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1

Mid-latitude VLF emissions observed in the topside ionosphere  

International Nuclear Information System (INIS)

Narrow-band VLF data have been processed from wide-band (50 Hz--30 kHz) tapes of Alouette-2 VLF electric field data by narrow-band amplifiers with a minimum reading circuit. The narrow-band VLF data are useful for studying large-scale latitudinal structures of VLF emissions. Narrow-band VLF emissions around 5 kHz are found at invariant latitudes from 620 to 540 in the morning topside-ionosphere. The 5 kHz VLF emissions seem to be in part the origin of ground VLF hiss (5 kHz +- 1 kHz) observed often at mid and low latitudes. (auth.)

1975-01-01

2

Some unusual discrete VLF emissions observed at a low-latitude ground station at Agra  

Directory of Open Access Journals (Sweden)

Full Text Available A detailed analysis of the VLF emissions data obtained during occasional whistler campaigns at the low-latitude ground station Agra (geomagnetic latitude 171' N, L = 1.15 has yielded some unusual discrete VLF emissions of the rising type. These include (1 emissions occurring at time intervals increasing in ge ommetrical progression, (2 emissions occuring simulta neously in different frequency ranges and (3 emissions observed during daytime. In the present study, the observed characteristics of these emissions are described and interpreted. It is shown that the increasing time delay between different components of the emissions match closely with the propagation time delays between different hops of a whistler of dispersion 19 s1/2, the unusual occurrence of the emissions in two different frequency ranges approximately at the same time may possibly be linked with their generation at two different locations, and the occurrence of emissions during daytime may be due to propagation under the influence of equatorial anomaly.

B. Singh

3

Correlation between lambda 4278 optical emissions and VLF wave events observed at L approximately 4 in the Antarctic  

Science.gov (United States)

The paper reports on one-to-one correlations observed at L of about 4 between bursts of ducted VLF noise in the 2 to 4-kHz range and optical emissions at lambda 4278. The optical observations were made at Siple Station, Antarctica, in the austral winter of 1977; the wave activity was recorded at Siple and its conjugate station Roberval, Can. Most of the events occurred near dawn during or shortly after substorm events. In most cases the plasmapause was equatorward of Siple, and the equatorial densities were low. The estimated precipitated energy fluxes ranged from 0.04 to 0.1 ergs/sq cm/s; the correlated VLF activity usually consisted of clusters of discrete rising tones or chorus of 1 to 10 s duration. The data were consistent with scattering of electrons into the loss cone over Siple by emissions triggered by waves propagating away from the equator after reflection in the ionosphere over Siple.

Helliwell, R. A.; Doolittle, J. H.; Armstrong, W. C.; Carpenter, D. L.; Mende, S. B.

1980-07-01

4

VLF wave emissions by pulsed and DC electron beams in space 1 : Spacelab-2 observations  

DEFF Research Database (Denmark)

During the Spacelab 2 space shuttle mission a 1-keV, 100-mA, square-wave-modulated, electron source (FPEG) and a plasma diagnostics subsatellite (PDP) were used to investigate the properties of radio waves generated by electron beams in space. A variety of electron beam pulsing sequences were executed to investigate specific properties of the beam-plasma-wave interaction. In addition to operations conducted with the PDP in the payload bay, several investigations were conducted with the PDP operated as a free-flying satellite at distances of several hundred meters from the orbiter. In this paper we present the results of three beam operation sequences which provide new information about the characteristics of wave generation by electron beams. Those sequences are (1) the ??DG flux tube connection? sequence in which the FPEG was operated with continuous electron emission while the orbiter maneuvered to connect the PDP and the orbiter on the same magnetic field line; (2) a ??Pulsed flux tube connection? sequence for which the electron beam was square-wave-modulated at 1.22 kHz; and (3) a ??Prox Ops? sequence in which the FPEG was again pulsed at 1.22 kHz while the PDP was mounted in the orbiter payload bay rather than operating as a free-flying satellite. Analysis of the amplitudes of VLF emissions from these FPEG sequences allows comparison of broadband emissions from the dc and pulsed electron beams, comparison of broadband and narrow-band emissions during the pulsed electron beam emissions, and investigation of the production and propagation properties of radio waves generated by dc and pulsed electron beams in space plasmas. Spectrograms showing the general characteristics of the ambient wave environment and the wave environment generated during these three sequences are presented. The results of electron beam-generated wave observations from the STS 3/OSS 1 mission were verified. Both dc and modulated electron beams produce copious broadband emissions. Square-wave-modulated electron beams produce narrow-band radiation at the pulsing frequency and its harmonics along with the broadband emissions. The time evolution and spectral structure of broadband and narrow-band emissions are analyzed. Our observations indicated that dc, 50-mA electron beams and pulsed, 50% duty cycle, 100-mA beams produce broadband radiation which is comparable in intensity and spectral shape at all points for which the wave field was sampled. Observation of the waves produced by the electron beam during the flux tube connections indicates that there are three zones of wave emissions characterized by the amplitude of waves in those spatial regions. Zone 1 is a highly disturbed region near the beam with very intense wave activity. Zone 2 is a region of wave activity which decreases rapidly with increasing distance from the beam, and zone 3 contains lower amplitude emissions which appear to be near-field contributions. The amplitude of narrow-band emissions is in good agreement with the predictions of theory for waves generated through the Cherenkovresonance with wave normal angles less than the resonance cone angle, and the harmonic structure of the narrow-band radiation is found to be dependent on the beam propagation characteristics.

Reeves, G.D.; Banks, P.M.

1988-01-01

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 Sodankyl (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 0.30.4 s formed the main ELF-VLF activity in the frequency range 1.02.5 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 4550 km and luminosity propagated inside it with velocity of about 1012 kms. We discuss a new approach to explain the 515 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

Satellite observations of banded VLF emissions in conjunction with energy-banded ions during very large geomagnetic storms  

Science.gov (United States)

Electromagnetic VLF emissions banded in frequency, coincident with warm energy-banded ions in the low latitude auroral zone, and associated with very strong geomagnetic storms, are observed separately on two low-earth polar orbiting satellites, FAST and DEMETER. Both satellites carry a full complement of field and particle detectors. The FAST satellite, launched August 21, 1996 into an elliptical polar orbit with perigee 350 km and apogee 4175 km, traversed the auroral zone four times per orbit across a wide range of altitudes and local times. The DEMETER satellite was launched on June 29, 2004 into a circular sun-synchronous polar orbit at altitude 710 km, with data recorded at all invariant latitudes less than ~65 degrees. The ion bands were first reported in association with the Halloween storms [Cattell et al., 2004; Kozyra et al., 2004, Yao et al., 2008]. Banded ions are observed on FAST during every large magnetic storm in discrete energy bands at energies ~10 eV - 10 keV and lasting up to 12 hrs. The energy flux peaks in the trapped population but is also evident in the precipitating ions, and in certain cases a significant upgoing ion component appears at low invariant latitudes. These bands were observed over several orbits at similar latitudes in both dawn and evening sectors, with the signature typically more pronounced in the dawn sector. In this study we focus on the coincidence of the energy-banded ions with observations of frequency-banded VLF electromagnetic emissions. During all of these very large storms, banded VLF emissions are evident in both the electric and magnetic field, appearing as discrete frequency bands between ~100 and ~1500 Hz separated by 75-150 Hz. These banded emissions persist for several FAST or DEMETER orbits, lasting up to 10 hrs, in both the northern and southern hemispheres. There appears to be a correlation between the banded wave observations and ion and electron density enhancements. Possible generation mechanisms for the banded emissions include EMIC waves generated in the equatorial ring current region which bounce to higher L-shells and propagate down auroral field lines to the spacecraft location.

Colpitts, C. A.; Cattell, C. A.; Kozyra, J. U.; Parrot, M.

2010-12-01

7

Early VLF perturbations observed in association with elves  

DEFF Research Database (Denmark)

VLF remote sensing is used to detect lower-ionospheric electron density changes associated with a certain type of transient luminous events known as elves. Both ground- and satellite-based observations of elves are analysed in relation to VLF data acquired at various receiver sites in Europe, the United States and Antarctica. Ground-based observations were performed during the EuroSprite2003 campaign, when five elves were captured by low-light cameras located in the Pyrenees. Analysis of VLF recordings from Crete shows early VLF perturbations accompanying all of the elves. A large dataset consisting of elves captured by the ISUAL (Imager of Sprites and Upper Atmospheric Lightning) payload on Taiwan's FORMOSAT-2 satellite over Europe and North America has also been analysed. Early/fast VLF perturbations were found to accompany some of the elves observed over Europe. However, no VLF perturbations were detected in relation to the elves observed by ISUAL over North America. The present analysis - based on the largest database of optical elve observations used for VLF studies so far - constitutes evidence of processes initiated by the lightning EMP (electromagnetic pulse) causing electron density changes in the lower ionosphere in line with theoretical predictions. It also proves that sub-ionospheric electron density changes associated with elves can intrude to lower heights and thus perturb VLF transmissions. The possibility of VLF detection, however, depends on several factors, e.g., the distance of the elve from the receiver and the transmitter-receiver great circle path (GCP), the altitude of the ionised region and the characteristics of the VLF transmitter, as well as the EMP energy, which occasionally may be sufficient to cause optical emissions but not ionisation.

Mika, A.; Haldoupis, C.

2006-01-01

8

Early VLF perturbations observed in association with elves  

Directory of Open Access Journals (Sweden)

Full Text Available VLF remote sensing is used to detect lower-ionospheric electron density changes associated with a certain type of transient luminous events known as elves. Both ground- and satellite-based observations of elves are analysed in relation to VLF data acquired at various receiver sites in Europe, the United States and Antarctica. Ground-based observations were performed during the EuroSprite2003 campaign, when five elves were captured by low-light cameras located in the Pyrenees. Analysis of VLF recordings from Crete shows early VLF perturbations accompanying all of the elves. A large dataset consisting of elves captured by the ISUAL (Imager of Sprites and Upper Atmospheric Lightning payload on Taiwan's FORMOSAT-2 satellite over Europe and North America has also been analysed. Early/fast VLF perturbations were found to accompany some of the elves observed over Europe. However, no VLF perturbations were detected in relation to the elves observed by ISUAL over North America. The present analysis based on the largest database of optical elve observations used for VLF studies so far constitutes evidence of processes initiated by the lightning EMP (electromagnetic pulse causing electron density changes in the lower ionosphere in line with theoretical predictions. It also proves that sub-ionospheric electron density changes associated with elves can intrude to lower heights and thus perturb VLF transmissions. The possibility of VLF detection, however, depends on several factors, e.g., the distance of the elve from the receiver and the transmitterreceiver great circle path (GCP, the altitude of the ionised region and the characteristics of the VLF transmitter, as well as the EMP energy, which occasionally may be sufficient to cause optical emissions but not ionisation.

. Mika

2006-09-01

9

Observations of the VLF quiet band phenomenon  

Science.gov (United States)

In 1979, VLF receivers were operated near Roberval, Canada. Data obtained from this experiment on July 23 near 12.16 UT show one hop signals at just below 3 kHz, originating from the VLF transmitter located at Siple Station, Antarctica. On the low-frequency side of the Siple signals, a 'quiet band' of background noise suppresion is visible, about 95 Hz in width. The time taken for the effect to develop is between 5 and 10 s and the recovery time of the noise is greater than about 20 s. The level of suppression is about 3 dB. The important aspect of these data is that, although growth is enhanced above the frequency of the Siple signals, on the lower border of the quiet band little or no enhancement is observed, in contrast to some theoretical models. These data are not of sufficient duration or simplicity to provide a decisive test of recent quiet band theories.

Matthews, J. P.

1986-10-01

10

VLF observation of long ionospheric recovery events  

Science.gov (United States)

We introduce a new class of Early/fast VLF events with recoveries of up to 20 min, much longer than typical Early/fast and Lightning-induced Electron Precipitation (LEP) events which recover to pre-event levels in $\\lesssim$200 s. Three distinct types of long recovery events are observed, each exhibiting different characteristics, with the observed features of at least some of the event types consistent with the possibility of persistent ionization at altitudes below 60 km as put forth by Lehtinen and Inan (2007).

Cotts, Benjamin R. T.; Inan, Umran S.

2007-07-01

11

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

12

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.

2012-12-01

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VLF saucers observed by multiple Cluster spacecraft in the AAR  

Science.gov (United States)

VLF saucer is a natural radio-wave phenomenon observed in the auroral zone since the 1960's. It has a characteristic V-shaped signature on electric field spectrograms in the VLF range. Many properties of VLF saucers have been established in the 1970's based on Alouette and Isis spacecraft. Further investigations continued thanks to satellites flying over the auroral zone such as Viking, Polar and FAST. Since 2006, the orbits of the ESA/NASA Cluster satellites are slowly evolving from a nominal polar orbit to an oblique one. Meanwhile, the original 19,000 km perigee of their orbits went down to a few hundred kilometres and then back up. During spring 2009, early winter 2009/2010 and late 2011, Cluster scientists could make use of this natural orbital drift to target a new key region of the magnetosphere: the Auroral Acceleration Region (AAR). We present new observations of VLF saucers with upward electron beams by multiple Cluster satellites in the AAR region and how these observations improve our knowledge on the VLF saucers source region.

Masson, A.; Berthomier, M.; Fazakerley, A. N.; Andre, M.; Taylor, M. G.; Escoubet, C. P.; Rauch, J.; Dcrau, P.; Pickett, J. S.; Laakso, H. E.

2012-12-01

14

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

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

CERN Multimedia

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

16

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

Directory of Open Access Journals (Sweden)

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 (~1520% 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=150500 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

17

A parametric study of the numerical simulations of triggered VLF emissions  

Directory of Open Access Journals (Sweden)

Full Text Available This work is concerned with the numerical modelling of VLF emissions triggered in the equatorial region of the Earth's magnetosphere, using a well established 1-D Vlasov Hybrid Simulation (VHS code. Although this code reproduces observed ground based emissions well there is some uncertainty regarding the magnitude of simulation parameters such as saturation wave amplitude, cold plasma density, linear growth rate and simulation bandwidth. Concentrating on emissions triggered by pulses of VLF radio waves from the transmitter at Siple Station, Antarctica (L=4.2, these parameters, as well as triggering pulse length and amplitude, are systematically varied. This parametric study leads to an understanding of the physics of the triggering process and also of how the properties of these emissions, particularly their frequency time profile, depend upon these parameters. The main results are that weak power input tends to generate fallers, intermediate power input gives stable risers and strong growth rates give fallers, hooks or oscillating tones. The main factor determining the frequency sweep rate - of either sign - turns out to be the cold plasma density, lower densities giving larger sweep rates.

D. Nunn

2005-12-01

18

Experience of short term earthquake precursors with VLFVHF electromagnetic emissions  

Directory of Open Access Journals (Sweden)

Full Text Available Electromagnetic anomalies (EMA covering a wide range of frequencies from ULF, VLF up to VHF have been observed before recent destructive earthquakes in continental Greece. We show that the features of these signals are possibly correlated with the fault model characteristics of the associated earthquake and with the degree of geotectonic heterogeneity within the focal zone. The time evolution of these electromagnetic sequences reveals striking similarities to that observed in laboratory acoustic and electromagnetic emissions during different stages of failure preparation process in rocks. If we consider that the same dynamics governs the large-scale earthquakes and the microscopic scale sample rheological structure, the results of this analysis suggest that the recorded EMA might reflect the nucleation phase of the associated impending earthquake. We focus on the rise of the statistical view of earthquakes. We find electro-magnetic fingerprints of an underlying critical mechanism. Finally, we conclude that it is useful to combine ULF and VLF-VHF field measurements in an attempt to enhance the understanding of the physics behind these observations and thus to improve the quality of earthquake prediction. Further, the identification of an EMA as a seismogenic one supports the characterization of a sequence of shocks as foreshocks at the time they occur, further helping the earthquake prediction effort.

K. Eftaxias

2003-01-01

19

A New Observation Technique Applied to Early/Fast VLF Scattering Events  

Science.gov (United States)

Early/fast very low frequency (VLF, 3-30 kHz) events are understood to result from ionospheric conductivity changes associated with lightning. Early/fast amplitude and phase perturbations have been observed coincidentally with various optical observations of transient luminous events (TLEs), including elves, sprites, and sprite halos, each of which can have temporal characteristics consistent with those of early/fast VLF events. It is yet unresolved, however, whether a specific type of TLE is directly related to the ionospheric conductivity changes responsible for the typical early/fast event. In this paper, we present spread spectrum VLF scattering observations of early/fast events. The spread spectrum analysis technique determines the amplitude and phase of a subionospherically propagating VLF signal as a function of time during the early/fast event and as a function of frequency across the 200 Hz bandwidth of the VLF transmission. VLF scattering observations, each identified with causative lightning logged by the National Lightning Detection Network (NLDN), are compared with the predictions of the Long-Wave Propagation Capability (LWPC) code, a three-dimensional earth-ionosphere waveguide propagation and scattering model. Theoretical predictions for VLF scattering from ionization changes associated with elves are compared with those associated with sprite halos, and each are compared with experimental observations. Results indicate that the observed frequency dependence of VLF scattering during early/fast events results from the combination of scattering source properties and Earth-ionosphere waveguide propagation effects. Observations are more consistent with the modeled amplitude perturbations associated with sprite halos than those with elves.

Kotovsky, D. A.; Moore, R. C.

2012-12-01

20

Interaction between ELF-VLF emission and magnetic pulsations: quasi-periodic ELF-VLF emissions associated with Pc 3--4 magnetic pulsations and their geomagnetic conjugacy  

International Nuclear Information System (INIS)

The characteristics of quasi-periodic (QP) ELF-VLF emissions with periods of 10--150 s and their relationships to magnetic pulsations are studied by using data obtained from Syowa and Mizuho Stations in Antarctica and at Husafell in Iceland, which is located near the geomagnetic conjugate point of Syowa. From the coherency analysis between QP emissions and Pc 3--4 magnetic pulsations it is found that the coherency between the D component of magnetic pulsations and the intensity fluctuations of QP's is much higher than that between the H component of magnetic pulsations and QP's. It is also found that the propagation time of magnetic pulsations (HM waves) from the interaction region between magnetic pulsations and QP's in the magnetosphere to the ground is 20--30 s. These properties are observed at conjugate-pair stations with good conjugacy. The results strongly suggest that QP emissions are modulated by compressional mode Pc 3--4 magnetic pulsations near the equatorial plane in the outer magnetosphere

1980-01-01

 
 
 
 
21

First optical observations of energetic electron precipitation at 4278 caused by a powerful VLF transmitter  

Science.gov (United States)

summary is presented of experimental optical observations at 4278 from close to a powerful (~150 kW) VLF transmitter (call sign JXN) with a transmission frequency of 16.4 kHz. Approximately 2.5 s after transmitter turn-on, a sudden increase in optical emissions at 4278 was detected using a dedicated camera/charge-coupled device (CCD) monitoring system recording at a frequency of 10 Hz. The optical signal is interpreted as a burst of electron precipitation lasting ~0.5 s, due to gyro-resonant wave-particle interactions between the transmitted wave and the magnetospheric electron population. The precipitation was centered on the zenith and had no detectable spatial structure. The timing of this sequence of events is in line with theoretical predictions and previous indirect observations of precipitation. This first direct measurement of VLF-induced precipitation at 4278 reveals the spatial and temporal extent of the resulting optical signal close to the transmitter.

Denton, M. H.; Kosch, M. J.; Borovsky, J. E.; Clilverd, M. A.; Friedel, R. H. W.; Ulich, T.

2014-04-01

22

Experimental observations of proton whistlers from the INJUN 3 vlf data  

Energy Technology Data Exchange (ETDEWEB)

A new VLF phenomenon named a proton whistler has been identified in the VLF data from Alouette 1 and INJUN 3 satellites. Two independent analyses on 12% of the proton whistler INJUN 3 data were conducted: a semi-monthly sample of data for INJUN 3's ten-month lifetime to determine the gross features of proton whistlers, and a local nighttime and local daytime study of proton whistlers. Six assertions are made from these experimental observations.

Shawhan, S.D.

1965-08-01

23

Subionospheric early VLF signal perturbations observed in one-to-one association with sprites  

DEFF Research Database (Denmark)

Observations on the night of 21 July 2003 of the ionospheric effects of a thunderstorm in central France are reported. From 0200 to 0315 UT, a camera system in the Pyrenees Mountains captured 28 sprites, triggered by + CG lightning as observed by the French METEORAGE lightning detection system. A narrowband VLF receiver located on Crete, at similar to 2200 km southeast of the storm, observed subionospheric VLF signals from six ground-based transmitters. The amplitude of one of the VLF signals, originating at a transmitter located similar to 150 km west of the storm and passing through the storm region, exhibited rapid onset perturbations occurring in a nearly one-to-one relationship with the optical sprites. These "early'' VLF events are consistent with a process of narrow-angle forward scattering from a volume of enhanced ionization above the storm with lateral sizes larger than the VLF radio wavelength. The many + CG and - CG discharges that did not produce sprites were also found to not be associated with detectable VLF amplitude perturbations, even though some of these discharges reached relatively large peak currents. The rapid onsets of several of the sprite-related VLF perturbations were followed by relatively long onset durations, ranging from similar to 0.5 to 2.5 s, indicating that these events were early but not "fast.'' These "early/slow'' events may suggest a slow process of ionization build-up in the lower ionosphere, following intense lightning discharges that also lead to sprites. A limited number of early VLF perturbation events were also associated with whistler-induced electron precipitation events, or classic Trimpi perturbations, undoubtedly produced by the precipitation of electrons due to whistler-mode waves injected into the magnetosphere by the same lightning flash that led to the production of the sprite.

Haldoupis, C.; Neubert, Torsten

2004-01-01

24

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

25

Subionospheric VLF signatures and characteristics in 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 Nanc-ay, 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 Nanc-ay 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 ?2 s 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. © 2005 Elsevier Ltd. All rights reserved.

Mika, A.; Haldoupis, C.

2005-01-01

26

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 interactio...

Rozhnoi, A.; Solovieva, M.; Molchanov, O.; Akentieva, O.; Berthelier, J. J.; Parrot, M.; Biagi, P. F.; Hayakawa, M.

2008-01-01

27

Exos-B/Siple Station VLF wave-particle interaction experiments 2. Transmitter signals and associated emissions  

International Nuclear Information System (INIS)

Interactions between coherent VLF waves and energetic particles in the magnetosphere have been studied in a joint program involving the Japanese high-altitude satellite EXOS-B and the Siple Station VLF transmitter. During the period July 15--September 7, 1979, transmissions to the EXOS-B satellite were carried out on 50 separate occasions when the spacecraft was within +- 60"0 longitude of the magnetic field lines linking Siple Station, Antarctica (76"0S, 84"0W geographic, Lapprox.4.1) with its conjugate station at Roberval, Canada. Of this total, 37 were carried out while the satellite was located in the 1000--1600 LT sector of the magnetosphere and 13 while in the 0300--0800 LT sector. The transmitter signals were detected on EXOS-B on 50% of the occasions when transmissions were attempted, and on 5 occasions the transmitter signals were observed to have triggered VLF emissions somewhere along their ray path between the ionosphere and the satellite. All 5 triggering events occurred in a 6-day period following a large magnetic storm that took place on August 13, 1979, with 2 events occurring in the 1130--1330 LT sector and 3 events occurring in the 0400--0600 LT sector. Analysis of the emission triggering events provided strong evidence that the triggering took place inside whistler-mode ducts and that the emissions reached the satellite only after being scattered at one end of the ducts by ionospheric irregularities. On at least one day, emissions were triggered by ducted echoes of the transmitter signals but not by the direct ducted pulses themselves. On another day a new type of triggered emission was observed. We conclude that in the noon sector of the magnetosphere the amplitude of nonducted signals from the Siple transmitter is generally less than the threshold level necessary for triggering in the nonducted mode

1983-01-01

28

Exos-B/Siple Station VLF wave-particle interaction experiments 2. Transmitter signals and associated emissions  

Energy Technology Data Exchange (ETDEWEB)

Interactions between coherent VLF waves and energetic particles in the magnetosphere have been studied in a joint program involving the Japanese high-altitude satellite EXOS-B and the Siple Station VLF transmitter. During the period July 15--September 7, 1979, transmissions to the EXOS-B satellite were carried out on 50 separate occasions when the spacecraft was within +- 60/sup 0/ longitude of the magnetic field lines linking Siple Station, Antarctica (76/sup 0/S, 84/sup 0/W geographic, Lapprox.4.1) with its conjugate station at Roberval, Canada. Of this total, 37 were carried out while the satellite was located in the 1000--1600 LT sector of the magnetosphere and 13 while in the 0300--0800 LT sector. The transmitter signals were detected on EXOS-B on 50% of the occasions when transmissions were attempted, and on 5 occasions the transmitter signals were observed to have triggered VLF emissions somewhere along their ray path between the ionosphere and the satellite. All 5 triggering events occurred in a 6-day period following a large magnetic storm that took place on August 13, 1979, with 2 events occurring in the 1130--1330 LT sector and 3 events occurring in the 0400--0600 LT sector. Analysis of the emission triggering events provided strong evidence that the triggering took place inside whistler-mode ducts and that the emissions reached the satellite only after being scattered at one end of the ducts by ionospheric irregularities. On at least one day, emissions were triggered by ducted echoes of the transmitter signals but not by the direct ducted pulses themselves. On another day a new type of triggered emission was observed. We conclude that in the noon sector of the magnetosphere the amplitude of nonducted signals from the Siple transmitter is generally less than the threshold level necessary for triggering in the nonducted mode.

Bell, T.F.; Inan, U.S.; Kimura, I.; Hashimoto, K.; Matsumoto, H.; Mukai, T.

1983-01-01

29

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 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.

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

2014-04-01

30

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

1984-01-01

31

Nonlinear mechanisms of lower band and upper band VLF chorus emissions in the magnetosphere  

International Nuclear Information System (INIS)

Complete text of publication follows. We develop a nonlinear wave growth theory of magnetospheric chorus emissions, taking into account the spatial inhomogeneity of the static magnetic field and the plasma density variation along the magnetic field line. We derive theoretical expressions for the nonlinear growth rate and the amplitude threshold for the generation of self-sustaining chorus emissions. We assume that nonlinear growth of a whistler-mode wave is initiated at the magnetic equator where the linear growth rate maximizes. Self-sustaining emissions become possible when the wave propagates away from the equator during which the increasing gradients of the static magnetic field and electron density provide the conditions for nonlinear growth. The amplitude threshold is tested against both observational data and self-consistent particle simulations of the chorus emissions. The self-sustaining mechanism can result in a rising tone emission covering the frequency range of 0.1 - 0.7 of the equatorial electron gyrofrequency. During propagation higher frequencies are subject to stronger dispersion effects that can destroy the self-sustaining mechanism. We obtain a pair of coupled differential equations for the wave amplitude and frequency. Solving the equations numerically, we reproduce a rising tone of VLF whistler-mode emissions that is continuous in frequency. Chorus emissions, however, characteristically occur in two distinct frequency ranges, a lower band and an upper band, separated at half the electron gyrofrequency. We explain the gap by means of the nonlinear damping of the longitudinal component of a slightly oblique whistler-mode wave packet propagating along the inhomogeneous static magnetic field.

2009-08-23

32

VLF/ELF wave activity in the vicinity of the polar cusp: Cluster observations  

Science.gov (United States)

Observations by the Cluster spacecraft of VLF/ELF wave activity show distinct signatures for different regions in the vicinity of high altitude polar cusps, which are identified by using magnetic field and plasma data along spacecraft trajectories. These waves include: (1) Broad band magnetic noise observed in the polar cusp at frequencies from several Hz to ~100 Hz, below the local electron cyclotron frequency, fce. Similar magnetic noise is also observed in the high latitude magnetosheath and the magnetopause boundary layer. (2) Strong broad band electrostatic emissions observed in the cusp, in the magnetosheath, and in the high latitude magnetopause boundary layer, at frequencies extending from several Hz to tens of kHz, with maximum intensities below ~100 Hz. (3) Narrow-band electromagnetic whistler waves at frequencies ~0.2-0.6 fce, frequently observed in the closed boundary layer (CBL) adjacent to the polar cusp. These waves are for the first time observed in this region to be accompanied by counter-streaming electron beams of ~100 eV, which suggests that the waves are excited by these electrons through wave-particle interaction. (4) Narrow-band electrostatic waves observed slightly above the local fce in the CBL. (5) Lion roars, observed in the high latitude magnetosheath, often in magnetic troughs of mirror mode oscillations. The above wave signatures can serve as indicators of the regions in the vicinity of the magnetospheric cusp.

Lin, N.; Lee, E. S.; Mcfadden, J.; Parks, G.; Wilber, M.; Maksimovic, M.; Cornilleau-Wehrlin, N.; Fazakarley, A.; Lucek, E.; Rme, H.; Santolik, O.; Zong, Q.-G.

2006-08-01

33

Rare ground-based observations of Siple VLF transmitter signals outside the plasmapause  

Science.gov (United States)

Signals from the Siple, Antarctica (L approximately 4.3), VLF transmitter observed at the conjugate ground station Roberval, Canada, have previously been found to propagate either within the outer plasmasphere or within the region of steep plasmapause density gradients, but on paths with equatorial electron density that is within a factor of 2 of nearby plasmaspheric levels. Here two cases in which propagation occurred just outside the plasmapause and at plasma trough density levels are reported. In one case a series of 1-s pulses and frequency ramps was observed; many of the pulses triggered risers with slopes of approximately 10 kHz/s, much steeper than those usually observed within the plasmasphere. In the other case, no evidence of triggered emissions was seen on the Siple pulses, but instead efficient echoing occurred and noise band precursors to large wave bursts were initiated. The wave bursts were of a type that has been previously identified as driving transient bursts of electron precipitation into the ionosphere. Both cases occurred under magnetic conditions more disturbed than those typical of strong Siple signal propagation in the outer plasmasphere.

Carpenter, D. L.; Miller, T. R.

1983-12-01

34

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

Energy Technology Data Exchange (ETDEWEB)

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.

Rash, J.P.S.; Scourfield, M.W.J. (Natal Univ., Durban (South Africa). Dept. of Physics)

1984-12-01

35

VLF and HF Plasma Waves Associated with Spread-F Plasma Depletions Observed on the C/NOFS Satellite  

Science.gov (United States)

The C/NOFS spacecraft frequently encounters structured plasma depletions associated with equatorial spread-F along its trajectory that varies between 401 km perigee and 867 km apogee in the low latitude ionosphere. We report two classes of plasma waves detected with the Vector Electric Field Investigation (VEFI) that appear when the plasma frequency is less than the electron gyro frequency, as is common in spread-F depletions where the plasma number density typically decreases below 10(exp 4)/cu cm. In these conditions, both broadband VLF waves with a clear cutoff at the lower hybrid frequency and broadband HF waves with a clear cutoff at the plasma frequency are observed. We interpret these waves as "hiss-type" emissions possibly associated with the flow of suprathermal electrons within the inter-hemispherical magnetic flux tubes. We also report evidence of enhanced wave "transients" sometimes embedded in the broader band emissions that are associated with lightning sferics detected within the depleted plasma regions that appear in both the VLF and HF data. Theoretical implications of these observations are discussed.

Pfaff, Robert; Freudenreich, H.; Schuck, P.; Klenzing, J.

2011-01-01

36

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 b...

Platino, M.; Inan, U. S.; Bell, T. F.; Pickett, J.; Kennedy, E. J.; Trotignon, J. G.; Rauch, J. L.; Canu, P.

2004-01-01

37

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ill...

Platino, M.; Inan, U. S.; Bell, T. F.; Pickett, J.; Kennedy, E. J.; Trotignon, J. G.; Rauch, J. L.; Canu, P.

2004-01-01

38

VLF emission triggering by a highly anisotropic energetic electron plasma  

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 Earths 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

D. Nunn

39

VLF/ELF wave activity in the vicinity of the polar cusp: Cluster observations  

Directory of Open Access Journals (Sweden)

Full Text Available Observations by the Cluster spacecraft of VLF/ELF wave activity show distinct signatures for different regions in the vicinity of high altitude polar cusps, which are identified by using magnetic field and plasma data along spacecraft trajectories. These waves include: (1 Broad band magnetic noise observed in the polar cusp at frequencies from several Hz to ~100 Hz, below the local electron cyclotron frequency, fce. Similar magnetic noise is also observed in the high latitude magnetosheath and the magnetopause boundary layer. (2 Strong broad band electrostatic emissions observed in the cusp, in the magnetosheath, and in the high latitude magnetopause boundary layer, at frequencies extending from several Hz to tens of kHz, with maximum intensities below ~100 Hz. (3 Narrow-band electromagnetic whistler waves at frequencies ~0.20.6 fce, frequently observed in the closed boundary layer (CBL adjacent to the polar cusp. These waves are for the first time observed in this region to be accompanied by counter-streaming electron beams of ~100 eV, which suggests that the waves are excited by these electrons through wave-particle interaction. (4 Narrow-band electrostatic waves observed slightly above the local fce in the CBL. (5 Lion roars, observed in the high latitude magnetosheath, often in magnetic troughs of mirror mode oscillations. The above wave signatures can serve as indicators of the regions in the vicinity of the magnetospheric cusp.

N. Lin

2006-08-01

40

On the possibility of precursors of earthquakes in VLF range observed by DEMETER Satellite  

Science.gov (United States)

Very Low Frequency (VLF) disturbances in the ionospheric electric field observed by DEMETER satellite prior to three different earthquakes that occurred during the years 2008-2009 have been presented. The electromagnetic wave data has been analyzed for few days before the earthquake with special attention to the variation in spectral characteristics and non-linear effects using the statistical and wavelet based techniques. Results indicate that the earthquake preparation process may disturb the ionospheric plasma and these disturbances can reach the non-linear stage leading to the strong variations in the electromagnetic field and plasma parameters. The enhancement in statistical parameters shows the coherent structure and intermittent phenomenon which is the signature of turbulence. The characteristics features of VLF disturbances have further been studied using the wavelet and bispectral analysis tools which provide useful information on the plasma turbulence.

Sondhiya, D. K.; Kumar, S.; Gwal, A. K.

2014-05-01

 
 
 
 
41

"Early/slow'' events : A new category of VLF perturbations observed in relation with sprites  

DEFF Research Database (Denmark)

Analysis of subionospheric VLF transmissions, observed in relation with sprites, has led to the identification of a new category of VLF perturbations caused by the direct effects of tropospheric lightning on the overlying lower ionosphere. They constitute a large subset of the so-called "early/fast'' events where now the term "fast,'' which implies rapid onset durations less than similar to 20 ms, does not apply. In contrast with early/fast, the perturbations have a gradual growth and thus "slow'' onset durations ranging from about 0.5 to 2.5 s; thus these events are labeled herein as "early/slow.'' They are indicative of a new physical process at work which, following a sprite-causative cloud-to-ground discharge, leads to a gradual buildup of conductivity changes in the lower ionosphere which must be responsible for the long onset durations of the observed perturbations. Analysis of broadband VLF sferic recordings, made with a two-channel receiver near the sprite producing storms, shows that the growth phaseof an early/slow event coincides with the occurrence of complex and dynamic lightning action. This is composed of a few sequential cloud-to-ground lightning strokes and clusters (bursts) of sferics which are attributable to intracloud lightning. We postulate that the long onset durations are due to secondary ionization buildup in the upper D region below the nighttime VLF reflection heights, caused mainly by the impact on sprite-produced electrons of sequential electromagnetic pulses radiated upward from horizontal in-cloud discharges.

Haldoupis, C.; Steiner, R.J.

2006-01-01

42

ISEE 1 observations of VLF line radiation in the earth's magnetosphere  

Science.gov (United States)

VLF line radiation in the magnetosphere is analyzed in an attempt to clarify the role of radiation from electric power lines in magnetospheric wave-particle interactions. Observations were made by the ISEE 1 satellite from October 1977 through August 1979 between L = 2 and L = 8 and 50 to 110 deg W longitude, a region encompassing the magnetic field lines linking the Eights, Siple and Roberval stations and in which VLF chorus activity had been linked to power line radiation. Line radiation was detected on 5 of 90 orbits, in all cases at frequencies below 4 kHz. The one event with a high S/N ratio exhibited lines changing frequency at rates from 22 to 6 Hz/min over a 9-min period. The radiation was detected at a time when whistler mode echoing was quite pronounced on lower L shells, and thus may have been a scattered component of line radiation echoing between hemispheres. It is concluded that very little of the background VLF wave energy in the outer magnetosphere is contained in line radiation, although the catalytic role of line radiation in controlling wave-particle interactions remains to be assessed.

Bell, T. F.; Inan, U. S.; Luette, J. P.

