WorldWideScience
 
 
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.)

2

Propagation and observations of vlf emissions in the auroral zone  

International Nuclear Information System (INIS)

Vlf data from the auroral zone ground stations at College and Bar I collected for almost a year and a half. The data contained many naturally occurring vlf emissions called hiss and chorus in the range of a few hundred Hz to a few kHz. Events indicated relationships of elf/vlf emissions with the manifestations of auroral substorm phenomena. The diurnal variation of the narrow band chorus emissions below approximately 4 kHz was found to peak around local noon and show a strong correlation with the large and anistropic (greater than or equal to 40 keV) electron flux at approximately 2000 km. Ground observations of wideband vlf hiss revealed that it is primarily a late evening phenomena and is closely related to the visual aurora. Examples of correlation between occurrences of vlf hiss and auroral activation indicate that there does exist a causal connection between the two, which may be due to the same precipitating particles responsible for both hiss and the auroral light. Comparison of the low-altitude polar orbiting Injun 5 satellite data with the ground vlf data clearly revealed that there is a definite scarcity of vlf events on the ground. Many of the near-auroral zone vlf events are frequently either reflected by, or heavily attenuated in, the lower ionosphere, and these losses in the lower ionosphere are the principal causes for the rarity of hiss and chorus emissions at the ground level. A separate computation for vlf signals which are observed by the high altitude OGO satellites and are generated in the equatorial plane of the magnetosphere indicates that these signals are more or less trapped in the magnetosphere at altitudes greater than or equal to 1 R/sub E/ and cannot reach the ground

3

Ulysses observations of escaping VLF emissions from Jupiter  

Science.gov (United States)

The Ulysses URAP experiment has detected Jovian radio emissions in the VLF range at distances from Jupiter in excess of 1.5 AU. The URAP observations represent the first synoptic observations of Jupiter in the VLF band, from 3 to 30 kHz. In this band lie the low-frequency extent of the bKOM emission, the escaping continuum emission, and the Jovian type IIIs. Initial results indicate that the continuum varies in frequency with the solar wind ram pressure at Jupiter, whereas, the Jovian type IIIs appear to be controlled to some extent by the planetary rotation, often appearing when system III longitude 100 deg faces the spacecraft.

Kaiser, M. L.; Desch, M. D.; Farrell, W. M.; Macdowall, R. J.; Stone, R. G.; Lecacheux, A.; Pedersen, B.-M.; Zarka, P.

1992-01-01

4

VLF emissions in the Venus foreshock - Comparison with terrestrial observations  

Science.gov (United States)

An examination is conducted of ELF/VLF emissions observed in the solar wind upstream of the Venus shock, for the 100 Hz-30 kHz range, using data from the Pioneer Venus Orbiter's electric field detector and magnetometer instruments. Detailed comparisons are made with terrestrial measurements for both the electron and ion foreshocks. The results obtained support the Crawford et al. (1990) identification of the Venus electron foreshock emissions as electron plasma oscillations, whose waves are generated in situ and act to isotropize the electron distributions.

Crawford, G. K.; Strangeway, R. J.; Russell, C. T.

1993-01-01

5

Identification of earthquake sources responsible for subsurface VLF electric field emissions observed at Agra  

Science.gov (United States)

Employing USGS earthquake data for Indian region and very low frequency (VLF, 3 kHz) subsurface electric field data obtained by using a borehole antenna at Agra in India, statistical analysis has been carried out to identify the earthquake sources responsible for VLF data. The correlation coefficient between occurrence number of VLF noise bursts and earthquakes are calculated and level of null hypothesis tested. The results show that seismic activities occurring close to the observing station and the main boundary fault located at the southern base of Himalaya are the main sources of VLF emissions recorded at the station.

Singh, Vikram; Singh, Birbal; Kumar, Manoj; Hayakawa, M.

6

Characteristics of ELF/VLF drifting emissions observed at low latitude station Varanasi during geomagnetic substorms  

International Nuclear Information System (INIS)

If the frequency within a set of periodic emissions changes significantly, the set is called drifting emissions. In this paper, characteristics of drifting ELF/VLF emissions are examined based on the ELF/VLF data recorded at low latitudes ground station Varanasi (geom. lat. 140 55/ N, long. 1540 E, L=1.07) during the period Jan., 1990 to Dec., 1990. Total seven strong events of drifting ELF/VLF emissions have been observed on 28-29 April, 1990 at pre-midnight sector out of which 3 events were analyzed in detail. The observed ELF/VLF emissions exhibit a regular frequency drifts, increasing as well as decreasing drift. The ELF/VLF emissions observed are mainly periodic emissions of rising and falling tone chorus. These emissions were observed during a geomagnetic storm period, when minimum Dst-index was -98 nT and KP-index ? 5. The repetition period, sweep rate and the frequency drift rate have been evaluated for all events. We have also computed the spectral power density, location of plasmapause, maximum intensity and maximum frequency attained. The generation mechanism of these drifting ELF/VLF emissions is explained in terms of a quasi-linear electron synchrotron instability model for wave excitation. The frequency drift in these emissions have been interpreted in terms of a combined effect of L-shell drift of energetic electrons and the change in convections electric field during the substorm developments. The computed maximum spectral power density of the wave varies between 1.8 x 10-21 to 4.08 x 10-22 Gauss2/Hz. The computed frequency drift rates of these drifting emissions are found in good agreement with that of experimentally observed values.

7

Characteristics of ELF/VLF drifting emissions observed at low latitude station Varanasi during geomagnetic substorms  

Energy Technology Data Exchange (ETDEWEB)

If the frequency within a set of periodic emissions changes significantly, the set is called drifting emissions. In this paper, characteristics of drifting ELF/VLF emissions are examined based on the ELF/VLF data recorded at low latitudes ground station Varanasi (geom. lat. 14{sup 0} 55{sup /} N, long. 154{sup 0} E, L=1.07) during the period Jan., 1990 to Dec., 1990. Total seven strong events of drifting ELF/VLF emissions have been observed on 28-29 April, 1990 at pre-midnight sector out of which 3 events were analyzed in detail. The observed ELF/VLF emissions exhibit a regular frequency drifts, increasing as well as decreasing drift. The ELF/VLF emissions observed are mainly periodic emissions of rising and falling tone chorus. These emissions were observed during a geomagnetic storm period, when minimum D{sub st}-index was -98 nT and K{sub P}-index {>=} 5. The repetition period, sweep rate and the frequency drift rate have been evaluated for all events. We have also computed the spectral power density, location of plasmapause, maximum intensity and maximum frequency attained. The generation mechanism of these drifting ELF/VLF emissions is explained in terms of a quasi-linear electron synchrotron instability model for wave excitation. The frequency drift in these emissions have been interpreted in terms of a combined effect of L-shell drift of energetic electrons and the change in convections electric field during the substorm developments. The computed maximum spectral power density of the wave varies between 1.8 x 10{sup -21} to 4.08 x 10{sup -22} Gauss{sup 2}/Hz. The computed frequency drift rates of these drifting emissions are found in good agreement with that of experimentally observed values.

Singh, Shubha; Singh, A K [Atmospheric Research Lab., Department of Physics, Banaras Hindu University, Varanasi- 221005 (India); Singh, R P, E-mail: abhay_s@rediffmail.co [V.C., V.K. S. University, Ara, Bihar (India)

2010-02-01

8

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

International Nuclear Information System (INIS)

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

9

ISEE-1 observations in the magnetosphere of VLF emissions triggered by nonducted coherent VLF waves during VLF wave-injection experiments  

International Nuclear Information System (INIS)

It is noted that recent data from the ISEE-1 spacecraft indicate that VLF emissions triggered by nonducted coherent VLF waves often possess spectral characteristics markedly different from those of emissions triggered by ducted waves. Emission triggering by nonducted waves is found to involve a strong path selectiveness. It is also established that emission triggering by nonducted waves can take place over a wide L-range and may involve inner radiation belt particles of energy up to 200 keV. It is concluded that the VLF emission generation process can occur under much more general conditions than previously believed on the basis of the results of ground-to-ground wave-injection experiments

10

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 17°1' 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

11

Generation mechanism for VLF chorus emissions observed at a low-latitude ground station  

Directory of Open Access Journals (Sweden)

Full Text Available A detailed spectral analysis of VLF chorus emissions observed at the low-latitude ground station Gulmarg (geomag. lat., 24° 26' N, geomag. long., 147° 9' E, L=1.28 during the strong magnetic activity on 7-8 March 1986 have been carried out, which shows that each chorus element originates from the upper edge of the underlying hiss band. To explain various temporal and spectral features of these emissions, a possible generation mechanism has been presented based on the backward wave oscillator regime of the magnetospheric cyclotron maser. On the basis of this model, we have computed various chorus parameters as well as some magnetospheric parameters affecting the generation process. A comparison of the observed chorus characteristics with the proposed generation mechanism shows a good agreement.

A. K. Singh

2004-06-01

12

Appearance of Enhanced VLF-Emissions on 8 KC/S Observed Along a n-S Chain of Stations.  

Science.gov (United States)

VLF-emissions on 8 kc/s have been recorded simultaneously along a chain of stations in N-S direction: Tromso, Lycksele, Oslo and Chambon la Foret, covering a latitude difference from 70 degrees to 48 degrees N. It is shown that the polar VLF-emissions rec...

L. Harang

1966-01-01

13

Coordinated Optical/VLF Lightning Observations  

Science.gov (United States)

We examine the coordinated optical and VLF emissions from lightning detected by the Los Alamos Sferic Array (LASA) during the summer of 2005. The sensor station located in Norman, OK that summer was equipped with an optical photodiode detector in addition to the VLF radio receiver usual to the LASA stations. We apply signal-to-noise ratio thresholds and require that the optical signal arrived within a specific temporal window about the VLF detection to claim coincidence, thus enabling a statistical assessment of the variations in optical emissions from various types of lightning discharges. We differentiate among lightning discharge types on the basis of the VLF waveform. Examination of 35,272 events finds that 43% of negative polarity cloud-to-ground discharges (CGs) have a coincident optical detection, while only 23% of negative polarity in-cloud discharges (ICs) show optical coincidence. Further, positive polarity VLF events are substantially less likely to show optical coincidence: 9% of positive ICs and 10% of positive CGs were optically detected. There is essentially no correlation observed, overall, between the intensity of the optical and VLF emissions from a given event, regardless of event type. Light & Jacobson (JGR, v107, p4756, 2002) found evidence that the type of discharge referred to as a "narrow bipolar event" (NBE) lacks corresponding optical emission, but the question remains open of whether they are completely dark or whether they do generate optical emissions which were simply below the detection threshold for that particular satellite-based data set. These ground-based data show that VLF NBEs are at least a factor of two to four less likely to show optical counterparts than other, more common types of lightning discharge. We attempt to set an upper limit to their optical emission in this work.

Light, T.; Hamlin, T.

2008-12-01

14

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

15

Auroral pulsations and accompanying VLF emissions  

Directory of Open Access Journals (Sweden)

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

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

V. R. Tagirov

16

Ground-based ELF/VLF chorus observations at subauroral latitudes—VLF-CHAIN Campaign  

Science.gov (United States)

We report observations of very low frequency (VLF) and extremely low frequency (ELF) chorus waves taken during the ELF/VLF Campaign observation with High-resolution Aurora Imaging Network (VLF-CHAIN) of 17-25 February 2012 at subauroral latitudes at Athabasca (L=4.3), Canada. ELF/VLF waves were measured continuously with a sampling rate of 100 kHz to monitor daily variations in ELF/VLF emissions and derive their detailed structures. We found quasiperiodic (QP) emissions whose repetition period changes rapidly within a period of 1 h without corresponding magnetic pulsations. QP emissions showed positive correlation between amplitude and frequency sweep rate, similarly to rising-tone elements. We found an event of nearly simultaneous enhancements of QP emissions and Pc1/electromagnetic ion cyclotron wave intensities, suggesting that the temperature anisotropy of electrons and ions developed simultaneously at the equatorial plane of the magnetosphere. We also found QP emissions whose intensity suddenly increased in association with storm sudden commencement without changing their frequency. Falling-tone ELF/VLF emissions were observed with their rate of frequency change varying from 0.7 to 0.05 kHz/s over 10 min. Bursty-patch emissions in the lower and upper frequency bands are often observed during magnetically disturbed periods. Clear systematic correlation between these various ELF/VLF emissions and cosmic noise absorption was not obtained throughout the campaign period. These observations indicate several previously unknown features of ELF/VLF emissions in subauroral latitudes and demonstrate the importance of continuous measurements for monitoring temporal variations in these emissions.

Shiokawa, Kazuo; Yokoyama, Yu; Ieda, Akimasa; Miyoshi, Yoshizumi; Nomura, Reiko; Lee, Sungeun; Sunagawa, Naoki; Miyashita, Yukinaga; Ozaki, Mitsunori; Ishizaka, Kazumasa; Yagitani, Satoshi; Kataoka, Ryuho; Tsuchiya, Fuminori; Schofield, Ian; Connors, Martin

2014-09-01

17

A search for ELF/VLF emissions induced by earthquakes as observed in the ionosphere by the DE 2 satellite  

Science.gov (United States)

ELF/VLF data from 63 DE 2 orbits coincident with large (magnitude not less than 5.0) earthquakes were examined individually and compared with control orbits not coincident with earthquakes. No unusual emissions coincident with the passing of the DE 2 satellite near an epicenter within a certain temporal and spatial window were identified for any orbit. About 63 percent of the orbits showed an ELF or VLF emission above 10 micro-V/m in at least one of the 20 channels when the satellite passed near and epicenter; 37 percent were quiet in all channels.

Henderson, T. R.; Sonwalkar, V. S.; Helliwell, R. A.; Inan, U. S.; Fraser-Smith, A. C.

1993-01-01

18

Effect of solar wind shock waves in VLF emission  

International Nuclear Information System (INIS)

Sc effects in VLF emission, detected in the middle latitudes, are compared to solar wind shock waves, identified according to the ISEE-3 satellite data, and a simultaneous increase of hourly values of the main solar wind parameters and interplanetary magnetic field strength according to the IMP satellite data. It is established that the given SC effects in VLF emission are related to shock waves come to the Earth. The conclusion is made concerning possible use of continuous terrestrial VLF observations to detect the moment of interaction between shock waves and magnetosphere

19

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

20

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 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.

Á. Mika

2006-09-01

 
 
 
 
21

Particle precipitation tied to unusual VLF emissions  

International Nuclear Information System (INIS)

Complete text of publication follows. Some unusual Very Low Frequency (VLF) emissions have been studied from the VLF data obtained from the SANAE IV, Antarctica. The emissions have vastly different forms, but do however show some similarities. The emissions occur during periods of low global geomagnetic activity (Kp <3), and mostly within a short time of a space weather condition which would result in increased plasma density within the magnetosphere. These conditions include geomagnetic storms, increased solar wind speed/proton density and a southward oriented Interplanetary Magnetic Filed (IMF). The aim of this work is to directly link the occurrence of emissions and particle precipitation. To this end we study data from the Finish chain of riometers (roughly meridional in the northern hemisphere), as well as riometers located at SANAE IV.

22

Simultaneous direction finding of VLF emissions in Japan and Europe, (1)  

International Nuclear Information System (INIS)

It was clarified that the VLF (very low frequency) emission observed at low latitude as that in Moshiri is not propagated from the auroral zone but generated as a result of the interaction between waves and particles in the vicinity of plasma pause. For the purpose of further pursuit for that point, the direction finding of VLF emissions accompanying mainly magnetic storms was performed at Moshiri and other two points in Europe (Brorfelde, Denmark and Chambon-la-Foret, France) in order to clarify the generating and propagating mechanisms of VLF emissions at the time of disturbances. The project was conducted for 3 years from the fiscal 1976, and the observations were successful, being able to obtain a number of significant data. The objects of observation were the intensity and incident direction of VLF emissions (Hiss), whistler, and isolated VLF emissions (riser, hook, and trigged emission). Incident direction finding was carried out by the field analysis method and the direction finding using a goniometer, which are complementary each other. The final conclusion is not yet presented because the data arrangement is underway. However, the following is due: most VLF emissions (Hiss) occurred accompanying geomagnetism disturbances. It is mainly generated at dawn. In European stations, most of VLF emissions were observed simultaneously, and were considered to be the same events by the comparison of spectra by means of sonagram and the comparison of hiss record. (Wakatsuki, Y.)

23

Relation of pulsations of cosmic radio noise and ELF - VLF emission  

International Nuclear Information System (INIS)

The relation of pulsations of cosmic radio noise absorption (CRNA) and ELF-VLF emission , as well as the dependence of this relation on location of the emission generation area projected on to the Earth surface, time of the day and geomagnetic disturbance level, are studied. Pulsations of the minute intervals of the periods were used as an indication of CRNA and ELF-VLF emission level variations. It is found that coincidence of the characteristic indications of similar ELF-VLF emission and CRNA modulation is observed at the CRNA stations outside the plasmosphere projection. It is experimentally observed that ELF-VLF emission, assigned to the class of long-term cyclotron noise bursts, from the extraplasmospheric area of a local source can be detected at more than 1000 km away from its projection onto the Earth surface

24

VLF emission bursts in the terrestrial and Venusian nightside troughs  

Science.gov (United States)

It is shown here that the 100-Hz emission bursts in the Venusian nightside ionosphere are remarkably similar to those of the terrestrial VLF saucer emissions in terms of their spatial and temporal characteristics and the properties of their magnetoplasma environment. It is proposed that the generation mechanism for such VLF sources should be considered as a viable alternative to lightning as a source of Venusian ionospheric whistler-mode emissions.

Maeda, Kaichi; Grebowsky, Joseph M.

1989-01-01

25

VLF emission stimulated by parallel electric fields  

Science.gov (United States)

Modifications in the growth of plasma waves by quasi-stationary electric fields of electromagnetic waves below the electron cyclotron frequency in a plasma are investigated analytically. The phenomena are believed to be active mechanisms in the appearance of quasi-stationary parallel electric potentials along field lines of the ambient geomagnetic field. The discussion is constrained to parallel wave propagation, which is most affected by the growth rates of whistlers and ion cyclotron waves. Operator calculus is employed to define a general dispersion relation for plasma waves in an applied electric field. The relation is used to explore loss-cone distributions, parallel propagation and VLF emissions in the magnetospheric plasma. Electric fields are assumed to excite plasma wave propagation in the latter.

Juhl, B.; Treumann, R. A.

1985-08-01

26

Frequency-time behavior of artificially stimulated vlf emissions  

International Nuclear Information System (INIS)

Artificially stimulated VLF emissions (ASE's) are emissions triggered in the magnetosphere by the whistler mode signals from VLF transmitters. These emissions may be separated into two classes, rising and falling, depending on whether the final value of df/dt is positive or negative. Several hundred ASE's triggered by three transmitters have been analyzed using the fast Fourier transform with a filter spacing of 25 Hz and an effective filter width of about 45 Hz. The study was limited to the initial frequency-time behavior of ASE's. Averages taken over many events reveal that both rising and falling tones show the same initial behavior. The emissions begin at the frequency of the triggering signal. Both tones initially rise in frequency, falling tones reversing slope at a point 25--300 Hz above the triggering signal. The slope of rising tones, particularly those triggered by NAA, often abruptly levels off in this same frequency range; as a result, a short (approximately 40 ms) plateau is formed that precedes the final rising phase. The initial frequency offset commonly observed in individual events appears to result from the frequent coincidence with this plateau of a peak in amplitude. Emissions stimulated by all three transmitters show essentially the same features; this finding indicates that their frequency behavior does not depend strongly on transmitter power. The process appears to be asymmetric in frequency; no evidence of initial growth below the triggering frequency has been found. (U.S.)

27

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

28

Quasi-periodic ELF/VLF wave emissions in the Earth's magnetosphere: comparison of satellite observations and modeling  

Directory of Open Access Journals (Sweden)

Full Text Available We present the results of a case study of quasi-periodic (QP ELF/VLF hiss emissions detected on board the Freja and Magion 5 satellites. Detailed analysis of available QP events revealed certain specific features of their dynamic spectra, which have not been reported earlier. In particular, we found an event with an increase in the frequency drift rate during the generation of a single element of QP emission, and an event with alteration of QP elements having different frequency drift rates. Another event demonstrates the possible relationship between QP hiss emissions and discrete VLF emissions. Properties of QP events are compared with parameters of energetic electrons and cold plasma, and other available data.

Possible scenarios for the formation of these emissions are discussed on the basis of self-consistent simulations of the cyclotron instability, employing the information obtained experimentally. It is shown that the generation regime of self-sustained pulsations can explain consistently our data set. We show that our numerical model is capable of explaining the mentioned specific features of the dynamic spectrum of QP emissions. Comparison of the modeling results with experimental data yields an estimate for the parameters not measured directly.

Key words. Magnetospheric physics (plasma waves and instabilities; energetic particles, precipitating; energetic particles, trapped

D. L. Pasmanik

2004-12-01

29

Similar behaviors of natural ELF/VLF ionospheric emissions and transmitter signals over seismic Adriatic regions  

Directory of Open Access Journals (Sweden)

Full Text Available We report on the analysis of ELF/VLF emissions observed by the Instrument Champ Electrique (ICE experiment onboard the DEMETER micro-satellite. We consider principally selected seismic events reported by Molchanov et al. (2006. These authors studied the VLF signals radiated by ground transmitters and received on board the DEMETER micro-satellite. They revealed a drop of the signals (scattering spot connected with the occurrence of large earthquakes. In our investigations, we proceed to a spectral analysis of ICE observations with the aim to find if the natural ionospheric VLF/ELF emissions show, or not, a similar ''drop'' in the intensity as it is the case of the VLF transmitter signal. We combine our results with those of Molchanov et al. (2006, and we discuss the origin of such interesting ionospheric features in the frame of the investigation of the pre-seismic electromagnetic emissions. We show that the geomagnetic activity is a key parameter which could disturb the natural VLF ionospheric emissions, and also the transmitter signal. We find that it is not possible to conclude the presence, or not, of a preseismic effect when the Kp-index is higher than one.

M. Y. Boudjada

2008-11-01

30

DE-1 observations of VLF transmitter signals and wave-particle interactions in the magnetosphere  

International Nuclear Information System (INIS)

A broadband VLF receiver on the DE-1 satellite measures signals injected into the magnetosphere by ground-based transmitters. VLF emissions triggered by these signals indicate that the waves interact strongly with trapped energetic particles in the magnetosphere. The propagation paths from the source to the satellite are deduced on the basis of the group time delay and Doppler shift. Although there are many different paths, emissions are triggered by the later-arriving pulses that have traversed the geomagnetic equator. First satellite-based observations of emission triggering by high-power communications transmitters and their possible inplications are discussed

31

Disturbance phenomena in VLF standard radio wave observation  

International Nuclear Information System (INIS)

Storm aftereffect, i.e. the phase disturbance after initiation of a magnetic storm has been revealed in the observation of VLF standard radio waves. In VLF long distance propagation at middle latitudes (L - 3), the phase disturbance for several days after the initiation of a magnetic storm is due to electron fall from the radiation belt. This has been confirmed by the comparison with electron flux detected by an artificial satellite. The correlations between VLF phase disturbance and magnetism activity or ionosphere absorption are described. The relation between winter anomaly and phase disturbance is also discussed. (Mori, K.)

32

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-12-15

33

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.

34

On the frequency modulation of VLF emissions  

Directory of Open Access Journals (Sweden)

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

M. Goncharova

35

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.; Décréau, P.; Pickett, J. S.; Laakso, H. E.

2012-12-01

36

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

37

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

CERN Document Server

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

Kachakhidze, Manana

2013-01-01

38

Observations of VLF Hiss at Very Low L Values.  

Science.gov (United States)

Observations of intense bursts of very-low-frequency (VLF) radio noise at low altitudes near the magnetic equator are reported using data from the Injun 3 satellite. The spectral characteristics of these radio noise events typically consist of hiss extend...

D. A. Gurnett

1967-01-01

39

Study of wave-particle interactions of VLF/ELF chorus waves observed at subauroral latitudes  

Science.gov (United States)

One of the mechanisms that cause energetic particle precipitation at low latitude side of auroral zone, such as pulsating auroras, is the VLF/ELF waves generated around magnetic equator which modulate particle precipitation through wave-particle interaction. In this model, correlations between pulsating auroras and VLF/ELF waves observed at ground are expected. Indeed, examples of such good correlations were reported previously (Tsuruda et al., 1981). In those days, however, it was difficult to analyze the frequency characteristics and wave forms in detail, since all data were in analog recordings. Therefore, we made a campaign observation of high-time resolution measurements of auroras and VLF/ELF waves at Athabasca (54.72N, 246.69E, MLAT=61.3) and Fort Vermillion (58.38N, 243.99E, MLAT=64.5), using two loop antennas(100kHz sampling), several auroral cameras(30-100Hz sampling) and induction magnetometers(64Hz sampling) for February 16-27, 2012. In this campaign, various types of chorus waves were observed, i.e., Q-P emissions with repeating periods of 20-60 seconds, rising/falling tones for which the emission frequency varies in a few seconds, patchy high-frequency burst waves, and so on. In order to investigate waveparticle interaction of these waves, we closely compare these VLF/ELF waves with the data of energetic particle precipitation obtained from all-sky cameras and riometers in Athabasca and Meanook (54.61N, 246.65E, MLAT=61.47). We also investigate local magnetic field variations and ULF wave variations to identify the cause of temporal variation of VLF/ELF waves.

Yokoyama, Y.; Shiokawa, K.; Miyoshi, Y.; Ozaki, M.; Ishizaka, K.; Yagitani, S.; Connors, M. G.

2012-12-01

40

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

International Nuclear Information System (INIS)

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

 
 
 
 
41

Regular noise background in VLF emission and global thunderstorm centers  

Science.gov (United States)

VLF emissions were recorded at high latitudes by loop-antenna measurements involving the azimuth rotation of the antenna plane. Ratios of regular-noise-background (RNB) amplitudes for different antenna positions were analyzed, and it is shown that the received radiation can be approximated by a model of two sources, one of which is localized while the other is 'isotropic' with respect to the azimuth. The azimuth angles of radiation arrival from localized sources are examined in detail, and a formula is obtained for the azimuth of signal arrival. An analysis of data obtained in autumn-winter periods at different measurement points shows that localized RBN sources are global thunderstorm centers.

Druzhin, G. I.; Toropchinova, T. V.; Shapaev, V. I.

1986-04-01

42

Narrowband VLF observations as validation of Plasmaspheric model  

Science.gov (United States)

PLASMON is a European Union FP7 project which will use observations of whistlers and field line resonances to construct a data assimilative model of the plasmasphere. This model will be validated by comparison with electron precipitation data derived from narrowband VLF observations of subionospheric propagation from the AARDDVARK network. A VLF receiver on Marion Island, located at 46.9° S 37.1° E (L = 2.60), is able to observe the powerful NWC transmitter in Australia over a 1.4 signal is thus very strong and exhibits an excellent signal-to-noise ratio. Data from the UltraMSK narrowband VLF receiver on Marion Island are used to examine evidence of particle precipitation along this path, thereby inferring the rate at which electrons are scattered into the bounce loss cone. This path covers a small range of L-values so that there is little ambiguity in the source of any peturbations. Perturbations detected on the path during geomagnetic storms should predominantly be responses to energetic electron precipitation processes occurring inside the plasmasphere. Comparisons will be made to preliminary plasmaspheric results from the PLASMON project.

Collier, Andrew; Clilverd, Mark; Rodger, C. J.; Delport, Brett; Lichtenberger, János

2012-07-01

43

VLF emission produced by a rarefied electron beam during active experiments in the Earth ionosphere: Conditions of observation of the emission  

Energy Technology Data Exchange (ETDEWEB)

The authors discuss the interpretation of active electron beam injection experiments in the ionosphere. They consider cases where the beams generate whistler wave packets. The observation of such wave generation phenomena depends upon the orientation of the reciever with respect to the beam source, and the injection angle with respect to the geomagnetic field. They consider the spectral characteristics of the whistlers generated as a function of the plasma density, and the energy transferred into these oscillation modes.

Lundin, B.; Chmyrev, V. [Institute of Terrestrial Magnetism, Moscow (Russian Federation); Krafft, C. [Universite Paris-Sud, Orsay (France)] [and others

1994-08-01

44

VLF subionospheric disturbances associated with earthquakes: Observations and numerical modeling  

Science.gov (United States)

Recently many experimental results have been reported concerning the ionospheric perturbation associated with major earthquakes. VLF/LF transmitter signal received by network observations are used to detect seismo-ionospheric signatures such as amplitude and phase anomalies. These signatures are due to the ionospheric perturbation located around the transmitter and receivers. However the physical properties of the perturbation such as electron density, spatial scale, and location have not been understood well. In this paper we performed the numerical modeling of the subionosperic VLF/LF signals including the various conditions of seismo-ionospheric perturbations by using a two-dimensional finite-difference time-domain (FDTD) method to determine the perturbation properties. The amplitude and phase for the various cases of an ionospheric perturbation are calculated relative to the normal condition (without perturbation) as functions of distance from the transmitter and distance between the transmitter and perturbation. These numerical results are compared with our observation. As a result, we found that the received transmitter amplitude depends greatly on the distance between the transmitter and ionopsheric perturbation, on the spaticl scale and height of the perturbations. Moreover results of modeled ionospheric perturbation for the recent 2011 off the pacific coast of Tohoku earthquake are compared with those from our VLF network experiment.

