WorldWideScience

Sample records for babcock-leighton flux-transport dynamo

  1. A THREE-DIMENSIONAL BABCOCK-LEIGHTON SOLAR DYNAMO MODEL

    International Nuclear Information System (INIS)

    Miesch, Mark S.; Dikpati, Mausumi

    2014-01-01

    We present a three-dimensional (3D) kinematic solar dynamo model in which poloidal field is generated by the emergence and dispersal of tilted sunspot pairs (more generally bipolar magnetic regions, or BMRs). The axisymmetric component of this model functions similarly to previous 2.5 dimensional (2.5D, axisymmetric) Babcock-Leighton (BL) dynamo models that employ a double-ring prescription for poloidal field generation but we generalize this prescription into a 3D flux emergence algorithm that places BMRs on the surface in response to the dynamo-generated toroidal field. In this way, the model can be regarded as a unification of BL dynamo models (2.5D in radius/latitude) and surface flux transport models (2.5D in latitude/longitude) into a more self-consistent framework that builds on the successes of each while capturing the full 3D structure of the evolving magnetic field. The model reproduces some basic features of the solar cycle including an 11 yr periodicity, equatorward migration of toroidal flux in the deep convection zone, and poleward propagation of poloidal flux at the surface. The poleward-propagating surface flux originates as trailing flux in BMRs, migrates poleward in multiple non-axisymmetric streams (made axisymmetric by differential rotation and turbulent diffusion), and eventually reverses the polar field, thus sustaining the dynamo. In this Letter we briefly describe the model, initial results, and future plans

  2. Solar Cycle Variability Induced by Tilt Angle Scatter in a Babcock-Leighton Solar Dynamo Model

    Science.gov (United States)

    Karak, Bidya Binay; Miesch, Mark

    2017-09-01

    We present results from a three-dimensional Babcock-Leighton (BL) dynamo model that is sustained by the emergence and dispersal of bipolar magnetic regions (BMRs). On average, each BMR has a systematic tilt given by Joy’s law. Randomness and nonlinearity in the BMR emergence of our model produce variable magnetic cycles. However, when we allow for a random scatter in the tilt angle to mimic the observed departures from Joy’s law, we find more variability in the magnetic cycles. We find that the observed standard deviation in Joy’s law of {σ }δ =15^\\circ produces a variability comparable to the observed solar cycle variability of ˜32%, as quantified by the sunspot number maxima between 1755 and 2008. We also find that tilt angle scatter can promote grand minima and grand maxima. The time spent in grand minima for {σ }δ =15^\\circ is somewhat less than that inferred for the Sun from cosmogenic isotopes (about 9% compared to 17%). However, when we double the tilt scatter to {σ }δ =30^\\circ , the simulation statistics are comparable to the Sun (˜18% of the time in grand minima and ˜10% in grand maxima). Though the BL mechanism is the only source of poloidal field, we find that our simulations always maintain magnetic cycles even at large fluctuations in the tilt angle. We also demonstrate that tilt quenching is a viable and efficient mechanism for dynamo saturation; a suppression of the tilt by only 1°-2° is sufficient to limit the dynamo growth. Thus, any potential observational signatures of tilt quenching in the Sun may be subtle.

  3. A Coupled 2 × 2D Babcock-Leighton Solar Dynamo Model. I. Surface Magnetic Flux Evolution

    Science.gov (United States)

    Lemerle, Alexandre; Charbonneau, Paul; Carignan-Dugas, Arnaud

    2015-09-01

    The need for reliable predictions of the solar activity cycle motivates the development of dynamo models incorporating a representation of surface processes sufficiently detailed to allow assimilation of magnetographic data. In this series of papers we present one such dynamo model, and document its behavior and properties. This first paper focuses on one of the model’s key components, namely surface magnetic flux evolution. Using a genetic algorithm, we obtain best-fit parameters of the transport model by least-squares minimization of the differences between the associated synthetic synoptic magnetogram and real magnetographic data for activity cycle 21. Our fitting procedure also returns Monte Carlo-like error estimates. We show that the range of acceptable surface meridional flow profiles is in good agreement with Doppler measurements, even though the latter are not used in the fitting process. Using a synthetic database of bipolar magnetic region (BMR) emergences reproducing the statistical properties of observed emergences, we also ascertain the sensitivity of global cycle properties, such as the strength of the dipole moment and timing of polarity reversal, to distinct realizations of BMR emergence, and on this basis argue that this stochasticity represents a primary source of uncertainty for predicting solar cycle characteristics.

  4. The Role of Magnetic Buoyancy in a Babcock-Leighton Type Solar ...

    Indian Academy of Sciences (India)

    tribpo

    J. Astrophys. Astr. (2000) 21, 381-385. The Role of Magnetic Buoyancy in a Babcock-Leighton. Type Solar Dynamo. Dibyendu Nandy* & Arnab Rai Choudhuri, ... model of the solar dynamo—which draws inspiration from the Babcock- .... are still of rather exploratory nature, since none of the authors have succeeded yet.

  5. Solar and Stellar Dynamos Saas-Fee Advanced Course 39 Swiss Society for Astrophysics and Astronomy

    CERN Document Server

    2013-01-01

    Astrophysical dynamos are at the heart of cosmic magnetic fields of a wide range of scales, from planets and stars to entire galaxies. This book presents a thorough, step-by-step introduction to solar and stellar dynamos. Looking first at the ultimate origin of cosmic seed magnetic fields, the antagonists of field amplification are next considered: resistive decay, flux expulsion, and flows ruled out by anti-dynamo theorems. Two kinematic flows that can act as dynamos are then studied: the Roberts cell and the CP-flow. Mean-field electrodynamics and derivation of the mean-field dynamo equations lead to the alpha Omega-dynamo, the flux transport dynamo, and dynamos based on the Babcock-Leighton mechanism. Alternatives to the mean-field theory are also presented, as are global MHD dynamo simulations. Fluctuations and grand minima in the solar cycle are discussed in terms of dynamo modulations through stochastic forcing and nonlinear effects. The book concludes with an overview of the major challenges in underst...

  6. Non-kinematic Flux-transport Dynamos Including the Effects of Diffusivity Quenching

    Energy Technology Data Exchange (ETDEWEB)

    Ichimura, Chiaki; Yokoyama, Takaaki [Department of Earth and Planetary Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2017-04-10

    Turbulent magnetic diffusivity is quenched when strong magnetic fields suppress turbulent motion in a phenomenon known as diffusivity quenching. Diffusivity quenching can provide a mechanism for amplifying magnetic field and influencing global velocity fields through Lorentz force feedback. To investigate this effect, we conducted mean field flux-transport dynamo simulations that included the effects of diffusivity quenching in a non-kinematic regime. We found that toroidal magnetic field strength is amplified by up to approximately 1.5 times in the convection zone as a result of diffusivity quenching. This amplification is much weaker than that in kinematic cases as a result of Lorentz force feedback on the system’s differential rotation. While amplified toroidal fields lead to the suppression of equatorward meridional flow locally near the base of the convection zone, large-scale equatorward transport of magnetic flux via meridional flow, which is the essential process of the flux-transport dynamo, is sustainable in our calculations.

  7. The Nature of Grand Minima and Maxima from Fully Nonlinear Flux Transport Dynamos

    Energy Technology Data Exchange (ETDEWEB)

    Inceoglu, Fadil; Arlt, Rainer [Leibniz-Institute for Astrophysics Potsdam, An der Sternwarte 16, D-14482, Potsdam (Germany); Rempel, Matthias, E-mail: finceoglu@aip.de [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 (United States)

    2017-10-20

    We aim to investigate the nature and occurrence characteristics of grand solar minimum and maximum periods, which are observed in the solar proxy records such as {sup 10}Be and {sup 14}C, using a fully nonlinear Babcock–Leighton type flux transport dynamo including momentum and entropy equations. The differential rotation and meridional circulation are generated from the effect of turbulent Reynolds stress and are subjected to back-reaction from the magnetic field. To generate grand minimum- and maximum-like periods in our simulations, we used random fluctuations in the angular momentum transport process, namely the Λ-mechanism, and in the Babcock–Leighton mechanism. To characterize the nature and occurrences of the identified grand minima and maxima in our simulations, we used the waiting time distribution analyses, which reflect whether the underlying distribution arises from a random or a memory-bearing process. The results show that, in the majority of the cases, the distributions of grand minima and maxima reveal that the nature of these events originates from memoryless processes. We also found that in our simulations the meridional circulation speed tends to be smaller during grand maximum, while it is faster during grand minimum periods. The radial differential rotation tends to be larger during grand maxima, while it is smaller during grand minima. The latitudinal differential rotation, on the other hand, is found to be larger during grand minima.

  8. Waldmeier's Rules in the Solar and Stellar Dynamos

    Science.gov (United States)

    Pipin, Valery; Kosovichev, Alexander

    2015-08-01

    The Waldmeier's rules [1] establish important empirical relations between the general parameters of magnetic cycles (such as the amplitude, period, growth rate and time profile) on the Sun and solar-type stars [2]. Variations of the magnetic cycle parameters depend on properties of the global dynamo processes operating in the stellar convection zones. We employ nonlinear mean-field axisymmetric dynamo models [3] and calculate of the magnetic cycle parameters, such as the dynamo cycle period, total magnetic and Poynting fluxes for the Sun and solar-type stars with rotational periods from 15 to 30 days. We consider two types of the dynamo models: 1) distributed (D-type) models employing the standard α - effect distributed in the whole convection zone, and 2) Babcock-Leighton (BL-type) models with a non-local α - effect. The dynamo models take into account the principal mechanisms of the nonlinear dynamo generation and saturation, including the magnetic helicity conservation, magnetic buoyancy effects, and the feedback on the angular momentum balance inside the convection zones. Both types of models show that the dynamo generated magnetic flux increases with the increase of the rotation rate. This corresponds to stronger brightness variations. The distributed dynamo model reproduces the observed dependence of the cycle period on the rotation rate for the Sun analogs better than the BL-type model. For the solar-type stars rotating more rapidly than the Sun we find dynamo regimes with multiple periods. Such stars with multiple cycles form a separate branch in the variability-rotation diagram.1. Waldmeier, M., Prognose für das nächste Sonnenfleckenmaximum, 1936, Astron. Nachrichten, 259,262. Soon,W.H., Baliunas,S.L., Zhang,Q.,An interpretation of cycle periods of stellar chromospheric activity, 1993, ApJ, 414,333. Pipin,V.V., Dependence of magnetic cycle parameters on period of rotation in nonlinear solar-type dynamos, 2015, astro-ph: 14125284

  9. Modeling a Shallow Solar Dynamo

    Science.gov (United States)

    Schatten, Kenneth H.

    2009-03-01

    Photospheric ephemeral regions (EPRs) cover the Sun like a magnetic carpet. From this, we update the Babcock - Leighton solar dynamo. Rather than sunspot fields appearing in the photosphere de novo from eruptions originating in the deep interior, we consider that sunspots form directly in the photosphere by a rapid accumulation of like-sign field from EPRs. This would only occur during special circumstances: locations and times when the temperature structure is highly superadiabatic and contains a large subsurface horizontal magnetic field (only present in the Sun’s lower latitudes). When these conditions are met, superadiabatic percolation occurs, wherein an inflow and downflow of gas scours the surface of EPRs to form active regions. When these conditions are not met, magnetic elements undergo normal percolation, wherein magnetic elements move about the photosphere in Brownian-type motions. Cellular automata (CA) models are developed that allow these processes to be calculated and thereby both small-scale and large-scale models of magnetic motions can be obtained. The small-scale model is compared with active region development and Hinode observations. The large-scale CA model offers a solar dynamo, which suggests that fields from decaying bipolar magnetic regions (BMRs) drift on the photosphere driven by subsurface magnetic forces. These models are related to observations and are shown to support Waldmeier’s findings of an inverse relationship between solar cycle length and cycle size. Evidence for significant amounts of deep magnetic activity could disprove the model presented here, but recent helioseismic observations of “butterfly patterns” at depth are likely just a reflection of surface activity. Their existence seems to support the contention made here that the field and flow separate, allowing cool, relatively field-free downdrafts to descend with little field into the nether worlds of the solar interior. There they heat by compression to form a

  10. Meridional Flow Observations: Implications for the current Flux Transport Models

    International Nuclear Information System (INIS)

    Gonzalez Hernandez, Irene; Komm, Rudolf; Kholikov, Shukur; Howe, Rachel; Hill, Frank

    2011-01-01

    Meridional circulation has become a key element in the solar dynamo flux transport models. Available helioseismic observations from several instruments, Taiwan Oscillation Network (TON), Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI), have made possible a continuous monitoring of the solar meridional flow in the subphotospheric layers for the last solar cycle, including the recent extended minimum. Here we review some of the meridional circulation observations using local helioseismology techniques and relate them to magnetic flux transport models.

  11. A Critical Assessment of the Flux Transport Dynamo Arnab Rai ...

    Indian Academy of Sciences (India)

    The important velocity fields, such as the differential rotation and the meridional arise out of the turbulent stresses in the solar convection zone and are very difficult to calculate from first principles. Until a dynamical model reproduces the velocity fields correctly, there is no hope that it will explain the behaviour of the magnetic.

  12. A Critical Assessment of the Flux Transport Dynamo Arnab Rai ...

    Indian Academy of Sciences (India)

    The second school of thought is due to Babcock. (1961) and Leighton (1964). Sunspot pairs forming out of the toroidal magnetic field have tilts produced by the Coriolis force (D'Silva & Choudhuri 1993)—tilts increas- ing with latitude in accordance with Joy's law. According to the Babcock–Leighton viewpoint, the decay of ...

  13. The Role of Magnetic Buoyancy in a Babcock-Leighton Type Solar ...

    Indian Academy of Sciences (India)

    tribpo

    2 (left) is a butterfly diagram for the toroidal field near the bottom of the. SCZ. This figure is obtained with Bc = 1 and f = 0.1 and the contour levels that we have plotted are: 0.5, 1,2, 4, 8 and 16 respectively. We clearly see an equatorward propagation of the fields with time, in keeping with the equatorward propagation.

  14. The solar dynamo and prediction of sunspot cycles

    Science.gov (United States)

    Dikpati, Mausumi

    2012-07-01

    Much progress has been made in understanding the solar dynamo since Parker first developed the concepts of dynamo waves and magnetic buoyancy around 1955, and the German school first formulated the solar dynamo using the mean-field formalism. The essential ingredients of these mean-field dynamos are turbulent magnetic diffusivity, a source of lifting of flux, or 'alpha-effect', and differential rotation. With the advent of helioseismic and other observations at the Sun's photosphere and interior, as well as theoretical understanding of solar interior dynamics, solar dynamo models have evolved both in the realm of mean-field and beyond mean-field models. After briefly discussing the status of these models, I will focus on a class of mean-field model, called flux-transport dynamos, which include meridional circulation as an essential additional ingredient. Flux-transport dynamos have been successful in simulating many global solar cycle features, and have reached the stage that they can be used for making solar cycle predictions. Meridional circulation works in these models like a conveyor-belt, carrying a memory of the magnetic fields from 5 to 20 years back in past. The lower is the magnetic diffusivity, the longer is the model's memory. In the terrestrial system, the great-ocean conveyor-belt in oceanic models and Hadley, polar and Ferrel circulation cells in the troposphere, carry signatures from the past climatological events and influence the determination of future events. Analogously, the memory provided by the Sun's meridional circulation creates the potential for flux-transport dynamos to predict future solar cycle properties. Various groups in the world have built flux-transport dynamo-based predictive tools, which nudge the Sun's surface magnetic data and integrated forward in time to forecast the amplitude of the currently ascending cycle 24. Due to different initial conditions and different choices of unknown model-ingredients, predictions can vary; so

  15. Nonlinear astrophysical dynamos: bifurcation of steady dynamos from oscillation dynamos

    International Nuclear Information System (INIS)

    Yoshimura, H.

    1978-01-01

    The nonlinear dynamo wave equation, which has been formulated to explore oscillating dynamos, is found also to have steady magnetic field condfigurations as its stable solutions. The solutions of the nonlinear wave equation, integrated numerically as the initial-boundary-value problem in the rotating spherical geometry, eventually bifurcate into a stationary oscillating state and a stationary steady state, depending on the initial condition adopted in the integration. Both states are stable with respect to small perturbations. In the steady-state solutions, the magnetic configuration is that of a helical tube so that the dynamo process, being controlled by the nonlinear process, adjusts itself to be exactly balanced with the diffusion process. The relative sensitivity of the bifurcation of the system depends on the structure of the dynamo system and the strength of the nonlinear process. We suggest that the magnetic fields of the Earth and planets, and the fields of non--solar-type magnetic stars, especially stars classified as oblique rotators, can be understood as special stationary solutions of the nonlinear dynamo wave equation, which can also have oscilating solutions. Thus the field reversal of so-called steady dynamos can be understood naturally as the transition governed by the wave nature of the equation between the two stationary states when some change occurs temporarily in the dynamics of the dynamos

  16. Predicting cycle 24 using various dynamo-based tools

    Directory of Open Access Journals (Sweden)

    M. Dikpati

    2008-02-01

    Full Text Available Various dynamo-based techniques have been used to predict the mean solar cycle features, namely the amplitude and the timings of onset and peak. All methods use information from previous cycles, including particularly polar fields, drift-speed of the sunspot zone to the equator, and remnant magnetic flux from the decay of active regions. Polar fields predict a low cycle 24, while spot zone migration and remnant flux both lead to predictions of a high cycle 24. These methods both predict delayed onset for cycle 24. We will describe how each of these methods relates to dynamo processes. We will present the latest results from our flux-transport dynamo, including some sensitivity tests and how our model relates to polar fields and spot zone drift methods.

  17. Evolution of Our Understanding of the Solar Dynamo During Solar Cycle 24

    Science.gov (United States)

    Munoz-Jaramillo, A.

    2017-12-01

    Solar cycle 24 has been an exciting cycle for our understanding of the solar dynamo: 1. It was the first cycle for which dynamo based predictions were ever used teaching us valuable lessons. 2. It has given us the opportunity to observe a deep minimum and a weak cycle with a high level of of observational detail . 3. It is full of breaktrhoughs in anelastic MHD dynamo simulations (regular cycles, buoyant flux-tubes, mounder-like events). 4. It has seen the creation of bridges between the kinematic flux-transport and anelastic MHD approaches. 5. It has ushered a new generation of realistic surface flux-transport simulations 6. We have achieved significant observational progress in our understanding of solar cycle propagation. The objective of this talk is to highlight some of the most important results, giving special emphasis on what they have taught us about solar cycle predictability.

  18. The lunar dynamo.

    Science.gov (United States)

    Weiss, Benjamin P; Tikoo, Sonia M

    2014-12-05

    The inductive generation of magnetic fields in fluid planetary interiors is known as the dynamo process. Although the Moon today has no global magnetic field, it has been known since the Apollo era that the lunar rocks and crust are magnetized. Until recently, it was unclear whether this magnetization was the product of a core dynamo or fields generated externally to the Moon. New laboratory and spacecraft measurements strongly indicate that much of this magnetization is the product of an ancient core dynamo. The dynamo field persisted from at least 4.25 to 3.56 billion years ago (Ga), with an intensity reaching that of the present Earth. The field then declined by at least an order of magnitude by ∼3.3 Ga. The mechanisms for sustaining such an intense and long-lived dynamo are uncertain but may include mechanical stirring by the mantle and core crystallization. Copyright © 2014, American Association for the Advancement of Science.

  19. Parameter optimization for surface flux transport models

    Science.gov (United States)

    Whitbread, T.; Yeates, A. R.; Muñoz-Jaramillo, A.; Petrie, G. J. D.

    2017-11-01

    Accurate prediction of solar activity calls for precise calibration of solar cycle models. Consequently we aim to find optimal parameters for models which describe the physical processes on the solar surface, which in turn act as proxies for what occurs in the interior and provide source terms for coronal models. We use a genetic algorithm to optimize surface flux transport models using National Solar Observatory (NSO) magnetogram data for Solar Cycle 23. This is applied to both a 1D model that inserts new magnetic flux in the form of idealized bipolar magnetic regions, and also to a 2D model that assimilates specific shapes of real active regions. The genetic algorithm searches for parameter sets (meridional flow speed and profile, supergranular diffusivity, initial magnetic field, and radial decay time) that produce the best fit between observed and simulated butterfly diagrams, weighted by a latitude-dependent error structure which reflects uncertainty in observations. Due to the easily adaptable nature of the 2D model, the optimization process is repeated for Cycles 21, 22, and 24 in order to analyse cycle-to-cycle variation of the optimal solution. We find that the ranges and optimal solutions for the various regimes are in reasonable agreement with results from the literature, both theoretical and observational. The optimal meridional flow profiles for each regime are almost entirely within observational bounds determined by magnetic feature tracking, with the 2D model being able to accommodate the mean observed profile more successfully. Differences between models appear to be important in deciding values for the diffusive and decay terms. In like fashion, differences in the behaviours of different solar cycles lead to contrasts in parameters defining the meridional flow and initial field strength.

  20. An Experimental MHD Dynamo

    International Nuclear Information System (INIS)

    Forest, C. B.

    2002-01-01

    The project is designed to understand current and magnetic field generation in plasmas and other magnetohydrodynamic systems. The experiments will investigate the generation of a dynamo using liquid Na

  1. BABCOCK–LEIGHTON SOLAR DYNAMO: THE ROLE OF DOWNWARD PUMPING AND THE EQUATORWARD PROPAGATION OF ACTIVITY

    Energy Technology Data Exchange (ETDEWEB)

    Karak, Bidya Binay; Cameron, Robert, E-mail: bkarak@ucar.edu [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany)

    2016-11-20

    The key elements of the Babcock–Leighton dynamos are the generation of poloidal field through decay and the dispersal of tilted bipolar active regions and the generation of toroidal field through the observed differential rotation. These models are traditionally known as flux transport dynamo models as the equatorward propagations of the butterfly wings in these models are produced due to an equatorward flow at the bottom of the convection zone. Here we investigate the role of downward magnetic pumping near the surface using a kinematic Babcock–Leighton model. We find that the pumping causes the poloidal field to become predominately radial in the near-surface shear layer, which allows the negative radial shear to effectively act on the radial field to produce a toroidal field. We observe a clear equatorward migration of the toroidal field at low latitudes as a consequence of the dynamo wave even when there is no meridional flow in the deep convection zone. Both the dynamo wave and the flux transport type solutions are thus able to reproduce some of the observed features of the solar cycle including the 11-year periodicity. The main difference between the two types of solutions is the strength of the Babcock–Leighton source required to produce the dynamo action. A second consequence of the magnetic pumping is that it suppresses the diffusion of fields through the surface, which helps to allow an 11-year cycle at (moderately) larger values of magnetic diffusivity than have previously been used.

  2. Dynamo: A Runtime Codesign Environment

    National Research Council Canada - National Science Library

    Quinn, Heather; Leeser, Miriam; Smith-King, L. A

    2004-01-01

    ...-up. Dynamo is a runtime system for generating hardware/software pipeline implementations. Dynamo balances the benefits of hardware and software implementations and takes overhead costs into account in order to accurately predict runtimes of hardware/software systems.

  3. A PROPOSED PARADIGM FOR SOLAR CYCLE DYNAMICS MEDIATED VIA TURBULENT PUMPING OF MAGNETIC FLUX IN BABCOCK–LEIGHTON-TYPE SOLAR DYNAMOS

    Energy Technology Data Exchange (ETDEWEB)

    Hazra, Soumitra; Nandy, Dibyendu [Department of Physical Sciences, Indian Institute of Science Education and Research, Kolkata (India)

    2016-11-20

    At present, the Babcock–Leighton flux transport solar dynamo models appear to be the most promising models for explaining diverse observational aspects of the sunspot cycle. The success of these flux transport dynamo models is largely dependent upon a single-cell meridional circulation with a deep equatorward component at the base of the Sun’s convection zone. However, recent observations suggest that the meridional flow may in fact be very shallow (confined to the top 10% of the Sun) and more complex than previously thought. Taken together, these observations raise serious concerns on the validity of the flux transport paradigm. By accounting for the turbulent pumping of magnetic flux, as evidenced in magnetohydrodynamic simulations of solar convection, we demonstrate that flux transport dynamo models can generate solar-like magnetic cycles even if the meridional flow is shallow. Solar-like periodic reversals are recovered even when meridional circulation is altogether absent. However, in this case, the solar surface magnetic field dynamics does not extend all the way to the polar regions. Very importantly, our results demonstrate that the Parker–Yoshimura sign rule for dynamo wave propagation can be circumvented in Babcock–Leighton dynamo models by the latitudinal component of turbulent pumping, which can generate equatorward propagating sunspot belts in the absence of a deep, equatorward meridional flow. We also show that variations in turbulent pumping coefficients can modulate the solar cycle amplitude and periodicity. Our results suggest the viability of an alternate magnetic flux transport paradigm—mediated via turbulent pumping—for sustaining solar-stellar dynamo action.

  4. Natural Dynamos: Introduction

    Czech Academy of Sciences Publication Activity Database

    Brestenský, J.; Ševčík, S.; Šimkanin, Ján; Marsenić, A.; Šoltis, T.

    Roč. 104, 5-6 ( 2010 ), s. 455-455, č. článku PII 929636498. ISSN 0309-1929 Institutional research plan: CEZ:AV0Z30120515 Keywords : hydromagnetic dynamos * magnetoconvection * hydromagnetic processes Subject RIV: DE - Earth Magnetism, Geodesy, Geography OBOR OECD: Physical geography Impact factor: 0.831, year: 2010

  5. Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars

    Science.gov (United States)

    Warnecke, J.; Rheinhardt, M.; Tuomisto, S.; Käpylä, P. J.; Käpylä, M. J.; Brandenburg, A.

    2018-01-01

    Aims: We investigate dynamo action in global compressible solar-like convective dynamos in the framework of mean-field theory. Methods: We simulate a solar-type star in a wedge-shaped spherical shell, where the interplay between convection and rotation self-consistently drives a large-scale dynamo. To analyze the dynamo mechanism we apply the test-field method for azimuthally (φ) averaged fields to determine the 27 turbulent transport coefficients of the electromotive force, of which six are related to the α tensor. This method has previously been used either in simulations in Cartesian coordinates or in the geodynamo context and is applied here for the first time to fully compressible simulations of solar-like dynamos. Results: We find that the φφ-component of the α tensor does not follow the profile expected from that of kinetic helicity. The turbulent pumping velocities significantly alter the effective mean flows acting on the magnetic field and therefore challenge the flux transport dynamo concept. All coefficients are significantly affected by dynamically important magnetic fields. Quenching as well as enhancement are being observed. This leads to a modulation of the coefficients with the activity cycle. The temporal variations are found to be comparable to the time-averaged values and seem to be responsible for a nonlinear feedback on the magnetic field generation. Furthermore, we quantify the validity of the Parker-Yoshimura rule for the equatorward propagation of the mean magnetic field in the present case.

  6. Quasi-geostrophic dynamo theory

    Science.gov (United States)

    Calkins, Michael A.

    2018-03-01

    The asymptotic theory of rapidly rotating, convection-driven dynamos in a plane layer is discussed. A key characteristic of these quasi-geostrophic dynamos is that the Lorentz force is comparable in magnitude to the ageostrophic component of the Coriolis force, rather than the leading order component that yields geostrophy. This characteristic is consistent with both observations of planetary dynamos and numerical dynamo investigations, where the traditional Elssasser number, ΛT = O (1) . Thus, while numerical dynamo simulations currently cannot access the strongly turbulent flows that are thought to be characteristic of planetary interiors, it is argued that they are in the appropriate geostrophically balanced regime provided that inertial and viscous forces are both small relative to the leading order Coriolis force. Four distinct quasi-geostrophic dynamo regimes are discussed, with each regime characterized by a unique magnetic to kinetic energy density ratio and differing dynamics. The axial torque due to the Lorentz force is shown to be asymptotically small for such quasi-geostrophic dynamos, suggesting that 'Taylor's constraint' represents an ambiguous measure of the primary force balance in a rapidly rotating dynamo.

  7. Magnetized Turbulent Dynamo in Protogalaxies

    Energy Technology Data Exchange (ETDEWEB)

    Leonid Malyshkin; Russell M. Kulsrud

    2002-01-28

    The prevailing theory for the origin of cosmic magnetic fields is that they have been amplified to their present values by the turbulent dynamo inductive action in the protogalactic and galactic medium. Up to now, in calculation of the turbulent dynamo, it has been customary to assume that there is no back reaction of the magnetic field on the turbulence, as long as the magnetic energy is less than the turbulent kinetic energy. This assumption leads to the kinematic dynamo theory. However, the applicability of this theory to protogalaxies is rather limited. The reason is that in protogalaxies the temperature is very high, and the viscosity is dominated by magnetized ions. As the magnetic field strength grows in time, the ion cyclotron time becomes shorter than the ion collision time, and the plasma becomes strongly magnetized. As a result, the ion viscosity becomes the Braginskii viscosity. Thus, in protogalaxies the back reaction sets in much earlier, at field strengths much lower than those which correspond to field-turbulence energy equipartition, and the turbulent dynamo becomes what we call the magnetized turbulent dynamo. In this paper we lay the theoretical groundwork for the magnetized turbulent dynamo. In particular, we predict that the magnetic energy growth rate in the magnetized dynamo theory is up to ten times larger than that in the kinematic dynamo theory. We also briefly discuss how the Braginskii viscosity can aid the development of the inverse cascade of magnetic energy after the energy equipartition is reached.

  8. A COUPLED 2 × 2D BABCOCK–LEIGHTON SOLAR DYNAMO MODEL. II. REFERENCE DYNAMO SOLUTIONS

    International Nuclear Information System (INIS)

    Lemerle, Alexandre; Charbonneau, Paul

    2017-01-01

    In this paper we complete the presentation of a new hybrid 2 × 2D flux transport dynamo (FTD) model of the solar cycle based on the Babcock–Leighton mechanism of poloidal magnetic field regeneration via the surface decay of bipolar magnetic regions (BMRs). This hybrid model is constructed by allowing the surface flux transport (SFT) simulation described in Lemerle et al. to provide the poloidal source term to an axisymmetric FTD simulation defined in a meridional plane, which in turn generates the BMRs required by the SFT. A key aspect of this coupling is the definition of an emergence function describing the probability of BMR emergence as a function of the spatial distribution of the internal axisymmetric magnetic field. We use a genetic algorithm to calibrate this function, together with other model parameters, against observed cycle 21 emergence data. We present a reference dynamo solution reproducing many solar cycle characteristics, including good hemispheric coupling, phase relationship between the surface dipole and the BMR-generating internal field, and correlation between dipole strength at cycle maximum and peak amplitude of the next cycle. The saturation of the cycle amplitude takes place through the quenching of the BMR tilt as a function of the internal field. The observed statistical scatter about the mean BMR tilt, built into the model, acts as a source of stochasticity which dominates amplitude fluctuations. The model thus can produce Dalton-like epochs of strongly suppressed cycle amplitude lasting a few cycles and can even shut off entirely following an unfavorable sequence of emergence events.

  9. A COUPLED 2 × 2D BABCOCK–LEIGHTON SOLAR DYNAMO MODEL. II. REFERENCE DYNAMO SOLUTIONS

    Energy Technology Data Exchange (ETDEWEB)

    Lemerle, Alexandre; Charbonneau, Paul, E-mail: lemerle@astro.umontreal.ca, E-mail: paulchar@astro.umontreal.ca [Département de physique, Université de Montréal, 2900 Boulevard Édouard-Montpetit, Montréal, QC, H3T 1J4 (Canada)

    2017-01-10

    In this paper we complete the presentation of a new hybrid 2 × 2D flux transport dynamo (FTD) model of the solar cycle based on the Babcock–Leighton mechanism of poloidal magnetic field regeneration via the surface decay of bipolar magnetic regions (BMRs). This hybrid model is constructed by allowing the surface flux transport (SFT) simulation described in Lemerle et al. to provide the poloidal source term to an axisymmetric FTD simulation defined in a meridional plane, which in turn generates the BMRs required by the SFT. A key aspect of this coupling is the definition of an emergence function describing the probability of BMR emergence as a function of the spatial distribution of the internal axisymmetric magnetic field. We use a genetic algorithm to calibrate this function, together with other model parameters, against observed cycle 21 emergence data. We present a reference dynamo solution reproducing many solar cycle characteristics, including good hemispheric coupling, phase relationship between the surface dipole and the BMR-generating internal field, and correlation between dipole strength at cycle maximum and peak amplitude of the next cycle. The saturation of the cycle amplitude takes place through the quenching of the BMR tilt as a function of the internal field. The observed statistical scatter about the mean BMR tilt, built into the model, acts as a source of stochasticity which dominates amplitude fluctuations. The model thus can produce Dalton-like epochs of strongly suppressed cycle amplitude lasting a few cycles and can even shut off entirely following an unfavorable sequence of emergence events.

  10. The Evolution of the Solar Magnetic Field: A Comparative Analysis of Two Models

    Science.gov (United States)

    McMichael, K. D.; Karak, B. B.; Upton, L.; Miesch, M. S.; Vierkens, O.

    2017-12-01

    Understanding the complexity of the solar magnetic cycle is a task that has plagued scientists for decades. However, with the help of computer simulations, we have begun to gain more insight into possible solutions to the plethora of questions inside the Sun. STABLE (Surface Transport and Babcock Leighton) is a newly developed 3D dynamo model that can reproduce features of the solar cycle. In this model, the tilted bipolar sunspots are formed on the surface (based on the toroidal field at the bottom of the convection zone) and then decay and disperse, producing the poloidal field. Since STABLE is a 3D model, it is able to solve the full induction equation in the entirety of the solar convection zone as well as incorporate many free parameters (such as spot depth and turbulent diffusion) which are difficult to observe. In an attempt to constrain some of these free parameters, we compare STABLE to a surface flux transport model called AFT (Advective Flux Transport) which solves the radial component of the magnetic field on the solar surface. AFT is a state-of-the-art surface flux transport model that has a proven record of being able to reproduce solar observations with great accuracy. In this project, we implement synthetic bipolar sunspots into both models, using identical surface parameters, and run the models for comparison. We demonstrate that the 3D structure of the sunspots in the interior and the vertical diffusion of the sunspot magnetic field play an important role in establishing the surface magnetic field in STABLE. We found that when a sufficient amount of downward magnetic pumping is included in STABLE, the surface magnetic field from this model becomes insensitive to the internal structure of the sunspot and more consistent with that of AFT.

  11. Numerical models of planetary dynamos

    International Nuclear Information System (INIS)

    Glatzmaier, G.A.; Roberts, P.H.

    1992-01-01

    We describe a nonlinear, axisymmetric, spherical-shell model of planetary dynamos. This intermediate-type dynamo model requires a prescribed helicity field (the alpha effect) and a prescribed buoyancy force or thermal wind (the omega effect) and solves for the axisymmetric time-dependent magnetic and velocity fields. Three very different time dependent solutions are obtained from different prescribed sets of alpha and omega fields

  12. Modelling total solar irradiance using a flux transport model

    Science.gov (United States)

    Dasi Espuig, Maria; Jiang, Jie; Krivova, Natalie; Solanki, Sami

    2014-05-01

    Reconstructions of solar irradiance into the past are of considerable interest for studies of solar influence on climate. Models based on the assumption that irradiance changes are caused by the evolution of the photospheric magnetic field have been the most successful in reproducing the measured irradiance variations. Our SATIRE-S model is one of these. It uses solar full-disc magnetograms as an input, and these are available for less than four decades. Thus, to reconstruct the irradiance back to times when no observed magnetograms are available, we combine the SATIRE-S model with synthetic magnetograms, produced using a surface flux transport model. The model is fed with daily, observed or modelled statistically, records of sunspot positions, areas, and tilt angles. To describe the secular change in the irradiance, we used the concept of overlapping ephemeral region cycles. With this technique TSI can be reconstructed back to 1700.

  13. A reconstruction of solar irradiance using a flux transport model

    Science.gov (United States)

    Dasi Espuig, Maria; Jiang, Jie; Krivova, Natalie; Solanki, Sami

    2013-04-01

    Reconstructions of solar irradiance into the past are of considerable interest for studies of solar influence on climate. Models based on the assumption that irradiance changes are caused by the evolution of the photospheric magnetic field have been the most successful in reproducing the measured irradiance variations. Our SATIRE-S model is one of these. It uses solar full-disc magnetograms as an input, and these are available for less than four decades. Thus, to reconstruct the irradiance back to times when no observed magnetograms are available, we combine the SATIRE-S model with synthetic magnetograms, produced using a surface flux transport model. The model is fed with daily, observed or modelled statistically, records of sunspot positions, areas, and tilt angles. To describe the secular change in the irradiance, we used the concept of overlapping ephemeral region cycles. With this technique TSI can be reconstructed back to 1610.

  14. On the saturation of astrophysical dynamos

    DEFF Research Database (Denmark)

    Dorch, Bertil; Archontis, Vasilis

    2004-01-01

    In the context of astrophysical dynamos we illustrate that the no-cosines flow, with zero mean helicity, can drive fast dynamo action and we study the dynamo's mode of operation during both the linear and non-linear saturation regimes. It turns out that in addition to a high growth rate...... in the linear regime, the dynamo saturates at a level significantly higher than normal turbulent dynamos, namely at exact equipartition when the magnetic Prandtl number Prm~ 1. Visualization of the magnetic and velocity fields at saturation will help us to understand some of the aspects of the non-linear dynamo...

  15. Turbulent dynamo action in stars

    International Nuclear Information System (INIS)

    Brandenburg, A.; Nordlund, A.; Ruokolainen, J.; Stein, R.F.; Tuominen, I.

    1990-01-01

    The way in which dynamo action amplifies magnetic fields in the Sun, the Earth, and indeed galaxies is a classic problem of theoretical physics. Here we present the results of direct simulations of turbulent compressible hydromagnetic convection with a stable overshoot layer underneath (to model the Sun). We find spontaneous dynamo action followed by saturation, with most of the generated magnetic field appearing as coherent flux tubes in the vicinity of strong downdrafts. Here both the generation and destruction of magnetic field is at its most vigorous, and which process ultimately dominates depends on the sizes of the magnetic Reynolds and magnetic Prandtl numbers. (orig.)

  16. ESTIMATING THE DEEP SOLAR MERIDIONAL CIRCULATION USING MAGNETIC OBSERVATIONS AND A DYNAMO MODEL: A VARIATIONAL APPROACH

    Energy Technology Data Exchange (ETDEWEB)

    Hung, Ching Pui; Jouve, Laurène; Brun, Allan Sacha [Laboratoire AIM Paris-Saclay, CEA/IRFU Université Paris-Diderot CNRS/INSU, F-91191 Gif-Sur-Yvette (France); Fournier, Alexandre [Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot UMR 7154 CNRS, F-75005 Paris (France); Talagrand, Olivier [Laboratoire de météorologie dynamique, UMR 8539, Ecole Normale Supérieure, Paris Cedex 05 (France)

    2015-12-01

    We show how magnetic observations of the Sun can be used in conjunction with an axisymmetric flux-transport solar dynamo model in order to estimate the large-scale meridional circulation throughout the convection zone. Our innovative approach rests on variational data assimilation, whereby the distance between predictions and observations (measured by an objective function) is iteratively minimized by means of an optimization algorithm seeking the meridional flow that best accounts for the data. The minimization is performed using a quasi-Newton technique, which requires knowledge of the sensitivity of the objective function to the meridional flow. That sensitivity is efficiently computed via the integration of the adjoint flux-transport dynamo model. Closed-loop (also known as twin) experiments using synthetic data demonstrate the validity and accuracy of this technique for a variety of meridional flow configurations, ranging from unicellular and equatorially symmetric to multicellular and equatorially asymmetric. In this well-controlled synthetic context, we perform a systematic study of the behavior of our variational approach under different observational configurations by varying their spatial density, temporal density, and noise level, as well as the width of the assimilation window. We find that the method is remarkably robust, leading in most cases to a recovery of the true meridional flow to within better than 1%. These encouraging results are a first step toward using this technique to (i) better constrain the physical processes occurring inside the Sun and (ii) better predict solar activity on decadal timescales.

  17. Incorporation of a Generalized Data Assimilation Module within a Global Photospheric Flux Transport Model

    Science.gov (United States)

    2016-03-31

    Table of Contents 1. INTRODUCTION...Traditional Photospheric Magnetic Flux Synoptic Maps .........................................................1 2.2 Photospheric Flux Transport Models...4 3. WH model evolved synoptic map (latitude vs. longitude

  18. A Vorticity-Magnetic Field Dynamo Instability

    OpenAIRE

    Blackman, Eric G.; Chou, Tom

    1997-01-01

    We generalize the mean field magnetic dynamo to include local evolution of the mean vorticity in addition to the mean magnetic field. The coupled equations exhibit a general mean field dynamo instability that enables the transfer of turbulent energy to the magnetic field and vorticity on larger scales. The growth of the vorticity and magnetic field both require helical turbulence which can be supplied by an underlying global rotation. The dynamo coefficients are derived including the backreac...

  19. Turbulent Liquid Metal Dynamo Experiments

    International Nuclear Information System (INIS)

    Forest, Cary

    2007-01-01

    The self-generation of magnetic fields in planets and stars--the dynamo effect--is a long-standing problem of magnetohydrodynamics and plasma physics. Until recently, research on the self-excitation process has been primarily theoretical. In this talk, I will begin with a tutorial on how magnetic fields are generated in planets and stars, describing the 'Standard Model' of self-excitation known as the alpha-omega dynamo. In this model, axisymmetric differential rotation can produce the majority of the magnetic field, but some non-axisymmetric, turbulence driven currents are also necessary. Understanding the conversion of turbulent kinetic energy in the fluid motion into electrical currents and thus magnetic fields, is a major challenge for both experiments and theory at this time. I will then report on recent results from a 1 meter diameter, spherical, liquid sodium dynamo experiment at the University of Wisconsin, in which the first clear evidence for these turbulence driven currents has been observed.

  20. New results on an equipartition dynamo

    DEFF Research Database (Denmark)

    Dorch, S. B. F.; Archontis, V.

    2006-01-01

    This contribution presents results from numerical computer experiments with a 3-d steady sine flow (with zero mean helicity) that drives fast dynamo action. The mode of operation of this so-called ``no-cosines" dynamo (recently dubbed ``the Archontis dynamo"" by David Galloway) was studied during...... significantly higher that intermittent turbulent dynamos: Namely very close to energy equipartition for high Reynolds numbers. The equipartition solution however is not turbulent but a laminar solution that acts as an attractor to other modes. Similarities and differences, in the way the magnetic field...

  1. Nonlinear MHD dynamo operating at equipartition

    DEFF Research Database (Denmark)

    Archontis, V.; Dorch, Bertil; Nordlund, Åke

    2007-01-01

    Context.We present results from non linear MHD dynamo experiments with a three-dimensional steady and smooth flow that drives fast dynamo action in the kinematic regime. In the saturation regime, the system yields strong magnetic fields, which undergo transitions between an energy-equipartition a......Context.We present results from non linear MHD dynamo experiments with a three-dimensional steady and smooth flow that drives fast dynamo action in the kinematic regime. In the saturation regime, the system yields strong magnetic fields, which undergo transitions between an energy......, and that it can saturate at a level significantly higher than intermittent turbulent dynamos, namely at energy equipartition, for high values of the magnetic and fluid Reynolds numbers. The equipartition solution however does not remain time-independent during the simulation but exhibits a much more intricate...

  2. Mechanically-forced dynamos (Invited)

    Science.gov (United States)

    Le Bars, M.

    2013-12-01

    It is a commonly accepted hypothesis that convection is responsible for planetary dynamos. However, the validity of the convective dynamo model can be questioned in various planets and moons as well as in asteroids, where the constraints from thermal evolution and compositional core models are sometimes difficult to reconcile with available data from paleomagnetism and in situ measurements. Over the last few years, researches have thus been pursued to find alternative mechanisms for sustaining intense three-dimensional motions in liquid cores, a necessary ingredient for planetary dynamo. In particular, mechanical forcings driven by libration, precession, nutation and tides, have received a renewed interest, following the first studies by Malkus in the 60's. A huge reservoir of energy is available in the rotational and orbital motions of all planetary systems. If planetary bodies were completely rigid and rotating at a constant spin rate, their fluid layers in the absence of convection would also behave rigidly and follow the spin of their boundaries. But small periodic perturbations of the shape of the core/mantle boundary (i.e. dynamic tides) and/or small periodic perturbations of the direction of the spin vector (i.e. precession and nutation) and/or small periodic perturbations of the spin rate (i.e. libration) systematically perturb this rigid state. Then, each of these small perturbations is capable of triggering instabilities in fluid layers, conveying energy from the spin and orbital motions to drive intense three-dimensional flows in the liquid cores. With the view to establish a general framework for planetary applications, I will present here the basic physical ingredients of these instabilities, which involve a resonance between the considered mechanical forcing and two inertial waves of the core. I will then review the numerical and experimental validations of this generic principle, and the few magnetohydrodynamic validations of their dynamo capacity

  3. Statistical simulation of the magnetorotational dynamo

    Energy Technology Data Exchange (ETDEWEB)

    Squire, J. [PPPL; Bhattacharjee, A. [PPPL

    2014-08-01

    We analyze turbulence and dynamo induced by the magnetorotational instability (MRI) using quasi-linear statistical simulation methods. We find that homogenous turbulence is unstable to a large scale dynamo instability, which saturates to an inhomogenous equilibrium with a very strong dependence on the magnetic Prandtl number (Pm). Despite its enormously reduced nonlinearity, the quasi-linear model exhibits the same qualitative scaling of angular momentum transport with Pm as fully nonlinear turbulence. This demonstrates the relationship of recent convergence problems to the large scale dynamo and suggests possible methods for studying astrophysically relevant regimes at very low or high Pm.

  4. Statistical Simulation of the Magnetorotational Dynamo

    Energy Technology Data Exchange (ETDEWEB)

    Squire, Jonathan [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Bhattacharjee, Amitava [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences; Max Planck Society, Garching (Germany). Max Planck Inst. for Astrophysik

    2015-02-01

    Turbulence and dynamo induced by the magnetorotational instability (MRI) are analyzed using quasilinear statistical simulation methods. It is found that homogenous turbulence is unstable to a large-scale dynamo instability, which saturates to an inhomogenous equilibrium with a strong dependence on the magnetic Prandtl number (Pm). Despite its enormously reduced nonlinearity, the dependence of the angular momentum transport on Pm in the quasilinear model is qualitatively similar to that of nonlinear MRI turbulence. This demonstrates the importance of the large-scale dynamo and suggests how dramatically simplified models may be used to gain insight into the astrophysically relevant regimes of very low or high Pm.

  5. Dynamos, Domains, and Paleomagnetic Poles

    Science.gov (United States)

    Kent, Dennis; Pan, Yongxin

    2011-05-01

    Earth's and Planetary Interiors: Observation and Numerical Models of Paleomagnetic and Planetary Magnetism; Beijing, China, 7-11 July 2010 ; The second international Beijing Earth and Planetary Interior Symposium (BEPIS; http://www.paleomag.net/meeting) was held at the Institute of Geology and Geophysics, Chinese Academy of Sciences (CAS), just down the road from the Bird's Nest and other iconic structures of the 2008 Beijing Olympics. The symposium was organized by Rixiang Zhu (CAS, Beijing, China) and Keke Zhang (Exeter University, Exeter, UK) and brought together more than 100 scientists, including 30 graduate students from 10 countries. Thirty-nine invited talks were organized along three major themes: planetary dynamos, paleomagnetism, and mineral magnetism. The talks were held in alternating and sometimes closely interleaved sessions and were supported by 40 poster presentations.

  6. Comments on the kinetic dynamo

    International Nuclear Information System (INIS)

    Fowler, T.K.

    1995-01-01

    It is conjectured that transport by parallel mass flow in a braided magnetic field, rather than hyper-resistivity, drives the dynamo effect after stochasticity is established. In this paper the authors do not attempt a rigorous proof of this conjecture, which requires showing that braiding introduces correlations analogous to those giving rise to the neoclassical bootstrap current. The authors do offer plausible arguments for the conjecture and show that it leads to interesting consequences if true. Namely, magnetic fluctuations would then scale with the magnetic Reynolds number S like B/B ∼ S -1/2 and the Rechester-Rosenbluth thermal diffusivity like χe ∝ S -1 . This scaling would explain the highest temperatures obtained in the CTX spheromak. It also suggests that a fully-bootstrapped current drive experiment could be carried out on-the DIII-D tokamak

  7. Dynamo generated by the centrifugal instability

    Science.gov (United States)

    Marcotte, Florence; Gissinger, Christophe

    2016-10-01

    We present a scenario for magnetic field amplification where an electrically conducting fluid is confined in a differentially rotating, spherical shell with thin aspect ratio. When the angular momentum sufficiently decreases outwards, a hydrodynamic instability develops in the equatorial region, characterized by pairs of counter-rotating toroidal vortices similar to those observed in cylindrical Couette flow. These spherical Taylor-Couette vortices generate a subcritical dynamo magnetic field dominated by nonaxisymmetric components. We show that the critical magnetic Reynolds number seems to reach a constant value at large Reynolds number and that the global rotation can strongly decrease the dynamo onset. Our numerical results are understood within the framework of a simple dynamical system, and we propose a low-dimensional model for subcritical dynamo bifurcations. Implications for both laboratory dynamos and astrophysical magnetic fields are finally discussed.

  8. Magnetic Field Amplification via Protostellar Disc Dynamos

    Science.gov (United States)

    Dyda, S.; Lovelace, R. V. E.; Ustyugova, G. V.; Koldoba, A. V.; Wasserman, I.

    2018-03-01

    We numerically investigate the generation of a magnetic field in a protostellar disc via an αΩ-dynamo and the resulting magnetohydrodynamic (MHD) driven outflows. We find that for small values of the dimensionless dynamo parameter αd the poloidal field grows exponentially at a rate σ ∝ Ω _K √{α _d}, before saturating to a value ∝ √{α _d}. The dynamo excites dipole and octupole modes, but quadrupole modes are suppressed, because of the symmetries of the seed field. Initial seed fields too weak to launch MHD outflows are found to grow sufficiently to launch winds with observationally relevant mass fluxes of order 10^{-9} M_{⊙}/{yr} for T Tauri stars. This suggests αΩ-dynamos may be responsible for generating magnetic fields strong enough to launch observed outflows.

  9. Riga dynamo experiment and its theoretical background

    International Nuclear Information System (INIS)

    Gailitis, Agris; Lielausis, Olgerts; Platacis, Ernests; Gerbeth, Gunter; Stefani, Frank

    2004-01-01

    It is widely believed that almost all magnetic fields in a natural environment are the result of the dynamo process - the field generation in moving nearly homogeneous electro-conducting fluids. This dynamo process occurs in the depths of celestial bodies such as the Earth, most of the planets, the Sun, other stars, and even galaxies. The Riga dynamo experiment is not intended as a model of any particular celestial body. It aims at demonstrating the basic dynamo mechanism - that the intense motion in a large volume of a good electro-conducting liquid creates a magnetic field. In the present paper, the set-up and the main results of this experiment are presented, with some focus on the theoretical interpretation of the data

  10. Time scales separation for dynamo action

    OpenAIRE

    Dormy, Emmanuel; Gerard-Varet, David

    2008-01-01

    International audience; The study of dynamo action in astrophysical objects classically involves two timescales: the slow diffusive one and the fast advective one. We investigate the possibility of field amplification on an intermediate timescale associated with time dependent modulations of the flow. We consider a simple steady configuration for which dynamo action is not realised. We study the effect of time dependent perturbations of the flow. We show that {some} vanishing {low frequency} ...

  11. Dynamo mode dynamics in reversed field pinches

    Science.gov (United States)

    Fitzpatrick, Richard

    1999-11-01

    Reversed field pinches (RFPs) are unstable to multiple m=1 tearing modes, resonant in the plasma core. These ``dynamo modes'' are ultimately responsible for the dynamo action which maintains the reversal of the edge toroidal magnetic field against ohmic decay. Unfortunately, the dynamo modes also generally disrupt magnetic flux surfaces in the core, thereby strongly degrading the plasma confinement. However, recent experiments in the Madison Symmetric Torus (MST) and the Reversed Field Experiment (RFX) indicate that a well-confined RFP plasma is a possibility provided that the amplitude of the dynamo modes is controlled, and the rotation of these modes is also maintained. An analytic formalism has been developed in order to investigate the nonlinear interaction of dynamo modes with one another, with static error-fields, and with eddy currents excited in the vacuum vessel or stabilizing shell. The dynamo modes are found to couple nonlinearly to form a toroidally localized magnetic structure which can be identified as the ``slinky mode,'' reported in many RFP experiments. As the mode amplitudes increase, the slinky mode forms via a series of bifurcations in which the overall mode structure and the plasma rotation profile both change discontinuously. The threshold amplitude for the onset of these bifurcations is similar to that observed experimentally. The absence of mode rotation in RFX (which gives rise to serious edge loading problems) is shown to be due to strong eddy currents excited in the resistive vacuum vessel. Dynamo modes are slowed down by these eddy currents to such an extent that they are easily locked by small static error-fields which would otherwise (i.e., in the absence of the vacuum vessel eddy currents) be unable to affect the mode rotation. Since MST does not possess a resistive vacuum vessel (in MST the thick stabilizing shell also plays the role of the vacuum vessel: in RFX there is a separate vacuum vessel inside the shell) there are no vacuum

  12. Mean-field magnetohydrodynamics and dynamo theory

    CERN Document Server

    Krause, F

    2013-01-01

    Mean-Field Magnetohydrodynamics and Dynamo Theory provides a systematic introduction to mean-field magnetohydrodynamics and the dynamo theory, along with the results achieved. Topics covered include turbulence and large-scale structures; general properties of the turbulent electromotive force; homogeneity, isotropy, and mirror symmetry of turbulent fields; and turbulent electromotive force in the case of non-vanishing mean flow. The turbulent electromotive force in the case of rotational mean motion is also considered. This book is comprised of 17 chapters and opens with an overview of the gen

  13. Alpha-effect dynamos with zero kinetic helicity.

    Science.gov (United States)

    Rädler, Karl-Heinz; Brandenburg, Axel

    2008-02-01

    A simple explicit example of a Roberts-type dynamo is given in which the alpha effect of mean-field electrodynamics exists in spite of pointwise vanishing kinetic helicity of the fluid flow. In this way, it is shown that alpha-effect dynamos do not necessarily require nonzero kinetic helicity. A mean-field theory of Roberts-type dynamos is established within the framework of the second-order correlation approximation. In addition, numerical solutions of the original dynamo equations are given that are independent of any approximation of that kind. Both theory and numerical results demonstrate the possibility of dynamo action in the absence of kinetic helicity.

  14. Converting DYNAMO simulations to Powersim Studio simulations

    Energy Technology Data Exchange (ETDEWEB)

    Walker, La Tonya Nicole; Malczynski, Leonard A.

    2014-02-01

    DYNAMO is a computer program for building and running 'continuous' simulation models. It was developed by the Industrial Dynamics Group at the Massachusetts Institute of Technology for simulating dynamic feedback models of business, economic, and social systems. The history of the system dynamics method since 1957 includes many classic models built in DYANMO. It was not until the late 1980s that software was built to take advantage of the rise of personal computers and graphical user interfaces that DYNAMO was supplanted. There is much learning and insight to be gained from examining the DYANMO models and their accompanying research papers. We believe that it is a worthwhile exercise to convert DYNAMO models to more recent software packages. We have made an attempt to make it easier to turn these models into a more current system dynamics software language, Powersim © Studio produced by Powersim AS2 of Bergen, Norway. This guide shows how to convert DYNAMO syntax into Studio syntax.

  15. TIDALLY DRIVEN DYNAMOS IN A ROTATING SPHERE

    International Nuclear Information System (INIS)

    Cébron, D.; Hollerbach, R.

    2014-01-01

    Large-scale planetary or stellar magnetic fields generated by a dynamo effect are mostly attributed to flows forced by buoyancy forces in electrically conducting fluid layers. However, these large-scale fields may also be controlled by tides, as previously suggested for the star τ-boo, Mars, or the early Moon. By simulating a small local patch of a rotating fluid, Barker and Lithwick have recently shown that tides can drive small-scale dynamos by exciting a hydrodynamic instability, the so-called elliptical (or tidal) instability. By performing global magnetohydrodynamic simulations of a rotating spherical fluid body, we investigate if this instability can also drive the observed large-scale magnetic fields. We are thus interested in the dynamo threshold and the generated magnetic field in order to test if such a mechanism is relevant for planets and stars. Rather than solving the problem in a geometry deformed by tides, we consider a spherical fluid body and add a body force to mimic the tidal deformation in the bulk of the fluid. This allows us to use an efficient spectral code to solve the magnetohydrodynamic problem. We first compare the hydrodynamic results with theoretical asymptotic results and numerical results obtained in a truly deformed ellipsoid, which confirms the presence of elliptical instability. We then perform magnetohydrodynamic simulations and investigate the dynamo capability of the flow. Kinematic and self-consistent dynamos are finally simulated, showing that the elliptical instability is capable of generating a dipole-dominated large-scale magnetic field in global simulations of a fluid rotating sphere

  16. Statistical Mechanics of Turbulent Dynamos

    Science.gov (United States)

    Shebalin, John V.

    2014-01-01

    Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much

  17. MAGNETIC FLUX TRANSPORT AND THE LONG-TERM EVOLUTION OF SOLAR ACTIVE REGIONS

    International Nuclear Information System (INIS)

    Ugarte-Urra, Ignacio; Upton, Lisa; Warren, Harry P.; Hathaway, David H.

    2015-01-01

    With multiple vantage points around the Sun, Solar Terrestrial Relations Observatory (STEREO) and Solar Dynamics Observatory imaging observations provide a unique opportunity to view the solar surface continuously. We use He ii 304 Å data from these observatories to isolate and track ten active regions and study their long-term evolution. We find that active regions typically follow a standard pattern of emergence over several days followed by a slower decay that is proportional in time to the peak intensity in the region. Since STEREO does not make direct observations of the magnetic field, we employ a flux-luminosity relationship to infer the total unsigned magnetic flux evolution. To investigate this magnetic flux decay over several rotations we use a surface flux transport model, the Advective Flux Transport model, that simulates convective flows using a time-varying velocity field and find that the model provides realistic predictions when information about the active region's magnetic field strength and distribution at peak flux is available. Finally, we illustrate how 304 Å images can be used as a proxy for magnetic flux measurements when magnetic field data is not accessible

  18. A spherical Taylor-Couette dynamo

    Science.gov (United States)

    Marcotte, Florence; Gissinger, Christophe

    2016-04-01

    We present a new scenario for magnetic field amplification in the planetary interiors where an electrically conducting fluid is confined in a differentially rotating, spherical shell (spherical Couette flow) with thin aspect-ratio. When the angular momentum sufficiently decreases outwards, a primary hydrodynamic instability is widely known to develop in the equatorial region, characterized by pairs of counter-rotating, axisymmetric toroidal vortices (Taylor vortices) similar to those observed in cylindrical Couette flow. We characterize the subcritical dynamo bifurcation due to this spherical Taylor-Couette flow and study its evolution as the flow successively breaks into wavy and turbulent Taylor vortices for increasing Reynolds number. We show that the critical magnetic Reynolds number seems to reach a constant value as the Reynolds number is gradually increased. The role of global rotation on the dynamo threshold and the implications for planetary interiors are finally discussed.

  19. Magnetic reversals from planetary dynamo waves

    DEFF Research Database (Denmark)

    Sheyko, Andrey; Finlay, Chris; Jackson, Andrew

    2016-01-01

    A striking feature of many natural dynamos is their ability to undergo polarity reversals. The best documented example is Earth's magnetic field, which has reversed hundreds of times during its history. The origin of geomagnetic polarity reversals lies in a magnetohydrodynamic process that takes...... place in Earth's core, but the precise mechanism is debated. The majority of numerical geodynamo simulations that exhibit reversals operate in a regime in which the viscosity of the fluid remains important, and in which the dynamo mechanism primarily involves stretching and twisting of field lines...... (the ratio of advection to Coriolis force). Instead, stretching of the magnetic field by a strong shear in the east-west flow near the imaginary cylinder just touching the inner core and parallel to the axis of rotation is crucial to the reversal mechanism in our models, which involves a process akin...

  20. The Alpha Dynamo Effects in Laboratory Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Hantao Ji; Stewart C. Prager

    2001-10-16

    A concise review of observations of the alpha dynamo effect in laboratory plasmas is given. Unlike many astrophysical systems, the laboratory pinch plasmas are driven magnetically. When the system is overdriven, the resultant instabilities cause magnetic and flow fields to fluctuate, and their correlation induces electromotive forces along the mean magnetic field. This alpha-effect drives mean parallel electric current, which, in turn, modifies the initial background mean magnetic structure towards the stable regime. This drive-and-relax cycle, or the so-called self-organization process, happens in magnetized plasmas in a timescale much shorter than resistive diffusion time, thus it is a fast and unquenched dynamo process. The observed alpha-effect redistributes magnetic helicity (a measure of twistedness and knottedness of magnetic field lines) but conserves its total value. It can be shown that fast and unquenched dynamos are natural consequences of a driven system where fluctuations are statistically either not stationary in time or not homogeneous in space, or both. Implications to astrophysical phenomena will be discussed.

  1. Total solar irradiance reconstruction since 1700 using a flux transport model

    Science.gov (United States)

    Dasi Espuig, Maria; Krivova, Natalie; Solanki, Sami K.; Jiang, Jie

    Reconstructions of solar irradiance into the past are crucial for studies of solar influence on climate. Models based on the assumption that irradiance changes are caused by the evolution of the photospheric magnetic fields have been most successful in reproducing the measured irradiance variations. Daily magnetograms, such as those from MDI and HMI, provide the most detailed information on the changing distribution of the photospheric magnetic fields. Since such magnetograms are only available from 1974, we used a surface flux transport model to describe the evolution of the magnetic fields on the solar surface due to the effects of differential rotation, meridional circulation, and turbulent diffusivity, before 1974. In this model, the sources of magnetic flux are the active regions, which are introduced based on sunspot group areas, positions, and tilt angles. The RGO record is, however, only available since 1874. Here we present a model of solar irradiance since 1700, which is based on a semi-synthetic sunspot record. The semi-synthetic record was obtained using statistical relationships between sunspot group properties (areas, positions, tilt angles) derived from the RGO record on one hand, and the cycle strength and phase derived from the sunspot group number (Rg) on the other. These relationships were employed to produce daily records of sunspot group positions, areas, and tilt angles before 1874. The semi-synthetic records were fed into the surface flux transport model to simulate daily magnetograms since 1700. By combining the simulated magnetograms with a SATIRE-type model, we then reconstructed total solar irradiance since 1700.

  2. The Hottest Hot Jupiters May Host Atmospheric Dynamos

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, T. M. [Department of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne (United Kingdom); McElwaine, J. N. [Planetary Science Institute, Tucson, AZ 85721 (United States)

    2017-06-01

    Hot Jupiters have proven themselves to be a rich class of exoplanets that test our theories of planetary evolution and atmospheric dynamics under extreme conditions. Here, we present three-dimensional magnetohydrodynamic simulations and analytic results that demonstrate that a dynamo can be maintained in the thin, stably stratified atmosphere of a hot Jupiter, independent of the presumed deep-seated dynamo. This dynamo is maintained by conductivity variations arising from strong asymmetric heating from the planets’ host star. The presence of a dynamo significantly increases the surface magnetic field strength and alters the overall planetary magnetic field geometry, possibly affecting star–planet magnetic interactions.