1982-05-01

43

The role of upstream ULF waves in the generation of quasi-periodic ELF-VLF emissions  

Directory of Open Access Journals (Sweden)

Full Text Available Recent work suggests that the quasi-periodic (QP modulation ~1050 s of naturally occurring ELF-VLF radio emissions (~0.55 kHz is produced by the compressional action of Pc3 magnetic pulsations on the source of the emissions. Whilst it is generally accepted that these magnetic pulsations have an exogenic source, it is not clear what the mechanism of their generation is. A study of QP emissions observed during 1988 at Halley, Antarctica, in conjunction with IMP-8 satellite solar wind data, shows that the occurrence and modulation frequency of the emissions are strongly dependent upon the direction and strength of the IMF, respectively. The observed relationships are very similar to those previously reported for Pc3 pulsations associated with upstream ion-cyclotron resonance, involving proton beams reflected at the bowshock. In comparing the observed QP modulation frequencies with upstream wave theory, agreement was found by considering wave excitation exclusively associated with a proton beam reflected from a position on the bowshock at which the shock normal is parallel to the ambient IMF direction. Other geometries were found to be either impropitious or uncertain. The work indicates the useful diagnostic role QP emissions could play in the study of compressional ULF waves in the upstream solar wind and in monitoring the IMF conditions responsible for their generation.

K. Morrison

44

VLF observation during Leonid Meteor Shower-2002 from Kolkata  

CERN Document Server

Using a Gyrator-II Loop antenna tuned at 19.0Khz, we monitored the meteor shower during 17-24th November, 2002. We observe the primary peak at 3h58m (UT) on the 19th of November, 2002. We distinctly observed several `beadlike' and `exponentially dropping' signals. The `beadlike' signals were more in abundance on the 18th of November, 2002, one day prior to the actual encounter.

Chakrabarti, S K; Acharyya, K; Mandal, S; Chakrabarti, S; Khan, R; Bose, B; Chakrabarti, Sandip K.

2002-01-01

45

VLF observation during Leonid Meteor Shower-2002 from Kolkata  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using a Gyrator-II Loop antenna tuned at 19.0Khz, we monitored the meteor shower during 17-24th November, 2002. We observe the primary peak at 3h58m (UT) on the 19th of November, 2002. We distinctly observed several `beadlike' and `exponentially dropping' signals. The `beadlike' signals were more in abundance on the 18th of November, 2002, one day prior to the actual encounter.

Chakrabarti, Sandip K.; Pal, S.; Acharyya, K.; Mandal, S.; Chakrabarti, S.; Khan, R.; Bose, B.

2005-01-01

46

Analysis of time-of-arrival observations performed during ELF/VLF wave generation experiments at HAARP  

Science.gov (United States)

Modulated high frequency (HF) heating of the lower ionosphere in the presence of auroral electrojet currents has become an important method for generating electromagnetic waves in the extremely-low frequency (ELF) and very-low frequency (VLF) bands. Recent research efforts focus on improving the efficiency of ELF/VLF wave generation. One method to do so involves the spatial mapping of modulated currents that result from HF heating for comparison with HF heating models. As a first step toward providing a spatial map of the modulated ionospheric currents, we introduce time-of-arrival (TOA) observations performed during a series of experimental research campaigns conducted at the High-frequency Active Auroral Research Program (HAARP) in Gakona, Alaska. The TOA method provides a measurement of the ELF/VLF amplitude and phase detected at a ground-based receiver as a function of time, and this information may be used to estimate the distribution of ELF/VLF source currents within the HF heated region. In an effort to test and improve the TOA method, the University of Florida conducted ELF/VLF wave generation experiments using the HAARP HF transmitter under varying ionospheric conditions and using various transmission formats. In this paper, we summarize our experimental results and compare observations with the predictions of a theoretical model.

Fujimaru, S.; Moore, R. C.

2011-06-01

47

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.

2013-06-17

48

Experimental Observations and Theoretical Modeling of VLF Scattering During LEP Events  

Science.gov (United States)

Recent experimental observations of very low frequency (VLF) scattering during lightning-induced election precipitation (LEP) events are presented. A spread spectrum analysis technique is applied to these observations, demonstrating a significant dependence on frequency. For LEP events, the scattered field amplitude and phase both exhibit strong frequency dependence, as do the event onset delays (relative to the causative lightning flash) and the event onset durations. The experimental observations are compared with the predictions of an Earth-ionosphere waveguide propagation and scattering model. The Long-Wave Propagation Capability (LWPC) code is used to demonstrate that the scattered field amplitude and phase depend sensitively on the electrical properties of the scattering body and the ionosphere between the scatterer and the receiver. The observed frequency-dependent onset times and durations, on the other hand, are attributed to the scattering source characteristics. These measurements can also be used to study radiation belt dynamics.

Mitchell, M. F.; Moore, R. C.

2012-12-01

49

On the occurrence of ground observations of ELF/VLF magnetospheric amplification induced by the HAARP facility  

Science.gov (United States)

The ionospheric heating facility of the High Frequency Active Auroral Research Program (HAARP) has been used extensively in the last 3 years for injection of ELF/VLF waves into the magnetosphere via modulated heating of the overhead auroral electrojet currents. Of particular interest are waves that are observed to be nonlinearly amplified after interaction with hot plasma electrons in the Earth's radiation belts. Past results have shown HAARP to be an effective platform for controlled studies of wave particle interactions in the Earth's magnetosphere. A summary of the experimental results is provided in the context of dependencies on geomagnetic conditions and transmitter parameters. It is deduced that the primary variable that is associated with successful ground observations of HAARP-induced magnetospheric amplification is availability of magnetospheric wave guiding structures. Such structures are found to be most prevalent under quiet geomagnetic conditions following a disturbance when the plasmapause extends to the latitude of the HAARP facility or higher. Strong electrojet currents and high amplitudes of generated ELF/VLF signals observed on the ground are poor indicators of observation probability on a day to day basis although variation of these variables can be important on minute and second timescales. Frequency-time formats with continuously increasing ELF/VLF frequency show preferential amplification as predicted by nonlinear theory of electron trapping. Amplification of signals is also found to be possible for signals with noncoherent bandwidths of up to 30 Hz.

Go?kowski, M.; Cohen, M. B.; Carpenter, D. L.; Inan, U. S.

2011-04-01

50

VLF observations of ionospheric disturbances in association with TLEs from the EuroSprite?2007 campaign  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two Very Low Frequency (VLF) AWESOME remote sensing systems located at Algiers, Algeria (36.45N, 3.28E) and Sebha, Libya (27.02N, 14.26E) monitor VLF signal perturbations for evidence of ionospheric disturbances. During the EuroSprite-2007 campaign a number of Transient Luminous Events (TLEs) were captured over the Mediterranean Sea by cameras at Pic du Midi (42.94N, 0.14E) and at Centre de Recherches Atmosphriques (CRA) in southwestern France (43.13N, 0.37E). The cameras ob...

Naitamor, S.; Alabdoadaim, M. A.; Cohen, M. B.; Cotts, B. R. T.; Soula, S.; Chanrion, Olivier Arnaud; Neubert, Torsten; Abdelatif, T.

2010-01-01

51

Unducted ulf energy from tropical lightning as a possible source of mid-latitude vlf emissions and electron precipitation  

International Nuclear Information System (INIS)

The model of Reeve and Rycroft (1976) for the generation of whistler precursors is shown to be a special case of a mechanism by which energy from tropical lightning may be directed into the plasmasphere so as to be able to resonate with energetic electrons just inside the plasmapause. The results of such a wave--particle interaction would b (1) to trigger VLF emissions which may under certain conditions be received on the ground as apparently spontaneous emissions and (2) to reduce the pitch angle of the resonant electrons, and thus cause them to be precipitated into the atmosphere at the foot of the field line just inside the plasmapause. Such precipitating electrons could significantly contribute, by secondary ionization, to the maintenance of the bottomside ionosphere at night

1976-12-01

52

Assessing global lightning activity with ELF/VLF observations, Schumann resonances and ionospheric potential  

International Nuclear Information System (INIS)

Complete text of publication follows. Global lightning activity is estimated from globally spaced ELF/VLF receivers and used to investigate the dynamics of the global atmospheric electric circuit. ELF/VLF radiation generated by lightning is known to propagate long distances in the Earth ionosphere waveguide, but propagation effects resulting from diurnal ionospheric variations often dominate received amplitudes at a fixed station. Day/night propagation effects thus make meaningful comparison and summation of activity across multiple stations difficult. Exact inversion of the propagation channel is possible only with knowledge of the location of each lightning impulse, a feat unattainable even with current detection networks. In a novel approach, propagation effects are accounted for using established monthly averages of lightning location provided by the Lightning Image Sensor (LIS) and applying known frequency specific attenuation parameters for daytime/nighttime ELF/VLF propagation. The method allows for quantification of daily lightning activity on a global scale using a small number of receiver sites. Obtained curves of daily lightning activity are compared to measurements of atmospheric electric field at mid and polar latitudes and also to lightning activity estimates based on Schumann resonances. For Schumann resonances we utilize a method of field decomposition that separates propagating and standing modes. It is found that in most examined cases daily global lightning activity and the atmospheric electric field are poorly correlated.

2009-08-23

53

Pulsating phenomena of auroral-zone x-rays associated with quasi-periodic VLF emissions and Pc 3 magnetic pulsations  

International Nuclear Information System (INIS)

A stratospheric balloon, carrying a Nal(Tl) scintillation counter for measuring 20 - 100 keV bremsstrahlung x-ray was launched from Stamsund (L = 5.6) in Norway during the recovery phase of a magnetospheric substorm. The scintillation counter recorded x-ray pulsations with periods of 20 - 30 s when the balloon was located at L = 5.4 - 4.8 and at 0950 - 1300 MLT. A rising tone type of quasi-periodic (QP) VLF emissions and Pc 3 magnetic pulsations observed at 160 km northeast of Stamsund, were closely associated with these x-ray pulsations. The one-to-one correspondence between occurrences of QP emissions and enhancements of x-ray count rate suggests that QP emissions (whistler mode waves) modulate the pitch angle diffusion rate of energetic electrons trapped in the magnetosphere through the cyclotron interaction. Further a close relation between QP emissions and Pc 3 magnetic pulsations suggests that compressional mode Pc 3 waves propagating in radial direction from the dayside magnetopause toward the earth modulate the growth rate of whistler mode waves. (author)

1985-01-01

54

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

Energy Technology Data Exchange (ETDEWEB)

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.

Rash, J.P.S.; Scourfield, M.W.J.; Dougherty, M.K. (Natal Univ., Durban (South Africa). Dept. of Physics)

1984-12-01

55

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

Directory of Open Access Journals (Sweden)

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 JuneNovember 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. Hller

2009-10-01

56

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

Directory of Open Access Journals (Sweden)

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 JuneNovember 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. Hller

2009-03-01

57

Plasma waves produced by an ion beam: observations by the VLF experiment on Porcupine  

International Nuclear Information System (INIS)

Results are presented from the VLF electric field experiments flown on Porcupine flights F3 and F4, which also had ejectable xenon ion sources. The xenon ion beam was found to produce plasma instabilities whose frequencies could be linked to the local proton gyrofrequency fsub(cH"+). The main energy in the instabilities lies at approximately 3kHz for events when the Xe"+ source is close to the rocket, and at approximately 7kHz when the source is farther away. Theory predicts that these frequencies should be the lower-hybrid-resonance and this implies that Xe"+ is the dominant ion in the first case and that it is the ambient plasma that dominates later. There is no discernable antenna spin-modulation during the Xe events which indicates that the wave k-vectors are not unidirectional. A theory is cited based on the 'setting up' of the proton cyclotron harmonic waves by the Xe"+ or O"+ cyclotron harmonic waves. The second Xe"+ event on both flights exhibited an, as yet, unexplained harmonic structure related to fsub(cH"+)/2. (Auth.)

1980-04-18

58

Possible production of lower hybrid parametric instabilities by VLF ground transmitter and by natural emissions  

International Nuclear Information System (INIS)

A parametric instability at the lower hybrid frequency which is known as the ion quasi-mode instability may be excited in the ionosphere. The instability considered is a three-wave interaction in which an incident whistler mode wave near the lower hybrid frequency dcays into a lower hybrid wave and an ion acoustic type of oscillation. Threshold calculations are made at intervals along the L = 4 magnetic field line starting at the earth's surface (the geomagnetic position of Siple Station, Antarctica) and proceeding to the equatorial plane. A model is developed for the ionospheric plasma parameters needed to evaluate the expression for threshold field strength. The field directly radiated by the Siple transmitter are not strong enough to meet the requirement for threshold. However, it is possible that the threshold can be met for Siple transmissions which are amplified by natural processes and also for natural emissions

1982-04-01

59

On the ionospheric perturbation associated with the 2007 Niigata Chuetsu-oki earthquake, as seen from subionospheric VLF/LF network observations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In order to investigate any precursory effect of ionospheric perturbations associated with the large 2007 Niigata Chuetsu-oki earthquake (16 July 2007) (magnitude, 6.8), we have made full use of our VLF/LF network observation in Japan by examing the four propagation paths; JJI transmitter (Kyusyu, Ebino)-MSR (Moshiri, Hokkaido), JJY transmitter (Fukushima)-MSR, JJY-KOC (Kochi) and JJI-CBA (Tateyama, Chiba). For the former two paths of JJI-MSR and JJY-MSR, we have observed significant propagat...

Hayakawa, M.; Horie, T.; Yoshida, M.; Kasahara, Y.; Muto, F.; Ohta, K.; Nakamura, T.

2008-01-01

60

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 Pyrnes 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 Mtorage 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

 
 
 
 
61

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 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.

2009-08-23

62

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

63

On the ionospheric perturbation associated with the 2007 Niigata Chuetsu-oki earthquake, as seen from subionospheric VLF/LF network observations  

Directory of Open Access Journals (Sweden)

Full Text Available In order to investigate any precursory effect of ionospheric perturbations associated with the large 2007 Niigata Chuetsu-oki earthquake (16 July 2007 (magnitude, 6.8, we have made full use of our VLF/LF network observation in Japan by examing the four propagation paths; JJI transmitter (Kyusyu, Ebino-MSR (Moshiri, Hokkaido, JJY transmitter (Fukushima-MSR, JJY-KOC (Kochi and JJI-CBA (Tateyama, Chiba. For the former two paths of JJI-MSR and JJY-MSR, we have observed significant propagation anomalies (both a decrease in nighttime average amplitude and an enhancement in nighttime amplitude fluctuation both satisfying the 2? (?: standard deviation criteria on 89 July, about one week before the earthquake. However, the lack of observation for the path from JJY-KOC, has enabled us to make no conclusion for this path. On the other hand, the path from JJI-CBA does not seem to be perturbed. Although this earthquake is very big and shallow, the amount of VLF anomaly for this earthquake is not so pronounced as expected, probably because the epicenter is not unfortunately located within the sensitive areas of any propagation paths. These observational facts suggest that the lower ionosphere above the epicenter is perturbed definitely prior to the earthquake, with radius of a few hundred kilometers.

M. Hayakawa

2008-06-01

64

Observations on GEOS-1 of whistler mode turbulence generated by a ground based VLF transmitter  

DEFF Research Database (Denmark)

Signals launched by the NLK Jim Creek transmitter in Alaska on 18.60 and 18.65 kHz have been observed on GEOS?1. Data for one pass over Alaska on June 11, 1977, are presented here. The peak amplitude of the signals is ?5 pT (0.6 mV/m), which is received when the satellite is close to exact conjugacy at 7500 km altitude. While the weaker signals received at some distance from conjugacy behave as expected from linear theory, the stronger signals received closer to conjugacy have features which indicate that some non?linear process is active. These features are: 1) a turbulent electric frequency spectrum 2) an increased electrostatic character of the waves. The threshold field amplitude of the supposed (but unidentified) non?linear interaction is ?1 pT.

Neubert, Torsten; Lefeuvre, F.

1983-01-01

65

Phase measurements of whistler mode signals from the Siple VLF transmitter  

Science.gov (United States)

A digital signal processing program has been developed to measure the phases of coherent VLF signals from analog tape recordings made in the field. The program uses a constant frequency pilot tone recorded with the VLF data to correct tape speed errors and reconstruct the signal phases. Several examples of whistler mode signals from the VLF transmitter at Siple Station, Antarctica, as received at Roberval, Quebec, are analyzed. Pulses with temporal growth show a relative phase advance with time, and thus a positive frequency offset from the transmitted signal, often from the beginning of the pulse. Amplitude beating is often seen toward the end of a pulse, sometimes with phase cycle-skipping as the emission becomes unlocked from the input signal. Current theories of wave-particle interaction are reviewed and found to explain some of the observed signal features, though no theory predicts the initial frequency offset of a growing pulse.

Paschal, E. W.; Helliwell, R. A.

1984-03-01

66

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

1988-09-01

67

VLF wave emissions by pulsed and DC electron beams in space 2 : Analysis of Spacelab-2 results  

DEFF Research Database (Denmark)

Experiments investigating the generation of radio frequency waves in space plasmas by the injection of artificial electron beams into ionospheric plasmas were conducted in July and August of 1985 on the Spacelab 2 space shuttle mission. Among the results were the production of broadband electromagnetic emissions from continuous and square-wave-modulated, low-power (1-keV, 50/100-mA) electron beams and the observation of narrow-band radiation from pulsed beam operations. Observations from the Spacelab 2 experiments were presented by Reeves et al. (1988b). This paper is a sequel to that earlier work and presents analysis of the observations. Observations of narrow-band radiation are compared with the predictions of a theory of wave generation by pulsed electron beams (Harker and Banks, 1987). Good agreement between observations and predictions is found for the s = 0, root 2 solutions which represent Cherenkov radiation with wave normal angles less than the Gendrin angle. For the broadband emissions, predictionsusing a single-ion, cold plasma theory are compared with the general features observed in the data. Broadband emissions from dc and pulsed electron beams also have features which can be understood in terms of the characteristics of whistler mode waves which are produced by the Cherenkov resonance. All observations were made within the near field of waves in this mode. Waves observed outside the predicted region of propagation are identified as near-field components. Study of wave amplitudes in a coordinate system defined by the orbiter velocity vector indicates the presence of a wake structure behind the beam. Large-amplitude waves observed in the beam and beam-wake regions may include additional, electrostatic contributions to the wave fields. The relative contributions of electromagnetic and electrostatic fields are discussed, and an order of magnitude estimate of the Poynting flux is presented.

Reeves, G.D.; Banks, P.M.

1990-01-01

68

X ray microbursts and VLF chorus  

International Nuclear Information System (INIS)

On January 4, 1978, at 1140 UT, a SuperArcas sounding rocket was launched from Siple Station, Antarctica (L = 4.2, 760S, 840W), during a geomagnetically disturbed period (Kp = 6--) with intense X ray and VLF chorus activity. The parachuted payload observed an intense microburst precipitation event of 10-minute duration. These data have been correlated with measurements of VLF chorus by receivers on the ground at both Siple and its magnetic conjugate point, Roberval, Quebec. Detailed one-to-one correspondence between the microbursts and the chorus was not a consistent feature of the data. Time series analysis of the data did indicate a significant correlation between the Siple X ray precipitation and the Roberval VLF waves with an arrival time delay of 0.1 +- 0.3 seconds

1982-11-01

69

X ray microbursts and VLF chorus  

Energy Technology Data Exchange (ETDEWEB)

On January 4, 1978, at 1140 UT, a SuperArcas sounding rocket was launched from Siple Station, Antarctica (L = 4.2, 76/sup 0/S, 84/sup 0/W), during a geomagnetically disturbed period (Kp = 6--) with intense X ray and VLF chorus activity. The parachuted payload observed an intense microburst precipitation event of 10-minute duration. These data have been correlated with measurements of VLF chorus by receivers on the ground at both Siple and its magnetic conjugate point, Roberval, Quebec. Detailed one-to-one correspondence between the microbursts and the chorus was not a consistent feature of the data. Time series analysis of the data did indicate a significant correlation between the Siple X ray precipitation and the Roberval VLF waves with an arrival time delay of 0.1 +- 0.3 seconds.

Roeder, J.L.; Benbrook, J.R.; Bering E.A. III; Sheldon, W.R.

1982-11-01

70

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 100300 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 60100 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

71

Variations of VLF/LF signals observed on the ground and satellite during a seismic activity in Japan region in MayJune 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 MayJune 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

72

Observations of plasma wave turbulence generated around large ionospheric spacecraft : Effects of motionally induced EMF and of electron beam emission  

DEFF Research Database (Denmark)

We report on observations of plasma wave turbulence generated during electron beam injections, spacecraft potential variations, and neutral gas emissions of the CHARGE 2 sounding rocket experiment. The payload was flown in a mother/daughter configuration, with the two sub-payloads electrically connected by an insulated, conducting tether. While tethered, the two platforms were separated, drifting apart in a direction perpendicular to both the magnetic field and to the spacecraft velocity, reaching a maximum distance of 426 m at the end of the flight. The mother carried a high-voltage (HV) system (0-460 V), biasing the mother negative relative to the daughter. The operation of the HV bias system simulated the motional emf induced in larger orbiting space structures like the Tethered Satellite System 1 (TSS 1) space shuttle mission scheduled for the spring of 1992. In addition, the mother carried an electron beam accelerator (1 keV, 0-46 mA). The daughter diagnostics included wave receivers (400 Hz to 10 MHz) connected to a pair of electric dipole antennas. Broadband ELF/VLF turbulence was generated both during electron beam emissions and when the HV bias system was operated, while turbulence in the HF range was observed only during electron beam emissions. As a result of the electrical connection through the tether, the ELF/VLF wave intensities show little variation with separation distance of the two payloads. Two sources of wave turbulence are proposed to account for the observations: (1) wave turbulence generated by the beam/spacecraft system in particular in the HF range, and (2) electron return currents to the daughter stimulating VLF noise during HV operations and electron beam emissions.

Neubert, Torsten; Sasaki, S.

1991-01-01

73

ELF/VLF wave generation using simultaneous CW and modulated HF heating of the ionosphere  

Science.gov (United States)

Experimental observations of ELF/VLF waves generated using the dual-beam heating capability of the High frequency Active Auroral Research Program (HAARP) HF transmitter in Gakona, Alaska, are compared with the predictions of an ionospheric HF heating model that accounts for the simultaneous propagation and absorption of multiple HF beams. The model output is used to assess three properties of the ELF/VLF waves observed on the ground: the ELF/VLF signal magnitude, the ELF/VLF harmonic ratio, and the ELF/VLF power law exponent. Ground-based experimental observations indicate that simultaneous heating of the ionosphere by a CW HF wave and a modulated HF wave generates significantly lower ELF/VLF magnitudes than during periods without CW heating, consistent with model predictions. Further modeling predictions demonstrate the sensitive dependence of ELF/VLF magnitude on the frequency and power of the CW signal. The ratio of ELF/VLF harmonic magnitudes is also shown to be a sensitive indicator of ionospheric modification, although it is somewhat less sensitive than the ELF/VLF magnitude. Last, the peak power level of the modulated HF beam was varied in order to assess the power dependence of ELF/VLF wave generation under both single- and dual-beam heating conditions. Experimental and theoretical results indicate that accurate evaluation of the ELF/VLF power law index requires high signal-to-noise ratio; it is thus a less sensitive indicator of ionospheric modification than either ELF/VLF magnitude or the ELF/VLF harmonic ratio.

Moore, R. C.; Agrawal, D.

2011-04-01

74

Quantitative measurements of LEP events using subionospheric VLF remote sensing  

Science.gov (United States)

Comparison of VLF experimental observations of LEP events with a comprehensive model of lightning-induced electron precipitation and the resulting ionospheric disturbance allows the measurement of such events with unprecedented quantitative detail. We examine the use of VLF remote sensing to quantitatively measure the precipitating flux associated with two representative LEP events. Observations of VLF signal perturbations recorded on the Holographic Array for Ionospheric/Lightning Research (HAIL) are interpreted using a comprehensive model of lightning-induced electron precipitation. The model consists of three major components: a test-particle model of the gyroresonant whistler-induced electron precipitation [Borntik et al., 2006]; a Monte Carlo simulation of the energy deposition into the ionosphere resulting from the calculated precipitation flux [Lehtinen, 2001]; and a model of VLF subionospheric signal propagation that takes into account the disturbed ionospheric density profiles [Chevalier and Inan, 2006]. For both cases, the model predicts VLF signal amplitude and phase perturbations within a factor of three of those observed, within the expected variability in trapped energetic flux levels. The modeled, precipitated energy flux (E>45 keV) peaks at ~110-2 [ergs s-1 cm-2], resulting in a peak loss of ~0.001% from a single flux tube at L~2.2, consistent with previous satellite measurements of LEP events [Voss et al., 1998]. A metric for quantitative interpretation of VLF signal perturbations in terms of precipitated electron flux is presented. A conversion metric ?, relating VLF signal amplitude perturbations to the time-integrated precipitation flux (100-300 keV) along the VLF signal path, of 1.10.21010 [el m-1/dB] is suggested for precipitation events of similar location and characteristics to the events examined in this work. Preliminary work on the occurrence rates of LEP events is also presented.

Peter, W.; Inan, U.

2006-12-01

75

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 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

1975-11-01

76

EXOS-B/Siple station VLF wave-particle interaction experiments. I - General description and wave-particle correlations  

Science.gov (United States)

The EXOS-B/Siple Station joint experiment on the triggering of VLF emissions by man-made signals causing some form of wave-particle interactions in the magnetosphere is presented, and results concerning wave-particle correlations are reported. In situ measurements of both energetic electron flux and VLF waves were made near the meridian connecting Siple Station, Antarctica with Roberval, Quebec, Canada in campaigns during July through September, 1979 and December 1979 through January 1980 at times of VLF transmission from Siple. Strong observed signals were found to be well correlated with a pancake pitch angle distribution of 0.3 to 6.9-keV electrons, and to exhibit a positive linear growth rate. Artificially stimulated emissions were observed to be accompanied by large electron fluxes in all energy channels in the equatorial interaction region, although the measured pitch angle distribution was not highly anisotropic. Results may be interpreted by the amplification of Siple signals by the cyclotron instability due to high pitch angle anisotropy (pancake distribution) and the triggering of emissions in the presence of high electron fluxes with some anisotropy and a sufficiently strong signal.

Kimura, I.; Hashimoto, K.; Matsumoto, H.; Mukai, T.; Bell, T. F.; Inan, U. S.; Helliwell, R. A.; Katsufrakis, J. P.

1983-01-01

77

Observational Evaluation of Mobile Source Emissions  

Science.gov (United States)

Ambient ratios of NOx, CO, and CO2 sampled by aircraft in Houston and Dallas during the 2000 and 2006 Texas Air Quality Study (TexAQS) are compared with each other and with observations at a Houston highway tunnel. From these measurements we estimate 2000 and 2006 emissions for Houston and Dallas mobile sources. The observations demonstrate time-of-day variations in the relative contributions from gasoline and diesel combustion which are consistent with known traffic patterns. We incorporate CO2 emissions derived from the Federal Highway Administration's motor vehicle fuel use statistics into the EPA's National Emission Inventory (NEI), resulting in an emission data set for NOx, CO, and CO2 with 4-km spatial and hourly temporal resolution. Comparison of the emission ratios derived from the TexAQS observations with this inventory allows a direct evaluation of the NEI mobile source NOx and CO emissions.

Frost, G. J.; McKeen, S.; Trainer, M.; Aikin, K.; Peischl, J.; Ryerson, T.; Holloway, J.; Petron, G.; Tans, P.; Harley, R.

2007-12-01

78

Siple Station, Antarctica, Statistics of Magnetospheric ELF/VLF Wave Growth  

Science.gov (United States)

Controlled experiments with ground-based ELF/VLF transmitters have proven invaluable in studying the interactions between whistler waves and energetic electrons in the radiation belts. These gyrosesonant interactions result in wave growth and nonlinear triggered emissions that can be observed both at the geomagnetic conjugate point after reflection and a second interhemispheric crossing. Most notably, the Siple Station transmitter in Antarctica at L=4.6, which operated at 0.5-5 kHz from 1973-1988, provided a wealth of examples that still have not been analyzed on a large scale. In 15 years of experiments, Siple Station transmitted a broad array of frequency-time formats, including tones, ramps, tone doublets, and chirps, under a variety of geomagnetic conditions. To enable more thorough and longer-term studies, data are now being digitized in mass from magnetic tapes, with additional processing to remove artifacts of the recording and digitization. We present initial statistics on the occurrence of amplified ELF/VLF waves at the conjugate location to Siple, Roberval, Quebec, and the signal near Siple Station after a second interhemispheric crossing. Using the transmitted tones and ramps, we analyze the correlation of the growth rates of ELF/VLF waves injected at Siple Station and the L-shells of the propagation paths with geomagnetic parameters (kp, ae, etc).

Li, J.; Cohen, M.; Harid, V.; Spasojevic, M.; Papon, J.; Carpenter, D.; Inan, U. S.

2011-12-01

79

Higher harmonic tweek sferics observed at low latitude: estimation of VLF reflection heights and tweek propagation distance  

Directory of Open Access Journals (Sweden)

Full Text Available Lightning generated signals recorded at a low-latitude station, Suva (18.2 S, 178.3 E Fiji, in the South Pacific region, during September 2003July 2004, are used to study the propagation features and the reflection heights of tweek atmospherics in the waveguide formed by the Earth's surface and the lower ionosphere. Tweeks are observed only during the local night and the maximum harmonic (n recorded is six. The occurrence of tweeks with higher n progressively decreases as n increases. The dispersed part of tweeks decreases as n increases. The attenuation factor has been calculated for tweeks with n=13. The ionospheric reflection heights obtained assuming the transverse magnetic mode of propagation for tweek signals vary from 8392 km. A higher harmonic of the same tweek is reflected from about 2.0 km higher than the lower harmonic. For 90% of tweeks, propagation distances are estimated to be between 10005000 km. Tweeks with lower n propagate longer distances than the tweeks with higher n.

S. Kumar

2008-06-01

80

X-ray microbursts and VLF chorus  

Science.gov (United States)

On January 4, 1978, at 1140 UT, a Super Arcas sounding rocket was launched from Siple Station, Antarctica (L = 4.2, 76 S, 84 W) during a geomagnetically disturbed period (K sub p = 6-) with intense X-ray and VLF chorus activity. The parachuted payload observed an intense microburst precipitation event of 10 minute duration. These data have been correlated with measurements of Very Low Frequency chorus by receivers on the ground at both Siple and its magnetic conjugate point, Roberval, Quebec. Detailed one-to-one correspondence between the microbursts and the chorus was not a consistent feature of the data. Time series analysis of the data did indicate a significant correlation between the Siple X-ray precipitation and the Roberval VLF waves with an arrival time delay of 0.1 + or - 0.

Roeder, J. L.; Benbrook, J. R.; Bering, E. A.; Sheldon, W. R.; Stansberry, E. G.

1985-09-01

 
 
 
 
81

X ray microbursts and VLF chorus  

Science.gov (United States)

On January 4, 1978, at 1140 UT, a SuperArcas sounding rocket was launched from Siple Station, Antarctica (L = 4.2, 76 deg S, 84 deg W), during a geomagnetically disturbed period (Kp = 6-) with intense X-ray and VLF chorus activity. The parachuted payload observed an intense microburst precipitation event of 10-minute duration. These data have been correlated with measurements of FLF chorus by receivers on the ground at both Siple and its magnetic conjugate point, Roberval, Quebec. Detailed one-to-one correspondence between the microbursts and the chorus was not a consistent feature of the data. Time series analysis fo the data did indicate a significant correlation between the Siple X-ray precipitation and the Roberval VLF waves with an arrival time delay of 0.1 + or 0.3.

Roeder, J. L.; Benbrook, J. R.; Bering, E. A., III; Sheldon, W. R.

1985-11-01

82

Quantifying Methane Emissions Using Satellite Observations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Methane is the second most influential anthropogenic greenhouse gas. There are large uncertainties in the magnitudes and trends of methane emissions from different source types and source regions. Satellite observations of methane offer dense spatial coverage unachievable by suborbital observations. This thesis evaluates the capabilities of using satellite observations of atmospheric methane to provide high-resolution constraints on continental scale methane emissions. In doing so, I seek to ...

Wecht, Kevin James

2013-01-01

83

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 MayJune 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 p...

Rozhnoi, A.; Solovieva, M.; Molchanov, O.; -f Biagi, P.; Hayakawa, M.; Schwingenschuh, K.; Boudjada, M.; Parrot, M.

2010-01-01

84

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 spinning dust and is consistent with spinning dust contributing 0.4 0.1 of the Galactic plane emission at 23 GHz.

2011-06-10

85

Optimizing an ELF/VLF Phased Array at HAARP  

Science.gov (United States)

The goal of this study is to maximize the amplitude of 1-5 kHz ELF/VLF waves generated by ionospheric HF heating and measured at a ground-based ELF/VLF receiver. The optimization makes use of experimental observations performed during ELF/VLF wave generation experiments at the High-frequency Active Auroral Research Program (HAARP) Observatory in Gakona, Alaska. During these experiments, the amplitude, phase, and propagation delay of the ELF/VLF waves were carefully measured. The HF beam was aimed at 15 degrees zenith angle in 8 different azimuthal directions, equally spaced in a circle, while broadcasting a 3.25 MHz (X-mode) signal that was amplitude modulated (square wave) with a linear frequency-time chirp between 1 and 5 kHz. The experimental observations are used to provide reference amplitudes, phases, and propagation delays for ELF/VLF waves generated at these specific locations. The presented optimization accounts for the trade-off between duty cycle, heated area, and the distributed nature of the source region in order to construct a "most efficient" phased array. The amplitudes and phases generated by modulated heating at each location are combined in post-processing to find an optimal combination of duty cycle, heating location, and heating order.

Fujimaru, S.; Moore, R. C.

2013-12-01

86

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

Science.gov (United States)

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.

Helliwell, R. A.; Katsufrakis, J. P.; Bell, T. F.; Raghuram, R.

1975-01-01

87

Observations of interstellar molecular hydrogen emission  

International Nuclear Information System (INIS)

A search for interstellar molecular hydrogen emission, as seen in the v = 1 ? 0 S(1) line, is presented. Seven objects show emission from vibrationally excited H2. Of the seven new sources, six are associated with planetary nebulae and one is associated with T Tauri. By considering the current theories of H2 excitation and comparing the emission line intensities from the new sources with the upper limits to emission from nine HII regions, it is concluded that excitation of the molecules originates in the boundary layers of strong shock waves. The new sources provide a basis for further study of interstellar H2 emission, planetary nebulae, and T Tauri stars. An in-depth study of the molecular hydrogen emission from the Orion nebula is presented. Intensity measurements of the v = 1 ? 0 S(0), S(1), S(2), and Q(3) transitions and the v = 2 ? 1 S(1) transition are used to derive a vibrational temperature of 2000 K +- 300 K and the associated column densities at the two emission peaks. Measurements of the v = 1 ? 0 Q(3)/S(1) intensity ratio are given. Comparison of this ratio with that observed in NGC 7027 leads to a 2.1 ? m extinction of 4.5 magnitudes to the emission region in Orion. A measurement of the Q(4)/S(2) intensity ratio gives a similar value. The extinction implies that the emission region inside the molecular cloud and probably near the BN/KL infrared cluster. The resultant rotational and vibrtional temperatures of H2 are found to be equal within the uncertainties. The measurements of Orion strongly imply that the vibrationally excited molecular hydrogen exists behind the discontinuity of a strong shock wave. A rough estimate of the energy involved in the shock indicates that no observed object in Orion could drive the shock. The results lend support to the suggestion that a supernova explosion occurred within the molecular cloud several thousand years ago

1978-01-01

88

Time-of-arrival analysis applied to ELF/VLF wave generation experiments at HAARP  

Science.gov (United States)

Time-of-arrival (TOA) analysis is applied to observations performed during ELF/VLF wave generation experiments at the High-frequency Active Auroral Research Program (HAARP) HF transmitter in Gakona, Alaska. In 2012, a variety of ELF/VLF wave generation techniques were employed to identify the dominant source altitude for each case. Observations were performed for beat-wave modulation, AM modulation, STF modulation, ICD modulation, and cubic frequency modulation, among others. For each of these cases, we identify the dominant ELF/VLF source altitude and compare the experimental results with theoretical HF heating predictions.

Moore, R. C.; Fujimaru, S.