Hobara, Y.; Iwamoto, M.; Ohta, K.; Hayakawa, M.

2011-12-01

45

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

International Nuclear Information System (INIS)

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

46

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 (~15–20% in comparison with ~100% in former area that is probably coincides with the rate of ionospheric turbulence.
– From two years statistics of observation in the selected 3 low-latitude regions and 1 middle-latitude region inside reception area of VLF signal from NWC transmitter we find a correlation of spectrum broadening neither with ion-cyclotron noise (f=150–500 Hz, which possibly means poor representation of the turbulence by the noise due to its mixture with natural ELF emission (which correlates with whistler, nor with magnetic storm activity.
– We find rather evident correlation of ion-cyclotron frequency noise, VLF signal depression and weak correlation of spectrum broadening with seismicity in the middle-latitude region over Japan. But in the low-latitude regions we do not find such a correlation. Statistical decrease of VLF signal supports our previous case study results. However rather weak spectrum broadening-seismicity statistical correlation means probably that passive scattering prevails upon nonlinear (active one.

A. Rozhnoi

2008-10-01

47

Acoustic-gravity waves in the nonisothermal atmosphere and its influence on the magnetospheric quasi-periodic vlf emissions  

Science.gov (United States)

We examine two mutually complementing tasks related to the theoretical analysis of acoustic-gravity disturbances in the Earth's atmosphere and its influence on magnetosphere processes. Our research is based on modern atmospherical models. We study waves propagation, absorption, and filtration. The atmospheric nonisothermicity is taken into account, for example, by introduction of a two-layered atmosphere temperature model. For a study of more delicate effects, a piecewise-linear model, for which the analytical solution is written by the hypergeometric functions, is employed. Also we consider an influence of acoustic-gravity waves on VLF electromagnetic wave excitation in the magnetosphere. This influence occurs as a result of the following processes: a modulation of the plasma density by acoustic-gravity waves in the ionosphere, a modulation of reflection from the ionosphere for VLF waves, and a modification of the magnetospheric resonator Q-factor for VLF waves. Variation of the magnetospheric resonator Q-factor has an influence on the operation of the plasma magnetospheric maser, where the active substances are radiation belts particles and the working modes are electromagnetic VLF waves (whistler-type waves). The plasma magnetospheric maser can be responsible for an excitation of self-oscillations. These self-oscillations are frequently characterized by alternating stages of accumulation and precipitation of energetic particles into the ionosphere during a pulse of whistler emissions. Numerical and analytical investigations of the response of self-oscillations to harmonic oscillations of the whistler reflection coefficient shows that even a small modulation rate can significantly changes the magnetospheric VLF emissions. Our results can explain the causes of the modulation of energetic electron fluxes and whistler wave intensity with a time scale from 10 to 150 seconds in the day-side magnetosphere. Such quasi-periodic VLF emissions are often observed in the sub-auroral and auroral magnetosphere and have a noticeable effect on the formation of the space weather phenomena.

Savina, Olga; Bespalov, Peter; Misonova, Vera; Petrov, Kiril

2014-05-01

48

Statistical investigation of six years of the Demeter measurements of the VLF quasi-periodic emissions  

Science.gov (United States)

Quasi-periodic (QP) VLF emissions are wideband emissions which are observed inside or near the plasmapause. They are characterized by a periodic modulation of the wave intensity with typical periods from several seconds up to a few minutes. The source region of QP emissions is probably located close to the geomagnetic equatorial plane. We have systematically analyzed six years of measurements from the Demeter spacecraft in order to determine the direction of propagation of QP emissions as a function of geomagnetic latitude, magnetic local time, L-parameter, and frequency. A large database of time-frequency structured QP emissions in the range from 0.1 to 1200 Hz has been used for our analysis.

Hayosh, M.; Nemec, F.; Santolik, O.; Parrot, M.

2013-12-01

49

Emissions of plasma waves from VLF to LF ranges in the magnetic polar regions  

International Nuclear Information System (INIS)

The data of natural plasma waves obtained from the initial three month observations of the planetary plasma sounder system are investigated, focusing on VLF to LF range phenomena in the polar ionosphere. It is disclosed that the dynamic spectrum of the auroral VLF hiss phenomena consists of the main portion and wings. The main portion whose lowest frequency is less than 1 kHz is associated with the leaked AKR phenomena, suggesting that the main portion is generated at the acceleration region of the auroral particles. The wings that have a cut-off frequency at several kHz, higher than the main portion, are formed as the result of the cut-off at the lower hybrid resonance frequency in side area of the source region. These features suggest that the auroral VLF hiss emissions are generated through the Landau type interactions with the auroral particles in the large wave number domain of the whisler mode which is of the nature of a electrostatic plasma wave. The detailed features of the LF hiss emissions are derived for the first time from the data with high time resolution in time and frequency. The auroral LF hiss emissions in a frequency range from 100 to 450 kHz have weak and relatively steady dynamic spectra showing a clear contrast with the leaked AKR phenomena which shows the very intense and highly variable feature. It is found that the generation of the LF hiss is sometimes taking place at the level of 500 km altitude. The upper hybrid mode wave are also generated in the polar ionosphere by the electron beams streaming down from the acceleration region, and the waves are observed in the form of locally trapped Z-mode waves that are converted while propagation through the inhomogenous media. (Kubozono, M.)

50

Prediction capabilities of VLF/LF Emission as the main Precursor of earthquake  

Science.gov (United States)

Recent satellite and ground-based observations proved that in earthquake preparation period in the seismogenic area VLF/LF and ULF electromagnetic emissions are fixed. According to the opinion of the authors of the present work 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 work 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 electromagnetic contour, synthesis of which, according to our opinion, is rather harmonious.

Kachakhidze, Manana; Kachakhidze, Nino

2014-05-01

51

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

52

Spread-spectrum VLF observations of early/fast and LEP events  

Science.gov (United States)

Subionospherically-propagating very low frequency (VLF) signals are sensitive to changes in the electrical properties of the D-region ionosphere. Lightning may produce such changes in the form of early/fast events and lightning-induced electron precipitation (LEP) events. While LEP events may be used to probe the energy distribution of electrons in the Earth's radiation belts, early/fast events are indicative of direct coupling of lightning energy to the overlying ionosphere and are closely associated with the occurrence of transient luminous events (TLEs). In this paper, we present observations of early/fast events and LEP events detected using narrowband (200-Hz) VLF transmitters. A spread-spectrum VLF analysis technique is employed to utilize the full 200-Hz bandwidth of the narrowband VLF signal and to analyze the effect of these events on VLF propagation as a function of frequency within the 200-Hz band. Observations underscore the utility of the spread-spectrum analysis technique.

Wang, T.; Moore, R. C.

2011-12-01

53

Quasiperiodic VLF emissions with short-period modulation and their relationship to whistlers: A case study  

Science.gov (United States)

study properties of quasiperiodic (QP) VLF emissions recorded on 24 December 2011 during the VLF campaign in northern Finland. The main attention is paid to interrelationships between different characteristic periods in the QP spectra. In particular, we analyze regular variations in the QP repetition intervals (1-10 min) during the event from 15:30 to 22 UT, their changes during substorms, and short periodic (several second) modulation observed within separate QP elements. We explained the variations of periods of QP emissions in terms of the model of auto-oscillation regime of the cyclotron instability in the magnetosphere. During the considered event lasting about 7 h we observed a regular increase in the time intervals between the QP elements. We relate this increase with weakening of the magnetospheric source of energetic electrons. Significant variations in the QP period occurred during substorms. These variations can be due to a substorm-related increase in the energetic-electron flux and/or due to the precipitation of these electrons into the ionosphere which changes the reflection coefficient of VLF waves. We analyze the fine structure of QP element spectra and reveal the periods related to the time scales of guided propagation of whistler mode waves along the magnetic field line, which suggests that ducted propagation regime took place for the QP emissions. The periods were about 6-9 s for frequencies 1.2-4 kHz, respectively, which was similar to the period of almost simultaneously observed two-hop whistlers. In the low-frequency part of QP spectra periodic emissions with shorter periods of about 3 s were observed. Analysis of fine structure of QP elements shows that their formation is affected by both linear effects (i.e., group-velocity dispersion) and quasi-linear effects related to the modification of the energetic electron distribution function. It allows us to observe the transition from purely linear to quasi-linear regime of wave-particle interactions in the spectra of these short periodic emissions. The nonlinear regime can be understood in terms of passive mode locking in magnetospheric cyclotron maser.

Manninen, J.; Demekhov, A. G.; Titova, E. E.; Kozlovsky, A. E.; Pasmanik, D. L.

2014-05-01

54

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

Science.gov (United States)

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

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

2013-12-01

55

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

Directory of Open Access Journals (Sweden)

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

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

D. Nunn

56

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

DEFF Research Database (Denmark)

Two Very Low Frequency (VLF) AWESOME remote sensing systems located at Algiers, Algeria (36.45°N, 3.28°E) and Sebha, Libya (27.02°N, 14.26°E) 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 (42.94°N, 0.14°E) and at Centre de Recherches Atmospheriques (CRA) in southwestern France (43.13°N, 0.37°E). The cameras observations are compared to collected VLF AWESOME data. We consider early VLF perturbations observed on 12-13, 17-18 October and 17-18 December, 2007. The data from the two VLF receivers confirm the association between TLEs and early VLF signal perturbations with the perturbations amplitudes dependent on the observation configuration i.e. whether the TLE is near the receiver, near the transmitter, or far from both and the scattering process. The results also reveal that the early VLF perturbations can occur in the absence of a TLE.

Chanrion, Olivier Arnaud; Neubert, Torsten

2010-01-01

57

Experience of short term earthquake precursors with VLF–VHF 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

58

Scientific heritage of Ya. I. Likhter, a pioneer of the studies of VLF emission (Devoted to centenary of Ya. Likhter)  

Science.gov (United States)

This work presents the most important results, some of which have been previously unknown, of long-term experimental studies of signals and emission in the ELF and VLF ranges carried by Ya.I. Likhter during ground-based and satellite observations. In addition, the possibility of using the research results obtained for the diagnostics of parameters and the state of the near Earth's plasma is shown.

Mikhailov, Yu. M.; Larkina, V. I.; Mikhailova, G. A.

2014-01-01

59

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

International Nuclear Information System (INIS)

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

60

Rare examples of early VLF events observed in association with ISUAL-detected gigantic jets  

Science.gov (United States)

We examine narrowband VLF observations and investigate the association of early VLF perturbations with gigantic jets recorded by the Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) instrument aboard FORMOSAT-2. From its inception in 2004 to April 2013, the ISUAL instrument has recorded 90 gigantic jets using a triggered camera. Stanford VLF receivers located around the world are used to detect perturbations to VLF transmitter signals associated with lightning. While nine gigantic jet events occurred within 100 km of a VLF transmitter-receiver great circle path, only four early VLF events were detected in association with three ISUAL gigantic jets. One of these is a moderate event of 0.4 dB amplitude change, and the others are very small. The recovery time of these events are less than a couple of minutes and so do not constitute the "long recovery" early VLF events that have been postulated to be associated with gigantic jets. We speculate on possible explanations for the lack of other events on monitored paths, including a lack of significant ionization produced in the D region ionosphere by the gigantic jet event, weak transmitter signals recorded by the receivers, or mode effects on transmitter paths.

Marshall, R. A.; Adachi, T.; Hsu, R.-R.; Chen, A. B.

2014-01-01

 
 
 
 
61

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

62

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

63

DE 1 VLF observations during Activny wave injection experiments  

Science.gov (United States)

We report on coordinated high-altitude satellite observations in support of one of the first space-based very low frequency (VLF) wave injection experiments, namely the USSR Aktivny mission. The Aktivny satellite (A) was designed to carry a VLF transmitter (nominal frequency approximately 10 kHz, transmitter power approximately 10 kW) coupled to a 20-m-diameter loop antenna in a nearly polar orbit (83 deg inclination, apogee approximately 2500 km, perigee approximately 500 km). We focus our attention on conjunction experiments between the Aktivny and DE 1 satellites. Because of problems in the deployment of the loop antenna, the radiated power capability of the antenna was significantly reduced. Although this substantially reduced the expectation of receiving detectable signal levels on the satellite, the DE 1/Aktivny conjunction experiments were nevertheless carried out as a means of possibly placing an upper limit on the radiated power. During the period November 1989 through April 1990, a total of 10 DE 1/Aktivny wave injection sessions were conducted. During each session the Aktivny transmitter operated at 10.537 kHz with 1 s On - 1 s Off format, for a period of 6 min centered around the conjunction time. During three conjunction periods (December 12, 26, and 27, 1989) both DE 1 and Aktivny were in the southern hemisphere, and DE 1 was at relatively low altitudes (ranging from 6211 to 14,810 km), thus providing the best conjunction possibilities according to the ray tracing criteria developed above. On most days, Omega transmitter signals as well as commonly occuring natural wave phenomena such as whistlers (0(+)) and hiss were clearly seen well above the background level, but there was no evidence of the Aktivny 1 s On/ 1 s Off pattern. Though no Aktivny signals were detected by the LWR on the DE 1 satellite, the experimental constraints allow us to place an upper limit on the total power radiated by the Aktivny transmitter in the whistler-mode. Using experimental parameters, and the minimum detectable signal level of 0.05 muV/m for LWR, we find the upper limit on the total power radiated by the Aktivny satellite in the whistler-mode to be approximately 10 mW. Several recommendations for future space-based wave injection experiments are presented.

Sonwalkar, V. S.; Inan, U. S.; Bell, T. F.; Helliwell, R. A.; Molchanov, O. A.; Green, J. L.

1994-01-01

64

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

Science.gov (United States)

summary is presented of experimental optical observations at 4278 Å 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 Å 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 Å 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

65

Anomalous Seismo-ionospheric Perturbations Observed in Sub-ionospheric VLF Signal  

Science.gov (United States)

Electromagnetic anomalies have been observed in sub-ionospheric VLF signal before recent earthquakes in Japan on 15 February, 2009, Nicobar Island, India on 10 August, 2009 and Kepulaun Mentawai Region, Indonesia on 16 Aug 2009. VLF signal transmitted from Hawaii, USA North West Cape, Australia is monitored continuously at our ground station Varanasi. Here we have tried to find out ionospheric perturbations revealed by VLF signals prior to the earthquake. We observed a significant enhancement in nighttime fluctuation several days before the earthquake. VLF radio waves show anomalous variations in amplitude from their day to day variability. It is fond that nighttime trend exhibit a significant decrease in amplitude several days before the earthquake. Apart form the decrease in amplitude it is also found that there is sudden enhancement in daytime amplitude, within 48 hours prior to the earthquake. The possible mechanisms for these ionospheric perturbations due to earthquake have been discussed.

Singh, Ashutosh Kumar; Singh, Rajesh; Singh, Abhay Kumar

66

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

67

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

Directory of Open Access Journals (Sweden)

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

J. Manninen

2012-12-01

68

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

69

Diurnal Variations of Quasi-Periodic and Periodic VLF emissions in the Outer Magnetosphere  

Science.gov (United States)

ELF-VLF receiver and search coil magnetometer data from four Antarctic stations during 1998 have been analyzed to study quasi-periodic emissions (QPs) and periodic emissions (PEs), which occur as ULF-range modulations of ELF-VLF signals between 0.5 kHz and ˜4 kHz. QPs are modulated at frequencies of 15-50 mHz, and PEs are modulated at frequencies of 100-500 mHz. The stations used covered a range of magnetic latitudes from -62° (Halley) to -74° (South Pole Station); two automated geophysical observatories (AGOs) were located at intermediate latitudes. Consistent with earlier studies, most QPs were observed with magnetic pulsations of identical period in the Pc 3-4 range (type I QPs). Of those QPs not observed with simultaneous magnetic pulsations (type II QPs), nearly all were accompanied by PEs. It is also notable that no PE events simultaneous with Pc 3-4 magnetic pulsations but without QPs were observed during the entire year at any station. Diurnal patterns of all categories of QP events show occurrence maxima in the noon or post-noon sectors. The total absence of type I QP occurrences without PEs on the nightside is consistent with the expected absence of Pc 3-4 pulsations there, because of their origin at the upstream bow shock. PEs, on the other hand, could be seen at all local times. Diurnal profiles showed no latitudinal or seasonal differences for most categories, except for a clear reversal of the profile of PE occurrence with latitude. In every multistation event studied, we have found QP and/or PE modulations to be simultaneous at all stations to within the 1-s sampling time of the data. This suggests that all such events originate a single, localized region, most probably near the plasmapause. In contrast, the magnetic pulsations showed little or no detailed correlation between stations. Both statistical and single event studies support the hypothesis that highly localized field-aligned currents stimulated by echoing whistlers (PEs) may be responsible for producing type II QPs on the same flux tubes, typically in the subauroral or auroral regions. In addition, we have noted that the small number of type II QP events we have observed without accompanying PEs is tightly clustered near local noon. The existence of a set of equatorially-localized, near-noon, compressional Pc 3-4 waves that evidently do not appear in ground records suggests that this category as well might be generated by ULF wave modulation of equatorial ELF/VLF wave growth.

Engebretson, M. J.; Posch, J. L.; Shelburne, G. A.; Halford, A. J.; Smith, A. J.; Spasojevich, M.; Inan, U. S.; Arnoldy, R. L.

2003-12-01

70

IMF's control of quasi-periodic ELF-VLF emissions  

Energy Technology Data Exchange (ETDEWEB)

Correlations among the magnitude of the interplanetary magnetic field (IMF), the modulation frequency of quasi-periodic (QP) ELF-VLF emissions observed at high-latitude conjugate-pair stations, Syowa station (L approx. 6.6) in Antarctica and Husafell in Iceland, and the dominant frequency of low-latitude Pc 3 magnetic pulsations observed at Hermanus (L approx. 1.8) located near the Syowa station's meridian in South Africa are examined using the data obtained during the conjugate campaign in 1977. The analysis shows that the modulation frequency of type 1 QP emissions, QP's associated with Pc 3 magnetic pulsations, is correlated well with the IMF magnitude. On the other hand, it has been recently established that the frequency of compressional Pc 3 waves in the magnetosphere is also controlled by the IMF magnitude. These observational results support the phenomenological model that compressional magnetic waves originating upstream of the earth's foreshock modulate the type 1 QP emissions near the equatorial plane in the outer magnetosphere.

Yumoto, K.; Sato, N.

1986-12-01

71

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 +- 600 longitude of the magnetic field lines linking Siple Station, Antarctica (760S, 840W 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 daypheric 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

72

VLF observations of ionospheric disturbances in association with TLEs from the Eurosprite-2007 campaign  

International Nuclear Information System (INIS)

Complete text of publication follows. Two Very Low Frequency (VLF) AWESOME remote sensing systems located at Algeria (Algiers 36.45 N, 3.28E) and Libya (Sebha 27.02N, 14.26E) monitor VLF signal perturbations for evidence of ionospheric disturbances. The observations from Eurosprite-2007 campaign of sprites and elves are compared to collected VLF AWESOME data. The types of perturbations considered in this study are early/fast, early/slow, observed in 12-13, 17-18 October and 17-18 December, 2007. The results obtained from this study indicate that a one-to-one association between sprites and/or elves with early VLF perturbations is not in general exact, small early perturbations can occur in absence of TLE events. This is unlike the results reported by Haldoupis et al. [2004] on the one-to-one association between sprites and VLF disturbances during Eurosprite-2003 campaign. Moreover, a number of early perturbations were recorded by AWESOME systems at (Algeria and Libya) were not accompanied by sprites and/or elves observed by Eurosprites- 2007 cameras.

73

Direct observation of radiation belt electrons precipitation by the controlled injection of VLF signals from a ground-based transmitter  

International Nuclear Information System (INIS)

Radiation belt electrons precipitated by controlled injection of VLF signals from a ground based transmitter have been directly observed for the first time. These observations were part of the SEEP (Stimulated Emission of Energetic Particles) experiment conducted during May-December 1982. Key elements of SEEP were the controlled modulation of VLF transmitters and a sensitive low altitude satellite payload to detect the precipitation. An outstanding example of time-correlated wave and particle data occurred from 8680 to 8740 seconds. U. T. on 17 August 1982 when the satellite passed near the VLF transmitter at Cutler, Maine (NAA) as it was being modulated with a repeated ON (3--s)/OFF (2--s) pattern. During each of twelve consecutive pulses from the transmitter the electron counting rate increased significantly after start of the ON period and reached a maximum about 2 seconds later. The measured energy spectra revealed that approximately 15 to 50 percent of the enhanced electron flux was concentrated near the resonant energies for first order cyclotron interactions occurring close to the magnetic equator with the nearly monochromatic waves emitted from the transmitter

74

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

75

On the origin of VLF hiss observed at middle and low latitudes  

International Nuclear Information System (INIS)

As to the origin of VLF hiss observed at middle and low latitudes, the theories presented are varied, though it has been believed that it is the propagation by waveguide mode from high to middle/low latitudes. After reviewing the studies made in this field, the subject is discussed on the basis of the latitude distribution of VLF-hiss activity observed with AL-2 between 05 LT and 10 LT at altitudes 2200--3000 km. In conclusion, the theory that the VLF hiss at middle and low latitudes is propagated from auroral zone, appears to be invalid. Instead, the entry of 5 kHz hiss at middle latitude into the space between ionosphere and ground from the source near plasmapause can be confirmed experimentally. (Mori, K.)

76

A relationship between solar proton events, ionospheric uplift observed at VLF and negative ionospheric storms  

Science.gov (United States)

Three consecutive magnetic storms during the month of September 1982 were found to be associated with solar proton events (SPE) observed over a number of high latitude VLF propagation paths. The penetration of solar protons into the auroral zone produced a marked reduction in reflection height at night for high latitude VLF paths resulting in a reduced diurnal phase shift. This effect has been known for some 50 years. However in this paper, a previously unidentified response is described consisting of an increase in the night 90 km reflection height over middle latitude and transequatorial VLF paths. Solar protons do not penetrate to these latitudes and this slight increase in VLF reflection height was associated with typical negative ionospheric storm effects in the F2 region. Dynamics at the 90 km base of the night ionosphere are little known and difficult to investigate except at VLF. These results are the first to suggest a response of the night ionospheric base to events leading to the well known negative ionospheric storm seen at greater heights. Such negative storms seen in the F2 region have been associated with an equatorward wind surge and change in neutral atmospheric chemistry driven by joule heating in the auroral zone produced by solar proton precipitation.

Lynn, K. J. W.

2013-12-01

77

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.; Rème, H.; Santolik, O.; Zong, Q.-G.

2006-08-01

78

Peculiarities of sudden commencement manifestation in VLF-emission generation and cosmic noise absorption  

Science.gov (United States)

The variation of the VLF emission and energetic particles precipitation (cosmic noise absorp-tion) parameters during the periods of magnetic storm sudden commencement (SC) are con-sidered. It was selected 13 events during the period 2003-2008. Among the selected events, the majority -the joint events, manifested both in riometric absorption and in the VLF emission generation, the events accompanied by only the VLF emission generation, the events manifested only in riometric absorption and also the events without the VLF emission and riometric ab-sorption. The VLF emission measurements carried out at Yakutsk station (L=3), and riometric absorption measurement conducted at the Yakut meridional chain of stations (MLat=190 deg). For the selected events were estimated azimuthal components of the solar wind electric fields (Esw) and induction electric fields (Ei), change of the field in the magnetosphere (?Bz), re-flecting the degree of the magnetosphere compression at L shell of Yakutsk, Kp index for the 6-hour interval prior to the SC. Analysis of variations of the parameters listed above, allowed us to note the following features of the considered events: • The SCs which were registered in the noon sector MLT, preceded by intervals with higher values of the Kp index (Kp=3-6) in comparison with the SCs in the other MLT sectors (Kp=1-4). • The SC which were registered in the noon MLT sector accompanied by Esw of eastward direction (Esw 0). • The SC which were not accompanied by the VLF emission and riometric absorption registered at small values of ?Bz = 6-8 nT and Ei = 0.7-0.9 mV/m. The direction of Esw (to the east) in such events is opposite to Ei direction, which were directed to the west. This work was supported by the Presidium of the Russian Academy of Sciences (program 16, part 3), by the RFBR grant No.09-05-98546 and also supported by the SB RAS project No.69.

Moiseyev, Alexey; Solovyev, Stepan; Boroev, Roman; Mullayarov, Viktor; Samsonov, Sergey; Du, Aimin

79

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

International Nuclear Information System (INIS)

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

80

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

 
 
 
 
81

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

Science.gov (United States)

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

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

2014-10-01

82

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

Directory of Open Access Journals (Sweden)

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

A. Rozhnoi

2014-04-01

83

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 Earth’s magnetic field as a function of frequency and of time. Due to the Cluster orbit, chorus emissions are often observed close to perigee, and the data analysis determines the direction of these waves. Three events observed during different levels of magnetic activity are reported. It is shown that the component of the Poynting vector parallel to the magnetic field changes its sense when the satellites cross the magnetic equator, which indicates that the chorus waves propagate away from the equator. Detailed analysis indicates that the source is located in close vicinity of the plane of the geomagnetic equator.

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

D. Nunn

84

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 ~0.2–0.6 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.

N. Lin

2006-08-01

85

Observations of VLF transmitter-induced depletions of inner zone electrons  

International Nuclear Information System (INIS)

Precipitation spikes of electrons, in which the energy spread of the peak is narrow (less than 50 keV) and the peak energy is a strong function of the location in L, have been observed in the region 1.5 < L < 2.0 and have been ascribed to interactions between waves from high power VLF transmitters on the ground and the precipitated electrons [Vampola and Kuck, 1978; Imhof et al., 1981]. On numerous occasions when these spikes were observed at low altitude by instrumentation on the S3-2 satellite, a significant depletion of electrons at the same energies was observed high on the field line. These depletions indicate that the loss rate of electrons due to VLF transmitters is significant and usually exceeds the rate at which radial diffusion is refilling those field lines. Electrons with energies between 36 keV and 317 keV in the region 1.9 < L < 1.6 were observed to have lifetimes limited to a few days by interactions with waves from VLF transmitters. Thus the outer edge of the inner zone is defined by this wave-particle process

86

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

CERN Document Server

The present paper deals with an attempt to check up the theoretical model of self-generated seismo-electromagnetic oscillations of LAI system on the basis of retrospective data. Application of the offered simple model enables one to explain qualitatively the mechanism of VLF electromagnetic emission initiated in the process of an earthquake preparation. It is worth to pay attention to the fact that frequency changes from MHz to kHz in electromagnetic emission spectrum comes to a good agreement with avalanche-like unstable model of fault formation. L'Aquila earthquake taken as an example to isolate reliably the Earth VLF emission from the magnetospheric electromagnetic emission of the same frequency range, MHD criterion is offered together with geomagnetic activity indexes. On the basis of the considered three earthquakes, according to the opinion of authors the model of self-generated seismo-electromagnetic oscillations of the LAI system will enable us to approach the problem of resolution of earthquake predi...

Kachakhidze, M; Kachakhidze, N

2012-01-01

87

Initial results of VLF Campaign observation with High-resolution Aurora Imaging Network (VLF-Chain) over Canada  

Science.gov (United States)

Whistler-mode waves in the VLF/ELF frequency range interact with high-energy (~10 keV) electrons to cause diffuse and pulsating auroras, and with MeV electrons in the radiation belts. However, simultaneous high-time resolution measurements of aurora and these waves have previously not been done sufficiently. We made a campaign observation of such high-time resolution measurements at Athabasca (54.72N, 246.69E, MLAT=61.3) and Fort Vermillion (58.38N, 243.99E, MLAT=64.5) using two loop antennas and several auroral cameras for February 16-26, 2012. The loop antennas at both stations measure east-west and north-south magnetic field variations with a sampling rate of 100 kHz. The panchromatic all-sky cameras at both stations measure auroras with a sampling rate of 30 Hz. The sampling timings of both instruments are corrected by GPS receivers. In addition we installed an oblique looking narrow-FoV EMCCD camera at Athabasca with a sampling rate of 100 Hz, to measure height variation of pulsating aurora. At Athabasca, routine measurements by an induction magnetometer, a proton photometer, an all-sky airglow imager, LF standard wave receiver, were also carried out. We also tried to compare these observations with satellite measurements by REIMEI, THEMIS, NOAA, and DMSP. In this presentation we will show initial results obtained from this comprehensive campaign of aurora and radio wave measurements at subauroral latitudes.

Shiokawa, Kazuo

2012-07-01

88

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

89

VLF electromagnetic noise bursts observed in a borehole and their relation with low-latitude hiss  

Science.gov (United States)

In an attempt to monitor subsurface VLF electric field changes associated with earthquakes, a borehole antenna has been installed at Bichpuri, Agra (Geograph. Lat. /27.2°N, Geograph. Long. /78°E, Geomag. Lat. 17.1°N,L=1.1) in India and observations have been taken since February, 1998 using an analog system. The electric field changes have been found to occur in the form of noise bursts of varying amplitudes and durations. A thorough analysis of the data of the year 1999 has shown occasional occurrence of large amplitudes, long duration (/~5-6h or more) noise bursts which show seasonal, stormtime, and diurnal variations similar to those of low latitude magnetospheric hiss observed on the ground. Similar noise bursts have also been recorded in the vertical terrestrial antenna operated in conjunction with the borehole antenna. This result indicates penetration of ionospheric/magnetospheric VLF signals to large depths in the crustal region and cautions for careful identification of potential seismogenic signals in VLF data.