  3. Magnetic dynamos in accreting planetary bodies

    Science.gov (United States)

    Golabek, Gregor; Labrosse, Stéphane; Gerya, Taras; Morishima, Ryuji; Tackley, Paul

    2013-04-01

    Laboratory measurements revealed ancient remanent magnetization in meteorites [1] indicating the activity of magnetic dynamos in the corresponding meteorite parent body. To study under which circumstances dynamo activity is possible, we use a new methodology to simulate the internal evolution of a planetary body during accretion and differentiation. Using the N-body code PKDGRAV [2] we simulate the accretion of planetary embryos from an initial annulus of several thousand planetesimals. The growth history of the largest resulting planetary embryo is used as an input for the thermomechanical 2D code I2ELVIS [3]. The thermomechanical model takes recent parametrizations of impact processes [4] and of the magnetic dynamo [5] into account. It was pointed out that impacts can not only deposit heat deep into the target body, which is later buried by ejecta of further impacts [6], but also that impacts expose in the crater region originally deep-seated layers, thus cooling the interior [7]. This combination of impact effects becomes even more important when we consider that planetesimals of all masses contribute to planetary accretion. This leads occasionally to collisions between bodies with large ratios between impactor and target mass. Thus, all these processes can be expected to have a profound effect on the thermal evolution during the epoch of planetary accretion and may have implications for the magnetic dynamo activity. Results show that late-formed planetesimals do not experience silicate melting and avoid thermal alteration, whereas in early-formed bodies accretion and iron core growth occur almost simultaneously and a highly variable magnetic dynamo can operate in the interior of these bodies. [1] Weiss, B.P. et al., Science, 322, 713-716, 2008. [2] Richardson, D. C. et al., Icarus, 143, 45-59, 2000. [3] Gerya, T.V and Yuen, D.J., Phys. Earth Planet. Int., 163, 83-105, 2007. [4] Monteux, J. et al., Geophys. Res. Lett., 34, L24201, 2007. [5] Aubert, J. et al

  4. Modelling astrophysical outflows via the unified dynamo-reverse dynamo mechanism

    Science.gov (United States)

    Lingam, Manasvi; Mahajan, Swadesh M.

    2015-04-01

    The unified dynamo-reverse dynamo (Dy-RDy) mechanism, capable of simultaneously generating large-scale outflows and magnetic fields from an ambient microscopic reservoir, is explored in a broad astrophysical context. The Dy-RDy mechanism is derived via the Hall magnetohydrodynamics, which unifies the evolution of magnetic field and fluid vorticity. It also introduces an intrinsic length-scale, the ion skin depth, allowing for the proper normalization and categorization of microscopic and macroscopic scales. The large-scale Alfvén Mach number MA, defining the relative `abundance' of the flow field to the magnetic field is shown to be tied to a microscopic scalelength that reflects the characteristics of the ambient short-scale reservoir. The dynamo (Dy), preferentially producing the large-scale magnetic field, is the dominant mode when the ambient turbulence is mostly kinetic, while the outflow producing reverse dynamo (RDy) is the principal manifestation of a magnetically dominated turbulent reservoir. It is conjectured that an efficient RDy may be the source of many observed astrophysical outflows that have MA ≫ 1.

  5. Some Recent Developments in Solar Dynamo Theory Arnab Rai ...

    Indian Academy of Sciences (India)

    providing a theoretical model of the observed poleward migration of the weak surface field. 4. The full dynamo model. Our aim now should be to use the helioseismically determined differential rotation to construct a dynamo model, in which the poloidal field is produced by the Babcock–. Leighton process and the meridional ...

  6. Some Recent Developments in Solar Dynamo Theory Arnab Rai ...

    Indian Academy of Sciences (India)

    Abstract. We discuss the current status of solar dynamo theory and describe the dynamo model developed by our group. The toroidal magnetic field is generated in the tachocline by the strong differential rotation and rises to the solar surface due to magnetic buoyancy to create active regions. The decay of these active ...

  7. Efficiency Measurement Using a Motor-Dynamo Module

    Science.gov (United States)

    Ng, Pun-hon; Wong, Siu-ling; Mak, Se-yuen

    2009-01-01

    In this article, we describe a simple method which can be used to measure the efficiency of a low power dc motor, a motor-converted dynamo and a coupled motor-dynamo module as a function of the speed of rotation. The result can also be used to verify Faraday's law of electromagnetic induction. (Contains 1 table and 8 figures.)

  8. MHD dynamo action in space plasmas

    International Nuclear Information System (INIS)

    Faelthammar, C.G.

    1984-05-01

    Electric currents are now recognized to play a major role in the physical process of the Earths magnetosphere as well as in distant astrophysical plasmas. In driving these currents MHD dynamos as well as generators of a thermoelectric nature are important. The primary source of power for the Earths magnetospheric process is the solar wind, which supplies a voltage of the order of 200 kV across the magnetosphere. The direction of the large-scale solar wind electric field varies of many different time scales. The power input to the magnetosphere is closely correlated with the direction of the large-scale solar wind electric field in such a fashion as to mimick the response of a half-wave rectifier with a down-to-dusk conduction direction. Behind this apparently simple response there are complex plasma physical processes that are still very incompletely understood. They are intimately related to auroras, magnetic storms, radiation belts and changes in magnetospheric plasma populations. Similar dynamo actions should occur at other planets having magnetospheres. Recent observations seem to indicate that part of the power input to the Earths magnetosphere comes through MHD dynamo action of a forced plasma flow inside the flanks of the magnetopause and may play a role in other parts of the magnetosphere, too. An example of a cosmical MHD connected to a solid load is the corotating plasma of Jupiters inner magnetosphere, sweeping past the plants inner satelites. In particular the electric currents thereby driven to and from the satellite Io have attracted considerable interest.(author)

  9. Could Giant Basin-Forming Impacts Have Killed Martian Dynamo?

    Science.gov (United States)

    Kuang, W.; Jiang, W.; Roberts, J.; Frey, H. V.

    2014-01-01

    The observed strong remanent crustal magnetization at the surface of Mars suggests an active dynamo in the past and ceased to exist around early to middle Noachian era, estimated by examining remagnetization strengths in extant and buried impact basins. We investigate whether the Martian dynamo could have been killed by these large basin-forming impacts, via numerical simulation of subcritical dynamos with impact-induced thermal heterogeneity across the core-mantle boundary. We find that subcritical dynamos are prone to the impacts centered on locations within 30 deg of the equator but can easily survive those at higher latitudes. Our results further suggest that magnetic timing places a strong constraint on postimpact polar reorientation, e.g., a minimum 16 deg polar reorientation is needed if Utopia is the dynamo killer.

  10. Reconstructing solar magnetic fields from historical observations. II. Testing the surface flux transport model

    Science.gov (United States)

    Virtanen, I. O. I.; Virtanen, I. I.; Pevtsov, A. A.; Yeates, A.; Mursula, K.

    2017-07-01

    Aims: We aim to use the surface flux transport model to simulate the long-term evolution of the photospheric magnetic field from historical observations. In this work we study the accuracy of the model and its sensitivity to uncertainties in its main parameters and the input data. Methods: We tested the model by running simulations with different values of meridional circulation and supergranular diffusion parameters, and studied how the flux distribution inside active regions and the initial magnetic field affected the simulation. We compared the results to assess how sensitive the simulation is to uncertainties in meridional circulation speed, supergranular diffusion, and input data. We also compared the simulated magnetic field with observations. Results: We find that there is generally good agreement between simulations and observations. Although the model is not capable of replicating fine details of the magnetic field, the long-term evolution of the polar field is very similar in simulations and observations. Simulations typically yield a smoother evolution of polar fields than observations, which often include artificial variations due to observational limitations. We also find that the simulated field is fairly insensitive to uncertainties in model parameters or the input data. Due to the decay term included in the model the effects of the uncertainties are somewhat minor or temporary, lasting typically one solar cycle.

  11. Reconstructing solar magnetic fields from historical observations: Testing the surface flux transport model

    Science.gov (United States)

    Virtanen, Iiro; Virtanen, Ilpo; Pevtsov, Alexei; Yeates, Anthony; Mursula, Kalevi

    2017-04-01

    We aim to use the surface flux transport model to simulate the long-term evolution of the photospheric magnetic field from historical observations. In this work we study the accuracy of the model and its sensitivity to uncertainties in its main parameters and the input data. We test the model by running simulations with different values of meridional circulation and supergranular diffusion parameters, and study how the flux distribution inside active regions and the initial magnetic field affect the simulation. We compare the results to assess how sensitive the simulation is to uncertainties in meridional circulation speed, supergranular diffusion and input data. We also compare the simulated magnetic field with observations. We find that there is generally good agreement between simulations and observations. While the model is not capable of replicating fine details of the magnetic field, the long-term evolution of the polar field is very similar in simulations and observations. Simulations typically yield a smoother evolution of polar fields than observations, that often include artificial variations due to observational limitations. We also find that the simulated field is fairly insensitive to uncertainties in model parameters or the input data. Due to the decay term included in the model the effects of the uncertainties are rather minor or temporary, lasting typically one solar cycle.

  12. A two-billion-year history for the lunar dynamo.

    Science.gov (United States)

    Tikoo, Sonia M; Weiss, Benjamin P; Shuster, David L; Suavet, Clément; Wang, Huapei; Grove, Timothy L

    2017-08-01

    Magnetic studies of lunar rocks indicate that the Moon generated a core dynamo with surface field intensities of ~20 to 110 μT between at least 4.25 and 3.56 billion years ago (Ga). The field subsequently declined to <~4 μT by 3.19 Ga, but it has been unclear whether the dynamo had terminated by this time or just greatly weakened in intensity. We present analyses that demonstrate that the melt glass matrix of a young regolith breccia was magnetized in a ~5 ± 2 μT dynamo field at ~1 to ~2.5 Ga. These data extend the known lifetime of the lunar dynamo by at least 1 billion years. Such a protracted history requires an extraordinarily long-lived power source like core crystallization or precession. No single dynamo mechanism proposed thus far can explain the strong fields inferred for the period before 3.56 Ga while also allowing the dynamo to persist in such a weakened state beyond ~2.5 Ga. Therefore, our results suggest that the dynamo was powered by at least two distinct mechanisms operating during early and late lunar history.

  13. MHD turbulent dynamo in astrophysics: Theory and numerical simulation

    Science.gov (United States)

    Chou, Hongsong

    2001-10-01

    This thesis treats the physics of dynamo effects through theoretical modeling of magnetohydrodynamic (MHD) systems and direct numerical simulations of MHD turbulence. After a brief introduction to astrophysical dynamo research in Chapter 1, the following issues in developing dynamic models of dynamo theory are addressed: In Chapter 2, nonlinearity that arises from the back reaction of magnetic field on velocity field is considered in a new model for the dynamo α-effect. The dependence of α-coefficient on magnetic Reynolds number, kinetic Reynolds number, magnetic Prandtl number and statistical properties of MHD turbulence is studied. In Chapter 3, the time-dependence of magnetic helicity dynamics and its influence on dynamo effects are studied with a theoretical model and 3D direct numerical simulations. The applicability of and the connection between different dynamo models are also discussed. In Chapter 4, processes of magnetic field amplification by turbulence are numerically simulated with a 3D Fourier spectral method. The initial seed magnetic field can be a large-scale field, a small-scale magnetic impulse, and a combination of these two. Other issues, such as dynamo processes due to helical Alfvénic waves and the implication and validity of the Zeldovich relation, are also addressed in Appendix B and Chapters 4 & 5, respectively. Main conclusions and future work are presented in Chapter 5. Applications of these studies are intended for astrophysical magnetic field generation through turbulent dynamo processes, especially when nonlinearity plays central role. In studying the physics of MHD turbulent dynamo processes, the following tools are developed: (1)A double Fourier transform in both space and time for the linearized MHD equations (Chapter 2 and Appendices A & B). (2)A Fourier spectral numerical method for direct simulation of 3D incompressible MHD equations (Appendix C).

  14. Mean-field theory and self-consistent dynamo modeling

    International Nuclear Information System (INIS)

    Yoshizawa, Akira; Yokoi, Nobumitsu

    2001-12-01

    Mean-field theory of dynamo is discussed with emphasis on the statistical formulation of turbulence effects on the magnetohydrodynamic equations and the construction of a self-consistent dynamo model. The dynamo mechanism is sought in the combination of the turbulent residual-helicity and cross-helicity effects. On the basis of this mechanism, discussions are made on the generation of planetary magnetic fields such as geomagnetic field and sunspots and on the occurrence of flow by magnetic fields in planetary and fusion phenomena. (author)

  15. 3-dimensional simulation of dynamo effect of reversed field pinch

    International Nuclear Information System (INIS)

    Koide, Shinji.

    1990-09-01

    A non-linear numerical simulation of the dynamo effect of a reversed field pinch (RFP) with finite beta is presented. It is shown that the m=-1, n=(9,10,11,....,19) modes cause the dynamo effect and sustain the field reversed configuration. The role of the m=0 modes on the dynamo effect is carefully examined. Our simulation shows that the magnetic field fluctuation level scales as S -0.2 or S -0.3 in the range of 10 3 5 , while Nebel, Caramana and Schnack obtained the fluctuation level is independent of S for a pressureless RFP plasma. (author)

  16. Introduction to Plasma Dynamo, Reconnection and Shocks

    Energy Technology Data Exchange (ETDEWEB)

    Intrator, Thomas P. [Los Alamos National Laboratory

    2012-08-30

    In our plasma universe, most of what we can observe is composed of ionized gas, or plasma. This plasma is a conducting fluid, which advects magnetic fields when it flows. Magnetic structure occurs from the smallest planetary to the largest cosmic scales. We introduce at a basic level some interesting features of non linear magnetohydrodynamics (MHD). For example, in our plasma universe, dynamo creates magnetic fields from gravitationally driven flow energy in an electrically conducting medium, and conversely magnetic reconnection annihilates magnetic field and accelerates particles. Shocks occur when flows move faster than the local velocity (sonic or Alfven speed) for the propagation of information. Both reconnection and shocks can accelerate particles, perhaps to gigantic energies, for example as observed with 10{sup 20} eV cosmic rays.

  17. Starspots: A Key to the Stellar Dynamo

    Directory of Open Access Journals (Sweden)

    Berdyugina Svetlana V.

    2005-12-01

    Full Text Available Magnetic activity similar to that of the Sun is observed on a variety of cool stars with external convection envelopes. Stellar rotation coupled with convective motions generate strong magnetic fields in the stellar interior and produce a multitude of magnetic phenomena including starspots in the photosphere, chromospheric plages, coronal loops, UV, X-ray, and radio emission and flares. Here I review the phenomenon of starspots on different types of cool stars, observational tools and diagnostic techniques for studying starspots as well as starspot properties including their temperatures, areas, magnetic field strengths, lifetimes, active latitudes and longitudes, etc. Evolution of starspots on various time scales allows us to investigate stellar differential rotation, activity cycles, and global magnetic fields. Together these constitute the basis for our understanding of stellar and solar dynamos and provide valuable constraints for theoretical models.

  18. Planetary Dynamos: Investigations of Saturn and Ancient Mars

    Energy Technology Data Exchange (ETDEWEB)

    Stanley, Sabine [University of Toronto

    2012-04-18

    Magnetic field observations by spacecraft missions have provided vital information on planetary dynamos. The four giant planets as well as Earth, Mercury and Ganymede have observable magnetic fields generated by active dynamos. In contrast, Moon and Mars only have remanent crustal fields from dynamo action in their early histories. A variety of magnetic field morphologies and intensities can be found in the solar system. We have found that some of the differences between planetary magnetic fields can be explained as the result of the presence of boundary thermal variations or stably-stratified layers. In this talk, I will discuss how dynamos are affected by these complications and discuss the implications for Mars’ magnetic dichotomy and Saturn’s extremely axisymmetric magnetic field.

  19. Direct numerical simulation of dynamo transition for nonhelical MHD

    Energy Technology Data Exchange (ETDEWEB)

    Nath, Dinesh; Verma, Mahendra K [Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Lessinnes, Thomas; Carati, Daniele [Physique Statistique et Plasmas, Universite Libre de Bruxellers, B-1050 Bruxelles (Belgium); Sarris, Ioannis [Department of Mechanical and Industrial Engineering, University of Thessaly, Volos (Greece)

    2010-02-01

    Pseudospectral Direct Numerical Simulation (DNS) has been performed to simulate dynamo transition for nonhelical magnetohydrodynamics turbulence. The numerical results are compared with a recent low-dimensional model [Verma et al. [13

  20. Energy transfers in dynamos with small magnetic Prandtl numbers

    KAUST Repository

    Kumar, Rohit

    2015-06-25

    We perform numerical simulation of dynamo with magnetic Prandtl number Pm = 0.2 on 10243 grid, and compute the energy fluxes and the shell-to-shell energy transfers. These computations indicate that the magnetic energy growth takes place mainly due to the energy transfers from large-scale velocity field to large-scale magnetic field and that the magnetic energy flux is forward. The steady-state magnetic energy is much smaller than the kinetic energy, rather than equipartition; this is because the magnetic Reynolds number is near the dynamo transition regime. We also contrast our results with those for dynamo with Pm = 20 and decaying dynamo. © 2015 Taylor & Francis.

  1. Magnetohydrodynamic dynamos in the presence of fossil magnetic fields

    International Nuclear Information System (INIS)

    Boyer, D.W.

    1982-01-01

    A fossil magnetic field embedded in the radiative core of the Sun has been thought possible for some time now. However, such a fossil magnetic field has, a priori, not been considered a visible phenomenon due to the effects of turbulence in the solar convection zone. Since a well developed theory (referred to herein as magnetohydrodynamic dynamo theory) exists for describing the regeneration of magnetic fields in astrophysical objects like the Sun, it is possible to quantitatively evaluate the interaction of a fossil magnetic field with the magnetohydrodynamic dynamo operating in the solar convection zone. In this work, after a brief description of the basic dynamo equations, a spherical model calculation of the solar dynamo is introduced. First, the interaction of a fossil magnetic field with a dynamo in which the regeneration mechanisms of cyclonic convection and large-scale, nonuniform rotation are confined to spherical shells is calculated. It is argued that the amount of amplification or suppression of a fossil magnetic field will be smallest for a uniform distribution of cyclonic convection and nonuniform rotation, as expected in the Sun. Secondly, the interaction of a fossil magnetic field with a dynamo having a uniform distribution of cyclonic convection and large-scale, nonuniform rotation is calculated. It is found that the dipole or quadrupole moments of a fossil magnetic field are suppressed by factors of -0.35 and -0.37, respectively

  2. DIPOLE COLLAPSE AND DYNAMO WAVES IN GLOBAL DIRECT NUMERICAL SIMULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Schrinner, Martin; Dormy, Emmanuel [MAG (ENS/IPGP), LRA, Ecole Normale Superieure, 24 Rue Lhomond, 75252 Paris Cedex 05 (France); Petitdemange, Ludovic, E-mail: martin@schrinner.eu [Previously at Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg, Germany. (Germany)

    2012-06-20

    Magnetic fields of low-mass stars and planets are thought to originate from self-excited dynamo action in their convective interiors. Observations reveal a variety of field topologies ranging from large-scale, axial dipoles to more structured magnetic fields. In this article, we investigate more than 70 three-dimensional, self-consistent dynamo models in the Boussinesq approximation obtained by direct numerical simulations. The control parameters, the aspect ratio, and the mechanical boundary conditions have been varied to build up this sample of models. Both strongly dipolar and multipolar models have been obtained. We show that these dynamo regimes in general can be distinguished by the ratio of a typical convective length scale to the Rossby radius. Models with a predominantly dipolar magnetic field were obtained, if the convective length scale is at least an order of magnitude larger than the Rossby radius. Moreover, we highlight the role of the strong shear associated with the geostrophic zonal flow for models with stress-free boundary conditions. In this case the above transition disappears and is replaced by a region of bistability for which dipolar and multipolar dynamos coexist. We interpret our results in terms of dynamo eigenmodes using the so-called test-field method. We can thus show that models in the dipolar regime are characterized by an isolated 'single mode'. Competing overtones become significant as the boundary to multipolar dynamos is approached. We discuss how these findings relate to previous models and to observations.

  3. Design of the Madison Dynamo Experiment

    Science.gov (United States)

    Kendrick, R. D.; Forest, C. B.; O'Connell, R.; Nornberg, M. D.; Spence, E. J.

    2004-11-01

    A spherical dynamo experiment has been constructed at the University of Wisconsin's liquid-sodium facility. The goals of the experiment are to observe and understand magnetic instabilities driven by flow shear in MHD systems, investigate MHD turbulence for magnetic Reynolds numbers of 100, and understand the role of fluid turbulence in current generation. Magnetic field generation is possible for only specific flow geometries. The experiment consists of a 1 m diameter, spherical stainless steel vessel filled with liquid sodium at 110 Celsius. The temperature of the vessel is maintained through an actively-heated-and-cooled oil heat-exchange system. Two 100 Hp motors with impellers drive flows in the liquid sodium with flow velocities near 15 m/s. Each shaft is sealed with an oil-buffered dual mechanical cartridge seal. The experiment is automated for remote operation and data logging. The melting and transfer of one metric ton of sodium to a storage vessel is discussed. Operating parameters and performance of the experiment are presented.

  4. Linking paleointensities and exsolution-driven dynamo

    Science.gov (United States)

    Du, Z.; Jackson, C.; Bennett, N.; Driscoll, P.; Deng, J.; Lee, K. K. M.; Greenberg, E.; Prakapenka, V. B.; Fei, Y.

    2017-12-01

    Origin of Earth's ancient magnetic field is an outstanding problem. Exsolution of MgO (O'Rourke and Stevenson, 2016, Badro et al., 2016) or SiO2 (Hirose et al., 2016) from the core during cooling has been proposed as a viable mechanism to drive an early geodynamo. We conducted new experiments on Mg partitioning between an iron-rich liquid and silicate/oxide melt. Our results indicate that MgO exsolution is limited and insufficient to drive an early geodynamo alone. In order to link the possible exsolution-driven dynamo and paleomagnetic observations, we constructed a thermal model by including the effect of exsolution. Our model predicts inner core nucleation (ICN) at 850 Ma and a nearly constant paleointensity using our experimentally determined data. Interestingly, strong exsolution in the form of either MgO or SiO2 would lead to a distinct trend in paleointensity after ICN. This potentially provides an observational test for the exsolution model and ICN.

  5. Measurement of the dynamo effect in a plasma

    International Nuclear Information System (INIS)

    Ji, H.; Prager, S.C.; Almagri, A.F.; Sarff, J.S.; Hirano, Y.; Toyama, H.

    1995-11-01

    A series of the detailed experiments has been conducted in three laboratory plasma devices to measure the dynamo electric field along the equilibrium field line (the α effect) arising from the correlation between the fluctuating flow velocity and magnetic field. The fluctuating flow velocity is obtained from probe measurement of the fluctuating E x B drift and electron diamagnetic drift. The three major findings are (1) the α effect accounts for the dynamo current generation, even in the time dependence through a ''sawtooth'' cycle; (2) at low collisionality the dynamo is explained primarily by the widely studied pressureless Magnetohydrodynamic (MHD) model, i.e., the fluctuating velocity is dominated by the E x B drift; (3) at high collisionality, a new ''electron diamagnetic dynamo'' is observed, in which the fluctuating velocity is dominated by the diamagnetic drift. In addition, direct measurements of the helicity flux indicate that the dynamo activity transports magnetic helicity from one part of the plasma to another, but the total helicity is roughly conserved, verifying J.B. Taylor's conjecture

  6. CHANGES OF THE SOLAR MERIDIONAL VELOCITY PROFILE DURING CYCLE 23 EXPLAINED BY FLOWS TOWARD THE ACTIVITY BELTS

    International Nuclear Information System (INIS)

    Cameron, R. H.; Schuessler, M.

    2010-01-01

    The solar meridional flow is an important ingredient in Babcock-Leighton type models of the solar dynamo. Global variations of this flow have been suggested to explain the variations in the amplitudes and lengths of the activity cycles. Recently, cycle-related variations in the amplitude of the P 1 2 term in the Legendre decomposition of the observed meridional flow have been reported. The result is often interpreted in terms of an overall variation in the flow amplitude during the activity cycle. Using a semi-empirical model based upon the observed distribution of magnetic flux on the solar surface, we show that the reported variations of the P 1 2 term can be explained by the observed localized inflows into the active region belts. No variation of the overall meridional flow amplitude is required.

  7. Dynamo transformation of the collisional R-T in a weakly ionized ...

    Indian Academy of Sciences (India)

    terms of dynamo transformation of neutral drag effect as a source to understand complete suppression of the usual collisional R-T and in turn linear driving of the NILF. It is therefore emphasized, worth calling it as the dynamo instability. Keywords. Ionosphere; mesosphere; partial ionization; irregularities; collisional; dynamo ...

  8. Feasible homopolar dynamo with sliding liquid-metal contacts

    OpenAIRE

    Priede, Jānis; Avalos-Zúñiga, Raúl

    2013-01-01

    We present a feasible homopolar dynamo design consisting of a flat, multi-arm spiral coil, which is placed above a fast-spinning metal ring and connected to the latter by sliding liquid-metal electrical contacts. Using a simple, analytically solvable axisymmetric model, we determine the optimal design of such a setup. For small contact resistance, the lowest magnetic Reynolds number, Rm~34.6, at which the dynamo can work, is attained at the optimal ratio of the outer and inner radii of the ri...

  9. Magnetic field saturation in the Riga dynamo experiment.

    Science.gov (United States)

    Gailitis, A; Lielausis, O; Platacis, E; Dement'ev, S; Cifersons, A; Gerbeth, G; Gundrum, T; Stefani, F; Christen, M; Will, G

    2001-04-02

    After the dynamo experiment in November 1999 [A. Gailitis et al., Phys. Rev. Lett. 84, 4365 (2000)] had shown magnetic field self-excitation in a spiraling liquid metal flow, in a second series of experiments emphasis was placed on the magnetic field saturation regime as the next principal step in the dynamo process. The dependence of the strength of the magnetic field on the rotation rate is studied. Various features of the saturated magnetic field are outlined and possible saturation mechanisms are discussed.

  10. Systematic parameter study of dynamo bifurcations in geodynamo simulations

    Science.gov (United States)

    Petitdemange, Ludovic

    2018-04-01

    We investigate the nature of the dynamo bifurcation in a configuration applicable to the Earth's liquid outer core, i.e. in a rotating spherical shell with thermally driven motions with no-slip boundaries. Unlike in previous studies on dynamo bifurcations, the control parameters have been varied significantly in order to deduce general tendencies. Numerical studies on the stability domain of dipolar magnetic fields found a dichotomy between non-reversing dipole-dominated dynamos and the reversing non-dipole-dominated multipolar solutions. We show that, by considering weak initial fields, the above transition disappears and is replaced by a region of bistability for which dipolar and multipolar dynamos coexist. Such a result was also observed in models with free-slip boundaries in which the geostrophic zonal flow can develop and participate to the dynamo mechanism for non-dipolar fields. We show that a similar process develops in no-slip models when viscous effects are reduced sufficiently. The following three regimes are distinguished: (i) Close to the onset of convection (Rac) with only the most critical convective mode (wave number) being present, dynamos set in supercritically in the Ekman number regime explored here and are dipole-dominated. Larger critical magnetic Reynolds numbers indicate that they are particularly inefficient. (ii) in the range 3 10) , the relative importance of zonal flows increases with Ra in non-magnetic models. The field topology depends on the magnitude of the initial magnetic field. The dipolar branch has a subcritical behavior whereas the multipolar branch has a supercritical behavior. By approaching more realistic parameters, the extension of this bistable regime increases. A hysteretic behavior questions the common interpretation for geomagnetic reversals. Far above the dynamo threshold (by increasing the magnetic Prandtl number), Lorentz forces contribute to the first order force balance, as predicted for planetary dynamos. When

  11. The Dynamo Dialectic: An Inside Look at the Current Solar Minimum

    Science.gov (United States)

    Miesch, M. S.

    2010-06-01

    Although the causal chain is by no means straightforward, variations among solar minima observed in the solar atmosphere and heliosphere must ultimately arise from the capricious nature of the dynamo operating in the solar interior. Given the highly turbulent conditions in the solar envelope, chaotic temporal variation should be expected. A deep understanding of long-term solar variability must come from a conceptual synthesis between the inherent disorder of a turbulent dynamo as manifested by the magnetic carpet and the patent order exhibited by the solar activity cycle. This is the dynamo dialectic, thesis-antithesis-synthesis; the solar dynamo is cyclic, the solar dynamo is chaotic, the solar dynamo is both. I will review our current understanding of how order and chaos coexist in the Sun based on simplified but illustrative systems including both mean-field dynamo models and 3D MHD convection simulations.

  12. Simulation study of dynamo structure in reversed field pinch

    International Nuclear Information System (INIS)

    Nagata, A.; Sato, K.I.; Ashida, H.; Amano, T.

    1992-10-01

    The dynamo structure in the reversed field pinch (RFP) is studied through the nonlinear dynamics of single-helicity mode. Simulation is concentrated upon the physical structure of nonlinear interactions of the plasma flow and magnetic fluctuation. The result indicates that when the initial equilibrium profile is deformed by resistive diffusion, the radial flow is driven near the core of the plasma. As this flow forms a vortex structure and magnetic fluctuation grows radially, the dynamo electric field is spirally induced just inside the reversal surface and then the toroidal flux is increased. This dynamo electric field correlates to nonlinear evolution of the kinetic energy of m=1 mode, and the increase of the toroidal flux is originated in the growth process of the magnetic energy of this mode. Consequently, the RFP configuration can be sustained by the single-helicity evolution of m=1 mode alone, and the electric field induced by the interactions of the toroidal velocity and the radial magnetic field is the most dominant source on the dynamo action. (author)

  13. Solar small-scale dynamo and polarity of sunspot groups

    Science.gov (United States)

    Sokoloff, D.; Khlystova, A.; Abramenko, V.

    2015-08-01

    In order to clarify a possible role of small-scale dynamo in formation of solar magnetic field, we suggest an observational test for small-scale dynamo action based on statistics of anti-Hale sunspot groups. As we have shown, according to theoretical expectations the small-scale dynamo action has to provide a population of sunspot groups which do not follow the Hale polarity law, and the density of such groups on the time-latitude diagram is expected to be independent on the phase of the solar cycle. Correspondingly, a percentage of the anti-Hale groups is expected to reach its maximum values during solar minima. For several solar cycles, we considered statistics of anti-Hale groups obtained by several scientific teams, including ours, to find that the percentage of anti-Hale groups becomes indeed maximal during a solar minimum. Our interpretation is that this fact may be explained by the small-scale dynamo action inside the solar convective zone.

  14. Solar Internal Rotation and Dynamo Waves: A Two Dimensional ...

    Indian Academy of Sciences (India)

    tribpo

    Solar Internal Rotation and Dynamo Waves: A Two Dimensional. Asymptotic Solution in the Convection Zone ... We calculate here a spatial 2 D structure of the mean magnetic field, adopting real profiles of the solar internal ... of the asymptotic solution in low (middle) and high (right panel) latitudes. field is shifted towards the ...

  15. Energy fluxes in helical magnetohydrodynamics and dynamo action

    Indian Academy of Sciences (India)

    his sabbatical leave. This work was supported in part by the Department of Science and. Technology, India. References. [1] H K Moffatt, Magnetic fields generation in electrically conducting fluids (Cambridge University. Press, Cambridge, 1978). [2] F Krause and K H Rädler, Mean-field magnetohydrodynamics and dynamo ...

  16. Solar Internal Rotation and Dynamo Waves: A Two Dimensional ...

    Indian Academy of Sciences (India)

    tribpo

    3Moscow State University, Department of Physics, 119899 Moscow, Russia. * e mail: gbelvedere@alpha4. ct. astro, it. Key words. Sun: magnetic fields, rotation, activity. Extended abstract. Here we outline how asymptotic models may contribute to the investigation of mean field dynamos applied to the solar convective zone.

  17. Precession Driven Instabilities and Dynamos in the Early Moon

    Science.gov (United States)

    Cebron, D.; Laguerre, R.; Noir, J.; Vidal, J.; Schaeffer, N.

    2017-12-01

    The Early Moon magnetic fields are probably due to a strong temporary dynamo, which may be due to lunar precession [1]. However, precession driven dynamos remain badly known, with only few studied cases [2,3,4]. Given the uncertainties of the early Moon precession, wider ranges of parameters need to be explored in order to assess if such lunar dynamos are possible. Using the efficient dynamo code XSHELLS, we have thus performed many simulations of precessing spherical shells, varying the parameters in a systematic way. This allows us to characterize the various excited instabilities, and to propose scaling laws. We also obtain that precession driven dynamos seem scarce and weak in our simulations, which makes difficult and uncertain the extrapolation of these dynamos to the Moon. However, our dynamo simulations, as every other in the literature, neglect the topographic torque effect on instabilities in order to use fast spectral codes [5]. By contrast, the topographic torque is dominant for the lunar core. Before exploring this effect numerically, which is a real challenge, we choose to study it theoretically. To do so, we have developed a novel global linear stability analysis of mechanically-driven flows in triaxial ellipsoids, with leading order viscous effects. Internal dissipation is obtained for the first time by extending the Greenspan's theory (1968) of geostrophic and inertial modes. By contrast with pioneering theories [6], we propose a new linear viscous model valid in arbitrary ellipsoid and for any precessing forcing. Then we perform the linear stability analysis by considering ellipsoidal perturbations of unprecedented spatial complexity with a self-consistent model of viscous damping. We show that forced precession-driven basic flows are bistable in triaxial ellipsoids. Then, we present the first stability analysis of precessing-flows in triaxial ellipsoids. [1] Dwyer et al. (2011), Nature, 479, 212-214.[2] Tilgner (2005), Phy. Fluids, 17, 034104

  18. Physical conditions for Jupiter-like dynamo models

    Science.gov (United States)

    Duarte, Lúcia D. V.; Wicht, Johannes; Gastine, Thomas

    2018-01-01

    The Juno mission will measure Jupiter's magnetic field with unprecedented precision and provide a wealth of additional data that will allow us to constrain the planet's interior structure and dynamics. Here we analyse 66 different numerical simulations in order to explore the sensitivity of the dynamo-generated magnetic field to the planets interior properties. Jupiter field models based on pre-Juno data and up-to-date interior models based on ab initio simulations serve as benchmarks. Our results suggest that Jupiter-like magnetic fields can be found for a number of different models. These complement the steep density gradients in the outer part of the simulated shell with an electrical conductivity profile that mimics the low conductivity in the molecular hydrogen layer and thus renders the dynamo action in this region largely unimportant. We find that whether we assume an ideal gas or use the more realistic interior model based on ab initio simulations makes no difference. However, two other factors are important. A low Rayleigh number leads to a too strong axial dipole contribution while the axial dipole dominance is lost altogether when the convective driving is too strong. The required intermediate range that yields Jupiter-like magnetic fields depends on the other system properties. The second important factor is the convective magnetic Reynolds number radial profile Rmc(r), basically a product of the non-axisymmetric flow velocity and electrical conductivity. We find that the depth where Rmc exceeds about 50 is a good proxy for the top of the dynamo region. When the dynamo region sits too deep, the axial dipole is once more too dominant due to geometric reasons. Extrapolating our results to Jupiter and the result suggests that the Jovian dynamo extends to 95% of the planetary radius. The zonal flow system in our simulations is dominated by an equatorial jet which remains largely confined to the molecular layer. Where the jet reaches down to higher

  19. Integral equation approach to time-dependent kinematic dynamos in finite domains

    International Nuclear Information System (INIS)

    Xu Mingtian; Stefani, Frank; Gerbeth, Gunter

    2004-01-01

    The homogeneous dynamo effect is at the root of cosmic magnetic field generation. With only a very few exceptions, the numerical treatment of homogeneous dynamos is carried out in the framework of the differential equation approach. The present paper tries to facilitate the use of integral equations in dynamo research. Apart from the pedagogical value to illustrate dynamo action within the well-known picture of the Biot-Savart law, the integral equation approach has a number of practical advantages. The first advantage is its proven numerical robustness and stability. The second and perhaps most important advantage is its applicability to dynamos in arbitrary geometries. The third advantage is its intimate connection to inverse problems relevant not only for dynamos but also for technical applications of magnetohydrodynamics. The paper provides the first general formulation and application of the integral equation approach to time-dependent kinematic dynamos, with stationary dynamo sources, in finite domains. The time dependence is restricted to the magnetic field, whereas the velocity or corresponding mean-field sources of dynamo action are supposed to be stationary. For the spherically symmetric α 2 dynamo model it is shown how the general formulation is reduced to a coupled system of two radial integral equations for the defining scalars of the poloidal and toroidal field components. The integral equation formulation for spherical dynamos with general stationary velocity fields is also derived. Two numerical examples - the α 2 dynamo model with radially varying α and the Bullard-Gellman model - illustrate the equivalence of the approach with the usual differential equation method. The main advantage of the method is exemplified by the treatment of an α 2 dynamo in rectangular domains

  20. Feasible homopolar dynamo with sliding liquid-metal contacts

    International Nuclear Information System (INIS)

    Priede, Jānis; Avalos-Zúñiga, Raúl

    2013-01-01

    We present a feasible homopolar dynamo design consisting of a flat, multi-arm spiral coil, which is placed above a fast-spinning metal ring and connected to the latter by sliding liquid-metal electrical contacts. Using a simple, analytically solvable axisymmetric model, we determine the optimal design of such a setup. For small contact resistance, the lowest magnetic Reynolds number, Rm≈34.6, at which the dynamo can work, is attained at the optimal ratio of the outer and inner radii of the rings R i /R o ≈0.36 and the spiral pitch angle 54.7°. In a setup of two copper rings with the thickness of 3 cm, R i =10 cm and R o =30 cm, self-excitation of the magnetic field is expected at a critical rotation frequency around 10 Hz

  1. Magnetic field dynamos and magnetically triggered flow instabilities

    Science.gov (United States)

    Stefani, F.; Albrecht, T.; Arlt, R.; Christen, M.; Gailitis, A.; Gellert, M.; Giesecke, A.; Goepfert, O.; Herault, J.; Kirillov, O. N.; Mamatsashvili, G.; Priede, J.; Rüdiger, G.; Seilmayer, M.; Tilgner, A.; Vogt, T.

    2017-07-01

    The project A2 of the LIMTECH Alliance aimed at a better understanding of those magnetohydrodynamic instabilities that are relevant for the generation and the action of cosmic magnetic fields. These comprise the hydromagnetic dynamo effect and various magnetically triggered flow instabilities, such as the magnetorotational instability and the Tayler instability. The project was intended to support the experimental capabilities to become available in the framework of the DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN). An associated starting grant was focused on the dimensioning of a liquid metal experiment on the newly found magnetic destabilization of rotating flows with positive shear. In this survey paper, the main results of these two projects are summarized.

  2. Hydromagnetic dynamos at the low Ekman and magnetic Prandtl numbers

    Czech Academy of Sciences Publication Activity Database

    Šimkanin, Ján

    2016-01-01

    Roč. 46, č. 3 (2016), s. 221-244 ISSN 1335-2806 R&D Projects: GA MŠk(CZ) LG13042 Institutional support: RVO:67985530 Keywords : hydromagnetic dynamo * magnetic Prandtl number * inertial forces Subject RIV: DE - Earth Magnetism, Geodesy, Geography https://www.degruyter.com/downloadpdf/j/congeo.2016.46.issue-3/congeo-2016-0014/congeo-2016-0014.pdf

  3. On chaos synchronization of a complex two coupled dynamos system

    Energy Technology Data Exchange (ETDEWEB)

    Mahmoud, Gamal M. [Department of Mathematics, Faculty of Science, Assiut University, Assiut 71516 (Egypt)]. E-mail: gmahmoud@aun.edu.eg; Aly, Shaban A. [Department of Mathematics, Faculty of Science, Al-Azhar University, Assiut 71511 (Egypt)]. E-mail: shhalyl2@yahoo.com; Farghaly, Ahmed A. [Department of Mathematics, Faculty of Science, Assiut University, Assiut 71516 (Egypt)]. E-mail: ahmed_l_66@yahoo.com

    2007-07-15

    The main objective of this work is to investigate the chaotic behavior and chaos synchronization of a complex two coupled dynamos system subject to different initial conditions. This system exhibits a chaotic attractor which is found numerically. The global synchronization and active control techniques are used in this investigation. The feedback gain matrix and Lyapunov function are calculated and used to show that the linear error dynamical system is asymptotically stable. The analytical results are tested numerically and excellent agreement is found.

  4. The dynamics of magnetic Rossby waves in spherical dynamo simulations: A signature of strong-field dynamos?

    Science.gov (United States)

    Hori, K.; Teed, R. J.; Jones, C. A.

    2018-03-01

    We investigate slow magnetic Rossby waves in convection-driven dynamos in rotating spherical shells. Quasi-geostrophic waves riding on a mean zonal flow may account for some of the geomagnetic westward drifts and have the potential to allow the toroidal field strength within the planetary fluid core to be estimated. We extend the work of Hori et al. (2015) to include a wider range of models, and perform a detailed analysis of the results. We find that a predicted dispersion relation matches well with the longitudinal drifts observed in our strong-field dynamos. We discuss the validity of our linear theory, since we also find that the nonlinear Lorentz terms influence the observed waveforms. These wave motions are excited by convective instability, which determines the preferred azimuthal wavenumbers. Studies of linear rotating magnetoconvection have suggested that slow magnetic Rossby modes emerge in the magnetostrophic regime, in which the Lorentz and Coriolis forces are in balance in the vorticity equation. We confirm this to be predominant balance for the slow waves we have detected in nonlinear dynamo systems. We also show that a completely different wave regime emerges if the magnetic field is not present. Finally we report the corresponding radial magnetic field variations observed at the surface of the shell in our simulations and discuss the detectability of these waves in the geomagnetic secular variation.

  5. A THEORETICAL STUDY OF THE BUILD-UP OF THE SUN’S POLAR MAGNETIC FIELD BY USING A 3D KINEMATIC DYNAMO MODEL

    Energy Technology Data Exchange (ETDEWEB)

    Hazra, Gopal; Choudhuri, Arnab Rai [Department of Physics, Indian Institute of Science, Bangalore, 560012 (India); Miesch, Mark S., E-mail: ghazra@physics.iisc.ernet.in, E-mail: arnab@physics.iisc.ernet.in, E-mail: miesch@ucar.edu [High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80301 (United States)

    2017-01-20

    We develop a three-dimensional kinematic self-sustaining model of the solar dynamo in which the poloidal field generation is from tilted bipolar sunspot pairs placed on the solar surface above regions of strong toroidal field by using the SpotMaker algorithm, and then the transport of this poloidal field to the tachocline is primarily caused by turbulent diffusion. We obtain a dipolar solution within a certain range of parameters. We use this model to study the build-up of the polar magnetic field and show that some insights obtained from surface flux transport models have to be revised. We present results obtained by putting a single bipolar sunspot pair in a hemisphere and two symmetrical sunspot pairs in two hemispheres. We find that the polar fields produced by them disappear due to the upward advection of poloidal flux at low latitudes, which emerges as oppositely signed radial flux and which is then advected poleward by the meridional flow. We also study the effect that a large sunspot pair, violating Hale’s polarity law, would have on the polar field. We find that there would be some effect—especially if the anti-Hale pair appears at high latitudes in the mid-phase of the cycle—though the effect is not very dramatic.

  6. The pDynamo Program for Molecular Simulations using Hybrid Quantum Chemical and Molecular Mechanical Potentials.

    Science.gov (United States)

    Field, Martin J

    2008-07-01

    The pDynamo program has been developed for the simulation of molecular systems using hybrid quantum chemical (QC) and molecular mechanical (MM) potentials. pDynamo is written in a mixture of the computer languages Python and C and is a successor to the previous version of Dynamo, now denoted fDynamo, that was written in Fortran 90 (J. Comput. Chem. 2000, 21, 1088). The current version of Dynamo has a similar range of functionality to the older one but extends it in some significant ways, including the addition of a density functional theory QC capability. This paper gives a general description of pDynamo and outlines some of the advantages and disadvantages that have been encountered in switching computer languages. Some technical aspects of the implementation of pDynamo's algorithms are also discussed and illustrated with the results of example calculations. pDynamo is available on the Web at the address http://www.pdynamo.org and is released under the CeCILL license which is equivalent to the GNU general public license but conforms to the principles of French law.

  7. A NEW SIMPLE DYNAMO MODEL FOR STELLAR ACTIVITY CYCLE

    Energy Technology Data Exchange (ETDEWEB)

    Yokoi, N.; Hamba, F. [Institute of Industrial Science, University of Tokyo, Tokyo 153-8505 (Japan); Schmitt, D. [Max-Planck Institut für Sonnensystemforschung, Göttingen D-37077 (Germany); Pipin, V., E-mail: nobyokoi@iis.u-tokyo.ac.jp [Institute of Solar–Terrestrial Physics, Russian Academy of Science, Irkutsk 664033 (Russian Federation)

    2016-06-20

    A new simple dynamo model for stellar activity cycle is proposed. By considering an inhomogeneous flow effect on turbulence, it is shown that turbulent cross helicity (velocity–magnetic-field correlation) enters the expression of turbulent electromotive force as the coupling coefficient for the mean absolute vorticity. This makes the present model different from the current α –Ω-type models in two main ways. First, in addition to the usual helicity ( α ) and turbulent magnetic diffusivity ( β ) effects, we consider the cross-helicity effect as a key ingredient of the dynamo process. Second, the spatiotemporal evolution of cross helicity is solved simultaneously with the mean magnetic fields. The basic scenario is as follows. In the presence of turbulent cross helicity, the toroidal field is induced by the toroidal rotation. Then, as in usual models, the α effect generates the poloidal field from the toroidal one. This induced poloidal field produces a turbulent cross helicity whose sign is opposite to the original one (negative production). With this cross helicity of the reversed sign, a reversal in field configuration starts. Eigenvalue analyses of the simplest possible model give a butterfly diagram, which confirms the above scenario and the equatorward migrations, the phase relationship between the cross helicity and magnetic fields. These results suggest that the oscillation of the turbulent cross helicity is a key for the activity cycle. The reversal of the cross helicity is not the result of the magnetic-field reversal, but the cause of the latter. This new model is expected to open up the possibility of the mean-field or turbulence closure dynamo approaches.

  8. Using Jupiter's gravitational field to probe the Jovian convective dynamo.

    Science.gov (United States)

    Kong, Dali; Zhang, Keke; Schubert, Gerald

    2016-03-23

    Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection.

  9. A homopolar disc dynamo experiment with liquid metal contacts

    OpenAIRE

    Avalos-Zúñiga, R. A.; Priede, J.; Bello-Morales, C. E.

    2017-01-01

    We present experimental results of a homopolar disc dynamo constructed at CICATA-Quer\\'etaro in Mexico. The device consists of a flat, multi-arm spiral coil which is placed above a fast-spinning metal disc and connected to the latter by sliding liquid-metal electrical contacts. Theoretically, self-excitation of the magnetic field is expected at the critical magnetic Reynolds number Rm~45, which corresponds to a critical rotation rate of about 10 Hz. We measured the magnetic field above the di...

  10. The magnetic universe geophysical and astrophysical dynamo theory

    CERN Document Server

    Rüdiger, Günther

    2004-01-01

    Magnetism is one of the most pervasive features of the Universe, with planets, stars and entire galaxies all having associated magnetic fields. All of these fields are generated by the motion of electrically conducting fluids, the so-called dynamo effect. The precise details of what drives the motion, and indeed what the fluid consists of, differ widely though. In this work the authors draw upon their expertise in geophysical and astrophysical MHD to explore some of these phenomena, and describe the similarities and differences between different magnetized objects. They also explain why magn

  11. Dramatically Enhanced Spin Dynamo with Plasmonic Diabolo Cavity.

    Science.gov (United States)

    Gou, Peng; Qian, Jie; Xi, Fuchun; Zou, Yuexin; Cao, Jun; Yu, Haochi; Zhao, Ziyi; Yang, Le; Xu, Jie; Wang, Hengliang; Zhang, Lijian; An, Zhenghua

    2017-07-13

    The applications of spin dynamos, which could potentially power complex nanoscopic devices, have so far been limited owing to their extremely low energy conversion efficiencies. Here, we present a unique plasmonic diabolo cavity (PDC) that dramatically improves the spin rectification signal (enhancement of more than three orders of magnitude) under microwave excitation; further, it enables an energy conversion efficiency of up to ~0.69 mV/mW, compared with ~0.27 μV/mW without a PDC. This remarkable improvement arises from the simultaneous enhancement of the microwave electric field (~13-fold) and the magnetic field (~195-fold), which cooperate in the spin precession process generates photovoltage (PV) efficiently under ferromagnetic resonance (FMR) conditions. The interplay of the microwave electromagnetic resonance and the ferromagnetic resonance originates from a hybridized mode based on the plasmonic resonance of the diabolo structure and Fabry-Perot-like modes in the PDC. Our work sheds light on how more efficient spin dynamo devices for practical applications could be realized and paves the way for future studies utilizing both artificial and natural magnetism for applications in many disciplines, such as for the design of future efficient wireless energy conversion devices, high frequent resonant spintronic devices, and magnonic metamaterials.

  12. A long-lived lunar dynamo driven by continuous mechanical stirring.

    Science.gov (United States)

    Dwyer, C A; Stevenson, D J; Nimmo, F

    2011-11-09

    Lunar rocks contain a record of an ancient magnetic field that seems to have persisted for more than 400 million years and which has been attributed to a lunar dynamo. Models of conventional dynamos driven by thermal or compositional convection have had difficulty reproducing the existence and apparently long duration of the lunar dynamo. Here we investigate an alternative mechanism of dynamo generation: continuous mechanical stirring arising from the differential motion, due to Earth-driven precession of the lunar spin axis, between the solid silicate mantle and the liquid core beneath. We show that the fluid motions and the power required to drive a dynamo operating continuously for more than one billion years and generating a magnetic field that had an intensity of more than one microtesla 4.2 billion years ago are readily obtained by mechanical stirring. The magnetic field is predicted to decrease with time and to shut off naturally when the Moon recedes far enough from Earth that the dissipated power is insufficient to drive a dynamo; in our nominal model, this occurred at about 48 Earth radii (2.7 billion years ago). Thus, lunar palaeomagnetic measurements may be able to constrain the poorly known early orbital evolution of the Moon. This mechanism may also be applicable to dynamos in other bodies, such as large asteroids.

  13. Can Superflares Occur on the Sun? A View from Dynamo Theory

    Science.gov (United States)

    Katsova, M. M.; Kitchatinov, L. L.; Livshits, M. A.; Moss, D. L.; Sokoloff, D. D.; Usoskin, I. G.

    2018-01-01

    Recent data from the Kepler mission has revealed the occurrence of superflares in Sun-like stars which exceed by far any observed solar flares in released energy. Radionuclide data do not provide evidence for occurrence of superflares on the Sun over the past eleven millennia. Stellar data for a subgroup of superflaring Kepler stars are analysed in an attempt to find possible progenitors of their abnormal magnetic activity. A natural idea is that the dynamo mechanism in superflaring stars differs in some respect from that in the Sun. We search for a difference in the dynamo-related parameters between superflaring stars and the Sun to suggest a dynamo mechanism as close as possible to the conventional solar/stellar dynamo but capable of providing much higher magnetic energy. Dynamo based on joint action of differential rotation and mirror asymmetric motions can in principle result in excitation of two types of magnetic fields. First of all, it is well-known in solar physics dynamo waves. The point is that another magnetic configuration with initial growth and further stabilisation can also be excited. For comparable conditions, magnetic field of second configuration is much stronger than that of the first one just because dynamo does not spend its energy for periodic magnetic field inversions but uses it for magnetic field growth. We analysed available data from the Kepler mission concerning the superflaring stars in order to find tracers of anomalous magnetic activity. As suggested in a recent paper [1], we find that anti-solar differential rotation or anti-solar sign of the mirror-asymmetry of stellar convection can provide the desired strong magnetic field in dynamo models. We confirm this concept by numerical models of stellar dynamos with corresponding governing parameters. We conclude that the proposed mechanism can plausibly explain the superflaring events at least for some cool stars, including binaries, subgiants and, possibly, low-mass stars and young

  14. IS THE SMALL-SCALE MAGNETIC FIELD CORRELATED WITH THE DYNAMO CYCLE?

    Energy Technology Data Exchange (ETDEWEB)

    Karak, Bidya Binay; Brandenburg, Axel, E-mail: bbkarak@nordita.org [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)

    2016-01-01

    The small-scale magnetic field is ubiquitous at the solar surface—even at high latitudes. From observations we know that this field is uncorrelated (or perhaps even weakly anticorrelated) with the global sunspot cycle. Our aim is to explore the origin, and particularly the cycle dependence, of such a phenomenon using three-dimensional dynamo simulations. We adopt a simple model of a turbulent dynamo in a shearing box driven by helically forced turbulence. Depending on the dynamo parameters, large-scale (global) and small-scale (local) dynamos can be excited independently in this model. Based on simulations in different parameter regimes, we find that, when only the large-scale dynamo is operating in the system, the small-scale magnetic field generated through shredding and tangling of the large-scale magnetic field is positively correlated with the global magnetic cycle. However, when both dynamos are operating, the small-scale field is produced from both the small-scale dynamo and the tangling of the large-scale field. In this situation, when the large-scale field is weaker than the equipartition value of the turbulence, the small-scale field is almost uncorrelated with the large-scale magnetic cycle. On the other hand, when the large-scale field is stronger than the equipartition value, we observe an anticorrelation between the small-scale field and the large-scale magnetic cycle. This anticorrelation can be interpreted as a suppression of the small-scale dynamo. Based on our studies we conclude that the observed small-scale magnetic field in the Sun is generated by the combined mechanisms of a small-scale dynamo and tangling of the large-scale field.

  15. Small-Scale Magnetic Helicity and Nonlinear Stabilization of the Dynamo

    Science.gov (United States)

    Sokoloff, D. D.; Yushkov, E. V.; Lukin, A. S.

    2017-12-01

    According to present-day ideas, nonlinear saturation of the astrophysical dynamo and, in particular, the solar dynamo, are based on the consideration of the magnetic helicity balance, to which the helicities of the large-scale magnetic field and small-scale field related to it contributed. We show that, in a mirrorasymmetric medium, the small-scale magnetic field generated by the small-scale dynamo also has a nonzero magnetic helicity, which also should be taken into account in the magnetic helicity balance.

  16. A Gailitis-type dynamo in the magnetic CP stars?

    International Nuclear Information System (INIS)

    Moss, D.

    1990-01-01

    In the Gailitis dynamo as originally formulated, axisymmetric laminar field motions confined to two thin, coaxial tori, symmetrically arranged with respect to an 'equatorial' plane, excite a large-scale non-axisymmetric magnetic field. The simplest mode is of the same topology as a dipole with axis perpendicular to the axis of symmetry of the motions. The topology of the fluid motions is the same as that of the rotationally driven meridional circulation, modified by magnetic or dissipative terms, that is believed to be present in the radiative envelopes of middle main-sequence stars. This paper investigates the possibility that a Gailitis-type mechanism, driven by the meridional circulation, might excite large-scale magnetic fields of 'perpendicular dipole' type in the magnetic CP stars. (author)

  17. Driving of Accretion Disk Variability by the Disk Dynamo

    Science.gov (United States)

    Hogg, J. Drew; Reynolds, Christopher S.

    2016-04-01

    Variability is a ubiquitous feature of emission from accreting objects, but many questions remain as to how the variability is driven and how it relates to the underlying accretion physics. In this talk I will discuss recent results from a long, semi-global MHD simulation of a thin accretion disk around a black hole used to perform a detailed study of the fluctuations in the internal disk stress and the influence these fluctuations have on the accretion flow. In the simulation, low frequency fluctuations of the effective α-parameter in the disk are linked to oscillations of the disk dynamo. These fluctuations in the effective alpha parameter drive “propagating fluctuations” in mass accretion rate through the disk that qualitatively resemble the variability from astrophysical black hole systems. The mass accretion rate has several of the ubiquitous phenomenological properties of black hole variability, including log-normal flux distributions, RMS-flux relationships, and radial coherence.

  18. Magnetism, dynamo action and the solar-stellar connection

    Science.gov (United States)

    Brun, Allan Sacha; Browning, Matthew K.

    2017-09-01

    The Sun and other stars are magnetic: magnetism pervades their interiors and affects their evolution in a variety of ways. In the Sun, both the fields themselves and their influence on other phenomena can be uncovered in exquisite detail, but these observations sample only a moment in a single star's life. By turning to observations of other stars, and to theory and simulation, we may infer other aspects of the magnetism—e.g., its dependence on stellar age, mass, or rotation rate—that would be invisible from close study of the Sun alone. Here, we review observations and theory of magnetism in the Sun and other stars, with a partial focus on the "Solar-stellar connection": i.e., ways in which studies of other stars have influenced our understanding of the Sun and vice versa. We briefly review techniques by which magnetic fields can be measured (or their presence otherwise inferred) in stars, and then highlight some key observational findings uncovered by such measurements, focusing (in many cases) on those that offer particularly direct constraints on theories of how the fields are built and maintained. We turn then to a discussion of how the fields arise in different objects: first, we summarize some essential elements of convection and dynamo theory, including a very brief discussion of mean-field theory and related concepts. Next we turn to simulations of convection and magnetism in stellar interiors, highlighting both some peculiarities of field generation in different types of stars and some unifying physical processes that likely influence dynamo action in general. We conclude with a brief summary of what we have learned, and a sampling of issues that remain uncertain or unsolved.

  19. An efficient method for computing the eigenfunctions of the dynamo equation

    Science.gov (United States)

    Schrinner, M.; Schmitt, D.; Jiang, J.; Hoyng, P.

    2010-09-01

    Aims: We present an elegant method of determining the eigensolutions of the induction and dynamo equations in a fluid embedded in a vacuum. Methods: The magnetic field is expanded in a complete set of functions. The new method is based on the biorthogonality of the adjoint electric current and the vector potential with an inner product defined by a volume integral over the fluid domain. The advantage of this method is that the velocity and the dynamo coefficients of the induction and the dynamo equation do not have to be differentiated and thus even numerically determined tabulated values of the coefficients produce reasonable results. Results: We provide test calculations and compare with published results obtained by the classical treatment based on the biorthogonality of the magnetic field and its adjoint. We especially consider dynamos with mean-field coefficients determined from direct numerical simulations of the geodynamo and compare with initial value calculations and the full MHD simulations.

  20. Towards the geophysical regime in numerical dynamo models: studies of rapidly-rotating convection driven dynamos with low Pm and constant heat flux boundary conditions

    DEFF Research Database (Denmark)

    Sheyko, A.A.; Finlay, Chris; Marti, P.

    We present a set of numerical dynamo models with the convection strength varied by a factor of 30 and the ratio of magnetic to viscous diffusivities by a factor of 20 at rapid rotation rates (E =nu/(2 Omega d^2 ) = 10-6 and 10-7 ) using a heat flux outer BC. This regime has been little explored...... on the structure of the dynamos and how this changes in relation to the selection of control parameters, a comparison with the proposed rotating convection and dynamo scaling laws, energy spectra of steady solutions and inner core rotation rates. Magnetic field on the CMB. E=2.959*10-7, Ra=6591.0, Pm=0.05, Pr=1....

  1. Solar Cycle Variability and Grand Minima Induced by Joy's Law Scatter

    Science.gov (United States)

    Karak, Bidya Binay; Miesch, Mark S.

    2017-08-01

    The strength of the solar cycle varies from one cycle to another in an irregular manner and the extreme example of this irregularity is the Maunder minimum when Sun produced only a few spots for several years. We explore the cause of these variabilities using a 3D Babcock--Leighton dynamo. In this model, based on the toroidal flux at the base of the convection zone, bipolar magnetic regions (BMRs) are produced with flux, tilt angle, and time of emergence all obtain from their observed distributions. The dynamo growth is limited by a tilt quenching.The randomnesses in the BMR emergences make the poloidal field unequal and eventually cause an unequal solar cycle. When observed fluctuations of BMR tilts around Joy's law, i.e., a standard deviation of 15 degrees, are considered, our model produces a variation in the solar cycle comparable to the observed solar cycle variability. Tilt scatter also causes occasional Maunder-like grand minima, although the observed scatter does not reproduce correct statistics of grand minima. However, when we double the tilt scatter, we find grand minima consistent with observations. Importantly, our dynamo model can operate even during grand minima with only a few BMRs, without requiring any additional alpha effect.

  2. Latitudinal migration of sunspots based on the ESAI database

    Science.gov (United States)

    Zhang, Juan; Li, Fu-Yu; Feng, Wen

    2018-01-01

    The latitudinal migration of sunspots toward the equator, which implies there is propagation of the toroidal magnetic flux wave at the base of the solar convection zone, is one of the crucial observational bases for the solar dynamo to generate a magnetic field by shearing of the pre-existing poloidal magnetic field through differential rotation. The Extended time series of Solar Activity Indices (ESAI) elongated the Greenwich observation record of sunspots by several decades in the past. In this study, ESAI’s yearly mean latitude of sunspots in the northern and southern hemispheres during the years 1854 to 1985 is utilized to statistically test whether hemispherical latitudinal migration of sunspots in a solar cycle is linear or nonlinear. It is found that a quadratic function is statistically significantly better at describing hemispherical latitudinal migration of sunspots in a solar cycle than a linear function. In addition, the latitude migration velocity of sunspots in a solar cycle decreases as the cycle progresses, providing a particular constraint for solar dynamo models. Indeed, the butterfly wing pattern with a faster latitudinal migration rate should present stronger solar activity with a shorter cycle period, and it is located at higher latitudinal position, giving evidence to support the Babcock-Leighton dynamo mechanism.

  3. Simulations of global-scale dynamo action in the Sun and other stars

    Science.gov (United States)

    Brown, Benjamin

    2011-04-01

    Our Sun is a magnetic star, and its eleven-year cycles of magnetic activity profoundly affect our modern technological society. The magnetic fields we see at the solar surface are built by dynamo processes in the Sun's sub-surface convection zone. There, global-scale plasma motions couple with rotation to build and rebuild the global-scale magnetic fields and drive cycles of magnetic activity, though the exact processes at work in solar and stellar dynamos remain elusive. The Sun is not the only magnetic star: indeed magnetism is a ubiquitous feature of stars that have convection zones near their surfaces. Observations of younger suns indicate that they rotate quite rapidly, have strong magnetic fields at their surfaces, and show signs of cyclic activity. Here we explore recent 3-D MHD simulations of the solar dynamo and of stellar dynamos in younger, more rapidly rotating solar-type stars. These are conducted with the anelastic spherical harmonic (ASH) code on modern supercomputers. These simulations of global-scale convection and dynamo action produce strikingly organized magnetic structures in the bulk of their convection zones. Wreaths of magnetic field fill the convection zone and can undergo regular cycles of polarity reversal. Indeed, we find that cyclic behavior is a common feature throughout the parameter space we have explored. Simulations like these are providing new views on the phenomena of solar and stellar dynamo action.