2012-12-01

89

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

90

Airborne observations of the infrared emission bands  

International Nuclear Information System (INIS)

Low resolution airborne spectra from 5 to 8 ?m are now available for a sample of 40 sources selected from the IRAS LRS Atlas with PAH emission features. A new emission band at 5.2 ?m, previously predicted for PAHs, has been found in 33 sources; it also correlates with the 7.7 ?m band. This extends the generic spectrum of narrow observed PAH features to 3.3, 5.2, 5.6, 6.2, 6.9, 7.7, 8.7, 11.3, and 12.7 ?m. From this sizeable sample of sources we define the relative strengths of most of these bands in three separate nebular environments: planetaries, HII regions, and reflection nebulae. There are significant differences in the generic spectra of PAHs in these different environments, particularly in the ratio of I (6.2)/I (7.7) and in the actual wavelength of the strong 7.7 ?m peak. New observations of southern nebulae, including the unusually carbon-rich [WC10] planetary nuclei and the apparently oxygen-rich object, NGC 6302, broadens the range of C/O over which we detect PAH features to 0.2-4.8. The addition of these planetaries strengthens our earlier claim that the fraction of total emission observed by IRAS that is carried by PAH emission is correlated with nebular gas-phase C/O ratio. The [WC10] nuclei also exhibit a strong plateau of emission linking the 6.2 and 7.7 ?m features

1989-09-01

91

Observations of Diffuse Ultraviolet Emission from Draco  

CERN Document Server

We have studied small scale (2 arcmin) spatial variation of the diffuse UV radiation using a set of 11 GALEX deep observations in the constellation of Draco. We find a good correlation between the observed UV background and the IR 100 micron flux, indicating that the dominant contributor of the diffuse background in the field is the scattered starlight from the interstellar dust grains. We also find strong evidence of additional emission in the FUV band which is absent in the NUV band. This is most likely due to Lyman band emission from molecular hydrogen in a ridge of dust running through the field and to line emissions from species such as C IV (1550 A) and Si II (1533 A) in the rest of the field. A strong correlation exists between the FUV/NUV ratio and the FUV intensity in the excess emission regions in the FUV band irrespective of the optical depth of the region. The optical depth increases more rapidly in the UV than the IR and we find that the UV/IR ratio drops off exponentially with increasing IR due ...

Sujatha, N V; Suresh, Rahul; Henry, Richard Conn; Bianchi, Luciana

2010-01-01

92

Associated ground-based observations of optical aurorae and discrete whistler waves  

International Nuclear Information System (INIS)

Discrete VLF wave emissions in association with auroral light intensity fluctuations have been recorded at L = 4 during simultaneous operation of a broadband VLF receiver and a low light level TV system. The correlated wave-particle interaction events are interpreted as being typical examples of the electron cyclotron resonance process responsible for the precipitation of energetic electrons in the vicinity of the plasmapause. A range of delay times between the correlated VLF wave and the optical signals, coupled with the frequency versus time characteristics of the VLF wave emissions, is consistent with the electron cyclotron source region being randomly located within 8,000 km of the equatorial plane. The events are shown to be triggered by ducted whistler mode waves that originate from the opposite hemisphere to that of the station at which the observations are made. Events characterized by VLF waves of rising tone are presumed to occur in a region of enhanced plasma density commonly observed within the plasma trough. It is proposed that this region is responsible for ducting the VLF waves from the source to ground

1990-01-01

93

TOA Analysis Applied to Improve ELF/VLF Wave Generation Efficiency at HAARP  

Science.gov (United States)

Time-of-arrival (TOA) analysis is applied to observations performed during ELF/VLF wave generation experiments at the High-frequency Active Auroral Research Program (HAARP) HF transmitter in Gakona, Alaska. Geometric modulation is used together with a variable pulse length modulation format to determine the ideal arc length maximizing the ELF/VLF signal magnitude observed on the ground. Observations indicate that the ELF/VLF signal magnitude increases with arc length to a certain extent, after which the magnitude decreases. The end result is that an optimal arc length is identified, maximizing ELF/VLF signal magnitude and minimizing the HF power required to produce that magnitude. A standard frequency analysis is presented together with the TOA analysis to provide a complete context for the experimental results.

Fujimaru, S.; Moore, R. C.

2011-12-01

94

Airborne observations of the infrared emission bands  

Science.gov (United States)

Earlier airborne studies of the infrared bands between 5 and 8 microns have now been extended to a sample of southern sources selected from the IRAS Low Resolution Spectra (LRS) atlas. The correlation between the strongest bands at 6.2 and 7.7 microns is now based on a total sample of 40 sources and is very strong. A new emission band at 5.2 microns, previously predicted for polycyclic aromatic hydrocarbons (PAHs), is recognized in 27 sources; it too correlates with the dominant 7.7 micron band, showing that the 5.2 micron feature also belongs to the generic spectrum of PAH features at 3.3, 5.6, 6.2, 6.2, 7.7, 8.7, 11.3, and 12.7 microns. Sufficient sources are had now to define the relative strengths of most of these bands in three separate nebular environments: planetaries, H II regions, and reflection nebulae. Significant variations are detected in the generic spectra of PAHs in these different environments which are echoed by variations in the exact wavelength of the strong 7.7 micron peak. The earlier suggestion that, in planetaries, the fraction of total emission observed by IRAS that is carried by the PAH emissions is correlated with nebular gas-phase C/O ratio is supported by the addition of newly-observed southern planetaries, including the unusually carbon-rich (WC10) nebular nuclei. These (WC10) nuclei also exhibit a strong plateau of emission linking the 6.2 and 7.7 micron features.

Cohen, M.; Wooden, Diane; Tielens, Alexander G. G. M.; Bregman, Jesse D.; Witteborn, Fred C.; Rank, D.; Allamandola, Louis J.

1989-01-01

95

Airborne observations of the infrared emission bands  

International Nuclear Information System (INIS)

Earlier airborne studies of the infrared bands between 5 and 8 microns have now been extended to a sample of southern sources selected from the IRAS Low Resolution Spectra (LRS) atlas. The correlation between the strongest bands at 6.2 and 7.7 microns is now based on a total sample of 40 sources and is very strong. A new emission band at 5.2 microns, previously predicted for polycyclic aromatic hydrocarbons (PAHs), is recognized in 27 sources; it too correlates with the dominant 7.7 micron band, showing that the 5.2 micron feature also belongs to the generic spectrum of PAH features at 3.3, 5.6, 6.2, 6.2, 7.7, 8.7, 11.3, and 12.7 microns. Sufficient sources are had now to define the relative strengths of most of these bands in three separate nebular environments: planetaries, H II regions, and reflection nebulae. Significant variations are detected in the generic spectra of PAHs in these different environments which are echoed by variations in the exact wavelength of the strong 7.7 micron peak. The earlier suggestion that, in planetaries, the fraction of total emission observed by IRAS that is carried by the PAH emissions is correlated with nebular gas-phase C/O ratio is supported by the addition of newly-observed southern planetaries, including the unusually carbon-rich (WC10) nebular nuclei. These (WC10) nuclei also exhibit a strong plateau of emission linking the 6.2 and 7.7 micron features

1989-12-01

96

Electron precipitation induced by VLF noise bursts at the plasmapause and detected at conjugate ground stations  

Science.gov (United States)

The observation of precipitation-induced amplitude perturbations in subionospherically propagating fixed-frequency VLF signals is considered. Simultaneous broadband VLF recordings (on magnetic tape in analog form) were made at Siple, Antarctica, and at its magnetic conjugate Roberval, Quebec, on September 11, 1973. These stations detected a series of approximately 20 VLF noise bursts and correlated amplitude perturbations of 17.8-kHz signals from the U.S. Navy VLF transmitter NAA (Cutler, ME). The noise bursts were found to occur at intervals of roughly 5 min over a several-hour period. Examples of individual bursts are shown. Two basic wave structures were observed, including a main body of each burst and, in some cases, a precursor noise band.

Dingle, B.; Carpenter, D. L.

1981-06-01

97

Whistler propagation in ionospheric density ducts: Simulations and DEMETER observations  

Science.gov (United States)

On 16 October 2009, the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite observed VLF whistler wave activity coincident with an ionospheric heating experiment conducted at HAARP. At the same time, density measurements by DEMETER indicate the presence of multiple field-aligned enhancements. Using an electron MHD model, we show that the distribution of VLF power observed by DEMETER is consistent with the propagation of whistlers from the heating region inside the observed density enhancements. We also discuss other interesting features of this event, including coupling of the lower hybrid and whistler modes, whistler trapping in artificial density ducts, and the interference of whistlers waves from two adjacent ducts.

Woodroffe, J. R.; Streltsov, A. V.; Vartanyan, A.; Milikh, G. M.

2013-11-01

98

Analysis of magnetospheric ELF/VLF wave amplification from the Siple Transmitter experiment  

Science.gov (United States)

Controlled experiments with dedicated ground-based ELF/VLF (0.3-30 kHz) transmitters are invaluable in investigating nonlinear whistler mode wave-particle interactions in the Earth's magnetosphere. The most productive such experiment operated between 1973 and 1988 near L=4 at Siple Station, Antarctica. A major effort has been undertaken to digitize and preserve a significant portion of the historical data set from the original magnetic tapes, and we describe here the data set and the processing techniques used to remove artifacts introduced during recording and playback. We analyze a commonly transmitted diagnostic format from 1986 and present statistics on the occurrence and properties of amplified ELF/VLF waves received by a ground-based receiver at the geomagnetic conjugate location to Siple at Lake Mistissini, Quebec. For the interval examined, only 11% of Siple transmissions are successfully received in the conjugate hemisphere with quiet geomagnetic conditions being significantly more conducive to successful reception. The total growth for the events examined is estimated to be 5-40 dB, and nonlinear growth rates are in the range of 20-350 dB/s. The observations show that as the nonlinear growth rate increases, the duration of nonlinear growth decreases. Significant linear correlation is found between the noise floor and the saturation level, with higher noise floors resulting from increases in natural magnetospheric emissions. Finally, we find a lack of correlation between the nonlinear growth rate and the noise, threshold, and saturation levels.

Li, J. D.; Spasojevic, M.; Harid, V.; Cohen, M. B.; Go?kowski, M.; Inan, U.

2014-03-01

99

Cassini CIRS Observations of Iapetus' Thermal Emission  

Science.gov (United States)

Cassini s Composite Infrared Spectrometer (CIRS, [1]) mapped Iapetus thermal emission from 7 to approx.300 microns during the spacecraft s December 31st 2004 flyby of the satellite. Short-wavelength spectra were obtained with the CIRS "FP3" (10 - 17 micron) and "FP4" (7 - 10 micron) detector arrays, each consisting of 1 x 10 pixels with a spatial resolution of 0.29 milliradians, while longer wavelength observations used the "FP1" detector, with a single-aperture detector with 4 milliradian diameter. The detectors are scanned across the target to build up an image cube with two spatial dimensions and one spectral dimension. CIRS daytime observations covered the dark terrain of Cassini Regio, except for high northern latitudes which were occupied by bright terrain, while nighttime observations covered a mixture of bright and dark terrain. The 120,000 km flyby distance provided a maximum spatial resolution of 35 km in the FP3 and FP4 detectors, and 500 km in the FP1 detector.

Spencer, J. R.; Pearl, J. C.; Segura, M.

2005-01-01

100

Constraining CO emission estimates using atmospheric observations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

2012-01-01

 
 
 
 
101

Non detection of lightning signature in the Huygens RLF_VLF data  

Science.gov (United States)

Long before Huygens landed on Titan, none of the two Voyager flybys had revealed any impulsive electromagnetic emission from Titan and the question of a possible lightning activity and related biochemistry reactions remained open. However, the modelling of the ionospheric altitude profile predicted the existence of multiple layers. The upper ones, induced by photons and precipitated energetic electrons were crossed by Cassini during its closest flybys, whereas the lower ionosphere, produced by galactic cosmic rays, was detected in situ during the descent of the Huygens probe. One of the main objectives of the Permittivity, Waves and Altimetry (PWA) experiment, a part of the Huygens Atmospheric Structure Instrument (HASI), was to measure in situ the electron and ion densities in the lower ionosphere with two different and overlapping techniques, a mutual impedance probe (MIP) and a relaxation probe (RP). MIP consists of a transmitting dipole that injects a known sinusoidal current in the medium and of a receiving dipole that measures the induced potential. The latter also measured the natural electromagnetic waves confined within the ionospheric cavity that could not be detected by the Voyager spacecraft, nor by Cassini. The two relevant frequency domains are the ELF range (~10-100 Hz), for the global Schumann resonance and its harmonics, and the VLF range (1-10 kHz), for the transverse resonances (tweeks). Average energy spectra were computed on board and telemetered to ground. The wideband electric receiver revealed the steady presence of an intense emission at 36 Hz throughout the descent, shown in fig. 1 that was reminiscent of a Schumann resonance [3,10]. The 36 Hz emission and its production mechanism was the subject of numerous investigations by the PWA team (see [1] and a companion presentation by Bghin et al., in GP3 Session ESPC-DPS2011- 194). No particular emission was observed in the VLF range. Another team of scientists led by J. Morente revisited the PWA data set and expressed a somewhat different opinion (see [5-7] for ELF and [4.8.9] for VLF). They claimed that these measurements carried the indication of a multitude of resonances and harmonics, thus irrefutably proving the existence of lightning activity on Titan. It can however be demonstrated that their interpretation is based on artefacts generated by an improper analysis of the data.

Hamelin, M.; Grard, R.; Bghin, C.; Berthelier, J. J.; Lopez-Moreno, J. J.; Simes, F.

2011-10-01

102

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

103

ELF and VLF activity associated with high latitude hole  

International Nuclear Information System (INIS)

Based upon observations from a series of polar orbiting OGO satellites, the properties and structure of a 'high latitude trough or hole' (HLT) or (HLH) in the topside ionosphere are summarized and correlated with the following terms, specifically in relation to ELF and VLF activity: (1) distinction from the midlatitude light ion trough (LIT) in H+ associated with the plasmapause; (2) a narrow, abrupt depletion in the concentrations of atomic ions H+, He+, O+, and N+; (3) molecular ion enhancements in NO+, O2+, and N2+; (4) the > 30 keV electron trapping boundary; (5) the > 30 keV electron precipitation; (6) the electric field reversal; (7) the convective flow reversal; (8) the polar cap boundary. These observations are often well correlated with ELF and VLF activity, exhibiting enhancements in broadband auroral hiss, ELF noise and/or auroral kilometric radiation in the HLH region. (Auth.)

1978-08-08

104

Ogo 5 observations of LHR noise, emissions, and whistlers near the plasmapause at several earth radii during a large magnetic storm.  

Science.gov (United States)

On May 15, 1969, Ogo 5 crossed the plasmapause during a major storm that produced severe geomagnetic disturbances (Kp up to 8-), large and rapid variations in ring-current intensity (as measured by Dst), intense low-latitude aurora, and persistent SAR arcs. Near the highly structured plasmasphere boundary, the electric- and magnetic-field sensors on Ogo 5 detected lower-hybrid-resonance noise bursts, whistlers, ELF hiss, and other discrete signals or emissions. Some LHR noise bursts were associated with whistlers, and these high-altitude phenomena resembled the corresponding ionospheric ones. This report contains a description of the VLF observations. We also show that intense ULF magnetic signals were present near the plasmapause, and we attempt to relate these observations to the predictions of various theories of proton ring-current decay and SAR-arc formation.

Scarf, F. L.; Fredricks, R. W.; Smith, E. J.; Frandsen, A. M. A.; Serbu, G. P.

1972-01-01

105

Full-wave modeling of transionospheric propagation of VLF waves  

Science.gov (United States)

The full-wave method (FWM) of N. G. Lehtinen and U. S. Inan (2008) is used to model trans-ionospheric propagation of VLF electromagnetic waves from ground-based transmitters up to satellite altitudes. Direct comparison with satellite observations indicates that the VLF wave intensities measured at satellite altitudes are substantially smaller than predicted. The apparent reduction in amplitude is attributed to the presence of irregularities in the ionosphere, which the waves encounter during their traversal of the lower ionosphere. Linear mode scattering from the irregularities convert the whistler waves into quasi-electrostatic whistler mode (QEWM) waves with wave normal angles near the resonance cone. Recent enhancements to the FWM are also described, which allow the minimization of an aliasing error encountered in taking the inverse Fourier transform.

Lehtinen, Nikolai G.; Inan, Umran S.

2009-02-01

106

The stopping time of the ULF/VLF wave and energetic (  

Science.gov (United States)

An elaboration of the Demeter observations made in the topside ionosphere above Greece reveals the following constrains with the great (M?6.4) earthquakes (EQs) occurred in the Greek territory: (1) ULF/VLF wave and electron precipitation (EP) activity was recorded by DEMETER for some days before the earthquake occurrence time, (2) all three phenomena (ULF/VLF/EP) ceased a few hours before all the Greek earthquakes. Therefore, we infer that the satellite observations above Greece during the period 2005-2010 are consistent with the stopping time of ULF/VLF/EP activity as a short time (few hours) earthquake predictor. These results for Greek EQs are in agreement with statistical results from an examination of the ULF/VLF/EP variations observed by DEMETER before the majority of the great (M?7) earthquakes occurred worldwide, during the same period (2005-2010). Precise statistical results of the ULF/VLF/EP beginning and stopping times before the M?7 before EQs are also presented in this work.

Anagnostopoulos, George; Athanasiou, Michael; Vassiliadis, Basil; Karli, Anna; Fotinopoulos, Stavros

2014-05-01

107

Simultaneous observations of electric field changes, wideband magnetic field pulses, and VHF emissions associated with K processes in lightning discharges  

Science.gov (United States)

studied simultaneous electric field changes, microsecond-scale (VLF/LF) magnetic field pulses, and VHF emissions associated with K processes in 37 cloud and 54 cloud-to-ground lightning flashes that occurred in a local convective thunderstorm in Shanghai. All the observed features were very similar for both types of flashes. Over 98% of the 1252 observed K changes were associated with detectable microsecond-scale pulses, although only about 26% of them were accompanied by large pulses whose amplitude exceeds by at least 50% the average amplitude of the five largest pulses in the flash. VHF bursts, which almost always coincide in time with microsecond-scale pulses, can occur either during K changes or during the gaps between K changes. About 9% of K changes were observed to be associated with regular pulse trains, with pulses in the train showing one-to-one correspondence to VHF bursts and occurring at a geometric mean interval of 6.9 s. Overall, our results indicate that small microsecond-scale pulses are an inherent feature of K processes. We infer that the K process can be viewed as a fast negative leader, but only those leaders with appreciable charge transfer show step/ramp-like K changes in electric field records.

Zhu, Baoyou; Zhou, Helin; Thottappillil, Rajeev; Rakov, Vladimir A.

2014-03-01

108

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 species

1994-07-24

109

Mg+ and other metallic emissions observed in the thermosphere  

Energy Technology Data Exchange (ETDEWEB)

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 deg. 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 propagation 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 species.

Gardner, J.A.; Viereck, R.A.; Murad, E.; Lai, S.T.; Knecht, D.J.

1994-11-17

110

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Kasahara, Y.; Muto, F.; Horie, T.; Yoshida, M.; Hayakawa, M.; Ohta, K.; Rozhnoi, A.; Solovieva, M.; Molchanov, O. A.

2008-01-01

111

100 Days of ELF/VLF Generation via HF Heating with HAARP (Invited)  

Science.gov (United States)

ELF/VLF radio waves are difficult to generate with conventional antennas. Ionospheric HF heating facilities generate ELF/VLF waves via modulated heating of the lower ionosphere. HF heating of the ionosphere changes the lower ionospheric conductivity, which in the presence of natural currents such as the auroral electrojet, creates an antenna in the sky when heating is modulated at ELF/VLF frequencies. We present a summary of nearly 100 days of ELF/VLF wave generation experiments at the 3.6 MW HAARP facility near Gakona, Alaska, and provide a baseline reference of ELF/VLF generation capabilities with HF heating. Between February 2007 and August 2008, HAARP was operated on close to 100 days for ELF/VLF wave generation experiments, at a variety of ELF/VLF frequencies, seasons and times of day. We present comprehensive statistics of generated ELF/VLF magnetic fields observed at a nearby site, in the 500-3500 Hz band. Transmissions with a specific HF beam configuration (3.25 MHz, vertical beam, amplitude modulation) are isolated so the data comparison is self-consistent, across nearly 5 million individual measurements of either a tone or a piece of a frequency-time ramp. There is a minimum in the average generation close to local midnight. It is found that generation during local nighttime is on average weaker, but more highly variable, with a small number of very strong generation periods. Signal amplitudes from day to day may vary by as much as 20-30 dB. Generation strengthens by ~5 dB during the first ~30 minutes of transmission, which may be a signature of slow electron density changes from sustained HF heating. Theoretical calculations are made to relate the amplitude observed to the power injected into the waveguide and reaching 250 km. The median power generated by HAARP and injected into the waveguide is ~0.05-0.1 W in this base-line configuration (vertical beam, 3.25 MHz, amplitude modulation), but may have generated hundreds of Watts for brief durations. Several efficiency improvements have improved the ELF/VLF wave generation efficiency further.

Cohen, M.; Golkowski, M.

2013-12-01

112

Tethered Aerostat VLF/LF Transmitter System Design Considerations.  

Science.gov (United States)

A tethered aerostat VLF/LF transmitter (TAVT) system is a cost-effective, survivable alternative for reconstituting VLF/LF communications connectivity to strategic forces in a post-attack environment. This paper describes the tradeoff design consideration...

R. L. Crawford T. C. Lamanna K. L. Jordon

1993-01-01

113

VLF saucers source region and generation revealed by the four Cluster satellites  

Science.gov (United States)

A VLF saucer is a natural radio-wave phenomenon observed in the auroral zone since the 1960's. It has a characteristic V-shaped signature on electric field spectrograms in the VLF range. Many properties of VLF saucers have been established in the 1970's based on Alouette and Isis spacecraft. Further investigations continued thanks to satellites flying over the auroral zone, such as Viking, Polar and FAST. Since 2006, the orbits of the ESA/NASA Cluster satellites are slowly evolving from a nominal polar orbit to an oblique one. Meanwhile, the perigee of their orbits, originally at 19,000 km, naturally decreased to a few hundred kilometres and since 2011 have been steadily increasing back to the original perigee. Since spring 2009, Cluster scientists can make use of this natural orbital drift to target a new key region of the magnetosphere: the Auroral Acceleration Region (AAR). The AAR continues to be targeted by the Cluster mission, with a recent data campaign achieved successfully in Spring 2013. On rare occasions, VLF saucers are observed by the Cluster spacecraft, as they need to fly close enough to their source to catch them. Unique observations of electrostatic VLF saucers by the four Cluster satellites will be presented. These data not only enable for the first time to triangulate their source region, but they also allow revisiting some of the hypotheses commonly used so far in the analysis of their source region. Finally, the multi-point observations of VLF saucers question fundamental aspects of their generation. Indeed, it is difficult to understand, based on previously published studies, how transient structures such as electron holes are able to support the continuous generation of these electrostatic waves during several minutes, as observed by Cluster.

Masson, A.; Berthomier, M.; Pickett, J. S.; Fazakerley, A. N.; Forsyth, C.; Escoubet, C.; Laakso, H. E.; Rauch, J.; Dcrau, P.

2013-12-01

114

Lightning and radar observations of hurricane Rita landfall  

Energy Technology Data Exchange (ETDEWEB)

Los Alamos National Laboratory (LANL) owns and operates an array of Very-Low Frequency (VLF) sensors that measure the Radio-Frequency (RF) waveforms emitted by Cloud-to-Ground (CG) and InCloud (IC) lightning. This array, the Los Alamos Sferic Array (LASA), has approximately 15 sensors concentrated in the Great Plains and Florida, which detect electric field changes in a bandwidth from 200 Hz to 500 kHz (Smith et al., 2002). Recently, LANL has begun development of a new dual-band RF sensor array that includes the Very-High Frequency (VHF) band as well as the VLF. Whereas VLF lightning emissions can be used to deduce physical parameters such as lightning type and peak current, VHF emissions can be used to perform precise 3d mapping of individual radiation sources, which can number in the thousands for a typical CG flash. These new dual-band sensors will be used to monitor lightning activity in hurricanes in an effort to better predict intensification cycles. Although the new LANL dual-band array is not yet operational, we have begun initial work utilizing both VLF and VHF lightning data to monitor hurricane evolution. In this paper, we present the temporal evolution of Rita's landfall using VLF and VHF lightning data, and also WSR-88D radar. At landfall, Rita's northern eyewall experienced strong updrafts and significant lightning activity that appear to mark a transition between oceanic hurricane dynamics and continental thunderstorm dynamics. In section 2, we give a brief overview of Hurricane Rita, including its development as a hurricane and its lightning history. In the following section, we present WSR-88D data of Rita's landfall, including reflectivity images and temporal variation. In section 4, we present both VHF and VLF lightning data, overplotted on radar reflectivity images. Finally, we discuss our observations, including a comparison to previous studies and a brief conclusion.

Henderson, Bradley G [Los Alamos National Laboratory; Suszcynsky, David M [Los Alamos National Laboratory; Hamlin, Timothy E [Los Alamos National Laboratory; Jeffery, C A [Los Alamos National Laboratory; Wiens, Kyle C [TEXAS TECH U.; Orville, R E [TEXAS A& M

2009-01-01

115

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

116

Airborne Observations of Ammonia Emissions from North Carolina Swine Facilities  

Science.gov (United States)

Ammonia (NH3) is the dominant gas-phase base in the troposphere. As a consequence, NH3 abundance influences particle formation and composition. Anthropogenic emissions of NH3 can react with sulfuric acid (H2SO4) and nitric acid (HNO3), photochemical oxidation products of sulfur dioxide (SO2) and nitrogen oxides (NOx (NO + NO2)), to form ammoniated particles that typically account for half or more of measured PM2.5 mass in the Eastern US. NH3 emissions are predominantly from agricultural sources, primarily livestock animal waste and crop fertilization. Accurate NH3 emissions estimates from these sources are necessary for developing effective particle control strategies. Swine facilities in North Carolina are one of the largest source of NH3 emissions in the Southeastern US. Airborne measurements of NH3 and particulate ammonium (NH4+) made aboard the NOAA WP-3D aircraft as part of the recent 2013 SENEX field campaign are used to quantify NH3 emissions from North Carolina swine facilities. The observed NH3 emissions are compared to swine facility emissions estimates from current emissions inventories. In addition, the NH3 emissions from swine facilities are placed in the broader context of NH3 sources through comparison to recent emissions observations from dairy facilities in California. The July 10 SENEX WP-3D flight track colored and sized by observed NH3 mixing ratios.

Nowak, J. B.; Neuman, J. A.; Liao, J.; Welti, A.; Middlebrook, A. M.; McKeen, S. A.; Trainer, M.; Parrish, D. D.

2013-12-01

117

Whistler induced suppression of VLF noise  

Science.gov (United States)

A class of suppression effects is investigated involving the reduction in amplitude of a natural VLF noise band following the reception of a whistler. Data acquired at South Pole Station during 1981 showed such suppression events on 20 percent of all winter days. A review of data from Siple, Byrd, Eights, and Palmer Stations in Antarctica and Roberval in Quebec, Canada, has identified many more events. The attenuation typically reaches a maximum of 3-5 dB in 5-10 s, and the noise band recovers to the pre-event amplitude 15-30 s after the whistler. The noise bands are generally mid-latitude hiss, but suppression associated with polar chorus has been seen. Regularly observed features of suppression events include multi-hop echoing of the driving whistler; confinement of the whistler echoes to the frequency band occupied by the suppressed noise; suppression during the first pass of the whistler; continuing suppression by the whistler echoes as the suppressed noise amplitude reaches a minimum and then recovers; and recovery of the noise band to the pre-event level. At the present level of understanding, it is concluded that whistler suppression and the Quiet Band effect are closely related.

Gail, W. B.; Carpenter, D. L.

1984-02-01

118

Showa Station and Iceland conjugate-point observations  

International Nuclear Information System (INIS)

Joint observations with France were conducted for 52 days from July 29 to September 18, 1977, at Husafell about 100 km away from the capital of Iceland, Reykjavik. Husafell is about 60 km distant from the geomagnetic conjugate point of Showa Station. The items observed in Iceland were two horizontal components of geomagnetic pulsation, VLF natural radio waves, fixed-direction photometer (4278 A) and aurora TV camera. These have been all observed continuously at Showa Station, so that detailed analyses of conjugate-point observations are possible. The observation point was at Husafell, while geomagnetic stations are at Reykjavik, Showa Station and Mizuho Station. This report is described on the intensity ratio of ELF/VLF band natural radiowaves, spectral analyses, the conjugate natures of QP emission, aurora chorus and aurora hiss, and the relation of QP emission to geomagnetic pulsation. (J.P.N.)

1978-11-01

119

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

120

Optimizing ELF/VLF generation via HF heating utilizing beam motion  

Science.gov (United States)

ELF/VLF (300 Hz - 30 kHz) waves are difficult to generate with conventional antennae due to their extraordinary long wavelengths, and the good conductance of the Earth at these frequencies. Recently, ELF and VLF waves have been generated using HF (3-10 MHz) heating of the lower ionosphere, in the presence of natural currents such as the auroral electrojet, which modulates the ionospheric conductivity and therefore turns the lower ionosphere into a large radiating element. The recently upgraded HAARP facility, near Gakona Alaska, utilizes 3.6 MW of HF power, along with an unprecedented ability to steer the HF heating beam over a large area extremely rapidly. Since the completion of the upgrade in 2007, the first successful implementation of techniques such as geometric modulation [Cohen et al. 2008, Borisov et al. 1998], and beam painting [Papadopoulos et al. 1989] have occurred. These results have shown as much as 7-11 dB improvement in the signal strengths, as well as the first ability to direct ELF/VLF signals via an unprecedented ELF/VLF phased array. Here, we use a combination of experimental and theoretical investigations to discuss the optimization of ELF/VLF generation via HF heating, including the effect of HF and ELF frequency on the amplitude and the directional pattern for various generation techniques. The experimental observations occur over an array of receivers across Alaska. The theoretical formulation utilizes a 3D model of the HF heating and subsequent electron cooling processes, leading to spatial structure of modulated ionospheric conductivities, the results of which are input into a model of ELF/VLF propagation in the Earth-ionosphere waveguide.

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

2008-12-01

 
 
 
 
121

Investigation of EM Emissions by the Electrodynamic Tether, Inclusive of an Observational Program (EMET)  

Science.gov (United States)

Our TSS-1/R investigation, which we shall refer to as EMET in this report, was an integral part of the effort by the TSS-1/R Investigators' Working Group (IWG) to come to an understanding of the complex interaction between the tethered satellite system and the ionosphere. All of the space-borne experiments were designed to collect data relevant to the local interaction. Only the ground- based experiments, EMET and its Italian counterpart Observations on the Earth's Surface of Electromagnetic Emissions (OESEE), held out any hope of characterizing the long range effects of the interaction. This was to be done by detecting electromagnetic waves generated by the system in the ionosphere, assuming the signal reached the Earth's surface with sufficient amplitude. As the type of plasma waves excited to carry charge away from the charge-exchange regions of the system at each end of the tether is one of the theoretical points about which there is greatest disagreement, a definitive identification of tether-generated waves could mark significant progress in the so-called current closure problem of electrodynamic tethers. Dr. Mario Grossi of the Smithsonian Astrophysical Observatory (SAO) initiated the investigation, and his experience in the field of ULF-ELF waves and their detection was invaluable throughout its course. Rice University had the responsibility of setting up the EMET ULF-VLF ground stations under a subcontract from SAO. Principal Investigator (PI) for the Rice effort was Prof. William E. Gordon, who was primary observer at the Arecibo Observatory during TSS-LR. Dr. Steve Noble handled major day-to-day operations, training, and planning for the ground-based measurements. Dr. James McCoy of NASA JSC, a member of the Mona/Arecibo team, was pilot for the numerous flights ferrying personnel and equipment between Puerto Rico and Mona Island. Final responsibility for the measurements rested with SAO, and the activities of field personnel and SAO investigators were closely co-ordinated during the mission. Dr. Enrico Lorenzini of SAO served as the eyes, ears, and brain of EMET in the Science Operations Area and PI table during the mission, whenever the PI was absent during the round-the-clock mission operations. The Rice University final report to SAO, which is included as an Appendix, contains details of the remote sites, means of communication, sensors, etc., as well as the affiliations of personnel involved in the data-gathering effort.

Estes, Robert D.

1998-01-01

122

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

1989-01-01

123

First observations of stimulated electromagnetic emission at Arecibo  

Energy Technology Data Exchange (ETDEWEB)

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.

Thide, B.; Hedberg, A. (Swedish Institute of Space Physics, Uppsala (Sweden)); Fejer, J.A.; Sulzer, M.P. (Arecibo Observatory (Puerto Rico))

1989-05-01

124

MSX Observations of Diffuse UV Emission in Orion  

CERN Document Server

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 a UV-IR ratio of 40 photons cm-2 s-1 sr-1 A-1 (MJy sr-1)-1. In the other two fields there was no structure in the diffuse emission nor was there any correlation with the IRAS emission.

Murthy, J; Paxton, L J; Price, S D; Murthy, Jayant

2001-01-01

125

SCIAMACHY formaldehyde observations: constraint for isoprene emissions 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, never studied before, 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. Observed columns present a bias less than 20% on average. The differences are discussed according to the errors on the model and the observations and the 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 21015 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. Perspectives of using SCIAMACHY observations as constraint for biogenic isoprene emissions with an adapted averaging are approached: this new constraint should help to reduce their uncertainties more than 50% in region of intense emissions.

G. Dufour

2008-11-01

126

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.)

1979-01-01

127

MSX Observations of Diffuse UV Emission in Orion  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

128

Observations of Anomalous Microwave Emission from HII regions  

CERN Document Server

In this brief review, I give a summary of the observations of Anomalous Microwave Emission (AME) from HII regions. AME has been detected in, or in the vicinity of, HII regions. Given the difficulties in measuring accurate SEDs over a wide range of frequencies and in complex environments, many of these detections require more data to confirm them as emitting significant AME. The contribution from optically thick free-free emission from UCHII regions may be also be significant in some cases. The AME emissivity, defined as the ratio of the AME brightness to the 100 micron brightness, is comparable to the value observed in high-latitude diffuse cirrus in some regions, but is significantly lower in others. However, this value is dependent on the dust temperature. More data, both at high frequencies (>5 GHz) and high resolution (~1 arcmin or better) is required to disentangle the emission processes in such complex regions.

Dickinson, Clive

2013-01-01

129

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

1989-01-15

130

Observation of beta-delayed proton emission from 24Al  

International Nuclear Information System (INIS)

Utilizing the 24Mg(p,n) reaction and a low-energy proton detector ball, beta-delayed proton emission from 24Al has been observed in the form of a quasicontinuum of protons from ?300 to 1100 keV. By making a comparsion with a previously known 24Al beta-delayed alpha branching ratio, a branching ratio for beta-delayed proton emission of (1.20.3)x10-5 has been determined

1994-10-01

131

Interpretation of EUV emissions observed by Mills et al.  

Science.gov (United States)

An explanation of the so-called hydrino continuum emissions proposed by Mills and Lu, most recently in [Eur. Phys. J. D 64, 65 (2011)], is presented using conventional atomic, plasma, and discharge physics. It is argued that the observed EUV emissions during their pulsed discharges originate from transitions in ions sputtered or evaporated from the electrodes. Such an interpretation removes their justification for the introduction of hydrino particles.

Phelps, A. V.; Clementson, J.

2012-05-01

132

Solar Flare Impulsive Phase Emission Observed with SDO/EVE  

Science.gov (United States)

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 Te = 5.8-7.2 allow the evolution of the DEM to be studied over a wide temperature range at 10 s 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 component from 7 to 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 emission was verified using Atmospheric Imaging Assembly images to be the flare ribbons and footpoints, indicating that the constructed DEMs represent the spatially average thermal structure of the chromospheric flare emission during the impulsive phase.

