WorldWideScience
1

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 altitgnals 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

2

Nonducted coherent VLF waves and associated triggered emissions observed on the ISEE-1 satellite  

Science.gov (United States)

A description is given of new observations of nonducted coherent VLF waves from ground-based transmitters and associated VLF emissions in the magnetosphere. The data reported were acquired by the Stanford University VLF Wave Injection Experiment on the ISEE-1 satellite. The experiment has four main components, including a broadband (1-32 kHz) VLF receiver on ISEE-1 connected to a long electric antenna, a broadband (1-20 kHz) controllable VLF transmitter located at Siple Station in the Antarctic, various VLF navigation and communications transmitters, and ground stations in the Antarctic and Canada. The main goal of the experiment is to acquire understanding of interactions between coherent VLF waves and energetic particles in the magnetosphere, in particular the whistler mode instability through which both natural and stimulated VLF emissions are produced.

Bell, T. F.; Inan, U. S.; Helliwell, R. A.

1981-01-01

3

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

4

On the observations of unique low latitude whistler-triggered VLF/ELF emissions  

Science.gov (United States)

A detailed analysis of the VLF/ELF wave data obtained during a whistler campaign under All India Coordinated Program of Ionosphere Thermosphere Studies (AICPITS) at our low latitude Indian ground station Jammu (geomag. lat. = 22° 26? N, L = 1.17) has yielded two types of unusual and unique whistler-triggered VLF/ELF emissions. These include (1) whistler-triggered hook emissions and (2) whistler-triggered long enduring discrete chorus riser emissions in VLF/ELF frequency range during night time. Such types of whistler-triggered emissions have not been reported earlier from any of the ground observations at low latitudes. In the present study, the observed characteristics of these emissions are described and interpreted. Dispersion analysis of these emissions show that the whistlers as well as emissions have propagated along a higher geomagnetic field line path with L-values lying ?L = 4, suggesting that these triggered emissions are to be regarded as mid-latitude emissions. These waves could have propagated along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal (PL) mode. The measured intensity of the triggered emissions is almost equal to that of the source waves and does not vary throughout the period of observation on that day. It is speculated that these emissions may have been generated through a process of resonant interaction of the whistler waves with energetic electrons. Parameters related to this interaction are computed for different values of L and wave amplitude. The proposed mechanism explains some aspects of the dynamic spectra.

Altaf, M.; Singh, K. K.; Singh, A. K.; Lalmani

5

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

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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

6

Simultaneous observation of various types of ELF/VLF emissions during daytime at a low latitude Indian ground station  

Science.gov (United States)

This paper reports unusual natural electromagnetic disturbances of various types in the ELF/VLF range received simultaneously during day time at a low latitude Indian ground station Jammu (geomag. lat., 220 26' N; L =1.17). A detailed spectrum analysis of the ELF/VLF data collected at Jammu over a time span of several years has yielded sum unusual and very interesting ELF/VLF emissions of different types recorded simultaneously during daytime on January 6, 1999. These include (1) discrete chorus riser emissions with multiple bands in the ELF range triggered from the sferic, (2) hook and inverted hook emissions in the ELF range triggered from the sferic, (3) double hook shaped emission in the ELF range, (4) long enduring ELF/VLF hiss triggered from the sferics and (5) band limited pulsing type of emissions in the ELF/VLF range. The observed characteristics of these ELF/VLF emissions occurring simultaneously are described. Our spectrum analysis clearly shows that these different type of emissions observed simultaneously are triggered by the lightning generated sferics, which is indicative of the embryonic effect of lightning in generating these observed emissions at Jammu. The various types of daytime emissions reported in this paper have been observed for the first time at a low latitude station. The unusual occurrence of these emissions in different frequency ranges may possibly be linked with their generation at different locations, and the occurrence of these emissions during daytime may be due to propagation to ground under the influence of equatorial anomaly in non-ducted mode of propagation. It is proposed that the different types of ELF/VLF emissions are generated through a process of resonant interaction of lightning generated whistler wave with energetic electrons.

Lalmani, Lalmani; Lalmani, Lalmani; Singh, A. K.

7

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

OpenAIRE

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 pr...

Singh, A. K.; Ro?nnmark, K.

2004-01-01

8

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

International Nuclear Information System (INIS)

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

9

Auroral pulsations and accompanying VLF emissions  

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

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

V. R. Tagirov

10

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

11

ELF/VLF emission and electrophonic sounds from Leonids identified  

Science.gov (United States)

Measurements of the ELF/VLF radio emission and electrophonic sounds were performed together with the video meteor observations during the activity of the Leonid meteor shower in 1998 over Mongolia. A number of ELF/VLF events were detected simultaneously with the observation of bright fireballs. One of them also with the electrophonic sound. For one event we have the electrophonic detected by the microphones and heard by observers, but the meteor is not directly visible on the video. This is the first unambiguous experimental confirmation that the ELF/VLF emission from a bright fireball can induce the electrophonic sound. Analysis of the complete data set is still in progress.

Vinkovic, Dejan

12

Irregular pulsations in simultaneous TV, IRIS and VLF observations  

OpenAIRE

The models of VLF emission generation are based on cyclotron wave-particle interaction mechanism. According to such models the generation of waves is accompanied by a modification of particles pitch-angle distribution, that can lead to their precipitation in a loss cone. The dissipation of energetic particles in the atmosphere is accompanied by excitation of auroral emissions at altitudes of 100-200 km, that is observed by optical instruments. If the precipitated particles are rather energeti...

Kozelov, B. V.; Titova, E. E.; Manninen, J.; Honary, F.; Marple, S.; Turunen, T.

2005-01-01

13

Observational detection of meteor-produced VLF electromagnetic radiation.  

Science.gov (United States)

In November 1998, the Croatian Physical Society's expedition to Mongolia was undertaken. The goal was to make measurements of the puzzling electrophonic sounds and very low frequency (VLF) radio emission from meteors during the anticipated Leonid meteor storm. During the night of 16/17 November 1998, an extremely high fireball activity of the Leonid meteors occurred. During this period, the authors performed measurements of the VLF radiation from meteors. They present a positive signal which consists of a sequence of sharp, short VLF bursts, coincident with the appearance of a meteor that was recorded by the video camera. This is the first completely controlled instrumental recording of such an event.

Garaj, S.; Vinkovic, D.; Zgrablic, G.; Kovacic, D.; Gradecak, S.; Biliskov, N.; Grbac, N.; Andreic, Z.

1999-09-01

14

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

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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

15

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

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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.

17

Magnetosphere VLF observation by satellite ISIS  

International Nuclear Information System (INIS)

On the basis of the VLF (50 Hz -- 30 kHz) electric field data from the satellite ISIS, the following works carried out in The Radio Research Laboratories are described: deuteron whistler and whistler duct, detection of plasmapause by LHR hiss, and the origin of 5 kHz hiss at low/middle latitudes. The deuteron whistlers are observable distinctly only at low latitude because of gyro-frequency and the frequency resolution of spectral analyzers. Whistler echo occurs when a whistler moves back and forth through a duct along the line of magnetic force, so it is considered that the ISIS satellite crosses the duct. The variation in ion composition around plasmapause obtained through LHR hiss is explainable by the plasamapause position and the magnetic storm effect on the plasamapause. Concerning the narrow band hiss of 5 kHz +- 1.0 kHz frequently observed on the ground at low/middle latitudes, it may occur around plasmapause, propagate through the ionosphere and then to the ground in waveguide mode, or otherwise, it may occur above the ionosphere and then propagate directly to the ground penetrating through the ionosphere. (J.P.N.)

18

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

CERN Document Server

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

Kachakhidze, Manana

2013-01-01

19

A test of incoherent Cerenkov radiation for VLF hiss and other magnetospheric emissions  

Science.gov (United States)

Consideration of incoherent Cerenkov radiation from intense fluxes of electrons in the magnetosphere as a source of VLF hiss and several other emission phenomena. A procedure for calculating the Cerenkov and cyclotron radiation power from a spectrum of electrons in a test volume is outlined, as well as a ray-tracing routine for determining the path that the emitted power follows through the magnetosphere. Comparisons are made between a VLF hiss event and an energetic particle spectrum observed simultaneously with the Injun 5 spacecraft. Calculated power and fields for incoherent Cerenkov radiation are two orders of magnitude below the observed VLf hiss values, although the spectral shapes are similar. It is concluded that a partially coherent or amplified Cerenkov source or an instability is located in the altitude range from 3000 to 10,000 km. Calculations regarding Cerenkov radiation as a possible source for other wave phenomena indicate that upper hybrid resonance noise and fast hisslers may be understood in terms of incoherent Cerenkov radiation, but that V-shaped VLF hiss, saucers, ELF hiss, and Io-related Jovian decametric radiation may not.

Taylor, W. W. L.; Shawhan, S. D.

1974-01-01

20

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

21

On the possible relations of non-Io DAM periodic bursts with Jovian VLF radio emission  

Science.gov (United States)

Periodic radio bursts of Jovian non-Io DAM[1], which are observed in the decametric frequency range of dynamic spectra as a series of reoccurring arc-like radio bursts with an averaged period of 10.07 hours, exhibit also strong correlation with a significant enhancement of the solar wind ram pressure around Jupiter. In this study we investigate the possible relations between the occurrence of the non-Io DAM periodic bursts and VLF components of the Jovian radiation such as narrow-band kilometric (nKOM) and "bulleye" radio emissions. The observations provided by Ulysses/URAP and Cassini/RPWS have shown that these VLF emissions are detected immediately after the passage of a solar wind pressure pulse, which crosses the Jovian magnetosphere every 13 or 26 days. This phenomenon can be explained by a strong interchange instability in the Io torus after strong solar wind pulses. We discuss the interchange instability, which can produce the VLF radio emission from the outer Io torus edge, as a possible mechanism of generation of the non-Io DAM periodic bursts.

Panchenko, M.; Rucker, H. O.; Farrell, W. M.

2011-10-01

22

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

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

A. Rozhnoi

2008-10-01

23

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

24

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

25

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

26

Atmospheric and ionospheric electrical parameter variations inferred from sub - ionospheric seismo - electromagnetic VLF/LF observations  

Science.gov (United States)

Subionospheric VLF/LF radio links are an essential tool to investigate seismo - electromagnetic phenomena. The propagation of very low (VLF) and low frequency (LF) frequency radio waves is mainly controlled by the index of refraction and electrical conductivity in the waveguide between the surface and the ionosphere. These parameters can be disturbed during seismic active periods by the lithospheric - atmospheric - ionospheric coupling. The signals of various navigational and time service transmitters are received by a European network of VLF/LF receivers. Several methods have been developed to analyse the received VLF/LF amplitude and phase in order to get information on the seismic activity along the radio path. We present a simple model for the estimation of the VLF/LF radio wave propagation parameters using mainly the amplitude observations of receivers in Italy, Austria and Russia. The main emphasis is on the L'Aquila earthquake from April 2009 with a magnitude of 6.3. This event has been observed with ground based VLF/LF radio links as well as with satellite VLF receivers. The influence of the electrophysical parameters in the immediate vicinity of the active-seismic region on ionospheric parameters is a hot debated issue, where definite physical answers are still expected to be found. Its consequences for the VLF/LF propagation in the sub-ionospheric waveguide are theoretically not well understood up to now, although empirically the issue is well established. For the analysis of pre-seismic activity the systematic variation of the terminator time (TT) and the night time amplitude variations (residual method) seem to be an important indicator. Therefore we studied theoretically the propagation and the influence of ionospheric parameter changes on the VLF/LF mode conversion at the solar terminator and near the seismic region. Our method is based on analytical models of Ledinegg et al. (1982). In particular, we will present prelininary results of the influence of conductivity variations in the wave guide on the received VLF/LF amplitude. This is a first step in solving the inverse problem of VLF/LF seismo-electromagnetism.

Schwingenschuh, K.; Eichelberger, H. U.; Besser, B. P.; Prattes, G.; Boudjada, M. Y.; Stangl, G.; Wolbang, D.; Rozhnoi, A.; Solovieva, M.; Biagi, P. F.; Friedrich, M.; Biernat, H.; Hayakawa, M.

2012-04-01

27

Statistical investigation of the VLF quasi-periodic emissions measured by the DEMETER spacecraft.  

Czech Academy of Sciences Publication Activity Database

. EGU, 2013. EGU2013-8852. ISSN 1607-7962.[EGU General Assembly 2013. 07.04.2013-12.04.2013, Vienna]Institucionální podpora: RVO:68378289Klí?ová slova: VLF quasi-periodic emissionsKód oboru RIV: DG - V?dy o atmosfé?e, meteorologie http://meetingorganizer.copernicus.org/EGU2013/EGU2013-8852.pdf

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

28

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

DEFF Research Database (Denmark)

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

Mika, A.; Haldoupis, C.

2005-01-01

29

Quasi-periodic VLF emissions with short-period modulation and their relationship to whistlers: a case study  

Science.gov (United States)

We study properties of quasiperiodic (QP) VLF emissions recorded on December 24, 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 hours 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 3.5--1.2 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 ???????? 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 nonlinear effects related

Titova, Elena; Demekhov, Andrei; Kozlovsky, Alexander; Manninen, Jyrki; Pasmanik, Dmitry

30

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

International Nuclear Information System (INIS)

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

31

Active Antenna for the VLF to HF Observer  

Science.gov (United States)

A simple and low cost method of fabricating an active antenna preamplifier system covering the range of 10 KHz to 10 MHz for use with tunable communications receivers is described. The same type of system can be used with airborne VLF navigation receivers. By operating a high impedance preamplifier as a wide band device directly at the base of a short vertical antenna, the signal can be driven back to the receiver on a length of coaxial cable. The antenna can be as short as I meter and still give excellent results when the capacity to ground at the antenna is low.

Burhans, R. W.

1979-01-01

32

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

Science.gov (United States)

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

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

2014-05-01

33

VLF noises triggered by whistlers as observed in the topside ionosphere  

Science.gov (United States)

ISIS-1, ISIS-2, and DE-1 VLF electric field data from Kashima station, Japan are used to investigate characteristics of whistler triggered emissions in the topside ionosphere. The occurrence rate for nonducted whistler triggered emission is shown to be distributed randomly between L = 2.0 and 4.2, while the occurrence rate of ducted whistler triggered emissions increases with latitudes between L = 1.5 and 2.9, attains a maximum at L = 2.7, and abruptly drops off at L = 3.0. The findings indicate that some whistler triggered emissions may be generated by the interaction of whistlers with magnetospheric electrons.

Nakamura, Yoshikatsu; Ondoh, Tadanori

1988-01-01

34

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

35

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

36

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

OpenAIRE

It is now well known that amplitude modulated HF transmissions into the ionosphere can be used to generate ELF/VLF signals using the so-called "electrojet antenna". Although most observations of the generated ELF/VLF signals have been made on the ground, several low and high-altitude satellite observations have also been reported (James et al., 1990). One of the important unknowns in the physics of ELF/VLF wave generation by ionospheric heating is the volume of the magnetosphere ill...

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

2004-01-01

37

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

Directory of Open Access Journals (Sweden)

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

M. Platino

2004-07-01

38

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

39

Subionospheric VLF Observations of Transmitter-Induced Precipitation of Inner Radiation Belt Electrons  

Science.gov (United States)

Ionospheric effects of energetic electron precipitation induced by controlled injection of VLF signals from a ground based transmitter are observed via subionospheric VLF remote sensing. The 21.4 kHz NPM transmitter in Lualualei, Hawaii is keyed ON-OFF in a periodic sequence lasting 30 minutes. The same periodicity is observed in the amplitude and phase of the sub-ionospherically propagating signals of the 24.8 kHz NLK (Jim Creek, Washington) and 25.2 kHz NLM (LaMoure, North Dakota) transmitters measured at Midway Island. The NLM and NLK signal paths pass underneath the region of electron precipitation induced by the NPM transmitter, as predicted theoretically on the basis of cyclotron resonance interaction between energetic electrons and obliquely propagating whistler-mode waves injected by NPM. The ionospheric disturbances are consistent with that caused by conductivity enhancements resulting from secondary ionization produced by the precipitation of pitch angle scattered electrons in the 100-300 keV energy range. Periodic perturbations of the NLK signal observed at Palmer, Antarctica suggest that energetic electrons are scattered into both the bounce and drift loss cones. Utilizing a comprehensive model of magnetospheric wave-particle interaction, ionospheric energy deposition, and subionospheric VLF propagation, the precipitated energy flux is estimated to peak at L ~ 2 and ~ 3 x 10-4 [ergs s-1 cm-2

Golkowski, M.; Inan, U.; Peter, W.

2006-12-01

40

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

41

Correlation between observed VLF phase deviation and solar X-ray flux during solar flares  

International Nuclear Information System (INIS)

Correlation between the observed phase deviation of GBR 16 kHz VLF signals and the solar X-ray flux in the bands 0.5-4 and 1-8 A during solar flare events has been studied. It is found that the unnormalized phase deviations show a better correlation with the observed X-ray flux than the correlation with the normalized phase deviations. The threshold X-ray flux to produce a detectable sudden phase anomaly (SPA) has been estimated. (author)

42

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)

43

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.

44

Whistlers observed at low-latitude ground-based VLF facility in Fiji  

Science.gov (United States)

The propagation features of nighttime whistlers to low-latitude station, Suva (-18.2°, 178.3°, geomag. lat. -22.1°, geomag. long. 253.5°, L=1.15), Fiji, from preliminary observations made during the period from September 2003 2005, are reported. The observations of ELF VLF signals commenced in September 2003 using the VLF set-up of World Wide Lightning Location Network at our station. The whistlers were observed during the severe magnetic storm of 20 22 November 2003 and moderate magnetic storm of 17 19 July 2005. A whistler with dispersion D=12.7 s1/2 occurred on 22 November at 00:11 h LT. On 20 July at 01:00 h LT, a short whistler with dispersion D=20.9 s1/2 and two whistler events having two-component whistlers with D=15.8, 16.7 s1/2 and 16.7, 17.3 s1/2 were observed. Non-ducted pro-longitudinal mode of the whistler propagation supported by negative latitudinal electron density gradients in the ionosphere that are enhanced by magnetic storms, seems most likely mode of propagation for the whistlers with dispersion of 12.7 17.3 s1/2 to this low-latitude station.

Kumar, Sushil; Anil, D.; Kishore, A.; Ramachandran, V.

2007-08-01

45

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

Energy Technology Data Exchange (ETDEWEB)

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.

Hardy, D.A.; Burke, W.J. (Hanscom Air Force Base, MA (United States)); Villalon, E. (Northeastern Univ., Boston, MA (United States))

1990-05-01

46

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

International Nuclear Information System (INIS)

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

47

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

Directory of Open Access Journals (Sweden)

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

Norbayah Yusop

2014-03-01

48

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

49

Whistler-triggered emissions observed by ISIS satellites  

Science.gov (United States)

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

Nakamura, Y.; Ondoh, T.

1989-01-01

50

Formation of wedge-like pattern on VLF spectrograms observed by DEMETER  

Science.gov (United States)

The DEMETER satellite has almost circular polar orbit, with the altitude ~ 700 km. At middle latitudes, DEMETER typically stays in the region where the height-dependent variation of the lower hybrid resonance (LHR) frequency profile forms a trough, i.e. inside the so-called LHR waveguide. In this region, LHR phenomena reveal themselves most distinctly. A striking example of such phenomena is provided by wedge-like events (WLE) registered sometimes on overview VLF spectrograms (time duration ~ 2 minutes, frequency range 0 - 20 kHz) during thunderstorm activity. A characteristic feature of these spectrograms is the presence of unusual upper and lower cutoff frequencies. The upper cutoff frequency varies rapidly, approximately in proportion to L-3, where L is McIlwain parameter on the satellite orbit. On the contrary, the lower cutoff frequency is almost constant, so that the cutoffs cross at larger L. Between these cutoffs, which thus form a wedge, intense whistlers are observed, whereas only 0+ whistlers and, probably, ducted whistlers are found outside the cutoffs. We present numerous examples of such spectrograms, and explain the formation of wedge-like structures by the wave propagation features in the inner magnetosphere, and specific position of the satellite with respect to the LHR maximum. In general terms, this explanation is as follows. WLE consists of whistler mode waves originating from lightnings and, thus, is related to thunderstorm activity. The wedge as such is formed by quasi-resonance whistler waves that cannot propagate in the region where the wave frequency is below local LHR frequency. Then, the lower frequency cutoff is determined by the LHR maximum, as quasi-resonant waves with lower frequencies originating in opposite hemisphere do not reach the satellite due to LHR reflection above it. The appearance of an upper cutoff frequency is due to another feature of unducted VLF wave propagation, which consists in trajectories merging into a limiting trajectory for waves with the same frequency, but starting from different latitudes in the opposite hemisphere. As the further increase of the initial latitude does not lead to an increase of the final L-shell in the opposite hemisphere, there appears a maximum L-shell on which the waves with the given frequency can be observed. This L-shell decreases with the increase of wave frequency due to a more pronounced bending towards lower L-shells for higher frequency waves. As the result, the accessible domain for quasi-resonance whistler-mode waves on the (L-f)-plane takes the wedge-like shape. The observed features of spectral intensity are also explained consistently by the above suggested model.

Shklyar, David; Parrot, Michel; Chum, Jaroslav; Santolik, Ondrej; Titova, Elena

2010-05-01

51

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

52

Whistler-triggered emissions observed by ISIS satellites  

Energy Technology Data Exchange (ETDEWEB)

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 f{sub LHR}. 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 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.

Nakamura, Y.; Ondoh, T. (Communications Research lab., Tokyo (Japan))

1989-01-01

53

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

OpenAIRE

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...

Ho?ller, H.; -d Betz, H.; Schmidt, K.; Calheiros, R. V.; May, P.; Houngninou, E.; Scialom, G.

2009-01-01

54

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.

55

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 gation 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.

56

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

57

Conjugacy of daytime ELF-VLF emission activities in the auroral zones  

Energy Technology Data Exchange (ETDEWEB)

Statistical characteristics of emission occurrence are examined, using 1 year of digital data of 750-Hz, 2-kHz, and 4-kHz intensity records. These waves were measured simultaneously at a conjugate pair of stations, namely Syowa Station in Antarctica and Husafell in Iceland. The following notable diurnal and seasonal variation and Kp dependence was found for the daytime emissions (04-14 MLT): (1) The 750-Hz emissions were mostly observed during the daytime around noon in both conjugate regions. The emission occurrence reached a maximum 1-3 hours earlier at Syowa than at Husafell during the equinox season. The seasonal variation of 750-Hz emission occurrence showed a maximum during local summer and a minimum during local winter at both stations. The ratio of the emission enhancement in summer to that at the equinox is higher at Husafell than at Syowa. The emissions mostly occurred during moderately disturbed conditions of Kp {approximately} 2-4 at both stations. (2) The 2-kHz emission occurrence reached a maximum around 13 MLT at Syowa and around 11 MLT at Husafell. Peaks of the emission occurrence during summer shifted to the afternoonside at Syowa and to the morningside at Husafell. The occurrences at Syowa reached a maximum during local summer and a minimum during winter. (3) The occurrence of 4-kHz emissions was much more frequent at Husafell than at Syowa. The emissions at Husafell occurred mostly in the morning ({approximately}08 MLT) and in local winter, and the occurrences became more frequent with increasing magnetic activity. On the bases of these statistical characteristics, the authors discuss the effects of sunlight and geomagnetic activity which cause an asymmetry of wave propagation from the magnetosphere to the ionosphere in the two hemispheres.