  4. INTERIOR STRUCTURE OF WATER PLANETS: IMPLICATIONS FOR THEIR DYNAMO SOURCE REGIONS

    International Nuclear Information System (INIS)

    Yunsheng Tian, Bob; Stanley, Sabine

    2013-01-01

    Recent discoveries of water-rich, sub-Neptunian- to Neptunian-massed exoplanets with short-period orbits present a new parameter space for the study of exoplanetary dynamos. We explore the geometry of the dynamo source region within this parameter space using 1D interior structure models. We model planets with four chemically distinct layers that consist of (1) an iron core, (2) a silicate layer, (3) an H 2 O layer, and (4) an H/He envelope. By varying the total planetary mass in the range of 1-19 M ⊕ , the mass fraction of the H/He envelope between 0.1% and 5.1%, and the equilibrium temperature between 100 K and 1000 K, a survey of the parameter space for potential dynamo source region geometries is conducted. We find that due to the nature of the phase diagram of water at pressure and temperature conditions of planetary interiors, two different dynamo source region geometries are obtainable. Specifically, we find that smaller planets, and planets with thicker H/He envelopes, are likely to be in the regime of a thick-shelled dynamo. Massive planets, and planets with thin H/He envelopes, are likely to be in the regime of a thin-shelled dynamo. Also, small variations of these parameters can produce large interior structure differences. This implies the potential to constrain these parameters based on observations of a planet's magnetic field signature.

  5. Solar-type dynamo behaviour in fully convective stars without a tachocline.

    Science.gov (United States)

    Wright, Nicholas J; Drake, Jeremy J

    2016-07-28

    In solar-type stars (with radiative cores and convective envelopes like our Sun), the magnetic field powers star spots, flares and other solar phenomena, as well as chromospheric and coronal emission at ultraviolet to X-ray wavelengths. The dynamo responsible for generating the field depends on the shearing of internal magnetic fields by differential rotation. The shearing has long been thought to take place in a boundary layer known as the tachocline between the radiative core and the convective envelope. Fully convective stars do not have a tachocline and their dynamo mechanism is expected to be very different, although its exact form and physical dependencies are not known. Here we report observations of four fully convective stars whose X-ray emission correlates with their rotation periods in the same way as in solar-type stars. As the X-ray activity-rotation relationship is a well-established proxy for the behaviour of the magnetic dynamo, these results imply that fully convective stars also operate a solar-type dynamo. The lack of a tachocline in fully convective stars therefore suggests that this is not a critical ingredient in the solar dynamo and supports models in which the dynamo originates throughout the convection zone.

  6. Ram pressure effects in the galactic plane and galactic dynamos in the no-z approximation

    Science.gov (United States)

    Moss, D.; Sokoloff, D.; Beck, R.

    2012-08-01

    Context. The magnetic field of galaxies is believed to be produced by internal dynamo action, but can be affected by motion of the galaxy through the surrounding medium. Observations of polarized radio emission of galaxies located in galaxy clusters have revealed noticeable features of large-scale magnetic configurations, including displacements of the magnetic structures from the optical images and tails, which are possible imprints of ram pressure effects arising from motion of the galaxies through the intracluster medium. Aims: We present a quantitative dynamo model, which attempts to describe the above effects. In contrast, to the traditional problem of a wind affecting a body with a prescribed magnetic field, we investigate how a non-magnetized wind flow affects a magnetic field that is being self-excited by galactic dynamo action. Methods: To isolate the leading physical effects, we exploit a simple dynamo model that can describe relevant effects. In particular, we use what is known as the "no-z" approximation for the mean-field dynamo equations. Results: In a suitable parametric range we obtain displacements of the large-scale magnetic field, as well as magnetic tails. However, the specific details of their locations are quite counterintuitive. The direction of displacement is perpendicular to, rather than parallel to, the wind direction. The point at which the tail emerges from the galaxy depends on details of the model. The tail is eventually directed downstream. In the simplest case the magnetic tail begins in the region where the wind decreases the total gas velocity. Any wind that penetrates the galaxy modifies the intrinsic dynamo action. These features are different from those found in ram-pressure models. Conclusions: Any determination of galactic motion through the cluster medium from observational data needs to take the effects of dynamo action into account.

  7. Dynamo saturation in direct simulations of the multi-phase turbulent interstellar medium

    Science.gov (United States)

    Bendre, A.; Gressel, O.; Elstner, D.

    2015-12-01

    The ordered magnetic field observed via polarised synchrotron emission in nearby disc galaxies can be explained by a mean-field dynamo operating in the diffuse interstellar medium (ISM). Additionally, vertical-flux initial conditions are potentially able to influence this dynamo via the occurrence of the magnetorotational instability (MRI). We aim to study the influence of various initial field configurations on the saturated state of the mean-field dynamo. This is motivated by the observation that different saturation behaviour was previously obtained for different supernova rates. We perform direct numerical simulations (DNS) of three-dimensional local boxes of the vertically stratified, turbulent interstellar medium, employing shearing-periodic boundary conditions horizontally. Unlike in our previous work, we also impose a vertical seed magnetic field. We run the simulations until the growth of the magnetic energy becomes negligible. We furthermore perform simulations of equivalent 1D dynamo models, with an algebraic quenching mechanism for the dynamo coefficients. We compare the saturation of the magnetic field in the DNS with the algebraic quenching of a mean-field dynamo. The final magnetic field strength found in the direct simulation is in excellent agreement with a quenched αΩ dynamo. For supernova rates representative of the Milky Way, field losses via a Galactic wind are likely responsible for saturation. We conclude that the relative strength of the turbulent and regular magnetic fields in spiral galaxies may depend on the galaxy's star formation rate. We propose that a mean field approach with algebraic quenching may serve as a simple sub-grid scale model for galaxy evolution simulations including a prescribed feedback from magnetic fields.

  8. Resolved magnetic dynamo action in the simulated intracluster medium

    Science.gov (United States)

    Vazza, F.; Brunetti, G.; Brüggen, M.; Bonafede, A.

    2018-02-01

    Faraday rotation and synchrotron emission from extragalactic radio sources give evidence for the presence of magnetic fields extending over ˜ Mpc scales. However, the origin of these fields remains elusive. With new high-resolution grid simulations, we studied the growth of magnetic fields in a massive galaxy cluster that in several aspects is similar to the Coma cluster. We investigated models in which magnetic fields originate from primordial seed fields with comoving strengths of 0.1 nG at redshift z = 30. The simulations show evidence of significant magnetic field amplification. At the best spatial resolution (3.95 kpc), we are able to resolve the scale where magnetic tension balances the bending of magnetic lines by turbulence. This allows us to observe the final growth stage of the small-scale dynamo. To our knowledge, this is the first time that this is seen in cosmological simulations of the intracluster medium. Our mock observations of Faraday rotation provide a good match to observations of the Coma cluster. However, the distribution of magnetic fields shows strong departures from a simple Maxwellian distribution, suggesting that the three-dimensional structure of magnetic fields in real clusters may be significantly different than what is usually assumed when inferring magnetic field values from rotation measure observations.

  9. Magnetorotational Turbulence and Dynamo in a Collisionless Plasma

    Science.gov (United States)

    Kunz, Matthew

    2017-10-01

    Low-luminosity black-hole accretion flows are collisionless. A kinetic approach is thus necessary to understand the transport of heat and angular momentum, the acceleration of particles, and the growth and structure of the magnetic field in these systems. I present results from the first 6D kinetic simulation of magnetorotational turbulence and dynamo, which was performed using the hybrid-kinetic particle-in-cell code Pegasus. Special attention will be paid to the transport of angular momentum by the anisotropic-pressure stress, as well as to the ion-Larmor-scale kinetic instabilities (firehose, mirror, ion-cyclotron) that regulate it. The latter endow the plasma with an effective viscosity that is biased with respect to the magnetic-field direction and spatiotemporally variable. Energy spectra suggest an Alfvén-wave cascade at large scales and a kinetic-Alfvén-wave cascade at small scales, with strong small-scale density fluctuations and weak nonaxisymmetric density waves. Ions undergo nonthermal particle acceleration, their distribution accurately described by a κ distribution. Dedicated nonlinear studies of firehose and mirror instabilities in a shearing plasma will also be presented as a complement to the study of the magnetorotational instability. The profits, perils, and price of using a kinetic approach are discussed.

  10. Nonlinear dynamo mode dynamics in reversed field pinches

    International Nuclear Information System (INIS)

    Fitzpatrick, Richard; Yu, Edmund P.

    2000-01-01

    The nonlinear dynamics of a typical dynamo mode in a reversed field pinch, under the action of the braking torque due to eddy currents excited in a resistive vacuum vessel and the locking torque due to a resonant error-field, is investigated. A simple set of phase evolution equations for the mode is derived: these equations represent an important extension of the well-known equations of Zohm et al. [Europhys. Lett. 11, 745 (1990)] which incorporate a self-consistent calculation of the radial extent of the region of the plasma which corotates with the mode; the width of this region being determined by plasma viscosity. Using these newly developed equations, a comprehensive theory of the influence of a resistive vacuum vessel on error-field locking and unlocking thresholds is developed. Under certain circumstances, a resistive vacuum vessel is found to strongly catalyze locked mode formation. Hopefully, the results obtained in this paper will allow experimentalists to achieve a full understanding of why the so-called ''slinky mode'' locks in some reversed field pinch devices, but not in others. The locking of the slinky mode is currently an issue of outstanding importance in reversed field pinch research. (c) 2000 American Institute of Physics

  11. Nonlinear dynamo mode dynamics in reversed field pinches

    Science.gov (United States)

    Fitzpatrick, Richard; Yu, Edmund P.

    2000-09-01

    The nonlinear dynamics of a typical dynamo mode in a reversed field pinch, under the action of the braking torque due to eddy currents excited in a resistive vacuum vessel and the locking torque due to a resonant error-field, is investigated. A simple set of phase evolution equations for the mode is derived: these equations represent an important extension of the well-known equations of Zohm et al. [Europhys. Lett. 11, 745 (1990)] which incorporate a self-consistent calculation of the radial extent of the region of the plasma which corotates with the mode; the width of this region being determined by plasma viscosity. Using these newly developed equations, a comprehensive theory of the influence of a resistive vacuum vessel on error-field locking and unlocking thresholds is developed. Under certain circumstances, a resistive vacuum vessel is found to strongly catalyze locked mode formation. Hopefully, the results obtained in this paper will allow experimentalists to achieve a full understanding of why the so-called "slinky mode" locks in some reversed field pinch devices, but not in others. The locking of the slinky mode is currently an issue of outstanding importance in reversed field pinch research.

  12. Nonlinear dynamo mode dynamics in reversed field pinches

    Energy Technology Data Exchange (ETDEWEB)

    Fitzpatrick, Richard [Institute for Fusion Studies, Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States); Yu, Edmund P. [Institute for Fusion Studies, Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States)

    2000-09-01

    The nonlinear dynamics of a typical dynamo mode in a reversed field pinch, under the action of the braking torque due to eddy currents excited in a resistive vacuum vessel and the locking torque due to a resonant error-field, is investigated. A simple set of phase evolution equations for the mode is derived: these equations represent an important extension of the well-known equations of Zohm et al. [Europhys. Lett. 11, 745 (1990)] which incorporate a self-consistent calculation of the radial extent of the region of the plasma which corotates with the mode; the width of this region being determined by plasma viscosity. Using these newly developed equations, a comprehensive theory of the influence of a resistive vacuum vessel on error-field locking and unlocking thresholds is developed. Under certain circumstances, a resistive vacuum vessel is found to strongly catalyze locked mode formation. Hopefully, the results obtained in this paper will allow experimentalists to achieve a full understanding of why the so-called ''slinky mode'' locks in some reversed field pinch devices, but not in others. The locking of the slinky mode is currently an issue of outstanding importance in reversed field pinch research. (c) 2000 American Institute of Physics.

  13. NONLINEAR DYNAMO IN A ROTATING ELECTRICALLY CONDUCTING FLUID

    Directory of Open Access Journals (Sweden)

    M. I. Kopp

    2017-05-01

    Full Text Available We found a new large-scale instability, which arises in the rotating conductive fluid with small-scale turbulence. Turbulence is generated by small-scale external force with a low Reynolds number. The theory is built simply by the method of multiscale asymptotic expansions. Nonlinear equations for vortex and magnetic perturbations obtained in the third order for small Reynolds number. It is shown that the combined effects of the Coriolis force and the small external forces in a rotating conducting fluid possible large-scale instability. The large-scale increments of the instability, correspond to generation as the vortex and magnetic disturbances. This type of instability is classified as hydrodynamic and MHD alpha-effect. We studied the stationary regimes of nonlinear equations of magneto-vortex dynamo. In the limit of weakly conducting fluid found stationary solutions in the form of helical kinks. In the limit of high conductivity fluid was obtained stationary solutions in the form of nonlinear periodic waves and kinks.

  14. Paleomagnetism of the moon and the problem of planetary dynamo fields

    International Nuclear Information System (INIS)

    Dolginov, S.S.

    1986-01-01

    It is shown within the scope of the precessional dynamo model that satellites of the moon, which, as has been proposed, existed in equatorial orbits 4-3.8 Gyr ago and whose fall to the surface relates to the formation of the maria (14) and a change in position of the axis of rotation of the moon (15), could have determined the generation of a strong dynamo field of 10 -4 T in which the ancient lunar rocks acquired thermoremanent magnetization. The strong dynamo field attenuated with the fall of the satellites to the surface of the moon, but a moderate dynamo field could have been generated with the precession of the moon under the perturbing effect of the gravitational field of the earth. This field also attenuated with the recession of the moon from the earth and its acquisition of synchronous rotation. If the distribution of the paleofields over the entire surface of the moon, which one can hope will be established, confirms the assumption of uniform magnetization of the lunar crest by a field of internal origin, then the planetary precessional dynamo model gets additional proof of the established cause-effect relation: If the source inducing the precessional motion disappears, then the magnetic field disappears

  15. How supercritical are stellar dynamos, or why do old main-sequence dwarfs not obey gyrochronology?

    Science.gov (United States)

    Kitchatinov, Leonid; Nepomnyashchikh, Alexander

    2017-09-01

    Asteroseismological determinations of stellar ages have shown that old main-sequence dwarfs do not obey gyrochronology. Their rotation is slow compared to young stars but faster than what gyrochronology predicts. This can be explained by the presence of a maximum rotation period beyond which the large-scale dynamo switches off and stops providing global magnetic fields necessary for stellar spin-down. Assuming this explanation, the excess of stellar dynamo parameters over their marginal values can be estimated for the given spectral type and rotation rate. The estimation gives the dynamo number for the Sun about 10 per cent above its critical value. The corresponding dynamo model provides - though with some further tuning - reasonable results for the Sun. Following the same approach, the differential rotation and marginal dynamo modes are computed for stars between 0.7 and 1.2 solar masses. With an increasing stellar mass, the differential rotation and the ratio of toroidal-to-poloidal field are predicted to increase while the field topology changes from dipolar to mixed quadrupolar-dipolar parity.

  16. Multiscale Variability of the Atmospheric Boundary Layer during DYNAMO

    Science.gov (United States)

    Johnson, R. H.; Ciesielski, P. E.

    2017-12-01

    Properties of the atmospheric boundary layer (ABL) over the central Indian Ocean are investigated using sounding data obtained during the Dynamics of the MJO (DYNAMO) field campaign in 2011-12. Observations from Gan Island on Addu Atoll, the R/V Revelle, and Male' in the Maldives are used to determine the frequency of well-mixed layers, as well as their mean thermodynamic and wind profiles. Well-mixed boundary layers or mixed layers were observed 68% of the time from the three sites, ranging from 100-m depth in recovering convective downdraft wakes to 925 m in undisturbed conditions, with a mean depth of 508 m. At Revelle, the site most representative of the open ocean, the ABL displayed a distinct signal of modulation by the October and November MJOs, with mixed layer depths gradually increasing through the suppressed phases as the sea surface temperature (SST) increased leading up to the active phases, followed by frequent ABL stabilization and shallow mixed layers in recovering wakes. A distinct diurnal cycle of mixed layer depths and properties was observed during the MJO suppressed phases in response to a diurnal cycle of the SST under the mostly light-wind, clear-sky conditions. The daytime growth of the mixed layer contributed to an afternoon maximum in cumulus cloud development and rainfall during the suppressed periods by allowing more boundary layer thermals to reach their condensation levels. The variability of the ABL on time scales ranging from convective to diurnal to monthly poses significant challenges for numerical simulations of the MJO and the tropical circulation in general.

  17. Finite-correlation-time effects in the kinematic dynamo problem

    International Nuclear Information System (INIS)

    Schekochihin, Alexander A.; Kulsrud, Russell M.

    2001-01-01

    Most of the theoretical results on the kinematic amplification of small-scale magnetic fluctuations by turbulence have been confined to the model of white-noise-like (δ-correlated in time) advecting turbulent velocity field. In this work, the statistics of the passive magnetic field in the diffusion-free regime are considered for the case when the advecting flow is finite-time correlated. A new method is developed that allows one to systematically construct the correlation-time expansion for statistical characteristics of the field such as its probability density function or the complete set of its moments. The expansion is valid provided the velocity correlation time is smaller than the characteristic growth time of the magnetic fluctuations. This expansion is carried out up to first order in the general case of a d-dimensional arbitrarily compressible advecting flow. The growth rates for all moments of the magnetic-field strength are derived. The effect of the first-order corrections due to the finite correlation time is to reduce these growth rates. It is shown that introducing a finite correlation time leads to the loss of the small-scale statistical universality, which was present in the limit of the δ-correlated velocity field. Namely, the shape of the velocity time-correlation profile and the large-scale spatial structure of the flow become important. The latter is a new effect, that implies, in particular, that the approximation of a locally-linear shear flow does not fully capture the effect of nonvanishing correlation time. Physical applications of this theory include the small-scale kinematic dynamo in the interstellar medium and protogalactic plasmas

  18. Marshall N. Rosenbluth Outstanding Doctoral Thesis Award: Magnetorotational turbulence and dynamo

    Science.gov (United States)

    Squire, Jonathan

    2017-10-01

    Accretion disks are ubiquitous in astrophysics and power some of the most luminous sources in the universe. In many disks, the transport of angular momentum, and thus the mass accretion itself, is thought to be caused by the magnetorotational instability (MRI). As the MRI saturates into strong turbulence, it also generates ordered magnetic fields, acting as a magnetic dynamo powered by the background shear flow. However, despite its importance for astrophysical accretion processes, basic aspects of MRI turbulence-including its saturation amplitude-remain poorly understood. In this talk, I will outline progress towards improving this situation, focusing in particular on the nonlinear shear dynamo and how this controls the turbulence. I will discuss how novel statistical simulation methods can be used to better understand this shear dynamo, in particular the distinct mechanisms that may play a role in MRI turbulence and how these depend on important physical parameters.

  19. Sustainment dynamo reexamined: nonlocal electrical conductivity of plasma in a stochastic magnetic field

    International Nuclear Information System (INIS)

    Jacobson, A.R.; Moses, R.W.

    1984-01-01

    The plasma dynamo is both an intriguing and a practical concept. The intrigue derives from attempting to explain naturally occurring and man-made plasmas whose strong field-aligned currents j/sub parallel/ apparently disobey the most naive Ohm's law j/sub parallel/ = sigma/sub parallel/E/sub parallel/. The practical importance derives from the dynamo's role both in formation and in sustainment of reversed-field pinch (RFP) and Spheromak fusion plasmas. We will examine certain features of the documented quasi-steady discharges on ZT-40M, and RFP in apparent need of a sustainment dynamo. We will show that the tail electrons (which carry j/sub parallel/) are probably wandering (along stochastic B Vector-field lines) over much of the minor radius in one mean-free-path

  20. Energy transfers and magnetic energy growth in small-scale dynamo

    KAUST Repository

    Kumar, Rohit Raj

    2013-12-01

    In this letter we investigate the dynamics of magnetic energy growth in small-scale dynamo by studying energy transfers, mainly energy fluxes and shell-to-shell energy transfers. We perform dynamo simulations for the magnetic Prandtl number Pm = 20 on 10243 grid using the pseudospectral method. We demonstrate that the magnetic energy growth is caused by nonlocal energy transfers from the large-scale or forcing-scale velocity field to small-scale magnetic field. The peak of these energy transfers moves towards lower wave numbers as dynamo evolves, which is the reason why the integral scale of the magnetic field increases with time. The energy transfers U2U (velocity to velocity) and B2B (magnetic to magnetic) are forward and local. Copyright © EPLA, 2013.

  1. Modelling the solar magnetism: from its internal origin to its manifestations at the surface

    International Nuclear Information System (INIS)

    Jouve, Laurene

    2008-01-01

    This thesis is part of the general study of dynamical processes involved in stars such as convection, rotation or magnetic fields and of their nonlinear interactions. The results of numerical simulations using the 2D finite element code STELEM and the pseudo-spectral 3D code ASH are presented. The first part of this work focuses on the global modeling of the solar dynamo. Through 2D simulations using mean-field theory, I studied the influence of a complex profile of meridional flow in Babcock-Leighton models. We show that there may be doubts about the ability of such models to reproduce the main characteristics of the solar cycle. In order to better constrain the effects of solar variability on the Earth climate, we present a first application in solar physics of sophisticated prediction methods which are used in meteorology. I also computed the first 3D MHD simulations in spherical geometry of a key step in the solar dynamo: the nonlinear evolution of magnetic structures from the base of the convection zone up to the surface where they produce active regions. Weak fields are likely to be modulated by convective motions, thus creating favored longitudes of emergence. If these structures are sufficiently arched, the orientation of bipolar spots corresponds to Joy's law. The introduction of an atmosphere in these models is a step towards a 3D global vision of our Sun. (author) [fr

  2. Non-linear dynamo waves in an incompressible medium when the turbulence dissipative coefficients depend on temperature

    Directory of Open Access Journals (Sweden)

    A. D. Pataraya

    1997-01-01

    Full Text Available Non-linear α-ω; dynamo waves existing in an incompressible medium with the turbulence dissipative coefficients depending on temperature are studied in this paper. We investigate of α-ω solar non-linear dynamo waves when only the first harmonics of magnetic induction components are included. If we ignore the second harmonics in the non-linear equation, the turbulent magnetic diffusion coefficient increases together with the temperature, the coefficient of turbulent viscosity decreases, and for an interval of time the value of dynamo number is greater than 1. In these conditions a stationary solution of the non-linear equation for the dynamo wave's amplitude exists; meaning that the magnetic field is sufficiently excited. The amplitude of the dynamo waves oscillates and becomes stationary. Using these results we can explain the existence of Maunder's minimum.

  3. DYNAMO-HIA--a Dynamic Modeling tool for generic Health Impact Assessments.

    Directory of Open Access Journals (Sweden)

    Stefan K Lhachimi

    Full Text Available BACKGROUND: Currently, no standard tool is publicly available that allows researchers or policy-makers to quantify the impact of policies using epidemiological evidence within the causal framework of Health Impact Assessment (HIA. A standard tool should comply with three technical criteria (real-life population, dynamic projection, explicit risk-factor states and three usability criteria (modest data requirements, rich model output, generally accessible to be useful in the applied setting of HIA. With DYNAMO-HIA (Dynamic Modeling for Health Impact Assessment, we introduce such a generic software tool specifically designed to facilitate quantification in the assessment of the health impacts of policies. METHODS AND RESULTS: DYNAMO-HIA quantifies the impact of user-specified risk-factor changes on multiple diseases and in turn on overall population health, comparing one reference scenario with one or more intervention scenarios. The Markov-based modeling approach allows for explicit risk-factor states and simulation of a real-life population. A built-in parameter estimation module ensures that only standard population-level epidemiological evidence is required, i.e. data on incidence, prevalence, relative risks, and mortality. DYNAMO-HIA provides a rich output of summary measures--e.g. life expectancy and disease-free life expectancy--and detailed data--e.g. prevalences and mortality/survival rates--by age, sex, and risk-factor status over time. DYNAMO-HIA is controlled via a graphical user interface and is publicly available from the internet, ensuring general accessibility. We illustrate the use of DYNAMO-HIA with two example applications: a policy causing an overall increase in alcohol consumption and quantifying the disease-burden of smoking. CONCLUSION: By combining modest data needs with general accessibility and user friendliness within the causal framework of HIA, DYNAMO-HIA is a potential standard tool for health impact assessment based

  4. Neoclassical tearing dynamo and self-sustainment of a bootstrapped tokamak

    International Nuclear Information System (INIS)

    Bhattacharjee, A.; Yuan, Y.

    1993-01-01

    It has been suggested by Boozer that a completely bootstrapped tokamak which requires no seed current is possible due to the open-quotes dynamo effectclose quotes caused by tearing modes. Numerical calculations have been carried out by Weening and Boozer confirming the feasibility of a completely bootstrapped tokamak. These calculations use the resistive MHD model, with the pressure profile held arbitrarily fixed. Several questions naturally arise. Is resistive MHD a good model in the low-collisionality regime of present-day tokamaks in which large bootstrap currents have been observed? Is it consistent to rely on pressure gradients to provide the bootstrap current, but then omit pressure gradients in investigating the tearing instabilities that provide the dynamo effect? And how realistic is it to assume that a strong pressure gradient is sustainable in the central region where current relaxation is expected to produce a dynamo effect? In this paper, the authors investigate the dynamo effect in a bootstrapped tokamak within the framework of the neoclassical MHD model which is more realistic than resistive MHD for the regime in question. Since neoclassical MHD includes trapped-particle effects, it can, in principle, provide an additional mechanism for exciting tearing modes which are known to be stabilized by temperature gradients. They investigate the properties of the dynamo field var-epsilon, and find that the original definition var-epsilon = 1 x b 1 > used in incompressible resistive MHD is no longer adequate; neoclassical MHD forces a redefinition of var-epsilon due to the requirements imposed by the helicity conservation constraint. Thus a completely steady-state bootstrapped tokamak sustained by a neoclassical tearing dynamo is realizable. However, they are pessimistic that such a tokamak, even if it were resistively stable, would be stable to ideal kink modes

  5. Effect of Chemistry on Electrodynamics in the Martian Dynamo Region using Multifluid MHD

    Science.gov (United States)

    Matheny, M. M.; Riousset, J. A.; Nykyri, K.

    2017-12-01

    Electromagnetic interactions between Mars remnant crustal magnetic fields and solar and planetary ions lead to time and space variations of the ionosphere. In this work, we continue the investigations started by Riousset et al. [JGR, 118, 2013; GRL, 41, 2014] and address the effect of chemistry on ion populations in the dynamo region, where ion dynamics are driven by collisions while electrons are still mostly magnetized. We adopt a mesoscale model to simulate dynamics of electrons and ions in the upper atmosphere ( 100-400 km). Our approach focuses on numerical studies using the Martian Multifluid Magnetohydrodynamic (MF-MHD) Model (M4). The dynamo is a region which varies in time and space due to the lack of a global planetary intrinsic magnetic field, the location of the remnant crustal fields, and the planetary rotation responsible for day/night transition and subsequent trans-terminator particle transfer. The time scales of atmospheric collisions, gyromotions, and chemical processes will be discussed in detail to support the selection of relevant reactions for mesoscale studies of the dynamo regions. Several schemes are available in the referenced literature [e.g., Najib et al., JGR, 116, A05204, 2011], and will be used as a basis for the chemistry scheme. The improved model will more accurately reflect changes in the population of planetary ions, which can alter the dynamo current, thereby also causing perturbations in the magnetic topology. The MAVEN mission has shown the importance of ion escape in the Martian atmospheric loss, and previous modeling studies [e.g., Riousset et al., 2014] have shown that electrodynamics in the dynamo region may impact upward transport of ions from the dynamo region, supporting the need for further studies of this region.

  6. Large-scale dynamo action due to α fluctuations in a linear shear flow

    Science.gov (United States)

    Sridhar, S.; Singh, Nishant K.

    2014-12-01

    We present a model of large-scale dynamo action in a shear flow that has stochastic, zero-mean fluctuations of the α parameter. This is based on a minimal extension of the Kraichnan-Moffatt model, to include a background linear shear and Galilean-invariant α-statistics. Using the first-order smoothing approximation we derive a linear integro-differential equation for the large-scale magnetic field, which is non-perturbative in the shearing rate S , and the α-correlation time τα . The white-noise case, τα = 0 , is solved exactly, and it is concluded that the necessary condition for dynamo action is identical to the Kraichnan-Moffatt model without shear; this is because white-noise does not allow for memory effects, whereas shear needs time to act. To explore memory effects we reduce the integro-differential equation to a partial differential equation, valid for slowly varying fields when τα is small but non-zero. Seeking exponential modal solutions, we solve the modal dispersion relation and obtain an explicit expression for the growth rate as a function of the six independent parameters of the problem. A non-zero τα gives rise to new physical scales, and dynamo action is completely different from the white-noise case; e.g. even weak α fluctuations can give rise to a dynamo. We argue that, at any wavenumber, both Moffatt drift and Shear always contribute to increasing the growth rate. Two examples are presented: (a) a Moffatt drift dynamo in the absence of shear and (b) a Shear dynamo in the absence of Moffatt drift.

  7. Constraining Fully Convective Magnetic Dynamos using Brown Dwarf Auroral Radio Emission

    Science.gov (United States)

    Kao, Melodie; Hallinan, Gregg; Pineda, J. Sebastian; Escala, Ivanna; Burgasser, Adam; Bourke, Stephen; Stevenson, David

    2017-05-01

    An important outstanding problem in dynamo theory is understanding how magnetic fields are generated and sustained in fully convective objects, spanning stars through planets. For fully convective dynamo models to accurately predict exoplanet magnetic fields, pushing measurements to include the coolest T and Y dwarfs at the substellar-planetary boundary is critical. A number of models for possible dynamo mechanisms in this regime have been proposed but constraining data on magnetic field strengths and topologies across a wide range of mass, age, rotation rate, and temperature are sorely lacking, particularly in the brown dwarf regime.Detections of highly circularly polarized pulsed radio emission provide our only window into magnetic field measurements for objects in the ultracool brown dwarf regime. However, these detections are very rare; previous radio surveys encompassing ∼60 L6 or later targets have yielded only one detection. We have developed a selection strategy for biasing survey targets by leveraging the emergence of magnetic activity that is driven by planet-like auroral processes in the coolest brown dwarfs. Using our selection strategy, we previously observed six late L and T dwarfs with the Jansky Very Large Array (VLA) at 4-8 GHz and detected the presence of highly circularly polarized radio emission for five targets. Our initial detections provided the most robust constraints on dynamo theory in this regime, confirming magnetic fields >2.5 kG. To further probe the mechanisms driving fully convective dynamos at the substellar-planetary boundary, we present magnetic field constraints for two Y-dwarfs and 8-12 GHz radio observations of late L and T dwarfs corresponding to >3.6 kG surface fields. We additionally present initial results for a comprehensive L and T dwarf survey spanning a wide range of rotation periods to test rotation-dominated dynamo models. Finally, we present a method for comparing magnetic field measurements derived from

  8. Surface flux transport simulations: Effect of inflows toward active regions and random velocities on the evolution of the Sun's large-scale magnetic field

    Science.gov (United States)

    Martin-Belda, D.; Cameron, R. H.

    2016-02-01

    Aims: We aim to determine the effect of converging flows on the evolution of a bipolar magnetic region (BMR), and to investigate the role of these inflows in the generation of poloidal flux. We also discuss whether the flux dispersal due to turbulent flows can be described as a diffusion process. Methods: We developed a simple surface flux transport model based on point-like magnetic concentrations. We tracked the tilt angle, the magnetic flux and the axial dipole moment of a BMR in simulations with and without inflows and compared the results. To test the diffusion approximation, simulations of random walk dispersal of magnetic features were compared against the predictions of the diffusion treatment. Results: We confirm the validity of the diffusion approximation to describe flux dispersal on large scales. We find that the inflows enhance flux cancellation, but at the same time affect the latitudinal separation of the polarities of the bipolar region. In most cases the latitudinal separation is limited by the inflows, resulting in a reduction of the axial dipole moment of the BMR. However, when the initial tilt angle of the BMR is small, the inflows produce an increase in latitudinal separation that leads to an increase in the axial dipole moment in spite of the enhanced flux destruction. This can give rise to a tilt of the BMR even when the BMR was originally aligned parallel to the equator.

  9. The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations

    Science.gov (United States)

    Nandy, Dibyendu; Bhowmik, Prantika; Yeates, Anthony R.; Panda, Suman; Tarafder, Rajashik; Dash, Soumyaranjan

    2018-01-01

    On 2017 August 21, a total solar eclipse swept across the contiguous United States, providing excellent opportunities for diagnostics of the Sun’s corona. The Sun’s coronal structure is notoriously difficult to observe except during solar eclipses; thus, theoretical models must be relied upon for inferring the underlying magnetic structure of the Sun’s outer atmosphere. These models are necessary for understanding the role of magnetic fields in the heating of the corona to a million degrees and the generation of severe space weather. Here we present a methodology for predicting the structure of the coronal field based on model forward runs of a solar surface flux transport model, whose predicted surface field is utilized to extrapolate future coronal magnetic field structures. This prescription was applied to the 2017 August 21 solar eclipse. A post-eclipse analysis shows good agreement between model simulated and observed coronal structures and their locations on the limb. We demonstrate that slow changes in the Sun’s surface magnetic field distribution driven by long-term flux emergence and its evolution governs large-scale coronal structures with a (plausibly cycle-phase dependent) dynamical memory timescale on the order of a few solar rotations, opening up the possibility for large-scale, global corona predictions at least a month in advance.

  10. New Mexico Liquid Metal αω -dynamo experiment: Most Recent Progress

    Science.gov (United States)

    Si, Jiahe; Sonnenfeld, Richard; Colgate, Art; Li, Hui

    2017-10-01

    The goal of the New Mexico Liquid Metal αω -dynamo experiment is to demonstrate a galactic dynamo can be generated through two phases, the ω-phase and α-phase by two semi-coherent flows in laboratory. We have demonstrated an 8-fold poloidal-to-toroidal flux amplification from differential rotation (the ω-effect) by minimizing turbulence in our apparatus. To demonstrate the α-effect, major upgrades are needed. The upgrades include building a helicity injection facility, mounting new 100hp motors and new sensors, designing a new data acquisition system capable of transmitting data from about 80 sensors in a high speed rotating frame with an overall 200kS/sec sampling rate. We hope the upgrade can be utilized to answer the question of whether a self-sustaining αω -dynamo can be implemented with a realistic lab fluid flow field, as well as to obtain more details to understand dynamo action in highly turbulent Couette flow.

  11. Instrumental Implementation of an Experiment to Demonstrate αω -dynamos in Accretion Disks

    Science.gov (United States)

    Si, Jiahe; Sonnenfeld, Richard; Colgate, Art; Li, Hui; Nornberg, Mark

    2016-10-01

    The New Mexico Liquid Metal αω -dynamo experiment is aimed to demonstrate a galactic dynamo. Our goal is to generate the ω-effect and α-effect by two semi-coherent flows in laboratory. Two coaxial cylinders are used to generate Taylor-Couette flows to simulate the differential rotation of accretion disks. Plumes induced by jets injected into the Couette flows are expected to produce helicities necessary for the α-effect. We have demonstrated an 8-fold poloidal-to-toroidal flux amplification from differential rotation (the ω-effect) by minimizing turbulence in our apparatus. To demonstrate the α-effect, the experimental apparatus is undergoing significant upgrade. We have constructed a helicity injection facility, and are also designing and testing a new data acquisition system capable of transmitting data in a high speed rotating frame. Additional magnetic field diagnostics will also be included. The upgrade is intended to answer the question of whether a self-sustaining αω -dynamo can be constructed with a realistic fluid flow field, as well as to obtain more details to understand dynamo action in highly turbulent Couette flow.

  12. Theory Tested by Means of the Stars. [viability of the alpha-omega dynamo model

    Science.gov (United States)

    Golub, L.

    1985-01-01

    The viability of the solar alpha-omega dynamo model was studied through examination of extreme stellar cases expected to show specific types of deviation from solar behavior. Observational data was taken from studies of main sequence stars with shallow convective zones, fully convective M-dwarfs, and a Pleiades X-ray survey.

  13. The role of dynamo fluctuations in anomalous ion heating, mode locking, and flow generation

    International Nuclear Information System (INIS)

    Terry, P.W.; Gatto, R.; Fiksel, G.; Fitzpatrick, R.; Hegna, C.C.

    2001-01-01

    Anomalous ion heating intrinsic to magnetic fluctuation-induced electron heat transport, the locking of global modes through wall conditions, and flow generation via the magnetic Reynolds stress all derive from the global, m=1 tearing modes familiar in the RFP as the dynamo modes. These important processes are investigated analytically and numerically, yielding new insights and predictions for comparison with experiment. (author)

  14. DYNAMO EFFECTS NEAR THE TRANSITION FROM SOLAR TO ANTI-SOLAR DIFFERENTIAL ROTATION

    International Nuclear Information System (INIS)

    Simitev, Radostin D.; Kosovichev, Alexander G.; Busse, Friedrich H.

    2015-01-01

    Numerical MHD simulations play an increasingly important role for understanding the mechanisms of stellar magnetism. We present simulations of convection and dynamos in density-stratified rotating spherical fluid shells. We employ a new 3D simulation code for obtaining the solution of a physically consistent anelastic model of the process with a minimum number of parameters. The reported dynamo simulations extend into a “buoyancy-dominated” regime where the buoyancy forcing is dominant while the Coriolis force is no longer balanced by pressure gradients, and strong anti-solar differential rotation develops as a result. We find that the self-generated magnetic fields, despite being relatively weak, are able to reverse the direction of differential rotation from anti-solar to solar-like. We also find that convection flows in this regime are significantly stronger in the polar regions than in the equatorial region, leading to non-oscillatory dipole-dominated dynamo solutions, and to a concentration of magnetic field in the polar regions. We observe that convection has a different morphology in the inner and the outer part of the convection zone simultaneously such that organized geostrophic convection columns are hidden below a near-surface layer of well-mixed highly chaotic convection. While we focus our attention on the buoyancy-dominated regime, we also demonstrate that conical differential rotation profiles and persistent regular dynamo oscillations can be obtained in the parameter space of the rotation-dominated regime even within this minimal model

  15. Inertial effects on thermochemically driven convection and hydromagnetic dynamos in a spherical shell

    Czech Academy of Sciences Publication Activity Database

    Šimkanin, Ján; Kyselica, Juraj; Guba, P.

    2018-01-01

    Roč. 212, č. 3 (2018), s. 2194-2205 ISSN 0956-540X Institutional support: RVO:67985530 Keywords : composition and structure of the core * dynamo * nonlinear differential equations * numerical modelling Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 2.414, year: 2016

  16. Magnetic and velocity fields in a dynamo operating at extremely small Ekman and magnetic Prandtl numbers

    Czech Academy of Sciences Publication Activity Database

    Šimkanin, Ján; Kyselica, Juraj

    2017-01-01

    Roč. 47, č. 4 (2017), s. 261-276 ISSN 1335-2806 R&D Projects: GA MŠk(CZ) LG13042 Institutional support: RVO:67985530 Keywords : hydromagnetic dynamo * magnetic Prandtl number * inertial forces Subject RIV: DE - Earth Magnetism, Geodesy, Geography OBOR OECD: Physical geography

  17. Sudden transitions and grand variations in the solar dynamo, past and future

    NARCIS (Netherlands)

    de Jager, C.; Duhau, S.

    2012-01-01

    The solar dynamo is the exotic dance of the sun's two major magnetic field components, the poloidal and the toroidal, interacting in anti-phase. On the basis of new data on the geomagnetic aa index, we improve our previous forecast of the properties of the current Schwabe cycle #24. Its maximum will

  18. MAGNETIC CYCLES IN A CONVECTIVE DYNAMO SIMULATION OF A YOUNG SOLAR-TYPE STAR

    International Nuclear Information System (INIS)

    Brown, Benjamin P.; Miesch, Mark S.; Browning, Matthew K.; Brun, Allan Sacha; Toomre, Juri

    2011-01-01

    Young solar-type stars rotate rapidly and many are magnetically active. Some appear to undergo magnetic cycles similar to the 22 yr solar activity cycle. We conduct simulations of dynamo action in rapidly rotating suns with the three-dimensional magnetohydrodynamic anelastic spherical harmonic (ASH) code to explore dynamo action achieved in the convective envelope of a solar-type star rotating at five times the current solar rotation rate. We find that dynamo action builds substantial organized global-scale magnetic fields in the midst of the convection zone. Striking magnetic wreaths span the convection zone and coexist with the turbulent convection. A surprising feature of this wreath-building dynamo is its rich time dependence. The dynamo exhibits cyclic activity and undergoes quasi-periodic polarity reversals where both the global-scale poloidal and toroidal fields change in sense on a roughly 1500 day timescale. These magnetic activity patterns emerge spontaneously from the turbulent flow and are more organized temporally and spatially than those realized in our previous simulations of the solar dynamo. We assess in detail the competing processes of magnetic field creation and destruction within our simulations that contribute to the global-scale reversals. We find that the mean toroidal fields are built primarily through an Ω-effect, while the mean poloidal fields are built by turbulent correlations which are not well represented by a simple α-effect. During a reversal the magnetic wreaths propagate toward the polar regions, and this appears to arise from a poleward propagating dynamo wave. As the magnetic fields wax and wane in strength and flip in polarity, the primary response in the convective flows involves the axisymmetric differential rotation which varies on similar timescales. Bands of relatively fast and slow fluid propagate toward the poles on timescales of roughly 500 days and are associated with the magnetic structures that propagate in the

  19. Analysis, Control, Synchronization and SPICE Implementation of a Novel 4-D Hyperchaotic Rikitake Dynamo System without Equilibrium

    Directory of Open Access Journals (Sweden)

    S. Vaidyanathan

    2014-11-01

    Full Text Available Chaos theory has wide applications and its importance can be seen by the voluminous publications on various applications in several branches of science, commerce and engineering. Control, tracking or regulation and synchronization of different types of chaotic systems are importance areas of research in the control literature and various methods have been adopted over the past few decades for tackling these research problems. Also, the discovery of novel chaotic and hyperchaotic systems in various applications, their qualitative properties and the control of such systems are also important research areas in chaos theory. This paper announces a novel 4-D hyperchaotic Rikitake dynamo system, which is derived by adding a state feedback control to the famous 3-D Rikitake two-disk dynamo system (1958. The frequent and irregular reversals of the Earth’s magnetic field inspired a number of early studies involving electrical currents within the Earth’s molten core. One of the first such models to exhibit reversals was Rikitake’s two-disk dynamo system (Rikitake, 1958. This paper discusses the qualitative properties of the novel hyperchaotic Rikitake dynamo system. We note that the novel hyperchaotic Rikitake dynamo system has no equilibrium points. The Lyapunov exponents of the hyperchaotic Rikitake dynamo system are found as �! = 0.09136, �! = 0.02198, �! = 0 and �! = −2.11190. The Kaplan-Yorke fractional dimension of the novel hyperchaotic Rikitake dynamo system is found as �!" = 3.05367. Next, this paper discusses control and synchronization of the novel hyperchaotic Rikitake dynamo system with unknown parameters using adaptive control method. The main results are established using Lyapunov stability theory and numerically illustrated using MATLAB. Finally, for the 4-D novel hyperchaotic system, an electronic circuit realization in SPICE has been described to confirm the feasibility of the theoretical hyperchaotic Rikitake dynamo

  20. Constraining the Date of the Martian Dynamo Shutdown by Means of Crater Magnetization Signatures

    Science.gov (United States)

    Vervelidou, Foteini; Lesur, Vincent; Grott, Matthias; Morschhauser, Achim; Lillis, Robert J.

    2017-11-01

    Mars is believed to have possessed a dynamo that ceased operating approximately 4 Ga ago, although the exact time is still under debate. The scope of this study is to constrain the possible timing of its cessation by studying the magnetization signatures of craters. The study uses the latest available model of the lithospheric magnetic field of Mars, which is based on Mars Global Surveyor data. We tackle the problem of nonuniqueness that characterizes the inversion of magnetic field data for the magnetization by inferring only the visible part of the magnetization, that is, the part of the magnetization that gives rise to the observed magnetic field. Further on, we demonstrate that a zero visible magnetization is a valid proxy for the entire magnetization being zero under the assumption of a magnetization distribution of induced geometry. This assumption holds for craters whose thermoremanent magnetization has not been significantly altered since its acquisition. Our results show that the dynamo shut off after the impacts that created the Acidalia and SE Elysium basins and before the crust within the Utopia basin cooled below its magnetic blocking temperature. Accounting for the age uncertainties in the dating of these craters, we estimate that the dynamo shut off at an N(300) crater retention age of 2.5-3.2 or an absolute model age of 4.12-4.14 Ga. Moreover, the Martian dynamo may have been weaker in its early stage, which if true implies that the driving mechanism of the Martian dynamo was not the same throughout its history.

  1. Hydromagnetic dynamos in rotating spherical fluid shells in dependence on the Prandtl number, density stratification and electromagnetic boundary conditions

    Czech Academy of Sciences Publication Activity Database

    Šoltis, T.; Šimkanin, Ján

    2014-01-01

    Roč. 44, č. 4 (2014), s. 293-312 ISSN 1335-2806 Institutional support: RVO:67985530 Keywords : hydromagnetic dynamo * non-uniform stratification * Prandtl number * penetrative convection * electromagnetic boundary conditions Subject RIV: DE - Earth Magnetism, Geodesy, Geography

  2. Lorentz violation bounds from torsion trace fermion sector and galaxy M51 data and chiral dynamos

    Energy Technology Data Exchange (ETDEWEB)

    Garcia de Andrade, L.C. [IF-UERJ, Departamento de Fisica Teorica, Rio de Janeiro, RJ (Brazil)

    2017-06-15

    Earlier we have computed a Lorentz violation (LV) bound for torsion terms via galactic dynamos and found bounds similar to the one obtained by Kostelecky et al. (Phys Rev Lett 100:111102, 2008) which is of the order of 10{sup -31} GeV. Their result was found making use of the axial torsion vector in terms of Dirac spinors and minimal torsion coupling in flat space-time of fermions. In this paper, a torsion dynamo equation obtained using the variation of the torsion trace and galaxy M51 data of 500 pc are used to place an upper bound of 10{sup -26} GeV in LV, which agrees with the one by Kostelecky and his group using an astrophysical framework background. Their lowest bound was obtained in earth laboratory using dual masers. One of the purposes of this paper is to apply the Faraday self-induction magnetic equation, recently extended to torsioned space-time, by the author to show that it lends support to physics in Riemann-Cartan space-time, in several distinct physical backgrounds. Backreaction magnetic effects are used to obtain the LV bounds. Previously Bamba et al. (JCAP 10:058, 2012) have used the torsion trace in their teleparallel investigation of the IGMF, with the argument that the torsion trace leads to less weaker effects than the other irreducible components of the torsion tensor. LV is computed in terms of a chiral-torsion-like current in the new dynamo equation analogous to the Dvornikov and Semikoz dynamo equation with chiral magnetic currents. Making use of the chiral-torsion dynamo equation we estimate the LV bounds in the early universe to be of the order of 10{sup -24} GeV, which was the order of the charged-lepton sector. Our main result is that it is possible to obtain more stringent bounds than the ones found in the fermion sector of astrophysics in the new revised 2017 data table for CPT and Lorentz violation by Kostelecky and Mewes. They found in several astrophysical backgrounds, orders of magnitude such as 10{sup -24} and 10{sup -23} Ge

  3. Lorentz violation bounds from torsion trace fermion sector and galaxy M 51 data and chiral dynamos

    Science.gov (United States)

    Garcia de Andrade, L. C.

    2017-06-01

    Earlier we have computed a Lorentz violation (LV) bound for torsion terms via galactic dynamos and found bounds similar to the one obtained by Kostelecky et al. (Phys Rev Lett 100:111102, 2008) which is of the order of 10^{-31} GeV. Their result was found making use of the axial torsion vector in terms of Dirac spinors and minimal torsion coupling in flat space-time of fermions. In this paper, a torsion dynamo equation obtained using the variation of the torsion trace and galaxy M51 data of 500 pc are used to place an upper bound of 10^{-26} GeV in LV, which agrees with the one by Kostelecky and his group using an astrophysical framework background. Their lowest bound was obtained in earth laboratory using dual masers. One of the purposes of this paper is to apply the Faraday self-induction magnetic equation, recently extended to torsioned space-time, by the author to show that it lends support to physics in Riemann-Cartan space-time, in several distinct physical backgrounds. Backreaction magnetic effects are used to obtain the LV bounds. Previously Bamba et al. (JCAP 10:058, 2012) have used the torsion trace in their teleparallel investigation of the IGMF, with the argument that the torsion trace leads to less weaker effects than the other irreducible components of the torsion tensor. LV is computed in terms of a chiral-torsion-like current in the new dynamo equation analogous to the Dvornikov and Semikoz dynamo equation with chiral magnetic currents. Making use of the chiral-torsion dynamo equation we estimate the LV bounds in the early universe to be of the order of 10^{-24} GeV, which was the order of the charged-lepton sector. Our main result is that it is possible to obtain more stringent bounds than the ones found in the fermion sector of astrophysics in the new revised 2017 data table for CPT and Lorentz violation by Kostelecky and Mewes. They found in several astrophysical backgrounds, orders of magnitude such as 10^{-24} and 10^{-23} GeV which are not so

  4. Large-scale dynamo of accretion disks around supermassive nonrotating black holes

    Directory of Open Access Journals (Sweden)

    Poplavsky A.L.

    2006-01-01

    Full Text Available In this paper one presents an analytical model of accretion disk magnetosphere dynamics around supermassive nonrotating black holes in the centers of active galactic nuclei. Based on general relativistic equations of magneto hydrodynamics, the nonstationary solutions for time-dependent dynamo action in the accretion disks, spatial and temporal distribution of magnetic field are found. It is shown that there are two distinct stages of dynamo process: the transient and the steady-state regimes, the induction of magnetic field at t > 6:6665 x 1011GM/c3 s becomes stationary, magnetic field is located near the innermost stable circular orbit, and its value rises up to ~ 105 G. Applications of such systems with nonrotating black holes in real active galactic nuclei are discussed.

  5. GLOBAL GALACTIC DYNAMO DRIVEN BY COSMIC RAYS AND EXPLODING MAGNETIZED STARS

    International Nuclear Information System (INIS)

    Hanasz, Michal; Woltanski, Dominik; Kowalik, Kacper

    2009-01-01

    We report the first results of the first global galactic-scale cosmic ray (CR)-MHD simulations of CR-driven dynamo. We investigate the dynamics of magnetized interstellar medium (ISM), which is dynamically coupled with CR gas. We assume that exploding stars deposit small-scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of CRs, accelerated in supernova shocks. We conduct numerical simulations with the aid of a new parallel MHD code PIERNIK. We find that the initial magnetization of galactic disks by exploding magnetized stars forms favorable conditions for the CR-driven dynamo. We demonstrate that dipolar magnetic fields supplied on small supernova remnant scales can be amplified exponentially by the CR-driven dynamo, to the present equipartition values, and transformed simultaneously to large galactic scales. The resulting magnetic field structure in an evolved galaxy appears spiral in the face-on view and reveals the so-called X-shaped structure in the edge-on view.

  6. The effect of tidal heating on core dynamos in the TRAPPIST-1 system

    Science.gov (United States)

    Knapp, Mary; Stamenkovic, Vlada

    2017-05-01

    The recent discovery of seven Earth-sized planets orbiting a nearby (12 pc) M8 dwarf TRAPPIST-1 (T1) presents the best opportunity yet to study the magnetic fields of small exoplanets. The T1 planets likely experience significant tidal heating due to their interaction with each other as well as their host star. The system bears a striking resemblance to an expanded version of the Galilean moons of the Jovian system. This similarity suggests that there may be magnetic interaction between the inner T1 planets and the host star, similar to Io and its flux tube, Europa's induced magnetic field, and Ganymede's intrinsic dynamo field. This work examines whether tidal effects enhance or suppress magnetic field generation in the T1 planets. Existing interior models developed in Stamenkovic et al. (2012) are adapted to include tidal heating and tailored specifically to the T1 planets in order to determine whether the interior energetics are favorable or unfavorable to a sustained magnetic dynamo over the lifetime of the system. Allowing for a range of planetary input parameters (core fraction, bulk composition, initial temperature, etc.), we quantify the influence of tidal heating on the likelihood of sustained core dynamos in the T1 planets.

  7. Ion heating and MHD dynamo fluctuations in the reversed field pinch

    International Nuclear Information System (INIS)

    Scime, E.E.

    1992-05-01

    Ion temperature measurements, time resolved to 10 μs, have been made in the Madison Symmetric Torus (MST) reversed field pinch (RFP) with a five channel charge exchange analyzer. The characteristic anomalously high ion temperature of RFP discharges has been observed in the MST. The evolution of the ion and electron temperature, as well as density and charge exchange power loss, were measured for a series of reproducible discharges. The ion heating expected from collisional processes with the electrons is calculated and shown too small to explain the measured ion temperatures. The charge exchange determined ion temperature is also compared to measurements of the thermally broadened CV 227.1 nm line. The ion temperature, T i ∼ 250 eV for I = 360 kA, increases by more than 100% during discrete dynamo bursts in MST discharges. Magnetic field fluctuations in the range 0.5 endash 5 MHz were also measured during the dynamo bursts. Structure in the fluctuation frequency spectrum at the ion cyclotron frequency appears as the bursts terminate, suggesting that the mechanism of ion heating involves the dissipation of dynamo fluctuations at ion cyclotron frequencies. Theoretical models for ion heating are reviewed and discussed in light of the experimental results. Similar electron heating mechanisms may be responsible for the discrepancy between measured and expected loop voltages in the RFP. The electrons, as well as the ions, may be heated by turbulent mechanisms, and a RFP energy budget including such phenomena is described

  8. Ab Initio Simulations of a Supernova-driven Galactic Dynamo in an Isolated Disk Galaxy

    Science.gov (United States)

    Butsky, Iryna; Zrake, Jonathan; Kim, Ji-hoon; Yang, Hung-I.; Abel, Tom

    2017-07-01

    We study the magnetic field evolution of an isolated spiral galaxy, using isolated Milky Way-mass galaxy formation simulations and a novel prescription for magnetohydrodynamic (MHD) supernova feedback. Our main result is that a galactic dynamo can be seeded and driven by supernova explosions, resulting in magnetic fields whose strength and morphology are consistent with observations. In our model, supernovae supply thermal energy and a low-level magnetic field along with their ejecta. The thermal expansion drives turbulence, which serves a dual role by efficiently mixing the magnetic field into the interstellar medium and amplifying it by means of a turbulent dynamo. The computational prescription for MHD supernova feedback has been implemented within the publicly available ENZO code and is fully described in this paper. This improves upon ENZO's existing modules for hydrodynamic feedback from stars and active galaxies. We find that the field attains microgauss levels over gigayear timescales throughout the disk. The field also develops a large-scale structure, which appears to be correlated with the disk’s spiral arm density structure. We find that seeding of the galactic dynamo by supernova ejecta predicts a persistent correlation between gas metallicity and magnetic field strength. We also generate all-sky maps of the Faraday rotation measure from the simulation-predicted magnetic field, and we present a direct comparison with observations.

  9. Ab Initio Simulations of a Supernova-driven Galactic Dynamo in an Isolated Disk Galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Butsky, Iryna [Astronomy Department, University of Washington, Seattle, WA 98195 (United States); Zrake, Jonathan; Kim, Ji-hoon; Yang, Hung-I; Abel, Tom [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Menlo Park, CA 94025 (United States)

    2017-07-10

    We study the magnetic field evolution of an isolated spiral galaxy, using isolated Milky Way–mass galaxy formation simulations and a novel prescription for magnetohydrodynamic (MHD) supernova feedback. Our main result is that a galactic dynamo can be seeded and driven by supernova explosions, resulting in magnetic fields whose strength and morphology are consistent with observations. In our model, supernovae supply thermal energy and a low-level magnetic field along with their ejecta. The thermal expansion drives turbulence, which serves a dual role by efficiently mixing the magnetic field into the interstellar medium and amplifying it by means of a turbulent dynamo. The computational prescription for MHD supernova feedback has been implemented within the publicly available ENZO code and is fully described in this paper. This improves upon ENZO 's existing modules for hydrodynamic feedback from stars and active galaxies. We find that the field attains microgauss levels over gigayear timescales throughout the disk. The field also develops a large-scale structure, which appears to be correlated with the disk’s spiral arm density structure. We find that seeding of the galactic dynamo by supernova ejecta predicts a persistent correlation between gas metallicity and magnetic field strength. We also generate all-sky maps of the Faraday rotation measure from the simulation-predicted magnetic field, and we present a direct comparison with observations.

  10. MAGNETIC QUENCHING OF TURBULENT DIFFUSIVITY: RECONCILING MIXING-LENGTH THEORY ESTIMATES WITH KINEMATIC DYNAMO MODELS OF THE SOLAR CYCLE

    International Nuclear Information System (INIS)

    Munoz-Jaramillo, Andres; Martens, Petrus C. H.; Nandy, Dibyendu

    2011-01-01

    The turbulent magnetic diffusivity in the solar convection zone is one of the most poorly constrained ingredients of mean-field dynamo models. This lack of constraint has previously led to controversy regarding the most appropriate set of parameters, as different assumptions on the value of turbulent diffusivity lead to radically different solar cycle predictions. Typically, the dynamo community uses double-step diffusivity profiles characterized by low values of diffusivity in the bulk of the convection zone. However, these low diffusivity values are not consistent with theoretical estimates based on mixing-length theory, which suggest much higher values for turbulent diffusivity. To make matters worse, kinematic dynamo simulations cannot yield sustainable magnetic cycles using these theoretical estimates. In this work, we show that magnetic cycles become viable if we combine the theoretically estimated diffusivity profile with magnetic quenching of the diffusivity. Furthermore, we find that the main features of this solution can be reproduced by a dynamo simulation using a prescribed (kinematic) diffusivity profile that is based on the spatiotemporal geometric average of the dynamically quenched diffusivity. This bridges the gap between dynamically quenched and kinematic dynamo models, supporting their usage as viable tools for understanding the solar magnetic cycle.

  11. EFFECTS OF LARGE-SCALE NON-AXISYMMETRIC PERTURBATIONS IN THE MEAN-FIELD SOLAR DYNAMO

    Energy Technology Data Exchange (ETDEWEB)

    Pipin, V. V. [Institute of Solar-Terrestrial Physics, Russian Academy of Sciences (Russian Federation); Kosovichev, A. G. [W.W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)

    2015-11-10

    We explore the response of a nonlinear non-axisymmetric mean-field solar dynamo model to shallow non-axisymmetric perturbations. After a relaxation period, the amplitude of the non-axisymmetric field depends on the initial condition, helicity conservation, and the depth of perturbation. It is found that a perturbation that is anchored at 0.9 R{sub ⊙} has a profound effect on the dynamo process, producing a transient magnetic cycle of the axisymmetric magnetic field, if it is initiated at the growing phase of the cycle. The non-symmetric, with respect to the equator, perturbation results in a hemispheric asymmetry of the magnetic activity. The evolution of the axisymmetric and non-axisymmetric fields depends on the turbulent magnetic Reynolds number R{sub m}. In the range of R{sub m} = 10{sup 4}–10{sup 6} the evolution returns to the normal course in the next cycle, in which the non-axisymmetric field is generated due to a nonlinear α-effect and magnetic buoyancy. In the stationary state, the large-scale magnetic field demonstrates a phenomenon of “active longitudes” with cyclic 180° “flip-flop” changes of the large-scale magnetic field orientation. The flip-flop effect is known from observations of solar and stellar magnetic cycles. However, this effect disappears in the model, which includes the meridional circulation pattern determined by helioseismology. The rotation rate of the non-axisymmetric field components varies during the relaxation period and carries important information about the dynamo process.

  12. Spectroscopic measurement of the MHD dynamo in the MST reversed field pinch

    International Nuclear Information System (INIS)

    Chapman, J.T.

    1998-09-01

    The author has directly observed the coupling of ion velocity fluctuations and magnetic field fluctuations to produce an MHD dynamo electric field in the interior of the MST reversed field pinch. Chord averaged ion velocity fluctuations were measured with a fast spectroscopic diagnostic which collects line radiation from intrinsic carbon impurities simultaneously along two lines of sight. The chords employed for the measurements resolved long wavelength velocity fluctuations of several km/s at 8--20 kHz as tiny, fast Doppler shifts in the emitted line profile. During discrete dynamo events the velocity fluctuations, like the magnetic fluctuations, increase dramatically. The toroidal and poloidal chords with impact parameters of 0.3 a and 0.6 a respectively, resolved fluctuation wavenumbers with resonance surfaces near or along the lines of sight indicating a radial velocity fluctuation width for each mode which spans only a fraction of the plasma radius. The phase between the measured toroidal velocity fluctuations and the magnetic fluctuations matches the predictions of resistive MHD while the poloidal velocity fluctuations exhibit a phase consistent with the superposition of MHD effects and the advection of a mean flow gradient past the poloidal line of sight. Radial velocity fluctuations resolved by a chord through the center of the plasma were small compared to the poloidal and toroidal fluctuations and exhibited low coherence with the magnetic fluctuations. The ensembled nonlinear product of the ion velocity fluctuations and fluctuations in the magnetic field indicates a substantial dynamo electric field which peaks during the periods of spontaneous flux generation

  13. Dynamo dominated accretion and energy flow: The mechanism of active galactic nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Colgate, S.A.; Li, H.

    1998-12-31

    An explanation of the magnetic fields of the universe, the central mass concentration of galaxies, the massive black hole of every galaxy, and the AGN phenomena has been an elusive goal. The authors suggest here the outlines of such a theoretical understanding and point out where the physical understanding is missing. They believe there is an imperative to the sequence of mass flow and hence energy flow in the collapse of a galactic mass starting from the first non-linearity appearing in structure formation following decoupling. This first non-linearity of a two to one density fluctuation, the Lyman-{alpha} clouds, ultimately leads to the emission spectra of the phenomenon of AGN, quasars, blazars, etc. The over-arching physical principle is the various mechanisms for the transport of angular momentum. They believe they have now understood the new physics of two of these mechanisms that have previously been illusive and as a consequence they impose strong constraints on the initial conditions of the mechanisms for the subsequent emission of the gravitational binding energy. The new phenomena described are: (1) the Rossby vortex mechanism of the accretion disk {alpha}-viscosity, and (2) the mechanism of the {alpha}-{Omega} dynamo in the accretion disk. The Rossby vortex mechanism leads to a prediction of the black hole mass and rate of energy release and the {alpha}-{Omega} dynamo leads to the generation of the magnetic flux of the galaxy (and the far greater magnetic flux of clusters) and separately explains the primary flux of energy emission as force-free magnetic energy density. This magnetic flux and magnetic energy density separately are the necessary consequence of the saturation of a dynamo created by the accretion disk with a gain greater than unity.

  14. Spectroscopic measurement of the MHD dynamo in the MST reversed field pinch

    Energy Technology Data Exchange (ETDEWEB)

    Chapman, James Tharp [Univ. of Wisconsin, Madison, WI (United States)

    1998-09-01

    The author has directly observed the coupling of ion velocity fluctuations and magnetic field fluctuations to produce an MHD dynamo electric field in the interior of the MST reversed field pinch. Chord averaged ion velocity fluctuations were measured with a fast spectroscopic diagnostic which collects line radiation from intrinsic carbon impurities simultaneously along two lines of sight. The chords employed for the measurements resolved long wavelength velocity fluctuations of several km/s at 8-20 kHz as tiny, fast Doppler shifts in the emitted line profile. During discrete dynamo events the velocity fluctuations, like the magnetic fluctuations, increase dramatically. The toroidal and poloidal chords with impact parameters of 0.3 a and 0.6 a respectively, resolved fluctuation wavenumbers with resonance surfaces near or along the lines of sight indicating a radial velocity fluctuation width for each mode which spans only a fraction of the plasma radius. The phase between the measured toroidal velocity fluctuations and the magnetic fluctuations matches the predictions of resistive MHD while the poloidal velocity fluctuations exhibit a phase consistent with the superposition of MHD effects and the advection of a mean flow gradient past the poloidal line of sight. Radial velocity fluctuations resolved by a chord through the center of the plasma were small compared to the poloidal and toroidal fluctuations and exhibited low coherence with the magnetic fluctuations. The ensembled nonlinear product of the ion velocity fluctuations and fluctuations in the magnetic field indicates a substantial dynamo electric field which peaks during the periods of spontaneous flux generation.

