WorldWideScience
1

World map of ELF/VLF emissions as observed by a low-orbiting satellite  

International Nuclear Information System (INIS)

Statistical studies were performed of the intensities of the ELF/VLF emissions observed by the low-orbiting satellite AUREOL-3. Data were obtained from filterbanks and the frequency range of observations extends from a few tens of Hz up to 15 kHz. The most important phenomena observed are ELF hiss and VLF hiss. Electric and magnetic components are used. Thus, representation of the waves intensities in geographical coordinates was made at different frequencies. The relative ability of natural waves (whistler, hiss) and man-made waves, such as powerful VLF transmitters or powerline harmonic radiations (PLHR), to precipitate particles in the slot region, is studied. Using geomagnetical representation, it is shown that ELF hiss is maximum between 06 and 20 Magnetic Local Time and in the invariant latitude range 500-700 as usual, but geographic representation indicates that the waves are intensified at the longitudes of VLF transmitters and near the South Atlantic Anomaly (SAA). The SAA plays a dominant role in the localization of the strongest ELF hiss. Weakest intensities are observed to the east of the SAA. As to the VLF hiss, the maximum intensity is related to regions of enhanced thunderstorm activity, and may be influenced by powerline harmonic radiations (PLHR) over USA. Comparisons with past work, experimental as well as theoretical, are made

2

Low-level VLF and LR radio emissions observed at earth and Jupiter  

Science.gov (United States)

Major observational features of magnetospheric VLF-LF radio noise that have been uncovered by the IMP, Hawkeye and ISEE satellites, are examined with emphasis on the capabilities of the noise to diagnose local and remote plasma parameters. The relationship of the radiation to not less than 1-mV/m electrostatic upper hybrid emissions is assessed, and indirect observational evidence suggests that upper noise is associated with the generation of the VLF-LF radiation. Theoretical luminosities of mechanisms including synchrotron radiation, linear mode conversion of upper hybrid waves and nonlinear scattering of upper hybrid waves off plasma density irregularities are estimated, and the wave-wave scattering hypothesis is considered to be a viable mechanism if the presence of low-frequency waves as a scattering agent can be established.

Barbosa, D. D.

1982-01-01

3

ABOVE: an Array for Broadband Observations of VLF/ELF Emissions  

Science.gov (United States)

Understanding particle acceleration and loss due to wave-particle interaction in the inner magnetosphere requires observations across a wide range of scales and from a variety of locations. High-altitude missions such as RBSP and THEMIS provide extremely detailed in-situ observations but at a very limited number of points. On the other hand, ground-based arrays can simultaneously monitor a great volume of space, but are necessarily remote observations. In between, low-altitude satellite and balloon missions provide coverage on intermediate scales and locations. All of these scales and locations are important to understanding this problem. The University of Calgary is deploying an array of ground-based VLF/ELF receivers and riometers (ABOVE: an Array for Broadband Observations of VLF/ELF Emissions) to augment existing Canadian ground-based facilities such as CARISMA, Norstar and SuperDARN. The ABOVE instruments monitor electromagnetic waves in a frequency rage covering chorus and hiss emissions, as well as electron precipitation into the atmosphere. The large physical scale monitored by these instruments will form an excellent complement to detailed but highly localized in-situ measurements (RBSP, THEMIS, etc.). This presentation will cover the details and current status of the ABOVE project, complementarity with other space-based and ground-based resources, and how potential users can immediately access ABOVE data to use in their research.

Cully, C. M.; Weatherwax, A. T.; Spanswick, E.; Donovan, E.

2012-12-01

4

Low-level VLF and LF radio emissions observed at earth and jupiter  

International Nuclear Information System (INIS)

This paper examines the current state of knowledge of VLF and LF radio wave emissions in the magnetosphere. Specifically, the properties of the low-level noise commonly referred to as continuum radiation are reviewed with emphasis of the capabilities of the noise to diagnose local and remote plasma parameters. The relationship of the radiation to > or =1-mV/m electrostatic upper hybrid emissions is critically assessed. There is a fair amount of indirect observational evidence to suggest that upper hybrid noise is associated with the generation of the VLF-LF radiation, and proposed theoretical mechanisms lean toward this interpretation also. However, no definitive association has been established to date. The theoretical luminosities of several mechanisms, which include synchrotron radiation, linear mode conversion of upper hybrid waves, and nonlinear scattering of upper hybrid waves off plasma density irregularities, are estimated. The wave-wave scattering hypothesis is adjudged to be a viable mechanism if the presence of low-frequency waves as a scattering agent can be established either theoretically or observationally. The alternate mechanisms are considered to be too weak as potential source, but efficiency-saving modifications may make the linear mode conversion hypothesis more competitive. Recommendations for future studies on this subject are given

5

Auroral pulsations and accompanying VLF emissions  

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Full Text Available Results of simultaneous TV observations of pulsating auroral patches and ELF-VLF-emissions in the morning sector carried out in Sodankylä (Finland on February 15, 1991 are presented. Auroral pulsating activity was typical having pulsating patches with characteristic periods of about 7 s. Narrow-band hiss emissions and chorus elements at intervals of 0.3–0.4 s formed the main ELF-VLF activity in the frequency range 1.0–2.5 kHz at the same time. The analysis of auroral images with time resolution of 0.04 s allowed perfectly separate analysis of spatial and temporal variations in the auroral luminosity. Mutual correspondence between the behaviour of the luminous auroral patches and the appearance of ELF noise type hiss emissions and VLF chorus trains was found in two intervals chosen for analysis. While the hiss emissions were associated with the appearance of luminosity inside a limited area close to the zenith, the structured VLF emissions were accompanied by rapid motion of luminosity inside the area. The spatial dimension of the pulsating area was about 45–50 km and luminosity propagated inside it with velocity of about 10–12 kms. We discuss a new approach to explain the 5–15 s auroral pulsation based on the theory of flowing cyclotron maser and relaxation characteristics of ionosphere.

Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions · Space plasma physics (wave-particle interactions

V. R. Tagirov

6

Simultaneous observations of quasi-periodic ELF/VLF wave emissions and electron precipitation by DEMETER satellite: A case study.  

Czech Academy of Sciences Publication Activity Database

Ro?. 118, ?. 7 (2013), s. 4523-4533. ISSN 2169-9380 R&D Projects: GA ?R(CZ) GAP209/11/2280; GA MŠk LH12231 Institutional support: RVO:68378289 Keywords : quasi-periodic ELF/VLF emissions in the magnetosphere * wave-particle interactions * demeter spacecraft measurements * whistler-mode waves Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 3.440, year: 2013 http://onlinelibrary.wiley.com/doi/10.1002/jgra.50179/abstract

Hayosh, Mykhaylo; Pasmanik, D. L.; Demekhov, A. G.; Santolík, Ond?ej; Parrot, M.; Titova, E. E.

2013-01-01

7

Non-typical ground-based quasi-periodic VLF emissions observed at L˜5.3 under quiet geomagnetic conditions at night  

Science.gov (United States)

Non-typical long lasting quasi-periodic (QP) VLF emissions have been recorded in Northern Finland at L?5.3 during the recent Finnish VLF campaign held in December 2011. Contrary to the typical daytime QP emissions, the night-time and early morning (00-05 UT) event reported here for the first time is a sequence of 1.5-3.5 kHz noise bursts lasting for several tens of seconds with an unusually long repetition period which gradually decreases from ?700 s to ?50 s. These QP emissions were observed under conditions of very quiet geomagnetic activity (Kp=0). In spite of that, the interplanetary magnetic field generally had a small southward component, and a high-latitude substorm occurred on the night-side. After this substorm, the repetition period of the VLF bursts suddenly dropped from ?200 s to?60 s and the spectral structure of QP wave changed. We attribute these QP emissions to auto-oscillations of the cyclotron instability of the Earth's radiation belts. According to the theory, the repetition period of the QP should be inversely proportional to the flux of the gyroresonant energetic electrons. Thus the increased flux of energetic electrons injected by the substorm probably led to the decreasing QP repetition periods.

Manninen, J.; Kleimenova, N. G.; Kozyreva, O. V.; Bespalov, P. A.; Kozlovsky, A. E.

2013-07-01

8

VLF/ELF radiation observation at Moshiri  

International Nuclear Information System (INIS)

VLF and ELF radiations have been observed at the Moshiri Observatory (magnetic latitude 34 deg. 07 min. N) since 1964. The mechanisms of VLF and ELF radiation occurrences revealed thus far and the problems for future study are described. At present, with a hiss recorder aimed at continuous radiation (the hiss type), observation is being made continuously at 8 kHz (band width = +-1.5 kHz), 5 kHz (+-1 kHz), 1.5 kHz (+-100 Hz) and 0.8 kHz (+-100 Hz) using a minimum-value detection circuit. At 5 kHz, observation is also proceeding at several time rates. Besides the above observation by hiss recorder, wide-band (0 - 10 kHz) observation (mainly for whistler) is continuing with magnetic tape. (Mori, K.)

9

Multistation observations of ELF/VLF whistler mode chorus  

Science.gov (United States)

An array of seven ELF/VLF receivers in Alaska is utilized for direction finding and determination of ionospheric exit point of whistler mode chorus waves from the Earth's magnetosphere. Each receiver records both orthogonal horizontal magnetic components of the chorus waves. All sites use GPS-synchronized sampling, allowing for the localization of ionospheric exit points utilizing both arrival azimuth and time of arrival lag between sites. Results show two distinct groups of cases, emissions with singular ionospheric exit points and those with multiple exit points. Singular exit point cases exhibit migration and mode conversion as a function of propagation distance from the source point. The multiple exit point case shows chorus waves impinging on the ionosphere over a spread in magnetic latitude, suggesting nonducted propagation. Ray tracing for this case is unable to reproduce the observations unless a cold plasma density different than that predicted by geomagnetic conditions is used. It is proposed that chorus elements cross the transionospheric boundary after experiencing scattering from meter-scale irregularities. Additionally, subionospheric VLF remote sensing is used to detect precipitation onto the ionosphere of energetic radiation belt electrons that have been pitch angle scattered by individual chorus emission packets. VLF perturbation signatures are consistent with precipitation fluxes being dominated by electrons with energies less than 1 MeV.

Go?Kowski, M.; Inan, U. S.

2008-08-01

10

First results of simultaneous recording of VLF emissions at two closely located points at auroral latitudes  

Science.gov (United States)

For the first time, simultaneous observations of very low frequency (VLF) emissions at auroral latitudes ( L = 5.3) are carried out at two points located at close geomagnetic latitudes and spaced in longitude by 400 km: the Finnish Kannuslehto station (? = 64.2°) and the Russian Lovozero observatory (? = 64.1°). A recording equipment with similar frequency responses was used. The first results of a comparison of simultaneous observations showed that, in the overwhelming majority of cases, bursts of VLF emission appeared at both points synchronously with an identical (more often right-handed) polarization of the magnetic field of VLF waves, which can be evidence in favor of large dimensions of the ionosphere exit region of VLF waves. A simultaneous burst of quasi-periodic VLF emissions that occurred on February 02, 2013, during a substorm at 23-24 UT is discussed in detail. Additionally, VLF bursts were recorded which were observed only at one point, e.g., the appearance of left-hand polarized periodic emissions (PEs) in band 2.5-4.0 kHz with a repetition period of 3-4 s.

Manninen, J.; Fedorenko, Yu. V.; Kleimenova, N. G.; Kozyreva, O. V.; Nikitenko, A. S.

2014-01-01

11

Perturbations of ionosphere-magnetosphere coupling by powerful VLF emissions from ground-based transmitters  

International Nuclear Information System (INIS)

The characteristics of the plasma-wave disturbances stimulated in the near-Earth plasma by powerful VLF radiation from ground-based transmitters are investigated. Radio communication VLF transmitters of about 1 MW in power are shown to produce artificial plasma-wave channels (density ducts) in the near-Earth space that originate in the lower ionosphere above the disturbing emission source and extend through the entire ionosphere and magnetosphere of the Earth along the magnetic field lines. Measurements with the onboard equipment of the DEMETER satellite have revealed that under the action of emission from the NWC transmitter, which is one of the most powerful VLF radio transmitters, the generation of quasi-electrostatic (plasma) waves is observed on most of the satellite trajectory along the disturbed magnetic flux tube. This may probably be indicative of stimulated emission of a magnetospheric maser.

12

Perturbations of ionosphere-magnetosphere coupling by powerful VLF emissions from ground-based transmitters  

Energy Technology Data Exchange (ETDEWEB)

The characteristics of the plasma-wave disturbances stimulated in the near-Earth plasma by powerful VLF radiation from ground-based transmitters are investigated. Radio communication VLF transmitters of about 1 MW in power are shown to produce artificial plasma-wave channels (density ducts) in the near-Earth space that originate in the lower ionosphere above the disturbing emission source and extend through the entire ionosphere and magnetosphere of the Earth along the magnetic field lines. Measurements with the onboard equipment of the DEMETER satellite have revealed that under the action of emission from the NWC transmitter, which is one of the most powerful VLF radio transmitters, the generation of quasi-electrostatic (plasma) waves is observed on most of the satellite trajectory along the disturbed magnetic flux tube. This may probably be indicative of stimulated emission of a magnetospheric maser.

Belov, A. S., E-mail: alexis-belov@yandex.ru; Markov, G. A.; Ryabov, A. O. [Lobachevsky Nizhni Novgorod State University (Russian Federation); Parrot, M. [Environment Physics and Chemistry Laboratory (France)

2012-12-15

13

The theory and simulation of falling frequency VLF emissions  

Science.gov (United States)

Recently a lot of progress has been made in the numerical simulation and theoretical understanding of rising frequency triggered emissions and rising frequency chorus. Both PIC[3,4,5] and Vlasov[1,2] codes produce risers in the negative inhomogeneity region downstream from the equator, and Vlasov codes have simulated fallers but with difficulty. In this paper using a Vlasov VHS simulation code[1] we confine the interaction region to be the positive inhomogeneity region upstream from the equator, thus suppressing the tendency of the code to only trigger risers. The emission generation region is in reality a thin cylindrical field aligned from which the generated fields radiate out. It is unreasonable to assume the fields radiated from a faller GR are transmitted to the downstream region without spreading loss or Landau damping. Furthermore due to energetic resonant electron drift and the fact that the mean group velocity will not be aligned with ambient B field we do not expect phase coherent wave particle interaction across the equator With this reduced interaction region it is found that the VHS code easily and reproducibly triggers falling tones. One example is presented of the numerical simulation of a faller. It is analysed in detail and is compared with VHS simulations of rising frequency emission and also rising frequency chorus. Following Omura [3] it is found that the sweeping frequency is due entirely to the frequency/wavenumber advective term. It has recently been shown [5,6] that the non linear resonant particle current component Jb plays a key role in setting up the required spatial gradient of frequency. The plots of in phase current in z/t space point to a generation point upstream from the equator where initial sweep rate is determined as being nonlinear frequency shift ?1 divided by the set up time which is of the order of the trapping time [5,6]. In the generation region itself we find that the current component parallel to Bw (Jb) is positive, whereas it is negative for risers. In addition examination of the resonant particle distribution function reveals an enhanced distribution function or 'hill' in the resonant particle trap, which is as expected for positive inhomogeneity factor S, again in contrast to the riser case where one has a 'hole' in velocity space in the trap. References 1. Nunn,D., Y. Omura, H. Matsumoto, I. Nagano, and S. Yagitani,(1997) "The numerical simulation of VLF chorus and discrete emissions observed on the Geotail satellite using a Vlasov code," J. Geophys. Res., 102, pp 27083-27097. 2.Nunn,D., O. Santolik, M. Rycroft, and V. Trakhtengerts,(2009), "On the numerical modelling of VLF chorus dynamical spectra," Ann. Geophys., 27, pp1-19. 3. Omura,Y., Y. Katoh, and D. Summers,(2008), "Theory and simulation of the generation of whistler-mode chorus," J.Geophys. Res., 113, A04223, doi:10.1029/2007JA012622. 4. Omura,Y., M. Hikishima, Y. Katoh, D. Summers, and S. Yagitani,(2009) "Nonlinear mechanisms of lower-band and upperband VLF chorus emissions in the magnetosphere," J. Geophys. Res., 114,. A07217, doi:10.1029/2009JA014206. 5. Omura, Y. and D. Nunn (2011),Triggering process of whistler mode chorus emissions in the magnetosphere, J. Geophys. Res., 116, A05205, doi:10.1029/2010JA016280. 6. Nunn,D. and Y. Omura (2012), A computational and theoretical analysis of falling frequency VLF emissions, J. Geophys. Res., in press.

Nunn, D.; Omura, Y.

2012-12-01

14

On the frequency modulation of VLF emissions  

Directory of Open Access Journals (Sweden)

Full Text Available The VLF-wave frequency modulation efficiency as a function of magnetosphere plasma parameters under the weak pitch-angle diffusion regime is studied. The study is based on the VLF growth-rate modulation both in the magnetosphere equatorial plane and after integrating along the magnetic field line. It is shown that for the typical quiet magnetosphere plasma parameters the relative shift of the maximum intensity frequency ??m/?m is approximately equal to relative disturbance of the magnetic field in the magnetosphere equatorial plane, but may exceed it when both electron temperature anisotropy and the parameter ???are small; here ? is the total-to-warm electron content ratio and ?? is the electron parallel beta. It is also shown that relative shift of the maximum intensity frequency ??m/?m after integrating along the field line is not less than 50% from its value at the equatorial plane, which allows the use of the equatorial-plasma-parameter data to estimate the VLF frequency modulation on the ground. The upper cut-off frequency modulation is considered as well. The calculated theoretical sonagrams show that this frequency modulation may be related to the non-dispersive and to the "inverted-V'' structures of QP hiss.

M. Goncharova

15

On the frequency modulation of VLF emissions  

Science.gov (United States)

The VLF-wave frequency modulation efficiency as a function of magnetosphere plasma parameters under the weak pitch-angle diffusion regime is studied. The study is based on the VLF growth-rate modulation both in the magnetosphere equatorial plane and after integrating along the magnetic field line. It is shown that for the typical quiet magnetosphere plasma parameters the relative shift of the maximum intensity frequency m/m is approximately equal to relative disturbance of the magnetic field in the magnetosphere equatorial plane, but may exceed it when both electron temperature anisotropy and the parameter alpha>∥ are small; here alpha> is the total-to-warm electron content ratio and ∥ is the electron parallel beta. It is also shown that relative shift of the maximum intensity frequency m/m after integrating along the field line is not less than 50% from its value at the equatorial plane, which allows the use of the equatorial-plasma-parameter data to estimate the VLF frequency modulation on the ground. The upper cut-off frequency modulation is considered as well. The calculated theoretical sonagrams show that this frequency modulation may be related to the non-dispersive and to the inverted-V'' structures of QP hiss. Acknowledgements. The work done by P. Henelius and E. Vilenius in programme development is gratefully acknowledged. Topical Editor D. Alcayde thanks I. Pryse and A. Vallance-Jones for their help in evaluating this paper.

Goncharova, M.; Lyatsky, W.

1996-11-01

16

Ring current electron trajectories associated with VLF emissions  

International Nuclear Information System (INIS)

Intensity enhancements of the ring current electrons associated with the VLF emissions during the geomagnetic storms and substorms, which have been observed by the equatorially orbiting S3-A satellite (Explorer 45), are so far limited only to electrons of energies below the order of 10 keV. Furthermore, onsets of the enhancement are detected in the lowest observable energy channel first, then shifting toward higher energies with time, a feature, which is opposite to the well-known energy dependence expected from the drift motion of electrons in the earth's dipole magnetic field. In order to explain these findings on the ring current electron enhancements, trajectories of electrons injected into the nightside of the magnetosphere from the geomagnetic tail are calculated by modifying Ejiri's calculations which were used for the interpretation of the nose events of the ring current protons observed also by the S3-A satellite. The results indicate that the electron intensity enhancements are limited to electrons below the order of 10keV simply because of the location of the observations which are initially confined to the dusk-midnight sector outside the plasmasphere. If the observations are made in the morning sector, where many VLF emissions such as chorus are observed, the enhancement should not be limited only to electrons below the order of 10 keV but should extend to electrons up to the order of 100 keV. The apparent inverse dispersion, i.e., t. The apparent inverse dispersion, i.e., the appearance of the enhancement at lower energies first, is also due to the location of the observations. Namely, if the observations are made in the morning sector outside the plasmasphere, the normal dispersion with the first enhancement by high-energy electrons should be seen. Since the adiabatic energy increase of charged particles during cross-magnetic field inward motion in the dipole field is largest for the 900 pitch angle particles, the energy at the source is lowest for 900 pitch angle electrons

17

ELF and VLF observations of ionospheric disturbances caused by extra-terrestrial origin  

Science.gov (United States)

Very Low Frequency (VLF) radio wave propagates within the Earth-ionosphere waveguide, and hence measurement of the VLF amplitude and phase can be utilized to study physics of phenomena taking place in the lower ionosphere below about 100 km. Observation of Extremely Low Frequency (ELF) radio wave is also a powerful tool to investigate ionospheric phenomena such as lightning. Here we present ELF and VLF observations of ionospheric disturbances caused by extraterrestrial phenomena. Cosmological Gamma-ray bursts has already been known as the origin of ionospheric disturbances. In addition to this, "magnetar" flares has also been recognized to affect the Earth's ionosphere. Ordinary neutron stars possess magnetic fields of about 10^12 Gauss, while magnetars are considered to have extremely strong magnetic fields of about 10^15 G. Some of the magnetars emit short-duration (~0.1 s) gamma-ray bursts repeatedly in active phases, thereby they are named as "Soft Gamma-ray Repeaters (SGRs)". As rare events, SGRs emit exceptionally bright gamma-ray flares "giant flares", whose peak fluxes exceed those of X-class large solar flares by several order of magnitudes. Recent sensitive measurement of ELF and VLF radio waves can observe ionospheric disturbances caused by these short-repeated and giant flares. Namely, we have found that transient ELF radio wave and Schumann resonance were caused by SGR giant flares in 2004. The emission mechanism is still unclear, but similarity of nuclear detonation in 1960's might give some hints to unveil the emission mechanism. Interesting application of VLF measurement of magnetar flare is that we can deduce the gamma-ray spectrum from VLF data. Intensive astronomical X-ray and gamma-ray observations have been performed by satellites in space using very sensitive detectors. Since SGR giant flare emits huge X-ray/gamma-ray flux, such sensitive detectors are affected by severe saturation problems and precise measurement is very difficult. In my presentation, we present how we deduce the photon spectrum from the VLF data. Using Monte Carlo method, we modeled ionization of lower ionosphere, and obtained altitude profile of electron number density. We then utilized Finite-Difference Time Domain (FDTD) method to simulate VLF propagation. The altitude profile and simulated amplitude change differs depending on the energy spectrum. Therefore, by comparing simulation results with the observation, we can infer the source spectrum as an inverse problem.

Tanaka, Y.; Hayakawa, M.; Hobara, Y.; Raulin, J.; Takahashi, Y.; Sato, M.; Terasawa, T.

2013-05-01

18

Prediction Capabilities of VLF/LF Emission as the Main Precursor of Earthquake  

CERN Document Server

Recent satellite and ground-based observations proved that in earthquake preparation period in the seismogenic area we have VLF/LF and ULF electromagnetic emissions. According to the opinion of the authors of the present paper this phenomenon is more universal and reliable than other earthquake indicators. Hypothetically, in case of availability of adequate methodological grounds, in the nearest future, earth VLF/LF electromagnetic emission might be declared as the main precursor of earthquake. In particular, permanent monitoring of frequency spectrum of earth electromagnetic emission generated in the earthquake preparation period might turn out very useful with the view of prediction of large (M 5) inland earthquakes. The present paper offers a scheme of the methodology according to which the reality of the above given hypothesis can be checked up. To prove the prediction capabilities of earth electromagnetic emission we have used avalanche-like unstable model of fault formation and an analogous model of ele...

Kachakhidze, Manana

2013-01-01

19

Study of VLF emissions apparently associated with earthquakes from ground-based and GEOS satellites data  

International Nuclear Information System (INIS)

VLF emissions, apparently associated with earthquakes, have been independently observed at the Kerguelen station(49 deg 26'S,70 deg 25'E) and on the GEOS-1 and GEOS-2 satellites, at frequencies under 10 kHz. The observations at Kerguelen have been made on magnetic antennas, on April 24 and 25 1980, in a period when three earthquakes of moderate intensity (M ? 4.7) took place near the station. The observations on the GEOS satellites have been made from magnetic and electric antennas during the period 1977-1981. The analysis has been performed selecting the cases for which, on the one hand, intense earthquakes (M>5) occurred in regions close to the satellite longitude (GEOS-2 is geostationary and its geographical longitude is ? 22 deg E) and, on the other hand, the satellite is operating in a VLF mode. Methods of distinction between correlations and coincidences are discussed

20

Excitation of sidebands due to nonlinear coupling between a VLF transmitter signal and a natural ELF emission  

International Nuclear Information System (INIS)

Symmetric sidebands are observed in the ionosphere by the AUREOL 3 satellite when it passes at a height of 1,200 km above the VLF transmitter at the Komsomolsk-on-Amur Alpha station (50 degree 5 N, 135 degree E, frequency 11.90 and 12.65 kHz). The sidebands are about 500 Hz off the carrier frequency of Alpha pulses. They are approximately 20 dB lower than the transmitter signal, and they appear only when ELF natural emission above the local proton gyrofrequency is observed. The data are presented and analyzed. The nonlinear coupling of the VLF transmitter signal to natural ELF emission is invoked to explain the symmetric sidebands. It is shown that the nonlinear current excited by the beats of VLF and ELF waves is strong enough to explain the sideband amplitude

21

Excitation of sidebands due to nonlinear coupling between a VLF transmitter signal and a natural ELF emission  

Science.gov (United States)

Symmetric sidebands are observed in the ionosphere by the AUREOL 3 satellite when it passes at a height of 1200 km above the VLF transmitter at the Komsomolsk-on-Amur Alpha station. The sidebands are about 500 Hz off the carrier frequency of Alpha pulses. They are approximately 20 dB lower than the transmitter signal, and they appear only when ELF natural emission above the local proton gyrofrequency is observed. The data are presented and analyzed. The nonlinear coupling of the VLF transmitter signal to natural ELF emission is invoked to explain the symmetric sidebands. It is shown that the nonlinear current excited by the beats of VLF and ELF waves is strong enough to explain the sideband amplitude.

Sotnikov, V. I.; Fiala, V.; Lefeuvre, F.; Lagoutte, D.; Mogilevskii, M.

1991-07-01

22

Excitation of sidebands due to nonlinear coupling between a VLF transmitter signal and a natural ELF emission  

Energy Technology Data Exchange (ETDEWEB)

Symmetric sidebands are observed in the ionosphere by the AUREOL 3 satellite when it passes at a height of 1,200 km above the VLF transmitter at the Komsomolsk-on-Amur Alpha station (50{degree}5 N, 135{degree} E, frequency 11.90 and 12.65 kHz). The sidebands are about 500 Hz off the carrier frequency of Alpha pulses. They are approximately 20 dB lower than the transmitter signal, and they appear only when ELF natural emission above the local proton gyrofrequency is observed. The data are presented and analyzed. The nonlinear coupling of the VLF transmitter signal to natural ELF emission is invoked to explain the symmetric sidebands. It is shown that the nonlinear current excited by the beats of VLF and ELF waves is strong enough to explain the sideband amplitude.

Sotnikov, V.I.; Fiala, V.; Lefeuvre, F.; Lagoutte, D. (Lab. de Physique et Chimie de l' Environnement, Orleans (France)); Mogilevsky, M. (Space Research Inst., Moscow (USSR))

1991-07-01

23

Statistical correlation of spectral broadening in VLF transmitter signal and low-frequency ionospheric turbulence from observation on DEMETER satellite  

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Full Text Available In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere. At present paper we investigate a possibility VLF signal-ionospheric turbulence interaction using additional characteristic of VLF signal-spectrum broadening. This characteristic is important for estimation of the interaction type: linear or nonlinear scattering. Our main results are the following:
– There are two zones of increased spectrum broadening, which are centered near magnetic latitudes ?=±10° and ?=±40°. Basing on the previous case study research and ground ionosonde registrations, probably it is evidence of nonlinear (active scattering of VLF signal on the ionospheric turbulence. However occurrence rate of spectrum broadening in the middle-latitude area is higher than in the near-equatorial zone (~15–20% in comparison with ~100% in former area that is probably coincides with the rate of ionospheric turbulence.
– From two years statistics of observation in the selected 3 low-latitude regions and 1 middle-latitude region inside reception area of VLF signal from NWC transmitter we find a correlation of spectrum broadening neither with ion-cyclotron noise (f=150–500 Hz, which possibly means poor representation of the turbulence by the noise due to its mixture with natural ELF emission (which correlates with whistler, nor with magnetic storm activity.
– We find rather evident correlation of ion-cyclotron frequency noise, VLF signal depression and weak correlation of spectrum broadening with seismicity in the middle-latitude region over Japan. But in the low-latitude regions we do not find such a correlation. Statistical decrease of VLF signal supports our previous case study results. However rather weak spectrum broadening-seismicity statistical correlation means probably that passive scattering prevails upon nonlinear (active one.

A. Rozhnoi

2008-10-01

24

A computational and theoretical analysis of falling frequency VLF emissions  

Science.gov (United States)

Recently much progress has been made in the simulation and theoretical understanding of rising frequency triggered emissions and rising chorus. Both PIC and Vlasov VHS codes produce risers in the region downstream from the equator toward which the VLF waves are traveling. The VHS code only produces fallers or downward hooks with difficulty due to the coherent nature of wave particle interaction across the equator. With the VHS code we now confine the interaction region to be the region upstream from the equator, where inhomogeneity factor S is positive. This suppresses correlated wave particle interaction effects across the equator and the tendency of the code to trigger risers, and permits the formation of a proper falling tone generation region. The VHS code now easily and reproducibly triggers falling tones. The evolution of resonant particle current JE in space and time shows a generation point at -5224 km and the wavefield undergoes amplification of some 25 dB in traversing the nonlinear generation region. The current component parallel to wave magnetic field (JB) is positive, whereas it is negative for risers. The resonant particle trap shows an enhanced distribution function or `hill', whereas risers have a `hole'. According to recent theory (Omura et al., 2008, 2009) sweeping frequency is due primarily to the advective term. The nonlinear frequency shift term is now negative (˜-12 Hz) and the sweep rate of -800 Hz/s is approximately nonlinear frequency shift divided by TN, the transition time, of the order of a trapping time.

Nunn, David; Omura, Yoshiharu

2012-08-01

25

Observations of Ionospheric ELF and VLF Wave Generation by Excitation of the Thermal Cubic Nonlinearity  

Science.gov (United States)

Extremely-low-frequency (ELF, 3-3000 Hz) and very-low-frequency (VLF, 3-30 kHz) waves generated by the excitation of the thermal cubic nonlinearity are observed for the first time at the High-Frequency Active Auroral Research Program high-frequency transmitter in Gakona, Alaska. The observed ELF and VLF field amplitudes are the strongest generated by any high frequency (HF, 3-30 MHz) heating facility using this mechanism to date. This manner of ELF and VLF generation is independent of naturally forming currents, such as the auroral electrojet current system. Time-of-arrival analysis applied to experimental observations shows that the thermal cubic ELF and VLF source region is located within the collisional D-region ionosphere. Observations are compared with the predictions of a theoretical HF heating model using perturbation theory. For the experiments performed, two X-mode HF waves were transmitted at frequencies ?1 and ?2, with |?2-2?1| being in the ELF and VLF frequency range. In contrast with previous work, we determine that the ELF and VLF source is dominantly produced by the interaction between collision frequency oscillations at frequency ?2-?1 and the polarization current density associated with the lower frequency HF wave at frequency ?1. This specific interaction has been neglected in past cubic thermal nonlinearity work, and it plays a major role in the generation of ELF and VLF waves.

Moore, R. C.; Fujimaru, S.; Kotovsky, D. A.; Go?kowski, M.

2013-12-01

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On the nonlinear triggering of VLF emissions by power line harmonic radiation  

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Full Text Available VLF ground data from Porojarvi in N. Finland has been presented. Spectrograms reveal frequent occurrence of power line harmonic radiation (PLHR, originating from the Finnish power system and from heavy industrial plant. The radiation is seen to penetrate the magnetosphere since numerous occurrences of PLHR triggered emissions are seen. Risers predominate but fallers and hooks are also observed. A well-established 1D Vlasov simulation code has been used to simulate these emissions, using plausible magnetospheric data for a range of L values from L = 4 to L = 5.5. The code is able to reproduce risers fallers and hooks in close agreement with observations. The results shed considerable insight into the generation structure of both risers and fallers.

Key words. Electromagnetics (numerical methods · Ionosphere (wave-particle interactions · Magnetospheric physics (plasma waves and instabilities

D. Nunn

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Electron precipitation and VLF emissions associated with cyclotron resonance interactions near the plasmapause  

International Nuclear Information System (INIS)

Correlated bursts of bremsstrahlung X rays and VLF emissions were recorded for approx.25 min at Siple Station, Antarctica, on January 2, 1971. The burst occurred quasi-periodically with spectral power predominantly in the period range 4--12 s. A typical VLF burst consisted of 3--5 rising elements of approx.0.1-s duration separated by approx.0.15 s and was confined to the frequency range 1.5--3.8 kHz. Evidence is presented to show that the bursts were triggered by the low-frequency tail of whistlers propagating from the northern hemisphere. The interpretation of the observations in terms of an equatorial cyclotron resonance interaction occurring at the outer edge of the plasmapause on the L=4.2 field line, offered initially by Rosenberg et al. (1971), is given further support by the more extensive analysis presented here of the electron energy-wave frequency relationship in the bursts and the propagation times for the resonant waves and electrons. It is inferred from the X ray data that the equatorial flux of trapped electrons was probably anisotropic and near the stable trapping limit at the time of this event. It is suggested that an important effect of the trigger signal is the increase of the anisotropy of the resonant electrons. Wave growth rates calculated in the random phase approximation for electron pitch angle distributions that might apply in this event can explain certain features of the VLF and precipitation data during and between the burstsuring and between the bursts

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New type of ensemble of quasi-periodic, long-lasting VLF emissions at the auroral zone  

Science.gov (United States)

A new type of the series of quasi-periodic (QP) very low frequency (VLF) emissions in frequency range of 1-5 kHz, and not associated with geomagnetic pulsations, has been discovered at auroral latitudes (L = 5.3) during the Finnish VLF campaign (held in December 2011). At least five unusually spectacular events, each with a duration of several hours, have been observed during the night under conditions of quiet geomagnetic activity (Kp = 0-1), although QPs usually occur during the daytime. Contrary to the QP emissions typically occurring during the day, the spectral structure of these QP events represented an extended, complicated sequence of repeated discrete rising VLF signals. Their duration was about 2-3 min each, with the repetition periods ranging from ~1 min to ~10 min. Two such nighttime non-typical events are reported in this paper. The fine structure of the separated QP elements may represent a mixture of the different frequency band signals, which seem to have independent origins. It was found that the periodic signals with lower frequency appear to trigger the strong dispersive upper frequency signals. The temporal dynamics of the spectral structure of the QPs studied were significantly controlled by some disturbances in the solar wind and interplanetary magnetic field (IMF). This finding is very important for future theoretical investigations because the generation mechanism of this new type of QP emissions is not yet understood.

Manninen, J.; Kleimenova, N. G.; Kozyreva, O. V.

2012-12-01

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New type of ensemble of quasi-periodic, long-lasting VLF emissions at the auroral zone  

Directory of Open Access Journals (Sweden)

Full Text Available A new type of the series of quasi-periodic (QP very low frequency (VLF emissions in frequency range of 1–5 kHz, and not associated with geomagnetic pulsations, has been discovered at auroral latitudes (L = 5.3 during the Finnish VLF campaign (held in December 2011. At least five unusually spectacular events, each with a duration of several hours, have been observed during the night under conditions of quiet geomagnetic activity (Kp = 0–1, although QPs usually occur during the daytime. Contrary to the QP emissions typically occurring during the day, the spectral structure of these QP events represented an extended, complicated sequence of repeated discrete rising VLF signals. Their duration was about 2–3 min each, with the repetition periods ranging from ~1 min to ~10 min. Two such nighttime non-typical events are reported in this paper. The fine structure of the separated QP elements may represent a mixture of the different frequency band signals, which seem to have independent origins. It was found that the periodic signals with lower frequency appear to trigger the strong dispersive upper frequency signals. The temporal dynamics of the spectral structure of the QPs studied were significantly controlled by some disturbances in the solar wind and interplanetary magnetic field (IMF. This finding is very important for future theoretical investigations because the generation mechanism of this new type of QP emissions is not yet understood.

J. Manninen

2012-12-01

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Subionospheric VLF signatures and their association with sprites observed during EuroSprite 2003  

DEFF Research Database (Denmark)

In this study, VLF observations during EuroSprite-2003 are analyzed in connection with many sprites observed above thunderstorms in central France. The sprites were detected with a sensitive camera from the Observatoire du Pic du Midi in the Pyrenees overlooking storms monitored by the French national lightning detection network. The VLF observations were made in Crete, Greece with a narrowband receiver, and in Nancay, France with a broadband receiver. The storms were in the vicinity of a VLF transmitter (HWV) at Le Blanc, France, whose signal was received on Crete, arriving over a great circle path that cut through the storms to the southeast. The Nancay broadband receiver was located near HWV to the northeast of the transmitter. This setup provided a unique observational set for investigation. The receiver in Crete observed early VLF perturbations in nearly one-to-one association with the sprites, which endorses the findings of earlier work based on EuroSprite-2003 observations from a single storm. While part of the sprite-related VLF perturbations were of the early/fast type, many classified as "early/slow" having onset durations up to similar to 2s and thus suggesting a new mechanism at work which may cause a slow build up of ionization after a sprite. The only elve in the data set was found to associate also with an early/fast VLF perturbation. Moreover, the analysis showed basically no early VLF events to occur in relation to the numerous +/- CG discharges that did not lead to sprites. Bandpass filtering of the broadband VLF signal revealed that only about 5% of the sprites were escorted by early VLF perturbations, possibly due to backscatter. Finally, by using all 131 sprites captured during EuroSprite-2003, the time lags of the sprites to the preceding +/- CG discharges were computed and analyzed. The time-lag distribution had a well defined tail suggesting that at least one third of the sprites observed were lagging the +/- CG discharges by more than 30 up to 300 ms. In addition these "long-delayed" sprites were not accompanied by any radio-sferics during the sprite observation period, in sharp contrast to the short-delayed sprites which were escorted nearly always by enhanced, burst-like, sferic activity. These observations endorse the notion of long delayed sprites reported in past studies, but also show that their occurrence is much more frequent than it was thought before.

Mika, A.; Haldoupis, C.

2005-01-01

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Electron and VLF travel time differences for wave-particle interactions at L=4: Pt. 1  

International Nuclear Information System (INIS)

The Cerenkov interaction has been invoked as a generation mechanism for very low frequency (VLF) auroral hiss. We examine the conditions at L=4 under which VLF Cerenkov radiation may be emitted by auroral electrons. The difference in travel time along the L=4 field line between the electrons and VLF taking part in the interaction, is calculated as a function of VLF wave frequency, auroral electron energy and equatorial electron density for two standard magnetospheric plasma distribution models and unducted VLF radiation. Ducting conditions are then invoked to consider VLF observed on the ground. A simple relationship is obtained which approximates the limited regime in auroral electron energy and ambient equatorial electron density where both the Cerenkov emission and ducting conditions are satisfied. The corresponding differences in electron and VLF travel times are examined and the significance of these results for ground-based observations of VLF and auroral emissions at an L=4 station such as Sanae, Antarctica, is discussed

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Statistical investigation of VLF quasiperiodic emissions measured by the DEMETER spacecraft  

Science.gov (United States)

We present a survey of quasiperiodic (QP) ELF/VLF emissions detected onboard the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite (altitude of about 700 km, nearly Sun-synchronous orbit at 10:30/22:30 LT). Six years of data have been visually inspected for the presence of QP emissions with modulation periods higher than 10 s and with frequency bandwidths higher than 200 Hz. It is found that these QP events occur in about 5% of daytime half orbits, while they are basically absent during the night. The events occur predominantly during quiet geomagnetic conditions following the periods of enhanced geomagnetic activity. Their occurrence and properties are systematically analyzed. QP emissions occur most often at frequencies from about 750 Hz to 2 kHz, but they may be observed at frequencies as low as 500 Hz and as high as 8 kHz. Modulation periods of QP events may range from about 10 to 100 s, with typical values of 20 s. Frequency drifts of the identified events are generally positive, but they are lower for events with larger modulation periods. The events are usually limited to higher L values (L > 2). The upper L shell boundary of their occurrence could not be identified using the DEMETER data, but they are found to extend up to at least L ~ 6. The occurrence rate of the events is significantly lower at the longitudes of the South Atlantic anomaly (by a factor of more than 2).

Hayosh, M.; N?mec, F.; Santolík, O.; Parrot, M.

2014-10-01

33

Direction finding of half-gyrofrequency VLF emissions in the off-equatorial region of the magnetosphere and their generation and propagation  

International Nuclear Information System (INIS)

The spectra of VLF/ELF emissions in the off-equatorial region in the outer magnetosphere are, on occasion, found to consist of upper and lower bands with a frequency gap between them. The wave normal directions of the upper band VLF emissions have been determined by means of wave distribution function analyses based first on the measurement of three magnetic field components only, and then with the additional use of an electric field component. It is found that the wave distribution functions are composed of two peaks whose central wave normal angles ? with respect to the magnetic field at a geomagnetic latitude of ? 17 degree are close to the local oblique resonance cone ?res but whose values of ? are always about 15 degree-20 degree less than ?res at a higher latitude of ?26 degree. This observed wave normal behavior is compared with the theoretical prediction from direct ray tracing studies using the hypothesis deduced from a previous investigation that the waves are generated at the equator with wave normals close to ?res. A combination of this comparison and inverse ray tracing in which the initial wave normal directions are those determined from the wave distribution analysis has yielded the results that the ? values of the upper band VLF emissions are very close to ?res at the equator and that the normalized frequency there, ?eq, is above 0.5. Hence the upper band VLF emissions are identified asLF emissions are identified as being half-gyrofrequency VLF emissions generated in the vicinity of the magnetic equator, with their wave normals close to ?res. The characteristics of propagation between the equatorial source region and the observing positions have been investigated by direct ray tracing. The generation mechanism is also discussed

34

Combined ULF and VLF observations of seismo-electro-magnetic phenomena in Europe  

Science.gov (United States)

A combined analysis of magnetic ultra-low-frequency (ULF) and electromagnetic very-low-frequency (VLF) fluctuations before, during and after earthquakes in south and south-east Europe is presented. The magnetic fluctuations are studied in the frame of the South European Geomagnetic Array (SEGMA) network. The fluxgate and searchcoil magnetometers, located in Italy, Bulgaria and Hungary perform measurements of fluctuations in the pico-Tesla and nano-Tesla range from milli-Hertz to 100 Hz. The properties of VLF radio links (10 kHz - 50 kHz) are studied in the frame of the European VLF/LF radio receiver network (INFREP). Single parameter studies of ULF and VLF variations in the vicinity of earthquakes in Europe have been performed in the last decade (Villante et al. 2010, Rozhnoi et al. 2009). We present the first results of a dual parameter study based on single parameter ULF and VLF observations. The proposed method provides the opportunity to decrease the number of false alerts. A dual parameter seismo-electro-magnetic reliability number is developed and compared with single parameter quality numbers. References: Rozhnoi, A., Solovieva, M., Molchanov, O., Schwingenschuh, K., Boudjada, M., Biagi, P. F., Maggipinto, T., Castellana, L., Ermini, A., and Hayakawa, M.: Anomalies in VLF radio signals prior the Abruzzo earthquake (M=6.3) on 6 April 2009, Nat. Hazards Earth Syst. Sci., 9, 1727-1732, doi:10.5194/nhess-9-1727-2009, 2009. Villante, U., De Lauretis, M., De Paulis, C., Francia, P., Piancatelli, A., Pietropaolo, E., Vellante, M., Meloni, A., Palangio, P., Schwingenschuh, K., Prattes, G., Magnes, W., and Nenovski, P.: The 6 April 2009 earthquake at L'Aquila: a preliminary analysis of magnetic field measurements, Nat. Hazards Earth Syst. Sci., 10, 203-214, doi:10.5194/nhess-10-203-2010, 2010.

Schwingenschuh, Konrad; Eichelberger, Hans; Wolbang, Daniel; Prattes, Gustav; Besser, Bruno; Boudjada, Mohammed Y.; Stangl, Günter; Magnes, Werner; Berghofer, Gerhard; Aydogar, Özer; Rozhnoi, Alexander; Solovieva, Maria; Vellante, Massimo; Villante, Umberto; Biagi, Pier F.

2014-05-01

35

Statistical investigation of VLF quasiperiodic emissions measured by the DEMETER spacecraft.  

Czech Academy of Sciences Publication Activity Database

Ro?. 119, ?. 10 (2014), s. 8063-8072. ISSN 2169-9380 R&D Projects: GA ?R(CZ) GAP209/11/2280; GA MŠk LH12231 Grant ostatní: Akademie v?d(CZ) M100421206 Institutional support: RVO:68378289 Keywords : VLF waves in ionosphere * QP emissions * DEMETER spacecraft Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.440, year: 2013 http://onlinelibrary.wiley.com/doi/10.1002/2013JA019731/abstract

Hayosh, Mykhaylo; N?mec, F.; Santolík, Ond?ej; Parrot, M.

2014-01-01

36

Comparison of FORTE satellite VHF and WWLLN ground-based VLF data on lightning emissions from the same thunderstorms  

Science.gov (United States)

We compare VHF satellite observations and VLF ground-based observations of lightning events within range of both of these dissimilar systems. Earlier work had compared FORTE VHF signals to National Lightning Detection Network (NLDN) signals for lightning in North America [Jacobson, et al., 2000]. That earlier work formed the basis for identifying certain lightning-stroke types over North America via their satellite-recorded VHF waveforms [Light, et al., 2001; Suszcynsky, et al., 2001]. We repeat that exercise for lightning strokes over the lightning-prone region of Australasia, and use the inferred stroke types to provide insight on the relative selection biases of satellite-based VHF and ground-based VLF lightning detection. Jacobson, A. R., et al. (2000), FORTE radio-frequency observations of lightning strokes detected by the National Lightning Detection Network, Journal of Geophysical Research, 105, 15,653. Light, T. E., et al. (2001), Coincident Radio Frequency and Optical Emissions from Lightning, Observed with the FORTE Satellite, Journal of Geophysical Research, 106, 28,223-228,231. Suszcynsky, D. M., et al. (2001), Coordinated Observations of Optical Lightning from Space using the FORTE Photodiode Detector and CCD Imager, Journal of Geophysical Research, 106, 17,897-817,906.

Jacobson, A. R.; Lay, E.; Holzworth, R.; Suszcynsky, D.

2006-12-01

37

Meteorological effects in the lower ionosphere as based on VLF/LF signal observations  

Directory of Open Access Journals (Sweden)

Full Text Available Very low and low frequency (VLF/LF data recorded in the Far Eastern stations Petropavlovsk-Kamchatsky (158.92° E, 53.15° N, Yuzhno-Sakhalinsk (142.75° E, 46.95° N and Yuzhno-Kurilsk (145.861° E, 44.03° N are investigated to study the meteorological effects in the lower ionosphere. The results demonstrate the sensitivity of the VLF/LF signals to the variations of atmospheric pressure, humidity, wind velocity and temperature, and the VLF/LF record at the station of Yuzhno-Kurilsk is found to be most sensitive to those variations of atmospheric parameters. The region under consideration is characterized by high winter cyclonic activity in midlatitudes and strong summer and autumn typhoon activity in low latitudes. VLF/LF signal variations during 8 tropical cyclones (TCs with different intensity are considered. Negative nighttime anomalies in the signal amplitude that are most probably caused by TC activity are found for 6 events. Those anomalies are observed during 1–2 days when TCs move inside the sensitivity zones of the subionospheric paths. Perturbations of the VLF signal observed during 2 TCs can be caused by both the TC influence and seismic activity, but no correlation between TC intensity and magnitude of the signal anomalies is found. Spectral analysis of the typhoon-induced disturbed signals revealed the fluctuations with time periods in the range of 7–16 and 15–55 min that corresponds to the range of internal gravity waves periods.

A. Rozhnoi

2014-04-01

38

Meteorological effects in the lower ionosphere as based on VLF/LF signal observations  

Science.gov (United States)

Very low and low frequency (VLF/LF) data recorded in the Far Eastern stations Petropavlovsk-Kamchatsky (158.92° E, 53.15° N), Yuzhno-Sakhalinsk (142.75° E, 46.95° N) and Yuzhno-Kurilsk (145.861° E, 44.03° N) are investigated to study the meteorological effects in the lower ionosphere. The results demonstrate the sensitivity of the VLF/LF signals to the variations of atmospheric pressure, humidity, wind velocity and temperature, and the VLF/LF record at the station of Yuzhno-Kurilsk is found to be most sensitive to those variations of atmospheric parameters. The region under consideration is characterized by high winter cyclonic activity in mid-latitudes and strong summer and autumn typhoon activity in low latitudes. VLF/LF signal variations during eight tropical cyclones (TCs) with different intensity are considered. Negative nighttime anomalies in the signal amplitude that are most probably caused by TC activity are found for six events. Those anomalies are observed during 1-2 days when TCs move inside the sensitivity zones of the subionospheric paths. Perturbations of the VLF signal observed during two TCs can be caused by both the TC influence and seismic activity, but no correlation between TC intensity and magnitude of the signal anomalies is found. Spectral analysis of the typhoon-induced disturbed signals revealed the fluctuations with time periods in the range of 7-16 and 15-55 min that corresponds to the range of internal gravity waves periods.

Rozhnoi, A.; Solovieva, M.; Levin, B.; Hayakawa, M.; Fedun, V.

2014-10-01

39

Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter  

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Full Text Available It is now well known that amplitude modulated HF transmissions into the ionosphere can be used to generate ELF/VLF signals using the so-called "electrojet antenna". Although most observations of the generated ELF/VLF signals have been made on the ground, several low and high-altitude satellite observations have also been reported (James et al., 1990. One of the important unknowns in the physics of ELF/VLF wave generation by ionospheric heating is the volume of the magnetosphere illuminated by the ELF/VLF waves. In an attempt to investigate this question further, ground-satellite conjunction experiments have recently been conducted using the four Cluster satellites and the HF heater of the High-Frequency Active Auroral Research Program (HAARP facility in Gakona, Alaska. Being located on largely closed field lines at L?4.9, HAARP is currently also being used for ground-to-ground type of ELF/VLF wave-injection experiments, and will be increasingly used for this purpose as it is now being upgraded for higher power operation. In this paper, we describe the HAARP installation and present recent results of the HAARP-Cluster experiments. We give an overview of the detected ELF/VLF signals at Cluster, and a possible explanation of the spectral signature detected, as well as the determination of the location of the point of injection of the HAARP ELF/VLF signals into the magnetosphere using ray tracing.

M. Platino

2004-07-01

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Propagation characteristics of ground observed VLF waves after emerging from the ducts in the ionosphere  

International Nuclear Information System (INIS)

Recent experimental results have shown that the VLF ducts extending high in the magnetosphere are terminated at the base of the protonosphere and the VLF waves emerging from these ducts are propagated downward in the nonducted mode of propagation. In this paper, results of the ray tracing computations carried out with a specific purpose of examining the conditions under which these partly nonducted waves are observed on the ground, are presented. The results show that, for ground observations, it is necessary that the waves should emerge from the ducts at a definite wave normal angle. This wave normal angle is well in the range of total wave normal angles which the ermerging waves may conceive at the base of the ducts at middle and high latitudes but lies outside the range at low latitudes. Various results related to whistler activity on the ground are discussed in the light of these results

41

In connection with identification of VLF emissions before L'Aquila earthquake  

Directory of Open Access Journals (Sweden)

Full Text Available The present paper deals with an attempt to check the theoretical model of self-generated seismo-electromagnetic oscillations of LAI system on the basis of retrospective data.

Application of the offered simple model enables one to explain qualitatively the mechanism of VLF electromagnetic emission initiated in the process of an earthquake preparation. Besides, the model enables us to associate telluric character geoelectric and geomagnetic perturbations incited by rock polarization and self-generated electromagnetic oscillations of lithosphere-atmosphere system.

L'Aquila earthquake taken as an example to isolate reliably the Earth VLF emission from the magnetospheric electromagnetic emission of the same frequency range, MHD criterion is offered together with geomagnetic activity indexes.

On the basis of the considered three earthquakes, according to the opinion of authors the model of self-generated seismo-electromagnetic oscillations of the LAI system will enable us to approach the problem of resolution of earthquake prediction with certain accuracy.

M. K. Kachakhidze

2012-04-01

42

Radiation belt precipitation due to man-made VLF transmissions. Satellite observations  

International Nuclear Information System (INIS)

Complete text of publication follows. In the more than four decades since the discovery of the Earth's Van Allen radiation belts, it has proven difficult to confirm the principal source and loss mechanisms that control radiation belt particles. It has been recognized for some time that the loss of radiation belt electrons in the inner belt beyond L?1.5 is dominated by pitch angle scattering in wave-particle interactions with whistler mode waves, although there has been uncertainty as to the relative importance of different wave types. Relatively recent theoretical calculations have led to the rather surprising conclusion that manmade VLF transmissions may dominate losses in the inner radiation belts. This finding has sparked considerable interest, suggesting practical human control of the radiation belts to protect Earth-orbiting systems from natural and nuclear injections of high energy electrons, generally known as Radiation Belt Remediation (RBR). While strong correlations between drift-loss cone enhancements and transmitter locations have been shown previously, particle enhancements have yet to be tied directly to VLF wave observations. The occurrence frequency of drift loss cone enhancements above transmitters has also previously been unknown. In this paper we combine wave and particle observations from the DEMETER satellite with ground based VLF recordings to examine the significance of the transmitter NWC on the inner radiation belt. Enhancements of drift-losadiation belt. Enhancements of drift-loss cone electron fluxes are observed eastward of the transmitter location, with cyclotron resonance taking place on the field line near the VLF transmitter location, followed by the eastward drift of electrons towards the South Atlantic Anomaly. Transmitters located under a nighttime ionosphere are favoured, due to the lower ionospheric absorption. 95% of orbital passes which met these conditions showed evidence of an interaction. A positive correlation exists between transmitter operation and the presence of such enhancements. Typical transmissions cause a ?400-fold increase in 300 keV drift-loss cone electrons. These observations provide conclusive evidence linking drift-loss cone electron flux enhancements and transmitter operation. Numerical magnitudes and occurrence rates experimentally detected here should allow a validation of models for wave and particle dynamics in the radiation belts.

43

Lightning-associated VLF perturbations observed at low latitude: Occurrence and scattering characteristics  

Science.gov (United States)

The occurrence of short-timescale (˜1-100 s) perturbations (early VLF events) on four Very Low Frequency (VLF) transmitter signals (call signs: NWC, NPM, VTX, NLK), recorded at Suva (18.1°S, 178.5°E, L = 1.16), shows the most frequent occurrence on the NWC signal and least on the VTX. Daytime early/fast events on the NWC transmission are (0.2-0.5 dB) with only negative amplitude perturbations with comparatively lower recovery times (10-30 s) as compared with most nighttime events with amplitude perturbations of 0.2-1.5 dB and recovery times of 20-80 s. The World-Wide Lightning Location Network detected causative lightnings for 74 of 453 early VLF events out of which 54 (73%) were produced due to narrow-angle scattering, and by 20 (27%) due to wide-angle scattering. The recovery (decay) of the scattered amplitude of early/fast events on the NWC signal shows both exponential and logarithmic forms, but the linear correlation coefficient is better with a logarithm fit. The first observations of early/slow events in daylight propagation are presented. Initial results on early/fast events with unusually long recoveries (?5 min) and strong perturbations (?1 dB) indicate that they are mainly observed on the transmissions from NPM and NLK in the nighttime only, with rare occurrence on other transmissions. Such unusually long recovery of early/fast events may be associated with large ionic conductivity perturbations associated with gigantic jets.

Kumar, Sushil; Kumar, Abhikesh

2013-01-01

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Observations of relativistic electron microbursts in association with VLF chorus  

Science.gov (United States)

The Solar, Anomalous and Magnetospheric Particle Explorer (SAMPEX) satellite frequently observes relativistic (>1 MeV) electron precipitation in the radiation belts at L shells of 4-6 with bursty temporal structure lasting MeV energies do not satisfy the first-order cyclotron resonance condition with chorus wave frequencies at the equator. However, MeV electrons may interact with chorus through higher-order resonances or off-equatorial interactions.

Lorentzen, K. R.; Blake, J. B.; Inan, U. S.; Bortnik, J.

2001-04-01

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Detection of VLF and LF emissions of fluorescent light for efficient management of power consumption  

International Nuclear Information System (INIS)

In this research work, a detection probe of Very Low Frequency and Low Frequency (LF) emissions of fluorescent light is developed by using low cost loop antenna. The developed loop antenna is able to operate at VLF and LF bandwidth. The developed antenna is tested and measured with signal generator and oscilloscope in order to verify the usefulness of antenna. The developed antenna is subsequently used to detect the signal emitted by the fluorescent light. The antenna probe is located at different distance in order to obtain the peak voltage of received signal. Besides that, the fluorescent light is switch on and off respectively in order to verify the source of signal. From the oscilloscope, the received signal is operating at approximately 28 KHz. Hence, the developed antenna probe can be used for efficient management of power consumption as 28 KHz signal is detected if the light is on.