Sato, Natsuo (National Institute of Polar Research, Tokyo (Japan)); Suzuki, Hiroyuki; Maezawa, Kiyoshi (Yamagata Univ. (Japan)); Saemundsson, T. (Univ. of Iceland, Reykjavik (Iceland))

1990-06-01

58

Emission of ELF/VLF Waves by a Modulated Electrojet upwards into the Ionosphere and into the Earth-Ionosphere Waveguide  

Science.gov (United States)

The modulation of the auroral electrojet by a ground-based ionosphere heating facility is calculated by solving a kinetic equation for electron distribution function. The resulting current is used to calculate the emission of ELF/VLF waves both into ionosphere and into the Earth-ionosphere waveguide. For this purpose, we developed a finite element method of calculation of electromagnetic field in a horizontally-stratified ionosphere filled with magnetized plasma, with arbitrary harmonically-varying current distribution and the direction of geomagnetic field. This method is proven to be stable against the loss of precision due to "swamping" of useful modes by evanescent waves. The electromagnetic field is calculated both in the Earth-Ionosphere waveguide (at arbitrary horizontal distance and direction) and in the ionosphere (as a whistler mode). The presented method requires less computational resources than traditional FDFD and FDTD methods. The calculated values are compared to ground and satellite observations of electrojet emissions from modulation by existing ionosphere heating facilities. In particular, we find that the emission of the whistler waves upward into the ionosphere is contained in a relatively narrow channel, even in the absence of ducting, due to a substantial horizontal size of the emitting region. We discuss the difference in the treatment of the heating of free electron by using the kinetic approach and the approach assuming a thermal (Maxwellian) distribution of electrons.

Lehtinen, N. G.; Inan, U. S.

2007-12-01

59

Rocket observations of the precipitation of electrons by ground VLF transmitters  

International Nuclear Information System (INIS)

Below an altitude of 400 km or less over the NASA Wallops Island range, stably trapped particles do not exist because of the South Atlantic Anomaly. In an experiment to measure scattered electrons at these altitudes (NASA flight 36:013), electron detectors clearly measured two monoenergetic electron peaks above the low background. The two monoernergetic peaks are attributed to the resonant interaction of electrons with VLF waves from Navy ground transmitters at Cutler, Maine, and Annapolis, Maryland. The transmitter signals were measured with electric and magnetic receivers aboard the rocket, and their propagation through the ionosphere and correlation with the precipitated electrons are discussed. In addition, energetic ions were also measured to be in the bounce loss cone during this rocket flight. Because of increased geomagnetic activity, it apears that the ring current extended inward to at least the L=2.5 magnetic shell and enhanced convection eroded the plasmasphere. The inward movement or compression of the plasmapause is consistent with a steep gradient in the equatorial cold plasma density and a localized equatorial interaction region needed to account for the monoenergetic elecrtron precipitation. The role of the geomagnetic activity in ''priming'' the trapped electron population for cyclotron resonance with VLF waves such that there is continuous scattering into the bounce loss cone remains uncertain. copyright American Geophysical Union 1989rican Geophysical Union 1989

60

Observation of ionospheric perturbation through ground-based VLF receiver and the DEMETER Satellite during some recent Solar Eclipses  

Science.gov (United States)

Solar eclipses always provide us a great opportunity to study upper atmosphere under a controlled experimental condition where extreme ultraviolet and X-rays from the sun are blocked gradually by the lunar disk in a predictable way. Thus, the strength of the source of high energy radiation becomes time dependent. In this paper, we report lower ionospheric response to two solar eclipses of July 22, 2009 (90.63%) and January 15, 2010 (75%) as observed by a ground-based VLF receiver at frequency 19.8 kHz placed at Khukurdaha ( 80 km away from Kolkata). We report perturbations in electron densities ionosphere during these two solar eclipses. Measurements of densities and temperatures of thermal electrons and ions were provided by instruments on board the DEMETER satellite, which flew near India during the time of partial solar obscuration. We clearly observe a significant decrease in plasma density, electron and ion temperatures along the orbit.

Kanta Maji, Surya; Chakrabarti, Sandip Kumar; Pal, Sujay

61

Propagation Characteristics and Generation Mechanism of ELF/VLF Hiss Observed at Low-latitude Ground Station ( L = 1.17)  

Science.gov (United States)

Extremely low frequency (ELF)/Very low frequency (VLF) hiss is whistler mode wave that interacts with energetic electrons in the magnetosphere. The characteristics features of ELF/VLF hiss observed at low latitude ground station Jammu (Geomag. lat. 22°16' N, L=1.17) are reported. It is observed that most of hiss events first propagate in ducted mode along higher L-values ( L = 4-5), after reaching lower edge of ionosphere excite the Earth-ionosphere waveguide and propagate towards equator to be received at low-latitude station Jammu. To understand the generation mechanism of ELF/VLF hiss, incoherent Cerenkov radiated power from the low-latitude and mid-latitude plasmasphere are evaluated. Considering this estimated power as an input for wave amplification through wave-particle interaction, the growth rate and amplification factor is evaluated which is too small to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of ELF/VLF hiss.

Singh, Kalpana; Singh, Rajesh; Singh, A. K.; Singh, R. P.

2007-04-01

62

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

63

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

64

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.

65

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

66

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

67

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

68

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.

69

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

70

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

71

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

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

A. A. Lubchich

2006-10-01

72

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

73

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

74

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

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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

75

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

76

Broadband VLF burst associated with ring current electrons  

International Nuclear Information System (INIS)

During the periods after the maximum phase of geomagnetic storms on 2 April 1972 a broadband VLF emission burst has been observed by the equatorially orbiting satellit S3-A (Explorer 45) along its inbound plasmapause crossings. The frequency band broadening takes place just outside of the nighttime plasmasphere, where the density of cold plasma has been known to be very low during the later phase of a geomagnetic storm. Instead of the gradual broadening of several hours duration, a burst type braodening of VLF emission lasting less than ten minutes was observed in the similar location. The magnetic field component of this emission is very weak and the frequency spreads below the local half electron cyclotron frequency. Corresponding enhancement of the anisotropic ring-current electrons is also very sudden and limited below the order of 10 keV without significant velocity dispersion, in contrast to the gradual broadening events. The cause of this type of emission band spreading can be attributed to the generation of the quasi-electrostatic whistler mode emissions of short wavelength by hot bi-maxwellian electrons surging into the domain of relatively low density magnetized cold plasma. The lack of energy dispersion in the enhanced electrons indicates that the inner edge of the plasma sheet, the source of these hot electrons, is not far from the location of this event

77

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

78

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

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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

79

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

80

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

81

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

82

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

Science.gov (United States)

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

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

2009-12-01

83

The statistics of natural ELF/VLF waves derived from a long continuous set of ground-based observations at high latitude  

Science.gov (United States)

This paper analyses a unique set of continuous high-quality well-calibrated observations of natural ELF/VLF radio waves, in the range 0.3-10 kHz, made at Halley Research Station, Antarctica (76oS,27oW,L=4.5) over one and a half solar cycles (1992-2007). Reference is also made to similar but shorter data sets obtained from other Antarctic stations. The observed waves vary over a very wide dynamic range, from the receiver noise level of wrt (at 1 kHz) up to 40-50 dB above it, over a wide range of timescales. However, the long continuous data set allows us to average out the random and aperiodic variations to extract the underlying dependence of the wave characteristics on local time, time of year, solar cycle, etc. Below about 5 kHz the received waves are predominantly whistler-mode waves, notably chorus, which are generated in the magnetosphere and propagate on geomagnetic field-aligned ("ducted") paths to low altitudes. At the top of the frequency range the observed waves are mostly atmospherics from tropical lightning. The spectrum, and dependence on local time and season, are discussed in terms of a source function and a propagation function from the source region through the ionosphere (in the case of the magnetospheric waves) and under the ionosphere. The dependence of the waves on latitude, geomagnetic activity, solar cycle and day of the week are also described.

Smith, A. J.; Horne, R. B.; Meredith, N. P.

2010-04-01

84

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

Directory of Open Access Journals (Sweden)

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

A. Rozhnoi

2010-03-01

85

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

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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

86

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

Science.gov (United States)

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

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

1985-01-01

87

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

Energy Technology Data Exchange (ETDEWEB)

Khabarovsk transmitter signals (15.0 kHz, 48{degrees}N, 135{degrees}E) were observed on the high-latitude ({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 detected signals from the Khabarovsk transmitter. On two days, August 23 and 27, 1989, observations of the Khabarovsk transmitter signals were simultaneously carried out at high altitude on the DE 1 satellite and at low altitude on 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 {le} 100 km scale size with a few percent enhancement in electron density, believed to be responsible for the observed multipath propagation. The authors report the first detection of an exterior caustic surface near L {approximately} 3.5 for VLF ground transmitter signals injected into the magnetosphere; the location of the caustic surface depended on the signal frequency, and the electric and magnetic fields decreased by several hundred decibels per L shell in the dark (shadow) side of the caustic. The authors also report the first direct detection of a magnetospheric duct as L = 2.94 which was believed to be responsible for the ducted propagation of Khabarovsk signals observed on the COSMOS 1809 satellite; the measured duct parameters were {Delta}L{approximately} 0.06 and {Delta}N{sub e}{approximately}10 -13%. 54 refs., 8 figs. 3 tabs.

Sonwalkar, V.S.; Inan, U.S.; Bell, T.F. [Stanford Univ., CA (United States)] [and others

1994-09-01

88

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

Science.gov (United States)

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

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

2014-10-01

89

Ground observation of electromagnetic emissions related to clusters of earthquakes  

Science.gov (United States)

ULF-VLF data obtained from three ground based experiments working at Agra station (geograph. Lat. 27.20N, Long. 780E) in India namely measurement of ultra low frequency (ULF) magnetic field emissions using a 3-component search coil magnetometer, vertical component of very low frequency (VLF) electric field emissions with a borehole antenna, and phase and amplitude of fixed frequency VLF transmitter signals using AbsPAL receiver are analysed in search of possible precursors of two major seismic activities that occurred in Sumatra (Indonesia) during post-tsunami period between January and April, 2005. These two major seismic events occurred as clusters of earthquakes during 27-29 January and 28-30 March, 2005. The results show that barring borehole all the experiments showed precursors due to these clusters of earthquakes. Such precursors were not seen in the case of isolated large magnitude earthquakes. Further, the precursory duration was influenced by the magnetic storm which occurred about a week before the clusters. The mechanism of ULF propagation to long distances between Sumatra and Agra, and perturbations in the ionosphere before the clusters are discussed.

Singh, Vikram; Singh, Birbal

2010-05-01

90

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

91

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

92

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

93

Anomalies observed in VLF and LF radio signals on the occasion of the western Turkey earthquake (Mw=5.7) at May 19, 2011  

Science.gov (United States)

Since 2009 a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers is operating in Europe in order to study the disturbances produced by the earthquakes on the propagation of these signals. In 2011 the network was formed by nine receivers, of which three are located in Italy and one is in Austria, Greece, Portugal, Romania, Russia and Turkey. On May 19, 2001 an earthquake (Mw=5.7) occurred in western Turkey, that is inside the "sensitive" area of the network. Evident anomalies were revealed both in the signals broadcasted by the TRT transmitter (180 kHz) located near Ankara and in a VLF signal coming from a transmitter located in western Europe and collected by the receiver TUR of the network located in eastern Turkey

Biagi, P. F.; Maggipinto, T.; Schiavulli, L.; Ligonzo, T.; Ermini, A.; Moldovan, I. A.; Silva, H. G.; Bezzeghoud, M.; Contadakis, M. E.; Arabelos, D. N.; Buyuksarac, A.

2012-10-01

94

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

95

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

International Nuclear Information System (INIS)

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

96

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

OpenAIRE

Signals of two Japanese transmitters (22.2 kHz and 40 kHz) recorded on the ground VLF/LF station in Petropavlovsk-Kamchatsky and on board the DEMETER French satellite have been analyzed during a seismic activity in Japan in May–June 2008. The period of analysis was from 18 April to 27 June. During this time two rather large earthquakes occurred in the north part of Honshu Island – 7 May (M=6.8) and 13 June (M=6.9). The ground and satellite data were p...

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

2010-01-01

97

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

OpenAIRE

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 observatio...

Pier Francesco Biagi; Masashi Hayakawa; Michel Parrot; Maria Solovieva; Alexander Rozhnoi; Konrad Schwingenschuh

2012-01-01

98

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

Directory of Open Access Journals (Sweden)

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

Pier Francesco Biagi

2012-09-01

99

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)

100

Observations of auroral broadband emissions by CLUSTER  

OpenAIRE

We present the results of a study based on several events of broadband ULF/ELF emissions observed in the auroral region by the CLUSTER multi-spacecraft at distances around 4–5 RE. These emissions, observed below the ion plasma frequency, are similar to the broadband emissions observed at lower altitudes (800–4000 km) by rockets (e.g. AMICIST) and satellites (e.g. FREJA and FAST). As successive passages of the four CLUSTER satellites through nearly the same regions show, the intensity of t...

Wahlund, J. E.; Yilmaz, A.; Backrud, M.; Sundkvist, D.; Vaivads, A.; Winningham, D.; Andre, M.; Balogh, A.; Bonnell, J.; Buchert, S.; Carozzi, T.; Cornilleau, N.; Dunlop, M.; Eriksson, A. I.; Fazakerley, A.

2003-01-01

101

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

102

ELF/VLF propagation measurements in the Atlantic during 1989  

Science.gov (United States)

The vertical electric field component was measured by a group of the Ukrainian Insitute of Radio Astronomy on board the Professor Zubov scientific vessel during April 1989 at latitudes from 30 deg S to 50 deg N. Results of the amplitude measurements in the Atlantic of natural ELF radio signals and those from the VLF navigation system 'Omega' at its lowest frequency of 10.2 kHz are given. Characteristics were obtained of the moving ship as the field-site for the ELF observations. Variations in the ELF radio noise amplitude recorded at tropical latitudes agree with the computed data for the model of three continental centers of lightning activity. The VLF results were obtained by the 'beat' technique providing the simplest narrow-band amplitude registration. Range dependencies of the field amplitudes from A (Norway), B (Liberia) and F (Argentina) stations have been analyzed. The VLF attentuation factor was estimated for the ambient day conditions along the four cardinal directions. This allowed the detection of a statistically significant attenuation difference between the east-west and west-east propagation paths. The VLF radio signal was also used as a probe to evaluate the effective height of the vertical electric antenna and to calibrate the ELF noise amplitudes.

Nickolaenko, A. P.

1995-06-01

103

Very diffused whistlers and chorus emissions observed in the equatorial magnetosphere  

Science.gov (United States)

Wide-band VLF electric field data of DE-1 received at Kashima, Japan for a substrom period (AL = - 520nT) on May 11, 1990 are used to study effect of plasma irregularities near the plasmapause on whistlers and L-dependency of VLF risers and falling waves. The DE-1 passed obliquely through the morning equatorial magnetosphere from geomagnetic latitude of 4.5 deg N, L = 3.3, and altitude of 13,750 km to 1.0 deg S, L = 2.5, and 10,030 km. Very diffused whistlers occurred from 1.0 deg S and L = 2.54 to 5.3 deg N and L = 2.80 for 0643 to 0646 MLT (geomagnetic local time), and a first normal whistler did at 7.9 deg N and L = 2.9. This implies that the very diffused whistlers were observed at geomagnetic latitudes below 5.8 deg N and L below 2.9. Frequency rising emissions (risers) occurred at frequency from 8 to 10 kHz and from 16 to 20 kHz at L above 3.1 and falling emissions did from frequency band from 8 to 6 kHz or that from 14 to 10 kHz in double frequency bands at L = 2.9 to 3.0. In summary, the very diffused whistlers were observed at geomagnetic latitudes below 5.8 degrees and for L below 2.9, while the frequency rising emissions and falling ones were observed at L above 2.9. Non-ducted whistlers scattered by plasma irregularities have large wave normal angles for f above f(LHR) and large electric fields parallel to wave vectors. Plasma irregularities exist near the equatorial plasmapause (Horwitz et al., 1986). The Doppler-shifted spectrum broadening of VLF waves propagating in the plasma irregularity due to the satellite motion is estimated at 100 Hz by the expression given by Bell et al.,(1983) for f(LHR) = 1 kHz and satellite velocity of 5 km/s at 2.6 Re (Earth radius). Spasojevic et al. (2003) have shown high irregularity density structures within the plasmaspheric plume observed by IMAGE EUV imager in continued substorm activity, amd also the base of plasmaspheric plume closer to the plasmasphere located at L = 2.0 to 2.3 in the morning sector. The plasmaspheric plume located between 2.6 and 3.3 Re wraps around the plasmapause between 0630 and 0400 MLT. These locations of plume irregularities are similar to those of the very diffused whistlers observed by the DE-1. Therefore, the very diffused whistlers seem to be due to the Doppler-shifted spectrum broadening of normal whistlers passing through the high irregularity density structures within the plasmspheric plume in the morning sector.

Ondoh, Tadanori

104

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

Energy Technology Data Exchange (ETDEWEB)

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

Hansen, H.J.; Scourfield, M.W.J. (Univ. of Natal, Durban (South Africa))

1990-01-01

105

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

International Nuclear Information System (INIS)

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

106

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

Science.gov (United States)

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

Ahmedov, Bobomurat

107

Ionosphere Activity Effects on Anthropogenic VLF Wave measured by DEMETER and Application to Earth Electromagnetic Survey  

Science.gov (United States)

Very Low Frequency (VLF) signal from the world-wide powerful VLF stations network, for navigation and military communication is commonly used for ground level electromagnetic survey in geophysics because part of the recorded signal is of internal origin, from induction in the Earth. This VLF signal has been observed also at satellite altitude during the DEMETER mission. The VLF electromagnetic field is recorded on the 15 - 20 kHz frequency band by the ICE et IMSC sensors on-board the spacecraft and provide simultaneously the electric and magnetic component of the electromagnetic signal. The waves transmitted by the ground-based VLF antennas propagate in free space and may pass through the ionosphere, depending on ionosphere properties or orientation of the wave vector relative to the Earth magnetic field. They can only cross the ionosphere and reach the satellite in the case of low ionosphere activities. The ionization varies according to time of day or season and it has been shown that man made VLF waves can precipitate radiation belt energetic electrons into the ionosphere. We study the effect of the interaction between VLF wave transmitted from ground and the ionosphere to analyze the contribution of ionosphere to the signal measured by DEMETER. We calculate the electromagnetic field of the VLF antennas placed on the surface of the Earth and transmitted through the ionosphere up to the satellite as a function of earth electrical resistivity. To compare with the data, we define the ratio between the electric and magnetic field that we call wave impedance. The comparison between the theoretical and observed impedance allows to deduce the average resistivity of the earth for shallow depth from the satellite data.

Leye, P. O.; Tarits, P.

2012-04-01

108

A VLF survey using current gathering phenomena for tracing buried faults of Fethiye-Burdur Fault Zone, Turkey  

Science.gov (United States)

Fethiye-Burdur Fault Zone (FBFZ) produces moderate to large earthquakes which can severely affect the surrounding cities spreading towards the basins of the region. In this study, with the aim of feature city planning, very low frequency electromagnetic (VLF) survey was carried out across (FBFZ) to locate subsurface faults covered by basin fills. VLF parameters such as the apparent resistivity, phase (VLF-R response) real and imaginary parts of tipper (VLF-EM response) were obtained using GBZ, a well known radio station in England at Oxford, which give a strong signal in our survey area with a suitable frequency (19.6 kHz) for our purposes. VLF method is called as VLF-EM, when it is only relying on the measurement of horizontal and vertical magnetic fields. However, when it includes measurement of horizontal electric field, providing resistivity values, it is referred as VLF-R method. In this study, the direction of horizontal electric field is perpendicular to fault strike describing the H-polarization mode. Although this mode produces strong VLF-R (resistivity) response, we also obtained quite clear and characteristic VLF-EM anomalies along some of the survey profiles. Both VLF-R and VLF-EM responses with the contribution of the vortex and gathered (direct) currents, in E and H-polarization modes, are reviewed and VLF anomalies observed over FBFZ are discussed. In FBFZ, current gathering anomalies become stronger in the presence of high conductivity contrast and in the presence of parallel fault branches separating the medium into resistors in series. In these conditions, changing electrical charge at the contacts of faults cause successive variations in E-field. As a result VLF-R response is strengthened and also secondary magnetic field which causes VLF-EM anomalies may be enhanced, in H-polarization mode. Interpretation of resistivity, phase and tipper data with current density pseudosections, over our survey lines, showed the location of buried faults of FBFZ beneath the sedimentary covers of the basins.

Gürer, A.; Bayrak, M.; Gürer, Ö. F.

2009-07-01

109

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

110

Observations of Diffuse Ultraviolet Emission from Draco  

OpenAIRE

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 th...

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

2010-01-01

111

Non detection of lightning signature in the Huygens RLF_VLF data  

Science.gov (United States)

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

Hamelin, M.; Grard, R.; Béghin, C.; Berthelier, J. J.; Lopez-Moreno, J. J.; Simões, F.

2011-10-01

112

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

113

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

114

Trapped electron losses by interactions with coherent VLF waves  

International Nuclear Information System (INIS)

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

115

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

116

The Graz seismo-electromagnetic VLF facility  

OpenAIRE

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...

Schwingenschuh, K.; Prattes, G.; Besser, B. P.; Moc?nik, K.; Stachel, M.; O?, Aydogar; Jernej, I.; Boudjada, M. Y.; Stangl, G.; Rozhnoi, A.; Solovieva, M.; Biagi, P. F.; Hayakawa, M.; Eichelberger, H. U.

2011-01-01

117

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 Suprathermal Ion Currents (GEODESIC) sounding rocket encountered more than 100 filamentary density cavities associated with enhanced plasma waves at ELF (magnetic wave power throughout the VLF band. GEODESIC also observed enhancements of ELF and VLF electric 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 the magnetic fields. This behavior is opposite to that predicted by previously published theories of LHCs based on passive scattering of externally incident auroral hiss. We argue that the GEODESIC cavities are active wave generation sites capable of radiating VLF waves into the surrounding plasma and producing VLF saucers, with energy supplied by cold, upward flowing electron beams composing the auroral return current. This interpretation is supported by the observation that the most intense waves, both inside and outside cavities, occurred in regions where energetic electron precipitation was largely inhibited or absent altogether. We suggest that the wave-enhanced cavities encountered by GEODESIC were qualitatively different from those observed by earlier spacecraft because of the fortuitous timing of the GEODESIC launch, which placed the payload at apogee within a substorm-related return current during its most intense phase, lasting only a few minutes.