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

2013-12-01

133

Excitation of whistler mode signals via injection of polarized VLF waves with the Siple transmitter  

International Nuclear Information System (INIS)

Whistler mode waves of various polarizations were transmitted by the Siple Station, Antarctica, VLF transmitter and received near the geomagnetic conjugate point at Lake Mistissini, Quebec. Crossed 21-km horizontal dipole antennas on top of the 2-km-thick ice sheet were used to transmit 2- to 4-kHz waves alternately with right-hand circular, left-hand circular, and linear polarizations. Excitation of a multiplicity of magnetospheric propagation paths and the received signal strength were observed to depend on the transmitter antenna polarization. Where whistler mode growth and emission triggering occurred, saturated peak values of received signals were independent of antenna polarization and initial injected power levels, in agreement with previous findings. Propagation paths of ducted Siple signals observed at Lake Mistissini were identified with propagation paths deduced from natural whistlers, from which the L shell values and equatorial number densities for the paths were calculated. A combination of L shell data and models of antenna coupling into the whistler mode may aid in the location of ducts. Dynamics Explorer I satellite recordings of unducted Siple signals showed trends similar to the ground data on ducted signals. The observations are discussed in the context of a simplified model of the coupling from the Siple antenna into the ionosphere, which provides reasonable agreement with observations. 14 refs

1992-01-01

134

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 21015 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

135

Beat excitation of whistler mode sidebands using the Siple VLF transmitter  

Science.gov (United States)

The process of whistler mode sideband generation in the magnetosphere was studied by transmitting two monochromatic signals closely spaced in frequency (Delta-f = 5-45 Hz) from the experimental VLF transmitter at Siple Station, Antarctica. The signals were observed following ducted magnetospheric propagation to the conjugate station at Roberval, Quebec. Sidebands up to seventh order were generated extending to + or - 100 Hz with respect to the average frequency of the carriers. New frequencies were observed both under conditions of little or no growth of the input signals and when one of the input signals did grow significantly. At times the sideband amplitudes exceeded the intensity of either input signal. A small signal mechanism is proposed in which emissions are triggered by each beat between the input waves but are then suppressed by the following beat. The energy from the phase bunched particles is believed to feed preferentially into the sidebands rather than causing growth of the input waves themselves. In this model, phase-trapping of resonant electrons by the wave is not required. The observed process of sideband generation provides a mechanism to break down the coherence of relatively narrowband waves in the magnetosphere and may thus account for existing evidence of the transformation of relatively coherent wave packets into broader more variable bands of noiselike signals.

Helliwell, R. A.; Inan, U. S.; Katsufrakis, J. P.; Carpenter, D. L.

1986-01-01

136

Thermal emission from isolated neutron stars: theoretical and observational aspects  

CERN Document Server

The possibility for direct investigation of thermal emission from isolated neutron stars was opened about 25 years ago with the launch of the first X-ray observatory, Einstein. A significant contribution to this study was provided by ROSAT in 1990's. The outstanding capabilities of the currently operating observatories, Chandra and XMM-Newton, have greatly increased the potential to observe and analyze thermal radiation from the neutron star surfaces. Confronting observational data with theoretical models of thermal emission, presumably formed in neutron star atmospheres, allows one to infer the surface temperatures, magnetic fields, chemical composition, and neutron star masses and radii. This information, supplemented with model equations of state and neutron star cooling models, provides an opportunity to understand the fundamental properties of the superdense matter in the neutron star interiors. I review the current status and most important results obtained from modeling neutron star thermal emission an...

Zavlin, V E

2007-01-01

137

100 days of ELF/VLF generation via HF heating with HAARP  

Science.gov (United States)

Extremely low frequency/very low frequency (ELF/VLF) radio waves are difficult to generate with conventional antennas. Ionospheric high frequency (HF) heating facilities generate ELF/VLF waves via modulated heating of the lower ionosphere. HF heating of the ionosphere changes the lower ionospheric conductivity, which in the presence of natural currents such as the auroral electrojet creates an antenna in the sky when heating is modulated at ELF/VLF frequencies. We present a summary of nearly 100 days of ELF/VLF wave generation experiments at the 3.6 MW High Frequency Active Auroral Research Program (HAARP) facility near Gakona, Alaska, at a variety of ELF/VLF frequencies, seasons, and times of day. We present comprehensive statistics of generated ELF/VLF magnetic fields observed at a nearby site, in the 500-3500 Hz band. Transmissions with a specific HF beam configuration (3.25 MHz, vertical beam, amplitude modulation) are isolated so the data comparison is self-consistent, across nearly 5 million individual measurements of either a tone or a piece of a frequency-time ramp. There is a minimum in the average generation close to local midnight. It is found that generation during local nighttime is on average weaker but more highly variable, with a small number of very strong generation periods. Signal amplitudes from day to day may vary by as much as 20-30 dB. Generation strengthens by 5 dB during the first 30 min of transmission, which may be a signature of slow electron density changes from sustained HF heating. Theoretical calculations are made to relate the amplitude observed to the power injected into the waveguide and reaching 250 km. The median power generated by HAARP and injected into the waveguide is 0.05-0.1 W in this baseline configuration (vertical beam, 3.25 MHz, amplitude modulation) but may have generated hundreds of watts for brief durations. Several efficiency improvements have improved the ELF/VLF wave generation efficiency further.

Cohen, M. B.; Go?kowski, M.

2013-10-01

138

On the altitude of the ELF/VLF source region generated during beat-wave HF heating experiments  

Science.gov (United States)

Modulated high frequency (HF, 3-10 MHz) heating of the ionosphere in the presence of the auroral electrojet currents is an effective method for generating extremely low frequency (ELF, 3-3000 Hz) and very low frequency (VLF, 3-30 kHz) radio waves. The amplitudes of ELF/VLF waves generated in this manner depend sensitively on the auroral electrojet current strength, which varies with time. In an effort to improve the reliability of ELF/VLF wave generation by ionospheric heating, recent experiments at the High-frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska, have focused on methods that are independent of the strength of the auroral electrojet currents. One such potential method is so-called beat-wave ELF/VLF generation. Recent experimental observations have been presented to suggest that in the absence of a significant D-region ionosphere (60-100 km altitude), an ELF/VLF source region can be created within the F-region ionosphere (150-250 km altitude). In this paper, we use a time-of-arrival analysis technique to provide direct experimental evidence that the beat-wave source region is located in the D-region ionosphere, and possibly the lower E-region ionosphere (100-120 km altitude), even when ionospheric diagnostics indicate a very weak D-layer. These results have a tremendous impact on the interpretation of recent experimental observations.

Moore, R. C.; Fujimaru, S.; Cohen, M.; Go?kowski, M.; McCarrick, M. J.

2012-09-01

139

Synoptic observations of Jupiter's radio emissions: average statistical properties observed by voyager  

International Nuclear Information System (INIS)

Observations of Jupiter's low-frequency radio emission collected over one-month intervals before and after each Voyager encounter have been analyzed to provide a synoptic view of the average statistical properties of the emissions. Compilations of occurrence probability, average power flux density, and average sense of circular polarization are presented as a function of central meridian longitude, phase of Io, and frequency. The results are compared with ground-based observations. The necessary geometrical conditions and preferred polarization sense for Io-related decametric emission observed by Voyager from above both the dayside and nightside hemispheres are found to be essentially the same as those observed in earth-based studies. On the other hand, there is a clear local time dependence in the Io-dependent decametric emission. The emission is prevalent at longitudes >200"0 when observed from over the dayside hemisphere but is dominant at longitudes >200"0 when observed from over the postmidnight sector. Decametric emission, which comprises the dynamic spectral lesser arcs near 10 MHz, displays a distinct, bimodal polarization pattern that is predominantly in the left-hand sense at longitudes below 150"0 and in the right-hand sense at longitudes above 150"0. The central meridian longitude distributions of occurrence probability and average flux density at hectometric wavelengths appear to depend significantly on both the observer's latitude and local time. Io appears to have an influence on average flux density of the emission down to below 2 MHz. The average power flux density sectrum of Jupiter's emission has a broad peak near 9 MHz. Intergration of the average spectrum over all frequencies and all longitudes gives a total radiated power for an equivalent isotropic source of 4 x 10"1"1 W

1981-09-30

140

Thermal emission from isolated neutron stars: theoretical and observational aspects  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The possibility for direct investigation of thermal emission from isolated neutron stars was opened about 25 years ago with the launch of the first X-ray observatory, Einstein. A significant contribution to this study was provided by ROSAT in 1990's. The outstanding capabilities of the currently operating observatories, Chandra and XMM-Newton, have greatly increased the potential to observe and analyze thermal radiation from the neutron star surfaces. Confronting observation...

Zavlin, Vyacheslav E.

2007-01-01

 
 
 
 
141

Isoprene and monoterpene emission rate variability: Observations with Eucalyptus and emission rate algorithm development  

Science.gov (United States)

Variability in the emission rates of isoprene and monoterpenes from individual leaves of Eucalyptus globulus was investigated with a laboratory gas exchange system and an environmental control leaf cuvette. For individual leaves, with constant environmental conditions, short-term (1 hour) fluctuations in isoprene emission rates were less than 3% while day-to-day fluctuations averaged 14%. Leaf-to-leaf variations were much larger (62%). Fluctuations with time and leaf-to-leaf variability in CO2 assimilation rates were of the same order as isoprene, while monoterpene variations were higher. Leaf age was identified as one of the factors contributing to leaf-to-leaf variability in CO2 assimilation and isoprene and monoterpene emission rates. Monoterpene emission rates were not influenced by light intensity or CO2 mixing ratio. The observed temperature dependence was the same for ?-pinene and 1,8-cineole (an oxygenated monoterpene) and is similar to the temperature dependence of monoterpene emission rates reported by other investigators. Isoprene emissions were slightly dependent on humidity (1-3% increase in emission per 10% increase in relative humidity) and responded only to very low (600 ppm) CO2 mixing ratios. Isoprene emission was associated with the abaxial leaf side, which contains stomatal pores, while monoterpenes were emitted primarily from the adaxial side, which lacks stomatal pores. The temperature and light dependence of isoprene emission closely resembles relationships observed for electron transport in plant chloroplasts. For this reason, we have used a mechanistic electron transport model as the basis for an empirical isoprene emission rate model. The emission rate variation predicted by this model was within 10% of observed values for 62% of the 255 observations at light-saturated conditions and temperatures between 23 and 33C. The entire data base includes over 600 observations at leaf temperatures ranging between 12 and 50C and light intensities between 0 and 2000 ?mol m-2 s-1. Nearly two thirds of the emission rates predicted for the entire data base were within a factor of 1.25, and 89% were within a factor of 2. The algorithms developed in this study provide a solid physiological basis for future efforts to model the biogenic flux of isoprene and monoterpenes into the atmosphere.

Guenther, Alex B.; Monson, Russell K.; Fall, Ray

1991-06-01

142

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

143

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

144

ULF-VLF electric field measurements during the 2001 Leonid storm  

Science.gov (United States)

The generation of electromagnetic waves by the impacts of meteors in the upper earth atmosphere has been as subject of controversial discussion during the last decades. While there is some evidence for emissions in the VF/VLF range (300 Hz - 30 kHz), the generation of ULF/ELF waves (3 Hz - 300 Hz) by meteor impacts is poorly demonstrated. As part of a comprehensive observation campaign undertaken by a team from the European Space Agency the vertical electric field has been monitored in parallel to optical video recordings of the 2001 Leonid storm in order to correlate optical observations and electric field measurement data. First, the instrumentation and recording equipment is introduced. Electric field measurement data in the frequency and time domain are presented. Particular attention is paid to the analysis of data in the 10 Hz - 300 Hz frequency range, which includes Schumann resonance frequencies. The results of a comparison of global ZHR data and the activity at selected ULF/ELF frequencies are shown. Preliminary conclusions are drawn, and methods for the improvements of results are suggested.

Trautner, R.; Koschny, D.; Witasse, O.; Zender, J.; Knfel, A.

2002-11-01

145

Equatorial Emissions Events in the Inner Magnetosphere from THEMIS Observations  

Science.gov (United States)

Two specific emission events near equator are found by analyzing wave data from SCM (Search Coil Magnetometer) and EFI (Electric Field Instrument) of THEMIS mission in the local afternoon sector for the year of 2008. These events are both with emissions of frequencies at about 70Hz and 110Hz, between the local proton gyrofrequency fcH+ and the lower hybrid frequency flhr, around 5RE. The analyzed wave vectors are shown to be nearly perpendicular to the ambient geomagnetic fields. The observed ion velocity distributions at the same time exhibit ring features at about 3600 km/sec in perpendicular velocity, which is larger than the local Alfvn velocity. Wave growth rates over different frequencies are calculated to compare with the emission intensity at different frequencies based on dispersion relation of magnetosonic waves.

Wang, K.; Chen, R.; Tam, W. Y.; Chen, L.; Jan, Y.; Yang, Y.

2013-12-01

146

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.; Guzmn, F.; Favre, M.; Wyndham, E. S.; Chuaqui, H.; Bhuyan, H.

2014-05-01

147

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

148

Observation of dispersive wave emission by temporal cavity solitons  

CERN Document Server

We examine a coherently-driven, dispersion-managed, passive Kerr fiber ring resonator and report the first direct experimental observation of dispersive wave emission by temporal cavity solitons. 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 cavity solitons under conditions where higher-order dispersion plays a significant role. Significantly, since temporal cavity solitons manifest themselves in monolithic microresonators, our results are likely to explain the origins of spectral features observed in broadband Kerr frequency combs.

Jang, Jae K; Murdoch, Stuart G; Coen, Stephane

2014-01-01

149

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 O_4 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

1985-01-01

150

GALEX OBSERVATIONS OF DIFFUSE ULTRAVIOLET EMISSION FROM DRACO  

International Nuclear Information System (INIS)

We have studied small-scale (2') spatial variation of the diffuse ultraviolet (UV) radiation using a set of 11 Galaxy Evolution Explorer deep observations in the constellation of Draco. We find a good correlation between the observed UV background and the infrared (IR) 100 ?m flux, indicating that the dominant contributor of the diffuse background in the field is scattered starlight from the interstellar dust grains. We also find strong evidence of additional emission in the far-ultraviolet (FUV) band which is absent in the near-ultraviolet (NUV) band. This is most likely due to Lyman band emission from molecular hydrogen in a ridge of dust running through the field and to line emissions from species such as C IV (1550 A) and Si II (1533 A) in the rest of the field. A strong correlation exists between the FUV/NUV ratio and the FUV intensity in the excess emission regions in the FUV band irrespective of the optical depth of the region. The optical depth increases more rapidly in the UV than the IR and we find that the UV/IR ratio drops off exponentially with increasing IR due to saturation effects in the UV. Using the positional details of Spitzer extragalactic objects, we find that the contribution of extragalactic light in the diffuse NUV background is 49 13 photons cm-2 sr-1 s-1 A-1 and is 30 10 photons cm-2 sr-1 s-1 A-1 in the FUV band.

2010-11-10

151

Large Radio Telescopes for Anomalous Microwave Emission Observations  

CERN Document Server

We discuss in this paper the problem of the Anomalous Microwave Emission (AME) in the light of ongoing or future observations to be performed with the largest fully steerable radio telescope in the world. High angular resolution observations of the AME will enable astronomers to drastically improve the knowledge of the AME mechanisms as well as the interplay between the different constituents of the interstellar medium in our galaxy. Extragalactic observations of the AME have started as well, and high resolution is even more important in this kind of observations. When cross-correlating with IR-dust emission, high angular resolution is also of fundamental importance in order to obtain unbiased results. The choice of the observational frequency is also of key importance in continuum observation. We calculate a merit function that accounts for the signal-to-noise ratio (SNR) in AME observation given the current state-of-the-art knowledge and technology. We also include in our merit functions the frequency depen...

Battistelli, E S; de Bernardis, P; Masi, S

2013-01-01

152

EUV emission lines and diagnostics observed with Hinode/EIS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quiet Sun and active region spectra from the Hinode/EIS instrument are presented, and the strongest lines from different temperature regions discussed. A list of emission lines recommended to be included in EIS observation studies is presented based on analysis of blending and diagnostic potential using the CHIANTI atomic database. In addition we identify the most useful density diagnostics from the ions covered by EIS.

Young, P. R.; Del Zanna, G.; Mason, H. E.; Dere, K. P.; Landi, E.; Landini, M.; Doschek, G. A.; Brown, C. M.; Culhane, J. L.; Harra, L. K.; Watanabe, T.; Hara, H.

2007-01-01

153

TIMS observations of surface emissivity in HAPEX-Sahel  

Science.gov (United States)

The Thermal Infrared Multispectral Scanner (TIMS) was flown on the NASA C-130 aircraft for a series of 12 flights during HAPEX-Sahel at altitudes ranging from 0.25 to 6 km (0.6 to 15 m resolution). TIMS provides coverage of the 8 to 12 micrometer thermal infrared band in 6 contiguous channels. Thus it is possible to observe the spectral behavior of the surface emissivity over this wavelength interval.

Schmugge, Thomas; Hook, Simon; Kahle, Anne

1995-01-01

154

In situ observations of medium frequency auroral radio emissions  

Science.gov (United States)

The auroral ionosphere is a region rich with plasma waves that can be studied both in space and on the ground. These waves may mediate energy exchange between particle populations and provide information about the local plasma properties and boundaries. Auroral medium frequency (MF) burst is an impulsive radio emission observed at ground-level from 1.3-4.5 MHz that is associated with local substorm onset. There have been two recent reports of impulsive, broadband, MF waves at high latitudes. Burchill and Pfaff [2005] reported observations from the FAST satellite of impulsive, broadband, MF and low frequency (LF) radio waves. Using data from the DEMETER satellite, Parrot et al. [2009] surveyed MF waves caused by lightning. This study did show a high-latitude population of MF waves. We investigate whether the waves observed by these two satellites are related to auroral MF burst. Using FAST satellite burst mode electric field data from high-latitude (> 60 degrees magnetic), low-altitude ( 3) from 1996-2002, we have found forty-four examples of impulsive MF waves, all of which are associated with impulsive LF waves. Although MF burst and the waves observed by FAST have similar spectral signatures, they have different magnetic local time dependencies, which suggests that they may be unrelated. A study of MF waves observed at high latitude by DEMETER is ongoing. In situ observations of MF burst could provide crucial information about this heretofore unexplained natural radio emission.

Broughton, M.; Labelle, J. W.; Pfaff, R. F.; Parrot, M.; Yan, X.; Burchill, J. K.

2013-12-01

155

Coherent whistler emissions in the magnetosphere Cluster observations  

Directory of Open Access Journals (Sweden)

Full Text Available The STAFF-SC observations complemented by the data from other instruments on Cluster spacecraft were used to study the main properties of magnetospheric lion roars: sporadic bursts of whistler emissions at f~0.10.2fe where fe is the electron gyrofrequency. Magnetospheric lion roars are shown to be similar to the emissions in the magnetosheath while the conditions for their generation are much less favorable: the growth rate of the cyclotron temperature anisotropy instability is much smaller due to a smaller number of the resonant electrons. This implies a nonlinear mechanism of generation of the observed wave emissions. It is shown that the observed whistler turbulence, in reality, consists of many nearly monochromatic wave packets. It is suggested that these structures are nonlinear Gendrin's whistler solitary waves. Properties of these waves are widely discussed. Since the group velocity of Gendrin's waves is aligned with the magnetic field, these well guided wave packets can propagate through many magnetic "bottles" associated with mirror structures, without being trapped.

I. Dandouras

2007-02-01

156

Coherent whistler emissions in the magnetosphere - Cluster observations  

Science.gov (United States)

The STAFF-SC observations complemented by the data from other instruments on Cluster spacecraft were used to study the main properties of magnetospheric lion roars: sporadic bursts of whistler emissions at f~0.1-0.2fe where fe is the electron gyrofrequency. Magnetospheric lion roars are shown to be similar to the emissions in the magnetosheath while the conditions for their generation are much less favorable: the growth rate of the cyclotron temperature anisotropy instability is much smaller due to a smaller number of the resonant electrons. This implies a nonlinear mechanism of generation of the observed wave emissions. It is shown that the observed whistler turbulence, in reality, consists of many nearly monochromatic wave packets. It is suggested that these structures are nonlinear Gendrin's whistler solitary waves. Properties of these waves are widely discussed. Since the group velocity of Gendrin's waves is aligned with the magnetic field, these well guided wave packets can propagate through many magnetic "bottles" associated with mirror structures, without being trapped.

Dubinin, E. M.; Maksimovic, M.; Cornilleau-Wehrlin, N.; Fontaine, D.; Travnicek, P.; Mangeney, A.; Alexandrova, O.; Sauer, K.; Fraenz, M.; Dandouras, I.; Lucek, E.; Fazakerley, A.; Balogh, A.; Andre, M.

2007-02-01

157

Observation of microwave emission from extensive air showers with CROME  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on the measurement of microwave radio signals from air showers with the CROME (Cosmic Ray Observation via Microwave Emission) experiment. CROME is located in the center of the KASCADE-Grande air shower array. The radio signals of the CROME antennas are stored for each high-energy trigger from the KASCADE-Grande array and matched o?ine with the KASCADE-Grande data. After almost one year of data taking microwave signals have been observed for more than ten air showers.

2013-01-01

158

XMM-Newton Observation of Solar Wind Charge Exchange Emission  

CERN Document Server

We present an XMM-Newton spectrum of diffuse X-ray emission from within the solar system. The spectrum is dominated by probable C VI lines at 0.37 keV and 0.46 keV, an O VII line at 0.56 keV, O VIII lines at 0.65 keV and ~0.8 keV, Ne IX lines at ~0.92 keV, and Mg XI lines at ~1.35 keV. This spectrum is consistent with that expected from charge exchange emission between the highly ionized solar wind and either interstellar neutrals in the heliosphere or material from Earth's exosphere. The emission is clearly seen as a low-energy (E<1.5 keV) spectral enhancement in one of a series of four observations of the Hubble Deep Field North. The X-ray enhancement is concurrent with an enhancement in the solar wind measured by ACE, Wind, and SoHO spacecraft. The solar wind enhancement reaches a flux level an order of magnitude more intense than typical fluxes at 1 AU, and has a significantly enhanced O^{+7}/O^{+6} ratio. Besides being of interest in its own right for studies of the solar system, this emission can hav...

Snowden, S L; Kuntz, K D

2004-01-01

159

Observations of the spectrum of the interplanetary dust emission  

Science.gov (United States)

Published data from satellite (IRAS), rocket-borne (ZIP), and balloon-borne (ARGO) spectroscopic observations of interplanetary dust emission in the FIR are compiled and analyzed, extending the spatial-distribution results of Salama et al. (1986) to evaluate the possible role of silicate and graphite grains in determining the FIR spectrum. The zodiacal dust spectra in the ecliptic plane at solar elongations epsilon = 45 and 90 deg are calculated on the basis of theoretical models and compared with the observations. A model based on a flat distribution of 10-micron-diameter silicate grains is shown to reproduce the observed spectrum at epsilon = 45 deg but not at epsilon = 90 deg, where a model with a mixture of silicate and graphite grains gives a better, but still unsatisfactory fit to the observations.

Salama, A.; de Bernardis, P.; Masi, S.; Moreno, G.

160

ISO observations of spirals Modelling the FIR emission  

CERN Document Server

ISO observations at 200 micron have modified our view of the dust component in spiral galaxies. For a sample of seven resolved spirals we have retrieved a mean temperature of 20K, about 10K lower than previous estimates based on IRAS data at shorter wavelengths. Because of the steep dependence of far-infrared emission on the dust temperature, the dust masses inferred from ISO fluxes are a factor of 10 higher than those derived from IRAS data only, leading to gas-to-dust ratios close to the value observed in the Galaxy. The scale-length of the 200 micron emission is larger than for the IRAS 100 micron emission, with colder dust at larger distances from the galactic centre, as expected if the interstellar radiation field is the main source of dust heating. The 200 micron scale-length is also larger than the optical, for all the galaxies in the sample. This suggests that the dust distribution is more extended than that of the stars.A model of the dust heating is needed to derive the parameters of the dust distri...

Bianchi, S; Davies, J I; Bianchi, Simone; Alton, Paul B.; Davies, Jonathan I.

1999-01-01

 
 
 
 
161

Lunar occultation observations of millimeter CO emission in S255  

International Nuclear Information System (INIS)

Observations of millimeter wavelength emission lines at the highest possible angular resolution are necessary to reveal the energetics and dynamics in compact regions of star formation activity. Lunar occultations of molecular clouds provide a means for obtaining angular resolution that is much better than that possible with a single radio telescope, and make it possible to study in more distant sources features at the same linear scale as those in Orion. The authors have recently used lunar occultations of the region around two infrared sources embedded in the S255 molecular cloud to determine the angular structure of the CO emission of the surrounding gas, and have found that this region closely resembles the core of the Orion molecular cloud. (Auth.)

1979-08-10

162

Experimental observation on anomalous emission in Mg vapor  

Energy Technology Data Exchange (ETDEWEB)

When the 3s3p 1P level of a Mg atom is resonantly excited by a laser, an anomalous emission with a wavelength of 5184 A can be observed, which corresponds to the transition for 3s4s 3S to 3s3p 3P2. According to the temporal behavior of this emission and its intensity dependence on atom density, it is believed that the experiment seems to show the transition from a spontaneous process to a cooperative process. The population inversion between 3s4s 3S and 3s3p 3P2 is created by inelastic collisions of the lower excited 3s3p 1P atoms. 8 references.

Zhang, D.; Chen, B.; Ju, R.; Zhao, X.

1985-08-01

163

Doppler-Shifted Flare Emissions Observed by SDO/EVE  

Science.gov (United States)

The EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory (SDO) has been obtaining unprecedented observations of solar variation on times scales of seconds during flares and over the rising phase of Solar Cycle 24 since its start of normal operations in May 2010. Unexpectedly, as first pointed out in Hudson et. al., Ap.j. (2011), even with EVE's spectral resolution of 0.1 nm and 'irradiance' measurements, EVE has the ability to very accurately determine Doppler shifts in all emissions during solar flares and coronal mass ejections (CMEs). The technique for deriving these absolute velocities is not straightforward, as the optical and instrumental effects must first be eliminated in order to separate the absolute plasma velocities from the instrument effects. This talk will discuss these efforts to eliminate the instrumental component, as well as show some of the first results of absolute velocities of multiple emissions at a wide range of temperatures during solar flares.

Chamberlin, Phillip C.

2012-01-01

164

Spicule emission profiles observed in He i 10 830  

Science.gov (United States)

Aims:Off-the-limb observations with high spatial and spectral resolution will help us understand the physical properties of spicules in the solar chromosphere. Methods: Spectropolarimetric observations of spicules in the He i 10 830 multiplet were obtained with the Tenerife Infrared Polarimeter on the German Vacuum Tower Telescope at the Observatorio del Teide (Tenerife, Spain). The analysis shows the variation of the off-limb emission profiles as a function of the distance to the visible solar limb. The ratio between the intensities of the blue and the red components of this triplet (R=I_blue/I_red) is an observational signature of the optical thickness along the light path, which is related to the intensity of the coronal irradiation. Results: We present observations of the intensity profiles of spicules above a quiet Sun region. The observable R as a function of the distance to the visible limb is also given. We have compared our observational results to the intensity ratio obtained from detailed radiative transfer calculations in semi-empirical models of the solar atmosphere assuming spherical geometry. The agreement is purely qualitative. We argue that future models of the solar chromosphere and transition region should account for the observational constraints presented here.

Snchez-Andrade Nuo, B.; Centeno, R.; Puschmann, K. G.; Trujillo Bueno, J.; Blanco Rodrguez, J.; Kneer, F.

2007-09-01

165

Radio emission from Colliding-Wind Binaries: Observations and Models  

CERN Multimedia

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

166

CBR anisotropy and galactic emission observations from Antarctica. [LMC; SMC  

Energy Technology Data Exchange (ETDEWEB)

In this paper we report the results of an experiment on the CBR anisotropy at 2 mm and 2.5 degrees angular resolution carried out during the Antarctic summer of 1987-88. We find evidence of statistical fluctuations at a level of T/T=2x10{sup {minus}4}, most of which can be ascribed to both atmospheric residual noise and/or patch galactic emission. In addition, we observed the Magellanic Clouds and obtained an excess of mm-wave radiation in dicating the presence of a cold dust component coexisting with the IRAS wa rm dust. (AIP)

Andreani, P.; Dall' Oglio, G.; Bari, M.D. (University of Rome, Physics Dept. P.leA. Moro 2,00185 Rome (Italy)); Martinis, L. (ENEA T.I.B., Frascati (Italy)); Piccirillo, L. (University of Rome, Physics Dept. P.LeA. Moro 2,00185 Rome (Italy) Istituto Superiore P.T., V.le Europe 190,00144 Rome (Italy)); Pizzo, L.; Santillo, C. (Unviersity of Rome, Physcis Dept, P.LeA. Moro 2,00185 Rome (Italy))

1990-01-15

167

CBR anisotropy and galactic emission observations from Antarctica  

International Nuclear Information System (INIS)

In this paper we report the results of an experiment on the CBR anisotropy at 2 mm and 2.5 degrees angular resolution carried out during the Antarctic summer of 1987-88. We find evidence of statistical fluctuations at a level of T/T=2x10-4, most of which can be ascribed to both atmospheric residual noise and/or patch galactic emission. In addition, we observed the Magellanic Clouds and obtained an excess of mm-wave radiation in dicating the presence of a cold dust component coexisting with the IRAS wa rm dust

1990-01-15

168

Impact of SPS heating on VLF, LF, and MF telecommunications systems ascertained by experimental means  

Energy Technology Data Exchange (ETDEWEB)

The results of experiments undertaken to assess the potential impact of the operation of the Satellite Power System on the D and E regions of the ionosphere, and on telecommunication systems that are dependent upon the structure of the lower ionosphere are summarized. Using the high-power high-frequency transmitter facility located at Platteville, Colorado, power densities comparable to the Satellite Power System can be delivered to the heights of 70 to 100 km above the surface of the earth. Observations of the performance of telecommunication systems that operate in the VLF, LF, and MF portions of the spectrum have been investigated during times when the ionosphere was modified with SPS comparable power density and when it was not. The results obtained indicte that the SPS, as currently configured with a peak power density of 23 mW/cm/sup 2/, will not adversely impact upon the performance of VLF, LF, and MF telecommunication systems.

Rush, C.M.; Violette, E.J.; Espeland, R.H.; Carroll, J.C.; Allen, K.C.

1980-07-01

169

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1988-08-01

170

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

1988-01-01

171

Magnetic storm associated enhanced particle precipitation in the South Atlantic anomaly - Evidence from VLF phase measurements  

Science.gov (United States)

Phase recordings of VLF signals transmitted almost entirely within the South Atlantic anomaly region are analyzed to determine the vertical extent of particle precipitation previously detected at E region heights. Signals at a frequency of 13.6 kHz were transmitted from Golfo Nuevo, Argentina and received at Atibaia, Brazil. Significant perturbations characterized by advancements in received signal phase indicative of VLF reflective layer lowering are observed during times of magnetic disturbances, particularly at night. Simultaneous measurements of sporadic E layer parameters over Cachoeira Paulista, Brazil also show enhancements in the blanketing frequency and the top reflected frequency at some delay with respect to magnetic disturbance onset. Results reveal magnetic storm associated ionization enhancements in the height region between about 110 to 70 km which is interpreted as high-energy charged particle precipitation in the South Atlantic magnetic anomaly.

Abdu, M. A.; Batista, I. S.; Piazza, L. R.; Massambani, O.

1981-09-01

172

Spectroscopic observations of 10 emission-line dwarf galaxies  

International Nuclear Information System (INIS)

Oxygen, helium, and neon abundances are derived from image-dissector scanner observations of 10 emission-line dwarf galaxies. The n(0)/n(H) ratios range from 0.025 to 0.5 the solar value, with the expected anticorrelation with gas temperature. Assuming that n(Ne"+"+)/n(O"+"+)roughly-equaln(Ne)/n(O), we find a value of 0.23 for this ratio, which is about 50% higher than the values quoted for Orion and the Magellanic Clouds. The mean ratio of n(He"+, He"+"+)/n(H"+) is 0.082 +- 0.007 for the five best observed galaxies: we do not detect any correlation of this ratio with the oxygen abundance. Reasons are given to refrain from deriving nitrogen abundances for these galaxies. It seems likely that the underlying continua in these galaxies come predominantly from mixtures of O-type stars and moderately hot giants and supergiants

1981-01-01

173

Observations of microwave continuum emission from air shower plasmas  

International Nuclear Information System (INIS)

We investigate a possible new technique for microwave detection of cosmic-ray extensive air showers which relies on detection of expected continuum radiation in the microwave range, caused by free-electron collisions with neutrals in the tenuous plasma left after the passage of the shower. We performed an initial experiment at the Argonne Wakefield Accelerator laboratory in 2003 and measured broadband microwave emission from air ionized via high-energy electrons and photons. A follow-up experiment at the Stanford Linear Accelerator Center in the summer of 2004 confirmed the major features of the previous Argonne Wakefield Accelerator observations with better precision. Prompted by these results we built a prototype detector using satellite television technology and have made measurements suggestive of the detection of cosmic-ray extensive air showers. The method, if confirmed by experiments now in progress, could provide a high-duty cycle complement to current nitrogen fluorescence observations.

2008-08-01

174

The Terminator Time in subionospheric VLF/LF diurnal variation as recorded by the Romanian VLF/LF radio monitoring system related to earthquake occurrence and volcano erruptions  

Science.gov (United States)

The Romanian VLF/LF monitoring system consisting in a radio receiver and the infrastructure that is necessary to record and transmit the collected data is part of the European international network named INFREP. Information on electromagnetic fields' intensities created by transmitters at a receiving site are indicating the quality of the propagation along the paths between the receivers and transmitters. Studying the ionosphere's influences on the electromagnetic waves' propagation along a certain path is a method to put into evidence possible modifications of its lower structure and composition as earthquakes' precursors. The VLF/LF receiver installed in Romania was put into operation in February 2009 and has already 3 years of testing, functioning and proving its utility in the forecast of some earthquakes or volcanic eruptions. Simultaneously we monitor, in the same site with the VLF/LF receiver, the vertical atmospheric electric field and different other meteorological parameters as: temperature, pressure or rainfall. The global magnetic conditions are emphasized with the help of Daily Geomagnetic Index Kp. At a basic level, the adopted analysis consists in a simple statistical evaluation of the signals by comparing the instantaneous values to the trend of the signal. In this paper we pay attention to the terminator times in subionospheric VLF/LF diurnal variation, which are defined as the times of minimum in amplitude (or phase) around sunrise and sunset. These terminator times are found to shift significantly just around the earthquake. In the case of Kobe earthquake, there were found significant shifts in both morning and evening terminator times and these authors interpreted the shift in terminator time in terms of the lowering of lower ionosphere by using the full-wave mode theory. A LabVIEW application which accesses the VLF/LF receiver through internet was developed. 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 appends daily files into monthly and anual 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. This type of representation, highlights the modification of the terminator time versus the length of the solar-day, improves the user's capability to detect possible propagation anomalies due to ionosphere conditions and allows a quick visual inspection of unexpected behaviors of transmission channels at different frequencies and paths. A very special result, was observed on the recordings made on the propagation path to Iceland (NRK, 37.5kHz). Recordings are made once a minute, for a period of 303 days. Icelandic channel propagation anomalies present in the range of 40-90 days are considered to be precursory phenomena associated with Eyjafjallajokull - Iceland, volcanic eruption occurred in April-May 2010.

Moldovan, I. A.; Moldovan, A. S.; Biagi, P. F.; Ionescu, C.; Schwingenschuh, K.; Boudjada, M. Y.

2012-04-01

175

Vlf radiations by some meteors: a reality ? perseids 2009 campaign. (French Title: Recherche de radiations vlf ventuelles par les mtores. campagne de mesures persides 2009 )  

Science.gov (United States)

Numerous credible reports about various audible sounds appearing simultaneously with visible meteors have been collected for centuries. Some theoretical works predict that an electromagnetic wave vector could be the reason for such simultaneous light and sound observations. The present study simply aims to observe the electromagnetic activity in the lower part of the radio spectrum during a meteor shower and to search for any interesting correlations with meteors detected by VHF forward scatter means. Preliminary results of the present study tend to show a significant correlation between certain meteors and the time-correlated corresponding ELF/VLF events.

Rault, J. L.

2010-09-01

176

Arecibo emission-absorption observations of Galactic OH  

International Nuclear Information System (INIS)

Observations of OH emission/absorption toward 19 low-Galactic-latitude background-continuum sources are reported. Data obtained at 1.665 and 1.667 GHz using the 12-m radio telescope at Arecibo Observatory during February-March 1984, are presented in extensive tables and graphs and characterized in detail, with reference to theoretical models. A total of 11 OH absorption features were detected toward nine of the sources, with an average of one feature of optical depth 0.02 or greater per 5 kpc of path length and an average column density of 1.6 x 10 to the 12th/sq cm (corrected to b = 90 deg). 35 references

1989-01-01

177

Observations of Microwave Continuum Emission from Air Shower Plasmas  

CERN Document Server

We investigate a possible new technique for microwave measurements of ultra-high energy cosmic ray (UHECR) extensive air showers which relies on detection of expected continuum radiation in the microwave range, caused by free-electron collisions with neutrals in the tenuous plasma left after the passage of the shower. We performed an initial experiment at the AWA (Argonne Wakefield Accelerator) laboratory in 2003 and measured broadband microwave emission from air ionized via high energy electrons and photons. A follow-up experiment at SLAC (Stanford Linear Accelerator Center) in summer of 2004 confirmed the major features of the previous AWA observations with better precision and made additional measurements relevant to the calorimetric capabilities of the method. Prompted by these results we built a prototype detector using satellite television technology, and have made measurements indicating possible detection of cosmic ray extensive air showers. The method, if confirmed by experiments now in progress, cou...