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Observation of beam-generated VLF hiss in a large laboratory plasma  

International Nuclear Information System (INIS)

The predicted instability of obliquely propagating whistler waves in a plasma penetrated by an electron beam is verified in a laboratory experiment. The observations support the model for the generation of auroral hiss and compare favorably with ground and satellite observations of VLF hiss. In contrast to the conventional small-diameter laboratory beam-plasma systems the present device is large in comparison to the characteristic whistler wavelength (lambdaapprox. =2-4 cm; beam and plasma diameter, 45 cm; length, 250 cm). Unstable whistlers can therefore propagate and grow oblique to the beam over many wavelengths before encountering the plasma boundaries. When a cold (1 eV), energetic (40 eV), low-density (n/sub b/approx. =108 cm-3) electron beam is injected along the magnetic field (B0=75G) into an initially cold (kT/sub e/approx. =1/4 eV), dense (n/sub e/approx. =1010 cm-3) background plasma, the spontaneous emission of broadband RF noise ranging from the lower hybrid frequency ?/sub l h/ to the electron cyclotron frequency ?/sub e/ is observed. By performing narrowband two-dimensional cross-correlation measurements between two small antennas the RF noise is identified from its dispersion characteristics ? (k) as whistler waves propagating near the oblique resonance angle theta=arccos (?/?/sub e/). The parallel phase velocity is close to the beam velocity (?/k9 or approx. =upsilon/sub b/). Although the iox. =upsilon/sub b/). Although the instability amplitude is far above the thermal noise level, it is not large enough to give rise to significant nonlinear effects. The instability saturates when the higher-frequency short-wavelength electrostatic instabiliy near the electron plasma frequency (s/sub p/2>>w/sub/ e/2) forms a plateau in the beam distribution. Time- and space-resolved electron pitch angle distribution function measurements are performed. The propagation of the whistlers out of the instability region and refraction into electromagnetic whistlers are observed

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Electron dispersion events in the morningside auroral zone and their relationship with VLF emissions  

International Nuclear Information System (INIS)

Energy/time dispersion events have been observed in the precipitating electron data in the energy range from 630 eV to 20 keV recorded by the J sensor on the low-altitude, polar-orbiting HILAT satellite. The dispersions are such that the higher-energy electrons are observed earlier in time than the lower-energy electrons The time interval for single dispersion event is from 1 to 2 s. Within an auroral pass in which such energy/time dispersion events are observed, there are typically several such events, and they can be spaced within the pass in either a periodic or aperiodic manner. The events are typically observed within and toward the equatorward edge of the region of diffuse auroral electron precipitation. During a given pass the events can be observed over a wide range of L shells. The occurrence of these events maximizes in the interval 0600-1,200 hours MLT. The energy/time dispersion is generally consistent with the electrons originating from a common source. The events are seen at L shells from 3.7 to greater than 15. The source distance for the electrons is inferred to be generally beyond the equator for events at L shells less than approximately 8 and before the equator for events at higher L shells. Because of the low energies at which the dispersions are observed, it is unlikely that their occurrence can be explained by resonant interaction with VLF waves. Based on circumstantial evidence from other reported observations common to the morning sector, and aations common to the morning sector, and alternative theoretical explanation is presented. According to this model the dispersion events result from impulsive interactions of the electrons with intense, asymmetric packets of VLF waves via the nonlinear, ponderomotive force

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Characteristic of Tweek Atmospherics Observed in Mid-latitude using AWESOME VLF Receiver  

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Full Text Available This study presents the analysis of tweek atmospherics received by AWESOME VLF receiver at station of Gakona (62.71°N, 143.99°W during four months observation from January to April 2011. Tweek which originates from lightning discharge are used to monitor the nighttime D-region ionosphere using the fundamental cut-off frequency to measure the variations of the lower ionosphere’s reflection height, the equivalent electron density at the reflection height and the propagation distance travel by tweeks. In this study, a total of 1316 tweeks are analyzed and from the analysis, it shows that equinox’s season has the highest tweek occurrence compared to winter season in March and April. The maximum harmonic (m of t weeks is found to be up to fourth ( m = 4 and tweeks with mode number one (m = 1 are more dominantly occurred. Our observations indicate that the equivalent electron densities for tweeks varies from 22-27 eL/cm3 in the altitude ranged of 75 to 91 km and demonstrate that these ELF/VLF signals travel considerable distances up to 6700 km from the causative lightning discharges. The ionospheric parameters for three locations (high, middle and low latitude respectively were compared and the results show that they are almost consistent for all the locations.

Norbayah Yusop

2014-03-01

49

Nonlinear wave-wave interactions in the subauroral ionosphere on the basis of ISIS-2 satellite observations of Siple station VLF signals  

Science.gov (United States)

Nonlinear wave-wave interaction between signals from a ground-based VLF transmitter and narrow-band ELF emissions in the subauroral ionosphere is studied by means of the bispectrum and bicoherence analysis. A bicoherence analysis has indicated that the sideband structures around the Siple transmitter signal received onboard the ISIS satellite are due to the nonlinear interaction between the Siple VLF signal and the pre-existing ELF emission.

Ohnami, S.; Hayakawa, M.; Bell, T. F.; Ondoh, T.

1993-01-01

50

Nighttime D region electron density profiles and variabilities inferred from broadband measurements using VLF radio emissions from lightning  

Science.gov (United States)

Lightning discharges radiate most of their electromagnetic energy in the very low frequency (VLF, 3-30 kHz) and extremely low frequency (ELF, 3-3000 Hz) bands and are, consequently, an effective tool for remotely sensing the nighttime ionospheric D region electron density profile. Using broadband lightning-generated VLF signals, we derived the night-to-night variations of the midlatitude ionospheric D region electron density profiles. For 16 nights, between 1 July and 4 August 2004, we examined measured VLF data from lightning occurring near the United States east coast (˜530-860 km away from Duke University) and received at Duke University from 0400 to 0600 UT. From these observed VLF radio atmospherics (sferics), we extracted the nighttime D region electron density profiles covering the range of electron densities from 100 to 103 cm-3, in the altitude range of approximately 70-95 km, using a two-dimensional, laterally homogenous model of VLF propagation in the Earth-ionosphere waveguide. The inferred electron density profile variabilities were in good agreement with those from past nighttime rocket experiments at similar latitudes. Using the rocket-measured profiles in our propagation simulations, we determined that the two-parameter exponential D region electron density profiles we inferred were the best exponential fit, in the electron density range of ˜3 to ˜500 cm-3, to the rocket-measured D region electron density profiles. In an initial effort to determine the sources of the observed variabilities, we compared the SAMPEX precipitating electron measurements to the electron density profiles inferred during July 2000. The results indicate that high-energy electron precipitation might account for at least part of the night-to-night variations of the D region electron densities at the midlatitudes.

Cheng, Zhenggang; Cummer, Steven A.; Baker, Daniel N.; Kanekal, Shrikanth G.

2006-05-01

51

Propagation characteristics of VLF hiss observed at low latitude ground stations  

International Nuclear Information System (INIS)

Propagation characteristics of VLF hiss observed at the low latitude ground stations of Moshiri (Geomag. lat. 34.30N) and Hiraiso (Geomag. Lat. 26.20N) in Japan during quiet and disturbed days are discussed in the light of both the ducted and nonducted modes of propagation. The ducted propagation is studied by computing the enhancement factors at different altitudes along the field lines where the hiss is likely to be generated, whereas the nonducted propagation is studied by making use of ray tracing computations. It is shown that the storm-time hiss, generated at small wave normal angles (wave normal below the field line) can propagate to low latitude ground stations in the nonducted mode of propagation under the influence of negative latitudinal gradients of ionization, whereas the quiet-time hiss, generated at relatively large wave normal angles, can propagate in the normal nonducted mode of propagation

52

Whistler-triggered emissions observed by ISIS satellites  

Science.gov (United States)

A statistical examination has been conducted of the ducted and nonducted whistler-triggered emissions (WTEs) observed by the ISIS satellites in the 1979-1981 period. Most WTEs are observed with simultaneous lower hybrid resonance in the topside ionosphere. The VLF emissions triggered by ducted whistlers frequently occur at L of 2-3, while those triggered by nonducted whistlers occur in the wider latitudinal regions at L of 2.2-4.3.

Nakamura, Y.; Ondoh, T.

1989-01-01

53

Whistler-triggered emissions observed by ISIS satellites  

International Nuclear Information System (INIS)

VLF emissions triggered by whistlers are often observed at middle and high latitudes in the topside ionosphere by ISIS satellites. Most of them are so-called LHR emissions lasting for a few seconds. Latitudinal distributions of the occurrence rate for the whistler-triggered emissions in the topside ionosphere have been obtained by using VLF electric field data received from the ISIS 1 and 2 satellites at Kashima station, Communications Research Laboratory, Japan. These VLF emissions are classified into two groups according to the type of whistlers, i.e., ducted whistlers with a continuous trace over the full frequency range of the spectrum and nonducted whistlers without a complete trace below fLHR. The latitudinal distribution of the occurrence rate for emissions triggered by ducted whistlers is considerably different from that for emissions triggered by nonducted whistlers, especially at high latitudes. The occurrence rate for the emissions by nonducted whistlers is distributed rather randomly in latitude between L = 2.0 and L = 4.2. The occurrence rate for emissions by ducted whistlers increases with latitudes between L = 1.5 and L = 2.9, and it attains a maximum of 0.33 at L = 2.7. It then abruptly drops to 0.1 at L = 3.0, and it remains below 0.1 between L = 3.0 and L = 4.0. The decrease of the occurrence rate for emissions by ducted whistlers at L = 3.0 seems to be caused by the decrease of the radiation belt electron flux near the slot region. These electron flux near the slot region. These results suggest that the VLF emissions triggered by ducted whistlers in the topside ionosphere are generated by the cyclotron resonant interaction of ducted whistlers with the magnetospheric electrons near the geomagnetic equatorial plane

54

Electron and VLF travel time differences for wave-particle interactions at L=4: Pt. 2  

International Nuclear Information System (INIS)

The cyclotron resonance or gyroresonance interaction has been widely invoked as a generation mechanism for discrete VLF emissions and plasmaspheric hiss. This interaction involves electrons and VLF waves travelling in opposite directions along a geomagnetic field line. We examine, for an interaction region in the equatorial plane at L=4, the energy of the resonant electrons as a function of VLF wave frequency and ambient equatorial electron density. Then for two different spatial configurations of the interaction and two standard plasma distribution models we examine the difference in travel times to a ground-based observer in the Southern hemisphere for the electrons and waves taking part in the interaction. This difference in travel times is shown as a function of VLF wave frequency and equatorial electron density. The results, and their significance for observations of auroral electrons and VLF at Sanae, Antarctica, are discussed and compared with similar results for the Cerenkov interaction discussed in an earlier paper

55

Spectral broadening of VLF transmitter signals and sideband structure observed on Aureol 3 satellite at middle latitudes  

International Nuclear Information System (INIS)

Electric and magnetic field wave data acquired on Aureol 3 satellite demonstrate the existence of a spectral broadening effect in which VLF transmitter signals from Alpha station (geographic coordinates, 50.5 degree N, 137 degree E) in USSR undergo a significant spectral broadening on electric fields as they propagate through the ionosphere up to the spacecraft in the altitude range of 500-2,000 km at middle latitudes (L ? 2). The spectral broadening phenomena may be divided into two types: (1) spectrally broadened components occurring without any association with ELF/VLF emissions under disturbed ionospheric conditions and (2) spectrally broadened components with predominant sideband structure in association with ELF emissions. Bicoherence computation results suggest a nonlinear mode coupling between the transmitter signal and ELF emission which produces sidebands that are quasi-electrostatic in nature. However, faint spectral broadened components in both types 1 and 2 may be connected with Doppler shift of quasi-electrostatic whistler mode waves with a broad spectrum of k near the resonance cone, due to scattering of the transmitter signals from ionospheric irregularities in the F region

56

Spectral broadening of VLF transmitter signals and sideband structure observed on Aureol 3 satellite at middle latitudes  

Energy Technology Data Exchange (ETDEWEB)

Electric and magnetic field wave data acquired on Aureol 3 satellite demonstrate the existence of a spectral broadening effect in which VLF transmitter signals from Alpha station (geographic coordinates, 50.5{degree}N, 137{degree}E) in USSR undergo a significant spectral broadening on electric fields as they propagate through the ionosphere up to the spacecraft in the altitude range of 500-2,000 km at middle latitudes (L {approximately} 2). The spectral broadening phenomena may be divided into two types: (1) spectrally broadened components occurring without any association with ELF/VLF emissions under disturbed ionospheric conditions and (2) spectrally broadened components with predominant sideband structure in association with ELF emissions. Bicoherence computation results suggest a nonlinear mode coupling between the transmitter signal and ELF emission which produces sidebands that are quasi-electrostatic in nature. However, faint spectral broadened components in both types 1 and 2 may be connected with Doppler shift of quasi-electrostatic whistler mode waves with a broad spectrum of k near the resonance cone, due to scattering of the transmitter signals from ionospheric irregularities in the F region.

Tanaka, Y.; Hayakawa, M. (Nagoya Univ., Aichi (Japan)); Lagoutte, D.; Lefeuvre, F. (Centre National de la Recherche Scientifique, Orleans (France)); Tajima, S. (Nagoya Univ., Aichi (Japan) Nippon Gakki Company Ltd., Hamamatsu (Japan))

1987-07-01

57

VLF emissions from a modulated electron beam in the auroral ionosphere  

International Nuclear Information System (INIS)

A discrete VLF frequency of 3 kHz was successfully radiated by a modulated electron beam on a rocket launched into an active aurora. Instrumentation on this flight included a programable electron accelerator on the aft section with various particle and field detectors on the aft sections as well as the ejected forward payload. The accelerator programmer included a current modulation period at fixed electron energy for 0.45-s duration approximately every 11 s throughout the flight. In each of these program steps, 4-kV electrons are current modulated at a 3-kHz rate between I/sub min/ = 0 or 10 mA and I/sub max/approx. =80 mA. The forward payload, which was ejected at about 10 m/s, included a pair of spherical double probes seperated by 2.75 m and connected to a VLF receiver operating between 30 Hz and 18 kHz. Both this broadband receiver output as well as various narrow band channel outputs were directly telemetered to ground. Post flight spectrum analysis of the broadband VLF data clearly indicates that signals during the 3-kHz accelerator modulation periods were propagated to the forward payload. A detailed analysis of these modulated pulses detected by the VLF receiver is presented. A time-delay analysis between the start of the modulation and detection at the forward payload indicates time delays up to 0.2 s. The electron beam is believed to have produced a beam-plasma discharge making a radiation efficiency calculation difficult. However, absolute received signal ficult. However, absolute received signal strength was about 1 mV/m at 1.4-km separation

58

Possible Seismic Influence on VLF Wave Intensity: Observations by a Low-Altitude Satellite.  

Czech Academy of Sciences Publication Activity Database

Vol. 2. Praha : MATFYZPRESS, Praha, 2008 - (Šafranková, J.; Pavl?, J.), s. 168-171 ISBN 978-80-7378-066-1. [Week of Doctoral Students 2008 /17./. Prague (CZ), 03.06.2008-06.06.2008] R&D Projects: GA ?R GA205/06/1267 Grant ostatní: CNRS/DREI(FR) PICS-3725 Institutional research plan: CEZ:AV0Z30420517 Keywords : seismo-electromagnetic effects * VLF electromagnetic waves * DEMETER Subject RIV: BL - Plasma and Gas Discharge Physics http://oberon.troja.mff.cuni.cz/~nemef1am/work/articles/08wds.pdf

N?mec, František; Santolík, Ond?ej; Parrot, M.

59

Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from preseismic activity.  

Czech Academy of Sciences Publication Activity Database

Ro?. 118, ?. 8 (2013), s. 5286-5295. ISSN 2169-9380 R&D Projects: GA ?R(CZ) GAP209/11/2280; GA ?R GA205/09/1253 Grant ostatní: European Community Seventh Framework Programme (FP7/2007-2013),(XE) 262005; AV ?R(CZ) M100431206. Institutional support: RVO:68378289 Keywords : DEMETER * VLF waves * preseismic activity * Earth-ionosphere waveguide Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 3.440, year: 2013 http://onlinelibrary.wiley.com/doi/10.1002/jgra.50469/abstract

Píša, David; N?mec, F.; Santolík, Ond?ej; Parrot, M.; Rycroft, M.

2013-01-01

60

Lightning characteristics observed by a VLF/LF lightning detection network (LINET in Brazil, Australia, Africa and Germany  

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Full Text Available This paper describes lightning characteristics as obtained in four sets of lightning measurements during recent field campaigns in different parts of the world from mid-latitudes to the tropics by the novel VLF/LF (very low frequency/low frequency lightning detection network (LINET. The paper gives a general overview on the approach, and a synopsis of the statistical results for the observation periods as a whole and for one special day in each region. The focus is on the characteristics of lightning which can specifically be observed by this system like intra-cloud and cloud-to-ground stroke statistics, vertical distributions of intra-cloud strokes or peak current distributions. Some conclusions regarding lightning produced NOx are also presented as this was one of the aims of the tropical field campaigns TROCCINOX (Tropical Convection, Cirrus and Nitrogen Oxides Experiment and TroCCiBras (Tropical Convection and Cirrus Experiment Brazil in Brazil during January/February 2005, SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere and TWP-ICE (Tropical Warm Pool – International Cloud Experiment during November/December 2005 and January/February 2006, respectively, in the Darwin area in N-Australia, and of AMMA (African Monsoon Multidisciplinary Analyses in W-Africa during June–November 2006.

Regional and temporal characteristics of lightning are found to be dependent on orographic effects (e.g. S-Germany, Brazil, Benin, land-sea breeze circulations (N-Australia and especially the evolution of the monsoons (Benin, N-Australia. Large intra-seasonal variability in lightning occurrence was found for the Australian monsoon between the strong convection during build-up and break phases and the weak wet monsoon phase with only minor lightning activity. Total daily lightning rates can be of comparable intensity in all regions with the heaviest events found in Germany and N-Australia. The frequency of occurrence of such days was by far the largest in N-Australia. In accordance with radar observed storm structures, the intra-cloud stroke mean emission heights were found distinctly different in Germany (8 km as compared to the tropics (up to 12 km in N-Australia. The fraction of intra-cloud strokes (compared to all strokes was found to be relatively high in Brazil and Australia (0.83 and 0.74, respectively as compared to Benin and Germany (0.67 and 0.69, respectively.

Using stroke peak currents and vertical location information, lightning NOx (LNOx production under defined standard conditions can be compared for the different areas of observation. LNOx production per standard stroke was found to be most efficient for the N-Australian and S-German thunderstorms whereas the yield from Brazilian and W-African strokes was nearly 40% less. On the other hand, the main NO contribution in Brazil was from intra-cloud (IC strokes whereas in Benin it was due to cloud-to-ground (CG components. For the German and Australian strokes both stroke types contributed similar amounts to the total NO outcome.

H. Höller

2009-03-01

61

Lightning characteristics observed by a VLF/LF lightning detection network (LINET in Brazil, Australia, Africa and Germany  

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Full Text Available This paper describes lightning characteristics as obtained in four sets of lightning measurements during recent field campaigns in different parts of the world from mid-latitudes to the tropics by the novel VLF/LF (very low frequency/low frequency lightning detection network (LINET. The paper gives a general overview on the approach, and a synopsis of the statistical results for the observation periods as a whole and for one special day in each region. The focus is on the characteristics of lightning which can specifically be observed by this system like intra-cloud and cloud-to-ground stroke statistics, vertical distributions of intra-cloud strokes or peak current distributions. Some conclusions regarding lightning produced NOx are also presented as this was one of the aims of the tropical field campaigns TROCCINOX (Tropical Convection, Cirrus and Nitrogen Oxides Experiment and TroCCiBras (Tropical Convection and Cirrus Experiment Brazil in Brazil during January/February 2005, SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere and TWP-ICE (Tropical Warm Pool-International Cloud Experiment during November/December 2005 and January/February 2006, respectively, in the Darwin area in N-Australia, and of AMMA (African Monsoon Multidisciplinary Analyses in W-Africa during June–November 2006.

Regional and temporal characteristics of lightning are found to be dependent on orographic effects (e.g. S-Germany, Brazil, Benin, land-sea breeze circulations (N-Australia and especially the evolution of the monsoons (Benin, N-Australia. Large intra-seasonal variability in lightning occurrence was found for the Australian monsoon between the strong convection during build-up and break phases and the weak active monsoon phase with only minor lightning activity. Total daily lightning stroke rates can be of comparable intensity in all regions with the heaviest events found in Germany and N-Australia. The frequency of occurrence of such days was by far the largest in N-Australia. In accordance with radar observed storm structures, the intra-cloud stroke mean emission heights were found distinctly different in Germany (8 km as compared to the tropics (up to 12 km in N-Australia. The fraction of intra-cloud strokes (compared to all strokes was found to be relatively high in Brazil and Australia (0.83 and 0.82, respectively as compared to Benin and Germany (0.64 and 0.69, respectively.

Using stroke peak currents and vertical location information, lightning NOx (LNOx production under defined standard conditions can be compared for the different areas of observation. LNOx production per standard stroke was found to be most efficient for the N-Australian and S-German thunderstorms whereas the yield from Brazilian and W-African strokes was nearly 40% less. On the other hand, the main NO contribution in Brazil was from intra-cloud (IC strokes whereas in Benin it was due to cloud-to-ground (CG components. For the German and Australian strokes both stroke types contributed similar amounts to the total NO outcome.

H. Höller

2009-10-01

62

Solar cycle and seasonal variation of plasma mass density inferred from ULF and VLF observations at low latitudes  

International Nuclear Information System (INIS)

Complete text of publication follows. ULF and VLF diagnosis of the magnetosphere plasma are both well established techniques that went through a great progress in the last decades. While the VLF diagnostic method was developed and applied even before the IGY, ground-based and satellite magnetometer records have been used to monitor the geomagnetic field line resonance (FLR) frequencies and hereby the plasma mass density (PMD) in the magnetosphere since the early 1990's. Now we have sufficiently long FLR observations to study its solar cycle dependence. FLR observations using the gradient-method started in Hungary (at L?1.9) in 1996, and have been more regular since 2000. The plasmaspheric equatorial electron density data were obtained by using whistler data recorded at Tihany (Hungary, L=1.8) since early 2002. The whistlers were analysed by a new whistler inversion method using a recent experimental filed aligned density distribution. The variation of noontime equatorial PMD shows clear solar cycle dependence with higher densities for higher sunspot numbers. In addition, a clear seasonal variation with a winter peak can also be observed, which is stronger during years near sunspot maximum. Similar solar cycle dependence of plasmaspheric equatorial electron densities were identified earlier from mid-latitude (L=2.5) whistler as well as from plasmaspheric altitude (?2000 km) satellite (e.g. Akebono) measurements. This behaviour was built in the plasmasphere models (was built in the plasmasphere models (e.g. IRI, FLIP). The seasonal variation, however, seems to be dependent on latitude and maybe even on longitude. While at L=2.5 (?110 deg W) Park (1978) reported an annual and a semiannual variation, the latter cannot be identified in our plasma mass density observations at L=1.9 (?18 deg E). Our PMD estimations were compared to F2 layer electron density (Juliusruh) and a strong correlation was found. This correlation is thought to be maintained by the ambipolar diffusion of plasma along the field lines. The solar cycle and seasonal variation of the F2 layer density, including the 'winter anomaly' is a well-described and partially understood phenomenon (e.g Zou et al, 2000). Our results support that FLR frequencies at low (and mid) latitudes are highly influenced by F2 region dynamics. An interhemispheric comparison (ULF data from HER, South Africa at L?1.8) of the FLR based PMD monitoring was also carried out. The inferred values and general trends were similar as expected, since in both cases the equatorial density of the same L-shell was estimated. During the investigated interval the F2 region was, however, highly asymmetric, the equatorial PMD correlates with the F2 electron density at the northern footpoint, but not with that at the southern footpoint.

63

Dependence of Characteristics of SURA Induced Artificial ULF/VLF Signals on Geomagnetic Activity  

Science.gov (United States)

A comprehensive study of artificial ionospheric signal generation in the ULF/VLF bands at SURA facility in Russia was conducted during the past 4 years. We investigated the influence of geomagnetic activity on the characteristics of artificial low-frequency signals under the background of increasing solar activity. No correlation of artificial ULF signals with variations of Earth's magnetic field was observed for weak geomagnetic disturbances (Kp ? 3) while the VLF signals increased in the growth phase of the geomagnetic perturbation. In case of strong magnetic storm (Kp ? 5+) a tendency of the amplitude of the ULF/VLF signals decrease with increasing magnetic disturbance was observed. Sometimes, the modulation of artificial ULF signals with a period of 15-30 s was detected in the decay phase of magnetic storms. During storm time, a change in the polarization of artificial VLF emissions was detected. The right polarization becomes predominant. Interpretation of observed peculiarities of artificial VLF signals is given in the context of the physical mechanism of ionospheric current drive by RF pumping.

Kotik, D. S.; Ryabov, A. V.; Ermakova, E. N.; Pershin, A. V.

2015-04-01

64

Study of solar flare induced D-region ionosphere changes using VLF amplitude observations at a low latitude site  

Science.gov (United States)

About 26 solar flare events from C2.56 to X3.2 classes were obtained and analyzed at Tay Nguyen University, Vietnam (12.56°N, 108.02°E) during May - December 2013 using very low frequency remote sensing to understand the responses of low latitude D-region ionosphere during solar flares. The observed VLF amplitude perturbations are used as the input parameters for the simulated Long Wavelength Propagation Capability (LWPC) program, using Wait's model of lower ionosphere, to calculate two Wait's parameters, viz. the reflection height (H') and the sharpness factor (?). The results reveal that when X-ray irradiance is increased, ? increased from 0.3 to 0.506 km-1, while H' decreased from 74 to 60 km. The electron density increased at the height of 74 km with 1-3 orders of magnitude during solar flares. These phenomena can be explained as: the ionization due to X-ray irradiance becomes greater than that due to cosmic rays and Lyman-? radiation, which increases the electron density profile. The present results are in agreement with the earlier results. The 3D representation of the electron density changes with altitude and time supports to fully understand the shape of the electron density changes due to X-ray flares. The shape variation of electron density is roughly followed to the variation of the amplitude perturbation and keeps this rule for different altitudes. It is also found that the electron density versus the height in lower latitude D-region ionosphere increases more rapidly during solar flares.

Tan, L. M.; Thu, N. N.; Ha, T. Q.; Marbouti, M.

2014-06-01

65

Longitudinal drift of substorm electrons as the reason of impulsive precipitation events and VLF emissions  

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Full Text Available Using the data from satellite CRRES and three geostationary LANL spacecraft, the propagation of an electron cloud from midnight to the evening sector is investigated. An electron cloud was injected during a weak isolated substorm that developed on a quiet geomagnetic background. It is found that within the local time sector from 03:00 until at least 08:00 MLT, the propagation of electrons at perpendicular pitch-angles is well described by a simple model of drift in the dipole magnetic field. The flux levels in the field-aligned electrons increase simultaneously with the flux at perpendicular pitch angles, which is attributed to the pitch angle diffusion by the whistler mode. This pitch-angle diffusion leads to precipitation of electrons from a drifting cloud and an increase in the ionospheric electron density, simultaneously observed above Tromsø, Norway, by the EISCAT UHF radar in the morning sector (04:40–05:25 MLT. The precipitation develops as quasi-periodic pulses with a period of about 100 s. We discuss the models of pulsating precipitation due to the whistler cyclotron instability and show that our observations can be explained by such a model.

A. A. Lubchich

2006-10-01

66

Simultaneous observations of VLF ground transmitter signals on the DE 1 and COSMOC 1809 satellites: Detection of a magnetospheric caustic and a duct  

Science.gov (United States)

Khabarovsk transmitter signals (15.0 kHz, 48 deg N, 135 deg E) were observed on the high-altitude (approximately 15000 km) Dynamic Explorer 1 (DE 1) and the low-altitude (approximately 960) km COSMOS 1809 satellites during a 9-day period in August 1989. On 7 out of 9 days the linear wave receiver (LWR) on the DE 1 satellite also detected signals from the Alpha transmitter (11.9-15.6 kHz) in Russia and an Omega transmitter (10.2-13.6 kHz) in Australia, as well as natural VLF emissions such as hiss, chorus, whistlers, and wideband impulsive signals. On two days, August 23 and 27, 1989, observations of the Khabarovsk transmitter signals were simultaneously carried out at high altitude on thre DE 1 satellite and at low altitude on the COSMOS 1809 satellite. Analysis of data from these 2 days has led to several new results on the propagation of whistler mode signals in the Earth's magnetosphere. New evidence was found of previously reported propagation phenomena, such as (1) confinement of transmitter signals in the conjugate hemisphere at ionospheric heights (approximately 1000 km), (2) observation of direct multipath propagation on both DE 1 and COSMOS 1809, (3) detection of ionospheric irregularities of is less than or equal to 100 km scale size with a few percent enhancement in electron density. We also report the first direct detection of a magnetospheric dust at L = 2.94 which was believed to be responsible for the ducted propagation of Khabarovsk signals observed in the COSMOS 1809 satellite. Our study also indicates that duct end points can extend down to at least approximately 1000 km. The peak electric and magnetic fields of ducted Khabarovsk transmitter signals at approximately 1000 km were 520 micro V/m and 36 pT respectively. Estimated field strengths of these signals inside the dust at the geomagnetic equator were 57 micro V/m and 12 pT for electric and magnetic field respectively. The results of two-dimensional ray tracing simulations were consistent with the observations of the nonducted whistler-mode propagation of Khabarovsk (15 kHz) and Alpha (11.9 kHz) signals from the transmitter location to the DE 1 and COSMOS 1809 satellites. Our results have direct implications for the question of accessibility of waves injected from the ground to various regions of the ionosphere and the magnetosphere.

Chmyrev, V. M.; Sobolev, Ya. P.; Ovcharenko, O. Ya.; Selegej, V.

1994-09-01

67

ELF/VLF signatures of sprite-producing lightning discharges observed during the 2005 EuroSprite campaign  

International Nuclear Information System (INIS)

Complete text of publication follows. During the summer of 2005, transient luminous events were optically imaged from the French Pyrenees as part of the EuroSprite campaign. Simultaneously, ELF (Extremely Low Frequency: 3-3000Hz) and broadband VLF (Very Low Frequency: 3-30 kHz) data were recorded continuously at two separate receivers in Israel, located about 3300 km from the area of the parent lightning discharges responsible for the generation of sprites. Additionally, narrowband VLF data were collected in Crete, at about 2300 km away from the region of sprites. The motivation for the present study was to identify the signature of the sprite-producing lightning discharges in the ELF and VLF electromagnetic frequency bands, to qualify and compare their parameters, and to study the influence of the thunderstorm activated region on its overlaying ionosphere. For the 15 sprites analyzed, their causative positive cloud-to-ground (+CG) discharges had peak current intensities between +8 and +130 kA whereas their charge moment changes (CMC) ranged from 500 to 3500 C · km. Furthermore, the peak current reported by the Meteorage lightning network are well correlated with the amplitudes of the VLF bursts, while showing poor correlation with the CMCs which were estimated using ELF methods. Additionally, more than one +CG was associated with 6 of the sprites, implying that lightning discharges that produce sprites can sometimes have multiple ground connections separated in timeiple ground connections separated in time and space. Finally, for a significant number of events (33%) an ELF transient was not associated with sprite occurrence, suggesting that long continuing current of tens of msec may not always be a necessary condition for sprite production, a finding which influences the estimation of the global sprite rate based on Schumann Resonance (SR) measurements.

68

ELF/VLF signatures of sprite-producing lightning discharges observed during the 2005 EuroSprite campaign  

Science.gov (United States)

During the summer of 2005, transient luminous events were optically imaged from the French Pyrénées as part of the EuroSprite campaign. Simultaneously, extremely low frequency (ELF: 3-3000 Hz) and broadband very low frequency (VLF: 3-30 kHz) data were recorded continuously at two separate receivers in Israel, located about 3300 km from the area of the parent lightning discharges responsible for the generation of sprites. Additionally, narrowband VLF data were collected in Crete, at about 2300 km away from the region of sprites. The motivation for the present study was to identify the signature of the sprite-producing lightning discharges in the ELF and VLF electromagnetic frequency bands, to qualify and compare their parameters, and to study the influence of the thunderstorm-activated region on its overlaying ionosphere. For the 15 sprites analyzed, their causative positive cloud-to-ground (+CG) discharges had peak current intensities between +8 and +130 kA whereas their charge moment changes (CMC) ranged from 500 to 3500 C km. Furthermore, the peak current reported by the Météorage lightning network are well correlated with the amplitudes of the VLF bursts, while showing poor correlation with the CMCs which were estimated using ELF methods. Additionally, more than one +CG was associated with six of the sprites, implying that lightning discharges that produce sprites can sometimes have multiple ground connections separated in time and space. Finally, for a significant number of events (33%) an ELF transient was not associated with sprite occurrence, suggesting that long continuing current of tens of ms may not always be a necessary condition for sprite production, a finding which influences the estimation of the global sprite rate based on Schumann resonance (SR) measurements.

Greenberg, E.; Price, C.; Yair, Y.; Haldoupis, C.; Chanrion, O.; Neubert, T.

2009-08-01

69

ELF/VLF signatures of sprite-producing lightning discharges observed during the 2005 EuroSprite campaign  

DEFF Research Database (Denmark)

During the summer of 2005, transient luminous events were optically imaged from the French Pyrénées as part of the EuroSprite campaign. Simultaneously, extremely low frequency (ELF: 3–3000 Hz) and broadband very low frequency (VLF: 3–30 kHz) data were recorded continuously at two separate receivers in Israel, located about 3300 km from the area of the parent lightning discharges responsible for the generation of sprites. Additionally, narrowband VLF data were collected in Crete, at about 2300 km away from the region of sprites. The motivation for the present study was to identify the signature of the sprite-producing lightning discharges in the ELF and VLF electromagnetic frequency bands, to qualify and compare their parameters, and to study the influence of the thunderstorm-activated region on its overlaying ionosphere. For the 15 sprites analyzed, their causative positive cloud-to-ground (+CG) discharges had peak current intensities between +8 and +130 kA whereas their charge moment changes (CMC) ranged from 500 to 3500 C km. Furthermore, the peak current reported by the Météorage lightning network are well correlated with the amplitudes of the VLF bursts, while showing poor correlation with the CMCs which were estimated using ELF methods. Additionally, more than one +CG was associated with six of the sprites, implying that lightning discharges that produce sprites can sometimes have multiple ground connections separated in time and space. Finally, for a significant number of events (33%) an ELF transient was not associated with sprite occurrence, suggesting that long continuing current of tens of ms may not always be a necessary condition for sprite production, a finding which influences the estimation of the global sprite rate based on Schumann resonance (SR) measurements.

Greenberg, E.; Price, C.

2009-01-01

70

VLF lightning noise tracks the solar rotation  

Science.gov (United States)

Lightning is the major source of VLF radiation in the atmosphere. From long term measurements of natural VLF radiation, we have discovered that at frequencies close to the Earth-ionosphere cutoff frequency (~2 KHz), the VLF "noise" shows a clear 27-day periodicity. Furthermore, the 27-day modulation is detected only during daylight hours, implying that this is not the lightning activity itself that is changing, but rather the waveguide parameters, that are sensitive to changing solar radiation. Although this 27-day period is quite fundamental to our Sun, it is only partially observable via the typical solar parameters such as sun spot number, Lyman alpha radiation and 10.7cm radio flux. We propose that continuous monitoring of broadband VLF radio noise may provide a new method for monitoring changes in the solar rotation rate.

Reuveni, Yuval; Price, Colin

2010-05-01

71

VLF transmissions observed at anomalously high latitude above the ionosphere in the conjugate hemisphere  

Science.gov (United States)

It is shown that whereas the plasmapause can guide both the NAA and GBR signals, the efficiency of this guidance depends on the position of the plasmapause. The plasmapause must be situated sufficiently equatorwards so that half of the equatorial electron gyrofrequency at the plasmapause position is greater than (or approximately equal to) the transmitter signal frequency. Ray tracing calculations in a realistic magnetosphere model suggest that for the 16 kHz GBR signal, the efficiency of guiding falls off when the L-value of the plasmapause is greater than 3.0; the guiding effectively ceases when this L-value exceeds 3.5. Guidance of the plasmapause gives rise to a wave field at a higher latitude than for nonguided propagation. This, it is pointed out, will only occur when the position of the plasmapause after geomagnetic storms is at a sufficiently low L-value. This is consistent with the experimental observations of anomalously high latitude signal reception following strong magnetic storms.

Denby, M.; Strangeways, H. J.; Bullough, K.

1984-01-01

72

Geographic distribution of lightning-induced electron pricipitation observed as VLF/LF perturbation events  

International Nuclear Information System (INIS)

Expected occurrence characteristics of lightning-induced electron precipitation (LEP) events at longitudes of the western (1100 W) versus eastern (710 W) Unted States are considered from the point of view of available trapped particle flux at the edge of the loss cone. Considered from the point of view of available trapped particle flux at the edge of the loss cone. Considering published data on nighttime fluxes of >68 keV electrons observed at L?2.5, and for ''direct'' precipitation into the northern hemisphere induced by northern hemisphere lightning, the occurrence rate and flux levels are expected to a factor of 20--200 higher in the west than in the east, assuming no significant variation in lightning source activity with longitude. Again assuming lightning sources in the north, it is predicted that at 710 W, ''mirrored'' precipitation into the southern hemisphere would involve precipitation fluxes 30--300 times higher than ''direct'' precipitation into the noerthern hemisphere. However, at 1100 W and again assuming lightning in the north, southern hemisphere precipitation would tend to be limited to that small fraction of particles that were initially scattered into the northern loss cone and that were then backscattered from the northern atmosphere so as to reach the south

73

Statistical analyses of spatial and time dependence of lightning whistlers observed by VLF/WBA onboard AKEBONO  

Science.gov (United States)

AKEBONO (EXOS-D) has been continuously operated for more than 24 years since 1989 to observe particles and plasma waves in the auroral region and the plasmasphere. It covers altitude region from 300 km to about 10,000 km with an inclination of 75 degree. Therefore, analyses of the data obtained by AKEBONO enable us to study how the magnetosphere varies depending on the local time, season and solar activity. The WBA (Wide Band Analyzer) is one of subsystems of the VLF instruments onboard AKEBONO. It measures one component of electric or magnetic analogue waveform at frequency band of 50 Hz - 15 kHz. Lightning whistler is one of typical waves frequently observed by the WBA. It is generated by lightning discharge and propagates along the geomagnetic field lines from northern to southern hemisphere and vice-versa. Their dispersions depend on their path length and electron density profile along their propagation path. We have been developed an automatic detection system of lightning whistlers from the spectrogram of the WBA receiver. In the present study, we statistically analyzed the data received at Uchinoura Space Center from 1989 to 2005, and got spatial and time distribution of lightning whistlers by the system. First, we found that lightning whistlers were mainly observed only inside the plasmasphere with L-value below 4. Next, we studied MLT (Magnetic Local Time) and seasonal dependences of occurrence frequency of the lightning whistlers. It is noted that the coverage of MLT and season of the AKEBONO orbit changes simultaneously, but we could successfully identified the MLT and seasonal dependences separately analyzing the long term observation data. Consequently lightning whistlers were mainly observed in the night-side (from 16 to 4 in MLT), while their occurrence frequency becomes quite small in the dayside (from 7 to 15 in MLT). Presumably this is caused by the condition of the ionosphere. In the dayside, it is difficult for whistler-mode wave to propagate into the plasmasphere but it can easily propagate in the night-side. About the seasonal dependence, we found two peaks of occurrence frequency of lightning whistlers. One is from December to January and another is from June to July. The source of lightning whistler is lightning discharge, whose occurrence frequency is known to become maximum in summer. Thus we can find two peaks of occurrence frequency which correspond to the lightning whistlers propagating from summer hemisphere to winter hemisphere. As a future work, we will study solar activity dependence of lightning whistlers. By normalizing the bias caused by MLT and seasonal dependences of lightning whistler based on the results derived in the present study, it is expected to clarify the solar activity dependence independent of the MLT and seasonal variation. It is also interesting to estimate the electron density profile using trends of whistler dispersion. The propagation time of whistler mode wave can be theoretically calculated using ray tracing technique under assumption of electron density profile model. By comparing the observed trends of dispersion along the AKEBONO trajectories with those theoretically derived, we can determine an appropriate electron density profile, and we can know the time variation of the electron density profile in the plasmasphere statistically.

Oike, Y.; Kasahara, Y.; Goto, Y.

2013-12-01

74

Ionospheric turbulence from ground-based and satellite VLF/LF transmitter signal observations for the Simushir earthquake (November 15, 2006  

Directory of Open Access Journals (Sweden)

Full Text Available

Signals from very low frequency (VLF/ low frequency (LF transmitters recorded on the ground station at Petropavlovsk-Kamchatsky and on board the French DEMETER satellite were analyzed for the Simushir earthquake (M 8.3; November 15, 2006. The period of analysis was from October 1, 2006, to January 31, 2007. The ground and satellite data were processed by a method based on the difference between the real signal at night-time and the model signal. The model for the ground observations was the monthly averaged signal amplitudes and phases, as calculated for the quiet days of every month. For the satellite data, a two-dimensional model of the signal distribution over the selected area was constructed. Preseismic effects were found several days before the earthquake, in both the ground and satellite observations.

 

Pier Francesco Biagi

2012-04-01

75

Optical Signatures of Ground-based VLF Transmitter-Induced Electron Precipitation from the Radiation Belts  

Science.gov (United States)

Ground-based VLF transmitters, although designed and built for long-range communication utilizing the efficient wave propagation in the Earth-ionosphere waveguide, nonetheless leak a small fraction of their radiated energy through the ionosphere and into the magnetosphere. The resulting whistler-mode waves propagate either obliquely or along field-aligned density enhancements known as ducts. In the equatorial region, these waves interact with 100—300 keV energetic electrons, which undergo pitch-angle and energy scattering through cyclotron resonance. Electrons near the bounce loss cone may be scattering into the loss cone, thus precipitating in the lower ionosphere at 60—100 km altitude in their subsequent half-bounce period. This precipitation creates significant ionization enhancements, which may be observed by subionospheric VLF probing techniques. Such observations have recently been reported but are still under debate, as direct VLF heating of the ionosphere may contribute to the measured signature. However, the ionization produced by these precipitating electrons will in turn produce optical emissions through excitation of the neutral atmospheric species, and it may be possible that these optical signatures will be observable. Currently experimental efforts are under way to detect this optical signature, which will not be produced by direct VLF heating, so that the measurement will constitute an unambiguous detection of VLF transmitter-induced precipitation. In this paper, we present model calculations that predict an observable optical signature. VLF waves are modeled using the Stanford ray-tracing program, and pitch-angle and energy scattering are calculated through cyclotron resonance. From the resulting precipitating flux, Monte Carlo model is next used to calculate the ionization profiles, as a function of altitude. Using known optical excitation rates, this ionization profile is then turned into optical emissions rates, and photons are propagated to a camera on the ground or a satellite location to find the expected Rayleigh brightness of the emitting region. Results show that the larger ground-based transmitters may produce observable optical emissions.

Marshall, R. A.; Inan, U. S.; Lehtinen, N. G.; Graf, K. L.; Bortnik, J.

2009-12-01

76

Variations of VLF/LF signals observed on the ground and satellite during a seismic activity in Japan region in May–June 2008  

Directory of Open Access Journals (Sweden)

Full Text Available Signals of two Japanese transmitters (22.2 kHz and 40 kHz recorded on the ground VLF/LF station in Petropavlovsk-Kamchatsky and on board the DEMETER French satellite have been analyzed during a seismic activity in Japan in May–June 2008. The period of analysis was from 18 April to 27 June. During this time two rather large earthquakes occurred in the north part of Honshu Island – 7 May (M=6.8 and 13 June (M=6.9. The ground and satellite data were processed by a method based on the difference between the real signal in nighttime and the model one. For ground observations a clear decrease in both signals has been found several days before the first earthquake. For the second earthquake anomalies were detected only in JJI signal. The epicenters of earthquakes were in reliable reception zone of 40 kHz signal on board the DEMETER. Signal enhancement above the seismic active region and significant signal intensity depletion in the magnetically conjugate area has been found for satellite observation before the first earthquake. Anomalies in satellite data coincide in time with those in the ground-based observation.

A. Rozhnoi

2010-03-01

77

Whistler-triggered VLF noise bursts observed on the DE-1 satellite and simultaneously at Antarctic ground stations  

Science.gov (United States)

Simultaneous observations of whistler-triggered very low-frequency noise bursts on the ground at Anarctic stations, Halley and Siple, and on the high-altitude satellite DE-1 are reported. Results of a case study from June 25, 1982 in which the satellite data were recorded near 25 deg south magnetic latitude and the L = 4.7 magnetic shell, are presented. Analysis indicates that the chorus bursts that are triggered in whistler ducts travel downwards in the ducts to low altitudes in the ionosphere, and that propagation to DE-1 is by upward reflection into a nonducted mode. A means of estimating the propagation characteristics of the wave bursts is provided by comparisons of nonducted signals from the Siple transmitter and discrete periodic emissions. The ducted-nonducted mode conversion process is a mechanism for the large-scale spreading into the magnetosphere of coherent whistler-mode wave energy which is generated, amplified, or triggered in small localized ducts. The DE-1 data show that a strong interaction exists between whistler-triggered noise bursts and prevailing hiss levels.

Smith, A. J.; Carpenter, D. L.; Inan, U. S.

1985-01-01

78

Low-mid latitude D region ionospheric perturbations associated with 22 July 2009 total solar eclipse: Wave-like signatures inferred from VLF observations  

Science.gov (United States)

We present first report on the periodic wave-like signatures (WLS) in the D region ionosphere during 22 July 2009 total solar eclipse using JJI, Japan, very low frequency (VLF) navigational transmitter signal (22.2 kHz) observations at stations, Allahabad, Varanasi and Nainital in Indian Sector, Busan in Korea, and Suva in Fiji. The signal amplitude increased on 22 July by about 6 and 7 dB at Allahabad and Varanasi and decreased by about 2.7, 3.5, and 0.5 dB at Nainital, Busan, and Suva, respectively, as compared to 24 July 2009 (normal day). The increase/decrease in the amplitude can be understood in terms of modal interference at the sites of modes converted at the discontinuity created by the eclipse intercepting the different transmitter-receiver great circle paths. The wavelet analysis shows the presence of WLS of period ~16-40 min at stations under total eclipse and of period ~30-80 min at stations under partial eclipse (~85-54% totality) with delay times between ~50 and 100 min at different stations. The intensity of WLS was maximum for paths in the partially eclipsed region and minimum in the fully eclipsed region. The features of WLS on eclipse day seem almost similar to WLS observed in the nighttime of normal days (e.g., 24 July 2009). The WLS could be generated by sudden cutoff of the photo-ionization creating nighttime like conditions in the D region ionosphere and solar eclipse induced gravity waves coming to ionosphere from below and above. The present observations shed additional light on the current understanding of gravity waves induced D region ionospheric perturbations.

Maurya, Ajeet K.; Phanikumar, D. V.; Singh, Rajesh; Kumar, Sushil; Veenadhari, B.; Kwak, Y.-S.; Kumar, Abhikesh; Singh, Abhay K.; Niranjan Kumar, K.

2014-10-01

79

Simultaneous observations of VLF ground transmitter signals on the DE 1 and COSMOS 1809 satellites: Detection of a magnetospheric caustic and a duct  

Science.gov (United States)

Khabarovsk transmitter signals (15.0 kHz, 48°N, 135°E) were observed on the high-altitude (~15000 km) Dynamic Explorer 1 (DE 1) and the low-altitude (~960) km COSMOS 1809 satellites during a 9-day period in August 1989. On 7 out of 9 days the linear wave receiver (LWR) on the DE 1 satellite detected signals from the Khabarovsk transmitter. In addition, the DE 1 satellite also detected signals from the Alpha transmitter (11.9-15.6 kHz) in Russia and an Omega transmitter (10.2-13.6 kHz) in Australia, as well as natural VLF emissins such as hiss, chorus, whistlers, and wideband impulsive signals. On two days, August 23 and 27, 1989, observations of the Khabarovsk transmitter signals were simultaneously carried out at high altitude on the DE 1 satellite and at low altitude on COSMOS 1809 satellite. Analysis of data from these 2 days has led to several new results on the propagation of whistler mode signals in the Earth's magnetosphere. New evidence was found of previously reported propagation phenomena, such as (1) confinement of transmitter signals in the conjugate hemisphere at ionospheric heights (~1000 km), (2) observation of direct multipath propagation on both DE 1 and COSMOS 1809, (3) detection of ionospheric irregularities of VLF ground transmitter signals injected into the magnetosphere; the location of the caustic surface depended on the signal frequency, and the electric and magnetic fields decreased by several hundred decibels per L shell in the dark (shadow) side of the caustic. We also report the first direct detection of a magnetospheric duct at L=2.94 which was believed to be responsible for the ducted propagation of Khabarovsk signals observed on the COSMOS 1809 satellite; the measured duct parameters were: ?L~0.06 and ?Ne~10-13%. The duct width at the equator was ~367 km. Our study also indicates that duct end points can extend down to at least ~1000 km. The peak electric and magnetic fields of ducted Khabarovsk transmitter signals at ~1000 km were 520 ?V/m and 36 pT respectively. Estimated field strengths of these signals inside the duct at the geomagnetic equator were 57 ?V/m and 12 pT for electric and magnetic field respectively. The results of two-dimensional ray tracing simulations were consistent with the observations of the nonducted whistler-mode propagation of Khabarovsk (15 kHz) and Alpha (11.9 kHz) signals from the transmitter location to the DE 1 and COSMOS 1809 satellites. Our results have direct implications for the question of accessibility of waves injected from the ground to various regions of the ionosphere and the magnetosphere. In situ measurements of electric and magnetic fields of Khabarovsk transmitter signals inside a duct may well prove to be the critical measurements needed to differentiate between the small signal and large signal theories of wave particle interactions.

Sonwalkar, V. S.; Inan, U. S.; Bell, T. F.; Helliwell, R. A.; Chmyrev, V. M.; Sobolev, Ya. P.; Ovcharenko, O. Ya.; Selegej, V.

1994-09-01

80

Observations of Jovian Synchrotron Emission  

Science.gov (United States)

On route to Saturn, the Cassini spacecraft flew past Jupiter and provided the first opportunity to observe the Jovian synchrotron radiation at a wavelength of 2.2 cm. Measurements were successfully carried out shortly after Jupiter closest approach using the radiometer subsystem of the Cassini Radar Instrument. The resulting data provide unique information on the highest energy electrons in Jupiter's magnetosphere. Earth-based radio telescopes have difficulty measuring the synchrotron radiation at wavelengths this short because of the difficulty in separating atmospheric thermal emission from the synchrotron radiation. The 2.2 cm Cassini radiometer was used to produce 20 maps covering two complete rotations of Jupiter in both horizontal and vertical linear polarization. Synchrotron emission was clearly detected distinct from the thermal emission as evidenced by its polarization and spatial distribution. A ground based campaign involving the VLA (operating at 20 and 90 cm) and the NASA Deep Space Network antennas (operating at 2.3, 8.5, 13.8 and 32 GHz) observed simultaneously with Cassini. The combined data set provides a complete picture of the electron energy spectrum and distribution in the Jovian inner radiation belts. Preliminary results from the observations and modeling efforts will be presented. The JPL contribution to this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Bolton, S. J.; Janssen, M.; Levin, S.; Sault, R.; Bastian, T.; Klein, M.; Gulkis, S.; Hofstadter, M.; Elachi, C.; Johnston, W.; Bunker, A.; Hamilton, G.; Liepack, O.; Roth, L.; West, R.; Dulk, G.; Leblanc, Y.; Thorne, R.; Roller, J.; McLeod, R.

2001-05-01

81

Ionospheric precursors of earthquakes recorded by VLF receiver at Tashkent IHY station  

Science.gov (United States)

Tashkent International Heliophysical Year (IHY) station is a member of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network being operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in Very Low Frequency (VLF) band. Regular monitoring of the D- and F-layers of ionosphere over Central Asia territory is being performed on the permanent basis starting year 2008. We have studied VLF amplitude anomalies related to the EQs occurred in 2008-2009 years with magnitude more than 5 on the path way from the VLF transmitters to the Tashkent station assuming that propagation of VLF ground-based transmitters signals can be perturbed by EQ preparation detectable from the ground-based measurements in the VLF bands. For analyzing narrowband data we have used the nighttime fluctuation (NF) method paying attention to the data obtained during the local nighttime (20:00 LT-04:00 LT) in Tashkent where the VLF receiver is operating. The mean nighttime amplitude (or trend) and nighttime fluctuation are found to increase significantly before the EQ occurred on the path way from the transmitters to the receiver. The obtained results have revealed an agreement with VLF amplitude anomalies observed in Tashkent VLF station during the strong EQs occurred on the path way from the transmitters to the receiver. Some results are presented to show the probing potentiality of VLF waves to predict short term EQs with high magnitude.

Tojiev, S. R.; Ahmedov, B. J.; Eshkuvatov, H. E.

2014-08-01

82

Detection of Magnetospherically Ducted VLF Signals Geomagnetically Conjugate to a Russian Alpha Transmitter at L=1.9  

Science.gov (United States)

The Russian 'Alpha' transmitters broadcast alternating pulses between 11-15 kHz for navigation. A fraction of the VLF energy escapes into the magnetosphere, is guided by ducts, amplified by interaction with radiation belt particles, and observed at the geomagnetic conjugate point. We analyze VLF data from Adelaide, Australia, conjugate to the Komsomolsk transmitter. An automated detection scheme separates the subionospheric and magnetospheric signals. We track availability of ducts at L=1.9 and find them present often. We connect the ground signal to the signal observed by the DEMETER spacecraft, which also observe triggered emissions and spectral broadening. We correlate to geomagnetic conditions to assess the role of wave growth and triggering from wave-particle interactions. We also find a strong diurnal variation in the magnetospheric signal, and apply a full-wave model of transionospheric propagation to include the effects of ionospheric absorption on both ends.

Cohen, M.; Golkowski, M.; Lehtinen, N. G.; Inan, U. S.; Parrot, M.

2011-12-01

83

VLF line radiation in the earth's magnetosphere and its association with power system radiation  

International Nuclear Information System (INIS)

In a recent experiment, discrete VLF emissions from the magnetosphere were triggered by a transmitter at Siple Station in Antarctica. Spectrograms of these signals as received at the conjugate point, Roberval, Quebec, showed changes in slope, entrainments, and cutoffs at frequencies (several kilohertz) close to the harmonic induction lines from the local 60-Hz power system. This observation led to the suggestion that harmonic radiation from the power system enters the magnetosphere and interacts with the triggered emissions. New evidence supporting this suggestion has been found in spectrograms of simultaneous recordings made at Roberval and at Siple Station in Antarctica. It is shown that line radiation, near harmonics of 60 Hz, travels along the earth's magnetic field in the whistler mode and is received in the conjugate hemisphere at Siple Station. Echoing of the line radiation between Siple and Roberval is often observed. The magnetospheric lines are usually shifted in frequency by 20--30 Hz with respect to the adjacent induction line, but their spacings are near 120 Hz. They may trigger and cut off emissions as do signals from VLF transmitters. Occasionally, magnetospheric lines are seen with spacings of only 20--30 Hz. This smaller frequency separation and the frequency shift of other lines spaced 120 Hz apart are related to the positive frequency offset of emissions triggered by VLF signals from the Omega navigation transmitters. Harmonic lines of reasonable amnsmitters. Harmonic lines of reasonable amplitude (approx.10-3 ?) are shown to enhance significantly the precipitation of 2-keV electrons over the eastern parts of the American continents near Lapprox.4. Some mid-latitude hiss bands appear to consist of sets of magnetospheric lines and their associated triggered emissions

84

Diurnal variation of VLF signals  

CERN Document Server

This paper presents an introduction to Chapman's theory of a production layer in the ionosphere relevant to the monitoring of VLF signals and Sudden Ionospheric Distubances (SIDs). It shows how the diurnal pattern of VLF signal strength can be derived, and how this pattern may be fitted to VLF signal strength measurements. It also shows through an example some of the possible problems for fitting this diurnal pattern (the fact that D-layer height cannot always be derived directly from measurements) and some of the advantages when a `fit' has been obtained (increased sensitivity of the instrument without any changes to hardware).

Kaye, Richard

2014-01-01

85

Propagation characteristics of omega signals and their triggered emissions observed by EXOS-D satellite  

International Nuclear Information System (INIS)

Omega signals have been frequently observed by the Japanese satellite EXOS-D (Akebono) in the magnetosphere. The authors have statistically analyzed VLF-WBA (wide-band analyzer) data in a period of 6 months, which were acquired by Kagoshima (KSC) and Prince Albert (PA) satellite tracking stations. About a quarter of the data obtained at KSC contain Omega signals from Australia and about a sixth of the data at PA contain those from North Dakota. Ray tracing calculations for the Australian Omega signals are consistent with the results of observations. 10 cases of triggered emissions are also found in the analyzed data. Amplitude and phase characteristics along an Omega pulse are investigated for the triggering event and an apparent phase lead, corresponding to a frequency increase by about 10 Hz was found at the center frequency of signals after the triggering starts

86

Propagation characteristics of omega signals and their triggered emissions observed by EXOS-D satellite  

Energy Technology Data Exchange (ETDEWEB)

Omega signals have been frequently observed by the Japanese satellite EXOS-D (Akebono) in the magnetosphere. The authors have statistically analyzed VLF-WBA (wide-band analyzer) data in a period of 6 months, which were acquired by Kagoshima (KSC) and Prince Albert (PA) satellite tracking stations. About a quarter of the data obtained at KSC contain Omega signals from Australia and about a sixth of the data at PA contain those from North Dakota. Ray tracing calculations for the Australian Omega signals are consistent with the results of observations. 10 cases of triggered emissions are also found in the analyzed data. Amplitude and phase characteristics along an Omega pulse are investigated for the triggering event and an apparent phase lead, corresponding to a frequency increase by about 10 Hz was found at the center frequency of signals after the triggering starts.