Singh, Birbal; Hayakawa, Masashi; Mishra, Pradeep K.; Singh, Raj Pal; Lakshmi, D. R.

2003-02-01

90

Study of long path VLF signal propagation characteristics as observed from Indian Antarctic station, Maitri  

Science.gov (United States)

To examine the quality and propagation characteristics of the Very Low Frequency (VLF) radio waves in a very long propagation path, Indian Centre for Space Physics, Kolkata, participated in the 27th Indian scientific expedition to Antarctica during 2007-2008. One Stanford University made AWESOME VLF receiving system was installed at the Indian Antarctic station Maitri and about five weeks of data were recorded successfully from the Indian transmitter VTX and several other transmitting stations worldwide. The quality of the signal from the VTX transmitter was found to be very good, consistent and highly stable in day and night. The signal shows the evidences of the presence of the 24 h solar radiation in the Antarctic region during local summer. Here we report the both narrow band and broadband VLF observations from this site. The diurnal variations of VTX signal (18.2 kHz) are presented systematically for Antarctica path and also compared the same with the variations for a short propagation path (VTX-Kolkata). We compute the spatial distribution of the VTX signal along the VTX-Antarctica path using the most well-known LWPC model for an all-day and all-night propagation conditions. The calculated signal amplitudes corresponding to those conditions relatively corroborate the observations. We also present the attenuation rate of the dominant waveguide modes corresponding to those propagation conditions where the effects of the Antarctic polar ice on the attenuation of different propagating waveguide modes are visible.

Sasmal, Sudipta; Pal, Sujay; Chakrabarti, Sandip K.

2014-10-01

91

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

Science.gov (United States)

We use VLF electromagnetic wave data measured by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite at an altitude of about 700 km to check for the presence of statistically significant changes of natural wave intensity (due to signals from lightning) related to preseismic activity. All the relevant data acquired by DEMETER during almost 6.5 years of the mission have been analyzed using a robust two-step data-processing schema. This enables us to compare data from the vicinity of about 8400 earthquakes with an unperturbed background distribution based on data collected during the whole DEMETER mission and to evaluate the statistical significance of the observed effects. We confirm previously reported results of a small but statistically significant decrease of the wave intensity (by ˜2 dB) at frequencies of about 1.7 kHz. The effect is observed for a few hours before the times of the main shocks; it occurs during the night. The effect is stronger between March and August, at higher latitudes and for the positions of hypocenters below the sea. We suggest an explanation based on changed properties of the lower boundary of the ionosphere, which leads to a decrease of the intensity of lightning-generated whistlers observed at the spacecraft altitude. This effect might result from a lowering of the ionosphere associated with an increase in the electrical conductivity of the lower troposphere due to an additional ionization of air molecules at the Earth's surface prior to earthquakes.

PíšA, David; N?Mec, FrantišEk; SantolíK, Ond?Ej; Parrot, Michel; Rycroft, Michael

2013-08-01

92

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

Directory of Open Access Journals (Sweden)

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

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

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

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

M. K. Kachakhidze

2012-04-01

93

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 ~10–50 s of naturally occurring ELF-VLF radio emissions (~0.5–5 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

94

The total solar eclipse of 23 October 1976 observed at VLF  

International Nuclear Information System (INIS)

VLF transmissions at 13.6 and 22.3 kHz from Omega Reunion, Omega Japan and NWC, were monitored at Melbourne during the total solar eclipse of 23 October 1976. The solar obscuration function for each path was calculated and compared with the phase deviation observed experimentally. The phase response was found to be a non-linear function of solar obscuration with a maximum phase deviation which was less than expected when compared with the normal diurnal phase variation. A differential equation was developed to model the observations. The effective time constant of ionospheric response was found to be four minutes and independent of reflection height. (author)

95

The natural VLF emission as diagnostics and estimation means of the fluxes of solar x ray bursts  

International Nuclear Information System (INIS)

The possibility to detect the chromospheric flares based on the natural VLF emission intensity data on the Earth's surface is considered. Diagnostics of the change of solar x ray burst flux at 0.5 to 4A and its estimation are discussed as possible

96

The natural VLF emission as diagnostics and estimation means of the fluxes of solar x ray bursts  

Science.gov (United States)

The possibility to detect the chromospheric flares based on the natural VLF emission intensity data on the Earth's surface is considered. Diagnostics of the change of solar x ray burst flux at 0.5 to 4A and its estimation are discussed as possible.

Murzaeva, N. N.

1989-01-01

97

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

98

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

International Nuclear Information System (INIS)

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

99

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.

100

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

International Nuclear Information System (INIS)

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

 
 
 
 
101

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

102

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

Science.gov (United States)

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

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

1993-01-01

103

Whistler-triggered emissions observed by ISIS satellites  

International Nuclear Information System (INIS)

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

104

A Satellite Study of VLF HISS.  

Science.gov (United States)

Broad-band VLF radio noises from about 4 kc/s to above 10 kc/s are frequently observed near the auroral zone with the Injun 3 satellite. These broad-band VLF radio noises are called VLF hiss. In this study we select VLF hiss events for analysis by requiri...

D. A. Gurnett

1966-01-01

105

Magnetospheric amplification and emission triggering by ELF/VLF waves injected by the 3.6 MW HAARP ionospheric heater  

Science.gov (United States)

The HF dipole array of the High Frequency Active Auroral Research Program (HAARP) in Gakona, Alaska, was recently upgraded to 180 elements, facilitating operations at a total radiated power level of 3.6 MW and an effective radiated power of ˜575 MW. In the first experiments at the new power level, the HAARP array is used for magnetospheric wave injection. Modulated heating of auroral electrojet currents in the ionosphere yields radiation in the ELF/VLF frequency range. The HAARP-generated signals are injected into the magnetosphere, where they propagate in the whistler mode in field-aligned "ducts," allowing them to be observed at the conjugate point on a ship-borne receiver and on autonomous buoy platforms. The observation of the 1-hop signals is accompanied by the observation of associated 2-hop components in the northern hemisphere, which have reflected from the ionospheric boundary in the southern hemisphere. The observed signals are accompanied by triggered emissions and exhibit temporal amplification of 15-25 dB/s and bandwidth broadening to ˜50 Hz. Amplification occurs at injected signal frequencies selected in near real time on the basis of observations of natural emission activity, and only certain components of the frequency-time formats transmitted are amplified. Observations at multiple sites and dispersion analysis show that the signals are injected into the magnetosphere directly above the HF heater. The duration of echo observation and the prevalence of 1-hop observations are consistent with statistics from 1986 Siple Station experiments. The particle-trapping wave amplitude near the magnetic equator is estimated in the range 0.1-0.4 pT and gyroresonance with 10 keV-100 keV electrons.

Go?Kowski, M.; Inan, U. S.; Gibby, A. R.; Cohen, M. B.

2008-10-01

106

Survey of ELF-VLF plasma waves in outer radiation belt observed by Cluster STAFF-SA experiment  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Various types of plasma waves have profound effects on acceleration and scattering of radiation belt particles. For the purposes of radiation belt modeling it is necessary to know statistical distributions of plasma wave parameters. This paper analyzes four years of plasma wave observations in the Earth's outer radiation belt obtained by the STAFF-SA experiment on board Cluster spacecraft. Statistical distributions of spectral density of different plasma waves observed in ELF-VLF range (...

Pokhotelov, D.; Lefeuvre, F.; Horne, R. B.; Cornilleau-wehrlin, N.

2008-01-01

107

A study of quasi-periodic ELF-VLF emissions at three Antarctic stations: evidence for off-equatorial generation?  

Directory of Open Access Journals (Sweden)

Full Text Available The spatial extent and temporal behaviour of quasi-periodic (QP intensity modulations of 0.5-2 kHz ELF-VLF signals were investigated in a comparative study of data collected at the Antarctic stations of South Pole (L=14, Halley (L=4, and Siple (L=4. Frequently, the waveforms of ELF-VLF signals simultaneously received at each site were identical. Although of similar frequency structure, the waveforms of the accompanying Pc3 magnetic pulsations did not show a one-to-one association. Whereas both are dayside phenomena, QP emissions occur over a smaller range of local times, and have a maximum of occurrence later in the day closer to local noon. QP emissions are identified with the periodic modulation of the electron pitch-angle distribution by the propagation of ULF compressional fast-mode waves through a region. However, contrary to previous ideas, rising-tone emissions do not represent the frequency-time signatures of such waves. In addition to generation close to the equatorial plane, we propose an additional high-latitude source of QP emissions. These emissions are associated with regions of minimum B produced by the dayside compression of the magnetosphere close to the magnetopause. Model magnetic field calculations of these minimum-B regions as a function of magnetic local time and invariant latitude are presented.

K. Morrison

108

Numerical modeling of seismo-ionospheric disturbances by FDTD method and comparison with experimental results from Japanese VLF observation network  

Science.gov (United States)

Recently many experimental results have been reported concerning the ionospheric perturbation associated with major earthquakes. VLF/LF transmitter signal received by network observations are used to detect seismo-ionospheric signatures such as amplitude and phase anomalies. These signatures are due to the ionospheric perturbation located around the transmitter and receivers. However the physical properties of the perturbation such as electron density, spatial scale, and location have not been understood well. In this paper we carried out the numerical simulation on the subionosperic VLF/LF signals including the various conditions of seismo-ionospheric perturbations by using a two-dimensional finite-difference time-domain (2D-FDTD) method to determine the perturbation properties. The amplitude and phase for the various cases of an ionospheric perturbation are calculated relative to the normal condition (without perturbation) as functions of distance from the transmitter and distance between the transmitter and perturbation. These numerical results are compared with our observation for several major earthquakes. As a result, we found that the received transmitter amplitude depends greatly on the distance between the transmitter and ionopsheric perturbation, on the spatial scale and height of the perturbations. Moreover results of modeled ionospheric perturbation for the recent 2011 off the pacific coast of Tohoku earthquake are compared with those from our VLF network experiment.

Hobara, Yasuhide; Ohta, Kenji; Iwamoto, Masahiko; Hayakawa, Masashi

2012-07-01

109

Observed Barium Emission Rates  

Science.gov (United States)

The barium releases from the CRRES satellite have provided an opportunity for verifying theoretically calculated barium ion and neutral emission rates. Spectra of the five Caribbean releases in the summer of 1991 were taken with a spectrograph on board a U.S. Air Force jet aircraft. Because the line of sight release densities are not known, only relative rates could be obtained. The observed relative rates agree well with the theoretically calculated rates and, together with other observations, confirm the earlier detailed theoretical emission rates. The calculated emission rates can thus with good accuracy be used with photometric observations. It has been postulated that charge exchange between neutral barium and oxygen ions represents a significant source for ionization. If so. it should be associated with emissions at 4957.15 A and 5013.00 A, but these emissions were not detected.

Stenbaek-Nielsen, H. C.; Wescott, E. M.; Hallinan, T. J.

1993-01-01

110

Observed barium emission rates  

Energy Technology Data Exchange (ETDEWEB)

The barium release from the CRRES satellite have provided an opportunity for verifying theoretically calculated barium ion and neutral emission rates. Spectra of the five Caribbean releases in the summer of 1991 were taken with a spectrograph on board a U.S. Air Force jet aircraft. Because the line of sight release densities are not known, only relative rates could be obtained. The observed relative rates agree well with the theoretically calculated rates and, together with other observations, confirm the earlier detailed theoretical emission rates. The calculated emission rates can thus with good accuracy be used with photometric observations. It has been postulated that charge exchange between neutral barium and oxygen ions represents a significant source for ionization. If so, it should be associated with emissions at 4957.15 {angstrom} and 5013.00 {angstrom}, but these emissions were not detected. 16 refs., 10 figs., 4 tabs.

Stenbaek-Nielsen, H.C.; Wescott, E.M.; Hallinan, T.J. [Univ. of Alaska, Fairbanks, AL (United States)

1993-10-01

111

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

International Nuclear Information System (INIS)

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

112

VLF emissions from a modulated electron beam in the auroral ionosphere  

International Nuclear Information System (INIS)

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

113

Multispacecraft observations of quasi-periodic emissions  

Science.gov (United States)

Quasi-periodic (QP) emissions are VLF electromagnetic waves in the frequency range of about 0.5-5 kHz which exhibit a periodic time modulation of the wave intensity. The modulation period is usually on the order of a few tens of seconds. The generation mechanism of these emissions is still not understood, but at least in some cases it appears to be related to ULF magnetic field pulsations which result in periodic modifications of the resonant conditions in the source region. We use multipoint measurements of QP emissions by the 4 Cluster spacecraft. The observations are obtained close to the equatorial region at radial distances of about 4 Earth radii, i.e. close to a possible generation region. A combined analysis of the high resolution data obtained by the WBD instruments and the ULF magnetic field data obtained by the FGM instruments allows for a detailed case-study analysis of these unique emissions. The presented analysis benefits from the recent close-separation configuration of three of the Cluster spacecraft (?20-100 km) and a related timing analysis, which would be impossible otherwise.

Nemec, Frantisek; Picket, Jolene S.; Santolik, Ondrej

2014-05-01

114

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 lthat in most examined cases daily global lightning activity and the atmospheric electric field are poorly correlated.

115

Storm time evolution of ELF/VLF waves observed by DEMETER satellite  

Science.gov (United States)

this paper, using the data of Sun-synchronous satellite (Detection of Electro-Magnetic Waves Transmitted from Earthquake Regions) DEMETER, we investigated the storm time variations of ELF/VLF waves during the intense coronal mass ejections (CME)-driven storms from 2005 to 2009. The results show that there is a good correlation between the enhancement of ELF/VLF waves and the CME events. Immidately following the enhanced wave activity driven by CMEs at the initial phase, the wave intensity decreases temporarily at the beginning of storm main phase. The strongest waves predominantly occur from the late main phase to early recovery phase. The ELF waves below 3 kHz are significantly intensified during the whole storm time, while the high-frequency waves above 3 kHz seem strengthened predominantly during the late main and early recovery phase. The ELF waves below 3 kHz can exist in a wide L shell range, with the intensity peaking at L ~ 3 and 4. High-frequency waves at f > 9 kHz exist mostly outside the plasmapause. The stronger ELF/VLF waves on the dayside can last longer time than those on the nightside.

Zhima, Zeren; Cao, JinBin; Liu, WenLong; Fu, HuiShan; Wang, TieYan; Zhang, XueMin; Shen, XuHui

2014-04-01

116

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)

117

ELF/VLF Wave-injection Experiments with HAARP  

Science.gov (United States)

The potential use of modulated HF heating of the lower ionosphere as a means to generate ELF/VLF waves has long been recognized. Located conveniently at L ? 4.9, thus lying on closed sub-auroral field lines most of the time, the High-Frequency Active Auroral Research Program (HAARP) heater in Gakona, Alaska is well positioned for the conduct of ELF/VLF wave-injection experiments for magnetospheric wave-particle interaction studies. Early results (2004) have alreay demonstrated that whistler-mode wave amplification can be initiated by ELF/VLf signals injected from HAARP, leading to multiple-hop propagation of signals between hemispheres and triggering of discrete emissions. With the upcomign completion of the upgrade of HAARP to full power (3.6 MW radiated), a new set of experiments have become possible, and the first opportunity for the conduct of such experiments is now before us. During February 23-March 6th, Stanford University personnel will be deploying two large Buoys equipped with ELF/VLF erceivers in the geomagneticaly conjugate region of HAARP, and will also conduct continuous ELF/VLF observations on the research ship which will deploy them. The experiments are aimed at generating specially designed ELF/VLF modulation formats, for initiation of wave growth, emission triggering and excitation of one-hop and two-hop whistler-mode waves. ELF/VLf observations will be conducted on teh ship and buoys near the conjugate region, but also on several distributed sites in Alaska as well as on teh DEMETER spacecraft. In this paper, we will discuss these experiments and present initial results from them. This papers constitutes a brief summary of the extensive work contributed by many other not-listed authors, at Stanford University, at AFRL, ONR, and at LPCE/CNRS in Orleans. The presenter listed as the single author is simply the team leader, listed solely for purposes of brevity.

Inan, U. S.

2007-05-01

118

EXOS-B/Siple station VLF wave-particle interaction experiment  

International Nuclear Information System (INIS)

It is well-known that ground-based VLF signals are often amplified or associated with VLF emissions in virtue of interactions with counterstreaming electrons in the magnetosphere. In order to clarify this mechanism of the wave-particle interaction, a Japanese satellite EXOS-B was used to monitor energetic electron flux as well as VLF signals transmitted from Siple Station in Antarctica, expecting to observe wave excitations by the interaction between the Siple signal and the energetic electrons. The preliminary results of the experiments are briefly discussed. (Auth.)

119

Characteristics of VLF and ELF sferics associated with TLEs observed in a combined aircraft and ground-based campaign in 2011  

Science.gov (United States)

In the period of a combined aircraft and ground-based campaign supported by NHK Cosmic Shore project, June 27 to July 10, 2011, we succeeded in capturing images for over a hundred of TLEs, including sprites, elves and blue jets. In order to investigate characteristics of lightning discharges producing TLEs, we installed a VLF observation system at Yucca Ridge Field Station, CO, and recorded sferics waveforms continuously through out the campaign period. The VLF observation system is composed of two horizontal magnetic loop antennas and a vertical electric dipole antenna, receiver, PC and GPS clock. The higher cutoff and sampling frequencies are 50 kHz and 80 kHz, respectively. In addition, we make use of waveform data recorded by the global ELF observation network (GEON) operated continuously by Hokkaido University. Based on these VLF and ELF waveform data, we can estimate charge moment changes (CMCs). Using not only the CMC values but also the precise location and peak currents of parent lightning discharges provided by existing lightning geolocation network, we can clarify the possible mechanisms, which cause a large variation in structures of TLEs. In this presentation, we introduce the availability of the sferics data recorded by VLF and ELF receivers for the observed TLEs and report the initial results of data analysis, namely, the relationship between the spatio-temporal structures of the representative TLEs observed in the campaign and the characteristics of parent lightning discharges, such as CMC values and associated pulse trains due to the intra-cloud discharge.

Kudo, T.; Takahashi, Y.; Sato, M.; Yanagi, Y.; Inoue, T.; Stenbaek-Nielsen, H. C.; McHarg, M. G.; Haaland, R. K.; Kammae, T.; Yair, Y.; Lyons, W. A.; Cummer, S. A.; Ahrns, J.; Yukman, P.; Warner, T. A.; Sonnenfeld, R. G.; Li, J.; Lu, G.

2011-12-01

120

Survey of ELF-VLF plasma waves in outer radiation belt observed by Cluster STAFF-SA experiment  

Directory of Open Access Journals (Sweden)

Full Text Available Various types of plasma waves have profound effects on acceleration and scattering of radiation belt particles. For the purposes of radiation belt modeling it is necessary to know statistical distributions of plasma wave parameters. This paper analyzes four years of plasma wave observations in the Earth's outer radiation belt obtained by the STAFF-SA experiment on board Cluster spacecraft. Statistical distributions of spectral density of different plasma waves observed in ELF-VLF range (chorus, plasmaspheric hiss, magnetosonic waves are presented as a function of magnetospheric coordinates and geomagnetic activity indices. Comparison with other spacecraft studies supports some earlier conclusions about the distribution of chorus and hiss waves and helps to remove the long-term controversy regarding the distribution of equatorial magnetosonic waves. This study represents a step towards the development of multi-spacecraft database of plasma wave activity in radiation belts.

D. Pokhotelov

2008-10-01

 
 
 
 
121

VLF Technique and Science in India  

Science.gov (United States)

Since IGY period (1957-58), natural and artificially produced Very Low Frequency (VLF) electromagnetic radiations are being recorded at large number of ground stations and on board satellites to study various wave-plasma interactive phenomena. The terrestrial propagation of these VLF radio waves are primarily enabled through the earth ionosphere wave guide (EIWG) system to long horizontal distances around the globe and ducted along the geomagnetic field lines into the conjugate hemisphere through the ionosphere-plasmasphere-magnetosphere routes. The time frequency spectra indicate presence of dispersion and various cut-off frequencies providing several types of received signals like whistlers, chorus, tweeks, hiss, hisslers etc., which can be heard on an earphone with distinguishing audio structures. While the VLF technique has been a very effective tool for studying middle and high latitude phenomena, the importance of various anomalous characteristics over the Indian low latitude stations provide potentially new challenges for their scientific interpretation and modelling. The ducted and non-ducted propagation, low latitude TRIMPI/TLE effects, D-region ionisation perturbations due to solar and stellar x- and ? ray emissions and detecting precursors of seismic activities are a few problems which will gain from low latitude studies. Since the conjugate points of Indian stations lie over the Indian oceanic region, the VLF propagation effects would be relatively noise free to observe rare and new phenomena requiring better SNR to detect such changes. The VLF signals emanating from the active seismic zones would require high sensitivity of the system and suitable network of transmitting and receiving stations. Results obtained on whistlers and related studies from a number of Indian stations covering geomagnetic latitude range between 13-24 °N are mentioned and reviewed in the background of theoretical understanding of the lightning return stroke signal elements, VLF propagation through cold plasma, ionospheric wave guide mode, electron precipitation due to cyclotron resonance and production of ionisation in the D-region due to solar/stellar UV/X/?-rays. Further use of the VLF technique in terms of improving both observational data for real time monitoring/modelling of geophysical phenomena and exploring space weather conditions are considered as part of a future Indian programme.

Chakravarty, S. C.

2010-10-01

122

VLF Technique and Science in India  

International Nuclear Information System (INIS)

Since IGY period (1957-58), natural and artificially produced Very Low Frequency (VLF) electromagnetic radiations are being recorded at large number of ground stations and on board satellites to study various wave-plasma interactive phenomena. The terrestrial propagation of these VLF radio waves are primarily enabled through the earth ionosphere wave guide (EIWG) system to long horizontal distances around the globe and ducted along the geomagnetic field lines into the conjugate hemisphere through the ionosphere-plasmasphere-magnetosphere routes. The time frequency spectra indicate presence of dispersion and various cut-off frequencies providing several types of received signals like whistlers, chorus, tweeks, hiss, hisslers etc., which can be heard on an earphone with distinguishing audio structures. While the VLF technique has been a very effective tool for studying middle and high latitude phenomena, the importance of various anomalous characteristics over the Indian low latitude stations provide potentially new challenges for their scientific interpretation and modelling. The ducted and non-ducted propagation, low latitude TRIMPI/TLE effects, D-region ionisation perturbations due to solar and stellar x- and ? ray emissions and detecting precursors of seismic activities are a few problems which will gain from low latitude studies. Since the conjugate points of Indian stations lie over the Indian oceanic region, the VLF propagation effects would be relatively noise free to observe rare and new phenomena requiring better SNR to detect such changes. The VLF signals emanating from the active seismic zones would require high sensitivity of the system and suitable network of transmitting and receiving stations. Results obtained on whistlers and related studies from a number of Indian stations covering geomagnetic latitude range between 13-24 deg. N are mentioned and reviewed in the background of theoretical understanding of the lightning return stroke signal elements, VLF propagation through cold plasma, ionospheric wave guide mode, electron precipitation due to cyclotron resonance and production of ionisation in the D-region due to solar/stellar UV/X/?-rays. Further use of the VLF technique in terms of improving both observational data for real time monitoring/modelling of geophysical phenomena and exploring space weather conditions are considered as part of a future Indian programme.

123

Decrease of VLF transmitter signal and Chorus-whistler waves before l'Aquila earthquake occurrence  

Directory of Open Access Journals (Sweden)

Full Text Available We investigate the VLF emissions observed by the Instrument Champ Electrique (ICE experiment onboard the DEMETER micro-satellite. We analyze intensity level variation 10 days before and after the occurrence of l'Aquila earthquake (EQ. We found a clear decrease of the VLF received signal related to ionospheric whistler mode (mainly Chorus emission and to signal transmitted by the DFY VLF station in Germany, few days (more than one week before the earthquake. The VLF power spectral density decreases of more than two orders of magnitude until the EQ, and it recovers to normal levels just after the EQ occurrence. The geomagnetic activity is principally weak four days before EQ and increases again one day before l'Aquila seismic event. Our results are discussed in the frame of short- and long-terms earthquakes prediction focusing on the crucial role of the magnetic field of the Earth.

M. Y. Boudjada

2010-07-01

124

Ion cyclotron bands in VLF saucers  

Science.gov (United States)

In the wideband VLF data obtained by the polar orbiting DE-1 satellite over the polar night ion trough region of the upper ionosphere, conspicuous frequency-band structures are found to occur both in absorption and emission, particularly associating with VLF saucers. The attenuation bands indicate that the ions of atomic hydrogen from the polar ionosphere are accelerated by the ac electric fields of VLF waves oscillating normal to the static magnetic field, analogous to a cyclotron accelerator. The observed frequencies of the cyclotron harmonics suggest that the acceleration is taking place in the layer below the satellite at a geocentric distance of less than about 1.5 earth radii. This example indicates the existence of upward propagating hiss at those altitudes inside the auroral zone. On the other hand, the frequency shifts of the emission bands are attributed to a combination of two different types of Doppler shift, one due to the orbital motion of the satellite and the other due to the upward motion of the medium at the emission source. This indicates the existence of an upward plasma flow at the source, with a velocity of the order of 20 km/s inside the saucer. The amount of this frequency shift decreases with increasing harmonic order, indicating a higher phase velocity for the electrostatic waves of higher harmonic order.

Maeda, Kaichi; Fung, Shing F.; Calvert, Wynne

1990-01-01

125

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 June–November 2006.

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

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

H. Höller

2009-10-01

126

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 June–November 2006.

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

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

H. Höller

2009-03-01

127

Characteristics of VLF atmospherics near the resonance frequency of earth-ionosphere waveguide 1.6-2.3 kHz by observations in the auroral region  

International Nuclear Information System (INIS)

Complete text of publication follows. Ground-based recording of ELF-VLF waves with right-handed (R) and left-handed (L) circular polarization has been performed in Northern Finland. Monitoring showed a difference in the behavior of VLF waves with R- and L-polarization. Well-defined amplitude maximum were observed in vicinity critical frequency of the first transverse resonance in Earth-ionosphere waveguide (around 1.6-2.3 kHz) for L waves only. Near this maxima waves have a perfect circular L-polarization. To study the features of VLF wave propagation near the first transverse resonance we calculated the parameters of waveguide modes from the full wave equation for night model of the ionosphere. Intensity of the signals in the near and far zones was calculated. Our calculations show that a maximum in the spectra of VLF waves near the critical frequencies of 1.6 - 2.3 kHz is due to small absorption of L waves and excitation of resonance waves in Earth-ionosphere waveguide.

128

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.)

129

Changes of VLF wave intensity observed by the DEMETER spacecraft in the vicinity of earthquakes  

Science.gov (United States)

We present a statistical study of variations of VLF wave intensity in the upper ionosphere based on data measured during the whole mission of the DEMETER satellite (?6.5 years). This spacecraft was operating between years 2004 and 2010 at the altitude of ?660 km. We have analyzed all available data measured close in time (48 hours before and 24 hours after the time of the main shock) and distance (satellite projection on the ground within 440 km from the earthquake epicenter) from large earthquakes (M?5). Data related to more than 12000 earthquakes with a magnitude greater than or equal to 5 according to the USGS earthquake catalog have been analyzed. We have compared these data with an unperturbed background distribution based on data collected during the whole DEMETER mission. We confirm the previously reported results of a statistically significant decrease of the wave intensity at frequencies of about 1.7 kHz. This effect seems to be related to a decrease of the lower ionospheric boundary. We demonstrate a strong seasonal dependence of the effect; it is stronger for months with higher thunderstorm activity (March - August). The effect is also stronger at larger geographic latitudes and for epicenters located below the sea. These dependencies can be explained by the characteristics of the wave propagation in the Earth-ionosphere waveguide.

Pisa, D.; Nemec, F.; Parrot, M.; Santolik, O.

2012-12-01

130

VLF waves in the foreshock  

Science.gov (United States)

Plasma waves observed in the VLF range upstream of planetary bow shocks not only modify the particle distributions, but also provide important information about the acceleration processes that occur at the bow shock. Electron plasma oscillations observed near the tangent field line in the electron foreshock are generated by electrons reflected at the bow shock through a process that has been referred to as Fast Fermi acceleration. Fast Fermi acceleration is the same as shock-drift acceleration, which is one of the mechanisms by which ions are energized at the shock. We have generated maps of the VLF emissions upstream of the Venus bow shock, using these maps to infer properties of the shock energization processes. We find that the plasma oscillations extend along the field line up to a distance that appears to be controlled by the shock scale size, implying that shock curvature restricsts the flux and energy of reflected electrons. We also find that the ion acoustic waves are observed in the ion foreshock, but at Venus these emissions are not detected near the ULF forshock boundary. Through analogy with terrestrial ion observations, this implies that the ion acoustic waves are not generated by ion beams, but are instead generated by diffuse ion distributions found deep within the ion foreshock. However, since the shock is much smaller at Venus, and there is no magnetosphere, we might expect ion distributions within the ion foreshock to be different than at the Earth. Mapping studies of the terrestrial foreshock similar to those carried out at Venus appear to be necessary to determine if the inferences drawn from Venus data are applicable to other foreshocks.

Strangeway, R. J.; Crawford, G. K.