Gorham, P W; Varner, G S; Beatty, J J; Connolly, A; Chen, P; Conde, M E; Gai, W; Hast, C; Hebert, C L; Miki, C; Konecny, R; Kowalski, J; Ng, J; Power, J G; Reil, K; Saltzberg, D; Stokes, B T; Walz, D

2007-01-01

178

Observations of CO emission from diffuse interstellar clouds  

International Nuclear Information System (INIS)

We report measurements of, and upper limits for, millimeter-wavelength CO emission from interstellar clouds which have previously been studied via optical absorption lines. Along with CO measurements made by the Copernicus satellite, the results can be used to place constraints on models for interstellar chemistry. Our results are roughly consistent with models in which CO is produced by gas-phase reactions, and we find evidence to support calculations that a necessary but not sufficient condition for detecting the millimeter-wavelength CO lines is that the total gas density be greater than about 1000 cm-3. Some of the clouds we have observed appear to be nearly self-gravitating and may therefore be in the very first stages of star formation

1976-11-01

179

VLA observations of formaldehyde emission from Rho Ophiuchi B  

International Nuclear Information System (INIS)

The 2(11)-2(12) H2CO K-doublet emission source in the Rho Ophiuchi B cloud core has been observed with an angular resolution of 10 arcsec. The core contains 1-4 solar masses of dense molecular gas within a region 0.05 x 0.02 pc in spatial extent. Maps with spectral resolution of 0.25 km/s exhibit structure on size scales approximately the same as the Jeans length, approximately 0.01 pc. Systematic variations in the positions of the peak line intensities with velocity suggest that the core may be comprised of at least two small rotating fragments. These fragments contain masses typical of low-mass stars and have densities and linear sizes expected of protostars. 13 references

1985-01-01

180

Observational Signatures of Lyman Alpha Emission from Early Galaxy Formation  

CERN Multimedia

The next generation of telescopes aim to directly observe the first generation of galaxies that initiated the reionization process in our Universe. The Lyman Alpha (Lya) emission line is robustly predicted to be the most prominent intrinsic spectral feature of these galaxies, making it an ideal target to search for and study high-redshift galaxies. I briefly discuss why Lya emitting galaxies (LAEs) provide a good probe of the intergalactic medium (IGM) during the Epoch of Reionization (EoR). I argue that if we wish to fully exploit LAEs as a probe of the EoR, it is important to understand what drives their observed redshift evolution after reionization is completed. One important uncertainty in interpreting existing LAE observations relates to the impact of the ionized IGM on Lya photons emitted by galaxies, which is strongly connected to the effects of scattering through HI in galactic outflows. Scattering through galactic outflows can also modify the Lya spectral line shape such that > 5% of the emitted Lya...

Dijkstra, Mark

2011-01-01

 
 
 
 
181

Spectroscopic observations of 10 emission-line dwarf galaxies  

Energy Technology Data Exchange (ETDEWEB)

Oxygen, helium, and neon abundances are derived from image-dissector scanner observations of 10 emission-line dwarf galaxies. The n(0)/n(H) ratios range from 0.025 to 0.5 the solar value, with the expected anticorrelation with gas temperature. Assuming that n(Ne/sup + +/)/n(O/sup + +/)roughly-equaln(Ne)/n(O), we find a value of 0.23 for this ratio, which is about 50% higher than the values quoted for Orion and the Magellanic Clouds. The mean ratio of n(He/sup +/, He/sup + +/)/n(H/sup +/) is 0.082 +- 0.007 for the five best observed galaxies: we do not detect any correlation of this ratio with the oxygen abundance. Reasons are given to refrain from deriving nitrogen abundances for these galaxies. It seems likely that the underlying continua in these galaxies come predominantly from mixtures of O-type stars and moderately hot giants and supergiants.

Kinman, T.D.; Davidson, K.

1981-01-01

182

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 Earths 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

183

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; Frie, Udo; Phler, Denis; Johnston, Paul; Kreher, Karin; Robinson, Andrew D.; Thomas, Alan; Harris, Neil R. P.; Platt, Ulrich

2014-05-01

184

Galactic neutral hydrogen emission-absorption observations from Arecibo  

International Nuclear Information System (INIS)

We have observed the interstellar medium in the directions of 27 extragalactic sources at high and intermediate galactic latitudes (vertical-barb/sup ii/vertical-bar>50) at 21 cm wavelength with the upgraded Arecibo telescope (HPBW=3'.2, gainapprox.6 K Jy-1). The small beam greatly reduces the uncertainty in the derived on-source emission profile and increases confidence that it corresponds to the same material as the absorption spectrum. Each region has been observed for approximately 2 hours to tetect optical depths as low as 10-2 in most cases. The data allow the derivation of optical depths, harmonic mean spin temperatures, and column densities for the neutral hydrogen as a function of velocity in the range -200-1 (LSR) with resolution as fine as 0.25 km s-1. Spin temperatures as high as 1000 K are evident with a significant fraction of the neutral hydrogen still hotter. The cooler material is distributed over all temperatures from 30 K to at least 800 K. At latitudes below vertical-barb/sup ii/vertical-bar0 values for the harmonic mean temperature T/sub spin/ in the range 100 K to 300 K are most common.We have detected 66 separate absorption features, tentatively associated with neutral hydrogen clouds, with central temperatures ranging from 30 to 500 K. These features conform well to the relationship T/sub spin/=45(1-e/sup -tau/)/sup -0.5/ (K), over a broad range of values of the optical depth. The velocity distribution of these clouds shows a significant negative-velocity ''tail'' at high and intermediate latitudes. The mean square velocity of the clouds seems to depend on optical depth: v/sub rms/ is greater (approx.11 km s-1) for the optically thin clouds (tau-1). High-negative-velocity emission (v-1) has been detected in six directions; in two of these corresponding absorption features are evident, indicating cool neutral material

1978-01-01

185

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

186

Regional nitrogen oxides emission trends in East Asia observed from space  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

2013-01-01

187

Co-ordinated observations of transient luminous events during the EuroSprite2003 campaign  

DEFF Research Database (Denmark)

During the Northern Hemisphere summer of 2003 a sprite observation campaign was conducted from Southern Europe and the magnetically conjugate region in South Africa. The campaign brought together a wide variety of instrumentation to investigate the effects of sprites on the mesosphere, and to search for signatures of the relativistic electron acceleration process in the magnetically conjugate hemisphere. Measurements in Europe included optical video imaging from a remote-controlled, semi-automatic camera system located at the Observatoire du Pic du Midi in the Pyrenees mountains in Southern France, infrasound observations from France, and ULF-HF electromagnetic observations from a number of locations. The measurements in South Africa included observations of optical emissions and VLF electromagnetic waves. The campaign was successful, with more than 100 sprites observed during 10 storms. The paper will give an overview of the campaign and some results. They include: (1) the first clear identification of infrasound from sprites, allowing independent (of optical observations) estimates of the energy input to the mesosphere, (2) the first detection of sprites triggered by intra-cloud lightning, a result that underscores the need for considering the complete thunderstorm source field resulting from both cloud-to-ground discharges and the intra-cloud discharges feeding them, and (3) a clear one-to-one relationship with sprites and early VLF events, suggesting that VLF ground transmitter signals can be an important tool for estimating ionisation and relaxation of ionised structures in sprites. No signatures of relativistic electrons were identified during the campaign.

Neubert, Torsten; Allin, Thomas Højgaard

2005-01-01

188

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.)

1979-05-26

189

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Dufour, G.; Wittrock, F.; Camredon, M.; Beekmann, M.; Richter, A.; Aumont, B.; Burrows, J. P.

2009-01-01

190

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

1993-01-01

191

Motorcycles, mopeds: polluting emissions and energy consumption. Initial observations  

Energy Technology Data Exchange (ETDEWEB)

The present French fleet of two-wheel vehicles is very heterogeneous (2- and 4-stroke engines with cubic capacity from 50 cm{sup 3} to 1300 cm{sup 3} and automatic or manual transmissions) and generally lacking in any anti-pollution system, which leads to high emission levels of carbon monoxide and unburned hydrocarbons. Mopeds have high emission levels compared to those of 4-wheel vehicles, which have decreased markedly since 1970. The following chart of limit values confirms that the gap between these two vehicle categories in polluting emissions has increased in just a few years. The implementation of more restrictive regulations about pollution emissions was delayed for a long time because of cumulative technological delays in comparison to private vehicles. But in the end a European directive differentiating two kinds of two-wheel vehicles: mopeds and motorcycles was voted in 1997 (no. 97/24). There are two stages (in 1999 and 2002 respectively) for lowering emissions levels for mopeds (engine size smaller than 50 cm{sup 3}). For motorcycles a single stage was set for 1999, with a second stage still under consideration. Given the high stakes in terms of decreased pollution emission rom the necessary technological leap for the shift from outmoded carburetor engines to more refined technology (injection + post-treatment) under ADEME's guidance, the issue of exhaust-pollution reduction of two-wheel vehicles was included in both the PRIMEQUAL programme, 'Automobile Pollution Emissions' and the PREDIT call for proposals, 'Cycle Fuel Engine Pollution Reduction' in 1999. Several projects of varying technical natures (evaluations of existing engines and technological studies of new solutions in engines and exhaust pollution reduction) have been implemented in partnership with specialist research laboratories (such as the IFP) and manufacturers and outfitters in the sector (Sagem, Arvin Exhaust, Peugeot Motorcycles). Moreover, as the principle for automobile air-conditioning had been retained, ADEME initiated a campaign for evaluating exhaust emissions and consumption by two-wheel vehicles in laboratory tests. This campaign makes it possible to obtain a 'photo' of present two-wheel emissions and consumption and to better gauge the stakes associated to the evolution of this category of vehicle. The goal of this present document is to establish the state of the art of what actually exists concerning the fleet and the levels of pollutant emissions through the findings of this testing campaign. (author)

Barbusse, St.

2001-05-01

192

Normal development of the fruitfly Drosophila in VLF magnetic fields  

International Nuclear Information System (INIS)

Attempts to substantiate irreversible actions of a variety of magnetic fields on the fruitfly, Drosophila melanogaster, have been successful and unsuccessful in about equal numbers. The most conspicuous mutagenic effects apparently induced by pulsed HF-fields failed to appear under continuous electromagnetic irradiation. This seems to correlate the observed damage with the VLF-components of the pulsed fields. The present investigation is motivated by the occurence of these components both in the atmosphere and in the vicinity of electrical appliances. A strain of normally viable wild type males and subnormally viable Attached-X y w females was used in which the yield and the sex ratio of the progeny indicate, respectively, the extent of developmental damage and of sex-linked recessive lethal mutation induced by the exposure to detrimental conditions. Evaluation of 73,800 flies from subsequent generations of a control group and two test groups raised in steady, or rotating, homogeneous 9.6 kHz magnetic fields of about 2.5 G did not reveal any developmental or hereditar load in the test groups. (orig.)

1977-01-01

193

Structure of VLF whistler mode sideband waves in the magnetosphere  

International Nuclear Information System (INIS)

An accurate determination is made of the sideband structure of ducted VLF whistler mode waves transmitted from Siple Station and observed at Lake Mistissini, Quebec. Single- and double-frequency experiments are described. It is shown that sideband spectra can be explained by nonlinear interactions between two or more lines in the magnetosphere, the line intensities required for such interactions being low. If one of the lines is a transmitted carrier, the other line can be as much as 40 dB lower in amplitude, implying that power line radiation (PLR) can be an important factor in sideband generation. It is shown that single-line sidebands are due to interactions between the input wave and harmonics of 60 Hz present within the duct (assumed to be PLR), and that double-line spectra are affected by their position relative to the same 60-Hz system of lines. A study of double-line spectra as a function of line separation and line amplitude ratio is made

1988-03-01

194

A generation mechanism for chorus emission  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A chorus generation mechanism is discussed, which is based on interrelation of ELF/VLF noise-like and discrete emissions under the cyclotron wave-particle interactions. A natural ELF/VLF noise radiation is excited by the cyclotron instability mechanism in ducts with enhanced cold plasma density or at the plasmapause. This process is accompanied by a step-like deformation of the energetic electron distribution function in the velocity space, which is situated at the boundary between resonant a...

Trakhtengerts, V. Y.

1999-01-01

195

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

196

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

1988-10-01

197

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 110 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

198

Extended Emission Sources Observed Via Two-Proton Correlations.  

Science.gov (United States)

Two-proton correlations were measured as a function of the total energy and relative momentum of the proton. The correlation is analyzed for different orientations of the relative momentum, which allows information on the size and lifetime of the emission...

T. C. Awes R. L. Ferguson F. E. Obenshain F. Plasil G. R. Young

1988-01-01

199

A generation mechanism for chorus emission  

Directory of Open Access Journals (Sweden)

Full Text Available A chorus generation mechanism is discussed, which is based on interrelation of ELF/VLF noise-like and discrete emissions under the cyclotron wave-particle interactions. A natural ELF/VLF noise radiation is excited by the cyclotron instability mechanism in ducts with enhanced cold plasma density or at the plasmapause. This process is accompanied by a step-like deformation of the energetic electron distribution function in the velocity space, which is situated at the boundary between resonant and nonresonant particles. The step leads to the strong phase correlation of interacting particles and waves and to a new backward wave oscillator (BWO regime of wave generation, when an absolute cyclotron instability arises at the central cross section of the geomagnetic trap, in the form of a succession of discrete signals with growing frequency inside each element. The dynamical spectrum of a separate element is formed similar to triggered ELF/VLF emission, when the strong wavelet starts from the equatorial plane. The comparison is given of the model developed using some satellite and ground-based data. In particular, the appearance of separate groups of chorus signals with a duration 2-10 s can be connected with the preliminary stage of the step formation. BWO regime gives a succession period smaller than the bounce period of energetic electrons between the magnetic mirrors and can explain the observed intervals between chorus elements.

Key words. Magnetospheric physics (Energetic particles trapped. Space plasma physics (wave-particle interactions; waves and instabilities

V. Y. Trakhtengerts

200

Principal component analysis of sub-ionospheric VLF propagation conditions  

International Nuclear Information System (INIS)

Complete text of publication follows. Very Low Frequency (VLF) waves propagate with insignificant attenuation in the Earth-ionosphere waveguide. Attenuation is, however, appreciably higher on illuminated paths due to the presence of the ionospheric D region. Propagation conditions may be monitored using a narrow-band receiver tuned to the stable signals from numerous VLF transmitters distributed across the surface of the Earth. The passage of the day-night terminator across the transmitter-receiver path has a characteristic signature on the amplitude and phase of the signal. Principal Component Analysis (PCA) has been applied to distinguish between the regular diurnal signal variation and exogenous perturbations.

2009-08-23

 
 
 
 
201

Mg{sup +} and other metallic emissions observed in the thermosphere  

Energy Technology Data Exchange (ETDEWEB)

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{sup +} and Ca{sup +} 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{sup +} 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 species.

Gardner, J.A. [PhotoMetrics, Inc., Woburn, MA (United States); Viereck, R.A.; Murad, E.; Lai, S.T.; Knecht, D.J.; Pike, C.P. [USAF Phillips Lab., Hanscom AFB, MA (United States). Spacecraft Interactions Branch; Broadfoot, A.L.; Anderson, E.R. [Univ. of Arizona, Tucson, AZ (United States). Lunar and Planetary Observatory; McNeil, W.J. [Radex, Inc., Bedford, MA (United States)

1994-12-31

202

SCIAMACHY formaldehyde observations: constraint for isoprene emissions over Europe?  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, never studied before, and investigate the influence of the diffe...

Dufour, G.; Wittrock, F.; Camredon, M.; Beekmann, M.; Richter, A.; Burrows, J.

2008-01-01

203

Extended emission sources observed via two-proton correlations  

International Nuclear Information System (INIS)

Two-proton correlations were measured as a function of the total energy and relative momentum of the proton. The correlation is analyzed for different orientations of the relative momentum, which allows information on the size and lifetime of the emission source to be extracted. The most energetic particles are emitted from a short- lived source of compound nucleus dimensions while the lower energy protons appear to be emitted from a source considerably larger than the compound nucleus. 9 refs., 3 figs

1988-06-06

204

Observation of J = 1 ? 0 emission from H15NC  

International Nuclear Information System (INIS)

Emission from the J = 1 ? 0 transition of H15NC has been detected in the direction of DR21(OH). The transition frequency of 88865.69 MHz was measured in the laboratory by microwave absorption spectroscopy. The 15N/13C isotopic abundance ratio of 1.01 for DR21(OH) is larger than those calculated from isotopes of HCN in other interstellar clouds, perhaps implying a localized enrichment in 15N in DR21(OH). (author)

1977-01-01

205

Interferometric observations of the mainline OH maser emission from OH127.8-0.0  

International Nuclear Information System (INIS)

The 1667-MHz OH maser emission from OH127.8-0.0 has been observed using MERLIN in its spectral line mode. These data were combined with previous MERLIN observations of the 1612-MHz emission to study in detail the relationship between the extended structures at the two frequencies. The structure observed is generally consistent with existing theories of maser pumping, although the lack of any mainline emission inside the well-defined eastern arc of 1612-MHz emission is difficult to explain. (author)

1985-09-01

206

Observations on some thermoluminescence emission centres in geological quartz  

Energy Technology Data Exchange (ETDEWEB)

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 110{sup o}C peak, which is used for pre-dose dating and the peak at 325{sup o}C, which is of significance for partial and selective bleach techniques and for optically stimulated luminescence (OSL) dating. Because the 325{sup o}C 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 375{sup o}C 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).

Scholefield, R.B.; Prescott, J.R.; Fox, P.J. [Adelaide Univ., SA (Australia). Dept. of Mathematical Physics; Franklin, A.D. [Maryland Univ., College Park, MD (United States). Dept. of Physics and Astronomy

1994-04-01

207

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)

1994-01-01

208

Estimation of NOx Emissions from megacities using mobile MAX-DOAS and satellite observations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The focus of this study is on the quantification of NOx emissions. We characterized and quantfified vertically integrated NO2 concentrations (VCDs) and NOx emissions by using mobile MAX-DOAS and satellite observations. The mobile MAX-DOAS observations are conducted on different circles around megacities. From the combination of MAX-DOAS

2012-01-01

209

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

210

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 observations a...

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

2010-01-01

211

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 observations a...

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

2009-01-01

212

Electric fields, electron precipitation, and VLF radiation during a simultaneous magnetospheric substorm and atmospheric thunderstorm  

International Nuclear Information System (INIS)

A balloon payload instrumented with a double-probe electric field detector and an X ray scintillation counter was launched from Roberval, Quebec, Canada (L=4.1) at 0828 UT (0328 LT) on July 9, 1975. A magnetospheric substorm was observed locally between 0815 and 1100 UT, which produced a maximum ?B of approx.500 nT at approx.0930 UT. A single-cell atmospheric thunderstorm developed northeast of Roberval beginning around 0925 UT which was most intense from approx.1000 to 1035 UT. Detailed study of the electrical properties of the thunderstorm, the X ray precipitation data, and VLF spheric data leads to three conclusions. First, the electrical coupling from the thunderstorm to the magnetosphere increases with frequency from dc to the VLF; for the observed storm the amplitude at the ionosphere of thunderstorm produced electric fields was not significant at frequencies below 0.1 Hz. Second, the atmospheric conductivity above the thunderstorm was observed to be about one-half the fair weather value prior to 1000 UT; decreased to about one-quarter the fair weather value at about 1000 UT; and remained depressed after the end of the thunderstorm. This result was contrary to that expected on the basis of previous work and is one which merits considerably more investigation. Third, the data show a high probability that half-hop whistlers initiated by sferics from the thunderstorm triggered energetic electron precipitation from the magnetosphere

1980-01-01

213

Electric fields, electron precipitation, and VLF radiation during a simultaneous magnetospheric substorm and atmospheric thunderstorm  

Energy Technology Data Exchange (ETDEWEB)

A balloon payload instrumented with a double-probe electric field detector and an X ray scintillation counter was launched from Roberval, Quebec, Canada (L=4.1) at 0828 UT (0328 LT) on July 9, 1975. A magnetospheric substorm was observed locally between 0815 and 1100 UT, which produced a maximum ..delta..B of approx.500 nT at approx.0930 UT. A single-cell atmospheric thunderstorm developed northeast of Roberval beginning around 0925 UT which was most intense from approx.1000 to 1035 UT. Detailed study of the electrical properties of the thunderstorm, the X ray precipitation data, and VLF spheric data leads to three conclusions. First, the electrical coupling from the thunderstorm to the magnetosphere increases with frequency from dc to the VLF; for the observed storm the amplitude at the ionosphere of thunderstorm produced electric fields was not significant at frequencies below 0.1 Hz. Second, the atmospheric conductivity above the thunderstorm was observed to be about one-half the fair weather value prior to 1000 UT; decreased to about one-quarter the fair weather value at about 1000 UT; and remained depressed after the end of the thunderstorm. This result was contrary to that expected on the basis of previous work and is one which merits considerably more investigation. Third, the data show a high probability that half-hop whistlers initiated by sferics from the thunderstorm triggered energetic electron precipitation from the magnetosphere.

Bering, E.A.; Rosenberg, T.J.; Benbrook, J.R.; Detrick, D.; Matthews, D.L.; Rycroft, M.J.; Saunders, M.A.; Sheldon, W.R.

1980-01-01

214

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

215

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

Science.gov (United States)

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 patterns 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). 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 1.8 higher than GFED v3 values. For savanna, woodland, and deforestation fires, early dry season NOx emission factors were a factor of ~1.5-2 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, supporting the hypothesis that prolonged dry spells may lead to an increase in the contribution of smoldering combustion from large-diameter fuels, offsetting 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.

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

2014-04-01

216

An Empirical Study of ELF and VLF Shield Cans.  

Science.gov (United States)

An empirical ELF and VLF study of 1/16- and 1/32-inch-thick shield cans (stainless steel, aluminum, copper, Polyform, annealed Hipernom, and annealed and unannealed cold-rolled steel, mumetal, and Co-Netic) was performed to investigate shielding effective...

J. R. Moser

1967-01-01

217

Saturation Effects in the VLF Scattering off Strongly Heated Ionosphere  

Science.gov (United States)

The HAARP ionospheric HF heating facility modifies the conductivity of the lower ionosphere, creating a perturbation in the propagation of VLF transmitter-generated waves. The changes in the VLF amplitude may be detected by ground-based receivers and satellites with VLF instruments. In order to quantify these effects, we introduce a novel computational technique which combines the Stanford FWM (full-wave method) with the method of moments (MoM) to calculate the scattering on localized strong perturbations in stratified media. The Born approximation, which was previously used for similar calculations [Lehtinen et al., 2010], neglects the scattered field inside the perturbation region and therefore becomes invalid when the scattered field is of the order of the incident field, which happens when the perturbation is strong (i.e., the relative change of the conductivity is ~1). On the contrary, the use of MoM allows us to calculate the effects of the total field and thus may be applied to situations with any level of perturbation. This technique is applied to the VLF scattering off ionospheric disturbances created by HF heating. We show how the field measured on the ground and at a satellite deviates from that calculated previously in the Born approximation by demonstrating saturation effects for strong heating.

Lehtinen, N. G.; Bell, T. F.; Inan, U. S.

2011-12-01

218

Observations at 843 MHz of quiescent emission from the flare star AT Mic  

Energy Technology Data Exchange (ETDEWEB)

The Molonglo Observatory Synthesis Telescope was used in 1983 and on four occasions in 1985 to map the 843-MHz continuum emission from a field including the flare star AT Mic. Quiescent emission, apparently from the star, was detected. The flux density varied from one observation to another, in the range 3 to 8 mJy at 843 MHz. These observations are thought to be the first reported of quiescent emission from a flare star at such a low frequency. The emission mechanism is not known.

Vaughan, A.E.; Large, M.I.

1986-11-15

219

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

220

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 20072011 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 20072011 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

 
 
 
 
221

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 Earths 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

222

An assessment of plasma instabilities or planetary lightning as a source for the VLF bursts detected at Venus  

Science.gov (United States)

Very low frequency (VLF) signals detected in the nightside ionosphere of Venus have generally been attributed to atmospheric lightning. However it has recently been suggested that these bursts could be generated by either whistler-mode or lower hybrid drift instabilities. It has previously been shown that the growth rate for whistler-mode instabilities in the nightside ionosphere is too small for appreciable growth at altitudes less than 200 km, where the VLF burst rate is highest. We show that the bursts are usually observed in regions of low electron beta, where whistler-mode attenuation is small. We further show that many of the bursts are detected in regions of high collision frequency, which stabilizes the lower hybrid drift instability. Lastly, the waves are also detected in regions where the wavelength required for Doppler-shift of lower hybrid waves to 100 Hz is shorter than the electron Larmor radius, which also argues against a lower hybrid drift instability. Planetary lightning is consequently a more likely source for the VLF bursts.

Strangeway, R. J.

1995-01-01

223

The National Emissions Inventory Significantly Overestimates NOx Emissions: Analysis of CMAQ and in situ observations from DISCOVER-AQ  

Science.gov (United States)

NOx and CO not only adversely impact human health, but they, along with associated VOCs, are also important precursors for O3 formation. While ambient NOx and CO concentrations have decreased dramatically over the past 10-20 years, O3 has remained a more recalcitrant problem, particularly in the Baltimore/Washington region. Reduction of O3 production requires that emissions inventories, such as the National Emissions Inventory (NEI), accurately capture total emissions of CO and NOx while also correctly apportioning them among different sectors. Previous evaluations of the NEI paint different pictures of its accuracy, with assertions that it overestimates either one or both of CO and NOx from anywhere between 25 percent to a factor of 2. These conflicting claims warrant further investigation. In this study, measurements of NOx and CO taken aboard the NOAA P3B airplane during the 2011 DISCOVER-AQ field campaign were used to determine the NOx/CO emissions ratio at 6 locations in the Washington/Baltimore region. An average molar emissions ratio of 12.8 1.2 CO/NOx was found by calculating the change in CO over the change in NOx from vertical concentration profiles in the planetary boundary layer. Ratios showed little variation with location. Observed values were approximately a factor of 1.35 - 1.75 times greater than that predicted by the annual, countywide emissions ratio from the 2008 NEI. When compared to a temporalized, gridded version of the inventory processed by SMOKE, ratio observations were greater than that predicted by inventories by up to a factor of 2. Comparison of the in situ measurements and remotely sensed observations from MOPITT of CO to the Community Multiscale Air Quality (CMAQ) model agree within 10-35 percent, with the model higher on average. Measurements of NOy by two separate analytical techniques, on the other hand, show that CMAQ consistently and significantly overestimates NOy concentrations. Combined with the CO observations, this indicates that the NEI overestimates NOx emissions by approximately a factor of 2. Comparison of the temporalized NEI to continuous monitoring of NOx emissions from point sources shows that, on average, agreement between observations and the NEI were within 5 percent. In a region where the NEI estimates on-road emissions can account for 50-75 percent of total NOx, the most likely source of error in the NOx inventory is in the on-road sector. Assumptions about the lifetime and efficacy of catalytic converters in the MOVES model should be investigated as a possible source of this error.

Anderson, D. C.; Dickerson, R. R.; Loughner, C.

2013-12-01

224

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Zavala, M.; Molina, Mario J.; Lei, Wenfang; Molina, Luisa Tan

2008-01-01

225

Spitzer Observations of Centaurus A: Infrared Synchrotron Emission from the Northern Lobe  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present measurements obtained with the Spitzer Space Telescope in five bands from 3.6-24 microns of the northern inner radio lobe of Centaurus A, the nearest powerful radio galaxy. We show that this emission is synchrotron in origin. Comparison with ultraviolet observations from GALEX shows that diffuse ultraviolet emission exists in a smaller region than the infrared but also coincides with the radio jet. We discuss the possibility, that synchrotron emission is responsib...

Brookes, M. H.; Lawrence, C. R.; Keene, J.; Stern, D.; Gorijan, V.; Werner, M.; Charmandaris, V.

2006-01-01

226

IUE observations of Mg2 emission form Miras  

Science.gov (United States)

A total of 61 well exposed low dispersion LWP observations were obtained from the brightest normal M-type Mira variables around their pulsation cycles. By observing Mg II throughout the cycle, the intent is to determine the shock luminosity and duration, and the density in the upper atmospheres of Miras. The data also provide a mechanism for probing the radiative cooling in postshock regions of the atmosphere as a function of time. A summary of data acquired for IUE programs SRHLW and MGIEB is presented.

Brugel, Edward W.

1987-01-01

227

Observations of CO J = 3 ? 2 emission from molecular clouds  

International Nuclear Information System (INIS)

Extensive observations in the J = 3 ? 2 transition of carbon monoxide at 345 GHz (870 ?m) have been obtained using an indium anti-monide heterodyne spectral-line receiver with the United Kingdom 3.8-m Infrared Telescope (UKIRT) at Mauna Kea. Mapping observations of up to 1/2 deg"2 areas are reported towards the sources NGC 1333, 2023, 2024 and 2068. These maps, obtained with a 55-arcsec beam, reveal a number of new molecular hotspots as well as confirming the previous detection of molecular cool-spots. High-quality spectra have been obtained towards the self-absorbed sources NGC 1333 IRS-1, NGC 2071, Mon R2, AFGL 961 and DR 21. These spectra are similar to those observed in lower CO transitions, but there is a tendency for the redshifted wing to be enhanced in the J = 3 ? 2 transition. Spectral observations are also reported for L 1551/HH-29. Analysis of the variation of gas kinetic temperature around several of the mapped sources shows close agreement with the expected grain kinetic temperature, assuming these sources to be irradiated by single central stars of a spectral class similar to that estimated from other methods. The present data support the previous model (from CO J = 1 ? 0 data) for NGC 2071 and show it to be a rotating cloud. (author)

1981-01-01

228

ENA Emission from Low Altitude: A Survey of Medium Energy Neutral Atom (MENA) Observations from IMAGE  

Science.gov (United States)

The precipitation of ring current ions into the upper atmosphere can provide a regionally important source of energy and ionization. The interaction of these ions with the upper atmosphere produces a non-isotropic Energetic Neutral Atom (ENA) emission that can be observed remotely by ENA imaging instrumentation on a suitably located spacecraft. We have recently developed a numerical algorithm for recognizing the signature of ENA emissions from low altitude in the IMAGE/MENA summary spectrograms. We use this algorithm to gather statistics on the observation of these emissions. We will present an overview of MENA observations of ENA emissions from low altitude throughout the IMAGE mission life, focusing on the spatial distributions of these emitted ENAs around Earth and the dependence of the emission on geomagnetic activity, especially the phase of the geomagnetic storm. Finally, we are working to extend our recognition algorithm to the TWINS data set and will provide a progress report on that activity.

Mackler, D.; Jahn, J.; McComas, D.; Pollock, C.; Schaefer, D.; Valek, P.

2008-12-01

229

Stimulation of Pc 1 geomagnetic pulsations by naturally occurring repetitive VLF activity  

Science.gov (United States)

Several different mechanisms have been suggested for the natural stimulation of Pc 1 geomagnetic pulsation events, including hydromagnetic noise in the magnetosphere, bursts of radiation from high-energy charged particles, or sferics from lightning discharges. Guided by the results of experiments to generate Pc 1 pulsations by VLF transmissions into the magnetosphere, and by the theory that has been developed in support of these experiments, is proposed: the stimulation of Pc 1 pulsation events by naturally occurring repetitive VLF signals. The VLF signals may be echoing whistlers, periodic chorus elements, or other periodic or quasi-periodic VLF wavetrains echoing along a geomagnetic field line. Preliminary support for this hypothesis is provided by a comparison of the Pc 1 pulsations and VLF activity occurring at Roberval, Quebec, during nine intervals of simultaneous Pc 1 pulsation and VLF measurement.

Fraser-Smith, A. C.; Helliwell, R. A.

1980-10-01

230

Observations of CO J = 3 ? 2 emission from molecular clouds  

International Nuclear Information System (INIS)

Observational studies of interstellar Carbon Monoxide have enabled astronomers to gather a wealth of information on the structure, energetics and kinematics of galactic molecular clouds. In this paper new data obtained using the 3.8 m United Kingdom Infrared Telescope (UKIRT) with the QMC and UKIRT submillimeter heterodyne receivers are reported. These cryogenic heterodyne systems have system noise temperatures varying between 270 K at 220 GHz and 400 K at 370 GHz. Spectra and maps have been obtained towards many galactic star formation regions (NGC 1333 (IRS-1), NGC 2071, Mon R2 and AFGL 961). Some of the observed data in the J = 1 ? 0, J = 2 ? 1 and J = 3 ? 2 CO transitions, where the data from lower transitions are collected from the literature using telescopes with similar beam sizes, are compared. (Auth.)

1981-06-26

231

Observation of lasing emission from carbon nanodots in organic solvents.  

Science.gov (United States)

Lasing is observed from carbon nanodots (C-dots) dispersed into a layer of poly(ethylene glycol) coated on the surface of optical fibers under 266 nm optical excitation. This is due to the enhancement of photoluminescence intensity via the esterification of carboxylic groups of the C-dots, and the formation of high-Q cylindrical microcavities to support second-type whispering gallery modes. PMID:22454321

Zhang, W F; Zhu, H; Yu, S F; Yang, H Y

2012-05-01

232

Some observational tests of x-ray pulsar emission models  

International Nuclear Information System (INIS)

The understanding of neutron star physics which relies heavily on knowing values of their mass, radius and magnetic field strength was studied. The only information about these till now comes from the surface radiation. Major uncertainties concerning the nature of the mass exchange and the accretion flow, the magnetopause structure, the infall deceleration, the actual pulsation mechanism and the atmosphere geometry are examined. The alternatives and several possible observational tests are discussed

1981-01-01

233

Observations and predictions of EUV emission from classical novae  

Energy Technology Data Exchange (ETDEWEB)

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.

Starrfield, S.; Truran, J.W.; Sparks, W.M.; Krautter, J.

1989-01-01

234

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

235

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

236

Relationship between ionospherically produced elf/vlf signals and the dynamo current system at Arecibo  

International Nuclear Information System (INIS)

This thesis describes a theoretical and experimental study of the relationship between the dynamo current system and the elf/vlf signals produced by periodic heating, via powerful h-f waves, of the lower ionosphere. Theory is developed that allows prediction of the direction of the major axis of the magnetic field polarization ellipse at ground level from the direction of the dynamo current system as deduced from magnetometer records. Single-slab and multi-slab ionospheric models are used to explain the effect of the lower D region upon the direction of the major axis of the magnetic field polarization ellipse at ground level. A sensitivity study shows that the D region collisions frequency is the most important factor in determining the relationship between the direction of the dynamo current system and the direction of the major axis of the magnetic field polarization ellipse major axis at ground level. Experimental evidence is presented to show that the direction of the major axis of the magnetic field polarization ellipse observed on the ground changes, as a function to time of day, in apparent synchronism with the changing direction of the dynamo current system. Evidence presented shows that the elf/vlf signals described in this work are ionospheric in origin

1984-01-01

237

Relationship between ionospherically produced elf/vlf signals and the dynamo current system at Arecibo  

Energy Technology Data Exchange (ETDEWEB)

This thesis describes a theoretical and experimental study of the relationship between the dynamo current system and the elf/vlf signals produced by periodic heating, via powerful h-f waves, of the lower ionosphere. Theory is developed that allows prediction of the direction of the major axis of the magnetic field polarization ellipse at ground level from the direction of the dynamo current system as deduced from magnetometer records. Single-slab and multi-slab ionospheric models are used to explain the effect of the lower D region upon the direction of the major axis of the magnetic field polarization ellipse at ground level. A sensitivity study shows that the D region collisions frequency is the most important factor in determining the relationship between the direction of the dynamo current system and the direction of the major axis of the magnetic field polarization ellipse major axis at ground level. Experimental evidence is presented to show that the direction of the major axis of the magnetic field polarization ellipse observed on the ground changes, as a function to time of day, in apparent synchronism with the changing direction of the dynamo current system. Evidence presented shows that the elf/vlf signals described in this work are ionospheric in origin.

Allshouse, R.L.

1984-01-01

238

A Broad View on the Interpretation of Electromagnetic Data (VLF, RMT, MT, CSTMT)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

239

Scalin features of VLF chorus observed by Magion-5.  