Sawada, Akira; Kishi, Youji; Yamamoto, Masayuki; Sakurai, Akihiro; Kasahara, Yoshiya; Kimura, Iwane (Kyoto Univ. (Japan))

1991-02-01

87

Ionospheric D region remote sensing using VLF radio atmospherics  

Science.gov (United States)

Lightning discharges radiate the bulk of their electromagnetic energy in the very low frequency (VLF, 3-30 kHz) and extremely low frequency (ELF, 3-3000 Hz) bands. This energy, contained in impulse-like signals called radio atmospherics or sferics, is guided for long distances by multiple reflections from the ground and lower ionosphere. This suggests that observed sferic waveforms radiated from lightning and received at long distances (>1000 km) from the source stroke contain information about the state of the ionosphere along the propagation path. The focus of this work is on the extraction of nighttime D region electron densities (in the altitude range of ˜70-95 km) from observed VLF sferics. In order to accurately interpret observed sferic characteristics, we develop a model of sferic propagation which is based on an existing frequency domain subionospheric VLF propagation code. The model shows that the spectral characteristics of VLF sferics depend primarily on the propagation path averaged ionospheric D region electron density profile, covering the range of electron densities from ˜100 to 103 cm-3. To infer the D region density from observed VLF sferics, we find the electron density profile that produces a modeled sferic spectrum that most closely matches an observed sferic spectrum. In most nighttime cases the quality of the agreement and the uncertainties involved allow the height of an exponentially varying electron density profile to be inferred with a precision of ˜0.2 km.

Cummer, S. A.; Inan, U. S.; Bell, T. F.

1998-11-01

88

Polars - multisite emission - multiwavelength observation  

CERN Document Server

We review the main observational characteristics of AM Herculis stars (polars) at X-ray, EUV, UV, IR and optical wavelengths. Particular emphasis is given to multi-epoch, multi-wavelength observations of the eclipsing polar HU Aqr (RX J2107.9-0518). In AM Herculis stars the broad-band spectral energy distribution from X-rays to the IR is governed by only very small structures: the hot accretion regions on the footpoints af accreting field lines. The most extended structures in the binary systems on the other hand, the mass-donating secondary stars and the accretion streams, distinctly appear only as Doppler-shifted emission or absorption lines. They can best be studied by investigating selected narrow spectral features in the optical, ultraviolet or the near infrared. In this contribution both aspects will be highlighted, the structure of the accretion regions as inferred from multi-wavelength observations with low or no spectral resolution, as well as the structure of the secondary stars and the accretion st...

Schwope, A D; Buckley, D; Ciardi, D R; Cropper, M; Horne, K; Howell, S; Mantel, K H; Metzner, A; O'Brien, K; Schwarz, R; Sirk, M; Steeghs, D; Still, M D; Thomas, H C; Schwope, Axel D.

1997-01-01

89

Features of artificial ULF/VLF signals induced by SURA facility under increased solar activity conditions  

Science.gov (United States)

It was conducted a comprehensive study of artificial ionospheric signal generation in the ULF/VLF bands at SURA facility during the past four years. We investigated the influence of geomagnetic activity on the characteristics of artificial low-frequency signals in recent years under the background of increasing solar activity. No correlation with variations of Earth's magnetic field was observed for weak geomagnetic disturbances (Kp increased for growth phase of the geomagnetic field perturbations during a small magnetic storms October 7, 2011 (Ki = 4 according to Moscow station). A similar pattern was traced in 2013 during storms March 21 (Kp = 5), May 24-25 (Kp = 5 +) and August 16 (Kp = 5 +). There are two possible reasons for the observed dependence - increasing the absorption of HF and VLF waves in the lower ionosphere, and / or reduction of the critical frequency of the F-layer, usually accompanied by a magnetic storm. The last factor is perhaps the most likely. This dependence was traced more convincingly on May 24-25, when during a storm time SURE had operated from evening until 6:00 MST in the morning. Signal amplitude explicitly followed the F- layer critical frequency variation. Some of the measurements in June 2012 were conducted during a magnetic storm on June 16-18, (Kp = 6). It was also found a decrease in the amplitude of the signal at the rise of the magnetic disturbance. In addition, during the daytime session 18.06.2012 during the recovery phase, it was detected modulation of artificial signals at frequencies 11 and 17 Hz with a period of 30 seconds. Note that the period of 30s is the main period of oscillation of the geomagnetic field line passing through the SURA facility, and more, the periods for torsional and the toroidal oscillation modes of this field line surprising coincidence for SURA geomagnetic latitude. Also the peculiarities were displayed in the polarization of artificial VLF signals during magnetic storms. Typically, the artificial emission is elliptically polarized at all frequencies of VLF signals with a predominance of the left- polarization. During a storm time, it was detected a change in the polarization of artificial VLF emissions. The right polarization becomes predominant. This fact can be associated with changes in ionospheric plasma parameters under a magnetic storm conditions. This work was supported by RFBR grants 13-02-0072 and 13-02-12074.

Kotik, Dmitry; Ryabov, Alexander; Pershin, Alexsander; Ermakova, Elena

90

Generation of ELF and VLF waves in the HF heater-modulated polar electrojet  

International Nuclear Information System (INIS)

Using the powerful HF heater to modulate the ionospheric electrojet current, ELF/VLF waves have been generated, as observed in many ionospheric heating experiments. The wave generation process can be understood as follows. As an amplitude modulated HF heater is transmitted to the ionosphere, the electron temperature of the electrojet in the D/E region of the ionosphere is modulated accordingly. This in turn causes modulation of the conductivity and thus of the electrojet current. Emissions are then produced at the modulation frequency and its harmonics. However, the analysis indicates that a thermal instability is also at work, helping the emission process to be more effective. In the lower ionosphere, ?en ? Te5/6, and thus increases with heating. On the other hand, the heating of the electrojet plasma by the HF heater is through electron neutral collisions. Such a positive feedback gives rise to a desired thermal instability for the ELF/VLF generation. Two heater-modulation schemes are considered in the present work. One modulates the heater with a rectangular periodic pulse. The other uses two overlapping heater waves (beat wave scheme) having a frequency difference equal to the desired modulation frequency. The nonlinear evolutions of the generated ELF/VLF waves are determined numerically. Their spectra are also evaluated. The results show that the signal quality of the emissions deteriorates with the modulation frequency. On thes with the modulation frequency. On the other hand, the field intensity of the emission at the fundamental modulation frequency increases with the modulation frequency

91

Anomalies Observed in VLF and LF Radio Signals on the Occasion of the Western Turkey Earthquake (Mw = 5.7 on May 19, 2011  

Directory of Open Access Journals (Sweden)

Full Text Available Since 2009 a network of VLF (20 - 60 kHz and LF (150 - 300 kHz radio receivers is operating in Europe in order to study the disturbances produced by the earthquakes on the propagation of these signals. In 2011 the network was formed by nine receivers, of which three are located in Italy and one is in Austria, Greece, Portugal, Romania, Russia and Turkey. On May 19, 2001 an earthquake (Mw = 5.7 occurred in western Turkey, that is inside the “sensitive” area of the network. The radio data collected during April-May 2011 were studied using the Wavelet spectra, the Principal Component Analysis and the Standard Deviation trends as different methods of analysis. Evident anomalies were revealed both in the signals broadcasted by the TRT transmitter (180 kHz located near Ankara and in a VLF signal coming from a transmitter located in Western Europe and collected by the receiver TUR of the network located in eastern Turkey. Evident precursor phases were pointed out. Some differences in the efficiency of the three analysis methods were revealed.

Pier Francesco Biagi

2012-09-01

92

ELF and VLF radio waves  

Science.gov (United States)

This review covers developments in ELF and VLF radio-wave propagation research over the last 50 years of the Journal of Atmospheric and Solar-Terrestrial Physics. A review of such a large field, over such a long period, cannot be fully comprehensive and the authors have therefore covered important areas which have they themselves have found interesting. The survey begins with a review of work on natural and man made sources of ELF and VLF radiation. This is followed by sections on experimental and theoretical studies of unperturbed (ambient) ELF and VLF radio propagation. Schumann resonance research, which is currently undergoing a renaissance, is then reviewed. A review of research into transient perturbations of ELF and VLF propagation follows, extending from the early work on nuclear explosions up to the current work on sprites. The review concludes with a brief summary of the VLF navigation systems of the USSR and USA, (Alpha and Omega) whose development and life-span covered most of the last 50 years.

Barr, R.; Jones, D. L.; Rodger, C. J.

2000-11-01

93

Peculiarities of VLF chorus propagation in the megnetosphere  

International Nuclear Information System (INIS)

Analysis of space characteristics of VLF chories illumination zone in the upper ionosphere is conducted according to ''Interkosmos-19'' satellite data. It is shown, that this zone is located in the area of L-shell which are smaller than plasmapause L-shell. With the increase of this zone magnetic activity its spatial dimensions reduce and the north zone boundary shifts in accordance with plasmapause position change whereas the lower one remains practically unchanged (L=2.0-2.5). Differences in the times of chorus element arrival to different latitudes in the upper ionosphere are determined. It is shown, that the observed space and time characteristics of VLF chorus can be explained by the effect of concentration gradient in the area of plasmapause on the trajectories of VLF-waves and their approach to ionosphere

94

Joint UTK-UBC, auroral-ULF-VLF research project in Canada  

International Nuclear Information System (INIS)

The joint project with an observation network in middle Canada is proceeding since 1975. Its purpose is to clarify the relation among incident particles and the related geomagnetic pulsation and VLF waves and thereby the interaction between particles and waves in the terrestrial magnetosphere, by the network from auroral zone to plasmapause. Observations of aurora by TV camera, ULF waves by induction magnetometer and approach orientation and altitude angle by VLF detection device, are carried out. ULF observation is made at number of points, and aurora and VLF-DF at several key stations. (Mori, K.)

95

ELF/VLF wave generation by modulated HF heating of the auroral electrojet  

Science.gov (United States)

The generation of electromagnetic waves in the Extremely Low Frequency (ELF, 3-3000 Hz) and Very Low Frequency (VLF, 3-30 kHz) bands by modulated High Frequency (HF, 3-30 MHz) heating of the auroral electrojet current system is investigated experimentally, and observations are compared against the predictions of a theoretical model. Experimental evidence is presented to demonstrate the regular occurrence of ELF/VLF amplitude saturation as a function of peak HF power level. The observed ELF/VLF amplitude saturation is examined as a function of modulation frequency and as a function of time of day. For modulation depths less than 100%, the dependence of ELF/VLF amplitude on average HF power is investigated, yielding an optimal average HF power level which maximizes the observed ELF/VLF amplitude. Observations of ELF/VLF amplitude saturation under a large range of geomagnetic conditions indicate that the identified saturation process occurs on a regular basis. Furthermore, observations indicate that the spatial distribution of the modulated ionospheric conductivity can be remotely sensed using ground based measurements of the horizontal component of the generated ELF/VLF magnetic flux density. Each of these experimental observations is interpreted in the context of an HF heating model which accounts for the Earth's magnetic field and for the altitudinal variation of several ionospheric constituents. This model indicates that the variation in ELF/VLF amplitude at low HF power levels is dominated by the HF self-absorption process, whereas the variation in ELF/VLF amplitude at high HF power levels results from the competition between the electron energy losses associated with the rotational excitation of molecular nitrogen and the vibrational excitation of molecular oxygen.

Moore, Robert C.

96

Characteristics of VLF/LF Sferics from Elve-producing Lightning Discharges  

Science.gov (United States)

Lightning return strokes radiate an electromagnetic pulse (EMP) which interacts with the D-region ionosphere; the largest EMPs produce new ionization, heating, and optical emissions known as elves. Elves are at least six times more common than sprites and other transient luminous events. Though the probability that a lightning return stroke will produce an elve is correlated with the return stroke peak current, many large peak current strokes do not produce visible elves. Apart from the lightning peak current, elve production may depend on the return stroke speed, lightning altitude, and ionospheric conditions. In this work we investigate the detailed structure of lightning that gives rise to elves by analyzing the characteristics of VLF/LF lightning sferics in conjunction with optical elve observations. Lightning sferics were observed using an array of six VLF/LF receivers (1 MHz sample-rate) in Oklahoma, and elves were observed using two high-speed photometers pointed over the Oklahoma region: one located at Langmuir Laboratory, NM and the other at McDonald Observatory, TX. Hundreds of elves with coincident LF sferics were observed during the summer months of 2013. We present data comparing the characteristics of elve-producing and non-elve producing lightning as measured by LF sferics. In addition, we compare these sferic and elve observations with FDTD simulations to determine key properties of elve-producing lightning.

Blaes, P.; Zoghzoghy, F. G.; Marshall, R. A.

2013-12-01

97

Evidence of a VLF transmission amplitude perturbation induced by a discrete meteor  

OpenAIRE

Modifications of the ionosphere D layer density and/or altitude by solar UV or XR bursts are frequently observed. inducing phase and/or amplitude modifications on VLF transmissions propagation. A perturbation of the amplitude of french and german VLF transmissions received at Pic du Midi observatory during the Geminids 2010 meteor shower has been observed, which is triggered by a large meteor ionized trail

Rault, Jean-louis

2011-01-01

98

ARCADE 2 OBSERVATIONS OF GALACTIC RADIO EMISSION  

International Nuclear Information System (INIS)

We use absolutely calibrated data from the ARCADE 2 flight in 2006 July to model Galactic emission at frequencies 3, 8, and 10 GHz. The spatial structure in the data is consistent with a superposition of free-free and synchrotron emission. Emission with spatial morphology traced by the Haslam 408 MHz survey has spectral index ?synch = -2.5 ± 0.1, with free-free emission contributing 0.10 ± 0.01 of the total Galactic plane emission in the lowest ARCADE 2 band at 3.15 GHz. We estimate the total Galactic emission toward the polar caps using either a simple plane-parallel model with csc |b| dependence or a model of high-latitude radio emission traced by the COBE/FIRAS map of C II emission. Both methods are consistent with a single power law over the frequency range 22 MHz to 10 GHz, with total Galactic emission toward the north polar cap TGal = 10.12 ± 0.90 K and spectral index ? = -2.55 ± 0.03 at reference frequency 0.31 GHz. Emission associated with the plane-parallel structure accounts for only 30% of the observed high-latitude sky temperature, with the residual in either a Galactic halo or an isotropic extragalactic background. The well-calibrated ARCADE 2 maps provide a new test for spinning dust emission, based on the integrated intensity of emission from the Galactic plane instead of cross-correlations with the thermal dust spatial morphology. The Galactic plane intensity measured by ARCADE 2 is fainter than predicted by models without sr than predicted by models without spinning dust and is consistent with spinning dust contributing 0.4 ± 0.1 of the Galactic plane emission at 23 GHz.

99

Constraining CO emission estimates using atmospheric observations  

OpenAIRE

We apply a four-dimensional variational (4D-Var) data assimilation system to optimize carbon monoxide (CO) emissions and to reduce the uncertainty of emission estimates from individual sources using the chemistry transport model TM5. In the first study only a limited amount of surface network observations from the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) is used to test the 4D-Var system. Uncertainty re...

Hooghiemstra, P. B.

2012-01-01

100

Ionospheric disturbances in D-layer recorded by VLF receiver at Tashkent IHY station  

Science.gov (United States)

Tashkent International Heliophysical Year (IHY) station is a member of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network being operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in Very Low Frequency (VLF) band. Regular monitoring of the D- and F-layers of ionosphere over Central Asia territory is being performed on the permanent basis starting year 2008. Solar flare events are permanently observed and the analysis showed that there is simultaneous correlation between the times of change of amplitude of the waves and the Solar flares. Features of the lightning discharge generated by radio atmospherics are studied and its effectiveness in D-region ionosphere diagnostics is explained. We have studied VLF amplitude anomalies related to the earthquakes (EQs) occurred in the recent years with magnitude more than 5 on the path way from the VLF transmitters to the Tashkent station assuming that propagation of VLF ground-based transmitters signals can be perturbed by EQ preparation can be detectable from the ground-based measurements in the VLF bands. For analyzing narrowband data we have used the Nighttime Fluctuation (NF) method paying attention to the data obtained during the local nighttime (20:00 LT-04:00 LT). The mean nighttime amplitude (or trend) and nighttime fluctuation are found to increase significantly before the EQ occurred on the path way from the transmitters to the receiver. The obtained results have revealed an agreement with VLF amplitude anomalies observed in Tashkent VLF station during the strong EQs occurred on the path way from the transmitters to the receiver. Some results are presented to show the probing potentiality of VLF waves to predict short term EQs with high magnitude.

Ahmedov, Bobomurat

101

Particle acceleration by intense auroral VLF turbulence  

International Nuclear Information System (INIS)

Broadband turbulence in the lower-hybrid to plasma frequency range is found in a variety of forms in the suprauroral region, most notably as auroral hiss and VLF saucers. When the turbulence is intense, it is observed to be associated with ion conics (ions heated transverse to the geomagnetic field) and 'counter-streaming' electron fluxes (heated in both directions parallel to the field). A review is presented of the dispersion and propagation characteristics of whistler resonance-cone waves, which comprise the turbulence. Plasma simulation and mesoscale (Monte Carlo) simulation techniques are used to illustrate the interaction of the ambient plasma with the turbulence. These calculations demonstrate how this interaction results in transverse heating of the ions and parallel heating of the electrons of the plasma, leading to the formation of the observed heated and accelerated particle fluxes. 50 refs

102

Simultaneous observations of quasi-periodic (QP) VLF wave emissions and related ULF fluctuations of the geomagnetic field.  

Czech Academy of Sciences Publication Activity Database

Pa?íž : COSPAR, 2014. C0.4-37-14. [COSPAR Scientific Assembly /40th/. 02.08.2014-10.08.2014, in Moscow, Russia, Moskva] Institutional support: RVO:68378289 http://adsabs. harvard .edu/abs/2014cosp...40E1176H

Hayosh, Mykhaylo; Santolík, O.; Parrot, M.; N?mec, F.

103

Observations and Models of Iapetus's Microwave Emissivity  

Science.gov (United States)

Iapetus is one of the most unusual moons in the solar system and is best known for its stark hemispherical albedo contrast at optical wavelengths. However, only a handful of previous observations have explored whether this contrast also manifests itself in the thermal emission. While Iapetus's daytime infrared brightness temperature only varies by about 10K, our observations with the Green Bank Telescope (GBT) have shown that Iapetus's microwave brightness temperature at the Ka-Band (26-40 GHz) can vary by as much as 60K, with effective emissivities dropping to less than 0.3 on the bright trailing hemisphere. We have also observed that the variation is substantially less at 3.3 mm. This behavior is unprecedented in the astronomical literature, but not entirely unprecedented in the literature from the remote sensing branch of climate science. Climate scientists have made extensive studies of Earth's microwave emissivities from 10 to 200 GHz and found similarly shaped features in dry snowpacks and glaciers. Here we present an attempt to model Iapetus's microwave emissivity using various snow models from the climate science literature and report on the final observations from a GBT observing campaign. This research has been supported by the NRAO pre-doc program and the Virginia Space Grant Consortium graduate fellowship program.

Ries, Paul

2012-01-01

104

Subionospheric VLF/LF Probing of Ionospheric Perturbations Associated with Earthquakes: A Possibility of Earthquake Prediction  

Science.gov (United States)

The VLF (Very Low Frequency) / LF (Low Frequency) receiving network has been established in Japan, which is composed of seven observing stations (Moshiri (Hokkaido), Chofu (Tokyo, UEC, University of Electro-Communications), Tateyama (Chiba), Shimizu (Shizuoka), Kasugai (Aichi), Maizuru (Kyoto) and Kochi (Kochi)), and three additional foreign stations have been established in Kamchatka, Taiwan and Indonesia. At each station we observe simultaneously several VLF/LF transmitter signals (two Japanese transmitters with call signals fo JJY (Fukushima), JJI (Miyazaki)), and foreign VLF transmitters (NWC (Western Australia, Australia), NPM (Hawaii, USA), NLK (Washington, USA)). This Japanese VLF/LF network is used to study the ionospheric perturbations associated with earthquakes, and we present two recent results; (1) a statistical result on the correlation between VLF/LF propagation anomalies and earthquakes, and (2) the latest results during the last six months on the two particular propagation paths; JJY-Moshiri and JJY-Taiwan. Then, we discuss the correlation of ionospheric perturbations with earthquakes in the sense of a possibility of earthquake prediction by means of VLF propagation anomalies.

Hayakawa, Masashi; Horie, Takumi; Muto, Fumiya; Kasahara, Yasushi; Ohta, Kenji; Liu, Jann-Yenq; Hobara, Yasuhide

105

NERO-The Neutron Emission Ratio Observer  

Science.gov (United States)

The Neutron Emission Ratio Observer (NERO), has been constructed for the use at the National Superconducting Cyclotron Laboratory to work in conjunction with the NSCL Beta Counting System in order to detect ?-delayed neutrons. The design of the detector provides high and flat efficiency for a wide range of neutron energies, as well as a low neutron background.

Lorusso, Giuseppe; Pereira, Jorque; Hosmer, Paul; Kratz, Karl Ludvig; Montes, Fernando; Reeder, Paul; Santi, Peter; Schatz, Hendrik

2007-10-01

106

More evidence for a one-to-one correlation between Sprites and Early VLF perturbations  

DEFF Research Database (Denmark)

Past studies have shown a correlation between sprites and early VLF perturbations, but the reported correlation varies widely from ?50% to 100%. The present study resolves these large discrepancies by analyzing several case studies of sprite and narrowband VLF observations, in which multiple transmitter?receiver VLF pairs with great circle paths (GCPs) passing near a sprite?producing thunderstorm were available. In this setup, the multiple paths act in a complementary way that makes the detection of early VLF perturbations much more probable compared to a single VLF path that can miss several of them, a fact that was overlooked in past studies. The evidence shows that visible sprite occurrences are accompanied by early VLF perturbations in a one?to?one correspondence. This implies that the sprite generation mechanism may cause also sub?ionospheric conductivity disturbances that produce early VLF events. However, the one?to?one visible sprite to early VLF event correspondence, if viewed conversely, appears notto be always reciprocal. This is because the number of early events detected in some case studies was considerably larger than the number of visible sprites. Since the great majority of the early events not accompanied by visible sprites appeared to be caused by positive cloud to ground (+CG) lightning discharges, it is possible that sprites or sprite halos were concurrently present in these events as well but were missed by the sprite?watch camera detection system. In order for this option to be resolved we need more studies using highly sensitive optical systems capable of detecting weaker sprites, sprite halos and elves.

Haldoupis, C.; Amvrosiadi, N.

2010-01-01

107

The latitude dependence of vlf radiation intensity  

Science.gov (United States)

Consideration is given to the differential latitude dependence of the spectral energy density of magnetospheric elf and vlf radiation. Expressions for the spectral wave energy density distributions predicted by the model of plasmaspheric elf hiss excitation in the equatorial magnetosphere proposed by Etcheto (1972, 1973), its modification by Sazhin to take into account magnetic field inhomogeneity and the model of ionospheric wave generation of Kovner et al. (1978) and St. Maurice (1978) are presented. The latitude distribution of the spectral energy density of low-frequency waves observed by Intercosmos 5 is shown to agree most nearly with the distribution obtained from the model of Sazhin, despite its close agreement with that of Etcheto in most other aspects.

Sazhin, S. S.; Sizova, L. Z.; Larkina, V. I.

1980-04-01

108

Radio Emissions Observed by Galileo near Io  

Science.gov (United States)

The Galileo spacecraft observed spin modulation of radio wave emissions near Io in the frequency range from about 600 kHz to about 1.2 MHz. Assuming transverse EM radiation, we have used the modulation of the high-frequency sweep-frequency receiver signals of the electric dipole antenna over many spins to estimate the plane through the source. The emission has a range of frequencies close to the local upper hybrid frequency of the plasma near Io. We conclude that the emission may be associated with either the plasma torus or magnetic flux tubes in the wake of Io (the Alfven current system). We postulate this emission may be associated with a free-energy source such as density gradients, energetic plasma beams and/or an electron distribution with a temperature anisotropy. All of these free-energy sources are observed or expected in the torus near Io. The observations are the first in the hectometric frequency range that have a source associated with Io or in the Io torus.

Menietti, J. D.; Gurnett, D. A.; Kurth, W. S.; Groene, J. B.; Granroth, L. J.

1998-01-01

109

Experimental evidence of the simultaneous occurrence of VLF chorus on the ground in the global azimuthal scale – from pre-midnight to the late morning  

Directory of Open Access Journals (Sweden)

Full Text Available Night-time VLF (very low frequency chorus bursts lasting about one hour have been recorded at Finnish temporal station Kannuslehto (CGM: 64.2°; 107.9°, L = 5.3 during two VLF campaigns (on 25 February–4 March 2008 and 27 March–17 April 2011. The chorus bursts were associated with substorm development. They were accompanied by riometer absorption enhancements, which occurred simultaneously within as large longitude areas as from pre-midnight (Sodankylä, ~22:00 MLT to the late morning (Tixie, ~03:00 MLT and Gakona, ~08:00 MLT longitudes. It was found that the pre-midnight chorus observed on the ground occurred simultaneously with VLF chorus emissions recorded in the late morning on the low-altitude DEMETER satellite crossing the similar geomagnetic latitudes on the opposite local time sector. For the first time some evidence of simultaneous chorus burst generation in the global longitudinal scale was found (from pre-midnight to the late morning by using direct comparison with satellite data as well as using non-direct indicator–azimuthally extended riometer absorption enhancements.

T. Turunen

2012-04-01

110

Initial Results from Awesome VLF Receiver Installed in Ecuador  

Science.gov (United States)

In this work we present the first results that we have derived from analysis of data obtained using the Atmospheric Weather Electromagnetic System for Observation Modeling and Education (Awesome) VLF receiver, designed and developed by Stanford University, USA. The receiver was installed under inter-institutional cooperation in the emerging Space Science division of the Quito Astronomical Observatory, and it is working properly since 2010. We have describe the performance characteristic of the Awesome system and the importance of having receivers at equator for monitoring the ionosphere and magnetosphere, recepting extremely low frequencies (ELF;30-3000 Hz) and very low frequencies (VLF; 3-30 KHz) electromagnetic waves, in order to better understanding the physical processes which take place in these media.

Lopez, Ericson

2012-07-01

111

Magion 5 observations of chorus-like emissions and their propagation features as inferred from ray-tracing simulation  

Directory of Open Access Journals (Sweden)

Full Text Available After reviewing briefly the present state of knowledge about chorus-like emissions, we present an overview of Magion 5 satellite observations of these emissions in the inner magnetosphere of the Earth. From the extensive VLF data recorded on board the Magion 5 satellite, we show examples of different types of discrete elements, representing rising and falling tones, and discuss their spectral properties, such as the bandwidth and the characteristic frequency as compared to the equatorial electron gyrofrequency. We analyse the possibility of satellite observation of discrete elements, assuming nonducted wave propagation from the source. As for the characteristic dimension of the generation region, we apply the figures obtained from the recently published correlation analysis of chorus emission recorded by four satellites in the Cluster experiment. We conclude that different frequencies in the chorus element should be emitted in a certain span of wave normal angles, so that the whole element could be observed far from the generation region.

Key words. Magnetospheric physics (plasmasphere; plasma waves and instabilities – Space plasma physics (wave-particle interactions – Ionosphere (wave propagation

J. Chum

112

Unexpected Very Low Frequency (VLF) Radio Events Recorded by the Ionospheric Satellite DEMETER  

Science.gov (United States)

DEMETER was a low Earth orbiting microsatellite in operation between July 2004 and December 2010. Its scientific objective was the study of ionospheric perturbations in relation to seismic activity and man-made activities. Its payload was designed to measure electromagnetic waves over a large frequency range as well as ionospheric plasma parameters (electron and ion densities, fluxes of energetic charged particles). This paper will show both expected and unusual events recorded by the satellite when it was in operation. These latter events have been selected from the DEMETER database because they are rare or even have never been observed before, because they have a very high intensity, or because they are related to abnormalities of the experiments under particular plasma conditions. Some events are related to man-made radio waves emitted by VLF ground-based transmitters or power line harmonic radiation. Natural waves, such as atypical quasi-periodic emissions or uncommon whistlers, are also shown.

Parrot, M.; Berthelier, J. J.; Blecki, J.; Brochot, J. Y.; Hobara, Y.; Lagoutte, D.; Lebreton, J. P.; N?mec, F.; Onishi, T.; Pinçon, J. L.; Píša, D.; Santolík, O.; Sauvaud, J. A.; Slominska, E.

2015-02-01

113

Binding of the baculovirus very late expression factor 1 (VLF-1 to different DNA structures  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Baculovirus genomes encode a gene called very late expression factor 1 (VLF-1 that is a member of the integrase (Int family of proteins. In this report we describe the binding properties of purified Autographa californica multiple capsid nucleopolyhedrovirus (AcMNPV VLF-1 to a number of different DNA structures including homologous regions. In addition, its enzymatic activity was examined. Results VLF-1 was expressed in a recombinant baculovirus as a fusion with both HA and HIS6 tags and its binding activity to different DNA structures was tested. No binding was evident to single and double strand structures, very low binding was observed to Y-forks, more binding was observed to three-way junctions, whereas cruciform structures showed high levels of binding. VLF-1 binding was affected by divalent cations; optimal binding to three-way junctions and cruciforms was 2 and 0 mM MgCl2, respectively. Homologous region (hr sequences was also examined including oligomers designed to expose the hr palindrome as a hairpin, linear double strand, or H-shaped structure. Efficient binding was observed to the hairpin and H-shaped structure. No topoisomerase or endonuclease activity was detected. Sedimentation analysis indicated that *VLF-1 is present as a monomer. Conclusions An HA- and HIS-tagged version of AcMNPV VLF-1 showed structure-dependent binding to DNA substrates with the highest binding affinity to cruciform DNA. These results are consistent with the involvement of VLF-1 in the processing of branched DNA molecules at the late stages of viral genome replication. We were unable to detect enzymatic activity associated with these complexes.

Mikhailov Victor S

2002-09-01

114

Theory of VLF Doppler signatures and their relation to magnetospheric density structure  

International Nuclear Information System (INIS)

The published spectrograms of signals from ground-based VLF transmitters observed aboard satellites show a wide variation from sample to sample. In general, the observed signals are Doppler shifted by the motion of the satellite, but in some published samples there is no observed Doppler shift. A ray tracing study of differing VLF Dopper signatures observed by the Ogo 4, FR 1, and Isis 2 VLF experiments has shown that each signature can be reproduced by a distinct class of electron density gradient models. Large positive and negative Doppler shifts (approx.100 Hz) are reproduced by a strong decreasing electron density gradient which interacts with the magnetic field curvature gradient between Lapprox.2 and Lapprox.3. Presence of a strong signal with no Doppler shift is shown to be a result of trapping of upgoing rays by steep density drop-offs. Merging of the spectral components in the Doppler shifted signals is interpreted in terms of scattering by small-scale field-aligned density irregularities. These results allow VLF Doppler observations to be used as a new diagnostic tool in determining magnetospheric density structure below Lapprox.3 and in estimating the effective coverage of the lower ionosphere by the ground-based VLF transmitter in the excitation hemisphere

115

Theory of VLF Doppler signatures and their relation to magnetospheric density structure  

Energy Technology Data Exchange (ETDEWEB)

The published spectrograms of signals from ground-based VLF transmitters observed aboard satellites show a wide variation from sample to sample. In general, the observed signals are Doppler shifted by the motion of the satellite, but in some published samples there is no observed Doppler shift. A ray tracing study of differing VLF Dopper signatures observed by the Ogo 4, FR 1, and Isis 2 VLF experiments has shown that each signature can be reproduced by a distinct class of electron density gradient models. Large positive and negative Doppler shifts (approx.100 Hz) are reproduced by a strong decreasing electron density gradient which interacts with the magnetic field curvature gradient between Lapprox.2 and Lapprox.3. Presence of a strong signal with no Doppler shift is shown to be a result of trapping of upgoing rays by steep density drop-offs. Merging of the spectral components in the Doppler shifted signals is interpreted in terms of scattering by small-scale field-aligned density irregularities. These results allow VLF Doppler observations to be used as a new diagnostic tool in determining magnetospheric density structure below Lapprox.3 and in estimating the effective coverage of the lower ionosphere by the ground-based VLF transmitter in the excitation hemisphere. (AIP)

Edgar, B.C.

1976-07-01

116

The nonlinear gyroresonance interaction between energetic electrons and coherent VLF waves propagating at an arbitrary angle with respect to the earth's magnetic field  

Science.gov (United States)

A theory is presented of the nonlinear gyroresonance interaction that takes place in the magnetosphere between energetic electrons and coherent VLF waves propagating in the whistler mode at an arbitrary angle psi with respect to the earth's magnetic field B-sub-0. Particularly examined is the phase trapping (PT) mechanism believed to be responsible for the generation of VLF emissions. It is concluded that near the magnetic equatorial plane gradients of psi may play a very important part in the PT process for nonducted waves. Predictions of a higher threshold value for PT for nonducted waves generally agree with experimental data concerning VLF emission triggering by nonducted waves.

Bell, T. F.

1984-01-01

117

LROC model observers for emission tomographic reconstruction  

Science.gov (United States)

Detection and localization performance with signal location uncertainty may be summarized by Figures of Merit (FOM's) obtained from the LROC curve. We consider model observers that may be used to compute the two LROC FOM's: ALROC and PCL, for emission tomographic MAP reconstruction. We address the case background-known-exactly (BKE) and signal known except for location. Model observers may be used, for instance, to rapidly prototype studies that use human observers. Our FOM calculation is an ensemble method (no samples of reconstructions needed) that makes use of theoretical expressions for the mean and covariance of the reconstruction. An affine local observer computes a response at each location, and the maximum of these is used as the global observer - the response needed by the LROC curve. In previous work, we had assumed the local observers to be independent and normally distributed, which allowed the use of closed form expressions to compute the FOM's. Here, we relax the independence assumption and make the approximation that the local observer responses are jointly normal. We demonstrate a fast theoretical method to compute the mean and covariance of this joint distribution (for the signal absent and present cases) given the theoretical expressions for the reconstruction mean and covariance. We can then generate samples from this joint distribution and rapidly (since no reconstructions need be computed) compute the LROC FOM's. We validate the results of the procedure by comparison to FOM's obtained using a gold-standard Monte Carlo method employing a large set of reconstructed noise trials.

Khurd, Parmeshwar; Gindi, Gene

2004-05-01

118

Trapped electron losses by interactions with coherent VLF waves  

International Nuclear Information System (INIS)

VLF whistler waves from lightning enter the magnetosphere and cause the precipitation of energetic trapped electrons by pitch angle scattering. These events, known as Lightning-induced Electron Precipitation (LEP) have been detected by satellite and rocket instruments and by perturbations of VLF waves traveling in the earth-ionosphere waveguide. Detailed comparison of precipitating electron energy spectra and time dependence are in general agreement with calculations of trapped electron interactions with ducted whistler waves. In particular the temporal structure of the precipitation and the dynamic energy spectra of the electrons confirm this interpretation of the phenomena. There are discrepancies between observed and measured electron flux intensities and pitch angle distributions, but these quantities are sensitive to unknown wave intensities and trapped particle fluxes near the loss cone angle. The overall effect of lightning generated VLF waves on the lifetime of trapped electrons is still uncertain. The flux of electrons deflected into the bounce loss cone by a discrete whistler wave has been measured in a few cases. However, the area of the precipitation region is not known, and thus the total number of electrons lost in an LEP event can only be estimated. While the LEP events are dramatic, more important effects on trapped electrons may arise from the small but numerous deflections which increase the pitch angle diffusion rate of the electron population. copysion rate of the electron population. copyright 1996 American Institute of Physics

119

Satellite observation of plasma-wave disturbances induced by high-power radio emission from the NWC transmitter  

International Nuclear Information System (INIS)

In this work, we present the results of in-situ measurements of the characteristics of electromagnetic and plasma disturbances in the ionospheric region modified by high-power emission from the NWC transmitter, which were obtained using the onboard equipment of the French microsatellite DEMETER. It is shown that under the influence of VLF emissions from the ground-based transmitters, artificial plasma-wave channels with typical transverse scales of about 1000 km can be formed in the ionospheric plasma.

120

Generation and Propagation Characteristics of Dual-Band Chorus Emissions Observed by Geotail  

Science.gov (United States)

We analyze the generation and propagation characteristics of chorus emissions observed by the wave form capture (WFC) and the sweep frequency analyzer (SFA) onboard the Geotail spacecraft in the dayside outer magnetosphere (L from 9 to 10). We examine any observational evidence, which may validate the nonlinear growth theory of the chorus emissions [1]. In the nonlinear growth theory a rising-tone element is initially generated continuously in the frequency range from 0.1 to 0.7 fce, where fce is the gyrofrequency in the generation region. Because of the nonlinear damping mechanism the rising-tone element is separated into upper and lower bands at half the local gyrofrequency (1/2 fce) through propagation [2]. As the rising-tone emissions are generated in the minimum-B region and propagate toward the larger-B regions along the geomagnetic field line, the upper cutoff of the lower-band chorus corresponds to 1/2 fce in the generation region, and the lower cutoff of the upper-band chorus corresponds to 1/2 fce at the observation point. In this study, we analyze the SFA spectrum data (consecutively over several hours) and WFC waveform data (several seconds) of the dual-band chorus emissions observed by Geotail. As a result, it is found that the upper cutoff of the lower-band chorus coincides with 1/2 fce at the minimum-B region estimated from the geomagnetic field line connecting to the Geotail position by using the Tsyganenko geomagnetic field model (TS04 model), whereas the lower cutoff of the upper-band chorus coincides with 1/2 fce locally at the observation point. We also examine the amplitude of a rising-tone emission using the WFC waveform data on the basis of the nonlinear growth theory. The amplitude at the generation region is estimated from the observed frequency sweep rate of the emission, and the nonlinear growth of the amplitude through propagation toward the observation point is calculated from the nonlinear growth rate, which is found consistent with the observed amplitude. We will also discuss the observational evidence for the threshold amplitudes and the optimum amplitudes required for triggering rising-tone chorus emissions in the generation region. [1] Omura Y., Y. Katoh and D. Summers (2008), Theory and simulation of the generation of whistler-mode chorus, J. Geophys. Res., 113, A04223, doi:10.1029/2007JA012622. [2] Omura Y., M. Hikishima, Y. Katoh, D. Summers, and S. Yagitani (2009), Nonlinear mechanisms of lower-band and upper-band VLF chorus emissions in the magnetosphere, J.Geophys. Res., 114, A07217, doi:10.1029/2009JA014206. [3] Omura Y., and D. Nunn (2011), Triggering process of whistler mode chorus emissions in the magnetosphere, J. Geophys. Res., 116, A05205, doi:10.1029/2010JA016280.

Yagitani, S.; Habagishi, T.; Mori, S.; Omura, Y.; Kojima, H.

2012-12-01

121

ULF/ELF emissions observed in Japan, possibly associated with the Chi-Chi earthquake in Taiwan  

Directory of Open Access Journals (Sweden)

Full Text Available ULF/ELF emission observation has been performed at Nakatsugawa observatory (geographic coordinates; 35.4° N, 137.5° E, Gifu prefecture since January 1999. The equipment consists of three-orthogonal magnetic sensors (induction coils, amplifiers, A/D converters and the data logger with a computer. The frequency range of observation is from 0.001 Hz to 50 Hz. The serious changes in ELF magnetic field intensity were detected on 20 September 1999, in such a way that the ELF noise level is found to increase by more than 5 dB from the normal level for about 1.5 h during 21:30–23:00 Japanese Standard Time on 20 September and also the upper limit extends up to 50 Hz. A careful comparison with the nearby lightning as detected by VLF, enables us to confirm that this abnormal ELF noise level increase is not due to the nearby lightning. The phase difference of these ELF emissions (BX , BY was measured, and indicates that these ELF emissions are linearly polarized, suggesting that they have propagated in the subionospheric waveguide over long distances. This polarization result enables us to perform goniometric direction finding and the result shows that the main direction of these ULF/ELF emissions is toward Taiwan. Hence, it is likely that such ULF/ELF emissions are associated with the Chi-Chi earth-quake in Taiwan at 02:27 Japanese Standard Time on 21 September 1999 (M = 7.6; depth 11 km.

K. Ohta

2001-01-01

122

ARCADE 2 Observations of Galactic Radio Emission  

CERN Document Server

We use absolutely calibrated data from the ARCADE 2 flight in July 2006 to model Galactic emission at frequencies 3, 8, and 10 GHz. The spatial structure in the data is consistent with a superposition of free-free and synchrotron emission. Emission with spatial morphology traced by the Haslam 408 MHz survey has spectral index beta_synch = -2.5 +/- 0.1, with free-free emission contributing 0.10 +/- 0.01 of the total Galactic plane emission in the lowest ARCADE 2 band at 3.15 GHz. We estimate the total Galactic emission toward the polar caps using either a simple plane-parallel model with csc|b| dependence or a model of high-latitude radio emission traced by the COBE/FIRAS map of CII emission. Both methods are consistent with a single power-law over the frequency range 22 MHz to 10 GHz, with total Galactic emission towards the north polar cap T_Gal = 0.498 +/- 0.028 K and spectral index beta = -2.55 +/- 0.03 at reference frequency 1 GHz. The well calibrated ARCADE 2 maps provide a new test for spinning dust emi...

Kogut, A; Levin, S M; Limon, M; Lubin, P M; Mirel, P; Seiffert, M; Singal, J; Villela, T; Wollack, E; Wünsche, C A

2009-01-01

123

Radio emission modelization - Observables and interpretation  

International Nuclear Information System (INIS)

Radio detection techniques of extensive air shower are currently being reinvested. Experiment with unprecedented quality of data are ongoing and different emission models are being investigated. We report here two complementary approaches of the geosynchrotron emission, trying to emphasize field features which can be confronted to experimental data or help its interpretation - among which a -v×B dependency.

124

Ray-based modeling of lightning-induced ionospheric effects on short range VLF skywave signals  

Science.gov (United States)

At locations close (~100-km) to a VLF transmitter, observation of the sky wave signal from the transmitter becomes possible by aligning a proximate magnetic loop antenna to null the ground signal. Previous observations using such an arrangement [e.g., Rodriguez et al. 1992], and [Pasko et al., 2002] show a very high degree of temporal variability in received signal amplitude. Observation of VLF signatures of Early/Fast and Lightning-induced Electron Precipitation (LEP) events under these constraints show an unusual number of remarkably large events, more than ten times larger than a typical long-distance path, and often exhibit non-exponential recovery, or no recovery at all. Because of the large spatial extent of LEP events compared to the sky wave path distances, at least portions of the disturbed region must necessarily be nearly overhead the receiver and/or transmitter and we can employ simple ray tracing techniques to determine the evolution of the scattered field from the ionospheric disturbance over time, taking into account path-length difference, absorption, ground, and ionospheric reflection coefficients and multiple hops. We present several examples of characteristic VLF perturbations observed on short paths, and interpret these in terms of a simple ray-path-based model of the VLF scattering from the lower ionosphere.

Cotts, B. R.; Inan, U. S.

2005-12-01

125

Lightning and ionospheric remote sensing using VLF/ELF radio atmospherics  

Science.gov (United States)

Lightning discharges radiate the bulk of their electromagnetic energy in the Very Low Frequency (VLF, 3- 30 kHz) and Extremely Low Frequency (ELF, 3-3000 Hz) frequency ranges. This energy, contained in impulse-like signals called radio atmospherics or sferics, is guided for long distances by multiple reflections from the ground and lower ionosphere. These two facts suggest that observed sferic waveforms radiated from lightning contain a great deal of information about both the state of the ionosphere along the propagation path and the dynamics of the current in the lightning return stroke. The aim of this dissertation is to develop and implement the necessary techniques to use sferic observations to determine the characteristics of the ionosphere and lightning. In this work, a quantitative model of sferic propagation is developed, and with it the spectral characteristics of VLF (> 1.5 kHz) sferics are shown to depend primarily on the propagation-path-averaged ionospheric D region electron density profile. Using this propagation model, a parameterized ionosphere is iteratively varied to find the theoretical sferic spectrum that agrees best with an observed sferic spectrum composed of the average of many individual sferic spectra. In most nighttime cases, the quality of the agreement allows the height of an exponentially-varying electron density profile to be inferred with a precision of 0.2 km. Since the general sferic waveform depends on the source current-moment waveform as well as the ionospherically- controlled propagation, the former quantity can be measured for individual discharges from observed sferics. Of particular interest are those lightning discharges associated with mesospheric optical emissions known as sprites. By using a robust deconvolution technique, source current-moment waveforms are extracted from individual observed ELF (< 1.5 kHz) sferics. The cases studied in detail show that optical emissions are sometimes produced with a smaller vertical charge-moment change than predicted by sprite production models. This suggests that mechanisms not considered in existing theories may play a role in sprite production.

Cummer, Steven Andrew

126

VLF Waves as Instigators and Diagnostics of Magnetosphere-Ionosphere Coupling  

Science.gov (United States)

In the terrestrial environment Very Low Frequency (VLF) radio waves originate principally from two sources: lightning discharges and wave-particle interactions. Whereas the former occur within the troposphere, the latter prevail in the ionosphere and magnetosphere. Within the magnetosphere the VLF signals propagate in the whistler mode, and are thus guided by the Earth's magnetic field while being subjected to dispersion. Lightning strokes, which liberate a brief but intense pulse of radiation, lead to the production of whistlers. During its passage through the magnetosphere the initial impulse is dispersed into a signal with a well defined frequency-time structure. Careful analysis of whistler traces allows the diagnosis of magnetospheric parameters. The identification of whistlers in broadband VLF data and their subsequent analysis has traditionally been an arduous process. However, recent advances have allowed for automated whistler detection and analysis. Extensive magnetospheric studies using whistler data are thus now feasible and there is the probability of real time analysis. Chorus and hiss are VLF phenomena which originate within the magnetosphere. Chorus is thought to arise via the amplification of VLF signals by an unstable electron population. The mechanism invoked is Doppler-shifted Cyclotron Resonance, where the wave frequency is Doppler-shifted up to the gyration frequency of the counter-streaming electrons. As energy is transferred from the particles to the waves, the particles' pitch angles are reduced and there is a diffusion of electrons into the loss cone. These electrons are subsequently precipitated into the ionosphere. Within the cavity formed by the surface of the Earth and the base of the ionosphere, VLF waves propagate in a waveguide mode. Under quiescent conditions both the upper and lower bound-aries of the waveguide are stable. However, the precipitation of electrons into the ionosphere causes a perturbation in the upper boundary, which leads to a modification in the propagation conditions within the waveguide. Signals from stable VLF transmitters are affected by these perturbations and may be used to study modifications in the profile of the lower ionosphere. Such modifications may also arise from solar flares and gamma-ray bursts. The study of VLF waves as a diagnostic tool for magnetosphere-ionosphere coupling will be reviewed and possibilities for linking ground and satellite observations will be discussed.

Collier, Andrew

127

Mg+ and other metallic emissions observed in the thermosphere  

International Nuclear Information System (INIS)

Limb observations of UV dayglow emissions from 80 to 300 km tangent heights were made in December, 1992, using the GLO instrument, which flew on STS-53 as a Hitchhiker-G experiment. STS-53 was at 330 km altitude and had an orbit inclination of 57 degree. The orbit placed the shuttle near the terminator for the entire mission, resulting in a unique set of observations. The GLO instrument consisted of 12 imagers and 9 spectrographs on an Az/El gimbal system. The data was obtained over 6 days of the mission. Emissions from Mg+ and Ca+ were observed, as were emissions from the neutral metallic species Mg and Na. The ultimate source of the metals is ablation of meteors; however, the spatial distribution of the emissions is controlled by upper mesospheric and thermospheric winds and, in the case of the ions, by the electromagnetic fields of the ionosphere. The observed Mg+ emission was the brightest of the metal emissions, and was observed near the poles and around the geomagnetic equator near sunset. The polar emissions were short-lived and intense, indicative of auroral activity. The equatorial emissions were more continuous, with several luminous patches propagating poleward over the period of several orbits. The instrumentation will be described, as will spatial and temporal variations of the metal emissions with emphasis on the metal ions. These observations will be compared to previous observations of thermospheric metallic speciesions of thermospheric metallic species

128

Optical signatures of radiation belt electron precipitation induced by ground-based VLF transmitters  

Science.gov (United States)

Numerical simulations are presented of optical emissions in the ionosphere due to electron precipitation caused by ground-based VLF transmitters. Ray tracing and precipitation calculations are made to estimate the flux precipitated from the inner magnetosphere for existing ground-based VLF transmitters as well as hypothetical transmitters with controlled parameters. The resulting precipitated fluxes are used to estimate ionization profiles through Monte Carlo simulations, and the ionization profiles are converted to photon volume emission rates. The results are extended over a range of L shells and longitudes. Results show that the NWC transmitter at North West Cape, Australia, creates the strongest optical signature because of its high power, latitude of ˜35°, and low frequency. The resulting optical signal has a peak of <0.1 R; however, we calculate that this should be detectable using sensitive photometric instruments and controlled modulation experiments.

Marshall, R. A.; Newsome, R. T.; Lehtinen, N. G.; Lavassar, N.; Inan, U. S.

2010-08-01

129

Excitation of VLF quasi-electrostatic oscillations in the ionospheric plasma  

Directory of Open Access Journals (Sweden)

Full Text Available A numerical solution of the dispersion equation for electromagnetic waves in a hot magnetized collisionless plasma has shown that, in a current-free ionospheric plasma, the distortion of the electron distribution function reproducing the downward flow of a thermal electron component and the compensating upward flow of the suprathermal electrons, which are responsible for the resulting heat flux, can destabilize quasi-electrostatic ion sound waves. The numerical analysis, performed with ion densities and electron temperature taken from the data recorded by the Interkosmos-24 (IK-24, Aktivny satellite, is compared with a VLF spectrum registered at the same time on board. This spectrum shows a wide frequency band emission below the local ion plasma frequency. The direction of the electron heat flux inherent to the assumed model of VLF emission generation is discussed

B. Lundin

130

Investigation of TEC and VLF space measurements associated to L'Aquila (Italy earthquakes  

Directory of Open Access Journals (Sweden)

Full Text Available In this study, we report on Total Electron Content (TEC and Very Low Frequency (VLF space measurements derived from Global Positioning System (GPS and DEMETER satellites, respectively. These measurements are associated with the earthquake (EQ of a magnitude of 6.3, which occurred on 6 April 2009, in L'Aquila (Italy. Anomaly features are derived from the analysis of TEC and VLF observations recorded two weeks before and after the seismic event occurrence. A TEC map with an interpolated regional pixel resolution of 1° × 1° × 15 min in latitude, longitude and time was generated, allowing for the checking of a possible presence of disturbances over the L'Aquila region. This analysis is combined with the study of the time profile associated to the VLF flux density variations recorded by the Instrument Champ Electrique (ICE experiment on-board DEMETER satellite. We discuss, on the one hand, the combination efficiency of the electronic density and the VLF electromagnetic measurements and, on the other hand, the difficulty to distinguish between global effects and regional ones related to the earthquake.

G. Stangl

2011-04-01

131

Study of latitudinal effects on VLF transmitter signals recorded by DEMETER/ICE experiment  

Science.gov (United States)

We report on VLF transmitter signals observed by the ‘Instrument Capteur Electrique' (ICE) experiment onboard the DEMETER micro-satellite. The DEMETER polar and circular sun-synchronous orbits lead to cover an invariant latitude range between -65° and +65° where up- and down-going half-orbits correspond to night-time (22:00 LT) and day-time (10:00 LT), respectively. The DEMETER orbit features permit to record signals emitted by some VLF ground-stations and detected by ICE experiment. We consider three transmitter signals emitted by stations in Europe (Germany, DFY, 16.58 kHz), in Asia (Japan, JP, 17.8 kHz) and in Australia (Australia, NWC, 19.8 kHz). We study the variation of these VLF signals taking into consideration the DEMETER satellite latitudes .We emphasis on latitudes where the satellite is close to the Earth's sub-auroral regions. We discuss particularly the presence, or not, of auroral magnetic activity effect on the VLF transmitter signals.

Boudjada, M. Y.; Schwingenschuh, K.; Berthelier, J. J.; Döller, R.; Galopeau, P. H. M.; Parrot, M.; Stangl, G.; Biernat, H.; Voller, W.; Besser, B.

2010-05-01

132

Elf Transients and Vlf Subionospheric Disturbances In Association With Sprites and Elves During Winter Lightning In Japan  

Science.gov (United States)

Recent findings of the optical emissions in the mesosphere in the various places over the world attract a lot of interests about the electrodynamic coupling between the light- ning in the troposphere, mesosphere and lower ionosphere. Red sprites and elves were observed in Japan during the winter of 1998/99 in Hokuriku region by the group of Tohoku Univ. In this paper we present the results of our winter lightning campaign especially focused our attention on the EM phenomena in association with optical emissions over Japan sea as a case study. Along with our objective we have the optical measurement (consisting of CCD camera and Spectrometer installed by Tohoku Uni- versity) to detect the sprite and elves, ELF transient measurement is used to extract the charge moment of the parent lightning strokes, VLF scattering measurement is a sensitive tool to obtain the ionospheric disturbances (electron temperature and den- sity perturbations), and the data from Japanese Lightning Detection Network recently covered all over Japan allow us to locate the event, time and its peak current. We analyze quantitatively the results from coordinated measurement and find the clear straightforward relationship between charge transfer of the parent discharge calculated from ELF (fSprites tend to associate with a large ionospheric disturbance (-13~.6 dB) with a large charge moment transfer (260~875 Ckm), whereas a large lightning peak current (+223~470kA) (or slow-tail amplitude) leading to the strong EMP is necessary to initiate elves, but with rather small ionospheric disturbances. The different characteristics between sprite and/or elve producing lightning and other conventional lightning will be dis- cussed as well. Furthermore preliminary results of winter lightning campaign in Japan (2001/02) with higher time resolution of VLF scattering measurement, ELF transients and ULF mea- surement with optical images of sprite will be presented.

Hobara, Y.; Hayakawa, M.; Ohta, K.; Fukunishi, H.; Williams, E. R.

133

Nighttime sensitivity of ionospheric VLF measurements to X-ray bursts from a remote cosmic source  

Science.gov (United States)

On 22 January 2009, a series of X-ray bursts were emitted by the soft gamma ray repeater SGR J1550-5418. Some of these bursts produced enhanced ionization in the nighttime lower ionosphere. These ionospheric disturbances were studied using X-ray measurements from the Anti-Coincidence Shield of the Spectrometer for Integral onboard the International Gamma-Ray Astrophysics Laboratory and simultaneous phase and amplitude records from two VLF propagation paths between the transmitter Naval Radio Station, Pearl Harbor (Hawaii) and the receivers Radio Observatorio do Itapetinga (Brazil) and Estação Antarctica Commandante Ferraz (Antarctic Peninsula). The VLF measurements have been obtained with an unprecedented high time resolution of 20 ms. We find that the illumination factor I (illuminated path length times the cosine of the zenith angle), which characterizes the propagation paths underlying the flaring object, is a key parameter which determines the sensitivity threshold of the VLF detection of X-ray bursts from nonsolar transients. For the present VLF measurements of bursts from SGR J1550-5418, it is found that for I ? 1.8 Mm, all X-ray bursts with fluence in the 25 keV to 2 MeV range larger than F25_min ~ 1.0 × 10-6 erg/cm2 produce a measurable ionospheric disturbance. Such a lower limit of the X-ray fluence value indicates that moderate X-ray bursts, as opposed to giant X-ray bursts, do produce ionospheric disturbances larger than the sensitivity limit of the VLF technique. Therefore, the frequency of detection of such events could be improved, for example by increasing the coverage of existing VLF receiving networks. The VLF detection of high-energy astrophysical bursts then appears as an important observational diagnostic to complement their detection in space. This would be especially important when space observations suffer from adverse conditions, like saturation, occultation from the Earth, or the passage of the spacecraft through the South Atlantic anomaly.

Raulin, Jean-Pierre; Trottet, Gérard; Giménez de Castro, C. Guillermo; Correia, Emilia; Macotela, E. Liliana

2014-06-01

134

OBSERVATION OF CORRELATED OPTICAL AND GAMMA EMISSIONS FROM GRB 081126  

International Nuclear Information System (INIS)

We present an analysis of time-resolved optical emissions observed from the gamma-ray burst GRB 081126 during the prompt phase. The analysis employed time-resolved photometry using optical data obtained by the TAROT telescope, using BAT data from the Swift spacecraft, and time-resolved spectroscopy at high energies from the GBM instrument onboard the Fermi spacecraft. The optical emission of GRB 081126 is found to be compatible with the second gamma emission pulse shifted by a positive time lag of 8.4 ± 3.9 s. This is the first well-resolved observation of a time lag between optical and gamma emissions during a gamma-ray burst. Our observations could potentially provide new constraints on the fireball model for gamma-ray burst early emissions. Furthermore, observations of time lags between optical and gamma ray photons provides an exciting opportunity to constrain quantum gravity theories.

135

Observational constraints on biogenic VOC emission model estimates (Invited)  

Science.gov (United States)

Chemistry and transport models require accurate estimates of biogenic volatile organic compound (BVOC) emissions in order to simulate the atmospheric constituents controlling air quality and climate, such as ozone and particles, and so the uncertainties associated with BVOC estimates may be limiting the development of effective air quality and climate management strategies. BVOC emission models include driving variables and algorithms that span scales from the leaf level to entire landscapes. While considerable effort has been made to improve BVOC emission models in the past decades, there have been relatively few attempts to quantify the uncertainties associated with these estimates or to rigorously assess emission modeling approaches. This presentation will summarize the availability of observations that can be used to constrain BVOC emission models including flux measurements (leaf enclosure, above canopy tower, and aircraft platforms) and ambient concentrations of BVOC and their products. Results from studies targeting specific BVOC emission processes (e.g., the response of isoprene emission to drought and the response of monoterpene emissions to bark beetle attack) will be shown and the application of these observations for BVOC model evaluation will be discussed. In addition, the results from multi-scale BVOC emission studies (leaf enclosure, whole canopy flux tower, regional aircraft eddy covariance) will be presented and a approach for incorporating these observations into a community model testbed will be described and used to evaluate regional BVOC emission models.