  15. Role of a continuous MHD dynamo in the formation of 3D equilibria in fusion plasmas

    Science.gov (United States)

    Piovesan, P.; Bonfiglio, D.; Cianciosa, M.; Luce, T. C.; Taylor, N. Z.; Terranova, D.; Turco, F.; Wilcox, R. S.; Wingen, A.; Cappello, S.; Chrystal, C.; Escande, D. F.; Holcomb, C. T.; Marrelli, L.; Paz-Soldan, C.; Piron, L.; Predebon, I.; Zaniol, B.; DIII-D, The; RFX-Mod Teams

    2017-07-01

    Stationary 3D equilibria can form in fusion plasmas via saturation of magnetohydrodynamic (MHD) instabilities or stimulated by external 3D fields. In these cases the current profile is anomalously broad due to magnetic flux pumping produced by the MHD modes. Flux pumping plays an important role in hybrid tokamak plasmas, maintaining the minimum safety factor above unity and thus removing sawteeth. It also enables steady-state hybrid operation, by redistributing non-inductive current driven near the center by electron cyclotron waves. A validated flux pumping model is not yet available, but it would be necessary to extrapolate hybrid operation to future devices. In this work flux pumping physics is investigated for helical core equilibria stimulated by external 3D fields in DIII-D hybrid plasmas. We show that flux pumping can be produced in a continuous way by an MHD dynamo emf. The same effect maintains helical equilibria in reversed-field pinch (RFP) plasmas. The effective MHD dynamo loop voltage is calculated for experimental 3D equilibrium reconstructions, by balancing Ohm’s law over helical flux surfaces, and is consistent with the expected current redistribution. Similar results are also obtained with more sophisticated nonlinear MHD simulations. The same modelling approach is applied to helical RFP states forming spontaneously in RFX-mod as the plasma current is raised above 0.8-1 MA. This comparison allows to identify the underlying physics common to tokamak and RFP: a helical core displacement modulates parallel current density along flux tubes, which requires a helical electrostatic potential to build up, giving rise to a helical MHD dynamo flow.

  16. The importance of wind-flux feedbacks during the November CINDY-DYNAMO MJO event

    Science.gov (United States)

    Riley Dellaripa, Emily; Maloney, Eric; van den Heever, Susan

    2015-04-01

    High-resolution, large-domain cloud resolving model (CRM) simulations probing the importance of wind-flux feedbacks to Madden-Julian Oscillation (MJO) convection are performed for the November 2011 CINDY-DYNAMO MJO event. The work is motivated by observational analysis from RAMA buoys in the Indian Ocean and TRMM precipitation retrievals that show a positive correlation between MJO precipitation and wind-induced surface fluxes, especially latent heat fluxes, during and beyond the CINDY-DYNAMO time period. Simulations are done using Colorado State University's Regional Atmospheric Modeling System (RAMS). The domain setup is oceanic and spans 1000 km x 1000 km with 1.5 km horizontal resolution and 65 stretched vertical levels centered on the location of Gan Island - one of the major CINDY-DYNAMO observation points. The model is initialized with ECMWF reanalysis and Aqua MODIS sea surface temperatures. Nudging from ECMWF reanalysis is applied at the domain periphery to encourage realistic evolution of MJO convection. The control experiment is run for the entire month of November so both suppressed and active, as well as, transitional phases of the MJO are modeled. In the control experiment, wind-induced surface fluxes are activated through the surface bulk aerodynamic formula and allowed to evolve organically. Sensitivity experiments are done by restarting the control run one week into the simulation and controlling the wind-induced flux feedbacks. In one sensitivity experiment, wind-induced surface flux feedbacks are completely denied, while in another experiment the winds are kept constant at the control simulations mean surface wind speed. The evolution of convection, especially on the mesoscale, is compared between the control and sensitivity simulations.

  17. Using Jupiter’s gravitational field to probe the Jovian convective dynamo

    Science.gov (United States)

    Kong, Dali; Zhang, Keke; Schubert, Gerald

    2016-01-01

    Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection. PMID:27005472

  18. Using dynamo theory to predict the sunspot number during solar cycle 21

    Science.gov (United States)

    Schatten, K. H.; Scherrer, P. H.; Svalgaard, L.; Wilcox, J. M.

    1978-01-01

    On physical grounds it is suggested that the polar field strength of the sun near a solar minimum is closely related to the solar activity of the following cycle. Four methods of estimating the polar magnetic field strength of the sun near solar minimum are employed to provide an estimate of the yearly mean sunspot number of cycle 21 at solar maximum of 140 + or - 20. This estimate may be considered a first-order attempt to predict the cycle activity using one parameter of physical importance based upon dynamo theory.

  19. A magnetic betelgeuse? Numerical simulations of non-linear dynamo action

    DEFF Research Database (Denmark)

    Dorch, S. B. F.

    2004-01-01

    Betelgeuse is an example of a cool super-giant displaying brightness fluctuations and irregular surface structures. Simulations by Freytag et al. (2002) of the convective envelope of the star have shown that the fluctuations in the star's luminosity may be caused by giant cell convection. A related...... question regarding the nature of Betelgeuse and supergiants in general is whether these stars may be magnetically active. If so, that may in turn also contribute to their variability. By performing detailed numerical simulations, I find that both linear kinematic and non-linear dynamo action are possible...

  20. Integration of Environmental Sensors with BIM: case studies using Arduino, Dynamo, and the Revit API

    Directory of Open Access Journals (Sweden)

    Kensek, K. M.

    2014-12-01

    Full Text Available This paper investigates the feasibility of connecting environmental sensors such as light, humidity, or CO2 receptors to a building information model (BIM. A base case was created in Rhino; using Grasshopper and Firefly, a simple digital model responded to lighting-levels detected by a photoresistor on an Arduino board. The case study was duplicated using Revit Architecture, a popular BIM software, and Dynamo, a visual programming environment, in an innovative application. Another case study followed a similar procedure by implementing the Revit API directly instead of using Dynamo. Then the process was reversed to demonstrate that not only could data could be sent from sensors to change the 3D model, but changes to parameters of a 3D model could effect a physical model through the use of actuators. It is intended that these virtual/physical prototypes could be used as the basis for testing intelligent façade systems before constructing full size mock-ups.Este estudio investiga la posibilidad de conectar sensores ambientales como de luz, humedad, o dióxido de carbono con un modelo de información de un edificio (siglas BIM en inglés. Un caso base fue creado en Rhino; usando Grasshopper and Firefly, donde un simple modelo digital respondió a niveles de luz detectados por un foto resistor en una tarjeta Arduino. El caso de estudio fue duplicado usando Revit Architecture, una herramienta popular en BIM, y Dynamo, un ambiente de programación gráfica, en una creativa aplicación. Un segundo caso de estudio siguió un procedimiento similar implementando Revit API directamente en vez de usar Dynamo. Entonces el proceso fue revertido para demostrar que no solamente la información podría ser enviada desde sensores para cambiar el modelo tridimensional, pero cambios en los parámetros de un modelo tridimensional podrían afectar un modelo físico mediante el uso de actuadores. Se espera que esos modelos virtuales puedan ser usados como base para

  1. Disorder in the Disk: The Influence of Accretion Disk Thickness on the Large-scale Magnetic Dynamo.

    Science.gov (United States)

    Hogg, J. Drew; Reynolds, Christopher S.

    2018-01-01

    The evolution of the magnetic field from the enigmatic large-scale dynamo is often considered a central feature of the accretion disk around a black hole. The resulting low-frequency oscillations introduced from the growth and decay of the field strength, along with the change in field orientation, are thought to be intimately tied to variability from the disk. Several factors are at play, but the dynamo can either be directly tied to observable signatures through modulation of the heating rate, or indirectly as the source of quasiperiodic oscillations, the driver of nonlinear structure from propagating fluctuations in mass accretion rate, or even the trigger of state transitions. We present a selection of results from a recent study of this process using a suite of four global, high-resolution, MHD accretion disk simulations. We systematically vary the scale height ratio and find the large-scale dynamo fails to develop above a scale height ratio of h/r ≥ 0.2. Using “butterfly” diagrams of the azimuthal magnetic field, we show the large-scale dynamo exists in the thinner accretion disk models, but fails to excite when the scale height ratio is increased, a feature which is also reflected in 2D Fourier transforms. Additionally, we calculate the dynamo α-parameter through correlations in the averaged magnetic field and turbulent electromotive force, and also generate synthetic light curves from the disk cooling. Using our emission proxy, we find the disks have markedly different characters as photometric fluctuations are larger and less ordered when the disk is thicker and the dynamo is absent.

  2. The Dynamo package for tomography and subtomogram averaging: components for MATLAB, GPU computing and EC2 Amazon Web Services.

    Science.gov (United States)

    Castaño-Díez, Daniel

    2017-06-01

    Dynamo is a package for the processing of tomographic data. As a tool for subtomogram averaging, it includes different alignment and classification strategies. Furthermore, its data-management module allows experiments to be organized in groups of tomograms, while offering specialized three-dimensional tomographic browsers that facilitate visualization, location of regions of interest, modelling and particle extraction in complex geometries. Here, a technical description of the package is presented, focusing on its diverse strategies for optimizing computing performance. Dynamo is built upon mbtools (middle layer toolbox), a general-purpose MATLAB library for object-oriented scientific programming specifically developed to underpin Dynamo but usable as an independent tool. Its structure intertwines a flexible MATLAB codebase with precompiled C++ functions that carry the burden of numerically intensive operations. The package can be delivered as a precompiled standalone ready for execution without a MATLAB license. Multicore parallelization on a single node is directly inherited from the high-level parallelization engine provided for MATLAB, automatically imparting a balanced workload among the threads in computationally intense tasks such as alignment and classification, but also in logistic-oriented tasks such as tomogram binning and particle extraction. Dynamo supports the use of graphical processing units (GPUs), yielding considerable speedup factors both for native Dynamo procedures (such as the numerically intensive subtomogram alignment) and procedures defined by the user through its MATLAB-based GPU library for three-dimensional operations. Cloud-based virtual computing environments supplied with a pre-installed version of Dynamo can be publicly accessed through the Amazon Elastic Compute Cloud (EC2), enabling users to rent GPU computing time on a pay-as-you-go basis, thus avoiding upfront investments in hardware and longterm software maintenance.

  3. Turbulent Dynamo Amplification of Magnetic Fields in Laser-Produced Plasmas: Simulations and Experiments

    Science.gov (United States)

    Tzeferacos, P.; Rigby, A.; Bott, A.; Bell, A.; Bingham, R.; Casner, A.; Cattaneo, F.; Churazov, E.; Forest, C.; Katz, J.; Koenig, M.; Li, C.-K.; Meinecke, J.; Petrasso, R.; Park, H.-S.; Remington, B.; Ross, J.; Ryutov, D.; Ryu, D.; Reville, B.; Miniati, F.; Schekochihin, A.; Froula, D.; Lamb, D.; Gregori, G.

    2017-10-01

    The universe is permeated by magnetic fields, with strengths ranging from a femtogauss in the voids between the filaments of galaxy clusters to several teragauss in black holes and neutron stars. The standard model for cosmological magnetic fields is the nonlinear amplification of seed fields via turbulent dynamo. We have conceived experiments to demonstrate and study the turbulent dynamo mechanism in the laboratory. Here, we describe the design of these experiments through large-scale 3D FLASH simulations on the Mira supercomputer at ANL, and the laser-driven experiments we conducted with the OMEGA laser at LLE. Our results indicate that turbulence is capable of rapidly amplifying seed fields to near equipartition with the turbulent fluid motions. This work was supported in part from the ERC (FP7/2007-2013, No. 256973 and 247039), and the U.S. DOE, Contract No. B591485 to LLNL, FWP 57789 to ANL, Grant No. DE-NA0002724 and DE-SC0016566 to the University of Chicago, and DE-AC02-06CH11357 to ANL.

  4. Hidden hyperchaos and electronic circuit application in a 5D self-exciting homopolar disc dynamo

    Science.gov (United States)

    Wei, Zhouchao; Moroz, Irene; Sprott, J. C.; Akgul, Akif; Zhang, Wei

    2017-03-01

    We report on the finding of hidden hyperchaos in a 5D extension to a known 3D self-exciting homopolar disc dynamo. The hidden hyperchaos is identified through three positive Lyapunov exponents under the condition that the proposed model has just two stable equilibrium states in certain regions of parameter space. The new 5D hyperchaotic self-exciting homopolar disc dynamo has multiple attractors including point attractors, limit cycles, quasi-periodic dynamics, hidden chaos or hyperchaos, as well as coexisting attractors. We use numerical integrations to create the phase plane trajectories, produce bifurcation diagram, and compute Lyapunov exponents to verify the hidden attractors. Because no unstable equilibria exist in two parameter regions, the system has a multistability and six kinds of complex dynamic behaviors. To the best of our knowledge, this feature has not been previously reported in any other high-dimensional system. Moreover, the 5D hyperchaotic system has been simulated using a specially designed electronic circuit and viewed on an oscilloscope, thereby confirming the results of the numerical integrations. Both Matlab and the oscilloscope outputs produce similar phase portraits. Such implementations in real time represent a new type of hidden attractor with important consequences for engineering applications.

  5. Generation of dynamo waves by spatially separated sources in the Earth and other celestial bodies

    Science.gov (United States)

    Popova, E.

    2017-12-01

    The amplitude and the spatial configuration of the planetary and stellar magnetic field can changing over the years. Celestial bodies can have cyclic, chaotic or unchanging in time magnetic activity which is connected with a dynamo mechanism. This mechanism is based on the consideration of the joint influence of the alpha-effect and differential rotation. Dynamo sources can be located at different depths (active layers) of the celestial body and can have different intensities. Application of this concept allows us to get different forms of solutions and some of which can include wave propagating inside the celestial body. We analytically showed that in the case of spatially separated sources of magnetic field each source generates a wave whose frequency depends on the physical parameters of its source. We estimated parameters of sources required for the generation nondecaying waves. We discus structure of such sources and matter motion (including meridional circulation) in the liquid outer core of the Earth and active layers of other celestial bodies.

  6. Study of electrode slice forming of bicycle dynamo hub power connector

    Science.gov (United States)

    Chen, Dyi-Cheng; Jao, Chih-Hsuan

    2013-12-01

    Taiwan's bicycle industry has been an international reputation as bicycle kingdom, but the problem in the world makes global warming green energy rise, the development of electrode slice of hub dynamo and power output connector to bring new hope to bike industry. In this study connector power output to gather public opinion related to patent, basis of collected documents as basis for design, structural components in least drawn to power output with simple connector. Power output of this study objectives connector hope at least cost, structure strongest, highest efficiency in output performance characteristics such as use of computer-aided drawing software Solid works to establish power output connector parts of 3D model, the overall portfolio should be considered part types including assembly ideas, weather resistance, water resistance, corrosion resistance to vibration and power flow stability. Moreover the 3D model import computer-aided finite element analysis software simulation of expected the power output of the connector parts manufacturing process. A series of simulation analyses, in which the variables relied on first stage and second stage forming, were run to examine the effective stress, effective strain, press speed, and die radial load distribution when forming electrode slice of bicycle dynamo hub.

  7. A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars.

    Science.gov (United States)

    Stello, Dennis; Cantiello, Matteo; Fuller, Jim; Huber, Daniel; García, Rafael A; Bedding, Timothy R; Bildsten, Lars; Aguirre, Victor Silva

    2016-01-21

    Magnetic fields play a part in almost all stages of stellar evolution. Most low-mass stars, including the Sun, show surface fields that are generated by dynamo processes in their convective envelopes. Intermediate-mass stars do not have deep convective envelopes, although 10 per cent exhibit strong surface fields that are presumed to be residuals from the star formation process. These stars do have convective cores that might produce internal magnetic fields, and these fields might survive into later stages of stellar evolution, but information has been limited by our inability to measure the fields below the stellar surface. Here we report the strength of dipolar oscillation modes for a sample of 3,600 red giant stars. About 20 per cent of our sample show mode suppression, by strong magnetic fields in the cores, but this fraction is a strong function of mass. Strong core fields occur only in red giants heavier than 1.1 solar masses, and the occurrence rate is at least 50 per cent for intermediate-mass stars (1.6-2.0 solar masses), indicating that powerful dynamos were very common in the previously convective cores of these stars.

  8. Simulations of Dynamo and Magnetorotational Instability in Madison Plasma Experiments and Astrophysical Disks

    Energy Technology Data Exchange (ETDEWEB)

    Ebrahimi, Fatima [Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences

    2018-02-22

    Magnetic fields are observed to exist on all scales in many astrophysical sources such as stars, galaxies, and accretion discs. Understanding the origin of large scale magnetic fields, whereby the field emerges on spatial scales large compared to the fluctuations, has been a particularly long standing challenge. Our physics objective are 1) what are the minimum ingredients for large-scale dynamo growth? 2) could a large-scale magnetic field grow out of turbulence and sustained despite the presence of dissipation? These questions are fundamental for understanding the large-scale dynamo in both laboratory and astrophysical plasmas. Here, we report major new findings in the area of Large-Scale Dynamo (magnetic field generation). First, we have identified the minimum conditions needed for large-scale field growth. Though quasilinear calculations and numerical simulations, we have shown that the combination of imposed non-axisymmetric fluctuations, even if not helical, and differential rotation (or linear shear in the Cartesian approximation) of the fluctuating field is sufficient to source the electromotive force and generate a large scale magnetic field. By computing planar averaged fields and power spectra in shearing box simulations, we also find large scale dynamo action in the early MRI growth phase - a previously unidentified feature. [F. Ebrahimi and E. Blackman, MNRAS 459, (1422-1431) 2016.& P. Bhat, F. Ebrahimi, and E. G. Blackman, Mon. Not. R. Astron. Soc. 462, 818 (2016)] Second, turbulence is needed to explain the accretion process, the inflow of matter on a central object, in astrophysical disks surrounding black holes and massive stars. Flow-driven magnetorotational instability has long been proposed to explain the transport of angular momentum in accretion disks. However, some initial seed magnetic field is needed to trigger this instability. The initial magnetic field in previous simulations has always been externally imposed, or had a significant

  9. Increasing Helicity to Achieve a Dynamo State on the Three-Meter Model of the Earth's Core

    Science.gov (United States)

    Rojas, R.; Perevalov, A.; Lathrop, D. P.

    2017-12-01

    Dynamo theory describes the generation of magnetic fields in the flows of conducting fluids, for example, in stars and planetary cores. Spherical Couette flows, which are flows between two concentric and independently rotating spheres, is one of the experimental models for achieving this task in the laboratory. We have performed dynamo state search in our three-meter spherical-Couette model reaching up to Reynolds number near 108 with amplifications of the field between 10-30% but without a self-sustained dynamo magnetic field. A recent numerical work [K. Finke and A. Tilgner. Phys. Rev. E, 86:016310, Jul 2012] suggested that a roughened inner core reduces the threshold for dynamo action. The mean flow would have more poloidal component than the one we are generating with our current smooth sphere setup. With baffles flow would be expelled radially outward on the equatorial plane and returned at the poles, with opposite helicities in the two hemispheres. Baffles welded on our smooth inner sphere are proposed to achieve this task. We are working to perform experiments on a scaled water model of our experimental setup with Reynolds number near 105 to measure the helicity improvements of different baffle designs in support of upcoming Three-Meter modifications. We gratefully acknowledge support from NSF EAR-1417148.

  10. Linear astrophysical dynamos in rotating spheres: Differential rotation, anisotropic turbulent magnetic diffusivity, and solar-stellar cycle magnetic parity

    International Nuclear Information System (INIS)

    Yoshimura, H.; Wang, Z.; Wu, F.

    1984-01-01

    Differential rotation dependence of the selection mechanism for magnetic parity of solar and stellar cycles is studied by assuming various differential rotation profiles inn the dynamo equation. The parity selection depends on propagation direction of oscillating magnetic fields in the form of dynamo waves which propagate along isorotation surfaces. When there is any radial gradient in the differential rotation, dynamo waves propagate either equatorward or poleward. In the former case, field systems of the two hemispheres approach each other and collide at the equator. Then, odd parity is selected. In the latter case, field systems of the two hemispheres recede from each other and do not collide at the equator, an even parity is selected. Thus the equatorial migration of wings of the butterfly iagram of the solar cycle and its odd parity are intrinsically related. In the case of purely latitudibnal differential rotation, dynamo waves propagate purely radially and growth rates of odd and even modes are nearly the same even when dynamo strength is weak when the parity selection mechanism should work most efficiently. In this case, anisotropy of turbulent diffusivity is a decisive factor to separate odd and even modes. Unlike in the case of radial-gradient-dominated differential rotation in which any difference between diffusivities for poloidal and toroidal fields enhancess the parity selection without changing the parity, the parity selection in the case of latitudinal-gradient-dominated differential rotation depends on the difference of diffusivities for poloidal and toroidal fields. When diffusivity for poloidal fields iss larger than that for toroidal fields, odd parity is selected; and when diffusivity for toroidal fields is larger, even parity is selected

  11. Kinematic Dynamo Action in the Presence of a Large Scale Velocity

    Science.gov (United States)

    Carvalho, J. C.

    1990-11-01

    RESUMEN. Se investiga la influencia de Un campo de velocidades de ran escala sobre la acci6n del tur bulento. Usando Un proceso de expansi6n, las soluciones se encuentran en el del movimiento lobal y de cizalla pequeflo y para randes de Reynolds. Se calcula la re jeneraci6n tica hasta un orden en el de expansi6n usando convectivas ciclotr6nicas para el campo turbulento de velocidad. ABSTRACT. The influence a scale velocity field upon the kinernatic turbulent dynamo action is . Usinj an expansion process, the solutions are found in the limit of small bulk motion and shear, and for Reynolds number. The majnetic is calculated up to second order in the expansion parameter usin cyclonic convective cells for the turbulent velocity field. Key o'td : HYDROMAGNETICS

  12. The Climate Variability & Predictability (CVP) Program at NOAA - DYNAMO Recent Project Advancements

    Science.gov (United States)

    Lucas, S. E.; Todd, J. F.; Higgins, W.

    2013-12-01

    The Climate Variability & Predictability (CVP) Program supports research aimed at providing process-level understanding of the climate system through observation, modeling, analysis, and field studies. This vital knowledge is needed to improve climate models and predictions so that scientists can better anticipate the impacts of future climate variability and change. To achieve its mission, the CVP Program supports research carried out at NOAA and other federal laboratories, NOAA Cooperative Institutes, and academic institutions. The Program also coordinates its sponsored projects with major national and international scientific bodies including the World Climate Research Programme (WCRP), the International Geosphere-Biosphere Programme (IGBP), and the U.S. Global Change Research Program (USGCRP). The CVP program sits within the Earth System Science (ESS) Division at NOAA's Climate Program Office. Dynamics of the Madden-Julian Oscillation (DYNAMO): The Indian Ocean is one of Earth's most sensitive regions because the interactions between ocean and atmosphere there have a discernable effect on global climate patterns. The tropical weather that brews in that region can move eastward along the equator and reverberate around the globe, shaping weather and climate in far-off places. The vehicle for this variability is a phenomenon called the Madden-Julian Oscillation, or MJO. The MJO, which originates over the Indian Ocean roughly every 30 to 90 days, is known to influence the Asian and Australian monsoons. It can also enhance hurricane activity in the northeast Pacific and Gulf of Mexico, trigger torrential rainfall along the west coast of North America, and affect the onset of El Niño. CVP-funded scientists participated in the DYNAMO field campaign in 2011-12. Results from this international campaign are expected to improve researcher's insights into this influential phenomenon. A better understanding of the processes governing MJO is an essential step toward

  13. Generating buoyant magnetic flux ropes in solar-like convective dynamos

    International Nuclear Information System (INIS)

    Nelson, N J; Miesch, M S

    2014-01-01

    Our Sun exhibits strong convective dynamo action which results in magnetic flux bundles emerging through the stellar surface as magnetic spots. Global-scale dynamo action is believed to generate large-scale magnetic structures in the deep solar interior through the interplay of convection, rotation and shear. Portions of these large-scale magnetic structures are then believed to rise through the convective layer, forming magnetic loops which then pierce the photosphere as sunspot pairs. Previous global simulations of three-dimensional magnetohydrodynamic convection in rotating spherical shells have demonstrated mechanisms whereby large-scale magnetic wreaths can be generated in the bulk of the convection zone. Our recent simulations have achieved sufficiently high levels of turbulence to permit portions of these wreaths to become magnetically buoyant and rise through the simulated convective layer through a combination of magnetic buoyancy and advection by convective giant cells. These buoyant magnetic loops are created in the bulk of the convective layer as strong Lorentz force feedback in the cores of the magnetic wreaths dampen small-scale convective motions, permitting the amplification of local magnetic energies to over 100 times the local kinetic energy. While the magnetic wreaths are largely generated the shearing of axisymmetric poloidal magnetic fields by axisymmetric rotational shear (the Ω-effect), the loops are amplified to their peak field strengths before beginning to rise by non-axisymmetric processes. This further extends and enhances a new paradigm for the generation of emergent magnetic flux bundles, which we term turbulence-enabled magnetic buoyancy. (paper)

  14. Dynamo action and magnetic activity during the pre-main sequence: Influence of rotation and structural changes

    Science.gov (United States)

    Emeriau-Viard, Constance; Brun, Allan Sacha

    2017-10-01

    During the PMS, structure and rotation rate of stars evolve significantly. We wish to assess the consequences of these drastic changes on stellar dynamo, internal magnetic field topology and activity level by mean of HPC simulations with the ASH code. To answer this question, we develop 3D MHD simulations that represent specific stages of stellar evolution along the PMS. We choose five different models characterized by the radius of their radiative zone following an evolutionary track, from 1 Myr to 50 Myr, computed by a 1D stellar evolution code. We introduce a seed magnetic field in the youngest model and then we spread it through all simulations. First of all, we study the consequences that the increase of rotation rate and the change of geometry of the convective zone have on the dynamo field that exists in the convective envelop. The magnetic energy increases, the topology of the magnetic field becomes more complex and the axisymmetric magnetic field becomes less predominant as the star ages. The computation of the fully convective MHD model shows that a strong dynamo develops with a ratio of magnetic to kinetic energy reaching equipartition and even super-equipartition states in the faster rotating cases. Magnetic fields resulting from our MHD simulations possess a mixed poloidal-toroidal topology with no obvious dominant component. We also study the relaxation of the vestige dynamo magnetic field within the radiative core and found that it satisfies stability criteria. Hence it does not experience a global reconfiguration and instead slowly relaxes by retaining its mixed poloidal-toroidal topology.

  15. Accretion disc dynamo activity in local simulations spanning weak-to-strong net vertical magnetic flux regimes

    Science.gov (United States)

    Salvesen, Greg; Simon, Jacob B.; Armitage, Philip J.; Begelman, Mitchell C.

    2016-03-01

    Strongly magnetized accretion discs around black holes have attractive features that may explain enigmatic aspects of X-ray binary behaviour. The structure and evolution of these discs are governed by a dynamo-like mechanism, which channels part of the accretion power liberated by the magnetorotational instability (MRI) into an ordered toroidal magnetic field. To study dynamo activity, we performed three-dimensional, stratified, isothermal, ideal magnetohydrodynamic shearing box simulations. The strength of the self-sustained toroidal magnetic field depends on the net vertical magnetic flux, which we vary across almost the entire range over which the MRI is linearly unstable. We quantify disc structure and dynamo properties as a function of the initial ratio of mid-plane gas pressure to vertical magnetic field pressure, β _0^mid = p_gas / p_B. For 10^5 ≥ β _0^mid ≥ 10 the effective α-viscosity parameter scales as a power law. Dynamo activity persists up to and including β _0^mid = 10^2, at which point the entire vertical column of the disc is magnetic pressure dominated. Still stronger fields result in a highly inhomogeneous disc structure, with large density fluctuations. We show that the turbulent steady state βmid in our simulations is well matched by the analytic model of Begelman et al. describing the creation and buoyant escape of toroidal field, while the vertical structure of the disc can be broadly reproduced using this model. Finally, we discuss the implications of our results for observed properties of X-ray binaries.

  16. Simulations of Magnetic Flux Emergence in Cool, Low-Mass Stars: Toward Linking Dynamo Action with Starspots

    Science.gov (United States)

    Weber, Maria Ann; Browning, Matthew; Nelson, Nicholas

    2018-01-01

    Starspots are windows into a star’s internal dynamo mechanism. However, the manner by which the dynamo-generated magnetic field traverses the stellar interior to emerge at the surface is not especially well understood. Establishing the details of magnetic flux emergence plays a key role in deciphering stellar dynamos and observed starspot properties. In the solar context, insight into this process has been obtained by assuming the magnetism giving rise to sunspots consists partly of idealized thin flux tubes (TFTs). Here, we present three sets of TFT simulations in rotating spherical shells of convection: one representative of the Sun, the second of a solar-like rapid rotator, and the third of a fully convective M dwarf. Our solar simulations reproduce sunspot observables such as low-latitude emergence, tilting action toward the equator following the Joy’s Law trend, and a phenomenon akin to active longitudes. Further, we compare the evolution of rising flux tubes in our (computationally inexpensive) TFT simulations to buoyant magnetic structures that arise naturally in a unique global simulation of a rapidly rotating Sun. We comment on the role of rapid rotation, the Coriolis force, and external torques imparted by the surrounding convection in establishing the trajectories of the flux tubes across the convection zone. In our fully convective M dwarf simulations, the expected starspot latitudes deviate from the solar trend, favoring significantly poleward latitudes unless the differential rotation is sufficiently prograde or the magnetic field is strongly super-equipartition. Together our work provides a link between dynamo-generated magnetic fields, turbulent convection, and observations of starspots along the lower main sequence.

  17. Seasonal Environmental Characteristics for the Tropical Cyclone Genesis in the Indian Ocean during the CINDY2011/DYNAMO Field Experiment

    Directory of Open Access Journals (Sweden)

    Aya Tsuboi

    2016-05-01

    Full Text Available This study investigated the seasonal environmental characteristics for tropical cyclone genesis (TCG over the Indian Ocean during the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 and the Dynamics of the Madden–Julian Oscillation (MJO (CINDY2011/DYNAMO field experiment and compare them with long-term climatological features. It was found that the spatial pattern of an empirical environmental index for TCG over the tropical Indian Ocean in 2011 is very similar to the feature composited over the years with high activity of MJO. The analyses of the contributions from each environmental factor indicated that relative humidity, absolute vorticity, and vertical velocity contribute to generate positive influences on the conditions for TCG in 2011. The influences of La Niña appear only through a shear effect over the Indian Ocean in 2011. Under the influences of active MJO events during the CINDY2011/DYNAMO period, the environmental conditions for TCG over the Indian Ocean are determined more strongly by MJO than by La Niña, through modifications of some environmental properties favorable for TCG. The environmental characteristics during CINDY2011/DYNAMO seem to be quite typical of the MJO active years; in such a case, the influences of El Niño/La Niña would not appear in determining the environmental conditions for TCG over the Indian Ocean.

  18. Dynamos in asymptotic-giant-branch stars as the origin of magnetic fields shaping planetary nebulae.

    Science.gov (United States)

    Blackman, E G; Frank, A; Markiel, J A; Thomas, J H; Van Horn, H M

    2001-01-25

    Planetary nebulae are thought to be formed when a slow wind from the progenitor giant star is overtaken by a subsequent fast wind generated as the star enters its white dwarf stage. A shock forms near the boundary between the winds, creating the relatively dense shell characteristic of a planetary nebula. A spherically symmetric wind will produce a spherically symmetric shell, yet over half of known planetary nebulae are not spherical; rather, they are elliptical or bipolar in shape. A magnetic field could launch and collimate a bipolar outflow, but the origin of such a field has hitherto been unclear, and some previous work has even suggested that a field could not be generated. Here we show that an asymptotic-giant-branch (AGB) star can indeed generate a strong magnetic field, having as its origin a dynamo at the interface between the rapidly rotating core and the more slowly rotating envelope of the star. The fields are strong enough to shape the bipolar outflows that produce the observed bipolar planetary nebulae. Magnetic braking of the stellar core during this process may also explain the puzzlingly slow rotation of most white dwarf stars.

  19. Galactic Dynamos and Density Wave Theory - Part Two - an Alternative Treatment for Strong Non-Axisymmetry

    Science.gov (United States)

    Subramanian, K.; Mestel, L.

    1993-12-01

    A steady density wave in a disc-like galaxy could lead to a spiral form for the crucial α-effect term in standard dynamo theory. We had earlier studied this problem under the thin-disc approximation and by effecting an approximate separation of variables between the z-dependence and the r, φ-dependences of the magnetic field. We return to this problem by making an alternative approximation of our equations, which allows a better treatment of the case of strong departures from axisymmetry, albeit with a cruder treatment of the z-dependence. The numerical solution of the equations reveals, as in our earlier work, the existence of rapidly growing, global, bisymmetric magnetic modes, corotating with the density wave. The modes extend several kiloparsecs around the radius r_c_ where the wave corotates with the gas. The magnetic spiral is closely aligned with the density wave in regions where it has maximum strength; leading within r_c_ and trailing outside. These results are remarkably similar to that obtained in our earlier work, under a very different approximation scheme, encouraging belief in the robustness of the results obtained in both papers.

  20. THE SMALL-SCALE DYNAMO AND NON-IDEAL MAGNETOHYDRODYNAMICS IN PRIMORDIAL STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Schober, Jennifer; Federrath, Christoph; Glover, Simon; Klessen, Ralf S. [Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Schleicher, Dominik [Institut fuer Astrophysik, Georg-August-Universitaet Goettingen, Friedrich-Hund-Platz, D-37077 Goettingen (Germany); Banerjee, Robi, E-mail: schober@stud.uni-heidelberg.de, E-mail: christoph.federrath@monash.edu, E-mail: glover@uni-heidelberg.de, E-mail: klessen@uni-heidelberg.de, E-mail: dschleic@astro.physik.uni-goettingen.de, E-mail: banerjee@hs.uni-hamburg.de [Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg (Germany)

    2012-08-01

    We study the amplification of magnetic fields during the formation of primordial halos. The turbulence generated by gravitational infall motions during the formation of the first stars and galaxies can amplify magnetic fields very efficiently and on short timescales up to dynamically significant values. Using the Kazantsev theory, which describes the so-called small-scale dynamo-a magnetohydrodynamical process converting kinetic energy from turbulence into magnetic energy-we can then calculate the growth rate of the small-scale magnetic field. Our calculations are based on a detailed chemical network and we include non-ideal magnetohydrodynamical effects such as ambipolar diffusion and Ohmic dissipation. We follow the evolution of the magnetic field up to larger scales until saturation occurs on the Jeans scale. Assuming a weak magnetic seed field generated by the Biermann battery process, both Burgers and Kolmogorov turbulence lead to saturation within a rather small density range. Such fields are likely to become relevant after the formation of a protostellar disk and, thus, could influence the formation of the first stars and galaxies in the universe.

  1. Sudden transitions and grand variations in the solar dynamo, past and future☆

    Directory of Open Access Journals (Sweden)

    De Jager Cornelis

    2012-06-01

    Full Text Available The solar dynamo is the exotic dance of the sun’s two major magnetic field components, the poloidal and the toroidal, interacting in anti-phase. On the basis of new data on the geomagnetic aa index, we improve our previous forecast of the properties of the current Schwabe cycle #24. Its maximum will occur in 2013.5 and the maximum sunspot number Rmax will then be 62 ± 12, which is within the bounds of our earlier forecasts. The subsequent analysis, based on a phase diagram, which is a diagram showing the relation between maximum sunspot numbers and minimum geomagnetic aa index values leads to the conclusion that a new Grand Episode in solar activity has started in 2008. From the study of the natural oscillations in the sunspot number time series, as found by an analysis based on suitable wavelet base functions, we predict that this Grand Episode will be of the Regular Oscillations type, which is the kind of oscillations that also occurred between 1724 and 1924. Previous expectations of a Grand (Maunder-type Minimum of solar activity cannot be supported. We stress the significance of the Hallstatt periodicity for determining the character of the forthcoming Grand Episodes. No Grand Minimum is expected to occur during the millennium that has just started.

  2. Sudden transitions and grand variations in the solar dynamo, past and future

    Science.gov (United States)

    De Jager, Cornelis; Duhau, Silvia

    2012-06-01

    The solar dynamo is the exotic dance of the sun's two major magnetic field components, the poloidal and the toroidal, interacting in anti-phase. On the basis of new data on the geomagnetic aa index, we improve our previous forecast of the properties of the current Schwabe cycle #24. Its maximum will occur in 2013.5 and the maximum sunspot number Rmax will then be 62 ± 12, which is within the bounds of our earlier forecasts. The subsequent analysis, based on a phase diagram, which is a diagram showing the relation between maximum sunspot numbers and minimum geomagnetic aa index values leads to the conclusion that a new Grand Episode in solar activity has started in 2008. From the study of the natural oscillations in the sunspot number time series, as found by an analysis based on suitable wavelet base functions, we predict that this Grand Episode will be of the Regular Oscillations type, which is the kind of oscillations that also occurred between 1724 and 1924. Previous expectations of a Grand (Maunder-type) Minimum of solar activity cannot be supported. We stress the significance of the Hallstatt periodicity for determining the character of the forthcoming Grand Episodes. No Grand Minimum is expected to occur during the millennium that has just started. The full text of all quoted papers by the two authors of this paper can be consulted at www.cdejager.com/sun-earth-publications/.

  3. Magnetorotational instability and dynamo action in gravito-turbulent astrophysical discs

    Science.gov (United States)

    Riols, A.; Latter, H.

    2018-02-01

    Though usually treated in isolation, the magnetorotational and gravitational instabilities (MRI and GI) may coincide at certain radii and evolutionary stages of protoplanetary discs and active galactic nuclei. Their mutual interactions could profoundly influence several important processes, such as accretion variability and outbursts, fragmentation and disc truncation, or large-scale magnetic field production. Direct numerical simulations of both instabilities are computationally challenging and remain relatively unexplored. In this paper, we aim to redress this neglect via a set of 3D vertically stratified shearing-box simulations, combining self-gravity and magnetic fields. We show that gravito-turbulence greatly weakens the zero-net-flux MRI. In the limit of efficient cooling (and thus enhanced GI), the MRI is completely suppressed, and yet strong magnetic fields are sustained by the gravito-turbulence. This turbulent `spiral wave' dynamo may have widespread application, especially in galactic discs. Finally, we present preliminary work showing that a strong net-vertical-flux revives the MRI and supports a magnetically dominated state in which the GI is secondary.

  4. On possible cosmic origin of the 11-year solar cycle

    Science.gov (United States)

    Kotov, V. A.; Sanchez, F. M.; Bizouard, K.

    2012-06-01

    In order to test Dicke's idea of a clock hidden inside the Sun and determine the initial phase of the solar cycle, the epochs of the extrema of the Wolf numbers observed over the past 400 years are examined. It is shown that extrema that obey the period P W equaled 11.07(4) years retain the initial phase, which cannot be explained in terms of local physics and concepts of the past century regarding the mechanism of the solar cycle based on the theory of a magnetic dynamo and the phenomenological model of the Babcock-Leighton cycle. It is suggested that the cycle has a cosmic (cosmological) origin. This is clearly indicated by the correlation of the cycle period with a holographic time-scale of the Universe, ( a 0 R 3)1/4/ c ≈ 11.0(4) years, where a 0 and R are the radii of the first Bohr orbit of a hydrogen atom and the observable Universe, respectively, and c is the speed of light. It is noted that there are other strict holographic relations that include a 0, R, P W , the wavelength of the microwave background radiation (with a temperature of 2.7 K), and a period of the global solar pulsations equal to 9600.6 s. The true physical nature of the governing mechanism for the 11-year cycle can perhaps only be understood based on modern concepts about the nonlocality of our world, which follows from Bell's theorem, which is grounded on the achievements of quantum mechanics at the turn of the 20th and 21st centuries, as well as using a model of a holographic Universe free of c.

  5. Small-scale dynamo magnetism as the driver for heating the solar atmosphere.

    Science.gov (United States)

    Amari, Tahar; Luciani, Jean-François; Aly, Jean-Jacques

    2015-06-11

    The long-standing problem of how the solar atmosphere is heated has been addressed by many theoretical studies, which have stressed the relevance of two specific mechanisms, involving magnetic reconnection and waves, as well as the necessity of treating the chromosphere and corona together. But a fully consistent model has not yet been constructed and debate continues, in particular about the possibility of coronal plasma being heated by energetic phenomena observed in the chromosphere. Here we report modelling of the heating of the quiet Sun, in which magnetic fields are generated by a subphotospheric fluid dynamo intrinsically connected to granulation. We find that the fields expand into the chromosphere, where plasma is heated at the rate required to match observations (4,500 watts per square metre) by small-scale eruptions that release magnetic energy and drive sonic motions. Some energetic eruptions can even reach heights of 10 million metres above the surface of the Sun, thereby affecting the very low corona. Extending the model by also taking into account the vertical weak network magnetic field allows for the existence of a mechanism able to heat the corona above, while leaving unchanged the physics of chromospheric eruptions. Such a mechanism rests on the eventual dissipation of Alfvén waves generated inside the chromosphere and that carry upwards the required energy flux of 300 watts per square metre. The model shows a topologically complex magnetic field of 160 gauss on the Sun's surface, agreeing with inferences obtained from spectropolarimetric observations, chromospheric features (contributing only weakly to the coronal heating) that can be identified with observed spicules and blinkers, and vortices that may be possibly associated with observed solar tornadoes.

  6. A small-scale dynamo in feedback-dominated galaxies - III. Cosmological simulations

    Science.gov (United States)

    Rieder, Michael; Teyssier, Romain

    2017-12-01

    Magnetic fields are widely observed in the Universe in virtually all astrophysical objects, from individual stars to entire galaxies, even in the intergalactic medium, but their specific genesis has long been debated. Due to the development of more realistic models of galaxy formation, viable scenarios are emerging to explain cosmic magnetism, thanks to both deeper observations and more efficient and accurate computer simulations. We present here a new cosmological high-resolution zoom-in magnetohydrodynamic (MHD) simulation, using the adaptive mesh refinement technique, of a dwarf galaxy with an initially weak and uniform magnetic seed field that is amplified by a small-scale dynamo (SSD) driven by supernova-induced turbulence. As first structures form from the gravitational collapse of small density fluctuations, the frozen-in magnetic field separates from the cosmic expansion and grows through compression. In a second step, star formation sets in and establishes a strong galactic fountain, self-regulated by supernova explosions. Inside the galaxy, the interstellar medium becomes highly turbulent, dominated by strong supersonic shocks, as demonstrated by the spectral analysis of the gas kinetic energy. In this turbulent environment, the magnetic field is quickly amplified via a SSD process and is finally carried out into the circumgalactic medium by a galactic wind. This realistic cosmological simulation explains how initially weak magnetic seed fields can be amplified quickly in early, feedback-dominated galaxies, and predicts, as a consequence of the SSD process, that high-redshift magnetic fields are likely to be dominated by their small-scale components.

  7. Manifestations of the MHD and kinetic dynamo through soft x-rays

    Energy Technology Data Exchange (ETDEWEB)

    Chartas, G.A.

    1991-08-01

    The underlying mechanisms that produce and sustain the reversed toroidal field in RFP's are investigated by analyzing 2Dx-ray emissivity reconstruction and by correlating the evolution of the hot electron properties to the reversed toroidal magnetic field. Reconnection of emissivity surfaces as seen in soft x-ray (SXR) reconstructing occur near the predicted resonant surface for the m=1, n=5, 6,-7 resistive tearing modes. Two distinct rates of reversed magnetic field generation are observed. First, in the MHD relaxation phase a sudden increase in B{sub t}(a) is detected. This event coincides with a large increase in the edge hot electron current density. The second mode of flux generation is observed t have a slower rate and occurs during the diffusion phase. A variation of the edge hot electron current density by a factor of four produced only a small change in the measured B{sub t}(a), implying the contributions of the hot electrons to the dynamo during the diffusion phase is small. {tilde T}{sub e}, / was measured to be approximately 60%, which is much larger than the corresponding quantity for the bulk component which is about 30%. Scaling of the magnetic Reynolds number with the diffusion and MHD relaxation time, {tau}{sub MHD} indicated that the {tau}{sub MHD} does not have a strong dependence on the Spitzer resistivity whereas the diffusion time does depend on the classical resistivity. SXR emission mode analysis during the transition from a rotating to a locked plasma shows a decrease in the m=1 Fourier Bastille component of the emissivity. This is due to the flattening of the emissivity profile as seen in the SXR reconstructions.

  8. Comparison of tobacco control scenarios: quantifying estimates of long-term health impact using the DYNAMO-HIA modeling tool.

    Science.gov (United States)

    Kulik, Margarete C; Nusselder, Wilma J; Boshuizen, Hendriek C; Lhachimi, Stefan K; Fernández, Esteve; Baili, Paolo; Bennett, Kathleen; Mackenbach, Johan P; Smit, H A

    2012-01-01

    There are several types of tobacco control interventions/policies which can change future smoking exposure. The most basic intervention types are 1) smoking cessation interventions 2) preventing smoking initiation and 3) implementation of a nationwide policy affecting quitters and starters simultaneously. The possibility for dynamic quantification of such different interventions is key for comparing the timing and size of their effects. We developed a software tool, DYNAMO-HIA, which allows for a quantitative comparison of the health impact of different policy scenarios. We illustrate the outcomes of the tool for the three typical types of tobacco control interventions if these were applied in the Netherlands. The tool was used to model the effects of different types of smoking interventions on future smoking prevalence and on health outcomes, comparing these three scenarios with the business-as-usual scenario. The necessary data input was obtained from the DYNAMO-HIA database which was assembled as part of this project. All smoking interventions will be effective in the long run. The population-wide strategy will be most effective in both the short and long term. The smoking cessation scenario will be second-most effective in the short run, though in the long run the smoking initiation scenario will become almost as effective. Interventions aimed at preventing the initiation of smoking need a long time horizon to become manifest in terms of health effects. The outcomes strongly depend on the groups targeted by the intervention. We calculated how much more effective the population-wide strategy is, in both the short and long term, compared to quit smoking interventions and measures aimed at preventing the initiation of smoking. By allowing a great variety of user-specified choices, the DYNAMO-HIA tool is a powerful instrument by which the consequences of different tobacco control policies and interventions can be assessed.

  9. Comparison of tobacco control scenarios: quantifying estimates of long-term health impact using the DYNAMO-HIA modeling tool.

    Directory of Open Access Journals (Sweden)

    Margarete C Kulik

    Full Text Available BACKGROUND: There are several types of tobacco control interventions/policies which can change future smoking exposure. The most basic intervention types are 1 smoking cessation interventions 2 preventing smoking initiation and 3 implementation of a nationwide policy affecting quitters and starters simultaneously. The possibility for dynamic quantification of such different interventions is key for comparing the timing and size of their effects. METHODS AND RESULTS: We developed a software tool, DYNAMO-HIA, which allows for a quantitative comparison of the health impact of different policy scenarios. We illustrate the outcomes of the tool for the three typical types of tobacco control interventions if these were applied in the Netherlands. The tool was used to model the effects of different types of smoking interventions on future smoking prevalence and on health outcomes, comparing these three scenarios with the business-as-usual scenario. The necessary data input was obtained from the DYNAMO-HIA database which was assembled as part of this project. All smoking interventions will be effective in the long run. The population-wide strategy will be most effective in both the short and long term. The smoking cessation scenario will be second-most effective in the short run, though in the long run the smoking initiation scenario will become almost as effective. Interventions aimed at preventing the initiation of smoking need a long time horizon to become manifest in terms of health effects. The outcomes strongly depend on the groups targeted by the intervention. CONCLUSION: We calculated how much more effective the population-wide strategy is, in both the short and long term, compared to quit smoking interventions and measures aimed at preventing the initiation of smoking. By allowing a great variety of user-specified choices, the DYNAMO-HIA tool is a powerful instrument by which the consequences of different tobacco control policies and

  10. Reducing and measuring fluctuations in the MST RFP: Enhancement of energy confinement and measurement of the MHD dynamo

    International Nuclear Information System (INIS)

    Den Hartog, D.J.; Almagri, A.F.

    1996-09-01

    A three- to five-fold enhancement of the energy confinement time in a reversed-field pinch (RFP) has been achieved in the Madison Symmetric Torus (MST) by reducing the amplitude of tearing mode fluctuations responsible for anomalous transport in the core of the RFP. By applying a transient poloidal inductive electric field to flatten the current density profile, the fluctuation amplitude b/B decreases from 1.5% to 0.8%, the electron temperature T e0 increases from 250 eV to 370 eV, the ohmic input power decreases from 4.5 MW to approximately 1.5 MW, the poloidal beta β 0 increases from 6% to 9%, and the energy confinement time τ E increases from 1 ms to ∼5 ms in I φ = 340 kA plasmas with density n = 1 x 10 19 m -3 . Current profile control methods are being developed for the RFP in a program to eliminate transport associated with these current-gradient-driven fluctuations. In addition to controlling the amplitude of the tearing modes, we are vigorously pursuing an understanding of the physics of these fluctuations. In particular, plasma flow, both equilibrium and fluctuating, plays a critical role in a diversity of physical phenomena in MST. The key results: 1) Edge probe measurements show that the MHD dynamo is active in low collisionality plasmas, while at high collisionality a new mechanism, the 'electron diamagnetic dynamo,' is observed. 2) Core spectroscopic measurements show that the toroidal velocity fluctuations of the plasma are coherent with the large-scale magnetic tearing modes; the scalar product of these two fluctuating quantities is similar to that expected for the MHD dynamo electromotive force. 3) Toroidal plasma flow in MST exhibits large radial shear and can be actively controlled, including unlocking locked discharges, by modifying E r with a robust biased probe. 24 refs

  11. Tropical deep convection, entrainment, and dilution during the dynamo field campaign

    Science.gov (United States)

    Hannah, Walter

    This dissertation presents a study of outstanding questions in tropical meteorology relating to tropical deep convection, entrainment, and dilution. Much of the discussion in this study will focus on an important convectively-coupled phenomenon in the tropical atmosphere known as the Madden-Julian Oscillation (MJO), which is an eastward propagating atmospheric disturbance over the Indian and West Pacific Oceans that dominates the tropical variability on intraseasonal timescales (30-90 days). A field campaign known as the "Dynamics of the MJO" (DYNAMO) was conducted in the boreal winter months from October 2011 through February 2012 to study the initialization of the MJO with in-situ observations. The first part of this study examines hindcast simulations of the first two MJO events during DYNAMO in a general circulation model (GCM). The model used for this is the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM5) version 5, which uses parameterized convection. In these simulations, an entrainment rate parameter is varied to test its effects on the representation of the MJO, following previous studies. Hindcast simulations with CAM5 reveal that the entrainment parameter can improve the representation of the MJO. However, analysis of the column integrated moist static energy (MSE) budget reveals that this improvement is the right answer for the wrong reason. CAM5 incorrectly enhances vertical MSE advection, which compensates for cloud radiative feedbacks that are too weak. A promising theory for the MJOs fundamental dynamics is that of a moisture mode. The second part of the study examines hindcasts using the super-parameterized version of CAM5 (SP-CAM) that uses embedded cloud-resolving models (CRM) to explicitly simulate convection on the sub-grid scale. SP-CAM was used for these hindcast simulations because previous studies have shown this type of model can reproduce the MJO much better than conventional GCMs. SP-CAM hindcasts yield

  12. A dynamo theory prediction for solar cycle 22: Sunspot number, radio flux, exospheric temperature, and total density at 400 km

    Science.gov (United States)

    Schatten, K. H.; Hedin, A. E.

    1986-01-01

    Using the dynamo theory method to predict solar activity, a value for the smoothed sunspot number of 109 + or - 20 is obtained for solar cycle 22. The predicted cycle is expected to peak near December, 1990 + or - 1 year. Concommitantly, F(10.7) radio flux is expected to reach a smoothed value of 158 + or - 18 flux units. Global mean exospheric temperature is expected to reach 1060 + or - 50 K and global total average total thermospheric density at 400 km is expected to reach 4.3 x 10 to the -15th gm/cu cm + or - 25 percent.

  13. A dynamo theory prediction for solar cycle 22 - Sunspot number, radio flux, exospheric temperature, and total density at 400 km

    Science.gov (United States)

    Schatten, K. H.; Hedin, A. E.

    1984-01-01

    Using the 'dynamo theory' method to predict solar activity, a value for the smoothed sunspot number of 109 + or - 20 is obtained for solar cycle 22. The predicted cycle is expected to peak near December, 1990 + or - 1 year. Concommitantly, F(10.7) radio flux is expected to reach a smoothed value of 158 + or - 18 flux units. Global mean exospheric temperature is expected to reach 1060 + or - 50 K and global total average total thermospheric density at 400 km is expected to reach 4.3 x 10 to the -15th gm/cu cm + or - 25 percent.

  14. DYNAMO: a Mars upper atmosphere package for investigating solar wind interaction and escape processes, and mapping Martian fields

    DEFF Research Database (Denmark)

    Chassefiere, E.; Nagy, A.; Mandea, M.

    2004-01-01

    DYNAMO is a small multi-instrument payload aimed at characterizing current atmospheric escape, which is still poorly constrained, and improving gravity and magnetic field representations, in order to better understand the magnetic, geologic and thermal history of Mars. The internal structure...... of periapsis 170 km), and in a lesser extent 2a, offers an unprecedented opportunity to investigate by in situ probing the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, and therefore the present atmospheric escape rate...

  15. Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander

    Science.gov (United States)

    2016-10-14

    lunar dynamo may have been variable in direction. Published by Elsevier Inc. 1 o a M s u t o F R P b w 1 r l h c i n...i n i t a n H ttp://dx.doi.org/10.1016/j.icarus.2016.09.038 019-1035/ Published by Elsevier Inc. rium and Serenitatis basins has...Bethell a , c a Department of Earth & Planetary Sciences , University of California Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA b Red Sky

  16. High Magnetic Shear Gain in a Liquid Sodium Stable Couette Flow Experiment: A Prelude to an α-Ω Dynamo

    International Nuclear Information System (INIS)

    Colgate, Stirling A.; Beckley, Howard; Si, Jiahe; Martinic, Joe; Westpfahl, David; Slutz, James; Westrom, Cebastian; Klein, Brianna; Schendel, Paul; Scharle, Cletus; McKinney, Travis; Ginanni, Rocky; Bentley, Ian; Mickey, Timothy; Ferrel, Regnar; Li, Hui; Pariev, Vladimir; Finn, John

    2011-01-01

    The Ω phase of the liquid sodium α-Ω dynamo experiment at New Mexico Institute of Mining and Technology in cooperation with Los Alamos National Laboratory has demonstrated a high toroidal field B φ that is ≅8xB r , where B r is the radial component of an applied poloidal magnetic field. This enhanced toroidal field is produced by the rotational shear in stable Couette flow within liquid sodium at a magnetic Reynolds number Rm≅120. Small turbulence in stable Taylor-Couette flow is caused by Ekman flow at the end walls, which causes an estimated turbulence energy fraction of (δv/v) 2 ∼10 -3 .

  17. A COUPLED 2 × 2D BABCOCK–LEIGHTON SOLAR DYNAMO MODEL. I. SURFACE MAGNETIC FLUX EVOLUTION

    International Nuclear Information System (INIS)

    Lemerle, Alexandre; Charbonneau, Paul; Carignan-Dugas, Arnaud

    2015-01-01

    The need for reliable predictions of the solar activity cycle motivates the development of dynamo models incorporating a representation of surface processes sufficiently detailed to allow assimilation of magnetographic data. In this series of papers we present one such dynamo model, and document its behavior and properties. This first paper focuses on one of the model’s key components, namely surface magnetic flux evolution. Using a genetic algorithm, we obtain best-fit parameters of the transport model by least-squares minimization of the differences between the associated synthetic synoptic magnetogram and real magnetographic data for activity cycle 21. Our fitting procedure also returns Monte Carlo-like error estimates. We show that the range of acceptable surface meridional flow profiles is in good agreement with Doppler measurements, even though the latter are not used in the fitting process. Using a synthetic database of bipolar magnetic region (BMR) emergences reproducing the statistical properties of observed emergences, we also ascertain the sensitivity of global cycle properties, such as the strength of the dipole moment and timing of polarity reversal, to distinct realizations of BMR emergence, and on this basis argue that this stochasticity represents a primary source of uncertainty for predicting solar cycle characteristics

  18. A COUPLED 2 × 2D BABCOCK–LEIGHTON SOLAR DYNAMO MODEL. I. SURFACE MAGNETIC FLUX EVOLUTION

    Energy Technology Data Exchange (ETDEWEB)

    Lemerle, Alexandre; Charbonneau, Paul; Carignan-Dugas, Arnaud, E-mail: lemerle@astro.umontreal.ca, E-mail: paulchar@astro.umontreal.ca [Département de physique, Université de Montréal, 2900 boul. Édouard-Montpetit, Montréal, QC, H3T 1J4 (Canada)

    2015-09-01

    The need for reliable predictions of the solar activity cycle motivates the development of dynamo models incorporating a representation of surface processes sufficiently detailed to allow assimilation of magnetographic data. In this series of papers we present one such dynamo model, and document its behavior and properties. This first paper focuses on one of the model’s key components, namely surface magnetic flux evolution. Using a genetic algorithm, we obtain best-fit parameters of the transport model by least-squares minimization of the differences between the associated synthetic synoptic magnetogram and real magnetographic data for activity cycle 21. Our fitting procedure also returns Monte Carlo-like error estimates. We show that the range of acceptable surface meridional flow profiles is in good agreement with Doppler measurements, even though the latter are not used in the fitting process. Using a synthetic database of bipolar magnetic region (BMR) emergences reproducing the statistical properties of observed emergences, we also ascertain the sensitivity of global cycle properties, such as the strength of the dipole moment and timing of polarity reversal, to distinct realizations of BMR emergence, and on this basis argue that this stochasticity represents a primary source of uncertainty for predicting solar cycle characteristics.

  19. Energetic Approach to Investigation of Chaotic Behavior of Low-Dimensional Dynamic Systems and its Illustration on a Two-Disc Rikitake Dynamo

    Czech Academy of Sciences Publication Activity Database

    Pánek, D.; Hrušák, J.; Doležel, Ivo

    2007-01-01

    Roč. 43, č. 596 (2007), s. 46-51 ISSN 0321-0499 R&D Projects: GA ČR(CZ) GA102/07/0496 Institutional research plan: CEZ:AV0Z20570509 Keywords : chaotic behavior * low-dimensional chaotic systems * Rikitake dynamo Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  20. A parallel implementation of an MHD code for the simulation of mechanically driven, turbulent dynamos in spherical geometry

    Science.gov (United States)

    Reuter, K.; Jenko, F.; Forest, C. B.; Bayliss, R. A.

    2008-08-01

    A parallel implementation of a nonlinear pseudo-spectral MHD code for the simulation of turbulent dynamos in spherical geometry is reported. It employs a dual domain decomposition technique in both real and spectral space. It is shown that this method shows nearly ideal scaling going up to 128 CPUs on Beowulf-type clusters with fast interconnect. Furthermore, the potential of exploiting single precision arithmetic on standard x86 processors is examined. It is pointed out that the MHD code thereby achieves a maximum speedup of 1.7, whereas the validity of the computations is still granted. The combination of both measures will allow for the direct numerical simulation of highly turbulent cases ( 1500

  1. New solar telescope in Big Bear: evidence for super-diffusivity and small-scale solar dynamos?

    International Nuclear Information System (INIS)

    Goode, Philip R; Abramenko, Valentyna; Yurchyshyn, Vasyl

    2012-01-01

    The 1.6 m clear aperture New Solar Telescope (NST) in Big Bear Solar Observatory (BBSO) is now providing the highest resolution solar data ever. These data have revealed surprises about the Sun on small-scales including the observation that bright points (BPs), which can be used as proxies for the intense, compact magnetic elements that are apparent in photospheric intergranular lanes. The BPs are ever more numerous on ever smaller spatial scales as though there were no limit to how small the BPs can be. Here we discuss high resolution NST data on BPs that provide support for the ideas that a turbulent regime of super-diffusivity dominates in the quiet Sun, and there are local dynamos operating near the solar surface. (comment)

  2. High magnetic shear gain in a liquid sodium stable couette flow experiment A prelude to an alpha - omega dynamo

    Energy Technology Data Exchange (ETDEWEB)

    Colgate, Stirling [Los Alamos National Laboratory; Li, Jui [Los Alamos National Laboratory; Finn, John [Los Alamos National Laboratory; Pariev, Vladimir [Los Alamos National Laboratory; Beckley, Howard [NM INSTIT. OF MINING AND TECH; Si, Jiahe [NM INSTIT. OF MINING AND TECH.; Martinic, Joe [NM INSTIT. OF MINING AND TECH.; Westpfahl, David [NM INSTIT. OF TECH.; Slutz, James [NM INSTIT. OF MINING AND TECH.; Westrom, Zeb [NM INSTIT. OF TECH.; Klein, Brianna [NM INSTIT. OF MINING AND TECH.

    2010-11-08

    The {Omega}-phase of the liquid sodium {alpha}-{Omega} dynamo experiment at NMIMT in cooperation with LANL has successfully demonstrated the production of a high toroidal field, B{sub {phi}} {approx_equal} 8 x B{sub r} from the radial component of an applied poloidal magnetic field, B{sub r}. This enhanced toroidal field is produced by rotational shear in stable Couette Row within liquid sodium at Rm {approx_equal} 120. The small turbulence in stable Taylor-Couette Row is caused by Ekman Row where ({delta}v/v){sup 2} {approx} 10{sup -3}. This high {Omega}-gain in low turbulence flow contrasts with a smaller {Omega}-gain in higher turbulence, Helmholtz-unstable shear flows. This result supports the ansatz that large scale astrophysical magnetic fields are created within semi-coherent large scale motions in which turbulence plays a diffusive role that enables magnetic flux linkage.

  3. Current drive drift waves as a possible mechanism for dynamo effect and transport in reversed field pinches

    International Nuclear Information System (INIS)

    Briguglio, S.; Romanelli, F.; Vlad, G.

    1986-01-01

    The possibility that a current driven drift wave turbulence may be responsible for the outward ion flux observed in Reversed Field Pinches (RFPs) is investigated; the latter flux was recently proposed as the driving mechanism of the dynamo sustaining the poloidal current in the external region of an RFP discharge. It is shown that this possibility can be supported by the linear theory of current driven drift waves. Finally, on the assumption that the transport is dominated by these instabilities, a scaling law for the temperature in RFPs is derived, which shows an approximately linear dependence on the current and a weak dependence on the size of the machine, in agreement with the experimental results. (author)

  4. Simulations of Cloud-Radiation Interaction Using Large-Scale Forcing Derived from the CINDY/DYNAMO Northern Sounding Array

    Science.gov (United States)

    Wang, Shuguang; Sobel, Adam H.; Fridlind, Ann; Feng, Zhe; Comstock, Jennifer M.; Minnis, Patrick; Nordeen, Michele L.