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

2012-02-01

118

Preamplifier Noise in VLF Receivers  

Science.gov (United States)

Noise specifications for junction field-effect transistors are presented in different ways depending on the particular semiconductor manufacturer. Arithmetic involved in converting these specifications to equivalent RMS noise in microvolts developed at the preamplifier input terminal is reviewed. These methods were useful for estimating the noise performance of high input impedance preamplifiers used with E-field antennas operating in the range of 1 KHz to 10 MHz. Both the JFET MPF-102 transistor and the COS/MOS CA3600 transistor array provided amplification for VLF receivers where the internally generated noise was well below the atmospheric noise level. The CA3600 transistor array provided better performance because of the more symmetrical complementary MOS transistor transfer characteristics than a single N-type biased JFET transistor. The CMOS amplifier resulted in self-compensating gain characteristics over a very wide temperature range from -55 to +125 C.

Burhans, R. W.

1978-01-01

119

A Study of diurnal and seasonal variations of the lower ionosphere using VLF Wave  

Science.gov (United States)

We have investigated the ionospheric variations using the VLF wave observed by SID (Sudden Ionospheric Disturbance) monitor. The SID monitor receives the VLF(Very Low Frequency) radio wave bounced off the ionosphere and obtains the data by sampling every five seconds. In this study, we have employed the data observed by SID monitor (22.2kHz) from October, 2008 to September, 2009, which has been tuned to the radio transmitter station JJI (32.04oN, 130.81oE) in Ebino, Japan and installed in KSA (Korea Science Academy of KAIST), Busan (35.23oN, 129.08oE). The result shows the diurnal and seasonal variations and the Sunrise-Sunset effect. We have found that the solar activity affects the variation of VLF strength. The strength of the received radio signal changes according to how much ionization has occurred and at what level of the ionosphere the VLF wave bounces from. In addition, we have verified the variation of VLF strength during the solar eclipse on July 22, 2009.

Mie Park, Sun; Ryu, Chung-Kwon; Jang, Jae-Son; Cho, Jun Gu

120

Remote sensing of ionospheric disturbances associated with energetic particle precipitation using the South Pole VLF beacon  

Science.gov (United States)

The Stanford University VLF beacon transmitter located at South Pole operates at 19.4 kHz, transmitting for 1 min intervals every 15 min throughout the day. The beacon serves as a tool to measure changes in the D region ionospheric conductivity owing to energetic particle precipitation and is capable of providing coverage that spans the Antarctic continent. We present VLF beacon signal amplitude and phase data measured at Palmer Station, Antarctica. Diurnal and seasonal variations are discussed first, followed by analysis of data from two periods of high geomagnetic activity, in July 2004 and in May 2005, with a phase advance and an amplitude depression of the beacon signal (as recorded at Palmer) observed for both cases. Data from the MEPED instrument aboard the NOAA-16 and 17 POES satellites show an increase in energetic electron (>100 keV) and proton (>16 MeV) precipitation fluxes coincident with the VLF beacon signal perturbations. The fluxes measured on POES are used as an aide to generate profiles of secondary ionization along the great circle path from South Pole to Palmer. These profiles are then applied to a quantitative model of subionospheric VLF signal propagation to estimate the phase and amplitude variations expected. Results indicate that the observed VLF amplitude and phase data are in reasonable agreement with theoretical calculations in both cases, indicating that the model captures the ionospheric disturbance in effect during both of the disturbed periods.

Chevalier, M. W.; Peter, W. B.; Inan, U. S.; Bell, T. F.; Spasojevic, Maria

2007-11-01

121

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

Science.gov (United States)

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

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

1972-01-01

122

A broad-band vlf-burst associated with ring-current electrons  

International Nuclear Information System (INIS)

Frequency band broadening takes place just outside of the nighttime plasmasphere, where the density of cold plasma is known to be very low during the later phase of a geomagnetic storm. Instead of the gradual broadening of several hours duration, a burst type broadening of VLF emission lasting less than ten minutes was observed by Explorer 45 in a similar location. The magnetic field component of this emission is very weak and the frequency spreads below the local half electron cyclotron frequency. Corresponding enhancement of the anisotropic ring current electrons is also very sudden and limited below the order of 10 keV without significant velocity dispersion, in contrast to the gradual broadening events. The cause of this type of emission band spreading can be attributed to the generation of the quasielectrostatic whistler mode emission of short wavelength by hot bimaxwellian electrons surging into the domain of relatively low density magnetized cold plasma. The lack of energy dispersion in the enhanced electrons indicates that the inner edge of the plasma sheet, the source of these hot electrons, is not far from the location of this event

123

Emilia Earthquake: VLF Transmitters and ELF Signal from the Central Italy Electromagnetic Network (CIEN)  

Science.gov (United States)

Use of a VLF (1-25 kHz) transmitter monitoring in connection with strong earthquakes has been studied by several authors over the last two decades. This has recently led to international cooperation which includes a network covering the whole of Europe (Hayakawa, 1994;Biagi, 2011). Its aim is to monitor the sub-ionospheric channels between VLF radio transmitters and receivers. In fact, sub-ionospheric channels, which are above the preparation zone of a future strong earthquake, have been observed in several cases preventing transmissions many days before the main shocks. To study this kind of phenomena, a network devoted to seismic monitoring of VLF transmitters and ELF signals ELF (4 Hz-1 kHz) was established in central Italy (Central Italy Electromagnetic Network, CIEN) was operating since 2006 and progressively extended to include 6 stations. The features of CIEN are described at first

Fidani, C.; Albarello, D.; Arcaleni, M.; Martinelli, G.; Siciliani, P. M.; Tardioli, S.; Vannucchi, A.

2012-10-01

124

Spin modulation of spectrally broadened VLF signals  

International Nuclear Information System (INIS)

The spectra of broadened VLF signals from ground transmitters received on the spinning ISIS spacecraft have a characteristic temporal dependence when the long receiving dipoles pass close to parallel to the earth's magnetic field direction. As the angle between the dipole and the field direction passes its minimum, the spectra evolve from having enhanced negative Doppler components to having enhanced positive Doppler components or vice versa. The relative orientation of the spin, spacecraft velocity, and magnetic field vectors determines whether the enhancement evolves from positive to negative Doppler or from negative to positive. Theoretical calculations of the Doppler spectra agree with observations from the ISIS spacecraft. These analyses show that wave vectors corresponding to broadened spectra are confined to a narrow range of azimuths about the magnetic field direction. The wave vectors are distributed through a range of polar angles with respect to the magnetic field direction. The wave vectors are distributed through a range of polar angles with respect to the magnetic field direction, possibly as the result of scattering of the upcoming waves in the ionosphere below the spacecraft. The technique has been used to deduce the preferred azimuth in the case of one spectrum

125

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

126

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

127

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

Directory of Open Access Journals (Sweden)

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

K. Ohta

2001-01-01

128

ARCADE 2 Observations of Galactic Radio Emission  

CERN Document Server

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

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

2009-01-01

129

Excitation of VLF quasi-electrostatic oscillations in the ionospheric plasma  

Directory of Open Access Journals (Sweden)

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

B. Lundin

130

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

International Nuclear Information System (INIS)

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

131

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

Energy Technology Data Exchange (ETDEWEB)

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

Mielke, T.A.; Elkins, C.J.; Helliwell, R.A.; Inan, U.S. (Stanford University, CA (United States))

1992-02-01

132

Possible Mg ii emission in B stars observed from Copernicus  

Energy Technology Data Exchange (ETDEWEB)

Four B stars, ..cap alpha.. Vir, ..beta.. Cen, ..cap alpha.. Gru, and ..beta.. Lib, were observed with the Copernicus Princeton Telescope Spectrometer at a resolution of 0.1 A in order to investigate the presence of chromospheric emission. Emission was observed in ..beta.. Cen and ..cap alpha.. Gru, while the results for ..cap alpha.. Vir and ..beta.. Lib were inconclusive. (AIP)

Kondo, Y.; Modisette, J.L.; Dufour, R.J.; Whaley, R.S.

1976-05-15

133

Possible Mg II emission in B stars observed from Copernicus  

Science.gov (United States)

Four B stars, Alpha Vir, Beta Cen, Alpha Gru, and Beta Lib, were observed with the Copernicus spectrometer at a resolution of 0.1 A in order to investigate the presence of chromospheric emission. Emission was observed in Beta Cen and Alpha Gru, while the results for Alpha Vir and Beta Lib were inconclusive.

Kondo, Y.; Whaley, R. S.; Modisette, J. L.; Dufour, R. J.

1976-01-01

134

Characteristics of lightning associated transient perturbations in low latitude VLF path  

Science.gov (United States)

Lightning can perturb the sub-ionospheric VLF propagation directly or indirectly. Direct perturbations in the sub-ionospheric VLF signals occur within 20 ms of the associated lightning discharges while the indirect perturbations occur through the lighting generated whistler mode waves in the magnetosphere. These whistler mode waves undergo cyclotron resonance with the trapped electrons in the magnetosphere. The electrons which are pitch angle scattered into the loss cone, precipitate into the ionosphere producing secondary ionization in the lower ionosphere. This process produce indirect VLF perturbations known as lightning induced electron precipitation (LEP) events. We have analyzed such events for the VTX-Kolkata and NWC-Kolkata path. We observed too many events. Some of them have positive shifts while others have negative shifts. We are trying to find the reasons behind such variations in amplitude shifts. We have fitted the events with FRED (Fast Rise Exponential Decay) function to characterize the onset and recovery time. We try to explain the positive and negative VLF amplitude deviation due to lightning events using the most well-known LWPC (Long Wavelength Propagation Capability) code.

Chakraborty, Suman; Chakrabarti, Sandip Kumar; Pal, Sujay

135

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

136

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

Science.gov (United States)

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

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

2014-06-01

137

Prompt Emission Observations of Swift BAT Bursts  

Science.gov (United States)

We review the prompt emission properties of Swift BAT gamma-ray bursts (GRBs). We present the global properties of BAT GRBs based on their spectral and temporal characteristics. The BAT T90 and T50 durations peak at 80 and 20 s, respectively. The peak energy (Epeak) of about 60% of BAT GRBs is very likely to be less than 1.00 keV. We also present the BAT characteristics of GRBs with soft spectra, so called Xray flashes (XRFs). We will compare the BAT GRBs and XRFs parameter distribution to the other missions.

Barthelmy, Scott

2009-01-01

138

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

139

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)

140

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

141

Observations and modelling of pulsed radio emission from CU Virginis  

CERN Document Server

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

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

2012-01-01

142

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

143

A new VLF/LF atmospheric noise model  

Science.gov (United States)

Atmospheric noise, originating essentially from lightning discharges, is the main disturbance of VLF/LF telecommunications. This paper characterizes atmospheric noise in the 10-80 kHz range and proposes a new model: very accurate low-frequency noise model (VALERIE). This model uses a new approach, which combines noise measurements with lightning data. The noise statistics were obtained from several years of measurements taken by the Délégation Générale de l'Armement (DGA)/Centre Technique des Systèmes Naval (CTSN) (Toulon, France) and the Space and Naval Warfare Systems (SPAWAR) (San Diego, California). Lightning data were provided by recent satellite observations made by NASA. A comparison of VALERIE predictions with measurements by cross validation showed an increase in accuracy compared to the current International Telecommunication Union (Geneva) model and a decreased average deviation. The model has been validated for the Atlantic area but may be extended as new measurements are collected.

Fieve, S.; Portala, P.; Bertel, L.

2007-06-01

144

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.)

145

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

International Nuclear Information System (INIS)

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

146

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

147

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

148

Egret observations of the extragalactic gamma-ray emission  

DEFF Research Database (Denmark)

The all-sky survey in high-energy gamma rays (E > 30 MeV) carried out by 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 as an almost uniformly distributed component that is generally believed to originate outside the Galaxy. Through a careful study and removal of the Galactic diffuse emission, the flux, spectrum, and uniformity of the extragalactic emission are deduced. The analysis indicates that the extragalactic emission is well described by a power-law photon spectrum with an index of -(2.10 +/- 0.03) in the 30 MeV to 100 GeV energy range. No large-scale spatial anisotropy or changes in the energy spectrum are observed in the deduced extragalactic emission. The most likely explanation for the origin of this extragalactic high-energy gamma-ray emission is that it arises primarily from unresolved gamma-ray-emitting blazars.

Sreekumar, P.; Bertsch, D.L.

1998-01-01

149

Observation of beta-delayed proton emission from 24Al  

International Nuclear Information System (INIS)

Utilizing the 24Mg(p,n) reaction and a low-energy proton detector ball, beta-delayed proton emission from 24Al has been observed in the form of a quasicontinuum of protons from ?300 to 1100 keV. By making a comparsion with a previously known 24Al beta-delayed alpha branching ratio, a branching ratio for beta-delayed proton emission of (1.2±0.3)x10-5 has been determined

150

EGRET Observations of the Extragalactic Gamma Ray Emission  

OpenAIRE

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

151

Solar Flare Impulsive Phase Emission Observed with SDO/EVE  

Science.gov (United States)

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

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

2013-12-01

152

Observations of interstellar H2O emission at 183 gigahertz  

Science.gov (United States)

Observations of the 183-GHz rotational transition of water vapor in interstellar molecular clouds are reported. The observations were made with a portable double-sideband superheterodyne radiometer used with the 91-cm Cassegrain telescope on board the Kuiper Airborne Observatory. An emission feature was detected in the direction of the Kleinmann-Low nebula in Orion with a peak antenna temperature of 15 K, a local standard of rest velocity of 8 km/sec, and a width of 15 km/sec. A plateau component of the emission profile is attributed to the 1-arcmin region characteristic of plateau emission from other observed molecules, with emission enhanced over that expected for thermal excitation, while the spike component observed is consistent with an optically thick source of the size of the molecular ridge in Orion at a temperature of 50 K and a column density greater than or equal to 3 x 10 to the 17th/sq cm, implying that H2O is one of the more abundant species in the Orion Molecular Cloud. Emission at 183 GHz was not detected in Sgr A, Sgr B2, W3, W43, W49, W51, DR 21, NGC 1333, NGC 7027, GL 2591 or the Rho Oph cloud; it may have been detected in M 17.

Waters, J. W.; Kakar, R. K.; Kuiper, T. B. H.; Roscoe, H. K.; Swanson, P. N.; Rodriguez Kuiper, E. N.; Kerr, A. R.; Thaddeus, P.; Gustincic, J. J.

1980-01-01

153

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1980-07-01

154

Effect of Earthquakes on Lower Ionosphere as Found by Subionospheric VLF Propagation  

Science.gov (United States)

Reliable VLF subionospheric signal effect related to the seismic activity was first reported by Hayakawa et al. (1996 a, b) in association with the great Kobe earthquake. We have analyzed the similar data around 10 other great earthquakes (magnitude M >6), in order to understand the main features of such an effect, and the following characteristics are emerged from our analysis:(a) This effect looks as transient oscillations with 5-10 days period, which are initiated a few days before a large earthquake and relaxed for a few days or weeks after it.(b) It is mainly related to crust earthquakes.(c) It cannot be observed outside the sensitivity zone of VLF transmitter (first Fresnel zone) even for very large earthquakes (M >7)

Hayakawa, M.; Molchanov, O. A.

155

Self-modulated vlf wave--electron interactions in the magnetosphere: A cause of auroral pulsations  

Energy Technology Data Exchange (ETDEWEB)

A model is developed for self-modulated pulsations in the outer trapped electron belts. The pulsations are a consequence of growth of VLF waves and removal of trapped electrons following an electron injection event. If too many electrons are removed by wave interactions, the system restores itself by building up the flux again to values exceeding the equilibrium flux, repeated through many cycles. Pulsations are shown to be possible for both broadband VLF wave generation and narrowband wave generation. The resulting electron orecipitation pulses are consistent with observations of pulsating aurorae on the morningside following a substorm injection event. The conditions for pulsations are quite stringent and favor trapped particle fluxes near the stable trapping limit. Individual pulses may be in or near strong diffusion.

Davidson, G.T.

1979-11-01

156

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

Directory of Open Access Journals (Sweden)

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

G. Dufour

2009-03-01

157

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

International Nuclear Information System (INIS)

The burst precipitation of energetic electrons (? 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 ? 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

158

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

Science.gov (United States)

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

Rault, J. L.

2010-09-01

159

Radio observations of peculiar emission-line Algol binary stars  

Science.gov (United States)

Twelve peculiar emission-line Algol (PELA) binaries were observed at cm wavelengths. Six of these objects, WW And (tentative), KX And, AM Aur, V644 Mon, DN Ori, and AY Per were detected at the 100 to 400 micro-Jy level, corresponding to luminosity densities of order 10 exp 17 erg/s/Hz. These luminosity densities, combined with nearly flat cm spectra and high brightness temperatures, are consistent with the nonthermal gyrosynchrotron radiation model proposed as the result of observations from the previous PELA survey. Also, the star V367 Cyg was reobserved at thirteen different orbital phases; no variability was found within the errors. V367 Cyg's lack of variability and well-determined average spectral index, however, imply the possibility of a different emission mechanism, thermal bremsstrahlung, although the nonthermal model cannot be entirely ruled out. The characteristic brightness temperature of thermal bremsstrahlung is only about 10,000 K, which means that the radius of the emission region would have to be much larger than previously assumed, about 10 AU. Suggestions for further observations of all previously observed PELAS are presented in order to determine the correct emission mechanism.

Elias, Nicholas M., II; Guedel, Manuel

1993-01-01

160

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

International Nuclear Information System (INIS)

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

161

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

162

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)

163

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

164

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 precipitan caused by energetic electrons precipitating from the earth's radiation belt following their injection deep into the magnetosphere during the magnetic storm

165

Quantitative study of substorm-associated VLF phase anomalies and precipitating energetic electrons on November 13, 1979  

International Nuclear Information System (INIS)

The phase anomalies associated with substorms are observed on VLF signals propagating on transauroral paths (transmitters at OMEGA-ALDRA (13.6 kHz), GBR (16.0 kHz), and OMEGA--NORTH DAKOTA (13.6 kHz)) which were continually received at Inubo, Japan, during the events on November 13, 1979. Detailed comparisons are made between these phase anomalies and geomagnetic bays, and quantitative relations are obtained with precipitating energetic electrons (E>30, E>100, and E>300 keV) detected on board the TIROS-N and NOAA 6 satellites. It is concluded that two types of VLF phase anomalies exist which, in turn, are associated with two phases in the history of energetic electron precipitation into the atmosphere. The first type of phase anomaly is associated with direct injection of energetic electrons into the outer magnetosphere and atmosphere which, in turn, is completely correlated in time with development of the auroral electrojet current system. The second type arises from energetic electrons which subsequently precipitate from a trapped electron population and has a delayed onset and prolonged duration. An excellent quantitative correlation is obtained between the logarithm of the electron flux and the magnitude of the phase anomaly on the OMEGA-ALDRA signal. From the local time characteristics of this quantitative relation it is deduced that the electrons with E>300 keV are the main source of D region ionization responsible for the VLF phase anomalyhe VLF phase anomaly

166

Optical emission spectroscopy observations of fast pulsed capillary discharge plasmas  

Science.gov (United States)

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

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

2014-05-01

167

Observations of field emission from amorphous carbon films  

International Nuclear Information System (INIS)

Full text.In the past few years there has been significant interest in several applications that could involve vacuum electron emission. One of the most discussed applications is for displays, high-power and high frequency devices. Metal and semiconductor field emitter arrays with the sharp points are prone to catastrophic failure at high current densities. Although semiconductor field emitters can yield high current densities (>1500 A/cm2), they are easily contaminated and will not operate after being exposed to oxygen. A third approach, currently under investigation involves using field emitters coated with wide-band gap (>5eV) materials having their conduction band close to the vacuum energy level, even in the presence of O2 and H2O background gases. A candidate material under investigation as a field emitter coating with enhanced emission properties is amorphous diamond. In this work field emission from amorphous carbon films prepared on Si substrates has been investigated. Field emission was observed at fields as low as 20 KV/cm. The samples were tested in the as grown form and after coating with thin films of Au. Thin vacuum deposited Au layers significantly improved the stability of the emission current. The experimental results show that, within the applied field range, the I-V characteristics are well described by the Fowler-Nordheim regime

168

ROSAT observations of X-ray emission from planetary nebulae  

CERN Document Server

We have searched the entire ROSAT archive for useful observations to study X-ray emission from Galactic planetary nebulae (PNs). The search yields a sample of 63 PNs, which we call the ROSAT PN sample. About 20-25% of this sample show X-ray emission; these include 13 definite detections and three possible detections (at a 2-sigma level). All X-ray sources in these PNs are concentrated near the central stars. Only A 30, BD+30 3639, and NGC 6543 are marginally resolved by the ROSAT instruments. Three types of X-ray spectra are seen in PNs. Type 1 consists of only soft X-ray emission (0.5 keV, and can be fitted by thin plasma emission models at temperatures of a few 10^6 K. Type 3 is a composite of a bright Type 1 component and a fainter Type 2 component. Unresolved soft sources with Type 1 spectra or the soft component of Type 3 spectra are most likely photospheric emission from the hot central stars. Absorption cross sections are large for these soft-energy photons; therefore, only large, tenuous, evolved PNs ...

Guerrero, M; Gruendl, R A; Guerrero, Martin A.; Chu, You-Hua; Gruendl, Robert A.

2000-01-01

169

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

170

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.nd.

171

TIMS observations of surface emissivity in HAPEX-Sahel  

Science.gov (United States)

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

Schmugge, Thomas; Hook, Simon; Kahle, Anne

1995-01-01

172

Observable Majoron Emission in Neutrinoless Double Beta Decay  

OpenAIRE

We consider a class of simplest Majoron models where neutrino- majoron couplings can be in the range $g \\sim 10^{-5}-10^{-3}$ leading to the observability of neutrinoless double beta decay with majoron emission. The majoron is a singlet of the electroweak gauge symmetry, thus avoiding conflict with the LEP data on Z decay, which rules out the triplet and doublet majoron models.

Berezhiani, Z.; Smirnov, A. Yu; Valle, J. W. F.

1992-01-01

173

Coherent whistler emissions in the magnetosphere – Cluster observations  

Directory of Open Access Journals (Sweden)

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

I. Dandouras

2007-02-01

174

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

175

XMM-Newton Observation of Solar Wind Charge Exchange Emission  

CERN Document Server

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

Snowden, S L; Kuntz, K D

2004-01-01

176

Lunar occultation observations of millimeter CO emission in S255  

International Nuclear Information System (INIS)

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

177

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

International Nuclear Information System (INIS)

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

178

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

International Nuclear Information System (INIS)

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

179

Structure of VLF whistler mode sideband waves in the magnetosphere  

Energy Technology Data Exchange (ETDEWEB)

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.