Guenther, A. B.

2013-12-01

136

Fast Emission Estimates in China Constrained by Satellite Observations (Invited)  

Science.gov (United States)

Emission inventories of air pollutants are crucial information for policy makers and form important input data for air quality models. Unfortunately, bottom-up emission inventories, compiled from large quantities of statistical data, are easily outdated for an emerging economy such as China, where rapid economic growth changes emissions accordingly. Alternatively, top-down emission estimates from satellite observations of air constituents have important advantages of being spatial consistent, having high temporal resolution, and enabling emission updates shortly after the satellite data become available. Constraining emissions from concentration measurements is, however, computationally challenging. Within the GlobEmission project of the European Space Agency (ESA) a new algorithm has been developed, specifically designed for fast daily emission estimates of short-lived atmospheric species on a mesoscopic scale (0.25 × 0.25 degree) from satellite observations of column concentrations. The algorithm needs only one forward model run from a chemical transport model to calculate the sensitivity of concentration to emission, using trajectory analysis to account for transport away from the source. By using a Kalman filter in the inverse step, optimal use of the a priori knowledge and the newly observed data is made. We apply the algorithm for NOx emission estimates in East China, using the CHIMERE model together with tropospheric NO2 column retrievals of the OMI and GOME-2 satellite instruments. The observations are used to construct a monthly emission time series, which reveal important emission trends such as the emission reduction measures during the Beijing Olympic Games, and the impact and recovery from the global economic crisis. The algorithm is also able to detect emerging sources (e.g. new power plants) and improve emission information for areas where proxy data are not or badly known (e.g. shipping emissions). The new emission estimates result in a better agreement between observations and simulations of air pollutant concentrations, facilitating improved air quality forecasts. The EU project MarcoPolo will combine these emission estimates from space with statistical information on e.g. land use, population density and traffic to construct a new up-to-date emission inventory for China.

Mijling, B.; van der A, R.

2013-12-01

137

Sunsat-2004 satellite and synoptic VLF payload  

Science.gov (United States)

Sunsat 2004 is a second satellite from the University of Stellenbosch, with intended suns-synchronous launch in late 2005. The first satellite, Sunsat, was launched in February 1999, and was Africa's first satellite The three-axis stabilised bus will normally point its main solar panel at the sun, but will rotate for imaging. The attitude determination and control system will use coarse sun sensors, magnetometers, rate gyros, and a star mapper, and use reaction wheels and torquer rods for actuation. The payloads include a multispectral pushbroom imager with less than 5m GSD, TV cameras, an Amateur Radio communications payload, and science experiments. The main South African science experiment is a VLF receiver. In the magnetosphere VLF waves play an important role in energy exchange processes with energetic particles. The wave-particle interactions can lead to particle precipitation into the atmosphere or introduce additional energy into particle populations in the magnetosphere. The former is important due to its effect on terrestrial communications while the latter is of interest, as it affects the environment in which satellites operate. A full understanding, of the magnetosphere and phenomena such as the aurora, airglow and particle precipitation, depends on comprehensive wave and particle models together with models of the background plasma density The energetic particle populations and background plasma densities have been extensively modelled using data from a large number of satellite, rocket and ground-based experiments but no comprehensive model of the wave environment exist. The proposed synoptic VLF experiment will start to address this need by locating and tracking the morphology of regions in the magnetosphere where waves are generated. The experiment would consist of a nine channel VLF receiver with a loop antenna. The data would be recorded on board and transmitted to ground stations at appropriate times. A number of additional science payloads are also being evaluated for the mission, and will be reported on in the paper.

Milne, Gw; Hughes, A.; Mostert, S.; Steyn, Wh

138

Suzaku Observations of Charge Exchange Emission from Solar System Objects  

Science.gov (United States)

Recent results of charge exchange emission from solar system objects observed with the Japanese Suzaku satellite are reviewed. Suzaku is of great importance to investigate diffuse X-ray emission like the charge exchange from planetary exospheres and comets. The Suzaku studies of Earth's exosphere, Martian exosphere, Jupiter's aurorae, and comets are overviewed.

Ezoe, Y.; Fujimoto, R.; Yamasaki, N. Y.; Mitsuda, K.; Ohashi, T.; Ishikawa, K.; Oishi, S.; Miyoshi, Y; Terada, N.; Futaana, Y.; Porter, F. S.; Brown, G. V.

2012-01-01

139

Tectonomagnetic and VLF electromagnetic signals in Central Italy  

Directory of Open Access Journals (Sweden)

Full Text Available Tectonomagnetic field observations from absolute magnetic field level measurements were undertaken in Central Italy in an area extending between latitude 41°N and 43°N and between longitude 13°E and 15°E. Moreover,natural electromagnetic signals from a system of two VLF search coil wide-band antennas were collected at the geomagnetic observatory of L Aquila (42º23'N, 13º19'E. The analysis of these data allowed the investigation of the electromagnetic properties of the study area at different time and spatial lengthscales. Tectonomagnetic field observations were obtained comparing data simultaneously recorded at three magnetometer stations using L'Aquila Observatory as a reference for differentiation. We report on the time evolution of magnetic and electromagnetic indicators related to local and regional seismic activity.

P. Palangio

2004-06-01

140

Observations and modelling of pulsed radio emission from CU Virginis  

CERN Document Server

We present 13 cm and 20 cm radio observations of the magnetic chemically peculiar star CU Virginis taken with the Australia Telescope Compact Array. We detect two circularly polarised radio pulses every rotation period which confirm previous detections. In the first pulse, the lower frequency emission arrives before the higher frequency emission and the ordering reverses in the second pulse. In order to explain the frequency dependence of the time between the two pulses, we construct a geometric model of the magnetosphere of CU Virginis, and consider various emission angles relative to the magnetic field lines. A simple electron cyclotron maser emission model, in which the emission is perpendicular to the magnetic field lines, is not consistent with our data. A model in which the emission is refracted through cold plasma in the magnetosphere is shown to have the correct pulse arrival time frequency dependence.

Lo, K K; Hobbs, G; Murphy, T; Gaensler, B M; Melrose, D; Ravi, V; Manchester, R M; Keith, M J

2012-01-01

141

Observations and modelling of pulsed radio emission from CU Virginis  

Science.gov (United States)

We present 13 and 20 cm radio observations of the magnetic chemically peculiar star CU Virginis taken with the Australia Telescope Compact Array. We detect two circularly polarized radio pulses every rotation period which confirm previous detections. In the first pulse, the lower frequency emission arrives before the higher frequency emission and the ordering reverses in the second pulse. In order to explain the frequency dependence of the time between the two pulses, we construct a geometric model of the magnetosphere of CU Virginis, and consider various emission angles relative to the magnetic field lines. A simple electron cyclotron maser emission model, in which the emission is perpendicular to the magnetic field lines, is not consistent with our data. A model in which the emission is refracted through cold plasma in the magnetosphere is shown to have the correct pulse arrival time frequency dependence.

Lo, K. K.; Bray, J. D.; Hobbs, G.; Murphy, T.; Gaensler, B. M.; Melrose, D.; Ravi, V.; Manchester, R. N.; Keith, M. J.

2012-04-01

142

Solar Flare Impulsive Phase Emission Observed with SDO/EVE  

OpenAIRE

Differential emission measures (DEMs) during the impulsive phase of solar flares were constructed using observations from the EUV Variability Experiment (EVE) and the Markov-Chain Monte Carlo method. Emission lines from ions formed over the temperature range log T = 5.8 - 7.2 allow the evolution of the DEM to be studied over a wide temperature range at 10s cadence. The technique was applied to several M- and X-class flares, where impulsive phase EUV emission is observable in...

Kennedy, Michael B.; Milligan, Ryan O.; Mathioudakis, Mihalis; Keenan, Francis P.

2013-01-01

143

Cluster observations and simulations of He+ EMIC triggered emissions  

Science.gov (United States)

EMIC triggered emissions have been reported in the inner magnetosphere at the edge of the plasmapause nightside [Pickett et al., 2010]. The generation mechanism proposed by Omura et al. [2010] is very similar to the one of the whistler chorus emissions and simulation results agree with observations and theory [Shoji et Omura, 2011]. The main characteristics of these emissions generated in the magnetic equatorial plane region are a frequency with time dispersion and a high level of coherence. The start frequency of previously mentioned observations is above half of the proton gyrofrequency. It means that the emissions are generated on the proton branch. On the He+ branch, generation of triggered emissions, in the same region, requests more energetic protons and the triggering process starts below the He+ gyrofrequency. It makes their identification in Cluster data rather difficult. Recent simulation results confirm the possibility of EMIC triggered emission on the He+ branch. In the present contribution we propose to compare a Cluster event to simulation results in order to investigate the possibility to identify observations to a He+ triggered emission. The impact of the observed waves on particle precipitation is also investigated.

Grison, B.; Shoji, M.; Santolik, O.; Omura, Y.

2012-12-01

144

Effects of HF heater-produced ionospheric depletions on the ducting of VLF transmissions: A ray tracing study  

Science.gov (United States)

Comprehensive three-dimensional ray tracing studies suggest that local large-scale ionospheric density perturbations caused by the HF heater at Arecibo significantly affect the amount of power from upgoing 28.5 kHz VLF transmissions that couples into plasmaspheric ducts on nearby magnetic field lines. Large density depletions can perturb the ray paths of upgoing VLF to enhance or reduce the total power in a local duct. Under certain conditions, ducted power may be enhanced up to 13 dB or attenuated up to 18 dB. The dependence of this effect on the location and cross-L drift of plasmaspheric ducts and the depth of the heater-induced depletion may explain the difficulty in obtaining consistent experimental observations. Nongeometrical optics effects from the heating and resultant structures on VLF propagation may also affect the ducted power distribution but are outside the scope of ray tracing analysis.

Starks, M. J.

2002-11-01

145

First observations of stimulated electromagnetic emission at Arecibo  

International Nuclear Information System (INIS)

The first observations of HF heater stimulated electromagnetic emissions induced in the low-latitude ionospheric plasma above Arecibo, Puerto Rico, are reported. Many systematic spectral features of the emissions bear a close resemblance to those observed in ionospheric modification experiments in the auroral zone and scale in accordance with detailed theory. This proves that these sideband emissions are not dependent on specific geophysical conditions but are due to fundamental interaction processes in the ionospheric plasma. The authors also report the discovery of unique, short-lived HF sideband emissions that are less systematic than those observed previously and accompanied by a quenching of the HF enhanced plasma and ion lines in the Arecibo 430 MHz incoherent scatter radar spectra

146

Memories of National Institute of Polar Research. Series A-19. Upper atmosphere physics: ELF emission in high latitudes: Ray path calculation and ground-satellite observations  

Science.gov (United States)

Results are presented of the study of the two kinds of the Extremely Low Frequency (ELF) ray propagation from the equatorial plane to the polar region with the observation of ELF and Very Low Frequency (VLF) waves by the International Satellite for Ionosphere Studies (ISIS) over Antarctica, ELF waves at Showa Station, Antarctica, and Bremsstrahlung X-rays by balloons. Conditions for the existence of penetrating ray paths are obtained from a two-dimensional ray tracing. Wave normal directions and arriving latitudes at low altitudes are also calculated. The calculated characteristics of ELF wave normals are compared with those from ISIS satellite observation in the altitude range of 1,450 to 3,500 km by means of spin-modulated characteristics and multi-ion cutoff characteristics of received ELF signals. Seasonal variation of ELF emission intensity at the ISIS satellite altitude and on the ground is attributable to a north-south asymmetry in the penetrating ray paths depending on a field-aligned electron density gradient in the both hemispheres. Another mode of ELF wave propagation, i.e., ducted propagation outside the plasmapause, is investigated for periodic emissions. ELF emissions observed on the ground are compared with Bremsstrahlung X-rays observed by balloons. Three balloon experiments were carried out in northern Norway and at Showa Station, Antarctica, and the observed Bremsstrahlung X-rays and ELF emissions were compared for three characteristic time scales: slow variations (a few tens of minutes), pulsations (from a few tens of seconds to several minutes) and bursts (less than 10 seconds).

Yamagishi, Hisao; Hoshiai, Takao; Ejiri, Masaki; Hirasawa, Takeo; Hiroi, Yoshikuni; Kaminuma, Katsutada; Kawaguchi, Sadao; Kokubun, Susumu; Kushiro, Ikuo; Mae, Shinji

1989-03-01

147

A balloon observation of the galactic far infrared emission  

International Nuclear Information System (INIS)

The observation of galactic far infrared emission using a balloon was made at the height of 30 km. An optical system for the observation was set on the balloon which made flight on May 25, 1978. The wavelength of measured far infrared emission was about 150 micrometer, and the emission from spread dust was able to be measured. The brightness distribution of far infrared emission is shown in a figure, and compared with the continuous emission of 5 GHz. The spread in the direction of galactic latitude is uniform. The full width at half maximum was about 1.5 degree. Concentration of the brightness was seen at the central region of the galaxy. The individual sources of far infrared emission were also seen. The brightness in the direction of l = 355 degree was low. An unidentified source was observed at l = 6.0 degree and b = -4.3 degree. The results were compared with the results of other observations. Dust in the central region of the galaxy, number of dust in the galactic disc, the distribution of heat source of dust and so on are discussed. (Kato, T.)

148

MSX Observations of Diffuse UV Emission in Orion  

OpenAIRE

We have observed intense diffuse radiation in the UV (1400 A - 2600 A) from three fields around M42 in Orion. Intensities of 20000 photons cm-2 s-1 sr-1 A-1 were observed to the east and west of M42 with 8000 photons cm-2 s-1 sr-1 A-1 south of the nebula. Enhanced emission, perhaps associated with a nearby complex of molecular clouds observed in CO, was detected in one of the fields. The IRAS 100 micron emission in that region is highly correlated with the UV intensity with ...

Murthy, Jayant; Henry, R. C.; Paxton, L. J.; Price, S. D.

2001-01-01

149

Observations of gamma-ray emission in solar flares  

International Nuclear Information System (INIS)

This paper reviews the observations of gamma-ray emission made from the OSO-7 satellite in connection with two solar flares in early August 1972. The details of the measurements and a preliminary interpretation of some of the observed features are given. (U.S.)

150

Extended emission sources observed via two-proton correlations  

International Nuclear Information System (INIS)

Two-particle correlations between light particles emitted in heavy-ion reactions may be used to extract information on the spatial extent and time development of the emission source. Such measurements have provided evidence for the formation and decay of localized regions of high excitation. An interesting aspect of these measurements is the observation that the less energetic particles are emitted from sources of larger apparent dimensions. This has been interpreted as an indication that the lower energy particles are emitted at a later, more equilibrated stage of the reaction. As originally pointed out by Koonin, the dependence of the two-particle correlation on the direction of the relative momentum, with respect to the direction of emission, may provide information on the source lifetime and shape. Although spatial and temporal effects are not strictly distinguishable, a long-lived spherical emission source will have a characteristically prolate appearance, elongated in the direction of emission. We present an analysis of the directional dependence of the two-proton correlation function and extract the shape of the proton emission source. The source shape is observed to vary from that of the compound nucleus for the emission of energetic protons to an extended spherical shape for the emission of low-energy protons, contrary to expectations for a long-lived evaporative source of compound nucleus dimensions. 2 figs

151

Progress on scanning field emission microscope development for surface observation  

International Nuclear Information System (INIS)

Fabrication technologies for X-band high gradient accelerating structures have been studied at KEK with SLAC, INFN and CERN. A scanning field emission microscope has been developed at KEK for the observation of the microscopic surface defects which may be related to the rf breakdown trigger. We present the progress on the experimental results of studying field emission characteristics by scanning an arbitrary area of 0.5 mmx0.5 mm on OFHC copper surface using a newly developed scanning field emission microscope.

152

Progress on scanning field emission microscope development for surface observation  

Energy Technology Data Exchange (ETDEWEB)

Fabrication technologies for X-band high gradient accelerating structures have been studied at KEK with SLAC, INFN and CERN. A scanning field emission microscope has been developed at KEK for the observation of the microscopic surface defects which may be related to the rf breakdown trigger. We present the progress on the experimental results of studying field emission characteristics by scanning an arbitrary area of 0.5 mmx0.5 mm on OFHC copper surface using a newly developed scanning field emission microscope.

Higashi, Y., E-mail: higashiy@post.kek.jp [KEK, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Higo, T.; Matsumoto, S.; Yokoyama, K.; Zhang Xiaowei [KEK, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Dolgashev, Valery; Tantawi, Sami [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Spataro, B. [INFN-LNF, 00044 Frascati (Italy)

2011-11-21

153

Studies of VLF Radio Waves for Sudden Ionospheric Disturbances (sid) in Kashmir Region  

Science.gov (United States)

It is recognized that the ionosphere may be sensitive to seismic effects, and the detection of ionospheric perturbations associated with seismicity would be useful for short term prediction of seismic events. To observe this effect, Indian Centre for Space Physics has installed an antenna and receiver system at Kashmir University to monitor the variation of the VLF signal transmitted from VTX. We present the preliminary results from this station.

Wani, M. R.; Iqbal, Naseer; Sasmal, Sudipta

2010-10-01

154

Studies of VLF radio waves for sudden ionospheric disturbances (SID) in Kashmir region  

International Nuclear Information System (INIS)

It is recognized that the ionosphere may be sensitive to seismic effects, and the detection of ionospheric perturbations associated with seismicity would be useful for short term prediction of seismic events. To observe this effect, Indian Centre for Space Physics has installed an antenna and receiver system at Kashmir University to monitor the variation of the VLF signal transmitted from VTX. We present the preliminary results from this station.

155

An automated analysis of DEMETER ionospheric plasma waves observations and its application to the search for anomalous emissions over the Great Sichuan EQ region  

Science.gov (United States)

Electric field observations in the VLF range from the ICE experiment onboard the CNES DEMETER micro-satellite have been analyzed to search for anomalies possibly related to the Great Sichuan Earthquake of May 12, 2008. This work was undertaken using results from a dedicated data processing that has been recently developed at LATMOS to perform an automated recognition and characterization of the various wave emissions that are regularly detected along the orbit of DEMETER. The data processing method and the associated algorithms will be first presented and a few typical results will be shown in order to provide a detailed understanding of the algorithm capabilities. As a first full-scale application of this method, a statistical study was conducted to analyze the plasma waves observed in day-time half orbits over a region of ~1000 kilometres extent centred on the Sichuan EQ epicentre and during a period of 20 days encompassing the day of the EQ. 5 years of observations have been used to derive the statistical distribution of various types of ionospheric plasma waves that can be compared to the signals detected during the seismic active period. The first outcome of our study was the detection of a localized variation in the characteristics of the electrostatic turbulence 6 days before the EQ that appears to be unique in the whole 5 year reference observations data base. We will discuss this result and its possible interpretations.

Onishi, Tatsuo; Berthelier, Jean-Jacques

2010-05-01

156

SCIAMACHY formaldehyde observations: constraint for isoprene emission estimates over Europe?  

Directory of Open Access Journals (Sweden)

Full Text Available Formaldehyde (HCHO is an important intermediate compound in the degradation of volatile organic compounds (VOCs in the troposphere. Sources of HCHO are largely dominated by its secondary production from VOC oxidation, methane and isoprene being the main precursors in unpolluted areas. As a result of the moderate lifetime of HCHO, its spatial distribution is determined by reactive hydrocarbon emissions. We focus here on Europe and investigate the influence of the different emissions on HCHO tropospheric columns with the CHIMERE chemical transport model in order to interpret the comparisons between SCIAMACHY and simulated HCHO columns. Europe was never specifically studied before for these purposes using satellite observations. The bias between measurements and model is less than 20% on average. The differences are discussed according to the errors on the model and the observations and remaining discrepancies are attributed to a misrepresentation of biogenic emissions. This study requires the characterisation of: (1 the model errors and performances concerning formaldehyde. The errors on the HCHO columns, mainly related to chemistry and mixed emission types, are evaluated to 2×1015 molecule/cm2 and the model performances evaluated using surface measurements are satisfactory (~13%; (2 the observation errors that define the needs in spatial and temporal averaging for meaningful comparisons. Using SCIAMACHY observations as constraint for biogenic isoprene emissions in an inverse modelling scheme reduces their uncertainties by about a factor of two in region of intense emissions. The retrieved correction factors for the isoprene emissions range from a factor of 0.15 (North Africa to a factor of 2 (Poland, the United Kingdom depending on the regions.

G. Dufour

2009-03-01

157

Statistical analysis of VLF radio emissions triggered by power line harmonic radiation and observed by the low-altitude satellite DEMETER.  

Czech Academy of Sciences Publication Activity Database

Ro?. 119, ?. 7 (2014), s. 5744-5754. ISSN 2169-9380 R&D Projects: GA ?R GAP205/10/2279; GA MŠk LH12231 Institutional support: RVO:68378289 Keywords : man-made waves * ionosphere Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.440, year: 2013 http://onlinelibrary.wiley.com/doi/10.1002/2014JA020139/abstract

Parrot, M.; N?mec, F.; Santolík, Ond?ej

2014-01-01

158

Rocket investigations of electron precipitation and VLF waves in the Antarctic upper atmosphere  

Science.gov (United States)

The results of two Antarctic rocket campaigns, primarily initiated to investigate electron precipitation stimulated by signals from the Siple-Station ground-based VLF transmitter, are presented. While the primary objective of the campaigns was not achieved, the Siple VLF transmitter facilitated a study of the wave environment in the ionosphere. Standing wave patterns in the ionosphere were observed for the first time by detectors flown aboard the Nike-Tomahawk rockets; the same detectors monitored a continuous signal from the transmitter through the neutral atmosphere and into the ionosphere, providing unique data for comparison with theoretical studies of wave propagation. The measurements of penetrating electron precipitation were interpreted in terms of a model of energetic electron precipitation from the trapped radiational belts.

Sheldon, W. R.; Benbrook, J. R.; Bering, E. A.

1988-08-01

159

Rocket investigations of electron precipitation and VLF waves in the Antarctic upper atmosphere  

International Nuclear Information System (INIS)

The results of two Antarctic rocket campaigns, primarily initiated to investigate electron precipitation stimulated by signals from the Siple-Station ground-based VLF transmitter, are presented. While the primary objective of the campaigns was not achieved, the Siple VLF transmitter facilitated a study of the wave environment in the ionosphere. Standing wave patterns in the ionosphere were observed for the first time by detectors flown aboard the Nike-Tomahawk rockets; the same detectors monitored a continuous signal from the transmitter through the neutral atmosphere and into the ionosphere, providing unique data for comparison with theoretical studies of wave propagation. The measurements of penetrating electron precipitation were interpreted in terms of a model of energetic electron precipitation from the trapped radiational belts. 52 references

160

Detection of variations of VLF/LF signals generated by lightning strokes and its analysis  

Science.gov (United States)

Lightnings which are produced in the Earth's atmosphere during thunderstorms are known to generate currents of 200 kA per stroke and cause broadband radio signals acting on antennas at the Earth's surface. In the present contribution, the newly developed theory of cosmic ray shower-runaway breakdown in thunderclouds predicted by Gurevich et al. is reconsidered and possible changes of the degree of ionization in thunderstorm regions are discussed. Moreover, estimates of the variations of electrical conductivity and electric fields during the electron avalanche are performed. The changes of the plasma parameters of the Earth's atmosphere may be strong enough, so that the altitudes, at which artificial VLF/LF signals are reflected in the atmosphere, are modified. Consequently, also the amplitudes and phases of the VLF/LF signals detected by radio stations may show observable variations. For instance, they should be detectable by the VLF/LF radio station VADar of the University of Technology Darmstadt constructed to predict possible earthquake precursors in Europe. First results of the analysis of VADar observations during thunderstorms using the Hilbert-Huang method are presented.

Ram Lee, Bo; Meister, Claudia-Veronika; Hoffmann, Dieter H. H.

2013-04-01

161

Quasi-periodic very low frequency emissions, very low frequency chorus, and geomagnetic Pc4 pulsations (Event on April 3, 2011)  

Science.gov (United States)

The results of an analysis of ground-based observations of very low frequency (VLF) emissions in Scandinavia ( L ˜ 5) in April 2011 are discussed. A detailed study is conducted of an non-typical event (April 3, 2011) of simultaneous generation of VLF chorus at frequencies below 3 kHz and quasi-periodic VLF emissions ( QP) in the band of 4-6 kHz, which were not discrete emissions but consisted of separate short (about 20 s) bursts of hiss. It is shown that these emissions were mainly characterized by right-hand polarization, which indicates the location of the exit point of waves from the ionosphere near the point of ground observations. Based on an analysis of the spectral characteristics of emissions, it is concluded that the generation regions of chorus and QP emissions were located at different L shells. The appearance of QP emissions coincided with the excitation of resonance geomagnetic pulsations of the Pc4 range in the magnetosphere with a period that was close to the quasi-period of repetition of spectral forms in QP emissions. However, based on the available data, it is not possible to conclude that these geomagnetic pulsations caused the quasi-periodic generation of bursts of VLF hiss. The time shift between the peaks of QP and geomagnetic pulsations was inconsistent and varied from one burst of hiss to another. It is suggested that the discussed QP emissions were a result of the development of self-oscillations in the Earth's radiation belts.

Manninen, J.; Kleimenova, N. G.; Kozyreva, O. V.; Bespalov, P. A.; Raita, T.

2012-02-01

162

GOME-2 satellite observations of NOx emissions from ships  

Science.gov (United States)

The volume of international shipping has been rapidly increasing over the last decades, and further increases are expected for the coming years. A large fraction of the shipping is close to coastal areas but for intercontinental transport, shipping routes also pass through the remote oceans. As the volume of transported goods is increasing, so is the amount of shipping related pollutant emissions into the marine boundary layer. As result of the lack of legislation on shipping emissions, in particular in international waters, in combination with substantial emission reductions for many land based sources, the relative importance of pollution from ships is increasing. Satellite observations of NO2 and HCHO by GOME and SCIAMACHY have been used to identify shipping emissions mainly in the Indian Ocean, where high vessel densities and low background pollution levels facilitate the detection of small signals. With the better spatial coverage of recent satellite instruments such as GOME-2 and OMI, the statistics improved and better detection limits can now be achieved. In this study, three years of GOME-2 data of NO2 have been systematically examined for shipping signals. Compared to previous studies, additional shipping tracks could be identified in the NO2 maps. Comparison with SCIAMACHY measurements shows interesting changes in the paths taken by the ships in the Gulf of Aden and the Indian Ocean. The observed patterns in ship emissions will be discussed with respect to reported vessel densities and GOME-2 measurement uncertainties.

Richter, Andreas; Hilboll, Andreas; Zien, Achim; Burrows, John P.

2010-05-01

163

Observational and theoretical advances in cosmological foreground emission  

Science.gov (United States)

Observational and theoretical work towards the separation of foreground emission from the cosmic microwave background is described. The bulk of this work is in the design, construction, and commissioning of the C-Band All-Sky Survey (C-BASS), an experiment to produce a template of the Milky Way Galaxy's polarized synchrotron emission. Theoretical work is the derivation of an analytical approximation to the emission spectrum of spinning dust grains. The performance of the C-BASS experiment is demonstrated through a preliminary, deep survey of the North Celestial Pole region. A comparison to multiwavelength data is performed, and the thermal and systematic noise properties of the experiment are explored. The systematic noise has been minimized through careful data processing algorithms, implemented both in the experiment's Field Programmable Gate Array (FPGA) based digital backend and in the data analysis pipeline. Detailed descriptions of these algorithms are presented. The analytical function of spinning dust emission is derived through the application of careful approximations, with each step tested against numerical calculations. This work is intended for use in the parameterized separation of cosmological foreground components and as a framework for interpreting and comparing the variety of anomalous microwave emission observations.

Stevenson, Matthew A.

164

Exos-B/Siple Station VLF wave-particle interaction experiments: 1. General description and wave-particle correlations  

International Nuclear Information System (INIS)

In situ measurements of both energetic particles and VLF waves have been carried out in a joint program involving the Japanese satellite EXOS-B and the Siple Station VLF transmitter. A general description of the experiment is given as well as some results concerning wave-particle correlations. Detailed analysis of the observed wave characteristics is given in a companion paper. Correlations of electron flux and pitch angle anisotropy in the energy range from 85 eV to 6.9 keV with waves in a range from 300 Hz to 9 kHz are examined. These electrons sometimes have a pitch angle distributions with a peak flux at 900 pitch angle (so-called pancake distribution). On five passes out of a total of 50 during the summer campaign in 1979, the energy of the electrons that showed a high pitch angle anisotropy shifted upward as the satellite moved into the plasmasphere, crossing the plasmapause in the equatorial region. In two cases out of five, strong Siple signals were observed in the geomagnetic equatorial region just outside the plasmapause, in association with such a pancake pitch angle distribution of electrons. The Siple signals are most likely amplified by the cyclotron instability due to the high pitch angle anisotropy (HPAA), although the flux of resonant electrons was relatively small. For three other cases of HPAA, the satellite location was so far away from the Siple meridian that the signal level, even if amplified, was too weak to be detected by the satell was too weak to be detected by the satellite. Emissions associated with Siple signals were detected on five (two equatorial and three high latitude) passes, which were all confined on 6 days after a large magnetic storm. On the days when the Siple triggered emissions were observed, the pitch angle anisotropy was low, but the electron flux at resonant energies in the equatorial region was four or five times larger than that on other non-triggering days in all energy channels from 85 eV to 6.9 keV

165

Vertical transport of surface fire emissions observed from space  

Science.gov (United States)

We use optimal estimation to infer the vertical distribution of surface emissions lofted from boreal and tropical biomass burning during June-October (JJASO) 2006. We use satellite observations of CO, a tracer of incomplete combustion, at thermal infrared and microwave wavelengths from Aura Tropospheric Emission Spectrometer (TES) and Microwave Limb Sounder (MLS), respectively. TES and MLS together typically provide two to three pieces of information. We use a maximum a posteriori (MAP) methodology to estimate emitted CO mass in five vertical regions spanning the troposphere and lower stratosphere, equivalent to estimating surface emissions. Correlations between neighboring vertical regions, due to vigorous mixing induced by surface heating, reduce the inversion to the information content provided by the data. We use a total of 1785 TES profile measurements, of which 672 are colocated with MLS. We define an injection height based on MAP statistics. We find that 10%-20% of boreal and tropical fire emissions, depending on the region, reach the free and upper troposphere during JJASO 2006. Our injection height estimates during two key pyroconvective events, Siberia (July) and Indonesia (October), qualitatively agree with measurements of aerosol index and attenuated backscatter from Aura Ozone Monitoring Instrument (OMI) and CALIPSO, respectively. Surface emissions inferred from our mass estimates agree with the Global Fire Emission Database biomass burning emission inventory to within ±10%. The small percentage of emissions injected above the boundary layer result in disproportionate changes in CO concentrations of more than 2-25 ppb and 15-160 ppb over boreal and tropical regions, respectively.

Gonzi, Siegfried; Palmer, Paul I.

2010-01-01

166

Excitation of guided ELF-VLF waves through modification of the F2 ionospheric layer by high-power radio waves  

International Nuclear Information System (INIS)

The possibility of controlled excitation of ELF-VLF electromagnetic waves through modification of the F2 ionospheric layer by high-power high-frequency emission is demonstrated in a natural experiment by using the Sura midlatitude heating facility. The excited low-frequency waves can be used to explore the near-Earth space and stimulate the excitation of a magnetospheric maser.

167

Observations of H2 emission from NGC 7538  

International Nuclear Information System (INIS)

Observations of the molecular hydrogen emission at 2 ?m in NGC 7538 are presented. A map of the ?=1-0S(1) line obtained at 24'' resolution indicates that the peak of the molecular line emission occurs between the interface of the visible H II region and the dense molecular cloud and the infrared cluster within the molecular cloud. The apparent luminosity in the S(1) line of approx.1.2L/sub sun/ is similar to that measured for Orion, approx.2.5L/sub sun/, before correction for extinction by overlying dust

168

Solar Flare Impulsive Phase Emission Observed with SDO/EVE  

CERN Document Server

Differential emission measures (DEMs) during the impulsive phase of solar flares were constructed using observations from the EUV Variability Experiment (EVE) and the Markov-Chain Monte Carlo method. Emission lines from ions formed over the temperature range log T = 5.8 - 7.2 allow the evolution of the DEM to be studied over a wide temperature range at 10s cadence. The technique was applied to several M- and X-class flares, where impulsive phase EUV emission is observable in the disk-integrated EVE spectra from emission lines formed up to 3 - 4 MK, and we use spatially-unresolved EVE observations to infer the thermal structure of the emitting region. For the nine events studied the DEMs exhibited a two component distribution during the impulsive phase, a low temperature component with peak temperature of 1 - 2 MK, and a broad high temperature one from 7 - 30 MK. A bimodal high temperature component is also found for several events, with peaks at 8 and 25 MK during the impulsive phase. The origin of the emissi...

Kennedy, Michael B; Mathioudakis, Mihalis; Keenan, Francis P

2013-01-01

169

Observations of H? emission profiles in Aditya tokamak  

International Nuclear Information System (INIS)

Emissions from the hydrogen Balmer alpha (? = 656.28 nm) has been recorded for a large number of plasma discharges in the Aditya tokamak using a 1m Czerny-Turner spectrometer equipped with an 1800 grooves/mm reflection grating. Eight simultaneous vertically collimated line-of-sights, using individual lens – fiber combination from a top port of the tokamak view a poloidal cross-section of the plasma. The line-of-sights can be moved along the major radius to obtain emissions from different major-radial positions on a shot–to–shot basis. Abel-like matrix inversion has been performed to obtain radial profile of volume emissivities from these chord-integrated intensities. Considerable H? emission is observed in the bulk plasma indicating a considerable neutral penetration. Further, a second peak in the H? radial profile has been observed at ?(r/a) ? +/- 0.3 -- +/- 0.5 in majority of discharges irrespective of the plasma column position. This observation suggests a considerable accumulation of neutrals in the region of ?(r/a) ? +/- 0.3 -- +/- 0.5. CV to CIII line ratio variations at the same location also suggest a substantial presence of neutrals explained by the charge-exchange, involving collisions between H-like carbon ions and neutral hydrogen atoms. (author)

170

Verification of the backward wave oscillator model of VLF chorus generation using data from MAGION 5 satellite  

OpenAIRE

We present a detailed study of chorus emissions in the magnetosphere detected on board Magion 5, when the satellite was not far from the magnetic equator. We determine the frequency sweep rate of more than 8500 electromagnetic VLF chorus elements. These results are compared with the backward wave oscillator (BWO) regime of chorus generation. Comparison of the frequency sweep rate with the BWO model shows: (i) There is a correlation between the frequency sweep rates and the chorus ampli...

Titova, E. E.; Kozelov, B. V.; Jiric?ek, F.; Smilauer, J.; Demekhov, A. G.; Yu Trakhtengerts, V.

2003-01-01

171

Verification of the backward wave oscillator model of VLF chorus generation using data from MAGION 5 satellite.  

Czech Academy of Sciences Publication Activity Database

Ro?. 21, - (2003), s. 1073-1081. ISSN 0992-7689 R&D Projects: GA AV ?R IAA3042201 Grant ostatní: INTAS(GB) 99-0502; RFBR(RU) 01-05-643829; RFBR(RU) 02-02-17109 Institutional research plan: CEZ:AV0Z3042911 Keywords : magnetospheric physics (VLF emissions, energetic particles) * space plasma physics (wave-particle interactions) Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 1.031, year: 2003

Titova, E. E.; Kozelov, B. V.; Ji?í?ek, František; Šmilauer, Jan; Demekhov, A. G.; Trakhtengerts, V. Yu.

2003-01-01

172

An unusual VLF signature structure recorded by the DEMETER satellite  

OpenAIRE

A type of electromagnetic phenomenon has been found in the electric VLF data measured by the low Earth orbit DEMETER satellite, which was nonidentified earlier as a different class of electromagnetic VLF events. The phenomenon, termed as “swallow-tailed whistler” (STW) after its shape, seems to be similar to a whistler, but following the main trace, an additional trace appears with monotonously increasing frequency. The secondary trace, lasting less than 80 ms within the recorded 20 kHz b...

Ferencz, Csaba; Lichtenberger, Janos; Hamar, Daniel; Ferencz, Orsolya E.; Steinbach, Peter; Szekely, Balazs; Parrot, Michel; Lefeuvre, Francois; Berthelier, Jean-jacques; Clilverd, Mark

2010-01-01

173

VLF wave propagation and determination of ionospheric parameters  

Science.gov (United States)

Characteristics and composition of the ionosphere were theoretically investigated by VLF wave propagation in the Earth-ionosphere waveguide. The exact mode equation is deduced and the calculation of the waveguide parameters v/c and alpha is explained. The ionospheric plasma parameters are determined by numerical simulation. Comparison of these calculations with the results of earlier VLF measurements and results from the literature shows good agreement.

Floery, E.; Riedler, W.

1982-06-01

174

Observation of dispersive wave emission by temporal cavity solitons.  

Science.gov (United States)

We examine a coherently-driven, dispersion-managed, passive Kerr fiber ring resonator and report, to the best of our knowledge, the first direct experimental observation of dispersive wave emission by temporal cavity solitons (CSs). Our observations are in excellent agreement with analytical predictions and they are fully corroborated by numerical simulations. These results lead to a better understanding of the behavior of temporal CSs under conditions where higher-order dispersion plays a significant role. Significantly, since temporal CSs manifest themselves in monolithic microresonators, our results are likely to explain the origins of spectral features observed in broadband Kerr frequency combs. PMID:25360913

Jang, Jae K; Erkintalo, Miro; Murdoch, Stuart G; Coen, Stéphane

2014-10-01

175

Optical emission spectroscopy observations of fast pulsed capillary discharge plasmas  

Science.gov (United States)

We present time resolved optical emission spectroscopic (OES) observations of a low energy, pulsed capillary discharage (PCD). The optical emission from the capillary plasma and plasma jets emitted from the capillary volume was recorded with with a SpectraPro 275 spectrograph, fitted with a MCP gated OMA system, with 15 ns time resolution. The discharge was operated with different gases, including argon, nitrogen, hydrogen and methane, in a repetitive pulsed discharge mode at 10-50 Hz, with, 10-12 kV pulses applied at the cathode side. The time evolution of the electron density was measured using Stark broadening of the H? line. Several features of the capillary plasma dynamics, such as ionization growth, wall effects and plasma jet evolution, are inferred from the time evolution of the optical emission.

Avaria, G.; Ruiz, M.; Guzmán, F.; Favre, M.; Wyndham, E. S.; Chuaqui, H.; Bhuyan, H.

2014-05-01

176

Observations and Theory of the Anomalous Microwave Emission  

Science.gov (United States)

The recently discovered Anomalous Microwave Emission (AME) presents a potential new probe of interstellar dust. Peaking at around 30GHz, having a width of several tens of GHz, and appearing to be highly dust-correlated, this continuum emission is commonly assumed to be due very small, rapidly spinning dust grains. Directed study of the AME may therefore provide a new handle on these grains and their environments. I will present three projects aimed at advancing our understanding of this emission. The first is a new, analytical derivation of radiation from spinning dust grains, bridging the gap between the precise models and realistic observations. The second is a joint CARMA/AMI survey of Planck Early Cold Clumps, searching for predicted spinning dust emission. The third is a correlation analysis of diffuse microwave emission from the North Celestial Pole, combining a new 5GHz map from the C-Band All-Sky Survey (C-BASS) with existing radio, WMAP, IRAS, and H? maps. This work was supported in part by the NSF (AST-1212217).

Stevenson, Matthew; Readhead, A. C.; Pearson, T. J.; Cleary, K.; Tibbs, C.; Villadsen, J.; Hirata, C. M.; Paladini, R.; Muchovej, S.; Grainge, K.; Perrott, Y.; Rumsey, C.; Scaife, A.; C-BASS Collaboration

2013-01-01

177

Ground and space observations of medium frequency auroral radio emissions  

Science.gov (United States)

The auroral zone is a rich source of natural radio emissions that can be observed in space and at ground-level. By studying these waves, scientists can gain insight into the plasma processes that generate them and use the near-Earth space environment as a large-scale plasma physics laboratory. This thesis uses both ground-level and in situ observations to study two kinds of natural radio emissions. First, we report observations of a new kind of auroral radio emission. The waves have frequencies ranging from 1.3-2.2 MHz, bandwidths ranging from 90-272 kHz, and durations ranging from 16-355 s. Spectral analysis of the waveform data has revealed that the emission has a complex combination of at least three kinds of fine structures. For model auroral electron distributions, calculations indicate that Langmuir waves could be excited at frequencies consistent with observations. The remainder of the thesis discusses auroral medium frequency (MF) burst, an impulsive, broadband natural radio emission observed at ground-level within a few minutes of local substorm onset. LaBelle [2011] proposed that MF burst originates as Langmuir/Z-mode waves on the topside of the ionosphere that subsequently mode convert to L-mode waves and propagate to ground-level. Using continuous waveform measurements and combined observations with the Sondrestrom Incoherent Scatter Radar, we have performed two tests of this mechanism. The results of these tests are consistent with the mechanism described in LaBelle [2011]. A survey of 8,624 half-orbits of the DEMETER spacecraft has revealed 68 observations of bursty MF waves. We have compared the wave properties of these waves to those of MF burst and have found that although it is uncertain, the balance of the evidence suggests that the bursty MF waves observed with DEMETER are the same phenomenon as the ground-level MF burst. Finally, we have used numerical simulations to model both the fine structure of MF burst and to estimate the attenuation the waves would experience due to Landau damping on the topside ionosphere and mode conversion on the bottomside ionosphere. The amount of Landau damping is sensitive to the ratio of secondary to background electrons nse/ne0. Ignoring collisional damping in the lower ionosphere, these calculations suggest that for nse/n e0burst could plausibly originate as Langmuir/Z-mode waves on the topside of the ionosphere.

Broughton, Matthew C.

178

VHE emission from extragalactic sources: open issues from MWL observations  

Energy Technology Data Exchange (ETDEWEB)

The Cherenkov telescopes observations together with Fermi/LAT survey and multi-wavelength (MWL) simultaneous coverage are posing new challenges to the description of extreme sources, such as BL Lacs, flat spectrum radio quasars (FSRQs), and radiogalaxies. We will review some of these new results threatening the conventional emission models. Among them: the difficulties of the usual description with single-zone SSC models of the SED of BL Lacs objects, when simultaneous very-high energy (VHE) and MWL observations are taken into account; the constraints on the location of the gamma-ray emission region as revealed by the MAGIC observations of the FSRQ PKS 1222+21; the firm VHE detection of somewhat unexpected sources such as the radiogalaxy IC 310 in the Perseus cluster of galaxies. We will also consider the interplay between intrinsic emission models and the interaction of gamma-rays with the extragalactic background light and intergalactic magnetic fields. These issues will be tackled in the framework of the results of MWL observations led by the MAGIC Cherenkov telescopes system.

Stamerra, A.

2013-06-15

179

Correlations between SAMPEX detected relativistic electron precipitation and perturbations in ground based VLF signals during periods of extreme geomagnetic disturbance  

International Nuclear Information System (INIS)

Complete text of publication follows. Bursts of relativistic (>1 MeV) electron precipitation from Earth's radiation belts are detected by the Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX), a low Earth orbiting satellite. During periods of enhanced geomagnetic activity, perturbations can be found in very low frequency (VLF) signals received by the Antarctic-Arctic Radiation-belt (Dynamic) Deposition - VLF Atmospheric Research Konsortium (AARDDVARK). One such class of these VLF perturbations have been termed FAST events, which are characterised by their large perturbation amplitude, both positive and negative, their temporal brevity (t?6. These FAST events are observed across multiple VLF channels and are thought to be caused by a 'rainstorm' of spatially small (tens of kilometres or less) bursts of precipitation striking the atmosphere. It is seen that periods of FAST event activity coincide with periods of SAMPEX detected relativistic electron precipitation, which are termed microbursts. SAMPEX is usually measuring both the drift and bounce-loss cones, while the AARDDVARK measurements are of local precipitation from the bounce-loss cone. A statistical analysis of the nature of the correlation between FAST events and SAMPEX precipitation during times of enhanced geomagnetic disturbance is currently being undertaken. Emphasis is being placed on periods during wasis is being placed on periods during which SAMPEX was viewing the bounce-loss cone but not the drift-loss cone.

180

Broad Iron Emission from Gravitationally Lensed Quasars Observed by Chandra  

CERN Document Server

Recent work has demonstrated the potential of gravitationally lensed quasars to extend measurements of black hole spin out to high-redshift with the current generation of X-ray observatories. Here we present an analysis of a large sample of 27 lensed quasars in the redshift range 1.0observed with Chandra, utilizing over 1.6 Ms of total observing time, focusing on the rest-frame iron K emission from these sources. Although the X-ray signal-to-noise (S/N) currently available does not permit the detection of iron emission from the inner accretion disk in individual cases in our sample, we find significant structure in the stacked residuals. In addition to the narrow core, seen almost ubiquitously in local AGN, we find evidence for an additional underlying broad component from the inner accretion disk, with a clear red wing to the emission profile. Based on simulations, we find the detection of this broader component to be significant at greater than the 3-sigma level. This implies that iron emission...

Walton, D J; Miller, J M; Reis, R C; Stern, D; Harrison, F A

2015-01-01

181

Deep 1.4-GHz observations of diffuse polarized emission  

CERN Document Server

Polarized diffuse emission observations at 1.4-GHz in a high Galactic latitude area of the northern Celestial hemisphere are presented. The 3.2 X 3.2 deg^2 field, centred at RA = 10h 58m, Dec = +42deg 18' (B1950), has Galactic coordinates l~172deg, b~+63deg and is located in the region selected as northern target of the BaR-SPOrt experiment. Observations have been performed with the Effelsberg 100-m telescope. We find that the angular power spectra of the E- and B-modes have slopes of beta_E = -1.79 +/- 0.13 and beta_B = -1.74 +/- 0.12, respectively. Because of the very high Galactic latitude and the smooth emission, a weak Faraday rotation action is expected, which allows both a fair extrapolation to Cosmic Microwave Background Polarization (CMBP) frequencies and an estimate of the contamination by Galactic synchrotron emission. We extrapolate the E-mode spectrum up to 32-GHz and confirm the possibility to safely detect the CMBP E-mode signal in the Ka band found in another low emission region (Carretti et a...

Carretti, E; Reich, W; Reich, P; Fürst, E; Bernardi, G; Cortiglioni, S; Sbarra, C

2006-01-01

182

Observationally compatible model for Jupiter's IO-related decametric emission  

International Nuclear Information System (INIS)

A model for Jupiter's Io-related decametric radiation was adjusted to provide a close fit to observed contours of emission occurrence probability on the plane of Io phase vs. the central meridian longitude for frequencies between 35 and 36 MHz. These observations were reported by Wilson, Warwick, and Libby in 1968. A nonlinear indirect emission mechanism was assumed in which Io-excited Alfven waves produce an electron beam, which in turn, after intermediate steps, results in the emission of fast extraordinary mode electromagnetic waves. This radiation is emitted into a hollow-cone beam attached to the Io flux tube at a point where the wave frequency is slightly higher than the electron cyclotron frequency. A five dipole representation of Jupiter's magnetic field was developed and used in this model; it closely matches of O4 field model and has the advantage of greater computational flexibility. The Voyager-determined distribution of electron number density vs. height above the cloud-top level was used. Appropriate adjustments were made to account for the Alfven wave propagation time between Io and the emission point

183

Electron beam-driven ion modes in a space plasma. I - Observations  

Science.gov (United States)

The VLF wave spectra detected by a separable payload during the continuous electron beam emissions of the BERT-1 rocket, are presented here. The observations include broadband turbulence attributed to a plasma cloud formed through beam ionization of ambient neutrals; electrostatic waves that vary with plasma density with frequency separations of approximately twice the hydrogen gyrofrequency; and electromagnetic modes near even harmonics of the hydrogen cyclotron frequency.

Donatelli, D. E.; Ernstmeyer, J.; Sydora, R.

184

Further observations on rhythmic emission of fragrance in flowers.  

Science.gov (United States)

Observations regarding floral fragrance and the rhythmicity of its emission in four plant species are reported. In the case of flowers of Hoya carnosa R. Br. which are characterized by circadian rhythmicity of scentedness (R. Altenburger and P. Matile, 1988, Planta 174, 248-252), temperature compensation of the free-running period as well as persistence of oscillations in permanent darkness have been demonstrated. A hitherto unidentified component of fragrance turned out to be identical to an unusual sesquiterpene recently discovered in cardamom oil (B. Maurer et al., 1986, Tetrahedron Lett. 27, 2111-2112). In Stephanotis floribunda Brongs. the rhythmic emission of fragrance is circadian in nature, but in a constant environment the oscillations of individual components are increasingly asynchronous. In excised flowers of Odontoglossum constrictum Lindl. the diurnal oscillations observed in a natural photoperiod are abolished under constant environmental conditions. They are resumed upon the return to a 12?12-h photoperiod. The absence of circadian control could also be demonstrated in excised flowers of Citrus medica L. In this species, too, the daily maxima of scent emission reappear upon the transfer of flowers to a 12?12-h light/ dark cycle. Results obtained upon the comparative analysis of volatiles in the headspace above the flowers and in petal extract indicate that the relative abundance of an individual compound in the floral fragrance is not a function of differential volatility. PMID:24201944

Altenburger, R; Matile, P

1990-01-01

185

GOME-2 satellite observations of NOx emissions from ships  

Energy Technology Data Exchange (ETDEWEB)

The volume of international shipping has been rapidly increasing over the last decades, and further increases are expected for the coming years. A large fraction of shipping is close to coastal areas but for intercontinental transport, shipping routes also pass through the remote oceans. As the volume of transported goods is increasing, so is the amount of shipping related pollutant emissions into the marine boundary layer. Satellite observations of NO{sub 2} and HCHO by GOME and SCIAMACHY have been used to identify shipping emissions mainly in the Indian Ocean, where high vessel densities and low background pollution levels facilitate the detection of small signals. With the better spatial coverage of recent satellite instruments such as GOME-2 and OMI, the statistics improved and better detection limits can now be achieved. In this study, three years of GOME-2 data of NO{sub 2} have been systematically examined for shipping signals. Compared to previous studies, additional shipping tracks could be identified in the NO2 maps. Comparison with SCIAMACHY measurements shows changes in the paths taken by the ships in the Gulf of Aden and the Indian Ocean. The observed patterns in ship emissions are discussed with respect to reported vessel densities and GOME-2 measurement uncertainties.

Richter, Andreas; Hilboll, Andreas; Zien, Achim; Burrows, John P. [Institut fuer Umweltphysik, Universitaet Bremen (Germany)

2010-07-01

186

Time-monitoring observations of Br? emission from young stars  

Science.gov (United States)

We present multiple epochs of near-infrared spectroscopy for a sample of 25 young stars, including T Tauri, Herbig Ae/Be, and FU Ori objects. Using the FSPEC instrument on the Bok 90-inch telescope, we obtained K-band spectra of the Br? transition of hydrogen, with a resolution of ?3500. Epochs were taken over a span of >1 yr, sampling time-spacings of roughly 1 d, 1 month, and 1 yr. The majority of our targets show Br? emission, and in some cases these are the first published detections. Time variability is seen in approximately half of the targets showing Br? emission. We compare the observed variability with expectations for rotationally modulated accretion on to the central stars and time-variable continuum emission or extinction from matter in the inner disc. Our observations are not entirely consistent with models of rotationally modulated magnetospheric accretion. Further monitoring, over a larger number of epochs, will facilitate more quantitative constraints on variability time-scales and amplitudes, and a more conclusive comparison with theoretical models.

Eisner, J. A.; Rieke, G. H.; Rieke, M. J.; Flaherty, K. M.; Stone, J. M.; Arnold, T. J.; Cortes, S. R.; Cox, E.; Hawkins, C.; Cole, A.; Zajac, S.; Rudolph, A. L.

2015-02-01

187

The large scale infrared emission in the galactic plane - observations  

International Nuclear Information System (INIS)

Infrared radiation is deeply involved in a variety of matters and processes in the galaxy. Near infrared radiation is predominantly emitted by late type stars which include the major part of the mass in the Galaxy and hence govern its dynamics. Short wavelength radiation (UV and visible) emitted from early type stars is easily absorbed by dust around the stars themselves or by interstellar dust, and reemitted in middle or far infrared regions. A variety of emission lines, fine structure lines of neutral and ionized heavy elements, as well as many molecular lines are also clustered in the middle and far infrared regions. Since their line intensities are generally very weak, and, moreover, spectroscopic observations demand relatively difficult techniques in their detection, the surveys so far done have been limited mostly to continuum emission. This article compiles them and discusses briefly their implications to the structure of the Galaxy in its inner region. (Auth.)

188

Study of ELF/VLF wave generation by HF heater-modulated electrojet  

Energy Technology Data Exchange (ETDEWEB)

Generation of ELF/VLF waves by the modulation of the electrojet by the powerful HF heater is of current interest. It is done by applying an amplitude modulated HF heater to modify the electron temperature of the electrojet in time. This in turn causes the modulation of the conductivity and thus, the electrojet current. Emissions are then produced at the modulation frequency and its harmonics. The present work extends the previous one of thermal instability to the nonlinear saturation regime. Two heater-modulation schemes are considered. One, corresponding to the one adopted in the Tromsq heating experiments, modulated the heater by a rectangular periodic pulse. The other one needs two overlapping heater waves (beat wave) having a frequency difference equal to the desired modulation frequency. It is essentially a sinusoidal amplitude modulation and is the approach adopted in the Arecibo heating experiments. The nonlinear evolutions of the generated ELF/VLF waves are determined numerically. Their spectra are also evaluated. The results show that the signal quality of the beat wave scheme is better (i.e., harmonic components have relatively lower intensities than that of the fundamental line). The field intensity of the emission at the fundamental modulation frequency is found to increase with the modulation frequency, consistent with the Tromsq results.

Kuo, S.P. [Polytechnic Univ., Farmingdale, NY (United States). Dept. of Electrical Engineering; Lee, M.C. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center; Kossey, P. [Phillips Lab., Hanscom AFB, MA (United States)

1997-12-31

189

Study of ELF/VLF wave generation by HF heater-modulated electrojet  

International Nuclear Information System (INIS)

Generation of ELF/VLF waves by the modulation of the electrojet by the powerful HF heater is of current interest. It is done by applying an amplitude modulated HF heater to modify the electron temperature of the electrojet in time. This in turn causes the modulation of the conductivity and thus, the electrojet current. Emissions are then produced at the modulation frequency and its harmonics. The present work extends the previous one of thermal instability to the nonlinear saturation regime. Two heater-modulation schemes are considered. One, corresponding to the one adopted in the Tromsq heating experiments, modulated the heater by a rectangular periodic pulse. The other one needs two overlapping heater waves (beat wave) having a frequency difference equal to the desired modulation frequency. It is essentially a sinusoidal amplitude modulation and is the approach adopted in the Arecibo heating experiments. The nonlinear evolutions of the generated ELF/VLF waves are determined numerically. Their spectra are also evaluated. The results show that the signal quality of the beat wave scheme is better (i.e., harmonic components have relatively lower intensities than that of the fundamental line). The field intensity of the emission at the fundamental modulation frequency is found to increase with the modulation frequency, consistent with the Tromsq results

190

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Foreground Emission  

Science.gov (United States)

The WMAP mission has mapped the full sky to determine the geometry, content, and evolution of the universe. Full sky maps are made in five microwave frequency bands to separate the temperature anisotropy of the cosmic microwave background (CMB) from foreground emission, including diffuse Galactic emission and Galactic and extragalactic point sources. We define masks that excise regions of high foreground emission, so CMB analyses can became out with minimal foreground contamination. We also present maps and spectra of the individual emission components, leading to an improved understanding of Galactic astrophysical processes. The effectiveness of template fits to remove foreground emission from the WMAP data is also examined. These efforts result in a CMB map with minimal contamination and a demonstration that the WMAP CMB power spectrum is insensitive to residual foreground emission. We use a Maximum Entropy Method to construct a model of the Galactic emission components. The observed total Galactic emission matches the model to less than 1% and the individual model components are accurate to a few percent. We find that the Milky Way resembles other normal spiral galaxies between 408 MHz and 23 GHz, with a synchrotron spectral index that is flattest (beta(sub s) approx. -2.5) near star-forming regions, especially in the plane, and steepest (beta(sub s) approx. -3) in the halo. This is consistent with a picture of relativistic cosmic ray electron generation in star-forming regions and diffusion and convection within the plane. The significant synchrotron index steepening out of the plane suggests a diffusion process in which the halo electrons are trapped in the Galactic potential long enough to suffer synchrotron and inverse Compton energy losses and hence a spectral steepening. The synchrotron index is steeper in the WMAP bands than in lower frequency radio surveys, with a spectral break near 20 GHz to beta(sub s) less than -3. The modeled thermal dust spectral index is also steep in the WMAP bands, with beta(sub d) approx. = 2.2. Our model is driven to these conclusions by the low level of total foreground contamination at approx. 60 GHz. Microwave and Ha measurements of the ionized gas agree well with one another at about the expected levels. Spinning dust emission is limited to less than 5% of the Ka-band foreground emission. A catalog of 208 point sources is presented. The reliability of the catalog is 98%, i.e., we expect five of the 208 sources to be statistically spurious. The mean spectral index of the point sources is alpha approx. 0(beta approx. -2). Derived source counts suggest a contribution to the anisotropy power from unresolved sources of (15.0 +/- 1.4) x 10(exp -3)micro sq K sr at Q-band and negligible levels at V-band and W-band. The Sunyaev-Zeldovich effect is shown to be a negligible "contamination" to the maps.