    2015-01-01

    The recently completed CINDY/DYNAMO field campaign observed two Madden-Julian oscillation (MJO) events in the equatorial Indian Ocean from October to December 2011. Prior work has indicated that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of these MJO events. The simulations are driven by the large-scale forcing data set derived from the DYNAMO northern sounding array observations, and carried out in a doubly periodic domain using the Weather Research and Forecasting (WRF) model. Simulated cloud properties and radiative fluxes are compared to those derived from the S-PolKa radar and satellite observations. To accommodate the uncertainty in simulated cloud microphysics, a number of single-moment (1M) and double-moment (2M) microphysical schemes in the WRF model are tested. The 1M schemes tend to underestimate radiative flux anomalies in the active phases of the MJO events, while the 2M schemes perform better, but can overestimate radiative flux anomalies. All the tested microphysics schemes exhibit biases in the shapes of the histograms of radiative fluxes and radar reflectivity. Histograms of radiative fluxes and brightness temperature indicate that radiative biases are not evenly distributed; the most significant bias occurs in rainy areas with OLR less than 150 W/ cu sq in the 2M schemes. Analysis of simulated radar reflectivities indicates that this radiative flux uncertainty is closely related to the simulated stratiform cloud coverage. Single-moment schemes underestimate stratiform cloudiness by a factor of 2, whereas 2M schemes simulate much more stratiform cloud.

  5. Predicting the health impact of lowering salt consumption in Turkey using the DYNAMO health impact assessment tool.

    Science.gov (United States)

    Erkoyun, E; Sözmen, K; Bennett, K; Unal, B; Boshuizen, H C

    2016-11-01

    To estimate the impact of three daily salt consumption scenarios on the prevalence and incidence of ischaemic heart disease (IHD) and cerebrovascular disease in 2025 in the Turkish population aged ≥30 years using the DYNAMO Health Impact Assessment tool. Statistical disease modelling study. DYNAMO health impact assessment was populated using data from Turkey to estimate the prevalence and incidence of IHD and cerebrovascular disease in 2025. TurkSTAT data were used for demographic data, and national surveys were used for salt consumption and disease-specific burden. Three salt consumption scenarios were modelled: (1) reference scenario: mean salt consumption stays the same from 2012-2013 until 2025; (2) gradual decline: daily salt intake reduces steadily by 0.47 g per year by lowering salt intake from bread by 50% and from table salt by 40% by 2025; and (3) World Health Organization (WHO) advice: daily salt intake of 5 g per day from 2013 until 2025. The gradual decline scenario would lead to a decrease in the prevalence of IHD and cerebrovascular disease by 0.3% and 0.2%, respectively, and a decrease in the incidence by 0.6 and 0.4 per 1000, respectively. Following WHO's advice would lead to a decrease in the prevalence of IHD and cerebrovascular disease by 0.8% and 0.5%, respectively, and a decrease in the incidence by 1.0 and 0.7 per 1000, respectively. This model indicates that Turkey can lower its future cardiovascular disease burden by following the gradual decline scenario. Following WHO's advice would achieve an even greater benefit. Copyright © 2016 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.

  6. RIEGER-TYPE PERIODICITY DURING SOLAR CYCLES 14–24: ESTIMATION OF DYNAMO MAGNETIC FIELD STRENGTH IN THE SOLAR INTERIOR

    Energy Technology Data Exchange (ETDEWEB)

    Gurgenashvili, Eka; Zaqarashvili, Teimuraz V.; Kukhianidze, Vasil; Ramishvili, Giorgi; Shergelashvili, Bidzina [Abastumani Astrophysical Observatory at Ilia State University, Tbilisi, Georgia (United States); Oliver, Ramon; Ballester, Jose Luis [Departament de Física, Universitat de les Illes Balears, E-07122, Palma de Mallorca (Spain); Hanslmeier, Arnold [IGAM, Institute of Physics, University of Graz, Universitätsplatz 5, A-8010 Graz (Austria); Poedts, Stefaan, E-mail: teimuraz.zaqarashvili@uni-graz.at [Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, B-3001, Leuven (Belgium)

    2016-07-20

    Solar activity undergoes a variation over timescales of several months known as Rieger-type periodicity, which usually occurs near maxima of sunspot cycles. An early analysis showed that the periodicity appears only in some cycles and is absent in other cycles. But the appearance/absence during different cycles has not been explained. We performed a wavelet analysis of sunspot data from the Greenwich Royal Observatory and the Royal Observatory of Belgium during cycles 14–24. We found that the Rieger-type periods occur in all cycles, but they are cycle dependent: shorter periods occur during stronger cycles. Our analysis revealed a periodicity of 185–195 days during the weak cycles 14–15 and 24 and a periodicity of 155–165 days during the stronger cycles 16–23. We derived the dispersion relation of the spherical harmonics of the magnetic Rossby waves in the presence of differential rotation and a toroidal magnetic field in the dynamo layer near the base of the convection zone. This showed that the harmonics of fast Rossby waves with m = 1 and n = 4, where m ( n ) indicates the toroidal (poloidal) wavenumbers, perfectly fit with the observed periodicity. The variation of the toroidal field strength from weaker to stronger cycles may lead to the different periods found in those cycles, which explains the observed enigmatic feature of the Rieger-type periodicity. Finally, we used the observed periodicity to estimate the dynamo field strength during cycles 14–24. Our estimations suggest a field strength of ∼40 kG for the stronger cycles and ∼20 kG for the weaker cycles.

  7. Emergence of Magnetic Flux Generated in a Solar Convective Dynamo. I. The Formation of Sunspots and Active Regions, and The Origin of Their Asymmetries

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Feng; Rempel, Matthias; Fan, Yuhong, E-mail: chenfeng@ucar.edu [High Altitude Observatory, NCAR, P.O. Box 3000, Boulder, CO, 80307 (United States)

    2017-09-10

    We present a realistic numerical model of sunspot and active region formation based on the emergence of flux bundles generated in a solar convective dynamo. To this end, we use the magnetic and velocity fields in a horizontal layer near the top boundary of the solar convective dynamo simulation to drive realistic radiative-magnetohydrodynamic simulations of the uppermost layers of the convection zone. The main results are as follows. (1) The emerging flux bundles rise with the mean speed of convective upflows and fragment into small-scale magnetic elements that further rise to the photosphere, where bipolar sunspot pairs are formed through the coalescence of the small-scale magnetic elements. (2) Filamentary penumbral structures form when the sunspot is still growing through ongoing flux emergence. In contrast to the classical Evershed effect, the inflow seems to prevail over the outflow in a large part of the penumbra. (3) A well-formed sunspot is a mostly monolithic magnetic structure that is anchored in a persistent deep-seated downdraft lane. The flow field outside the spot shows a giant vortex ring that comprises an inflow below 15 Mm depth and an outflow above 15 Mm depth. (4) The sunspots successfully reproduce the fundamental properties of the observed solar active regions, including the more coherent leading spots with a stronger field strength, and the correct tilts of bipolar sunspot pairs. These asymmetries can be linked to the intrinsic asymmetries in the magnetic and flow fields adapted from the convective dynamo simulation.

  8. The DYNAMO Orbiter Project: High Resolution Mapping of Gravity/Magnetic Fields and In Situ Investigation of Mars Atmospheric Escape

    Science.gov (United States)

    Smrekar, S.; Chassefiere, E.; Forget, F.; Reme, H.; Mazelle, C.; Blelly, P. -L.; Acuna, M.; Connerney, J.; Purucker, M.; Lin, R.

    2000-01-01

    Dynamo is a small Mars orbiter planned to be launched in 2005 or 2007, in the frame of the NASA/CNES Mars exploration program. It is aimed at improving gravity and magnetic field resolution, in order to better understand the magnetic, geologic and thermal history of Mars, and at characterizing current atmospheric escape, which is still poorly constrained. These objectives are achieved by using a low periapsis orbit, similar to the one used by the Mars Global Surveyor spacecraft during its aerobraking phases. The proposed periapsis altitude for Dynamo of 120-130 km, coupled with the global distribution of periapses to be obtained during one Martian year of operation, through about 5000 low passes, will produce a magnetic/gravity field data set with approximately five times the spatial resolution of MGS. Low periapsis provides a unique opportunity to investigate the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, therefore atmospheric escape, which may have played a crucial role in removing atmosphere, and water, from the planet. There is much room for debate on the importance of current atmosphere escape processes in the evolution of the Martian atmosphere, as early "exotic" processes including hydrodynamic escape and impact erosion are traditionally invoked to explain the apparent sparse inventory of present-day volatiles. Yet, the combination of low surface gravity and the absence of a substantial internally generated magnetic field have undeniable effects on what we observe today. In addition to the current losses in the forms of Jeans and photochemical escape of neutrals, there are solar wind interaction-related erosion mechanisms because the upper atmosphere is directly exposed to the solar wind. The solar wind related loss rates, while now comparable to those of a modest comet, nonetheless occur continuously, with the intriguing possibility of important cumulative and

  9. Data acquisition in a high-speed rotating frame for New Mexico Institute of Mining and Technology liquid sodium αω dynamo experiment.

    Science.gov (United States)

    Si, Jiahe; Colgate, Stirling A; Li, Hui; Martinic, Joe; Westpfahl, David

    2013-10-01

    New Mexico Institute of Mining and Technology liquid sodium αω-dynamo experiment models the magnetic field generation in the universe as discussed in detail by Colgate, Li, and Pariev [Phys. Plasmas 8, 2425 (2001)]. To obtain a quasi-laminar flow with magnetic Reynolds number R(m) ~ 120, the dynamo experiment consists of two co-axial cylinders of 30.5 cm and 61 cm in diameter spinning up to 70 Hz and 17.5 Hz, respectively. During the experiment, the temperature of the cylinders must be maintained to 110 °C to ensure that the sodium remains fluid. This presents a challenge to implement a data acquisition (DAQ) system in such high temperature, high-speed rotating frame, in which the sensors (including 18 Hall sensors, 5 pressure sensors, and 5 temperature sensors, etc.) are under the centrifugal acceleration up to 376g. In addition, the data must be transmitted and stored in a computer 100 ft away for safety. The analog signals are digitized, converted to serial signals by an analog-to-digital converter and a field-programmable gate array. Power is provided through brush/ring sets. The serial signals are sent through ring/shoe sets capacitively, then reshaped with cross-talk noises removed. A microcontroller-based interface circuit is used to decode the serial signals and communicate with the data acquisition computer. The DAQ accommodates pressure up to 1000 psi, temperature up to more than 130 °C, and magnetic field up to 1000 G. First physics results have been analyzed and published. The next stage of the αω-dynamo experiment includes the DAQ system upgrade.

  10. SMALL-SCALE AND GLOBAL DYNAMOS AND THE AREA AND FLUX DISTRIBUTIONS OF ACTIVE REGIONS, SUNSPOT GROUPS, AND SUNSPOTS: A MULTI-DATABASE STUDY

    Energy Technology Data Exchange (ETDEWEB)

    Muñoz-Jaramillo, Andrés; Windmueller, John C.; Amouzou, Ernest C.; Longcope, Dana W. [Department of Physics, Montana State University, Bozeman, MT 59717 (United States); Senkpeil, Ryan R. [Department of Physics, Purdue University, West Lafayette, IN 47907 (United States); Tlatov, Andrey G. [Kislovodsk Mountain Astronomical Station of the Pulkovo Observatory, Kislovodsk 357700 (Russian Federation); Nagovitsyn, Yury A. [Pulkovo Astronomical Observatory, Russian Academy of Sciences, St. Petersburg 196140 (Russian Federation); Pevtsov, Alexei A. [National Solar Observatory, Sunspot, NM 88349 (United States); Chapman, Gary A.; Cookson, Angela M. [San Fernando Observatory, Department of Physics and Astronomy, California State University Northridge, Northridge, CA 91330 (United States); Yeates, Anthony R. [Department of Mathematical Sciences, Durham University, South Road, Durham DH1 3LE (United Kingdom); Watson, Fraser T. [National Solar Observatory, Tucson, AZ 85719 (United States); Balmaceda, Laura A. [Institute for Astronomical, Terrestrial and Space Sciences (ICATE-CONICET), San Juan (Argentina); DeLuca, Edward E. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Martens, Petrus C. H., E-mail: munoz@solar.physics.montana.edu [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States)

    2015-02-10

    In this work, we take advantage of 11 different sunspot group, sunspot, and active region databases to characterize the area and flux distributions of photospheric magnetic structures. We find that, when taken separately, different databases are better fitted by different distributions (as has been reported previously in the literature). However, we find that all our databases can be reconciled by the simple application of a proportionality constant, and that, in reality, different databases are sampling different parts of a composite distribution. This composite distribution is made up by linear combination of Weibull and log-normal distributions—where a pure Weibull (log-normal) characterizes the distribution of structures with fluxes below (above) 10{sup 21}Mx (10{sup 22}Mx). Additionally, we demonstrate that the Weibull distribution shows the expected linear behavior of a power-law distribution (when extended to smaller fluxes), making our results compatible with the results of Parnell et al. We propose that this is evidence of two separate mechanisms giving rise to visible structures on the photosphere: one directly connected to the global component of the dynamo (and the generation of bipolar active regions), and the other with the small-scale component of the dynamo (and the fragmentation of magnetic structures due to their interaction with turbulent convection)

  11. Dynamo in protostars

    Indian Academy of Sciences (India)

    It is found in many stars, planets, galax- ies, interstellar medium, etc., and it is believed to induce inflow of matter or accretion in astrophysical disc and immersed cloud, collimated jets and outflows, magnetic break- ing, and protostellar winds. The magnetic field plays a crucial role in all stages of the evolution of a protostar.

  12. Nonlinearity in a dynamo

    Czech Academy of Sciences Publication Activity Database

    Hejda, Pavel; Reshetnyak, M.

    2010-01-01

    Roč. 104, č. 5-6 (2010), s. 491-504 ISSN 0309-1929 R&D Projects: GA AV ČR IAA300120704 Institutional research plan: CEZ:AV0Z30120515 Keywords : Boussinesq convection * geostrophy * quenching * triads Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 0.831, year: 2010

  13. Dynamo in protostars

    Indian Academy of Sciences (India)

    ... Bidya Binay Karak2 3 Rohit Kumar1. Department of Physics, Indian Institute of Technology, Kanpur 208 016, India; Department of Physics, Indian Institute of Science, Bangalore 560 012, India; Nordita KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-106 91 Stockholm, Sweden ...

  14. Evidence for an impact-induced magnetic fabric in Allende, and exogenous alternatives to the core dynamo theory for Allende magnetization

    Science.gov (United States)

    Muxworthy, Adrian R.; Bland, Phillip A.; Davison, Thomas M.; Moore, James; Collins, Gareth S.; Ciesla, Fred J.

    2017-10-01

    We conducted a paleomagnetic study of the matrix of Allende CV3 chondritic meteorite, isolating the matrix's primary remanent magnetization, measuring its magnetic fabric and estimating the ancient magnetic field intensity. A strong planar magnetic fabric was identified; the remanent magnetization of the matrix was aligned within this plane, suggesting a mechanism relating the magnetic fabric and remanence. The intensity of the matrix's remanent magnetization was found to be consistent and low ( 6 μT). The primary magnetic mineral was found to be pyrrhotite. Given the thermal history of Allende, we conclude that the remanent magnetization was formed during or after an impact event. Recent mesoscale impact modeling, where chondrules and matrix are resolved, has shown that low-velocity collisions can generate significant matrix temperatures, as pore-space compaction attenuates shock energy and dramatically increases the amount of heating. Nonporous chondrules are unaffected, and act as heat-sinks, so matrix temperature excursions are brief. We extend this work to model Allende, and show that a 1 km/s planar impact generates bulk porosity, matrix porosity, and fabric in our target that match the observed values. Bimodal mixtures of a highly porous matrix and nominally zero-porosity chondrules make chondrites uniquely capable of recording transient or unstable fields. Targets that have uniform porosity, e.g., terrestrial impact craters, will not record transient or unstable fields. Rather than a core dynamo, it is therefore possible that the origin of the magnetic field in Allende was the impact itself, or a nebula field recorded during transient impact heating.

  15. Trends in ultracool dwarf magnetism. II. The inverse correlation between X-ray activity and rotation as evidence for a bimodal dynamo

    International Nuclear Information System (INIS)

    Cook, B. A.; Williams, P. K. G.; Berger, E.

    2014-01-01

    Observations of magnetic activity indicators in solar-type stars exhibit a relationship with rotation with an increase until a 'saturation' level and a moderate decrease in activity in the very fastest rotators ('supersaturation'). While X-ray data have suggested that this relationship is strongly violated in ultracool dwarfs (UCDs; spectral type ≳M7), the limited number of X-ray detections has prevented firm conclusions. In this paper, we analyze the X-ray activity-rotation relation in 38 UCDs. Our sample represents the largest catalog of X-ray active UCDs to date, including seven new and four previously unpublished Chandra observations presented in a companion paper. We identify a substantial number of rapidly rotating UCDs with X-ray activity extending two orders of magnitude below the expected saturation level and measure a 'supersaturation'-type anticorrelation between rotation and X-ray activity. The scatter in UCD X-ray activity at a fixed rotation is ∼3 times larger than that in earlier-type stars. We discuss several mechanisms that have been proposed to explain the data, including centrifugal stripping of the corona, and find them to be inconsistent with the observed trends. Instead, we suggest that an additional parameter correlated with both X-ray activity and rotation is responsible for the observed effects. Building on the results of Zeeman-Doppler imaging of UCD magnetic fields and our companion study of radio/X-ray flux ratios, we argue that this parameter is the magnetic field topology, and that the large scatter in UCD X-ray fluxes reflects the presence of two dynamo modes that produce distinct topologies.

  16. Electron-positron processes and spectral evolution in black hole accretion disk dynamo models for AGN sources of the cosmic X-ray and γ ray backgrounds

    International Nuclear Information System (INIS)

    Leiter, D.

    1983-01-01

    This work discusses a black hole accretion disk dynamo model for Active Galactic Nuclei (AGN) sources of the cosmic X-ray and γ ray backgrounds which involves both thermal and nonthermal accretion disk processes around greater than or equal to 10 8 M/sub sun/ Kerr black holes. Before black hole spin-up to the Kerr metric state, the large value of the compactness parameter L(luminosity)/r(size of emitting region) > 10 30 erg/cm-sec associated with the L/L/sub Edd/ less than or equal to l luminosity ratio in Precursor Active Galaxies (PAG) suppresses all nonthermal emission mechanisms. In this PAG state the resulting emission is predominantly thermal and is due to Comptonization of soft photons by an electron-positron plasma, generated within the hot accretion disk region by γ + γ reversible e+/- processes in the transrelativistic regime. While the underlying plasma in the PAG accretion disk hot inner region may be optically thin initially, the overall effect of the copious γ + γ reversible e+/- generated electron-positron plasma is to push the overall optical depth to tau greater than or equal to 1. This has two main effects: a) it causes the resulting Comptonized spectrum of X-radiation from PAG to be associated with a flat spectral index comparable to that of the residual Cosmic X-ray Background (CXB), and b) the copious γ + γ reversible e+/- within the hot accretion disk region play the role of a phase transition thermostat, and act to maintain the temperature of the hot inner region at greater than or equal to 109 0 K. 16 references

  17. Asia: The Global Telecom Dynamo.

    Science.gov (United States)

    McClelland, Stephen; Weiss, Edward; Sujarto, P. J.; Nakorn, Pria; Kim, B. A.; Chan, Lily; Bromby, Robin

    1997-01-01

    In a 1995 study, Moody's Investors Research found that companies and governments in the Pacific Rim would require $363 billion for essential telecom infrastructure by the end of the decade. Examines the state of communications in Hong Kong, Indonesia, Malaysia, the Philippines, Singapore, South Korea, Taiwan, Thailand, Australia, and New Zealand.…

  18. Dynamo: A Runtime Codesign Environment

    National Research Council Canada - National Science Library

    Quinn, Heather; Leeser, Miriam; Smith-King, L. A

    2004-01-01

    .... Signal and image processing applications are especially attractive for implementation on FPGAs as their computationally intensive and massively parallel algorithms can effectively take advantage...

  19. Magnetoconvection and the Solar Dynamo

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... Astronomical Observatory & Theoretical Astrophysics Center, Juliane Maries Vej 30, 2100 Copenhagen ɸ, Denmark; The Royal Swedish Academy of Sciences, Stockholm Observatory, SE-13336 Saltsjöbaden, Sweden; Dept. of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, ...

  20. Multi-scale harmonic model for solar and climate cyclical variation throughout the Holocene based on Jupiter-Saturn tidal frequencies plus the 11-year solar dynamo cycle

    Science.gov (United States)

    Scafetta, Nicola

    2012-05-01

    The Schwabe frequency band of the Zurich sunspot record since 1749 is found to be made of three major cycles with periods of about 9.98, 10.9 and 11.86 years. The side frequencies appear to be closely related to the spring tidal period of Jupiter and Saturn (range between 9.5 and 10.5 years, and median 9.93 years) and to the tidal sidereal period of Jupiter (about 11.86 years). The central cycle may be associated to a quasi-11-year solar dynamo cycle that appears to be approximately synchronized to the average of the two planetary frequencies. A simplified harmonic constituent model based on the above two planetary tidal frequencies and on the exact dates of Jupiter and Saturn planetary tidal phases, plus a theoretically deduced 10.87-year central cycle reveals complex quasi-periodic interference/beat patterns. The major beat periods occur at about 115, 61 and 130 years, plus a quasi-millennial large beat cycle around 983 years. We show that equivalent synchronized cycles are found in cosmogenic records used to reconstruct solar activity and in proxy climate records throughout the Holocene (last 12,000 years) up to now. The quasi-secular beat oscillations hindcast reasonably well the known prolonged periods of low solar activity during the last millennium such as the Oort, Wolf, Spörer, Maunder and Dalton minima, as well as the 17 115-year long oscillations found in a detailed temperature reconstruction of the Northern Hemisphere covering the last 2000 years. The millennial three-frequency beat cycle hindcasts equivalent solar and climate cycles for 12,000 years. Finally, the harmonic model herein proposed reconstructs the prolonged solar minima that occurred during 1900-1920 and 1960-1980 and the secular solar maxima around 1870-1890, 1940-1950 and 1995-2005 and a secular upward trending during the 20th century: this modulated trending agrees well with some solar proxy model, with the ACRIM TSI satellite composite and with the global surface temperature

  1. Harmonic model for solar and climate cyclical variation throughout the Holocene based on Jupiter-Saturn tidal frequencies plus the 11-year solar dynamo cycle

    Science.gov (United States)

    Scafetta, N.

    2012-12-01

    We show that the Schwabe frequency band of the Zurich sunspot record since 1749 is made of three major cycles that are closely related to the spring tidal period of Jupiter and Saturn (~9.93 year), to the tidal sidereal period of Jupiter (about 11.86 years) and to a central cycle that may be associated to a quasi-11-year solar dynamo cycle. The central harmonic is approximately synchronized to the average of the two planetary frequencies. A harmonic model based on the above two planetary tidal frequencies and on the exact dates of Jupiter and Saturn planetary tidal phases, plus a theoretically deduced 10.87-year central cycle reveals major beat periods occurring at about 115, 61 and 130 years, plus a quasi-millennial large beat cycle around 983 years. Equivalent synchronized cycles are found in cosmogenic solar proxy records used to reconstruct solar activity and in proxy climate records throughout the Holocene (last 12,000 years) up to now. The quasi-secular beat oscillations hindcast reasonably well the known prolonged periods of low solar activity during the last millennium such as the Oort, Wolf, Sporer, Maunder and Dalton minima, as well as the 17 115-year long oscillations found in a detailed temperature reconstruction of the Northern Hemisphere covering the last 2000 years. The millennial three-frequency beat cycle hindcasts equivalent solar and climate cycles for 12,000 years. Finally, the harmonic model herein proposed reconstructs the prolonged solar minima around 1900-1920 and 1960-1980, the secular solar maxima around 1870-1890, 1940-1950 and 1995-2005, and a secular upward trending during the 20th century. The latter modulated trending agrees well with some solar proxy model, with the ACRIM TSI satellite composite and with the global surface temperature modulation since 1850. The model forecasts a new prolonged solar minimum during 2020-2045, which is produced by the minima of both the 61 and 115-year reconstructed cycles. Finally, the model predicts

  2. Journal of Astrophysics and Astronomy | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... A Critical Assessment of the Flux Transport Dynamo ... Then, we critically examine the inadequacies of the model and the challenge posed by some recent observational data about meridional circulation, arriving at a conclusion ... Department of Physics, Indian Institute of Science, Bangalore 560 012, India.

  3. Sunspot Cycle Prediction Using Multivariate Regression and Binary ...

    Indian Academy of Sciences (India)

    49

    engineering decision making. In the present study, the sunspot cycle prediction has been carried out by a hybrid model which employs ...... 6) Dikpati M, De Toma G and Gilman P A 2006 Predicting the strength of solar cycle 24 using a flux-transport dynamo-based tool; Geophys Res lett. 33(5). L05102. 7) Drecher P E, Little ...

  4. Speed of Meridional Flows and Magnetic Flux Transport on the Sun

    Czech Academy of Sciences Publication Activity Database

    Švanda, Michal; Kosovichev, A.G.; Zhao, J.

    2007-01-01

    Roč. 607, č. 1 (2007), L69-L72 ISSN 0004-637X Grant - others:EU(XE) ESA-PECS project No. 98030 Institutional research plan: CEZ:AV0Z10030501 Source of funding: V - iné verejné zdroje Keywords : Sun * activity * atmospheric motions Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 6.405, year: 2007

  5. Forecasting F10.7 with Solar Magnetic Flux Transport Modeling (Postprint)

    Science.gov (United States)

    2012-04-03

    thought to propagate down field lines and heat chromospheric material at the foot points that in turn rises back into the corona [e.g., Cargill and...389, doi:10.1007/BF00151460. Cargill , P. J., and J. A. Klimchuk (2004), Nanoflare heating of the cor- ona revisited, Astrohys. J., 605, 911–920, doi

  6. Chandrasekhar–Kendall functions in astrophysical dynamos

    Indian Academy of Sciences (India)

    Some of the contributions of Chandrasekhar to the field of magnetohydrodynamics are highlighted. Particular emphasis is placed on the Chandrasekhar–Kendall functions that allow a decomposition of a vector field into right- and left-handed contributions. Magnetic energy spectra of both contributions are shown for a new ...

  7. Full sphere hydrodynamic and dynamo benchmarks

    KAUST Repository

    Marti, P.

    2014-01-26

    Convection in planetary cores can generate fluid flow and magnetic fields, and a number of sophisticated codes exist to simulate the dynamic behaviour of such systems. We report on the first community activity to compare numerical results of computer codes designed to calculate fluid flow within a whole sphere. The flows are incompressible and rapidly rotating and the forcing of the flow is either due to thermal convection or due to moving boundaries. All problems defined have solutions that alloweasy comparison, since they are either steady, slowly drifting or perfectly periodic. The first two benchmarks are defined based on uniform internal heating within the sphere under the Boussinesq approximation with boundary conditions that are uniform in temperature and stress-free for the flow. Benchmark 1 is purely hydrodynamic, and has a drifting solution. Benchmark 2 is a magnetohydrodynamic benchmark that can generate oscillatory, purely periodic, flows and magnetic fields. In contrast, Benchmark 3 is a hydrodynamic rotating bubble benchmark using no slip boundary conditions that has a stationary solution. Results from a variety of types of code are reported, including codes that are fully spectral (based on spherical harmonic expansions in angular coordinates and polynomial expansions in radius), mixed spectral and finite difference, finite volume, finite element and also a mixed Fourier-finite element code. There is good agreement between codes. It is found that in Benchmarks 1 and 2, the approximation of a whole sphere problem by a domain that is a spherical shell (a sphere possessing an inner core) does not represent an adequate approximation to the system, since the results differ from whole sphere results. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.

  8. Chandrasekhar–Kendall functions in astrophysical dynamos

    Indian Academy of Sciences (India)

    see figure 2b), where the peak of the spectrum at k ≡ km travels to smaller wavenumbers. The effect of this is also evident in real space in that larger scale patches of magnetic field. (a). (b). Figure 2. Spectra of magnetic energy of the negatively ...

  9. Hand-held Dynamo-metry

    NARCIS (Netherlands)

    Ploeg, Rutger Jan Otto van der

    1992-01-01

    This study describes the application of a hand-held dynamometer that was designed to measure muscle strength in normal individuals and neurological patients in a simple way, comparable to manual muscle testing. Zie: Summary

  10. Solar Field Mapping and Dynamo Behavior

    Directory of Open Access Journals (Sweden)

    Kenneth H. Schatten

    2012-01-01

    Full Text Available We discuss the importance of the Sun’s large-scale magnetic field to the Sun-Planetary environment. This paper narrows its focus down to the motion and evolution of the photospheric large-scale magnetic field which affects many environments throughout this region. For this purpose we utilize a newly developed Netlogo cellular automata model. The domain of this algorithmic model is the Sun’s photosphere. Within this computational space are placed two types of entities or agents; one may refer to them as bluebirds and cardinals; the former carries outward magnetic flux and the latter carries out inward magnetic flux. One may simply call them blue and red agents. The agents provide a granularity with discrete changes not present in smooth MHD models; they undergo three processes: birth, motion, and death within the photospheric domain. We discuss these processes, as well as how we are able to develop a model that restricts its domain to the photosphere and allows the deeper layers to be considered only through boundary conditions. We show the model’s ability to mimic a number of photospheric magnetic phenomena: the solar cycle (11-year oscillations, the Waldmeier effect, unipolar magnetic regions (e.g. sectors and coronal holes, Maunder minima, and the march/rush to the poles involving the geometry of magnetic field reversals. We also discuss why the Sun sometimes appears as a magnetic monopole, which of course requires no alteration of Maxwell’s equations.

  11. Can short time delays influence the variability of the solar cycle?

    Science.gov (United States)

    Jouve, Laurène; Proctor, Michael R. E.; Lesur, Geoffroy

    2011-08-01

    We present the effects of introducing results of 3D MHD simulations of buoyant magnetic fields in the solar convection zone in 2D mean-field Babcock-Leighton models. In particular, we take into account the time delay introduced by the rise time of the toroidal structures from the base of the convection zone to the solar surface. We find that the delays produce large temporal modulation of the cycle amplitude even when strong and thus rapidly rising flux tubes are considered. The study of a reduced model reveals that aperiodic modulations of the solar cycle appear after a sequence of period doubling bifurcations typical of non-linear systems. We also discuss the memory of such systems and the conclusions which may be drawn concerning the actual solar cycle variability.

  12. Reproducing the Photospheric Magnetic Field Evolution during the Rise of Cycle 24 with Flux Transport by Supergranules

    Science.gov (United States)

    Hathaway, David; Upton, Lisa

    2012-01-01

    We simulate the transport of magnetic flux in the Sun s photosphere by an evolving pattern of cellular horizontal flows (supergranules). Characteristics of the simulated flow pattern can match observed characteristics including the velocity power spectrum, cell lifetimes, and cell motions in longitude and latitude. Simulations using an average, and north-south symmetric, meridional motion of the cellular pattern produce polar magnetic fields that are too weak in the North and too strong in the South. Simulations using cellular patterns with meridional motions that evolve with the observed changes in strength and north-south asymmetry will be analyzed to see if they reproduce the polar field evolution observed during the rise of Cycle 24.

  13. Flux-cutting and flux-transport effects in type-II superconductor slabs in a parallel rotating magnetic field

    International Nuclear Information System (INIS)

    Cortes-Maldonado, R.; Perez-Rodrigues, F.; Espinosa-Rosales, J.E.; Carballo-Sanchez, A.F.

    2011-01-01

    The magnetic response of irreversible type-II superconductor slabs subjected to in-plane rotating magnetic field is investigated by applying the circular, elliptic, extended-elliptic, and rectangular flux-line-cutting critical-state models. Specifically, the models have been applied to explain experiments on a PbBi rotating disk in a fixed magnetic field Ha, parallel to the flat surfaces. Here, we have exploited the equivalency of the experimental situation with that of a fixed disk under the action of a parallel magnetic field, rotating in the opposite sense. The effect of both the magnitude H a of the applied magnetic field and its angle of rotation α s upon the magnetization of the superconductor sample is analyzed. When H a is smaller than the penetration field H p , the magnetization components, parallel and perpendicular to H a , oscillate with increasing the rotation angle. On the other hand, if the magnitude of the applied field, H a , is larger than H p , both magnetization components become constant functions of αs at large rotation angles. The evolution of the magnetic induction profiles inside the superconductor is also studied.

  14. The Current Status of Kinematic Solar Dynamo Models

    Indian Academy of Sciences (India)

    tribpo

    observation is the equatorward migration of the belt of sunspots, which leads to the well-known butterfly diagram. We believe that the sunspots are produced by the magnetic buoyancy of a strong toroidal magnetic field underneath the Sun's surface—an idea first propounded by Parker (1955a). Hence, the butterfly diagram.

  15. Helicity of Solar Active Regions from a Dynamo Model Piyali ...

    Indian Academy of Sciences (India)

    is an indicator of how stressed the active region flux system is and it is known to play an important role in the flaring .... P. C. acknowledges CSIR for financial support. References. Abramenko, V. I., Wang, T., Yurchishin, V. B. 1997, Solar Phys., 174, 291. Bao, S., Zhang, H. 1998, ApJ, 496, L43. Canfield, R. C., Pevtsov, A. A. ...

  16. The Current Status of Kinematic Solar Dynamo Models

    Indian Academy of Sciences (India)

    Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately.

  17. A Remarkable Recent Transition in the Solar Dynamo

    NARCIS (Netherlands)

    de Jager, C.; Akasofu, S.-I.; Duhau, S.; Livingston, W.C.; Nieuwenhuijzen, H.; Potgieter, M.S.

    2016-01-01

    We summarize the major aspects of the remarkable, fairly long lasting period(∼ 2005 to ∼ 2010) of low solar activity, that we will call the Transition. It is the transitionalstage between the Grand Maximum of the 20th century and a forthcoming (most probablyRegular) episode of solar activity. The

  18. Global Solar Dynamo Models: Simulations and Predictions Mausumi ...

    Indian Academy of Sciences (India)

    predict mean solar cycle features by assimilating magnetic field data from previous cycles. Key words. Sun—magnetic fields: .... recently published the steps for building such a model (see Fig. 2) and re-confirmed the results of the calibrated .... with different or time-varying meridional circulation, but that remains for the future.

  19. Solar Internal Rotation and Dynamo Waves: A Two Dimensional ...

    Indian Academy of Sciences (India)

    Author Affiliations. Gaetano Belvedere1 Kirill Kuzanyan2 Dmitry Sokoloff3. Department of Physics and Astronomy, University of Catania, Astronomy Unit, Via Santa Sofia 78, 95125 Catania, Italy. IZMIRAN, Troitsk, Moscow Region, 142092 Russia. Moscow State University, Department of Physics, 119899 Moscow, Russia.

  20. Procyon: New Candidate for the Dynamo Clinical Trial

    Science.gov (United States)

    Ayres, Thomas

    2017-08-01

    This is the third year of a joint Chandra/HST program to follow the evolution of the high-energy (X-ray and UV) activity cycles of the nearby mid-F subgiant Procyon. This bright star has high-energy attributes that are similar to the Sun, yet it is a hotter star, at the edge of the region in the H-R diagram where surface convection occurs (the power source for stellar magnetic activity). The HST part is to record STIS UV spectra of the bright star on a semiannual basis at high echelle resolution and high S/N, especially to capture the FUV Fe XII 124,134 nm coronal forbidden lines, which can tie together the non-simultaneous Chandra X-ray and HST pointings; as well as to record other key high-energy species like Si IV, C IV, and N V. The latter display Doppler-shifted, bimodal distorted emission profiles that signify high-powered dynamics in the interface regions of the stellar atmosphere between the super-hot corona (>1 MK) and the cold photosphere (<6000 K). The associated flows are a hot topic in contemporary solar physics, and one focus of a new space-based solar imaging spectrometer called IRIS. The solar and stellar FUV views are strongly complementary. The HST part of the program has two general objectives: (1) follow changes in the FUV spectra associated with any slowly evolving X-ray activity cycle of Procyon; and (2) combine the multiple epochs of echelle spectra to provide the highest possible S/N for identifying weak, but diagnostically important, emission lines (absorption, in some cases), and for decomposing the high-temperature line profiles (e.g., Si IV, C IV) into multiple dynamical components (which are though to be symptomatic of coronal heating and cooling processes).

  1. The Solar Wind Source Cycle: Relationship to Dynamo Behavior

    Science.gov (United States)

    Luhmann, J. G.; Li, Y.; Lee, C. O.; Jian, L. K.; Petrie, G. J. D.; Arge, C. N.

    2017-12-01

    Solar cycle trends of interest include the evolving properties of the solar wind, the heliospheric medium through which the Sun's plasmas and fields interact with Earth and the planets -including the evolution of CME/ICMEs enroute. Solar wind sources include the coronal holes-the open field regions that constantly evolve with solar magnetic fields as the cycle progresses, and the streamers between them. The recent cycle has been notably important in demonstrating that not all solar cycles are alike when it comes to contributions from these sources, including in the case of ecliptic solar wind. In particular, it has modified our appreciation of the low latitude coronal hole and streamer sources because of their relative prevalence. One way to understand the basic relationship between these source differences and what is happening inside the Sun and on its surface is to use observation-based models like the PFSS model to evaluate the evolution of the coronal field geometry. Although the accuracy of these models is compromised around solar maximum by lack of global surface field information and the sometimes non-potential evolution of the field related to more frequent and widespread emergence of active regions, they still approximate the character of the coronal field state. We use these models to compare the inferred recent cycle coronal holes and streamer belt sources of solar wind with past cycle counterparts. The results illustrate how (still) hemispherically asymmetric weak polar fields maintain a complex mix of low-to-mid latitude solar wind sources throughout the latest cycle, with a related marked asymmetry in the hemispheric distribution of the ecliptic wind sources. This is likely to be repeated until the polar field strength significantly increases relative to the fields at low latitudes, and the latter symmetrize.

  2. Global Solar Dynamo Models: Simulations and Predictions Mausumi ...

    Indian Academy of Sciences (India)

    planetary medium by man, solar cycle predictions have considerable practical value. Starting with solar cycle 22 ... arises from global instabilities in the overshoot tachocline (see Dikpati & Gilman. 2001 for details). .... meridional flow, if that flow changes from one cycle to the next or within a given cycle, the length of that ...

  3. Helicity of Solar Active Regions from a Dynamo Model Piyali ...

    Indian Academy of Sciences (India)

    Key words. MHD—Sun: activity—Sun: magnetic fields—sunspots. 1. Introduction. Typically, solar active regions are known to have helicity associated with them and the ... hemisphere and positive in the southern hemisphere), in spite of a very large statistical ... When a new toroidal flux tube with positive Bφ moves upwards.

  4. Relationships between radiation, clouds, and convection during DYNAMO.

    Science.gov (United States)

    Ciesielski, Paul E; Johnson, Richard H; Jiang, Xianan; Zhang, Yunyan; Xie, Shaocheng

    2017-03-16

    The relationships between radiation, clouds, and convection on an intraseasonal time scale are examined with data taken during the Dynamics of the Madden-Julian Oscillation (MJO) field campaign. Specifically, column-net, as well as vertical profiles of radiative heating rates, computed over Gan Island in the central Indian Ocean (IO) are used along with an objective analysis of large-scale fields to examine three MJO events that occurred during the 3 month period (October to December 2011) over this region. Longwave (LW) and shortwave radiative heating rates exhibit tilted structures, reflecting radiative effects associated with the prevalence of shallow cumulus during the dry, suppressed MJO phase followed by increasing deep convection leading into the active phase. As the convection builds going into the MJO active phase, there are increasingly top-heavy anomalous radiative heating rates while the column-net radiative cooling rate progressively decreases. Temporal fluctuations in the cloud radiative forcing, being quite sensitive to changes in high cloudiness, are dominated by LW effects with an intraseasonal variation of ~0.4-0.6 K/d. While both the water vapor and cloud fields are inextricably linked, it appears that the tilted radiative structures are more related to water vapor effects. The intraseasonal variation of column-net radiative heating enhances the convective signal in the mean by ~20% with a minimum in this enhancement ~10 days prior to peak MJO rainfall and maximum ~7 days after. This suggests that as MJO convective envelope weakens over the central IO, cloud-radiative feedbacks help maintain the mature MJO as it moves eastward.

  5. Energy fluxes in helical magnetohydrodynamics and dynamo action

    Indian Academy of Sciences (India)

    Renormalized viscosity, renormalized resistivity, and various energy fluxes are calculated for helical magnetohydrodynamics using perturbative field theory. The calculation is of first-order in perturbation. Kinetic and magnetic helicities do not affect the renormalized parameters, but they induce an inverse cascade of ...

  6. Energy fluxes in helical magnetohydrodynamics and dynamo action

    Indian Academy of Sciences (India)

    Abstract. Renormalized viscosity, renormalized resistivity, and various energy fluxes are calcu- lated for helical magnetohydrodynamics using perturbative field theory. The calculation is of first- order in perturbation. Kinetic and magnetic helicities do not affect the renormalized parameters, but they induce an inverse cascade ...

  7. The Current Status of Kinematic Solar Dynamo Models

    Indian Academy of Sciences (India)

    tribpo

    magnetic buoyancy of a strong toroidal magnetic field underneath the Sun's surface—an idea first propounded by Parker (1955a). Hence, the butterfly diagram implies an equatorward migration of the subsurface toroidal field. Although the sunspots are the regions of strongest magnetic field on the solar surface, there. 373 ...

  8. Intercomparison of the finite difference and nodal discrete ordinates and surface flux transport methods for a LWR pool-reactor benchmark problem in X-Y geometry

    International Nuclear Information System (INIS)

    O'Dell, R.D.; Stepanek, J.; Wagner, M.R.

    1983-01-01

    The aim of the present work is to compare and discuss the three of the most advanced two dimensional transport methods, the finite difference and nodal discrete ordinates and surface flux method, incorporated into the transport codes TWODANT, TWOTRAN-NODAL, MULTIMEDIUM and SURCU. For intercomparison the eigenvalue and the neutron flux distribution are calculated using these codes in the LWR pool reactor benchmark problem. Additionally the results are compared with some results obtained by French collision probability transport codes MARSYAS and TRIDENT. Because the transport solution of this benchmark problem is close to its diffusion solution some results obtained by the finite element diffusion code FINELM and the finite difference diffusion code DIFF-2D are included

  9. SIMULATION STUDY OF HEMISPHERIC PHASE-ASYMMETRY IN THE SOLAR CYCLE

    Energy Technology Data Exchange (ETDEWEB)

    Shukuya, D.; Kusano, K., E-mail: kusano@nagoya-u.jp [Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 4648601 (Japan)

    2017-01-20

    Observations of the Sun suggest that solar activities systematically create north–south hemispheric asymmetries. For instance, the hemisphere in which sunspot activity is more active tends to switch after the early half of each solar cycle. Svalgaard and Kamide recently pointed out that the time gaps of polar field reversal between the northern and southern hemispheres are simply consequences of the asymmetry of sunspot activity. However, the mechanism underlying the asymmetric feature in solar cycle activity is not yet well understood. In this paper, in order to explain the cause of the asymmetry from the theoretical point of view, we investigate the relationship between the dipole- and quadrupole-type components of the magnetic field in the solar cycle using the mean-field theory based on the flux transport dynamo model. As a result, we found that there are two different attractors of the solar cycle, in which either the north or the south polar field is first reversed, and that the flux transport dynamo model explains well the phase-asymmetry of sunspot activity and the polar field reversal without any ad hoc source of asymmetry.

  10. SOLAR CYCLE PROPAGATION, MEMORY, AND PREDICTION: INSIGHTS FROM A CENTURY OF MAGNETIC PROXIES

    Energy Technology Data Exchange (ETDEWEB)

    Munoz-Jaramillo, Andres; DeLuca, Edward E. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Dasi-Espuig, Maria [Max-Planck-Institut fuer Sonnensystemforschung, D-37191 Katlenburg-Lindau (Germany); Balmaceda, Laura A., E-mail: amunoz@cfa.harvard.edu, E-mail: edeluca@cfa.harvard.edu, E-mail: dasi@mps.mpg.de, E-mail: lbalmaceda@icate-conicet.gob.ar [Institute for Astronomical, Terrestrial and Space Sciences (ICATE-CONICET), San Juan (Argentina)

    2013-04-20

    The solar cycle and its associated magnetic activity are the main drivers behind changes in the interplanetary environment and Earth's upper atmosphere (commonly referred to as space weather). These changes have a direct impact on the lifetime of space-based assets and can create hazards to astronauts in space. In recent years there has been an effort to develop accurate solar cycle predictions (with aims at predicting the long-term evolution of space weather), leading to nearly a hundred widely spread predictions for the amplitude of solar cycle 24. A major contributor to the disagreement is the lack of direct long-term databases covering different components of the solar magnetic field (toroidal versus poloidal). Here, we use sunspot area and polar faculae measurements spanning a full century (as our toroidal and poloidal field proxies) to study solar cycle propagation, memory, and prediction. Our results substantiate predictions based on the polar magnetic fields, whereas we find sunspot area to be uncorrelated with cycle amplitude unless multiplied by area-weighted average tilt. This suggests that the joint assimilation of tilt and sunspot area is a better choice (with aims to cycle prediction) than sunspot area alone, and adds to the evidence in favor of active region emergence and decay as the main mechanism of poloidal field generation (i.e., the Babcock-Leighton mechanism). Finally, by looking at the correlation between our poloidal and toroidal proxies across multiple cycles, we find solar cycle memory to be limited to only one cycle.

  11. Magnetoconvection and the Solar Dynamo A. Nordlund1, S. Β. F ...

    Indian Academy of Sciences (India)

    tribpo

    , that is able to wind up an initially poloidal magnetic field into a strong, toroidal magnetic flux system, 2) magnetic flux storage, which is able to keep the magnetic field in the convection zone, while the toroidal field strength is building up, 3).

  12. Impact of Convection on Surface Fluxes Observed During LASP/DYNAMO 2011

    Science.gov (United States)

    2014-12-01

    a heat sink and a source of water vapor. Such cooling effects bring the second controlling process: convective-scale downdrafts that bring down...conducted in the vicinity of overcast conditions and a few small showers . Again, this flight was made nearly collocated with the R/V Revelle. Twenty... showers in the vicinity of Diego Garcia. The P-3 operated in the vicinity of Diego Garcia completing 11 LL. Further analysis occurred on the four LL

  13. Chaotic dynamics of the magnetic field generated by dynamo action in a turbulent flow

    Energy Technology Data Exchange (ETDEWEB)

    Petrelis, F; Fauve, S [Laboratoire de Physique Statistique, CNRS UMR 8550, Ecole Normale Superieure, 24 rue Lhomond, F-75005 Paris (France)], E-mail: petrelis@lps.ens.fr

    2008-12-10

    We present models related to the results of a recent experiment (the 'VKS experiment') showing the generation of a magnetic field by a fully turbulent flow of liquid sodium. We first discuss the geometry of the mean magnetic field when the two coaxial impellers driving the flow counter-rotate at the same frequency. We then show how we expect this geometry to be modified when the impellers rotate at different frequencies. We also show that, in the latter case, dynamical regimes of the magnetic field can be easily understood from the interaction of modes with dipolar (respectively quadrupolar) symmetry. In particular, this interaction generates magnetic field reversals that have been observed in the experiment and display a hierarchy of timescales similar to the Earth's magnetic field: the duration of the steady phases is widely distributed, but is always much longer than the time needed to switch polarity. In addition to reversals, several other large scale features of the generated magnetic field are obtained when varying the governing parameters of the flow. These results are also understood in the framework of the same model.

  14. A Magnetic Betelgeuse? Numerical Simulations of Non-linear Dynamo Action

    OpenAIRE

    Dorch, S. B. F.

    2003-01-01

    Betelgeuse is an example of a cool super-giant displaying brightness fluctuations and irregular surface structures. Simulations by Freytag et al. (2002) of the convective envelope of the star have shown that the fluctuations in the star's luminosity may be caused by giant cell convection. A related question regarding the nature of Betelgeuse and supergiants in general is whether these stars may be magnetically active. If so, that may in turn also contribute to their variability. By performing...

  15. The magnetic field of Betelgeuse: a local dynamo from giant convection cells?

    OpenAIRE

    Auriere, M.; Donati, J. -F.; Konstantinova-Antova, R.; Perrin, G.; Petit, P.; Roudier, T.

    2010-01-01

    Betelgeuse is an M supergiant with a complex and extended atmosphere, which also harbors spots and giant granules at its surface. A possible magnetic field could contribute to the mass loss and to the heating of the outer atmosphere. We observed Betelgeuse, to directly study and infer the nature of its magnetic field. We used the new-generation spectropolarimeter NARVAL and the least square deconvolution (LSD) method to detect circular polarization within the photospheric absorption lines of ...

  16. A theory of ionospheric dynamo for complete model of terrestrial space at high and medium latitudes

    International Nuclear Information System (INIS)

    Vardanyan, Yu.S.

    1992-01-01

    A multi-layer model of terrestrial cosmic space at high and medium latitudes is considered in the approximation of infinite conductivity of the Earth taking into account the ambipolar diffusion processes in upper layers of ionosphere. 14 refs

  17. Dynamo-HIA-a dynamic modeling tool for generic health impact assessments

    NARCIS (Netherlands)

    S.K. Lhachimi (Stefan); W.J. Nusselder (Wilma); H.A. Smit (Henriëtte); P.H.M. Van Baal (Pieter); P. Baili (Paolo); K. Bennett (Kathleen); E. Fernández (Esteve); M.C. Kulik (Margarete); T. Lobstein (Tim); J. Pomerleau (Joceline); J.P. Mackenbach (Johan); H.C. Boshuizen (Hendriek)

    2012-01-01

    textabstractBackground: Currently, no standard tool is publicly available that allows researchers or policy-makers to quantify the impact of policies using epidemiological evidence within the causal framework of Health Impact Assessment (HIA). A standard tool should comply with three technical

  18. DYNAMO-HIA - A Dynamic Modelling tool for generic Health Impact Assessments

    NARCIS (Netherlands)

    Lhachimi, S.K.; Nusselder, W.J.; Smit, H.A.; Baal, van P.; Bailli, P.; Bennett, K.; Fernández, E.; Kulik, M.C.; Lobstein, T.; Pomerleau, J.; Mackenbach, J.P.; Boshuizen, H.C.

    2012-01-01

    Background Currently, no standard tool is publicly available that allows researchers or policy-makers to quantify the impact of policies using epidemiological evidence within the causal framework of Health Impact Assessment (HIA). A standard tool should comply with three technical criteria

  19. The interhemispheric and F region dynamo currents revisited with the Swarm constellation

    DEFF Research Database (Denmark)

    Luehr, Hermann; Kervalishvili, Guram; Michaelis, Ingo

    2015-01-01

    Based on magnetic field data sampled by the Swarm satellite constellation it is possible for the first time to determine uniquely F region currents at low latitudes. Initial results are presented from the first 200days of formation flight (17 April to 5 November 2014). Detailed results have been...

  20. Degenerate Hopf bifurcation in a self-exciting Faraday disc dynamo

    Indian Academy of Sciences (India)

    School of Statistics and Management, Shanghai University of Finance and Economics, Shanghai 200433, People's Republic of China; Guangxi Colleges and Universities Key Laboratory of Complex System Optimization and Big Data Processing, Yulin Normal University, Yulin 537000, Guangxi, People's Republic of China ...

  1. The thermal evolution and dynamo generation of Mercury with an Fe-Si core

    Science.gov (United States)

    Knibbe, Jurrien

    2017-04-01

    The present day partially liquid (as opposed to fully solidified) Fe-rich core of Mercury is traditionally explained by assuming a substantial amount of S to be present in the core (e.g. Grott et al., 2011), because S lowers the core's melting temperature. However, this assumption has problematic implications: Mercury's large Fe-rich core and measured low FeO surface content are indicative of an oxygen poor bulk composition, which is consistent with the volatile-poor material that is expected to have condensed from the solar nebula close to the Sun. In contrast, S is a moderately volatile element. Combined with the high S content of Mercury's crust and (likely) mantle, as indicated by the measured high S/Si surface fraction, the resulting high planetary S abundance is difficult to reconcile with a volatile poor origin of the planet. Additionally, the observed low magnetic field strength is most easily explained if compositional buoyancy fluxes are absent [Manglik et al., 2010], yet such fluxes are produced upon solidifying a pure Fe inner core from Fe-S liquid. Alternatively, both Mercury's high S/Si and Mg/Si surface ratios (Nittler et al., 2011) may indicate that a siderophile fractionation of Si and lithophile fractionation of S took place during Mercury's core-mantle differentiation. This fractionation behaviour of these elements is supported by metal/silicate partitioning experiments that have been performed at the low oxygen conditions inferred for Mercury [e.g. Chabot et al., 2014]. Mercury's bulk composition, in terms of S/Si and Fe/Si ratios, would also approach that of meteorites that are considered as potential building blocks of the planet if the core is Si-rich and S-poor. Here we simulate the thermal evolution of Mercury with an Fe-Si core. Results show that an Fe-Si core can remain largely molten until present, without the need for S. An Fe-Si core also has interesting implications for Mercury's core-convection regime and magnetic field generation. The non-preferential Si fractionation between solid and liquid metal does not produce a compositional gradient, such that compositional buoyancy fluxes are negligible. Additionally, thermally driven core convection is more efficient as a result of a high latent heat release upon solidifying Si-rich metal. Implications of this scenario for Mercury's magnetic field strength and geometry need to be further examined.

  2. Degenerate Hopf bifurcation in a self-exciting Faraday disc dynamo

    Indian Academy of Sciences (India)

    Weiquan Pan

    2017-05-31

    May 31, 2017 ... [10] V T Pham, C Volos, S Jafari, Z C Wei and X Wang, Int. J. Bifur- cat. Chaos 24, 1450073 (2014). [11] Z C Wei, I Moroz and A P Liu, Turk. J. Math. 38, 672 (2014). [12] Z C Wei, I Moroz, Zhen Wang, Julien Clinton Sprott and T. Kapitaniak, Int. J. Bifurcat. Chaos 26, 1650125 (2016). [13] S M Zoldi and H S ...

  3. Dynamo transformation of the collisional R-T in a weakly ionized ...

    Indian Academy of Sciences (India)

    It is obvious to note the difference between usual R-T and NILF mode of instabilities. Now let us consider a situation when the relative neutral flow produces an internal effective gravity in the equilibrium but is not perturbed by the resulting instability. For a quick estimation of the growth rate of the resulting instability due to ...

  4. Degenerate Hopf bifurcation in a self-exciting Faraday disc dynamo

    Indian Academy of Sciences (India)

    Weiquan Pan

    2017-05-31

    May 31, 2017 ... 2Guangxi Colleges and Universities Key Laboratory of Complex System Optimization and Big Data Processing,. Yulin Normal University, Yulin 537000, Guangxi, People's Republic of ..... Now we apply the Hopf bifurcation theory to analyse the complex dynamical bifurcations. 4.1 Hopf bifurcation at E0.

  5. Marketing Plan of SK Dynamo České Budějovice

    OpenAIRE

    Kramář, Jan

    2012-01-01

    The major goal of this bachelor work is a detailed marketing situational analysis of a current club marketing plan. The marketing plan will be proposed on basis of detailed marketing situational analysis. The club may use the marketing plan as a source for written processing.

  6. A Standard Law for the Equatorward Drift of the Sunspot Zones

    Science.gov (United States)

    Hathaway, David H.

    2012-01-01

    The latitudinal location of the sunspot zones in each hemisphere is determined by calculating the centroid position of sunspot areas for each solar rotation from May 1874 to June 2012. When these centroid positions are plotted and analyzed as functions of time from each sunspot cycle maximum there appears to be systematic differences in the positions and equatorward drift rates as a function of sunspot cycle amplitude. If, instead, these centroid positions are plotted and analyzed as functions of time from each sunspot cycle minimum then most of the differences in the positions and equatorward drift rates disappear. The differences that remain disappear entirely if curve fitting is used to determine the starting times (which vary by as much as 8 months from the times of minima). The sunspot zone latitudes and equatorward drift measured relative to this starting time follow a standard path for all cycles with no dependence upon cycle strength or hemispheric dominance. Although Cycle 23 was peculiar in its length and the strength of the polar fields it produced, it too shows no significant variation from this standard. This standard law, and the lack of variation with sunspot cycle characteristics, is consistent with Dynamo Wave mechanisms but not consistent with current Flux Transport Dynamo models for the equatorward drift of the sunspot zones.

  7. Nanomagnetic intergrowths in Fe-Ni meteoritic metal: The potential for time-resolved records of planetesimal dynamo fields

    DEFF Research Database (Denmark)

    Bryson, James F.J.; Church, Nathan S.; Kasama, Takeshi

    2014-01-01

    Nanoscale intergrowths unique to the cloudy zones (CZs) of meteoritic metal display novel magnetic behaviour with the potential to reveal new insight into the early development of magnetic fields on protoplanetary bodies. The nanomagnetic state of the CZ within the Tazewell IIICD iron meteorite has...... with its [001] magnetic easy axis oriented along one of three 〈100〉 crystallographic directions of the parent taenite phase. Micromagnetic simulations demonstrate that switching occurs via the nucleation and propagation of domain walls through individual tetrataenite particles. The switching field (Hs......) varies with the length scale of the matrix phase (Lm), with Hs > 1 T for Lm ∼10 nm (approaching the intrinsic switching field for isolated single domain tetrataenite) and 0.2

  8. High Performance Computing Application: Solar Dynamo Model Project II, Corona and Heliosphere Component Initialization, Integration and Validation

    Science.gov (United States)

    2015-06-24

    the corona required to provide such conditions were still steady-state in formulation, anchored to a synoptic magnetogram describing a snapshot of the...state in their text that “a complete picture requires a comprehensive model of all of the processes considered together.” For convenience, however, they...updated magnetic field synoptic data, J. Geophys. Res., 117, A08110, doi:10.1029/2011JA017494. Yeates, A. R., D. H. Mackay, and A. A. van

  9. Comparison of tobacco control scenarios: Quantifying estimates of long-term health impact using the dynamo-hia modeling tool

    NARCIS (Netherlands)

    M.C. Kulik (Margarete); W.J. Nusselder (Wilma); H.C. Boshuizen (Hendriek); S.K. Lhachimi (Stefan); E. Fernández (Esteve); P. Baili (Paolo); K. Bennett (Kathleen); J.P. Mackenbach (Johan); H.A. Smit (Henriëtte)

    2012-01-01

    textabstractBackground: There are several types of tobacco control interventions/policies which can change future smoking exposure. The most basic intervention types are 1) smoking cessation interventions 2) preventing smoking initiation and 3) implementation of a nationwide policy affecting

  10. Comparison of tobacco control scenarios: quantifying estimates of long-term health impact using the DYNAMO-HIA modeling tool

    NARCIS (Netherlands)

    Kulik, M.C.; Nusselder, W.J.; Boshuizen, H.C.; Lhachimi, S.K.; Fernández, E.; Baili, P.; Bennett, K.; Mackenbach, J.P.; Smit, H.A.

    2012-01-01

    Background There are several types of tobacco control interventions/policies which can change future smoking exposure. The most basic intervention types are 1) smoking cessation interventions 2) preventing smoking initiation and 3) implementation of a nationwide policy affecting quitters and

  11. Topology of a dissipative spin: Dynamical Chern number, bath-induced nonadiabaticity, and a quantum dynamo effect

    Science.gov (United States)

    Henriet, Loïc; Sclocchi, Antonio; Orth, Peter P.; Le Hur, Karyn

    2017-02-01

    We analyze the topological deformations of the ground state manifold of a quantum spin-1/2 in a magnetic field H =H (sinθ cosϕ ,sinθ sinϕ ,cosθ ) induced by a coupling to an ohmic quantum dissipative environment at zero temperature. From Bethe ansatz results and a variational approach, we confirm that the Chern number associated with the geometry of the reduced spin ground state manifold is preserved in the delocalized phase for α <1 . We report a divergence of the Berry curvature at αc=1 for magnetic fields aligned along the equator θ =π /2 . This divergence is caused by the complete quenching of the transverse magnetic field by the bath associated with a gap closing that occurs at the localization Kosterlitz-Thouless quantum phase transition in this model. Recent experiments in quantum circuits have engineered nonequilibrium protocols to access topological properties from a measurement of a dynamical Chern number defined via the out-of-equilibrium spin expectation values. Applying a numerically exact stochastic Schrödinger approach we find that, for a fixed field sweep velocity θ (t )=v t , the bath induces a crossover from (quasi)adiabatic to nonadiabatic dynamical behavior when the spin bath coupling α increases. We also investigate the particular regime H /ωc≪v /H ≪1 with large bath cutoff frequency ωc, where the dynamical Chern number vanishes already at α =1 /2 . In this regime, the mapping to an interacting resonance level model enables us to analytically describe the behavior of the dynamical Chern number in the vicinity of α =1 /2 . We further provide an intuitive physical explanation of the bath-induced breakdown of adiabaticity in analogy to the Faraday effect in electromagnetism. We demonstrate that the driving of the spin leads to the production of a large number of bosonic excitations in the bath, which strongly affect the spin dynamics. Finally, we quantify the spin-bath entanglement and formulate an analogy with an effective model at thermal equilibrium.

  12. Small-scale dynamo action during the formation of the first stars and galaxies. I. The ideal MHD limit

    NARCIS (Netherlands)

    Schleicher, D. R. G.; Banerjee, R.; Sur, S.; Arshakian, T. G.; Klessen, R. S.; Beck, R.; Spaans, M.

    2010-01-01

    We explore the amplification of magnetic seeds during the formation of the first stars and galaxies. During gravitational collapse, turbulence is created from accretion shocks, which may act to amplify weak magnetic fields in the protostellar cloud. Numerical simulations showed that such turbulence

  13. Does the planetary dynamo go cycling on? Re-examining the evidence for cycles in magnetic reversal rate

    Science.gov (United States)

    Melott, Adrian L.; Pivarunas, Anthony; Meert, Joseph G.; Lieberman, Bruce S.

    2018-01-01

    The record of reversals of the geomagnetic field has played an integral role in the development of plate tectonic theory. Statistical analyses of the reversal record are aimed at detailing patterns and linking those patterns to core-mantle processes. The geomagnetic polarity timescale is a dynamic record and new paleomagnetic and geochronologic data provide additional detail. In this paper, we examine the periodicity revealed in the reversal record back to 375 million years ago (Ma) using Fourier analysis. Four significant peaks were found in the reversal power spectra within the 16-40-million-year range (Myr). Plotting the function constructed from the sum of the frequencies of the proximal peaks yield a transient 26 Myr periodicity, suggesting chaotic motion with a periodic attractor. The possible 16 Myr periodicity, a previously recognized result, may be correlated with `pulsation' of mantle plumes and perhaps; more tentatively, with core-mantle dynamics originating near the large low shear velocity layers in the Pacific and Africa. Planetary magnetic fields shield against charged particles, which can give rise to radiation at the surface and ionize the atmosphere, which is a loss mechanism particularly relevant to M stars. Understanding the origin and development of planetary magnetic fields can shed light on the habitable zone.