1995-01-01

131

VLF Radio Waves from Meteors  

Science.gov (United States)

To find the origin of electrophonic sounds produced by fireballs [1,2], a great number of project started, but only a few relevant data till now exist [3]. The effort to finding VLF emission from weak meteors with our group was inconclusive [4], probably because all the produced VLF radio waves of the meteors were at altitudes above the ionosphere, so the emitted radio waves were reflected towards space. There also exists the possibility that the signal to noise ratio was too small, or perhaps that some technical problems occurred [5]. The VLF emissions detected in some situations after faint meteors by others seem to be of dubious provenance [6,7]. Many open questions exist here, and to collect the necessary data in the search for the solutions, a planned new electronic equipment is described.

Korlevic, K.

132

Unique Observation of a Solar Flare by Lunar Occultation During the 2010 Annular Solar Eclipse Through Ionospheric Disturbances of VLF Signals  

Science.gov (United States)

Very Low Frequency (VLF) radio waves propagate through the Earth-ionosphere waveguide. Irregularities caused by excess or deficient extreme ultra-violet and X-rays, which otherwise sustain the ionosphere, change the waveguide properties and hence the signals are modified. We report the results of monitoring of the NWC transmitter (19.8 kHz) by a receiver placed at Khukurdaha (22°27'N, 87°45'E) during the partial solar eclipse (75 %) of 15th January, 2010. The propagation path from the transmitter to the receiver crosses the annular eclipse belt. We got a clear depression in the data during the period of the eclipse. Most interestingly, there was also a X-ray flaring activity in the sun on that day which reached its peak (C-type) right after the time when the eclipse reached its maximum. We saw the effects of the occultation of this flare in our VLF signal since a part of the X-ray active region was clearly blocked by the moon. We quantitatively compared by using analogies with previous observations and found best fitting parameters for the time when the flare was occulted. We then reconstructed the VLF signal in the absence of the occulted flare. To our knowledge, this is the first such incident where the solar flare was observed through lunar occultation and that too during a partial eclipse.

Maji, Surya K.; Chakrabarti, Sandip K.; Mondal, Sushanta K.

2012-06-01

133

Unique observation of a Solar Flare by Lunar Occultation during the 2010 Annular Solar Eclipse through ionospheric disturbances in VLF waves  

Science.gov (United States)

Very Low Frequency (VLF) radio waves propagate through the Earth-ionosphere waveguide. Irregularities caused by excess or deficient solar extreme ultra-violet and X-rays, which otherwise sustain the ionosphere, changes the waveguide properties and hence the signals are modified. We report the results of monitoring of the NWC transmitter (19.8kHz) by a receiver placed at Khukurdaha (~80 km away from Kolkata) during the partial solar eclipse (75%) of 15th January, 2010. The receiving station and the transmitter were on two opposite sides of the annular eclipse belt. We got a clear depression in the data during the period of partial eclipse. Most interestingly, there was also a flaring activity in the sun on that day which reached its peak (C-type) just after the time when the eclipse was near maximum. We saw effects of the occultation of this flare in our VLF signal since a part of the active region was clearly blocking the moon. We model this occultation, and reconstructed the VLF signal in the absence of the flare. To our knowledge, this is the first such incident where the solar flare was observed through lunar occultation and that too during a partial eclipse.

Kanta Maji, Surya; Chakrabarti, Sandip Kumar

2012-07-01

134

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

International Nuclear Information System (INIS)

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

135

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

136

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

Science.gov (United States)

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

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

2014-06-01

137

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

Directory of Open Access Journals (Sweden)

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

A. A. Lubchich

2006-10-01

138

Manifestation of Earth's diurnal periods in VLF radiation  

Science.gov (United States)

Spectral analysis of the registered data of natural VLF noise at the frequencies of 0.7, 1.2, and 5.3 kHz for 1997-2006 as well as of direction-finding data of atmospherics in the frequency range of 3-60 kHz for 2002-2006 has been carried out. The analysis has shown that in VLF noise envelope spectra and direction-finding data there are diurnal maxima that coincide with the periods of the Earth's rotation relative to the Sun (1440 min) and relative to the stars (1436 min). The highest amplitude in spectral components coincides with the period of the Earth's rotation relative to the Sun, and it is observed for the radiation registered form the southwesterly direction. It has been shown that not only the X-ray emission the Sun but also the X-ray emission of the galaxy affect the level of ionosphere D layer ionization.

Druzhin, G. I.; Mel'nikov, A. N.; Cherneva, N. V.

2014-07-01

139

Coherent generation of VLF hiss  

International Nuclear Information System (INIS)

VLF hiss is proposed to result from convective beam amplification of incoherent Cerenkov whistler radiation by the beam of precipitating auroral electrons. The beam amplification mechanism is investigated by using the lowest-order WKB wave kinetic equation and linear growth rates. It is shown that incoherent Cerenkov radiation cannot produce strong VLF hiss without beam amplification and that the beam amplification mechanism can account for the observed bandwidth and power fluxes of strong VLF hiss when the electron gyrofrequency is less than the electron plasma frequency. The theory is not adequate for high frequencies when the electron plasma frequency is less than the electron gyrofrequency, because nonlinear processes are important for frequencies near the plasma frequency

140

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

Science.gov (United States)

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

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

1994-01-01

 
 
 
 
141

VLF imaging of the Venus foreshock  

Science.gov (United States)

VLF plasma wave measurements obtained from the Pioneer Venus Orbiter Electric Field Detector (OEFD) have been used to construct statistical images of the Venus foreshock. Our data set contains all upstream measurements from an entire Venus year (approximately 200 orbits). Since the foreshock VLF characteristics vary with Interplanetary Magnetic Field (IMF) orientation we restrict the study to IMF orientations near the nominal Parker spiral angle (25 to 45). Our results show a strong decrease in 30 kHz wave intensity with both foreshock depth and distance. There is also an asymmetry in the 30 kHz emissions from the upstream and downstream foreshocks. The ion foreshock is characterized by strong emissions in the 5.4 kHz OEFD channel which are positioned much deeper in the foreshock than expected from terrestrial observations. No activity is observed in the region where field aligned ion distributions are expected. ULF wave activity, while weaker than at Earth, shows similar behavior and may indicate the presence of similar ion distributions.

Crawford, G. K.; Strangeway, R. J.; Russell, C. T.

1993-01-01

142

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

143

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.

144

Compton Gamma Ray Observatory/BATSE observations of energetic electrons scattered by cyclotron resonance with waves from powerful VLF transmitters  

Science.gov (United States)

To obtain a better understanding of the wave-particle mechanisms responsible for the loss of electrons from the radiation belts, energetic electron data from the Burst and Transient Source Experiment (BATSE) on the NASA's Compton Gamma Ray Observatory (GRO) was studied. Powerful ground-based VLF transmitters resonantly scatter electrons from the inner radiation belt onto trajectories from which they precipitate into the atmosphere as they drift eastward. 563 instances in which the satellite traversed a cloud of energetic electrons which had been scattered into quasi-trapped trajectories were identified. From the longitude distribution, it was concluded that waves from the VLF transmitter NWC at 114 deg E are the origin of 257 of the events, and waves from UMSat 44 deg E related to 45 more. In another 177 cases the electrons had drifted from the longitude of these transmitters to a location in the western hemisphere. The previously reported seasonal variation in the frequency of occurrence of cyclotron resonance interaction is confirmed with the continuous coverage provided by GRO. The frequency of occurrence of the cyclotron resonance interactions is largest before sunrise, which we attribute to the diurnal variations in the transmission VLF waves through the ionosphere. For the first time, unique very narrow sheets of electrons occurring in the aftermath of a large geomagnetic storm are reported.

Datlowe, Dayton W.; Imhof, William L.

1994-01-01

145

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

146

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 8–9 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

147

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

Science.gov (United States)

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

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

2013-12-01

148

VLF wave emissions by pulsed and dc electron beams in space. II - Analysis of Spacelab 2 results  

Science.gov (United States)

Results are presented from experiments on the generation of radio frequency waves in space plasmas by the injection of artificial electron beams into ionospheric plasmas that were conducted on the Spacelab 2 Space Shuttle mission. The observations of narrow-band radiation (Reeves et al., 1988) are compared with the prediction of a theory of wave generation by pulsed electron beams (Harker and Banks, 1987). Good agreement is found between the observations and predictions for the s = 0, root 2 solutions representing Cerenkov radiation with wave normal angles less than the Gendrin angle. Also, for broadband emissions, predictions using a single-ion cold plasma theory are compared with the observed features. The broadband dc and pulsed electron beam emissions also have features that can be explained in terms of the characteristics of whistler mode waves produced by Cerenkov resonance.

Reeves, G. D.; Banks, P. M.; Neubert, T.; Harker, K. J.; Gurnett, D. A.

1990-01-01

149

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

150

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

Directory of Open Access Journals (Sweden)

Full Text Available

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

 

Pier Francesco Biagi

2012-04-01

151

Characteristics of VLF atmospherics near the resonance frequency of the Earth-ionosphere waveguide 1.6–2.3 kHz by observations in the auroral region  

Directory of Open Access Journals (Sweden)

Full Text Available Recordings of ELF-VLF waves with the right-hand (RH and the left-hand (LH circular polarization were made in Northern Finland. Analysis showed a difference between the RH and LH polarized waves. A pronounced maximum of the wave amplitude was observed at the first critical frequency of the Earth-ionosphere waveguide (the first transverse resonance around 1.6–2.3 kHz. The wave had the circular LH polarization at this maximum. To interpret observations, we computed the characteristics of the waveguide modes by using the full wave solution in the night model of the ionosphere. Computations show that the spectral maximum at the first transverse resonance frequency arises from a small absorption of the LH polarized radio wave in the magnetized ionosphere plasma, forming the upper boundary of the Earth-ionosphere waveguide.

J. Manninen

2010-01-01

152

Observations of whistler-type echoes on signals of a ground VLF transmitter on board the Interkosmos-19 satellite  

International Nuclear Information System (INIS)

Whistler-type echoes were received on board the Interkosmos 19 satellite with signals at frequencies between 10.2 and 13.6 kHz from a VLF transmitter of the Omega navigation system located in the auroral zone (66.4 deg N, 13.2 deg E, L 5). The echoes occur predominately in periods of low geomagnetic activity the occurrence region in the outer ionosphere has the dimension of about 1000 km, and its position is about L 2.5 and L 4.4. The delay of the echo signal is practically the same during one satellite pass, but its values for different satellite revolutions lie between 2.5 and 3.5 s. The experimental results are consistent with the theory of nonlinear ducting assuming quasi-ducting of whistler waves in the equatorial region due to interaction with ion cyclotron waves that permanently exist in this region

153

Modeling solar flare induced lower ionosphere changes using VLF/LF transmitter amplitude and phase observations at a midlatitude site  

Directory of Open Access Journals (Sweden)

Full Text Available Remote sensing of the ionosphere bottom using long wave radio signal propagation is a still going strong and inexpensive method for continuous monitoring purposes. We present a propagation model describing the time development of solar flare effects. Based on monitored amplitude and phase data from VLF/LF transmitters gained at a mid-latitude site during the currently increasing solar cycle no. 24 a parameterized electron density profile is calculated as a function of time and fed into propagation calculations using the LWPC (Long Wave Propagation Capability. The model allows to include lower ionosphere recombination and attachment coefficients, as well as to identify the relevant forcing X-ray wavelength band, and is intended to be a small step forward to a better understanding of the solar–lower ionosphere interaction mechanisms within a consistent framework.

E. D. Schmitter

2013-04-01

154

VLF versus MF heating of the lower ionosphere  

International Nuclear Information System (INIS)

The perturbation in the signal strength of a VLF transmitter by another transmitter heating the ionosphere on the great circle path to the receiver is calculated for two cases: The NAA-Palmer path heated by the VLF transmitter, NAU, and the Omega Norway-Skibotn path heated by the MF transmitter, heating, near Tromsoe. Comparison implies either that VLF heating is over 100 times more effective than MF heating in terms of the perturbation produced, per RF heating watt, in VLF propagation in the Earth-ionosphere wave-guide or that the observed effect at Palmer is fortuitous or spurious

155

VLF versus MF heating of the lower ionosphere  

Energy Technology Data Exchange (ETDEWEB)

The perturbation in the signal strength of a VLF transmitter by another transmitter heating the ionosphere on the great circle path to the receiver is calculated for two cases: The NAA-Palmer path heated by the VLF transmitter, NAU, and the Omega Norway-Skibotn path heated by the MF transmitter, heating, near Tromsoe. Comparison implies either that VLF heating is over 100 times more effective than MF heating in terms of the perturbation produced, per RF heating watt, in VLF propagation in the Earth-ionosphere wave-guide or that the observed effect at Palmer is fortuitous or spurious.

Dowden, R.L.; Adams, C.D.D. (Univ. of Otago, Dunedin (New Zealand))

1991-08-01

156

The quantitative relationship between VLF phase deviations and 1-8 A solar X-ray fluxes during solar flares  

International Nuclear Information System (INIS)

An attempt is made to investigate the quantitative relationship between VLF phase deviations in SPA (sudden phase anomalies) events and associated solar X-ray fluxes in the 1 to 8 A band during solar flares. The phase deviations (?phi) of the 18.6 kHz VLF wave transmitted from NLK, USA are used in this analysis which were recorded at Nishinomiya, Japan during the period June 1974 to May 1975. The solar X-ray fluxes (F0) in the 1 to 8 A band are estimated from fsub(min) variations using the empirical expression given by Sato (J.Geomag.Geoelectr.;27: 95(1975)), because no observed data were available on the 1 to 8 a X-ray fluxes during the period of the VLF observation. The result shows that the normalized phase variation, ?phi/coschisub(min), where chisub(min) represents the minimum solar zenith angle on the VLF propagation path, increases with increasing logF0. A theoretical explanation for this is presented assuming that enhanced ionizations produced in the lower ionosphere by a monochromatic solar X-ray emission are responsible for the VLF phase deviations. Also it is found that a threshold X-ray flux to produce a detectable SPA effect is approximately 1.5 x 10-3 cm-2 sec-1 in the 1 to 8 a band. (author)

157

On the amplification of VLF hiss  

International Nuclear Information System (INIS)

Based on the model calculation of VLF hiss power flux spectrum resulting from convective beam amplification of incoherent Cerenkov whistler radiation by the beam of precipitating auroral electrons, the altitude dependence of power flux levels is examined. Their strong altitude dependence suggests that non-linear processes are important in determining the spectrum of VLF hiss at high altitude. It is also shown that estimated power fluxes inside the electron precipitation region at low altitude might not reach as high levels as observed when the electron beam is weak. In this case, wave propagation outside of the precipitation region will account for the high power flux levels as well as significant magnetic components of VLF hiss observed especially at low altitude. In addition, it is shown that the transformation of the electron beam in transit to lower altitudes, determined from Liouville's theorem, may influence appreciably VLF hiss power flux spectrum. Finally, it is pointed out that two types of VLF hiss spectrum observed at the ground level can be accounted for by the difference in strength of the electron beam. (author)

158

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

159

Detection of whistlers by the Belgian VLF antenna : Statistical analysis and comparison with Cluster data and a plasmaspheric model  

Science.gov (United States)

Whistlers are VLF (3-30 kHz) emissions initiated by lightning, propagating along magnetic field lines, observed on ground and in space. Whistler wave analysis is an effective tool for studying the plasmasphere. Whistlers acquire particular frequency-time characteristics while they propagate through the magnetospheric plasma, and in particular through the plasmasphere. Their propagation time depends on the plasma density along their propagation paths. It is possible to derive the plasmaspheric electron density distribution from these propagation times. We therefore have started a project to detect whistlers with VLF measurements. A VLF antenna has been installed in 2011 in Humain, Belgium (50.11°N, 5.15°E). The VLF antenna is made of two perpendicular magnetic loops, oriented North-South and East-West, and with an area of approximately 50 m2 each. This antenna is part of AWDAnet, the Automatic Whistler Detector and Analyzer system's network. This network covers low, mid and high magnetic latitudes, including conjugate locations. We use the AWDA system to automatically retrieve electron density profiles from whistler measurements made in Belgium. On this poster, results of whistler occurrence are shown, as well as a comparison with density data obtained from the WHISPER instrument onboard Cluster and from a plasmaspheric model. We also present the possibilities to install a similar VLF antenna at the Belgian Antarctica station.

Darrouzet, Fabien; Ranvier, Sylvain; De Keyser, Johan; Lamy, Hervé; Pierrard, Viviane; Borremans, Kris; Décréau, Pierrette; Lichtenberger, Janos

2014-05-01

160

Detection of whistlers by the Belgian VLF antenna : Statistical analysis and comparison with Cluster data  

Science.gov (United States)

Whistlers are VLF (3-30 kHz) emissions initiated by lightning, propagating along magnetic field lines, observed on ground and in space. Whistler wave analysis is an effective tool for studying the plasmasphere. Whistlers acquire particular frequency-time characteristics while they propagate through the magnetospheric plasma, and in particular through the plasmasphere. Their propagation time depends on the plasma density along their propagation paths. It is possible to derive the plasmaspheric electron density distribution from these propagation times. We therefore have started a project to detect whistlers with VLF measurements. A VLF antenna has been installed in early 2011 in Humain, Belgium (50.11^°N, 5.15^°E). The VLF antenna is made of two perpendicular magnetic loops, oriented North-South and East-West, and with an area of approximately 50 m2 each. This antenna is part of AWDAnet, the Automatic Whistler Detector and Analyzer system's network. This network covers low, mid and high magnetic latitudes, including conjugate locations. We use the AWDA system to retrieve automatically electron density profiles from whistler measurements made in Belgium. In this poster, the first results of whistler occurrence are shown, as well as the first comparison with density measurements made with the WHISPER instrument onboard Cluster.

Darrouzet, Fabien; Ranvier, Sylvain; De Keyser, Johan; Lamy, Hervé; Lichtenberger, Janos; Décréau, Pierrette

2013-04-01

 
 
 
 
161

Initial results from AWESOME VLF receiver in equatorial region of Vietnam  

Science.gov (United States)

A new AWESOME VLF receiver has been setup at Nha Trang station in Vietnam during the year 2012 under ISWI program. The VLF receiver is designed and developed by Stanford University, USA. It is a part of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in very low frequency (VLF). Some of the initial results obtained from the preliminary analysis of the VLF data recorded at the station are presented. Keyword: VLF frequency, AWESOME receiver, Ionosphere.

Vinh, Hao; Lan, Hoang Thai

162

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

163

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

International Nuclear Information System (INIS)

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

164

VLF remote sensing of the auroral electrojet  

Energy Technology Data Exchange (ETDEWEB)

The authors present data taken to test the use of phase and amplitude variations in ground based VLF wave propogation measurements as a means of determining the location of the auroral electrojet. High-energy (> 300 keV) precipitating electrons at the edge of the electrojet can induce phase and amplitude variations in VLF waves propogating through that region of the atmosphere. The authors present measurements made in conjunction with conventional magnetometer measurements as a way to validate this technique. Satellite measurements of field-aligned currents were available for one night of observations.

Cummer, S.A.; Bell, T.F.; Inan, U.S. [Stanford Univ., Stanford, CA (United States)] Zanetti, L.J. [Johns Hopkins Univ., Laurel, MD (United States)

1996-03-01

165

Observation of light emissions in superconducting cavities  

International Nuclear Information System (INIS)

In order to investigate the light emissions associated to the electron emission in a superconducting RF cavity, an optical observation system is mounted on the 'mushroom' cavity. After an intentional contamination of the cavity with alumina particles, stable luminous spots are observed around the contaminated area. (authors)

166

ULF wave generation through particle precipitation induced by VLF transmitters  

International Nuclear Information System (INIS)

Recent experiments have shown that significant fluxes (10-1 erg/cm2 s) of energetic electrons can be precipitated into the ionosphere at times when VLF emissions are triggered in the magnetosphere by whistlers. If similar fluxes can be produced during the artificial triggering of VLF emissions by ground- or satellite-based VLF transmitters, then a powerful tool would be available for studying the dynamics of the lower ionosphere. In the present paper we explore the feasibility of a technique to stimulate ULF waves in the ionosphere using the tool of controlled particle precipitation. Periodic (period of >1/2 s) transmissions from a VLF ground-based transmitter are used to trigger VLF emissions and precipitate energetic electrons. The periodic precipitated flux modifies the conductivity of the D and E regions, inducing periodic changes in current flow which in turn result in the generation of Pc 1 ULF waves. Calculations indicate that ULF wave amplitudes of 1 ? may be produced in this process. Furthermore, steady state magnetic field perturbations may reach 100 ? at ground level. Since both these amplitudes would be readily measurable with present techniques, the results lend plausibility to the idea of attempting to produce detectable ULF waves by using ground- or satellite-based VLF transmitters

167

ELF and VLF signatures of sprites registered onboard the low altitude satellite DEMETER  

Directory of Open Access Journals (Sweden)

Full Text Available We report the observation of ELF and VLF signature of sprites recorded on the low altitude satellite DEMETER during thunderstorm activity. At an altitude of ~700 km, waves observed on the E-field spectrograms at mid-to-low latitudes during night time are mainly dominated by up-going 0+ whistlers. During the night of 20 July 2007 two sprites have been observed around 20:10:08 UT from the observatory located on the top of the mountain ?nie?ka in Poland (50°44'09" N, 15°44'21" E, 1603 m and, ELF and VLF data have been recorded by the satellite at about 1200 km from the region of thunderstorm activity. During this event, the DEMETER instruments were switched in the burst mode and it was possible to register the wave forms. It is shown that the two sprites have been triggered by two intense +CG lightning strokes (100 kA occurring during the same millisecond but not at the same location. Despite the distance DEMETER has recorded at the same time intense and unusual ELF and VLF emissions. It is shown that the whistler wave propagates from the thunderstorm regions in the Earth-ionosphere guide and enters in the ionosphere below the satellite. They last several tens of milliseconds and the intensity of the ELF waveform is close to 1 mV/m. A particularly intense proton whistler is also associated with these emissions.

J. B??cki

2009-06-01

168

The results of experimental studies of VLF-ULF electromagnetic emission by rock samples due to mechanical action  

Science.gov (United States)

The paper presents the results of laboratory experiments on electromagnetic emissions excitation (the electric component of electromagnetic fields) by rock samples due to different forms of mechanical stress applications. It was shown that samples generate electric impulses with different spectra when the impact action, gradual loading or dynamic friction is applied. It was ascertained that level and spectral compositions of signals, generated by rock samples, change with an increasing number of hits. It was found that strong electromagnetic signals, generated while rock samples were fracturing, were accompanied by repetitive weak but perceptible variations in the electric field intensity in short frequency ranges.

Panfilov, A. A.

2014-06-01

169

Lightning--induced electron precipitation events observed at L-2.4 as phase and amplitude perturbations on subionospheric VLF signals  

International Nuclear Information System (INIS)

Lightning-induced electron precipitation (LEP) events are studied using the Trimpi effect, in which the precipitation-induced ionization enhancements in the lower ionosphere (D region) give rise to rapid perturbations of subionospheric VLF signals. In 1983,the phase and amplitude of signals from the NPM transmitter in Hawaii (23.4 kHz) and the Omega transmitter in Argentina (12.9 kHz) were measured at Palmer, Antarctica (L-2.4), together with the magnetospheric whistler background. The long baseline and over-sea great circle paths from these two sources make it possible for the observed perturbations to be interpreted using a single waveguide mode theory. Analytical expressions are used to relate the magnitude of the phase perturbations to differential changes in ionospheric reflection height along a segment of the propagation path. The predicted relationship between relative perturbation sizes on the two different signals is compared with measurements. From this information, the whistler-induced flux levels are inferred to be in the 10/sup -4/--10/sup -2/ erg cm/sup -2/ s/sup -1/ range and the precipitation regions are inferred to be roughly ''circular'' in shape, rather than elongated along L shells. Measured amplitude changes tended to be small (--0.5 dB) and negative, as expected from a single-mode theory, but the ratios of simultaneous amplitude and phase perturbations were slightly larger than the theory predicts, probably due to the effects of an additional mode(s). An assessment of the relative detectability of amplitude versus phase perturbations favors phase perturbations by -- 10 dB, irrespective of the detection scheme used. copyright American Geophysical Union 1987

170

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

171

Lightning VLF wave propagation from source, through ionosphere to inner magnetosphere using WWLLN and Van Allen Probes  

Science.gov (United States)

Lightning produces strong broadband radio waves, called "sferics", which propagate in the Earth-ionosphere waveguide and are detected thousands kilometers away from their source. Global real-time detection of lightning strokes including their time, location and energy, is conducted with the World Wide Lightning Location Network (WWLLN). In the ionosphere, these sferics couple into very low frequency (VLF) whistler waves which propagate obliquely to the Earth's magnetic field. Lightning generated VLF whistler dispersion in the ionosphere has been previously observed both from thunderstorm rockets and low altitude satellites. Previous studies also show a clear match and related attenuation between sferics detected by WWLLN and VLF whistlers observed by C/NOFS satellite. This global study can now be expanded to the magnetosphere using data from the Van Allen Probes (formerly known as the Radiation Belt Storm Probes (RBSP)) with high sampling rates for vector electric and magnetic fields, and extended altitude cover from ~600km to ~5 Re above the ground. In our work, we will show the one-to-one coincidence between WWLLN sferics and RBSP VLF whistlers. This talk will explore the relationship between these one to one lightning whistler waves with stimulated emissions such as lower hybrid waves, and possible energy deposition as the large amplitude lightning whistlers propagate into the outer magnetosphere.

Zheng, H.; Holzworth, R. H.; Brundell, J. B.; Wygant, J. R.; Mozer, F.; Hospodarsky, G. B.; Jacobson, A. R.; Hutchins, M. L.; Bonnell, J. W.; Breneman, A. W.; Kersten, K.

2013-12-01

172

Auroral activities and related ULF-VLF waves  

International Nuclear Information System (INIS)

Characteristics of ULF-VLF waves in the auroral zone were examined, especially in relation with auroral activities, on the basis of four campaign data of aurora (TV), VLF (Direction Finding) and ULF waves, which were carried out during IMS in Manitoba, Canada. In ULF range, Pi-2 pulsations were shown to occur associated with local auroral expansions, with principal axis of oscillation in direction toward the region of expansions and Pi-C pulsation in the dawn sector was related to auroral pulsations. Pc-1 was also examined showing a characteristic difference between fanshaped Pc-1 and non structured Pc-1. In VLF range, hiss emission is related to local activity of discrete aurora in its arrival direction, chorus emission is related to pulsating forms. The arrival direction of chorus emission in the daytime was sometimes found to move very rapidly. (author)

173

Ionosphere-magnetosphere studies using ground based VLF radio propagation technique: an Indian example  

Science.gov (United States)

Since IGY period (1957-58), natural and artificially produced Very Low Frequency (VLF) elec-tromagnetic radiations are being recorded at large number of ground stations all over the world and on-board satellites to study various radio wave-thermal/energetic plasma interactive pro-cesses related to earth's ionosphere-plasmasphere-magnetosphere environment. The terrestrial propagation of these VLF radio waves are primarily enabled through the earth ionosphere wave guide (EIWG) mode to long horizontal distances around the globe and ducted along the ge-omagnetic field lines into the conjugate hemisphere through the plasmasphere-magnetosphere regions. The time frequency spectra of the received signals indicate presence of dispersion (wave/group velocities changing with frequency) and various cut-off frequencies based on the width of the EIWG, electron gyro and plasma frequencies etc., providing several types of received signals like whistlers, chorus, tweeks, hiss and hisslers which can be heard on loud-speakers/earphones with distinguishing audio structures. While the VLF technique has been a very effective tool for studying middle and high latitude phenomena, the importance of the similar and anomalous observations over the Indian low latitude stations provide potentially new challenges for their scientific interpretation and modelling. The ducted and non-ducted magnetospheric propagation, pro-longitudinal (PL) mode, low latitude TRIMPI/TLE (Tran-sient Luminous Emissions) or other effects of wave-particle/wave-wave interactions, effects due to ionospheric irregularities and electric fields, full wave solutions to D-region ionisation per-turbations due to solar and stellar energetic X-and ? ray emissions during normal and flaring conditions are a few problems which have been addressed in these low latitude studies over India. Since the conjugate points of Indian stations lie over the Indian oceanic region, the VLF propagation effects would be relatively free from sferics at least in some seasons providing a noise free environment for observing rare and new phenomena requiring better SNR to detect such changes, The VLF signals from the active seismic zones or other electro-geological sources would require high sensitivities of the system and suitable network of transmitting and receiv-ing stations designed for targeted data and applications. Some new results over Indian and other regions show evidences of earthquake related seismo-geological VLF emissions with the potential of being used as a prognostic tool, change in ozone and ion production in the night time middle atmosphere due to transit of stellar x-ray/? ray sources. Results obtained on whistlers and related studies from a number of Indian stations covering geomagnetic latitude range between 13-24 N will be mentioned and reviewed in the background of theoretical understanding of the lightning return stroke signal elements, VLF propagation through cold plasma, ionospheric wave guide mode, electron precipitation due to cyclotron resonance and production of atomic oxygen O (3 P) and ionisation in the mesosphere due to solar/stellar UV/X/?rays. Use of future VLF techniques in terms of improving ground based observations, critical analysis of available satellite data in the context and real time moni-toring/modelling of earth's geosphere and space weather conditions will be considered for a possible programme of a developing country.