Czech Academy of Sciences Publication Activity Database

. Sapporo : Solarterrestrial environment laboratory Nagoya University, Radio science center for space and atmosphere Kyoto University, 2000. s. 238.[The first S-Ramp Conference. 02.10.2000-06.10.2000, Sapporo]Grant CEP: GA Mk OK 162; GA AV ?R IAA3042801Vzkumn zm?r: CEZ:AV0Z3042911Kd oboru RIV: BL - Fyzika plazmatu a vboje v plynech

Kozelov, B. V.; Titova, E. E.; Trakhtengerts, V. Y.; Ji??ek, Frantiek; T?ska, Pavel

240

Estimating Aerosol Emissions by Assimilating Remote Sensing Observations into a Global Transport Model  

Directory of Open Access Journals (Sweden)

Full Text Available We present a fixed-lag ensemble Kalman smoother for estimating emissions for a global aerosol transport model from remote sensing observations. We assimilate AERONET AOT and AE as well as MODIS Terra AOT over ocean to estimate the emissions for dust, sea salt and carbon aerosol and the precursor gas SO2. For January 2009, globally dust emission decreases by 26% (to 3,244 Tg/yr, sea salt emission increases by 190% (to 9073 Tg/yr, while carbon emission increases by 45% (to 136 Tg/yr, compared with the standard emissions. Remaining errors in global emissions are estimated at 62% (dust, 18% (sea salt and 78% (carbons, with the large errors over land mostly due to the sparseness of AERONET observations. The new emissions are verified by comparing a forecast run against independent MODIS Aqua AOT, which shows significant improvement over both ocean and land. This paper confirms the usefulness of remote sensing observations for improving global aerosol modelling.

Teruyuki Nakajima

2012-11-01

 
 
 
 
241

The observation of chemiluminescent NiO* emissions in the laboratory and in the night airglow  

Directory of Open Access Journals (Sweden)

Full Text Available The recent finding of an orange spectral feature in OSIRIS/Odin spectra of the night airglow near 87 km has raised interest in the origin of the emission. The feature was positively identified as the chemiluminescent FeO* emission where the iron is of meteoric origin. Since the meteorite source of atomic metals in the mesosphere contains both iron and nickel, with Ni being typically 6 % of Fe, it is expected that faint emissions involving Ni should also be present in the night airglow. The present study summarizes the laboratory observations of chemiluminescent NiO* emissions and includes a search for the NiO* signature in the night airglow. A very faint previously unidentified "continuum" extending longwave of 440 nm has been detected in the night airglow spectra obtained with two space-borne limb viewing instruments. Through a comparison with laboratory spectra this continuum is identified as arising from the NiO* emission. The altitude profile of the new airglow emission has also been measured. The similarity of the altitude profiles of the FeO* and NiO* emissions also suggests the emission is NiO as both can originate from reaction of the metal atoms with mesospheric ozone. The observed NiO* to FeO* ratio exhibits considerable variability; possible causes of this observed variation are briefly discussed.

W. F. J. Evans

2011-09-01

242

Observation of stimulated emission from an MBE grown GaN film on sapphire  

Energy Technology Data Exchange (ETDEWEB)

The authors report the first observation of optically pumped stimulated emission from an GaN epilayer at 77K and at room temperature grown by reactive ion-beam molecular beam epitaxy. The observed uv optical emission profile was a nonlinear function of the pump power density, with line narrowing at threshold power densities. The similarity in the emission profile as compared with those of films grown with low-pressure metal-organic chemical vapor deposition and metal-organic vapor phase epitaxy techniques will be noted.

Yung, K.; Yee, J.; Koo, J. [Lawrence Livermore National Lab., CA (United States); Rubin, M.; Newman, N.; Fu, T.; Ross, J. [Lawrence Berkeley Lab., CA (United States)

1993-11-12

243

100 eV electron temperatures in the Maryland centrifugal experiment observed using electron Bernstein emission  

Science.gov (United States)

Thermal electron Bernstein emission has been observed at the second harmonic of the electron cyclotron frequency at the mid-plane of the Maryland Centrifugal eXperiment. The emission is received in the X-mode polarization and coupled to the Bernstein wave by the B-X mode conversion process. The average B-X coupling efficiency is approximately 20%. The observed emission indicates thermal electron temperatures an excess of 100 eV in the core of the rotating plasma. The measured electron temperature is consistent with recent ion temperature measurements and indicates that the total energy confinement time exceeds 500 ?s.

Reid, R. R.; Romero-Talams, C. A.; Young, W. C.; Ellis, R. F.; Hassam, A. B.

2014-06-01

244

Constraints on ship NOx emissions in Europe using OMI NO2 observations  

Science.gov (United States)

Strong emissions of gases and particulate matter by ships affect the composition of the marine boundary layer, with important consequences for climate change, air quality and public health. Because hardly any regulations for the maritime sector exist in international waters, ships are still allowed to burn low-grade marine heavy fuel. As a result, ships emit large quantities of nitrogen oxides (NO x = NO + NO 2), important precursors for ozone (O 3) and particulate matter formation. Previous studies showed that global ship NO x emission inventories amount to 3.0-10.4 Tg N per year (15-30% of total NO x emissions), with most of these emissions within 400 km of the densely populated coastal regions. However, as individual measurements of ship emissions are sparse, and these few measurements are extrapolated, these bottom-up inventories suffer from large uncertainties. In this study we provide top-down constraints on ship NO x emissions in major European ship routes, using observed NO 2 columns from the Ozone Monitoring Instrument (OMI) and NO 2 columns simulated with the nested (0.5o0.67o) version of the GEOS-Chem chemistry transport model. Two simulations were performed using a plume-in-grid treatment of ship NO x emissions: (1) using EMEP and (2) using AMVER-ICOADS as ship emission inventory. We ensure consistency between the retrievals and model simulations by using the high-resolution GEOS-Chem NO 2 profiles as a priori. The OMI observations suggest that NO x emissions from the (2001) AMVER-ICOADS inventory are too low by a factor of 16 over the ship lane between Spain and the English Channel, and a factor of 10 over the lane between Cairo and Sicily. When comparing the OMI observations against the more recent (2005) EMEP inventory, our method unambiguously shows that ship emissions in the Mediterranean Sea are geographically misplaced by up to 150 km. EMEP emission totals however agree reasonably well with our OMI-constrained emissions over the eastern Mediterranean Sea. We present a new European ship emissions inventory for 2005-2006 which is based on the EMEP and AMVER-ICOADS inventories, and constrained with OMI NO 2 observations. Our work shows that satellite observations are essential in evaluating and improving our knowledge of both the location and magnitude of bottom-up emission inventories over sparsely monitored areas such as European seas, with important implications for exceedances of air quality standards in coastal regions.

Vinken, G. C.; Boersma, F.; van Donkelaar, A.; Zhang, L.

2012-12-01

245

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

246

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

247

Mapping Isoprene Emissions over North America using Formaldehyde Column Observations from Space  

Science.gov (United States)

I] We present a methodology for deriving emissions of volatile organic compounds (VOC) using space-based column observations of formaldehyde (HCHO) and apply it to data from the Global Ozone Monitoring Experiment (GOME) satellite instrument over North America during July 1996. The HCHO column is related to local VOC emissions, with a spatial smearing that increases with the VOC lifetime. lsoprene is the dominant HCHO precursor over North America in summer, and its lifetime (approx. = 1 hour) is sufficiently short that the smearing can be neglected. We use the Goddard Earth Observing System global 3-D model of tropospheric chemistry (GEOS-CHEM) to derive the relationship between isoprene emissions and HCHO columns over North America and use these relationships to convert the GOME HCHO columns to isoprene emissions. We also use the GEOS-CHEM model as an intermediary to validate the GOME HCHO column measurements by comparison with in situ observations. The GEOS-CHEM model including the Global Emissions Inventory Activity (GEIA) isoprene emission inventory provides a good simulation of both the GOME data (r(sup 2) = 0.69, n = 756, bias = +l1 %) and the in situ summertime HCHO measurements over North America (r(sup 2) = 0.47, n = 10, bias = -3%). The GOME observations show high values over regions of known high isoprene emissions and a day-to-day variability that is consistent with the temperature dependence of isoprene emission. Isoprene emissions inferred from the GOME data are 20% less than GEIA on average over North America and twice those from the U S . EPA Biogenic Emissions Inventory System (BEIS2) inventory. The GOME isoprene inventory when implemented in the GEOS-CHEM model provides a better simulation of the HCHO in situ measurements thaneitherGEIAorBEIS2 (r(sup 2) = 0.71,n= 10, bias = -10 %).

Palmer, Paul I.; Jacob, Daniel J.; Fiore, Arlene M.; Martin, Randall V.; Chance, Kelly; Kurosu, Thomas P.

2004-01-01

248

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

249

Chandra Observations and Modeling of Geocoronal Charge Exchange X-Ray Emission During Solar Wind Gusts  

Science.gov (United States)

Solar wind charge exchange (SWCX) X-rays are emitted when highly charged solar wind ions such as O7+ collide with neutral gas. The best known examples of this occur around comets, but SWCX emission also arises in the Earth's tenuous outer atmosphere and throughout the heliosphere as neutral H and He from the interstellar medium flows into the solar system. This geocoronal and heliospheric emission comprises much of the soft X-ray background and is seen in every X-ray observation. Geocoronal emission, although usually weaker than heliospheric emission, arises within a few tens of Earth radii and therefore responds much more quickly (on time scales of less than an hour) to changes in solar wind intensity than the widely distributed heliospheric emission.We have studied a dozen Chandra observations when the flux of solar wind protons and O7+ ions was at its highest. These gusts of wind cause correspondingly abrupt changes in geocoronal SWCX X-ray emission,which may or may not be apparent in Chandra data depending on a given observation's line of sight through the magnetosphere. We compare observed changes in the X-ray background with predictions from a fully 3D analysis of SWCX emission based on magnetospheric simulations using the BATS-R-US model.

Kornbleuth, Marc; Wargelin, Bradford J.; Juda, Michael

2014-06-01

250

Experiments on whistler wave filamentation and VLF hiss in a laboratory plasma  

Science.gov (United States)

With the development of a large magnetized plasma source it has become possible to investigate space plasma physics problems in the laboratory. First, the nonlinear effects associated with the excitation of a large amplitude whistler wave have been explored. It is found that the radiation pressure of the wave and thermal effects give rise to a field-aligned density depression in which the wave becomes completely trapped. Hyperfine filaments with diameters small compared with the parallel wavelength are observed. Second, the stability of oblique whistler waves in the presence of an electron beam has been studied. A broadband whistler instability is observed and identified as a Cherenkov interaction between beam electrons and whistlers propagating near the resonance cone. These observations confirm the present model for the generation of VLF hiss in the aurora.

Stenzel, R. L.

1977-01-01

251

Detection of karst structures using airborne EM and VLF  

International Nuclear Information System (INIS)

Through the combined use of multi-frequency helicopter electromagnetic and VLF data, it is possible to detect and delineate a wide variety of karst structures and possibly to assess their interconnectedness. Multi-frequency EM Can detect karst features if some element of the structure is conductive. This conductive aspect may derive from thick, moist soils in the depression commonly associated with a doline, from conductive fluids in the cavity, or from conductive sediments in the cavity if these occupy a significant portion of it. Multiple loop configurations may also increase the likelihood of detecting karst features. Preliminary evidence indicates total field VLF measurements may be able to detect interconnected karst pathways, so long as the pathways are water or sediment filled. Neither technique can effectively detect dry, resistive air-filled cavities

1994-10-23

252

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

253

Emissions of Biogenic Volatile Organic Compounds and Observations of VOC Oxidation at Harvard Forest  

Science.gov (United States)

The contribution of biogenic volatile organic compounds (BVOCs) to oxidant concentrations and secondary organic aerosol (SOA) production in forested environments depends on the emission rates of these compounds. Recent findings have suggested that the emission rates of BVOCs and the range of species emitted could be larger than previously thought. In this study, Proton Transfer Reaction Mass Spectrometry (PTR-MS) was used to obtain fast (vinyl ketone + methacrolein and terpene oxidation products were also measured. Isoprene is the dominant emitted species, with peak emission rates and midday mixing ratios of ca. 4 mg isoprene m-2 h-1 and ca. 5 ppbv, respectively. Isoprene emission rates are expected to vary with temperature and radiation (PAR) levels, and are compared to standard emission algorithms based on these parameters. Interannual variability in isoprene emission rates is also observed, and contributing factors are explored. In contrast to isoprene, maximum monoterpene concentrations typically were less than 1 ppbv and occurred in the early evening, with a local minimum at midday. Monoterpene fluxes are about an order of magnitude smaller than those of isoprene. The amplitude of the flux diurnal cycle suggests monoterpene emissions at Harvard Forest may exhibit light dependence as well as temperature dependence. Fluxes of oxygenated VOCs, including methanol, acetone, methyl ethyl ketone, and oxygenated terpenes that have rarely been observed previously, are also reported, and the dependence of their emission rates on factors such as time of year, temperature, radiation levels, and meteorological conditions are investigated.

McKinney, K. A.; Pho, T.; Vasta, A.; Lee, B. H.

2009-12-01

254

ELF/VLF Wave Generation with the HAARP Facility  

Science.gov (United States)

The recently upgraded HAARP facility, near Gakona, Alaska, utilizes 3.6 MW of HF (3-10 MHz) power along with an unprecedented ability to steer the HF heating beam over a large area extremely rapidly. In recent decades, HF heating has been successfully utilized to generate ELF/VLF (500 Hz - 10 kHz) radiation, via amplitude modulation of the HF beam. Through the temperature-dependent conductivity of the D-region ionospheric plasma, the lower ionosphere effectively becomes a large radiating antenna in the presence of currents, such as the naturally forming auroral electrojet. A variety of scientific and practical applications would benefit from more effective ability to generate and steer these generated signals, such as magnetospheric injection and study of subsequent wave-particle interactions, ionospheric diagnostics, and long-range communications, especially since additional upgrades to existing HF facilities are difficult. Some recent studies have focused on two particular efforts, known as geometric modulation and beam painting, to boost the generated amplitudes and implement more directional control, using motion of the HF beam. We discuss a set of experimental and theoretical efforts exploring the generation of these ELF/VLF waves, and their coupling to propagating signals in the Earth-ionosphere waveguide and the magnetosphere, utilizing HAARPs upgraded capabilities and an array of ELF/VLF receivers across Alaska. The theoretical formulation utilizes a 3D model of the HF collisional heating and subsequent collisional electron cooling processes, leading to spatial structure of modulated ionospheric conductivities, the results of which are input into an analytical model of ELF/VLF propagation in the Earth-ionosphere waveguide.

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

2009-12-01

255

The Search for VLF Precursors to Major Earthquakes: A Case Study with the M9.0 Earthquake of 11-Mar-2011 (Invited)  

Science.gov (United States)

It has been proposed that Very Low Frequency (VLF, 3-30 kHz) radio remote sensing may be used to detect ionospheric changes which may precede major earthquakes by hours or days. We report the results of a search for VLF precursors to the M9.0 Tohoku earthquake of 11-Mar-2011, the fifth most powerful earthquake in recorded history. Broadband and narrowband radio recordings were made at a site in Onagawa, Japan located ~102 km from the epicenter. The receiver operated for about two minutes after the start of the earthquake, after which the receiver lost power. Examination of the VLF data shows no radio emissions preceding or coincident with the onset of the earthquake. However, once the secondary seismic waves reached the receiver, a number of impulses and diffuse noise bands arose which may result from the entire power grid shaking or from radio emissions from compressing or fracturing rocks. Examination of the ELF data (0.2-1 kHz) shows no precursor effect in the hours preceding the seismic activity. We also examine the amplitudes of VLF subionospherically propagating transmitter signals going back months before the earthquake. We apply previously proposed techniques to extract properties of the diurnal amplitude profile that have been thought to correlate with earthquake precursors, but find no anomalous effect despite the remarkable intensity of the earthquake and proximity of the receiver to the epicenter. In general there are anomalous deviations but they cannot be reliably correlated with seismic activity. We also report the results of a global search for a lightning precursor effect on lightning flash rates, using the GLD360 network.

Cohen, M.; Kosovichev, P.; Marshall, R. A.; Droscoll, A.; Scherrer, D. K.

2013-12-01

256

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

Energy Technology Data Exchange (ETDEWEB)

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.

Kuo, S.P. [Polytechnic Univ., Farmingdale, NY (United States). Weber Research Inst.; Lee, M.C. [Massachusetts Inst. of Technology, Cambridge, MA (United States). Plasma Fusion Center

1995-12-31

257

Relative changes in CO emissions over megacities based on observations from space  

Science.gov (United States)

Urban areas are large sources of several air pollutants, with carbon monoxide (CO) among the largest. Yet measurement from space of their CO emissions remains elusive due to its long lifetime. Here we introduce a new method of estimating relative changes in CO emissions over megacities. A new multichannel Measurements of Pollution in the Troposphere (MOPITT) CO data product, offering improved sensitivity to the boundary layer, is used to estimate this relative change over eight megacities: Moscow, Paris, Mexico, Tehran, Baghdad, Los Angeles, Sao Paulo, and Delhi. By combining MOPITT observations with wind information from a meteorological reanalysis, changes in the CO upwind-downwind difference are used as a proxy for changes in emissions. Most locations show a clear reduction in CO emission between 2000-2003 and 2004-2008, reaching -43% over Tehran and -47% over Baghdad. There is a contrasted agreement between these results and the MACCity and Emission Database for Global Atmospheric Research v4.2 inventories.

Pommier, Matthieu; McLinden, Chris A.; Deeter, Merritt

2013-07-01

258

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

259

Observations of oxidation products above a forest imply biogenic emissions of very reactive compounds  

Directory of Open Access Journals (Sweden)

Full Text Available Vertical gradients of mixing ratios of volatile organic compounds have been measured in a Ponderosa pine forest in Central California (38.90 N, 120.63 W, 1315m. These measurements reveal large quantities of previously unreported oxidation products of short lived biogenic precursors. The emission of biogenic precursors must be in the range of 13-66mol m-2h-1 to produce the observed oxidation products. That is 6-30 times the emissions of total monoterpenes observed above the forest canopy on a molar basis. These reactive precursors constitute a large fraction of biogenic emissions at this site, and are not included in current emission inventories. When oxidized by ozone they should efficiently produce secondary aerosol and hydroxyl radicals.

R. Holzinger

2005-01-01

260

Two components of the coronal emission revealed by EUV spectroscopic observations  

CERN Document Server

Recent spectroscopic observations have revealed the ubiquitous presence of blueward asymmetries of emission lines formed in the solar corona and transition region. These asymmetries are most prominent in loop footpoint regions, where a clear correlation of the asymmetry with the Doppler shift and line width determined from the single Gaussian fit is found. Such asymmetries suggest at least two emission components: a primary component accounting for the background emission and a secondary component associated with high-speed upflows. The latter has been proposed to play a vital role in the coronal heating process and there is no agreement on its properties. Here we slightly modify the initially developed technique of Red-Blue (RB) asymmetry analysis and apply it to both artificial spectra and spectra observed by the EUV Imaging Spectrometer onboard Hinode, and demonstrate that the secondary component usually contributes a few percent of the total emission, has a velocity ranging from 50 to 150 km s-1 and a Gau...

Tian, Hui; De Pontieu, Bart; Martinez-Sykora, Juan; Sechler, Marybeth; Wang, Xin

2011-01-01

 
 
 
 
261

Near-infrared observation of the circumsolar dust emission during the 1983 solar eclipse  

International Nuclear Information System (INIS)

The authors have carried out observations of near-infrared brightness distributions of the solar corona, using a balloon-borne photometer at a balloon altitude, during the total eclipse on 11 June 1983 in Indonesia. As they report here, emissions in excess of the strong coronal background emission were recorded in some of the scans at approx. 4 R solar mass from the Sun. The spatial distribution of the excess emission implies the existence of a circumsolar ring of dust lying approximately in the ecliptic plane. (author)

1983-06-11

262

Observation of bistable upconversion emission in Tm,Yb codoped yttria nanocrystal  

Science.gov (United States)

Nonlinear upconversion emission properties in Tm and Yb codoped yttria nanocrystal have been studied under 973 nm laser excitation. Intrinsic bistability and hysteresis have been observed for the bright blue upconversion luminescence of Tm3+ ions at room temperature. The mechanism of the Tm3+ bistable emission is mainly related to laser-induced local thermal effects which cause the enhancement of sequential multi-photon energy transfer upconversion of Yb3+-Tm3+ pairs.

Li, L.; Li, H.; Zhang, X. L.; Peng, Y. F.; Nie, M.; Jiang, B.; Zhang, X. W.; Li, R. M.

2010-11-01

263

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 four-dimensional 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 time scales of weeks to months, short compared with the lifetime of methane. Observing System Simulation Experiments (OSSEs have been performed to demonstrate the feasibility of the method and to investigate the utility of SCIAMACHY observations for methane source estimation. The impact of a number of parameters on the error in the methane emission field retrieved has been analysed. These parameters include the measurement error, the error introduced by the presence of clouds, and the spatial resolution of the emission field. It is shown that 4D-var is an efficient method to deal with large amounts of satellite data and to retrieve emissions at high resolution. Some important conclusions regarding the SCIAMACHY measurements can be drawn. (i The observations at their estimated precision of 1.5 to 2% will contribute considerably to uncertainty reduction in monthly, subcontinental (~500 km methane source strengths. (ii Systematic measurement errors well below 1% have a dramatic impact on the quality of the derived emission fields. Hence, every effort should be made to identify and remove such systematic errors. (iii It is essential to take partly cloudy pixels into account in order to achieve sufficient spatial coverage. (iv The uncertainty in measured cloud parameters may at some point become the limiting factor for methane emission retrieval, rather than the uncertainty in measured methane itself.

J. F. Meirink

2006-01-01

264

Observations and interpretation of the infrared emission from supernova SN1987A  

Energy Technology Data Exchange (ETDEWEB)

Infrared spectrophotometric observations of SN1987A from the Kuiper Airborne Observatory are presented for the wavelength range 1.5 to 12.5 microns for five epochs at about 60, 260, 415, 615, and 777 days after the explosion. These data are combined with the ultraviolet, optical, infrared (UVOIR) measurements from ESO/CTIO and SAAO in order to characterize the continuum by three components: a photospheric contribution, free-free radiation, and the infrared emission from dust characterized by greybody radiation. Line flux measurements from the continuum substracted spectra are given, including the Brackett, Pfund, and Humphreys series of hydrogen and neutral and singly-ionized nickel and argon from the core ejecta. Carbon monoxide and silicon monoxide vibration bands are identified in the spectra. A simple analysis of the hydrogen line and free-free emission is presented. Dust radiative equilibrium calculations are performed. At 415 days, excess infrared emission, not accountable by circumstellar dust, was observed. At 615 and 777 days, this new component dominated the infrared continuum and is evidence for dust condensation in the ejecta of SN1987A. The shape of the infrared emission from newly formed dust is well characterized by the Planck curve, i.e., by a greybody, and therefore the grains which formed in the ejecta are either large or their emission arises from optically thick clumps. The radiative equilibrium temperature of the observed greybody emission indicates that the dust is in the metal-rich volume of the ejected core.

Wooden, D.H.

1989-01-01

265

Observations and interpretation of the infrared emission from supernova SN1987A  

International Nuclear Information System (INIS)

Infrared spectrophotometric observations of SN1987A from the Kuiper Airborne Observatory are presented for the wavelength range 1.5 to 12.5 microns for five epochs at about 60, 260, 415, 615, and 777 days after the explosion. These data are combined with the ultraviolet, optical, infrared (UVOIR) measurements from ESO/CTIO and SAAO in order to characterize the continuum by three components: a photospheric contribution, free-free radiation, and the infrared emission from dust characterized by greybody radiation. Line flux measurements from the continuum substracted spectra are given, including the Brackett, Pfund, and Humphreys series of hydrogen and neutral and singly-ionized nickel and argon from the core ejecta. Carbon monoxide and silicon monoxide vibration bands are identified in the spectra. A simple analysis of the hydrogen line and free-free emission is presented. Dust radiative equilibrium calculations are performed. At 415 days, excess infrared emission, not accountable by circumstellar dust, was observed. At 615 and 777 days, this new component dominated the infrared continuum and is evidence for dust condensation in the ejecta of SN1987A. The shape of the infrared emission from newly formed dust is well characterized by the Planck curve, i.e., by a greybody, and therefore the grains which formed in the ejecta are either large or their emission arises from optically thick clumps. The radiative equilibrium temperature of the observed greybody emission indicates that the dust is in the metal-rich volume of the ejected core

1989-01-01

266

Observations and interpretation of the infrared emission from supernova SN1987A  

Science.gov (United States)

Infrared spectrophotometric observations of SN1987A from the Kuiper Airborne Observatory are presented for the wavelength range 1.5 to 12.5 microns for five epochs at about 60, 260, 415, 615, and 777 days after the explosion. These data are combined with the ultraviolet, optical, infrared (UVOIR) measurements from ESO/CTIO and SAAO in order to characterize the continuum by three components: a photospheric contribution, free-free radiation, and the infrared emission from dust characterized by greybody radiation. Line flux measurements from the continuum substracted spectra are given, including the Brackett, Pfund, and Humphreys series of hydrogen and neutral and singly-ionized nickel and argon from the core ejecta. Carbon monoxide and silicon monoxide vibration bands are identified in the spectra. A simple analysis of the hydrogen line and free-free emission is presented. Dust radiative equilibrium calculations are performed. At 415 days, excess infrared emission, not accountable by circumstellar dust, was observed. At 615 and 777 days, this new component dominated the infrared continuum and is evidence for dust condensation in the ejecta of SN1987A. The shape of the infrared emission from newly formed dust is well characterized by the Planck curve, i.e., by a greybody, and therefore the grains which formed in the ejecta are either large or their emission arises from optically thick clumps. The radiative equilibrium temperature of the observed greybody emission indicates that the dust is in the metal-rich volume of the ejected core.

Wooden, Diane Holland

267

Toward observationally constrained high space and time resolution CO2 urban emission inventories  

Science.gov (United States)

The spatial patterns of greenhouse gas (GHG) emission and sequestration are currently studied primarily by sensor networks and modeling tools that were designed for global and continental scale investigations of sources and sinks. In urban contexts, by design, there has been very limited investment in observing infrastructure, making it difficult to demonstrate that we have an accurate understanding of the mechanism of emissions or the ability to track processes causing changes in those emissions. Over the last few years, our team has built a new high-resolution observing instrument to address urban CO2 emissions, the BErkeley Atmospheric CO2 Observing Network (BEACON). The 20-node network is constructed on a roughly 2 km grid, permitting direct characterization of the internal structure of emissions within the San Francisco East Bay. Here we present a first assessment of BEACON's promise for evaluating the effectiveness of current and upcoming local emissions policy. Within the next several years, a variety of locally important changes are anticipated--including widespread electrification of the motor vehicle fleet and implementation of a new power standard for ships at the port of Oakland. We describe BEACON's expected performance for detecting these changes, based on results from regional forward modeling driven by a suite of projected inventories. We will further describe the network's current change detection capabilities by focusing on known high temporal frequency changes that have already occurred; examples include a week of significant freeway traffic congestion following the temporary shutdown of the local commuter rail (the Bay Area Rapid Transit system).

Maness, H.; Teige, V. E.; Wooldridge, P. J.; Weichsel, K.; Holstius, D.; Hooker, A.; Fung, I. Y.; Cohen, R. C.

2013-12-01

268

Observations, theory and implications of thermal emission from gamma-ray bursts  

CERN Multimedia

Recent analyses show evidence for a thermal emission component that accompanies the non-thermal emission during the prompt phase of GRBs. First, we show the evidence for the existence of this component; Second, we show that this component is naturally explained by considering emission from the photosphere, taking into account high latitude emission from optically thick relativistically expanding plasma. We show that the thermal flux is expected to decay at late times as F_BB ~ t^{-2}, and the observed temperature as T ~ t^{-\\alpha}, with \\alpha ~ 1/2 - 2/3. These theoretical predictions are in very good agreement with the observations. Finally, we discuss three implications of this interpretation: (a) The relation between thermal emission and high energy, non-thermal spectra observed by Fermi. (b) We show how thermal emission can be used to directly measure the Lorentz factor of the flow and the initial radius of the jet. (c) We show how the lack of detection of the thermal component can be used to constrain ...

Pe'er, Asaf

2010-01-01

269

Observations of Far-Ultraviolet Diffuse Emission from the Small Magellanic Cloud  

CERN Document Server

We report the first observations of far-ultraviolet (FUV: 1000 -- 1150 \\AA) diffuse radiation from the Small Magellanic Cloud (SMC) using observations from the {\\em Far Ultraviolet Spectroscopic Explorer (FUSE)}. The strength of FUV diffuse surface brightness in the SMC ranges from the detection limit of 2000 photons cm$^{-2}$ s$^{-1}$ sr$^{-1}$ \\AA$^{-1}$ to a maximum of $3 \\times 10^{5}$ photons cm$^{-2}$ s$^{-1}$ sr$^{-1}$ \\AA$^{-1}$ at 1004 \\AA. The contribution of diffuse emission to the total radiation field was found to be 34% at 1004 \\AA to 44% at 1117 \\AA with a maximum observed uncertainty of 30%. There is a striking difference between the FUV diffuse fraction from the SMC and the Large Magellanic Cloud (LMC) with the SMC fraction being higher probable because the higher dust albedo. The FUV diffuse emission correlates with H$\\alpha$ emission in the H {\\small II} regions of the SMC.

Pradhan, Ananta C; Pathak, Amit

2011-01-01

270

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.)

1980-01-01

271

OBSERVATIONS OF FAR-ULTRAVIOLET DIFFUSE EMISSION FROM THE SMALL MAGELLANIC CLOUD  

International Nuclear Information System (INIS)

We report the first observations of far-ultraviolet (FUV: 1000-1150 ) diffuse radiation from the Small Magellanic Cloud (SMC) using observations from the Far-Ultraviolet Spectroscopic Explorer. The strength of FUV diffuse surface brightness in the SMC ranges from the detection limit of 2000 photons cm2 s1 sr1 Ŗ1 to a maximum of 3 105 photons cm2 s1 sr1 Ŗ1 at 1004 . The contribution of diffuse emission to the total radiation field was found to be 34% at 1004 to 44% at 1117 with a maximum observed uncertainty of 30%. There is a striking difference between the FUV diffuse fraction from the SMC and the Large Magellanic Cloud with the SMC fraction being higher probably because of the higher dust albedo. The FUV diffuse emission correlates with H? emission in the H II regions of the SMC.

2011-12-10

272

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 (\

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

2005-01-01

273

Observation of Extended VHE Emission from the Supernova Remnant IC 443 with VERITAS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present evidence that the very-high-energy (VHE, E > 100 GeV) gamma-ray emission coincident with the supernova remnant IC 443 is extended. IC 443 contains one of the best-studied sites of supernova remnant/molecular cloud interaction and the pulsar wind nebula CXOU J061705.3+222127, both of which are important targets for VHE observations. VERITAS observed IC 443 for 37.9 hours during 2007 and detected emission above 300 GeV with an excess of 247 events, resulting in a si...

Veritas, Collaboration; Acciari, V. A.; Aliu, E.; Arlen, T.; Aune, T.; Bautista, M.; Beilicke, M.; Benbow, W.; Bradbury, S. M.; Buckley, J. H.; Bugaev, V.; Butt, Y.; Byrum, K.; Cannon, A.; Celik, O.

2009-01-01

274

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

1982-01-01

275

Detection efficiency of the VLF World-Wide Lightning Location Network (WWLLN: initial case study  

Directory of Open Access Journals (Sweden)

Full Text Available An experimental Very Low Frequency (VLF World-Wide Lightning Location Network (WWLLN has been developed through collaborations with research institutions across the world, providing global real-time locations of lightning discharges. As of April 2006, the network included 25 stations providing coverage for much of the Earth. In this paper we examine the detection efficiency of the WWLLN by comparing the locations from this network with lightning location data purchased from a commercial lightning location network operating in New Zealand. Our analysis confirms that WWLLN favours high peak current return stroke lightning discharges, and that discharges with larger currents are observed by more stations across the global network. We then construct a first principles detection efficiency model to describe the WWLLN, combining calibration information for each station with theoretical modelling to describe the expected amplitudes of the VLF sferics observed by the network. This detection efficiency model allows the prediction of the global variation in WWLLN lightning detection, and an estimate of the minimum CG return stroke peak current required to trigger the network. There are strong spatial variations across the globe, primarily due to station density and sensitivity.

The WWLLN is currently best suited to study the occurrence and impacts of high peak-current lightning. For example, in 2005 about 12% of the global elve-producing lightning will have been located by the network. Since the lightning-EMP which produce elves has a high mean rate (210 per minute it has the potential to significantly influence the ionosphere on regional scales.

C. J. Rodger

2006-12-01

276

Estimating European volatile organic compound emissions using satellite observations of formaldehyde from the Ozone Monitoring Instrument  

Directory of Open Access Journals (Sweden)

Full Text Available Emission of non-methane Volatile Organic Compounds (VOCs to the atmosphere stems from biogenic and human activities, and their estimation is difficult because of the many and not fully understood processes involved. In order to narrow down the uncertainty related to VOC emissions, which negatively reflects on our ability to simulate the atmospheric composition, we exploit satellite observations of formaldehyde (HCHO, an ubiquitous oxidation product of most VOCs, focusing on Europe. HCHO column observations from the Ozone Monitoring Instrument (OMI reveal a marked seasonal cycle with a summer maximum and winter minimum. In summer, the oxidation of methane and other long-lived VOCs supply a slowly varying background HCHO column, while HCHO variability is dominated by most reactive VOC, primarily biogenic isoprene followed in importance by biogenic terpenes and anthropogenic VOCs. The chemistry-transport model CHIMERE qualitatively reproduces the temporal and spatial features of the observed HCHO column, but display regional biases which are attributed mainly to incorrect biogenic VOC emissions, calculated with the Model of Emissions of Gases and Aerosol from Nature (MEGAN algorithm. These "bottom-up" or a-priori emissions are corrected through a Bayesian inversion of the OMI HCHO observations. Resulting "top-down" or a-posteriori isoprene emissions are lower than "bottom-up" by 40% over the Balkans and by 20% over Southern Germany, and higher by 20% over Iberian Peninsula, Greece and Italy. We conclude that OMI satellite observations of HCHO can provide a quantitative "top-down" constraint on the European "bottom-up" VOC inventories.

G. Curci

2010-12-01

277

Estimating European volatile organic compound emissions using satellite observations of formaldehyde from the Ozone Monitoring Instrument  

Directory of Open Access Journals (Sweden)

Full Text Available Emission of non-methane Volatile Organic Compounds (VOCs to the atmosphere stems from biogenic and human activities, and their estimation is difficult because of the many and not fully understood processes involved. In order to narrow down the uncertainty related to VOC emissions, which negatively reflects on our ability to simulate the atmospheric composition, we exploit satellite observations of formaldehyde (HCHO, an ubiquitous oxidation product of most VOCs, focusing on Europe. HCHO column observations from the Ozone Monitoring Instrument (OMI reveal a marked seasonal cycle with a summer maximum and winter minimum. In summer, the oxidation of methane and other long-lived VOCs supply a slowly varying background HCHO column, while HCHO variability is dominated by most reactive VOC, primarily biogenic isoprene followed in importance by biogenic terpenes and anthropogenic VOCs. The chemistry-transport model CHIMERE qualitatively reproduces the temporal and spatial features of the observed HCHO column, but display regional biases which are attributed mainly to incorrect biogenic VOC emissions, calculated with the Model of Emissions of Gases and Aerosol from Nature (MEGAN algorithm. These "bottom-up" or a-priori emissions are corrected through a Bayesian inversion of the OMI HCHO observations. Resulting "top-down" or a-posteriori isoprene emissions are lower than "bottom-up" by 40% over the Balkans and by 20% over Southern Germany, and higher by 20% over Iberian Peninsula, Greece and Italy. The inversion is shown to be robust against assumptions on the a-priori and the inversion parameters. We conclude that OMI satellite observations of HCHO can provide a quantitative "top-down" constraint on the European "bottom-up" VOC inventories.