Bennett, C. L.; Hill, R. S.; Hinshaw, G.; Nolta, M. R.; Odegard, N.; Page, L.; Spergel, D. N.; Weiland, J. L.; Wright, E. L.; Halpern, M.

2003-01-01

191

FERMI Observations of Gamma -Ray Emission From the Moon  

Science.gov (United States)

We report on the detection of high-energy ? -ray emission from the Moon during the first 24 months of observations by the Fermi Large Area Telescope (LAT). This emission comes from particle cascades produced by cosmicray (CR) nuclei and electrons interacting with the lunar surface. The differential spectrum of the Moon is soft and can be described as a log-parabolic function with an effective cutoff at 2-3 GeV, while the average integral flux measured with the LAT from the beginning of observations in 2008 August to the end of 2010 August is F(greater than100 MeV) = (1.04 plus or minus 0.01 [statistical error] plus or minus 0.1 [systematic error]) × 10(sup -6) cm(sup -2) s(sup -1). This flux is about a factor 2-3 higher than that observed between 1991 and 1994 by the EGRET experiment on board the Compton Gamma Ray Observatory, F(greater than100 MeV)˜5×10(sup -7) cm(sup -2) s(sup -1), when solar activity was relatively high. The higher gamma -ray flux measured by Fermi is consistent with the deep solar minimum conditions during the first 24 months of the mission, which reduced effects of heliospheric modulation, and thus increased the heliospheric flux of Galactic CRs. A detailed comparison of the light curve with McMurdo Neutron Monitor rates suggests a correlation of the trends. The Moon and the Sun are so far the only known bright emitters of gamma-rays with fast celestial motion. Their paths across the sky are projected onto the Galactic center and high Galactic latitudes as well as onto other areas crowded with high-energy gamma-ray sources. Analysis of the lunar and solar emission may thus be important for studies of weak and transient sources near the ecliptic.

Abdo, A. A.; Ackermann, M.; Ajello, M.; Atwoo, W. B.; Baldini, I.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Gehrels, N.; Hays, E.; Thompson, D. J.; McEnery, J. E.; Troja, E.

2012-01-01

192

Fermi Observations of ?-Ray Emission from the Moon  

Science.gov (United States)

We report on the detection of high-energy ?-ray emission from the Moon during the first 24 months of observations by the Fermi Large Area Telescope (LAT). This emission comes from particle cascades produced by cosmic-ray (CR) nuclei and electrons interacting with the lunar surface. The differential spectrum of the Moon is soft and can be described as a log-parabolic function with an effective cutoff at 2-3 GeV, while the average integral flux measured with the LAT from the beginning of observations in 2008 August to the end of 2010 August is F(>100\\ MeV) =(1.04+/- 0.01\\,{[statistical\\ error]}+/- 0.1\\,{[systematic\\ error]})\\times 10^{-6} cm-2 s-1. This flux is about a factor 2-3 higher than that observed between 1991 and 1994 by the EGRET experiment on board the Compton Gamma Ray Observatory, F(>100 MeV) ? 5 × 10-7 cm-2 s-1, when solar activity was relatively high. The higher ?-ray flux measured by Fermi is consistent with the deep solar minimum conditions during the first 24 months of the mission, which reduced effects of heliospheric modulation, and thus increased the heliospheric flux of Galactic CRs. A detailed comparison of the light curve with McMurdo Neutron Monitor rates suggests a correlation of the trends. The Moon and the Sun are so far the only known bright emitters of ?-rays with fast celestial motion. Their paths across the sky are projected onto the Galactic center and high Galactic latitudes as well as onto other areas crowded with high-energy ?-ray sources. Analysis of the lunar and solar emission may thus be important for studies of weak and transient sources near the ecliptic.

Abdo, A. A.; Ackermann, M.; Ajello, M.; Atwoo, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Casandjian, J. M.; Cecchi, C.; Charles, E.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Digel, S. W.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Favuzzi, C.; Fegan, S. J.; Focke, W. B.; Fortin, P.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gehrels, N.; Germani, S.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Gomez-Vargas, G. A.; Grenier, I. A.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Hays, E.; Hill, A. B.; Horan, D.; Hou, X.; Hughes, R. E.; Iafrate, G.; Jackson, M. S.; Jóhannesson, G.; Johnson, A. S.; Kamae, T.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Mazziotta, M. N.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orienti, M.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Parent, D.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Poon, H.; Porter, T. A.; Prokhorov, D.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Rochester, L. S.; Roth, M.; Sadrozinski, H. F.-W.; Sanchez, D. A.; Sbarra, C.; Schalk, T. L.; Sgrò, C.; Share, G. H.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Stawarz, ?.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, D. L.; Wood, K. S.; Yang, Z.; Zimmer, S.

2012-10-01

193

Radio emission from Colliding-Wind Binaries: Observations and Models  

CERN Document Server

We have developed radiative transfer models of the radio emission from colliding-wind binaries (CWB) based on a hydrodynamical treatment of the wind-collision region (WCR). The archetype of CWB systems is the 7.9-yr period binary WR140, which exhibits dramatic variations at radio wavelengths. High-resolution radio observations of WR140 permit a determination of several system parameters, particularly orbit inclination and distance, that are essential for any models of this system. A model fit to data at orbital phase 0.9 is shown, and some short comings of our model described.

Dougherty, S M; O'Connor, E P

2005-01-01

194

Precipitation of inner zone electrons by whistler mode waves from the VLF transmitters UMS and NWC  

International Nuclear Information System (INIS)

The precipitation of energetic electrons which are commonly observed in the drift loss cone east of 600 east longitude between Lapprox.1.6 and Lapprox.1.8 can be accounted for by a Doppler-shifted cyclotron resonance between the electrons and nonducted whistler mode waves from high-power, ground-based VLF transmitters. A ray-tracing analysis using a diffusive-equilibrium model shows that 17.1-kHz waves starting with vertical wave normals between 230 and 310 magnetic latitude cross the magnetic equator between Lapprox.1.6 and f Lapprox.1.8 with wave normals of approximately 630. A relativistic cyclotron-resonance analysis for the same model plasmasphere using the ray-tracing results gives an energy versus L shell dependence for the precipitated ray electron which is in excellent agreement with the observed dependence. The primary VLF transmitter is most probably the UMS transmitter located near Gorki, USSR. It transmits on 17.1 kHz. VLF records covering this frequency band were available for only three of the time periods when electrons were observed. In two cases UMS was transmitting at the time required to account for the observations. In the third case a higher frequency is required to fit the data. At the time, the NWC transmitter at North West Cape, Australia was operating at 22.3 kHz. These data are consistent with a model in which weak pitch angle scattering by whistler mode waves from NWC does not completely fill the ves from NWC does not completely fill the drift loss cone at the longitude of NWC

195

The low ionosphere electron density changes during events of the extreme solar activity as deduced from VLF measurements  

International Nuclear Information System (INIS)

Complete text of publication follows. It is well known that solar X-ray flares increase the electron density at the lower ionosphere edge and that it can be detected from changes in the VLF propagation through Earth-ionosphere waveguide. The influence of the CME and SEP events, usually accompanying the extreme X-ray flares, on the electron density at the ionosphere-atmosphere boundary, can be also studied using the VLF data and appropriate choice of the processes introduced into continuity equation. Several examples of electron density disturbances, induced by X class flares: X1.3 at 1054 UT on July 2005, X17 class flare at 1740 UT on September 7, 2005, X9 at 1018 UT on December 5 2006 and accompanying events, are analyzed. The lack of the proportionality between VLF amplitude/phase (determined by electron density) and X-ray irradiance in the case of huge flares, indicates that processes else than photoionization-dissociative recombination take place. The continuity equation, including the three-body recombination is solved. The time variation of the electron density height profile N(z,t) during disturbed conditions is evaluated and compared with calculations, obtained from the Wait's N(z,t) model developed for the simulation of VLF propagation. The accordance in the order of magnitude was found. Also, the effects of the series of events in period from January 15 - 22, 2005, were analyzed. The VLF recordings reveal the absence of regular diurnal pattern in amplitude a of regular diurnal pattern in amplitude and phase, suggesting that the high level of electron density persists through night hours. It can be explained by impact of energetic particles, colliding with atmospheric neutrals. The X-ray emission released in 'bremsstrahlung' process cause the ionization of atmospheric constituents. The VLF signals on two traces, NAA/24 kHz (Maine, USA - Belgrade) and GQD/22.1 kHz (Skelton, UK - Belgrade), were recorded by AbsPal system and used in this study.

196

Clusters of galaxies: observational properties of the diffuse radio emission  

Science.gov (United States)

Clusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures. The luminous matter of clusters consists of galaxies and of an embedding intracluster medium (ICM), which has been heated to temperatures of tens of millions degrees, and thus is detected through its thermal emission in the soft X-ray regime. Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission. The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolutionary stage, and are crucial for a comprehensive physical description of the intracluster medium. They play an important role in the cluster formation and evolution. We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos. We discuss their classification and properties. We report published results up to date and obtain and discuss statistical properties. We present the properties of large-scale magnetic fields in clusters and in even larger structures: filaments connecting galaxy clusters. We summarize the current models of the origin of these cluster components, and outline the improvements that are expected in this area from future developments thanks to the new generation of radio telescopes.

Feretti, Luigina; Giovannini, Gabriele; Govoni, Federica; Murgia, Matteo

2012-05-01

197

Subionospheric VLF signatures of nighttime D region perturbations in the vicinity of lightning discharges  

International Nuclear Information System (INIS)

A 12-hour sequence of perturbations of subionospheric VLF signals observed in association with lightning provided preliminary evidence that the ionospheric regions perturbed in these events may be confined to within ? 150 km of the lightning discharges, and that intracloud flashes as well as cloud-to-ground lightning may be important in producing the perturbations. High-resolution analysis of event signatures indicated the presence of two different classes of events. For one set of events, observed during the most active central 6 hours of the observations period, a ? 0.6-s delay between the causative lightning and VLF event onset and a ? 1-s onset duration was observed, consistent with previously suggested models of the gyroresonant whistler-paritcle interaction that leads to particle precipitation and perturbation of the Earth-ionosphere waveguide. However, another set of events, observed during the first 2 hours of the observation period, exhibited a very different temporal signature, characterized by a much smaller (<50 ms) delay and sometimes also very short (< 50 ms) rise times. Such events are possibly related to previously reported cases of similarly early/fast events and may involve a more direct coupling between the lightning discharge and the lower ionosphere

198

Role of Geomagnetic Disturbances on VLF Whistler Wave Activity at Low Latitudes (P32)  

Science.gov (United States)

rppatel123@rediffmail.com The disturbances on solar surfaces lead to the enhanced injection of energetic charged particles in to the inner magnetosphere, which modifies the electrodynamic features of ionosphere and magnetosphere. The electrodynamic properties control the generation and propagation characteristics of VLF waves. At Varanasi station, which is one of the low latitude stations in India, we have recorded VLF waves from 1992 onwards. The source of VLF wave is natural lightning discharges. Whistler activity varies with latitude having maximum around 500 geomagnetic latitude. The occurrence rate is low at low latitudes and also depends on the solar and geomagnetic conditions. In this paper, we report the results derived from the statistical analysis of whistler waves recorded at Varanasi during the period January 1990 December 1999. The monthly occurrence rate is obtained which shows maximum during January to March. Seasonal variation of the occurrence rate is also studied. In order to study the role of geomagnetic disturbances on the occurrence rate, we have used Kp index and its variation. It is observed that the occurrence probability monotonically increases with ?Kp values. It is observed that when ?Kp > 10, the occurrence rate is greater than the average value. This tendency is found to be in good agreement with those reported by other workers. In addition, we also present the probability of observation of whistler waves during the weak/intense geomagnetic storm. Detailed result of occurrence of whistler waves during the main phase and recovery phase of geomagnetic storms will also be presented. An attempt will be made to present explanation of these statistical results.

Patel, R. P.; Singh, S.; Singh, A. K.; Singh, R. P.

2006-11-01

199

On the numerical modelling of VLF chorus dynamical spectra  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents a study of the use of a one-dimensional Vlasov Hybrid Simulation (VHS computer code to simulate the dynamical spectra (i.e. frequency versus time spectrograms of ELF/VLF chorus signals (from ~a fraction to ~10 kHz. Recently excellent measurements of chorus have been made in the source region close to the geomagnetic equator aboard the four spacecraft Cluster mission. Using Cluster data for wave amplitude, which is up to 300 pT, local gyrofrequency, cold plasma density, and L-shell, observed chorus signals are reproduced with remarkable fidelity and, in particular, sweep rates in the range 1–10 kHz result as observed. Further, we find that the sweep rate is a falling function of increasing cold plasma density, again in accord with observations. Finally, we have satisfactorily simulated the rather rare falling frequency elements of chorus which are sometimes observed aboard Cluster in the generation region. For both rising and falling chorus we have presented detailed structural analyses of the generation regions. The main contributor to the frequency sweep rate is primarily the establishment of wave number/frequency gradients across the generation region by the out of phase component of the resonant particle current. The secondary contributor is the shortening of the wavelength of resonant particle current relative to that of the wave field. In view of the close agreement between observation and simulation, we conclude that nonlinear electron cyclotron resonance is indeed the mechanism underlying the generation of chorus signals just outside the plasmasphere.

D. Nunn

2009-06-01

200

Neon Line Emission Observed in Keck/HIRES Sky Spectra  

Science.gov (United States)

Over the last three years, detailed studies of the sky spectra from the W. M. Keck (I) 10-meter telescope and the HIRES echelle spectrometer have been carried out. Many atomic and molecular emissions have been observed in the nightglow for the first time. For O2 in particular, an entire new range of molecular bands in the Atmospheric Band system has been found, following initial identifications by D.E. Osterbrock and collaborators. At the beginning co-added spectra were used, so as to optimize the identification of weak spectral features [Osterbrock et al. PASP, 110, 1499 (1998)]. We are now using individual 50-minute spectra, making it possible to use time as a variable. Of spectral lines normally associated with light pollution, by far the most prominent in Keck/HIRES sky spectra are those of neon, of which 36 have so far been identified, in the spectral range 5800-8100 Å. They exhibit a great deal of variability with time, but during a given night the variation is not random. At the most intense the summed intensity of the neon lines is on the order of 30 rayleighs (R), with the strong 5852 Å line having an intensity of ~ 2 R. At other times, the 5852 Å line is weaker by a factor of 50. The mercury line at 5461 Å is typically weaker than the Ne [5852] line, and at its maximum does not exceed 1 R. Particularly noteworthy is the fact that the neon and mercury lines are not correlated in time, as would be expected if they originate with a city source. Urban mercury radiation normally outshines that from neon by two orders of magnitude (cf. Lick Observatory observations). The highest neon intensities are observed when the telescope is pointed in a southerly direction, and no significant neon emission is observed at the azimuth of the closest city, Hilo. Approximately one-hundred 50-minute sky spectra, taken in 1993-1997, have been evaluated for this study. Continuing analysis reveals that argon and xenon lines also appear in some spectra; noteworthy is the fact that emission from the three atoms is uncorrelated in time. This work has been supported by the NSF Aeronomy program.

Cosby, P. C.; Huestis, D. L.; Slanger, T. G.

2000-12-01

201

ELF/VLF wavefield measurements made at the time of launch of Skylark SL1424  

International Nuclear Information System (INIS)

The Skylark SL1424, was launched at 04:14:22 UT on 1978 November 10 from the Andoya rocket range in northern Norway, when an ELF/VLF chorus event was observed by the GEOS 2 satellite and with a network of ground-based receivers. The satellite above the equator, the rocket in the ionosphere and the ground-based receivers were all approximately in magnetic conjugacy. Frequency against time spectrograms are presented of the wavefield obtained using all these receivers during the rocket flight. Accurate timing permits a comparative study of individual chorus elements. (Auth.)

202

Surface slope characteristics from Thermal Emission Spectrometer emission phase function observations  

Science.gov (United States)

It is possible to obtain surface roughness characteristics, by measuring a single surface from multiple emission angles and azimuths in the thermal infrared. Surfaces will have different temperatures depending on their orientation relative to the sun. A different proportion of sunlit versus shaded surfaces will be in the field of view based on the viewing orientation, resulting in apparent temperature differences. This difference in temperature can be utilized to calculate the slope characteristics for the observed area. This technique can be useful for determining surface slope characteristics not resolvable by orbital imagery. There are two main components to this model, a surface DEM, in this case a synthetic, two dimensional sine wave surface, and a thermal model (provided by H. Kieffer). Using albedo, solar longitude, slope, azimuth, along with several other parameters, the temperature for each cell of the DEM is calculated using the thermal model. A temperature is then predicted using the same observation geometries as the Thermal Emission Spectrometer (TES) observations. A temperature difference is calculated for the two complementary viewing azimuths and emission angles from the DEM. These values are then compared to the observed temperature difference to determine the surface slope. This method has been applied to TES Emission Phase Function (EPF) observations for both the spectrometer and bolometer data, with a footprint size of 10s of kilometers. These specialized types of TES observations measure nearly the same surface from several angles. Accurate surface kinetic temperatures are obtained after the application of an atmospheric correction for the TES bolometer and/or spectrometer. Initial results include an application to the northern circumpolar dunes. An average maximum slope of ~33 degrees has been obtained, which makes physical sense since this is near the angle of repose for sand sized particles. There is some scatter in the data from separate observations, which may be due to the large footprint size. This technique can be better understood and characterized by correlation with high resolution imagery. Several different surface maps will also be tested in addition to the two dimensional sine wave surface. Finally, by modeling the thermal effects on different particle sizes and land forms, we can further interpret the scale of these slopes.

Edwards, C. S.; Bandfield, J. L.; Christensen, P. R.

2006-12-01

203

Clusters of galaxies : observational properties of the diffuse radio emission  

CERN Document Server

Clusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures...(abridged)... Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission. The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolut...

Feretti, Luigina; Govoni, Federica; Murgia, Matteo

2012-01-01

204

Satellite observations indicate substantial spatiotemporal variability in biomass burning NOx emission factors for South America  

OpenAIRE

Biomass burning is an important contributor to global total emissions of NOx (NO+NO2). Generally bottom-up fire emissions models calculate NOx emissions by multiplying fuel consumption estimates with static biome-specific emission factors, defined in units of grams of NO per kilogram of dry matter consumed. Emission factors are a significant source of uncertainty in bottom-up fire emissions modeling because relatively few observations are available to characterize the large ...

Castellanos, P.; Boersma, K. F.; Werf, G. R.

2014-01-01

205

Scientific observation results of the magnetosphere  

International Nuclear Information System (INIS)

The results of observation of the magnetosphere with the satellite EXOS-B are described. Experiment on plasma wave excitation including cyclotron frequency radiation of electrons and electron density distribution in the magnetosphere: Plasma wave excitation over the whole magnetosphere by applying a high-frequency oscillating electric field using the EXOS-B is the first attempt, enabling new experiments on wave phenomena. Observation of magnetosphere plasma waves including terrestrial kilometric radiation (TKR), (n + 1/2) f sub( h) radiation, and emission of solar radio waves and VLF radio waves: In nature, variety of electromagnetic waves and plasma waves are received. VLF Doppler observation: From the Doppler effect of radio waves, wave propagation of whistler mode is observable. Electric field and impedance measurement: From impedance measurement, the detection of plasma resonance is possible. Magnetic field measurement: In this measurement, magnetic pulsation is detected. Observation of high-energy particle flux: Energy spectra are shown. Electron beam emission: The beam emitted disturbs plasma. Monitoring of solar battery elements: They deteriorated due to radiation. (J.P.N.)

206

On the statistical correlation between the ionospheric perturbations as detected by subionospheric VLF/LF propagation anomalies and earthquakes  

Directory of Open Access Journals (Sweden)

Full Text Available Relatively long-period (4 years data on different propagation paths by means of Japanese-Pacific VLF/LF network observation, are used to obtain further statistical significance on the correlation of ionospheric perturbations as revealed by VLF/LF propagation anomalies with earthquakes. Earthquakes with magnitude greater than 6.0, taken place only within the fifth Fresnel zone of each great-circle path are selected for the correlation study. It is finally found based on the superimposed epoch analysis that the nighttime trend (average amplitude exhibits a significant decrease exceeding 2? (?: standard deviation several days before the earthquake and the nighttime fluctuation exceeds the corresponding 2? again several days before the earthquake when the earthquake depth is smaller than 30 km (shallow earthquakes. However, when we treat all earthquakes including deep earthquakes, the trend shows a significant decrease (just approaching 2? line, and the nighttime fluctuation shows a less significant broad enhancement before the EQ.

Y. Kasahara

2008-07-01

207

Airborne VLF measurements and mapping of ground conductivity in Sweden  

Science.gov (United States)

Airborne VLF data are routinely collected by The Geological Survey of Sweden (SGU) as part of its bedrock mapping programme. In this paper we demonstrate that the novel Tensor VLF technique developed at Uppsala University and SGU can provide useful qualitative and quantitative information about the electrical conductivity distribution in the upper few hundred meters. Single transmitter scalar VLF maps emphasize those conductive structures that have dominant strikes in the direction of the transmitter. The tensor tipper (essentially the vertical magnetic field from currents along the strike direction) calculated from multiple transmitters is dependent only upon the underlying conductivity structure. Transformation of the tipper into the peaker (the horizontal divergence) has proven to enhance the lateral resolution while the transformation to the apparent resistivity can be used to discriminate different rock types. Two case histories from the application of VLF data are presented in this study. Two dimensional structures can be quantitatively modelled by modern inversion methods developed originally for deep electromagnetic MT soundings. Direct inversion of the real and imaginary parts of the tipper provides more quantitative information about the subsurface resistivity distribution.

Pedersen, Laust B.; Persson, Lena; Bastani, Mehrdad; Byström, Sören

2009-03-01

208

Numerical modelling of VLF radio wave propagation through earth-ionosphere waveguide and its application to sudden ionospheric disturbances  

CERN Document Server

In this thesis, we theoretically predict the normal characteristics of Very Low Frequency (3~30 kHz) radio wave propagation through Earth-ionosphere waveguide corresponding to normal behavior of the D-region ionosphere. We took the VLF narrow band data from the receivers of Indian Centre for Space Physics (ICSP) to validate our models. Detection of sudden ionospheric disturbances (SIDs) are common to all the measurements. We apply our theoretical models to infer the D-region characteristics and to reproduce the observed VLF signal behavior corresponding to such SIDs. We develop a code based on ray theory to simulate the diurnal behavior of VLF signals over short propagation paths (2000~3000 km). The diurnal variation from this code are comparable to the variation obtained from a more general Long Wave Propagation Capability (LWPC) code which is based on mode theory approach. We simulate the observational results obtained during the Total Solar Eclipse of July 22, 2009 in India. We also report and simulate a h...

Pal, Sujay

2015-01-01

209

A new approach for monitoring the 27-day solar rotation using VLF radio noise on the Earth's surface  

International Nuclear Information System (INIS)

Complete text of publication follows. The Sun is a very dynamic star, with variability on all time scales, from minutes to decades and centuries. One of the dominant periods of the Sun's variation is related to the solar rotation of ?27 days. Although this period is quite fundamental to our Sun, it is only partially observable via the typical solar parameters such as sun spot number, Lyman alpha radiation and 10.7cm radio flux. We have discovered a very robust indicator of this 27 day rotation from measurements of VLF radio noise at the Earth's surface. While VLF radio noise spans the frequency range of 3-30 kHz, the solar rotation is only observed at frequencies close the Earth-ionosphere waveguide cutoff frequency (?2 kHz). Furthermore, the 27-day solar rotation is detected only during daylight hours, implying a 27-day periodicity in the day-time collision frequency between free electrons and neutral air molecules in the lower part of the ionosphere. We propose that continuous monitoring of VLF radio noise at frequencies close to the waveguide cutoff will provide a new method of monitoring changes in the solar rotation rate.

210

Source location of chorus emissions observed by Cluster  

Directory of Open Access Journals (Sweden)

Full Text Available One of the objectives of the Cluster mission is to study sources of various electromagnetic waves using the four satellites. This paper describes the methods we have applied to data recorded from the STAFF spectrum analyser. This instrument provides the cross spectral matrix of three magnetic and two electric field components. This spectral matrix is analysed to determine, for each satellite, the direction of the wave normal relative to the Earth’s magnetic field as a function of frequency and of time. Due to the Cluster orbit, chorus emissions are often observed close to perigee, and the data analysis determines the direction of these waves. Three events observed during different levels of magnetic activity are reported. It is shown that the component of the Poynting vector parallel to the magnetic field changes its sense when the satellites cross the magnetic equator, which indicates that the chorus waves propagate away from the equator. Detailed analysis indicates that the source is located in close vicinity of the plane of the geomagnetic equator.

Key words. Magnetospheric physics (plasma waves and instabilities; storms and substorms; Space plasma physics (waves and instabilities

M. Parrot

211

Observations of Coastal IO Emissions on the Southern Hemisphere and Emission Potential of Different Seaweed Species  

Science.gov (United States)

At coastal sites reactive iodine species emitted by seaweed in the intertidal zone during low tide are known to have an important influence on the atmospheric chemistry. However, many underlying mechanisms are presently not understood. Also coastal studies were focused on a few locations on the northern hemisphere and their predominant seaweed species laminaria digitata and ascophyllum nodosum. Therefore the spatial emission and extent of the areas where halogen chemistry is of importance needs to be much better quantified. Especially in the mid latitudes of the southern hemisphere RHS measurements are very sparse. Here we report the first observations of coastal iodine monoxide (IO) in the southern hemisphere during the HALMA/MAORI campaign which was carried out in February to March 2013 on the east coast of New Zealand's South Island at Shag Point located north of Dunedin. To detect IO we used a mobile Open Light Path Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) instrument and a stationary Long Path (LP)-DOAS Instrument, which was furthermore used to measure BrO, O3 and I2. The measurement path was positioned over the water and mainly measured air masses that only passes over submerged seaweed forests. With the CE-DOAS placed close to exposed seaweed patches (mainly Macrocystis Pyrifera) we were able to observe high IO mixing ratios of up to 50 ppt (2ppt detection limit). However, the LP-DOAS did not detect IO above the detection limit of 0.7 ppt. This is consistent with previous observations which found that seaweed only emits halogens when exposed to air. To further investigate the emission potential of the seaweed species we setup a Teflon chamber around the CE-DOAS and measured the emissions of five different species for several hours. Additionally the air in the chamber was probed by a compact gas chromatograph (?DIRAC) for measurements of halocarbons and a TEI Ozone monitor. We found very high IO mixing ratios of up to 500 ppt for four seaweed species which correlated with high levels of halocarbons (CH3I, CH2Br2, CH2BrI and CH2BrCl up to 100ppt, CHBr3 up to 600ppt). These results, the similarities and differences in the emission behavior and implications for atmospheric chemistry are discussed.

Horbanski, Martin; Schmitt, Stefan; Frieß, Udo; Pöhler, Denis; Johnston, Paul; Kreher, Karin; Robinson, Andrew D.; Thomas, Alan; Harris, Neil R. P.; Platt, Ulrich

2014-05-01

212

EMISSION PATTERNS OF SOLAR TYPE III RADIO BURSTS: STEREOSCOPIC OBSERVATIONS  

International Nuclear Information System (INIS)

Simultaneous observations of solar type III radio bursts obtained by the STEREO A, B, and WIND spacecraft at low frequencies from different vantage points in the ecliptic plane are used to determine their directivity. The heliolongitudes of the sources of these bursts, estimated at different frequencies by assuming that they are located on the Parker spiral magnetic field lines emerging from the associated active regions into the spherically symmetric solar atmosphere, and the heliolongitudes of the spacecraft are used to estimate the viewing angle, which is the angle between the direction of the magnetic field at the source and the line connecting the source to the spacecraft. The normalized peak intensities at each spacecraft Rj = Ij /?Ij (the subscript j corresponds to the spacecraft STEREO A, B, and WIND), which are defined as the directivity factors are determined using the time profiles of the type III bursts. It is shown that the distribution of the viewing angles divides the type III bursts into: (1) bursts emitting into a very narrow cone centered around the tangent to the magnetic field with angular width of ?2° and (2) bursts emitting into a wider cone with angular width spanning from ? – 100° to ?100°. The plots of the directivity factors versus the viewing angles of the sources from all three spacecraft indicate that the type III emissions are very intense along the tangent to the spiral magnetic field lines atspiral magnetic field lines at the source, and steadily fall as the viewing angles increase to higher values. The comparison of these emission patterns with the computed distributions of the ray trajectories indicate that the intense bursts visible in a narrow range of angles around the magnetic field directions probably are emitted in the fundamental mode, whereas the relatively weaker bursts visible to a wide range of angles are probably emitted in the harmonic mode.

213

Aperture synthesis observations of solar and stellar radio emission  

International Nuclear Information System (INIS)

The work presented in this thesis relied upon the radio astronomical instrument, The Very Large Array. The thesis is divided into three major sections. In the first the author applied maximum entropy-type image reconstruction techniques, using both single dish and iterferometer data, to generate full disk images of the Sun at a wavelength ? ? 21 cm. Using a set of six such images obtained during the Sun's decline from sunspot maximum to minimum, he has noted a number of previously unreported phenomena. Among these: (1) a systematic decrease in quiet Sun's brightness temperature as it declined to minimum; (2) a systematic decrease in the Sun's radius at 21 cm; (3) evidence for the evolution of polar coronal holes during the course of the solar cycle. The observed variation, though not noted previously at radio wavelengths, is entirely consistent with white light K coronagraph data. The results reported here explain the conflicting nature of a number of past observations. In the second section of the thesis, he presents the results of a long term survey of magnetic cataclysmic variables (CVs). Cataclysmic variables are close binary systems which contain a white dwarf accreting mass from a late-type secondary, typically a dwarf of spectral type, G, K, or M. The survey resulted in the detection of two out of the eighteen systems observed. In the third section of the thesis, he presents new results on flare stars in the solar neighborhood and in the Pleiades. He has sucborhood and in the Pleiades. He has successfully employed the technique of dynamic spectroscopy to constrain the mechanisms(s) for radio flaring on other stars. The second part of section three is devoted to a search for radio emission from flare stars in the Pleiades which was motivated by the evolutionary questions raised by flare stars and the Pleiades lower main sequence

214

Unmanned Airborne Magnetic and VLF Investigations: Effective Geophysical Methodology for the Near Future  

Directory of Open Access Journals (Sweden)

Full Text Available Airborne geophysical investigations are now recognized as a powerful tool for geological-geophysical mapping, mineral prospecting, environmental assessments, ecological monitoring, etc. Currently, however, there are two main drawbacks to effective application of these investigations: (a the difficulty of conducting geophysical surveys at low altitudes, (b heightened danger for the aircraft crew, especially in regions with a rugged topography. Unmanned or so-called Remote Operated Vehicles (ROV surveys are not bound by these limitations. The new unmanned generation of small and maneuvering vehicles can fly at levels of a few (even one meters above the Earth’s surface, and thus follow the relief, while simultaneously making geophysical measurements. In addition, ROV geophysical investigations have extremely low exploitation costs. Finally, measurements of geophysical fields at different observation levels can provide new, unique geological-geophysical information. This chapter discusses future geophysical integration into ROV of measurements of magnetic and VLF electromagnetic fields. The use of GPS with improved wide-band Kalman filtering will be able to provide exact geodetic coordinates. A novel interpreting system for complex environments is presented that includes non-conventional methods for localizing targets in noisy backgrounds, filtering temporary variations from magnetic and VLF fields, eliminating terrain relief influence, quantitative analysis of the observed anomalies and their integrated examination. This system can be successfully applied at various scales for analysis of geophysical data obtained by ROVs to search for useful minerals, geological mapping, the resolution of many environmental problems, and geophysical monitoring of dangerous geological phenomena.

Lev Eppelbaum

2011-08-01

215

Inversion of airborne tensor VLF data using integral equations  

Science.gov (United States)

The Geological Survey of Sweden has been collecting airborne tensor very low frequency data (VLF) over several decades, covering large parts of the country. The data has been an invaluable source of information for identifying conductive structures that can among other things be related to water-filled fault zones, wet sediments that fill valleys or ore mineralizations. Because the method only uses two differently polarized plane waves of very similar frequency, vertical resolution is low and interpretation is in most cases limited to maps that are directly derived from the data. Occasionally, 2-D inversion is carried out along selected profiles. In this paper, we present for the first time a 3-D inversion for tensor VLF data in order to further increase the usefulness of the data set. The inversion is performed using a non-linear conjugate gradient scheme (Polak-Ribière) with an inexact line-search. The gradient is obtained by an algebraic adjoint method that requires one additional forward calculation involving the adjoint system matrix. The forward modelling is based on integral equations with an analytic formulation of the half-space Green's tensor. It avoids typically required Hankel transforms and is particularly amenable to singularity removal prior to the numerical integration over the volume elements. The system is solved iteratively, thus avoiding construction and storage of the dense system matrix. By using fast 3-D Fourier transforms on nested grids, subsequently farther away interactions are represented with less detail and therefore with less computational effort, enabling us to bridge the gap between the relatively short wavelengths of the fields (tens of metres) and the large model dimensions (several square kilometres). We find that the approximation of the fields can be off by several per cent, yet the transfer functions in the air are practically unaffected. We verify our code using synthetic calculations from well-established 2-D methods, and trade modelling accuracy off against computational effort in order to keep the inversion feasible in both respects. Our compromise is to limit the permissible resistivity to not fall below 100 ?m to maintain computational domains as large as 10 × 10 km2 and computation times on the order of a few hours on standard PCs. We investigate the effect of possible local violations of these limits. Even though the conductivity magnitude can then not be recovered correctly, we do not observe any structural artefacts related to this in our tests. We invert a data set from northern Sweden, where we find an excellent agreement of known geological features, such as contacts or fault zones, with elongated conductive structures, while high resistivity is encountered in probably less disturbed geology, often related to topographic highs, which have survived predominantly glacial erosion processes. As expected from synthetic studies, the resolution is laterally high, but vertically limited down to the top of conductive structures.

Kamm, Jochen; Pedersen, Laust B.

2014-08-01

216

Regional nitrogen oxides emission trends in East Asia observed from space  

OpenAIRE

Due to changing economic activity, emissions of air pollutants in East Asia change rapidly in space and time. Monthly emission estimates of nitrogen oxides derived from satellite observations provide valuable insight in the evolution of anthropogenic activity on a regional scale. We present the first results of a new emission estimation algorithm, specifically designed to use daily satellite observations of column concentrations for fast updates of emissions of short-lived atmospheric ...

Mijling, B.; R. J. van der A; Zhang, Q.

2013-01-01

217

The South America VLF Network - SAVNET: Achievements, Latest Results and Future Directions  

Science.gov (United States)

In this paper we present recent results obtained by the South America VLF Network (SAVNET). The use of the VLF technique by tracking subionospheric propagation anomalies appears as a very promising tool to study various aspects of Space Weather disturbances. On long timescales it is possible to indirectly monitor the solar Lyman-alpha radiation along the solar cycles. Short time phenomena like solar explosive events can be observed with 100% probability, even for the small intensity events. The effect of high-energy precipitating solar particles can be tracked in the low ionosphere. The same technique is also relevant to study the ionospheric perturbations caused by geomagnetic storms on typical timescales of a day to few days. Extra solar and terrestrial high-energy phenomena are naturally detected in the very sensitive low ionospheric plasma, as Gamma-ray bursts and Soft Gamma-ray repeaters. Finally, the remote sensing of the low ionosphere is also used to search for seismic-electromagnetic effects prior to Earthquakes. At the present time, SAVNET is composed of nine (9) tracking receiver stations in Brazil, Peru, Argentina and Mexico. In this presentation we will describe our future plans for expanding the array. Eastern Europe, Ecuador and Asia are good host candidates to participate in these forthcoming activities. The array expansion is necessary to improve the probability detection of very high-energy remote phenomena, and to demonstrate that these processes of great astrophysical importance can be easily detected using a cheap and simple technique.

Raulin, J.

2013-05-01

218

Modeling of the Very Low Frequency (VLF radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry  

Directory of Open Access Journals (Sweden)

Full Text Available X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~ 60 to 100 km in excess of what is expected from a quiet sun. Very Low Frequency (VLF radio wave signals reflected from the D region are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the lower ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the VLF signal change. We did the modeling of the VLF signal along the NWC (Australia to IERC/ICSP (India propagation path and compared the results with observations. The agreement is found to be very satisfactory.

S. Palit

2013-03-01

219

Modeling of very low frequency (VLF radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry  

Directory of Open Access Journals (Sweden)

Full Text Available X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia to IERC/ICSP (India propagation path and compared the results with observations. The agreement is found to be very satisfactory.

S. Palit

2013-09-01

220

Binding of the baculovirus very late expression factor 1 (VLF-1) to different DNA structures  

OpenAIRE

Abstract Background Baculovirus genomes encode a gene called very late expression factor 1 (VLF-1) that is a member of the integrase (Int) family of proteins. In this report we describe the binding properties of purified Autographa californica multiple capsid nucleopolyhedrovirus (AcMNPV) VLF-1 to a number of different DNA structures including homologous regions. In addition, its enzymatic activity was examined. Results VLF-1 was expressed in a recombinant baculovirus as a fusion with both HA...

Mikhailov Victor S; Rohrmann George F

2002-01-01

221

En bred syn på Tolkning av Elektromagnetiska Data (VLF, RMT, MT, CSTMT)  

OpenAIRE

The resolution power of single Very Low Frequency (VLF) data and multi-frequency Radiomagnetotelluric (RMT) data in delineating conductive structures typical for the sedimentary cover and crystalline basement in Scandinavia is studied with a view to future developments of the technique to increasing the frequency range into the LW radio band. Airborne and ground VLF data are interpreted and correlated with RMT measurements made on the ground to better understand the resolution power of VLF da...

Oskooi, Behrooz

2004-01-01

222

Observations of terrestrial far UV emissions by the FAUST telescope  

Science.gov (United States)

The Far Ultraviolet Space Telescope ('FAUST') furnishes precise photometry for extended astronomical objects in the 1400-1800 A wavelength interval, and constitutes a part of the Atlas-1 mission. On several occasions during this flight, FAUST was turned toward the earth in order to obtain terrestrial nightglow, auroral and Shuttleglow emissions. It is found that auroral precipitation activity dominates in the high magnetic latitude; outside it, diffuse emission is seen to slowly vary over the nightside.

Chakrabarti, Supriya; Sasseen, Timothy P.; Lampton, Michael; Bowyer, Stuart

1993-03-01

223

Worldwide monitoring of VLF-LF propagation and atmospheric noise  

Science.gov (United States)

A joint effort is underway between The Johns Hopkins University Applied Physics Laboratory and the Space and Naval Warfare (SPAWAR) Systems Center, San Diego, to deploy monitoring equipment capable of characterizing worldwide VLF-LF radio wave propagation and atmospheric noise levels. The monitoring equipment consists of a PC-based spectrum analyzer and orthogonal ferrite core magnetic loop antennas. The analyzer performs continuous measurements of the radio spectrum from 12 to 62 kHz and records time histories of VLF-LF signals (equivalent vertical electric field strength), noise amplitude probability distribution, noise impulsiveness, and average noise field strength. Data are downloaded via the Internet to a central database server. The Internet connection also provides for system reconfiguration and clock synchronization. Data collected by the monitoring network will be used to improve communication coverage forecasts and to analyze transient and long-term propagation effects. This paper provides an overview of the monitoring network and samples of data collected by it.

Tomko, A. A.; Hepner, T.

2001-03-01

224

Effect of rectification of vlf waves in the earth's magnetosphere  

International Nuclear Information System (INIS)

This paper discusses the results of an experiment on the detection of a rectified magnetospheric signal (RMS) arising in the action of a strong, modulated, low-frequency wave on the magnetospheric plasma. The signal develops at the modulation frequency of the transmitter and arrives at the receiver with a delay ? 3-5 sec. A possible mechanism of RMS generation in the region of resonance absorption of a vlf wave in the magnetosphere is discussed

225

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations Foreground Emission  

CERN Document Server

Full sky maps are made in five microwave frequency bands to separate the temperature anisotropy of the CMB from foreground emission. We define masks that excise regions of high foreground emission. The effectiveness of template fits to remove foreground emission from the WMAP data is examined. These efforts result in a CMB map with minimal contamination and a demonstration that the WMAP CMB power spectrum is insensitive to residual foreground emission. We construct a model of the Galactic emission components. We find that the Milky Way resembles other normal spiral galaxies between 408 MHz and 23 GHz, with a synchrotron spectral index that is flattest (beta ~ -2.5) near star-forming regions, especially in the plane, and steepest (beta ~ -3) in the halo. The significant synchrotron index steepening out of the plane suggests a diffusion process in which the halo electrons are trapped in the Galactic potential long enough to suffer synchrotron and inverse Compton energy losses and hence a spectral steepening. Th...

Bennett, C; Hinshaw, G; Nolta, M R; Odegard, N; Page, L; Spergel, D N; Weiland, J L; Wright, E L; Halpern, M; Jarosik, N C; Kogut, A J; Limon, M; Meyer, S S; Tucker, G S; Wollack, E

2003-01-01

226

Megacity Carbon: Observing system study for tracking Los Angeles greenhouse gas emission trends  

Science.gov (United States)

Future greenhouse gas (GHG) mitigation agreements will require independent quantification of anthropogenic emission trends. Atmospheric observations contain information about true and total GHG emissions, and therefore provide a foundation for monitoring, verifying, and validating anthropogenic GHG emissions. Atmospheric observations also are strongly influenced by biospheric fluxes, presenting a challenge for disentanglement and attribution. Megacities provide an optimal target for atmospheric monitoring of human-derived emissions. Intense anthropogenic emissions are concentrated in small spatial areas, creating a strong and detectable local signal, facilitating observation and attribution. The Megacity Carbon project aims to capitalize on these strong signals, by developing and demonstrating atmospheric observing systems to track GHG emission trends. To quantitatively track emission changes with time, we must carefully consider observing network design. Here we present a modeling study of different observing systems in the Los Angeles basin. By using a high-resolution Lagrangian Particle Dispersion model, we test different observations sensitivity to emissions in the basin. We employ a Bayesian approach to quantitatively assess the performance of different network designs, and explore the strengths and weaknesses of different observing techniques (ie in-situ point vs. total column observations). We'll present a recommended network design for Los Angeles, and a recommended method to design observing systems in other Megacities.

Kort, E. A.; Miller, C. E.; Duren, R.; Eldering, A.; Sander, S.; Newman, S.

2012-04-01

227

Subionospheric VLF/LF radio waves propagation characteristics before, during and after the Sofia, Bulgaria Mw=5.6 earthquake occurred on 22 May 2012  

Science.gov (United States)

In 2009, INFREP, a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers, was put into operation in Europe having as principal goal, the study of disturbances produced by the earthquakes on the propagation properties of these signals. On May 22nd, 2012 an earthquake with Mw=567 occurred in Bulgaria, near Sofia, inside the "sensitive" area of the INFREP VLF/LF electromagnetic network. The data collected on different frequencies, during April-May 2012 were studied using different methods of analysis: daily correlation methods, spectral approaches and terminator time techniques, in order to find out possible connections between the seismic activity and the subionospheric propagation properties of radio waves. The studies were performed with the help of a specially designed LabVIEW application, which accesses the VLF/LF receiver through internet. This program opens the receiver's web-page and automatically retrieves the list of data files to synchronize the user-side data with the receiver's data. Missing zipped files are also automatically downloaded. The application performs primary, statistical correlation and spectral analysis, appends daily files into monthly and annual files and performs 3D colour-coded maps with graphic representations of VLF and LF signals' intensities versus the minute-of-the-day and the day-of-the-month, facilitating a near real-time observation of VLF and LF electromagnetic waves' propagation. Another feature of the software is the correlation of the daily recorded files for the studied frequencies by overlaying the 24 hours radio activity and taking into account the sunrise and sunset. Data are individually processed (spectral power, correlations, differentiation, filtered using bandpass, lowpass, highpass). JTFA spectrograms (Cone-Shaped Distribution CSD, Gabor, Wavelet, short-time Fourier transform STFT, Wigner-Ville Distribution WVD, Choi-Williams Distribution CWD) are used, too.

Moldovan, Iren Adelina; Emilian Toader, Victorin; Nenovski, Petko; Biagi, Pier Francesco; Maggipinto, Tommaso; Septimiu Moldovan, Adrian; Ionescu, Constantin

2013-04-01

228

Microprocessor implementation of an FFT for ionospheric VLF observations  

Science.gov (United States)

A fast Fourier transform algorithm is implemented on a CMOS microprocessor for application to very low-frequency electric fields (less than 10 kHz) sensed on high-altitude scientific balloons. Two FFT's are calculated simultaneously by associating them with conjugate symmetric and conjugate antisymmetric results. One goal of the system was to detect spectral signatures associated with fast time variations present in natural signals such as whistlers and chorus. Although a full evaluation of the system was not possible for operational reasons, a measure of the system's success has been defined and evaluated.

Elvidge, J.; Kintner, P.; Holzworth, R.

1984-01-01

229

VLF Tan Delta Measurement for Used XLPE Power Cables  

Energy Technology Data Exchange (ETDEWEB)

Medium voltage power cables in nuclear power plants are currently managed through the visual inspection or by monitoring environmental factors such as the temperature and radiation levels. However, these methods are insufficient to monitor aging degradation of power cables. The NRC requires an additional monitoring program to detect the aged degradation, especially for safety-related power cables which are inaccessible or installed underground. EPRI suggested that very low frequency (VLF) tan {delta} test be included in MV power cable diagnostic programs. In addition, the VLF tan {delta} test was recently adopted for domestic submarine distribution cable diagnostics. KEPRI suggested that the impacts of leakage current should be controlled in VLF tan {delta} test for the submarine cables. As a pre-process to develop such a program, tan {delta} tests have been performed for 4.16 kV cables which were removed from the domestic nuclear power plant after approximate 30 years of service to analyze the degradation of long time serviced cables and the effect of leakage current from the both ends of cables

Lim, Woo Sang; Ha, Che Wung; Joo, Kwang Ho [Korea Hydro and Nuclear Power Co., Daejeon (Korea, Republic of)

2011-05-15

230

VLF Tan Delta Measurement for Used XLPE Power Cables  

International Nuclear Information System (INIS)

Medium voltage power cables in nuclear power plants are currently managed through the visual inspection or by monitoring environmental factors such as the temperature and radiation levels. However, these methods are insufficient to monitor aging degradation of power cables. The NRC requires an additional monitoring program to detect the aged degradation, especially for safety-related power cables which are inaccessible or installed underground. EPRI suggested that very low frequency (VLF) tan ? test be included in MV power cable diagnostic programs. In addition, the VLF tan ? test was recently adopted for domestic submarine distribution cable diagnostics. KEPRI suggested that the impacts of leakage current should be controlled in VLF tan ? test for the submarine cables. As a pre-process to develop such a program, tan ? tests have been performed for 4.16 kV cables which were removed from the domestic nuclear power plant after approximate 30 years of service to analyze the degradation of long time serviced cables and the effect of leakage current from the both ends of cables

231

Type II Radio Emission and Solar Particle Observations  

CERN Document Server

The 28 October 2003 flare gave us the unique opportunity to compare the acceleration time of high-energy protons with the escaping time of those particles which have been measured onboard spacecraft and by neutron monitors network as GLE event. High-energy emission time scale and shock wave height and velocity time dependencies were also studied.

Kuznetsov, S N; Yushkov, B; Yu, B; Myagkova, I N; Kudela, K; Belov, A V; Caroubalos, C; Hilaris, A; Mavromichalaki, H; Moussas, X; Preka-Papadema, P; 10.1142/S0217751X05029873

2010-01-01

232

Analysis of narrowband emission observed in the Saturn magnetosphere.  

Czech Academy of Sciences Publication Activity Database

Ro?. 114, - (2009), A06206/1-A06206/13. ISSN 0148-0227 Institutional research plan: CEZ:AV0Z30420517 Keywords : narrowband emission * Saturn magnetosphere * Cassini Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.082, year: 2009

Menietti, J. D.; Ye, S.; Y.; Yoon, P. H.; Santolík, Ond?ej; Rymer, A. M.; Gurnett, D. A.; Coates, A. J.

2009-01-01

233

Modification of the ionosphere by VLF wave-induced electron precipitation  

International Nuclear Information System (INIS)

Very low frequency (VLF) waves propagating in the whistler mode in the magnetosphere are known to cause precipitation of energetic electrons at middle latitudes. The interactions between the waves and electrons trapped in the magnetic field are believed to occur through cyclotron resonance. As a monochromatic wave propagates along a field line, the condition for resonance can be satisfied by electrons of a minimum energy at the equator and higher energies at increasing latitudes. Resonant interactions occurring in a field aligned region extending several thousand kilometers on both sides of the equator can therefore result in a precipitation flux with a wide range of energies. Electrons which are scattered into the loss cone will collide with the constituents of the ionosphere, causing additional ionization optical emissions, x-rays and heating. A computational technique is introduced which allows the temporal shape of pulse of precipitation to be modeled. A realistic energy distribution is used to weigh the contribution to the total precipitation energy flux resulting from resonant interactions in each segment of the duct. Wave growth along the path is found to affect the shape of the pulse. In its simplest application, the model sets limits on the time window in which a precipitation event can occur. The model arrival times are shown to agree with experimental correlations of VLF waves and effects of precipitation occurring on three occasions, thus supporting the ason three occasions, thus supporting the assumption, that the precipitation results from cyclotron resonant scattering. Various techniques that have been employed for detecting wave-induced precipitation are compared. A quantitative analysis of the use of an HF radar for this purpose is introduced, based on the changes in the phase and group paths of the radar signals that are reflected from the perturbed ionosphere

234

Comparison of two schemes for the generation of ELF/VLF waves in the HF heater-modulated polar electrojet  

International Nuclear Information System (INIS)

Two schemes for the generation of ELF/VLF waves in the HF heater-modulated polar electrojet has been studied. Under the illumination of an amplitude-modulated HF heater wave, the electron temperature of the electrojet is modulated accordingly. This, in turn, causes the modulation of the conductivity and, thus, the current intensity of the electrojet. Emissions are then produced at the modulation frequency and its harmonics. In one scheme, the HF heater is modulated by a rectangular periodic pulse. The other is the beat-wave scheme, namely, two overlapping heater waves have a frequency difference equal to the selected modulation frequency that is essentially equivalent to a sinusoidal amplitude modulation. The nonlinear evolutions of the generated ELF/VLF waves are determined numerically. Their spectra are also evaluated. The results show that the signal quality of the second (beat-wave) scheme is better. The field intensity of the emissions at the fundamental modulation frequency is found to increase with the modulation frequency in consistence with the Tromso experiments

235

Satellite observations indicate substantial spatiotemporal variability in biomass burning NOx emission factors for South America  

Directory of Open Access Journals (Sweden)

Full Text Available Biomass burning is an important contributor to global total emissions of NOx (NO + NO2. Generally bottom-up fire emissions models calculate NOx emissions by multiplying fuel consumption estimates with static biome specific emission factors, defined in units of grams of NO per kilogram of dry matter consumed. Emission factors are a significant source of uncertainty in bottom-up fire emissions modeling because relatively few observations are available to characterize the large spatial and temporal variability of burning conditions. In this paper we use NO2 tropospheric column observations from the Ozone Monitoring Instrument (OMI from the year 2005 over South America to calculate monthly NOx emission factors for four fire types: deforestation, savanna/grassland, woodland, and agricultural waste burning. In general, the spatial trends in NOx emission factors calculated in this work are consistent with emission factors derived from in situ measurements from the region, but are more variable than published biome specific global average emission factors widely used in bottom up fire emissions inventories such as the Global Fire Emissions Database (GFED v3. Satellite based NOx emission factors also indicate substantial temporal variability in burning conditions. Overall, we found that deforestation fires have the lowest NOx emission factors, on average 30 % lower than the emission factors used in GFED v3. Agricultural fire NOx emission factors were the highest, on average a factor of 2 higher than GFED v3 values. For savanna, woodland, and deforestation fires early dry season NOx emission factors were a factor of ~1.5–2.0 higher than late dry season emission factors. A minimum in the NOx emission factor seasonal cycle for deforestation fires occurred in August, the time period of severe drought in South America in 2005. Our results support the hypothesis that prolonged dry spells may lead to an increase in the contribution of smoldering combustion from large diameter fuels to total fire emissions, which would lower the overall modified combustion efficiency (MCE and NOx emission factor, and offset the higher combustion efficiency of dryer fine fuels. We evaluated the OMI derived NOx emission factors with SCIAMACHY NO2 tropospheric column observations and found improved model performance in regions dominated by fire emissions.

P. Castellanos

2013-08-01

236

Geomagnetic indices for prediction of ionospheric irregularities producing VLF scintillations  

International Nuclear Information System (INIS)

Complete text of publication follows. Great diversity of the ionospheric phenomena leads to a variety of irregularity types with spatial size from many thousands of kilometers to few centimeters and lifetimes from days to fractions of second. Since the ionosphere strongly influences the propagation of radio waves, signal distortions caused by these irregularities affect short-wave transmissions on Earth, transionospheric satellite communications and navigation. In this work the solar wind and the equatorial ionosphere parameters, Kp, Dst, AU, AL indices characterized contribution of different magnetospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the space weather effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict scintillations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of electron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind - magnetosphere ionosphere during magnetic storms have progressed greatly. We have examined scintillation relation to magnetospheric and ionospheric currents and show that the factonospheric currents and show that the factor, which presents during magnetic storms to fully inhibit scintillation, is the positive Bz-component of the IMF. During the positive Bz IMF F layer cannot raise altitude where scintillations are formed. The auroral indices and Kp do better for the prediction of the ionospheric scintillations at the equator. The interplanetary magnetic field data and models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, foF2, and the equatorial geomagnetic variations with the polar ionosphere currents and the solar wind. Taking into account the time delay between the solar wind and the ionosphere phenomena, the relationship between the solar wind, geomagnetic indices and the ionosphere parameters can be used for predicting of scintillations.

237

Inverse modeling of European CH4 emissions: sensitivity to the observational network  

OpenAIRE

Inverse modeling is widely employed to provide “top-down” emission estimates using atmospheric measurements. Here, we analyze the dependence of derived CH4 emissions on the sampling frequency and density of the observational surface network, using the TM5-4DVAR inverse modeling system and synthetic observations. This sensitivity study focuses on Europe. The synthetic observations are created by TM5 forward model simulations. The inversions of these synthetic observ...

Villani, M. G.; Bergamaschi, P.; Krol, M. C.; Meirink, J. F.; Dentener, F.

2010-01-01

238

XMM Observations of X-Ray Emission from Supernovae  

Science.gov (United States)

Of the six proposed targets, only one observation was performed. The observation resulted in a 28ks observation of SN 1998S. At the time of writing the proposal, our target list only contained previously unknown X-ray supernovae. Between submission of the proposal and the actual observation, a Chandra DDT observation resulted in the detection of SN 1998S. Since SN 1998S was observed with Chandra five times before the XMM-Newton observation was made, the data did not yield enough new information to warrant a separate SN 1998S publication. The key science results of that observation were presented in a review article (by Immler and Lewin); the results were also presented at two conferences.

Immler, Stefan; Lewin, Walter

2003-01-01

239

Observation of increases in emission from modern vehicles over time in Hong Kong using remote sensing  

International Nuclear Information System (INIS)

In this study on-road gaseous emissions of vehicles are investigated using remote sensing measurements collected over three different periods. The results show that a high percentage of gaseous pollutants were emitted from a small percentage of vehicles. Liquified Petroleum Gas (LPG) vehicles generally have higher gaseous emissions compared to other vehicles, particularly among higher-emitting vehicles. Vehicles with high vehicle specific power (VSP) tend to have lower CO and HC emissions while petrol and LPG vehicles tend to have higher NO emissions when engine load is high. It can be observed that gaseous emission factors of petrol and LPG vehicles increase greatly within 2 years of being introduced to the vehicle fleet, suggesting that engine and catalyst performance deteriorate rapidly. It can be observed that LPG vehicles have higher levels of gaseous emissions than petrol vehicles, suggesting that proper maintenance of LPG vehicles is essential in reducing gaseous emissions from vehicles. - Highlights: ? Emissions collected in 3 different periods to examine changes in emission over time. ? LPG vehicles generally emit more gaseous pollutants compared to other vehicles. ? Large increase in emissions from modern petrol/LPG vehicles after 2 years' operation. ? CO and NO emissions of modern diesel vehicles are similar to those of older vehicles. - Remote sensing measurements show large increases in gaseous emissions from vehicles in Hong Kong after 2 years ofcles in Hong Kong after 2 years of operation, indicating that engine and catalyst performance deteriorate rapidly.