Chakravarty, Subhas

174

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

Directory of Open Access Journals (Sweden)

Full Text Available We present a detailed study of chorus emissions in the magnetosphere detected on board Magion 5, when the satellite was not far from the magnetic equator. We determine the frequency sweep rate of more than 8500 electromagnetic VLF chorus elements. These results are compared with the backward wave oscillator (BWO regime of chorus generation. Comparison of the frequency sweep rate with the BWO model shows: (i There is a correlation between the frequency sweep rates and the chorus amplitudes. The frequency sweep rate increases with chorus amplitude, in accordance with expectations from the BWO model; (ii The chorus growth rate, estimated from the frequency sweep rate, is in accord with that inferred from the BWO generation mechanism; (iii The BWO regime of chorus generation ensures the observed decrease in the frequency sweep rate of the chorus elements with increasing L-shell.

Key words. Magnetospheric physics (VLF emissions, energetic particles – Space plasma physics (wave-particle interactions

E. E. Titova

175

Observation of light emissions in superconducting cavities; Observation d`emissions lumineuses dans une cavite supraconductrice  

Energy Technology Data Exchange (ETDEWEB)

In order to investigate the light emissions associated to the electron emission in a superconducting RF cavity, an optical observation system is mounted on the `mushroom` cavity. After an intentional contamination of the cavity with alumina particles, stable luminous spots are observed around the contaminated area. (authors) 3 refs., 2 figs.

Caruette, A.; Fouaidy, M.; Hammoudi, N.; Junquera, T.; Le Goff, A.; Lesrel, J.; Maissa, S. [Services Techniques, Inst. de Physique Nucleaire, Paris-11 Univ., 91 - Orsay (France)

1999-11-01

176

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

177

Vlf wave-wave interaction experiments in the magnetosphere  

International Nuclear Information System (INIS)

VLF wave-wave interaction experiments were carried out by injecting various forms of VLF pulses into the magnetosphere from a 21.2 km dipole antenna at Siple, Antarctica. The injected signals propagate along a geomagnetic field line and often interact strongly with energetic electrons trapped in the radiation belts near the equator. Signals may be amplified and trigger emissions. These signals may then interact with one another through these energetic electrons. This report is divided into three parts. In the first part, simulations of VLF pulses propagating in the magnetosphere are carried out. In the second part, it is found for the first time that a 10 ms gap in a triggering wave can induce emission, which may then interact with the post-gap signals. In the third part, sideband triggering is reported for the first time

178

VLF wave stimulation experiments in the magnetosphere from Siple Station, Antarctica  

International Nuclear Information System (INIS)

The experimental methods used in the VLF stimulation experiments at the Siple Station, Antarctica, are described together with the results of observations and their interpretations. Consideration is given to the equipment employed in the experiments, with special attention to the Jupiter VLF transmitter, and to the methodology used to stimulate VLF signals. Data are presented on the following types of experiments: (1) single-frequency growth and triggering, (2) frequency ramp, (3) multifrequency, and (3) noise simulation. The possibilities for new controlled VLF wave injection experiments in the earth's magnetospheric plasma are discussed. 44 references

179

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

Science.gov (United States)

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

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

2014-08-01

180

VLF wave intensity in the plasmasphere due to tropospheric lightning  

Science.gov (United States)

climatology of VLF (very low frequency) wave intensity from lightning in the plasmasphere is constructed. Starting from Optical Transient Detector/Lightning Imaging Sensor (OTD/LIS) lightning data representing 1995-2005, a climatology of strikes is assembled with 1° × 1° latitude-longitude spatial resolution, averaged into 2 h bins for each month of the year. Assuming a linear relationship between optical flash rate and VLF power flux, and that the VLF amplitude drops off as one over distance, a proxy for VLF power is developed. A typical lightning spectrum is applied and the values are scaled by appropriate transionospheric absorptions for each time and place. These values are mapped along geomagnetic field lines in order to compare them to E-field spectral densities measured by the DEMETER satellite between 2005 and 2009. An overview of the DEMETER survey mode data is presented which leads to the best scaling of the lightning VLF climatology in LEO (low earth orbit). The resulting data set represents a monthly, 2-hour, solar minimum climatology of VLF wave intensity from lightning in LEO. Finally, the E-field spectral densities are converted to Poynting flux, mapped to the plasmasphere, and converted to B-field spectral densities. Good overall agreement is found with previous observations and estimates. This new climatology is expected to have a significant impact on calculations of pitch-angle diffusion for relativistic electrons in the inner radiation belt.

Colman, J. J.; Starks, M. J.

2013-07-01

 
 
 
 
181

VLF-EM surveys at Chalk River, Ontario  

International Nuclear Information System (INIS)

Airborne DIGHEMII electromagnetic (EM) and airborne and ground Very Low Frequency Electromagnetic (VLF-EM) surveys were carried out at Chalk River prior to September 1979. All surveys were run in two directions perpendicular to the azimuths of the two VLF transmitters used (NAA, Cutler, Maine and NSS, Annapolis, Maryland). Both airborne and ground data show responses corresponding to the fracture sets mapped geologically. the order of increasing sensitivity of the techniques to small rock fractures is airborne DIGHEMII, airborne VLF-EM and ground VLF-EM. Comparison of azimuthal distribution of EM anomaly sets with geological mapping demonstrates that a VLF-EM survey in one direction only will not give a complete picture of fracture distribution. With two transmitters whose azimuths are roughly orthogonal, and with a survey in the corresponding two directions responses will be observed from all fractures that are electrical conductors. In the Chalk River area, overburden is generally resistive, and does not strongly influence results. In areas of thick or conductive cover, VLF-EM techniques should be used with caution

182

Radio observational constraints on pulsar emission mechanisms  

International Nuclear Information System (INIS)

A discussion is made of those observations that place constraints on the pulsar emission mechanism and its location in the pulsar magnetosphere. After reviewing the salient features of pulsar radiation, a number of issues are confronted, including (1) whether coherence is broadband or narrowband and, accordingly, (2) whether the emission frequency is mapped into radius and/or magnetic polar angle; and (3) whether pulse structure (micropulses and subpulses) represents angular or temporal structure. It is proposed that pulse nulling, mode changing, and quantized drift rates for subpulses are related to discrete states of the particle flow in polar cap models. (Auth.)

183

Further observations of 4fceauroral roar emissions  

Science.gov (United States)

Recently Sato et al. [2012] reported on the first observations of auroral roar emissions near 4 times the ionospheric electron cyclotron frequency (fce) with a passive receiver installed in Svalbard, Norway. The initial observations, performed for about a year, showed that 4fce roar emissions were detected from 5.27 to 5.70 MHz during moderate geomagnetic disturbances in 22 days between May and September 2011 only from noon to evening, while no event occurred during the 2010-2011 winter season. An analysis of a typical event showed that the electron density profile measured from EISCAT Svalbard dynasonde satisfied the condition that the upper frequency of the 4fce roar was nearly equal to both upper hybrid resonance frequency (fUH) and 4fce at 238-km altitude. Examination of 2011-2012 polarization measurement data in Iceland reveals four events of 4fce roar emissions, whose observed polarization character indicates not only L-O mode but also R-X mode electromagnetic waves in some cases. Although the initial observations in Svalbard support the idea that the origin of 4fce roar is mode conversion to the L-O mode of upper hybrid waves favorably generated under the condition of fUH ~ 4fce, nonlinear coupling of two upper hybrid waves may also works in the bottomside auroral ionosphere to generate R-X mode 4fce roar. Reference: Sato, Y., T. Ono, N. Sato, and Y. Ogawa (2012), First observations of 4fce auroral roar emissions, Geophys. Res. Lett., 39, L07101, doi:10.1029/2012GL051205.

Sato, Y.; Ono, T.; Sato, N.; Ogawa, Y.; Yamagishi, H.; Kadokura, A.

2012-12-01

184

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

185

Diurnal variation of VLF signals  

CERN Document Server

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

Kaye, Richard

2014-01-01

186

Observing H2 Emission in Forming Galaxies  

CERN Document Server

We study the H2 cooling emission of forming galaxies, and discuss their observability using the future infrared facility SAFIR. Forming galaxies with mass >10^11 Msun emit most of their gravitational energy liberated by contraction in molecular hydrogen line radiation, although a large part of thermal energy at virialization is radiated away by the H Ly alpha emission. For more massive objects, the degree of heating due to dissipation of kinetic energy is so great that the temperature does not drop below 10^4 K and the gravitational energy is emitted mainly by the Ly alpha emission. Therefore, the total H2 luminosity attains the peak value of about 10^42 ergs/s for forming galaxies whose total mass 10^11 Msun. If these sources are situated at redshift z=8, they can be detected by rotational lines of 0-0S(3) at 9.7 micron and 0-0S(1) at 17 micron by SAFIR. An efficient way to find such H2 emitters is to look at the Ly alpha emitters, since the brightest H2 emitters are also luminous in the Ly alpha emission.

Omukai, K

2003-01-01

187

On the relationship between lightning peak current and Early VLF perturbations  

Science.gov (United States)

Lightning strokes are known to cause direct heating and ionization of the D region, some of which are detected via scattering of VLF transmitter signals and are known as Early VLF events. The disturbed ionosphere typically recovers in many tens of seconds. New experimental evidence is presented demonstrating that the scattering pattern and onset amplitude of Early VLF events are strongly related to both the magnitude and polarity of causative lightning peak current. Observations of Early VLF events at nine Stanford VLF receiver sites across the continental United States are combined with lightning geolocation data from the National Lightning Detection Network (NLDN). During January and March 2011, NLDN recorded 7769 intense lightning discharges with high peak currents (>100 kA) generating 1250 detected Early VLF events. We show that the size of the scattered field due to the ionospheric disturbance increases with the peak current intensity of the causative lightning discharge. The most intense peak currents of >+200 and <-250 kA disturb VLF transmitter signals as far as ˜400 km away from the lightning stroke. Early VLF event detection probability also increases rapidly with peak current intensity. On the other hand, the observed VLF amplitude change is not significantly dependent on the peak current intensity. Stroke polarity is also important, with positive strokes being ˜5 times more likely to generate Early VLF disturbances than negative strokes of the same intensity. Intense positive cloud-to-ground lightning discharges, especially when occurring over the sea, are also more likely to produce Early VLF events with long recovery (many minutes).

Salut, M. M.; Cohen, M. B.; Ali, M. A. M.; Graf, K. L.; Cotts, B. R. T.; Kumar, Sushil

2013-11-01

188

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

189

Radiometrically accurate FTS for atmospheric emission observations  

Science.gov (United States)

The calibration and operational performance of an FTIR-based airborne high-resolution interferometer sounder (HIS) for use in broadband measurements of atmospheric emission at 3.8-16.6 microns are described. The radiometric and wavelength calibration procedures in the laboratory involved the use of reference black bodies at 300 and 245 K and the known wavelength of the HIS HeNe laser (corrected for FOV effects), respectively. The atmospheric verification program included downlooking observations from the NASA U2/ER2 aircraft (where resolving power of 1800-3800 was demonstrated) and uplooking observations from the ground; good agreement with data from balloon-borne radiosondes is obtained, with absolute temperature uncertainties of less than 0.5 K and reproducibilities of 0.1-0.2 K over most of the measurement domain.

Revercomb, H. E.; Smith, W. L.; Stromovsky, L. A.; Knuteson, R. O.; Buijs, H.

1989-01-01

190

k vector measurements of VLF signals by the satellite EXOS-D  

Science.gov (United States)

This paper presents the results of determinations of the wave normal, or k vector, and the Poynting vector directions of VLF and ELF emissions, using data from the PFX receiver subsystem of VLF instruments aboard the EXOS-D satellite to measure two components of E and three components of B fields. It is shown that, using the Means (1972) method, the PFX subsystem can determine reasonably well the direction of the k vector and Poynting vector of coherent VLF signals. The refractive index deduced from the E and B fields agreed well with the refractive index calculated by the Appleton Hartree formula.

Yamamoto, Masayuki; Ito, Yoshihiko; Kishi, Yoji; Sawada, Akira; Kimura, Iwane

1991-02-01

191

INSPIRE: A VLF Radio Project for High School Students  

Science.gov (United States)

Since 1988 the Interactive NASA Space Physics Ionospheric Radio Experiment, or INSPIRE, has given students the opportunity to build research-quality VLF radio receivers and make observations of both natural and stimulated radio waves in the atmosphere. Any high school science class is eligible to join the INSPIRE volunteer observing network and…

Marshall, Jill A.; Pine, Bill; Taylor, William W. L.

2007-01-01

192

Disturbances in VLF signal caused by tsunami  

Science.gov (United States)

One of the few experimental techniques which can monitor perturbations of the ionization within the lower ionosphere uses long-wave (i.e., VLF and LF) probing. Here we present the first measurements of the response of the lower ionosphere driven by tsunamis caused by the November 15, 2006 (Kuril region) and the March 11, 2011 (Tohoku region) earthquakes. We used data from VLF receiver stations in Petropavlovsk-Kamchatsky (PTK) and Yuzhno-Sakhalinsk (YSH) in Russia. To analyze the VLF signal variations observed after the first earthquake the subionospheric NPM - PTK path was used because it lies along the propagation direction of the tsunami. The signal propagating along this path exhibited a significant decrease in amplitude during nighttime observations together with phase variations. To study the case of the Tohoku earthquake we employed data from two receivers: Petropavlovsk-Kamchatsky and Yuzhno-Sakhalinsk. This tsunami propagated approximately along the Hawaii - Yuzhno-Sakhalinsk path. Analysis showed that the signals received at both stations are very similar except for those from NPM transmitter which show large differences in comparison to the other transmitters. For this particular pair of propagation paths the signal recorded in Petropavlovsk-Kamchatsky traveled along an undisturbed path whereas that measured at Yuzhno-Sakhalinsk clearly showed an anomalous decrease in amplitude together with an increase in phase. The wavelet spectrograms of the data revealed the frequency of the maximum spectral amplitude in the range of periods of 8-30 min which corresponds to the internal gravity wave periods. These periods are in compliance with the periods observed in data recorded by the DART sensor buoys. A qualitative interpretation of the observed effects was suggested in terms of the interaction of internal gravity waves with lower ionosphere.

Levin, Boris; Solovieva, Maria; Rozhnoi, Alexander; Shalimov, Sergei; Hayakawa, Masashi; Hobara, Yasuhide

2013-04-01

193

Peculiarities of VLF chorus propagation in the megnetosphere  

International Nuclear Information System (INIS)

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

194

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

International Nuclear Information System (INIS)

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

195

New Observations of UV Emissions from Europa  

Science.gov (United States)

The recent top prioritization of the Europa Jupiter System Mission for the next outer solar system flagship mission is refocusing attention on Europa and the other Galilean satellites and their contextual environments in the Jupiter system. Surface sputtering by magnetospheric plasma generates a tenuous atmosphere for Europa, dominated by 02 gas. This tenuous gas is in turn excited by plasma electrons, producing ultraviolet and visible emissions. Two sets of imaging observations have been published to date, UV images from the Hubble Space Telescope, and visible eclipse images from Cassini. Three additional sets of HST UV observations were acquired in February 2007, April 2007 and June 2009. The signal to noise ratio in these data are not high, however, given the paucity of data and its increasing importance in terms of planning for EJSM, we have attempted to extract as much new information as possible from these data. This talk will summarize our analysis to date, and discuss them in terms of existing models, which attempt to explain the image morphology either in terms of the underlying source production and loss processes, or in terms of the plasma interaction with the exosphere.

McGrath, Melissa; Sparks, William

2009-01-01

196

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

Directory of Open Access Journals (Sweden)

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

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

J. Chum

197

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

198

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

199

Rocket experiment on spontaneously and artificially stimulated VLF plasma waves in the ionosphere  

International Nuclear Information System (INIS)

In situ active experiments on the nonlinear wave-wave and wave-particle interactions in the ionospheric plasma were performed by a Japanese sounding rocket K-9M-41. Both spontaneously and artificially stimulated plasma waves in the VLF range were observed. When a large amplitude electron plasma wave was transmitted from the rocket, parametrically excited ion acoustic waves were observed in addition to natural emissions such as whistlers, LHR emissions, and hisslike emissions. It was also found that 'risers' were triggered by the LHR emissions, which seem to be very similar to a phenomenon of the so-called ASE (artificially stimulated emissions). When a slow electron beam with energy lower than 3 eV was ejected from the rocket, a new type of periodic U-shaped discrete emission was observed which was excited through a wave-particle interaction. The frequency of these emissions is lower than the LHR frequency and decreases as the beam energy is increased. Spectrograms of the observed plasma are presented, and some are analyzed theoretically. (auth)

200

Rocket experiment on spontaneously and artificially stimulated VLF plasma waves in the ionosphere  

International Nuclear Information System (INIS)

In situ active experiments on the nonlinear wave-wave and wave-particle interactions in the ionospheric plasma were performed by a Japanese sounding rocket K-9M-41. Both spontaneously and artificially stimulated plasma waves in the VLF range were observed. When a large amplitude electron plasma wave was transmitted from the rocket, parametrically excited ion acoustic waves were observed in addition to natural emissions such as whistlers, LHR emissions, and hisslike emissions. It was also found that 'risers' were triggered by the LHR emissions, which seem to be very similar to a phenomenon of the so-called ASE (artificially stimulated emissions). When a slow electron beam with energy lower than 3 eV was ejected from the rocket, a new type of periodic U-shaped discrete emission was observed which was excited through a wave-particle interaction. The frequency of these emissions is lower than the LHR frequency and decreases as the beam energy is increased. Spectrograms of the observed plasma waves are presented, and some are analyzed theoretically

 
 
 
 
201

Observation of the helium 10830 A airglow emission in midlatitude  

International Nuclear Information System (INIS)

The helium 10830 A airglow in twilight was observed by a tilting filter photometer. Over three years observation reveals the seasonal variation and the solar zenith angle dependence of the helium emission. The enhancement of the emission was observed in winter. The solar zenith angle dependence was also investigated. The observation results show that the conjugate photoelectrons and the diurnal variation of the exsospheric temperature affect the helium emission. (author)

202

The origin of VLF-motions during RIPEX  

Science.gov (United States)

Very low-frequency motions (VLF), with frequencies less than 0.004 Hz, were persistently present during the RIP-current EXperiment (RIPEX) at Sand City, Monterey Bay, and reached intensities similar to the infragravity motions (Macmahan et al, 2002). The origin of the observed VLF-motions is not well understood at present. Modeling efforts by Reniers et al. [2002], utilizing a 2D flow model operating on the wave-group time-scale, showed that a good match with the observed VLF-motions could be obtained. However similar results could be achieved by decreasing the lateral mixing and omitting the wave-group forcing. A more detailed analysis will be performed to assess the effects of wave-group forcing, lateral mixing and wave-current interaction to examine the origin of the VLF motions observed during RIPEX. Results of this assessment will be presented at the meeting. MacMahan, J., A.J.H.M. Reniers, E.B. Thornton and T. Stanton, 2002: Ripex: rip-current pulsation measurements, to appear in Proceedings of the 28nd International Conference on Coastal Engineering, Am. Soc. of Civ. Eng., Cardiff. Reniers, A.J.H.M., J. MacMahan, E.B. Thornton and T. Stanton, 2002: RIPEX: rip-current pulsation modeling, to appear in Proceedings of the 28nd International Conference on Coastal Engineering, Am. Soc. of Civ. Eng., Cardiff.

Reniers, A.; Macmahan, J.; Thornton, E.; Stanton, T.

2002-12-01

203

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

Science.gov (United States)

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

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

2012-12-01

204

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

205

ELF-VLF noise radiation at latitudes of the day-time polar cusp  

International Nuclear Information System (INIS)

Space-time distribution of noise ELF-VLF radiations within high latitude day-time sector is considered on the basis of ground and satellite observations. VLF-noises (polar choirs) are shown to occupy in the ionospheric heights the space from plasmapause projection up to projection of equatorial boundary of day-time polar cusp, where intensity of noises abruptly, by jump drops by 30-50 dB. In ground observatories near the cusp projection the intensity of VLF radiation even at small (? 250 km) distances differs by 2-3 times, even at similar time variations of flash amplitudes

206

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Rault, Jean-louis

2011-01-01

207

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

208

IUE observations of the Jovian dayglow emission  

International Nuclear Information System (INIS)

IUE spectra of Jupiter are examined in light of recent models put forward to explain the anomalously bright ultraviolet emissions seen from the upper atmospheres of the outer planets. Chi-squared fits of the IUE spectra with model spectra produced by two proposed excitation mechanisms, electron impact and fluorescence of solar radiation, result in consistently higher?2 values for the solar fluorescence model. The authors find no conclusive evidence in the IUE data for the dominance of solar fluorescence over electron excitation in producing the Jovian dayglow emission

209

Extended lateral heating of the nighttime ionosphere by ground?based VLF transmitters  

Science.gov (United States)

The effects of ground?based very low frequency (VLF) transmitters on the lower ionosphere are investigated. Controlled modulation experiments are performed with the 21.4 kHz, 424 kW VLF transmitter NPM in Lualualei, Hawaii, and physical effects of the NPM transmissions are studied with a subionospherically propagating VLF probe signal. Observed perturbations to the probe signal are consistent neither with expectations from transmitter?induced electron precipitation nor to off?path scattering from a concentrated heating region near the transmitter but rather appear to be the result of scattering from extended lateral heating of the ionosphere by the NPM transmitter. A large?scale computational modeling framework confirms theoretically that this form of ionospheric heating can account for the observed probe signal modulations, establishing that the lateral extent of ionospheric heating due to VLF transmitters is several thousand kilometers, significantly greater than previously recognized.

Graf, K. L.; Spasojevic, M.; Marshall, R. A.; Lehtinen, N. G.; Foust, F. R.; Inan, U. S.

2013-12-01

210

The Graz seismo-electromagnetic VLF facility  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper we describe the Graz seismo-electromagnetic very low frequency (VLF facility, as part of the European VLF receiver network, together with the scientific objectives and results from two years operation. After a brief technical summary of the present system – with heritage from a predecessor facility – i.e. hardware, software, operational modes and environmental influences, we discuss results from statistical data and scientific events related to terrestrial VLF propagation over Europe.

K. Schwingenschuh

2011-04-01

211

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

212

On the modulation of VLF radiation  

International Nuclear Information System (INIS)

In order to explain the VLF hissing modulation, being excited in the high ionosphere in the form of plasma waves, estimated numerically is a time of linear pumping of plasma waves in ionosphere. This estimate is compared with the experimental data on VLF radiation modulation. It is shown that the correspondance between the calculation and experimental dispersion can serve a confirmation of the fact that wide-band VLF hissing modulation which is not related to the geomagnetic fluctuations, is caused by the VLF radiation generation in the form of plasma waves by the flux of epithermal electrons, modulated according to the density

213

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

214

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

Science.gov (United States)

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

Ahmedov, Bobomurat

215

Intensity fluctuations of mid-latitude background VLF-noises and the interplanetary magnetic field  

International Nuclear Information System (INIS)

Influence of interplanetary magnetic field (IMF) sector structure polarity and also variations of solar wind velocity and density on the intensity of mid-latitude VLF background noises are studied. For analysis continuous observations of VLF radiations in Magadan Observatory (phi=53.7 deg, L=2.7) from November, 1972 to June, 1973 were used. It is shown that IMF sector sign has no sufficient effect on the level of mid-latitude VLF background noises at the frequences f < 4-5 kHz. In magnetoperturbed periods when IMF Bsub(z)-component was directed to the South and the Earth was in the region of high-speed plasma flux, in mid-latitudes abatement of intensity of VLF background noises was seen

216

About interrelation of the auroral X-ray and VLF radiation of the upper atmosphere  

International Nuclear Information System (INIS)

The time relationships between the auroral X radiation and the very-low-frequency (VLF) radiation of the upper atmosphere are analyzed. The data of a number of synchronous observations of X-ray bremmstrahlung in the stratosphere and of ground-based measurements of VLF radiation for the period of 1967-1970 were used. The X radiation was detected on balioons with gas-discharge and scintillation counters in the region of Tixy Bay. It was found that the Earth atmosphere is invaded by fluxes of X radiation (of electrons) with energies from several tens to hundreds of keV, which reveal a relationship with VLF radiation. This points to a correlation between dynamic processes assosiated with electron acceleration and generation of VLF radiations

217

Particle acceleration by intense auroral VLF turbulence  

Science.gov (United States)

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

Retterer, John M.; Jasperse, J. R.; Chang, Tom

1990-01-01

218

OBSERVATION OF CORRELATED OPTICAL AND GAMMA EMISSIONS FROM GRB 081126  

International Nuclear Information System (INIS)

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

219

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

220

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

Science.gov (United States)

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

Mijling, B.; van der A, R.

2013-12-01

 
 
 
 
221

Recovery signatures of lightning-associated VLF perturbations as a measure of the lower ionosphere  

Energy Technology Data Exchange (ETDEWEB)

A new model of the physical processes associated with subionospheric VLF signal perturbations caused by lightning-induced electron precipitation (LEP) bursts is developed to diagnose the state of the lower ionosphere (e.g., electron number density and rate coefficients for various chemical reactions) on the basis of measurements of VLF recovery signatures. The model accounts for the energy spectrum of the electron bursts precipitated by lightning-generated whistlers, the chemical relaxation of enhanced secondary ionization in the nightime D region due to LEP bursts, and quantitatively treats the resultant effects on propagation of the VLF signal in the Earth-ionosphere waveguide. Application of the model to experimental data obtained for the VLF propagation path from NPM station (Hawaii) to Palmer station (Antarctica) indicates that effective electron detachment rate {gamma}, enhanced secondary ionization profile (e.g., energy content of LEP bursts), as well as the ambient electron density distribution, may be estimated using observed subionospheric VLF recovery signatures. The effective detachment rate was identified as {approximately}10{sup 18} N s{sup {minus}1}, where N is total number density of neutrals. Model indicates in particular that the attachment-detachment processes play the dominant role in recovery of subionospheric VLF signal perturbations on timescales {approximately}100 s, and that the observed perturbations of the NPM-Palmer signal correspond to the LEP bursts consisting of relatively soft (< 250 keV) electrons. 33 refs., 24 figs.

Pasko, V.P.; Inan, U.S. [Stanford Univ., CA (United States)

1994-09-01

222

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 µs. 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

223

Scintrex Magnetometer/VLF: Earth and Environment  

...Scintrex Magnetometer/VLF: Earth and Environment Faculty of Environment Leeds.ac.uk Portal Site map Contact Us School of Earth and Environment Home Admissions & Study Research Business & Consultancy People Intranet You are here: Earth and Environment Intranet logs & nbspScintrex... Logfile for Scintrex Magnetometer/VLF Add a new log entry Displaying results 1 to 2 out of 2 ...

224

Modeling the relaxation of early VLF perturbations associated with transient luminous events  

International Nuclear Information System (INIS)

Complete text of publication follows. Studies show that Early VLF perturbations, characterized by abrupt signal onsets and long recoveries, occur often in relation with Transient Luminous Events (TLEs), that is, sprites, sprite halos, and elves. Also, most of the Early VLF events are attributed to forward scattering of sub-ionospheric VLF transmissions incident upon horizontally elongated disturbances of elevated ionization in the upper D region between about 70 and 90 km. This concept is supported by the similarity of Early VLF event recoveries to those of LEPs (Lightning induced Electron Precipitation events), which are due to electron density enhancements in the upper D region caused by lightning and whistler-induced precipitation of radiation belt electrons. Here, the simplified Glukhov-Pasko-Inan (GPI) model, that has been developed for LEP investigations, is applied to simulate Early VLF event recoveries observed simultaneously with sprites in the D region. The present study shows that: 1) Early VLF events with long (short) recoveries are likely to come from higher altitudes of about 80 to 90km (lower altitudes of about 70 to 80 km) and under conditions of low (high) electron density elevations relative to ambient values, 2) although negative ion and positive cluster ion production plays a role in electron density relaxation at lower heights, the electron-single ion dissociative recombination is likely the key process at upper D region heights that defines the relaxation of Early VLF perturbations, and 3) the estimated electron density increases responsible for Early VLF events reach typical values between 104 and 105 cm-3 in the upper D region ionosphere.

225

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

226

Suzaku Observations of Charge Exchange Emission from Solar System Objects  

Science.gov (United States)

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

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

2012-01-01

227

Observation of Polarised Microwave Emission from Cosmic Ray Air Showers  

CERN Document Server

We report on the first direct measurement of the basic features of microwave radio emission from extensive air showers. Using a trigger provided by the KASCADE-Grande air shower array, the signals of the microwave antennas of the CROME (Cosmic-Ray Observation via Microwave Emission) experiment have been read out and searched for signatures of radio emission by high-energy air showers. Microwave signals have been detected for more than 30 showers with energies above $3\\times10^{16}$\\,eV. The observations presented in this Letter are consistent with a mainly forward-beamed, coherent and polarised emission process in the GHz frequency range. An isotropic, unpolarised radiation is disfavoured as the dominant emission model. The measurements show that microwave radiation offers a new means of studying air showers at very high energy.