  14. Information Theoretic Approach to Discovering Causalities in the Solar Cycle

    Science.gov (United States)

    Wing, Simon; Johnson, Jay R.; Vourlidas, Angelos

    2018-02-01

    The causal parameters and response lag times of the solar cycle dynamics are investigated with transfer entropy, which can determine the amount of information transfer from one variable to another. The causal dependency of the solar cycle parameters is bidirectional. The transfer of information from the solar polar field to the sunspot number (SSN) peaks at lag time (τ) ∼ 30–40 months, but thereafter it remains at a persistently low level for at least 400 months (∼3 solar cycles) for the period 1906–2014. The latter may lend support to the idea that the polar fields from the last three or more solar cycles can affect the production of the SSN of the subsequent cycle. There is also a similarly long-term information transfer from the SSN to the polar field. Both the meridional flow speed and flux emergence (proxied by the SSN) transfer information to the polar field, but one transfers more information than the other, depending on the lag times. The meridional flow speed transfers more information than the SSN to the polar field at τ ∼ 28–30 months and at τ ∼ 90–110 months, which may be consistent with some flux transfer dynamo models and some surface flux transport models. However, the flux emergence transfers more information than the meridional flow to the polar field at τ ∼ 60–80 months, which may be consistent with a recently developed surface flux transport model. The transfer of information from the meridional flow to the SSN peaks at τ ∼ 110–120 months (∼1 solar cycle).

  15. Babcock Redux: An Amendment of Babcock's Schematic of the Sun's Magnetic Cycle

    Science.gov (United States)

    Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.

    2017-08-01

    We amend Babcock's original scenario for the global dynamo process that sustains the Sun's 22-year magnetic cycle. The amended scenario fits post-Babcock observed features of the magnetic activity cycle and convection zone, and is based on ideas of Spruit & Roberts (1983, Nature, 304, 401) about magnetic flux tubes in the convection zone. A sequence of four schematic cartoons lays out the proposed evolution of the global configuration of the magnetic field above, in, and at the bottom of the convection zone through sunspot Cycle 23 and into Cycle 24. Three key elements of the amended scenario are: (1) as the net following-polarity magnetic field from the sunspot-region Ω-loop fields of an ongoing sunspot cycle is swept poleward to cancel and replace the opposite-polarity polar-cap field from the previous sunspot cycle, it remains connected to the ongoing sunspot cycle's toroidal source-field band at the bottom of the convection zone; (2) topological pumping by the convection zone's free convection keeps the horizontal extent of the poleward-migrating following-polarity field pushed to the bottom, forcing it to gradually cancel and replace old horizontal field below it that connects the ongoing-cycle source-field band to the previous-cycle polar-cap field; (3) in each polar hemisphere, by continually shearing the poloidal component of the settling new horizontal field, the latitudinal differential rotation low in the convection zone generates the next-cycle source-field band poleward of the ongoing-cycle band. The amended scenario is a more-plausible version of Babcock's scenario, and its viability can be explored by appropriate kinematic flux-transport solar-dynamo simulations. A paper giving a full description of our dynamo scenario is posted on arXiv (http://arxiv.org/abs/1606.05371).This work was funded by the Heliophysics Division of NASA's Science Mission Directorate through the Living With a Star Targeted Research and Technology Program and the Hinode

  16. An econometric investigation of the sunspot number record since the year 1700 and its prediction into the 22nd century

    Science.gov (United States)

    Travaglini, Guido

    2015-09-01

    Solar activity, as measured by the yearly revisited time series of sunspot numbers (SSN) for the period 1700-2014 (Clette et al., 2014), undergoes in this paper a triple statistical and econometric checkup. The conclusions are that the SSN sequence: (1) is best modeled as a signal that features nonlinearity in mean and variance, long memory, mean reversion, 'threshold' symmetry, and stationarity; (2) is best described as a discrete damped harmonic oscillator which linearly approximates the flux-transport dynamo model; (3) its prediction well into the 22nd century testifies of a substantial fall of the SSN centered around the year 2030. In addition, the first and last Gleissberg cycles show almost the same peak number and height during the period considered, yet the former slightly prevails when measured by means of the estimated smoother. All of these conclusions are achieved by making use of modern tools developed in the field of Financial Econometrics and of two new proposed procedures for signal smoothing and prediction.

  17. Transport of Internetwork Magnetic Flux Elements in the Solar Photosphere

    Science.gov (United States)

    Agrawal, Piyush; Rast, Mark P.; Gošić, Milan; Bellot Rubio, Luis R.; Rempel, Matthias

    2018-02-01

    The motions of small-scale magnetic flux elements in the solar photosphere can provide some measure of the Lagrangian properties of the convective flow. Measurements of these motions have been critical in estimating the turbulent diffusion coefficient in flux-transport dynamo models and in determining the Alfvén wave excitation spectrum for coronal heating models. We examine the motions of internetwork flux elements in Hinode/Narrowband Filter Imager magnetograms and study the scaling of their mean squared displacement and the shape of their displacement probability distribution as a function of time. We find that the mean squared displacement scales super-diffusively with a slope of about 1.48. Super-diffusive scaling has been observed in other studies for temporal increments as small as 5 s, increments over which ballistic scaling would be expected. Using high-cadence MURaM simulations, we show that the observed super-diffusive scaling at short increments is a consequence of random changes in barycenter positions due to flux evolution. We also find that for long temporal increments, beyond granular lifetimes, the observed displacement distribution deviates from that expected for a diffusive process, evolving from Rayleigh to Gaussian. This change in distribution can be modeled analytically by accounting for supergranular advection along with granular motions. These results complicate the interpretation of magnetic element motions as strictly advective or diffusive on short and long timescales and suggest that measurements of magnetic element motions must be used with caution in turbulent diffusion or wave excitation models. We propose that passive tracer motions in measured photospheric flows may yield more robust transport statistics.

  18. Q GSM tegi konkurentidele dünamo / Aivar Hundimägi

    Index Scriptorium Estoniae

    Hundimägi, Aivar, 1975-

    2004-01-01

    Mobiilsideoperaatorile Q GSM (praegune Tele2) edu taganud turundusstrateegiatest. Lisad: Q GSMi Dynamo teenuspaketi eesmärgid; Q GSMist sai Tele2. Diagramm: 2000. aastal turule toodud Dynamo pakett tõi murrangu

  19. Solar small-scale magnetoconvection

    DEFF Research Database (Denmark)

    Stein, R. F.; Nordlund, Å.

    2006-01-01

    Turbulent Compressible Convection; Dynamo Action Driven; Magnetic-Fields; Numerical Simulations; Photospherical; Convection; Flux Separation; Granulation; Equations; Stars; Overshoot......Turbulent Compressible Convection; Dynamo Action Driven; Magnetic-Fields; Numerical Simulations; Photospherical; Convection; Flux Separation; Granulation; Equations; Stars; Overshoot...

  20. Plaadid / Ants Tõnisson

    Index Scriptorium Estoniae

    Tõnisson, Ants

    2004-01-01

    Uutest heliplaatidest Erkki Hyva "Varjust rambini", Goldie Lookin Chain "Greatest Hits", Dynamo Productions "Get It Together", Shyne "Godfather Buried Alive", Kenny Dope "Brazilika", Soulwax "Any Minute Now"

  1. Heliospheric Magnetic Fields, Energetic Particles, and the Solar Cycle

    Indian Academy of Sciences (India)

    tribpo

    of the solar dynamo, even if the energy densities of the mass motions involved in the dynamo action vastly exceed planetary effects. On longer terms, the changing interstellar environment may certainly influence the extent of the heliosphere, and some back-reaction of those boundary conditions on SW sources and on flare ...

  2. Mechanism of Cyclically Polarity Reversing Solar Magnetic Cycle as ...

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... We briefly describe historical development of the concept of solar dynamo mechanism that generates electric current and magnetic field by plasma ... The dynamo is the driver of the cyclically polarity reversing solar magnetic cycle. ... Department of Astronomy, University of Tokyo, Tokyo, Japan 113-0033.

  3. Mechanism of Cyclically Polarity Reversing Solar Magnetic Cycle as ...

    Indian Academy of Sciences (India)

    tribpo

    solar dynamo mechanism that generates electric current and magnetic field by plasma flows inside the .... on the flow which makes the flow pattern twist and propagate to drive the dynamo must be strong enough to .... drive electric current in cosmos, Elsassar, a friend of Einstein, proposed that non- axisymmetric flows could ...

  4. Untitled

    Indian Academy of Sciences (India)

    Geomagnetic S and L tides 345. A decreasing trend is also shown by the Samplitudes in D during winter and the phase angle differs from that in summer by about 150°. This suggests that, like the L dynamo, S dynamo also may fail to establish in the winter hemisphere,. However, an examination of the D daygraphs does not ...

  5. Fulltext PDF

    Indian Academy of Sciences (India)

    Abstract. In this paper, we estimate the magnetic Reynolds number of a typical protostar before and after deuterium burning, and claim for the existence of dynamo process in both the phases, because the magnetic Reynolds number of the protostar far exceeds the critical magnetic Reynolds number for dynamo action.

  6. Magnetohydrodynamics of accretion disks

    International Nuclear Information System (INIS)

    Torkelsson, U.

    1994-04-01

    The thesis consists of an introduction and summary, and five research papers. The introduction and summary provides the background in accretion disk physics and magnetohydrodynamics. The research papers describe numerical studies of magnetohydrodynamical processes in accretion disks. Paper 1 is a one-dimensional study of the effect of magnetic buoyancy on a flux tube in an accretion disk. The stabilizing influence of an accretion disk corona on the flux tube is demonstrated. Paper 2-4 present numerical simulations of mean-field dynamos in accretion disks. Paper 11 verifies the correctness of the numerical code by comparing linear models to previous work by other groups. The results are also extended to somewhat modified disk models. A transition from an oscillatory mode of negative parity for thick disks to a steady mode of even parity for thin disks is found. Preliminary results for nonlinear dynamos at very high dynamo numbers are also presented. Paper 3 describes the bifurcation behaviour of the nonlinear dynamos. For positive dynamo numbers it is found that the initial steady solution is replaced by an oscillatory solution of odd parity. For negative dynamo numbers the solution becomes chaotic at sufficiently high dynamo numbers. Paper 4 continues the studies of nonlinear dynamos, and it is demonstrated that a chaotic solution appears even for positive dynamo numbers, but that it returns to a steady solution of mixed parity at very high dynamo numbers. Paper 5 describes a first attempt at simulating the small-scale turbulence of an accretion disk in three dimensions. There is only find cases of decaying turbulence, but this is rather due to limitations of the simulations than that turbulence is really absent in accretion disks

  7. Planetary Magnetism

    International Nuclear Information System (INIS)

    Russell, C.T.

    1980-01-01

    Planetary spacecraft have now probed the magnetic fields of all the terrestrial planets, the moon, Jupiter, and Saturn. These measurements reveal that dynamos are active in at least four of the planets, Mercury, the earth, Jupiter, and Saturn but that Venus and Mars appear to have at most only very weak planetary magnetic fields. The moon may have once possessed an internal dynamo, for the surface rocks are magnetized. The large satellites of the outer solar system are candidates for dynamo action in addition to the large planets themselves. Of these satellites the one most likely to generate its own internal magnetic field is Io

  8. The Evolution of Stellar Dynamos; Survey for Low Mass Members of NGC2232; An X-Ray Survey of the Open Cluster CR140; Towards a Better Understanding of the Rotation-Activity Relation for Solar-Type Members of the Pleiades

    Science.gov (United States)

    Stauffer, John R.; Petre, Robert (Technical Monitor)

    2000-01-01

    This grant was originally awarded to Dr. Charles Prosser, who died tragically in a car accident in Tucson in 1998. We had hoped to finish the work Charles had started, which involved analysis of ROSAT data for three programs (observations of the clusters NGC2232, Crl4O and the Pleiades) and also analysis of optical data for each cluster in order to allow interpretation of the ROSAT observations. The Pleiades portion of the program was completed during the past year, and a paper published. We have obtained optical imaging of the other two clusters, and those data are being analyzed. Dr. Brian Patten intends to complete analysis of the ROSAT observations and to combine those data with the optical photometry, but progress on those efforts has been slow due to the press of other work (Dr. Patten is responsible for the pipeline processing of data from SWAS). We intend to publish those results as soon as we can, but it will now be completed without further support from this grant.

  9. Clustering of Emerging Flux

    Science.gov (United States)

    Ruzmaikin, A.

    1997-01-01

    Observations show that newly emerging flux tends to appear on the Solar surface at sites where there is flux already. This results in clustering of solar activity. Standard dynamo theories do not predict this effect.

  10. Studies on magnetic dynamics in RFX

    International Nuclear Information System (INIS)

    Martini, S.; Piovan, R.; Bolzonella, T.; Chitarin, G.; Innocente, P.; Sonato, P.; Terranova, D.; Zanca, P.; Zollino, G.

    2001-01-01

    The RFP configuration is maintained by an intrinsic dynamo mechanism associated to resistive MHD tearing modes. These dynamo modes are responsible for field line stochasticity and have a strong influence on plasma confinement. RFX results relevant to the subject are discussed both in terms of the influence of the magnetic boundary and of the characteristics of the RFP enhanced confinement regimes. The dynamo modes are often locked in phase and to the wall, which spoils the stabilising effect of the conducting shell and leads to severe plasma-wall interactions. The driven rotation of the locked dynamo modes has been studied in RFX by means of a new Toroidal Field Modulation System. A rotating toroidally localised perturbation of the toroidal magnetic field couples to the modes and induces their rotation. (author)

  11. Studies on magnetic dynamics in RFX

    International Nuclear Information System (INIS)

    Martini, S.; Piovan, R.; Bolzonella, T.; Chitarin, G.; Innocente, P.; Sonato, P.; Terranova, D.; Zanca, P.; Zollino, G.

    1999-01-01

    The RFP configuration is maintained by an intrinsic dynamo mechanism associated to resistive MHD tearing modes. These dynamo modes are responsible for field line stochasticity and have a strong influence on plasma confinement. RFX results relevant to the subject are discussed both in terms of the influence of the magnetic boundary and of the characteristics of the RFP enhanced confinement regimes. The dynamo modes are often locked in phase and to the wall, which spoils the stabilising effect of the conducting shell and leads to severe plasma-wall interactions. The driven rotation of the locked dynamo modes has been studied in RFX by means of a new Toroidal Field Modulation System. A rotating toroidally localised perturbation of the toroidal magnetic field couples to the modes and induces their rotation. (author)

  12. Plaadid / Valner Valme

    Index Scriptorium Estoniae

    Valme, Valner, 1970-

    2004-01-01

    Uutest plaatidest "Gilles Peterson. Erldwide Exclusives", Jonny Cash "My Mother's Hymn Book", Pharmac Hooligans "Imovane", The Housemartins "The Best of The Housemartins", Snow Patrol "Final Straw", Dynamoe "Coming Home"

  13. Core Processes: Earth's eccentric magnetic field

    DEFF Research Database (Denmark)

    Finlay, Chris

    2012-01-01

    Earth’s magnetic field is characterized by a puzzling hemispheric asymmetry. Calculations of core dynamo processes suggest that lopsided growth of the planet’s inner core may be part of the cause.......Earth’s magnetic field is characterized by a puzzling hemispheric asymmetry. Calculations of core dynamo processes suggest that lopsided growth of the planet’s inner core may be part of the cause....

  14. THERMODYNAMIC LIMITS ON MAGNETODYNAMOS IN ROCKY EXOPLANETS

    International Nuclear Information System (INIS)

    Gaidos, Eric; Conrad, Clinton P.; Manga, Michael; Hernlund, John

    2010-01-01

    To ascertain whether magnetic dynamos operate in rocky exoplanets more massive or hotter than the Earth, we developed a parametric model of a differentiated rocky planet and its thermal evolution. Our model reproduces the established properties of Earth's interior and magnetic field at the present time. When applied to Venus, assuming that planet lacks plate tectonics and has a dehydrated mantle with an elevated viscosity, the model shows that the dynamo shuts down or never operated. Our model predicts that at a fixed planet mass, dynamo history is sensitive to core size, but not to the initial inventory of long-lived, heat-producing radionuclides. It predicts that rocky planets larger than 2.5 Earth masses will not develop inner cores because the temperature-pressure slope of the iron solidus becomes flatter than that of the core adiabat. Instead, iron 'snow' will condense near or at the top of these cores, and the net transfer of latent heat upward will suppress convection and a dynamo. More massive planets can have anemic dynamos due to core cooling, but only if they have mobile lids (plate tectonics). The lifetime of these dynamos is shorter with increasing planet mass but longer with higher surface temperature. Massive Venus-like planets with stagnant lids and more viscous mantles will lack dynamos altogether. We identify two alternative sources of magnetic fields on rocky planets: eddy currents induced in the hot or molten upper layers of planets on very short-period orbits, and dynamos in the ionic conducting layers of 'ocean' planets with ∼10% mass in an upper mantle of water (ice).

  15. Magneto-Fluid Dynamics Fundamentals and Case Studies of Natural Phenomena

    CERN Document Server

    Lorrain, Paul; Houle, Stéphane

    2006-01-01

    This book concerns the generation of electric currents and of electric space charges inside conducting media that move in magnetic fields. The authors postulate nothing but the Maxwell equations. They discuss at length the disk dynamo, which serves as a model for the natural self-excited dynamos that generate magnetic fields such as that of sunspots. There are 36 Examples and 13 Case Studies. The Case Studies concern solar phenomena -- magnetic elements, sunspots, spicules, coronal loops -- and the Earth's magnetic field.

  16. Lifetime, turnover time, and fast magnetic field regeneration in random flows

    International Nuclear Information System (INIS)

    Tanner, S. E. M.

    2007-01-01

    The fast dynamo is thought to be relevant in the regeneration of magnetic fields in astrophysics where the value of the magnetic Reynolds number (Rm) is immense. The fast dynamo picture is one in which chaotic flows provide a mechanism for the stretching of magnetic field lines. Furthermore, a cascade of energy down to small scales results in intermittent regions of a small-scale, intense magnetic field. Given this scenario it is natural to invoke the use of kinematic random flows in order to understand field regeneration mechanisms better. Here a family of random flows is used to study the effects that L, the lifetime of the cell, and τ, the turnover time of the cell, may have on magnetic field regeneration. Defining the parameter Γ=L/τ, it has been varied according to Γ>1, Γ<1, Γ∼O(1). In the kinematic regime, dynamo growth rates and Lyapunov exponents are examined at varying values of Rm. The possibility of fast dynamo action is considered. In the nonlinear regime, magnetic and kinetic energies are examined. Results indicate that there does appear to be a relationship between Γ and dynamo efficiency. In particular, the most efficient dynamos seem to operate at lower values of Γ

  17. Magnetodynamo lifetimes for rocky, Earth-mass exoplanets with contrasting mantle convection regimes

    Science.gov (United States)

    van Summeren, Joost; Gaidos, Eric; Conrad, Clinton P.

    2013-05-01

    We used a thermal model of an iron core to calculate magnetodynamo evolution in Earth-mass rocky planets to determine the sensitivity of dynamo lifetime and intensity to planets with different mantle tectonic regimes, surface temperatures, and core properties. The heat flow at the core-mantle boundary (CMB) is derived from numerical models of mantle convection with a viscous/pseudoplastic rheology that captures the phenomenology of plate-like tectonics. Our thermal evolution models predict a long-lived ( 8 Gyr) field for Earth and similar dynamo evolution for Earth-mass exoplanets with plate tectonics. Both elevated surface temperature and pressure-dependent mantle viscosity reduce the CMB heat flow but produce only slightly longer-lived dynamos ( 8-9.5 Gyr). Single-plate ("stagnant lid") planets with relatively low CMB heat flow produce long-lived ( 10.5 Gyr) dynamos. These weaker dynamos can cease for several billions of years and subsequently reactivate due to the additional entropy production associated with inner core growth, a possible explanation for the absence of a magnetic field on present-day Venus. We also show that dynamo operation is sensitive to the initial temperature, size, and solidus of a planet's core. These dependencies would severely challenge any attempt to distinguish exoplanets with plate tectonics and stagnant lids based on the presence or absence of a magnetic field.

  18. Health Impacts of Increased Physical Activity from Changes in Transportation Infrastructure: Quantitative Estimates for Three Communities.

    Science.gov (United States)

    Mansfield, Theodore J; MacDonald Gibson, Jacqueline

    2015-01-01

    Recently, two quantitative tools have emerged for predicting the health impacts of projects that change population physical activity: the Health Economic Assessment Tool (HEAT) and Dynamic Modeling for Health Impact Assessment (DYNAMO-HIA). HEAT has been used to support health impact assessments of transportation infrastructure projects, but DYNAMO-HIA has not been previously employed for this purpose nor have the two tools been compared. To demonstrate the use of DYNAMO-HIA for supporting health impact assessments of transportation infrastructure projects, we employed the model in three communities (urban, suburban, and rural) in North Carolina. We also compared DYNAMO-HIA and HEAT predictions in the urban community. Using DYNAMO-HIA, we estimated benefit-cost ratios of 20.2 (95% C.I.: 8.7-30.6), 0.6 (0.3-0.9), and 4.7 (2.1-7.1) for the urban, suburban, and rural projects, respectively. For a 40-year time period, the HEAT predictions of deaths avoided by the urban infrastructure project were three times as high as DYNAMO-HIA's predictions due to HEAT's inability to account for changing population health characteristics over time. Quantitative health impact assessment coupled with economic valuation is a powerful tool for integrating health considerations into transportation decision-making. However, to avoid overestimating benefits, such quantitative HIAs should use dynamic, rather than static, approaches.

  19. Two populations of the solar magnetic field

    Science.gov (United States)

    Obridko, V. N.; Livshits, I. M.; Sokoloff, D. D.

    2017-12-01

    Dynamo theory suggests that there are two types of solar dynamo, namely the conventional mean-field dynamo, which produces large- and small-scale magnetic fields involved in the activity cycle, and also the small-scale dynamo, which produces a cycle independent small-scale magnetic field. The relative contribution of the two mechanisms to solar magnetism remains a matter of scientific debate, which includes the opinion that the contribution of the small-scale dynamo is negligible. Here, we consider several tracers of magnetic activity that separate cycle-dependent contributions to the background solar magnetic field from those that are independent of the cycle. We call background fields the magnetic fields outside active regions and give further development of this concept. The main message of our paper is that background fields include two relative separate populations. The background fields with a strength up to 100 Mx cm-2 are very poorly correlated with the sunspot numbers and vary little with the phase of the cycle. In contrast, stronger magnetic fields demonstrate pronounced cyclic behaviour. We discuss how this result can be included in the above-mentioned concepts of solar dynamo studies.

  20. The Role of Scale and Model Bias in ADAPT's Photospheric Eatimation

    Energy Technology Data Exchange (ETDEWEB)

    Godinez Vazquez, Humberto C. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hickmann, Kyle Scott [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Arge, Charles Nicholas [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Henney, Carl [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-05-20

    The Air Force Assimilative Photospheric flux Transport model (ADAPT), is a magnetic flux propagation based on Worden-Harvey (WH) model. ADAPT would be used to provide a global photospheric map of the Earth. A data assimilation method based on the Ensemble Kalman Filter (EnKF), a method of Monte Carlo approximation tied with Kalman filtering, is used in calculating the ADAPT models.

  1. Optimization of magnetic amplification by flow constraints in turbulent liquid sodium

    International Nuclear Information System (INIS)

    Nornberg, M. D.; Taylor, N. Z.; Forest, C. B.; Rahbarnia, K.; Kaplan, E.

    2014-01-01

    Direct measurements of the vector turbulent emf in a driven two-vortex flow of liquid sodium were performed in the Madison Dynamo Experiment [K. Rahbarnia et al., Astrophys. J. 759, 80 (2012)]. The measured turbulent emf is anti-parallel with the mean current and is almost entirely described by an enhanced resistivity, which increases the threshold for a kinematic dynamo. We have demonstrated that this enhanced resistivity can be mitigated by eliminating the largest-scale eddies through the introduction of baffles. By tailoring the flow to reduce large-scale components and control the helical pitch, we have reduced the power required to drive the impellers, doubled the magnetic flux generated by differential rotation, and increased the decay time of externally applied magnetic fields. Despite these improvements, the flows remain sub-critical to the dynamo instability due to the reemergence of turbulent fluctuations at high flow speeds

  2. Mars' core and magnetism.

    Science.gov (United States)

    Stevenson, D J

    2001-07-12

    The detection of strongly magnetized ancient crust on Mars is one of the most surprising outcomes of recent Mars exploration, and provides important insight about the history and nature of the martian core. The iron-rich core probably formed during the hot accretion of Mars approximately 4.5 billion years ago and subsequently cooled at a rate dictated by the overlying mantle. A core dynamo operated much like Earth's current dynamo, but was probably limited in duration to several hundred million years. The early demise of the dynamo could have arisen through a change in the cooling rate of the mantle, or even a switch in convective style that led to mantle heating. Presently, Mars probably has a liquid, conductive outer core and might have a solid inner core like Earth.

  3. Planetary Magnetism

    Science.gov (United States)

    Connerney, J. E. P.

    2007-01-01

    The chapter on Planetary Magnetism by Connerney describes the magnetic fields of the planets, from Mercury to Neptune, including the large satellites (Moon, Ganymede) that have or once had active dynamos. The chapter describes the spacecraft missions and observations that, along with select remote observations, form the basis of our knowledge of planetary magnetic fields. Connerney describes the methods of analysis used to characterize planetary magnetic fields, and the models used to represent the main field (due to dynamo action in the planet's interior) and/or remnant magnetic fields locked in the planet's crust, where appropriate. These observations provide valuable insights into dynamo generation of magnetic fields, the structure and composition of planetary interiors, and the evolution of planets.

  4. Magnetic spiral arms in galaxy haloes

    Science.gov (United States)

    Henriksen, R. N.

    2017-08-01

    We seek the conditions for a steady mean field galactic dynamo. The parameter set is reduced to those appearing in the α2 and α/ω dynamo, namely velocity amplitudes, and the ratio of sub-scale helicity to diffusivity. The parameters can be allowed to vary on conical spirals. We analyse the mean field dynamo equations in terms of scale invariant logarithmic spiral modes and special exact solutions. Compatible scale invariant gravitational spiral arms are introduced and illustrated in an appendix, but the detailed dynamical interaction with the magnetic field is left for another work. As a result of planar magnetic spirals `lifting' into the halo, multiple sign changes in average rotation measures forming a regular pattern on each side of the galactic minor axis, are predicted. Such changes have recently been detected in the Continuum Halos in Nearby Galaxies-an EVLA Survey (CHANG-ES) survey.

  5. Asymmetric flux generation and its relaxation in reversed field pinch

    International Nuclear Information System (INIS)

    Arimoto, H.; Masamune, S.; Nagata, A.

    1985-02-01

    The toroidally asymmetric flux enhancement [''dynamo effect''] and the axisymmetrization of the enhanced fluxes that follows in the setting up phase of Reversed Field Pinch are investigated on the STP-3[M] device. A rapid increase in the toroidal flux generated by the dynamo effect is first observed near the poloidal and toroidal current feeders. Then, this inhomogeneity of the flux propagates toroidally towards the plasma current. The axisymmetrization of the flux is attained just after the maximum of plasma current. The MHD activities decrease significantly after this axisymmetrization and the quiescent period is obtained. (author)

  6. Effects of pulsed electric field on ULQ and RFP plasmas

    International Nuclear Information System (INIS)

    Watanabe, M.; Saito, K.; Suzuki, T.

    1997-01-01

    Dynamo activity and self-organization processes are investigated using the application of pulsed poloidal and toroidal electric fields on ULQ and RFP plasmas. Synchronized to the application of the pulsed electric fields, the remarkable responses of the several plasma parameters are observed. The plasma has a preferential magnetic field structure, and the external perturbation activates fluctuation to maintain the structure through dynamo effect. This process changes the total dissipation with the variation of magnetic helicity in the system, showing that self organization accompanies an enhanced dissipation. (author)

  7. Large-scale perturbations of magnetohydrodynamic regimes linear and weakly nonlinear stability theory

    CERN Document Server

    Zheligovsky, Vladislav

    2011-01-01

    New developments for hydrodynamical dynamo theory have been spurred by recent evidence of self-sustained dynamo activity in laboratory experiments with liquid metals. The emphasis in the present volume is on the introduction of powerful mathematical techniques required to tackle modern multiscale analysis of continous systems and there application to a number of realistic model geometries of increasing complexity. This introductory and self-contained research monograph summarizes the theoretical state-of-the-art to which the author has made pioneering contributions.

  8. Coronal Structures as Tracers of Sub-Surface Processes

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... The origin of the field is beneath the turbulent convection zone, where the magnetic field is not a master but a slave, and one can wonder how much the coronal magnetic field ``remembers" its dynamo origin. Surprisingly, it does. We will describe several observational phenomena that indicate a close ...

  9. Fulltext PDF

    Indian Academy of Sciences (India)

    ing the data set, in units of Carrington Rotations (CRs), for Sunspot Area (SA) and soft X-ray flare index. (FISXR). We find from three solar ... magnetic helicity requires probably that dynamo gen- erated magnetic field be ..... X-axis represents the random variables (i.e., data values) and Y-axis the probability density function.

  10. Magnetostrophic balance as the optimal state for turbulent magnetoconvection.

    Science.gov (United States)

    King, Eric M; Aurnou, Jonathan M

    2015-01-27

    The magnetic fields of Earth and other planets are generated by turbulent convection in the vast oceans of liquid metal within them. Although direct observation is not possible, this liquid metal circulation is thought to be dominated by the controlling influences of planetary rotation and magnetic fields through the Coriolis and Lorentz forces. Theory famously predicts that planetary dynamo systems naturally settle into the so-called magnetostrophic state, where the Coriolis and Lorentz forces partially cancel, and convection is optimally efficient. Although this magnetostrophic theory correctly predicts the strength of Earth's magnetic field, no laboratory experiments have reached the magnetostrophic regime in turbulent liquid metal convection. Furthermore, computational dynamo simulations have as yet failed to produce a magnetostrophic dynamo, which has led some to question the existence of the magnetostrophic state. Here, we present results from the first, to our knowledge, turbulent, magnetostrophic convection experiments using the liquid metal gallium. We find that turbulent convection in the magnetostrophic regime is, in fact, maximally efficient. The experimental results clarify these previously disparate results, suggesting that the dynamically optimal magnetostrophic state is the natural expression of turbulent planetary dynamo systems.

  11. Canonical Models of Geophysical and Astrophysical Flows: Turbulent Convection Experiments in Liquid Metals

    Directory of Open Access Journals (Sweden)

    Adolfo Ribeiro

    2015-03-01

    Full Text Available Planets and stars are often capable of generating their own magnetic fields. This occurs through dynamo processes occurring via turbulent convective stirring of their respective molten metal-rich cores and plasma-based convection zones. Present-day numerical models of planetary and stellar dynamo action are not carried out using fluids properties that mimic the essential properties of liquid metals and plasmas (e.g., using fluids with thermal Prandtl numbers Pr < 1 and magnetic Prandtl numbers Pm ≪ 1. Metal dynamo simulations should become possible, though, within the next decade. In order then to understand the turbulent convection phenomena occurring in geophysical or astrophysical fluids and next-generation numerical models thereof, we present here canonical, end-member examples of thermally-driven convection in liquid gallium, first with no magnetic field or rotation present, then with the inclusion of a background magnetic field and then in a rotating system (without an imposed magnetic field. In doing so, we demonstrate the essential behaviors of convecting liquid metals that are necessary for building, as well as benchmarking, accurate, robust models of magnetohydrodynamic processes in Pm ≪  Pr < 1 geophysical and astrophysical systems. Our study results also show strong agreement between laboratory and numerical experiments, demonstrating that high resolution numerical simulations can be made capable of modeling the liquid metal convective turbulence needed in accurate next-generation dynamo models.

  12. Mechanism of Cyclically Polarity Reversing Solar Magnetic Cycle as ...

    Indian Academy of Sciences (India)

    tribpo

    axisymmetric flow twisted by Coriolis force with spatial scale of the order of the diameter of the Sun. An example of .... are defined as those flows that cannot feel the influence of Coriolis force strongly enough to act as a dynamo and .... and hence centrifugal force is acting on the body. However, according to the principle.

  13. Magnetic fields driven by tidal mixing in radiative stars

    Science.gov (United States)

    Vidal, Jérémie; Cébron, David; Schaeffer, Nathanaël; Hollerbach, Rainer

    2018-04-01

    Stellar magnetism plays an important role in stellar evolution theory. Approximatively 10 per cent of observed main sequence (MS) and pre-main-sequence (PMS) radiative stars exhibit surface magnetic fields above the detection limit, raising the question of their origin. These stars host outer radiative envelopes, which are stably stratified. Therefore, they are assumed to be motionless in standard models of stellar structure and evolution. We focus on rapidly rotating, radiative stars which may be prone to the tidal instability, due to an orbital companion. Using direct numerical simulations in a sphere, we study the interplay between a stable stratification and the tidal instability, and assess its dynamo capability. We show that the tidal instability is triggered regardless of the strength of the stratification (Brunt-Väisälä frequency). Furthermore, the tidal instability can lead to both mixing and self-induced magnetic fields in stably stratified layers (provided that the Brunt-Väisälä frequency does not exceed the stellar spin rate in the simulations too much). The application to stars suggests that the resulting magnetic fields could be observable at the stellar surfaces. Indeed, we expect magnetic field strengths up to several Gauss. Consequently, tidally driven dynamos should be considered as a (complementary) dynamo mechanism, possibly operating in radiative MS and PMS stars hosting orbital companions. In particular, tidally driven dynamos may explain the observed magnetism of tidally deformed and rapidly rotating Vega-like stars.

  14. Locked modes and plasma-wall interaction in a reversed-field pinch with a resistive shell and carbon first wall

    International Nuclear Information System (INIS)

    Hokin, S.; Bergsaaker, H.; Brunsell, P.

    2001-01-01

    The Extrap-T2 reversed-field pinch has concluded operation in the OHTE RFP configuration with a resistive shell. This paper summarizes our observations and conclusions regarding wall-locked modes, dynamo activity and plasma-wall interaction with a resistive shell and graphite first wall

  15. Locked modes and plasma-wall interaction in a reserved-field pinch with a resistive shell and carbon first wall

    International Nuclear Information System (INIS)

    Hokin, S.; Bergsaaker, H.; Brunsell, P.

    1999-01-01

    The Extrap-T2 reversed-field pinch has concluded operation in the OHTE RFP configuration with a resistive shell. This paper summarizes our observations and conclusions regarding wall-locked modes, dynamo activity and plasma-wall interaction with a resistive shell and graphite first wall

  16. Arts: Hot tickets 2017

    Science.gov (United States)

    Jones, Nicola

    2017-01-01

    Robots, DNA and electricity bask in the limelight, as Blade Runner reboots, Kazakhstan gets energetic and a 'space tapestry' rolls out. It's quite a year -- and key anniversaries hit, too, for Canada, the anthropology dynamo the Peabody Museum and architect Frank Lloyd Wright. Nicola Jones reports.

  17. Journal of Astrophysics and Astronomy | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... Later, the concept was successfully applied in studies of different solar processes from solar dynamo to flare and CME phenomena. Although no silver bullet, helicity has proven to be a very useful “tool” in answering many still-puzzling questions about origin and evolution of solar magnetic fields. I present ...

  18. Polar cap magnetic field reversals during solar grand minima: could pores play a role?

    Czech Academy of Sciences Publication Activity Database

    Švanda, Michal; Brun, A.S.; Roudier, T.; Jouve, L.

    2016-01-01

    Roč. 586, February (2016), A123/1-A123/11 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GA14-04338S Institutional support: RVO:67985815 Keywords : dynamo * Sun * magnetic fields Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  19. Solar Filaments as Tracers of Subsurface Processes

    Indian Academy of Sciences (India)

    tribpo

    Filaments are clouds of relatively cool and dense gas in the solar atmosphere. ... First-tier filaments may be related to a peculiar feature of the solar dynamo. .... Still, an appeal to subsurface processes should be resisted, but surface motion models have been able to reproduce neither the pattern of filament field orientations ...

  20. Carbon as the dominant light element in the lunar core

    NARCIS (Netherlands)

    Steenstra, E.S.; Lin, Y.; Rai, N.; Jansen, M.; van Westrenen, W.

    2016-01-01

    Geophysical and geochemical observations point to the presence of a light element in the lunar core, but the exact abundance and type of light element are poorly constrained. Accurate constraints on lunar core composition are vital for models of lunar core dynamo onset and demise, core formation

  1. Effects of discontinuous magnetic permeability on magnetodynamic problems

    KAUST Repository

    Guermond, J.-L.

    2011-07-01

    A novel approximation technique using Lagrange finite elements is proposed to solve magneto-dynamics problems involving discontinuous magnetic permeability and non-smooth interfaces. The algorithm is validated on benchmark problems and is used for kinematic studies of the Cadarache von Kármán Sodium 2 (VKS2) experimental fluid dynamo. © 2011 Elsevier Inc.

  2. The Influence of Metallicity on Stellar Differential Rotation and Magnetic Activity

    Science.gov (United States)

    Karoff, Christoffer; Metcalfe, Travis S.; Santos, Ângela R. G.; Montet, Benjamin T.; Isaacson, Howard; Witzke, Veronika; Shapiro, Alexander I.; Mathur, Savita; Davies, Guy R.; Lund, Mikkel N.; Garcia, Rafael A.; Brun, Allan S.; Salabert, David; Avelino, Pedro P.; van Saders, Jennifer; Egeland, Ricky; Cunha, Margarida S.; Campante, Tiago L.; Chaplin, William J.; Krivova, Natalie; Solanki, Sami K.; Stritzinger, Maximilian; Knudsen, Mads F.

    2018-01-01

    Observations of Sun-like stars over the past half-century have improved our understanding of how magnetic dynamos, like that responsible for the 11 yr solar cycle, change with rotation, mass, and age. Here we show for the first time how metallicity can affect a stellar dynamo. Using the most complete set of observations of a stellar cycle ever obtained for a Sun-like star, we show how the solar analog HD 173701 exhibits solar-like differential rotation and a 7.4 yr activity cycle. While the duration of the cycle is comparable to that generated by the solar dynamo, the amplitude of the brightness variability is substantially stronger. The only significant difference between HD 173701 and the Sun is its metallicity, which is twice the solar value. Therefore, this provides a unique opportunity to study the effect of the higher metallicity on the dynamo acting in this star and to obtain a comprehensive understanding of the physical mechanisms responsible for the observed photometric variability. The observations can be explained by the higher metallicity of the star, which is predicted to foster a deeper outer convection zone and a higher facular contrast, resulting in stronger variability.

  3. Applications of computer modeling to fusion research. Progress report, 1988--1989

    Energy Technology Data Exchange (ETDEWEB)

    Dawson, J.M.

    1989-12-31

    Progress achieved during this report period is presented on the following topics: Development and application of gyrokinetic particle codes to tokamak transport, development of techniques to take advantage of parallel computers; model dynamo and bootstrap current drive; and in general maintain our broad-based program in basic plasma physics and computer modeling.

  4. Applications of computer modeling to fusion research

    Energy Technology Data Exchange (ETDEWEB)

    Dawson, J.M.

    1989-01-01

    Progress achieved during this report period is presented on the following topics: Development and application of gyrokinetic particle codes to tokamak transport, development of techniques to take advantage of parallel computers; model dynamo and bootstrap current drive; and in general maintain our broad-based program in basic plasma physics and computer modeling.

  5. equatorial electrojet strength in the african sector during high

    African Journals Online (AJOL)

    Preferred Customer

    electrojet current. The electric fields that drive the equatorial electrojet current have been found to consist of three components with different origins. (Reddy, 1981): a) an electric field originating in the dynamo action of the global scale wind system in the lower atmosphere, which is the driving electric field on quiet days with ...

  6. Turundustegu 2000 : ego pani end maksma / Margo Kokerov

    Index Scriptorium Estoniae

    Kokerov, Margo, 1978-

    2001-01-01

    Marketingi Instituudi, Turunduskeskuse ja Emori korraldatud konkursist Eesti Turundustegu 2000. Ülevaade finaaltöödest - A. Le Coq'i turuosa kasv, Dynamo kõnepakett, Eesti väljapanek Expo 2000-1, Hiirte juust ja Ego järelmaksukaart

  7. Keynote Address: Outstanding Problems in Solar Physics

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... The solar neutrino problem; Structure of the solar interior (helioseismology); The solar magnetic field (dynamo, solar cycle, corona); Hydrodynamics of coronal loops; MHD oscillations and waves (coronal seismology); The coronal heating problem; Self-organized criticality (from nanoflares to giant flares) ...

  8. Recent Advances in Atmospheric, Solar-Terrestrial Physics and Space Weather From a North-South network of scientists [2006-2016] PART A: TUTORIAL

    Science.gov (United States)

    Amory-Mazaudier, C.; Menvielle, M.; Curto, J-J.; Le Huy, M.

    2017-12-01

    This paper reviews scientific advances achieved by a North-South network between 2006 and 2016. These scientific advances concern Solar Terrestrial Physics, Atmospheric Physics and Space Weather. In this part A, we introduce knowledge on the Sun-Earth system. We consider the physical process of the dynamo which is present in the Sun, in the core of the Earth and also in the regions between the Sun and the Earth, the solar wind-magnetosphere and the ionosphere. Equations of plasma physics and Maxwell's equations will be recalled. In the Sun-Earth system there are permanent dynamos (Sun, Earth's core, solar wind - magnetosphere, neutral wind - ionosphere) and non-permanent dynamos that are activated during magnetic storms in the magnetosphere and in the ionosphere. All these dynamos have associated electric currents that affect the variations of the Earth's magnetic field which are easily measurable. That is why a part of the tutorial is also devoted to the magnetic indices which are indicators of the electric currents in the Sun-Earth system. In order to understand some results of the part B, we present some characteristics of the Equatorial region and of the electrodynamics coupling the Auroral and Equatorial regions.

  9. Ed Lorenz: Father of the 'Butterfly Effect'

    Indian Academy of Sciences (India)

    IAS Admin

    similar to Lorenz system arise in very different contexts like lasers, dynamos, thermosyphons, brushless DC mo- tors, electric circuits, chemical reactions and forward osmosis. Also, chaotic behavior was observed experi- mentally in laser systems, Josephson junctions, plasma systems and nonlinear electronic circuits.

  10. Atmospheric solar tides and their electrodynamic effects

    International Nuclear Information System (INIS)

    Forbes, J.M.; Lindzen, R.S.

    1977-01-01

    In this final part of a three-part study, the polarization electric field generated by E-region dynamo action is considered, and its consistency with presently available experimental measurements is established. This serves as an independent check on some of the results and conclusions described in Parts I and II (Forbes and Lindzen, J. Atmos. Terr. Phys.; 38:897,911 (1976)). Incoherent scatter measurements of ionospheric drifts are reviewed from the point of view of determining the origin of the polarization electric field in the quiet-time ionosphere, and are compared with the theoretical dynamo electric fields which drive the current systems in Parts I and II. The analysis indicates that the polarization fields originating from E-region dynamo action are consistent with daytime F-region drift measurements, but are in poor agreement at night. This supports previous suggestions that electric fields generated by the plasmaspheric and F-region dynamos are short-circuited by the high E-region conductivity during the day, but contribite strongly to the night-time electric field. (author)

  11. Geomagnetic secular variation as a window on the dynamics of Earth's core (Invited)

    Science.gov (United States)

    Jackson, A.

    2010-12-01

    One of the forefront questions of planetary geophysics is to understand how magnetic fields can be spontaneously created by so-called dynamo action. Giant strides have been taken in recent years in understanding the theory of convectively driven dynamos; yet equally important is the marriage between theory and observation. I will argue that we are on the cusp of a new level of understanding brought about by new methods for incorporating observations and theory. In 1950 Sir Edward Bullard wrote an influential paper entitled "The westward drift of the Earth's magnetic field", with coauthors C Freedman, H Gellman and J Nixon. A comprehensive study of observations was tied together with the then nascent dynamo theory to infer properties of the dynamics of the core. Sixty years on, we have a much enriched understanding of the theory of convectively driven dynamos, and an even more comprehensive database of observations stretching back several centuries. Equally important are the new satellite observations that provide global coverage with unprecedented accuracy over the last decade. In this talk I will try to show how the interplay between theory and observation can lead to understanding of force balances in the core, and interactions between the core and the overlying mantle.

  12. Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven ...

    Indian Academy of Sciences (India)

    tribpo

    Key words. Sun—dynamo, helicity, turbulent convection. Extended abstract. Recent numerical simulations lead to the result that turbulence is much more mag- netically driven than believed. ... positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicity which is negative ...

  13. 1 INTRODUCTION 2 THE FELLOWSHIP

    Indian Academy of Sciences (India)

    2000-04-01

    Apr 1, 2000 ... activity, helioseismology, dynamo mechanisms, cycle variation in the quiet corona ... technology. Guest Editor: T.S. Gill. Pramana, Vol. 55, Nos 5/6, November/December 2000, pp. 643–966. The fourteenth national symposium on plasma ..... produced by in vitro fertilization (IVF) embryo transfer procedure.

  14. A Well-Known but Still Surprising Generator

    Science.gov (United States)

    Haugland, Ole Anton

    2014-01-01

    The bicycle generator is often mentioned as an example of a method to produce electric energy. It is cheap and easily accessible, so it is a natural example to use in teaching. There are different types, but I prefer the old side-wall dynamo. The most common explanation of its working principle seems to be something like the illustration in Fig.…

  15. Effects of Brinkman number on thermal-driven convective spherical ...

    African Journals Online (AJOL)

    Brinkman number effects on the thermal-driven convective spherical dynamos are studied analytically. The high temperature of the Earth's inner core boundary is usually conducted by the viscous, electrically conducting fluid of the outer core to the core mantle boundary as the Earth cools. The problem considers conducting ...

  16. Applications of computer modeling to fusion research

    International Nuclear Information System (INIS)

    Dawson, J.M.

    1989-01-01

    Progress achieved during this report period is presented on the following topics: Development and application of gyrokinetic particle codes to tokamak transport, development of techniques to take advantage of parallel computers; model dynamo and bootstrap current drive; and in general maintain our broad-based program in basic plasma physics and computer modeling

  17. Journal of Astrophysics and Astronomy | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... The origin of the field is beneath the turbulent convection zone, where the magnetic field is not a master but a slave, and one can wonder how much the coronal magnetic field ``remembers" its dynamo origin. Surprisingly, it does. We will describe several observational phenomena that indicate a close ...

  18. The intercrater plains of Mercury and the Moon: Their nature, origin and role in terrestrial planet evolution. Thermal models of Mercury. Ph.D. Thesis

    Science.gov (United States)

    Leake, M. A.

    1982-01-01

    Recent and more complex thermal models of Mercury and the terrestrial planets are discussed or noted. These models isolate a particular aspect of the planet's thermal history in an attempt to understand that parameter. Among these topics are thermal conductivity, convection, radiogenic sources of heat, other heat sources, and the problem of the molten core and regenerative dynamo.

  19. Effects of Brinkman number on thermal-driven convective spherical ...

    African Journals Online (AJOL)

    Michael Horsfall

    Theoretical Physics Group; Department of Physics, University of Port Harcourt, Port Harcourt, Nigeria. *Corresponding author ... illustrate enhancement of dynamo actions, demonstrating that magnetic field generation with time is possible. Moreover ..... The steady state flow variables define the absence of convective motion ...

  20. Power supply for magnetic coils in thermonuclear devices

    International Nuclear Information System (INIS)

    Shimada, Ryuichi; Tamura, Sanae; Kishimoto, Hiroshi.

    1981-01-01

    Purpose: To decrease the load fluctuations in an external power supply, as well as to increase the operation efficiency capacity of thermonuclear devices. Constitution: Electrical power with the same frequency as that of a dynamo generator is supplied by a power supply-driving power source including a frequency converter and the like to DC converters for driving plasma-exciting and -controlling coils. At the same time, the electrical power from the frequency converter is supplied to the dynamo generator with flywheel to add accumulate energies to the EC converters. Accordingly, the energy for the great power pulses in a short time comprises the sum of the energy supplied from the dynamo generator with flywheel and the energy supplied continuously from the outside to eliminate the need of providing a stand-by period for the re-acceleration of the dynamo generator with flywheel even if the scale of the thermonuclear device is enlarged and energy consumed in one cycle is increased, whereby the decrease in the operation efficiency can be prevented and the capacity of the flywheel can be reduced. (Yoshino, Y.)

  1. Smart multi-application energy harvester using Arduino | Rizman ...

    African Journals Online (AJOL)

    This paper presents a Smart Multi-App Harvester Energy Using Arduino for energy harvesting. The system consists of a few mechanical parts such as solar, thermal plate and dynamo (for kinetic) to harvest the energy. The objectives of the project are to harvest the wasted energy from the mechanical parts and used it as a ...

  2. Educating pain | Olivier | South African Journal of Philosophy

    African Journals Online (AJOL)

    As is pointed out, Nietzsche's contention that pain is the most powerful aid to mnemonics, originates from his philosophy of pain as the main condition of all forms of creation. The title “educating (bilden) pain” expresses Nietsche's advocacy of an education towards pain as the dynamo of creation. In this paper I explore how ...

  3. COMPARISON OF CHAOTIC AND FRACTAL PROPERTIES OF POLAR FACULAE WITH SUNSPOT ACTIVITY

    Energy Technology Data Exchange (ETDEWEB)

    Deng, L. H.; Xiang, Y. Y.; Dun, G. T. [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216 (China); Li, B., E-mail: wooden@escience.cn [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Shandong University at Weihai, Weihai 264209 (China)

    2016-01-15

    The solar magnetic activity is governed by a complex dynamo mechanism and exhibits a nonlinear dissipation behavior in nature. The chaotic and fractal properties of solar time series are of great importance to understanding the solar dynamo actions, especially with regard to the nonlinear dynamo theories. In the present work, several nonlinear analysis approaches are proposed to investigate the nonlinear dynamical behavior of the polar faculae and sunspot activity for the time interval from 1951 August to 1998 December. The following prominent results are found: (1) both the high- and the low-latitude solar activity are governed by a three-dimensional chaotic attractor, and the chaotic behavior of polar faculae is the most complex, followed by that of the sunspot areas, and then the sunspot numbers; (2) both the high- and low-latitude solar activity exhibit a high degree of persistent behavior, and their fractal nature is due to such long-range correlation; (3) the solar magnetic activity cycle is predictable in nature, but the high-accuracy prediction should only be done for short- to mid-term due to its intrinsically dynamical complexity. With the help of the Babcock–Leighton dynamo model, we suggest that the nonlinear coupling of the polar magnetic fields with strong active-region fields exhibits a complex manner, causing the statistical similarities and differences between the polar faculae and the sunspot-related indicators.

  4. Spatially Resolved Images and Solar Irradiance Variability R ...

    Indian Academy of Sciences (India)

    Abstract. The Sun is the primary source of energy that governs both the terrestrial climate and near-earth space environment. Variations in UV irradiances seen at earth are the sum of global (solar dynamo) to regional. (active region, plage, network, bright points and background) solar mag- netic activities that can be ...

  5. Subject Index

    Indian Academy of Sciences (India)

    Global Solar Dynamo Models: Simulations and Predictions (Mausumi Dikpati &. Peter A. Gilman), 29. Prediction of Peaks in Wolf Numbers in Cycle 24 according to .... Microflares as Possible Sources for Coronal Heating (Meera Gupta, Rajmal Jain,. Jayshree Trivedi & A. P. Mishra), 171. Damping of Slow Magnetoacoustic ...

  6. Sustainable Design with Respect to LCA Using Parametric Design and BIM Tools

    DEFF Research Database (Denmark)

    Tsikos, Marios; Negendahl, Kristoffer

    minimize their design’s environmental impacts. To achieve this, this study evaluated the potential of integrating LCA into BIM, developed and proposed an Integrated Dynamic Model using Revit, Dynamo and Excel. The Integrated Dynamic model was used in case studies the results of which were compared...

  7. Stoked nondynamos: sustaining field in magnetically non-closed systems

    International Nuclear Information System (INIS)

    Byington, B M; Brummell, N H; Stone, J M; Gough, D O

    2014-01-01

    Much effort has gone into identifying and classifying systems that might be capable of dynamo action, i.e. capable of generating and sustaining magnetic field indefinitely against dissipative effects in a conducting fluid. However, it is difficult, if not almost technically impossible, to derive a method of determining in both an absolutely conclusive and a pragmatic manner whether a system is a dynamo or not in the nonlinear regime. This problem has generally been examined only for closed systems, despite the fact that most realistic situations of interest are not strictly closed. Here we examine the even more complex problem of whether a known nondynamo closed system can be distinguished pragmatically from a true dynamo when a small input of magnetic field to the system is allowed. We call such systems ‘stoked nondynamos’ owing to the ‘stoking’ or augmentation of the magnetic field in the system. It may seem obvious that magnetic energy can be sustained in such systems since there is an external source, but crucial questions remain regarding what level is maintained and whether such nondynamo systems can be distinguished from a true dynamo. In this paper, we perform 3D nonlinear numerical simulations with time-dependent ABC forcing possessing known dynamo properties. We find that magnetic field can indeed be maintained at a significant stationary level when stoking a system that is a nondynamo when not stoked. The maintained state results generally from an eventual rough balance of the rates of input and decay of magnetic field. We find that the relevance of this state is dictated by a parameter κ representing the correlation of the resultant field with the stoking forcing function. The interesting regime is where κ is small but non-zero, as this represents a middle ground between a state where the stoking has no effect on the pre-existing nondynamo properties and a state where the effect of stoking is easily detectable. We find that in this regime, (a

  8. Sawteeth in the MST reversed field pinch

    International Nuclear Information System (INIS)

    Beckstead, J.A.

    1990-09-01

    A dynamo mechanism has been used in astrophysics to explain the self-generation of the magnetic fields observed throughout the universe. This same type of phenomenon is believed to occur in the reversed field pinch (RFP) plasmas. The RFP dynamo has been a major theoretical and experimental investigation since the first observations of the self-reversal process in early pinch research. A discrete dynamo event has been observed in the experimental RFP plasmas; this event is termed the RFP sawtooth. This phenomenon is similar to the sawtooth phenomenon observed in tokamak plasmas, but the two events differ in many respects. Both events are a result of the inward diffusion of the plasma current density. This causes the plasma to become unstable to the m = 1 tearing modes. It has been shown theoretically that the nonlinear interaction of these modes can generate the reversed toroidal field in the RFP. This thesis is a study of the RFP sawtooth phenomenon on the MST RFP. This includes experimental observations as well as 1-D numerical simulations of the sawtooth rise-time. During the rise-time of the sawtooth, the plasma is undergoing a purely diffusive process -- no dynamo is occurring during this phase. The dynamo only occurs during the sawtooth crash. During the rise-time, the m = 1 modes are observed to grow, and nonlinear interactions are observed prior to the sawtooth crash. At the time of the crash, many of the plasma profiles are flattened; these include the current density, the plasma temperature and the plasma density. The period of the sawteeth is observed to increase with the plasma current, as well as the magnetic Reynolds number, S

  9. Thermal conductivity of the electrode gap of a thermionic converter, filled with inert gases, at low pressures

    Science.gov (United States)

    Modin, V. A.; Nikolaev, Iu. V.

    1986-05-01

    Experimental data are presented on the thermal conductivity of the electrode gap of a thermionic converter filled with He, Ar, and Xe in the pressure range 40-550 Pa. The need to account for the coefficients of thermal accommodation of the emitter - inert-gas - collector system in this range is shown. The accommodation coefficients for different temperature regimes are measured and expressions are obtained for calculating the heat flux transported by the inert gases into the electrode gap.

  10. Thermal conductivity of the electrode gap of a thermionic converter, filled with inert gases, at low pressures

    International Nuclear Information System (INIS)

    Modin, V.A.; Nikolaev, Y.V.

    1985-01-01

    Experimental data is presented on the thermal conductivity of the electrode gap of a thermionic converter filled with He, Ar, and Xe in the pressure range 40--550 Pa. The need to account for the coefficients of thermal accommodation of the emitter-inert-gas-collector system in this range is shown. The accommodation coefficients for different temperature regimes are measured and expressions are obtained to calculate the heat flux transported by the inert gases in the electrode gap

  11. Photospheric Driving of Non-Potential Coronal Magnetic Field Simulations

    Science.gov (United States)

    2016-09-19

    linear combination of the L1 and L2 norms (called L1 -penalized least-squares). These methods are capable of producing smoother and more realistic...reduce spurious electric fields. A new technique was developed for sparse reconstruction of electric field based on L1 -minimization, which allowed a...technique, with test cases taken from (a) a simple flux transport model (with known electric field) and (b) a two-month ADAPT sequence. A comparison of

  12. Convection and magnetic field generation in the interior of planets (August Love Medal Lecture)

    Science.gov (United States)

    Christensen, U. R.

    2009-04-01

    Thermal convection driven by internal energy plays a role of paramount importance in planetary bodies. Its numerical modeling has been an essential tool for understanding how the internal engine of a planet works. Solid state convection in the silicate or icy mantles is the cause of endogenic tectonic activity, volcanism and, in the case of Earth, of plate motion. It also regulates the energy budget of the entire planet, including that of its core, and controls the presence or absence of a dynamo. The complex rheology of solid minerals, effects of phase transitions, and chemical heterogeneity are important issues in mantle convection. Examples discussed here are the convection pattern in Mars and the complex morphology of subducted slabs that are observed by seismic tomography in the Earth's mantle. Internally driven convection in the deep gas envelopes of the giant planets is possibly the cause for the strong jet streams at the surfaces that give rise to their banded appearance. Modeling of the magnetohydrodynamic flow in the conducting liquid core of the Earth has been remarkably successful in reproducing the primary properties of the geomagnetic field. As an examplefor attempts to explain also secondary properties, I will discuss dynamo models that account for the thermal coupling to the mantle. The understanding of the somewhat enigmatic magnetic fields of some other planets is less advanced. Here I will show that dynamos that operate below a stable conducting layer in the upper part of the planetary core can explain the unusual magnetic field properties of Mercury and Saturn. The question what determines the strength of a dynamo-generated magnetic field has been a matter of debate. From a large set of numerical dynamo simulations that cover a fair range of control parameters, we find a rule that relates magnetic field strength to the part of the energy flux that is thermodynamically available to be transformed into other forms of energy. This rules predicts

  13. Compensating Faraday Depolarization by Magnetic Helicity in the Solar Corona

    Energy Technology Data Exchange (ETDEWEB)

    Brandenburg, Axel; Ashurova, Mohira B. [Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303 (United States); Jabbari, Sarah, E-mail: brandenb@nordita.org [School of Mathematical Sciences and Monash Centre for Astrophysics, Monash University, Clayton, VIC 3800 (Australia)

    2017-08-20

    A turbulent dynamo in spherical geometry with an outer corona is simulated to study the sign of magnetic helicity in the outer parts. In agreement with earlier studies, the sign in the outer corona is found to be opposite to that inside the dynamo. Line-of-sight observations of polarized emission are synthesized to explore the feasibility of using the local reduction of Faraday depolarization to infer the sign of helicity of magnetic fields in the solar corona. This approach was previously identified as an observational diagnostic in the context of galactic magnetic fields. Based on our simulations, we show that this method can be successful in the solar context if sufficient statistics are gathered by using averages over ring segments in the corona separately for the regions north and south of the solar equator.

  14. Mars' Inner Core

    Science.gov (United States)

    1997-01-01

    This figure shows a cross-section of the planet Mars revealing an inner, high density core buried deep within the interior. Dipole magnetic field lines are drawn in blue, showing the global scale magnetic field that one associates with dynamo generation in the core. Mars must have one day had such a field, but today it is not evident. Perhaps the energy source that powered the early dynamo has shut down. The differentiation of the planet interior - heavy elements like iron sinking towards the center of the planet - can provide energy as can the formation of a solid core from the liquid.The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO. JPL is an operating division of California Institute of Technology (Caltech).

  15. Introduction to magnetohydrodynamics

    CERN Document Server

    Thompson, Ian

    2016-01-01

    Magnetohydrodynamics (MHD) plays a crucial role in astrophysics, planetary magnetism, engineering and controlled nuclear fusion. This comprehensive textbook emphasizes physical ideas, rather than mathematical detail, making it accessible to a broad audience. Starting from elementary chapters on fluid mechanics and electromagnetism, it takes the reader all the way through to the latest ideas in more advanced topics, including planetary dynamos, stellar magnetism, fusion plasmas and engineering applications. With the new edition, readers will benefit from additional material on MHD instabilities, planetary dynamos and applications in astrophysics, as well as a whole new chapter on fusion plasma MHD. The development of the material from first principles and its pedagogical style makes this an ideal companion for both undergraduate students and postgraduate students in physics, applied mathematics and engineering. Elementary knowledge of vector calculus is the only prerequisite.

  16. Stochastic Modelling, Analysis, and Simulations of the Solar Cycle Dynamic Process

    Science.gov (United States)

    Turner, Douglas C.; Ladde, Gangaram S.

    2018-03-01

    Analytical solutions, discretization schemes and simulation results are presented for the time delay deterministic differential equation model of the solar dynamo presented by Wilmot-Smith et al. In addition, this model is extended under stochastic Gaussian white noise parametric fluctuations. The introduction of stochastic fluctuations incorporates variables affecting the dynamo process in the solar interior, estimation error of parameters, and uncertainty of the α-effect mechanism. Simulation results are presented and analyzed to exhibit the effects of stochastic parametric volatility-dependent perturbations. The results generalize and extend the work of Hazra et al. In fact, some of these results exhibit the oscillatory dynamic behavior generated by the stochastic parametric additative perturbations in the absence of time delay. In addition, the simulation results of the modified stochastic models influence the change in behavior of the very recently developed stochastic model of Hazra et al.

  17. Primordial magnetic fields in hybrid inflation

    CERN Document Server

    Davis, A C; Davis, Anne Christine; Dimopoulos, Konstantinos

    1997-01-01

    We show that, during hybrid inflation, a primordial magnetic field can be created, sufficiently strong to seed the galactic dynamo and generate the observed galactic magnetic fields. Considering the inflaton dominated regime, our field is produced by the Higgs--field gradients, resulting from a grand unified phase transition. The evolution of the field is followed from its creation through to the epoch of structure formation, subject to the relevant constraints. We find that it is always possible to create a magnetic field of sufficient magnitude, provided the phase transition occurs during the final 15 e-foldings of the inflationary period. the achieved field can be coherent over large distances and, for some parameter space, it is strong enough to dispense with the galactic dynamo.

  18. Investigation of transitions from order to chaos in dynamical systems. Final technical report, period ending May 31, 1996

    International Nuclear Information System (INIS)

    Schmidt, G.