240

Observations on some thermoluminescence emission centres in geological quartz  

International Nuclear Information System (INIS)

We report measurements of three-dimensional thermoluminescence emission spectra of samples of geological quartz, derived from Australian sediments. The emphasis is on peaks of particular practical interest for thermoluminescence sediment dating, viz. the 110oC peak, which is used for pre-dose dating and the peak at 325oC, which is of significance for partial and selective bleach techniques and for optically stimulated luminescence (OSL) dating. Because the 325oC peak can be bleached to essentially zero, it can be isolated in a given spectrum by subtracting the bleached spectrum from the unbleached spectrum. By including both peaks in the same spectrum, it is demonstrated that they do not emit at the same wavelength, although this does not necessarily mean that the emission is from different emission centres. The 375oC peak, which is important in total bleach methods, emits at a distinguishable wavelength. The use of bleaching and subtraction in practical dating is discussed. (Author)

241

Regional nitrogen oxides emission trends in East Asia observed from space  

Directory of Open Access Journals (Sweden)

Full Text Available Due to changing economic activity, emissions of air pollutants in East Asia change rapidly in space and time. Monthly emission estimates of nitrogen oxides derived from satellite observations provide valuable insight in the evolution of anthropogenic activity on a regional scale. We present the first results of a new emission estimation algorithm, specifically designed to use daily satellite observations of column concentrations for fast updates of emissions of short-lived atmospheric constituents on a~mesoscopic scale (~ 0.25° × 0.25°. The algorithm is used to construct a monthly NOx emission time series for 2007–2011 from tropospheric NO2 observations of GOME-2 for East Chinese provinces and surrounding countries. The new emission estimates correspond well with the bottom-up inventory of EDGAR v4.2, but are smaller than the inventories of INTEX-B and MEIC. They reveal a strong positive trend during 2007–2011 for almost all Chinese provinces, related to the country's economic development. We find a 41% increment of NOx emissions in East China during this period, which shows the need to update emission inventories in this region on a regular basis. Negative emission trends are found in Japan and South Korea, which can be attributed to a combined effect of local environmental policy and global economic crises. Analysis of seasonal variation distinguishes between regions with dominant anthropogenic or biogenic emissions. For regions with a mixed anthropogenic and biogenic signature, the opposite seasonality can be used for an estimation of the separate emission contributions. Finally, the non-local concentration/emission relationships calculated by the algorithm are used to quantify the direct effect of regional NOx emissions on tropospheric NO2 concentrations outside the region. For regions such as North Korea and Beijing province, a substantial part of the tropospheric NO2 originates from emissions elsewhere.

B. Mijling

2013-07-01

242

Regional nitrogen oxides emission trends in East Asia observed from space  

Science.gov (United States)

Due to changing economic activity, emissions of air pollutants in East Asia are changing rapidly in space and time. Monthly emission estimates of nitrogen oxides derived from satellite observations provide valuable insight into the evolution of anthropogenic activity on a regional scale. We present the first results of a new emission estimation algorithm, specifically designed to use daily satellite observations of column concentrations for fast updates of emissions of short-lived atmospheric constituents on a mesoscopic scale (~ 0.25° × 0.25°). The algorithm is used to construct a monthly NOx emission time series for the period 2007-2011 from tropospheric NO2 observations of GOME-2 for East Chinese provinces and surrounding countries. The new emission estimates correspond well with the bottom-up inventory of EDGAR v4.2, but are smaller than the inventories of INTEX-B and MEIC. They reveal a strong positive trend during 2007-2011 for almost all Chinese provinces, related to the country's economic development. We find a 41% increment of NOx emissions in East China during this period, which shows the need to update emission inventories in this region on a regular basis. Negative emission trends are found in Japan and South Korea, which can be attributed to a combined effect of local environmental policy and global economic crises. Analysis of seasonal variation distinguishes between regions with dominant anthropogenic or biogenic emissions. For regions with a mixed anthropogenic and biogenic signature, the opposite seasonality can be used for an estimation of the separate emission contributions. Finally, the non-local concentration/emission relationships calculated by the algorithm are used to quantify the direct effect of regional NOx emissions on tropospheric NO2 concentrations outside the region. For regions such as North Korea and the Beijing municipality, a substantial part of the tropospheric NO2 originates from emissions elsewhere.

Mijling, B.; van der A, R. J.; Zhang, Q.

2013-12-01

243

Coronal emission line profile observations at total solar eclipses. I  

International Nuclear Information System (INIS)

A 25-cm aperture f/8.0 telescope was operated aboard a U.S. Air Force-Energy Research and Development Administration aircraft at the 30 May 1965 and 12 November 1966 total solar eclipses. A fixed path Fabry-Perot interferometer spectrograph with 0.008-nm resolution was developed to photographically record intensity vs wavelength profiles of the coronal emission lines Fe XIV (530.3 nm), Fe X(637.4 nm) and Ca XV (569.4 nm). A pressure scanned Fabry-Perot interferometer was developed with a photoelectric detector and recorder. Photoelectric tracking was used in 1965 and gyroscopic tracking with photoelectric updating provided improved tracking in 1966. Photographic interferometer data were obtained out to 1.79 R(sun) in 1965 at 530.3 nm. Doppler shifts are determined and indicate generally small velocities of coronal material. Results in Fe XIV and Fe X were obtained in 1966. No Ca XV emission was detected in 1966. (Auth.)

244

Lion roar emissions observed by the CLUSTER and THEMIS spacecraft  

Science.gov (United States)

Lion roars are intense, narrow-band whistler-mode emissions sporadically occurring in the Earth's magnetosheath. We present a statistical study based on the CLUSTER data recorded during years 2001 and 2005. We have used the spectral analyzer STAFF-SA which is processing signals from three magnetic and two electric sensors. Frequency and power properties of lion roars have been investigated and generally correspond to previous results. We have also studied their spatial distribution. We have compared the field-aligned component of the Poynting flux and the local magnetic field in order to predict the source region. Our result shows that lion roars are mainly propagating toward the Earth. We thus expect that the source region is more often close to the bow shock. The SCM and EFI instruments on-board THEMIS provide measurements of all six components of the magnetic and electric field. It allows us to investigate properties of lion roar emissions. We present case studies of selected events.

Krupar, V.; Santolik, O.; Maksimovic, M.; Cornilleau-Wehrlin, N.; Angelopoulos, V.; Le Contel, O.; Bonnell, J.; Auster, U.

2008-12-01

245

Optimizing the emission inventory of volatile organic compounds (VOCs) based on network observations  

Science.gov (United States)

Hourly observations of 56 non-methane hydrocarbons (NMHCs) performed by a network of photochemical assessment monitoring stations (PAMS) at 11 locations across Taiwan were used to evaluate 56 speciated emissions and the resulting simulations of an air quality model. Based on the PAMS observations at two urban sites, emission modification was made for the 56 PAMS species in the model. To further test the applicability of this emission correction approach, the same modified emissions were subject to seven different meteorological conditions and comparison with observations of all the 11 PAMS sites. Originally there was a minimum of only 8 of 56 species showed agreement with observations for the worst of the 11 PAMS sites and 28 of 56 species for the best site. With modified emissions, the number increased to 13-52 species across the 11 PAMS sites, demonstrating that the simple urban based correction procedure has broad applicability. When applying this modification of PAMS emissions to the simulations of other air quality gases, SO2 and NOx showed small changes compared with observations (-0.27% and -2.51%, respectively), while total VOC concentrations showed significant changes (+15.28%) as a result of the adjustment in VOC emissions (+26.7%). Although VOCs are the precursor of ozone, the relatively large changes in VOC did not seem to affect ozone formation to the similar extent, only resulting in the changes of average O3 by 2.9 ppb (+9.41%). It shows that although the emission modification improves individual VOC simulations, the performance in oxidant simulation is still largely unaltered. Although the original U.S. VOC emission profiles can capture the general features of ambient VOCs, further optimization of emissions may still be needed by referencing extensive observations, so that emissions can better fit domestic conditions and accuracy in model simulations can be improved.

Chen, Sheng-Po; Liu, Wen-Tzu; Ou-Yang, Chang-Feng; Chang, Julius S.; Wang, Jia-Lin

2014-02-01

246

Sensitivity analysis of methane emissions derived from SCIAMACHY observations through inverse modelling  

OpenAIRE

Satellite observations of trace gases in the atmosphere offer a promising method for global verification of emissions and improvement of global emission inventories. Here, an inverse modelling approach based on fourdimensional variational (4D-var) data assimilation is presented and applied to synthetic measurements of atmospheric methane. In this approach, emissions and initial concentrations are optimised simultaneously, thus allowing inversions to be carried out on t...

Meirink, J. F.; Eskes, H. J.; Goede, A. P. H.

2006-01-01

247

Some problems of VLF wave propagation in the magnetosphere  

International Nuclear Information System (INIS)

The geometric optical picture of very low frequency (VLF) wave propagation in the Earth plasmasphere under the assumption of the geomagnetic field dipolarity is studied. It is shown by means of numerical calculations that in the preequatorial region a wave becomes electrostatic one. If the wave frequency is not too small as compared with the equatorial value of the cyclotron frequency at the initial ?-shell, all trajectories begin focusing at the approach to the equator and finish in the opposite hemispheres on near ?-shells. For these conditions analytical solutions of the geometric optics equations are obtained

248

VLF study of low magnitude Earthquakes (4.5  

Science.gov (United States)

In the course of the European VLF/LF radio receiver network (International Network for Frontier Research on Earthquake Precursors, INFREP), radio signals in the frequency range from 10-50 kilohertz are received, continuously recorded (temporal resolution 20 seconds) and analyzed in the Graz/Austria knot. The radio signals are generated by dedicated distributed transmitters and detected by INFREP receivers in Europe. In case the signal is crossing an earthquake preparation zone, we are in principle able to detect seismic activity if the signal to noise ratio is high enough. The requirements to detect a seismic event with the radio link methods are given by the magnitude M of the Earthquake (EQ), the EQ preparation zone and the Fresnel zone. As pointed out by Rozhnoi et al. (2009), the VLF methods are suitable for earthquakes M>5.0. Furthermore, the VLF/LF radio link gets only disturbed if it is crossing the EQ preparation zone which is described by Molchanov et al. (2008). In the frame of this project I analyze low seismicity EQs (M?5.6) in south/eastern Europe in the time period 2011-2013. My emphasis is on two seismic events with magnitudes 5.6 and 4.8 which we are not able to adequately characterize using our single parameter VLF method. I perform a fine structure analysis of the residua of various radio links crossing the area around the particular 2 EQs. Depending on the individual paths not all radio links are crossing the EQ preparation zone directly, so a comparative study is possible. As a comparison I analyze with the same method the already good described EQ of L'Aquila/Italy in 2009 with M=6.3 and radio links which are crossing directly the EQ preparation zone. In the course of this project we try to understand in more detail why it is so difficult to detect EQs with 4.5Hayakawa: Seismo-Electromagnetics and related Phenomena: History and latest results, Terrapub, 2008.

Wolbang, Daniel; Biernat, Helfried; Schwingenschuh, Konrad; Eichelberger, Hans; Prattes, Gustav; Besser, Bruno; Boudjada, Mohammed; Rozhnoi, Alexander; Solovieva, Maria; Biagi, Pier Francesco; Friedrich, Martin

2014-05-01

249

The Observation and Direction Findings of ULF Electromagnetic Emissions Possibly Associated with Earthquakes  

Science.gov (United States)

Chubu University has established ULF/ELF electromagnetic observation network in order to study seismo-electromagnetics. We have observed ULF electromagnetic emissions radiated from the direction of the epicentral region of the 2004 Mid Niigata Prefecture (Ohta et al., 2005) and the 2004 Sumatra earthquakes (Ohta et al., 2007). In this study, we estimated the direction angle of the ULF emissions observed at three observation stations (Nakatsugawa, Shinojima and Minami Izu) before earthquakes. We found that ULF emissions observed at Nakatsugawa station have been propagated possibly from the direction of the epicenter of the 2007 Noto Hantou earthquake. And also we found that ULF emissions observed at three observation stations have been propagated possibly from the epicentral area of the 2008 Iwate-Miyagi Nairiku earthquake. However, the number of ULF emissions whose direction angle was pointed to the epicenter was not outstandingly large. If we don’t know the location of the earthquake, this would make us to misguide the location of the epicenter. The observed ULF emissions possibly propagated from the epicentral region were not so convincing enough. And so we need more event studies.

Izutsu, J.; Ohta, K.; Hayakawa, M.

2009-12-01

250

Neptunyl(vi) centred visible LMCT emission directly observable in the presence of uranyl(vi).  

Science.gov (United States)

Room temperature detection of neptunyl(vi) LMCT emission in a coordination compound and in the presence of uranyl(vi) is reported for the first time. Differences in the excitation profiles of the complexes enable spectral editing so either exclusively neptunyl(vi) or uranyl(vi) emission is observed or a sum of the two. PMID:25531574

Woodall, Sean D; Swinburne, Adam N; Lal Banik, Nidhu; Kerridge, Andrew; Di Pietro, Poppy; Adam, Christian; Kaden, Peter; Natrajan, Louise S

2015-03-12

251

Radiofrequency molecular emission spectra observed toward zeta Ophiuchi  

International Nuclear Information System (INIS)

The most intense radiofrequency emission from 12CO and 12CH in the direction of zeta Oph resides in a component at V/sub sun/=-14.4 km s-1 (V/sub 1sr/=-0.7 km s-1) whose FWHM is less than 0.5 km s-1; the nominal b-value of such a line is = exclamation2sigma-1. If this exceptionally narrow-lined cloud contains the bulk of the absorbing material toward zeta Oph (as is usually assumed), there may lurk in the spectra of many species substantial abundances which have previously gone undetected. The extent of this hidden contribution depends on the physical conditions believed to exist in the neutral and molecule-bearing gas. Although the density of this gas is usually assumed to be quite large, n (H) >103 cm-3, we show that some of the evidence available at present is consistent with and indicative of more rarified conditions. If this is the case, the depletions of many species have been greatly overestimated. The most direct probe of the physical conditions in the -14.4 km s-1 cloud would be a better determination of the C II column density, based on a search for damping wings such as have been recently shown to the present in O I

252

Radiofrequency molecular emission spectra observed toward zeta Ophiuchi  

Energy Technology Data Exchange (ETDEWEB)

The most intense radiofrequency emission from /sup 12/CO and /sup 12/CH in the direction of zeta Oph resides in a component at V/sub sun/=-14.4 km s/sup -1/ (V/sub 1sr/=-0.7 km s/sup -1/) whose FWHM is less than 0.5 km s/sup -1/; the nominal b-value of such a line is = exclamation2sigma<0.3 km s/sup -1/. If this exceptionally narrow-lined cloud contains the bulk of the absorbing material toward zeta Oph (as is usually assumed), there may lurk in the spectra of many species substantial abundances which have previously gone undetected. The extent of this hidden contribution depends on the physical conditions believed to exist in the neutral and molecule-bearing gas. Although the density of this gas is usually assumed to be quite large, n (H) >10/sup 3/ cm/sup -3/, we show that some of the evidence available at present is consistent with and indicative of more rarified conditions. If this is the case, the depletions of many species have been greatly overestimated. The most direct probe of the physical conditions in the -14.4 km s/sup -1/ cloud would be a better determination of the C II column density, based on a search for damping wings such as have been recently shown to the present in O I.

Liszt, H.S.

1979-11-01

253

Observations and predictions of EUV emission from classical novae  

International Nuclear Information System (INIS)

Theoretical modeling of novae in outburst predicts that they should be active emitters of radiation both in the EUV and soft X-ray wavelengths twice during the outburst. The first time is very early in the outburst when only an all sky survey can detect them. This period lasts only a few hours. They again become bright EUV and soft X-ray emitters late in the outburst when the remnant object becomes very hot and is still luminous. The predictions imply both that a nova can remain very hot for months to years and that the peak temperature at this time strongly depends upon the mass of the white dwarf. It is important to observe novae at these late times because a measurement of both the flux and temperature can provide information about the mass of the white dwarf, the tun-off time scale, and the energy budget of the outburst. We review the existing observations of novae in late stages of their outburst and present some newly obtained data for GQ Mus 1983. We then provide results of new hydrodynamic simulations of novae in outburst and compare the predictions to the observations. 43 refs., 6 figs

254

Temperature and Emission-Measure Profiles Along Long-Lived Solar Coronal Loops Observed with TRACE  

OpenAIRE

We report an initial study of temperature and emission measure distributions along four steady loops observed with the Transition Region and Coronal Explorer (TRACE) at the limb of the Sun. The temperature diagnostic is the filter ratio of the extreme-ultraviolet 171-angstrom and 195-angstrom passbands. The emission measure diagnostic is the count rate in the 171-angstrom passband. We find essentially no temperature variation along the loops. We compare the observed loop str...

Lenz, Dawn D.; Deluca, Edward E.; Golub, Leon; Rosner, Robert; Bookbinder, Jay A.

1999-01-01

255

Direct observation of thermionic emission pattern of hemispherical single-crystal LaB6  

Science.gov (United States)

Thermionic emission pattern from a hemispherical LaB6 cathode of orientation was made using an experimental setup similar to Martin's experiment. The emission pattern from a clean surface has clearly indicated that the bright region consists of (100) spot surrounded by four (210) spots. This suggests that the bright spots (except for the center spot in the cross-over images observed for , , and LaB6 cathodes correspond to (210) spots as deduced by Oshima et al. Emission patterns at different vacuum conditions are also observed to find that a specific emission pattern appears with good reproducibility corresponding to the change of vacuum condition, leading to existence of enhanced thermionic emission.

Shimizu, R.; Onoda, H.; Hagiwara, H.; Ishii, S.

1981-10-01

256

Energy and dynamic characteristics of the envelope of VLF chorus bursts  

International Nuclear Information System (INIS)

Some VLF chorus types are singled out which differ one from ahother by energy spectra as well as by dynamic characteristics. VLF data evaluations are presented of some parameters of a magnetospheric plasma and electron fluxes responsible for the generation of the VLF radiation. It is concluded that the investigation of chorus energy spectra makes it possible to specify the location of their generation region and opens new possibilities for diagnostics of angular and energy characteristics of electrons injected into the magnetosphere in the substorm period

257

Phenomenology of Neptune's radio emissions observed by the Voyager planetary radio astronomy experiment  

Science.gov (United States)

The Neptune flyby in 1989 added a new planet to the known number of magnetized planets generating nonthermal radio emissions. We review the Neptunian radio emission morphology as observed by the planetary radio astronomy experiment on board Voyager 2 during a few weeks before and after closest approach. We present the characteristics of the two observed recurrent main components of the Neptunian kilometric radiation, i.e., the 'smooth' and the 'bursty' emissions, and we describe the many specific features of the radio spectrum during closest approach.

Pedersen, B. M.; Lecacheux, A.; Zarka, P.; Aubier, M. G.; Kaiser, M. L.; Desch, M. D.

1992-01-01

258

Modeled and observed ozone sensitivity to mobile-source emissions in Mexico City  

Directory of Open Access Journals (Sweden)

Full Text Available The emission characteristics of mobile sources in the Mexico City Metropolitan Area (MCMA have changed significantly over the past few decades in response to emission control policies, advancements in vehicle technologies and improvements in fuel quality, among others. Along with these changes, concurrent non-linear changes in photochemical levels and criteria pollutants have been observed, providing a unique opportunity to understand the effects of perturbations of mobile emission levels on the photochemistry in the region using observational and modeling approaches. The observed historical trends of ozone (O3, carbon monoxide (CO and nitrogen oxides (NOx suggest that ozone production in the MCMA has changed from a low to a high VOC-sensitive regime over a period of 20 years. Comparison of the historical emission trends of CO, NOx and hydrocarbons derived from mobile-source emission studies in the MCMA from 1991 to 2006 with the trends of the concentrations of CO, NOx, and the CO/NOx ratio during peak traffic hours also indicates that fuel-based fleet average emission factors have significantly decreased for CO and VOCs during this period whereas NOx emission factors do not show any strong trend, effectively reducing the ambient VOC/NOx ratio.

This study presents the results of model analyses on the sensitivity of the observed ozone levels to the estimated historical changes in its precursors. The model sensitivity analyses used a well-validated base case simulation of a high pollution episode in the MCMA with the mathematical Decoupled Direct Method (DDM and the standard Brute Force Method (BFM in the 3-D CAMx chemical transport model. The model reproduces adequately the observed historical trends and current photochemical levels. Comparison of the BFM and the DDM sensitivity techniques indicates that the model yields ozone values that increase linearly with NOx emission reductions and decrease linearly with VOC emission reductions only up to 30% from the base case. We further performed emissions perturbations from the gasoline fleet, diesel fleet, all mobile (gasoline plus diesel and all emission sources (anthropogenic plus biogenic. The results suggest that although large ozone reductions obtained in the past were from changes in emissions from gasoline vehicles, currently significant benefits could be achieved with additional emission control policies directed to regulation of VOC emissions from diesel and area sources that are high emitters of alkenes, aromatics and aldehydes.

M. Zavala

2009-01-01

259

Modeled and observed ozone sensitivity to mobile-source emissions in Mexico City  

Directory of Open Access Journals (Sweden)

Full Text Available The emission characteristics of mobile sources in the Mexico City Metropolitan Area (MCMA have changed significantly over the past few decades in response to emission control policies, advancements in vehicle technologies and improvements in fuel quality, among others. Along with these changes, concurrent non-linear changes in photochemical levels and criteria pollutants have been observed, providing a unique opportunity to understand the effects of perturbations of mobile emission levels on the photochemistry in the region using observational and modeling approaches. The observed historical trends of ozone (O3, carbon monoxide (CO and nitrogen oxides (NOx suggest that ozone production in the MCMA has changed from a low to a high VOC-sensitive regime over a period of 20 years. Comparison of the historical emission trends of CO, NOx and hydrocarbons derived from mobile-source emission studies in the MCMA from 1991 to 2006 with the trends of the concentrations of CO, NOx, and the CO/NOx ratio during peak traffic hours also indicates that fuel-based fleet average emission factors have significantly decreased for CO and VOCs during this period whereas NOx emission factors do not show any strong trend, effectively reducing the ambient VOC/NOx ratio.

This study presents the results of model analyses on the sensitivity of the observed ozone levels to the estimated historical changes in its precursors. The model sensitivity analyses used a well-validated base case simulation of a high pollution episode in the MCMA with the mathematical Decoupled Direct Method (DDM and the standard Brute Force Method (BFM in the 3-D CAMx chemical transport model. The model reproduces adequately the observed historical trends and current photochemical levels. Comparison of the BFM and the DDM sensitivity techniques indicates that the model yields ozone values that increase linearly with NOx emission reductions and decrease linearly with VOC emission reductions only up to 30% from the base case. We further performed emissions perturbations from the gasoline fleet, diesel fleet, all mobile (gasoline plus diesel and all emission sources (anthropogenic plus biogenic. The results suggest that although large ozone reductions obtained in the past were from changes in emissions from gasoline vehicles, currently significant benefits could be achieved with additional emission control policies directed to regulation of VOC emissions from diesel and area sources that are high emitters of alkenes, aromatics and aldehydes.

M. Zavala

2008-08-01

260

Observation of Solar Wind Charge Exchange Emission from Exospheric Material in and Outside Earth's Magnetosheath  

Science.gov (United States)

A long XMM-Newton exposure is used to observe solar wind charge exchange (SWCX) emission from exospheric material in and outside Earth s magnetosheath. The light curve of the O VII (0.5-0.62 keV) band is compared with a model for the expected emission, and while the emission is faint and the light curve has considerable scatter, the correlation is significant to better than 99.9%. This result demonstrates the validity of the geocoronal SWCX emission model for predicting a contribution to astrophysical observations to a scale factor of order unity (1.36). The results also demonstrate the potential utility of using X-ray observations to study global phenomena of the magnetosheath which currently are only investigated using in situ measurements.

Snowden, S. L.; Collier, M. R.; Cravens, T.; Kuntz, K. D.; Lepri, S. T.; Robertson, I.; Tomas, L.

2008-01-01

261

Assimilation of FRP Observations for Global Fire Emission Estimation in MACC-II  

Science.gov (United States)

We present the Global Fire Assimilation System (GFAS) that is run routinely at ECMWF by the MACC-II project in preparation of the operational GMES atmospheric service. The GFAS currently combines Fire Radiative Power (FRP) observations from the polar orbiting MODIS instruments and applies a quality control, a partial cloud cover correction and observation gap filling with a Kalman filter to generate daily global FRP maps. These are subsequently used to calculate the daily average dry matter combustion rate and emission rates for 40 atmospheric trace constituents in real time with a time lag of 7 hours. The emission estimates are consistent with the GFED3 emission dataset, but FRP appears to have a lower detection threshold than the burnt area observations used in GFED3. The emissions are further validated with the atmospheric composition models of MACC by comparing the simulated smoke plumes with atmospheric observations. The temporal and spatial patterns of the emissions are shown to be realistic. However, a general mismatch between various aerosol smoke emission rates from bottom-up and top-down inventories is evident. Upcoming upgrades of GFAS will include FRP observations from the geostationary instruments aboard Meteosat-9, GOES-East and GOES-West and improve the temporal resolution to one hour.

Kaiser, J. W.; Benedetti, A.; Detmers, R.; Heil, A.; Morcrette, J.-J.; Schultz, M. G.; van der Werf, G. R.; Wooster, M. J.; Xu, W.

2012-04-01

262

Space-based observations of nitrogen dioxide: Trends in anthropogenic emissions  

Science.gov (United States)

Space-based instruments provide routine global observations, offering a unique perspective on the spatial and temporal variation of atmospheric constituents. In this dissertation, trends in regional-scale anthropogenic nitrogen oxide emissions (NO + NO2 ? NOx) are investigated using high resolution observations from the Ozone Monitoring Instrument (OMI). By comparing trends in OMI observations with those from ground-based measurements and an emissions inventory, I show that satellite observations are well-suited for capturing changes in emissions over time. The high spatial and temporal resolutions of the observations provide a uniquely complete view of regional-scale changes in the spatial patterns of NO 2. I show that NOx concentrations have decreased significantly in urban regions of the United States between 2005 and 2011, with an average reduction of 32 ± 7%. By examining day-of-week and interannual trends, I show that these reductions can largely be attributed to improved emission control technology in the mobile source fleet; however, I also show that the economic downturn of the late 2000's has impacted emissions. Additionally, I describe the development of a high-resolution retrieval of NO2 from OMI observations known as the Berkeley High Resolution (BEHR) retrieval. The BEHR product uses higher spatial and temporal resolution terrain and profile parameters than the operational retrievals and is shown to provide a more quantitative measure of tropospheric NO2 column density. These results have important implications for future retrievals of NO2 from space-based observations.

Russell, Ashley Ray

263

Spitzer observations of the thermal emission from WASP-43b  

CERN Document Server

WASP-43b (Hellier et al.; Gillon et al.) is one of the closest-orbiting hot Jupiters, with a semimajor axis a = 0.01526 +/- 0.00018 AU and a period of only 0.81 days. However, it orbits one of the coolest stars with a hot Jupiter (K7V, Tstar = 4520 +/- 120 K), giving the planet a modest equilibrium temperature of Teq = 1440 +/- 40 K, assuming zero Bond albedo and uniform planetary energy redistribution. This has resulted in strong signal-to-noise-ratio (S/N) observations and deep eclipses in both Warm Spitzer channels (3.6 and 4.5 microns). The eclipse depths and brightness temperatures from our jointly fit model are 0.346 +/- 0.013% and 1684 +/- 24 K at 3.6 microns and 0.382 +/- 0.015% and 1485 +/- 24 K at 4.5 microns. The eclipse timings improved the estimate of the orbital period, P, by a factor of three (P = 0.81347459 +/- 2.1x10-7 days) compared to Gillon et al. and put an upper limit on the eccentricity (e = 0.007+0.013-0.004). We use our Spitzer eclipse depths with two previously reported ground-based ...

Blecic, Jasmina; Madhusudhan, Nikku; Stevenson, Kevin B; Hardy, Ryan A; Cubillos, Patricio E; Hardin, Matthew; Nymeyer, Sarah; Anderson, David R; Hellier, Coel; Smith, Alexis M S; Cameron, Andrew Collier

2013-01-01

264

Electric and VLF-MT survey of Tegatayama tunnel; Tegatayama tunnel no denki tansa oyobi VLF tansa  

Energy Technology Data Exchange (ETDEWEB)

To survey the structure at the depth between 20 and 30 m, field tests were conducted by means of vertical electric and VFL-MT (magnetotelluric) survey. Tegatayama tunnel has a total length of 276 m, width of 7.5 m, and height of 4.7 m, and the depth from the surface is about 28 m near the top of mountain. Near the tunnel, the thickness of surface soil is about 60 cm, which consists of clay soil including soft mudstone gravel. It was found that terrace deposit is distributed up to the depth of 8 m, and that mudstone is distributed below the depth of 8 m. Weighted four-electrode method was adopted for the vertical electrical survey. Measurements were conducted at the immediately above the tunnel, 10 m apart from the center of tunnel in the right and left, and 20 m apart from the center in the east. For the VLF-MT method, component of frequency 22.2 kHz was used. As a result of the tests, it was difficult to illustrate the existence of tunnel from the vertical electrical survey only at one point. Feature of the tunnel could be well illustrated by means of the VLF-MT method. 3 refs., 9 figs.

Nishitani, T. [Akita University, Akita (Japan). Mining College

1997-05-27

265

Patterns in atmospheric carbonaceous aerosols in China: emission estimates and observed concentrations  

Directory of Open Access Journals (Sweden)

Full Text Available China is experiencing severe carbonaceous aerosol pollution driven mainly by large emissions resulting from intensive use of solid fuels. To gain a better understanding of the levels and trends of carbonaceous aerosol emissions and the resulting ambient concentrations at the national scale, we update an emission inventory of anthropogenic organic carbon (OC and elemental carbon (EC and employ existing observational studies to analyze characteristics of these aerosols including temporal, spatial, and size distributions, and the levels and shares of secondary organic carbon (SOC in total OC. We further use ground observations to test the levels and inter-annual trends of the calculated national and provincial emissions of carbonaceous aerosols, and propose possible improvements in emission estimation for the future. The national OC emissions are estimated to have increased 29% from 2000 (2127 Gg to 2012 (2749 Gg and EC by 37% (from 1356 to 1857 Gg. The residential, industrial, and transportation sectors contributed an estimated 76 ± 2, 19 ± 2 and 5 ± 1% of the total emissions of OC, respectively, and 52 ± 3, 32 ± 2 and 16 ± 2% of EC. Updated emission factors based on the most recent local field measurements, particularly for biofuel stoves, lead to considerably lower emissions of OC compared to previous inventories. Compiling observational data across the country, higher concentrations of OC and EC are found in northern and inland cities, while larger OC/EC and SOC/OC ratios are found in southern cities, due to the joint effects of primary emissions and meteorology. Higher SOC/OC ratios are estimated at rural and remote sites compared to urban ones, attributed to more emissions of OC from biofuel use, more biogenic emissions of volatile organic compound (VOC precursors to SOC, and/or transport of aged aerosols. For most sites, higher concentrations of OC, EC, and SOC are observed in colder seasons, while SOC/OC is reduced, particularly at rural and remote sites, attributed partly to weaker atmospheric oxidation and SOC formation compared to summer. Enhanced SOC formation from oxidization and anthropogenic activities like biomass combustion is judged to have crucial effects on severe haze events characterized by high particle concentrations. Several observational studies indicate an increasing trend in ambient OC/EC (but not in OC or EC individually from 2000 to 2010, confirming increased atmospheric oxidation of OC across the country. Combining the results of emission estimation and observations, the improvement over prior emission inventories is indicated by inter-annual comparisons and correlation analysis. It is also indicated, however, that the estimated growth in emissions might be faster than observed growth, and that some sources with high primary OC/EC like burning of biomass are still underestimated. Further studies to determine changing emission factors over time in the residential sector and to compare to other measurements such as satellite observations are thus suggested to improve understanding of the levels and trends of primary carbonaceous aerosol emissions in China.

H. Cui

2015-03-01

266

Numerical Simulations Of The Effect Of Localised Ionospheric Perturbations On Subionospheric VLF Propagation  

Science.gov (United States)

Electron density and temperature changes in the D-region of the ionosphere are sensitively manifested as changes in the amplitude and phase of subionospheric Very Low Frequency (VLF) signals propagating beneath the perturbed region. Disturbances (either in electron density or temperature) in the D region cause significant scattering of VLF waves propagating in the earth-ionosphere waveguide, leading to measurable changes in the amplitude and phase of the VLF waves. We analyze Lightning-induced electron precipitation (LEP) events during period 2008 - 2009 at Belgrade station on subionospheric VLF signals from four transmitters (DHO/23.4 kHz, Germany; GQD/22.1 kHz, UK; NAA/24.0 kHz USA and ICV/20.9 kHz Italy).

Šulic, D.; Nina, A.; Sreckovic, V.

2010-07-01

267

Substorm-related VLF chorus events: local-time dependence and relationship to newly-injected clouds of drifting energetic electrons  

International Nuclear Information System (INIS)

VLF chorus is a naturally occurring, electromagnetic wave phenomenon that is generated in the earth's magnetosphere during interactions between VLF waves and energetic electrons. The macrostructure of a 9-day period of VLF ground station data, recorded at two Antarctic stations, Halley Bay and Siple, has been studied using compressed time-scale spectrograms. A magnetically quiet period was chosen for analysis, within which isolated substorms occurred. It has been found that chorus frequently occurs in events, the most characteristic feature of which is an initial rise in the upper cut-off frequency of the chorus band. The events are typically observed in the midnight to 16:00 MLT sector. They are correlated with disturbances of about 100 to 750 gammas in the AE magnetic activity index, or substorms, and with energetic electron flux enhancements measured by ATS 6 at geosynchronous orbit. In addition, parameters scaled from the upper and lower cut-off frequency variations of the events have a local-time dependence. During substorms, satellites consistently encounter clouds of energetic electrons that have been injected into the nightside outer radiation zone. It is believed that the time-developing characteristics, and local-time dependencies of the chorus events are a reflection of the time-developing characteristics of clouds of energetic electrons that have recently been injected during substorms. Two interpretations of the chorus events have been investigated based horus events have been investigated based on this theory

268

Effect of D.C. testing water tree deteriorated cable and a preliminary evaluation of V.L.F. as alternate  

International Nuclear Information System (INIS)

This paper reports that according to the experience of some power utilities, the application of industry recommended high voltage d.c. field tests on 5-35 kV extruded dielectric cables, containing water trees, sometimes causes further deterioration of the insulation. Tests conducted on laboratory aged 15 kV ethylene propylene rubber (EP) and 15 and 28 kV crosslinked polyethylene (XLPE) insulated cables indicate that d.c. proof tests in accordance with AEIC specifications an IEEE test guides without flashover do not appear to cause further deterioration. Depending on the degree of cable aging and the level of test voltage, when flashovers take place, damage may be inflicted to XLPE cables. No damage was observed on aged EP cable, at the same test levels. Because of the aforementioned power utility experience, some users have requested an alternate field proof test. Tests conducted on new XLPE and EP cables indicate that damage to the insulation structure can be detected using VLF (0.1 Hz) voltage at approximately one-third the d.c. voltage level. Field tests conducted on severely tree deteriorated 15 kV polyethylene (PE) cable using AEIC recommended d.c. voltage level of about five times operating voltage level caused cable failure; VLF voltage levels up to two times operating voltage did not. VLF voltage appears to be a suitable alternate to d.c. voltage for field proof testing

269

Ion cyclotron emissions observed by the satellite Akebono in the vicinity of the magnetic equator  

International Nuclear Information System (INIS)

Ion wave observations by a wave measuring instrument named ELF on board the Akebono satellite, interesting ELF emissions in the frequency ranges above the cyclotron frequencies of He(+) and/or O(+) ions have been detected. It is proposed that these emissions are due to electromagnetic ion cyclotron waves, which might have been generated by the ion cyclotron resonant instability due to a temperature anisotropy of hot H(+) ions, trapped along the magnetic field lines around the geomagnetic equatorial plane. In order to confirm the characteristics of these ELF emissions, statistical characteristics, refractive index, and wave normal direction of the emissions are first estimated. The propagation characteristics of these ELF emissions are examined by ray tracing for ion cyclotron waves in the magnetosphere using both cold and hot plasma models. 18 refs

270

Observations of the microwave emission of Venus from 1.3 to 3.6 cm  

International Nuclear Information System (INIS)

An account is given of the methodology as well as the results of coordinated Venus emission observations conducted at four wavelengths between 1.35 and 3.6 cm; the results are compared with other observations and with calculated mission spectra, with a view to suggestions that the microwave spectrum of Venus could be sensitive to the subcloud abundance of such constituents as SO2 and gaseous H2SO4. The observed emission spectrum is consistent with an average subcloud abundance of gaseous H2SO4 in equatorial and midlatitude regions of about 5 ppm. An upper limit is established for the subcloud SO2 abundance. 19 refs

271

The Near-Infrared Broad Emission Line Region of Active Galactic Nuclei -- I. The Observations  

CERN Document Server

We present high quality (high signal-to-noise ratio and moderate spectral resolution) near-infrared (near-IR) spectroscopic observations of 23 well-known broad-emission line active galactic nuclei (AGN). Additionally, we obtained simultaneous (within two months) optical spectroscopy of similar quality. The near-IR broad emission line spectrum of AGN is dominated by permitted transitions of hydrogen, helium, oxygen, and calcium, and by the rich spectrum of singly-ionized iron. In this paper we present the spectra, line identifications and measurements, and address briefly some of the important issues regarding the physics of AGN broad emission line regions. In particular, we investigate the excitation mechanism of neutral oxygen and confront for the first time theoretical predictions of the near-IR iron emission spectrum with observations.

Landt, Hermine; Ward, Martin J; Elvis, Martin; Peterson, Bradley M; Korista, Kirk T; Karovska, Margarita

2007-01-01

272

Fast, simultaneous and robust VLF-EM data denoising and reconstruction via multivariate empirical mode decomposition  

Science.gov (United States)

The measurement of Very Low Frequency Electromagnetic (VLF-EM) is important in many different applications, i.e, environmental, archeological, geotechnical studies, etc. In recent years, improving and enhancing VLF-EM data containing complex numbers (bivariate) was presented by several authors in order to produce reliable models, generally using univariate empirical mode decomposition (EMD). Applying univariate EMD separately on each data is problematic. This results in a different number of misaligned Intrinsic Mode Functions (IMFs) which can complicate the selection of some IMFs for denoising process. Thus, a filtering method based on the multivariate empirical mode decomposition (MEMD) approach to decompose simultaneously bivariate data is proposed. In this paper we address two issues by employing the recently introduced noise assisted MEMD (N-A MEMD) for improving bivariate VLF-EM data. Firstly, the N-A MEMD to decompose bivariate measurement of the VLF-EM data into IMFs and a residue is defined as VLF-EM signal or unwanted noise. Secondly, the proposed method is used to enhance VLF-EM data and to reject unwanted noise. Finally, the proposed method is applied to a synthetic data with two added sinusoids. To demonstrate the robustness of the N-A MEMD method, the method was tested on added-noise synthetic data sets and the results were compared to the Ensemble EMD (EEMD) and Bivariate EMD (BEMD). The N-A MEMD gave more robust and accurate results than the EEMD and BEMD methods and the method required less CPU time to obtain the IMFs compared to EEMD. The method was also tested on several field data sets. The results indicate that the filtered VLF-EM data based on the N-A MEMD make the data easier to interpret and to be analyzed further. In addition, the 2D resistivity profile estimated from the inversion of filtered VLF-EM data results was appropriate to the geological condition.

Sungkono; Bahri, Ayi S.; Warnana, Dwa D.; Monteiro Santos, Fernando A.; Santosa, Bagus J.

2014-06-01

273

Atmospheric observations and emissions estimates of methane and nitrous oxide from regional to global scale  

Science.gov (United States)

Methane (CH4) and Nitrous Oxide (N2O) are the two most significant anthropogenic, long-lived, non-CO2 greenhouse gases, together perturbing the earth's energy balance by an amount comparable to that of CO2. This dissertation will focus on the use of atmospheric observations to quantify emissions of CH4 and N2O. First top-down emissions constraints on the regional scale, covering large areas of the U.S and southern Canada, are derived from airborne observations made in Spring of 2003. Using a receptor-oriented Lagrangian particle dispersion model provides robust validation of bottom-up emission estimates from EDGAR 32FT2000 and GEIA inventories. It is found that EDGAR CH4 emission rates are slightly low by a factor of 1.08 +/- 0.15 (2 sigma), while both EDGAR and GEIA N2O emissions are significantly too low, by factors of 2.62 +/- 0.50 and 3.05 +/- 0.61 respectively. This analysis is then extended over a full calendar year in 2004 with observations from NOAA's tall tower and aircraft profile network. EDGAR 32FT2000 CH 4 emissions are found to be consistent with observations, though the newer EDGAR v4.0 reduces CH4 emissions by 30%, and this reduction is not consistent with this study. Scaling factors found for N2O in May/June of 2003 (2.62 & 3.05) are found to hold for February-May of 2004, suggesting inventories are significantly too low in primary growing season coincident with significant fertilizer inputs. A new instrument for airborne observation of CO2, CH 4, N2O, and CO is introduced, and its operation and in-field performance are highlighted (demonstrated 1-sec precisions of 20 ppb, 0.5 ppb, 0.09 ppb, and 0.15 ppb respectively). Finally, global N2O observations collected with this sensor on the HIPPO (Hlaper Pole to Pole Observations) campaign are assessed. Comparison with a global model and subsequent inversion indicates strong, episodic inputs of nitrous oxide from tropical regions are necessary to bring observations and model in agreement. Findings highlight the strong temporal variability of nitrous oxide emissions, and the necessity of using full vertical profile observations in deriving emissions from atmospheric measurements.

Kort, Eric Adam

2011-12-01

274

Observations of the 10 micrometer natural laser emission from the mesospheres of Mars and Venus  

International Nuclear Information System (INIS)

Observations of the total flux and center to limb dependence of the nonthermal emission occurring in the cores of the 9.4 and 10.4 micrometers CO2 bands on Mars are compared to a theoretical model based on this mechanism. The model successfully reproduces the observed center to limb dependence of this emission, to within the limits imposed by the spatial resolution of the observations of Mars and Venus. The observed flux from Mars agrees closely with the prediction of the model the flux observed from Venus is 74% of the flux predicted by the model. This emission is used to obtain the kinetic temperatures of the Martian and Venusian mesospheres. For Mars near 70 km altitude, a rotational temperature analysis using five lines gives T 135 + or - 20 K. The frequency width of the emission is also analyzed to derive a temperature of 126 + or - 6 K. In the case of the Venusian mesosphere near 109 km, the frequency width of the emission gives T 204 + or - 10 K

275

CAN A LONG NANOFLARE STORM EXPLAIN THE OBSERVED EMISSION MEASURE DISTRIBUTIONS IN ACTIVE REGION CORES?  

Energy Technology Data Exchange (ETDEWEB)

All theories that attempt to explain the heating of the high-temperature plasma observed in the solar corona are based on short bursts of energy. The intensities and velocities measured in the cores of quiescent active regions, however, can be steady over many hours of observation. One heating scenario that has been proposed to reconcile such observations with impulsive heating models is the 'long nanoflare storm', where short-duration heating events occur infrequently on many sub-resolution strands; the emission of the strands is then averaged together to explain the observed steady structures. In this Letter, we examine the emission measure distribution predicted for such a long nanoflare storm by modeling an arcade of strands in an active region core. Comparisons of the computed emission measure distributions with recent observations indicate that the long nanoflare storm scenario implies greater than five times more 1 MK emission than is actually observed for all plausible combinations of loop lengths, heating rates, and abundances. We conjecture that if the plasma had 'super coronal' abundances, the model may be able to match the observations at low temperatures.

Mulu-Moore, Fana M.; Winebarger, Amy R. [NASA Marshall Space Flight Center, VP 62, Huntsville, AL 35812 (United States); Warren, Harry P., E-mail: fanamariam.mulumoore@nasa.gov [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)

2011-11-20

276

MULTIWAVELENGTH OBSERVATIONS OF GRB 110731A: GeV EMISSION FROM ONSET TO AFTERGLOW  

International Nuclear Information System (INIS)

We report on the multiwavelength observations of the bright, long gamma-ray burst GRB 110731A, by the Fermi and Swift observatories, and by the MOA and GROND optical telescopes. The analysis of the prompt phase reveals that GRB 110731A shares many features with bright Large Area Telescope bursts observed by Fermi during the first three years on-orbit: a light curve with short time variability across the whole energy range during the prompt phase, delayed onset of the emission above 100 MeV, extra power-law component and temporally extended high-energy emission. In addition, this is the first GRB for which simultaneous GeV, X-ray, and optical data are available over multiple epochs beginning just after the trigger time and extending for more than 800 s, allowing temporal and spectral analysis in different epochs that favor emission from the forward shock in a wind-type medium. The observed temporally extended GeV emission is most likely part of the high-energy end of the afterglow emission. Both the single-zone pair transparency constraint for the prompt signal and the spectral and temporal analysis of the forward-shock afterglow emission independently lead to an estimate of the bulk Lorentz factor of the jet ? ? 500-550.

277

Estimating Sulfur hexafluoride (SF6) emissions in China using atmospheric observations and inverse modeling  

Science.gov (United States)

With a global warming potential of around 22800 over a 100-year time horizon, sulfur hexafluoride (SF6) is one of the greenhouse gases regulated under the Kyoto Protocol. Global SF6 emissions have been increasing since circa the year 2000. The reason for this increase has been inferred to be due to rapidly increasing emissions in developing countries that are not obligated to report their annual emissions to the United Nations Framework Convention on Climate Change, notably China. In this study, SF6 emissions during the period 2006-2012 for China and other East Asian countries were determined using in-situ atmospheric measurements and inverse modeling. We performed various inversion sensitivity tests, which show the largest uncertainties in the a posteriori Chinese emissions are associated with the a priori emissions used and their uncertainty, the station network, as well as the meteorological input data. The overall relative uncertainty of the a posteriori emissions in China is estimated to be 17% in 2008. Based on sensitivity tests, we employed the optimal parameters in our inversion setup and performed yearly inversions for the study period. Inversion results show that the total a posteriori SF6 emissions from China increased from 1420 × 245 Mg/yr in 2006 to 2741 × 472 Mg/yr in 2009 and stabilized thereafter. The rapid increase in emissions reflected a fast increase in SF6 consumption in China, a result also found in bottom-up estimates. The a posteriori emission map shows high emissions concentrated in populated parts of China. During the period 2006-2012, emissions in northwestern and northern China peaked around the year 2009, while emissions in eastern, central and northeastern China grew gradually during almost the whole period. Fluctuating emissions are observed for southwestern China. These regional differences should be caused by changes of provincial SF6 usage and by shifts of usage among different sectors. Fig. 1. Footprint emission sensitivity obtained from FLEXPART 20-day backward simulations based on ECMWF input data averaged for the period 2006-2012 for all three stations. Black dots represent the corresponding measurement stations.

Fang, X.; Thompson, R.; Saito, T.; Yokouchi, Y.; Li, S.; Kim, J.; Kim, K.; Park, S.; Graziosi, F.; Stohl, A.

2013-12-01

278

Electron beam injection during active experiments. I - Electromagnetic wave emissions  

Science.gov (United States)

The wave emissions produced in Echo 7 experiment by active injections of electron beams were investigated to determine the properties of the electromagnetic and electrostatic fields for both the field-aligned and cross-field injection in such experiments and to evaluate the sources of free energy and relative efficiencies for the generation of the VLF and HF emissions. It is shown that, for typical beam energies in active experiments, electromagnetic effects do not substantially change the bulk properties of the beam, spacecraft charging, and plasma particle acceleration. Through simulations, beam-generated whistlers; fundamental z-mode and harmonic x-mode radiation; and electrostatic electron-cyclotron, upper-hybrid, Langmuir, and lower-hybrid waves were identified. The characteristics of the observed wave spectra were found to be sensitive to both the ratio of the electron plasma frequency to the cyclotron frequency and the angle of injection relative to the magnetic field.

Winglee, R. M.; Kellogg, P. J.

1990-01-01

279

The impact of PMSE and NLC particles on VLF propagation  

Directory of Open Access Journals (Sweden)

Full Text Available PMSE or Polar Mesosphere Summer Echoes are a well-known phenomenon in the summer northern polar regions, in which anomalous VHF/UHF radar echoes are returned from heights ~85km. Noctilucent clouds and electron density biteouts are two phenomena that sometimes occur together with PMSE. Electron density biteouts are electron density depletion layers of up to 90%, which may be several kms thick. Using the NOSC Modefndr code based on Wait's modal theory for subionospheric propagation, we calculate the shifts in received VLF amplitude and phase that occur as a result of electron density biteouts. The code assumes a homogeneous background ionosphere and a homogeneous biteout layer along the Great Circle Path (GCP corridor, for transmitter receiver path lengths in the range of 500–6000km.

For profiles during the 10h about midnight and under quiet geomagnetic conditions, where the electron density at 85km would normally be less than 500el/cc, it was found that received signal perturbations were significant, of the order of 1–4dB and 5–40° of phase. Perturbation amplitudes increase roughly as the square root of frequency. At short range perturbations are rather erratic, but more consistent at large ranges, readily interpretable in terms of the shifts in excitation factor, attenuation factor and v/c ratios for Wait's modes. Under these conditions such shifts should be detectable by a well constituted experiment involving multiple paths and multiple frequencies in the north polar region in summer. It is anticipated that VLF propagation could be a valuable diagnostic for biteout/PMSE when electron density at 85km is under 500el/cc, under which circumstances PMSE are not directly detectable by VHF/UHF radars.

Key words. Electromagnetism (wave propagation – Ionosphere (polar ionosphere – Radioscience (ionospheric propagation

D. Nunn

2004-04-01

280

Why is observable radio recombination line emission from galactic HII regions always close to LTE  

International Nuclear Information System (INIS)

There is no evidence for significant deviations from LTE in single-dish observations of radio recombination line emission from galactic HII regions. This is in agreement with the known properties of HII regions, particularly their density variations and limited range of excitation parameters; the optimum configuration for strong observable non-LTE effects, low electron density and high emission measure, simply does not exist in galactic HII regions, and the observed lines are emitted under near-LTE conditions. Models of the Orion Nebulae and NGC 6604 are presented which fit all available data and show only weak stimulated emission. It is concluded that reliable electron temperatures can indeed be obtained from straightforward analysis of appropriate radio recombination lines. (orig.)

281

AMI OBSERVATIONS OF THE ANOMALOUS MICROWAVE EMISSION IN THE PERSEUS MOLECULAR CLOUD  

International Nuclear Information System (INIS)

We present observations of the known anomalous microwave emission region, G159.6–18.5, in the Perseus molecular cloud at 16 GHz performed with the Arcminute Microkelvin Imager Small Array. These are the highest angular resolution observations of G159.6–18.5 at microwave wavelengths. By combining these microwave data with infrared observations between 5.8 and 160 ?m from the Spitzer Space Telescope, we investigate the existence of a microwave-infrared correlation on angular scales of ?2'. We find that the overall correlation appears to increase toward shorter infrared wavelengths, which is consistent with the microwave emission being produced by electric dipole radiation from small, spinning dust grains. We also find that the microwave-infrared correlation peaks at 24 ?m (6.7?), suggesting that the microwave emission is originating from a population of stochastically heated small interstellar dust grains rather than polycyclic aromatic hydrocarbons.

282

Observation of solar high energy gamma and X-ray emission and solar energetic particles  

CERN Document Server

We considered 18 solar flares observed between June 2010 and July 2012, in which high energy >100 MeV {\\gamma}-emission was registered by the Large Area Telescope (LAT) aboard FermiGRO. We examined for these {\\gamma}-events soft X-ray observations by GOES, hard X-ray observations by the Anti-Coincidence Shield of the SPectrometer aboard INTEGRAL (ACS SPI) and the Gamma-Ray burst Monitor (GBM) aboard FermiGRO. Hard X-ray and {\\pi}0-decay {\\gamma}-ray emissions are used as tracers of electron and proton acceleration, respectively. Bursts of hard X-ray were observed by ACS SPI during impulsive phase of 13 events. Bursts of hard X-ray >100 keV were not found during time intervals, when prolonged hard {\\gamma}-emission was registered by LAT/FermiGRO. Those events showing prolonged high-energy gamma-ray emission not accompanied by >100 keV hard X-ray emission are interpreted as an indication of either different acceleration processes for protons and electrons or as the presence of a proton population accelerated du...

Struminsky, Alexei

2015-01-01

283

HST observations of the (O III) emission-line region in Markarian 78  

Science.gov (United States)

We present the results of Hubble Space Telescope (HST) observations of Mrk 78, a Seyfert 2 galaxy. Observations were taken with the Faint Object Camera using the F550M, F502M (which includes the (O III) lambda lambda-4959, 5007 emission lines), and F130M filters. These are medium band filters centered at 5500, 5020, and 1300 A, respectively. The (O III) image shows a biconical shape with a full opening angle of 40 deg, elongated in the direction of the radio structure, with its apex approximately coincident with the center of both the radio and optical continuum. A resolved (0.8 sec in extent) obscuring region is present close to the center of the cone. The UV image confirms the result that emission from the nucleus is not seen directly. Our results provide a strong observational support for the 'occultation/reflection' model for Seyfert 2 galaxies. We discuss the relation between radio and emission-line regions and propose a pure photoionization origin for the (O III) emission. Finally, we test the occultation model by comparing our observations with the Infrared Astronomy Satellite (IRAS) data: a strongly anisotropic nuclear source is required to meet the energy requirement derived from the analysis of the far-infrared emission.

Capetti, A.; Macchetto, F.; Sparks, W. B.; Boksenberg, A.

1994-01-01

284

The observable effects of a photospheric component on GRB's and XRF's prompt emission spectrum  

CERN Document Server

A thermal radiative component is likely to accompany the first stages of the prompt emission of Gamma-ray bursts (GRB's) and X-ray flashes (XRF's). We analyze the effect of such a component on the observable spectrum, assuming that the observable effects are due to a dissipation process occurring below or near the thermal photosphere. We consider both the internal shock model and a 'slow heating' model as possible dissipation mechanisms. For comparable energy densities in the thermal and the leptonic component, the dominant emission mechanism is Compton scattering. This leads to a nearly flat energy spectrum (\

Peér, A; Rees, Martin J; Pe'er, Asaf; M\\'esz\\'aros, Peter; Rees, Martin J.

2005-01-01

285

Observation of surface modification and secondary particle emission in HCI-surface interaction  

International Nuclear Information System (INIS)

We have observed secondary particle emission in collision of HCI with Si and HOPG surfaces. For HOPG, we have measured the number of secondary electrons and the number of dot structures on the surface as the imprint of the incidence by STM. The single ion impact is surely observable with almost 100% efficiency by detecting an event of the secondary electron emission. For hydrogen terminated Si(111), H+, H2+, H3+, C+ and Si+ ions have been detected. The proton sputtering yield, which depends on the charge of HCI, has been examined

286

Observations of SiO maser emission from R Leo during its summer 1981 maximum  

International Nuclear Information System (INIS)

The 7-mm J = 1?0, v = 1 and v = 2 SiO maser emission from the Mira variable R Leo has been closely sampled in time near the summer 1981 optical maximum in order to observe possible phase-dependent effects. A significant broadening of both v = 1 and v = 2 emission, accompanied by profile changes, was observed between phases 0.95 and 0.98. If these changes are attributed to the expected passage of the shock front, the line formation region can be inferred to be very close to the photosphere of the star, and the radial extent of the line formation region may be crudely estimated

287

Radio emission observations as a new window in observing the Universe  

Science.gov (United States)

We are all the time bombard by cosmic particles, the so-called cosmic rays. Since a century from their discovery, it is not clearly known yet where do they come from, how they are produced and accelerated to extremely high energies which cannot be reproduced at the world largest and most powerful human-made particle accelerator LHC at CERN. Nevertheless, the Universe can be observed through its cosmic messengers. Large arrays are being equipped with detectors to observe the avalanche of billions of particles which develops in adequate media like air, water, ice, and salt in mines. Huge efforts are being made by many scientists over the entire world in research and development of a new method opening a new window in observing and understanding the Universe. An overview on the innovative radio detection in air of ultra-high energy cosmic ray induced air showers is given.

Isar, Paula Gina

2012-11-01

288

Sea ice effective microwave emissivities from satellite passive microwave and infrared observations  

Science.gov (United States)

Near-simultaneous images from the temperature-humidity IR radiometer and dual-polarization scanning multichannel microwave radiometer of the Nimbus 7 satellite are used to investigate microwave sea ice emissivities on a global scale. Emissivities in several Arctic region study areas are found to be approximately constant during a nine-month pereiod covering the fall, winter and spring months, in the cases of both first-year and multiyear ice. During the onset of summer, emissivity increases of about 30 percent are observed at 37 GHz in multiyear ice. A multichannel cluster analysis over very large study areas during winter indicates considerable variability in emissivities of consolidated ice clusters at 37 GHz, and only 1/3 as much variability at 18 GHz. If the variability within each cluster is quantified and taken into account by means of multispectral analysis, data on ice thickness and surface characteristics may also be obtained.

Comiso, J. C.

1983-01-01

289

Modeling and observations of the radio frequency emissions from terrestrial gamma-ray flashes  

Science.gov (United States)

We develop a model of the radio frequency (RF) emissions from terrestrial gamma-ray flashes (TGFs). As runaway electrons traverse the high field region of a thundercloud, they ionize the air and generate electrical currents, from both the energetic electrons and the low-energy electrons and ions. These electrical currents, which are distinct from the currents produced by lightning, can be quite large, reaching many tens of kA-km. It is found that the radio frequency emissions that result can be easily measured and provide additional information about the source mechanisms of TGFs, plus key properties such as the number of runaway electrons in the flash. In this presentation, we discuss the RF emissions produced by several TGF models and compare these emissions with TGF observations made by the Duke magnetic field sensors.

Dwyer, J. R.; Cummer, S. A.

2012-12-01

290

Observed effects of soil organic matter content on the microwave emissivity of soils  

Science.gov (United States)

In order to determine the significance of organic matter content on the microwave emissivity of soils when estimating soil moisture, field experiments were conducted in which 1.4 GHz microwave emissivity data were collected over test plots of sandy loam soil with different organic matter levels (1.8, 4.0, and 6.1 percent) for a range of soil moisture values. Analyses of the observed data show only minor variation in microwave emissivity due to a change in organic matter content at a given moisture level for soils with similar texture and structure. Predictions of microwave emissivity made using a dielectric model for aggregated soils exhibit the same trends and type of response as the measured data when appropriate values for the input parameters were utilized.

O'Neill, P. E.; Jackson, T. J.