G. Curci

2010-08-01

278

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 > 60and 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

279

Worldwide biogenic soil NOx emissions inferred from OMI NO2 observations  

Science.gov (United States)

Biogenic NOx emissions from soils are a large natural source with substantial uncertainties in global bottom-up estimates (ranging from 4 to 27 Tg N yr-1). We reduce this range in emission estimates, and present a top-down soil NOx emission inventory for 2005 based on retrieved tropospheric NO2 columns from the Ozone Monitoring Instrument (OMI). We used a state-of-science soil NOx emission inventory (Hudman et al., 2012) as a priori in the GEOS-Chem chemistry transport model to identify 11 regions where tropospheric NO2 columns are dominated by soil NOx emissions. Strong correlations between soil NOx emissions and simulated NO2 columns indicated that spatial patterns in simulated NO2 columns in these regions indeed reflect the underlying soil NOx emissions. Subsequently, we used a mass-balance approach to constrain emissions for these 11 regions on all major continents using OMI observed and GEOS-Chem simulated tropospheric NO2 columns. We found that responses of simulated NO2 columns to changing NOx emissions were suppressed over low NOx regions, and accounted for these non-linearities in our inversion approach. In general, our approach suggests that emissions need to be increased in most regions. Our OMI top-down soil NOx inventory amounts to 10.0 Tg N for 2005 when only constraining the 11 regions, and 12.9 Tg N when extrapolating the constraints globally. Substantial regional differences exist (ranging from -40% to +90%), and globally our top-down inventory is 4-35% higher than the GEOS-Chem a priori (9.6 Tg N yr-1). We evaluated NO2 concentrations simulated with our new OMI top-down inventory against surface NO2 measurements from monitoring stations in Africa, the USA, and Europe. Although this comparison is complicated by several factors, we find an encouraging improved agreement when using the OMI top-down inventory compared to using the a priori inventory. To our knowledge, this study provides, for the first time, specific constraints on soil NOx emissions on all major continents using OMI NO2 columns. Our results rule out the high end of reported soil NOx emission estimates, and suggest that global emissions are most likely around 10-13 Tg N yr-1.

Vinken, G. C. M.; Boersma, K. F.; Maasakkers, J. D.; Adon, M.; Martin, R. V.

2014-06-01

280

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

 
 
 
 
281

Fire emissions simulated by prescribing burned area observations in a global vegetation model  

Science.gov (United States)

The emissions of trace gases and aerosols from large vegetation fires into the atmosphere have an important climate impact. In this study we integrate observed burned area into a global vegetation model to derive global fire emissions. A global continuous burned area products provided by GFED (Global Fire Emissions Dataset) were obtained from MODIS (and pre-MODIS) satellites and are available for the time period 1997-2011. We integrate the global burned area product into the global vegetation model JSBACH, a land part of the Earth-System model developed at the Max Planck Institute for Meteorology. JSBACH simulates land biomass in terms of carbon, which can be combined with the satellite burned area information to derive fire carbon emissions. Some assumptions on fire fuel consumptions have to be made during the integration of satellite burned area into the JSBACH. This includes processes such as tree mortality and combustion completeness, i.e. how much of the vegetation biomass gets combusted during a fire. Partially, this information can be also obtained from measurements. In this study we follow closely the approach of GFED, incorporating also GFED supplemental information, to simulate fuel consumption in JSBACH. And we compare simulated by this approach fire carbon emissions with the fire emissions from GFED. Global vegetation models often use prescribed land cover maps. The simulated in the JSBACH vegetation biomass and thus the simulated fire carbon emissions critically depend on the land cover distribution. In our study we derive fire carbon emissions using two different land cover parameterizations, based on two different satellite datasets. We will present the results obtained from simulations using the JSBACH standard MODIS based vegetation distribution and compare them to the results derived using the recently released ESA CCI land cover satellite product to demonstrate the sensitivity of simulated fire carbon emissions to the underlying land cover distribution.

Khlystova, Iryna G.; Wilkenskjeld, Stiig; Kloster, Silvia

2014-05-01

282

Reduction of black carbon aerosols in Tokyo: Comparison of real-time observations with emission estimates  

Science.gov (United States)

Black carbon (BC) aerosols alter the radiation budget both directly (by absorbing solar visible radiation) and indirectly (by acting as cloud condensation nuclei) and cause adverse health effects. The absorbing efficiency and direct radiative effect of BC strongly depend on its mass concentration (MBC) and type of emission source. In the present study, we report measurements of MBC at the Research Center for Advanced Science and Technology (RCAST), located at the center of the urban boundary of Tokyo, using an EC-OC analyzer from 2003 to 2005 and a filter-based Continuous Soot Monitoring System (COSMOS) during 2007-2010. The results indicate that MBC have decreased significantly from 2.6 ?g m-3 to 0.5 ?g m-3 (80% reduction) between 2003 and 2010. Vehicular emissions are the dominant source of BC in Tokyo, and the observed reduction in MBC is mainly attributed to the stringent regulations of particulate matter exhaust from vehicles imposed by the Japanese government. In addition, this observation is also supported from emission estimates using diurnal-weekly variations of MBC in Tokyo and explains the observed reduction to within about 20%. This is the first clear evidence of a significant reduction in BC emissions in Tokyo and shows that measures taken to reduce BC emissions from traffic sources have a strong effect on air quality in a mega-city and also reduce the climate impact of traffic emissions. We highlight the importance of long-term and reliable measurements in detecting BC trends and for the validation and regulation of emission control measures in mega-cities.

Kondo, Y.; Ram, K.; Takegawa, N.; Sahu, L.; Morino, Y.; Liu, X.; Ohara, T.

2012-07-01

283

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)

2004-01-01

284

Observation of density fluctuations from the infrared bremsstrahlung emission on TFTR  

Energy Technology Data Exchange (ETDEWEB)

The infrared emission of beam heated TFTR discharges is studied using the high collection efficiency TFTR Thompson scattering system. It is found that emission in the vicinity of 9800 A can be used to study fluctuations in the bremsstrahlung emission. Low-frequency ({lt}40 kHz) fluctuations that are associated with MHD modes and high-frequency ({gt}200 kHz) bursts of fluctuations are observed. Both coherent and incoherent fluctuations exist. In some cases, the observed coherent fluctuations can be interpreted as being due to density fluctuations as high as 5%. The rms value of broadband density turbulence in the near central regions of the plasma is estimated to be about 1%.

Grek, B.; Bartolick, J.; Johnson, D. (Princeton Plasma Physics Laboratory, Princeton University, New Jersey 08544 (United States))

1992-10-01

285

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

286

Megamaser galaxy Markarian 273. I. VLA observations of the hydroxyl emission  

International Nuclear Information System (INIS)

The hydroxyl megamaser emission in Mrk 273 was observed with the VLA in its high-resolution A array. The radio continuum source is extended at 18 cm; observations published by Ulvestad and Wilson (1984) reveal a double at 6 cm where the stronger component is resolved into a triple at 2 cm. The OH emission is certainly associated only with the stronger component of the 6-cm double and possibly only with the stongest component of the 2-cm triple. Unfortunately, the three velocity-resolved components of the OH line are not spatially resolved, and no information on the molecular disk rotation properties of this galaxy can be determined. This is very different from the VLA results of the megamaser prototype in IC 4553, where the emission is associated with all the continuum components and actually mimics the spatial structure of the radio continuum. Relevant properties of the known megamasers are listed and compared. 22 references

1987-01-01

287

Observation of phase transitions in hydrogenated Yttrium films via normalized infrared emissivity  

International Nuclear Information System (INIS)

The direct observation of a sequence of phase transitions during hydrogenation of Y thin films has been realized through the use of in situ isothermal infrared emissivity measurements. The formation of different phases, ?-Y(H), YH2 and YH3, has been identified based on the observation of changes in the slope of the normalized IR emissivity vs. time curve during hydrogen loading. The presence of ?-Y(H), YH2 and YH3 was confirmed by ex situ X-ray diffraction, transmission electron microscopy, and prompt gamma activation analysis. Transmission electron microscopy further demonstrated epitaxial orientation relationships between the Al2O3 substrate, Ti buffer layer, the as-deposited Y film, as well as its hydrides. These results clearly demonstrate the power of IR emissivity imaging to monitor, in real time, the formation of hydride phases of both metallic and insulating character near the surface of a thin-film sample.

2010-02-04

288

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

Science.gov (United States)

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 version 2.1 of the Model of Emissions of Gases and Aerosols from Nature (MEGANv2.1), using leaf area data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) 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 122 Tg yr-1 (including biogenic, pyrogenic, and anthropogenic sources), an increase of 60% from the a priori global flux of 76 Tg yr-1. Global terrestrial methanol emissions are thus nearly 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. Inversions testing the sensitivity of optimized fluxes to model errors in OH, dry deposition, and oceanic uptake of methanol, as well as to the assumed a priori constraint, lead to global fluxes ranging from 118 to 126 Tg yr-1. 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.

Wells, K. C.; Millet, D. B.; Cady-Pereira, K. E.; Shephard, M. W.; Henze, D. K.; Bousserez, N.; Apel, E. C.; de Gouw, J.; Warneke, C.; Singh, H. B.

2014-03-01

289

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 24 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

290

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 FRP 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 by a factor of 24 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

2012-01-01

291

Chandra X-ray Observations of Jovian Low-latitude Emissions: Morphological, Temporal, and Spectral Characteristics  

Science.gov (United States)

Chandra observed X-rays from Jupiter during 24-26 February 2003 for about 40 hours with the ACIS-S and HRC-I instruments. The analysis of Jovian low-latitude "disk" Xray emissions are presented and compared with the high-latitude "auroral" emissions. We report the first Chandra ACIS-S measured X-ray spectrum (0.3-2 keV) of Jupiter's low-latitude disk The disk X-ray emission is harder and extends to higher energies than the auroral spectrum. The temporal variation in the Jovian disk X-rays is on an average consistent with those in the solar X-rays observed by GOES, and TIMED/SSE. Contrary to the auroral X-rays, the disk emissions are uniformly distributed over Jupiter; no indication of longitudinal dependence or correlation with surface magneh field strength is visible. Also, unlike the approx. 40 +/- 20 min periodic oscillations seen in the auroral X-ray emissions, the disk emissions do not show any periodic oscillations. The disk spectrum seems to be consistent with resonant and fluorescent scattering of solar X-rays by the Jovian upper atmosphere. Jupiter's disk is found to be about 50% dimmer in soft X-rays in February 2003 compared that in December 2000, which is consistent with the decrease in solar activity. No evidence of lightning-induced X-rays is seen in the Chandra X-ray data. The Jovian disk spectra observed with Chandra-ACIS is stronger than that observed with XMM-Newton two months later during April 28-29, 2003. The XMM-Newton Xray image of Jupiter shows evidence of limb darkening on the anti-sunward side as seen from Earth, as well as an asymmetry with respect to the subsolar point: suggesting a solar driven process.

Bhardwaj, Anil; Elsner, Ronald F.; Gladstone, G. Randall; Cravens, Thomas E.; Waiate J. Hunter, Jr.; Branduardi-Raymont, Graziella; Ford, Peter

2004-01-01

292

Using Lunar Observations to Assess Terra MODIS Thermal Emissive Bands Calibration  

Science.gov (United States)

MODIS collects data in both the reflected solar and thermal emissive regions using 36 spectral bands. The center wavelengths of these bands cover the3.7 to 14.24 micron region. In addition to using its on-board calibrators (OBC), which include a full aperture solar diffuser (SD) and a blackbody (BB), lunar observations have been scheduled on a regular basis to support both Terra and Aqua MODIS on-orbit calibration and characterization. This paper provides an overview of MODIS lunar observations and their applications for the reflective solar bands (RSB) and thermal emissive bands (TEB) with an emphasis on potential calibration improvements of MODIS band 21 at 3.96 microns. This spectral band has detectors set with low gains to enable fire detection. Methodologies are proposed and examined on the use of lunar observations for the band 21 calibration. Also presented in this paper are preliminary results derived from Terra MODIS lunar observations and remaining challenging issues.

Xiong, Xiaoxiong; Chen, Hongda

2010-01-01

293

Effects of LatticeQCD EoS and Continuous Emission on Some Observables  

International Nuclear Information System (INIS)

Effects of lattice-QCD-inspired equations of state and continuous emission on some observables are discussed, by solving a 3D hydrodynamics. The particle multiplicity as well ? 2 are found to increase in the mid-rapidity. We also discuss the effects of the initial-condition fluctuations

2006-04-11

294

The observation of chemiluminescent NiO* emissions in the laboratory and in the night airglow  

Directory of Open Access Journals (Sweden)

Full Text Available The recent finding of an orange spectral feature in OSIRIS/Odin spectra of the night airglow near 85 km has raised interest in the origin of the emission. The feature was positively identified as the chemiluminescent FeO* emission where the iron is of meteoric origin. Since the meteorite source of atomic metals in the mesosphere contains both iron and nickel, with Ni being typically 6% of Fe, it is expected that faint emissions involving Ni should also be present in the night airglow. The present study summarizes the laboratory observations of chemiluminescent NiO* emissions and includes a search for the NiO* signature in the night airglow. A faint previously unidentified "continuum" extending longwave of 440 nm has been identified in night airglow spectra obtained with two space-borne limb viewing instruments and through a comparison with laboratory spectra this continuum is identified as arising from the NiO* emission. The FeO* and NiO* emissions both originate from a reaction of the metal atoms with mesospheric ozone and so support the presence of NiO* in the night airglow.

A. L. Broadfoot

2011-04-01

295

EGRET observations of extended high-energy emissions from the nuclear line flares of June 1991  

Science.gov (United States)

EGRET onboard the Compton Gamma Ray Observatory observed four energetic X-type solar flares during June 1991. Two of these flares were in the EGRET spark chamber field of view and were observed to have high energy gamma ray emission lasting hours after the impulsive phase of the flare. Measurements of all four flares were obtained by the EGRET large NaI spectrometer.

Schneid, E. J.; Brazier, K. T. S.; Kanbach, G.; von Montigny, C.; Mayer-Hasselwander, H. A.; Bertsch, D. L.; Fichtel, C. E.; Hartman, R. C.; Hunter, S. D.; Thompson, D. J.; Dingus, B. L.; Sreekumar, P.; Lin, Y. C.; Michelson, P. F.; Nolan, P. L.; Kniffen, D. A.; Mattox, J. R.

1994-12-01

296

The Predicted Signature of Neutrino Emission in Observations of Pulsating Pre-White Dwarf Stars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Pre-white dwarf (PWD) star evolution can be driven by energy losses from neutrino interactions in the core. Unlike solar neutrinos, these are not the by-product of nuclear fusion, but instead result from electron scattering processes in the hot, dense regions of the PWD core. We show that the observed rate of period change in cool PWD pulsators will constrain neutrino emission in their cores, and we identify appropriate targets for future observation. Such a measurement will...

O Brien, M. Sean; Kawaler, Steven D.

2000-01-01

297

Observations of secondary emission chamber degradation from very high intensity proton beams at the AGS  

Energy Technology Data Exchange (ETDEWEB)

Degradation of Secondary Emission Chamber (SEC) efficiencies has been seen in the past. As a result, instruments in use today are built to minimize any such effects. With beam intensities as high as 6 x 10{sup 13} protons per pulse incident on these devices the authors are again observing significant degradation in SEC efficiencies. In this report the authors will present observations of these effects and methods they have developed to cope with them.

Brown, K.A.; Chiang, I.H.; Pendzick, A.; Tallerico, T.

1997-08-01

298

Observations of secondary emission chamber degradation from very high intensity proton beams at the AGS  

International Nuclear Information System (INIS)

Degradation of Secondary Emission Chamber (SEC) efficiencies has been seen in the past. As a result, instruments in use today are built to minimize any such effects. With beam intensities as high as 6 x 10"1"3 protons per pulse incident on these devices the authors are again observing significant degradation in SEC efficiencies. In this report the authors will present observations of these effects and methods they have developed to cope with them

1997-05-12

299

Comparing optimized CO emission estimates using MOPITT or NOAA surface network observations  

Science.gov (United States)

This paper compares two global inversions to estimate carbon monoxide (CO) emissions for 2004. Either surface flask observations from the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) or CO total columns from the Measurement of Pollution in the Troposphere (MOPITT) instrument are assimilated in a 4D-Var framework. Inferred emission estimates from the two inversions are consistent over the Northern Hemisphere (NH). For example, both inversions increase anthropogenic CO emissions over Europe (from 46 to 94 Tg CO/yr) and Asia (from 222 to 420 Tg CO/yr). In the Southern Hemisphere (SH), three important findings are reported. First, due to their different vertical sensitivity, the stations-only inversion increases SH biomass burning emissions by 108 Tg CO/yr more than the MOPITT-only inversion. Conversely, the MOPITT-only inversion results in SH natural emissions (mainly CO from oxidation of NMVOCs) that are 185 Tg CO/yr higher compared to the stations-only inversion. Second, MOPITT-only derived biomass burning emissions are reduced with respect to the prior which is in contrast to previous (inverse) modeling studies. Finally, MOPITT derived total emissions are significantly higher for South America and Africa compared to the stations-only inversion. This is likely due to a positive bias in the MOPITT V4 product. This bias is also apparent from validation with surface stations and ground-truth FTIR columns. Our results show that a combined inversion is promising in the NH. However, implementation of a satellite bias correction scheme is essential to combine both observational data sets in the SH.

Hooghiemstra, P. B.; Krol, M. C.; Bergamaschi, P.; de Laat, A. T. J.; van der Werf, G. R.; Novelli, P. C.; Deeter, M. N.; Aben, I.; Rckmann, T.

2012-03-01

300

Technique for Building and Calibrating VLF/LF Receive Loop Antennas.  

Canada Institute for Scientific and Technical Information (Canada)

The strategic VLF/LF submarine communications program involves several VLF and LF transmitter antennas located around the world. The Naval Command, Control and Ocean Surveillance Center (NCCOSC), Research, Development, Test and Evaluation Division (NRAD) is often tasked to baseline the antenna's performance before and after changes are made. One parameter useful in this process is measurement of the VLF/LF transmit antenna's magnetic field strength. The antenna's magnetic field strength provides information on the antenna's effective height, radiated power, and efficiency. Prior to making these measurements, the VLF/LF receive loop must first be calibrated in a Helmholtz coil. Determining magnetic field strength can then be accomplished by taking readings with the VLF/LF receive loop antenna while in the field of the transmit antenna. The voltage induced around the receive loop is measured by a selective level meter (Hewlett Packard 3486C0). Distance from the transmitting antenna to the VLF/LF receive loop is provided using Global Positioning System (GPS) instruments. Antenna current is measured in the helix house of the transmit antenna with a time stamp data recorder. Many of the transmit antenna's performance characteristics can be derived with the above measurements. The purpose of this document is to detail the construction method for building the VLF/LF receive loop antenna as designed by Mr. Don Watt of Watt Engineering. The second portion of this report describes the Helmholtz loop calibration procedure.

1997-01-01

 
 
 
 
301

Constraints on Eurasian ship NOx emissions using OMI NO2 observations and GEOS-Chem  

Science.gov (United States)

Ships emit large quantities of nitrogen oxides (NOx = NO + NO2), important precursors for ozone (O3) and particulate matter formation. Ships burn low-grade marine heavy fuel due to the limited regulations that exist for the maritime sector in international waters. Previous studies showed that global ship NOx emission inventories amount to 3.0-10.4 Tg N per year (15-30% of total NOx emissions), with most emissions close to land and affecting air quality in densely populated coastal regions. Bottom-up inventories depend on the extrapolation of a relatively small number of measurements that are often unable to capture annual emission changes and can suffer from large uncertainties. Satellites provide long-term, high-resolution retrievals that can be used to improve emission estimates. In this study we provide top-down constraints on ship NOx emissions in major European ship routes, using observed NO2 columns from the Ozone Monitoring Instrument (OMI) and NO2 columns simulated with the nested (0.50.67) version of the GEOS-Chem chemistry transport model. We use a plume-in-grid treatment of ship NOx emissions to account for in-plume chemistry in our model. We ensure consistency between the retrievals and model simulations by using the high-resolution GEOS-Chem NO2 profiles as a priori. We find evidence that ship emissions in the Mediterranean Sea are geographically misplaced by up to 150 km and biased high by a factor of 4 as compared to the most recent (EMEP) ship emission inventory. Better agreement is found over the shipping lane between Spain and the English Channel. We extend our approach and also provide constraints for major ship routes in the Red Sea and Indian Ocean. Using the full benefit of the long-term retrieval record of OMI, we present a new Eurasian ship emission inventory for the years 2005 to 2010, based on the EMEP and AMVER-ICOADS inventories, and top-down constraints from the satellite retrievals. Our work shows that satellite retrievals can improve the characterization of emission locations, magnitudes and trends over sparsely monitored areas such as seas or oceans.

Vinken, Geert C. M.; Boersma, Folkert; van Donkelaar, Aaron; Zhang, Lin

2013-04-01

302

Inhibited spontaneous emission of quantum dots observed in a 3D photonic band gap  

CERN Document Server

We present time-resolved emission experiments of semiconductor quantum dots in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study is made of crystals with a range of pore radii to tune the band gap relative to the emission frequency. The decay rates averaged over all dipole orientations are inhibited by up to a factor of 12\\times in the photonic band gap, and enhanced up to 2\\times outside the gap, in quantitative agreement with theory. We discuss the effects of spatial inhomogeneity, non-zero non-radiative decay, and transition dipole orientations on the observed inhibition in the band gap.

Leistikow, M D; Huisman, S R; Lagendijk, A; Vos, W L

2011-01-01

303

New polarimetric observations and a two pole model for the cyclotron emission from AM Herculis  

International Nuclear Information System (INIS)

We present high signal-to-noise ratio phase dependent linear polarization and intensity data on AM Herculis which show the presence of structured linear pulses in the optical and near IR regions. The data have been analysed to construct a detailed model which reproduces closely the observed pulse structure and polarization angle variations and clearly demonstrates the presence of two interfering cyclotron emission regions located close to the foot points of a closed field line in an offset dipole field distribution. Both emission regions are linearly extended on the white dwarf surface. (author)

1991-07-01

304

Dust emissivity in the Submm/Mm: SCUBA and SIMBA observations of Barnard 68  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have observed the dark cloud Barnard 68 with SCUBA at 850 um and with SIMBA at 1.2 mm. The submillimetre and millimetre dust emission correlate well with the extinction map of Alves, Lada and Lada (2001).The A_V/850um correlation is clearly not linear and suggests lower temperatures for the dust in the inner core of the cloud. Assuming a model for the temperature gradient, we derive the cloud-averaged dust emissivities (normalised to the V-Band extinction efficiency) at 8...

Bianchi, S.; Goncalves, J.; Albrecht, M.; Caselli, P.; Chini, R.; Galli, D.; Walmsley, M.

2003-01-01

305

The near infrared emission band observed in electron irradiated Xe and Xe in other rare gases  

International Nuclear Information System (INIS)

The near-infrared emission spectra were studied for xenon diluted with krypton, argon, and neon, respectively, in order to estimate the origin of an emission band at 1260 nm which was previously observed at several hundred Torr(1 Torr = 133.2 Pa) of pure Xe irradiated with pulses of high-energy electrons. A continuous band around 1260 nm was observed only in Xe-Ar mixtures. This band appeared at Xe pressures above 20 Torr(diluted in 600 Torr of Ar) while it was detected above 190 Torr in pure Xe. In Xe-Ar mixtures, three emission lines due to Xe 5d(3/2)_1 were also observed at 1700, 2020, and 2650 nm. On the basis of the reported kinetic data for the reactions of rare gas mixtures, the present results led to the conclusion that the band at 1260 nm was due to emission from highly excited excimer states, of which the dissociation limits were higher Rydberg states above the energy level of the Xe_2"+ ion. (author)

1985-01-01

306

Observational Characteristics of Radio Emission Related to Multi-polar Magnetic Configuration  

Science.gov (United States)

We present a large complex radio burst and its associated fast time structures observed on 2001 April 10 in the frequency range of 0.65 7.6 GHz. The NoRH radio image observation shows very complex radio source structures which include preexisting, newly emerging, submerging/cancelling polarities and a bipolar, a tripolar (a `bipolar + remote unipolar'), and a quadrupolar structure. This suggests that the radio burst is generated from a very complicated loop structure. According to the spectral and image observations, we assume that the beginning of this flare was caused by a single bipolar loop configuration with a `Y-type' reconnection structure. A composite of radio continuum and fast time structures is contained in this flare. The various fast radio emission phenomena include normal and reverse drifting type III bursts, and slowly drifting and no-drift structures. The tripolar configurations may form a double-loop with a `three-legged' structure, which is an important source of the various types of fast time structures. The two-loop reconnection model can lead simultaneously to electron acceleration and corona heating. We have also analyzed the behaviors of coronal magnetic polarities and the emission processes of different types radio emission qualitatively. Interactions of a bipolar or multi-polar loop are consistent with our observational results. Our observations favor the magnetic reconnection configurations of the `inverted Y-type' (bipolar) and the `three-legged' structures (tripolar or quadrupolar).

Wang, Min; Xie, Rui-Xiang; Xu, Chun; Shi, Shuo-Biao; Yan, Yi-Hua

2005-10-01

307

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

308

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

309

Methane emissions from West Siberian mud volcanoes: observations near Khanty-Mansiysk  

Science.gov (United States)

Recent studies have shown that mud volcanoes are important methane sources. We found mud volcanoes with high methane emissions in the floodplains of West Siberia middle taiga zone (25-40 km from Khanty-Mansiysk city). Despite of the minor area in comparison with surrounding methane-emitting wetlands, their methane emission rate reach 0.2 kg.m2h-1 that appears to be 1000 to 100000 times higher than that for wetlands. Probability density distribution of the observed methane emission rates is close to log-normal. Methanotrophic communities oxidizing emitted methane were found around seepages. Molecular identification of bacteria community composition using pmoA gen detects both type II and type I of methanotrophic bacteria (Gammaproteobacteria and Alphaproteobacteria classes, respectively) with type I dominating. Microorganisms similar to the authentic psychrophile Methylobacter psychrophiles (previously detected only in tundra soils) were also found among the later as well as a number of unidentified methanotrophs belonging to unknown taxon.

Glagolev, M.; Maksyutov, S.; Oshkin, I.; Kleptsova, I.; Dedysh, S.

2011-12-01

310

A multi-observational Characterisation of Dust Emission from Sources within complex Terrain  

Science.gov (United States)

Recent studies using satellite observations show that numerous dust sources are located in the foothills of the Saharan mountains. Generally, dust emission is closely related to sediment supply and surface wind. Thus, dust emission can be inhibited by either lack of high wind speeds or by unsuitable surface characteristics. Significant rainfall and flash flood events have been proposed to lead to changes in pluvial sediment supplies in mountain drainage systems. These sediments are suitable for dust uplift and assumed to have a main contribution to the dust emission fluxes over these areas. This mechanism could help to explain the observed marked interannual variability of some dust sources, which is currently not well understood. This study uses a novel combination of airborne and space-borne measurements to explore dust sources within complex terrain. It consists of two main parts: First, dust emission forced by the break-down of nocturnal low-level jets is investigated by analysing data from the RAIN4DUST/FENNEC-France aircraft campaign in June 2011 based at Fuerteventura, Spain. Local dust emission over North Mauritania is observed using a combination of different measurement systems flying aboard the French Falcon FA20, such as high resolution aerial ground camera, high-resolution lidar instrument and drop-sondes. The orientation of the flight legs allows for the characterisation of the evolution of a developing dust plume in time and space combining information on ground surface structure and vertical dust distribution. Supplementary analysis of model simulations and satellite remote sensing products provide additional information on the location of dust sources and dust transport paths. Second, the role of pluvial sediment supply for dust emission in desert valleys is investigated. For a selected area over West Africa ENVISAT SAR (synthetic aperture radar) measurements from 2003-2010 are analysed to identify changes in surface sediments through loss of coherence between two consecutive images. Results from this study highlight the contribution of flash floods for dust sources located within complex terrain. Together the two approaches provide a detailed picture of dust emission from sources within complex terrain revealing controls on dust emission from both atmospheric factors and sediment supply.

Schepanski, K.; Marnas, F.; Flamant, C.; Chaboureau, J.-P.; Kocha, C.; Pelon, J.; Lavaysse, C.; Wright, T. J.; Knippertz, P.

2012-04-01

311

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 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.

2012-03-26

312

Implications of the pion-decay gamma emission and neutron observations with CORONAS-F/SONG  

Science.gov (United States)

We analyzed the high-energy gamma and neutron emissions observed by the SONG instrument onboard the CORONAS-F satellite during August 25, 2001, October 28, 2003, November 4, 2003, and January 20, 2005 solar flares. These flares produced neutrons and/or protons recorded near Earth. The SONG response was consistent with detection of the pion-decay gamma emission and neutrons in these events. We compared time profiles of various electromagnetic emissions and showed that the maximum of the pion-decay-emission coincided in time best of all with the soft X-ray derivative, dISXR/dt, maximum. We evaluated the energy of accelerated ions and compared it with the energy deposited by accelerated electrons. The ion energy becomes comparable or even higher than the electron energy from a certain step of flare development. So the time profile of dISXR/dt is a superposition of energy deposited by both fractions of accelerated particles. This result allowed us to use a time profile of dISXR/dt as a real proxy of time behavior of the energy release at least during major flare analysis. In particular the time interval when the dISXR/dt value exceeds 0.9 of its maximum can be used as a unified reference point for the calculations of time delay between the high-energy proton acceleration and GLE onset. Analysis of the total set of pion-decay emission observations shows that such temporal closeness of pion-decay emission maximum and the soft X-ray derivative maximum is typical but not obligatory.

Kurt, V.; Yushkov, B.; Kudela, K.

2013-05-01

313

Observation of novel radioactive decay by spontaneous emission of complex nuclei  

International Nuclear Information System (INIS)

Two years of experimental investigation on the subject of spontaneous emission of intermediate-mass fragments is described in this manuscript. A short introduction on this subject and a historical review are presented in chapter 1. In chapter 2, the author describe the experimental methods which led to the observation of 14C emission in polycarbonate etched-track detectors from the isotopes 222Ra, 223Ra, 224Ra and 226Ra at the branching ratios with respect to ?-decay of (3.7 +/- 0.6) x 10-10, (6.1 +/- 1.0) x 10-10, (4.3 +/- 1.2) x 10-10 and (2.9 +/- 1.0) x 10-11 respectively. Branching ratio limits for heavy-ion emission from 221Fr, 221Ra and 225Ac were determined to be at -14, -13 and -13 respectively for the 90% C.L. The emission of 24Ne from 232U at a branching ratio of (2.0 +/- 0.5) x 10-12 has been discovered using polyethylene terephthalate etched-track plastics. A confirmation of 24Ne and/or 25Ne emission from 233U at a branching ratio of (5.3 +/- 2.3) x 10-13 is also reported. In chapter 3, three models of intermediate-mass decay are discussed-the analytic superasymmetric fission model, the model by Shi and Swiatecki, and a model based on a square-well + Coulomb potential

1986-01-01

314

Observations of artificial and natural optical emissions at the HAARP facility  

Directory of Open Access Journals (Sweden)

Full Text Available Extensive optical observations have been carried out at the High Frequency Active Auroral Research Program (HAARP ionospheric heating facility since it began operations in 1999. A number of modern optical diagnostic instruments are hosted at remote sites as well as the main transmitter facility, which has recently been expanded from the initial 960 kW prototype configuration to its full 3.6 MW design capability. Upgrades to optical diagnostics have allowed a number of interesting new observations to be made at the 960 kW power level since 2004. Systematic beam-swinging experiments generating quantifiable levels of optical emission at various regions in the sky for the first time clearly show that emission intensity is very sensitive to distance from the magnetic zenith, and drops off rapidly at about 15 zenith angle in directions other than magnetic south. High temporal resolution measurements of emissions in the 557.7 nm green line at start-up and in short transmitter pulses demonstrate that localized irregularities are preferentially excited in the initial seconds of heating, with evolution into a more homogenous spot occurring over a period of about 1 min. High-quality emission altitude profiles at both 630.0 and 557.7 nm have recently been isolated from side-looking data, spanning an altitude extent of over 200 km, which has allowed determination of the effective lifetime of O (1D over an unprecedented altitude range. An innovative automated remote imager network utilizing low-cost mirror optics has been designed and deployed to make such measurements routinely. Observations of natural optical emissions at the site have revealed the common presence of highly structured but faint co-rotating subauroral precipitation that acts to suppress excitation of artificial F region optical emissions in areas of active precipitation. The observed spatial modulation of artificial optical emissions by structured precipitation is consistent with localized absorption of HF waves in the ionospheric D layer enhanced by the energetic particle precipitation.

T. Pedersen

2008-05-01

315

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

316

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

317

Simultaneous optical/gamma-ray observations of GRB 121217's prompt emission  

CERN Document Server

Since the advent of the Swift satellite it has been possible to obtain precise localisations of GRB positions of sub-arcsec accuracy within seconds, facilitating ground-based robotic telescopes to automatically slew to the target within seconds. This has yielded a plethora of observational data for the afterglow phase of the GRB, but the quantity of data (<2 keV) covering the initial prompt emission still remains small. Only in a handful of cases has it been possible obtain simultaneous coverage of the prompt emission in a multi-wavelength regime (gamma-ray to optical), as a result of: observing the field by chance prior to the GRB (e.g. 080319B/naked-eye burst), long-prompt emission (e.g., 080928, 110205A) or triggered on a pre-cursor (e.g., 041219A, 050820A, 061121). This small selection of bursts have shown both correlated and uncorrelated gamma-ray and optical light curve behaviour, and the multi-wavelength emission mechanism remains far from resolved (i.e. single population synchrotron self-Component,...

Elliott, J; Schmidl, S; Greiner, J; Gruber, D; Oates, S; Kobayashi, S; Zhang, B; Cummings, J R; Filgas, R; Gehrels, N; Grupe, D; Kann, D A; Klose, S; Krhler, T; Guelbenzu, A Nicuesa; Rau, A; Rossi, A; Siegel, M; Schady, P; Sudilovsky, V; Tanga, M; Varela, K

2013-01-01

318

Observations of 3.2-3.6 micron emission features in comet Halley  

International Nuclear Information System (INIS)

Ground-based spectroscopic observations of the emission feature near 3.3 microns discovered in comet Halley by the Vega 1 spacecraft are reported. At a resolution of Delta gamma/gamma = 0.012 the emission consists of several components between 3.2 and 3.6 microns, and appears to be a superposition of C-H group bands. The feature is observed out to several thousand kilometers from the nucleus and does not appear to be thermal radiation from the grains responsible for the 4-20 micron continuum. Molecular scattering or emission by a component of cool (less than 400 K) grains would require near cosmic abundance of carbon. Hotter grains would radiate strongly enough to reduce the abundance requirement. The band shape is similar, but not identical, to interstellar absorption at 3.4 microns, to spectra of organic extracts from carbonaceous chondrites, and to spectra of some synthesized materials, such as QCCs (as discussed by Sakata and colleagues in 1984). A newly found emission at 3.52 + or 0.02 microns is evidence for oxygen containing organic molecules, possibly formaldehyde or methanol. 22 references

1986-01-01

319

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; Grard, Jean-Claude; Grodent, Denis

2011-01-01

320

Searching for meteor ELF /VLF signatures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

For more than two centuries, credible reports about various audible sounds appearing simultaneously with visible meteors have been collected. Knowing that the sound velocity is much lower than the light velocity, it was impossible to explain such a phenomenon until some theories predicted that an electromagnetic wave vector could be the reason for such simultaneous light and sound observations. Several optical/sound/radio recording campaigns have been performed in the last decades but with no...

Rault, J. -l

2010-01-01

 
 
 
 
321

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

Science.gov (United States)

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.

Meng, L.; Hess, P. G. M.; Mahowald, N. M.; Yavitt, J. B.; Riley, W. J.; Subin, Z. M.; Lawrence, D. M.; Swenson, S. C.; Jauhiainen, J.; Fuka, D. R.

2012-07-01

322

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 19932004 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 (150346 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

323

Estimates of surface methane emissions over Europe using observed surface concentrations and the FLEXPART trajectory model  

Science.gov (United States)

We use surface methane observations from nine European ground stations, and the FLEXPART Lagrangian transport model to obtain surface methane emissions for 2010. Our inversion shows the strongest emissions from the Netherlands and the coal mines in Upper Silesia Poland. This is qualitatively consistent with the EDGAR surface flux inventory. We also report significant surface fluxes from wetlands in southern Finland during July and August and reduced wetland fluxes later in the year. Our simulated methane surface concentration captures at least half of the daily variability in the observations, suggesting that the transport model is correctly simulating the regional transport pathways over Europe. We also use our trajectory model to determine whether future space-based remote sensing instruments (MERLIN) will be able to detect both natural and anthropogenic changes in the surface flux strengths.

Weaver, C. J.; Kiemle, C.; Kawa, S. R.; Aalto, T.; Necki, J.; Steinbacher, M.; Arduini, J.; Apadula, F.; Berkhout, H.; Hatakka, J.; O'Doherty, S.