    1996-01-01

    It has been recently conjectured that chaotic flows in conductive fluids can generate fast dynamos, where the magnetic field increases exponentially in time such processes could be responsible for the generation of solar and terrestrial magnetic fields. The author studied realistic flows, like those arising from the Rayleigh Benard instability. First the flow was studied computationally as well as analytically, to give a clear description of its properties, relevant ranges of parameter and regions of chaotic flow. Once this task was accomplished computational studies were carried out to see if such flows are capable of fast dynamo action. In addition, the author carried out preliminary investigations on other applications of chaotic dynamics, like emittance growth in electron beams, and the relationship between stochastic webs and percolation theory

  19. Adaptive web data extraction policies

    Directory of Open Access Journals (Sweden)

    Provetti, Alessandro

    2008-12-01

    Full Text Available Web data extraction is concerned, among other things, with routine data accessing and downloading from continuously-updated dynamic Web pages. There is a relevant trade-off between the rate at which the external Web sites are accessed and the computational burden on the accessing client. We address the problem by proposing a predictive model, typical of the Operating Systems literature, of the rate-of-update of each Web source. The presented model has been implemented into a new version of the Dynamo project: a middleware that assists in generating informative RSS feeds out of traditional HTML Web sites. To be effective, i.e., make RSS feeds be timely and informative and to be scalable, Dynamo needs a careful tuning and customization of its polling policies, which are described in detail.

  20. Magnetic field generation by pointwise zero-helicity three-dimensional steady flow of an incompressible electrically conducting fluid

    Science.gov (United States)

    Rasskazov, Andrey; Chertovskih, Roman; Zheligovsky, Vladislav

    2018-04-01

    We introduce six families of three-dimensional space-periodic steady solenoidal flows, whose kinetic helicity density is zero at any point. Four families are analytically defined. Flows in four families have zero helicity spectrum. Sample flows from five families are used to demonstrate numerically that neither zero kinetic helicity density nor zero helicity spectrum prohibit generation of large-scale magnetic field by the two most prominent dynamo mechanisms: the magnetic α -effect and negative eddy diffusivity. Our computations also attest that such flows often generate small-scale field for sufficiently small magnetic molecular diffusivity. These findings indicate that kinetic helicity and helicity spectrum are not the quantities controlling the dynamo properties of a flow regardless of whether scale separation is present or not.

  1. Remanent magnetism at Mars

    Science.gov (United States)

    Curtis, S. A.; Ness, N. F.

    1988-01-01

    It is shown that a strong case can be made for an intrinsic magnetic field of dynamo origin for Mars earlier in its history. The typical equatorial magnetic field intensity would have been equal to about 0.01-0.1 gauss. The earlier dynamo activity is no longer extant, but a significant remanent magnetic field may exist. A highly non-dipole magnetic field could result from the remanent magnetization of the surface. Remanent magnetization may thus play an important role in the Mars solar wind interactions, in contrast to Venus with its surface temperatures above the Curie point. The anomalous characteristics of Mars'solar wind interaction compared to that of Venus may be explicable on this basis.

  2. Mercury's thermal history and the generation of its magnetic field

    International Nuclear Information System (INIS)

    Schubert, G.; Ross, M.N.; Stevenson, D.J.; Spohn, T.

    1988-01-01

    Thermal history of Mercury's interior is examined using the model of Stevenson et al. (1983), extended to include the effects of tidal heating in Mercury's solid inner core. The implications of Mercury's thermal history for the source of the planet's magnetic field are discussed. It is shown that the major results of this model are similar to the results obtained with the Stevenson et al. model, except for the addition of inner-core tidal dissipation. It is concluded that the extended model properly characterizes Mercury's internal structure and thermal history, and that the criteria for dynamo generation are not properly satisfied. Alternative explanations, including the possibility of a weak thermoelectric dynamo, are examined

  3. The Origin and Dynamics of Solar Magnetism

    CERN Document Server

    Thompson, M. J; Culhane, J. L; Nordlund, Å; Solanki, S. K; Zahn, J.-P

    2009-01-01

    The articles collected in this volume present all aspects of solar magnetism: from its origin in the solar dynamo to its evolution and dynamics that create the variability of solar phenomena, its well-known 11-year activity cycle that leads to the ever-changing pattern of sunspots and active regions on the Sun. Several contributions deal with the solar dynamo, the driver of many solar phenomena. Other contributions treat the transport and emergence of the magnetic flux through the outer layers of the Sun. The coupling of magnetic fields from the surface to the solar corona and beyond is also described, together with current studies on the predictability of solar activity. This book is aimed at researchers and graduate students working in solar physics and space science. It provides a full review of our current understanding of solar magnetism by the foremost experts in the field.

  4. Turbulent convection in liquid metal with and without rotation

    OpenAIRE

    King, Eric M.; Aurnou, Jonathan M.

    2013-01-01

    The magnetic fields of Earth and other planets are generated by turbulent, rotating convection in liquid metal. Liquid metals are peculiar in that they diffuse heat more readily than momentum, quantified by their small Prandtl numbers, . Most analog models of planetary dynamos, however, use moderate fluids, and the systematic influence of reducing is not well understood. We perform rotating Rayleigh–Bénard convection experiments in the liquid metal gallium over a range of nondimensional bu...

  5. Vers une plus grande collaboration régionale — le CRDI appuie le ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    26 janv. 2011 ... Bien qu'ils aient souvent de la difficulté à se démarquer face à la véritable dynamo économique qu'est la Chine, des pays tels que le Laos, le Cambodge et le Vietnam, qui tentaient d'échapper à la guerre il y a à peine 25 ans, connaissent une croissance explosive encore plus remarquable. Renaissance ...

  6. On the Origin of Ultra High Energy Cosmic Rays II

    Energy Technology Data Exchange (ETDEWEB)

    Fowler, T K; Colgate, S; Li, H; Bulmer, R H; Pino, J

    2011-03-08

    We show that accretion disks around Active Galactic Nuclei (AGNs) could account for the enormous power in observed ultra high energy cosmic rays {approx}10{sup 20} eV (UHEs). In our model, cosmic rays are produced by quasi-steady acceleration of ions in magnetic structures previously proposed to explain jets around Active Galactic Nuclei with supermassive black holes. Steady acceleration requires that an AGN accretion disk act as a dynamo, which we show to follow from a modified Standard Model in which the magnetic torque of the dynamo replaces viscosity as the dominant mechanism accounting for angular momentum conservation during accretion. A black hole of mass M{sub BH} produces a steady dynamo voltage V {proportional_to} {radical}M{sub BH} giving V {approx} 10{sup 20} volts for M{sub BH} {approx} 10{sup 8} solar masses. The voltage V reappears as an inductive electric field at the advancing nose of a dynamo-driven jet, where plasma instability inherent in collisionless runaway acceleration allows ions to be steadily accelerated to energies {approx} V, finally ejected as cosmic rays. Transient events can produce much higher energies. The predicted disk radiation is similar to the Standard Model. Unique predictions concern the remarkable collimation of jets and emissions from the jet/radiolobe structure. Given MBH and the accretion rate, the model makes 7 predictions roughly consistent with data: (1) the jet length; (2) the jet radius; (3) the steady-state cosmic ray energy spectrum; (4) the maximum energy in this spectrum; (5) the UHE cosmic ray intensity on Earth; (6) electron synchrotron wavelengths; and (7) the power in synchrotron radiation. These qualitative successes motivate new computer simulations, experiments and data analysis to provide a quantitative verification of the model.

  7. Comparative Magnetic Minima: Characterizing Quiet Times in the Sun and Stars. Symposium of the International Astronomical Union (286th) Held in Mendoza, Argentina on October 3-7, 2011

    Science.gov (United States)

    2011-10-01

    Contributed Talk – Is the Small-scale Quiet Sun Dynamo a Pedestal for Solar (and Stellar) Activity? Karel Schrijver (Presentation file) 12:15 – 12:35...Presentation file) Discussion and Summary (Chair: Cristina Mandrini) 15:00 – 16:00 Discussion led by Karel Schrijver Can We Establish if We Are...a grand minimum was led by Karel Schrijver. Thirty one poster presentations were put up and remained during the entire meeting. A public outreach

  8. Energy Flow Exciting Field-Aligned Current at Substorm Expansion Onset

    Science.gov (United States)

    Ebihara, Y.; Tanaka, T.

    2017-12-01

    At substorm expansion onset, upward field-aligned currents (FACs) increase abruptly, and a large amount of electromagnetic energy starts to consume in the polar ionosphere. A question arises as to where the energy comes from. Based on the results obtained by the global magnetohydrodynamics simulation, we present energy flow and energy conversion associated with the upward FACs that manifest the onset. Our simulations show that the cusp/mantle region transmits electromagnetic energy to almost the entire region of the magnetosphere when the interplanetary magnetic field is southward. Integral curve of the Poynting flux shows a spiral moving toward the ionosphere, probably suggesting the pathway of electromagnetic energy from the cusp/mantle dynamo to the ionosphere. The near-Earth reconnection initiates three-dimensional redistribution of the magnetosphere. Flow shear in the near-Earth region results in the generation of the near-Earth dynamo and the onset FACs. The onset FACs are responsible to transport the electromagnetic energy toward the Earth. In the near-Earth region, the electromagnetic energy coming from the cusp/mantle dynamo is converted to the kinetic energy (known as bursty bulk flow) and the thermal energy (associated with high-pressure region in the inner magnetosphere). Then, they are converted to the electromagnetic energy associated with the onset FACs. A part of electromagnetic energy is stored in the lobe region during the growth phase. The release of the stored energy, together with the continuously supplied energy from the cusp/mantle dynamo, contributes to the energy supply to the ionosphere during the expansion phase.

  9. Model of High-Energy-Density Battery Based on SiC Schottky Diodes

    Science.gov (United States)

    2006-10-01

    experimental values. 12 6. References 1. Blanchard, James P. Stretching the Boundaries of Nuclear Technology. The Bridge 32.4, 2002, 29-34. 2...32.2, 3-4. 4. Lal, Amit; Blanchard, James . The Daintiest Dynamos. IEEE Spectrum Sept. 2004, 36-41. 5. Lal, A.; Blanchard, James . By Harvesting...MATTS BLDG 305 ABERDEEN PROVING GROUND MD 21005-5001 US ARMY TRADOC BATTLE LAB INTEGRATION & TECHL DIRCTRT ATTN ATCD-B 10 WHISTLER LANE

  10. Isotope Generated Electron Density in Silicon Carbide Direct Energy Converters

    Science.gov (United States)

    2006-10-01

    Blanchard, James P. Stretching the Boundaries of Nuclear Technology. The Bridge 32.4 (2002): 29-34. 2. Ahearne, John F. The Future of Nuclear... James . The Daintiest Dynamos. IEEE Spectrum Sept. 2004, 36-41. 5. Lal, A.; Blanchard, James . By Harvesting Energy From Radioactive Specks...ODDRE (R&AT) THE PENTAGON WASHINGTON DC 20301-3080 US ARMY TRADOC BATTLE LAB INTEGRATION & TECHL DIRCTRT ATTN ATCD-B 10 WHISTLER LANE FT

  11. Sustained Magnetorotational Turbulence in Local Simulations of Stratified Disks with Zero Net Magnetic Flux

    DEFF Research Database (Denmark)

    W. Davis, S.; M. Stone, J.; Pessah, Martin Elias

    2010-01-01

    We examine the effects of density stratification on magnetohydrodynamic turbulence driven by the magnetorotational instability in local simulations that adopt the shearing box approximation. Our primary result is that, even in the absence of explicit dissipation, the addition of vertical gravity ....... Confirming the results of previous studies, we find oscillations in the large scale toroidal field with periods of ~10 orbits and describe the dynamo process that underlies these cycles....

  12. Iron snow in the Martian core?

    Science.gov (United States)

    Davies, Christopher J.; Pommier, Anne

    2018-01-01

    The decline of Mars' global magnetic field some 3.8-4.1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core. The dynamo was probably powered by planetary cooling and so its termination is intimately tied to the thermochemical evolution and present-day physical state of the Martian core. Bottom-up growth of a solid inner core, the crystallization regime for Earth's core, has been found to produce a long-lived dynamo leading to the suggestion that the Martian core remains entirely liquid to this day. Motivated by the experimentally-determined increase in the Fe-S liquidus temperature with decreasing pressure at Martian core conditions, we investigate whether Mars' core could crystallize from the top down. We focus on the "iron snow" regime, where newly-formed solid consists of pure Fe and is therefore heavier than the liquid. We derive global energy and entropy equations that describe the long-timescale thermal and magnetic history of the core from a general theory for two-phase, two-component liquid mixtures, assuming that the snow zone is in phase equilibrium and that all solid falls out of the layer and remelts at each timestep. Formation of snow zones occurs for a wide range of interior and thermal properties and depends critically on the initial sulfur concentration, ξ0. Release of gravitational energy and latent heat during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies at least 400 km of the core. Snow zones can be 1.5-2 Gyrs old, though thermal stratification of the uppermost core, not included in our model, likely delays onset. Models that match the available magnetic and geodetic constraints have ξ0 ≈ 10% and snow zones that occupy approximately the top 100 km of the present-day Martian core.

  13. Symposium 3 of JENAM 2011

    CERN Document Server

    Georgieva, Katya; Nagovitsyn, Yury; The sun : new challenges

    2012-01-01

    These are the proceedings of the Symposium 3 of JENAM 2011 on new scientific challenges posed by the Sun. The topics covered are   1. The unusual sunspot minimum, which poses challenges to the solar dynamo theory 2. The Sun’s Terra-Hertz emission, which opens a new observational window 3. Corona wave activity 4. Space weather agents - initiation, propagation, and forecasting In 21 in-depth contributions, the reader will be presented with the latest findings.

  14. Combat aircraft mission tradeoff models for conceptual design evaluation

    OpenAIRE

    Malakhoff, Lev A

    1988-01-01

    A methodology is developed to address the analyses of combat aircraft attrition. The operations of an aircraft carrier task force are modeled using the systems dynamics simulation language DYNAMO. The three mission-roles include: surface attack, lighter escort, and carrier defense. The level of analysis is performed over the entire campaign, going beyond the traditional single·sortie analysis level. These analyses are performed by determining several measures of effectiveness (...

  15. Nonlinear reversed field pinch dynamics with nonideal boundaries

    International Nuclear Information System (INIS)

    Ho, Y.L.; Prager, S.C.

    1991-03-01

    The nonlinear behavior of the reversed field pinch bounded by a resistive shell or a distant conducting wall is investigated with a three-dimensional magnetohydrodynamic code. Nonlinear interaction between modes enhances fluctuation levels as the conducting wall is removed. The enhanced fluctuation induced v x b electric field, which produces the dynamo effect, suppresses toroidal current and enhances surface helicity dissipation. Thus, loop voltage must increase to sustain the current and maintain helicity balance. 46 refs., 21 figs., 2 tabs

  16. Proceedings of an International school and workshop on Plasma astrophysics, 24 August-3 September 1988, Varenna, Italy

    Energy Technology Data Exchange (ETDEWEB)

    Guyenne, T.D.; Hunt, J.J. (European Space Research and Technology Centre, Noordwijk (Netherlands)) (eds.)

    1989-01-01

    These volum proceedings on plasma astrophysics contain 63 contributions which are all in INIS scope. They are subdiveded intot the following categories: results of space projects, solar wind and planetary magnetospheres, sun and normal stars, interstellar medium and schock waves, reconnection of magnetic fields in space and dynamos, acceleration mechanisms and cosmic rays, accretion, disks compact objects and active galaxies, galactic structure dynamics and cosmology, and laboratory plasma physics. (author). refs.; tabs.

  17. The Effect of "Rogue" Active Regions on the Solar Cycle

    Science.gov (United States)

    Nagy, Melinda; Lemerle, Alexandre; Labonville, François; Petrovay, Kristóf; Charbonneau, Paul

    2017-11-01

    The origin of cycle-to-cycle variations in solar activity is currently the focus of much interest. It has recently been pointed out that large individual active regions with atypical properties can have a significant impact on the long-term behavior of solar activity. We investigate this possibility in more detail using a recently developed 2×2D dynamo model of the solar magnetic cycle. We find that even a single "rogue" bipolar magnetic region (BMR) in the simulations can have a major effect on the further development of solar activity cycles, boosting or suppressing the amplitude of subsequent cycles. In extreme cases, an individual BMR can completely halt the dynamo, triggering a grand minimum. Rogue BMRs also have the potential to induce significant hemispheric asymmetries in the solar cycle. To study the effect of rogue BMRs in a more systematic manner, a series of dynamo simulations were conducted, in which a large test BMR was manually introduced in the model at various phases of cycles of different amplitudes. BMRs emerging in the rising phase of a cycle can modify the amplitude of the ongoing cycle, while BMRs emerging in later phases will only affect subsequent cycles. In this model, the strongest effect on the subsequent cycle occurs when the rogue BMR emerges around cycle maximum at low latitudes, but the BMR does not need to be strictly cross-equatorial. Active regions emerging as far as 20° from the equator can still have a significant effect. We demonstrate that the combined effect of the magnetic flux, tilt angle, and polarity separation of the BMR on the dynamo is via their contribution to the dipole moment, δ D_{BMR}. Our results indicate that prediction of the amplitude, starting epoch, and duration of a cycle requires an accurate accounting of a broad range of active regions emerging in the previous cycle.

  18. Constructing a Plastic Bottle Wind Turbine as a Practical Aid for Learning about Using Wind Energy to Generate Electricity

    Science.gov (United States)

    Appleyard, S. J.

    2009-01-01

    A simple horizontal axis wind turbine can be easily constructed using a 1.5 l PET plastic bottle, a compact disc and a small dynamo. The turbine operates effectively at low wind speeds and has a rotational speed of 500 rpm at a wind speed of about 14 km h[superscript -1]. The wind turbine can be used to demonstrate the relationship between open…

  19. Primordial magnetic fields from metric perturbations

    CERN Document Server

    Maroto, A L

    2001-01-01

    We study the amplification of electromagnetic vacuum fluctuations induced by the evolution of scalar metric perturbations at the end of inflation. Such perturbations break the conformal invariance of Maxwell equations in Friedmann-Robertson-Walker backgrounds and allow the growth of magnetic fields on super-Hubble scales. We estimate the strength of the fields generated by this mechanism on galactic scales and compare the results with the present bounds on the galactic dynamo seed fields.

  20. Control volume method for the thermal convection problem in a rotating spherical shell: test on the benchmark solution

    Czech Academy of Sciences Publication Activity Database

    Hejda, Pavel; Reshetnyak, M.

    2004-01-01

    Roč. 48, č. 4 (2004), s. 741-746 ISSN 0039-3169 R&D Projects: GA AV ČR KSK3012103 Grant - others:RFFR(RU) 03-05-64074; EC(XE) HPRI-CT-1999-00026 Institutional research plan: CEZ:AV0Z3012916 Keywords : liquid core * dynamo benchmark * finite volume method Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 0.447, year: 2004

  1. Solar influences on atmospheric circulation

    Czech Academy of Sciences Publication Activity Database

    Georgieva, K.; Kirov, B.; Koucká Knížová, Petra; Mošna, Zbyšek; Kouba, Daniel; Asenovska, Y.

    90-91, SI (2012), s. 15-25 ISSN 1364-6826. [IAGA/ICMA/CAWSES-II TG4 Workshop on Vertical Coupling in the Atmosphere-Ionosphere System /4./. Prague, 14.02.2011-18.02.2011] Institutional support: RVO:68378289 Keywords : Solar activity * North Atlantic Oscillation * Solar dynamo * Solar activity Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 1.417, year: 2012 http://www.sciencedirect.com/science/article/pii/S1364682612001393

  2. Formation, stratification, and mixing of the cores of Earth and Venus

    OpenAIRE

    Jacobson, Seth A.; Rubie, David C.; Hernlund, John; Morbidelli, Alessandro; Nakajima, Miki

    2017-01-01

    Earth possesses a persistent, internally-generated magnetic field, whereas no trace of a dynamo has been detected on Venus, at present or in the past, although a high surface temperature and recent resurfacing events may have removed paleomagnetic evidence. Whether or not a terrestrial body can sustain an internally generated magnetic field by convection inside its metallic fluid core is determined in part by its initial thermodynamic state and its compositional structure, both of which are i...

  3. Paleomagnetism of Hadean to Neoarchean Detrital Zircons from the Jack Hills, Western Australia

    Science.gov (United States)

    Sciascia Borlina, C.; Weiss, B. P.; Lima, E. A.; Fu, R. R.; Bell, E. A.; Alexander, E.; Kirkpatrick, H.; Wielicki, M. M.; Harrison, M.; Ramezani, J.; Harrison, R.; Einsle, J. F.

    2017-12-01

    Determining the evolution of the Earth's magnetic field through geologic time will constrain the thermal evolution of the core and the mechanisms that have powered the geodynamo. Previous paleomagnetic studies indicate that an active dynamo existed at least as early as 3.5 billion years (Ga) ago. However, the history of the dynamo prior to this time and, in particular, its time of origin are largely unknown. One potential remanence carrier of the earlier geomagnetic field are 3.0-4.4 Ga detrital zircon crystals from the Jack Hills and other sites in the Yilgarn craton of Western Australia. Here we report new geomagnetic paleointensity data from Jack Hills zircons to assess whether they contain robust records of the early geodynamo. We studied the paleomagnetism of zircons that were selected based on a stringent set of criteria including concordant (>90%) U-Pb dates older than 3.5 Ga, minimal cracks and metamictization (to minimize the likelihood of containing secondary ferromagnetic deposits that may not have been removed after hydrochloric acid washing), and the presence of sharp (≤10 μm) internal Li-rich domains correlated with growth zonation (suggesting that they may have not been heated above the magnetite Curie temperature since their formation). All zircons that we have analyzed thus far exhibited unsuitable magnetic recording properties (demagnetize unstably and experience thermochemical alteration below 500oC) and therefore do not provide robust paleointensity constraints on the early dynamo. These results differ significantly from those of another recent paleomagnetic study that suggested that Jack Hills zircons contain records of a substantial dynamo extending back to 4.2 Ga. Reconciliation between these two studies is necessary so that the existence of the geodynamo before 3.5 Ga can be accepted.

  4. Classroom

    Indian Academy of Sciences (India)

    IAS Admin

    the ring and the dipole can rotate only about the X-axis. Figure 2. Figure 1 redrawn so as to give the angles and the sense of ring motion. Also shown is the magnetic dipole. (S. N) pivoted freely at the ring centre. the current I(t) induced in the metallic ring due to its rotation ! relative to B. It is essentially a dynamo-motor.

  5. 低炭素社会の実現に向けたナノ水力発電機による地域活性化の取り組み

    OpenAIRE

    笠井, 利浩; Kasai, Toshihiro; 谷内, 眞之助; Taniuchi, Shinnosuke; 藤田, 輝雄; Fujita, Teruo; 小林, 拓矢; Kobayashi, Takuya,

    2015-01-01

    A demonstration experiment of pico size hydroelectric power generation was performed in Kamiajimi area, Fukui-city from 2012. In this report, the installation activity of nano size hydroelectric power generation illumination that we did in 2014 will be presented. A nano size hydroelectric generator using a bicycle wheel with a hub dynamo and the LED illumination unit using power LED elements was developed. A workshop to make nano size hydroelectric generators was held with residents of Kamiaj...

  6. On geodynamo integrations conserving momentum flux

    Science.gov (United States)

    Wu, C.; Roberts, P. H.

    2012-12-01

    The equations governing the geodynamo are most often integrated by representing the magnetic field and fluid velocity by toroidal and poloidal scalars (for example, MAG code [1]). This procedure does not automatically conserve the momentum flux. The results can, particularly for flows with large shear, introduce significant errors, unless the viscosity is artificially increased. We describe a method that evades this difficulty, by solving the momentum equation directly while properly conserving momentum. It finds pressure by FFT and cyclic reduction, and integrates the governing equations on overlapping grids so avoiding the pole problem. The number of operations per time step is proportional to N3 where N is proportional to the number of grid points in each direction. This contrasts with the order N4 operations of standard spectral transform methods. The method is easily parallelized. It can also be easily adapted to schemes such as the Weighted Essentially Non-Oscillatory (WENO) method [2], a flux based procedure based on upwinding that is numerically stable even for zero explicit viscosity. The method has been successfully used to investigate the generation of magnetic fields by flows confined to spheroidal containers and driven by precessional and librational forcing [3, 4]. For spherical systems it satisfies dynamo benchmarks [5]. [1] MAG, http://www.geodynamics.org/cig/software/mag [2] Liu, XD, Osher, S and Chan, T, Weighted Essentially Nonoscillatory Schemes, J. Computational Physics, 115, 200-212, 1994. [3] Wu, CC and Roberts, PH, On a dynamo driven by topographic precession, Geophysical & Astrophysical Fluid Dynamics, 103, 467-501, (DOI: 10.1080/03091920903311788), 2009. [4] Wu, CC and Roberts, PH, On a dynamo driven topographically by longitudinal libration, Geophysical & Astrophysical Fluid Dynamics, DOI:10.1080/03091929.2012.682990, 2012. [5] Christensen, U, et al., A numerical dynamo benchmark, Phys. Earth Planet Int., 128, 25-34, 2001.

  7. Predicting Automotive Interior Noise Including Wind Noise by Statistical Energy Analysis

    OpenAIRE

    Yoshio Kurosawa

    2017-01-01

    The applications of soundproof materials for reduction of high frequency automobile interior noise have been researched. This paper presents a sound pressure prediction technique including wind noise by Hybrid Statistical Energy Analysis (HSEA) in order to reduce weight of acoustic insulations. HSEA uses both analytical SEA and experimental SEA. As a result of chassis dynamo test and road test, the validity of SEA modeling was shown, and utility of the method was confirmed.

  8. Mercury's magnetic field and interior

    International Nuclear Information System (INIS)

    Connerney, J.E.P.; Ness, N.F.

    1988-01-01

    The magnetic-field data collected on Mercury by the Mariner-10 spacecraft present substantial evidence for an intrinsic global magnetic field. However, studies of Mercury's thermal evolution show that it is most likely that the inner core region of Mercury solidified or froze early in the planet's history. Thus, the explanation of Mercury's magnetic field in the framework of the traditional planetary dynamo is less than certain

  9. Plasmas physics research in the MST toroidal confinement device

    International Nuclear Information System (INIS)

    1992-01-01

    Summaries of work completed during this report period are given for the following: (1) anomalous ion heating and dynamo fluctuations, (2) current density fluctuations and ambipolarity of transport, (3) measurement of nonlinear coupling of tearing fluctuations, (4) soft x-ray observation of tearing mode phase-locking, (5) locked modes, sawteeth, and field errors in MST, and (6) boronization using a boron- carbide limiter

  10. Solen må aldrig skinne, og Sofie må aldrig smile

    DEFF Research Database (Denmark)

    Nielsen, Jakob Isak

    2012-01-01

    Som producent på alle tre sæsoner af Forbrydelsen har Piv Bernth spillet en vigtig rolle i Forbrydelsens tilblivelsesproces og har sammen med Søren Sveistrup været seriens dynamo. I april 2012 blev Bernth udnævnt til DRs nye dramachef og skal i samarbejde med fiktionschef Nadia Kløvedal Reich være...

  11. A Comparison of the Democratic Security Policy in Colombia and Provincial Reconstruction Teams in Iraq

    Science.gov (United States)

    2009-09-01

    Reforma Agraria - Incora was created to redistribute land. Over time, it did have some success in marginal areas. But it failed to prove the dynamo...Record. Bureau of Democracy, Human Rights, and Labor . Available at: www.state.gov. 62 Ibid., 1. 63 Presidency of the Republic, “Democratic Security and...assessment, statistics show a significan 2000 .”68 C. DEMOBILIZATION The process of demobilization in Colombia is currently an area of contention for

  12. MAGNETIC ACTIVITY CYCLES IN THE EXOPLANET HOST STAR {epsilon} ERIDANI

    Energy Technology Data Exchange (ETDEWEB)

    Metcalfe, T. S.; Mathur, S. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); Buccino, A. P.; Mauas, P. J. D.; Petrucci, R. [Instituto de Astronomia y Fisica del Espacio (CONICET), C.C. 67 Sucursal 28, C1428EHA-Buenos Aires (Argentina); Brown, B. P. [Department of Astronomy and Center for Magnetic Self-Organization, University of Wisconsin, Madison, WI 53706-1582 (United States); Soderblom, D. R. [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Henry, T. J. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302 (United States); Hall, J. C. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Basu, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States)

    2013-02-01

    The active K2 dwarf {epsilon} Eri has been extensively characterized both as a young solar analog and more recently as an exoplanet host star. As one of the nearest and brightest stars in the sky, it provides an unparalleled opportunity to constrain stellar dynamo theory beyond the Sun. We confirm and document the 3-year magnetic activity cycle in {epsilon} Eri originally reported by Hatzes and coworkers, and we examine the archival data from previous observations spanning 45 years. The data show coexisting 3-year and 13-year periods leading into a broad activity minimum that resembles a Maunder minimum-like state, followed by the resurgence of a coherent 3-year cycle. The nearly continuous activity record suggests the simultaneous operation of two stellar dynamos with cycle periods of 2.95 {+-} 0.03 years and 12.7 {+-} 0.3 years, which, by analogy with the solar case, suggests a revised identification of the dynamo mechanisms that are responsible for the so-called 'active' and 'inactive' sequences as proposed by Boehm-Vitense. Finally, based on the observed properties of {epsilon} Eri, we argue that the rotational history of the Sun is what makes it an outlier in the context of magnetic cycles observed in other stars (as also suggested by its Li depletion), and that a Jovian-mass companion cannot be the universal explanation for the solar peculiarities.

  13. Oscillatory Convection in Rotating Liquid Metals

    Science.gov (United States)

    Bertin, Vincent; Grannan, Alex; Aurnou, Jonathan

    2016-11-01

    We have performed laboratory experiments in a aspect ratio Γ = 2 cylinder using liquid gallium (Pr = 0 . 023) as the working fluid. The Ekman number varies from E = 4 ×10-5 to 4 ×10-6 and the Rayleigh number varies from Ra = 3 ×105 to 2 ×107 . Using heat transfer and temperature measurements within the fluid, we characterize the different styles of low Pr rotating convective flow. The convection threshold is first overcome in the form of a container scale inertial oscillatory mode. At stronger forcing, wall-localized modes develop, coexisting with the inertial oscillatory modes in the bulk. When the strength of the buoyancy increases further, the bulk flow becomes turbulent while the wall modes remain. Our results imply that rotating convective flows in liquid metals do not develop in the form of quasi-steady columns, as in Pr = 1 planetary and stellar dynamo models, but in the form of oscillatory motions. Therefore, convection driven dynamo action in low Pr fluids can differ substantively than that occurring in typical Pr = 1 numerical models. Our results also suggest that low wavenumber, wall modes may be dynamically and observationally important in liquid metal dynamo systems. We thank the NSF Geophysics Program for support of this project.

  14. Self-similar energetics in large clusters of galaxies.

    Science.gov (United States)

    Miniati, Francesco; Beresnyak, Andrey

    2015-07-02

    Massive galaxy clusters are filled with a hot, turbulent and magnetized intra-cluster medium. Still forming under the action of gravitational instability, they grow in mass by accretion of supersonic flows. These flows partially dissipate into heat through a complex network of large-scale shocks, while residual transonic (near-sonic) flows create giant turbulent eddies and cascades. Turbulence heats the intra-cluster medium and also amplifies magnetic energy by way of dynamo action. However, the pattern regulating the transformation of gravitational energy into kinetic, thermal, turbulent and magnetic energies remains unknown. Here we report that the energy components of the intra-cluster medium are ordered according to a permanent hierarchy, in which the ratio of thermal to turbulent to magnetic energy densities remains virtually unaltered throughout the cluster's history, despite evolution of each individual component and the drive towards equipartition of the turbulent dynamo. This result revolves around the approximately constant efficiency of turbulence generation from the gravitational energy that is freed during mass accretion, revealed by our computational model of cosmological structure formation. The permanent character of this hierarchy reflects yet another type of self-similarity in cosmology, while its structure, consistent with current data, encodes information about the efficiency of turbulent heating and dynamo action.

  15. DATA ASSIMILATION APPROACH FOR FORECAST OF SOLAR ACTIVITY CYCLES

    Energy Technology Data Exchange (ETDEWEB)

    Kitiashvili, Irina N., E-mail: irina.n.kitiashvili@nasa.gov [NASA Ames Research Center, Moffett Field, Mountain View, CA 94035 (United States)

    2016-11-01

    Numerous attempts to predict future solar cycles are mostly based on empirical relations derived from observations of previous cycles, and they yield a wide range of predicted strengths and durations of the cycles. Results obtained with current dynamo models also deviate strongly from each other, thus raising questions about criteria to quantify the reliability of such predictions. The primary difficulties in modeling future solar activity are shortcomings of both the dynamo models and observations that do not allow us to determine the current and past states of the global solar magnetic structure and its dynamics. Data assimilation is a relatively new approach to develop physics-based predictions and estimate their uncertainties in situations where the physical properties of a system are not well-known. This paper presents an application of the ensemble Kalman filter method for modeling and prediction of solar cycles through use of a low-order nonlinear dynamo model that includes the essential physics and can describe general properties of the sunspot cycles. Despite the simplicity of this model, the data assimilation approach provides reasonable estimates for the strengths of future solar cycles. In particular, the prediction of Cycle 24 calculated and published in 2008 is so far holding up quite well. In this paper, I will present my first attempt to predict Cycle 25 using the data assimilation approach, and discuss the uncertainties of that prediction.

  16. Turbulent magnetohydrodynamics in liquid metals

    International Nuclear Information System (INIS)

    Berhanu, Michael

    2008-01-01

    In electrically conducting fluids, the electromagnetic field is coupled with the fluid motion by induction effects. We studied different magnetohydrodynamic phenomena, using two experiments involving turbulent flows of liquid metal. The first mid-sized uses gallium. The second, using sodium, is conducted within the VKS (Von Karman Sodium) collaboration. It has led to the observation of the dynamo effect, namely converting a part of the kinetic energy of the fluid into magnetic energy. We have shown that, depending on forcing conditions, a statistically stationary dynamo, or dynamical regimes of magnetic field can be generated. In particular, polarity reversals similar to those of Earth's magnetic field were observed. Meanwhile, experiment with Gallium has been developed to study the effects of electromagnetic induction by turbulent flows in a more homogeneous and isotropic configuration than in the VKS experiment. Using data from these two experiments, we studied the advection of magnetic field by a turbulent flow and the induced fluctuations. The development of probes measuring electrical potential difference allowed us to further highlight the magnetic braking of a turbulent flow of Gallium by Lorentz force. This mechanism is involved in the saturation of the dynamo instability. (author) [fr

  17. a Millennium of Geomagnetism

    Science.gov (United States)

    Stern, David P.

    2002-11-01

    The history of geomagnetism began around the year 1000 with the discovery in China of the magnetic compass. Methodical studies of the Earth's field started in 1600 with William Gilbert's De Magnete [Gilbert, 1600] and continued with the work of (among others) Edmond Halley, Charles Augustin de Coulomb, Carl Friedrich Gauss, and Edward Sabine. The discovery of electromagnetism by Hans Christian Oersted and André-Marie Ampére led Michael Faraday to the notion of fluid dynamos, and the observation of sunspot magnetism by George Ellery Hale led Sir Joseph Larmor in 1919 to the idea that such dynamos could sustain themselves naturally in convecting conducting fluids. From that came modern dynamo theory, of both the solar and terrestrial magnetic fields. Paleomagnetic studies revealed that the Earth's dipole had undergone reversals in the distant past, and these became the critical evidence in establishing plate tectonics. Finally, the recent availability of scientific spacecraft has demonstrated the intricacy of the Earth's distant magnetic field, as well as the existence of magnetic fields associated with other planets and with satellites in our solar system.

  18. Estimating the Magnetic Field Strength in Hot Jupiters

    Energy Technology Data Exchange (ETDEWEB)

    Yadav, Rakesh K. [Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 (United States); Thorngren, Daniel P., E-mail: rakesh_yadav@fas.harvard.edu [Department of Physics, University of California, Santa Cruz, CA (United States)

    2017-11-01

    A large fraction of known Jupiter-like exoplanets are inflated as compared to Jupiter. These “hot” Jupiters orbit close to their parent star and are bombarded with intense starlight. Many theories have been proposed to explain their radius inflation and several suggest that a small fraction of the incident starlight is injected into the planetary interior, which helps to puff up the planet. How will such energy injection affect the planetary dynamo? In this Letter, we estimate the surface magnetic field strength of hot Jupiters using scaling arguments that relate energy available in planetary interiors to the dynamo-generated magnetic fields. We find that if we take into account the energy injected in the planetary interior that is sufficient to inflate hot Jupiters to observed radii, then the resulting dynamo should be able generate magnetic fields that are more than an order of magnitude stronger than the Jovian values. Our analysis highlights the potential fundamental role of the stellar light in setting the field strength in hot Jupiters.

  19. Evolution in Cloud Population Statistics of the MJO: From AMIE Field Observations to Global Cloud-Permiting Models

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Chidong [Univ. of Miami, Coral Gables, FL (United States)

    2016-08-14

    Motivated by the success of the AMIE/DYNAMO field campaign, which collected unprecedented observations of cloud and precipitation from the tropical Indian Ocean in Octber 2011 – March 2012, this project explored how such observations can be applied to assist the development of global cloud-permitting models through evaluating and correcting model biases in cloud statistics. The main accomplishment of this project were made in four categories: generating observational products for model evaluation, using AMIE/DYNAMO observations to validate global model simulations, using AMIE/DYNAMO observations in numerical studies of cloud-permitting models, and providing leadership in the field. Results from this project provide valuable information for building a seamless bridge between DOE ASR program’s component on process level understanding of cloud processes in the tropics and RGCM focus on global variability and regional extremes. In particular, experience gained from this project would be directly applicable to evaluation and improvements of ACME, especially as it transitions to a non-hydrostatic variable resolution model.

  20. EXPLAINING THE COEXISTENCE OF LARGE-SCALE AND SMALL-SCALE MAGNETIC FIELDS IN FULLY CONVECTIVE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Yadav, Rakesh K.; Poppenhaeger, Katja; Wolk, Scott J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Christensen, Ulrich R.; Gastine, Thomas [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Morin, Julien [LUPM, Université de Montpellier, CNRS, Place Eugène Bataillon, F-34095 (France); Reiners, Ansgar, E-mail: rakesh.yadav@cfa.harvard.edu [Institut für Astrophysik, Universität Göttingen, Friedrich Hund Platz 1, D-37077 Göttingen (Germany)

    2015-11-10

    Despite the lack of a shear-rich tachocline region, low-mass fully convective (FC) stars are capable of generating strong magnetic fields, indicating that a dynamo mechanism fundamentally different from the solar dynamo is at work in these objects. We present a self-consistent three-dimensional model of magnetic field generation in low-mass FC stars. The model utilizes the anelastic magnetohydrodynamic equations to simulate compressible convection in a rotating sphere. A distributed dynamo working in the model spontaneously produces a dipole-dominated surface magnetic field of the observed strength. The interaction of this field with the turbulent convection in outer layers shreds it, producing small-scale fields that carry most of the magnetic flux. The Zeeman–Doppler-Imaging technique applied to synthetic spectropolarimetric data based on our model recovers most of the large-scale field. Our model simultaneously reproduces the morphology and magnitude of the large-scale field as well as the magnitude of the small-scale field observed on low-mass FC stars.

  1. Self-organisation and intermittent coherent oscillations in the EXTRAP T2 reversed field pinch

    International Nuclear Information System (INIS)

    Cecconello, M.; Malmberg, J.A.; Sallander, E.; Drake, J.R.

    2002-01-01

    Many reversed-field pinch (RFP) experiments exhibit a coherent oscillatory behaviour that is characteristic of discrete dynamo events and is associated with intermittent current profile self-organisation phenomena. However, in the vast majority of the discharges in the resistive shell RFP experiment EXTRAP T2, the dynamo activity does not show global, coherent oscillatory behaviour. The internally resonant tearing modes are phase-aligned and wall-locked resulting in a large localised magnetic perturbation. Equilibrium and plasma parameters have a level of high frequency fluctuations but the average values are quasi-steady. For some discharges, however, the equilibrium parameters exhibit the oscillatory behaviour characteristic of the discrete dynamo events. For these discharges, the trend observed in the tearing mode spectra, associated with the onset of the discrete relaxation event behaviour, is a relative higher amplitude of m = 0 mode activity and relative lower amplitude of the m = 1 mode activity compared with their average values. Global plasma parameters and model profile calculations for sample discharges representing the two types of relaxation dynamics are presented

  2. Self-Organisation and Intermittent Coherent Oscillations in the EXTRAP T2 Reversed Field Pinch

    Science.gov (United States)

    Cecconello, M.; Malmberg, J.-A.; Sallander, E.; Drake, J. R.

    Many reversed-field pinch (RFP) experiments exhibit a coherent oscillatory behaviour that is characteristic of discrete dynamo events and is associated with intermittent current profile self-organisation phenomena. However, in the vast majority of the discharges in the resistive shell RFP experiment EXTRAP T2, the dynamo activity does not show global, coherent oscillatory behaviour. The internally resonant tearing modes are phase-aligned and wall-locked resulting in a large localised magnetic perturbation. Equilibrium and plasma parameters have a level of high frequency fluctuations but the average values are quasi-steady. For some discharges, however, the equilibrium parameters exhibit the oscillatory behaviour characteristic of the discrete dynamo events. For these discharges, the trend observed in the tearing mode spectra, associated with the onset of the discrete relaxation event behaviour, is a relative higher amplitude of m = 0 mode activity and relative lower amplitude of the m = 1 mode activity compared with their average values. Global plasma parameters and model profile calculations for sample discharges representing the two types of relaxation dynamics are presented.

  3. Effects of the Observed Meridional Flow Variations since 1996 on the Sun's Polar Fields

    Science.gov (United States)

    Hathaway, David H.; Upton, Lisa

    2013-01-01

    The cause of the low and extended minimum in solar activity between Sunspot Cycles 23 and 24 was the small size of Sunspot Cycle 24 itself - small cycles start late and leave behind low minima. Cycle 24 is small because the polar fields produced during Cycle 23 were substantially weaker than those produced during the previous cycles and those (weak) polar fields are the seeds for the activity of the following cycle. The polar fields are produced by the latitudinal transport of magnetic flux that emerged in low-latitude active regions. The polar fields thus depend upon the details of both the flux emergence and the flux transport. We have measured the flux transport flows (differential rotation, meridional flow, and supergranules) since 1996 and find systematic and substantial variation in the meridional flow alone. Here we present experiments using a Surface Flux Transport Model in which magnetic field data from SOHO/MDI and SDO/HMI are assimilated into the model only at latitudes between 45-degrees north and south of the equator (this assures that the details of the active region flux emergence are well represented). This flux is then transported in both longitude and latitude by the observed flows. In one experiment the meridional flow is given by the time averaged (and north-south symmetric) meridional flow profile. In the second experiment the time-varying and north-south asymmetric meridional flow is used. Differences between the observed polar fields and those produced in these two experiments allow us to ascertain the effects of these meridional flow variations on the Sun s polar fields.

  4. Significance of Dungey-cycle flows in Jupiter's and Saturn's magnetospheres, and their identification on closed equatorial field lines

    Directory of Open Access Journals (Sweden)

    S. V. Badman

    2007-05-01

    Full Text Available We consider the contribution of the solar wind-driven Dungey-cycle to flux transport in Jupiter's and Saturn's magnetospheres, the associated voltages being based on estimates of the magnetopause reconnection rates recently derived from observations of the interplanetary medium in the vicinity of the corresponding planetary orbits. At Jupiter, the reconnection voltages are estimated to be ~150 kV during several-day weak-field rarefaction regions, increasing to ~1 MV during few-day strong-field compression regions. The corresponding values at Saturn are ~25 kV for rarefaction regions, increasing to ~150 kV for compressions. These values are compared with the voltages associated with the flows driven by planetary rotation. Estimates of the rotational flux transport in the "middle" and "outer" magnetosphere regions are shown to yield voltages of several MV and several hundred kV at Jupiter and Saturn respectively, thus being of the same order as the estimated peak Dungey-cycle voltages. We conclude that under such circumstances the Dungey-cycle "return" flow will make a significant contribution to the flux transport in the outer magnetospheric regions. The "return" Dungey-cycle flows are then expected to form layers which are a few planetary radii wide inside the dawn and morning magnetopause. In the absence of significant cross-field plasma diffusion, these layers will be characterized by the presence of hot light ions originating from either the planetary ionosphere or the solar wind, while the inner layers associated with the Vasyliunas-cycle and middle magnetosphere transport will be dominated by hot heavy ions originating from internal moon/ring plasma sources. The temperature of these ions is estimated to be of the order of a few keV at Saturn and a few tens of keV at Jupiter, in both layers.

  5. What can we learn about Mars from satellite magnetic field measurements?

    Science.gov (United States)

    Morschhauser, A.; Mittelholz, A.; Thomas, P.; Vervelidou, F.; Grott, M.; Johnson, C.; Lesur, V.; Lillis, R. J.

    2017-12-01

    The Mars orbiters MGS and MAVEN provide vector magnetic field data for Mars at a variety of altitudes, locations, and local times. In spite of the abundance of data, there are many open questions concerning the crustal magnetic field of Mars. In this contribution, we present our efforts to estimate the shutdown time of the Martian core dynamo and to estimate Martian paleopole locations, using magnetic field satellite data and models derived from these data [1]. Models are primarily based on MGS data, and we shortly present our recent advances to include MAVEN data. There exists some controversy concerning the timing of the Martian core dynamo shutdown [e.g., 2-5]. We address this question by studying the so-called visible magnetization [6-7] of impact craters larger than 400 km in diameter, and conclude that the dynamo ceased to operate in the Noachian period [8]. Further, paleopole locations have been used to constrain the dynamics of the Martian core dynamo [e.g. 4-5, 9]. However, such estimates are limited by the inherent non-uniqueness of inferring magnetization from magnetic field measurements. Here, we discuss how estimated paleopoles are influenced by this non-uniqueness and the limited signal-to-noise ratio of satellite measurements [6]. Furthermore, we discuss how paleopole locations may still be obtained from satellite magnetic field measurements. In this context, we present some new paleopole estimates for Mars including estimates of uncertainties. References: [1] A. Morschhauser et al. (2014), JGR, doi: 10.1002/2013JE004555 [2] R.J. Lillis et al. (2015), JGR, doi: 10.1002/2014je004774 [3] L.L. Hood et al. (2010), Icarus, doi: 10.1016/j.icarus.2010.01.009 [4] C. Milbury et al. (2012), JGR, doi: 10.1029/2012JE004099 [5] B. Langlais and M. Purucker (2007), PSS, 10.1016/j.pss.2006.03.008 [6] F. Vervelidou et al., On the accuracy of paleopole estimations from magnetic field measurements, GJI, under revision 2017 [7] D. Gubbins et al. (2011), GJI, doi: 10

  6. Large scale magnetic fields from torsion modes and massive photon inflation

    Science.gov (United States)

    Garcia de Andrade, L. C.

    2017-10-01

    Previously, Barrow and Tsagas (2008 Phys. Rev. D 77 107302) showed that a slower decay of magnetic fields are present in open Friedmann universes, with traditional Maxwell equations. In their paper magnetic fields of the order of B˜ 10-33~G , which are far below the value required to seed galactic dynamos, were obtained. In this paper, galactic dynamo seeds of the order of B˜ 10-23~G are obtained from massive electrodynamics in an Einstein-Cartan-Proca expanding universe of de Sitter type. Slow decay of magnetic fields in photon-torsion coupling in quantum electrodynamics (Garcia de Andrade 2011 Phys. Lett. B 468 28) have been recently shown by the author Garcia de Andrade (2012 Phys. Lett. B 711 143) to also not be able to seed galactic dynamos. Torsion modes are constrained by the field equations. Spacetime torsion is shown to be explicitly responsible for the slow decay of a cosmic magnetic field. In the absence of massive photon torsion coupling the magnetic field decay is of the order B˜ t-\\frac{3{2}} , when torsion turns on B˜ t-1.2 . The pure massive-photon-torsion contribution amplifies the magnetic field by B_torsion˜ t0.1 which characterizes an extremely slow magnetic dynamo action due to purely torsion gravitational effects. Recently Barrow, Tsagas and Yamamoto (2012 Phys. Rev. D 86 023535) have obtained superadiabatic amplification of B-fields in Friedmann open cosmology which lies within {10-20~G} and 10-12~G which falls very comfortably within the limits to seed galactic dynamos. The are other simple solutions where a B-field decays as B˜ a-1 , a relatively weak photon-torsion coupling approximation. These solutions are obtained for de Sitter and Friedmann metrics. Numerical values as displayed in this new version of the paper specifically for GUT phases of inflation with and without massive photons; without photons we obtain the well known value of GR which is B_GUT˜ 1048~G while for the values with massive photons one obtains B_GUT/γ˜ 10

  7. Viscosity in the edge of tokamak plasmas

    International Nuclear Information System (INIS)

    Stacey, W.M.

    1993-05-01

    A fluid representation of viscosity has been incorporated into a set of fluid equations that are maximally ordered in the ''short-radial-gradient-scale-length'' (srgsl) ordering that is appropriate for the edge of tokamak plasmas. The srgsl ordering raises viscous drifts and other viscous terms to leading order and fundamentally alters the character of the fluid equations. A leasing order viscous drift is identified. Viscous-driven radial particle and energy fluxes in the scrape-off layer and divertor channel are estimated to have an order unity effect in reducing radial peaking of energy fluxes transported along the field lines to divertor collector plates

  8. Experimental validation of calculation schemes connected with PWR absorbers and burnable poisons

    International Nuclear Information System (INIS)

    Klenov, P.

    1995-10-01

    In France 80% of electricity is produced by PWR reactors. For a better exploitation of these reactors a modular computer code Apollo-II has been developed. his code compute the flux transport by discrete ordinate method or by probabilistic collisions on extended configurations such as reactor cells, assemblies or little cores. For validation of this code on mixed oxide fuel lattices with absorbers an experimental program Epicure in the reactor Eole was induced. This thesis is devoted to the validation of the Apollo code according to the results of the Epicure program. 43 refs., 65 figs., 1 append

  9. Plasma Transport and Magnetic Flux Circulation in Saturn's Magnetosphere

    Science.gov (United States)

    Neupane, B. R.; Delamere, P. A.; Ma, X.; Wilson, R. J.

    2017-12-01

    Radial transport of plasma in the rapidly rotating magnetospheres is an important dynamical process. Radial transport is due to the centrifugally driven interchange instability and magnetodisc reconnection, allowing net mass to be transported outward while conserving magnetic flux. Using Cassini Plasma Spectrometer instrument (CAPS) data products (e.g., Thomsen et al., [2010]; Wilson et al., [2017]) we estimate plasma mass and magnetic flux transport rates as functions of radial distance and local time. The physical requirement for zero net magnetic flux transport provides a key benchmark for assessing the validity of our mass transport estimate. We also evaluate magnetodisc stability using a two-dimensional axisymmetric equilibrium model [Caudal, 1986]. Observed local properties (e.g., specific entropy and estimates of flux tube mass and entropy content) are compared with modeled equilibrium conditions such that departures from equilibrium can be correlated with radial flows and local magnetic field structure. Finally, observations of specific entropy indicate that plasma is non-adiabatic heated during transport. However, the values of specific entropy are well organized in inner magnetosphere (i.e. L<10), and become widely scattered in the middle magnetosphere, suggesting that the transport dynamics of the inner and middle magnetosphere are different.

  10. Space Weather Forecasts Driven by the ADAPT Model

    Science.gov (United States)

    Henney, C. J.; Arge, C. N.; Shurkin, K.; Schooley, A. K.; Hock, R. A.; White, S.

    2015-12-01

    In this presentation, we highlight recent progress to forecast key space weather parameters with the ADAPT (Air Force Data Assimilative Photospheric flux Transport) model. Driven by a magnetic flux transport model, ADAPT evolves global solar magnetic maps forward 1 to 7 days in the future to provide realistic estimates of the solar near-side field distribution used to forecast the solar wind, F10.7 (i.e., the solar 10.7 cm radio flux), extreme ultraviolet (EUV) and far ultraviolet (FUV) irradiance. Input to the ADAPT model includes solar near-side estimates of the inferred photospheric magnetic field from space-based (i.e., HMI) and ground-based (e.g., GONG & VSM) instruments. We summarize the recent findings that: 1) the sum of the absolute value of strong magnetic fields, associated with sunspots, is shown to correlate well with the observed daily F10.7 variability (Henney et al. 2012); and 2) the sum of the absolute value of weak magnetic fields, associated with plage regions, is shown to correlate well with EUV and FUV irradiance variability (Henney et al. 2015). In addition, recent progress to utilize the ADAPT global maps as input to the Wang-Sheeley-Arge (WSA) coronal and solar wind model is presented. We also discuss the challenges of observing less than half of the solar surface at any given time and the need for future magnetograph instruments near L1 and L5.

  11. Probing Magnetic Fields of Early Galaxies

    Science.gov (United States)

    Kohler, Susanna

    2017-06-01

    How do magnetic fields form and evolve in early galaxies? A new study has provided some clever observations to help us answer this question.The Puzzle of Growing FieldsDynamo theory is the primary model describing how magnetic fields develop in galaxies. In this picture, magnetic fields start out as weak seed fields that are small and unordered. These fields then become ordered and amplified by large-scale rotation and turbulence in galaxy disks and halos, eventually leading to the magnetic fields we observe in galaxies today.Schematic showinghow to indirectly measure protogalactic magnetic fields. The measured polarization of a background quasar is altered by the fields in a foreground protogalaxy. Click for a closer look! [Farnes et al. 2017/Adolf Schaller/STSCI/NRAO/AUI/NSF]To test this model, we need observations of the magnetic fields in young protogalaxies. Unfortunately, we dont have the sensitivity to be able to measure these fields directly but a team of scientists led by Jamie Farnes (Radboud University in the Netherlands) have come up with a creative alternative.The key is to find early protogalaxies that absorb the light of more distant background objects. If a protogalaxy lies between us and a distant quasar, then magnetic fields of the protogalaxy if present will affect the polarization measurements of the background quasar.Observing Galactic Building BlocksTop: Redshift distribution for the background quasars in the authors sample. Bottom: Redshift distribution for the foreground protogalaxies the authors are exploring. [Farnes et al. 2017]Farnes and collaborators examined two types of foreground protogalaxies: Damped Lyman-Alpha Absorbers (DLAs) and Lyman Limit Systems (LLSs). They obtained polarimetric data for a sample of 114 distant quasars with nothing in the foreground (the control sample), 19 quasars with DLAs in the foreground, and 27 quasars with LLSs in the foreground. They then used statistical analysis techniques to draw conclusions about

  12. The Oscillatory Nature of Rotating Convection in Liquid Metal

    Science.gov (United States)

    Aurnou, J. M.; Bertin, V. L.; Grannan, A. M.

    2016-12-01

    Earth's magnetic field is assumed to be generated by fluid motions in its liquid metal core. In this fluid, the heat diffuses significantly more than momentum and thus, the ratio of these two diffusivities, the Prandtl number Pr=ν/Κ, is well below unity. The convective flow dynamics of liquid metal is very different from Pr ≈ 1 fluids like water and those used in current dynamo simulations. In order to characterize rapidly rotating thermal convection in low Pr number fluids, we have performed laboratory experiments in a cylinder using liquid gallium (Pr ≈ 0.023) as the working fluid. The Ekman number, which characterizes the effect of rotation, varies from E = 4 10-5 to 4 10-6 and the dimensionless buoyancy forcing (Rayleigh number, Ra) varies from Ra =3 105 to 2 107. Using heat transfer measurements (Nusselt number, Nu) as well as temperature measurements within the fluid, we characterize the different styles of low Pr rotating convective flow. The convection threshold is first overcome in the form of a container scale inertial oscillatory mode. At stronger forcing, wall-localized modes are identified for the first time in liquid metal laboratory experiments. These wall modes coexist with the bulk inertial oscillatory modes. When the strengh of the buoyancy increases, the bulk flow becomes turbulent while the wall modes remain. Our results imply that rotating convective flows in liquid metals do not develop in the form of quasi-steady columns, as in Pr ≈ 1 dynamo models, but in the form of oscillatory motions. Therefore, the flows that drive thermally-driven dynamo action in low Pr geophysical and astrophysical fluids can differ substantively than those occuring in current-day Pr ≈ 1 numerical models. In addition, our results suggest that relatively low wavenumber, wall-attached modes may be dynamically important in rapidly-rotating convection in liquid metals.

  13. Pathway and conversion of energy incident on auroral and sub-auroral ionosphere at substorm expansion onset

    Science.gov (United States)

    Ebihara, Y.; Tanaka, T.

    2017-12-01

    One explanation for SAPS/SAID is the poleward ionospheric electric field arising from a pair of Region 1 and Region 2 field-aligned currents (FACs). At substorm expansion onset, the FACs are intensified, resulting in intensification of energy incident on the auroral and sub-auroral ionosphere. Where does the energy comes from? Based on the results obtained by the global magnetohydrodynamics (MHD) simulation, we present energy flow and energy conversion associated with the Region 1 and Region 2 FACs that are intensified at the onset of substorm expansion. The cusp/mantle region transmits electromagnetic energy to almost the entire region of the magnetosphere. A part of electromagnetic energy is stored in the lobe in the growth phase. When reconnection takes place in the near-Earth tail region, the stored energy is released in addition to the continuously supplied one from the cusp/mantle dynamo. Two types of pathways of energy seem to be involved in the generation of the near-Earth dynamo that is associated with FACs at the expansion onset. The first type is related to the earthward fast flow in the plasma sheet. The electromagnetic energy coming from the lobe splits into the thermal energy and the kinetic energy. The kinetic energy is then converted to the thermal energy and the electromagnetic energy, in association of flow braking. The second type is that the plasma coming from the lobe goes into the inner magnetosphere directly. The electromagnetic energy is converted to the thermal energy, followed by the electromagnetic energy at off-equator. The near-Earth dynamo region seems to be embedded in the magnetospheric convection system. In this sense, the expansion onset may be regarded as a sudden, local intensification of the convection.

  14. Long-lived magnetism on chondrite parent bodies

    Science.gov (United States)

    Shah, Jay; Bates, Helena C.; Muxworthy, Adrian R.; Hezel, Dominik C.; Russell, Sara S.; Genge, Matthew J.

    2017-10-01

    We present evidence for both early- and late-stage magnetic activity on the CV and L/LL parent bodies respectively from chondrules in Vigarano and Bjurböle. Using micro-CT scans to re-orientate chondrules to their in-situ positions, we present a new micron-scale protocol for the paleomagnetic conglomerate test. The paleomagnetic conglomerate test determines at 95% confidence, whether clasts within a conglomerate were magnetized before or after agglomeration, i.e., for a chondritic meteorite whether the chondrules carry a pre- or post-accretionary remanent magnetization. We found both meteorites passed the conglomerate test, i.e., the chondrules had randomly orientated magnetizations. Vigarano's heterogeneous magnetization is likely of shock origin, due to the 10 to 20 GPa impacts that brecciated its precursor material on the parent body and transported it to re-accrete as the Vigarano breccia. The magnetization was likely acquired during the break-up of the original body, indicating a CV parent body dynamo was active ∼9 Ma after Solar System formation. Bjurböle's magnetization is due to tetrataenite, which transformed from taenite as the parent body cooled to below 320 °C, when an ambient magnetic field imparted a remanence. We argue either the high intrinsic anisotropy of tetrataenite or brecciation on the parent body manifests as a randomly orientated distribution, and a L/LL parent body dynamo must have been active at least 80 to 140 Ma after peak metamorphism. Primitive chondrites did not originate from entirely primitive, never molten and/or differentiated parent bodies. Primitive chondrite parent bodies consisted of a differentiated interior sustaining a long-lived magnetic dynamo, encrusted by a layer of incrementally accreted primitive meteoritic material. The different ages of carbonaceous and ordinary chondrite parent bodies might indicate a general difference between carbonaceous and ordinary chondrite parent bodies, and/or formation location in the

  15. Measurement of magnetic turbulence structure and nonlinear mode coupling of tearing fluctuations in the Madison Symmetric Torus reversed field pinch edge

    International Nuclear Information System (INIS)

    Assadi, S.

    1994-01-01

    Linear and nonlinear magnetohydrodynamic (MHD) stability of current-driven modes are studied in the MST reversed field pinch. Measured low frequency (f < 35 kHz) magnetic fluctuations are consistent with the global resistive tearing instabilities predicted by 3-D MHD simulations. At frequencies above 35 kHz, the magnetic fluctuations were detected to be localized and externally resonant. Discrete dynamo events, ''sawtooth oscillations,'' have been observed in the experimental RFP plasmas. This phenomenon causes the plasma to become unstable to m = 1 tearing modes. The modes that may be important in different phases of these oscillations are identified. These results then assist in nonlinear studies and also help to interpret the spectral broadening of the measured data during a discrete dynamo event. Three-wave nonlinear coupling of spectral Fourier modes is measured in the MST by applying bispectral analysis to magnetic fluctuations measured at the plasma edge at 64 toroidal locations and 16 poloidal locations, permitting observation of coupling over 8 poloidal and 32 toroidal modes. Comparison to bispectra predicted by resistive MHD computation indicates reasonably good agreement. However, during the crash phase of the sawtooth oscillation the nonlinear coupling is strongly enhanced, concomitant with a broadened k-spectrum. During the sawtooth formation the plasma is undergoing a pure diffusive process. The dynamo only occurs during the sawtooth crash. High frequency activity prior to a sawtooth crash is caused by nonlinear frequency (small-scale) mode coupling. Growth rate and coupling coefficients of toroidal mode spectra are calculated by statistical modeling. Temporal evolution of edge toroidal mode spectra has been predicted by transfer function analysis. The driving sources of electrostatic fields are different than for the magnetic fields. The characteristics of tearing modes can be altered by external field errors and addition of impurities to the plasma

  16. Why does substorm-associated auroral surge travel westward?

    Science.gov (United States)

    Ebihara, Y.; Tanaka, T.

    2018-01-01

    A substorm is a long-standing unsolved issue in solar-terrestrial physics. One of the big challenges is to explain reasonably the evolution of the morphological structure of the aurora associated with the substorm. The sudden appearance of a bright aurora and an auroral surge traveling westward (westward traveling surge, WTS) are noticeable features of the aurora during the substorm expansion phase. By using a global magnetohydrodynamics (MHD) simulation, we obtained the following results regarding the WTS. When the interplanetary magnetic field turns southward, a persistent dynamo appears in the cusp/mantle region, driving the two-cell magnetospheric convection. Then, the substorm growth phase begins. When magnetic reconnection takes place in the magnetotail, plasma is accelerated earthward in the plasma sheet, and accelerated toward the equatorial plane in the lobe. The second dynamo appears in the near-Earth region, which is closely associated with the generation of the field-aligned current (FAC) on the nightside. When the FAC reaches the ionosphere, the aurora becomes bright, and the onset of the expansion phase begins. In the ionosphere, the conductivity is intensified in the bright aurora due to the precipitation of accelerated electrons. The conductivity gradient gives rise to the overflow of the Hall current, which acts as the third dynamo. The overflow results in the accumulation of space charge, which causes a divergent electric field. The divergent electric field generates a thin, structured upward FAC adjacent to the bright aurora. The opposite process takes place on the opposite side of the bright aurora. In short, the upward FAC increases (appearance of aurora) at the leading edge of the surge, and decreases (disappearance of aurora) at the trailing edge of the surge. By repeating these processes, the surge seems to travel westward.

  17. Magnetic field evolution in dwarf and Magellanic-type galaxies

    Science.gov (United States)

    Siejkowski, H.; Soida, M.; Chyży, K. T.