Sa, L.A.D.; Helliwell, R.A. (Stanford Univ., CA (United States))

1988-03-01

180

Normal development of the fruitfly Drosophila in VLF magnetic fields  

International Nuclear Information System (INIS)

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

181

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

182

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

183

FERMI Observations of Gamma -Ray Emission From the Moon  

Science.gov (United States)

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

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

2012-01-01

184

CBR anisotropy and galactic emission observations from Antarctica  

International Nuclear Information System (INIS)

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

185

Observations of SN 1987A: the narrow emission lines  

International Nuclear Information System (INIS)

The observations of narrow emission lines of Hell, CIII, NIII, NIV, NV and OIII in the short-wavelegth spectrum of SN 1987A are presented and discussed. It is shown that they originate from a circumstellar shell, which is at least a light year in size and whose nitrogen abundance relative to both carbon and oxygen is greatly enhanced as compared with cosmic values. Because of its characteristics, this shell is likely to be the remnant of the wind ejected by the progenitor star when it was a red supergiant

186

Effects of large-scale precipitations of relativistic magnetospheric electrons during and after the geomagnetic storm on November 27-28, 1990 according to VLF wave propagation data  

International Nuclear Information System (INIS)

By an example of ionospheric effects of an isolated geomagnetic storm are considered possibilities of the VLF wave monitoring of D region disturbances, caused by intrusion of relativistic (> 0.3 MeV) and subrelativistic (0.04-0.3 MeV) magnetospheric electrons. During and after the storm is observed large-scale prolonged (4-5 days) precipitation of the particles, caused the VLF wave phase anomalies at some spatially separated extended routes. Anomalies correlate closely between themselves and their value and duration correlate with the Dst index of the geomagnetic activity. 26 refs., 2 figs., 2 tabs

187

Observations of a complete sample of emission-line galaxies  

International Nuclear Information System (INIS)

Optical spectroscopic and broad-band imaging observations were obtained for all 172 emission-line galaxy (ELG) candidates in Lists IV and V of the University of Michigan Curtis Schmidt Objective Prism (UM) Survey. These data allow for the accurate determination of the completeness limits and selection characteristics of the survey and provide valuable information about the physical nature of the survey constituents. The UM survey is found to be comprehensive in the sense that it includes a wide range of types of active galaxies. Analysis of the data shows that the completeness characteristics of this survey are most accurately parameterized using emission-line flux and equivalent width. This result leads to the definition of a complete sample of UM galaxies which is used to determine the relative populations of the various types, of ELGs found in the survey. Important insights into the physical conditions in the emission-line regions of these objects are gained by the use of line-ratio diagnostic diagrams. A previously unrecognized segregation of the galaxies with H II region-like spectra by their ELG type is seen in these diagrams

188

On the numerical modelling of VLF chorus dynamical spectra  

Directory of Open Access Journals (Sweden)

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

D. Nunn

2009-06-01

189

EGRET Observations of Diffuse Gamma-Ray Emission in Monoceros  

Science.gov (United States)

We present a study of the diffuse, high-energy gamma-ray emission observed toward Monoceros by the EGRET instrument on the Compton Gamma-Ray Observatory. The EGRET data for this region (l = 210-250arcdeg , b = -15 - +20arcdeg ) include two observations, viewing periods 510.0 and 510.5, taken specifically for this work. The diffuse emission, largely produced by cosmic-ray interactions with interstellar gas, is used to trace the variation of the density of high-energy cosmic rays across the outer Galaxy in the third quadrant. This study complements an earlier work for the second quadrant (Digel et al. 1996, ApJ, 463, 609). Both regions contain segments of the Perseus arm, but the gap between the local arm and the Perseus arm in Monoceros is great enough that the density of cosmic rays in the interarm region can be measured separately. The density inferred from the gamma-ray emissivity of the gas is found to be significantly less in the interarm than in the local or Perseus arms. This finding supports models of Galactic cosmic rays which assume that cosmic rays are coupled to interstellar gas. For the local molecular clouds in Monoceros, which include Mon R2 and CMa OB1, we are also able to measure the mass-calibrating ratio N(H_2)/WCO=(1.56 +/- 0.29)*E(20) cm(-2) (K km s(-1) )(-1) , and set limits on the variation of cosmic-ray density within the clouds.

Digel, S. W.; Grenier, I. A.; Hunter, S. D.; Dame, T. M.; Thaddeus, P.

1998-05-01

190

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

International Nuclear Information System (INIS)

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

191

Periodic Jovian radio emission observed in decametric frequency range.  

Science.gov (United States)

We report the observations of the periodic Jovian non-Io radio emission recorded by Cassini, Wind and STEREO spacecraft in the decametric frequency range. The main group of these periodic radio features is observed as a series of arc-like radio bursts reoccurring with an averaged period of 10.07 hours or ~1.5% longer than the rotation rate of the planet's magnetosphere. The sources of these bursts sub-corotate with Jupiter being active during several Jupiter rotations. In most of the observed episodes the burst has small negative frequency drift in the time-frequency coordinates similar to vertex-late arcs of the Io-DAM. Besides this main group of periodic burst, we have also found two other groups of the periodic features rarely observed in the radio spectra - 1) "vertex-early" periodic non-Io DAM bursts or arcs with positive frequency drift and 2) non-arc periodic radio features. In contrast to the main group of the periodic non-Io bursts these "vertex-early" bursts reoccurred with the period close to the Jupiter rotation and typically were observed during 7-10 Jupiter rotations. The other rare group of the periodic non-arc radio features which are observed in form of broad beamed radio emission lacked clear discrete features. In our study we analyzed the properties of the different morphological groups of the periodic non-Io DAM bursts. This study comprise the determination of the averaged period of the bursts repetition as well as examination of our data for the existence of active Jovian longitudes at which periodic bursts of the different morphological groups occur more often. Additionally, on basis of observations over more than one Jupiter's 11.86 year orbital period we have also checked the dependence of the morphology of the periodic bursts on the declination of the Jovigraphic equatorial plane with respect to the ecliptic plane. We also suggest that the different morphological groups of the periodic features may have different origins and may be attributed to different particle dissipation processes in the Jovian magnetosphere.

Panchenko, M.; Rucker, H. O.

2012-09-01

192

Observations of Microwave Continuum Emission from Air Shower Plasmas  

CERN Document Server

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

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

2007-01-01

193

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

Directory of Open Access Journals (Sweden)

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

Y. Kasahara

2008-07-01

194

Significance of VLF transmitter in the precipitation on inner belt electrons  

International Nuclear Information System (INIS)

From the low-altitude satellite P78-1, narrow and sometimes multiple peaks have been observed in the energy spectra of electrons from 68 to 1120 keV precipitating in the drift loss cone from the inner radiation belt. Simultaneously, measurements of the plasma wave environment at higher altitudes on the same field lines have been made with the ISEE plasma wave experiment in many cases. The peaks in electron energy are sometimes extremely narrow, being of the order of 20-keV wide after the instrument resolution is unfolded. The plasma wave observations in these cases reveal the frequent presence of single and sometimes multiple monochromatic frequencies in the 10kHz to 25-kHz range that are attributed to ground-based VLF transmitters. The plasma wave experiment also provides electron plasma density profiles. The variations of the peak energies with L value and the nearly simultaneous and spatially coordinated narrow band wave frequencies strongly support the conclusion that the narrow peaks in the electron spectra result from cyclotron resonance interactions with the waves produced by ground-based VLF transmitters and that the effect of two or more transmitters are sometimes observed simultaneously

195

Common antenna preamplifier-isolator for VLF-LF receivers  

Science.gov (United States)

A modified high impedance preamplifier circuit which provides outputs to drive an Omega-VLF receiver and an ADF-LF receiver from a common antenna on general aviation aircraft is reported. The preamplifier was evaluated with fixed ground station receivers and results show the burn out problem of the first stage MOSFET during very close lightning discharges was eliminated.

Burhans, R. W.

1975-01-01

196

The European VLF/LF radio network: current status  

Science.gov (United States)

For several years researches about correlation between seismicity and disturbances in radio broadcasting are being carried out: in particular, the Japanese Pacific VLF radio network and the European VLF-LF radio network have been developed during the last years. The European network has been developed starting from two LF receivers located in central Italy in 1996. Up to now, 11 receivers of a new type, able to sample the VLF and LF intensity of ten radio signals, are being into operation in different European countries. The daily updating of data is effective and the data bank is located at the Department of Physics of the University of Bari (Italy) which is the central node of the network. In order to discover anomalies, the software able to carry out automatically a daily data analysis by the Wavelet spectra method has been planned and realized. At the moment, the software operates on four signals (two LF and two VLF) collected by one of the receiver located in Italy. If the anomaly is particularly strong a warning system gives an advise on the work station into operation in the central node of the Network. In any case, before assuming an anomaly as a seismic anomaly, geomagnetic and meteorological data must be checked as well as any possible instrumental malfunction. At present these controls are carried out only discontinuously by the researchers of the Bari Team.

Biagi, Pier Francesco; Maggipinto, Tommaso; Ermini, A.

2014-11-01

197

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

198

Anchoring Atmospheric Density Models Using Observed Shuttle Plume Emissions  

Science.gov (United States)

Atmospheric number densities at a given low-earth orbit (LEO) altitude can vary by more than an order of magnitude, depending on such parameters as diurnal variations and solar activity. The MSIS atmospheric model, which includes these dependent variables as input, is reported as being accurate to ±15%. Improvement to such models requires accurate direct atmospheric measurement. Here, a means of anchoring atmospheric models is offered through measuring the size and shape of atomic line or molecular band radiance resulting from the atmospheric interaction from rocket engine plumes or gas releases in LEO. Many discrete line or band emissions, ranging from the infrared to the ultraviolet may be suitable. For this purpose we are focusing on NH(A?X), centered at 316 nm. This emission is seen in the plumes of the Shuttle Orbiter PRCS engines, is expected in the plume of any amine fueled engine, and can be observed from remote sensors in space or on the ground. The atmospheric interaction of gas releases or plumes from spacecraft in LEO are understood by comparison of observed radiance with that predicted by Direct Simulation Monte Carlo (DSMC) models. The recent Extended Variable Hard Sphere (EVHS) improvements in treating hyperthermal collisions has produced exceptional agreement between measured and modeled steady-state Space Shuttle OMS and PRCS 190-250 nm Cameron band plume radiance from CO(a?X), which is understood to result from a combination of two- and three-step mechanisms. Radiance from NH(A?X) in far field plumes is understood to result from a simpler single-step process of the reaction of a minor plume species with atomic oxygen, making it more suitable for use in determining atmospheric density. It is recommended that direct retrofire burns of amine fueled engines be imaged in a narrow band from remote sensors to reveal atmospheric number density. In principal the simple measurement of the distance between the engine exit and the peak in the steady-state radiance from LEO spacecraft can indicate atmospheric density to ~1% accuracy. Use of this radiance requires calibration by an accurate independent measurement associated with a well-resolved steady-state image of it.

Dimpfl, W. L.; Bernstien, L. S.

2010-12-01

199

Inversion of airborne tensor VLF data using integral equations  

Science.gov (United States)

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

Kamm, Jochen; Pedersen, Laust B.

2014-08-01

200

Excitation of guided ELF-VLF waves through modification of the F{sub 2} ionospheric layer by high-power radio waves  

Energy Technology Data Exchange (ETDEWEB)

The possibility of controlled excitation of ELF-VLF electromagnetic waves through modification of the F{sub 2} ionospheric layer by high-power high-frequency emission is demonstrated in a natural experiment by using the Sura midlatitude heating facility. The excited low-frequency waves can be used to explore the near-Earth space and stimulate the excitation of a magnetospheric maser.

Markov, G. A.; Belov, A. S.; Komrakov, G. P. [Lobachevsky State University (Russian Federation); Parrot, M. [Environmental Physics and Chemistry Laboratory (France)

2012-03-15

201

Observations of exoelectron emission associated with heterogeneous catalysis  

Science.gov (United States)

It is suggested that the exoelectron emission from the catalyst may be used to monitor the rate of oxidation of CO and CH4 over palladium catalysts. Indirect heating of the catalyst and atmospheric pressure have no effect upon this monitoring system. Although the mechanism relating catalysis to exoelectron emission is not clear, it is considered possible that electron emission is triggered by the adsorption-desorption cycle.

Hoenig, S. A.; Utter, M. G.

1977-01-01

202

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

203

A generation mechanism of chorus emissions using BWO theory  

International Nuclear Information System (INIS)

In this paper, discrete VLF chorus emissions recorded at low latitude ground station Jammu (geomag. Lat. = 220 26/ 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.

204

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

Directory of Open Access Journals (Sweden)

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

S. Palit

2013-09-01

205

VLF study of low magnitude Earthquakes (4.5  

Science.gov (United States)

In the course of the European VLF/LF radio receiver network (International Network for Frontier Research on Earthquake Precursors, INFREP), radio signals in the frequency range from 10-50 kilohertz are received, continuously recorded (temporal resolution 20 seconds) and analyzed in the Graz/Austria knot. The radio signals are generated by dedicated distributed transmitters and detected by INFREP receivers in Europe. In case the signal is crossing an earthquake preparation zone, we are in principle able to detect seismic activity if the signal to noise ratio is high enough. The requirements to detect a seismic event with the radio link methods are given by the magnitude M of the Earthquake (EQ), the EQ preparation zone and the Fresnel zone. As pointed out by Rozhnoi et al. (2009), the VLF methods are suitable for earthquakes M>5.0. Furthermore, the VLF/LF radio link gets only disturbed if it is crossing the EQ preparation zone which is described by Molchanov et al. (2008). In the frame of this project I analyze low seismicity EQs (M?5.6) in south/eastern Europe in the time period 2011-2013. My emphasis is on two seismic events with magnitudes 5.6 and 4.8 which we are not able to adequately characterize using our single parameter VLF method. I perform a fine structure analysis of the residua of various radio links crossing the area around the particular 2 EQs. Depending on the individual paths not all radio links are crossing the EQ preparation zone directly, so a comparative study is possible. As a comparison I analyze with the same method the already good described EQ of L'Aquila/Italy in 2009 with M=6.3 and radio links which are crossing directly the EQ preparation zone. In the course of this project we try to understand in more detail why it is so difficult to detect EQs with 4.5LF radio link methods and why it is so important that the radio links are crossing directly the preparation zone, respectively how a VLF/LF path is affected if it misses the preparation zone tight. References [1] A. Rozhnoi et al.: Anomalies in VLF radio signals prior Abruzzo earthquake (M=6.3) on 6 April 2009, National Hazards and Earth System Sciences, 9, 1727-1732, 2009. [2] A. Molchanov, M. Hayakawa: Seismo-Electromagnetics and related Phenomena: History and latest results, Terrapub, 2008.

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

2014-05-01

206

Further sounding rocket observations of structured whistler mode auroral emissions  

Science.gov (United States)

Two recent sounding rockets were launched into active auroral substorms from Poker Flat, Alaska: CHARM on 27 February 2007 and SIERRA on 14 January 2002. Both payloads included HF wave receivers. As previously reported, the SIERRA HF receiver recorded short-lived, periodic, time-dispersed features at 200-600 kHz (“stripes”), in which high-frequency components precede low frequencies, leading to a nearly linear frequency-time signature. These features coincided with a region identified as Alfvénic and dominated by suprathermal electron bursts and 10-110 eV downward going ions poleward of the main inverted V auroral arc. The CHARM experiment, using different electric field sensors, confirmed the occurrence of the stripe features with characteristics similar to those observed with SIERRA. The most promising mechanism to explain stripes is a cyclotron resonance between downgoing Z mode waves and upgoing electron conics in the topside ionosphere at altitudes of 3000-5000 km. These electron conics resonate with successively lower-frequency waves as they ascend, leading to emissions in which lower frequencies are delayed relative to higher frequencies; detailed modeling reproduces even fairly subtle nonlinear features of the stripes’ frequency-time signature. The resulting structured Z mode waves then convert to whistler mode waves, which propagate to rocket altitudes. Previous simulations have shown that electron conics can be generated by Alfvénic acceleration and retain the periodicity of the driving Alfvén wave. If this acceleration could be driven by Alfvén waves at the frequency of the periodicity of the stripes, it could explain this periodicity and would be consistent with their correlation with an Alfvénic region.

Colpitts, C. A.; LaBelle, J.; Kletzing, C. A.; Yoon, P. H.

2010-10-01

207

Detection of karst structures using airborne EM and VLF  

International Nuclear Information System (INIS)

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

208

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

209

Observations of terrestrial far UV emissions by the FAUST telescope  

Science.gov (United States)

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

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

1993-01-01

210

Location accuracy of long distance VLF lightning locationnetwork  

OpenAIRE

An experimental VLF WorldWide Lightning Location (WWLL) network is being developed to provide realtime locations of cloud to ground lightning discharges occurring throughout the globe. This network has expanded from a limited number of stations in the Western Pacific to its current state of 11 stations, in most longitude sectors, with additional stations planned in the near future. As part of the initial testing phase of the WWLL the network has operated in a simple mode, sending the station ...

Rodger, C. J.; Brundell, J. B.; Dowden, R. L.; Thomson, N. R.

2004-01-01

211

Determining foreground contamination in cosmic microwave background observations: Diffuse Galactic emission in the MAXIMA-Ifield  

International Nuclear Information System (INIS)

Observations of the cosmic microwave background (CMB) can be contaminated by diffuse foreground emission from sources such as Galactic dust and synchrotron radiation. In these cases, the morphology of the contaminating source is known from observations at different frequencies, but not its amplitude at the frequency of interest for the CMB. We develop a technique for accounting for the effects of such emission in this case, and for simultaneously estimating the foreground amplitude in the CMB observations. We apply the technique to CMB data from the MAXIMA-1 experiment, using maps of Galactic dust emission from combinations of IRAS and DIRBE observations, as well as compilations of Galactic synchrotron emission observations. The spectrum of the dust emission over the 150-450 GHz observed by MAXIMA is consistent with preferred models, but the effect on CMB power spectrum observations is negligible

212

Modification of the ionosphere by VLF wave-induced electron precipitation  

International Nuclear Information System (INIS)

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

213

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

214

Observations that can unravel the coherent radio emission mechanism in pulsars  

CERN Document Server

Searching for the physical mechanism that can excite the coherent radio emission in pulsars is still an enigmatic problem. A wealth of high quality observations exist, which over the years have been instrumental in putting stringent constraints to pulsar emission models. In this article we will discuss the observational results that strongly suggests that pulsar radio emission is excited by coherent curvature radiation. We will also mention issues that remain to be resolved.

Mitra, Dipanjan

2013-01-01

215

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

Directory of Open Access Journals (Sweden)

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

P. Castellanos

2013-08-01

216

Infrared emission from X-ray binaries - IRAS observations  

International Nuclear Information System (INIS)

Theoretical calculations show that detectable amounts of FIR radiation can be produced by accretion disks around compact sources. Here, the HEAO A-1 Catalog (Wood et al., 1984) and Bradt and McClintock (1983) are used to select a likely set of candidate sources, and the IRAS Point Source Catalog and IRAS Serendipitous Survey Catalog are used to search for characteristic IR emission from sources in fields around them. Eighty-one candidates with 242 IRAS field sources were examined and color corrected. Eight of these have IR flux measurements which are consistent with emisison from an accretion disk S/N, although other mechanisms for their IR emission cannot yet be ruled out. Most have poor positional corespondences and must be considered suspect as identifications. 34 refs

217

XMM Observations of X-Ray Emission from Supernovae  

Science.gov (United States)

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

Immler, Stefan; Lewin, Walter

2003-01-01

218

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.

219

Emission of linalool from Valencia orange blossoms and its observation in ambient air  

Science.gov (United States)

Emission measurements made over a 5-month period of a Valencia orange tree showed the significant emission of the terpenoid linalool (C 10H 18O) from Valencia orange blossoms. The average annual emission rate of this Olinda Valencia orange, derived from emission measurements which include the blossoming season, is a factor of ˜10 higher than the average annual emission rate derived from measurements taken outside of the blossom season. Ambient monoterpene and linalool concentrations were measured in Riverside, California, in the spring and supported the chamber plant emissions data, with linalool concentrations as high as 17 ?g m -3 being observed in an orange grove. These results show that current biogenic emission inventories which are formulated from limited survey data, generally not including seasonal variations in the vegetative emissions, can be subject to large uncertainties.

Arey, Janet; Corchnoy, Stephanie B.; Atkinson, Roger

220

A theoretical and experimental study of non-ducted VLF waves after propagation through the magnetosphere.  

Science.gov (United States)

The nonducted propagation of artificial VLF waves through the magnetosphere has been studied by means of data obtained by the FR-1 satellite experiment, in which fixed frequency (16.8 kHz) waves radiated by a transmitter at the ground (at L equals 2.1) are received by the satellite, at 750 km altitude, both in the zone close to the transmitter and in the conjugate zone. From the wave-normal directions and Doppler shifts measured in the conjugate zone, it has been possible to identify waves that have been propagated from the Northern to the Southern Hemisphere in both ducted and nonducted modes. In this paper, the main features of the nonducted wave have been interpreted by ray tracing in models of the magnetosphere. The results improve our understanding as to why very few whistlers are observed on the ground at low latitudes.

Cerisier, J. C.

1973-01-01

221

Comparisons of emissivity observations from satellites and the ground at the CRCS Dunhuang Gobi site  

Science.gov (United States)

sets of field-measured hyperspectral resolution infrared (IR) emissivity spectra were taken from the China Radiometric Calibration Sites (CRCS) Dunhuang site in China, with one representing daytime and the other representing nighttime. Comparisons of the two sets show that the daytime emissivity is smaller than the nighttime emissivity in almost the entire spectrum between 7.5 and 14 µm, strong field evidence to support emissivity diurnal variations, which have been reported in previous studies using satellite observations. These emissivities are used as a reference to evaluate three different emissivity products from the same site: the Atmospheric Infrared Sounder (AIRS) operational emissivity products, the Moderate Resolution Imaging Spectroradiometer (MODIS) operational emissivity products, and the University of Wisconsin-Madison Hyperspectral Resolution IR emissivity (UWIREMIS) database. The AIRS emissivity does not agree as well with the field measurements when compared to that from MODIS and the UWIREMIS despite the fact that AIRS is hyperspectral; the likely cause for the disagreement is cloud contamination due to AIRS' large footprint. MODIS has the advantage of high spatial resolution and visible/near-infrared channels to help the cloud mask and is therefore less affected by cloud contamination. The V4.1 MODIS emissivity agrees better with the field measurement than the UWIREMIS, while the V5 does not do as well. The UWIREMIS emissivity, on the other hand, has the advantage of hyperspectral resolution, which makes it more useful for applications. The temporal analysis of the three satellite-based emissivity products is also presented.

Zhang, Yong; Li, Zhenglong; Li, Jun

2014-11-01

222

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

Science.gov (United States)

An experimental Very Low Frequency (VLF) World-Wide Lightning Location Network (WWLLN) has been developed through collaborations with research institutions across the world, providing global real-time locations of lightning discharges. As of April 2006, the network included 25 stations providing coverage for much of the Earth. In this paper we examine the detection efficiency of the WWLLN by comparing the locations from this network with lightning location data purchased from a commercial lightning location network operating in New Zealand. Our analysis confirms that WWLLN favours high peak current return stroke lightning discharges, and that discharges with larger currents are observed by more stations across the global network. We then construct a first principles detection efficiency model to describe the WWLLN, combining calibration information for each station with theoretical modelling to describe the expected amplitudes of the VLF sferics observed by the network. This detection efficiency model allows the prediction of the global variation in WWLLN lightning detection, and an estimate of the minimum CG return stroke peak current required to trigger the network. There are strong spatial variations across the globe, primarily due to station density and sensitivity. The WWLLN is currently best suited to study the occurrence and impacts of high peak-current lightning. For example, in 2005 about 12% of the global elve-producing lightning will have been located by the network. Since the lightning-EMP which produce elves has a high mean rate (210 per minute) it has the potential to significantly influence the ionosphere on regional scales.

Rodger, C. J.; Werner, S.; Brundell, J. B.; Lay, E. H.; Thomson, N. R.; Holzworth, R. H.; Dowden, R. L.