1990-01-01

291

Observation of soft X-ray emission from the supernova remnant HB9  

International Nuclear Information System (INIS)

The HEAO-1 A-2 experiment has observed soft X-ray emission from the old supernova remnant HB9 which lies close to the previously identified X-ray source, Capella. Most of the X-ray emission appears to originate from the southern half of the remnant where the optical and radio emission are brightest. The measured flux from HB9 is approximately 5 x 10-11 erg cm-2 s-1 between 0.3 and 2 keV for an inferred thermal bremsstrahlung spectrum with T approximately 3.4 x 106K and Nsub(x) approximately 3.5 x 1021H-atom cm-2. The spectral data and the low optical obscuration in the direction of the remnant suggest that HB9 is a good candidate for the detection of [Fe XIV] coronal line emission. (author)

292

Observations of O VI Emission from the Diffuse Interstellar Medium toward l = 113°, b = 71°  

Science.gov (United States)

Emission from O VI (??1032, 1038) in the diffuse interstellar medium was observed in two, long Far Ultraviolet Spectroscopic Explorer (FUSE) observations at l~=113.0d and b~=70.7d (near the quasar HS 1307+4617). The observed intensities are 2580+/-380 (random) +/-360 (systematic) and 1100+/-160 (random) +/-160 (systematic) photons cm-2 s-1 sr-1 in the 1032 and 1038 Å emission lines, respectively. The electron density, thermal pressure, and depth of the emitting gas are calculated from the observed intensities. The velocity of the emitting material is about +10 km s-1 relative to the local standard of rest and less than +30 km s-1 relative to the H I along the line of sight. The similarity suggests that the highly ionized gas is quiescent and not recently shock heated. Emission from the C II 3 s2 S1/2 to 2p2 P3/2 transition at 1037 Å is also observed, and upper limits are placed on the intensities of ultraviolet line emission from C I, C III, N I, N II, Mg II, Si II, S II, S III, S IV, S VI, Fe II, and Fe III.

Shelton, R. L.

2002-04-01

293

Multiwavelength observations of GRB 110731A: GeV emission from onset to afterglow  

CERN Document Server

We report on the multiwavelength observations of the bright, long gamma-ray burst \\GRB, by the \\Fermi and \\Swift observatories, and by the MOA and GROND optical telescopes. The analysis of the prompt phase reveals that \\GRB shares many features with bright Large Area Telescope bursts observed by \\Fermi during the first 3 years on-orbit: a light curve with short time variability across the whole energy range during the prompt phase, delayed onset of the emission above 100 MeV, extra power law component and temporally extended high-energy emission. In addition, this the first GRB for which simultaneous GeV, X-ray, and optical data are available over multiple epochs beginning just after the trigger time and extending for more than 800 s, allowing temporal and spectral analysis in different epochs that favor emission from the forward shock in a wind-type medium. The observed temporally extended GeV emission is most likely part of the high-energy end of the afterglow emission. Both the single-zone pair transparenc...

,

2012-01-01

294

Variations of the spectral index of dust emissivity from Hi-GAL observations of the Galactic plane  

OpenAIRE

Variations in the dust emissivity are critical for gas mass determinations derived from far-infrared observations, but also for separating dust foreground emission from the Cosmic Microwave Background (CMB). Hi-GAL observations allow us for the first time to study the dust emissivity variations in the inner regions of the Galactic plane at resolution below 1 degree. We present maps of the emissivity spectral index derived from the combined Herschel PACS 160 \\mu m, SPIRE 250 ...

Paradis, D.; Veneziani, M.; Noriega-crespo, A.; Paladini, R.; Piacentini, F.; Bernard, J. P.; Bernardis, P.; Calzoletti, L.; Faustini, F.; Martin, P.; Masi, S.; Montier, L.; Natoli, P.; Ristorcelli, I.; Thompson, M. A.

2010-01-01

295

Emission Height and Temperature Distribution of White-Light Emission Observed by Hinode/SOT from the 2012 January 27 X-class Solar Flare  

OpenAIRE

White-light emissions were observed from an X1.7 class solar flare on 27 January 2012, using three continuum bands (red, green, and blue) of the Solar Optical Telescope (SOT) onboard the Hinode satellite. This event occurred near the solar limb, and so differences in locations of the various emissions are consistent with differences in heights above the photosphere of the various emission sources. Under this interpretation, our observations are consistent with the white-ligh...

Watanabe, Kyoko; Shimizu, Toshifumi; Masuda, Satoshi; Ichimoto, Kiyoshi; Ohno, Masanori

2013-01-01

296

Development of a L-band ocean emissivity electromagnetic model using observations from the Aquarius Radiometer  

Science.gov (United States)

The Aquarius/SAC-D ocean salinity measurement mission was launched into polar orbit during the summer of 2011. The prime sensor is an L-band radiometer/scatterometer developed jointly by NASA Goddard Space Flight Center and the Jet Propulsion Laboratory. This paper deals with the development of an ocean emissivity model using AQ radiometer brightness temperature (Tb) observations. This model calculates the ocean surface emissivity as a function of ocean salinity, sea surface temperature, surface wind speed and direction. One unique aspect of this model is that it calculates ocean emissivity over wide ranges of Earth incidence angles (EIAs) from nadir to > 60°and ocean wind speeds from 0 m/s to > 70 m/s. This physical electromagnetic model with empirical coefficients follows the form of Stogryn [1967] that treats the ocean as a mixture of foam and clean rough water. The CFRSL ocean surface emissivity (?ocean) is modeled as a linear sum of foam (?foam) and foam-free seawater (?rough) emissivities, according to ?ocean = FF * ?foam + (1 - FF) * ?rough (1) where FF is the fractional area coverage by foam. The foam emissivity is modeled as ?foam = Q(freq, U10, EIA) (2) where Q( ) is the empirical dependence of foam emissivity on radiometer frequency, the 10-m neutral stability wind speed and EIA according to El-Nimri [2010]. Following Stogryn, the foam-free seawater emissivity (?rough) is modeled ?rough = ?smooth +??excess (3) where ?smooth = (1 - ?) is the smooth surface emissivity, ? is the Fresnel power reflection coefficient, and ??excess is the wind-induced excess emissivity, given by ??excess = G(freq, U10, WDir, EIA) (4) Where G( ) is the empirical signature of foam-free rough ocean, which depends upon the surface wind speed and wind direction. This function is determined empirically from measured AQ radiometer Tb's associated with surface wind vector from collocated NOAA GDAS numerical weather model. Ocean emissivity calculations are compared to AQ ocean surface Tb's normalized by collocated SST. Results are parametrically presented in a series of two dimensional graphs that illustrate the dependence of ocean emissivity on EIA, SST, salinity, U10 and wind direction. References: A. Stogryn, 1967, "The apparent temperature of the sea at microwave frequencies," IEEE Trans. Antennas Propag., vol. AP-15, no. 2, pp. 278-286, Mar. S. El-Nimri et al., 2010, "An improved C-band ocean surface emissivity model at hurricane force wind speeds over a wide range of earth incidence angles," IEEE Geosci. Rem. Sens. Letters, vol. 7, NO. 4, October.

Hejazin, Y.; Jones, W.; El-Nimri, S.

2012-12-01

297

PANCHROMATIC OBSERVATIONS OF THE TEXTBOOK GRB 110205A: CONSTRAINING PHYSICAL MECHANISMS OF PROMPT EMISSION AND AFTERGLOW  

Energy Technology Data Exchange (ETDEWEB)

We present a comprehensive analysis of a bright, long-duration (T{sub 90} {approx} 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb, and BOOTES telescopes when the gamma-ray burst (GRB) was still radiating in the {gamma}-ray band, with optical light curve showing correlation with {gamma}-ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to {gamma}-ray (1 eV to 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission ({approx}1100 s), a bright (R = 14.0) optical emission hump with very steep rise ({alpha} {approx} 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission (R{sub GRB} {approx} 3 Multiplication-Sign 10{sup 13} cm), initial Lorentz factor of the outflow ({Gamma}{sub 0} {approx} 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget.

Zheng, W. [Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, MI 48109 (United States); Shen, R. F. [Department of Astronomy and Astrophysics, University of Toronto, Toronto, Ontario M5S 3H4 (Canada); Sakamoto, T. [Center for Research and Exploration in Space Science and Technology (CRESST), NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Beardmore, A. P. [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); De Pasquale, M. [Mullard Space Science Laboratory, University College London, Holmbury Road, Holmbury St. Mary, Dorking RH5 6NT (United Kingdom); Wu, X. F.; Zhang, B. [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States); Gorosabel, J. [Instituto de Astrofisica de Andalucia (IAA-CSIC), 18008 Granada (Spain); Urata, Y. [Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan (China); Sugita, S. [EcoTopia Science Institute, Nagoya University, Furo-cho, chikusa, Nagoya 464-8603 (Japan); Pozanenko, A. [Space Research Institute (IKI), 84/32 Profsoyuznaya St., Moscow 117997 (Russian Federation); Nissinen, M. [Taurus Hill Observatory, Haerkaemaeentie 88, 79480 Kangaslampi (Finland); Sahu, D. K. [CREST, Indian Institute of Astrophysics, Koramangala, Bangalore 560034 (India); Im, M. [Center for the Exploration of the Origin of the Universe, Department of Physics and Astronomy, FPRD, Seoul National University, Shillim-dong, San 56-1, Kwanak-gu, Seoul (Korea, Republic of); Ukwatta, T. N. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Andreev, M. [Terskol Branch of Institute of Astronomy of RAS, Kabardino-Balkaria Republic 361605 (Russian Federation); Klunko, E., E-mail: zwk@umich.edu, E-mail: rfshen@astro.utoronto.ca, E-mail: zhang@physics.unlv.edu [Institute of Solar-Terrestrial Physics, Lermontov St., 126a, Irkutsk 664033 (Russian Federation); and others

2012-06-01

298

PANCHROMATIC OBSERVATIONS OF THE TEXTBOOK GRB 110205A: CONSTRAINING PHYSICAL MECHANISMS OF PROMPT EMISSION AND AFTERGLOW  

International Nuclear Information System (INIS)

We present a comprehensive analysis of a bright, long-duration (T90 ? 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb, and BOOTES telescopes when the gamma-ray burst (GRB) was still radiating in the ?-ray band, with optical light curve showing correlation with ?-ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to ?-ray (1 eV to 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission (?1100 s), a bright (R = 14.0) optical emission hump with very steep rise (? ? 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission (RGRB ? 3 × 1013 cm), initial Lorentz factor of the outflow (?00 ? 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget.

299

Modelling of X-ray emission supernova remnants observed by the European satellite XMM-Newton  

International Nuclear Information System (INIS)

This thesis deals with the X-ray emission of supernova remnants (SNRs) observed by the European satellite XMM-Newton. In SNRs, the matter heated to millions of degrees shines brightly in X-rays. This emission depends on the hydrodynamical evolution of the SNR, on the chemical composition of the ejected matter and on the ambient medium. Moreover, the blast-wave is considered to be the prime site of the production and the acceleration of cosmic-rays in our Galaxy. XMM-Newton is one of the first to allow the investigation of these different aspects thanks to its spatially-resolved spectroscopy and its very good sensitivity. l first studied Kepler's SNR (SN 1604) whose X-ray emission is dominated by the ejecta. Its observation has allowed to obtain information on the nucleosynthesis products, on their spatial distribution and on the temperature structure in the shocked ejecta. This gives strong constraints on the physics of the explosion and on the progenitor's type. l have shown also that the X-ray emission at the shock is likely to be non-thermal. Then, l studied the SNR G347.3-0.5 whose X-ray emission is entirely due to the synchrotron radiation of relativistic (TeV) electrons accelerated at the shock. From five pointing, l made a full mapping of the X-ray emission characteristics (brightness, absorption and spectral index) at small scale. Combined to radio observations, these results have indicated a clear interaction between the SNR and molecular clouds located at 1 kpc and not at 6 kpc as previously estimated. Lastly, in the framework of a self-similar hydrodynamical model coupled with non-linear particle acceleration, l have obtained the synchrotron emission profile in SNRs, including the adiabatic and radiative losses of the accelerated electrons. (author)

300

Interferometer Observations of Subparsec-scale Infrared Emission in the Nucleus of NGC 4151  

CERN Document Server

We report novel, high-angular resolution interferometric measurements that imply the near-infrared nuclear emission in NGC 4151 is unexpectedly compact. We have observed the nucleus of NGC 4151 at 2.2 microns using the two 10-meter Keck telescopes as an interferometer and find a marginally resolved source ~0.1 pc in diameter. Our measurements rule out models in which a majority of the K band nuclear emission is produced on scales larger than this size. The interpretation of our measurement most consistent with other observations is that the emission mainly originates directly in the central accretion disk. This implies that AGN unification models invoking hot, optically thick dust may not be applicable to NGC 4151.

Swain, M; Akeson, R L; Monnier, J; Millan-Gabet, R; Serabyn, E; Creech-Eakman, M J; Belle, G; Beletic, J; Beichman, C; Boden, A; Booth, A; Colavita, M M; Gathright, J; Hrynevych, M; Koresko, C; Mignant, D L; Ligon, R; Mennesson, B; Neyman, C; Sargent, A; Shao, M; Thompson, R; Unwin, S; Wizinowich, P

2003-01-01

301

Observation of Fluorescence Emissions from Single-Bubble Sonoluminescence in Water doped with Quinine  

CERN Document Server

Sonoluminescence is a phenomenon involving the transduction of sound into light. The detailed mechanism as well as the energy-focusing potentials are not yet fully explored and understood. So far only optical photons are observed, while emissions in the ultra-violet range are only inferred. By doping the fluorescent dye quinine into water with dilute sulphuric acid, the high energy photons can be converted into the optical photons with slower decay constants. These sonoluminescence and fluorescent emissions were observed in coincidence, and the emitted energy of the two modes can be differentiated by their respective timing profiles. Plans for using this technique as a diagnostic tool to quantitatively study ultra-violet and other high energy emissions in sonoluminescence are discussed.

Lu, J Q; Lin, F K; Liu, Y H

2005-01-01

302

Biomass burning emissions estimated with a global fire assimilation system based on observed fire radiative power  

Directory of Open Access Journals (Sweden)

Full Text Available The Global Fire Assimilation System (GFASv1.0 calculates biomass burning emissions by assimilating Fire Radiative Power (FRP observations from the MODIS instruments onboard the Terra and Aqua satellites. It corrects for gaps in the observations, which are mostly due to cloud cover, and filters spurious FRP observations of volcanoes, gas flares and other industrial activity. The combustion rate is subsequently calculated with land cover-specific conversion factors. Emission factors for 40 gas-phase and aerosol trace species have been compiled from a literature survey. The corresponding daily emissions have been calculated on a global 0.5° × 0.5° grid from 2003 to the present. General consistency with the Global Fire Emission Database version 3.1 (GFED3.1 within its accuracy is achieved while maintaining the advantages of an FRP-based approach: GFASv1.0 makes use of the quantitative information on the combustion rate that is contained in the observations, and it detects fires in real time at high spatial and temporal resolution. GFASv1.0 indicates omission errors in GFED3.1 due to undetected small fires. It also exhibits slightly longer fire seasons in South America and North Africa and a slightly shorter fire season in Southeast Asia. GFASv1.0 has already been used for atmospheric reactive gas simulations in an independent study, which found good agreement with atmospheric observations. We have performed simulations of the atmospheric aerosol distribution with and without the assimilation of MODIS aerosol optical depth (AOD. They indicate that the emissions of particulate matter need to be boosted with a factor of 2–4 to reproduce the global distribution of organic matter and black carbon. This discrepancy is also evident in the comparison of previously published top-down and bottom-up estimates. For the time being, a global enhancement of the particulate matter emissions by 3.4 is recommended. Validation with independent AOD and PM10 observations recorded during the Russian fires in summer 2010 show that the global Monitoring Atmospheric Composition and Change (MACC aerosol model with GFASv1.0 aerosol emissions captures the smoke plume evolution well when organic matter and black carbon are enhanced by the recommended factor. In conjunction with the assimilation of MODIS AOD, the use of GFASv1.0 with enhanced emission factors quantitatively improves the forecast of the aerosol load near the surface sufficiently to allow air quality warnings with a lead time of up to four days.

J. W. Kaiser

2011-07-01

303

Quantifying global terrestrial methanol emissions using observations from the TES satellite sensor  

Directory of Open Access Journals (Sweden)

Full Text Available We employ new global space-based measurements of atmospheric methanol from the Tropospheric Emission Spectrometer (TES with the adjoint of the GEOS-Chem chemical transport model to quantify terrestrial emissions of methanol to the atmosphere. Biogenic methanol emissions in the model are based on MEGANv2.1 emission algorithms, using MODIS leaf area and GEOS-5 assimilated meteorological fields. We first carry out a pseudo observation test to validate the overall approach, and find that the TES sampling density is sufficient to accurately quantify regional- to continental-scale methanol emissions using this method. A global inversion of two years of TES data yields an optimized annual global surface flux of 117 Tg yr?1 (including biogenic, pyrogenic, and anthropogenic sources, an increase of 56% from the a priori global flux of 75 Tg yr?1. Global terrestrial methanol emissions are thus approximately 25% those of isoprene (~540 Tg yr?1, and are comparable to the combined emissions of all anthropogenic volatile organic compounds (~100–200 Tg yr?1. Our a posteriori terrestrial methanol source leads to a strong improvement of the simulation relative to an ensemble of airborne observations, and corroborates two other recent top-down estimates (114–120 Tg yr?1 derived using in-situ and space-based measurements. The TES data imply a relatively modest revision of model emissions over most of the tropics, but a significant upward revision in midlatitudes, particularly over Europe and North America. We interpret the inversion results in terms of specific source types using the methanol:CO correlations measured by TES, and find that biogenic emissions are overestimated relative to biomass burning and anthropogenic emissions in central Africa and southeastern China, while they are underestimated in regions such as Brazil and the US. Based on our optimized emissions, methanol accounts for >25% of the photochemical source of CO and HCHO over many parts of the northern extratropics during springtime, and contributes ~6% of the global secondary source of those compounds annually.

K. C. Wells

2013-08-01

304

Resonant behavior observed in electron field emission from acid functionalized multiwall carbon nanotubes  

OpenAIRE

Acid functionalized multiwall carbon nanotube ink was deposited onto carbon fiber fabric via dip coating. Repeatable staircaselike current-field curves were observed in the field emission data. These atypical curves are attributed to resonant tunneling through localized surface states in a quantum well structure, which arises due to the presence of the surface carboxylic functional group.

Lyth, Sm; Silva, Srp

2009-01-01

305

Fermi-LAT Observations of Two Gamma-Ray Emission Components from the Quiescent Sun  

CERN Document Server

We report the detection of high-energy gamma rays from the quiescent Sun with the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope (Fermi) during the first 18 months of the mission. These observations correspond to the recent period of low solar activity when the emission induced by cosmic rays is brightest. For the first time, the high statistical significance of the observations allows clear separation of the two components: the point-like emission from the solar disk due to cosmic ray cascades in the solar atmosphere, and extended emission from the inverse Compton scattering of cosmic ray electrons on solar photons in the heliosphere. The observed integral flux (>100 MeV) from the solar disk is (4.6 +/- 0.2 [statistical error] +1.0/-0.8 [systematic error]) x10^{-7} cm^{-2} s^{-1}, which is ~7 times higher than predicted by the "nominal" model of Seckel et al. (1991). In contrast, the observed integral flux (>100 MeV) of the extended emission from a region of 20 deg radius centered on...

Abdo, A A

2011-01-01

306

The observable effects of a photospheric component on GRB's and XRF's prompt emission spectrum  

OpenAIRE

A thermal radiative component is likely to accompany the first stages of the prompt emission of Gamma-ray bursts (GRB's) and X-ray flashes (XRF's). We analyze the effect of such a component on the observable spectrum, assuming that the observable effects are due to a dissipation process occurring below or near the thermal photosphere. We consider both the internal shock model and a 'slow heating' model as possible dissipation mechanisms. For comparable energy densities in th...

Pe Er, Asaf; Me?sza?ros, Peter; Rees, Martin J.

2005-01-01

307

Observations of the Far-Infrared Emission Lines of OI and CII in Planetary Nebulae  

Science.gov (United States)

The authors have made observations of the far-infrared, fine structure emission lines [O I] 63 ?m, [O I] 145 ?m, and [C II] 158 ?m in the protoplanetary nebulae AFGL 2688 and AFGL 618, and the classical planetary nebulae IC 418 and NGC 7027. The observations were made with the UC Berkeley tandem Fabry-Perot spectrometer aboard the Kuiper Airborne Observatory in October, 1983.

Ellis, H. B., Jr.; Werner, W. M.

1985-07-01

308

Aperture optimization in emission imaging using ideal observers for joint detection and localization  

OpenAIRE

For the familiar 2-class detection problem (signal present/absent), ideal observers have been applied to optimization of pinhole and collimator parameters in planar emission imaging. Given photon noise and background and signal variability, such experiments show how to optimize an aperture to maximize detectability of the signal. Here, we consider a fundamentally different, more realistic task in which the observer is required to both detect and localize a signal. The signal is embedded in a ...

Zhou, Lili; Khurd, Parmeshwar; Kulkarni, Santosh; Rangarajan, Anand; Gindi, Gene

2008-01-01

309

SHARC-II 350 micron Observations of Thermal Emission from Warm Dust in z>=5 Quasars  

OpenAIRE

We present observations of four z>= SDSS quasars at 350 micron with the SHARC-II bolometer camera on the Caltech Submillimeter Observatory. These are among the deepest observations that have been made by SHARC-II at 350 micron, and three quasars are detected at >=3 sigma significance, greatly increasing the sample of 350 micron (corresponds to rest frame wavelengths of =5), detected high-redshift quasars. The derived rest frame far-infrared (FIR) emission in the three detected ...

Wang, Ran; Wagg, Jeff; Carilli, Chris L.; Benford, Dominic J.; Dowell, C. Darren; Bertoldi, Frank; Walter, Fabian; Menten, Karl M.; Omont, Alain; Cox, Pierre; Strauss, Michael A.; Fan, Xiaohui; Jiang, Linhua

2007-01-01

310

Relationship between long-term phase advances in high-latitude VLF wave propagation and solar energetic particle fluxes  

Science.gov (United States)

Anomalous advances of OMEGA VLF navigation system (10.2-kHz) signals during three extended periods (totaling 60 days) of solar cosmic ray event activity during 1982 are examined and compared with energetic proton, alpha particle, and electron precipitation into the polar cap ionosphere. Time profiles of the OMEGA 10.2-kHz Hawaii-to-Norway path phase advance are found to be almost congruent with the time profiles of the logarithms of the energetic proton fluxes precipitating into the polar cap as determined from instruments aboard the polar orbiting NOAA-6 satellite and the GOES-2 geostationary satellite. Although both energetic alpha particles and electrons contribute to the anomalous phase advance experienced by the 10.2-kHz Hawaii-to-Norway OMEGA signal, a simple, empirical algorithm reasonably relates the observed phase advance to the observed differential fluxes of 6-MeV solar cosmic ray protons.

Sauer, Herbert H.; Spjeldvik, Walther N.; Steele, F. Kenneth

1987-06-01

311

FUSE Observations of the Cygnus Loop OVI Emission from a Nonradiative Shock  

CERN Document Server

We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of a Balmer filament in the northeast region of the Cygnus Loop supernova remnant. The data consist of one spectrum obtained through the 30"x30" (LWRS) aperture and three spectra at adjacent positions obtained through the 4"x20" (MDRS) aperture. The nonradiative shocks in the region giving rise to these faint optical filaments produce strong OVI 1032,1038 emission, which is detected in all the spectra. The OVI emission is resolved by FUSE into a strong component centered at 0 km/s, and weaker components centered at +/- 140 km/s. The MDRS spectra allow us to study the variation of OVI emission in the post-shock structure. We find that the zero velocity emission is associated directly with the Balmer filament shock, while the high velocity emission comes from a more uniformly distributed component elsewhere along the line of sight. We also find that the shocks producing the emission at +/- 140 km/s have velocities between 180 km/s and 220 km/...

Sankrit, R; Sankrit, Ravi; Blair, William P.

2001-01-01

312

Observational constraints on the external shock prior emission hypothesis of GRBs  

CERN Document Server

An intriguing hypothesis, i.e. there exists a decaying X-ray emission component before the GRB trigger, has been suggested to interpret the shallow decay phase of the X-ray afterglow detected in many {\\em Swift} GRBs. If this "prior emission" is from an external shock, one would expect a corresponding optical emission component during the GRB prompt emission phase. In this paper we apply the available prompt optical emission data (both detections and upper limits) to constrain such a scenario. We fit the shallow and normal decay segments of the XRT light curves with a $T_0$-shifted single power law, and extrapolate the X-ray flux back to the time of the early optical observations. We then use the synchrotron spectrum predicted by the standard external shock model to extrapolate from the X-ray flux to the optical band, and obtain the possible range of the predicted optical flux. Finally, we compare the predictions with the observations. In the cases where later optical data are available, we also compare the s...

Birnbaum, Tesla; Zhang, Bin-Bin; Liang, En-Wei

2011-01-01

313

Diffuse X-ray emission from the Carina Nebula observed with Suzaku  

International Nuclear Information System (INIS)

A number of giant HII regions are associated with soft diffuse X-ray emission. Among these, the Carina Nebula possesses the brightest soft diffuse emission. The required plasma temperature and thermal energy can be produced by collisions or termination of fast winds from main-sequence or embedded young O stars, but the extended emission is often observed from regions apart from massive stellar clusters. The origin of the X-ray emission is unknown. The XIS CCD camera onboard Suzaku has the best spectral resolution for extended soft sources so far, and is therefore capable of measuring key emission lines in the soft band. Suzaku observed the core and the eastern side of the Carina Nebula (Car-D1) in 2005 Aug. and 2006 June, respectively. Spectra of the south part of the core and Car-D1 similarly showed strong L-shell lines of iron ions and K-shell lines of silicon ions, while in the north of the core these lines were much weaker. Fitting the spectra with an absorbed thin-thermal plasma model showed kT - 0.2, 0.6 keV and NH - 1 - 2x1021 cm-2 with a factor of 2-3 abundance variation in oxygen, magnesium, silicon and iron. The plasma might originate from an old supernova, or a super shell of multiple supernovae. (author)

314

Space-based observations of fire NOx emission coefficients: a global biome-scale comparison  

Directory of Open Access Journals (Sweden)

Full Text Available Biomass burning represents both a significant and highly variable source of NOx to the atmosphere. This variability stems from both the episodic nature of fires, and from fire conditions such as the modified combustion efficiency of the fire, the nitrogen content of the fuel and possibly other factors that have not been identified or evaluated by comparison with observations. Satellite instruments offer an opportunity to observe emissions from wildfires, providing a large suite of measurements which allow us to study mean behavior and variability on the regional scale in a statistically rigorous manner. Here we use space-based measurements of fire radiative power from the Moderate Resolution Imaging Spectroradiometer in combination with NO2 tropospheric column densities from the Ozone Monitoring Instrument to measure mean emission coefficients (ECs in g NO MJ?1 from fires for global biomes, and across a wide range of smaller-scale ecoregions, defined as spatially-distinct clusters of fires with similar fuel type. Mean ECs for all biomes fall between 0.250–0.362 g NO MJ?1, a range that is smaller than found in previous studies of biome-scale emission factors. The majority of ecoregion ECs fall within or near this range, implying that under most conditions, mean fire emissions per unit energy are similar between different regions regardless of fuel type or spatial variability. In contrast to these similarities, we find that about 24% of individual ecoregion ECs deviate significantly (p x emissions.

A. K. Mebust

2013-08-01

315

Vizualization of Daytime Temperature Observations of N2 Lyman-Birge-Hopfield Emission as Observed by the HIRAAS Experiment  

Science.gov (United States)

The High Resolution Airglow and Aurora Spectroscopy (HIRAAS) experiment was successfully launched on the USAF Advanced Research and Global Observation Satellite (ARGOS) and has monitored the thermospheric and ionospheric airglow since May 1999 using three ultraviolet spectrographs. Over 240 Gigabytes of science measurements from the HIRAAS experiment have been accumulated to this date. The High-resolution Ionospheric and Thermospheric Spectrograph (HITS) is a far- and extreme-ultraviolet (FUV/EUV) Rowland circle spectrograph sensing the 500-1500 Å passband with 0.5-Å spectral resolution. The Low Resolution Airglow and Auroral Spectrograph (LORAAS) instrument measures the EUV and FUV over the 800-1700 Å passband with 18-Å spectral resolution. Thermospheric temperature can be inferred from the rotational temperature of N2 in far-ultraviolet Lyman-Birge-Hopfied (LBH) emission when the band shapes are measured with sufficient spectral resolution. Dayside observations of molecular nitrogen LBH bands have been acquired by both HITS and LORAAS. Additionally, the HITS spectrograph periodically operates in stare mode at 200km and 120km tangent altitudes in the 1440-1560 Å passband. Techniques have been developed for retrieving termperature from the LBH (1-1) band in this passband. Using data mining and visualization techniques we compare the temperature distribution derived from the LBH emission observed by HITS and LORAAS over the time coverage of June 2000 and global coverage of the low and mid latitudes. The results will be discussed with respect to excitation mechanisms, geolocation, and geomagnetic activity effects.

Fortna, C. B.; Budzien, S. A.; Dymond, K. F.; Thonnard, S. E.; Nicholas, A. C.; McCoy, R. P.; Wolfram, K. D.

2001-05-01

316

DEMETER observations of bursty MF emissions and their relation to ground-level auroral MF burst  

Science.gov (United States)

A survey of medium frequency (MF) electric field data from selected orbits of the Detection of Electro-Magnetic Emissions Transmitted from Earthquakes (DEMETER) spacecraft reveals 68 examples of a new type of bursty MF emissions occurring at high latitudes associated with auroral phenomena. These resemble auroral MF burst, a natural radio emission observed at ground level near local substorm onsets. Similar to MF burst, the bursty MF waves observed by DEMETER have broadband, impulsive frequency structure covering 1.5-3.0 MHz, amplitudes of 50-100 ?V/m, an overall occurrence rate of ˜0.76% with higher occurrence during active times, and strong correlation with auroral hiss. The magnetic local time distribution of the MF waves observed by DEMETER shows peak occurrence rate near 18 MLT, somewhat earlier than the equivalent peak in the occurrence rate of ground level MF burst, though propagation effects and differences in the latitudes sampled by the two techniques may explain this discrepancy. Analysis of solar wind and SuperMAG data suggests that while the bursty MF waves observed by DEMETER are associated with enhanced auroral activity, their coincidence with substorm onset may not be as exact as that of ground level MF burst. One conjunction occurs in which MF burst is observed at Churchill, Manitoba, within 8 min of MF emissions detected by DEMETER on field lines approximately 1000 km southeast of Churchill. These observations may plausibly be associated with the same auroral event detected by ground level magnetometers at several Canadian observatories. Although it is uncertain, the balance of the evidence suggests that the bursty MF waves observed with DEMETER are the same phenomenon as the ground level MF burst. Hence, theories of MF burst generation in the ionosphere, such as beam-generated Langmuir waves excited over a range of altitudes or strong Langmuir turbulence generating a range of frequencies within a narrow altitude range, need to be revisited to see whether they predict in situ detection of MF burst.

Broughton, M. C.; LaBelle, J.; Parrot, M.

2014-12-01

317

AMI observations of Lynds dark nebulae: further evidence for anomalous cm-wave emission  

Science.gov (United States)

Observations at 14.2 to 17.9GHz made with the Arcminute Microkelvin Imager (AMI) Small Array towards 14 Lynds dark nebulae with a resolution of ~2arcmin are reported. These sources are selected from the Submillimetre Common-User Bolometre Array (SCUBA) observations of Visser, Richer & Chandler as small angular diameter clouds well matched to the synthesized beam of the AMI Small Array. Comparison of the AMI observations with radio observations at lower frequencies with matched uv-plane coverage is made, in order to search for any anomalous excess emission which can be attributed to spinning dust. Possible emission from spinning dust is identified as a source within a 2-arcmin radius of the SCUBA position of the Lynds dark nebula, exhibiting an excess with respect to lower frequency radio emission. We find five sources which show a possible spinning dust component in their spectra. These sources have rising spectral indices in the frequency range 14.2-17.9GHz with ?17.914.2 = -0.7 +/- 0.7 to -2.9 +/- 0.4, where S ~ ?-?. Of these five one has already been reported, L1111, we report one new definite detection, L675 (16?), and three new probable detections (L944, L1103 and L1246). The relative certainty of these detections is assessed on the basis of three criteria: the extent of the emission, the coincidence of the emission with the SCUBA position and the likelihood of alternative explanations for the excess. Extended microwave emission makes the likelihood of the anomalous emission arising as a consequence of a radio counterpart to a protostar or a protoplanetary disc unlikely. We use a 2-arcmin radius in order to be consistent with the IRAS identifications of dark nebulae, and our third criterion is used in the case of L1103 where a high flux density at 850?m relative to the far-infrared data suggests a more complicated emission spectrum. We kindly request that any reference to this paper cites `AMI Consortium: Scaife et al. 2009'. Issuing author - e-mail: as595@mrao.cam.ac.uk

AMI Consortium; Scaife, Anna M. M.; Hurley-Walker, Natasha; Green, David A.; Davies, Matthew L.; Franzen, Thomas M. O.; Grainge, Keith J. B.; Hobson, Michael P.; Lasenby, Anthony N.; Pooley, Guy G.; Rodríguez-Gonzálvez, Carmen; Saunders, Richard D. E.; Scott, Paul F.; Shimwell, Timothy W.; Titterington, David J.; Waldram, Elizabeth M.; Zwart, Jonathan T. L.

2009-12-01

318

MAGIC observes very high energy gamma ray emission from PKS 1424 +240  

Science.gov (United States)

The MAGIC collaboration reports the observation of very high energy gamma ray emission above 100GeV from PKS 1424 +240, categorized as an Intermediate BL Lac object. The distance of this source is unknown. The discoveries of high-energy and very high energy gamma ray emissions from this source were reported earlier this year by Fermi (Abdo et al., arXiv:0902.1340; Abdo et al., arXiv:0902.1559) and 9 days ago by VERITAS (ATEL #2084), respectively.

Teshima, Masahiro

2009-06-01

319

Impact of Asian emissions on observations at Trinidad Head, California, during ITCT 2K2  

Science.gov (United States)

Field measurements of a wide suite of trace gases and aerosols were carried out during April and May 2002, along with extensive chemical transport modeling, as part of the NOAA Intercontinental Transport and Chemical Transformation study. Here, we use a combination of in-situ ground-based measurements from Trinidad Head, CA, chemical transport modeling, and backward trajectory analysis to examine the impact of long-range transport from Asia on the composition of air masses arriving at the California coast at the surface. The impact of Asian emissions is explored in terms of both episodic enhancements and contribution to background concentrations. We find that variability in CO concentrations at the ground site was largely driven by North American emissions, and that individual Asian plumes did not cause any observable pollution enhancement episodes at Trinidad Head. Despite this, model simulations suggest that Asian emissions were responsible for 33% of the CO observed at Trinidad Head, providing a larger mean contribution than direct emissions from any other region of the globe. Surface ozone levels were found to depend primarily on local atmospheric mixing, with surface deposition leading to low concentrations under stagnant conditions. Model simulations suggested that on average 4 ± 1 ppb of ozone (10% of observed) at Trinidad Head was transported from Asia.

Goldstein, Allen H.; Millet, Dylan B.; McKay, Megan; Jaeglé, Lyatt; Horowitz, Larry; Cooper, Owen; Hudman, Rynda; Jacob, Daniel J.; Oltmans, Sam; Clarke, Andrew

2004-12-01

320

P-MaNGA Galaxies: Emission Lines Properties - Gas Ionisation and Chemical Abundances from Prototype Observations  

CERN Document Server

MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a SDSS-IV survey that will obtain spatially resolved spectroscopy from 3600 \\AA\\ to 10300 \\AA\\ for a representative sample of over 10000 nearby galaxies. In this paper we present the analysis of nebular emission line properties using observations of 14 galaxies obtained with P-MaNGA, a prototype of the MaNGA instrument. By using spatially resolved diagnostic diagrams we find extended star formation in galaxies that are centrally dominated by Seyfert/LINER-like emission, illustrating that galaxy characterisations based on single fibre spectra are necessarily incomplete. We observe extended (up to $\\rm 1 R_{e}$) LINER-like emission in the central regions of three galaxies. We make use of the $\\rm EW(H \\alpha)$ to argue that the observed emission is consistent with ionisation from hot evolved stars. Using stellar population indices we conclude that galactic regions which are ionised by a Seyfert/LINER-like radiation field are also devoid of recent st...

Belfiore, F; Bundy, K; Thomas, D; Maraston, C; Wilkinson, D; Sánchez, S F; Bershady, M; Blanc, G A; Bothwell, M; Cales, S L; Coccato, L; Drory, N; Emsellem, E; Fu, H; Gelfand, J; Law, D; Masters, K; Parejko, J; Tremonti, C; Wake, D; Weijmans, A; Yan, R; Xiao, T; Zhang, K; Zheng, T; Bizyaev, D; Kinemuchi, K; Oravetz, D; Simmons, A

2014-01-01

321

Efficiency and Sensitivity Analysis of Observation Networks for Atmospheric Inverse Modelling with Emissions  

CERN Document Server

The controllability of advection-diffusion systems, subject to uncertain initial values and emission rates, is estimated, given sparse and error affected observations of prognostic state variables. In predictive geophysical model systems, like atmospheric chemistry simulations, different parameter families influence the temporal evolution of the system.This renders initial-value-only optimisation by traditional data assimilation methods as insufficient. In this paper, a quantitative assessment method on validation of measurement configurations to optimize initial values and emission rates, and how to balance them, is introduced. In this theoretical approach, Kalman filter and smoother and their ensemble based versions are combined with a singular value decomposition, to evaluate the potential improvement associated with specific observational network configurations. Further, with the same singular vector analysis for the efficiency of observations, their sensitivity to model control can be identified by deter...

Wu, Xueran; Jacob, Birgit

2015-01-01

322

Observation of implosion dynamics by line emissions from direct-drive fusion capsules  

International Nuclear Information System (INIS)

Line emissions from Ar-doped fusion capsules were observed to investigate influence of drive uniformity on implosion behavior. To manipulate the drive non-uniformity, in particular of the mode number 6, the laser focus position was set in two representative cases. A fusion capsule was directly irradiated with 12 beams of partially-coherent green light. Imploded core plasmas were diagnosed by observing spatial distribution and time history of the Ar line emissions. Clear differences were obtained between the two irradiation cases despite the calculated irradiation uniformities for the two cases being identical. The experimental result was compared with two-dimensional fluid simulations post-processed with an X-ray spectrum analysis code. Drive uniformity and associated perturbation growth at the pusher-fuel boundary are discussed as a plausible reason for the observed differences. (orig.)

323

Antenna vector impedance measurement by the EXOS-D (AKEBONO) very low frequency plasma waves instrument (VLF)  

International Nuclear Information System (INIS)

Antenna impedance has been measured on board the EXOS-D (Akebono) satellite by imposing a constant current at VLF. The impedance is obtained in a complex form, i.e., as a resistance and a capacitance. This is essential to obtain the absolute electric field intensities of the VLF waves. A critical frequency below which the resistive part becomes important is also obtained

324

Conjugate observations of quasi-periodic emissions by Cluster and DEMETER spacecraft  

Science.gov (United States)

AbstractQuasi-periodic (QP) emissions are electromagnetic emissions at frequencies of about 0.5-4 kHz that are characterized by a periodic time modulation of the wave intensity. Typical periods of this modulation are on the order of minutes. We present a case study of a large-scale long-lasting QP event observed simultaneously on board the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) and the Cluster spacecraft. The measurements by the Wide-Band Data instrument on board the Cluster spacecraft enabled us to obtain high-resolution frequency-time spectrograms of the event close to the equatorial region over a large range of radial distances, while the measurements by the STAFF-SA instrument allowed us to perform a detailed wave analysis. Conjugate observations by the DEMETER spacecraft have been used to estimate the spatial and temporal extent of the emissions. The analyzed QP event lasted as long as 5 h and it spanned over the L-shells from about 1.5 to 5.5. Simultaneous observations of the same event by DEMETER and Cluster show that the same QP modulation of the wave intensity is observed at the same time at very different locations in the inner magnetosphere. ULF magnetic field fluctuations with a period roughly comparable to, but somewhat larger than the period of the QP modulation were detected by the fluxgate magnetometers instrument on board the Cluster spacecraft near the equatorial region, suggesting these are likely to be related to the QP generation. Results of a detailed wave analysis show that the QP emissions detected by Cluster propagate unducted, with oblique wave normal angles at higher geomagnetic latitudes.

N?Mec, F.; SantolíK, O.; Parrot, M.; Pickett, J. S.; Hayosh, M.; Cornilleau-Wehrlin, N.

2013-01-01

325

WRF Simulations of Los Angeles Region Carbon-dioxide Emissions: Comparisons with Column Observations  

Science.gov (United States)

California’s South coast air basin, a densely populated urban area (15 million people) with huge CO2 emissions (~200 Tg/year) distributed over a large area (~10(6) km2) that is bounded by mountains on three sides, is a good candidate for flux verification. Recently ground based solar tracking Fourier transform spectrometer measurements of columnar CO2, CO, CH4 and N2O at high temporal resolution (minutes) have been made from the Jet Propulsion Laboratory (Wunch et al., GRL 2009). Observations show large (up to 8 ppm) and variable increases in column CO2 that are attributed to anthropogenic emissions that are modulated by atmospheric dynamics. We perform nested grid simulations using the Weather Research Forecast model with constructed and reported spatio-temporally gridded CO2 emissions for this region during March 23 to 28, 2008. We predict largest CO2 increases of ~40 ppm at the surface, and simulate large rising plumes during midday. Our model reproduces the observed timing of the late afternoon drop in the column CO2 that results from when the boundary layer is higher than the mountains resulting in venting. Simulations capture the observed day-to-day variability in CO2 accumulation, particularly the small increase on March 27 due to flows from the north. We use combine our simulations and observations to assess available emissions inventories (CARB, EDGAR and VULCAN) for this region. We plan to gather some single-time snapshots of CO2 gradients from GOSAT and check for consistency and report satellite retrieval algorithms that are less sensitive to aerosols, water and surface reflectance. Our goal is to help develop integrated remote sensing and modeling methods top down verification of bottoms up greenhouse gas emissions.

Dubey, M. K.; Costigan, K. R.; Chylek, P.; Wunch, D.; Wennberg, P. O.

2009-12-01

326

Observations of volatile organic compounds during ARCTAS – Part 1: Biomass burning emissions and plume enhancements  

Directory of Open Access Journals (Sweden)

Full Text Available Mixing ratios of a large number of volatile organic compounds (VOCs were observed by the Trace Organic Gas Analyzer (TOGA on board the NASA DC-8 as part of the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS field campaign. Many of these VOCs were observed concurrently by one or both of two other VOC measurement techniques on board the DC-8: proton-transfer-reaction mass spectrometry (PTR-MS and whole air canister sampling (WAS. A comparison of these measurements to the data from TOGA indicates good agreement for the majority of co-measured VOCs. The ARCTAS study, which included both spring and summer deployments, provided opportunities to sample a large number of biomass burning (BB plumes with origins in Asia, California and Central Canada, ranging from very recent emissions to plumes aged one week or more. For this analysis, identified BB plumes were grouped by flight, source region and, in some cases, time of day, generating 40 individual plume groups, each consisting of one or more BB plume interceptions. Normalized excess mixing ratios (EMRs to CO were determined for each of the 40 plume groups for up to 19 different VOCs or VOC groups, many of which show significant variability, even within relatively fresh plumes. This variability demonstrates the importance of assessing BB plumes both regionally and temporally, as emissions can vary from region to region, and even within a fire over time. Comparisons with literature confirm that variability of EMRs to CO over an order of magnitude for many VOCs is consistent with previous observations. However, this variability is often diluted in the literature when individual observations are averaged to generate an overall regional EMR from a particular study. Previous studies give the impression that emission ratios are generally consistent within a given region, and this is not necessarily the case, as our results show. For some VOCs, earlier assumptions may lead to significant under-prediction of emissions in fire emissions inventories. Notably, though variable between plumes, observed EMRs of individual light alkanes are highly correlated within BB emissions. Using the NCAR master mechanism chemical box model initialized with concentrations based on two observed scenarios, i.e., fresh Canadian BB and fresh Californian BB, both plumes are expected to experience primarily decreases in oxygenated VOCs during the first 2.5 days, such that any production in the plumes of these compounds is less than the chemical loss. Comparisons of the modeled EMRs to the observed EMRs from BB plumes estimated to be three days in age or less indicate overall good agreement and, for most compounds, no significant difference between BB plumes in these two regions.

A. Hills

2011-05-01

327

Circumstellar Debris Disks : Observational Studies of Cold Dust and Gas Emission in Planetary Nurseries  

Science.gov (United States)

Planetary systems form in disks of gas and dust surrounding newborn stars. The young circumstellar environment is characterized by frequent collisions between rocky bodies, leading to a continuous production of small dust grains. Such collisional processing persists in leftover debris disks or belts akin to the Solar System's asteroid and Kuiper belts, during the star's entire main-sequence lifetime. This thesis presents observations of thermal emission from cold dust in extended debris disks, in addition to spatially resolved observations of dust scattered light and gas emission in nearby debris disk systems. A total of 30 debris disk candidates identified from infrared excess were observed at submillimeter (submm) wavelengths with the Atacama Pathfinder EXperiment (APEX) telescope in search for dust at radial distances corresponding to the Kuiper belt or beyond. Two observing campaigns with the PolCor instrument at the Nordic Optical Telescope (NOT), performing optical polarimetric coronagraphy to resolve scattered light from nearby disks were also carried out. The edge-on debris disk surrounding the star ? Pictoris was explored using integral-field spectroscopy with the Very Large Telescope (VLT) in an attempt to map the spatial distribution of previously detected gas. The APEX observations detected 14 exo-Kuiper belts, out of which 7 were new discoveries in the submm region. Modeling of the spectral energy distribution from available photometry and detected submm fluxes allowed us to study the dependence of the fractional dust luminosity and characteristic radial dust distance on stellar spectral type and age. The results indicate a decrease in fractional dust luminosity as t-?, where t is the age of the system and ? = 0.8-2.0. From the VLT data we retrieved the first complete image of Ca II and Fe I emission in the disk of ? Pictoris. Subsequent modeling demonstrated that the anomalous vertical structure of the observed Ca II emission can be explained by an optically thick disk midplane.

Nilsson, Ricky

2012-05-01

328

Study of the NWC electrons belt observed on DEMETER Satellite  

CERN Document Server

We analyzed the data from 2007 to 2008, which is observed by IDP onboard DEMETER satellite, during ten months of NWC working and seven months of NWC shutdown. The characteristic of the space instantaneous electron belts, which come from the influence of the VLF transmitted by NWC, is studied comprehensively. The main distribution region of the NWC electron belts and the flux change are given. We also studied the distribution characteristic of the average energy spectrum in different magnetic shell at the height of DEMETER orbit and the difference of the average energy spectrum of the electrons in the drift loss-cone between day and night. As a result, the powerful power of NWC transmitter and the 19.8 kHz narrow bandwidth VLF emission not only created a momentary electrons enhancement region, which strides 180 degree in them longitude direction and from 1.6 to 1.9 in L value, with the rise of the electrons flux reaching to 3 orders of magnitude mostly, but also induced the enhancement or loss of electrons in ...

Li, Xinqiao; Wang, Ping; Wang, Huanyu; Lu, Hong; Zhang, Xuemin; Huang, Jianping; Shi, Feng; Yu, Xiaoxia; Xu, Yanbing; Meng, Xiangcheng; Wang, Hui; Zhao, Xiaoyun; Parrot, M

2010-01-01

329

Correcting atmospheric effects in thermal ground observations for hyperspectral emissivity estimation  

Science.gov (United States)

Knowledge of Land surface temperature is of crucial importance in energy balance studies and environmental modeling. Accurate retrieval of land surface temperature (LST) demands detailed knowledge of the land surface emissivity. Measured radiation by remote sensing sensors to land surface temperature can only be performed using a-priori knowledge of the emissivity. Uncertainties in the retrieval of this emissivity can cause huge errors in LST estimations. The retrieval of emissivity (and LST) is per definition an underdetermined inversion, as only one observation is made while two variables are to be estimated. Several researches have therefore been performed on measuring emissivity, such as the normalized emissivity method, the temperature-emissivity separation (TES) using the minimum and maximum difference of emissivity and the use of vegetation indices. In each of these approaches atmospherically corrected radiance measurements by remote sensing sensors are correlated to ground measurements. Usually these ground measurements are performed with the ground equivalent of the remote sensing sensors; the CIMEL 312-2 has the same spectral bands as ASTER. This way parameterizations acquired this way are only usable for specific sensors and need to be redone for newer sensors. Recently hyperspectral thermal radiometers, such as the MIDAC, have been developed that can solve this problem. By using hyperspectral observations of emissivity, together with sensor simulators, ground measurements of different satellite sensor can be simulated. This facilitates the production of validation data for the different TES algorithms. However before such measurements can be performed extra steps of processing need to be performed. Atmospheric correction becomes more important in hyperspectral observations than for broadband observations, as energy levels measured per band is lower. As such the atmosphere has a relative larger contribution if bandwidths become smaller. The goal of this research was to enhance current methods for estimation of hyperspectral emissivity from field measurements. In particular the research focused on the atmospheric correction of the hyperspectral data, and the estimation of emissivity and temperature. For this, radiation measurements over different vegetation types were performed using the MIDAC thermal hyperspectral radiometer. The measurements of thermal radiation were performed in 2012 during ESA`s REFLEX fieldcampaign and each consisted of rapid acquisition of 4 targets: a hot and cold black-body (with predefined temperature), a gold plate and the vegetation-component of interest (vegetation/soil). The high spectral resolution of the measurement (at 0.5 cm-1 resolution) enables the characterization of individual gaseous absorption features and consequently allows for the atmospheric correction. Atmospheric correction of the 4 measurements was performed by creating a simple atmospheric correction model on basis of MODTRAN simulations. These MODTRAN outputs were converted to band resolutions using the spectral sensitivity of the MIDAC instrument. This approach enabled the estimation of different gas concentrations, such as C02 and H20, and at the same time atmospherically correct the raw measurements. Afterwards the data of the vegetation-component and gold plate (Infragold standard) were calibrated against the measurements of the hot/cold black bodies. Using the measurement of the gold plate the measured radiation from the vegetation-component was corrected for incoming radiation. Afterwards the temperature and emissivity of the vegetation-component was determined by fitting the atmospherically corrected data against the Planck curve. The success of the methodology was tested against measurements performed simultaneously with the MIDAC acquisitions. The atmospheric correction approach was tested by comparing the retrieved gaseous concentrations with LICOR 7500 measurements of these constituents. The TES estimations were evaluated by comparing the retrieved temperature with measurements of the vegetation-compon

Timmermans, Joris; Buitrago, Maria

2014-05-01

330

Gamma-ray emission from the Moon as observed by Fermi  

International Nuclear Information System (INIS)

The Large Area Telescope (LAT) on board the Fermi satellite is exploring the gamma-ray sky in the energy range from 20 MeV to > 300 GeV. Since the start of the science phase of th emission the LAT has detected high-energy gamma rays from the Moon. This emission is produced by interactions of cosmic-rays nuclei with the lunar surface and depends on the level of solar activity. Moon was detected by EGRET on CGRO with low statistics, but Fermi is the only gamma-ray mission capable of detecting the Moon over the full 24th solar cycle. Here it is reported the detection of gamma-ray emission from the Moon during the first 18 months of observation showing the status of the analysis and interpretation.

331

Observation of soft X-ray emission from the supernova remnant HB9  

Science.gov (United States)

The number of known X-ray emitting supernova remnants in our galaxy has significantly grown as a result of the soft X-ray survey by the HEAO-1 spacecraft. The HEAO-1 A-2 experiment has observed soft X-ray emission from the old supernova remnant HB9 which lies close to the previously identified X-ray source, Capella. Spectral data and the low optical obscuration in the direction of the remnant suggest that HB9 is a good candidate for detecting Fe XIV coronal forbidden-line emission. Mapping of the coronal line emission in association with the imaging X-ray data expected from HEAO-2 would allow the temperature profile of the emitting shell to be determined in a manner similar to that used by Tuohy, Nousek, and Garmire (1979) for the Cygnus Loop, which is in a similar evolutionary phase to HB9.

Tuohy, I. R.; Clark, D. H.; Garmire, G. P.

1979-01-01

332

Lightning as an embryonic source of VLF hiss  

International Nuclear Information System (INIS)

Data from the DE 1 satellite show that lightning-generated whistlers often trigger hiss emissions that endure for up to 10- to 20-s periods. The data consist of the measured electric and magnetic fields in the frequency range of 1.5 kHz to 6.0 kHz, during 22 DE 1 passes during the period December 28, 1986 to January 18, 1987. The whistler-triggered hiss emissions were observed on 16 of the passes, and they generally exhibited the following characteristics: (1) emission spectra were wide band (1-2 kHz) and rather structureless, (2) well-defined and sustained fading patterns were observed at twice the spin frequency over 10- to 20-s periods, (3) the spin fading characteristics of the triggered hiss bursts were similar to those reported for background plasmaspheric hiss, indicating a large wave normal angle with respect to the ambient magnetic field. The results indicate that lightning-generated whistlers may be an important embryonic source for magnetospheric hiss and that whistlers and emissions triggered by them often constitute the dominant wave activity in the ? 1.5- to 6-kHz range on L shells of 3.5 to 5 in the afternoon sector during geomagnetically quiet periods. Through cyclotron and Landau resonant scattering, it is likely that these lightning-generated waves play a dominant role in the loss of ?0.5- to 50-keV electrons trapped on these field lines in the afternoon sector. Through anisotropic proton instability, these waves can also interact with ring curreaves can also interact with ring current protons in the range of several tens of keV leading to a loss mechanism for ring current protons

333

Constraints on ship NOx emissions in Europe using OMI NO2 observations  

Science.gov (United States)

About 90% of world trade is transported by oceangoing ships, and seaborne trade has been shown to have increased by about 5% per year in the past decade. Global ship traffic is currently not regulated under international treaties (e.g. Kyoto protocol) and ships are still allowed to burn low-grade bunker fuel. As a result, ships emit large quantities of nitrogen oxides (NOx = NO + NO2), important precursors for ozone (O3) and particulate matter formation. Previous studies indicated that the global NOx emissions from shipping are in the range 3.0-10.4 Tg N per year (15-30% of total global NOx emissions). Because most ships sail within 400 km of the coast, it is important to understand the contribution of ship emissions to atmospheric composition in the densely populated coastal regions. Chemistry Transport Models (CTMs), in combination with emission inventories, are used to simulate atmospheric concentrations of air pollutants to assess the impact of ship emissions. However, these bottom-up inventories, based on extrapolation of a few engine measurements and strong assumptions, suffer from large uncertainties. In this study we provide top-down constraints on ship NOx emissions in Europe using satellite observations of NO2 columns. We use the nested version of the GEOS-Chem model (0.5°-0.667°) to simulate tropospheric NO2 columns over Europe for the years 2005-2006, using our plume-in-grid treatment of ship NOx emissions. We improve the NO2 retrievals from the Ozone Monitoring Instrument (OMI v2.0) by replacing the coarse a priori (TM4) vertical NO2 profiles (2°-3°) with the high-resolution GEOS-Chem profiles. This ensures consistency between the retrievals and model simulations. GEOS-Chem simulations of tropospheric NO2 columns show remarkable quantitative agreement with the observed OMI columns over Europe (R2=0.89, RMS difference < 0.2-1015 molec. cm-2), providing confidence in the ability of the model to simulate NO2 pollution over the European mainland. We proceed and show quantitative comparisons of simulated and observed columns over two distinct ship tracks in Europe (west of France and Mediterranean Sea). Our comparisons suggest that both the AMVER-ICOADS and EMEP inventories provide too low NOx emissions for these ship tracks, with important implications for exceedances of air quality standards in coastal regions.

Vinken, G. C. M.; Boersma, K. F.

2012-04-01

334

New Radio Observations of Anomalous Microwave Emission in the H II Region RCW175  

Science.gov (United States)

We have observed the H II region RCW175 with the 64 m Parkes telescope at 8.4 GHz and 13.5 GHz in total intensity, and at 21.5 GHz in both total intensity and polarization. High angular resolution ranging from 1 to 2.4 arcmin, high sensitivity, and polarization capability enable us to perform a detailed study of the different constituents of the H II region. For the first time, we resolve three distinct regions at microwave frequencies, two of which are part of the same annular diffuse structure. Our observations enable us to confirm the presence of anomalous microwave emission (AME) from RCW175. Fitting the integrated flux density across the entire region with the currently available spinning dust models, using physically motivated assumptions, indicates the presence of at least two spinning dust components: a warm component (T gas = 5800 K) with a relatively large hydrogen number density n H = 26.3/cm3 and a cold component (T gas = 100 K) with a hydrogen number density of n H = 150/cm3. The present study is an example highlighting the potential of using high angular-resolution microwave data to break model parameter degeneracies. Thanks to the spectral coverage and angular resolution of the Parkes observations, we have been able to derive one of the first AME/excess maps, at 13.5 GHz, showing clear evidence that the bulk of the anomalous emission arises in particular from one of the source components, with some additional contribution from the diffuse structure. A cross-correlation analysis with thermal dust emission has shown a high degree of correlation with one of the regions within RCW175. In the center of RCW175, we find an average polarized emission at 21.5 GHz of 2.2 ± 0.2(rand.) ± 0.3(sys.)% of the total emission, where we have included both systematic and statistical uncertainties at 68% CL. This polarized emission could be due to sub-dominant synchrotron emission from the region and is thus consistent with very faint or non-polarized emission associated with AME.