    2018-03-01

    Aims: Low-mass galaxies radio observations show in many cases surprisingly high levels of magnetic field. The mass and kinematics of such objects do not favour the development of effective large-scale dynamo action. We attempted to check if the cosmic-ray-driven dynamo can be responsible for measured magnetization in this class of poorly investigated objects. We investigated how starburst events on the whole, as well as when part of the galactic disk, influence the magnetic field evolution. Methods: We created a model of a dwarf/Magellanic-type galaxy described by gravitational potential constituted from two components: the stars and the dark-matter halo. The model is evolved by solving a three-dimensional (3D) magnetohydrodynamic equation with an additional cosmic-ray component, which is approximated as a fluid. The turbulence is generated in the system via supernova explosions manifested by the injection of cosmic-rays. Results: The cosmic-ray-driven dynamo works efficiently enough to amplify the magnetic field even in low-mass dwarf/Magellanic-type galaxies. The e-folding times of magnetic energy growth are 0.50 and 0.25 Gyr for the slow (50 km s-1) and fast (100 km s-1) rotators, respectively. The amplification is being suppressed as the system reaches the equipartition level between kinetic, magnetic, and cosmic-ray energies. An episode of star formation burst amplifies the magnetic field but only for a short time while increased star formation activity holds. We find that a substantial amount of gas is expelled from the galactic disk, and that the starburst events increase the efficiency of this process.

  18. Origin and Evolution of Magnetic Field in PMS Stars: Influence of Rotation and Structural Changes

    International Nuclear Information System (INIS)

    Emeriau-Viard, Constance; Brun, Allan Sacha

    2017-01-01

    During stellar evolution, especially in the pre-main-sequence phase, stellar structure and rotation evolve significantly, causing major changes in the dynamics and global flows of the star. We wish to assess the consequences of these changes on stellar dynamo, internal magnetic field topology, and activity level. To do so, we have performed a series of 3D HD and MHD simulations with the ASH code. We choose five different models characterized by the radius of their radiative zone following an evolutionary track computed by a 1D stellar evolution code. These models characterized stellar evolution from 1 to 50 Myr. By introducing a seed magnetic field in the fully convective model and spreading its evolved state through all four remaining cases, we observe systematic variations in the dynamical properties and magnetic field amplitude and topology of the models. The five MHD simulations develop a strong dynamo field that can reach an equipartition state between the kinetic and magnetic energies and even superequipartition levels in the faster-rotating cases. We find that the magnetic field amplitude increases as it evolves toward the zero-age main sequence. Moreover, the magnetic field topology becomes more complex, with a decreasing axisymmetric component and a nonaxisymmetric one becoming predominant. The dipolar components decrease as the rotation rate and the size of the radiative core increase. The magnetic fields possess a mixed poloidal-toroidal topology with no obvious dominant component. Moreover, the relaxation of the vestige dynamo magnetic field within the radiative core is found to satisfy MHD stability criteria. Hence, it does not experience a global reconfiguration but slowly relaxes by retaining its mixed stable poloidal-toroidal topology.

  19. Origin and Evolution of Magnetic Field in PMS Stars: Influence of Rotation and Structural Changes

    Energy Technology Data Exchange (ETDEWEB)

    Emeriau-Viard, Constance; Brun, Allan Sacha, E-mail: constance.emeriau@cea.fr, E-mail: sacha.brun@cea.fr [Laboratoire AIM Paris-Saclay CEA/DSM—CNRS—Université Paris Diderot, IRFU/DAp CEA Paris-Saclay, F-91191 Gif-sur-Yvette Cedex (France)

    2017-09-01

    During stellar evolution, especially in the pre-main-sequence phase, stellar structure and rotation evolve significantly, causing major changes in the dynamics and global flows of the star. We wish to assess the consequences of these changes on stellar dynamo, internal magnetic field topology, and activity level. To do so, we have performed a series of 3D HD and MHD simulations with the ASH code. We choose five different models characterized by the radius of their radiative zone following an evolutionary track computed by a 1D stellar evolution code. These models characterized stellar evolution from 1 to 50 Myr. By introducing a seed magnetic field in the fully convective model and spreading its evolved state through all four remaining cases, we observe systematic variations in the dynamical properties and magnetic field amplitude and topology of the models. The five MHD simulations develop a strong dynamo field that can reach an equipartition state between the kinetic and magnetic energies and even superequipartition levels in the faster-rotating cases. We find that the magnetic field amplitude increases as it evolves toward the zero-age main sequence. Moreover, the magnetic field topology becomes more complex, with a decreasing axisymmetric component and a nonaxisymmetric one becoming predominant. The dipolar components decrease as the rotation rate and the size of the radiative core increase. The magnetic fields possess a mixed poloidal-toroidal topology with no obvious dominant component. Moreover, the relaxation of the vestige dynamo magnetic field within the radiative core is found to satisfy MHD stability criteria. Hence, it does not experience a global reconfiguration but slowly relaxes by retaining its mixed stable poloidal-toroidal topology.

  20. Magnetic properties of Proxima Centauri b analogues

    Science.gov (United States)

    Zuluaga, Jorge I.; Bustamante, Sebastian

    2018-03-01

    The discovery of a planet around the closest star to our Sun, Proxima Centauri, represents a quantum leap in the testability of exoplanetary models. Unlike any other discovered exoplanet, models of Proxima b could be contrasted against near future telescopic observations and far future in-situ measurements. In this paper we aim at predicting the planetary radius and the magnetic properties (dynamo lifetime and magnetic dipole moment) of Proxima b analogues (solid planets with masses of ∼ 1 - 3M⊕ , rotation periods of several days and habitable conditions). For this purpose we build a grid of planetary models with a wide range of compositions and masses. For each point in the grid we run the planetary evolution model developed in Zuluaga et al. (2013). Our model assumes small orbital eccentricity, negligible tidal heating and earth-like radiogenic mantle elements abundances. We devise a statistical methodology to estimate the posterior distribution of the desired planetary properties assuming simple lprior distributions for the orbital inclination and bulk composition. Our model predicts that Proxima b would have a mass 1.3 ≤Mp ≤ 2.3M⊕ and a radius Rp =1.4-0.2+0.3R⊕ . In our simulations, most Proxima b analogues develop intrinsic dynamos that last for ≥4 Gyr (the estimated age of the host star). If alive, the dynamo of Proxima b have a dipole moment ℳdip >0.32÷2.9×2.3ℳdip , ⊕ . These results are not restricted to Proxima b but they also apply to earth-like planets having similar observed properties.

  1. Using SpF to Achieve Petascale for Legacy Pseudospectral Applications

    Science.gov (United States)

    Clune, Thomas L.; Jiang, Weiyuan

    2014-01-01

    Pseudospectral (PS) methods possess a number of characteristics (e.g., efficiency, accuracy, natural boundary conditions) that are extremely desirable for dynamo models. Unfortunately, dynamo models based upon PS methods face a number of daunting challenges, which include exposing additional parallelism, leveraging hardware accelerators, exploiting hybrid parallelism, and improving the scalability of global memory transposes. Although these issues are a concern for most models, solutions for PS methods tend to require far more pervasive changes to underlying data and control structures. Further, improvements in performance in one model are difficult to transfer to other models, resulting in significant duplication of effort across the research community. We have developed an extensible software framework for pseudospectral methods called SpF that is intended to enable extreme scalability and optimal performance. Highlevel abstractions provided by SpF unburden applications of the responsibility of managing domain decomposition and load balance while reducing the changes in code required to adapt to new computing architectures. The key design concept in SpF is that each phase of the numerical calculation is partitioned into disjoint numerical kernels that can be performed entirely inprocessor. The granularity of domain decomposition provided by SpF is only constrained by the datalocality requirements of these kernels. SpF builds on top of optimized vendor libraries for common numerical operations such as transforms, matrix solvers, etc., but can also be configured to use open source alternatives for portability. SpF includes several alternative schemes for global data redistribution and is expected to serve as an ideal testbed for further research into optimal approaches for different network architectures. In this presentation, we will describe our experience in porting legacy pseudospectral models, MoSST and DYNAMO, to use SpF as well as present preliminary

  2. Spheromak Physics Development

    International Nuclear Information System (INIS)

    Hooper, E.B.

    1997-01-01

    The spheromak is a Magnetic Fusion Energy (MFE) configuration, which is a leading alternative to the tokamak. It has a simple geometry which offers an opportunity to achieve the promise of fusion energy if the physics of confinement, current drive, and pressure holding capability extrapolate favorably to a reactor. Recent changes in the US MFE program, taken in response to budget constraints and programmatic directions from Congress, include a revitalization of an experimental alternative concept effort. Detailed studies of the spheromak were consequently undertaken to examine the major physics issues which need to be resolved to advance it as a fusion plasma, the optimum configuration for an advanced experiment, and its potential as a reactor. As a result of this study, we conclude that it is important to evaluate several physics issues experimentally. Such an experiment might be appropriately be named the Sustained Spheromak Physics Experiment (SSPX). It would address several critical issues, the solution to which will provide the physics basis to enable an advanced experiment. The specific scientific goals of SSPX would be to: * Demonstrate that electron and ion temperatures of a few hundred electron volts can be achieved in a steady-state spheromak plasma sustained by a magnetic dynamo (''helicity injection''). * Relate energy confinement quantitatively to the magnetic turbulence accompanying the dynamo and use this knowledge to optimize performance. * Measure the magnetic field profiles and magnetic turbulence in the plasma and relate these to the science of the magnetic dynamo which drives the current in the plasma. * Examine experimentally the pressure holding capability (''beta limit'') of the spheromak. * Understand the initial phases of the transition of the plasma from an equilibrium supported by a magnetic-flux conserving wall to one supported by external coils

  3. Mercury's global evolution: New views from MESSENGER

    Science.gov (United States)

    Hauck, S. A., II; Byrne, P. K.; Denevi, B. W.; Grott, M.; McCoy, T.; Stanley, S.

    2015-12-01

    MESSENGER's exploration of Mercury has revealed the planet's rich and dynamic history and provided new constraints on the processes that control its internal evolution. Mercury's surface records evidence of an extensive geological history. This evidence includes resurfacing by impacts and volcanism prior to the end of the late heavy bombardment (LHB) and a subsequent rapid waning of effusive volcanism. Volcanism is an important indicator of the history of melt production. Thousands of globally distributed, contractional tectonic landforms collectively have accommodated a decrease in Mercury's radius of 5-7 km since the end of the LHB. Such contraction results from planetary cooling and crystallization within Mercury's metallic core. Measurements of surface chemistry have provided constraints on internal radiogenic heat production necessary to understand more fully Mercury's thermal evolution. Elemental abundances also reveal that Mercury is strongly chemically reduced, suggesting that the core's iron is alloyed with silicon as well as sulfur, which constrains the dynamics and crystallization of the metallic core. Magnetometer observations show that Mercury's dynamo-generated, dominantly dipolar field is displaced ~500 km northward along the rotation axis. Low-altitude magnetic field observations late in the mission led to the discovery of crustal magnetization in Mercury's ancient crust, dating to at least 3.7 Ga, which places a new constraint on the timing of the dynamo. Monte Carlo parameterized mantle convection models, constrained by these observations, indicate that for global contraction of 7 km or less, mantle convection persists to the present ~40% of the time, with the likelihood of modern convection decreasing with less global contraction. Slow present cooling in these models indicates that dynamo generation is strongly influenced by both a static layer at the top of the core and convective motions within the core driven by compositional buoyancy.

  4. Planetary Geophysics and Tectonics

    Science.gov (United States)

    Zuber, Maria

    2005-01-01

    The broad objective of this work is to improve understanding of the internal structures and thermal and stress histories of the solid planets by combining results from analytical and computational modeling, and geophysical data analysis of gravity, topography and tectonic surface structures. During the past year we performed two quite independent studies in the attempt to explain the Mariner 10 magnetic observations of Mercury. In the first we revisited the possibility of crustal remanence by studying the conditions under which one could break symmetry inherent in Runcorn's model of a uniformly magnetized shell to produce a remanent signal with a dipolar form. In the second we applied a thin shell dynamo model to evaluate the range of intensity/structure for which such a planetary configuration can produce a dipole field consistent with Mariner 10 results. In the next full proposal cycle we will: (1) develop numerical and analytical and models of thin shell dynamos to address the possible nature of Mercury s present-day magnetic field and the demise of Mars magnetic field; (2) study the effect of degree-1 mantle convection on a core dynamo as relevant to the early magnetic field of Mars; (3) develop models of how the deep mantles of terrestrial planets are perturbed by large impacts and address the consequences for mantle evolution; (4) study the structure, compensation, state of stress, and viscous relaxation of lunar basins, and address implications for the Moon s state of stress and thermal history by modeling and gravity/topography analysis; and (5) use a three-dimensional viscous relaxation model for a planet with generalized vertical viscosity distribution to study the degree-two components of the Moon's topography and gravity fields to constrain the primordial stress state and spatial heterogeneity of the crust and mantle.

  5. The Efficiency of Magnetic Field Amplification at Shocks by Turbulence

    Science.gov (United States)

    Ji, Suoqing; Oh, S. Peng; Ruszkowsi, M.; Markevitch, M.

    2016-01-01

    Turbulent dynamo field amplification has often been invoked to explain the strong field strengths in thin rims in supernova shocks (approx.100 micrograms) and in radio relics in galaxy clusters (approx. micrograms). We present high-resolution magnetohydrodynamic simulations of the interaction between pre-shock turbulence, clumping and shocks, to quantify the conditions under which turbulent dynamo amplification can be significant. We demonstrate numerically converged field amplification which scales with Alfven Mach number, B/B0 varies as MA, up to MA approx.150.This implies that the post-shock field strength is relatively independent of the seed field. Amplification is dominated by compression at low MA, and stretching (turbulent amplification) at high MA. For high MA, the B-field grows exponentially and saturates at equipartition with turbulence, while the vorticity jumps sharply at the shock and subsequently decays; the resulting field is orientated predominately along the shock normal (an effect only apparent in 3D and not 2D). This agrees with the radial field bias seen in supernova remnants. By contrast, for low MA, field amplification is mostly compressional, relatively modest, and results in a predominantly perpendicular field. The latter is consistent with the polarization seen in radio relics. Our results are relatively robust to the assumed level of gas clumping. Our results imply that the turbulent dynamo may be important for supernovae, but is only consistent with the field strength, and not geometry, for cluster radio relics. For the latter, this implies strong pre-existing B-fields in the ambient cluster outskirts.

  6. Comment on Lockwood and Davis, "On the longitudinal extent of magnetopause reconnection pulses"

    Directory of Open Access Journals (Sweden)

    W. J. Heikkila

    1999-02-01

    Full Text Available Lockwood and Davis (1996 present a concise description of magnetopause reconnection pulses, with the claimed support of three types of observations: (1 flux transfer events (FTE, (2 poleward-moving auroral forms on the dayside, and (3 steps in cusp ion dispersion characteristics. However, there are a number of errors and misconceptions in the paper that make their conclusions untenable. They do not properly take account of the fact that the relevant processes operate in the presence of a plasma. They fail to notice that the source of energy (a dynamo with E · J<0 must be close to the region of dissipation (the electrical load with E · J>0 in transient phenomena, since energy (or information cannot travel faster than the group velocity of waves in the medium (here the Alfvén velocity VA. In short, Lockwood and Davis use the wrong contour in their attempt to evaluate the electromotive force (emf. This criticism goes beyond their article: a dynamo is not included in the usual definition of reconnection, only the reconnection load. Without an explicit source of energy in the assumed model, the idea of magnetic reconnection is improperly posed. Recent research has carried out a superposed epoch analysis of conditions near the dayside magnetopause and has found the dynamo and the load, both within the magnetopause current sheet. Since the magnetopause current is from dawn to dusk, the sign of E · J reflects the sign of the electric field. The electric field reverses, within the magnetopause; this can be discovered by an application of Lenz's law using the concept of erosion of the magnetopause. The net result is plasma transfer across the magnetopause to feed the low latitude boundary layer, at least partly on closed field lines, and viscous interaction as the mechanism by which solar wind plasma couples to the magnetosphere.

  7. Presenting the science of the Sun to the general public

    Science.gov (United States)

    Choudhuri, Arnab Rai

    2016-07-01

    Although the science behind the Sun is so fascinating, there has not been sufficient worldwide effort in presenting this science to the general public. My recently published popular science book "Nature's Third Cycle: A Story of Sunspots" (Oxford University Press, 2015) is probably the first popular science book introducing the phenomenology of the solar cycle along with a non-technical account of dynamo theory. I shall discuss my perspective of the challenges involved in presenting the science of the Sun to the public. The Amazon link of my book is: http://www.amazon.co.uk/Natures-Third-Cycle-Story-Sunspots/dp/0199674752/

  8. The Effect of Rotating a Faraday Disc Perpendicular to an Applied Magnetic Field Theory and Experiment

    Science.gov (United States)

    Mazuruk, Konstantin; Grugel, Richard N.

    2003-01-01

    A magnetohydrodynamic model that examines the effect of rotating an electrically conducting cylinder with a uniform external magnetic field applied orthogonal to its axis is presented. Noting a simple geometry, it can be classified as a fundamental dynamo problem. For the case of an infinitely long cylinder, an analytical solution is obtained and analyzed in detail. A semi-analytical model was developed that considers a finite cylinder. Experimental data from a spinning brass wheel in the presence of Earth's magnetic field were compared to the proposed theory and found to fit well.

  9. Suppression of turbulent resistivity in turbulent Couette flow

    International Nuclear Information System (INIS)

    Si, Jiahe; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe; Colgate, Stirling A.; Li, Hui; Nornberg, Mark D.

    2015-01-01

    Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations

  10. X-ray emission regimes and rotation sequences in M 35 . An updated model of stellar activity evolution on the main sequence

    Science.gov (United States)

    Gondoin, P.

    2013-08-01

    Context. Late-type stars in young open clusters show two kinds of dependence of their X-ray emission on rotation. They also tend to group into two main sub-populations that lie on narrow sequences in diagrams where their rotation periods are plotted against their (B - V) colour indices. A correlation between these two regimes of X-ray emission and the rotation sequences has been recently observed in the M 34 open cluster. Sun-like M 34 stars also show a drop of their X-ray to bolometric luminosity ratio by about one order of magnitude at a Rossby number of about 0.3. Aims: The present study looks for similar connections between X-ray activity and rotation in an other open cluster. The aim is to consolidate a model of X-ray activity evolution on the main sequence and to provide observational constraints on dynamo processes in the interiors of late-type stars. Methods: The paper compares XMM-Newton measurements of X-ray stellar emission in M 35 with X-ray luminosity distributions derived from rotation period measurements assuming either an X-ray regime transition at a critical Rossby number or a correlation between X-ray emission regimes and rotation sequences. Results: This second hypothesis could account for the low number of M 35 stars detected in X-rays. A model of X-ray activity evolution is proposed based on the correlation. One major output is that the transition from saturated to non-saturated X-ray emission occurs at Rossby numbers between about 0.13 and 0.4 for each star depending on its mass and initial period of rotation on the ZAMS. This prediction agrees with observations of stellar X-ray emission in M 34. It explains the large range of X-ray luminosities observed among Sun-like stars in young open clusters. Conclusions: I conclude that the correlation between X-ray emission regimes and rotation sequences could be a fundamental property of the early evolution of stellar magnetic activity on the main sequence. I argue that the angular momentum

  11. Tiny Stars, Strong Fields: Exploring the Origin of Intense Magnetism in M Stars

    Science.gov (United States)

    Toomre, Juri

    The M-type stars are becoming dominant targets in searches for Earth-like planets that could occupy their habitable zones. The low masses and luminosities of M-dwarf central stars make them very attractive for such exoplanetary hunts. The habitable zone of M dwarfs is close to the star due to their low luminosity. Thus possibly habitable planets will have short orbital periods, making their detection feasible both with the transit method (used by Kepler, K2 and soon with TESS) and with the radial velocity approaches. Yet habitability on a planet likely requires both solid surfaces and atmospheres, but also a favorable radiation environment. It is here that the M-dwarf central stars raise major theoretical puzzles, for many of them exhibit remarkably intense and frequent flaring, despite their modest intrinsic luminosities. The super-flares release their energy both in white light and in X-rays, and can be thousands of times brighter than the strongest solar flares. Such striking events must have magnetic origins, likely from fields built by convective dynamos operating in their interiors. Further, recent observations suggest that the surface of some M stars is carpeted with magnetic fields of 3 kG or more. Such field strengths are reminiscent of a sunspot, but here instead cover much of the stellar surface. With M stars now taking center stage in the search for Earthlike planets, it is crucial to begin to understand how convective dynamos may be able to build intense magnetic fields involved with super-flares and vast star spots, and how they depend upon the mass and rotation rate of these stars. We propose to use major 3-D MHD simulations with our Anelastic Spherical Harmonic (ASH) code to study the coupling of turbulent convection, rotation, and magnetism within full spherical domains such as the interior of an M dwarf. This permits the exploration of the magnetic dynamos that must be responsible for the evolving magnetism and intense activity of many M dwarfs

  12. Magnetic field interpretation for the outburst of CH Cygni

    International Nuclear Information System (INIS)

    Wdowiak, T.J.

    1977-01-01

    The possible appearance of kilogauss magnetic structure in and above the photosphere of a red giant during helium-shell flash is examined as a mechanism for the outburst of the apparently single star, CH Cyg. Strong magnetic fields created by dynamo action in a temporary connection zone of a red giant core, by virtue of their intrinsic buoyancy, would rise quickly to the stellar surface. It is suggested that if the field is coupled with the large-scale convective structure of the envelope, the energy contained and rate of release would be sufficient to produce the emission features of the spectrum of CH Cyg

  13. Iron snow in the Martian Core?

    Science.gov (United States)

    Davies, C. J.; Pommier, A.

    2017-12-01

    The decline of Mars' global magnetic field some 3.8-4.1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core. The termination of the dynamo is intimately tied to the thermochemical evolution of the core-mantle system and therefore to the present-day physical state of the Martian core. The standard model predicts that the Martian dynamo failed because thermal convection stopped and the core remained entirely liquid until the present. Here we consider an alternative hypothesis that the Martian core crystallized from the top down in the so-called iron snow regime. We derive energy-entropy equations describing the long-timescale thermal and magnetic evolution of the core that incorporate the self-consistent formation of a snow layer that freezes out pure iron and is assumed to be on the liquidus; the iron sinks and remelts in the deeper core, acting as a possible source for magnetic field generation. Compositions are in the FeS system, with a sulfur content up to 16 wt%. The values of the different parameters (core radius, density and CMB pressure) are varied within bounds set by recent internal structure models that satisfy existing geodetic constraints (planetary mass, moment of inertia and tidal Love number). The melting curve and adiabat, CMB heat flow and thermal conductivity were also varied, based on previous experimental and numerical works. We observe that the formation of snow zones occurs for a wide range of interior and thermal structure properties and depends critically on the initial sulfur concentration. Gravitational energy release and latent heat effects arising during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies a significant fraction of the core. Our results suggest that snow zones can be 1.5-2 Gyrs old, though thermal stratification of the uppermost core, not included in our model, likely delays onset. Models that match the available

  14. AGARD (Advisory Group for Aerospace Research & Development) Index of Publications, 1986-1988

    Science.gov (United States)

    1989-08-01

    mmate nrmsOorn~esdsgn methods app~cabf. 81 coco Moderer ateortaeet w-. pWIapre through t a etues, i n hede- lidruetor of changes9 tn tl stage c 22 N89...N489- 18026 and aesnansrocrsp5P.0r63 fax", spacecratt p095 N87-20357 lotorero Control aN -5-k orerr sgreonry25N8 143 Dynamo modelrng an? deferral coco ...01.0114890 lech ~dstyn the* analysis RESEARCH AIRCRAFT Tasole. Wi 111100 in distributedt 10001101f0embedded . 1 highly loablis gui/aoce 804 -.. 00 -werfl

  15. PCAST warns against slashing Federal science budget

    Science.gov (United States)

    Carlowicz, Michael

    With the congressional cost-cutting dynamo rolling through the 1996 budget process, a group of academic and industry science advisors has assumed the role of traffic cop, cautioning legislators on both sides of the aisle to [slow down!] Invoking economic productivity, the quality of American life, and national security, the 19 members of the President's Committee of Advisors on Science and Technology (PCAST) have warned both political parties that a budget balanced through severe cuts in research funding will cost the country more than it saves.

  16. Design and construction of the small wind generator called “AR-SF-500” for the ore milling to a laborator y scale

    OpenAIRE

    Romero Baylón, Alfonso; UNMSM; Flores Chávez, Silvana; UNMSM; Pacheco, Werner; UNMSM

    2014-01-01

    The small wind generator called “AR-SFWP- 500” has a dynamo that generated a potency of 500 watts, which characterize for having in its internal structure, the called “permanent magnet” for working with small wind generators, such as employing in rural zones, where there is a lack of electric energy. In this sense, the purpose of the paper, treats explaining the process of design and construction of the Small Wind Generator AR-SFWP- 500, whose principle of functioning is based in transform th...

  17. Electron reflectometry as a probe of the Martian crust and atmosphere

    Science.gov (United States)

    Lillis, Robert James

    This thesis is devoted to the expansion of the technique of electron reflectometry from its prior purpose in mapping lunar crustal magnetic fields to the same purpose at Mars, where the presence of a substantial atmosphere considerably complicates matters. Previous work, using magnetometer data from the Mars Global Surveyor (MGS) spacecraft, established the existence of surprisingly strong crustal remanent magnetic fields and placed important constraints both upon the properties of the crustal magnetic sources responsible for the fields and upon the timing and orientation of Mars's ancient core dynamo. To build upon this work, I have analyzed pitch angle distributions of magnetically reflecting solar wind electrons measured by the MGS Magnetometer/ Electron Reflectometer (MAG/ER) to create a map of Martian crustal magnetic fields at ~195 km altitude, giving greater spatial resolution and sensitivity than was previously possible using magnetometer data alone. Low magnetic fields measured above most volcanoes indicate thermal demagnetization of the crust by magmatism and underplating after the cessation of the core dynamo, while relatively high fields measured above the Hadriaca Patera volcano imply that Martian volcanism predates this cessation and is significantly older than any exposed volcanic surface. The geographic and size distribution of demagnetization signatures of impact craters and the suggested presence of magnetic edge effects, indicates that (1) crustal magnetization occurs at typically shallower depths in the northern Martian lowlands than in the southern highlands and (2) the typical crustal magnetic coherence scale, is >100 km. A comparison of crater retention ages with magnetic signatures of some of the oldest impact basins on Mars confirms that Mars's core dynamo ceased operating early in the planet's history, >4 billion years ago. Significant differences in magnetization between geologically contemporary basins suggests that the dynamo's final

  18. Geomagnetic and sunspot activity associations and ionospheric effects of lightning phenomena at Trivandrum near dip equator

    Science.gov (United States)

    Girish, T. E.; Eapen, P. E.

    2008-12-01

    From a study of thunder/lightning observations in Trivandrum (near dip equator) for selected years between 1853 and 2005, we could find an inverse relation of the same with sunspot activity and associations with enhancements in diurnal range of local geomagnetic declination. The results seem to suggest lightning-associated modulation of E-region dynamo currents in the equatorial ionosphere and the thunderstorm activity near dip equator probably acts as a moderator to regulate electric potential gradient changes in the global electric circuit due to solar activity changes.

  19. Investigating stellar surface rotation using observations of starspots

    DEFF Research Database (Denmark)

    Korhonen, Heidi Helena

    2011-01-01

    Rapid rotation enhances the dynamo operating in stars, and thus also introduces significantly stronger magnetic activity than is seen in slower rotators. Many young cool stars still have the rapid, primordial rotation rates induced by the interstellar molecular cloud from which they were formed...... information on the rotation of the star. At times even information on the spot rotation at different stellar latitudes can be obtained, similarly to the solar surface differential rotation measurements using magnetic features as tracers. Here, I will review investigations of stellar rotation based...

  20. The case for a primordial galactic field

    International Nuclear Information System (INIS)

    Kulsrud, R.

    1989-01-01

    Two possible theories of the origin of the galactic magnetic field are discussed. It is shown that the first theory, of its generation by a fast magnetic dynamo, is limited by the properties of the interstellar medium which suppress the small scale motions in the turbulence, and thus inhibit the generation of the field from a small seed field. The second theory that the galactic field is a relic of a general cosmic magnetic field existing prior to formation of our galaxy is discussed. It is pointed out that such a field would evolve to a field very similiar to that which we see today. (author). 4 refs

  1. Self-consistent mean field forces in turbulent plasmas: Current and momentum relaxation

    International Nuclear Information System (INIS)

    Hegna, C.C.

    1997-08-01

    The properties of turbulent plasmas are described using the two-fluid equations. Under some modest assumptions, global constraints for the turbulent mean field forces that act on the ion and electron fluids are derived. These constraints imply a functional form for the parallel mean field forces in the Ohm's law and the momentum balance equation. These forms suggest that the fluctuations attempt to relax the plasma to a state where both the current and the bulk plasma momentum are aligned along the mean magnetic field with proportionality constants that are global constants. Observations of flow profile evolution during discrete dynamo activity in reversed field pinch experiments are interpreted

  2. Spectral modeling of magnetohydrodynamic turbulent flows.

    Science.gov (United States)

    Baerenzung, J; Politano, H; Ponty, Y; Pouquet, A

    2008-08-01

    We present a dynamical spectral model for large-eddy simulation of the incompressible magnetohydrodynamic (MHD) equations based on the eddy damped quasinormal Markovian approximation. This model extends classical spectral large-eddy simulations for the Navier-Stokes equations to incorporate general (non-Kolmogorovian) spectra as well as eddy noise. We derive the model for MHD flows and show that the introduction of an eddy damping time for the dynamics of spectral tensors, in the absence of equipartition between the velocity and magnetic fields, leads to better agreement with direct numerical simulations, an important point for dynamo computations.

  3. Hyper-resistivity produced by tearing mode turbulence

    International Nuclear Information System (INIS)

    Strauss, H.R.

    1986-01-01

    Tearing mode turbulence produces a hyper-resistivity or effective anomalous electron viscosity. The hyper-resistivity is calculated for the mean magnetic field quasilinearly, and for long-wavelength modes using the direct interaction approximation. The hyper-resistivity accounts for current relaxation in reversed-field pinch experiments, and gives a magnetic fluctuation sealing of S -1 /sup // 3 . It causes enhanced tearing mode growth rates in the turbulent phase of tokamak disruptions. In astrophysics, it limits magnetic energy growth due to the dynamo effect, and may explain rapid reconnection phenomena such as solar flares

  4. Relaxing Oscillation of the Machine-Unit

    Directory of Open Access Journals (Sweden)

    Bohumil Skala

    2008-01-01

    Full Text Available To understand the behavior of the Earth´s geomagnetic field, many theories have been created. One of the possible approaches is the Rikitake dynamo and chaotic theory. This paper describes the first step, i.e. how to verify the chaotic theory simulated result by a practical test. This first step is the oscillating machine unit. The asynchronous motor working point is moving from the stable part of its torque characteristic to the labile part due to the enormous loading. In the labile part the speed slows down and loading has to be decreased. Then the motor moves back to the stable part of characteristic.

  5. Automatic carriage for radiographing weldings from the inside of pipelines by means of x-rays and relevant devices

    International Nuclear Information System (INIS)

    Gambini, A.; Capitelli, G.

    1975-01-01

    A tandem radiography vehicle for use in pipelines includes a carriage assembly, having an internal combustion engine and a dynamo-alternator motor for driving the vehicle, and powering an x-ray tube. Electronic circuitry for controlling the operation and power to the x-ray tube are included. A compass control system on the carriage is activated by a magnet externally positioned on the pipeline for positioning the vehicle at a weld inspection area. Means for segregating exhaust from the engine are also disclosed. (U.S.)

  6. IoT Vending: modelo inteligente en la nube para máquinas Vending

    OpenAIRE

    Boces Vela, David

    2015-01-01

    El presente proyecto es un trabajo de estudio e implementación de la suite AWS de Amazon, concretamente de sus servicios AWS Internet of Things, AWS Lambda y AWS DynamoDB. Se ha creado un modelo de negocio en la nube, que toma decisiones en tiempo real en función de la interacción de la máquinas de venta y los clientes. Gracias a este modelo, la empresa propietaria de estas máquinas puede automatizar muchas de las tareas de gestión y mantenimiento de las mismas. En todo momento se tiene...

  7. Magnetic processes in astrophysics theory, simulations, experiments

    CERN Document Server

    Rüdiger, Günther; Hollerbach, Rainer

    2013-01-01

    In this work the authors draw upon their expertise in geophysical and astrophysical MHD to explore the motion of electrically conducting fluids, the so-called dynamo effect, and describe the similarities and differences between different magnetized objects. They also explain why magnetic fields are crucial to the formation of the stars, and discuss promising experiments currently being designed to investigate some of the relevant physics in the laboratory. This interdisciplinary approach will appeal to a wide audience in physics, astrophysics and geophysics. This second edition covers such add

  8. Suppression of turbulent resistivity in turbulent Couette flow

    Science.gov (United States)

    Si, Jiahe; Colgate, Stirling A.; Sonnenfeld, Richard G.; Nornberg, Mark D.; Li, Hui; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe

    2015-07-01

    Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.

  9. Suppression of turbulent resistivity in turbulent Couette flow

    Energy Technology Data Exchange (ETDEWEB)

    Si, Jiahe, E-mail: jsi@nmt.edu; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe [New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 (United States); Colgate, Stirling A.; Li, Hui [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Nornberg, Mark D. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

    2015-07-15

    Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.

  10. Magnetohydrodynamics and the earth's core selected works by Paul Roberts

    CERN Document Server

    Soward, Andrew M

    2003-01-01

    Paul Roberts'' research contributions are remarkable in their diversity, depth and international appeal. Papers from the Paul Roberts'' Anniversary meeting at the University of Exeter are presented in this volume. Topics include geomagnetism and dynamos, fluid mechanics and MHD, superfluidity, mixed phase regions, mean field electrodynamics and the Earth''s inner core. An incisive commentary of the papers puts the work of Paul Roberts into historical context. Magnetohydrodynamics and the Earth''s Core provides a valuable source of reference for graduates and researchers working in this area of geoscience.

  11. Evolution in Cloud Population Statistics of the MJO. From AMIE Field Observations to Global-Cloud Permitting Models final report Version 1

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Min [Univ. of Wyoming, Laramie, WY (United States)

    2016-01-08

    Methods of convective/stratiform precipitation classification and surface rain rate estimation based on the Atmospheric Radiation Measurement (ARM) program cloud radar measurements were developed and evaluated. Simultaneous and collocated observations of the Ka-band ARM zenith radar (KAZR), two scanning precipitation radars (NCAR S-PolKa and Texas A&M University SMART-R), and surface precipitation during the DYNAMO/AMIE field campaign were used. The motivation of this study is to apply the unique long-term ARM cloud radar observations without accompanying precipitation radars to the study of cloud lifecycle and precipitation features under different weather and climate regimes.

  12. A self-consistent theory of radial transport of field-aligned current by microturbulence

    International Nuclear Information System (INIS)

    Terry, P.W.

    1990-02-01

    The radial transport of field-aligned current due to collisionless microturbulence is examined self-consistently. The self-consistent treatment of mode coupling shown to constrain the transport in such a way that the relaxation of current gradients is regulated solely by electrostatic fluctuations which couple to ion dissipation, even in the presence of temperature gradients and temperature anisotropy. As a consequence, the radial flux of parallel current induced by collisionless microinstabilities is insufficient to account for the dynamo in reversed field pinch plasmas. 26 refs

  13. Turbulent dispersion of many particles

    Science.gov (United States)

    Pratt, J.; Busse, A.; Muller, W. C.

    2017-12-01

    We demonstrate the utility of the convex hull to analyze dispersion of groups of many Lagrangian tracer particles in turbulence. We examine dispersion in turbulent flows driven by convection, relevant to geophysical flows and the spread of contaminants in the atmosphere, and in turbulent flows affected by magnetic fields, relevant to stellar winds and stellar interiors. Convex hull analysis can provide new information about local dispersion, in the form of the surface area and volume for a cluster of particles. We use dispersive information to examine the local anisotropy that occurs in these turbulent settings, and to understand fundamental characteristics of heat transfer and the small-scale dynamo.

  14. X-ray emission from open star clusters with Spectrum-Rontgen-Gamma

    DEFF Research Database (Denmark)

    Singh, K.P.; Ojha, D.K.; Schnopper, H.W.

    1998-01-01

    The study of X-ray emission from co-evolving populations of stars in open dusters is extremely important for understanding the dynamo activity among the stars. With this objective, we propose to observe a number of open clusters in the X-ray and UV bands using SPECTRUM-Rontgen-Gamma. The high...... throughput of SPECTRUM-Rontgen-Gamma will help detect main sequence stars like Sun in middle-aged and old clusters. We will study the relationships between various parameters - age, rotation, abundance, UBV colors, X-ray luminosity, coronal temperature etc. X-ray spectra of younger and brighter populations...

  15. Studies on the transformation of fibrinogen to fibrin. Radiation effects. Observation by electron microscopy

    International Nuclear Information System (INIS)

    Marguerie de Rotrou, G.; Hollard, D.; Suscillon, M.; Cuong, M.; Vitry, F. de

    1968-01-01

    The authors used electron microscopy, thrombo-dynamo-graphy and spectrophotometry, to study the damage caused by X rays on the fibrinogen molecule and fibrin-formation process. This process is highly disturbed by increasing doses of irradiation from 0 to 3.10 5 roentgen. Electron microscopy observation shows interesting data on the structure of the plug, formed by irradiated fibrinogen solution. This study also lead the authors to propose a new model of the fibrinogen molecule and a schema explaining observed striations and granular appearance of the fibrin fibers surface. (authors) [fr

  16. The origin of lunar palaeomagnetism

    International Nuclear Information System (INIS)

    Runcorn, S.K.

    1978-01-01

    Using the new determination of magnetic field anomalies over part of the Moon's surface which has recently been interpreted (Hood et al. J. Geophys. Res. Lett.; 5:305 (1978)) in terms of magnetized areas of the lunar surface it is shown in this work that palaeomagnetic pole positions can be calculated and that these are so clustered on the lunar surface that there is evidence against meteoritic or cometary processes as explanations of the remanent magnetization of the Apollo rocks. It is concluded that the Moon had a magnetic field in its early history produced by dynamo processes in a fluid electrically conducting core. (U.K.)

  17. A New Disintegrative Capture Theory for the Origin of the Moon

    OpenAIRE

    Noerdlinger, Peter D.

    2012-01-01

    The object that resulted in the creation of the Moon started in the same orbital path as Earth around the Sun, but at Earth's L4. This proto-Moon (PM) was 4 times less massive than the usual Giant Impact (GI) object "Theia" and was captured into Earth orbit. It had a 32% Iron-Nickel-Sulfur core supporting a dynamo, which explains magnetized lunar rocks. Following capture, it was torn apart by tidal forces and its core of iron plastered itself, with some of its rock mantle, on the surface of E...

  18. Lunar magnetism

    Science.gov (United States)

    Hood, L. L.; Sonett, C. P.; Srnka, L. J.

    1984-01-01

    Aspects of lunar paleomagnetic and electromagnetic sounding results which appear inconsistent with the hypothesis that an ancient core dynamo was the dominant source of the observed crustal magnetism are discussed. Evidence is summarized involving a correlation between observed magnetic anomalies and ejecta blankets from impact events which indicates the possible importance of local mechanisms involving meteoroid impact processes in generating strong magnetic fields at the lunar surface. A reply is given to the latter argument which also presents recent evidence of a lunar iron core.

  19. Energetic particles precipitation from the magnetosphere above the epicenter of approaching earthquake

    International Nuclear Information System (INIS)

    Gal'perin, Yu.I.; Gladyshev, V.A.; Dzhordzhio, N.V.; Larkina, V.I.; Mogilevskij, M.M.

    1992-01-01

    A survey of seismo-magnetospheric effects and a discussion of possible processes leading to the respective particles precipitation enhancements are presented. It is supposed that ELF electromagnetic noises mostly in the 0.1-10 Hz range are exicited by MHD-waves generated in the ionospheric dynamo-region above the epicenter zone under the action of weak but relatively large-scale (tens of km) intra-acoustic waves originating from staggering of geological blocks with periods of order of minutes

  20. Physical properties of the planet Mercury

    Science.gov (United States)

    Clark, Pamela E.

    1988-01-01

    The global physical properties of Mercury are summarized with attention given to its figure and orbital parameters. The combination of properties suggests that Mercury has an extensive iron-rich core, possibly with a still-functioning dynamo, which is 42 percent of the interior by volume. Mercury's three major axes are comparable in size, indicating that the planet is a triaxial ellipsoid rather than an oblate spheroid. In terms of the domination of its surface by an intermediate plains terrane, it is more Venus- or Mars-like; however, due to the presence of a large metallic magnetic core, its interior may be more earth-like.

  1. Magnetic field of Mercury and models of thermal evolution

    International Nuclear Information System (INIS)

    Sharpe, H.N.; Strangway, D.W.

    1976-01-01

    Recent planetary probes have performed in situ measurements of the magnetic fields of all the terrestrial planets. Consideration is given to the origin of these fields, with attention to the equilibrium-- condensation hypothesis for the formation of the solar system. In particular, it is shown that Mercury's present day magnetic field could have been acquired during or shortly after a cold accretion or that it could be due to a presently operating dynamo, resulting from a 'hot evolution'. Two parameters which would help to distinguish between these possibilities are the present-day surface heat flow and the moment of inertia

  2. ARM MJO Investigation Experiment on Gan Island (AMIE-Gan) Science Plan

    Energy Technology Data Exchange (ETDEWEB)

    Long, CL; Del Genio, A; Deng, M; Fu, X; Gustafson, W; Houze, R; Jakob, C; Jensen, M; Johnson, R; Liu, X; Luke, E; May, P; McFarlane, S; Minnis, P; Schumacher, C; Vogelmann, A; Wang, Y; Webster, P; Xie, S; Zhang, C

    2011-04-11

    The overarching campaign, which includes the ARM Mobile Facility 2 (AMF2) deployment in conjunction with the Dynamics of the Madden-Julian Oscillation (DYNAMO) and the Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011) campaigns, is designed to test several current hypotheses regarding the mechanisms responsible for Madden-Julian Oscillation (MJO) initiation and propagation in the Indian Ocean area. The synergy between the proposed AMF2 deployment with DYNAMO/CINDY2011, and the corresponding funded experiment on Manus, combine for an overarching ARM MJO Investigation Experiment (AMIE) with two components: AMF2 on Gan Island in the Indian Ocean (AMIE-Gan), where the MJO initiates and starts its eastward propagation; and the ARM Manus site (AMIE-Manus), which is in the general area where the MJO usually starts to weaken in climate models. AMIE-Gan will provide measurements of particular interest to Atmospheric System Research (ASR) researchers relevant to improving the representation of MJO initiation in climate models. The framework of DYNAMO/CINDY2011 includes two proposed island-based sites and two ship-based locations forming a square pattern with sonde profiles and scanning precipitation and cloud radars at both island and ship sites. These data will be used to produce a Variational Analysis data set coinciding with the one produced for AMIE-Manus. The synergy between AMIE-Manus and AMIE-Gan will allow studies of the initiation, propagation, and evolution of the convective cloud population within the framework of the MJO. As with AMIE-Manus, AMIE-Gan/DYNAMO also includes a significant modeling component geared toward improving the representation of MJO initiation and propagation in climate and forecast models. This campaign involves the deployment of the second, marine-capable, AMF; all of the included measurement systems; and especially the scanning and vertically pointing radars. The campaign will include sonde

  3. Global Plasma Turbulence Simulations of q=3 Sawtoothlike Events in the RTP Tokamak

    Science.gov (United States)

    de Baar, M. R.; Thyagaraja, A.; Hogeweij, G. M.; Knight, P. J.; Min, E.

    2005-01-01

    A two-fluid computer model of electromagnetic tokamak turbulence, CUTIE, is used to study the dynamic structure and turbulent transport in the Rijnhuizen Tokamak Project tokamak. A discharge with dominant, off-axis electron cyclotron heating is the main focus of the simulations which were extended over several resistive diffusion times. CUTIE reproduces the turbulent transport and MHD phenomena of the experiment. The noninductive components of the current density profile, viz., the dynamo current and the bootstrap current, are identified as key players in the turbulent transport and its suppression and in off-axis MHD events.

  4. Twenty years later: The war did (not begin at Maksimir an anthropological analysis of the media narratives about a never ended football game

    Directory of Open Access Journals (Sweden)

    Đorđević Ivan

    2012-01-01

    Full Text Available The aim of this work is an analysis of the media narratives about the never ended football match between Dynamo Zagreb and Red Star Belgrade on May 13 1990. The article focuses on the media coverage twenty years after the incident in the context of the game's acquired mythic status, symbolically marking the beginning of the war in former Yugoslavia. The object of the analysis are Serbian and Croatian media with the aim of revealing the strategies of representing this event in the period of the normalization of the relations in the region. [Projekat Ministarstva nauke Republike Srbije, br. 177026: Cultural Heritage and Identity

  5. Conductivity and dissociation in liquid metallic hydrogen and implications for planetary interiors.

    Science.gov (United States)

    Zaghoo, Mohamed; Silvera, Isaac F

    2017-11-07

    Liquid metallic hydrogen (LMH) is the most abundant form of condensed matter in our solar planetary structure. The electronic and thermal transport properties of this metallic fluid are of fundamental interest to understanding hydrogen's mechanism of conduction, atomic or pairing structure, as well as the key input for the magnetic dynamo action and thermal models of gas giants. Here, we report spectrally resolved measurements of the optical reflectance of LMH in the pressure region of 1.4-1.7 Mbar. We analyze the data, as well as previously reported measurements, using the free-electron model. Fitting the energy dependence of the reflectance data yields a dissociation fraction of 65 ± 15%, supporting theoretical models that LMH is an atomic metallic liquid. We determine the optical conductivity of LMH and find metallic hydrogen's static electrical conductivity to be 11,000-15,000 S/cm, substantially higher than the only earlier reported experimental values. The higher electrical conductivity implies that the Jovian and Saturnian dynamo are likely to operate out to shallower depths than previously assumed, while the inferred thermal conductivity should provide a crucial experimental constraint to heat transport models. Published under the PNAS license.

  6. Magnetostrophic Rotating Magnetoconvection

    Science.gov (United States)

    King, Eric; Aurnou, Jonathan

    2016-11-01

    Planetary magnetic fields are generated by turbulent convection within their vast interior liquid metal cores. Although direct observation is not possible, this liquid metal circulation is thought to be dominated by the controlling influences of Coriolis and Lorentz forces. Theory famously predicts that local-scale convection naturally settles into the so-called magnetostrophic state, where the Coriolis and Lorentz forces partially cancel, and convection is optimally efficient. To date, no laboratory experiments have reached the magnetostrophic regime in turbulent liquid metal convection. Furthermore, computational dynamo simulations have as yet failed to produce a globally magnetostrophic dynamo, which has led some to question the existence of the magnetostrophic state. Here, we present results from the first turbulent magnetostrophic rotating magnetoconvection experiments using the liquid metal gallium. We find that turbulent convection in the magnetostrophic regime is, in fact, maximally efficient. The experimental results clarify these previously disparate results, suggesting that the fluid dynamics saturate in magnetostrophic balance within turbulent liquid metal, planetary cores. The authors thank the NSF Geophysics Program for financial support.

  7. The sunspot cycle and solar magnetic fields. I - The mechanism as inferred from observation. II - The interaction of flux tubes with the convection zone

    Science.gov (United States)

    Giovanelli, R. G.

    The first part of the present work notes that solar magnetic and velocity field observations can be used to derive the course of events in the solar cycle; such observations differ from those of conventional dynamo theories in the matters of polar field reversal, the sunspot cycle, and the torsional oscillation. In the second part, the mechanisms of interaction between flux tubes or ropes and the convection zone are examined for their relevance to the sunspot cycle. The mechanisms encompass floating, transport, and the penetration of gas from outside the tubes. All previous studies are noted to contain one or more major errors, rendering their conclusions invalid. These errors invariably involve the assumption that Archimede's principle is applicable to flux ropes, that gas entry can be disregarded, or, in some cases, that floating criteria substantially depend on local phenomena. Attention is given to: (1) the transport of flux tubes by the slow poleward motions, and to the even slower systems that carry tube extensions downwards to depths of about 150 Mm and then equatorwards; (2) their magnetic field strengths; and (3) the amplitudes of the torsional oscillation. All major cycle observations are concluded to be accounted for by the novel dynamo mechanism discussed.

  8. Laboratory astrophysics using differential rotation of unmagnetized plasma at large magnetic Reynolds number

    Science.gov (United States)

    Weisberg, David

    2016-10-01

    Differentially rotating plasma flow has been measured in the Madison Plasma Dynamo Experiment (MPDX). Spherical cusp-confined plasmas have been stirred both from the plasma boundary using electrostatic stirring in the magnetized edge and in the plasma core using weak global fields and cross-field currents to impose a body-force torque. Laminar velocity profiles conducive to shear-driven MHD instabilities like the dynamo and the MRI are now being generated and controlled with magnetic Reynolds numbers of Rm new quasi-1D ambipolar diffusion model is presented to explain measurements of cusp loss widths that do not fit the classic hybrid gyroradius theory. Emissive electrode discharge is shown to be an efficient method for plasma heating, but limits on input heating power have been observed (believed to be caused by the formation of double-layers at anodes). These confinement studies have culminated in large (R = 1.4 m), warm (Te 1), steady-state plasmas. Results of the ambipolar transport model are good fits to measurements of pressure gradients and fluid drifts in the cusp, and offer a predictive tool for future cusp-confined devices. Hydrodynamic modeling is shown to be a good description for measured plasma flows, where ion viscosity proves to be an efficient mechanism for transporting momentum from the magnetized edge into the unmagnetized core. In addition, the body-force stirring technique produces velocity profiles conducive to MRI experiments where dΩ / dr MHD instabilities.

  9. The magnetized universe: its origin and dissipation through acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Colgate, Stirling [Los Alamos National Laboratory; Li, Hui [Los Alamos National Laboratory; Kronberg, Philip [Los Alamos National Laboratory

    2010-09-02

    Problems of a magnetic universe and some, possible solutions: The greater the total energy of an astrophysical phenomena, the more restricted are the possible explanations. Magnetic energy is the most challenging because its origin is still considered problematic. We suggest that it is evident that the universe is magnetized because of radio lobes, extra galactic cosmic rays, an observed Faraday rotation measure, and the polarized emission of extra galactic radio structures. The implied energies are so large that only the formation of supermassive black holes, (SMBHs) at the center of every galaxy are remotely energetic enough to supply this immense energy, {approx} (1/10)10{sup 8} M{sub {circle_dot}}c{sup 2}. (Only a galaxy cluster of 1000 galaxies has comparable energy, but is inversely rare.) Yet this energy appears to be largely transformed into accelerated relativistic particles, both electrons and ions. Only a large-scale coherent dynamo within the accretion disk forming the massive black hole makes a reasonable starting point. The subsequent winding of this dynamo derived flux by conducting, angular-momentum-dominated accreting matter produces the immense, coherent magnetic fluxes. We imbed this explanation in a list of similar phenomena at smaller scale and look for physical consistency among the various phenomena, especially the conversion of force-free magnetic energy into acceleration.

  10. Van der Pol and the history of relaxation oscillations: Toward the emergence of a concept

    Science.gov (United States)

    Ginoux, Jean-Marc; Letellier, Christophe

    2012-06-01

    Relaxation oscillations are commonly associated with the name of Balthazar van der Pol via his paper (Philosophical Magazine, 1926) in which he apparently introduced this terminology to describe the nonlinear oscillations produced by self-sustained oscillating systems such as a triode circuit. Our aim is to investigate how relaxation oscillations were actually discovered. Browsing the literature from the late 19th century, we identified four self-oscillating systems in which relaxation oscillations have been observed: (i) the series dynamo machine conducted by Gérard-Lescuyer (1880), (ii) the musical arc discovered by Duddell (1901) and investigated by Blondel (1905), (iii) the triode invented by de Forest (1907), and (iv) the multivibrator elaborated by Abraham and Bloch (1917). The differential equation describing such a self-oscillating system was proposed by Poincaré for the musical arc (1908), by Janet for the series dynamo machine (1919), and by Blondel for the triode (1919). Once Janet (1919) established that these three self-oscillating systems can be described by the same equation, van der Pol proposed (1926) a generic dimensionless equation which captures the relevant dynamical properties shared by these systems. Van der Pol's contributions during the period of 1926-1930 were investigated to show how, with Le Corbeiller's help, he popularized the "relaxation oscillations" using the previous experiments as examples and, turned them into a concept.

  11. JOINT INVERSE CASCADE OF MAGNETIC ENERGY AND MAGNETIC HELICITY IN MHD TURBULENCE

    International Nuclear Information System (INIS)

    Stepanov, R.; Frick, P.; Mizeva, I.

    2015-01-01

    We show that oppositely directed fluxes of energy and magnetic helicity coexist in the inertial range in fully developed magnetohydrodynamic (MHD) turbulence with small-scale sources of magnetic helicity. Using a helical shell model of MHD turbulence, we study the high Reynolds number MHD turbulence for helicity injection at a scale that is much smaller than the scale of energy injection. In a short range of scales larger than the forcing scale of magnetic helicity, a bottleneck-like effect appears, which results in a local reduction of the spectral slope. The slope changes in a domain with a high level of relative magnetic helicity, which determines that part of the magnetic energy is related to the helical modes at a given scale. If the relative helicity approaches unity, the spectral slope tends to –3/2. We show that this energy pileup is caused by an inverse cascade of magnetic energy associated with the magnetic helicity. This negative energy flux is the contribution of the pure magnetic-to-magnetic energy transfer, which vanishes in the non-helical limit. In the context of astrophysical dynamos, our results indicate that a large-scale dynamo can be affected by the magnetic helicity generated at small scales. The kinetic helicity, in particular, is not involved in the process at all. An interesting finding is that an inverse cascade of magnetic energy can be provided by a small-scale source of magnetic helicity fluctuations without a mean injection of magnetic helicity

  12. The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

    International Nuclear Information System (INIS)

    Christensen-Dalsgaard, Joergen; Carpenter, Kenneth G; Schrijver, Carolus J; Karovska, Margarita

    2011-01-01

    The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is a 'Landmark/Discovery Mission' in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ('NASA Space Science Vision Missions' (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

  13. Design Analysis And Applications Of A Regenerative Bicycle Ergometer

    Directory of Open Access Journals (Sweden)

    Chukwuneke J. L.

    2015-08-01

    Full Text Available Man needs to do some form of physical work in other to remain healthy this work is similar to the work done by any machine or equipment and thus should be channeled to give useful output but rather it is usually dissipated into the environment in form of heat. The regenerative bicycle ergometer takes advantage of the greater power generated by the limbs and arms thus conserves converts and stores the energy dissipated by the rider with an ideal mechanical advantage of 7.6 it strategically uses simple mechanisms to magnify its work and then converts this mechanical energy into electrical energy by the use of a dynamo with a speed ratio of 108.5 and a transmission efficiency of 89 the rider pedals 27rpm to obtain the dynamos rated input of 2600rpm giving an output of 12.6volts. The regenerative bicycle ergometer is designed and constructed to perform all the core functions of a bicycle ergometer having an allowable load of 116.5kg and a maximum resistance of 65.33N which is equivalent to a mass of 6.66kg. The energy converted is stored in a 12volts battery making its use flexible clean and meeting the energy demands of man.

  14. Assessing the Impact of Small-Scale Magnetic Morphology on Solar Variability

    Science.gov (United States)

    Peck, Courtney; Rast, Mark; Criscuoli, Serena

    2017-08-01

    Spectral solar irradiance (SSI), the radiant energy flux per wavelength of the Sun received at Earth, is an important driver of chemical reactions in the Earth’s atmosphere. Accurate measurements of SSI are therefore necessary as an input for global climate models. While models and observations of the spectrally-integrated total solar irradiance (TSI) variations agree within ˜ 95%, they can disagree on the sign and magnitude of the SSI variations. In this work, we examine the contribution of currently-unresolved small-scale magnetic structures to SSI variations in the photosphere. We examine the emergent spectra of two atmospheres with differing imposed-field conditions — one with a small-scale dynamo and the other with a predominantly vertical magnetic field — with similar mean field strengths at wavelengths spanning from visible to infrared. Comparing the radiative output at various viewing angles of pixels of equal vertical magnetic field strength between the two simulations, we find that the small-scale dynamo simulations produce higher radiative output than those in the predominantly vertical field simulation. This implies that the radiative output of a small magnetic structure depends on the magnetic morphology of the environment in which it is embedded, which is currently not included in SSI models. We deduce the effect on inferred irradiance by comparing the disk-integrated irradiance of these two atmospheres with standard 1D model atmospheres used in SSI modeling.

  15. Phase Equilibria of a S- and C-Poor Lunar Core

    Science.gov (United States)

    Righter, K.; Pando, K.; Go, B. M.; Danielson, L. R.; Habermann, M.

    2016-01-01

    The composition of the lunar core can have a large impact on its thermal evolution, possible early dynamo creation, and physical state. Geochemical measurements have placed better constraints on the S and C content of the lunar mantle. In this study we have carried out phase equilibrium studies of geochemically plausible S- and C-poor lunar core compositions in the Fe-Ni-S-C system, and apply them to the early history of the Moon. We chose two bulk core compositions, with differing S and C content based on geochemical analyses of S and C trapped melts in Apollo samples, and on the partitioning of S and C between metal and silicate. This approach allowed calculation of core S and C contents - 90% Fe, 9% Ni, 0.5% C, and 0.375% S by weight; a second composition contained 1% each of S and C. Experiments were carried out from 1473K to 1973K and 1 GPa to 5 GPa, in piston cylinder and multi- anvil apparatuses. Combination of the thermal model of with our results, shows that a solid inner core (and therefore initiation of a dynamo) may have been possible in the earliest history of the Moon (approximately 4.2 Ga ago), in agreement with. Thus a volatile poor lunar core may explain the thermal and magnetic history of the Moon.

  16. Astrophysical Phenomenology and the MRI: Progress, Challenges, and Laboratory Connections

    Science.gov (United States)

    Blackman, Eric

    2010-05-01

    The MRI shows excellent promise as a mechanism for generating turbulence with properties needed to transport angular momentum in sufficiently ionized accretion engines. However, it remains a long-term challenge to incorporate what is learned from the MRI into robust practical improvements to current mean field spectral and phenomenological models of accretion engines. We do not understand disk phenomenology nearly as well as stellar phenomenology. In this respect, I discuss how the study of accretion disk theory currently parallels that of mean field dynamo theory, the 21st century version of which has found success through a symbiosis of analytic modeling and numerical simulations. In fact, the two theories are actually complementary components of what should be a unified theory: mean field dynamos prioritize the induction equation whereas mean field accretion theory prioritize the momentum equation. Indeed, much of what has yet to be understood in the application of the MRI to realistic systems is its role in the generation of dynamically significant large-scale fields, which in turn can power coronae and jets. Finally, I discuss how our understanding of the interplay between disks, coronae, and jets may benefit from laboratory plasma studies.

  17. Forecast of the Next Solar Activity Cycle and Thereafter

    Science.gov (United States)

    Duhau, S.; de Jager, C.

    2008-05-01

    Solar variability is controlled by the internal dynamo which is a nonlinear system. It is therefore unpredictable in principle (Tobias, 2004). Yet we have found that the system shows regularities, in line with what can be expected from chaos theory (Duhau ad de Jager, 2008). It is dominated by an attractor state to which the system returns more or less regularly. In addition we distinguish between Grand Maxima, Grand Minima and periods of a more regular oscillation around the attractor state level. Here, we show that the dynamo system is presently undergoing a transition from the recent Grand Maximum to another regime. This transition started in 2000 and is expected to end around the maximum of cycle #24, that we foresee for 2012 - 2013. At that time the maximum sunspot number Rmax will be 70 ± 17, where the 'error' is the largest conceivable deviation from the expected value. At that time a period of lower solar activity will start. That period will most probably be a regular quasiperiodic episode, as occurred between 1730 and 1925. It is characterized by the superposition of weak 'regular' Gleissberg cycle and decadal oscillations. These last will be negative and might turn out to be very strong, as around 1810, in which case a Dalton-type Grand Minimum would develop. This moderate to low-activity episode is expected to last for an integer number of Gleissberg cycles.

  18. Simulating solar MHD

    Directory of Open Access Journals (Sweden)

    M. Schüssler

    Full Text Available Two aspects of solar MHD are discussed in relation to the work of the MHD simulation group at KIS. Photospheric magneto-convection, the nonlinear interaction of magnetic field and convection in a strongly stratified, radiating fluid, is a key process of general astrophysical relevance. Comprehensive numerical simulations including radiative transfer have significantly improved our understanding of the processes and have become an important tool for the interpretation of observational data. Examples of field intensification in the solar photosphere ('convective collapse' are shown. The second line of research is concerned with the dynamics of flux tubes in the convection zone, which has far-reaching implications for our understanding of the solar dynamo. Simulations indicate that the field strength in the region where the flux is stored before erupting to form sunspot groups is of the order of 105 G, an order of magnitude larger than previous estimates based on equipartition with the kinetic energy of convective flows.

    Key words. Solar physics · astrophysics and astronomy (photosphere and chromosphere; stellar interiors and dynamo theory; numerical simulation studies.

  19. The magnetic tides of Honolulu

    Science.gov (United States)

    Love, Jeffrey J.; Rigler, Erin Joshua

    2013-01-01

    We review the phenomenon of time-stationary, periodic quiet-time geomagnetic tides. These are generated by the ionospheric and oceanic dynamos, and, to a lesser-extent, by the quiet-time magnetosphere, and they are affected by currents induced in the Earth's electrically conducting interior. We examine historical time series of hourly magnetic-vector measurements made at the Honolulu observatory. We construct high-resolution, frequency-domain Lomb-periodogram and maximum-entropy power spectra that reveal a panorama of stationary harmonics across periods from 0.1 to 10000.0-d, including harmonics that result from amplitude and phase modulation. We identify solar-diurnal tides and their annual and solar-cycle sideband modulations, lunar semi-diurnal tides and their solar-diurnal sidebands, and tides due to precession of lunar eccentricity and nodes. We provide evidence that a method intended for separating the ionospheric and oceanic dynamo signals by midnight subsampling of observatory data time series is prone to frequency-domain aliasing. The tidal signals we summarize in this review can be used to test our fundamental understanding of the dynamics of the quiet-time ionosphere and magnetosphere, induction in the ocean and in the electrically conducting interior of the Earth, and they are useful for defining a quiet-time baseline against which magnetospheric-storm intensity is measured.

  20. Primordial magnetic field amplification from turbulent reheating

    International Nuclear Information System (INIS)

    Calzetta, Esteban; Kandus, Alejandra

    2010-01-01

    We analyze the possibility of primordial magnetic field amplification by a stochastic large scale kinematic dynamo during reheating. We consider a charged scalar field minimally coupled to gravity. During inflation this field is assumed to be in its vacuum state. At the transition to reheating the state of the field changes to a many particle/anti-particle state. We characterize that state as a fluid flow of zero mean velocity but with a stochastic velocity field. We compute the scale-dependent Reynolds number Re(k), and the characteristic times for decay of turbulence, t d and pair annihilation t a , finding t a d . We calculate the rms value of the kinetic helicity of the flow over a scale L and show that it does not vanish. We use this result to estimate the amplification factor of a seed field from the stochastic kinematic dynamo equations. Although this effect is weak, it shows that the evolution of the cosmic magnetic field from reheating to galaxy formation may well be more complex than as dictated by simple flux freezing