2006-12-01

223

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

Directory of Open Access Journals (Sweden)

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

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

C. J. Rodger

2006-12-01

224

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

225

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)

226

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.)

227

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

228

Observations and calculations of atmospheric helium 10830 emission  

Science.gov (United States)

Observations and computer model calculations of helium excitation and transport were carried out. The following conclusions can be drawn: (1) the dawn helium density in the thermosphere is greater than the dusk helium density by 50 per cent or more, in contrast to the static diffusion models but in agreement with the dynamic models; (2) the computed He 10830 intensities are inconsistent with the observations when use of the new Penning ionization cross section for loss of atomic oxygen is used; (3) conjugate photoelectron precipitation is responsible for excitation of atmospheric helium at middle latitudes, but it is not evident in the observations at the equator or Brazil (L equals 1.1); (4) the computations predict greater conjugate effects than observed, leading to the possibility of strong interhemispheric absorption.

Christensen, A. B.

1974-01-01

229

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)

230

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

OpenAIRE

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

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

2006-01-01

231

Solar Flare Impulsive Phase Footpoint Emission Observed with SDO/EVE  

Science.gov (United States)

The differential emission measure of solar flare plasmas was 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 - 7.4 allow for the evolution of the DEM to be studied over a wide temperature range at 10s cadence. The DEM construction technique is applied to several M and X-class flares where impulsive phase EUV emission is observable in the disk-integrated EVE spectra. The emission is verified using AIA images to be originating from the flare ribbons and footpoints and EVE observations are used to infer the thermal structure of the EUV emitting flare chromosphere. For the nine events studied the constructed differential emission measures have a two component distribution during the impulsive phase. The low temperature component has peak temperatures of 1 - 2 MK, and a high temperature component peaking at 10 MK.

Kennedy, Michael; Milligan, R. O.; Mathioudakis, M.

2013-07-01

232

Parity violating observables in radiative neutrino pair emission from metastable atoms  

CERN Document Server

We report on a possibility of measuring parity violating effects in radiative neutrino pair emission from metastable atoms; asymmetric angular distribution of emitted photons from oriented atoms and emergent circular polarization. Their observation, along with the continuous photon energy spectrum which has 6 thresholds, may be interpreted as events being a combined weak and QED process, emission of $\\gamma \

Yoshimura, M; Sasao, N; Yamaguchi, T

2009-01-01

233

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.)

234

Observations of OI 7774 emission excited by conjugate photoelectrons. [ionosonde data analhysis  

Science.gov (United States)

Observations and computer calculations of O I 7774 A airglow emissions excited by conjugate photoelectrons have been carried out. The observations were made at McDonald Observatory, Texas using a 2 m grille spectrometer from December 1972 to June 1973. The zenithal emission intensity during conjugate photoelectron precipitation was fairly constant at 2-4 R until conjugate sunset, after which it diminished steadily and ceased near a conjugate solar zenith angle of 105 (plus or minus 3) deg. A predawn enhancement in both O I 7774 A and forbidden O I 6300 A was observed to commence near 102 deg. The computations utilize the two-stream technique of Nagy and Banks (1970) to obtain the escaping photoelectron flux and the local excitation rates of the oxygen emissions. Good agreement with the observations is obtained for the dependence of the emission rate on conjugate solar zenith angle.

Christensen, A. B.

1975-01-01

235

Observations of the 145.5 micron (OI) emission line in the Orion nebula  

Science.gov (United States)

A first set of observations of the (OI) 3P to 3P1 (145.5 micron) transition was obtained. The line was observed both in a beam centered on the Trapezium, and in a 7 times wider beam encompassing most of the Orion Nebula. A wide beam map of the region was constructed which shows that most of the emission is confined to the central regions of the nebula. These observations may be compared with reported measurement of the 3P1 to 3P2 (63.2 micron) transition in Orion and are consistent with optically thin emission in the 145.5 micron line and self-adsorbed 63.2 micron emission lines. Mechanisms are discussed for the excitation of neutral oxygen. It is included that much of the observed emission originates in the thin, radio-recombination-line-emitting CII/HI envelope bordering on the HII region.

Stacey, G. J.; Smyers, S. D.; Kurtz, N. T.; Harwit, M.

1982-01-01

236

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

237

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

238

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

239

Observation of valence band electron emission from n-type silicon field emitter arrays  

Science.gov (United States)

Electron emission from the valence band of n-type Si field emitter arrays is reported. High electrostatic field at the surface of Si was achieved by reducing the radius of the emitter tip. Using oxidation sharpening, 1 ?m aperture polycrystalline Si gate, n-type Si field emitter arrays with small tip radius (˜10 nm) were fabricated. Three distinct emission regions were observed: conduction band emission at low gate voltages, saturated current emission from the conduction band at intermediate voltages, and valence band plus conduction band emission at high gate voltages. Emission currents at low and high voltages obey the Fowler-Nordheim theory. The ratio of the slopes of the corresponding Fowler-Nordheim fits for these two regions is 1.495 which is in close agreement with the theoretical value of 1.445.

Ding, Meng; Kim, Han; Akinwande, Akintunde I.

1999-08-01

240

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

241

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

Energy Technology Data Exchange (ETDEWEB)

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

Reid, R. R., E-mail: remington.r.reid@gmail.com [U.S. Naval Research Laboratory, Washington, DC 20375 (United States); Romero-Talamás, C. A. [Department of Engineering, University of Maryland Baltimore County, Baltimore, Maryland 21250 (United States); Young, W. C. [CPLA, University of Wisconsin, Madison, Wisconsin 53706 (United States); Ellis, R. F.; Hassam, A. B. [IREAP, University of Maryland, College Park, Maryland 20742 (United States)

2014-06-15

242

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

International Nuclear Information System (INIS)

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

243

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

244

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

245

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

Directory of Open Access Journals (Sweden)

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

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

M. Zavala

2008-08-01

246

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

247

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1997-05-27

248

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

Science.gov (United States)

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

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

2012-04-01

249

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

Science.gov (United States)

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

Šulic, D.; Nina, A.; Sreckovic, V.

2010-07-01

250

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

Science.gov (United States)

On 18 January 2011, at 20:23 UTC, an earthquake of magnitude 7.2 occurred in south-western Pakistan (latitude 28.73(°) N, longitude 63.93(°) E) at a depth of 68 km. We present the results of the analysis of very low frequency (VLF) radio signals, received at three stations located in India. We analyze the VLF signals around this earthquake day and look for possible precursory effects of this earthquake. For our analysis, we use four different VLF propagation paths. These propagation paths are DHO-IERC (Sitapur), VTX-Pune, VTX-ICSP (Indian Centre for Space Physics, Kolkata) and NWC-IERC. We observed significant shifts of the “sunrise terminator time” (SRT) for DHO-IERC and VTX-Pune paths. For DHO-IERC path, the SRT of the VLF signals shifted towards night time three days before the earthquake day, and in the case of VTX-Pune path it shifted towards night time just one day before the earthquake day. For VTX-Kolkata path, the shift of SRT is four days before the earthquake day, but here the shift is not so strong, somewhere between 2sigma and 3sigma lines. For the other two paths, namely, DHO-IERC and VTX-Pune, the terminator time shifts crossed the 3sigma line. We found no significant shifts of SRT for NWC-IERC propagation path. Higher deviation in the VTX-Pune path as compared to VTX-ICSP path could be due to the proximity of the former to the epicenter. Similarly, DHO-IERC path is over the epicenter while NWC-IERC path is totally away from the epicenter. This could be the reason why the effect in DHO-IERC path is stronger than that in NWC-IERC path.

Ray, Suman; Chakrabarti, Sandip Kumar

251

Observation of green emission from Ce{sup 3+}-doped gadolinium oxide nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Green emission at around 500 nm is observed in Gd{sub 2}O{sub 3}:Ce{sup 3+} nanoparticles and the intensity is highly dependent on the concentration of Ce{sup 3+} in the nanoparticles. The luminescence of this emission displays both picosecond (ps) and millisecond (ms) lifetimes. The ms lifetime is over four orders of magnitude longer than typical luminescence lifetimes (10-40 ns) of Ce{sup 3+} in traditional Ce{sup 3+} doped phosphors and therefore likely originates from defect states. The picosecond lifetime is shorter than the typical Ce{sup 3+} value and is also likely due to defect or surface states. When the samples are annealed at 700 {sup o}C, 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 Gd{sub 2}O{sub 3} undoped nanoparticles, which is attributed to the stabilizer, polyethylene glycol biscarboxymethyl ether. On aging, the undoped particles show similar emission to the doped particles with similar luminescence lifetimes. When Eu{sup 3+} ions are co-doped in Gd{sub 2}O{sub 3}:Ce nanoparticles, both the green emission and the emission at 612 nm from Eu{sup 3+} are observed.

Kuan Woo, Boon [Department of Physics, University of Texas at Arlington, Arlington, TX 76019-0059 (United States); Joly, Alan G. [Pacific Northwest National Laboratory, Richland, WA 99352 (United States); Chen, Wei, E-mail: weichen@uta.ed [Department of Physics, University of Texas at Arlington, Arlington, TX 76019-0059 (United States)

2011-01-15

252

Observation of green emission from Ce3+-doped gadolinium oxide nanoparticles  

International Nuclear Information System (INIS)

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 (ps) and millisecond (ms) lifetimes. The ms 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. On 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.

253

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

254

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

International Nuclear Information System (INIS)

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

255

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

Science.gov (United States)

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

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

2014-06-01

256

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

Science.gov (United States)

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

Steffes, Paul G.; Jenkins, Jon M.; Klein, Michael J.

1990-01-01

257

Panchromatic Observations of the Textbook GRB 110205A: Constraining Physical Mechanisms of Prompt Emission and Afterglow  

Science.gov (United States)

We present a comprehensive analysis of a bright, long duration (T(sub 90) approx. 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb and BOOTES telescopes when the GRB was still radiating in the gamma-ray band. Thanks to its long duration, nearly 200 s of observations were obtained simultaneously from optical, X-ray to gamma-ray (1 eV - 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution across 6 orders of magnitude in energy during the prompt emission phase. In particular, by fitting the time resolved prompt spectra, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard GRB synchrotron emission model in the fast cooling regime. Although the prompt optical emission is brighter than the extrapolation of the best fit X/ -ray spectra, it traces the -ray light curve shape, suggesting a relation to the prompt high energy emission. The synchrotron + synchrotron self-Compton (SSC) scenario is disfavored by the data, but the models invoking a pair of internal shocks or having two emission regions can interpret the data well. Shortly after prompt emission (approx. 1100 s), a bright (R = 14.0) optical emission hump with very steep rise ( alpha approx. 5.5) was observed which we interpret as the emission from the reverse shock. It is the first time that the rising phase of a reverse shock component has been closely observed.

Zheng, W.; Shen, R. F.; Sakamoto, T.; Beardmore, A. P.; De Pasquale, M.; Wu, X. F.; Gorosabel, J.; Urata, Y.; Sugita, S.; Zhang, B.; Pozanenko, A.; Nissinen, M.; Sahu, D. K.; Im, M.; Ukwatta, T. N.; Andreev, M.; Klunko, E.; Volnova, A.; Akerlof, C. W.; Anto, P.; Barthelmy, S. D.; Breeveld, A.; Carsenty, U.; Gehrels, N.; Sonbas, E.

2011-01-01

258

The impact of PMSE and NLC particles on VLF propagation  

Directory of Open Access Journals (Sweden)

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

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

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

D. Nunn

2004-04-01

259

Submillimeter Array Observations of CS J=14--13 Emission from the Evolved Star IRC+10216  

OpenAIRE

We present imaging observations of the evolved star IRC+10216 in the CS J=14--13 line at 685.4 GHz and associated submillimeter continuum at about 2'' resolution made with the partially constructed Submillimeter Array. The CS J=14--13 line emission from the stellar envelope is well resolved both spatially and spectrally. The strong central concentration of the line emission provides direct evidence that CS is a parent molecule that forms close to the stellar photosphere, in ...

Young, K. H.; Hunter, T. R.; Wilner, D. J.; Gurwell, M. A.

2004-01-01

260

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

OpenAIRE

This paper compares two global inversions to estimate carbon monoxide (CO) emissions for 2004. Either surface flask observations from the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) or CO total columns from the Measurement of Pollution in the Troposphere (MOPITT) instrument are assimilated in a 4D-Var framework. Inferred emission estimates from the two inversions are consistent over the Northern H...

Hooghiemstra, P. B.; Krol, M. C.; Bergamaschi, P.; Laat, A. T. J.; Werf, G. R.; Novelli, P. C.; Deeter, M. N.; Aben, I.; Ro?ckmann, T.

2012-01-01

261

On the emissivity of wire-grid polarizers for astronomical observations at mm-wavelengths  

OpenAIRE

We have measured, using a custom setup, the emissivity of metallic wire-grids, suitable for polarimeters and interferometers at mm and far infrared wavelengths. We find that the effective emissivity of these devices is of the order of a few %, depending on fabrication technology and aging. We discuss their use in astronomical instruments, with special attention to Martin Puplett Interferometers in low-background applications, like astronomical observations of the Cosmic Micr...

Schillaci, Alessandro; Battistelli, Elia; Alessandro, Giuseppe D.; Bernardis, Paolo; Masi, Silvia

2012-01-01

262

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

OpenAIRE

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...

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

2007-01-01

263

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

Directory of Open Access Journals (Sweden)

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

J. F. Meirink

2006-01-01

264

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)

265

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

Science.gov (United States)

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

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

2013-12-01

266

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

International Nuclear Information System (INIS)

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

267

C2 emission features in the Red Rectangle. A combined observational laboratory study  

Science.gov (United States)

Context. The Red Rectangle proto-planetary nebula (HD 44179) is known for a number of rather narrow emission features superimposed on a broad extended red emission (ERE) covering the 5000-7500 Å regime. The origin of these emission features is unknown. Aims: The aim of the present work is to search for potential carriers by combining new observational and laboratory data. This also allows to interpret spectral emission features in terms of actual physical conditions like temperature and density constraints and to trace chemical processes in the outflows of the Red Rectangle. Methods: Observational spectra have been obtained with the EMMI-NTT at offsets of 3'', 6'', 7'', 11'', 16'' and 20'' distance to the central star HD 44179. The spectra are compared to the outcome of a time-gated laser induced fluorescence laboratory study of an expanding acetylene plasma using a special supersonic pin-hole discharge source. With this set-up the hydrocarbon chemistry in the Red Rectangle nebula is simulated under laboratory controlled conditions. The plasma source has the unique feature to generate electronically and vibrationally excited species at low rotational temperatures. The comparison is facilitated by a simple model for fluorescent emission in the nebula. Results: Two of the astronomically observed narrow emission bands can be assigned as originating from unresolved rovibronic progressions within the d3?_g ? a3?_u Swan system of the C2 radical. The band appearance corresponds to a rotational temperature between 200 and 1000 K. The emission is driven by absorption in the C2 Phillips bands followed by intersystem crossing from the singlet to the triplet state and pumping in the Swan bands. Conclusions: These observations imply an active (photo)chemistry in the ejecta of the Red Rectangle. Based on observations collected at the European Southern Observatory, Chile. Program ID: 080.C-0814(A).

Wehres, N.; Romanzin, C.; Linnartz, H.; van Winckel, H.; Tielens, A. G. G. M.

2010-07-01

268

Observations of the event of May 16, 1981 in optical light and in kilometric radio emission  

International Nuclear Information System (INIS)

We present the results of Prognoz-8 observations of radio emission in the range 2160-540 kHz for the event of May 16, 1981. We pick out active periods on the basis of the optical data, and we compare radio bursts with activity phenomena observed in Halpha-filtergrams during preflare, maximum, and post-maximum phases of the flare. In the explosive phase, at the time when two ribbons of emission form, we observed a burst of radio emission similar to type III burst, with a rapid frequency drift. Estimates of the speed of the excitation agent yield the value V = 0.72c. We propose that at great heights (R = 8-20 R.), particles break out of the shockfront. During the post-maximum period, when arched structures existed in the flare, we observeno special phenomena in kilometric radiation, apart from small noise bursts

269

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

Energy Technology Data Exchange (ETDEWEB)

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

Tibbs, C. T. [Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States); Scaife, A. M. M. [School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom); Dickinson, C.; Davies, R. D.; Davis, R. J.; Watson, R. A. [Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL (United Kingdom); Paladini, R. [NASA Herschel Science Center, California Institute of Technology, Pasadena, CA 91125 (United States); Grainge, K. J. B., E-mail: ctibbs@ipac.caltech.edu [Astrophysics Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2013-05-10

270

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

International Nuclear Information System (INIS)

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

271

AMI Observations of the Anomalous Microwave Emission in the Perseus Molecular Cloud  

Science.gov (United States)

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

Tibbs, C. T.; Scaife, A. M. M.; Dickinson, C.; Paladini, R.; Davies, R. D.; Davis, R. J.; Grainge, K. J. B.; Watson, R. A.

2013-05-01

272

Recent developments in Fire Emission Monitoring in MACC-II using Fire Radiative Power Observations  

Science.gov (United States)

We will present the latest developments of the Global Fire Assimilation System (GFAS), which has been implemented by the MACC-II project in order to provide accurate fire biomass burning emission estimates for the real time and retrospective Copernicus/GMES atmospheric monitoring and forecasting services. Accurate fire emissions have been shown to be a crucial input for air quality forecasts even when satellite-based atmospheric observations are being assimilated. On the other hand, comparisons of the simulated smoke plumes and atmospheric observations provide information on the accuracy of the bottom-up fire emission estimates. The emission estimates of GFAS are generally consistent with those of the GFED inventory, but they are available with 1-day temporal resoution and in real time. There are also a few small systematic differences between the emission estimates of the two inventories. The general consistency is achieved by assimilating Fire Radiative Power (FRP) observations from the MODIS instruments, and by a conversion of the daily FRP to dry matter combustion rate that depends on the fire type. Emission rates for forty smoke constituents are subsequently calculated from the dry matter combustion rate. The emisson estimates have been validated against atmospheric observations of aerosol optical depth, carbon monoxide, ozone, nitrogen dioxide and formaldehyde using the atmospheric models of MACC. The GFAS data are currently produced with resolutions of 1 day and 0.1 deg, and a time lag of seven hours. They cover the period since January 2003 and are publicly available. In the future, the inclusion of FRP products from the geostationary satellites Meteosat-9, GOES-East, and GOES-West will lead to a finer temporal resolution as well as to an improved accuracy of the daily emission estimates. Estimates of smoke injection height will also become available

Kaiser, Johannes W.; Andela, Niels; Heil, Angelika; Paugam, Ronan; Schultz, Martin G.; van der Werf, Guido R.; Wooster, Martin J.; Remy, Samuel

2013-04-01

273

Plasma waves observed by sounding rockets  

International Nuclear Information System (INIS)

Observations of plasma wave phenomena have been conducted with several rockets launched at Kagoshima Space Center, Kyushu, Japan, and at Showa Base, Antarctica. This report presents some results of the observations in anticipation of having valuable comments from other plasma physicists, especially from those who are concerned with laboratory plasma. In the K-9M-41 rocket experiment, VLF plasma waves were observed. In this experiment, the electron beam of several tens of uA was emitted from a hot cathode when a positive dc bias changing from 0 to 10V at 1V interval each second was applied to a receiving dipole antenna. The discrete emissions with 'U' shaped frequency spectrum were observed for the dc bias over 3 volts. The U emissions appeared twice per spin period of the rocket. Similar rocket experiment was performed at Showa Base using a loop and dipole antenna and without hot cathode. Emissions were observed with varying conditions. At present, the authors postulate that such emissions may be produced just in the vicinity of a rocket due to a kind of wake effect. (Aoki, K.)

274

Fine spectral structures in Jovian decametric radio emission observed by ground-based radio telescope.  

Science.gov (United States)

Jupiter with the largest planetary magnetosphere in the solar system emits intense coherent non-thermal radio emission in a wide frequency range. This emission is a result of a complicated interaction between the dynamic Jovian magnetosphere and energetic particles supplying the free energy from planetary rotation and the interaction between Jupiter and the Galilean moons. Decametric radio emission (DAM) is the strongest component of Jovian radiation observed in a frequency range from few MHz up to 40 MHz. This emission is generated via cyclotron maser mechanism in sources located along Jovian magnetic field lines. Depending on the time scales the Jovian DAMexhibits different complex spectral structures. We present the observations of the Jovian decametric radio emission using the large ground-based radio telescope URAN- 2 (Poltava, Ukraine) operated in the decametric frequency range. This telescope is one of the largest low frequency telescopes in Europe equipped with high performance digital radio spectrometers. The antenna array of URAN-2 consists of 512 crossed dipoles with an effective area of 28 000m2 and beam pattern size of 3.5 x 7 deg. (at 25 MHz). The instrument enables continuous observations of the Jovian radio during long period of times. Jovian DAM was observed continuously since Sep. 2012 (depending on Jupiter visibility) with relatively high time-frequency resolution (4 kHz - 100ms) in the broad frequency range (8-32MHz). We have detected a big amount of the fine spectral structures in the dynamic spectra of DAM such as trains of S-bursts, quasi-continuous narrowband emission, narrow-band splitting events and zebra stripe-like patterns. We analyzed mainly the fine structures associated with non-Io controlled DAM. We discuss how the observed narrowband structures which most probably are related to the propagation of the decametric radiation in the Jupiter's ionosphere can be used to study the plasma parameters in the inner Jovian magnetosphere.

Panchenko, M.; Brazhenko, A. I.; Shaposhnikov, V. E.; Konovalenko, A. A.; Rucker, H. O.

2014-04-01

275

Cluster Observations Whistler-mode Propagation Inside and Outside the Plasmasphere  

Science.gov (United States)

ELF/VLF Chorus emissions and lightning- generated whistlers are two types of whistler mode waves commonly detected in the inner regions of the Earth's magnetosphere. Lightning-generated whistlers are generally observed in the region 2lightning strikes on Earth, and can travel relatively longer distances into the magnetosphere with relatively broad wave fronts. Recently the Cluster spacecraft have provided a unique opportunity to obtain four simultaneous measurements of these ELF/VLF whistler mode waves at four separate points in space. In the present paper we use CLUSTER data to compare the time signatures of both chorus emissions and whistlers in order to determine how the spectral properties of these waves vary with position. In particular we determine differences in the frequency spectrum of the lightning-generated whistlers, both inside and outside the plasmasphere, and use these differences to test the hypothesis that whistlers propagating outside the plasmasphere are often strongly coupled to lower hybrid waves in regions where the plasma density profile is irregular. In the case of chorus emissions, we compare the frequency shifts of individual chorus elements as measured on the CLUSTER spacecraft and use this data to determine the spatial and temporal characteristics of the chorus source regions

Platino, M.; Inan, U. S.; Bell, T. F.; Gurnett, D. A.; Pickett, J. S.