Smida, R; Engel, R; Arteaga-Velazquez, J C; Bekk, K; Bertaina, M; Bluemer, J; Bozdog, H; Brancus, I M; Chiavassa, A; Cossavella, F; Di Pierro, F; Doll, P; Fuchs, B; Fuhrmann, D; Grupen, C; Haungs, A; Heck, D; Hoerandel, J R; Huber, D; Huege, T; Kampert, K -H; Kang, D; Klages, H; Kleifges, M; Kroemer, O; Link, K; Luczak, P; Ludwig, M; Mathes, H J; Mayer, H J; Mathys, S; Melissas, M; Morello, C; Neunteufel, P; Oehlschlaeger, J; Palmieri, N; Pekala, J; Pierog, T; Rautenberg, J; Rebel, H; Riegel, M; Roth, M; Salamida, F; Schieler, H; Schoo, S; Schroeder, F G; Sima, O; Stasielak, J; Toma, G; Trinchero, G C; Unger, M; Weber, M; Weindl, A; Wilczynski, H; Will, M; Wochele, J; Zabierowski, J

2013-01-01

228

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

Directory of Open Access Journals (Sweden)

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

T. Turunen

2012-04-01

229

Spatial observations of dust emission in NGC 7027  

International Nuclear Information System (INIS)

NGC 7027 was mapped in each of five spectral bands between 8.7 and 23 ?m with a spatial resolution of 3.5 arcsec. Two new scientific results are presented: (1) Analysis of the observations shows that the dust in NGC 7027 contains two spatially distinct components, one of which is associated with and links the unidentified emission features at 8.6 and 11.3 ?m; the second component may be graphite. (2) High-quality observations indicate that thermal emission by dust in NGC 7027 is spatially coextensive with emission by ionized hydrogen over a broad spectral range in the midinfrared (approx.8--28 ?m). No significant emission above the approx.1% level was found outside the region of ionized hydrogen in any spectral band observed. The intensity distribution of the observed infrared emission was successfully modeled by emission from within the walls of a hollow cylinder, similar to the model for 5-GHz radio emission proposed by Scott [Mon. Not. R. Astron. Soc. 161, 35P (1973)

230

Evaluating China's black carbon emissions using surface observations: sensitivity to observation representativeness and transport model error  

Science.gov (United States)

Atmospheric measurements of BC concentrations at representative locations provide invaluable independent datasets to evaluate bottom-up BC emissions, particularly when used in conjunction with chemical transport models. A few studies have evaluated China's BC emission inventory using surface observations, but their 'top-down' estimates of Chinese BC emissions vary greatly. This study examines the sensitivity of 'top-down' quantification of Chinese BC emissions to the choice of observational data and to transport model errors associated with grid resolution, wet deposition, and transport. Using hourly measurements of BC obtained with optical methods at two rural sites in China (Miyun and Chongming), we performed a detailed analysis of the model-observation comparison to filter out those observations not representative of regional emissions or heavily influenced by the model's transport errors instead of by emissions. The observed BC to CO correlation and its variation with precipitation were used to evaluate the model's wet deposition process and to quantify the wet deposition bias on BC emission estimate. By comparing top-down BC emission estimate derived from carefully-selected hourly observations with that from mere monthly-mean observations, we provided the error estimate for top-down emissions due to observation representativeness and model error. After better quantifying these errors, we evaluated China's bottom-up BC inventory of Zhang et al. [2009] by region and found that this inventory underestimated BC emissions from Center China, North China Plain and Yangtze River Delta region while overestimated emissions from Northeast China and Center South China. Our top-down estimate of BC emissions over China as a whole is 20%-40% higher than the bottom-up inventory.

Wang, Y.; Wang, X.; Hao, J.; Kondo, Y.; Irwin, M.; Munger, J. W.; Zhao, Y.

2012-12-01

231

Very low frequency (VLF) hiss in Jupiter's magnetosphere  

International Nuclear Information System (INIS)

The particle energy required to generate the observed VLF hiss in the Jovian magnetosphere has been computed under longitudinal and transverse resonance condition. It is shown that the minimum energy required by electrons to generate VLF hiss under the longitudinal resonance condition lies in the range of 100 eV-1 keV for the wave frequencies of 2-10 kHz, while the corresponding energy range for the transverse resonance condition for the same frequency range comes out to be 8 keV-40 keV. Further, the average radiated power by the Cerenkov process in the Jupiter's magnetosphere at L = 5.6 Rj by electrons of energy 10 eV, 100 eV, and 1 keV for the wave frequency of 5 kHz has also been computed. (Auth.)

232

Deriving emissions on regional to global scales from atmospheric observations  

Science.gov (United States)

Trace-gas observations can provide information about emissions on both global and regional spatial scales. Reliable 'top-down' global estimates are possible for a trace gas when its global mean atmospheric concentration and rate of change can be derived from atmospheric observations, provided loss rates are known. Global emission rates for long-lived ozone-depleting gases and substitute chemicals (e.g., HCFCs and HFCs) have been derived in this way with a range in different modeling approaches. The first part of this talk will discuss this method, its limitations, and the consistency of these emissions with estimates derived from inventories. The second half of the presentation will focus on deriving U.S. emissions of ozone-depleting and greenhouse gases from air samples regularly collected across the continental U.S. Mixing ratio enhancements provide information about recent emissions. A number of techniques have been used to assess both absolute and relative emission magnitudes of ozone-depleting and greenhouse gases from the continental U.S. over multi-annual periods. The extensive nature of the ongoing sampling program has allowed us to identify that emissions of some chemicals vary with season and by region. These results reaffirm that a fairly comprehensive sampling network is required to derive unbiased, top-down emission estimates for such trace gases.

Montzka, S. A.; Miller, B. R.; Siso, C.; Sweeney, C.; Andrews, A. E.; Miller, J. B.; Fischer, M. L.; Wang, H.

2011-12-01

233

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

International Nuclear Information System (INIS)

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

234

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

Directory of Open Access Journals (Sweden)

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

Mikhailov Victor S

2002-09-01

235

Outer zone electron precipitation produced by a VLF transmitter  

International Nuclear Information System (INIS)

By means of high-resolution pitch angle measurements made by a magnetic-focusing electron spectrometer on the S3-3 satellite while in the drift loss cone region of the magnetosphere, characteristics of fluxes of 108- to 654-keV electron precipitated in the inner zone, in the slot region, and in the outer zone of the magnetosphere are all shown to be consistent with the precipitation's having been produced by the same ground-based VLF transmitter, UMS. Pitch angle measurements are used to locate the longitude of precipitation. The temporal pattern of transmitter operation obtained from synoptic data from a ground-based VLF receiver is used along with drift rate calculations to predict the electron energies as a function of L shell which should be observable by the S3-3 instrument. The predicted energy response is then compared with the in situ observations, getting complete agreement. Finally, wave-particle resonance calculations are made for each of the three regions. The study indicates that ground-based VLF transmitters, which have previously been shown to produce precipitation in the inner zone and slot regions, are almost certainly instrumental in precipitating electrons in the outer zone also. copyright American Geophysical Union 1988

236

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 2×1015 molecule/cm2 and the model performances evaluated using surface measurements are satisfactory (~13%; (2 the observation errors that define the needs in spatial and temporal averaging for meaningful comparisons. 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

237

Observations of gamma-ray emission in solar flares  

International Nuclear Information System (INIS)

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

238

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

239

EGRET Observations of the Extragalactic Gamma Ray Emission  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The all-sky survey in high-energy gamma rays (E$>$30 MeV) carried out by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma-Ray Observatory provides a unique opportunity to examine in detail the diffuse gamma-ray emission. The observed diffuse emission has a Galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation as well an almost uniformly distributed component that is generally believed to originate o...

Sreekumar, P.

1997-01-01

240

Trapped electron losses by interactions with coherent VLF waves  

International Nuclear Information System (INIS)

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

 
 
 
 
241

Trapped electron losses by interactions with coherent VLF waves  

Energy Technology Data Exchange (ETDEWEB)

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

Walt, M.; Inan, U.S. [Space, Telecommunications and Radioscience Laboratory, Stanford University, Stanford, California (United States); Voss, H.D. [Lockheed Missiles and Space Co. (United States)

1996-07-01

242

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

243

Applicability of ELF/VLF ambient magnetic fields  

International Nuclear Information System (INIS)

ELF and VLF emanations and fields are worth special consideration because they behave differently from normal electromagnetic inteference, modern technology is more susceptible to ELF/VLF, they are difficult to attentuate, and they raise possible safety considerations. This set of diagrams and figures from a presented talk defines ELF and VLF terminology and addresses the important issues of ELF/VLF ambient magnetic fields. Means of measuring ELF/VLF fields are listed and possible effects of ELF/VLF are described, including induction currents, power harmonics, video display sensitivity, and personnel safety

244

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

245

More on ELF, VLF, and meteors  

Science.gov (United States)

In the frame of an electrophonic meteors study during the 2009 Perseids shower, preliminary results were presented during the 2009 International Meteor Conference in Porec, Croatia. Further data gathering, including VHF and ELF/VLF radio and photographic records, was performed at the Pic du Midi observatory and at the Guzet ski station during the 2010 Geminids shower. Correlations between radio and photo data, and the influence of a large meteor on the propagation of some VLF radio transmissions are presented here.

Rault, J.-L.

2012-01-01

246

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

Directory of Open Access Journals (Sweden)

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

G. Dufour

2009-03-01

247

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.)

248

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 >2000 when observed from over the dayside hemisphere but is dominant at longitudes >2000 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 1500 and in the right-hand sense at longitudes above 1500. 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 1011 W

249

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

250

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.; Décréau, P.

2013-12-01

251

Observations of H2 emission from NGC 7538  

International Nuclear Information System (INIS)

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

252

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

253

Observations of H? emission profiles in Aditya tokamak  

International Nuclear Information System (INIS)

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

254

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 Alfvén 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

255

Observation of dispersive wave emission by temporal cavity solitons.  

Science.gov (United States)

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

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

2014-10-01

256

ELF/VLF wave disturbances detected by the DEMETER satellite over the HAARP transmitter  

Science.gov (United States)

We report observations of electromagnetic the ELF/VLF wave disturbances by the DEMETER satellite (670 km altitude) overflying the HAARP heating facility (62.39(°) N, 145.15(°) W, L = 4.9). The HAARP HF transmitter operated at the maximum available power of 3.6 MW, O-mode polarization, and the beam directed towards the magnetic zenith. ELF/VLF waves caused by the HAARP heating are detected by the DEMETER satellite when the HF radio wave frequency was close to the critical frequency (foF2) of the ionospheric F2 layer but below it. ELF/VLF wave disturbances observed above the HAARP transmitter were detected by electrical antennas in an area with characteristic size 10 (2) km. We analyze amplitude and polarization spectra of the ELF disturbances and compare them with the characteristics of natural ELF hiss above HAARP. The VLF wave disturbances in the topside ionosphere above the HAARP transmitter were detected in the frequency ranges 8-17 kHz and 15-18 kHz which are close to the lower hybrid resonance frequency f _LHR in the heating region and its second harmonic (2f _LHR), respectively. In the case where the HAARP HF power was modulated, the detected VLF waves were also modulated with the same frequency whereas in the ELF frequency range the modulation period of the HAARP power was not observed. Possible mechanisms of generation of the ELF/VLF disturbances produced by the HAARP transmitter in the topside ionosphere are discussed.

Titova, Elena; Demekhov, Andrei; Parrot, Michel; Mogilevsky, Mikhail; Mochalov, Alexey; Pashin, Anatoly

257

VHE emission from extragalactic sources: open issues from MWL observations  

Energy Technology Data Exchange (ETDEWEB)

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

Stamerra, A.

2013-06-15

258

VHE emission from extragalactic sources: open issues from MWL observations  

Science.gov (United States)

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

Stamerra, A.

2013-06-01

259

Characteristics of a New MSK-Demodulator Applied to VLF Remote Sensing  

Science.gov (United States)

Very Low Frequency (VLF) transmitters operate around the globe primarily for communications with submarines. These signals propagate in the Earth-ionosphere waveguide with relatively low attenuation, and they make excellent signal probes for ionospheric remote sensing. Many VLF transmitter signals are modulated using Minimum-Shift Keying (MSK). In this work, we present a complete analysis of a new signal processing method for MSK-modulated VLF signals with the purpose to produce reliable amplitude and phase measurements for ionospheric remote sensing. We analyze the bit-error rate and the resulting amplitude and phase measurements as a function of signal-to-noise ratio under different background noise environments. We also compare the new method to other methods presently in use. We highlight the transient response characteristics by analyzing naturally occurring ionospheric events observed in the Northern and Southern hemispheres.

Mitchell, M.; Moore, R. C.

2013-12-01

260

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

 
 
 
 
261

Polar cap optical emissions observed from the ISIS2 satellite  

International Nuclear Information System (INIS)

The application of polar orbiting scientific satellites to the study of polar cap phenomena has led to significant advances in our understanding of polar cap processes. The ISIS2 satellite, which is in a circular orbit 1400 km above the earth's surface, has provided monochromatic optical images of the high latitude region since April 1971. The 5577 Angstroem emission from atomic oxygen and the 3914 Angstroem emission from the First Negative bands of N2+ have been monitored by the auroral scanning photometer, and the 6300 Angstroem emission from atomic oxygen has been obtained by means of the red line photometer. In order to view the entire polar cap during a single pass of the satellite, several restrictive conditions have to be met which limit the quantity of useful data. Nevertheless, there have been a sufficient number of satisfactory observations to allow the characteristic features of high latitude emission to be identified. In the sections that follow, a summary of results of observations of dayside aurora and polar cap arcs is given. (orig./WL)

262

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.

263

Scattering of protons of the radiation belt on the whistler mode of vlf radiation  

International Nuclear Information System (INIS)

Fluxes of quasitrapped protons with E /sub p/ ? 1 MeV are recorded on the Interkosmos-5 earth satellite at low altitudes in the region of L ? 3-3.5 in periods of the recovery phase of magnetic storms. The observed fluxes are explained by the scattering of protons of the radiation belt on the whistler mode of vlf radiation. The scattering mechanism is analyzed for quiet and magnetically disturbed times. The energies of protons interacting with the whistler mode of vlf radiation are given as a function of L. The scattering efficiency is compared with that for scattering due to other mechanisms

264

Scattering of radiation belt protons on the whistler mode of VLF radiation  

International Nuclear Information System (INIS)

On the ''Interkosmos-5'' satellite during the period of the recovery phase of magnetic storms quasi-captured proton fluxes with Esub(p) approximately 1 MeV in the L approximately 3-3.5 region are detected at low altitudes. The observed fluxes are explained by scattering of radiation belt protons on the whistler of VLF-radiations. The scattering mechanism is considered for quite and magnetodisturbed time. The energy values of protons interacting with the whistler mode of VLF radiations depending on L are given. The scattering efficiency is compared with the scattering for account of other mechanisms

265

EUV emission lines and diagnostics observed with Hinode/EIS  

CERN Document Server

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; 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

266

VLF propagation in disturbed environments  

Science.gov (United States)

Long-range VLF/LF propagation of transverse magnetic (TM) and transverse electric (TE) signals at frequencies from 10 to 50 kHz is considered. Model ionospheres corresponding to solar proton events or spread-debris nuclear environments are used in full wave calculations. Such disturbances constrict the Earth ionosphere waveguide, increasing excitation factors and attenuation rates. The signals are therefore usually degraded beyond a few megameters, although either enhancement or degradation can occur at shorter distances. Ohmic heating of heavy ions in the lower ionosphere is the main loss mechanism for intense disturbances. Only TM modes are efficiently radiated by ground based transmitters. However, TE signals can be important for air-to-air links with terminal elevations of 20 kft or more, and nearly horizontal trailing wire antennas. Air-to-air TE signals propagate better than TM modes over poorly conducting ground such as exists throughout Greenland and much of Canada, and can fill nulls in the TM signal. For paths over highly conducting ground, TM modes suffer less degradation than TE signals during intense disturbances; but, for ground conductivities less than about 0.0001mhos/m, TM signals are more adversely affected than TE signals.

Field, E. C., Jr.

1982-02-01

267

Quasi-periodic emissions observed by Cluster and DEMETER spacecraft  

Science.gov (United States)

Quasi-periodic (QP) emissions are electromagnetic emissions in the frequency range of about 0.5-4 kHz that are characterized by a periodic modulation of wave intensity. Typical periods of this modulation are on the order of minutes. Although there are many observations of these events by ground-based instruments, satellite observations are still rather sparse. Nevertheless, these are of great importance, as they allow us to analyze wave properties in situ, close to the probable generation region, and, moreover, they are not affected by the wave propagation in the Earth-ionosphere waveguide. We present a survey of QP events observed by the WBD instruments on board the four Cluster spacecraft during their perigee passes at radial distances of about 4 RE. Moreover, a conjugate observation of a QP event by Cluster spacecraft and by the low-altitude DEMETER spacecraft has been identified. Simultaneous observations of the same event by several different spacecraft enable us to distinguish between spatial and temporal variations of the phenomenon. It is shown that during a QP event, the same modulation is observed at the same time at very different locations of the inner magnetosphere. The results of a detailed wave analysis based on multi-component measurements by the STAFF-SA instruments indicate that the emissions propagate unducted, with oblique wave normal angles at larger geomagnetic latitudes. Finally, ULF magnetic field data are inspected for the presence of magnetic field fluctuations with a period corresponding to the period of modulation and a possible generation mechanism of the events is discussed.

Nemec, F.; Santolik, O.; Parrot, M.; Hayosh, M.; Pickett, J. S.; Cornilleau-Wehrlin, N.

2012-12-01

268

Observation of microwave emission from extensive air showers with CROME  

Directory of Open Access Journals (Sweden)

Full Text Available 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.

Wilczy?ski H.

2013-06-01

269

Matched filtering for the measurement of conjugately ducted VLF transmissions  

Science.gov (United States)

The application of matched filtering to the problem of very low frequency (VLF) radio signals ducted between magnetically conjugate points on the Earth by ionospheric plasma structures has been examined theoretically and implemented in recent field experiments. With accurate knowledge of the source VLF transmission the subionospheric component of the received waveform can be effectively removed, and the characteristics of the remaining ducted signal can be accurately estimated. Although the technique has been shown not to produce strictly consistent estimates of the subionospheric and ducted signal amplitudes, it is able to efficiently recover the transit delays and amplitudes of ducted man-made whistler mode emissions for reasonable values of the relevant signal-to-noise ratios. This is substantiated by the use of matched filtering to analyze data collected by radio receivers placed at the conjugate ends of a magnetic field line, thereby recovering the amplitudes and transit delays of ducted signals with time resolution as small as 30 s. An arbitrary degree of accuracy can be obtained in these measurements through the use of bit stream extraction and comparison. Further correlation analysis can be performed to extract Doppler shifts due to drifting ducts, and the small time resolution makes possible studies of ducting under rapidly changing conditions.

Starks, M. J.; Lee, M. C.

2000-03-01

270

Observations and modeling of forward and reflected chorus waves captured by THEMIS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Discrete ELF/VLF chorus emissions are the most intense electromagnetic plasma waves observed in the radiation belts of the Earth's magnetosphere. Chorus emissions, whistler-mode wave packets propagating roughly along magnetic field lines from a well-localized source in the vicinity of the magnetic equator to polar regions, can be reflected at low altitudes. After reflection, wave packets can return to the equatorial plane region. Understanding of whistler wave propagation and reflection ...

Agapitov, O.; Krasnoselskikh, V.; Yu. Zaliznyak; Angelopoulos, V.; Le Contel, O.; Rolland, G.

2011-01-01

271

Strong ionospheric perturbations generated by powerful VLF ground-based transmitters  

Science.gov (United States)

This paper is related to the first in-situ observations of strong ionospheric perturbations close to powerful VLF transmitters. NWC in Australia is one of the most powerful VLF transmitters in the world and it is located at a low L-shell value (L=1.49). Waves and plasma parameters are recorded by the low orbiting satellite DEMETER. Electrostatic waves from HF to ELF ranges are generated and strong turbulence appears. Fluctuations of electron and ion densities are observed as well as increase of temperature. The perturbations are well located to the geographic North of the transmitter and cover a surface of ~ 500,000 km2. This area is centred at the altitude of the satellite (700 km) around the magnetic field line which has a foot at the location of the transmitter. This phenomenon is due to the electron and ion heating of the ionosphere induced by the powerful transmitter VLF wave. A much smaller effect is also observed in the Northern hemisphere at the conjugated location. This ionospheric perturbation observed for the first time is in addition to the already known precipitation of the energetic particles which interact with the VLF wave of the transmitter through a cyclotron resonance mechanism. NAA in US which has the same power as NWC is located at a much higher L value (3.0). Ionospheric perturbations from this transmitter is also detected although intense natural noise is present in this sub-auroral area.

Parrot, M.; Sauvaud, J.; Berthelier, J.; Lebreton, J.

2007-05-01

272

Fermi Observations of ?-Ray Emission from the Moon  

Science.gov (United States)

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

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

2012-10-01

273

Observations of the Solar Continuum Radio Emission at Decameter Wavelengths  

Science.gov (United States)

Results of study of the continuum radio emission of the Sun in the decameter range are presented. Observations were carried out with radio telescope URAN-2 in summer months in 2008-2009. Radio fluxes at frequencies 20 MHz and 25 MHz in frequency band 250 kHz were obtained during the time, when there were no active regions on the solar disk. Their average values for two years were 670 Jy and 850 Jy at frequencies 20 MHz and 25 MHz correspondingly. These fluxes are in agreement with high frequency values.

Brazhenko, Anatoliy I.; Mel'Nik, Valentin N.; Konovalenko, Alexander A.; Abranin, Edward P.; Dorovskyy, Vladimir V.; Vashchishin, Rostislav V.; Frantzusenko, Anatoly V.; Rucker, Helmut O.

2010-01-01

274

Observation of heavy cluster emission from radioactive 230U nuclei  

International Nuclear Information System (INIS)

230Pa was produced with the reaction 232Th (p, 3n) 230Pa in the irradiation powder targets of ThO2 with 35 MeV proton beam. Sources of 230Pa?230U + ?- were prepared by radiochemical method. Using solid-state track registration detectors, two events of 230U decay with heavy cluster emission have been observed. The preliminary branching ratio to ?-decay comes out to be B = ?Ne/?? = (1.3 ± 0.8) x 10-14

275

Excitation of VLF quasi-electrostatic oscillations in the ionospheric plasma  

Directory of Open Access Journals (Sweden)

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

B. Lundin

276

Theoretical predictions for VLF radio propagation  

Science.gov (United States)

The very low frequency (VLF, 3 to 30 kHz) part of the radio frequency spectrum is characterized by low attenuation rate, high phase and frequency stability, and high signal to noise ratio. Consequently, VLF radio propagation is used for many practical applications, e.g., frequency standardization, clock synchronization, and reliable long-distance radio communications. Because of the distinct advantages of VLF radio propagation, the U.S. Navy will be conducting a balloon-to-balloon-borne cross link communication experiment to study the characteristics of VLF altitude radio propagation. In this Technical Report, an attempt has been made to make theoretical computations of the vertical components of the individual and multimode field strengths as a function of distance based on mode theory. The variations of various ionospheric parameters, e.g., attenuation rates, the heights of the ionospheric reflection point, the height gain factors for an appropriate combination of the transmitting and receiving antenna elevations, along with the presence of the Earth's geomagnetic field, especially for the East-West propagation, have been duly considered.

Paul, M. P.

1983-08-01

277

OSSE Observations of Gamma-Ray Emission from Centaurus A  

Science.gov (United States)

Results are reported on hard X-ray and soft gamma-ray observations of Centaurus A during 1991-1994 with the Oriented Scintillation Spectrometer Experiment (OSSE) on NASA's Compton Gamma Ray Observatory (CGRO). Long-term intensity changes by a factor of 2-3 were measured over this period. Short-term variations by as much as 25% on timescales as short as 12 hr were detected in most of the observations. No evidence for gamma-ray line emission was detected at sensitivities much improved over previous observations. An intensity-dependent evolution of the 50-1000 keV spectral shape was observed which can be characterized as an exponentially cut-off power law with an intensity-dependent cutoff energy ranging from ˜300 keV at the highest observed level to ˜700 keV at the lowest levels. A broken power-law model with an intensity- correlated break above ˜120 keV describes the observed spectral changes equally well. Best-fit spectral breaks vary from ?? 0.25±0.1 at the lowest levels to ?? 0.7±0.15 at the highest observed intensity. Below 120 keV the spectra at all intensities can be fitted with photon spectral index ? 1.70±0.08, in agreement with previous X-ray measurements. Contemporaneous measurements by the EGRET instrument on CGRO require additional spectral softening in the MeV region relative to broken power-law extrapolations of the OSSE measurements. At the maximum observed intensity, the luminosity of Cen A appears to peak at ˜200 keV with L?(50-1000 keV) ?7 × 1042 ergs s-1, implying a minimum black hole mass of only ?5 × 104 solar masses for Eddington-limited accretion.

Kinzer, R. L.; Johnson, W. N.; Dermer, C. D.; Kurfess, J. D.; Strickman, M. S.; Grove, J. E.; Kroeger, R. A.; Grabelsky, D. A.; Purcell, W. R.; Ulmer, M. P.; Jung, G. V.; McNaron-Brown, K.

1995-08-01

278

Strong Magnetic Field Fluctuations within Filamentary Auroral Density Cavities Interpreted as VLF Saucer Sources  

Science.gov (United States)

The Geoelectrodynamics and Electro-Optical Detection of Electron and SuprathermalIon Currents (GEODESIC) sounding rocket encountered more than 100 filamentary densitycavities associated with enhanced plasma waves at ELF (3 kHz) and VLF (310 kHz)frequencies and at altitudes of 800990 km during an auroral substorm. These cavities weresimilar in size (20 m diameter in most cases) to so-called lower-hybrid cavities (LHCs)observed by previous sounding rockets and satellites; however, in contrast, many of theGEODESIC cavities exhibited up to tenfold enhancements in magnetic wave powerthroughout the VLF band. GEODESIC also observed enhancements of ELF and VLFelectric fields both parallel and perpendicular to the geomagnetic field B0 within cavities,though the VLF E field increases were often not as large proportionally as seen in themagnetic fields. This behavior is opposite to that predicted by previously published theoriesof LHCs based on passive scattering of externally incident auroral hiss. We argue thatthe GEODESIC cavities are active wave generation sites capable of radiating VLF wavesinto the surrounding plasma and producing VLF saucers, with energy supplied by cold,upward flowing electron beams composing the auroral return current. This interpretation issupported by the observation that the most intense waves, both inside and outside cavities,occurred in regions where energetic electron precipitation was largely inhibited orabsent altogether. We suggest that the wave-enhanced cavities encountered by GEODESICwere qualitatively different from those observed by earlier spacecraft because of thefortuitous timing of the GEODESIC launch, which placed the payload at apogee within asubstorm-related return current during its most intense phase, lasting only a few minutes.

Knudsen, D. L.; Kabirzadeh, R.; Burchill, J. K.; Pfaff, Robert F.; Wallis, D. D.; Bounds, S. R.; Clemmons, J. H.; Pincon, J.-L.

2012-01-01

279

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

Science.gov (United States)

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

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

280

Spectral character of VLF sferics propagating inside the Earth-ionosphere waveguide during two recent solar eclipses  

Science.gov (United States)

Effects of solar eclipses on the propagation characteristics of worldwide VLF sferics from lightning activity require more investigation. An attempt was made on the occasion of two solar eclipses during 22nd July, 2009 and 15th January, 2010 to study the effects of the two eclipses on the propagation characteristics of VLF sferics in the Earth-ionosphere waveguide. Identical experimental setups were used to study the VLF sferics during the two eclipse events. The spectral character of VLF sferics propagating inside the waveguide is studied at a fixed receiver location (23.75°N, 91.25°E) at six discrete frequencies in between 3 and 20 kHz. During both the eclipse events, it is observed that VLF sferics at all the six discrete frequencies is increased from the mean normal average ambient level. The increment peaks around 10-12 kHz with an overall increment of 6.4 dB with respect to its ambient level. The VLF spectral character of enhancement of sferics show similar characters in two eclipses. The percentage decrease in electron density using standard modeling equations is found to be 90% at the height of 71 km for both the eclipses, supporting linear variation of electron density with solar radiation at the D-region of the ionosphere. The results are explained qualitatively on the basis of a decrease in electron density at the lower ionosphere modifying the reflection coefficient which affected the propagation of VLF sferics in Earth-ionosphere waveguide during eclipsed condition.

Guha, Anirban; De, Barin Kumar; Choudhury, Abhijit; Roy, Rakesh

2012-04-01

 
 
 
 
281

The VLF-EM imaging of potential collapse on the LUSI embankment  

Science.gov (United States)

Collapse and overtopping repeatedly occur in LUSI Embankment. Discontinuities (crack or fracture) in the embankment are major reasons for embankment failures or collapses. Very-low frequency electromagnetic (VLF-EM) measurement is essentially a non-destructive technique which displays subsurface 2-D cross section of resistivity. The cross section result has the possibility of detecting discontinuities and liquid saturation in embankment before it collapsed by observing which part of it in the cross section has low resistivity. This paper presents results of a survey conducted at the LUSI embankment in Eastern Java, Indonesia in a part of potential collapse. VLF-EM profiles measured along the embankment crest provided an overview of the whole embankment and served to detect anomalous zones. The noise assisted multivariate empirical mode decomposition (NA-MEMD) is applied to reject unwanted VLF-EM noise and Inv2DVLF software is applied to obtain result of 2-D resistivity models. In the selected area, the drill log and the standard penetration test (SPT) value gave detailed information about subsurface layer below embankment. This information is valuable for supporting 2-D resistivity image obtained from VLF-EM data inversion. Furthermore, the low resistivity in embankment layer is associated to discontinuities (fracture, crack or fault) along the embankment which caused its collapse.

Sungkono; Husein, Alwi; Prasetyo, Hardi; Bahri, Ayi S.; Monteiro Santos, Fernando A.; Santosa, Bagus J.