2013-12-01

324

Observations of the Prompt Gamma-Ray Emission of GRB 070125  

CERN Multimedia

The long, bright gamma-ray burst GRB 070125 was localized by the Interplanetary Network. We present light curves of the prompt gamma-ray emission as observed by Konus-WIND, RHESSI, Suzaku-WAM, and Swift-BAT. We detail the results of joint spectral fits with Konus and RHESSI data. The burst shows moderate hard-to-soft evolution in its multi-peaked emission over a period of about one minute. The total burst fluence as observed by Konus is $1.75 \\times 10^{-4}$ erg/cm$^2$ (20 keV-10 MeV). Using the spectroscopic redshift z = 1.547, we find that the burst is consistent with the Amati $E_{peak,i}-E_{iso}$ and the Ghirlanda $E_{peak,i}-E_\\gamma$ correlations.

Bellm, Eric C; Pal'shin, Valentin; Yamaoka, Kazutaka; Bandstra, Mark E; Boggs, Steven E; Hong, Soojing; Kodaka, Natsuki; Kozyrev, A S; Litvak, M L; Mitrofanov, I G; Nakagawa, Yujin E; Ohno, Masanori; Onda, Kaori; Sanin, A B; Sugita, Satoshi; Tashiro, Makoto; Tretyakov, V I; Urata, Yuji; Wigger, Claudia

2007-01-01

325

Gamma-ray bursts, their high energy emission as observed by EGRET  

Science.gov (United States)

Gamma-ray bursts are among the most powerful events in the universe. These events release most of their energy as photons with energies in the range from 30keV to a few MeV, with a smaller fraction of the energy radiated in radio, optical and soft X-ray afterglows. Several experiments had advocated observing their prompt hard X-ray emission as well as their afterglows in all wavelengths. Thus, huge steps toward a complete understanding of gamma-ray burst afterglows have been done. Nevertheless, radiation above MeV energies has not been fully explored and understood. In particular, the Energetic Gamma Ray Experiment Telescope (EGRET, 1991-2000) observed emission at GeV energies at the same time and delayed from the keV emission for one burst. The GRB emission in the MeV-GeV range will not be further explored by another experiment until 2006. This thesis studies GRB emission in the MeV-GeV energies by a deeper analysis of EGRET data. First, upper limits for prompt and delayed GRB emission in the energy range of 0.02-30 GeV are calculated for bursts that were in the field of view of the EGRET Spark Chambers but were not detected. Secondly, EGRET data from its calorimeter TASC, in the energy range of 1-200 MeV is combined with BATSE data in the energy range of 0.025-2 MeV to better describe the GRB spectra in the MeV regime and its time evolution. Two special bursts that show an extra contribution to their spectra mainly above 10 MeV and up to 200 MeV are discussed. Characterization of the extra contribution to the spectra found in GRB941017 and GRB980923 is done. Also, limits to the existence of this extra contribution are calculated by analyzing TASC and Spark Chamber data finding evidence of this extra contribution in another burst, GRB910503. This emission is not explained by the known non-thermal electron radiation. Therefore this result implies that another radiation mechanism must exist in this gamma-ray burst and is responsible for more than 3 times as much energy release as previously observed. Other possible theoretical implications are also discussed.

Gonzalez Sanchez, Maria Magdalena

326

A study of the behavior of the terminator time shifts using multiple VLF propagation paths during the Pakistan earthquake (M = 7.2) of 18 January 2011  

Science.gov (United States)

On 18 January 2011, at 20:23 UTC, an earthquake of magnitude 7.2 occurred in southwestern Pakistan (latitude 2844' N, longitude 6356' E) at a depth of 68 km. We present the results of the analysis of very low frequency (VLF) radio signals, received at three stations located in India. We analyze the VLF signals around this earthquake day and look for possible precursory effects of this earthquake. For our analysis, we use four different VLF propagation paths. These propagation paths are DHO-IERC (Sitapur), VTX-Pune, VTX-ICSP (Indian Centre for Space Physics, Kolkata) and NWC-IERC. We observed significant shifts of the "sunrise terminator time" (SRT) for DHO-IERC and VTX-Pune paths. For DHO-IERC path, the SRT of the VLF signals shifted towards nighttime three days before the earthquake day, and in the case of VTX-Pune path it shifted towards nighttime just one day before the earthquake day. For VTX-Kolkata path, the shift of SRT is four days before the earthquake day, but here the shift is not so strong, somewhere between 2? and 3? lines. For the other two paths, namely, DHO-IERC and VTX-Pune, the terminator time shifts crossed the 3? line. We found no significant shifts of SRT for NWC-IERC propagation path. Higher deviation in the VTX-Pune path as compared to VTX-ICSP path could be due to the proximity of the former to the epicenter. Similarly, DHO-IERC path is over the epicenter while NWC-IERC path is totally away from the epicenter. This could be the reason why the effect in DHO-IERC path is stronger than that in NWC-IERC path.

Ray, S.; Chakrabarti, S. K.

2013-06-01

327

A study of the behavior of the terminator time shifts using multiple VLF propagation paths during the Pakistan earthquake (M = 7.2 of 18 January 2011  

Directory of Open Access Journals (Sweden)

Full Text Available On 18 January 2011, at 20:23 UTC, an earthquake of magnitude 7.2 occurred in southwestern Pakistan (latitude 2844' N, longitude 6356' E at a depth of 68 km. We present the results of the analysis of very low frequency (VLF radio signals, received at three stations located in India. We analyze the VLF signals around this earthquake day and look for possible precursory effects of this earthquake. For our analysis, we use four different VLF propagation paths. These propagation paths are DHOIERC (Sitapur, VTXPune, VTXICSP (Indian Centre for Space Physics, Kolkata and NWCIERC. We observed significant shifts of the "sunrise terminator time" (SRT for DHOIERC and VTXPune paths. For DHOIERC path, the SRT of the VLF signals shifted towards nighttime three days before the earthquake day, and in the case of VTXPune path it shifted towards nighttime just one day before the earthquake day. For VTXKolkata path, the shift of SRT is four days before the earthquake day, but here the shift is not so strong, somewhere between 2? and 3? lines. For the other two paths, namely, DHOIERC and VTXPune, the terminator time shifts crossed the 3? line. We found no significant shifts of SRT for NWCIERC propagation path. Higher deviation in the VTXPune path as compared to VTXICSP path could be due to the proximity of the former to the epicenter. Similarly, DHOIERC path is over the epicenter while NWCIERC path is totally away from the epicenter. This could be the reason why the effect in DHOIERC path is stronger than that in NWCIERC path.

S. Ray

2013-06-01

328

Radio Emission from 3D Relativistic Hydrodynamic Jets: Observational Evidence of Jet Stratification  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present the first radio emission simulations from high resolution three dimensional relativistic hydrodynamic jets, which allow for a study of the observational implications of the interaction between the jet and external medium. This interaction gives rise to a stratification of the jet where a fast spine is surrounded by a slow high energy shear layer. The stratification, and in particular the large specific internal energy and slow flow in the shear layer largely deter...

Aloy, Miguel-angel; Gomez, Jose-luis; Ibanez, Jose-maria; Marti, Jose-maria; Mueller, Ewald

1999-01-01

329

Evidence from sub-millimetre observations for thermal dust emission in NGC4151  

Science.gov (United States)

Observations of the Seyfert 1 galaxy NGC4151 using the UKT14 bolometer on the James Clerk Maxwell Telescope are reported. A 5 sigma upper limit of 200 mJy in an 11 arcsec aperture is found. Comparison with an earlier measurement at 155 microns indicates that at least half of the 155-micron flux is due to thermal dust emission. The remainder may be from a synchrotron source which becomes self-absorbed at wavelengths of less than 80 microns.

Edelson, R. A.; Gear, W. K. P.; Malkan, M. A.; Robson, E. I.

1988-01-01

330

Isoprene emissions in Africa inferred from OMI observations of formaldehyde columns  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use 20052009 satellite observations of formaldehyde (HCHO) columns from the OMI instrument to infer biogenic isoprene emissions at monthly 1 1 resolution over the African continent. Our work includes new approaches to remove biomass burning influences using OMI absorbing aerosol optical depth data (to account for transport of fire plumes) and anthropogenic influences using AATSR satellite data for persistent small-flame fires (gas flaring). The resulting biogenic HCHO colu...

2012-01-01

331

Isoprene Emissions in Africa Inferred from OMI Observations of Formaldehyde Columns  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use 20052009 satellite observations of formaldehyde (HCHO) columns from the OMI instrument to infer biogenic isoprene emissions at monthly 1 1 resolution over the African continent. Our work includes new approaches to remove biomass burning influences using OMI absorbing aerosol optical depth data (to account for transport of fire plumes) and anthropogenic influences using AATSR satellite data for persistent small-flame fires (gas flaring). The resulting biogenic HCHO columns (?HC...

2012-01-01

332

Observation of triatomic ionic excimers: Emission spectra of Kr{sub 2}{sup +}Cs  

Energy Technology Data Exchange (ETDEWEB)

Triatomic ionic excimers have now been observed. Alkali rare-gas triatomic ionic molecules have been produced by electron beam excitation. Emission spectra centered at {approximately}159 nm due to Kr{sub 2}{sup +}Cs radiative decay were recorded. Lifetime and binding energy of the lowest excited state are estimated; the ground state is repulsive. Two formation channels for these triatomic ions are proposed and their rate coefficients estimated. {copyright} {ital 1997 American Institute of Physics.}

Delaporte, P.; Voitik, M.; Sentis, M. [Institut de Recherche sur les Phenomenes Hors Equilibre, U.M.R. 6594 C.N.R.S. Aix-Marseille I II Universities, 13288 Marseille Cedex 9 (France)

1997-05-01

333

Observations and interpretation of energetic particle-driven ion cyclotron emission from JET DT plasmas  

Energy Technology Data Exchange (ETDEWEB)

Ion cyclotron emission (ICE) excited by collective instability of fusion {alpha}-particles has been observed during deuterium-tritium experiments with radio-frequency heating and neutral beam injection (NBI) in JET. A model based on classical {alpha}-particle confinement is broadly consistent with this data. ICE spectra from discharges with high power NBI also show evidence of ion hybrid wave excitation by beam ions, relevant to {alpha}-channelling. (author)

McClements, K.; Dendy, R.; Hunt, C. [and others

2000-03-01

334

The properties of ULF/VLF signals generated by the SURA facility without ionospheric currents modulation  

Science.gov (United States)

During the last three years the comprehensive study of ionospheric generation of the artificial signals in ULF/VLF band was carried out at SURA facility. This research was stimulated by successive HAARP experiments on detection the low frequency signals genreated due the action of the ponderomotive forces. Two experimental campaigns under different ionospheric, geomagnetic and facility operation mode conditions was undertaken every year from 2010 to 2012. Here we are summarizing the main features of the artificial ULF/VLF signals observed in vicinity the SURA site. The signals in the 2-20 Hz band were observed in the small area around the facility with the radius approximately 15 km. It was not signal detection at the 30 km distance. The maximum of the amplitude was detected in the nearest receiving point about 3 km away from the transmitting array. The amplitude increased about 3 times when the beam was inclined on16 degrees to the south so the footprint of the geomagnetic field line comes close to the point of observation. The ULF signals increased slightly when the SURA operating frequency overlaps the critical foF2 frequency. As a rule the daytime signals are smaller then nighttime one. No any correlation was observed with geomagnetic disturbances. The time delay of the ionospheric ULF signals measured by phase method was estimated as 300-400 ms. Polarization of the ULF signals has a pronounced elliptical character. Sometimes it was linear. The part of measurements in June 2012 was coincide with magnetic storm (June 16-18, Kp=6). It was observed broadening of the signal line at frequencies of 11 and 17 Hz up to 0.2 Hz at the recovery stage of the storm at June 18 (see the figure). This fact can be interpreted as the result of the signal interaction with the radiation belt protons appeared over there during the storm time. In 2012 campaigns it was firstly observed at SURA signals on frequencies of several kilohertz at nightime which could not be explained by traditional mechanism of ionospheric current modulation. Also this signals displayed unusual behavior during the magnetic storm deceasing in the amplitude. The work was supported by RFBR grants 11-02-00419, 11-02-97104 and RF Ministry of education and science by state contract 16.518.11.7066.;

Kotik, D. S.; Raybov, A. V.; Ermakova, E. N.

2012-12-01

335

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 on this theory

1979-01-01

336

VLF/LF Radio Sounding of Ionospheric Perturbations Associated with Earthquakes  

Directory of Open Access Journals (Sweden)

Full Text Available It is recently recognized that the ionosphere is very sensitive to seismic effects,and the detection of ionospheric perturbations associated with earthquakes, seems to bevery promising for short-term earthquake prediction. We have proposed a possible use ofVLF/LF (very low frequency (3-30 kHz /low frequency (30-300 kHz radio sounding ofthe seismo-ionospheric perturbations. A brief history of the use of subionospheric VLF/LFpropagation for the short-term earthquake prediction is given, followed by a significantfinding of ionospheric perturbation for the Kobe earthquake in 1995. After showingprevious VLF/LF results, we present the latest VLF/LF findings; One is the statisticalcorrelation of the ionospheric perturbation with earthquakes and the second is a case studyfor the Sumatra earthquake in December, 2004, indicating the spatical scale and dynamicsof ionospheric perturbation for this earthquake.

Masashi Hayakawa

2007-07-01

337

Results on VLF long-distance propagation received at Brazil and at Antarctic Peninsula  

Science.gov (United States)

Recent results are presented of VLF long-distance propagation obtained at Itapetinga Radio Observatory, Atibaia, Brazil, and at Antarctic Station Commandante Ferraz, King George Island, Antarctic Peninsula. The signals originated in North West Cape, Australia.

Piazza, L. R.; Mendesdacosta, A.; Kaufmann, P.; Kuntz, V. L. R.; Paesleme, N. M.; Macedomoura, M. S. S.

1987-03-01

338

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

CERN Document Server

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).

Sulic, D; Sreckovic, V

2014-01-01

339

Radiation Parameters of the VLF Transmitting Station NWC, North West Cape, Australia.  

Science.gov (United States)

The U.S. Naval Research Laboratory experimentally determined the radiation parameters, radiation resistance and effective height, of the very low frequency (VLF) transmitting station NWC at the U.S. Naval Communication Station, North West Cape, Australia....

W. E. Garner J. E. Raudenbush C. B. Brookes

1967-01-01

340

OBSERVATIONS OF FAR-ULTRAVIOLET DIFFUSE EMISSION FROM THE SMALL MAGELLANIC CLOUD  

Energy Technology Data Exchange (ETDEWEB)

We report the first observations of far-ultraviolet (FUV: 1000-1150 A) diffuse radiation from the Small Magellanic Cloud (SMC) using observations from the Far-Ultraviolet Spectroscopic Explorer. The strength of FUV diffuse surface brightness in the SMC ranges from the detection limit of 2000 photons cm{sup -2} s{sup -1} sr{sup -1} A{sup -1} to a maximum of 3 Multiplication-Sign 10{sup 5} photons cm{sup -2} s{sup -1} sr{sup -1} A{sup -1} at 1004 A. The contribution of diffuse emission to the total radiation field was found to be 34% at 1004 A to 44% at 1117 A with a maximum observed uncertainty of 30%. There is a striking difference between the FUV diffuse fraction from the SMC and the Large Magellanic Cloud with the SMC fraction being higher probably because of the higher dust albedo. The FUV diffuse emission correlates with H{alpha} emission in the H II regions of the SMC.

Pradhan, Ananta C.; Murthy, Jayant [Indian Institute of Astrophysics, Bangalore 560 034 (India); Pathak, Amit, E-mail: acp@iiap.res.in [Present address: Department of Physics, Tezpur University, Tezpur 784 028 (India)

2011-12-10

 
 
 
 
341

XMM-Newton observations of X-ray emission from Jupiter  

CERN Multimedia

We present the results of two XMM-Newton observations of Jupiter carried out in 2003 for 100 and 250 ks (or 3 and 7 planet rotations) respectively. X-ray images from the EPIC CCD cameras show prominent emission from the auroral regions in the 0.2 - 2.0 keV band: the spectra are well modelled by a combination of emission lines, including most prominently those of highly ionised oxygen (OVII and OVIII). In addition, and for the first time, XMM-Newton reveals the presence in both aurorae of a higher energy component (3 - 7 keV) which is well described by an electron bremsstrahlung spectrum. This component is found to be variable in flux and spectral shape during the Nov. 2003 observation, which corresponded to an extended period of intense solar activity. Emission from the equatorial regions of Jupiter's disk is also observed, with a spectrum consistent with that of solar X-rays scattered in the planet's upper atmosphere. Jupiter's X-rays are spectrally resolved with the RGS which clearly separates the prominent...

Branduardi-Raymont, G; Elsner, R F; Gladstone, G R; Ramsay, G; Rodrguez, P; Soria, R; Waite, J H; Cravens, T E

2005-01-01

342

Topographic Effects on the Surface Emissivity of a Mountainous Area Observed by a Spaceborne Microwave Radiometer  

Directory of Open Access Journals (Sweden)

Full Text Available A simulation study to understand the influence of topography on the surfaceemissivity observed by a satellite microwave radiometer is carried out. We analyze theeffects due to changes in observation angle, including the rotation of the polarization plane.A mountainous area in the Alps (Northern Italy is considered and the information on therelief extracted from a digital elevation model is exploited. The numerical simulation refersto a radiometric image, acquired by a conically-scanning radiometer similar to AMSR-E,i.e., flying at 705 km of altitude with an observation angle of 55°. To single out the impacton surface emissivity, scattering of the radiation due to the atmosphere or neighboringelevated surfaces is not considered. C and X bands, for which atmospheric effects arenegligible, and Ka band are analyzed. The results indicate that the changes in the localobservation angle tend to lower the apparent emissivity of a radiometric pixel with respectto the corresponding flat surface characteristics. The effect of the rotation of thepolarization plane enlarges (vertical polarization, or attenuates (horizontal polarizationthis decrease. By doing some simplifying assumptions for the radiometer antenna, theconclusion is that the microwave emissivity at vertical polarization is underestimated,whilst the opposite occurs for horizontal polarization, except for Ka band, for which bothunder- and overprediction may occur. A quantification of the differences with respect to aflat soil and an approximate evaluation of their impact on soil moisture retrieval areyielded.

Frank S. Marzano

2008-03-01

343

Detection of near-source ground motions associated with VLF (very low frequency) earthquakes beneath the forearc slope of the Nankai trough by broadband ocean bottom seismometers  

Science.gov (United States)

Occurrence of submarine VLF events along the Nankai trough and Ryukyu trench has been reported based on dense seismic networks over the Japanese islands. The seismic waves are dominated by 10-30 s Rayleigh waves, whereas short-period P and S arrivals are hardly seen. Through a period from August 2008 to September 2009, we deployed three broadband ocean bottom seismographs (BBOBS) off the Kii Peninsula, where VLF events are known to have occurred in 2004 as an aftershock activity of the off-Kii Peninsula earthquake (M7.4). The BBOBS equipped with a three-component CMG-3T broadband sensor (Guralp Systems Ltd.) that senses ground motions at periods from 0.02 to 360 s with a sampling rate of 100 Hz at 24-bit resolutions. Numerous VLF events occurred in March 2009 within a distance range of about 10 km from the BBOBS stations. The records of a VLF event are characterized by the dominance of a 10-s wave group with a small apparent velocity of about 0.4 km/s, the association of much longer period components (>100 s) and the simultaneous association of much higher frequency components (1-8 Hz). The onsets of P and S arrivals are in general difficult to read. The displacement function was calculated at each observational site for several VLF events by correcting for the instrumental response. The function shows in general a gradual rise to a sub-millimeter level that can be regarded as a static displacement of the seafloor. The rise time on the order of 20-100 s is anomalously long relative to M4-class ordinary earthquakes for which the rise time is on the order of 1 s. We located the high-frequency sources by cross-correlating the envelopes of high-frequency S wave trains at different stations and by using the three-dimensional velocity model of Nakanishi et al. (2002) (Obana et al., in this meeting). The sources are mainly located in the accretionary prism of the Nankai Trough. We made a full waveform inversion for the moment tensors and source time functions of several VLF events, using finite-difference synthetic seismograms computed for a 2.5-dimensional structure model consistent with the previous seismic explosion studies (Okamoto et al., in this meeting). The moment tensor solutions of the VLF events consistently indicate low-angle thrusts with the moment magnitudes of 3.7-4.5. The sources are located at depths of 6-8 km within the accretionary prism, many of which scatter around the decollement. The moment functions show anomalously long durations of at least 20-40 s, consistent with the displacement function obtained at each BBOBS station, suggesting that much slower processes take place at the VLF sources than at the normal earthquake sources. These solutions were examined in detail by a forward approach where 3-dimensional FDM simulations of wave generation and propagation were made using the realistic 3-dimensional velocity structure including the Q-effect. The results indicate that the high-frequency content of seismic waves depends strongly on source depth in a range 3-10 km so that it may carry important information about the source depth.

Sugioka, H.; Ito, A.; Okamoto, T.; Nakamura, T.; Ishihara, Y.; Obana, K.; Fukao, Y.; Araki, E.; Kodaira, S.; Suetsugu, D.; Kinoshita, M.

2010-12-01

344

Observation of temporal behavior of the emission frequency from an ultrashort, high-power, and compact millimeter-wave source  

International Nuclear Information System (INIS)

The authors demonstrated observation of emission frequency chirping of millimeter-wave emission from a time-varying plasma produced by a nanosecond UV laser pulse. By using a heterodyne interferometer the time-resolved frequency of the emission from a dc to ac radiation converter source was observed to range from 20 to 32 GHz due to the rapid plasma creation. This chirped pulse is suitable for application in various novel dense plasma diagnostics

2007-03-12

345

Azimuthal dependence of the sea surface microwave emission at grazing observation angles  

Energy Technology Data Exchange (ETDEWEB)

The dependence of the sea-surface microwave emission on the angle between the direction of observation and the wind direction is investigated. On the basis of the analysis of airborne measurements (in the 1.5 cm band) and theoretical calculations, it is shown that, for vertical polarization, the angle effect is determined by the azimuthal anisotropy of gravity-capillary waves (as in the case of nadir observations). For horizontal polarization, however, it is necessary to take into account the contribution of large gravity waves and foam. 22 refs.

Irisov, V.G.; Kuz' min, A.V.; Trokhimovskii, IU.G.; Etkin, V.S. (AN SSSR, Institut Kosmicheskikh Issledovanii, Moscow (USSR))

1990-12-01

346

Characterization of kraft pulp mill particulate emissionsA 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.

347

The Predicted Signature of Neutrino Emission in Observations of Pulsating Pre-White Dwarf Stars  

CERN Document Server

Pre-white dwarf (PWD) star evolution can be driven by energy losses from neutrino interactions in the core. Unlike solar neutrinos, these are not the by-product of nuclear fusion, but instead result from electron scattering processes in the hot, dense regions of the PWD core. We show that the observed rate of period change in cool PWD pulsators will constrain neutrino emission in their cores, and we identify appropriate targets for future observation. Such a measurement will tell us whether the theories of lepton interactions correctly describe the production rates and therefore neutrino cooling of PWD evolution. This would represent the first test of standard lepton theory in dense plasma.

O'Brien, M S; Kawaler, Steven D.

2000-01-01

348

Observations of X-rays and Thermal Dust Emission from the Supernova Remnant Kes 75  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present Spitzer Space Telescope and Chandra X-ray Observatory observations of the composite Galactic supernova remnant Kes 75 (G29.7-0.3). We use the detected flux at 24 microns and hot gas parameters from fitting spectra from new, deep X-ray observations to constrain models of dust emission, obtaining a dust-to-gas mass ratio M_dust/M_gas ~0.001. We find that a two-component thermal model, nominally representing shocked swept-up interstellar or circumstellar material and...

Morton, T. D.; Slane, P.; Borkowski, K. J.; Reynolds, S. P.; Helfand, D. J.; Gaensler, B. M.; Hughes, J. P.

2007-01-01

349

Observati'onal experience of emission spectrum rapid variations of the NGC 1275 peculiar galaxy nucleus  

International Nuclear Information System (INIS)

The search for possible variations in the NGC 1275 galaxy nucleus spectrum was carried out in a scale of one day. 126 spectrogramms obtained during 23 observational series on the 6-m telescope in four nights 12-15 January 1977 were used for the investigation. All the equivalent widths of 11 emission lines obtained in optical spectral region are tabulated. These observations permit in conclude that in a case of a day the continuous spectrum changes by two times and in the Hsub(?) flux by 50%

350

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)

1980-01-01

351

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

352

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 EarthIonosphere 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; Torbjrn Sundberg; Collier, Andrew B.; Etienne Koen; Stephen Meyer

2011-01-01

353

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 EarthIonosphere 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.

Stephen Meyer

2011-09-01

354

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

355

Energy Spectra of the Soft X-ray Diffuse Emission in Fourteen Fields Observed with Suzaku  

CERN Multimedia

The soft diffuse X-ray emission of twelve fields observed with Suzaku are presented together with two additional fields from previous analyses. All have galactic longitudes 65 deg < l < 295 deg to avoid contributions from the very bright diffuse source that extends at least 30 deg from the Galactic center. The surface brightnesses of the Suzaku nine fields for which apparently uncontaminated ROSAT All Sky Survey (RASS) were available were statistically consistent with the RASS values, with an upper limit for differences of 17e-6 c s-1 amin-2 in R45-band. The OVII and OVIII intensities are well correlated to each other, and OVII emission shows an intensity floor at ~2 photons s-1 cm-2 str-1 (LU). The high-latitude OVIII emission shows a tight correlation with excess of OVII emission above the floor, with OVIII intensity = 0.5 x [(OVII intensity) - 2 LU], suggesting that temperatures averaged over different line-of-sight show a narrow distribution around ~0.2 keV. We consider that the offset intensity of ...

Yoshino, T; Yamasaki, N Y; Takei, Y; Hagihara, T; Masui, K; Bauer, M; McCammon, D; Fujimoto, R; Wang, Q D; Yao, Y

2009-01-01

356

A Chandra Observation of the Diffuse Emission in the Face-on Spiral NGC 6946  

CERN Document Server

This paper describes the {\\it Chandra} observation of the diffuse emission in the face-on spiral NGC 6946. Overlaid on optical and H${\\alpha}$ images, the diffuse emission follows the spiral structure of the galaxy. An overlay on a 6 cm polarized radio intensity map confirms the phase offset of the polarized emission. We then extract and fit the spectrum of the unresolved emission with several spectral models. All model fits show a consistent continuum thermal temperature with a mean value of 0.25$\\pm$0.03 keV. Additional degrees of freedom are required to obtain a good fit and any of several models satisfy that need; one model uses a second continuum component with a temperature of 0.70$\\pm$0.10 keV. An abundance measure of 3$^{+1.95}_{-1.90}$ for Si differs from the solar value at the 90% confidence level; the net diffuse spectrum shows the line lies above the instrumental Si feature. For Fe, the abundance measure of 0.67$\\pm$0.13 is significant at 99%. Multiple gaussians also provide a good fit. Two of the...

Schlegel, E M; Petre, R

2003-01-01

357

EGRET Observations of the Diffuse Gamma-Ray Emission in Orion Analysis Through Cycle 6  

CERN Document Server

We present a study of the high-energy diffuse emission observed toward Orion by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory. The total exposure by EGRET in this region has increased by more than a factor of two since a previous study. A simple model for the diffuse emission adequately fits the data; no significant point sources are detected in the region studied ($l = 195^\\circ$ to $220^\\circ$ and $b = -25^\\circ to -10^\\circ$) in either the composite dataset or in two separate groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion is found to be $(1.65 \\pm 0.11) \\times 10^{-26} {s sr}^{-1}$ for E > 100 MeV, and the differential emissivity is well-described as a combination of contributions from cosmic-ray electrons and protons with approximately the local density. The molecular mass calibrating ratio is $N(H_2)/W_{CO} = (1.35 \\pm 0.15) \\times 10^{20} cm^{-2} (K km/s)^{-1}$.

Digel, S W; Hunter, S D; Mukherjee, R; Xu, F

1999-01-01

358

A climatology of dust emission events from northern Africa using long-term surface observations  

Science.gov (United States)

Long-term (1984-2012) surface observations from 70 stations in the Sahara and Sahel are used to explore the diurnal, seasonal and geographical variations in dust emission events and thresholds. The frequency of dust emission (FDE) is calculated using the present weather codes of SYNOP reports. Thresholds are estimated as the wind speed for which there is a 50% probability of dust emission and are then used to calculate strong wind frequency (SWF) and dust uplift potential (DUP), where the latter is an estimate of the dust-generating power of winds. Stations are grouped into six coherent geographical areas for more in-depth analysis. FDE is highest at stations in Sudan and overall peaks in spring north of 23 N. South of this, where stations are directly influenced by the summer monsoon, the annual cycle in FDE is more variable. Thresholds are highest in northern Algeria, lowest in the latitude band 16-21 N and have greatest seasonal variations in the Sahel. Spatial variability in thresholds partly explain spatial variability in frequency of dust emission events on an annual basis. However, seasonal variations in thresholds for the six grouped areas are not the main control on seasonal variations in FDE. This is demonstrated by highly correlated seasonal cycles of FDE and SWF which are not significantly changed by using a fixed, or seasonally varying, threshold. The likely meteorological mechanisms generating these patterns such as low-level jets and haboobs are discussed.

Cowie, S. M.; Knippertz, P.; Marsham, J. H.

2014-03-01

359

Using Swift observations of prompt and afterglow emission to classify GRBs  

CERN Multimedia

We present an analysis of early BAT and XRT data for 107 gamma--ray bursts (GRBs) observed by the Swift satellite. We use these data to examine the behaviour of the X-ray light curve and propose a classification scheme for GRBs based on this behaviour. As found for previous smaller samples, the earliest X-ray light curve can be well described by an exponential which relaxes into a power law, often with flares superimposed. The later emission is well fit using a similar functional form and we find that these two functions provide a good description of the entire X-ray light curve. For the prompt emission, the transition time between the exponential and the power law gives a well-defined timescale, T_p, for the burst duration. We use T_p, the spectral index of the prompt emission, beta_p, and the prompt power law decay index, alpha_p to define four classes of burst: short, slow, fast and soft. Bursts with slowly declining emission have spectral and temporal properties similar to the short bursts despite having ...

O'Brien, P T

2007-01-01

360

Survey observations of emission-line stars in the Orion region  

International Nuclear Information System (INIS)

Survey observations were conducted for H alpha-emission stars in the Orion region using the Kiso Schmidt telescope and partly the CTIO Curtis Schmidt telescope. In the area of about 25 square degrees, a total of 236 H alpha-emission objects, mostly supposed to be T Tau type stars, have been detected among which 155 are new ones including 6 non-stellar objects. Celestial coordinates and V-magnitude are measured for the detected objects. Eye estimation of the H alpha-emission intensity is also made at three epochs in a time span of about two years, where notable variation of H alpha intensity was found in 68 out of 236 objects. Besides a remarkable concentration along the northern dark cloud complex, a loose concentration is noticed near the Orion Belt region, fairly well coinciding with the distribution of the Orion OBIb association members. A comparison with the Av-map is also made to see the relationship between the distribution of emission-line objects and that of interstellar dust

1989-12-01

 
 
 
 
361

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.

2010-07-10

362

On the effectiveness of the vlf-em method For ground water prospecting in the Basement terrains, Sinai, Egypt  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The VLF-EM method is proved to be an effective, fast and inexpensive tool for ground water prospecting in the basement terrains of Southern Sinai. The resistive shallow alluvial deposits increase the penetration depth of the received VLF waves to as deep as 40 meters which is very reasonable to detect the water bearing alluvium in the studied areas. The measured horizontal and vertical components of the resultant VLF-EM field were used to calculate the apparent resistivities of the conductive...

Shendi, El-arabi Hendi

1997-01-01

363

On the complete characterization of the physical observables of radio emissions from arbitrary sources  

Science.gov (United States)

Like all forms of electromagnetic radiation, radio emissions of cosmic origin contain a diversity of physical observables that are constants of motion. Each of these observables carry unique information about the physics of the source(s) from which the radiation emanates and the medium through which it propagates. While the electromagnetic observables used in present-day radio and radar studies of space are limited to the energy (radiometry) and the linear momentum (radio astronomy, space radio and radar applications), the angular momentum and the boost momentum of the radiation are typically discarded and thereby important information wasted. We show how all electromagnetic observables can be measured and analysed, yielding information about vorticity and other topological properties as well as turbulence of radio sources and propagation media. Both theoretical predictions and experimental results confirming these predictions will be presented.

Thid, Bo; Tamburini, Fabrizio

2014-05-01

364

Characterization of gaseous pollutant and particulate matter emission rates from a commercial broiler operation part I: Observed trends in emissions  

Science.gov (United States)

This paper characterizes the emission rates of size fractionated particulate matter, inorganic aerosols, acid gases, ammonia and methane measured over four flocks at a commercial broiler chicken facility. Mean emission rates of each pollutant, along with sampling notes, were reported in this paper, the first in a series of two. Sampling notes were needed because inherent gaps in data may bias the mean emission rates. The mean emission rates of PM 10 and PM 2.5 were 5.0 and 0.78 g day -1 [Animal Unit, AU] -1, respectively, while inorganic aerosols mean emission rates ranged from 0.15 to 0.46 g day -1 AU -1 depending on the season. The average total acid gas emission rate was 0.43 g day -1 AU -1 with the greatest contribution from nitrous and nitric acids and little contribution from sulfuric acid (as SO 2). Ammonia emissions were seasonally dependent, with a mean emission rate of 66.0 g day -1 AU -1 in the cooler seasons and 94.5 g day -1 AU -1 during the warmer seasons. Methane emissions were relatively consistent with a mean emission rate of 208 g day -1 AU -1. The diurnal pattern in each pollutant's emission rate was relatively consistent after normalizing the hourly emissions according to each daily mean emission rate. Over the duration of a production cycle, all the measured pollutants' emissions increased proportionally to the total live mass of birds in the house, with the exception of ammonia. Interrelationships between pollutants provide evidence of mutually dependent release mechanisms, which suggests that it may be possible to fill data gaps with minimal data requirements. In the second paper (Roumeliotis, T.S., Dixon, B.J., Van Heyst, B.J. Characterization of gaseous pollutants and particulate matter emission rates from a commercial broiler operation part II: correlated emission rates. Atmospheric Environment, 2010.), regression correlations are developed to estimate daily mean emission rates for data gaps and, using the normalized hourly diurnal patterns from this paper, emission factors were generated for each pollutant.

Roumeliotis, Taylor S.; Dixon, Brad J.; Van Heyst, Bill J.

2010-10-01

365

Mid-infrared emission of galactic nuclei: TIMMI2 versus ISO observations and models  

CERN Document Server

We investigate the mid-infrared radiation of galaxies that are powered by a starburst or by an AGN. For this end, we compare the spectra obtained at different spatial scales in a sample of infrared bright galaxies. ISO observations which include emission of the nucleus as well as most of the host galaxy are compared with TIMMI2 spectra of the nuclear region. We find that ISO spectra are generally dominated by strong PAH bands. However, this is no longer true when inspecting the mid-infrared emission of the pure nucleus. Here PAH emission is detected in starbursts whereas it is significantly reduced or completely absent in AGNs. A physical explanation of these new observational results is presented by examining the temperature fluctuation of a PAH after interaction with a photon. It turns out that the hardness of the radiation field is a key parameter for quantifying the photo-destruction of small grains. Our theoretical study predicts PAH evaporation in soft X-ray environments. Radiative transfer calculations...

Siebenmorgen, R; Spoon, H W W

2004-01-01

366

OBSERVATION OF EXTENDED VERY HIGH ENERGY EMISSION FROM THE SUPERNOVA REMNANT IC 443 WITH VERITAS  

International Nuclear Information System (INIS)

We present evidence that the very high energy (VHE, E > 100 GeV) gamma-ray emission coincident with the supernova remnant IC 443 is extended. IC 443 contains one of the best studied sites of supernova remnant/molecular cloud interaction and the pulsar wind nebula CXOU J061705.3+222127, both of which are important targets for VHE observations. VERITAS observed IC 443 for 37.9 hr during 2007 and detected emission above 300 GeV with an excess of 247 events, resulting in a significance of 8.3 standard deviations (?) before trials and 7.5? after trials in a point-source search. The emission is centered at 6h16m51s + 22030'11'' (J2000) 0.003stat 0.008sys, with an intrinsic extension of 0.016 0.003stat 0.004sys. The VHE spectrum is well fit by a power law (dN/dE = N 0 x (E/TeV)-?) with a photon index of 2.99 0.38stat 0.3sys and an integral flux above 300 GeV of (4.63 0.90stat 0.93sys) x 10-12 cm-2 s-1. These results are discussed in the context of existing models for gamma-ray production in IC 443.

2009-06-20

367

Observation of Extended VHE Emission from the Supernova Remnant IC 443 with VERITAS  

CERN Document Server

We present evidence that the very-high-energy (VHE, E > 100 GeV) gamma-ray emission coincident with the