2004-12-01

276

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

OpenAIRE

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

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

2010-01-01

277

Worldwide biogenic soil NOx emissions inferred from OMI NO2 observations  

Science.gov (United States)

Biogenic NOx emissions from soils are a large natural source with substantial uncertainties in global bottom-up estimates (ranging from 4 to 15 Tg N yr-1). We reduce this range in emission estimates, and present a top-down soil NOx emission inventory for 2005 based on retrieved tropospheric NO2 columns from the Ozone Monitoring Instrument (OMI). We use a state-of-science soil NOx emission inventory (Hudman et al., 2012) as a priori in the GEOS-Chem chemistry transport model to identify 11 regions where tropospheric NO2 columns are dominated by soil NOx emissions. Strong correlations between soil NOx emissions and simulated NO2 columns indicate that spatial patterns in simulated NO2 columns in these regions indeed reflect the underlying soil NOx emissions. Subsequently, we use a mass-balance approach to constrain emissions for these 11 regions on all major continents using OMI observed and GEOS-Chem simulated tropospheric NO2 columns. We find that responses of simulated NO2 columns to changing NOx emissions are suppressed over low NOx regions, and account for these non-linearities in our inversion approach. In general, our approach suggests that emissions need to be increased in most regions. Our OMI top-down soil NOx inventory amounts to 10.0 Tg N for 2005 when only constraining the 11 regions, and 12.9 Tg N when extrapolating the constraints globally. Substantial regional differences exist (ranging from -40% to +90%), and globally our top-down inventory is 4-35% higher than the GEOS-Chem a priori (9.6 Tg N yr-1). We evaluate NO2 concentrations simulated with our new OMI top-down inventory against surface NO2 measurements from monitoring stations in Africa, the USA and Europe. Although this comparison is complicated by several factors, we find an encouraging improved agreement when using the OMI top-down inventory compared to using the a priori inventory. To our knowledge, this study provides, for the first time, specific constraints on soil NOx emissions on all major continents using OMI NO2 columns. Our results rule out the low end of reported soil NOx emission estimates, and suggest that global emissions are most likely around 12.9 ± 3.9 Tg N yr-1.

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

2014-09-01

278

Worldwide biogenic soil NOx emissions inferred from OMI NO2 observations  

Directory of Open Access Journals (Sweden)

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

G. C. M. Vinken

2014-06-01

279

VLF long-range lightning location using the arrival time difference technique (ATD)  

Science.gov (United States)

A new network of VLF receiving systems is currently being developed in the USA to support NASA's Tropical Rain Measuring Mission (TRMM). The new network will be deployed in the east coast of the US, including Puerto Rico, and will be operational in late 1995. The system should give affordable, near real-time, accurate lightning locating capabilities at long ranges and with extended coverage. It is based on the Arrival Time Difference (ATD) method of Lee (1986; 1990). The ATD technique is based on the estimation of the time of arrival of sferics detected over an 18 kHz bandwith. The ground system results will be compared and complemented with satellite optical measurements gathered with the already operational Optical Transient Detector (OTD) instrument and in due course with its successor the Lightning Imaging Sensor (LIS). Lightning observations are important to understand atmospheric electrification phenomena, discharge processes, associated phenomena on earth (e.g. whistlers, explosive Spread-F) and other planets. In addition, lightning is a conspicuous indicator of atmospheric activity whose potential is just beginning to be recognized and utilized. On more prosaic grounds, lightning observations are important for protection of life, property and services.

Ierkic, H. Mario

1996-01-01

280

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

International Nuclear Information System (INIS)

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

281

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

International Nuclear Information System (INIS)

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

282

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

CERN Document Server

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

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

2003-01-01

283

X-ray emission from supernovae: a review of the observations  

International Nuclear Information System (INIS)

Supernovae have been expected to be X-ray sources for many years. This paper reviews the observations that have detected or placed upper limits on the emission of X-rays from supernovae. A firm upper limit exists on X-ray emission from Type Ia supernovae based upon an observation of SN 1992A (parent galaxy: NGC 1380) made with ROSAT. The type II supernovae detected include SN 1978K (NGC 1313), SN 1980K (NGC 6946), SN 1986J (NGC 891), SN 1987A (Large Magellanic Cloud), and, most recently, SN 1993J (NGC 3031). These supernovae emit X-rays by at least two different processes. The author briefly reviews the proposed emission mechanisms. (author)

284

X-ray emission from supernovae: a review of the observations  

Energy Technology Data Exchange (ETDEWEB)

Supernovae have been expected to be X-ray sources for many years. This paper reviews the observations that have detected or placed upper limits on the emission of X-rays from supernovae. A firm upper limit exists on X-ray emission from Type Ia supernovae based upon an observation of SN 1992A (parent galaxy: NGC 1380) made with ROSAT. The type II supernovae detected include SN 1978K (NGC 1313), SN 1980K (NGC 6946), SN 1986J (NGC 891), SN 1987A (Large Magellanic Cloud), and, most recently, SN 1993J (NGC 3031). These supernovae emit X-rays by at least two different processes. The author briefly reviews the proposed emission mechanisms. (author)

Schlegel, E.M. [NASA Goddard Space Flight Center, Greenbelt, MD (United States)

1995-11-01

285

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

Directory of Open Access Journals (Sweden)

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

J. W. Kaiser

2012-01-01

286

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

Science.gov (United States)

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

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

2004-01-01

287

Using lunar observations to assess Terra MODIS thermal emissive bands calibration  

Science.gov (United States)

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

Xiong, Xiaoxiong; Chen, Hongda

2010-09-01

288

Observation of selectively excited continuous vacuum ultraviolet emission in molecular hydrogen  

International Nuclear Information System (INIS)

Vacuum ultraviolet continuous emission from selectively excited vibrational levels of the B 1?+/sub u/ state of molecular hydrogen into the dissociation continuum of the electronic ground state has been observed. The intensity distribution in the continuous spectra measured quantitatively proves the theory of Dalgarno, Herzberg, and Stephens. The new radiative dissociation process makes tunable vacuum ultraviolet laser action in molecular hydrogen appear feasible

289

The 9- to 12-?m atmospheric ozone emission observed in the SPIRIT 1 experiment  

International Nuclear Information System (INIS)

Spectra of ozone ?3 emission in an auroral nighttime sky were obtained in the Spectral Infrared Interferometric Telescope experiment. High-quality hot band spectra reveal spectral structure not previously observable and provide a critical test of ozone radiance models. The limb radiance profile is in good agreement with previous data below ?95 km, but above this it falls off more rapidly

290

Observations of the 145.5 micron [O I] emission line in the Orion Nebula  

International Nuclear Information System (INIS)

We have obtained a first set of observations of the [O I] 3P0 -3P1 (145.5 ?m) transition. We observed the line both in a 1' x 1' beam centered on the Trapezium and in a 7' x 7' beam encompassing most of the Orion Nebula. We also have constructed a wide-beam (7' x 7') map of the region which shows that most of the emission is confined to the central regions of the nebula. These observations may be compared with reported measurement of the 3P1-3P2 (63.2 ?m) transition in Orion and are consistent with optically thin emission in the 145.5 ?m line and self-absorbed 63.2 ?m emission lines. We discuss mechanisms for the excitation of neutral oxygen and conclude that much of the observed emission originates in the thin, radio recombination line-emitting C II/H I envelope bordering on the H II region

291

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

OpenAIRE

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

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

2008-01-01

292

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

OpenAIRE

A simulation study to understand the influence of topography on the surface emissivity observed by a satellite microwave radiometer is carried out. We analyze the effects due to changes in observation angle, including the rotation of the polarization plane. A mountainous area in the Alps (Northern Italy) is considered and the information on the relief extracted from a digital elevation model is exploited. The numerical simulation refers to a radiometric image, acquired by a conically-scanning...

Marzano, Frank S.; Nazzareno Pierdicca; Luca Pulvirenti

2008-01-01

293

X-ray observations of emission line galaxies with the Einstein Observatory  

International Nuclear Information System (INIS)

Four emission line galaxies, NGC 1365, 2992, 5506 and 7582, previously recognized as X-ray emitters in the range 1042-1043 erg/sec, have been observed with the Einstein Observatory Imaging Proportional Counter (IPC), in one case (NGC 2992) also with the High Resolution Imager (HRI). The Monitor Proportional Counter (MPC) data collected during these and other observations represent an important complement. This note summarizes the results. (orig./WL)

294

The visible and total emission of flares deduced from Sun-as-a-star observations.  

Science.gov (United States)

During solar flares, the impact of the accelerated particles on the chromosphere results in heating of the surrounding materials that then dissipate the received energy though electromagnetic emission at all wavelengths. The most dramatic increase occurs in the extreme ultraviolet and soft X-rays emission coming from the hot coronal plasma. However, small increases of the visible emission that are less easily detectable can contain a significant part of the total radiated energy. The statistical analysis of solar irradiance observations allows to quantify the energy radiated by the flare at all wavelengths and reveals that the visible component constitutes the core of the total emission for most of the flares. We discuss the origin of this white light emission and how its energy compares with the energy released in the soft X-ray and extreme ultraviolet spectral ranges. We next investigate how the spectral distribution of the flare energy evolves with the flare X-ray class and we estimate the power law exponent for the frequency distribution of the total flare emission.

Kretzschmar, Matthieu

2012-07-01

295

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

Directory of Open Access Journals (Sweden)

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

A. L. Broadfoot

2011-04-01

296

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

Directory of Open Access Journals (Sweden)

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

A. K. Mebust

2013-08-01

297

Observational constraints on the external shock prior emission hypothesis of GRBs  

CERN Document Server

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

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

2011-01-01

298

Verification of anthropogenic emissions of China by satellite and ground observations  

Science.gov (United States)

An integrated emission inventory of China was validated through comparing the Community Multi-scale Air Quality (CMAQ) simulations with the NO 2 and SO 2 column retrieved from Ozone Monitoring Instrument (OMI), Aerosol Optical Depth (AOD) retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS), and ground observations of SO 2, NO 2, PM 10, PM 2.5 and its components. The model simulations were performed for year 2005. The model generally reproduces both spatial distribution and seasonal variation of tropospheric NO 2, SO 2 column densities and AOD in China that have been observed by OMI and MODIS. The correlation coefficients between model simulated and satellite observed NO 2 column densities, SO 2 column densities and AOD over east China are 0.90, 0.85 and 0.79, and the normalized mean bias (NMBs) are -8%, 1%, and -8% respectively, which are comparable with the errors from satellite retrievals. The surface concentrations of NO 2, SO 2, and PM 10 given by CMAQ model are also comparable with those observed in Beijing, Shanghai, and Guangzhou, with the NMBs ranging from 1% to 18%, -3% to -25%, and -12% to 18%, respectively. The results suggest that the anthropogenic emissions of SO 2, NOx, and PM 10 used in this study are in line with both the satellite and ground observations therefore are of acceptable accuracy. There is overestimation for SO 2 and underestimation for PM 10 in some industry-intensive areas because of the inaccuracy of spatial and temporal allocations. The CMAQ model also significantly underestimates the PM 2.5 concentration in Beijhjing, mainly due to the limitation of secondary organic aerosol (SOA) formation mechanism used in the model and the underestimation of primary OC and EC emissions. Therefore more efforts shall be made to improve the primary emission estimates of OC and EC, as well as the temporal allocation factor of SO 2 and PM 10 emissions.

Wang, Shuxiao; Xing, Jia; Chatani, Satoru; Hao, Jiming; Klimont, Zbigniew; Cofala, Janusz; Amann, Markus

2011-11-01

299

Earth observations for estimating greenhouse gas emissions from deforestation in developing countries  

International Nuclear Information System (INIS)

In response to the United Nations Framework Convention on Climate Change (UNFCCC) process investigating the technical issues surrounding the ability to reduce greenhouse gas (GHG) emissions from deforestation in developing countries, this paper reviews technical capabilities for monitoring deforestation and estimating emissions. Implementation of policies to reduce emissions from deforestation require effective deforestation monitoring systems that are reproducible, provide consistent results, meet standards for mapping accuracy, and can be implemented at the national level. Remotely sensed data supported by ground observations are key to effective monitoring. Capacity in developing countries for deforestation monitoring is well-advanced in a few countries and is a feasible goal in most others. Data sources exist to determine base periods in the 1990s as historical reference points. Forest degradation (e.g. from high impact logging and fragmentation) also contribute to greenhouse gas emissions but it is more technically challenging to measure than deforestation. Data on carbon stocks, which are needed to estimate emissions, cannot currently be observed directly over large areas with remote sensing. Guidelines for carbon accounting from deforestation exist and are available in approved Intergovernmental Panel on Climate Change (IPCC) reports and can be applied at national scales in the absence of forest inventory or other data. Key constraints for implementing programs Key constraints for implementing programs to monitor greenhouse gas emissions from deforestation are international commitment of resources to increase capacity, coordination of observations to ensure pan-tropical coverage, access to free or low-cost data, and standard and consensual protocols for data interpretation and analysis

300

Quenched carbonaceous composite - Fluorescence spectrum compared to the extended red emission observed in reflection nebulae  

Science.gov (United States)

The photoluminescence (fluorescence) of a film of the laboratory-synthesized quenched carbonaceous composite (filmy QCC) is shown to have a single broad emission feature with a peak wavelength that varies from 670 to 725 nm, and coincides with that of the extended red emission observed in reflection nebulae. The rapid decay of the filmy QCC red fluorescence in air and of the stable blue fluorescence of the filmy QCC dissolved in liquid Freon suggests that the red fluorescence originates from the interaction of active chemical species and aromatic components in the filmy QCC. A material similar in nature to that of the filmy QCC may be a major component of interstellar dust.

Sakata, Akira; Wada, Setsuko; Narisawa, Takatoshi; Asano, Yoichi; Iijima, Yutaka; Onaka, Takashi; Tokunaga, Alan T.

1992-01-01

301

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

CERN Document Server

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

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

2011-01-01

302

Model for the VLF/LF radio signal anomalies formation associated with earthquakes  

Science.gov (United States)

The influence of quasi-static electric field of seismic origin on the characteristics of the internal gravity waves (IGWs) in the Earth's ionosphere is considered. The electric field in the ionosphere arises due to the injection of charged aerosols into the atmosphere, formation of an EMF in the near Earth atmosphere and perturbation of the conductive electric current in the global electric circuit. Amplification of the electric current in seismic zone is accompanied by the formation of perturbation of the lower ionosphere that affects the amplitude and phase of VLF/LF signals. The action of the electric field on the IGWs is connected with the appearance of the Ampere's force in the ionosphere. In the spectral range of these waves the latter acts on the neutral component of the ionosphere plasma. As the result of this interaction the ionosphere starts to support the discrete spectrum of oscillations. Periods of their maximums increase as numbers of natural sequence. The existence of such peculiarities of the waves in the ionosphere is confirmed by observations.

Sorokin, V. M.; Pokhotelov, O. A.

2014-12-01

303

Recent FUSE Observations of Diffuse O VI Emission from the Interstellar Medium  

CERN Document Server

We present new results from our survey of diffuse O VI-emitting gas in the interstellar medium with the Far Ultraviolet Spectroscopic Explorer (FUSE). Background observations obtained since 2005 have yielded eleven new O VI detections of 3-sigma significance, and archival searches have revealed two more. An additional 15 sight lines yield interesting upper limits. Combined with previous results, these observations reveal the large-scale structure of the O VI-bearing gas in the quadrant of the sky centered on the Magellanic Clouds. The most prominent feature is a layer of low-velocity O VI emission extending more than 70 degrees from the Galactic plane. At low latitudes (|b| < 30 degrees), the emission comes from narrow, high-density conductive interfaces in the local ISM. At high latitudes, the emission is from extended, low-density regions in the Galactic halo. We also detect O VI emission from the interface region of the Magellanic System, a structure recently identified from H I observations. These are ...

Dixon, W Van Dyke

2008-01-01

304

Lightning as an embryonic source of VLF hiss  

International Nuclear Information System (INIS)

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

305

Ground-based observation of MF auroral radio emissions in the polar cap and cusp regions  

Science.gov (United States)

Recent ground-based observations have detected MF auroral radio emissions called MF burst and auroral roar. It is interpreted that origin of both emissions is upper hybrid waves generated in the ionosphere by auroral electrons. Some theoretical studies [e.g. Weatherwax et al., 2002] have proposed that MF burst which has a broad band spectrum is generated at an altitude of few hundred kilometers over a wide altitude range while auroral roar is excited in altitudes where a condition of fuh ~ nfce (n=2, 3) is met, which leads to its narrow band spectrum. The polarization spectrum observation at the Husafell observatory in Iceland, which started in 2005, revealed the polarization characteristics of 3fce roar and the relationship with energy of precipitating electrons [Sato et al., 2008]. However, occurrence rate is low because the observation site is located in the auroral zone. We install a new instrument for MF auroral radio emissions at Longyearbyen in Svalbard. The observation at Longyearbyen has several advantages: higher occurrence rate can be expected in the polar cap region, and simultaneous observations with EISCAT Svalbard Radar (ESR) and other ground-based observations can be easily obtained. The instrument consists of two types of observation systems. One is designed for the continuous observation of spectrum in a frequency range below 6 MHz. The other is designed to obtain waveform data in a frequency range below 4 MHz by an A/D converter with a sampling speed of 10MSPS. By using the wave form data, the arrival direction angle of a received radio wave can be estimated. In this presentation, we will introduce the purpose of the observation and the detail of the instrument, and report some initial results.

Sato, Y.; Ono, T.; Kumamoto, A.; Sato, N.; Fujii, R.; Kadokura, A.; Oagawa, Y.; Nozawa, S.

2008-12-01

306

Study of the NWC electrons belt observed on DEMETER Satellite  

CERN Document Server

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

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

2010-01-01

307

Estimating aerosol emissions by assimilating observed aerosol optical depth in a global aerosol model  

Directory of Open Access Journals (Sweden)

Full Text Available This study estimates the emission fluxes of a range of aerosol species and aerosol precursor at the global scale. These fluxes are estimated by assimilating daily total and fine mode aerosol optical depth (AOD at 550 nm from the Moderate Resolution Imaging Spectroradiometer (MODIS into a global aerosol model of intermediate complexity. Monthly emissions are fitted homogenously for each species over a set of predefined regions. The performance of the assimilation is evaluated by comparing the AOD after assimilation against the MODIS observations and against independent observations. The system is effective in forcing the model towards the observations, for both total and fine mode AOD. Significant improvements for the root mean square error and correlation coefficient against both the assimilated and independent datasets are observed as well as a significant decrease in the mean bias against the assimilated observations. The assimilation is more efficient over land than over ocean. The impact of the assimilation of fine mode AOD over ocean demonstrates potential for further improvement by including fine mode AOD observations over continents. The Angström exponent is also improved in African, European and dusty stations. The estimated emission flux for black carbon is 14.5 Tg yr?1, 119 Tg yr?1 for organic matter, 17 Pg yr?1 for sea salt, 82.7 TgS yr?1 for SO2 and 1383 Tg yr?1 for desert dust. They represent a difference of +45%, +40%, +26%, +13% and ?39% respectively, with respect to the a priori values. The initial errors attributed to the emission fluxes are reduced for all estimated species.

N. Huneeus

2012-01-01

308

EVLA Observation of Centimeter Continuum Emission from Protostars in Serpens South  

Science.gov (United States)

Serpens South is a protocluster with an unusually high abundance of Class 0 and I protostars, suggesting it is in a very early phase of star formation and may eventually form a star cluster. Following its discovery in 2008 with the Spitzer space telescope, infrared and millimeter observations and analysis quickly followed, however, Serpens South has yet to be fully explored in the radio. Radio observations at centimeter wavelengths have long been used as a tool to probe the dynamical processes of young protostars that are still heavily shrouded in their protostellar envelopes and thus cannot be seen at longer wavelengths. Radio observations then become an important tool in understanding Serpens South due to its young age. To this end, we have conducted EVLA C band continuum observations of the central region of the Serpens South protostellar cluster in order to map the centimeter continuum emission in a region of high Class 0 / I protostellar surface density. We report the detection of centimeter emission corresponding to protostars identified by Spitzer, and to protostars identified but blended by Herschel. We characterize their centimeter emission, and put them in context with previous Spitzer and Herschel infrared and far-infrared observations, as well as IRAM millimeter observations. Additionally, we make an assessment of the protostars' bolometric luminosity, and compare them to the known protostellar 3.6 cm to 6.0 cm luminosity vs. bolometric luminosity relation. With the EVLA, we present a mid-resolution map of centimeter emission from the central region of Serpens South with the highest sensitivity to date, with a beam size of ~5 arcseconds and rms on the order of 15 microJansky.

Kern, Nicholas S.; Tobin, John J.; Keown, Jared A.; Gutermuth, Robert A.

2015-01-01

309

New Ecuadorian VLF and ELF receiver for study the ionosphere  

Science.gov (United States)

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

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

310

Systematic errors in VLF direction-finding of whistler ducts  

International Nuclear Information System (INIS)

Several methods of determining the azimuthal bearing of whistler-mode waves propagating from their ionospheric exit-point to a ground-based receiver are outlined. The relative merits of their use for the location of the position of whistler ducts is discussed. The systematic error in the azimuthal bearing due to multipath propagation and wave polarisation (when applicable) is evaluated for six different VLF direction-finding systems. These are the 4 parameter A and B methods, the crossed loops goniometer, the NPE (no polarisation error) method, the field analysing method and the frequency tracking direction-finder. The multipath error for all these direction-finders is generally fairly large and fluctuates fairly rapidly with wave frequency. However, it is shown that for direction-finders for which there is also a polarisation error, this error tends to cancel out the error due to multipath propagation. This results in a combined error which is generally significantly smaller than either error source alone. (author)

311

Systematic errors in VLF direction-finding of whistler ducts  

International Nuclear Information System (INIS)

In the previous paper it was shown that the systematic error in the azimuthal bearing due to multipath propagation and incident wave polarisation (when this also constitutes an error) was given by only three different forms for all VLF direction-finders currently used to investigate the position of whistler ducts. In this paper the magnitude of this error is investigated for different ionospheric and ground parameters for these three different systematic error types. By incorporating an ionosphere for which the refractive index is given by the full Appleton-Hartree formula, the variation of the systematic error with ionospheric electron density and latitude and direction of propagation is investigated in addition to the variation with wave frequency, ground conductivity and dielectric constant and distance of propagation. The systematic bearing error is also investigated for the three methods when the azimuthal bearing is averaged over a 2 kHz bandwidth. This is found to lead to a significantly smaller bearing error which, for the crossed-loops goniometer, approximates the bearing error calculated when phase-dependent terms in the receiver response are ignored. (author)

312

The European VLF/LF Radio Network: the current status  

Science.gov (United States)

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

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

2014-05-01

313

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

OpenAIRE

We report observations of molecular oxygen (O$_2$) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O2 lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km/s with line widths 3 km/s; however, the transition at 1121 GHz is not detected. The observed line characteristics, combined with the results of earlier observations, suggest that the region responsible for the O$_2$ emission is 9" (6e16 cm) in size, and is located close to t...