Battistelli, E. S.; Carretti, E.; Cruciani, A.; de Bernardis, P.; Génova-Santos, R.; Masi, S.; Naldi, A.; Paladini, R.; Piacentini, F.; Tibbs, C. T.; Verstraete, L.; Ysard, N.

2015-03-01

335

Intensity enhancement on the wavelength of the HeI 5876 A emission observed at high latitude  

International Nuclear Information System (INIS)

From ground-based spectrometric observation an emission on the wavelength of the HeI 5876 A line is identified during aurora. The emission is slightly Doppler shifted towards the blue side when the direction of observation is above magnetic horizon. The spectral form of this emission resembles that of an atomic line, not a molecular rotational band. It is likely that this emission is the HeI 5876 A line originating essentially from solar wind ?-particles. The relative weakness of this emission on the latitude of the polar cleft may be a consequence of the generally low energy of the particle influx in this region. (author)

336

FUSE Observations of the Cygnus Loop: O VI Emission from a Nonradiative Shock  

Science.gov (United States)

We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of a Balmer filament in the northeast region of the Cygnus Loop supernova remnant. The data consist of one spectrum obtained through the 30''×30'' (LWRS) aperture and three spectra at adjacent positions obtained through the 4''×20'' (MDRS) aperture. The nonradiative shocks in the region giving rise to these faint optical filaments produce strong O VI ??1032, 1038 emission, which is detected in all the spectra. The O VI emission is resolved by FUSE into a strong component centered at 0 km s-1 and weaker components centered at +/-140 km s-1. The MDRS spectra allow us to study the variation of O VI emission in the postshock structure. We find that the zero-velocity emission is associated directly with the Balmer filament shock, while the high-velocity emission comes from a more uniformly distributed component elsewhere along the line of sight. We also find that the shocks producing the emission at +/-140 km s-1 have velocities between 180 and 220 km s-1, if we assume that the ram pressure driving them is the same as for the zero-velocity component shock. In the context of the cavity model for the Cygnus Loop, the interaction of the blast wave with the spherical shell that forms most of the cavity wall can naturally give rise to the similar red- and blueshifted components that are observed. Based on data obtained for the Guaranteed Time Team by the NASA-CNES FUSE mission operated by the Johns Hopkins University. Financial support to US participants has been provided by NASA contract NAS 5-32985.

Sankrit, Ravi; Blair, William P.

2002-01-01

337

Probing the origin of VHE emission from M 87 with MWL observations in 2010  

International Nuclear Information System (INIS)

The large majority of extragalactic very high energy (VHE; E >100 GeV) sources belongs to the class of active galactic nuclei (AGN), in particular the BL Lac sub-class. AGNs are characterized by an extremely bright and compact emission region, powered by a super-massive black hole (SMBH) and an accretion disk, and relativistic outflows (jets) detected all across the electro-magnetic spectrum. In BL Lac sources the jet axis is oriented close to the line of sight, giving rise to a relativistic boosting of the emission. In radio galaxies, on the other hand, the jet makes a larger angle to the line of sight allowing to resolve the central core and the jet in great details. The giant radio galaxy M 87 with its proximity (16 Mpc) and its very massive black hole ((3-6)x109MSun) provides a unique laboratory to investigate VHE emission in such objects and thereby probe particle acceleration to relativistic energies near SMBH and in jets. M 87 has been established as a VHE emitter since 2005. The VHE emission displays strong variability on time-scales as short as a day. It has been subject of a large joint VHE and multi-wavelength (MWL) monitoring campaign in 2008, where a rise in the 43 GHz VLBA radio emission of the innermost region (core) was found to coincide with a flaring activity at VHE. This had been interpreted as a strong indication that the VHE emission is produced in the direct vicinity of the SMBH black hole. In 2010 again a flare at VHE was dk hole. In 2010 again a flare at VHE was detected triggering further MWL observations with the VLBA, Chandra, and other instruments. At the same time M 87 was also observed with the Fermi/LAT telescope at GeV energies and the European VLBI Network (EVN). In this contribution preliminary results from the campaign will be presented.

338

Panchromatic observations of the textbook GRB 110205A: constraining physical mechanisms of prompt emission and afterglow  

CERN Document Server

We present a comprehensive analysis of a bright, long duration (T90 ~ 257 s) GRB 110205A at redshift z= 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb and BOOTES telescopes when the GRB was still radiating in the gamma-ray band. Nearly 200 s of observations were obtained simultaneously from optical, X-ray to gamma-ray, which makes it one of the exceptional cases to study the broadband spectral energy distribution across 6 orders of magnitude in energy during the prompt emission phase. By fitting the time resolved prompt spectra, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard GRB synchrotron emission model in the fast cooling regime. Although the prompt optical emission is brighter than the extrapolation of the best fit X/gamma-ray spectra, it traces the gamma-ray light curve shape, suggesting a relation to the prompt high energy emission. The synchrotron + SSC scenario is disfavored by the data, but the models i...

Zheng, W; Sakamoto, T; Beardmore, A P; Pasquale, M; Wu, X F; Gorosabel, J; Urata, Y; Sugita, S; Zhang, B; Pozanenko, A; Nissinen, M; Sahu, D K; Im, M; Ukwatta, T N; Andreev, M; Klunko, E; Volnova, A; Akerlof, C W; Anto, P; Barthelmy, S D; Breeveld, A; Carsenty, U; Castillo-Carri'on, S; Castro-Tirado, A J; Chester, M M; Chuang, C J; Cunniffe, R; Postigo, A; Duffard, R; Flewelling, H; Gehrels, N; Guver, T; Guziy, S; Hentunen, V P; Huang, K Y; Jelínek, M; Koch, T S; Kub'anek, P; Kuin, P; McKay, T A; Mottola, S; Oates, S R; O'Brien, P; Page, M J; Pandey, S B; Pulgar, C; Rujopakarn, W; Rykoff, E; Salmi, T; S'anchez-Ramírez, R; Schaefer, B E; Sergeev, A; Sonbas, E; Sota, A; Tello, J C; Yamaoka, K; Yost, S A; Yuan, F

2011-01-01

339

High Resolution Observations of the Near-Infrared Emission from NGC 6822 Hubble V  

CERN Document Server

We observed Hubble V, the brightest HII region complex in the dwarf irregular galaxy NGC 6822, at near-infrared (1.8--2.4 um) wavelengths using the Cooled Grating Spectrometer 4 (CGS4) at the United Kingdom Infra-Red Telescope (UKIRT). The line emission maps of Hubble V show the typical structure of a photo-dissociation region (PDR) where an ionized core, traced by compact He I emission (2.0587 um) and Br_gamma emission (2.1661 um), is surrounded by an outer layer traced by molecular hydrogen (H_2) emission. The measured line ratios of H_2 2-1 S(1) (2.2477 um) / 1-0 S(1) (2.1218 um) from 0.2 to 0.6 and the un-shifted and un-resolved line profiles suggest that the H_2 emission originates purely from a PDR. By comparing the H_2 results with a PDR model, we conclude that Hubble V is equivalent to a dense (10^{4.5} cm^{-3}) and warm PDR. In this environment, most of the H_2 molecules are excited by far-UV photons (with a field strength of 10^{2-4} times that of the average interstellar field), although collisiona...

Lee, S; Lee, S G; Davis, C J; Kaufman, M J; Mochizuki, K; Jaffe, D T; Lee, Sungho; Pak, Soojong; Lee, Sang-Gak; Davis, Christopher J.; Kaufman, Michael J.; Mochizuki, Kenji; Jaffe, Daniel T.

2004-01-01

340

AMI observations of Lynds Dark Nebulae: further evidence for anomalous cm-wave emission  

CERN Document Server

Observations at 14.2 to 17.9 GHz made with the AMI Small Array towards fourteen Lynds Dark Nebulae with a resolution of 2' are reported. These sources are selected from the SCUBA observations of Visser et al. (2001) as small angular diameter clouds well matched to the synthesized beam of the AMI Small Array. Comparison of the AMI observations with radio observations at lower frequencies with matched uv-plane coverage is made, in order to search for any anomalous excess emission which can be attributed to spinning dust. Possible emission from spinning dust is identified as a source within a 2' radius of the Scuba position of the Lynds dark nebula, exhibiting an excess with respect to lower frequency radio emission. We find five sources which show a possible spinning dust component in their spectra. These sources have rising spectral indices in the frequency range 14.2--17.9 GHz. Of these five one has already been reported, L1111, we report one new definite detection, L675, and three new probable detections (L9...

Scaife, Anna M M; Green, David A; Davies, Matthew L; Franzen, Thomas M O; Grainge, Keith J B; Hobson, Michael P; Lasenby, Anthony N; Pooley, Guy G; Rodriguez-Gonzalvez, Carmen; Saunders, Richard D E; Scott, Paul F; Shimwell, Timothy W; Titterington, David J; Waldram, Elizabeth M; Zwart, Jonathan T L

2009-01-01

341

Atmospheric observations of carbon monoxide and fossil fuel CO2 emissions from East Asia  

DEFF Research Database (Denmark)

Flask samples from two sites in East Asia, Tae-Ahn Peninsula, Korea (TAP), and Shangdianzi, China (SDZ), were measured for trace gases including CO2, CO and fossil fuel CO2(CO(2)ff, derived from Delta(CO2)-C-14 observations). The five-year TAP record shows high CO(2)ff when local air comes from the Korean Peninsula. Most samples, however, reflect air masses from Northeastern China with lower CO(2)ff. Our small set of SDZ samples from winter 2009/2010 have strongly elevated CO(2)ff. Biospheric CO2 contributes substantially to total CO2 variability at both sites, even in winter when non-fossil CO2 sources (including photosynthesis, respiration, biomass burning and biofuel use) contribute 20-30% of the total CO2 enhancement. Carbon monoxide (CO) correlates strongly with CO(2)ff. The SDZ and TAP far-field (China influenced) samples have CO: CO(2)ff ratios (R-CO:CO2ff) of 47 +/- 2 and 44 +/- 3 ppb/ppm respectively, consistent with recent bottom-up inventory estimates and other observational studies. Locally influenced TAP samples fall into two distinct data sets, ascribed to air sourced from South Korea and North Korea. The South Korea samples have low R-CO:CO2ff of 13 +/- 3 ppb/ppm, slightly higher than bottom-up inventories, but consistent with emission ratios for other developed nations. We compare our CO(2)ff observations with modeled CO(2)ff using the FLEXPART Lagrangian particle dispersion model convolved with a bottom-up CO(2)ff emission inventories. The modeled annual mean CO(2)ff mole fractions are consistent with our observations when the model inventory includes the reported 63% increase in Chinese emissions from 2004 to 2010, whereas a model version which holds Chinese emissions flat is unable to replicate the observations.

Turnbull, Jocelyn C.; Tans, Pieter P.

2011-01-01

342

The European VLF/LF Radio Network: the current status  

Science.gov (United States)

Since 2009 a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers has been put into operation in Europe in order to study earthquakes precursors. At the moment the network consists of eleven receivers four of which are located in Italy, two in Greece and one in Portugal, Romania, Malta, Cyprus and Turkey. The data (sampling rate of 1min) are downloaded automatically at the end of each day and they are stored in the server located at the Department of Physics of the University of Bari (Italy), that is the central node of the network. Still, in some case, problems of connection exist. The different trends are open and visible on the web site: http://beta.fisica.uniba.it/infrep/Hom.aspx. The data files can be downloaded by the same web site but they are protected by username and password. Among the different methods of data analysis the Wavelet spectra appear to be the most sensitive ones. The software able to apply this technique on the radio data automatically at the end of each day has been planned and realized. At the moment it operates on four signals collected by one of the Italian receivers; if an anomaly stands up and it is over a fixed threshold a warning advise appears. In the web site, this activity is protected by a specific username and password.

Biagi, Pier Francesco; Maggipinto, Tommaso; Schiavulli, Luigi; Ligonzo, Teresa; Colella, Roberto; Ermini, Anita; Martinelli, Giovanni; Palangio, Paolo; Moldovan, Iren; Silva, Hugo; Contadakis, Michael; Frantzis, Xenophon; Katzis, Konstantinos; Buyuksarac, Aydin; D'Amico, Sebastiano

2014-05-01

343

New Ecuadorian VLF and ELF receiver for study the ionosphere  

Science.gov (United States)

Crucial physical phenomena occur in the equatorial atmosphere and ionosphere, which are currently understudied and poorly understood. Thus, scientific campaigns for monitoring the equatorial region are required in order to provide the necessary data for the physical models. Ecuador is located in strategic geographical position where these studies can be performed, providing quality data for the scientific community working in understanding the nature of these physical systems. The Quito Astronomical Observatory (QAO) of National Polytechnic School is moving in this direction by promoting research in space sciences for the study of the equatorial zone. With the participation and the valuable collaboration of international initiatives such us AWESOME, MAGDAS, SAVNET and CALLISTO, the Quito Observatory is establishing a new space physics division on the basis of the International Space Weather Initiative. As part of this project, in the QAO has been designed a new system for acquisition and processing VLF and ELF signals propagating in the ionosphere. The Labview Software is used to filtering, processing and conditioning the received signals, avoiding in this way 60 percent of the analog components present in a common receiver. The same software have been programmed to create the spectrograms and the amplitude and phase diagrams of the radio signals. The data is stored neatly in files that can be processed even with other applications.

Lopez, Ericson; Montenegro, Jefferson; Vasconez, Michael; Vicente, Klever

344

Validation of Satellite-Observed Volcanic Emissions with Ground-Based NOVAC-Measurements  

Science.gov (United States)

The observation of volcanic gas emissions with satellite instruments permits the long-term monitoring of the volcanic sulphur dioxide (SO2) emissions in near-real time. Besides studying the climate and meteorological effects that huge injections of SO2 during from volcanic eruptions or passive degassing phases may cause in the atmosphere, one can compare the degassing data with additional geophysical parameters to gain insights into chemical and geological processes occurring inside volcanoes. Next to the continuous long-term data set, another crucial advantage of the satellite measurements is the availability of data at inaccessible volcanoes, where ground-based measurements are impossible or dangerous to carry out. However, it is of key importance to validate satellite remote sensing data with ground-based measurements (where they are available) in order to implement a reliable and accurate vertical column density retrieval. While such validation has proven non-trivial in the past due to the differences in viewing geometry and observed spatial scales between ground-based and satellite measurements, the recent availability of a global network of ground-based volcanic gas emission measurements together with novel satellite instrumentation now provides the necessary framework to advance such efforts. Since its start in 2005, ground-based DOAS measurements of volcanic gas emissions have been conducted in the scope of the NOVAC (Network for Observation of Volcanic and Atmospheric Change) project. The project database now offers vast amounts of ground-based measurement data from numerous volcanoes on four different continents. Combined with the improved spatial resolution of novel satellite instruments, the data offers new possibilities for validation of satellite retrievals. Here we present first results of comparisons of volcanic SO2 emission measurements from the GOME-2 instrument on MetOp with ground-based data from the NOVAC network.

Hörmann, Christoph; Kern, Christoph; Bobrowski, Nicole; Vogel, Leif; Mies, Kornelia; Beirle, Steffen; Galle, Bo; Platt, Ulrich; Wagner, Thomas

2010-05-01

345

Modeling radio emission attenuation lanes observed by the Galileo and Cassini spacecraft  

Science.gov (United States)

The Cassini gravity-assisted flyby of Jupiter provided an opportunity to investigate radio emission attenuation lanes that were previously observed in the Voyager and Galileo data. The Cassini radio and plasma wave science (RPWS) investigation is the most advanced plasma wave instrument to visit the Jovian system, measuring electric fields over the frequency range from 1 Hz to 16 MHz with high spectral and temporal resolution. The narrow attenuation lanes in the hectometric emission vary in frequency with system III longitude. The lanes have been modeled in the past assuming a high-latitude cyclotron maser instability source region with emission that is efficiently scattered when the ray path is nearly tangent to the Io L-shell (Gurnett et al., 1998). In the current study we carried out ray tracing of radio emission for multiple frequencies and source regions in a magnetosphere that includes an Io L-shell filled with plasma. The half-width of the density distribution perpendicular to the magnetic field line and the central plasma density of the Io L-shell were fitting parameters. We have used the joint Galileo/Cassini observations at numerous frequencies and radial distances extending to 140 RJ to place constraints on model parameters. The results confirm the suggestion that wave refraction can produce the attenuation lanes. We have also been able to restrict the range of possible hectometric source regions and plasma parameters associated with the density model of the Io L-shell.

Menietti, J. D.; Gurnett, D. A.; Hospodarsky, G. B.; Higgins, C. A.; Kurth, W. S.; Zarka, P.

2003-08-01

346

Space-based observational approaches for carbon dioxide emissions treaty assessment  

Science.gov (United States)

There is increasing demand for methodologies to support the assessment of international treaties on carbon dioxide (CO2) emissions. The situation is complicated by the fact that the treaty protocols under consideration require the evaluation of the net global CO2 emissions (total anthropogenic emissions less sequestration or accumulation in long-term carbon stocks) on spatial scales of nation states (~100 km). These signals must also be disentangled from the large natural CO2 sources and sinks with high confidence. The current state of the art for observationally driven estimates of global CO2 fluxes comes from the TRANSCOM experiment and is limited to spatial resolutions of order 10,000 km (~25 global regions). Simulations of satellite data from the Greenhouse Gas Observations Satellite (GOSAT) or the Orbiting Carbon Observatory (OCO) sensors have shown the potential to reduce flux uncertainties by a factor of 10 or more while increasing the number of regions to ~100. We will present a series of flux inversion simulations using constellations of up to 4 OCO-like satellites that demonstrate the ability of space-based measurements to deliver weekly global CO2 fluxes on a 1° x 2.5° spatial resolution (~100 km x 200 km or 30,000 global regions) with flux uncertainties that are consistent with those needed to support the assessment of treaties regulating CO2 emissions.

Miller, Charles; Baker, David; Duren, Riley; Crisp, David

2010-05-01

347

HST/ACS Observations of Europa's Atmospheric UV Emission at Eastern Elongation  

CERN Document Server

We report results of a Hubble Space Telescope (HST) campaign with the Advanced Camera for Surveys to observe Europa at eastern elongation, i.e. Europa's leading side, on 2008 June 29. With five consecutive HST orbits, we constrain Europa's atmospheric \\ion{O}{1} 1304 \\A and \\ion{O}{1} 1356 \\A emissions using the prism PR130L. The total emissions of both oxygen multiplets range between 132 $\\pm$ 14 and 226 $\\pm$ 14 Rayleigh. An additional systematic error with values on the same order as the statistical errors may be due to uncertainties in modelling the reflected light from Europa's surface. The total emission also shows a clear dependence of Europa's position with respect to Jupiter's magnetospheric plasma sheet. We derive a lower limit for the O$_2$ column density of 6 $\\times$ 10$^{18}$ m$^{-2}$. Previous observations of Europa's atmosphere with STIS in 1999 of Europa's trailing side show an enigmatic surplus of radiation on the anti-Jovian side within the disk of Europa. With emission from a radially symm...

Saur, Joachim; Roth, Lorenz; Nimmo, Francis; Strobel, Darrell F; Retherford, Kurt D; McGrath, Melissa A; Schilling, Nico; Gérard, Jean-Claude; Grodent, Denis

2011-01-01

348

Multispacecraft Cluster observations of quasiperiodic emissions close to the geomagnetic equator  

Science.gov (United States)

We present a detailed analysis of three electromagnetic wave events observed by the Cluster Wide-Band Data instruments at frequencies of a few kilohertz, which exhibit a periodic time modulation of the wave intensity (quasiperiodic emissions). The events were measured when crossing the geomagnetic equator at radial distances of about 3-4 RE during the close separation campaign in July-October 2013. Coincident compressional magnetic field pulsations with the magnitude on the order of a few tenths of nanotesla were detected in two events. Their period corresponded to the modulation period of the quasiperiodic emissions in one event, while it was about double in the other. A possible explanation for this discrepancy between the two periods is given. Although Cluster 1, Cluster 3, and Cluster 4 were close to each other, Cluster 2 was located by more than 0.5 RE closer to the Earth. The same quasiperiodic modulation was observed by all Cluster spacecraft, but the emissions detected by Cluster 2 had a noticeable time delay. This can be explained by the wave propagation from the generation region located at larger radial distances, close to the plasmapause. The large range of L shells where the emissions are detected thus appears to be due to the unducted propagation from a spatially limited source. The frequency-time structure of individual elements forming the events is evaluated, and it is shown that the time dependence of the intensity modulation can be approximated by a simple model.

N?mec, F.; Pickett, J. S.; Santolík, O.

2014-11-01

349

Evolution of magnetotelluric, total magnetic field, and VLF field parameters in Central Italy: relations to local seismic activity  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetotelluric data were collected at Collemeluccio (41.72°N, 14.37°E in Central Italy from summer 1991 to spring 1998. Analyzed by means of tensor decomposition on the geoelectric potential and robust estimation on the geomagnetic field, this set of data allowed the investigation of the electric properties at different time-periods. The variation of some indicators, related to the phenomenon of electromagnetic induction, is presented here in its time evolution and compared to local and regional seismic activity. Tectonomagnetic field observations from absolute magnetic field level in Central Italy were also made on data simultaneously recorded at four magnetometer stations, using L'Aquila Geomagnetic Observatory as a reference for differentiation. Recent results gathered from a system of two VLF search coil wide-band antennas, installed in the L'Aquila Observatory, are also discussed in relation to local seismic activity.

T. Ernst

2001-06-01

350

Generation of VLF Mode Instability by Generalized Distribution Function in the Presence of Parallel AC Electric Field in Uranus  

International Nuclear Information System (INIS)

VLF (very low frequency) mode instability with parallel AC electric field was studied for generalized loss-cone distribution with an index j, which is reducible to bi-Maxwellian, loss-cone and delta function for j = 0,1 and ?. The particle trajectories and dispersion relation are obtained through a kinetic approach and method of characteristic solutions. The calculations are compared with the observations of low frequency waves of Voyager 2. The growth rate of plasma parameters suited to magnetosphere of Uranus is obtained. It is inferred that the magnitude as well as frequency of AC (alternating current) field increases the growth rate and widen the band width significantly. In addition to temperature anisotropy, particles in plasma having generalized loss-cone distribution provide an additional source of energy.

351

Scaling graphs of heart rate time series in athletes demonstrating the VLF, LF and HF regions.  

Science.gov (United States)

Scaling analysis of heart rate time series has emerged as a useful tool for the assessment of autonomic cardiac control. We investigate the heart rate time series of ten athletes (five males and five females), by applying detrended fluctuation analysis (DFA). High resolution ECGs are recorded under standardized resting conditions over 30 min and subsequently heart rate time series are extracted and artifacts filtered. We find three distinct regions of scale invariance, which correspond to the well-known VLF, LF and HF bands in the power spectra of heart rate variability. The scaling exponents alpha are alpha(HF): 1.15 [0.96-1.22], alpha(LF): 0.68 [0.57-0.84], alpha(VLF): 0.83[0.82-0.99], p VLF, LF and HF ranges, respectively. PMID:16868343

Baumert, Mathias; Brechtel, Lars M; Lock, Juergen; Voss, Andreas; Abbott, Derek

2006-09-01

352

Inverse modelling of European N2O emissions: assimilating observations from different networks  

Directory of Open Access Journals (Sweden)

Full Text Available We describe the setup and first results of an inverse modelling system for atmospheric N2O, based on a four-dimensional variational (4DVAR technique and the atmospheric transport zoom model TM5. We focus in this study on the European domain, utilizing a comprehensive set of quasi-continuous measurements over Europe, complemented by N2O measurements from the Earth System Research Laboratory of the National Oceanic and Atmospheric Administration (NOAA/ESRL cooperative global air sampling network. Despite ongoing measurement comparisons among networks parallel measurements at a limited number of stations show that significant offsets exist among the different laboratories. Since the spatial gradients of N2O mixing ratios are of the same order of magnitude as these biases, the direct use of these biased datasets would lead to significant errors in the derived emissions. Therefore, in order to also use measurements with unknown offsets, a new bias correction scheme has been implemented within the TM5-4DVAR inverse modelling system, thus allowing the simultaneous assimilation of observations from different networks. The N2O bias corrections determined in the TM5-4DVAR system agree within 0.1 ppb (dry-air mole fraction with the bias derived from the measurements at monitoring stations where parallel NOAA discrete air samples are available. The N2O emissions derived for the northwest European countries for 2006 show good agreement with the bottom-up emission inventories reported to the United Nations Framework Convention on Climate Change (UNFCCC. Moreover, the inverse model can significantly narrow the uncertainty range reported in N2O emission inventories, while the lack of measurements does not allow for better emission estimates in southern Europe. Several sensitivity experiments were performed to test the robustness of the results. It is shown that also inversions without detailed a priori spatio-temporal emission distributions are capable to reproduce major regional emission patterns within the footprint of the existing atmospheric network, demonstrating the strong constraints of the atmospheric observations on the derived emissions.

C. Brühl

2010-11-01

353

Inverse modelling of European N2O emissions: assimilating observations from different networks  

Directory of Open Access Journals (Sweden)

Full Text Available We describe the setup and first results of an inverse modelling system for atmospheric N2O, based on a four-dimensional variational (4DVAR technique and the atmospheric transport zoom model TM5. We focus in this study on the European domain, utilizing a comprehensive set of quasi-continuous measurements over Europe, complemented by N2O measurements from the Earth System Research Laboratory of the National Oceanic and Atmospheric Administration (NOAA/ESRL cooperative global air sampling network. Despite ongoing measurement comparisons among networks parallel measurements at a limited number of stations show that significant offsets exist among the different laboratories. Since the spatial gradients of N2O mixing ratios are of the same order of magnitude as these biases, the direct use of these biased datasets would lead to significant errors in the derived emissions. Therefore, in order to also use measurements with unknown offsets, a new bias correction scheme has been implemented within the TM5-4DVAR inverse modelling system, thus allowing the simultaneous assimilation of observations from different networks. The N2O bias corrections determined in the TM5-4DVAR system agree within ~0.1 ppb (dry-air mole fraction with the bias derived from the measurements at monitoring stations where parallel NOAA discrete air samples are available. The N2O emissions derived for the northwest European and east European countries for 2006 show good agreement with the bottom-up emission inventories reported to the United Nations Framework Convention on Climate Change (UNFCCC. Moreover, the inverse model can significantly narrow the uncertainty range reported in N2O emission inventories for these countries, while the lack of measurements does not allow to reduce the uncertainties of emission estimates in southern Europe. Several sensitivity experiments were performed to test the robustness of the results. It is shown that also inversions without detailed a priori spatio-temporal emission distributions are capable to reproduce major regional emission patterns within the footprint of the existing atmospheric network, demonstrating the strong constraints of the atmospheric observations on the derived emissions.

C. Brühl

2011-03-01

354

An explanation for experimental observations of harmonic cyclotron emission induced by fast ions  

International Nuclear Information System (INIS)

An explanation, supported by numerical simulations and analytical theory, is given for the harmonic cyclotron emission induced by fast ions in tokamak plasmas - particular, for the emission observed at low harmonics in deuterium-deuterium md deuterium-tritium experiments in the Joint European Tokamak. We show that the first proton harmonic is one of the highest spectral peaks whereas the first alpha is weak. We also compare the relative spectral amplitudes of different harmonics. Our results axe consistent with the experimental observations. The simulations verify that the instabilities are caused by a weak relativistic mass effect. Simulation that a nonuniform magnetic field leads to no appreciable change in the growth and saturation amplitude of the waves

355

The Direction Finding of ULF Emissions Observed before the 2007 Noto Hantou and the 2008 Iwate-Miyagi Nairiku Earthquakes  

Science.gov (United States)

Chubu University has established ULF/ELF electromagnetic observation network in order to study seismo-electromagnetics. We estimate the direction angle of the ULF emissions observed at three observation stations (Nakatsugawa, Shinojima and Minami Izu) before the 2007 Noto Hantou and 2008 Iwate-Miyagi Nairiku earthquakes. As a result of analysis, we found that observed ULF emissions have been propagated possibly from the direction of the epicenter of the 2007 Noto Hantou earthquake and the 2008 Iwate-Miyagi Nairiku earthquake. However, the observed ULF emissions possibly propagated from the epicentral region were not so convincing enough, and so we need more event studies.

Izutsu, Jun; Ohta, Kenji; Hayakawa, Masashi

356

Sensitivity of wetland methane emissions to model assumptions: application and model testing against site observations  

Directory of Open Access Journals (Sweden)

Full Text Available Methane emissions from natural wetlands and rice paddies constitute a large proportion of atmospheric methane, but the magnitude and year-to-year variation of these methane sources are still unpredictable. Here we describe and evaluate the integration of a methane biogeochemical model (CLM4Me; Riley et al., 2011 into the Community Land Model 4.0 (CLM4CN in order to better explain spatial and temporal variations in methane emissions. We test new functions for soil pH and redox potential that impact microbial methane production in soils. We also constrain aerenchyma in plants in always-inundated areas in order to better represent wetland vegetation. Satellite inundated fraction is explicitly prescribed in the model, because there are large differences between simulated fractional inundation and satellite observations, and thus we do not use CLM4-simulated hydrology to predict inundated areas. A rice paddy module is also incorporated into the model, where the fraction of land used for rice production is explicitly prescribed. The model is evaluated at the site level with vegetation cover and water table prescribed from measurements. Explicit site level evaluations of simulated methane emissions are quite different than evaluating the grid-cell averaged emissions against available measurements. Using a baseline set of parameter values, our model-estimated average global wetland emissions for the period 1993–2004 were 256 Tg CH4 yr?1 (including the soil sink and rice paddy emissions in the year 2000 were 42 Tg CH4 yr?1. Tropical wetlands contributed 201 Tg CH4 yr?1, or 78% of the global wetland flux. Northern latitude (>50 N systems contributed 12 Tg CH4 yr?1. However, sensitivity studies show a large range (150–346 Tg CH4 yr?1 in predicted global methane emissions (excluding emissions from rice paddies. The large range is sensitive to (1 the amount of methane transported through aerenchyma, (2 soil pH (±100 Tg CH4 yr?1, and (3 redox inhibition (±45 Tg CH4 yr?1. Results are sensitive to biases in the CLMCN and to errors in the satellite inundation fraction. In particular, the high latitude methane emission estimate may be biased low due to both underestimates in the high-latitude inundated area captured by satellites and unrealistically low high-latitude productivity and soil carbon predicted by CLM4.

L. Meng

2012-07-01

357

Negative differential conductance observed in electron field emission from band gap modulated amorphous-carbon nanolayers  

OpenAIRE

Amorphous-carbon (a-C)-based quantum confined structures were synthesized by pulsed laser deposition. In these structures, electrons are confined in a few nanometer thick sp(2) rich a-C layer, which is bound by the vacuum barrier and a 3 nm thick sp(3) rich a-C base layer. In these structures anomalous field emission properties, including negative differential conductance and repeatable switching effects, are observed when compared to control samples. These properties will be discussed in ter...

Tsang, Wm; Henley, Sj; Stolojan, V.; Silva, Srp

2006-01-01

358

Temperature variations in the mesopause region according to the hydroxyl-emission observations at midlatitudes  

Science.gov (United States)

The seasonal temperature variations in the mesopause region and the inter-day and nighttime temperature variability, the measure of which is standard deviations, have been studied based on the hydroxyl emission spectral observations at the Zvenigorod station of the Obukhov Institute of Atmospheric Physics in 2000-2011 and Institute of Solar Terrestrial Physics geophysical station (Tory) in 2008-2011. The long-term variations in all temperature variability parameters have been analyzed.

Perminov, V. I.; Semenov, A. I.; Medvedeva, I. V.; Pertsev, N. N.

2014-03-01

359

Detection and characterization of a 500 mic dust emissivity excess in the Galactic Plane using Herschel/Hi-GAL observations  

OpenAIRE

Past and recent observations have revealed unexpected variations in the FIR-mm dust emissivity. In the Herschel spectral range, those are often referred to as a 500{\\mu}m emission excess. Several dust emission models have been developed to interpret astrophysical data in the FIR-mm domain. However, these are commonly unable to fully reconcile theoretical predictions with observations. In contrast, the recently revised two level system (TLS) model seems to provide a promising...

Paradis, D.; Paladini, R.; Noriega-crespo, A.; Me?ny, C.; Piacentini, F.; Thompson, M. A.; Marshall, D. J.; Veneziani, M.; Bernard, J. -p; Molinari, S.

2011-01-01

360

Assessment of ground-based atmospheric observations for verification of greenhouse gas emissions from an urban region  

OpenAIRE

International agreements to limit greenhouse gas emissions require verification to ensure that they are effective and fair. Verification based on direct observation of atmospheric greenhouse gas concentrations will be necessary to demonstrate that estimated emission reductions have been actualized in the atmosphere. Here we assess the capability of ground-based observations and a high-resolution (1.3 km) mesoscale atmospheric transport model to determine a change in greenhouse gas emissions ...

Mckain, Kathryn; Wofsy, Steven C.; Nehrkorn, Thomas; Eluszkiewicz, Janusz; Ehleringer, James R.; Stephens, Britton B.

2012-01-01

361

Low-dimensional models for the estimation of anthropogenic CO2 emissions from atmospheric observations  

Science.gov (United States)

The estimation of anthropogenic fossil fuel emissions using atmospheric observations of CO2 has recently attracted increasing interest due to its relevance to monitoring of CO2 mitigation treaties and programs. To date, techniques to perform large-scale inversions had primarily been developed within the context of understanding biospheric and oceanic fluxes. Such fluxes tend to vary relatively smoothly in space and time, making it possible to use multiGaussian models to parameterize and regularize such inversions, predicated on limited measurements of CO2 concentrations. However, the spatial distribution of anthropogenic emissions is non-stationary and multiscale, and therefore makes the use of multiGaussians models less suitable. Thus, a need exists to identify how anthropogenic emissions may be represented in a low-dimensional manner (i.e., with few parameters), for use in top-down estimation. Certain aspects of the spatial extent of anthropogenic emissions can be represented using easily measurable proxies such as nightlights, population density and GDP; in fact, fossil fuel inventories regularly use them to disaggregate regional emission budgets to finer spatial resolutions. However, such proxies can also be used to construct a priori models for anthropogenic emissions, which can then be updated, with data, through inverse modeling. In this presentation, we compare 3 low-dimensional parameterizations to characterize anthropogenic sources. The models are derived from images of nightlights over the continental USA, but adopt different arguments to achieve their dimensionality reduction. In the first model, we threshold nightlights and fit bivariate Gaussian kernels over clusters to represent emission sources; the emission field is modeled as a weighted sum of the kernels. The second approach models emissions as a weighted superposition of a filtered nightlight-distribution and a multiresolution defect, modeled with Haar wavelet. The nightlight-based methods assume that emissions from sources not associated with human habitation and nightlights e.g., electricity production, are known from exogenous sources e.g., http://carma.org. The third model employs blended interpolation from a limited set of estimation points. This third method is designed to augment our parameterization with complex geographic features, such as highways. The models are tested and validated using a synthetic data experiment where the Vulcan database is used as the truth. Total emissions and the first-order moments are used as the metrics of comparison, for tests conducted at various spatial scales and increasing model complexity (i.e., number of independent model parameters). The models are then used in an inversion setting to conduct an observing system simulation experiment (OSSE). The Vulcan database acts as the emission source. An Ensemble Kalman Filter, with a simplified transport model, is used to perform the inversion. The fitted models are competed with each other by conducting posterior predictive checks, with typical ensemble metrics serving as the discriminants.

van Bloemen Waanders, B.; Ray, J.; McKenna, S. A.; Yadav, V.; Michalak, A. M.

2011-12-01

362

Herschel HIFI observations of O$_2$ toward Orion: special conditions for shock enhanced emission  

CERN Document Server

We report observations of molecular oxygen (O$_2$) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O2 lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km/s with line widths 3 km/s; however, the transition at 1121 GHz is not detected. The observed line characteristics, combined with the results of earlier observations, suggest that the region responsible for the O$_2$ emission is 9" (6e16 cm) in size, and is located close to the H2 Peak 1position (where vibrationally-excited H$_2$ emission peaks), and not at Peak A, 23" away. The peak O2 column density is 1.1e18/cm2. The line velocity is close to that of 621 GHz water maser emission found in this portion of the Orion Molecular Cloud, and having a shock with velocity vector lying nearly in the plane of the sky is consistent with producing maximum maser gain along the line-of-sight. The enhanced O$_2$ abundance compared to that generally found in dense interstellar clouds can be explained by passage of a low-velo...

Chen, Jo-Hsin; Viti, Serena; Snell, Ronald; Lis, Dariusz C; Benz, Arnold; Bergin, Edwin; Black, John; Caselli, Paola; Encrenaz, Pierre; Falgarone, Edith; Goicoechea, Javier R; Hjalmarson, Ake; Hollenbach, David; Kaufman, Michael; Melnick, Gary; Neufeld, David; Pagani, Laurent; van der Tak, Floris; van Dishoeck, Ewine; Yildiz, Umut A

2014-01-01

363

Recent increases in trifluoromethane (HFC-23) global emissions and early atmospheric changes observed for other hydrofluorocarbons  

Science.gov (United States)

Trifluoromethane (HFC-23) is an unintended by-product of chlorodifluoromethane (HCFC-22) production and has a 100-yr global warming potential of 14,800. Firn-air and ambient air measurements of HFC-23 from three firn sampling excursions to Antarctica between 2001 and 2009 are used to construct a consistent atmospheric history for this chemical in the Southern Hemisphere. The results show continued increases in the atmospheric abundance of HFC-23 and imply substantial increases in HFC-23 global emissions since 2003. These emission increases are coincident with rapidly increasing HCFC-22 production in developing countries and are observed despite efforts in recent years to limit emissions of HFC-23 through the Kyoto Protocol’s Clean Development Mechanism. These results will be considered along with new observations of additional HFCs from archived air, firn air, and ongoing flask-air measurements. Considered together, atmospheric increases observed for hydrochlorofluorocarbons and hydrofluorocarbons accounted for ~9% of the increase in total direct radiative forcing from anthropogenic gases during 2003-2008, an addition that was slightly larger than attributable to N2O over this same period.

Montzka, S. A.; Miller, B. R.; Battle, M. O.; Aydin, K. M.; Fahey, D. W.; Hall, B. D.; Miller, L.; Verhulst, K. R.; Saltzman, E.; McFarland, M.

2009-12-01

364

State of the hydrothermal activity of Soufrière of Guadeloupe volcano inferred by VLF surveys  

Science.gov (United States)

La Soufrière (1467 m) is the active island arc volcano of Guadeloupe Island in the Lesser Antilles arc. Its historical eruptions are more or less violent phreatic outbursts the last of which, in 1976-1977, led to the evacuation of nearly 70 000 persons. The subsurface structure of the volcano consists of calderas, craters, and avalanche amphitheatres nested within the composite pile of eruptive products. Since the last magmatic eruption, dated ca. 1440 AD, the four phreatic eruptions have developed radial fractures on Soufrière dome favouring the development of a huge active hydrothermal system emphasized by a tropical environment. After the eruptions, the thermal state and the stable ground water flow are completely disorganised during several years during which the slow mineralization of rocks is becoming again preponderant. Sealing of fractures and decay of rocks permeability act as a cap for upward thermal transfers. Therefore Soufrière dome operates as a valve, resealing the hydrothermal system underlying the volcano thus providing over pressurization that could lead to the next phreatic eruption. In 1992 new small seismic swarms have appeared. Several of them are recorded every year while the emission of acid gas slowly increases. In order to recognise the superficial electrical resistive and conductive zones (less than 100 m depth) as well as the cavities on Soufrière volcano, we have made Very Low Frequency (VLF) surveys in 2000. Electrical conductive zones are clearly associated with major radial faults starting from the summit in which the hydrothermal activity takes place. In the continuation of these active hydrothermal fractures hot springs are located down slope. Conversely some of the resistive zones are associated with inactive clayed and sealed or opened faults. The distribution of the conductive zones allows detailing the state of the superficial part of the hydrothermal system of La Soufrière. The distribution of vertical clayed zones associated with major faults supposes Soufrière dome constituted of more or less consolidated blocks joined side by side and lying on the hydrothermally floor of crater Amic.

Zlotnicki, J.; Vargemezis, G.; Mille, A.; Bruère, F.; Hammouya, G.

2006-04-01

365

Microwave, X-ray emission and SID associated with 13 May 1981 solar flare  

International Nuclear Information System (INIS)

Correlated optical, microwave, X-ray observations and the resulting SID effect have been analyzed for the double ribbon solar flare of class 3B observed on 13 May 1981. X-ray flux in the 0.5-4A and 1-8A bands has been estimated using the observed SPA data of 16 kHz VLF signals. The radio source responsible for the emission of microwave bursts seems to consist of two components, i.e. thermal and non-thermal components generating two distinct features in the time profiles of the observed radio bursts. The values of magnetic field perpendicular to electron velocity have been estimated as H1 approx. 380 gauss, electron energy as E approx. 1.4 MeV and the angular size of microwave bursts source as phi approx. 30 arc sec. (author)

366

(12)CO (3-2) & (1-0) emission line observations of nearby starburst galaxy nuclei  

Science.gov (United States)

New measurements of the (12)CO (1-0) and (12)CO (3-2) line emission are presented for the nuclei of seven nearby starburst galaxies selected from a complete sample of 21 nearby starburst galaxies for which the nuclear star formation rates are measured to be comparable to the archetype starburst galaxies M82 and NGC 253. The new observations capitalize on the coincidence between the beam size of the 45 m Nobeyama telescope at 115 GHz and that of the 15 m James Clerk Maxwell Telescope at 345 GHz to measure the value of the (12)CO (3-2)/(1-0) emission line ratio in a 15 sec (less than or equal to 2.5 kpc) diameter region centered on the nuclear starburst. In principle, the (12)CO (3-2)/(1-0) emission line ratio provides a measure of temperature and optical depth for the (12)CO gas. The error weighted mean value of the (12)CO (3-2)/(1-0) emission line ratio measured for the seven starburst galaxy nuclei is -0.64 +/- 0.06. The (12)CO (3-2)/(1-0) emission line ratio measured for the starburst galaxy nuclei is significantly higher than the average value measured for molecular gas in the disk of the Galaxy, implying warmer temperatures for the molecular gas in starburst galaxy nuclei. On the other hand, the (12)CO (3-2)/(1-0) emission line ratio measured for the starburst galaxy nuclei is not as high as would be expected if the molecular gas were hot, greater than 20 K, and optically thin, tau much less than 1. The total mass of molecular gas contained within the central 1.2-2.8 kpc diameter region of the starburst galaxy nuclei ranges from 10(exp 8) to 10(exp 9) solar mass. While substantial, the molecular gas mass represents only a small percentage, approximately 9%-16%, of the dynamical mass in the same region.

Devereux, Nicholas; Taniguchi, Yoshiaki; Sanders, D. B.; Nakai, N.; Young, J. S.

1994-01-01

367

Solar flares detected by the new narrowband VLF receiver at SANAE IV  

Scientific Electronic Library Online (English)

Full Text Available SciELO South Africa | Language: English Abstract in english A narrowband receiver was installed at the SANAE IV base in Antarctica to monitor specific very low frequency (VLF) radio signals from transmitters around the world. VLF waves propagating through the Earth-Ionosphere Waveguide are excellent probes of the varying properties of the lower region of the [...] ionosphere. This paper describes the set-up of the narrowband system and demonstrates its capabilities with data from a set of solar flares on 08 February and 12 February 2010.

Hanna, Dahlgren; Torbjörn, Sundberg; Andrew B., Collier; Etienne, Koen; Stephen, Meyer.

2011-10-01

368

Multiwavelength observations of GRB 110731A: GeV emission from onset to afterglow  

OpenAIRE

We report on the multiwavelength observations of the bright, long gamma-ray burst \\GRB, by the \\Fermi and \\Swift observatories, and by the MOA and GROND optical telescopes. The analysis of the prompt phase reveals that \\GRB shares many features with bright Large Area Telescope bursts observed by \\Fermi during the first 3 years on-orbit: a light curve with short time variability across the whole energy range during the prompt phase, delayed onset of the emission above 100 MeV...

Collaboration, The Fermi-lat; Collaboration, Fermi-gbm; Collaboration, Swift; Collaboration, Grond; Collaboration, The Moa

2012-01-01

369

The position angle of Jupiter's linearly polarized synchrotron emission - observations extending over 16 years  

International Nuclear Information System (INIS)

Parkes, Owens Valley and Goldstone measurements are presented, showing the variation with central meridian longitude of the position angle of Jupiter's linearly polarized synchrotron emission at wavelengths of 21, 13, 11 and 6 cm; the observations span a total time interval greater than one Jovian orbital period. The form of the position angle versus longitude curve shows a slight dependence on wavelength and epoch. The epoch dependence appears to reflect Jupiter's changing aspect with respect to the Earth. The observations yield a Jovian rotation period agreeing to within about 0.02 s with that derived from the decametric burst measurements, implying a highly stable inner magnetic field configuration. (author)

370

Characterization of kraft pulp mill particulate emissions—A summary of existing measurements and observations  

Science.gov (United States)

Particulate matter emission sources at a kraft pulp mill include kraft recovery furnaces, lime kilns, smelt dissolving tanks and power boilers. Chemical and physical characteristics of these paniculate emissions are reviewed. Measurements of particle size distributions for these sources made with cascade impactors and microscopic counting techniques both before and after paniculate control devices such as multiple cyclones, wet scrubbers, and electrostatic precipitalors are discussed. In general, particles with equivalent diameters less than 3 jim comprise the bulk of the controlled paniculate emissions from all sources. Sodium sulfate is the dominant paniculate emission from kraft recovery furnaces, smelt dissolving tanks and lime kilns. Results from a field investigation of the relationship between human observations of near-stack plume opacity and measured in-stack paniculate concentrations and opacities are summarized. Trained cenified panels of observers were used in the investigation to estimate plume opacities from two kraft recovery furnaces, a combination wood/coal-fired boiler, and a combination wood/oil-fired boiler at four different pulp mill locations. Plume opacities were varied from near-zero to 45 % by adjustment of the paniculate control equipment operation. The effects of different background viewing conditions, observer positions, observer experience levels, and plume characteristics are enumerated. It is concluded that there can be substantial variations between measured in-stack opacities and human perceptions of near-stack plume opacities. The degree of agreement between the human judgements and measured in-stack opacities is significantly affected by the background viewing conditions. It is further shown that even with a panel of six or seven trained observers with similar visual acuity, there can be significant departures of individual opacity readings from the panel mean opacity. Although this investigation deals with questions of human observations of near-stack opacity, it is likely that other studies concerned with human perceptions of visibility impairment at greater downwind distances will have to also address the inherently subjective nature of human visual observations and the effects of background viewing conditions. These factors will make it difficult to correlate human visual observations of plume characteristics to instrumental measures of opacity or opacity-related parameters made at the source.

Pinkerton, John E.; Blosser, Russell O.

371

Emission ratios of anthropogenic volatile organic compounds in northern mid-latitude megacities: Observations versus emission inventories in Los Angeles and Paris  

Science.gov (United States)

Ground-based and airborne volatile organic compound (VOC) measurements in Los Angeles, California, and Paris, France, during the Research at the Nexus of Air Quality and Climate Change (CalNex) and Megacities: Emissions, Urban, Regional and Global Atmospheric Pollution and Climate Effects, and Integrated Tools for Assessment and Mitigation (MEGAPOLI) campaigns, respectively, are used to examine the spatial variability of the composition of anthropogenic VOC urban emissions and to evaluate regional emission inventories. Two independent methods that take into account the effect of chemistry were used to determine the emission ratios of anthropogenic VOCs (including anthropogenic isoprene and oxygenated VOCs) over carbon monoxide (CO) and acetylene. Emission ratios from both methods agree within ±20%, showing the reliability of our approach. Emission ratios for alkenes, alkanes, and benzene are fairly similar between Los Angeles and Paris, whereas the emission ratios for C7-C9 aromatics in Paris are higher than in Los Angeles and other French and European Union urban areas by a factor of 2-3. The results suggest that the emissions of gasoline-powered vehicles still dominate the hydrocarbon distribution in northern mid-latitude urban areas, which disagrees with emission inventories. However, regional characteristics like the gasoline composition could affect the composition of hydrocarbon emissions. The observed emission ratios show large discrepancies by a factor of 2-4 (alkanes and oxygenated VOC) with the ones derived from four reference emission databases. A bias in CO emissions was also evident for both megacities. Nevertheless, the difference between measurements and inventory in terms of the overall OH reactivity is, in general, lower than 40%, and the potential to form secondary organic aerosols (SOA) agrees within 30% when considering volatile organic emissions as the main SOA precursors.

Borbon, Agnes; Gilman, J. B.; Kuster, W. C.; Grand, N.; Chevaillier, S.; Colomb, A.; Dolgorouky, C.; Gros, V.; Lopez, M.; Sarda-Esteve, R.; Holloway, J.; Stutz, J.; Petetin, H.; McKeen, S.; Beekmann, M.; Warneke, C.; Parrish, D. D.; Gouw, J. A.

2013-02-01

372

FERMI OBSERVATIONS OF HIGH-ENERGY GAMMA-RAY EMISSION FROM GRB 090217A  

International Nuclear Information System (INIS)

The Fermi observatory is advancing our knowledge of gamma-ray bursts (GRBs) through pioneering observations at high energies, covering more than seven decades in energy with the two on-board detectors, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Here, we report on the observation of the long GRB 090217A which triggered the GBM and has been detected by the LAT with a significance greater than 9?. We present the GBM and LAT observations and on-ground analyses, including the time-resolved spectra and the study of the temporal profile from 8 keV up to ?1 GeV. All spectra are well reproduced by a Band model. We compare these observations to the first two LAT-detected, long bursts GRB 080825C and GRB 080916C. These bursts were found to have time-dependent spectra and exhibited a delayed onset of the high-energy emission, which are not observed in the case of GRB 090217A. We discuss some theoretical implications for the high-energy emission of GRBs.

373

Volcanic emissions from AIRS observations: detection methods, case study, and statistical analysis  

Science.gov (United States)

Monitoring volcanic emissions is important for many reasons, most notably for impacts on climate and possible hazards for human health or aviation safety. Satellite instruments allow for long-term monitoring of volcanic emissions on a global scale. In this paper we introduce new detection indices for volcanic ash and sulfur dioxide (SO2) that are optimized for radiance measurements of the Atmospheric InfraRed Sounder (AIRS). Radiative transfer calculations are used to determine the sensitivity of the ash index (AI) on the aerosol optical depth and the SO2 index (SI) on the SO2 column density. A case study on AIRS observations after the eruption of the Puyehue Cordon-Caulle, Chile, in June 2011 demonstrates that the new indices work in practice. A statistical analysis of a ten-year record (2002 to 2013) of AIRS data provides AI thresholds that help to better discriminate volcanic emissions from regular events such as dust storms. We compared our new SI with the AIRS operational product and found that it is more sensitive and better suppresses interfering background signals. Our new volcanic emission data products have been successfully applied in other scientific studies.

Hoffmann, Lars; Griessbach, Sabine; Meyer, Catrin I.

2014-10-01

374

On the nature of prominence emission observed by SDO/AIA  

CERN Document Server

The Prominence-Corona Transition Region (PCTR) plays a key role in the thermal and pressure equilibrium of solar prominences. Our knowledge of this interface is limited and several major issues remain open, including the thermal structure and, in particular, the maximum temperature of the detectable plasma. The high signal-to-noise ratio of images obtained by the Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory clearly show that prominences are often seen in emission in the 171 and 131 bands. We investigate the temperature sensitivity of these AIA bands for prominence observation, in order to infer the temperature content in an effort to explain the emission. Using the CHIANTI atomic database and previously determined prominence differential emission measure distributions, we build synthetic spectra to establish the main emission-line contributors in the AIA bands. We find that the Fe IX line always dominates the 171 band, even in the absence of plasma at > 10^6 K temperatures, while th...

Parenti, Susanna; Heinzel, Petr; Golub, Leon

2012-01-01

375

ON THE NATURE OF PROMINENCE EMISSION OBSERVED BY SDO/AIA  

International Nuclear Information System (INIS)

The prominence-corona transition region (PCTR) plays a key role in the thermal and pressure equilibrium of solar prominences. Our knowledge of this interface is limited and several major issues remain open, including the thermal structure and, in particular, the maximum temperature of the detectable plasma. The high signal-to-noise ratio of images obtained by the Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory clearly shows that prominences are often seen in emission in the 171 and 131 bands. We investigate the temperature sensitivity of these AIA bands for prominence observations, in order to infer the temperature content in an effort to explain the emission. Using the CHIANTI atomic database and previously determined prominence differential emission measure distributions, we build synthetic spectra to establish the main emission-line contributors in the AIA bands. We find that the Fe IX line always dominates the 171 band, even in the absence of plasma at >106 K temperatures, while the 131 band is dominated by Fe VIII. We conclude that the PCTR has sufficient plasma emitting at >4 × 105 K to be detected by AIA.

376

ON THE NATURE OF PROMINENCE EMISSION OBSERVED BY SDO/AIA  

Energy Technology Data Exchange (ETDEWEB)

The prominence-corona transition region (PCTR) plays a key role in the thermal and pressure equilibrium of solar prominences. Our knowledge of this interface is limited and several major issues remain open, including the thermal structure and, in particular, the maximum temperature of the detectable plasma. The high signal-to-noise ratio of images obtained by the Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory clearly shows that prominences are often seen in emission in the 171 and 131 bands. We investigate the temperature sensitivity of these AIA bands for prominence observations, in order to infer the temperature content in an effort to explain the emission. Using the CHIANTI atomic database and previously determined prominence differential emission measure distributions, we build synthetic spectra to establish the main emission-line contributors in the AIA bands. We find that the Fe IX line always dominates the 171 band, even in the absence of plasma at >10{sup 6} K temperatures, while the 131 band is dominated by Fe VIII. We conclude that the PCTR has sufficient plasma emitting at >4 Multiplication-Sign 10{sup 5} K to be detected by AIA.

Parenti, S. [Royal Observatory of Belgium, 1180 Bruxelles (Belgium); Schmieder, B. [Observatoire de Paris, LESIA, 92195 Meudon (France); Heinzel, P. [Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondrejov (Czech Republic); Golub, L., E-mail: s.parenti@oma.be [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2012-07-20

377

Detection and Characterization of Cold Interstellar Dust and PAH Emission from COBE Observations  

CERN Document Server

Using data obtained by the DIRBE and FIRAS instruments on the COBE spacecraft we present the mean 3.5-1000 um dust spectrum from the high latitude cirrus clouds. These data represent the most comprehensive wavelength coverage of dust emission, and first strong evidence for the presence of PAHs in cirrus. The COBE data are well fit with a dust model consisting of a mixture of PAH molecules and bare astronomical silicate and graphite grains. From the model we derive the size distribution, abundances relative to the total hydrogen column density, and relative contribution of each dust component to the observed IR emission. The model provides a good fit to the FIRAS spectrum in the 140-500 um wavelength regime, but leaves an excess Galactic emission component at 500-1000 um. The nature of this component is still unresolved. The model requires about 85% of the solar carbon abundance to be locked up in dust, a third of that in PAHs. The remaining ~ 15% is in the gas as inferred from the [C II] 158 um line emission ...

Dwek, E

1996-01-01

378

Hard X-ray emission from Serpens X-1 as observed by INTEGRAL  

CERN Document Server

We here report results of an INTEGRAL observation of the X-ray burst and atoll source Ser X-1 performed on May 2003. The object was observed for a total of 400 ks but nearly 8 degrees off-axis due to the amalgamation with an observation of SS 433, the pointing target source. Ser X-1 was detected up to 30 keV with unprecedented positional accuracy for a high-energy emission; a sharp spectral drop is evident beyond this energy. Significant variability is seen in the 20-30 keV light curve. Comparison with previous observations indicates that the source was in its high (banana) state and displayed a soft spectrum during the INTEGRAL pointing. A (non simultaneous) broadband radio-to-gamma-rays broad-band spectral energy distribution for Ser X-1 is also presented for the first time.

Masetti, N; Palazzi, E; Amati, L; Caroli, E; Di Cocco, G; Frontera, F; Orlandini, M

2004-01-01

379

Direct Observation of Coronal Magnetic Fields by Vector Tomography of the Coronal Emission Line Polarizations  

CERN Document Server

This article presents the first direct "observation" of the global-scale, 3D coronal magnetic fields of Carrington Rotation (CR) Cycle 2112 using vector tomographic inversion techniques. The Vector tomographic inversion uses observational measurements of the Fe {\\sc{xiii}} 10747 \\AA\\ Hanle effect polarization signals by the Coronal Multichannel Polarimeter (CoMP) and coronal density and temperature structures derived from scalar tomographic inversion of STEREO/EUVI coronal emission lines (CELs) intensity images as inputs to derive a coronal magnetic field model that best reproduces the observed polarization signals. While independent verifications of the vector tomography results cannot be performed, we compared the tomography inverted coronal magnetic fields with those constructed by MagnetoHydroDynamic (MHD) simulation based on observed photospheric magnetic fields of CR 2112 and 2113. We found that the MHD model for CR 2112 is qualitatively consistent with the tomography inverted result for most of the rec...

Kramar, M; Tomczyk, S

2015-01-01

380

Gamma-Ray Emission in Dissipative Pulsar Magnetospheres: From Theory to Fermi Observations  

Science.gov (United States)

We compute the patterns of ?-ray emission due to curvature radiation in dissipative pulsar magnetospheres. Our ultimate goal is to construct macrophysical models that are able to reproduce the observed ?-ray light curve phenomenology recently published in the Second Fermi Pulsar Catalog. We apply specific forms of Ohm's law on the open field lines using a broad range for the macroscopic conductivity values that result in solutions ranging, from near-vacuum to near-force-free. Using these solutions, we generate model ?-ray light curves by calculating realistic trajectories and Lorentz factors of radiating particles under the influence of both the accelerating electric fields and curvature radiation reaction. We further constrain our models using the observed depende