2014-10-01

282

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

Directory of Open Access Journals (Sweden)

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

G. Stangl

2011-04-01

283

Effects of Geomagnetic effect on Sub-ionospheric VLF-LF Signals Propagation  

Science.gov (United States)

Abstract: To investigate the effect of geomagnetic storm on subionospheric VLF-LF signal propagation, we analyze the variation in amplitude of VLF-LF signal using advanced complex continuous wavelet transform techniques. We analyze the VLF signal transmitted form ICV (20.27 kHz) located at Isola di Tavolara (40.55o N, 9.430 E), Italy and DH038 (23.40 kHz) Rhauderfehn (53.040 N, 7.340 E) Germany and one LF signal transmitted form NRK (37.50 kHz) transmitter located at Grindavik (63.510 N, 22.280 E), Iceland. We observed significant absorption in amplitude of these signals during the geomagnetic storm compared to their ambient values for the same period during the adjacent 7 days. The signal strength along their propagation paths was controlled by the storm associated decrease in ionization in the D-region of the ionosphere. Waveguide mode theory calculations show that the elevation of the height of lower ionosphere boundary of Earth-ionosphere waveguide was significantly decreased during this period. Key words: Subionospheric VLF-LF propagation, Complex Wavelet Transform, Geomagnetic activity and Earth-ionosphere waveguide

Sondhiya, Deepak Kumar; Gwal, Ashok Kumar; Verma, Shivali; Kasde, Satish Kumar; Sonakia, Anjana

284

ELF and VLF radiation from the polar electrojet antenna  

International Nuclear Information System (INIS)

An approximate evaluation is made of the ELF/VLF dipole moment of the polar electrojet antenna established by ionospheric heating via the use of powerful HF waves amplitude modulated with frequencies in the ELF/VLF range. The theory of reciprocity is used to determine the magnitude of the ELF/VLF waveguide excitation produced by such a dipole immersed in the ionosphere. Propagation under a series of ionospheres ranging from quiet auroral nighttime to disturbed auroral daytime is considered. 32 references

285

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

286

Extreme Ultraviolet Emission from Flare Stars Observed with EUVE  

Science.gov (United States)

The Extreme Ultraviolet Explorer (EUVE) satellite recently completed an all-sky survey in the extreme ultraviolet (EUV) from 70 -- 700 Angstroms@. Data were collected on numerous late-type and flare stars both during the survey and during pointed calibration observations. We present results from the EUVE observations of dKe and dMe flare stars. Quiescent fluxes are given for those sources which were detected, and comparisons made to previous EUV and X-ray measurements of the coronal emission from these objects. EUV flares have also been observed from several stars, including AU Mic, AT Mic, Prox Cen and YZ CMi. Light curves for these objects are presented, along with flare frequencies, peak luminosities and total flare energies. Comparisons are made to flare frequencies and energies derived from optical and X-ray measurements. In a few cases, temperatures are derived from multi-band measurements or from simultaneous spectra taken during the flares. This work has been supported by NASA contracts NAS5-30180 and NAS5-29298.

Vedder, P. W.; Patterer, R. J.; Drake, J.; Cully, S.; Brown, A.; Pettersen, B.

1993-05-01

287

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

288

VLF radio propagation conditions. Computational analysis techniques  

International Nuclear Information System (INIS)

Complete text of publication follows. Very low frequency (VLF) radio waves propagate within the Earth-ionosphere waveguide with very little attenuation. Modifications of the waveguide geometry effect the propagation conditions, and hence, the attenuation. Changes in the ionosphere, such as the presence of the D-region during the day, or the precipitation of energetic particles, are the main causes of this modification. Using narrowband receivers monitoring VLF transmitters, the amplitude and phase of these signals are recorded. Multivariate data analysis techniques, namely Principal Component Analysis (PCA) and Singular Spectrum Analysis (SSA), are applied to the data in order to determine parameters, such as seasonal and diurnal changes, affecting the variation of these signals. Transient effects may then be easier to detect.

289

Analysis of coronal emissions observed at meter wavelengths  

Science.gov (United States)

We present an extensive analysis of large and medium scale radio sources observed with the Nançay Radioheliograph at 169 MHz, over more than four solar rotations in 1984 (during the declining phase of the solar cycle). The large scale emission is dominated by the coronal plateau, the radio counterpart of the coronal plasma sheet, which had an oscillatory structure around the equator. Medium scale local sources include both faint noise storm continua and thermal sources. Noise storm continua have greater brightness (8 105 to 3.8 106 K) and smaller diameter than thermal sources. We present distributions of brightness temperatures, sizes as well as longitude and latitude of the thermal sources and we study their location with respect to faculae and neutral lines. Based on their rotation rate, we estimate their altitude at 70 000 km. We find that most thermal sources at 169 MHz are located between faculae and neutral lines and we present a geometrical model to account for this observation, according to which these sources are located in the upper leg of large scale loops. A small number of thermal sources is closer to neutral lines; these might be loops at the base of isolated coronal streamers.

Lantos, P.; Alissandrakis, C. E.

1999-11-01

290

Source location of chorus emissions observed by Cluster  

Directory of Open Access Journals (Sweden)

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

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

M. Parrot

291

Analysis and Modeling of Jovian Radio Emissions Observed by Galileo  

Science.gov (United States)

Our studies of Jovian radio emission have resulted in the publication of five papers in refereed journals, with three additional papers in progress. The topics of these papers include the study of narrow-band kilometric radio emission; the apparent control of radio emission by Callisto; quasi-periodic radio emission; hectometric attenuation lanes and their relationship to Io volcanic activity; and modeling of HOM attenuation lanes using ray tracing. A further study of the control of radio emission by Jovian satellites is currently in progress. Abstracts of each of these papers are contained in the Appendix. A list of the publication titles are also included.

Menietti, J. D.

2003-01-01

292

Two Daytime Observations of Atomic Nitrogen Emissions in the Thermosphere.  

Science.gov (United States)

The NII 2143 A doublet and the NI 8680 A multiplet have been observed in the daytime thermosphere as part of two rocket experiments conducted during moderate-to -high levels of solar activity. An ultraviolet grating spectrometer, a single channel photometer and a near-infrared grating spectrometer with a CCD detector were used in the experiments. Spectral data were obtained during limb viewing at tangent altitudes between 120 and 230 km. Molecular band shapes are calculated, and the atomic emissions are isolated by spectral fitting using a chi-square analysis. The ratio between the strengths of the doublet lines at 2139 A and 2143 A is found to be 0.58 +/- 0.08. The measured intensity of the NII 2143 A doublet is consistent with production by photodissociative ionization, based on solar flux and photoelectron models and laboratory cross sections for photon and electron impact excitation. The experiment used to detect the NI 8680 A multiplet reveals spectral intensities higher than predicted for photoelectron impact excitation, and photon impact on N_2 is shown to play the dominant role in the production of the NI 8680 A emission. The magnitude of a cross section for this process is obtained from the data by assuming that the wavelength dependence is described by the excitation function measured for the NI 1200 A line. The peak value of the NI 8680 A photoexcitation cross section is found to be 1.5times10^{-19} cm^2, accurate to within a factor of 5.

Bucsela, Eric John

293

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

International Nuclear Information System (INIS)

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

294

Electrostatic waves stimulated by coherent VLF signals propagating in and near the inner radiation belt  

International Nuclear Information System (INIS)

Recent ISEE 1 satellite observations indicate that electrostatic waves are commonly stimulated by coherent VLF electromagnetic whistler mode signals propagating on magnetic field lines in, and near, the inner radiation belt. Evidence for the existence of the electrostatic waves consists of apparent bandwidth increases of up to 300 Hz in the electric field component of 10 to 15 kHz signals from ground-based VLF transmitters observed in the inner radiation belt. During the period July through December 1983, the effect was observed on 60% of the satellite orbits which penetrated the inner radiation belts (L?2), and in many cases the effect was observed continuously from the magnetic equator at L?2 down to perigee. The effect appeared in signals propagating from sources in both the northern and southern hemispheres

295

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

Science.gov (United States)

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

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

2014-05-01

296

Solar eclipse effects on HF and VLF propagation  

International Nuclear Information System (INIS)

A multifrequency oblique-incidence experiment performed during the 10 July 1972 total solar eclipse is described. A definite correlation of VLF phase, HF signal strength, and geomagnetic field behaviour on eclipse day is demonstrated. Because of the relatively high transmitter powers available, ionospheric non-linearities observed during the eclipse period provided additional diagnostic information on oblique-incidence phenomena which are particularly sensitive to inverted ?.E is not equal to 0 along the propagation path. Turbulence is suggested as a major suppressant of charge-coupled effects in the lower ionosphere. If the observed eclipse behaviour is interpreted entirely in terms of atmospheric irregularities, severe but realistic constraints on mid-eclipse conditions are implied. At mid-eclipse a nearly impulsive perturbation presumably caused by a re-entering rocket was also noted. (author)

297

Tectonomagnetic and VLF electromagnetic signals in Central Italy  

Directory of Open Access Journals (Sweden)

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

P. Palangio

2004-06-01

298

Periodic bursts observed in Jovian decametric radio emission  

Science.gov (United States)

Dynamic radio spectra of Jovian decametric radio emission (DAM) acquired by STEREO/ WAVES, Wind/WAVES and Cassini/RPWS instruments have been analyzed in a frequency range from few MHz up to ˜16 MHz during the time interval between the years 2002-2008. The non-Io component of the DAM, which is the subject of our study, appears mainly in a form of arcs in time-frequency coordinates and is generally modulated by the Jovian ˜9.925 - hour rotation period (System III). Nevertheless, we have found several unusual episodes when non-Io related bursts recurred with a period of ˜10.07 hour which is ˜1.5% longer than the System III and shorter than the period of System IV (System III + 3%). The bursts were observed in a frequency range from ˜4-5 MHz to ˜12-16 MHz. Typically, the bursts recurred very periodically during several Jovian days with decreasing intensity and displayed negative drift in time-frequency domain. All bursts were detected within the same sector of Jovian Central Meridian Longitude (III), between 300° and 60° (via 360°) of CML (III), close to the region of non-Io-C source. The absence of any correlation with the position of Io has been found. Since the bursts were observed sequentially by STEREO-A and STEREO-B, as well as by Wind and Cassini during several Jovian rotations with proper time delay we can conclude that the source of the periodic bursts sub-corotates with Jupiter and it may be active during longer periods of time. The possible relation between the Io plasma torus and ˜10.07-hour periodic bursts of the DAM is discussed.

Panchenko, M.; Rucker, H. O.; Kaiser, M. L.; Bougeret, J. L.; Gurnett, D. A.

2009-12-01

299

Parametric excitation of ELF-waves and ion acceleration due to injection of strong VLF-waves into the ionosphere  

International Nuclear Information System (INIS)

It is shown according to the data from the Kosmos-1809 satellite that propagation of a strong whistler VLF-wave through the ionosphere is followed by generation of ELF waves and acceleration of ionospheric ions. Excitation of ELF waves correlated with the VLF transmitter pulses occurred in the 70-400 Hz frequency range with the intensity peak of about 8x10-6 V/m Hz1/2 140-180 Hz frequencies. Amplification of an ion flux in the VLF wave area took place in the 15-700 eV energy range. The maximum intensity of (2-4)x104 cm-2xs-1xeV-1xsr-1 was observed at 20-70 eV energies. The accelerated ion fluxes are anisotropic. The experimental results are explained by the mechanism of superthermal ion acceleration by electromagnetic ion-cyclotron waves excited in the ionospheric plasma during parametric instability of wistlers

300

Observations of neutral iron emission in twilight spectra  

Science.gov (United States)

A method is presented for the analysis of twilight airglow spectra that may be contaminated by atmospheric continuum emission of unknown brightness. The necessity of correcting for this continuum emission when measuring weak airglow features in twilight is illustrated by application of the method to the neutral iron line at 3860 A.

Tepley, C. A.; Meriwether, J. W., Jr.; Walker, J. C. G.; Mathews, J. D.

1981-01-01

 
 
 
 
301

Propagation and bouncing period of VLF waves through inhomogeneous magnetosphere  

International Nuclear Information System (INIS)

The effects of small scale field aligned and non-field aligned plasma inhomogeneities on the VLF wave propagation through the magnetosphere have been studied. It has been shown that the plasma inhomogeneities help the VLF wave guiding in magnetosphere. The expressions for phase and group refractive indices and bounce period have been obtained. It has been demonstrated that the VLF wave bounce period decreases due to the non-field aligned plasma inhomogeneities help the VLF wave guiding in magnetosphere. The expressions for phase and group refractive indices and bounce period have been obtained. It has been demonstrated that the VLF wave bounce period decreases due to the non-field aligned plasma inhomogeneities. (author)

302

Rocketborne Observations of Atmospheric Infrared Emissions in the Auroral Region.  

Science.gov (United States)

This paper briefly reviews the preliminary results of spectral measurements of IR atmospheric emissions in the wavelength region from 1.6 to 23 micrometers. These measurements were achieved using cryogenic spectrometers on six recent rocket flights for co...

A. T. Stair, K. D. Baker, J. C. Ulwick, D. J. Baker

1975-01-01

303

Extended radio emission in clusters of galaxies: recent Westerbork observations  

International Nuclear Information System (INIS)

The authors present radio emission results for five clusters studied with the WSRT: (i) Coma cluster - radio halo detected; (ii) Perseus cluster; (iii) Hercules cluster; (iv) A 2256; and (v) A1314. (U.M.G.)

304

VLF wave modulation by ion-cyclotron oscillations at heavy ion injection into the ionosphere  

International Nuclear Information System (INIS)

COMBI experiment data demonstrating modulation of VLF-waves by ion-cyclotron waves are studied and analyzed. Explanation of these observations is suggested on the basis of quasilinear generation of low-hybrid oscillations by ion beam. Stabilization of beam instability is reached due to the balance between the rate of wave generation under Cherenkov interaction with beam ions and rate of wave energy absorption by electrons. 14 refs

305

Fast emission estimates in China and South Africa constrained by satellite observations  

Science.gov (United States)

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

Mijling, Bas; van der A, Ronald

2013-04-01

306

The effect of weather on VLF measurements  

International Nuclear Information System (INIS)

Complete text of publication follows. The VLF experiment running at SANAE IV, Antarctica, has long been plagued by an unknown form of intermittent interference. Previously the prime suspect for this interference was the HF Radar, part of the SUPERDarn network, operated at SANAE IV. However, this instrument was not operational during the second half of 2008, and yet the interference was still prevalent. It is well known that the wind can set up mechanical oscillations in the antenna elements, causing periodic modulations in the loop area. We show evidence linking high wind speeds to this interference.

307

Subionospheric VLF imaging of lightning-induced electron precipitation from the magnetosphere  

International Nuclear Information System (INIS)

High-resoluton measurements of subionospheric VLF signals at multiple sites are used as a new tool to assess the spatial distribution and occurrence of ionospheric disturbances associated with lightning-induced electron precipitation. Simultaneous observations in California, Saskatchewan, and Quebec of VLF signals from multiple sources allow the monitoring of event activity over a course grid covering the continental US. Association of the observed VLF signal perturbations with lightning is often made on the basis of time correlation with prominent radio atmospherics. Simultaneous observations of individual events on subionospheric paths that cross one another are used to locate the disturbed ionospheric region(s). Absence of perturbations on nearby paths permits assessment of the spatial exstent of the region with a varying degree of accuracy, depending on the distribution of signal paths. In one case distinctly different onset delays (with respect to causative discharges) consistent with predictions of whistler-particle scattering theory were found, and were interpreted as being due to two separate regions separated in L value by ? 0.4 L being excited in individual events. Occurrence statistics over the course of October 1987 exhibit generally higher levels of activity at the lower-latitude end of the 2 100 km off the great circle paths is not significant

308

Observation method of the Barkhausen jumps by sound emission  

International Nuclear Information System (INIS)

The recording of acoustic emission, accompanying remagnetization of ferromagnetics and conditioned by the Barkhausen jumps, has been described. The use of acoustic method in combination with traditional electromagnetic method of the Barkhausen effect recording when studying the remagnetization processes permits to separate the remagnetization process at the expense of 180 deg - and 90 deg - domain shifts. Experiments on nickel and structural steel 34KhN3M have shown a linear connection between mean qUadratic values of acoustic emission signals and magnetostriction value. Using the method suggested it is possible to record the presence of magnetostriction > or approximately 0.35x10-6

309

? vector measurements of VLF signals by the satellite EXOS-D  

International Nuclear Information System (INIS)

On board the EXOS-D (Akebono) satellite is a five channel PFX subsystem of VLF instruments, working to determine the wave normal of ? vector and Poynting vector directions by measuring two components of E and three components of B fields using wire and loop antennas. In order to confirm the characteristics or capability of determining the ? vector and the Poynting vector of a coherent VLF Omega signal transmitted from Australia have been analyzed. The observed Omega signal has been found to be right-handed polarized with Poynting vector is making a small angle with the geomagnetic field and lies nearly on the plane constructed by the geomagnetic field and ? vector. The refractive index deduced from the E and B fields well agrees with that calculated by Appleton Hartree formula

310

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

311

Methane emissions from Alaska in 2012 from CARVE airborne observations.  

Science.gov (United States)

We determined methane (CH4) emissions from Alaska using airborne measurements from the Carbon Arctic Reservoirs Vulnerability Experiment (CARVE). Atmospheric sampling was conducted between May and September 2012 and analyzed using a customized version of the polar weather research and forecast model linked to a Lagrangian particle dispersion model (stochastic time-inverted Lagrangian transport model). We estimated growing season CH4 fluxes of 8 ± 2 mg CH4?m(-2)?d(-1) averaged over all of Alaska, corresponding to fluxes from wetlands of [Formula: see text] mg CH4?m(-2)?d(-1) if we assumed that wetlands are the only source from the land surface (all uncertainties are 95% confidence intervals from a bootstrapping analysis). Fluxes roughly doubled from May to July, then decreased gradually in August and September. Integrated emissions totaled 2.1 ± 0.5 Tg CH4 for Alaska from May to September 2012, close to the average (2.3; a range of 0.7 to 6 Tg CH4) predicted by various land surface models and inversion analyses for the growing season. Methane emissions from boreal Alaska were larger than from the North Slope; the monthly regional flux estimates showed no evidence of enhanced emissions during early spring or late fall, although these bursts may be more localized in time and space than can be detected by our analysis. These results provide an important baseline to which future studies can be compared. PMID:25385648

Chang, Rachel Y-W; Miller, Charles E; Dinardo, Steven J; Karion, Anna; Sweeney, Colm; Daube, Bruce C; Henderson, John M; Mountain, Marikate E; Eluszkiewicz, Janusz; Miller, John B; Bruhwiler, Lori M P; Wofsy, Steven C

2014-11-25

312

Beta-delayed proton emission observed in new lanthanide isotopes  

International Nuclear Information System (INIS)

Several new measurements of proton emission decay isotopes are reported. Protons were measured in coincidence with positrons, gammas and x-rays. Isotopes were produced by 200-500 MeV heavy ion fusion reactions. Half-lives are reported for dysprosium, gadolinium, cerium, neodymium and lanthanum isotopes and representative cerium proton spectra are shown

313

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

International Nuclear Information System (INIS)

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

314

Signature of burst particle precipitation on VLF signals propagating in the Antarctic earth-ionosphere waveguide  

Energy Technology Data Exchange (ETDEWEB)

The burst precipitation of energetic electrons ({ge} 40 keV), induced by interactions with lightning-generated whistler mode waves, has been observed to cause phase and amplitude perturbations on subionospheric VLF signals (Trimpi events). With a knowledge of the propagation characteristics of the subionospheric signal, analysis of the perturbation details can lead to estimates of the energy, extent, and location of the precipitation. Trimpi events have been observed on VLF signals propagating at high latitudes (L {ge} 4) over Antarctica, on 3.79-kHz signals as they propagate from Siple toward VLF receivers at Halley and South Pole stations. To simulate the effects of precipitation, localized depressions in the ionospheric reflection height are introduced over the great circle propagation paths in the model, and it is seen that, while the amplitude (up to 6 dB) Trimpi events at Halley cannot be reproduced. Calculations are presented which show that signals echoing from precipitation patches located away from the great circle path could be the cause of such signatures.

Cotton, P.D. (Univ. of Sheffield (United Kingdom)); Smith, A.J. (Natural Environment Research Council, Cambridge (United Kingdom))

1991-11-01

315

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

316

The auroral 6300 angstrom emission: Observations and modeling  

International Nuclear Information System (INIS)

Measurements of the auroral atomic oxygen (3P-1D) emission line at 6300 angstrom made by the Atmosphere Explorer visible airglow experiment are analyzed using a tomographic inversion. Emission altitude profiles are compared to the results from an electron transport and chemical reaction model. The model incorporates measurements of the energetic electron flux, neutral composition, ion composition, and electron density. Reasonable correspondence is obtained using primarily the classical sources of O(1D) excitation: electron impact on atomic oxygen and dissociative recombination of O2+. The reaction of N(2D) with O2 is considered to be a minor source. Small contribution are also calculated for cascade from O(1S), electron impact dissociation of O2, reaction of N+ with O2, and energy transfer from O+(2D) and thermal electrons to O(3P). A possible minor source from the quenching of N(2D) or N(2P) by O(3P) is also discussed

317

Rashba-type surface emission observed on W(110)  

International Nuclear Information System (INIS)

In this contribution we discuss surface related spectral features of bcc W(110) by means of angle- and spin-resolved photoemission. For more than thirty years Tungsten serves as a prototypical material for studying spin-orbit effects in simple metals. Also, it is used for a quite long time in electron polarimeters. Nevertheless, there still remain some pecularities in its electronic structure concerning surface emission. It is known that a surface resonance exists on W(110) dispersing around anti ? in the vicinity of the Fermi level. But not much is understood concerning surface emission for higher binding energies. From our investigation we found that surface emission dominates the E(k parallel) intensity distribution measured along ?N. The spin analysis reveals a Rashba-like behavior for features related to the spin-orbit induced symmetry gap existing at anti ?. The theoretical analysis has been performed in the framework of the fully relativistic version of the one-step model of photoemission.

318

Observations of twilight helium 10830 A emission with an tilting filter photometer  

International Nuclear Information System (INIS)

A tilting filter photometer was used to observe the helium 10830 A emission in twilight. The observed intensities of the helium emission show the seasonal variation. The enhancement occurs in winter. It agrees with the previous observation of Christensen et al. It was observed also that the solar zenith angle dependencies of the intensity variations differ in the evening and morning twilights. It can be explained by the asymmetry of the exospheric temperature in evening and morning qualitatively. (author)

319

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

International Nuclear Information System (INIS)

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

320

Cold plasma diagnostics using satellite measurements of VLF signals from ground transmitters  

International Nuclear Information System (INIS)

A new diagnostic technique to obtain the cold plasma density profile in the magnetosphere is introduced. This method uses satellite measurements of group delay and pulse duration of VLF signals from ground transmitters in conjunction with a detailed ray tracing analysis. An iterative method is involved. This method starts with an approximate density profile, computes the ray paths for that profile, and then compares the properties of the rays that reach the satellite location with the actual satellite measurements. The density profile is then modified to account for any discrepancies between the two results. The same process is repeated with the new profile until one has reasonable agreement between the data and ray tracing results. This method is applied to the case of an Imp 6 pass on June 28, 1973, where strong signals from the Siple VLF transmitter were observed for over 25 min. Good agreement is found between the results of the new technique and the well-known ground whistler techniques of cold plasma diagnostics. The results also serve to illustrate the wide diversity paths of propagation from ground transmitters to high-altitude satellites during VLF wave injection experiments

 
 
 
 
321

Analysis of auroral infrared emissions observed during the ELIAS experiment  

Directory of Open Access Journals (Sweden)

Full Text Available The ELIAS (Earth Limb Infrared Atmospheric Structure experiment was flown from the Poker Flat Research Range, Alaska in 1983 and successfully monitored visible and infrared emissions from an IBC III+ aurora. Measurements were performed in both staring and scanning modes over several hundred seconds. The data for short- and mid-wave infrared regions have been analyzed in terms of auroral excitation of the NO and NO+ vibrational bands. Auroral excitation efficiencies and kinetic implications are presented.

G. E. Caledonia

322

Lightning-induced effects on VLF/LF radio propagation  

Science.gov (United States)

In recent years, at least two different ways in which energy from lightning discharges couples into the lower ionosphere and the radiation belts have come to the fore. In this paper, we briefly review these recent results especially from the point of view of their effects on VLF/LF radio propagation in the earth-ionosphere wave guide. We separately discuss two different mechanisms of coupling, namely lightning-induced electron precipitation, and lightning-induced heating and ionization of the lower ionosphere. We also discuss a planned active VLF wave-injection experiment designed to investigate ionospheric heating by VLF waves under controlled conditions and to generate ELF waves by modulated VLF heating.

Inan, U. S.; Rodriguez, J. V.

1993-01-01

323

Lower ionosphere electron density profiling with data from VLF receivers  

Science.gov (United States)

In this work we present the method for estimation of Wait's parameters H? and ? directly from measured electrical intensities of distant VLF transmitters. A very simple approach using Earth-ionosphere waveguide with highly conductive walls is used.

Hube?ák, Josef; Šlégr, Jan

2014-01-01

324

Coronal emission line profile observations at total solar eclipses. I  

International Nuclear Information System (INIS)

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

325

Energetic electron precipitation and VLF phase disturbances at middle latitudes following the magnetic storm of December 6, 1971  

International Nuclear Information System (INIS)

Enhanced fluxes of electrons precipitating over middle latitudes (L approx. 3--4) were detected by the polar-orbiting satellite 1971-089A following a period of magnetic activity starting on December 16, 1971. The electron fluxes measured in 256 differential channels between 130 and 2800 keV have been coordinated with phase observations of VLF radio waves propagating in the earth-ionosphere waveguide. The VLF paths in question, NLK (near Seattle, Washington) and GBR (at Rugby, England) to APL (near Washington, D. C.), cover approx. =1200 in longitude and range from L approx. 2.5 to L approx. 4.0 in invariant latitude. These paths showed marked daytime and nighttime phase advances from 1650 UT on December 17 (in excess of 10 ?s during maximum disturbance). The phase values did not return to prestorm levels before December 22--23. The unusual presence of these daytime VLF disturbances is offered as evidence for the widespread precipitation at low L shell vales of nearly relativistic electrons (E/sub e/> approx.200 keV) which would be required to penetrate below approx.70-km altitude to affect the daytime VLF transmissions. Wave guide mode calculations using D region electron density profiles deduced from the satellite particle data predict phase advances which agree reasonably well with the observed values. It is concluded that the observed long-lived VLF phase disturbances can be explained by excess D region ionization caused by energetic electrons precipitating from the earth's radiation belt following their injection deep into the magnetosphere during the magnetic storm

326

Detecting organic groundwater contamination using electrical resistivity and VLF surveys  

Energy Technology Data Exchange (ETDEWEB)

Geophysical methods can be helpful in mapping areas of contaminated soil and groundwater. Electrical resistivity (ER) and very low frequency electromagnetic (VLF EM) induction surveys were carried out at a site of shallow hydrocarbon contamination. Previously installed monitoring wells facilitated analysis of water chemistry to enhance interpretation of the geophysical data. The ER and VLF EM data correlate well and were used to map the contaminant plume, which was delineated as an area of high apparent and interval resistivities.

Benson, A.K.; Payne, K.L. [Brigham Young Univ., Provo, UT (United States). Dept. of Geology; Stubben, M.A. [Univ. of Arizona, Tucson, AZ (United States)

1995-12-31

327

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

International Nuclear Information System (INIS)

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. (author)

328

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

International Nuclear Information System (INIS)

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

329

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

330

Skycorr: Sky emission subtraction for observations without plain sky information  

Science.gov (United States)

Skycorr is an instrument-independent sky subtraction code that uses physically motivated line group scaling in the reference sky spectrum by a fitting approach for an improved sky line removal in the object spectrum. Possible wavelength shifts between both spectra are corrected by fitting Chebyshev polynomials and advanced rebinning without resolution decrease. For the correction, the optimized sky line spectrum and the automatically separated sky continuum (without scaling) is subtracted from the input object spectrum. Tests show that Skycorr performs well (per cent level residuals) for data in different wavelength regimes and of different resolution, even in the cases of relatively long time lags between the object and the reference sky spectrum. Lower quality results are mainly restricted to wavelengths not dominated by airglow lines or pseudo continua by unresolved strong emission bands.

Noll, S.; Kausch, W.; Kimeswenger, S.; Barden, M.; Jones, A. M.; Modigliani, A.; Szyszka, C.; Taylor, J.

2014-08-01

331

Beta-delayed proton emission observed in new lanthanide isotopes  

International Nuclear Information System (INIS)

The following new, beta-delayed proton emitters have been observed at the on-line isotope separator OASIS: 120La (2.8+-2s), 122La (8.7+-.7s), 123Ce (3.8+-.2s), 141Dy (1.0+-.2s), 141Gd, and 143Dy (3.2+-.6s). Z-identification was achieved through observation of characteristic X-rays in coincidence with protons. (orig./HSI)

332

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

333

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 fo...

Kaiser, J. W.; Heil, A.; Andreae, M. O.; Benedetti, A.; Chubarova, N.; Jones, L.; -j Morcrette, J.; Razinger, M.; Schultz, M. G.; Suttie, M.; Werf, G. R.