Chen, Jo-hsin; Goldsmith, Paul F.; Viti, Serena; Snell, Ronald; Lis, Dariusz C.; Benz, Arnold; Bergin, Edwin; Black, John; Caselli, Paola; Encrenaz, Pierre; Falgarone, Edith; Goicoechea, Javier R.; Hjalmarson, Ake; Hollenbach, David; Kaufman, Michael

2014-01-01

314

Correcting atmospheric effects in thermal ground observations for hyperspectral emissivity estimation  

Science.gov (United States)

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

Timmermans, Joris; Buitrago, Maria

2014-05-01

315

VLA Observations of Carbon 91$\\alpha$ Recombination Line Emission in W49 North  

CERN Document Server

We have detected C91$\\alpha$ (8.5891 GHz) emission toward 4 ultra-compact \\HII regions (\\UCHII s; W49G, J, L & C) in the W49 North massive star forming region with the Very Large Array (VLA) at 3\\arcsec resolution. No carbon line emission was detected toward \\UCHII s W49F, A, O, S and Q at this frequency to a 3$\\sigma$ level of 2 mJy. We also observed the same region in the C75$\\alpha$ line (15.3 GHz) with no detection at a 3$\\sigma$ level of 6 mJy with a 1\\arcsec.7 beam. Detection of line emission toward these sources add supporting data to the earlier result of \

Roshi, D A; De Pree, C G; Goss, W M

2006-01-01

316

Observation of sporadic emissions from the sun and Jupiter with high temporal and spectral resolutions  

International Nuclear Information System (INIS)

Several instability phenomena in plasmas lead to the emission of very intense radioelectric waves. In the case of the solar corona and the magnetosphere of Jupiter, these emissions can be extremely short (1msec) and can have a very narrow spectrum (1kHz). They must not be considered as a noise but as a nonstationary signal. Instruments have been developed at Meudon and Nancay observatories to study these emissions in the decameter range with high temporal and spectral resolutions: frequency scanning spectrographs and multichannel spectrographs. A few results of dynamical spectra obtained with these devices are presented. The problems related with their sensitivity are discussed: in this wave range, the sensitivity is limited by the continuous noise received from the back of the sky but it also depends on the shape of the observed spectrum

317

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

Directory of Open Access Journals (Sweden)

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

T. Ernst

2001-06-01

318

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

International Nuclear Information System (INIS)

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

319

Results of VLF campaigns in Summer, Winter and during Solar Eclipse in Indian Subcontinent and Beyond  

International Nuclear Information System (INIS)

VLF propagation effects are generally understood in terms of the earth-ionosphere waveguide. However, details of the theory are still incomplete. Particularly important are the newly emerging fields of VLF Astronomy where the ionosphere is treated as a giant detector for extraterrestrial energetic phenomena and the subject of lithosphere-ionosphere coupling where the the disturbances of this giant detector is influenced by terrestrial events, especially earthquakes and other seismic activities. We review the activities of our group in these fields. In particular, we concentrate on the results of the VLF campaigns we conducted using over a dozen receiving stations in Summer, in Winter and during the Total Solar eclipse in July, 2009. We also discuss briefly the results we obtained in Antarctica and their implications.

320

Chandra Observations of Extended X-Ray Emission in ARP 220  

Science.gov (United States)

We resolve the extended X-ray emission from the prototypical ultraluminous infrared galaxy Arp 220. Extended, faint, edge-brightened, soft X-ray lobes outside the optical galaxy are observed to a distance of 1CL 15 kpc on each side of the nuclear region. Bright plumes inside the optical isophotes coincide with the optical line emission and extend 1 1 kpc from end to end across the nucleus. The data for the plumes cannot be fitted by a single-temperature plasma and display a range of temperatures from 0.2 to 1 keV. The plumes emerge from bright, diffuse circumnuclear emission in the inner 3 kpc centered on the Ha peak, which is displaced from the radio nuclei. There is a close morphological correspondence between the Ha and soft X-ray emission on all spatial scales. We interpret the plumes as a starburst-driven superwind and discuss two interpretations of the emission from the lobes in the context of simulations of the merger dynamics of Arp 220.

McDowell, J. C.; Clements, D. L.; Lamb, S. A.; Shaked, S.; Hearn, N. C.; Colina, L.; Mundell, C.; Borne, K.; Baker, A. C.; Arribas, S.

2003-01-01

321

A Suzaku Observation of the Neutral Fe-line Emission from RCW 86  

Science.gov (United States)

The newly operational X-ray satellite Suzaku observed the supernova remnant (SNR) RCW 86 in February 2006 to study the nature of the 6.4 keV emission line first detected with the Advanced Satellite for Cosmology and Astronomy (ASCA). The new data confirms the existence of the line, localizing it for the first time inside a low temperature emission region and not at the locus of the continuum hard X-ray emission. We also report the first detection of a 7.1 keV line that we interpret as the K(beta) emission from neutral or low-ionized iron. The Fe-K line features are consistent with a non-equilibrium plasma of Fe-rich ejecta with n(sub e) less than or approx. equal to 10(exp 9)/cu cm s and kT(sub e) > 1 keV. We found a sign that Fe K(alpha) line is intrinsically broadened 47 (35-57) eV (99% error region). Cr-K line is also marginally detected, which is supporting the ejecta origin for the Fe-K line. By showing that the hard continuum above 3 keV has different spatial distribution from the Fe-K line, we confirmed it to be synchrotron X-ray emission.

Ueno, Masaru; Sato, Rie; Kataoka, Jun; Bamba, Aya; Harrus, Ilana; Hiraga, Junko; Hughes, John P.; Kilbourne, Caroline A.; Koyama, Katsuji; Kokubun, Motohide; Nakajima, Hiroshi; Ozaki, Masanobu; Petre, Robert; Takahashi, Tadayuki; Tanaka, Takaaki; Tomida, Hiroshi; Yamaguchi, Hiroya

2007-01-01

322

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

CERN Document Server

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

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

2011-01-01

323

Jovian non-thermal radio emission observed by STEREO/WAVES  

Science.gov (United States)

Solar TErrestrial RElations Observatory (STEREO) consists of two 3-axis-stabilized identical spacecraft (STEREO-A and STEREO-B), launched on Oct. 25, 2006. The WAVES experiment onboard STEREO is a radio burst tracer which observes the generation and evolution of the radio disturbances from the Sun to the orbit of Earth. Being mainly dedicated for measuring solar radio bursts, SWAVES also provided unique observations of the Jovian planetary radio emission. For the first time Jovian radiation is observed stereoscopically by two identical spacecraft in a frequency range from few kHz up to 16 MHz. The data recorded during more than two years (Nov 2006 - Dec 2008) of mission operations is analyzed. A big amount of the events of non-Io and Io controlled "arc-like" decametric components of the Jovian radiation (DAM) as well as hectometric emission (HOM) has been recorded. The unique stereoscopic observations by STEREO provide the opportunity to determine the propagation characteristics of the Jovian non-thermal radiation such as directivity and beam width of the emission cone. First results will be presented.

Rucker, H. O.; Panchenko, M.; Shaposhnikov, V. E.; Melnik, V. N.; Boudjada, M. Y.; Stereo Team

2009-04-01

324

Improved model of isoprene emissions in Africa using OMI satellite observations of formaldehyde: implications for oxidants and particulate matter  

OpenAIRE

We use a 2005–2009 record of isoprene emissions over Africa derived from OMI satellite observations of formaldehyde (HCHO) to better understand the factors controlling isoprene emission on the scale of the continent and evaluate the impact of isoprene emissions on atmospheric composition in Africa. OMI-derived isoprene emissions show large seasonality over savannas driven by temperature and leaf area index (LAI), and much weaker seasonality over equatorial ...

Marais, E. A.; Jacob, D. J.; Guenther, A.; Chance, K.; Kurosu, T. P.; Murphy, J. G.; Reeves, C. E.; Pye, H. O. T.

2014-01-01

325

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

CERN Document Server

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

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

2013-01-01

326

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

CERN Document Server

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

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

2011-01-01

327

Multispacecraft Cluster observations of quasiperiodic emissions close to the geomagnetic equator  

Science.gov (United States)

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

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

2014-11-01

328

Statistical studies of non-Io Jupiter DAM emissions observed at Nançay during solar cycle 23 (1995-2001)  

Science.gov (United States)

Non-Io (or Io-independent) Jupiter decameter emissions observed by the Nançay decametric array during the rising phase of solar cycle 23 (1995-2001) are studied. About 700 emissions have been recorded during that period. From the statistical studies, several conclusions were obtained. It was observed that most of emissions (~91%) are Right-Hand elliptically polarized and from the so-called "A" source (i.e. northern hemisphere and for Jovian longitude of observer in the range ~200° to 320°). The relative contributions to emissions is (in decreasing order) from sources "A", "B" (northern, 100°-200°), C (southern, 300°-400°), and D (southern, 0°-80°). Considering all emissions, the average duration is ~22 min, the average maximum frequency is ~24 MHz and the average power is ~2.4 dB above the sky background. RH emissions reach higher frequencies than LH (Left-Hand) ones. Their duration and average power are similar, but peak values are higher for RH emissions. The number of emissions roughly follows the sunspot cycle. In relation to the solar cycle variation, it was observed that Jupiter radio emissions have on the average a longer duration during the rising phase. The maximum frequency of emissions is similar on the average for all phases, but extreme values (maximum) are seen during rising and solar maximum epochs. The emissions power is higher during the rising and maximum phases (similar in both) than during solar minimum.

Echer, E.; Zarka, P.; Denis, L.

2008-12-01

329

Quantification of Shipping Emissions in the Eastern Mediterranean and Comparison with Satellite Observations  

Science.gov (United States)

Shipping is considered as one of the main emission sources worldwide. Recent studies suggest that, in the Mediterrenean, ship emissions are responsible for 10-50% of black carbon, 2-12% ozone in the surface layer and 5-20% for nitrogen dioxide atmospheric column burden (Marmer et al., 2009). It is, therefore, essential to have an accurate emissions estimation for ships. Marmara Sea, an inland sea connecting the Mediterrenean to the Black Sea, has significant marine activity. Marmara region, surrounding the Marmara Sea, has over 30 million population (including Istanbul megacity) with significant emission sources (e.g., on-road traffic, industry). Emission amounts from ships can be calculated based on two different methodologies, one is according to the total amount of bunker fuels for maritime transport sold which is called top down approach and the other is shipping activity-based bottom-up approach. The top-down estimation method is not suitable for calculations of shipping emissions in Turkey since fuel sales cannot be accurately obtained. Also, top-down approaches possibly have some errors, since data assumptions for the average engine power, engine operating hours and emission factors are the most important uncertain inputs. Previously, a few studies based on bottom-up aproach have been carried on about shipping emissions in Marmara Sea according to the shipping statistics belong to Istanbul and Canakkale Straits and port regions. These studies were mainly depending on very rough assumptions such as avearage ship speed, fixed ships routes, generalized engine types and average fuel consumptions. Deniz C. (2008) estimated shipping emissions in 2003, for Marmara Sea and Turkish Straits as 111,000 tons for NOx, 87,000 tons for SO2, 5,451,000 tons for CO2, 4762 tons for PM. Although- between 2003 and 2008- there is approximately 15% increase in number of ships passsing through Turkish Straits, this study shows that, shippings emissions for the same region are estimated to be more than 3 times of previous studies. In this study, Automatic Information System (AIS) records of marine vessels (having 1 minute temporal resolution) for over 10,000 ships operating at the study area (including Marmara Sea, Istanbul and Canakkale Straits and some parts of Black Sea and Aegian Sea) were obtained from Turkish Undersecretariat for Maritime Affairs for the period between August 2008 and August 2009. These records include the position of the ships, gross tonnage and ship types. Using energy based emission factors for each operation mode, minute-by-minute emissions were estimated. Annual emission totals for merchant ships were estimated as 605,000 tons for NOX; 495,000 tons for SO2; 25,600 tons for HC; 53,300 tons for PM and 29,630,000 tons for CO2. This paper presents the methodology and the findings of the emissions estimates for ships. The results will also be compared to satellite observations. For this purpose, CO measurements from MOPITT and SO2 measurements from OMI will be utilized.

Kilic, A.; Unal, A.; Kindap, T.; Karaca, M.; Khan, M. N.

2010-12-01

330

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

Scientific Electronic Library Online (English)

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

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

2011-10-01

331

Fractal characteristics of the ground-observed ULF emissions in relation to geomagnetic and seismic activities  

Science.gov (United States)

Results of fractal analysis of ultra-low-frequency (ULF) emissions registered at a low-latitude observatory, Guam (geomagnetic coordinates ?m=9°N, ?m=225°), and at a high-latitude drifting station, North Pole-30 (?m=75°N, ?m=172°), are presented. The first set of data covers a long period of observations (20 months) including the strong (Ms=8) Guam earthquake of 8 August 1993. The second set of data covers a short period of observations (21 days) in April 1989 during the preparation phase of the big magnetic storm of 25 April 1989. Definite peculiarities in the behavior of ULF emission scaling (fractal) characteristics have been found, which are discussed on the basis of the self-organized criticality concept. The principal common peculiarity for magnetosphere ionosphere and lithosphere systems is detection of flicker noise (?˜1, D0˜2) in a certain frequency range on the preparation phase of strong magnetospheric and seismic events.

Smirnova, N. A.; Hayakawa, M.

2007-11-01

332

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

Science.gov (United States)

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

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

2013-12-01

333

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

Directory of Open Access Journals (Sweden)

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

L. Meng

2012-07-01

334

Isoprene Emissions in Africa Inferred from OMI Observations of Formaldehyde Columns  

OpenAIRE

We use 2005–2009 satellite observations of formaldehyde (HCHO) columns from the OMI instrument to infer biogenic isoprene emissions at monthly 1 × 1° resolution over the African continent. Our work includes new approaches to remove biomass burning influences using OMI absorbing aerosol optical depth data (to account for transport of fire plumes) and anthropogenic influences using AATSR satellite data for persistent small-flame fires (gas flaring). The resulting biogenic H...

Marais, E. A.; Jacob, D. J.; Kurosu, T. P.; Chance, K.; Murphy, J. G.; Reeves, C.; Mills, G.; Casadio, S.; Millet, D. B.; Barkley, M. P.; Paulot, F.; Mao, J.

2012-01-01

335

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

OpenAIRE

Sonoluminescence is a phenomenon involving the transduction of sound into light. The detailed mechanism as well as the energy-focusing potentials are not yet fully explored and understood. So far only optical photons are observed, while emissions in the ultra-violet range are only inferred. By doping the fluorescent dye quinine into water with dilute sulphuric acid, the high energy photons can be converted into the optical photons with slower decay constants. These sonolumin...

Lu, J. Q.; Wong, H. T.; Lin, F. K.; Liu, Y. H.

2005-01-01

336

Observation of hard X-rays line emission from Her X-1  

International Nuclear Information System (INIS)

We present the results of a hard X-ray measurement of the binary source Her X-1, carried out with a balloon borne X-ray telescope consisting of two Multiwire Proportional Counters, having 900 cm2 sensitive area each and spectral resolution of 15% and 24% FWHM respectively at 60 keV. The source was observed during the 'Mid-on' state. Our data confirm the previously reported high energy emission line overimposed on the low energy thermal spectrum. (orig.)

337

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

OpenAIRE

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

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

1999-01-01

338

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

OpenAIRE

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

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

2011-01-01

339

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

Science.gov (United States)

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

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

2011-12-01

340

Dust emission mechanisms in the central Sahara: new insights from remote field observations  

Science.gov (United States)

North Africa is the world's largest source of mineral aerosol (dust). The Fennec Project, an international consortium led by the University of Oxford, is the first project to systematically instrument the remote central Sahara Desert. These observations have, among others, provided new insights into the atmospheric mechanisms of dust emission. Bordj Badji Mokhtar, in south-west Algeria, is within kilometres of the centre of the global mean summer dust maximum. The site, operated by Fennec partners ONM Algerie, has been heavily instrumented since summer 2011. During the Intensive Observation Period (IOP) in June 2011, four main emission mechanisms were observed and documented: cold pool outflows, low level jets (LLJs), monsoon surges and dry convective plumes. Establishing the relative importance of dust emission mechanisms has been a long-standing research goal. A detailed partitioning exercise of dust events during the IOP shows that 45% of the dust over BBM was generated by local emission in cold pool outflows, 14% by LLJs and only 2% by dry convective plumes. 27% of the dust was advected to the site rather than locally emitted and 12% of the dust was residual or ';background' dust. The work shows the primacy of cold pool outflows for dust emission in the region and also the important contribution of dust advection. In accordance with long-held ideas, the cube of wind speed is strongly correlated with dust emission. Surprisingly however, particles in long-range advection (>500km) were found to be larger than locally emitted dust. Although a clear LLJ wind structure is evident in the mean diurnal cycle during the IOP (12m/s peak winds at 935hPa between 04-05h), LLJs are only responsible for a relatively small amount of dust emission. There is significant daily variability in LLJ strength; the strongest winds are produced by a relatively small number of events. The position and strength of the Saharan Heat Low is strongly associated with the development (or otherwise) of LLJs. However, the presence of a LLJ is not a guarantee of dust emission. Momentum calculations show that dust emission always occurs if momentum mixes down to the surface, but mix-down does not always happen - particularly if the surface temperature inversion is strong or ground heating is weak. Fennec findings are not only providing new insights into dust emission processes, they are also an excellent test-bed for models and satellite algorithms in a region where high-quality ';ground-truthing' measurements have been scarce. Conditions of (relatively) high water vapour appear to be a common cause of error. In one model, wind speeds in the core of monsoon LLJs are underestimated by 8.5m/s compared to observations.

Allen, C.; Washington, R.; Engelstaedter, S.

2013-12-01

341

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

Directory of Open Access Journals (Sweden)

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

Frank S. Marzano

2008-03-01

342

XMM-Newton observations of X-ray emission from Jupiter  

CERN Document Server

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

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

2005-01-01

343

Groundbased Observations of Io [OI]6300 A Emission During the Galileo 124, 125, and Cassini Encounters  

Science.gov (United States)

For the past 12 years, we have conducted a synoptic study of [OI] 6300 A emission from Io using the high-resolution (R 120,000) stellar spectrograph at the National Solar Observatory McMath-Pierce telescope. We showed in a recent paper that this emission allows us to use Io as a localized probe of the three-dimensional plasma torus structure. We report on selected recent spectroscopic observations of Io [OI] 6300 A emission obtained during the Galileo I24 (1999-Oct-11) and I25 (1999-Nov-26) encounters with Io and the Cassini Jupiter encounter (closest approach 2000-Dec-30). The exposure time for each spectrum was 15 minutes, with a 5.2 x 5.2 aperture centered on Io. We obtained over 100 spectra for the I24 encounter during 1999 October 9-13, over 100 spectra for the I25 encounter during 1999 November 24-30, and for the Cassini Jupiter flyby almost 600 spectra from 2000 December to 2001 January 21. We use our database of observations to track long- and short-term variations in torus structure. We compare our results to Galileo, Cassini, HST, and other groundbased contemporaneous observations to gain insight into torus variability and structure.

Oliversen, R. J.; Morgenthaler, J. P.; Scherb, F.; Woodward, R. C.; Smyth, W. H.; Lupie, O. L.

2003-01-01

344

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

CERN Document Server

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

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

2014-01-01

345

Improved retrieval of global land emissivity from AMSR-E observations  

Science.gov (United States)

This research dissertation aims to improve our understandings of land surface emissivity using estimates from the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) and to investigate the effect of penetration depth of the microwave signal and its effect on the retrieval of this variable. Microwave observations at low frequencies exhibit more sensitivity to surface and subsurface properties with little interference from the atmosphere. The AMSR-E sensor has two additional lower frequencies, at 6.9 and 10.65 GHz (C- and X-band, respectively) with respect to its preceding sensors. Observations at these low frequencies penetrate deeper into the soil layer. Ancillary data used in the analysis, such as surface skin temperature and cloud mask, are obtained from International Satellite Cloud Climatology Project (ISCCP). Atmospheric properties are obtained from the TIROS Operational Vertical Sounder (TOVS) observations to determine the small upwelling and downwelling atmospheric emissions as well as the atmospheric transmission. The difference in depth of originations causes an inconsistency between diurnal variation of infrared and microwave brightness temperatures, which can lead to more than 10% difference between day and night estimates of land emissivity. In this study, the diurnal cycle of microwave brightness temperature is constructed at different channels using a constellation of satellites which comprises AMSR-E and other SSM/I sensors. Differences in phase and amplitude were observed between the microwave and infrared diurnal cycles. These differences seem to be consistent with land cover and soil texture maps. A principal component analysis (PCA) is conducted to evaluate spatial variation of diurnal cycle of brightness temperature at global scale. A lookup table of effective physical temperature representative of the contributing layers of the microwave signal at each channel and month is adopted based on the diurnal cycle of brightness temperature. The implementation of the proposed effective temperature diurnal cycle lookup table showed that it can significantly mitigate the differences between day and night retrieved emissivities from AMSR-E observations. Therefore, a global product of instantaneous land emissivity that accounts for the difference in penetration depth between thermal and microwave temperatures is proposed.

Norouzi, Hamidreza

2011-12-01

346

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

International Nuclear Information System (INIS)

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

347

EGRET Observations of Monoceros: Diffuse Gamma-Ray Emission in the Outer Galaxy  

Science.gov (United States)

We present an analysis of the diffuse gamma-ray emission observed toward Monoceros by the Energetic Gamma-Ray Experiment Telescope (EGRET). The region studied, l=210deg-250°, b=-15deg to +20deg, has kinematically well-defined segments of the local and Perseus arms and is one of the best regions for the study of variations of cosmic-ray density across the outer Galaxy. The local gamma-ray emissivity is (1.81+/-0.17)×10-26 s-1 sr-1 for energies greater than 100 MeV. For energies greater than 300 MeV, the gamma-ray emissivity in Monoceros is consistent with that of other local clouds studied with EGRET, which suggests that the density of GeV cosmic-ray protons does not vary significantly on scales of less than 1 kpc. As with other local clouds studied with EGRET, an excess of emissivity is observed above 1 GeV relative to that predicted from the cosmic-ray spectrum at the Earth. The gamma-ray emissivity is apparently enhanced in the Perseus arm relative to the interarm regions, although to a much lesser degree than predicted by the model of Hunter et al. The molecular mass calibrating ratio, X=N(H2)/WCO, is (1.64+/-0.31)×1020 cm-2 (K km s-1)-1 in the local clouds and is apparently about the same (to within 50%) in Maddalena's cloud. An uncataloged, marginally significant (~4.5 ?) unidentified point source near (215.5d, 0.5d) with a flux of (1.4+/-0.5)×10-7 cm-2 s-1 (>100 MeV) is suggested by the data.

Digel, S. W.; Grenier, I. A.; Hunter, S. D.; Dame, T. M.; Thaddeus, P.