2012-01-01

334

Radio observational constraints on Galactic 3D-emission models  

Digital Repository Infrastructure Vision for European Research (DRIVER)

(Abridged) We constrain simulated all-sky maps in total intensity, linear polarization, and rotation measure (RM) by observations. We test a number of large-scale magnetic field configurations and take the properties of the warm interstellar medium into account. From a comparison of simulated and observed maps we are able to constrain the regular large-scale Galactic magnetic field in the disk and the halo of the Galaxy. The local regular field is 2 microG and the average ra...

Sun, X. H.; Reich, W.; Waelkens, A.; Enßlin, T.

2007-01-01

335

Coronal emission line profile observations at total solar eclipses. II  

International Nuclear Information System (INIS)

High resolution spectra of the coronal emission line Fe XIV at 530.3 nm obtained at the 30 May 1965 total solar eclipse are analyzed and interpreted. Deconvolution techniques that preserve the line intensity vs wavelength profile shape are developed to obtain further resolution improvement. The west limb coronal enhancement is determined to have temperatures less than 3 MK and turbulent velocities of approximately 25 kms-1 decreasing with altitude. Temperature gradients provide evidence for marginal solar wind flow from this enhancement. Above the quiet photosphere in the southwest quadrant the comparison of line and continuum intensities and consideration of line width suggest to us the coronal region is filled with inhomogeneous plasma, dense enough in localized regions to maintain collisional excitation. Solar wind flow from this region obtains when turbulent velocities are assumed to contribute to the line broadening. This region is identified as a coronal hole and it is suggested that coronal material is heated by the quiet photosphere below. (Auth.)

336

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

337

Suzaku Observations of Abell 1795: Cluster Emission to R_200  

CERN Document Server

We report Suzaku observations of the galaxy cluster Abell 1795 that extend to r_200 ~ 2 Mpc, the radius within which the mean cluster mass density is 200 times the cosmic critical density. These observations are the first to probe the state of the intracluster medium in this object at r > 1.3 Mpc. We sample two disjoint sectors in the cluster outskirts (1.3 0.4 Mpc and find that it falls relatively rapidly (T ~ r^-0.9), reaching a value about one third of its peak at the largest radius we can measure it. Assuming the intracluster medium is in hydrostatic equilibrium and is polytropic, we find a polytropic index of 1.3 +0.3-0.2 and we estimate a mass of 4.1 +0.5-0.3 x 10^14 M_solar within 1.3 Mpc, somewhat (2.7-sigma) lower than that reported by previous observers. However, our observations provide evidence for departure from hydrostatic equilibrium at radii as small as r ~ 1.3 Mpc ~ r_500 in this apparently regular and symmetrical cluster.

Bautz, Marshall W; Sanders, Jeremy S; Arnaud, Keith A; Mushotzky, Richard F; Porter, F Scott; Hayashida, Kiyoshi; Henry, J Patrick; Hughes, John P; Kawaharada, Madoka; Makashima, Kazuo; Sato, Mitsuhiro; Tamura, Takayuki

2009-01-01

338

Radio emission from dusty galaxies observed by AKARI  

Science.gov (United States)

We probe radio-infrared correlation for two samples of extragalactic sources from the local Universe from the AKARI All-Sky Catalogue. The first, smaller sample (1053 objects) was constructed by the cross-correlation of the AKARI/FIS All-Sky Survey Bright Source Catalogue, the AKARI IRC All-Sky Survey Point Source Catalogue and the NRAO VLA Sky Survey, i.e. it consists of sources detected in the mid- and far-infrared by AKARI, and at the 1.4 GHz radio frequency by NRAO. The second, larger sample (13,324 objects) was constructed by the cross-correlation of only the AKARI/FIS All-Sky Survey Bright Source Catalogue and the NRAO VLA Sky Survey, i.e. it consists of sources detected in the far-infrared and radio, without a condition to be detected in the mid-infrared. Additionally, all objects in both samples were identified as galaxies in the NED and/or SIMBAD databases, and a part of them is known to host active galactic nuclei (AGNs). For the present analysis, we have restricted our samples only to sources with known redshift z. In this paper, we analyse the far-infrared-radio correlation for both of these samples. We compare the ratio of infrared and radio emission from normal star-forming dusty galaxies and AGNs in both samples. For the smaller sample we obtained =2.14 for AGNs and =2.27 for normal galaxies, while for the larger sample =2.15 for AGNs and =2.22 for normal galaxies. An average value of the slope in both samples is ~2.2, which is consistent with the previous measurements from the literature.

Pepiak, A.; Pollo, A.; Takeuchi, T. T.; Solarz, A.; Jurusik, W.

2014-10-01

339

Propagational Assessment of VLF Navigation Signals in North America and the North Atlantic.  

Science.gov (United States)

Requirements for vlf navigation signals are summarized. Various signals, both vlf communications and Omega and both day and night, are evaluated theoretically. Signal-to-noise ratio and signal structure are considered. Special attention is directed toward...

E. R. Swanson, M. J. Dick

1975-01-01

340

ALMA Capabilities for Observations of Spectral Line Emission  

CERN Document Server

The Atacama Large Millimeter/submillimeter Array (ALMA) combines large collecting area and location on a high dry site to provide it with unparalleled potential for sensitive millimeter/submillimeter spectral line observations. Its wide frequency coverage, superb receivers and flexible spectrometer will ensure that its potential is met. Since the 1999 meeting on ALMA Science\\cite{RefA}, the ALMA team has substantially enhanced its capability for line observations. ALMA's sensitivity increased when Japan joined the project, bringing the 16 antennas of the Atacama Compcat Array (ACA), equivalent to eight additional 12m telescopes. The first four receiver cartridges for the baseline ALMA (Japan's entry has brought two additional bands to ALMA's receiver retinue) have been accepted, with performance above the already-challenging specifications. ALMA's flexibility has increased with the enhancement of the baseline correlator with additional channels and flexibility, and with the addition of a separate correlator f...

Wootten, A

2007-01-01

 
 
 
 
341

Observations and predictions of EUV emission from classical novae  

International Nuclear Information System (INIS)

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

342

Observations of CO and 13CO emission from the molecular complexes in Orion  

International Nuclear Information System (INIS)

Microwave emission from the J = 1 ? 0 transition of 12O16O and 13O16O was observed over an area of 28 square degrees in the Orion region. The observations reveal the existence of two giant molecular complexes, a northern and a southern cloud, which are roughly aligned with the dust clouds in which Ori A and Ori B are embedded. Peaks in both CO and 13CO emisson can be identified with regions of prominent emission and reflection nebulae. Observable CO emission from the northern cloud covers about 750 pc2, while emission from the southern cloud covers about 1500 pc2. Observable 13CO emission is seen only in the inner 33% core area in both the northern and southern clouds in which CO emission is found. The total mass of the molecular complexes, derived from the LTE 13CO column density related to molecular hydrogen column density, is > 7 x 104 M sub solar, thus a sizable fraction of matter in the Orion region is in the form of molecular hydrogen. Although the northern and southern complexes are in the same region in the sky and at the same distance, the two clouds appear to be separate entities. The CO and 13Co emission is localized around the emission and reflection nebulae in the northern cloud, while emission in the southern cloud is concentrated in a ridge which extends along the length of the cloud. The emission in the northern cloud has no systematic velocity structure, while the CO emission in the southern cloud has a velocity gradient that is indicative of rotation

343

Top-down estimate of China's black carbon emissions using surface observations: Sensitivity to observation representativeness and transport model error  

Science.gov (United States)

This study examines the sensitivity of "top-down" quantification of Chinese black carbon (BC) emissions to the temporal resolution of surface observations and to the transport model error associated with the grid resolution and wet deposition. At two rural sites (Miyun in North China Plain and Chongming in Yangtze River Delta), the model-inferred emission bias based on hourly BC observations can differ by up to 41% from that based on monthly mean observations. This difference relates to the intrinsic inability of the grid-based model in simulating high pollution plumes, which often exert a larger influence on the arithmetic mean of observations at monthly time steps. Adopting the variation of BC to carbon monoxide correlation slope with precipitation as a suitable measure to evaluate the model's wet deposition, we found that wet removal of BC in the model was too weak, due in part to the model's underestimation of large precipitation events. After filtering out the observations during high pollution plumes and large precipitation events for which the transport model error should not be translated into the emission error, the inferred emission bias changed from -11% (without filtering) to -2% (with filtering) at the Miyun site, and from -22% to +1% at the Chongming site. Using surface BC observations from three more rural sites (located in Northeast, Central, and Central South China, respectively) as constraints, our top-down estimate of total BC emissions over China was 1.80 ± 0.65 Tg/yr in 2006, 0.5% lower than the bottom-up inventory of Zhang et al. (2009) but with smaller uncertainty.

Wang, Xuan; Wang, Yuxuan; Hao, Jiming; Kondo, Yutaka; Irwin, Martin; Munger, J. William; Zhao, Yongjing

2013-06-01

344

The plasma wave environment of an auroral arc. 3. VLF hiss  

International Nuclear Information System (INIS)

Intense auroral hiss was observed by a sounding rocket payload under circumstances that have allowed detailed comparison of the hiss spectrum with the predictions of a convective beam amplification hiss production model. Auroral hiss was first encountered at the poleward edge of the diffuse aurora, and was observed for the rest of the flight. A maximum intensity of 10-8(V/m)2/Hz at 30 kHz was seen in the dark region. Electron distribution functions were seen with ?f/?vparallel > 0 and a large enough slope to have produced appreciable VLF amplification. These distributions were found in a region a few kilometers wide on the equatorward boundary of the arc. A model distribution function has been fitted to one of the observed distributions and used as input into an auroral beam noise generation model. Reasonable assumptions about the distribution of cold plasma and width of the unstable region yields a predicted VLF spectrum in good agreement with observation. Several secondary results were also obtained. The observed VLF hiss does not appear to have been produced by a payload-plasma interaction. The intensity of the hiss measured in situ, above the ionosphere, was greater equatorward of the arc than within the arc, thus ruling out the ionospheric transmission model as an explanation for this intensity pattern. Quasi-linear back reaction on the electron distribution was not found to be significant in this case. The correlation between 0.1-0.7 keV electron flux and hiss intensity was not better than the correlation with the flux of 5-keV electrons

345

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

346

Assessing Greenhouse Gas emissions in the Greater Toronto Area using atmospheric observations (Invited)  

Science.gov (United States)

Urban areas are said to be responsible for approximately 75% of anthropogenic Greenhouse Gases (GHGs) emissions while comprising only two percent of the land area [1]. This limited spatial expansion should facilitate a monitoring of anthropogenic GHGs from atmospheric observations. As major sources of emissions, cities also have a huge potential to drive emissions reductions. To effectively manage emissions, cities must however, first measure and report these publicly [2]. Modelling studies and measurements of CO2 from fossil fuel burning (FFCO2) in densely populated areas does, however, pose several challenges: Besides continuous in-situ observations, i.e. finding an adequate atmospheric transport model, a sufficiently fine-grained FFCO2 emission model and the proper background reference observations to distinguish the large-scale from the local/urban contributions to the observed FFCO2 concentration offsets ( ?FFCO2) are required. Pilot studies which include the data from two 'sister sites*' in the vicinity of Toronto, Canada helped to derive flux estimates for Non-CO2 GHGs [3] and improve our understanding of urban FFCO2 emissions. Our 13CO2 observations reveal that the contribution of natural gas burning (mostly due to domestic heating) account for 80%×7% of FFCO2 emissions in the Greater Toronto Area (GTA) during winter. Our 14CO2 observations in the GTA, furthermore, show that the local offset of CO2 (?CO2) between our two sister sites can be largely attributed to urban FFCO2 emissions. The seasonal cycle of the observed ?FFCO2 in Toronto, combined with high-resolution atmospheric modeling, helps to independently assess the contribution from different emission sectors (transportation, primary energy and industry, domestic heating) as predicted by a dedicated city-scale emission inventory, which deviates from a UNFCCC-based inventory. [1] D. Dodman. 2009. Blaming cities for climate change? An analysis of urban greenhouse gas emissions inventories. Environment and Urbanization, 21,185. [2] Arikan Y., Desaim R., Bhatia P. and W. K. Fong, 2012 Global Protocol for Community-Scale Greenhouse Gas Emissions (GPC), C40 Cities Climate Leadership group, available at: http://www.c40.org [3] Vogel, F. R., Ishizawa, M., Chan, E., Chan, D., Hammer, S., Levin, I., & Worthy, D. E. J. (2012). Regional non-CO2 greenhouse gas fluxes inferred from atmospheric measurements in Ontario, Canada. Journal of Integrative Environmental Sciences, 9(1), 41-55. *The term 'sister sites' refers to sites that share a common background signal (i.e. common large scale influence), while significantly differing sensitivities to urban GHG emissions. In our case: Egbert, Ontario and Downsview, Toronto, Ontario.

Vogel, F. R.; Chan, E.; Huang, L.; Levin, I.; Worthy, D.

2013-12-01

347

A generation mechanism of chorus emissions using BWO theory  

Energy Technology Data Exchange (ETDEWEB)

In this paper, discrete VLF chorus emissions recorded at low latitude ground station Jammu (geomag. Lat. = 22{sup 0} 26{sup /} N, L = 1.17) are reported and their characteristics based on complete spectral analysis have been carried out. These discrete chorus emissions are generated during a strong geomagnetic storm period of 2-7 May, 1998. We have computed the sweep rate, repetition period, source region, and drift rate of the individual chorus elements. It is observed that the sweep rate increases with time. To explain the various temporal and spectral features of these emissions, a possible generation mechanism has been presented based on the backward wave oscillator (BWO) regime in the magnetospheric cyclotron maser. On the basis of this model, we have computed some discrete chorus emission parameters as well as magnetospheric parameters relevant to the generation process. A comparison of the computed and observed magnetospheric parameters has been presented. These results show a good agreement with the BWO model.

Singh, Ashutosh K; Singh, K K; Singh, A K; Patel, R P [Department of Physics, M. M. H. P. G. College, Ghaziabad (India); Singh, R, E-mail: abhay_s@rediffmail.co [Indian Institute of Geomagnetism, Navi Mumbai (India)

2010-02-01

348

A dynamic bandwidth and phase linearity measurement technique for 4-channel MSK VLF antenna systems  

Science.gov (United States)

This paper presents a method for performing dynamic measurements of antenna bandwidth and phase linearity parameters for VLF transmitter systems. These measurements were undertaken in support of both National and NATO VLF MSK upgrade programs and relate to VLF transmitting antenna characteristics required in order to comply with STANAG 5030.

Harrington, M. D.

1993-05-01

349

Factorization of air pollutant emissions: projections versus observed trends in Europe.  

Science.gov (United States)

This paper revisits the emission scenarios of the European Commission's 2005 Thematic Strategy on Air Pollution (TSAP) in light of today's knowledge. We review assumptions made in the past on the main drivers of emission changes, i.e., demographic trends, economic growth, changes in the energy intensity of GDP, fuel-switching, and application of dedicated emission control measures. Our analysis shows that for most of these drivers, actual trends have not matched initial expectations. Observed ammonia and sulfur emissions in European Union in 2010 were 10% to 20% lower than projected, while emissions of nitrogen oxides and particulate matter exceeded estimates by 8% to 15%. In general, a higher efficiency of dedicated emission controls compensated for a lower-than-expected decline in total energy consumption as well as a delay in the phase-out of coal. For 2020, updated projections anticipate lower sulfur and nitrogen oxide emissions than those under the 2005 baseline, whereby the degree to which these emissions are lower depends on what assumptions are made for emission controls and new vehicle standards. Projected levels of particulates are about 10% higher, while smaller differences emerge for other pollutants. New emission projections suggest that environmental targets established by the TSAP for the protection of human health, eutrophication and forest acidification will not be met without additional measures. PMID:25058894

Rafaj, Peter; Amann, Markus; Siri, José G

2014-10-01

350

Application of satellite observations for timely updates to global anthropogenic NOx emission inventories  

Science.gov (United States)

Anthropogenic emissions of nitrogen oxides (NOx) can change rapidly due to economic growth or control measures. Bottom-up emissions estimated using source-specific emission factors and activity statistics require years to compile and can become quickly outdated. We present a method to use satellite observations of tropospheric NO2 columns to estimate changes in NOx emissions. We use tropospheric NO2 columns retrieved from the SCIAMACHY satellite instrument for 2003-2009, the response of tropospheric NO2 columns to changes in NOx emissions determined from a global chemical transport model (GEOS-Chem), and the bottom-up anthropogenic NOx emissions for 2006 to hindcast and forecast the inventories. We evaluate our approach by comparing bottom-up and hindcast emissions for 2003. The two inventories agree within 6.0% globally and within 8.9% at the regional scale with consistent trends in western Europe, North America, and East Asia. We go on to forecast emissions for 2009. During 2006-2009, anthropogenic NOx emissions over land increase by 9.2% globally and by 18.8% from East Asia. North American emissions decrease by 5.7%.

Lamsal, L. N.; Martin, R. V.; Padmanabhan, A.; van Donkelaar, A.; Zhang, Q.; Sioris, C. E.; Chance, K.; Kurosu, T. P.; Newchurch, M. J.

2011-03-01

351

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

352

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

Science.gov (United States)

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

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

1992-01-01

353

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

354

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

355

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

356

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

357

Pioneer 10 ultraviolet photometer observations of Jovian UV emission in 1973  

Science.gov (United States)

The Pioneer 10 ultraviolet measurements obtained during the Jupiter encounter in 1973 have been further examined by using improved data handling and analysis techniques. The Pioneer 10 observations of Jupiter and its satellites during the encounter have been carefully reviewed in order to improve our understanding of the morphology of the Io plasma torus and Jupiter's upper atmosphere and to investigate the possible existence of other emission source such as Europa. In addition, the morphology of Io's bimodal torus observed during the Pioneer 10 encounter has been compared with the Voyager observations obtained approximately 6 years after the Pioneer 10 flyby and significant differences in the torus characteristics are found. The Io torus in 1973 was more similar to the 1992 Ulysses observations of a longitudinally asymmetric ring than to the complete ring observed by Voyager. Pioneer 10 observed a significantly dimmer Io torus and Jupiter upper atmosphere in the EUV compared to the Voyager observations. Apart from the torus and Jupiter, Pioneer 10 observed additional emissions which have been attributed to Io itself. Three distinct possibilities have been discussed to explain these additional emissions. The most likely is that Pioneer 10 observed volcanism on Io. There is also evidence of Pioneer 10 observing emissions from Europa. The present analysis clearly shows that the Jovian system in 1973 was significantly different from that observed in 1979.

Wu, F. M.; Gangopadhyay, P.; Judge, D. L.

1995-01-01

358

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

International Nuclear Information System (INIS)

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

359

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

360

Inverse Modeling of Texas NOx Emissions using OMI NO2 Observations  

Science.gov (United States)

Uncertain emissions inventories for nitrogen oxides (NOx) are among the leading causes of uncertainty in simulating ozone concentrations and their sensitivities to emissions. Emission inventories from regulatory modeling are typically derived from bottom-up approaches. Satellite observations of NO2 column densities can provide top-down estimates of NOx emissions. Most of the major metropolitan regions in Texas exceed the proposed ozone standards, so accurate emissions inventories to inform attainment efforts are a high priority. Here, we apply NO2 column densities observed by OMI to estimate NOx emission rates over Texas and surrounding states. Modeling episodes developed for recent ozone attainment planning efforts are used to simulate relationships between NOx emissions and NO2 concentrations, using the Decoupled Direct Method (DDM) in CAMx. Inverse modeling uses these sensitivity relationships to estimate a posteriori emissions. Results are compared across alternate inverse modeling approaches that differ in the extent to which they retain the spatial structure of the a priori inventory. We also test the impact of including lightning NO emissions in the a priori inventory, and of incorporating ground-based measurements of NOx along with satellite data in the inversions. The resulting a posteriori emissions estimates are applied in the attainment modeling episodes, to evaluate their impact on model estimates of ozone concentrations and sensitivities to control strategies. At the same time, collaborators on this NASA-funded project are developing GOES satellite-based photolysis rates for these episodes. The relative impacts of satellite-based NOx emissions and photolysis rates will be compared.

Cohan, D. S.; Tang, W.

2011-12-01

 
 
 
 
361

Observation of green emission from Ce3+ doped gadolinium oxide nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Green emission at around 500 nm is observed in Gd2O3:Ce3+ nanoparticles and the intensity is highly dependent on the concentration of Ce3+ in the nanoparticles. The luminescence of this emission displays both picosecond and millisecond lifetimes. The msec lifetime is over four orders of magnitude longer than typical luminescence lifetimes (10-40 ns) of Ce3+ in traditional Ce3+ doped phosphors and therefore likely originates from defect states. The picosecond lifetime is shorter than the typical Ce3+ value and is also likely due to defect or surface states. When the samples are annealed at 700 oC, this emission disappears possibly due to changes in the defect moieties or concentration. In addition, a blue emission at around 430 nm is observed in freshly-prepared Gd2O3 undoped nanoparticles which is attributed to the stabilizer, polyethylene glycol biscarboxymethyl ether. Upon aging, the undoped particles show similar emission to the doped particles with similar luminescence lifetimes. When Eu3+ ions are co-doped in Gd2O3:Ce nanoparticles, both the green emission and the emission at 612 nm from Eu3+ are observed.

Woo, Boon K.; Joly, Alan G.; Chen, Wei

2011-01-01

362

Estimation of the emission cone width of Jovian DAM using STEREO/WAVES observations  

Science.gov (United States)

The SWAVES experiment onboard the Solar TErrestrial RElations Observatory (STEREO) is mainly dedicated to measuring solar radio emission, but also provides unique stereoscopic observations of the Jovian radio emission in a frequency range from a few kHz up to 16 MHz. Stereoscopic observations provided by STEREO-A and -B allow to unambiguously determinate sources of the observed radio emissions from the dynamic spectra by means of the knowledge of the time delay between sequential detection of the radio bursts from the same source, i.e. solar radio bursts, Jovian Io dependent or Io independent DAM. Using the limited number of the stereoscopic observations of the Jovian radio emission from Wind and Cassini, Kaiser et al. [2000] determined the thickness of the hollow cone of the DAM emission by means of correlation analysis of the observed spectra. In particular, it has been found that the averaged emission cone wall thickness is approximately 1.5 degree. The angular separation, as seen from Jupiter, between the two STEREO spacecraft, orbiting the Sun, approximately twice per year is less than 2.5 degree during several time spans from 2007-2009. Therefore, the method described in Kaiser et al. [2000] is applied to determine the statistically confident results of the beaming width of the Io and non-Io DAM observed during this time. Altogether 70 radio events, in particular 49 Io- and 21 non-Io-related radio events have been observed. We have determined the averaged width of the emission cone wall for Io- and non-Io events as of about 1 degree. These results confirm the previous findings.

Zörweg, P.; Panchenko, M.; Rucker, H. O.

2011-10-01

363

The south America VLF NETwork (SAVNET: Development, installation status, first results  

Directory of Open Access Journals (Sweden)

Full Text Available The South America VLF Network, a new observing facility at Very Low Frequencies is presented. It has been recently installed at different locations in Latin America (in Brazil, Peru and Argentina. It consists of a net- work of seven Very Low Frequency tracking receivers with the main scientific objective of monitoring the solar activity on short (minutes to hours and long (years time scales. Other objectives include a better understanding of the spatial structure of the South Atlantic Magnetic Anomaly, the study of atmospheric phenomena and the search for genuine seismic-electromagnetic effects.

P. Kaufmann

2009-07-01

364

Concentric structures observed in oxygen molecular airglow emission from the International Space Station  

Science.gov (United States)

Concentric structures in airglow emissions have been observed by ground based imagers. Some of concentric structures in airglow are said to be caused from the lower atmospheric disturbance. The whole images of these structures were not able to observe only by using ground based imagers since their field of views are smaller than the spatial scale of the concentric structures. Thus, the relationship between the structures in airglow emission and the lower atmosphere is not clarified yet. Visible and near-infrared spectrographic imager (VISI) was installed on the Exposure Facility of Japanese Experimental Module of the International Space Station at August, 2012. Nominal observation of VISI started in October 2012. This imager observes the airglow emission with two field-of-views in the nadir direction from ISS. Concentric structure of 762-nm O _{2} emission was observed on June 1, 2013 by VISI. This is the first case that the image from the edge to the center of the concentric structure was observed by a single imager from the space. The distance from the edge of the structure to the center estimated from the wave fronts in this case was 2,000 km. Atmospheric gravity waves whose wavelength was 80 km had estimated to propagate from its center with 110 m/s of phase velocity. There were active clouds under the center of the concentric structure at time of this VISI observation. This concentric structure is estimated to had brought from the vertical propagation from the tropospheric disturbance and atmospheric gravity wave had propagated in horizontal direction in the emission layer. Propagation in concentric structure was also seen in the F region by the GPS total electron content observations. Other concentric structures in airglow emission are also found in the VISI observations. Some statistical studies of the spatial scale and wavelengths dominant in these structures are also discussed in this study.

Akiya, Yusuke; Otsuka, Yuichi; Yamazaki, Atsushi; Saito, Akinori; Tsugawa, Takuya; Sakanoi, Takeshi; Nishioka, Michi; Hozumi, Yuta

365

Airborne VLF Measurements and Variations of Ground Conductivity: A Tutorial  

Science.gov (United States)

Airborne very low frequency (VLF) data are routinely collected by national agencies and commercial companies together with other passive geophysical measurements of the static magnetic field and radiometric data. The purpose of this paper is to demonstrate that both standard three-component VLF and tensor VLF (TVLF) data contain a lot of useful quantitative and qualitative information about the electrical conductivity distribution in the upper few hundred meters of the crystalline basement. We first give a new derivation of the fundamental transfer functions (the tipper) used in the TVLF technique. We then show that the tipper can be estimated from simultaneous measurements of the wave magnetic fields from at least two transmitters with somewhat different frequencies, and present a simple model by which the maximum error introduced by the difference in frequencies can be found. Single transmitter scalar VLF maps emphasise those conductive structures that have dominant strikes in the direction of the transmitter. Multiple transmitter transfer functions are dependent only upon the underlying conductivity structure. Two dimensional structures can be quantitatively modelled by modern inversion methods developed originally for deep electromagnetic magnetotelluric (MT) soundings. In such cases three-component VLF measurements can be modelled easily upon appropriate rotation of the co-ordinate system to “strike” co-ordinates. Single frequency transfer functions (tippers) have real and imaginary parts that carry information on not only lateral contrasts in conductivity, as usually stated in text books, but, taken together, they provide a robust tool for determining the background conductivity level away from distinct conductors, and they can also be used to discriminate between deep and shallow conductors. Based upon simulations using multi-frequency data, it can be concluded that such a new development would dramatically increase the resolving power of airborne VLF measurements.

Pedersen, Laust B.; Oskooi, Behrooz

2004-03-01

366

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

367

What can we learn from observations about the trend in reactive nitrogen emissions?  

Science.gov (United States)

Reactive nitrogen include compounds that are chemically, biologically, or radiatively active. Two important constituents are oxidized nitrogen (NOx), emitted largely from combustion, and ammonia (NH3), emitted largely from agriculture. A series of studies, including emission measurements and ambient observations, indicate NOx emissions in the US have decreased substantially over recent years. However, the trend in ammonia is not clear. This talk will focus on how we can use in situ and remote-sensing observations, as well as chemical transport models and inverse-modeling techniques to (1) improve our understanding of spatial and temporal emissions, (2) quantify the contribution from anthropogenic and natural sources, and (3) identify trends to determine progress toward regulatory goals. Finally, this talk will conclude with suggestions for how to incorporate the extensive findings from top-down emission inventory analysis into the regulatory decision-making process.

Pinder, R. W.

2011-12-01

368

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.

369

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)

370

Evidence for X-ray emission from flare stars observed by ANS  

International Nuclear Information System (INIS)

Observations that detected the first X-ray emission from flare stars are described. An X-ray flare was detected from YZ CMi at 0.28 keV and approx.1--7 keV, although no optical or radio coverage was available. During a very large optical flare from UV Ceti, X-ray emission at (only) 0.28 keV was detected. Upper limits for X-ray emission from several small optical flares of UV Ceti are presented. Implications for X-ray flare models, the diffuse X-ray background, and low-energy cosmic-ray flux are mentioned

371

FERMI LARGE AREA TELESCOPE OBSERVATIONS OF TWO GAMMA-RAY EMISSION COMPONENTS FROM THE QUIESCENT SUN  

International Nuclear Information System (INIS)

We report the detection of high-energy ?-rays from the quiescent Sun with the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope (Fermi) during the first 18 months of the mission. These observations correspond to the recent period of low solar activity when the emission induced by cosmic rays (CRs) is brightest. For the first time, the high statistical significance of the observations allows clear separation of the two components: the point-like emission from the solar disk due to CR cascades in the solar atmosphere and extended emission from the inverse Compton (IC) scattering of CR electrons on solar photons in the heliosphere. The observed integral flux (?100 MeV) from the solar disk is (4.6 ± 0.2[statistical error]+1.0-0.8[systematic error]) x 10-7 cm-2 s-1, which is ?7 times higher than predicted by the 'nominal' model of Seckel et al. In contrast, the observed integral flux (?100 MeV) of the extended emission from a region of 20 deg. radius centered on the Sun, but excluding the disk itself, (6.8 ± 0.7[stat.]+0.5-0.4[syst.]) x 10-7 cm-2 s-1, along with the observed spectrum and the angular profile, is in good agreement with the theoretical predictions for the IC emission.

372