2001-07-01

348

Spectral structure and generation mechanism of ducted VLF whistler mode sideband waves  

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 transmissions are analyzed. Single-frequency sidebands are shown to be due to interactions between the input wave and harmonics of 60 Hz present within the duct. Sideband spectra are explained as due to wave-wave interactions occurring in the magnetosphere through electron cyclotron resonances, the line intensities required for such interactions being low. Resonances can be located outside or inside the wave potential wells. Application of the KAM theorem to the electron equations of motion shows the possible sideband radiation frequencies. Both external and trapped resonances generate the same radiation spectrum with frequencies given by a very simple formula. The carrier trapping frequencies do not affect the sideband wave frequencies, and do not impose sharp constraints on either the spectrum bandwidth, the sideband line separation, or the maximum interacting carrier frequency separation. It was found that the inhomogeneity of the magnetic field of the earth introduces phase shifts on the equilibrium positions of the resonances discussed. Those phase shifts, whether time dependent or not, will be translated at the receiving station as frequency shifts in the observed sidebands. A strong enough inhomogeneity will destroy a resonance completely. It was found that trapped resocompletely. It was found that trapped resonances are much more resilient to the effects of the inhomogeneity than external resonances, this being the reason why extremely weak carriers can produce sizable and readily observable sidebands when they interact with stronger carriers

349

Spectral structure and generation mechanism of ducted VLF whistler mode sideband waves  

Energy Technology Data Exchange (ETDEWEB)

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 transmissions are analyzed. Single-frequency sidebands are shown to be due to interactions between the input wave and harmonics of 60 Hz present within the duct. Sideband spectra are explained as due to wave-wave interactions occurring in the magnetosphere through electron cyclotron resonances, the line intensities required for such interactions being low. Resonances can be located outside or inside the wave potential wells. Application of the KAM theorem to the electron equations of motion shows the possible sideband radiation frequencies. Both external and trapped resonances generate the same radiation spectrum with frequencies given by a very simple formula. The carrier trapping frequencies do not affect the sideband wave frequencies, and do not impose sharp constraints on either the spectrum bandwidth, the sideband line separation, or the maximum interacting carrier frequency separation. It was found that the inhomogeneity of the magnetic field of the earth introduces phase shifts on the equilibrium positions of the resonances discussed. Those phase shifts, whether time dependent or not, will be translated at the receiving station as frequency shifts in the observed sidebands. A strong enough inhomogeneity will destroy a resonance completely. It was found that trapped resonances are much more resilient to the effects of the inhomogeneity than external resonances, this being the reason why extremely weak carriers can produce sizable and readily observable sidebands when they interact with stronger carriers.

Desa, L.A.D.

1990-01-01

350

Investigation of VLF and HF waves showing seismo-ionospheric anomalies induced by the 29 September 2009 Samoa earthquake (Mw=8.1  

Directory of Open Access Journals (Sweden)

Full Text Available In Samoa Islands, a powerful earthquake took place at 17:48:10.99 UTC (06:48:10.99 LT on 29 September 2009 with a magnitude Mw=8.1. Using ICE (Instrument Champ Electrique and IMSC (Instrument Magnetic Search Coil experiments onboard the DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions satellite we have surveyed possible variations in electromagnetic signals transmitted by the ground-based VLF transmitter NPM in Hawaii and in HF plasma waves close to the Samoa earthquake during the seismic activity. The indices Dst and Kp were used to distinguish pre-earthquake anomalies from the other anomalies related to the geomagnetic activities. In a previous study we have shown that anomalies in IAP (plasma analyzer and ISL (Langmuir probe experiments onboard the DEMETER and also TEC (Total Electron Content data appear 1 to 5 days before the Samoa earthquake. In this paper we show that the anomalies in the VLF transmitter signal and in the HF range appear with the same time scale. The lack of significant geomagnetic activities indicates that these anomalous behaviors could be regarded as seismo-ionospheric precursors. It is also shown that comparative analysis is more effective in seismo-ionospheric studies.

M. Parrot

2010-05-01

351

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

Science.gov (United States)

Flask samples from two sites in East Asia, Tae-Ahn Peninsula, Republic of Korea (TAP), and Shangdianzi, People's Republic of China (SDZ), were measured for a suite of trace gases and isotopes, including CO2, CO and ?14CO2. We use the ?14CO2 measurements to quantify the contribution of recently added fossil fuel CO2 (CO2ff) in each sample. Our five-year record from TAP, on the western edge of Korea, shows high pollution events when local air comes from the Korean Peninsula. Most samples at this site, however, reflect air masses from further afield in Northeastern China and typically have lower CO2ff values. SDZ is about 100km northeast of Beijing, and our small set of samples from winter 2009/2010 have strongly elevated CO2ff. Biospheric CO2 also contributes substantially to variability in total CO2 at both sites, even in winter when non-fossil CO2 sources (including photosynthesis, respiration, biomass burning and biofuel use) contribute 20-30% of the total CO2 enhancement over background. Carbon monoxide (CO) is also elevated, and correlates strongly with CO2ff. The SDZ samples, and the TAP far-field (China influenced) samples have CO to CO2ff emission ratios (RCO:CO2ff) of 47±2 and 44±3 ppb/ppm respectively, in agreement with recent bottom-up inventory estimates and consistent with other observational studies. Locally influenced TAP samples fall into two distinct datasets, ascribed to air sourced from either South Korea or North Korea. The South Korea samples are characterized by high CO2ff values and low RCO:CO2ff of 13±3 ppb/ppm, slightly higher than two available bottom-up inventory estimates, but quite consistent with emission ratios for other developed nations. We also compare our CO2ff observations with modeled CO2ff using the FLEXPART Lagrangian particle dispersion model, convolved with a bottom-up CO2ff emission inventory which includes the reported increase in Chinese emissions of 63% from 2004 to 2010. At SDZ, the model replicates the observations quite well. At TAP, the model performs well on an annual basis, although it is unable to capture the variability on individual days. The modeled time trend is consistent with our observations, whereas a model version which holds Chinese emissions flat at 2004 levels is unable to replicate the observed CO2ff.

Turnbull, J. C.; Tans, P. P.; Lehman, S. J.; Baker, D. F.; Conway, T. J.; Chung, Y. S.; Gregg, J.; Miller, J. B.; Southon, J. R.; Zhou, L.

2011-12-01

352

Observation 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, including the Earth's tenuous outer atmosphere (exosphere or geocorona) and hydrogen and helium from the local interstellar medium drifting through the heliosphere. This geocoronal and heliospheric emission comprises a significant and varying fraction of the soft X-ray background (SXRB) and is seen in every X-ray observation, with the intensity dependent on solar wind conditions and observation geometry. Under the right conditions, geocoronal emission can increase the apparent SXRB by roughly an order of magnitude for an hour or more. In this work, we study a dozen occasions when the near-Earth solar wind flux was exceptionally high. These gusts of wind lead to abrupt changes in SWCX X-ray emission around Earth, which may or may not be seen by X-ray observatories depending on their line of sight. Using detailed three-dimensional magnetohydrodynamical simulations of the solar wind's interaction with the Earth's magnetosphere, and element abundances and ionization states measured by ACE, we model the time-dependent brightness of major geocoronal SWCX emission lines during those gusts and compare with changes in the X-ray background measured by the Chandra X-ray Observatory. We find reasonably good agreement between model and observation, with measured geocoronal line brightnesses averaged over 1 hr of up to 136 photons s-1 cm-2 sr-1 in the O VII K? triplet around 564 eV.

Wargelin, B. J.; Kornbleuth, M.; Martin, P. L.; Juda, M.

2014-11-01

353

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

Science.gov (United States)

We present a study of the high-energy diffuse emission observed toward Orion by EGRET on the Compton Gamma Ray Observatory. The total exposure by EGRET in this region has increased by more than a factor of 2 since a previous study. A simple model for the diffuse emission adequately fits the data; no significant point sources are detected in the region studied (l=195deg to 220° and b=-25deg to -10°) in either the composite data set or in two separate groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion is found to be (1.65+/-0.11)×10-26 s-1 sr-1 for E >100 MeV, and the differential emissivity is well described as a combination of contributions from cosmic-ray electrons and protons with approximately the local density. The molecular mass calibrating ratio is N(H2)/WCO=(1.35+/-0.15)×1020 cm-2 (K km s-1)-1.

Digel, S. W.; Aprile, E.; Hunter, S. D.; Mukherjee, R.; Xu, F.

1999-07-01

354

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

Science.gov (United States)

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

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

2014-08-01

355

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

CERN Document Server

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

Schlegel, E M; Petre, R

2003-01-01

356

Whistler-triggered chorus emissions observed during daytime at low latitude ground station Jammu  

Science.gov (United States)

In this paper, we present whistler-triggered chorus emission recorded during daytime at low latitude ground station Jammu (geomag. Lat. = 22 degree 26 minute N; L = 1.17) during the period from 1996 to 2003. After analysis of the eight years collected data, we found out 29 events, which are definitely identified as chorus emission triggered by whistlers. During the observation period the magnetic activity is high. Analysis shows that the whistlers have propagated along the geomagnetic field line having L-values lying between L = 1.9 and 4.4. These waves could have propagated along the geomagnetic field lines either in ducted mode or pro-longitudinal mode. The measured relative intensity of the triggered emission and whistler wave is approximately the same and also varies from one event to another. It is proposed that these waves are generated through a process of wave-particle interaction and wave-wave interactions. Related parameters of this interaction are computed for different L-value and wave amplitude. With the help of dynamic spectra of these emissions, the proposed mechanisms are explained.

Pratap Patel, Ravindra; Singh, K. K.; Singh, A. K.; Singh, R. P.

357

Fe XXIV emission in solar flares observed with the NRL/ATM XUV slitless spectrograph  

International Nuclear Information System (INIS)

During the Skylab Mission, the NRL slitless spectrograph photographed a number of flares in the 170-600 A region with a spatial resolution approaching 2ins. At flare maximum the 2s 2Ssub(1/2) - 2p 2Psub(1/2,3/2) transitions of Fe XXIV are present and show the location of the (approx.)20 x 106deg plasma with respect to the surface magnetic field and chromospheric (HeII) emissions. Three examples are discussed (two only briefly). In the small, intense disk flare of 1973, August 9 the high temperature region appears at the foot of a low altitude arch. The estimated electron density is 5 x 1011cm-3. In the limb flare of 1974, January 15 the hot X-ray emitting component is at a very low altitude compared to the flare loops. In the impulsive double ribbon flare of 1973, June 15 the Fe XXIV emission is centered over the neutral line, forming a bridge-like structure between magnetic regions of opposite polarity. The estimated electron density is 5 x 1010cm-3. The Fe XXIV emission was visible 8 to 10 min as compared with a calculated cooling time by conduction of only 5 min. The lengthened life of the emission may be associated with the observed 'turbulence', which inhibits the heat conduction, or alternatively, with a slower energy release prolonged beyond the end of the burst phase. (Auth.)

358

The O(1S dayglow emission as observed by the WIND imaging interferometer on the UARS  

Directory of Open Access Journals (Sweden)

Full Text Available Volume emission rate profiles of the O(1D-1S 5577 Å dayglow measured by the WIND imaging interferometer on the Upper Atmosphere Research Satellite are analyzed to examine the O(1S excitation mechanisms in the sunlit lower thermosphere and upper mesosphere. The observed emission profiles are compared with theoretical profiles calculated using a model which takes into account all of the known daytime sources of O(1S. These include photoelectron impact on atomic oxygen, dissociative recombination of O+2, photodissociation of molecular oxygen, energy transfer from metastable N2(A3?+u and three body recombination of atomic oxygen. Throughout most of the thermosphere the measured and modelled emission rates are in reasonably good agreement, given the limitations of the model, but in the region below 100 km, where the oxygen atom recombination source is likely to dominate, the measured emission rates are considerably larger than those modelled using the MSIS-90 oxygen atom densities. This discrepancy is discussed in terms of possible inadequacies in the MSIS-90 model atmosphere and/or additional sources of O(1S at low altitude.

B. H. Solheim

359

Volcanic emissions from AIRS observations: detection methods, case study, and statistical analysis  

Science.gov (United States)

Monitoring volcanic emissions is important for many reasons, most notably for impacts on climate and possible hazards for human health or aviation safety. Satellite instruments allow for long-term monitoring of volcanic emissions on a global scale. In this paper we introduce new detection indices for volcanic ash and sulfur dioxide (SO2) that are optimized for radiance measurements of the Atmospheric InfraRed Sounder (AIRS). Radiative transfer calculations are used to determine the sensitivity of the ash index (AI) on the aerosol optical depth and the SO2 index (SI) on the SO2 column density. A case study on AIRS observations after the eruption of the Puyehue Cordon-Caulle, Chile, in June 2011 demonstrates that the new indices work in practice. A statistical analysis of a ten-year record (2002 to 2013) of AIRS data provides AI thresholds that help to better discriminate volcanic emissions from regular events such as dust storms. We compared our new SI with the AIRS operational product and found that it is more sensitive and better suppresses interfering background signals. Our new volcanic emission data products have been successfully applied in other scientific studies.

Hoffmann, Lars; Griessbach, Sabine; Meyer, Catrin I.

2014-10-01

360

Adjoint inverse modeling of NO x emissions over eastern China using satellite observations of NO 2 vertical column densities  

Science.gov (United States)

A four-dimensional variational data assimilation system for optimization of NO x emissions (RC4-NO x) was developed. A parameterized NO x chemistry scheme was introduced into the RC4-NO x system, and key parameters such as chemical production and loss terms of NO x were calculated in advance using the Community Multiscale Air Quality (CMAQ) modeling system. RC4-NO x was applied to optimize NO x emissions over eastern China (EC) in July 1996, 1999, and 2002 using Global Ozone Monitoring Experiment (GOME) satellite observations of NO 2 vertical column densities (VCDs) and a priori emissions from the Regional Emission Inventory in Asia (REAS). After assimilation, RC4-NO x generally reproduced the spatial distribution, regional averaged values, and time evolution of GOME NO 2 VCDs. Over EC, a priori emissions were reduced by 20% in 1996 and by 8% in 1999, whereas a posteriori emissions were almost the same as a priori emissions in 2002. A priori emissions in the Beijing region were reduced by optimization over the whole simulation period. A posteriori emissions over the Yangtze Delta were larger than a priori emissions in 2002, although they were smaller in both 1996 and 1999. As in other areas, a priori emissions over the North China Plain were reduced in 1996; but those over the eastern part of the plain were increased in 1999, and the area of increased emissions moved slightly westward in 2002. In each region, the growth rates of a posteriori emissions during both 1996-1999 and 1999-2002 became generally larger than those of a priori emissions, and the trends of a posteriori emissions became similar to those of GOME NO 2 VCDs. Our inverse modeling analysis indicates that the rate of increase of NO x emissions over EC from 1996 to 2002 was much larger for a posteriori emissions (49%) than for a priori emissions (19%).

Kurokawa, Jun-ichi; Yumimoto, Keiya; Uno, Itushi; Ohara, Toshimasa

361

Hard X-ray emission from Serpens X-1 as observed by INTEGRAL  

CERN Document Server

We here report results of an INTEGRAL observation of the X-ray burst and atoll source Ser X-1 performed on May 2003. The object was observed for a total of 400 ks but nearly 8 degrees off-axis due to the amalgamation with an observation of SS 433, the pointing target source. Ser X-1 was detected up to 30 keV with unprecedented positional accuracy for a high-energy emission; a sharp spectral drop is evident beyond this energy. Significant variability is seen in the 20-30 keV light curve. Comparison with previous observations indicates that the source was in its high (banana) state and displayed a soft spectrum during the INTEGRAL pointing. A (non simultaneous) broadband radio-to-gamma-rays broad-band spectral energy distribution for Ser X-1 is also presented for the first time.

Masetti, N; Palazzi, E; Amati, L; Caroli, E; Di Cocco, G; Frontera, F; Orlandini, M

2004-01-01

362

Gamma-Ray Emission in Dissipative Pulsar Magnetospheres: From Theory to Fermi Observations  

Science.gov (United States)

We compute the patterns of ?-ray emission due to curvature radiation in dissipative pulsar magnetospheres. Our ultimate goal is to construct macrophysical models that are able to reproduce the observed ?-ray light curve phenomenology recently published in the Second Fermi Pulsar Catalog. We apply specific forms of Ohm's law on the open field lines using a broad range for the macroscopic conductivity values that result in solutions ranging, from near-vacuum to near-force-free. Using these solutions, we generate model ?-ray light curves by calculating realistic trajectories and Lorentz factors of radiating particles under the influence of both the accelerating electric fields and curvature radiation reaction. We further constrain our models using the observed dependence of the phase lags between the radio and ?-ray emission on the ?-ray peak separation. We perform a statistical comparison of our model radio-lag versus peak-separation diagram and the one obtained for the Fermi standard pulsars. We find that for models of uniform conductivity over the entire open magnetic field line region, agreement with observations favors higher values of this parameter. We find, however, significant improvement in fitting the data with models that employ a hybrid form of conductivity, specifically, infinite conductivity interior to the light cylinder and high but finite conductivity on the outside. In these models the ?-ray emission is produced in regions near the equatorial current sheet but modulated by the local physical properties. These models have radio lags near the observed values and statistically best reproduce the observed light curve phenomenology. Additionally, they also produce GeV photon cut-off energies.

Kalapotharakos, Constantinos; Harding, Alice K.; Kazanas, Demosthenes

2014-10-01

363

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

Science.gov (United States)

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 is critical to a correct description of wave-particle interaction in the radiation belts. We focus on properties of reflected chorus emissions observed by the THEMIS (Time History of Events and Macroscale Interactions During Substorms) spacecraft Search Coil Magnetometer (SCM) and Electric Field Instrument (EFI) at ELF/VLF frequencies up to 4 kHz at L?8. We determine the direction of the Poynting flux and wave vector distribution for forward and reflected chorus waves. Although both types of chorus waves were detected near the magnetic equator and have similar, discrete structure and rising tones, reflected waves are attenuated by a factor of 10-30 and have 10% higher frequency than concurrently-observed forward waves. Modeling of wave propagation and reflection using geometrical optics ray-tracing allowed us to determine the chorus source region location and explain observed propagation characteristics. We find that reflected wave attenuation at a certain spatial region is caused by divergence of the ray paths of these non-ducted emissions, and that the frequency shift is caused by generation of the reflected waves at lower L-shells where the local equatorial gyrofrequency is larger.

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

2011-03-01

364

Emissions of mercury in southern Africa derived from long-term observations at Cape Point, South Africa  

Science.gov (United States)

Mercury emissions in South Africa have so far been estimated only by a bottom-up approach from activities and emission factors for different processes. In this paper we derive GEM/CO (GEM being gaseous elemental mercury, Hg0), GEM/CO2, GEM/CH4, CO/CO2, CH4/CO2, and CH4/CO emission ratios from plumes observed during long-term monitoring of these species at Cape Point between March 2007 and December 2009. The average observed GEM/CO, GEM/CO2, GEM/CH4, CO/CO2, CH4/CO2, and CH4/CO emission ratios were 2.40 ± 2.65 pg m-3 ppb-1 (n = 47), 62.7 ± 80.2 pg m-3 ppm-1 (n = 44), 3.61 ± 4.66 pg m-3 ppb-1 (n = 46), 35.6 ± 25.4 ppb ppm-1 (n = 52), 20.2 ± 15.5 ppb ppm-1 (n = 48), and 0.876 ± 1.106 ppb ppb-1 (n = 42), respectively. The observed CO/CO2, CH4/CO2, and CH4/CO emission ratios agree within the combined uncertainties of the observations and emissions with the ratios calculated from EDGAR (version 4.2) CO2, CO, and CH4 inventories for South Africa and southern Africa (South Africa, Lesotho, Swaziland, Namibia, Botswana, Zimbabwe, and Mozambique) in 2007 and 2008 (inventories for 2009 are not available yet). Total elemental mercury emission of 13.1, 15.2, and 16.1 t Hg yr-1 are estimated independently using the GEM/CO, GEM/CO2, and GEM/CH4 emission ratios and the annual mean CO, CO2, and CH4 emissions, respectively, of South Africa in 2007 and 2008. The average of these independent estimates of 14.8 t GEM yr-1 is much less than the total emission of 257 t Hg yr-1 shown by older inventories which are now considered to be wrong. Considering the uncertainties of our emission estimate, of the emission inventories, and the fact that emission of GEM represents 50-78 % of all mercury emissions, our estimate is comparable to the currently cited GEM emissions in 2004 and somewhat smaller than emissions in 2006. A further increase of mercury emissions due to increasing electricity consumption will lead to a more pronounced difference. A quantitative assessment of the difference and its significance, however, will require emission inventories for the years of observations (2007-2009) as well as better data on the speciation of the total mercury emissions in South Africa.

Brunke, E.-G.; Ebinghaus, R.; Kock, H. H.; Labuschagne, C.; Slemr, F.

2012-08-01

365

UV and EUV Emissions at the Flare Foot-points Observed by AIA  

CERN Document Server

A solar flare is composed of impulsive energy release events by magnetic reconnection, which forms and heats flare loops. Recent studies have revealed a two-phase evolution pattern of UV 1600\\AA\\ emission at the feet of these loops: a rapid pulse lasting for a few seconds to a few minutes, followed by a gradual decay on timescales of a few tens of minutes. Multiple band EUV observations by AIA further reveal very similar signatures. These two phases represent different but related signatures of an impulsive energy release in the corona. The rapid pulse is an immediate response of the lower atmosphere to an intense thermal conduction flux resulting from the sudden heating of the corona to high temperatures (we rule out energetic particles due to a lack of significant hard X-ray emission). The gradual phase is associated with the cooling of hot plasma that has been evaporated into the corona. The observed footpoint emission is again powered by thermal conduction (and enthalpy), but now during a period when appr...

Qiu, Jiong; Longcope, Dana W; James,; Klimchuk, A; Wen-Juan,; Liu,

2013-01-01

366

HST WFC3 Early Release Science: Emission-Line Galaxies from IR Grism Observations  

CERN Document Server

We present grism spectra of emission--line galaxies (ELGs) from 0.6--1.6 microns from the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). These new infrared grism data augment previous optical Advanced Camera for Surveys G800L (0.6--0.95 micron) grism data in GOODS--South, extending the wavelength covereage well past the G800L red cutoff. The ERS grism field was observed at a depth of 2 orbits per grism, yielding spectra of hundreds of faint objects, a subset of which are presented here. ELGs are studied via the \\Ha, \\OIII, and \\OII\\ emission lines detected in the redshift ranges 0.2$\\cle$z$\\cle$1.6, 1.2$\\cle$z$\\cle$2.4 and 2.0$\\cle$z$\\cle$3.6 respectively in the G102 (0.8--1.1 microns; R$\\sim$210) and G141 (1.1--1.6 microns; R$\\sim$130) grisms. The higher spectral resolution afforded by the WFC3 grisms also reveals emission lines not detectable with the G800L grism (e.g., \\SII\\ and \\SIII\\ lines). From these relatively shallow observations, line luminosities, star--formation rates, and grism s...

Straughn, A N; Kuemmel, M; Walsh, J R; Cohen, S H; Gardner, J P; Windhorst, R A; O'Connell, R W; Pirzkal, N; Meurer, G; McCarthy, P J; Hathi, N P; Malhotra, S; Rhoads, J; Balick, B; Bond, H E; Calzetti, D; Disney, M J; Dopita, M A; Frogel, J A; Hall, D N B; Holtzman, J A; Kimble, R A; Luppino, G; Paresce, F; Saha, A; Silk, J I; Trauger, J T; Walker, A R; Whitmore, B C; Young, E T

2010-01-01

367

Volcanic carbon dioxide emissions: observation strategies using GOSAT FTS SWIR data  

Science.gov (United States)

About one tenth of the Earth’s human population lives under direct threat of volcanic hazards. Being able to provide sufficiently early and scientifically sound warning is a key to volcanic hazard mitigation. Forecasting volcanic eruptions is based on epidemiological and probabilistic analyses of monitoring data. In times of crisis, the extremely short time for decisions, validation and response leads to a quest for the earliest possible indicators of unrest. Among the first potential signals of ascending magma is the exsolution of volatiles contained in magma induced by dynamic depressurization, crystallization, and temperature variations. The three most abundant gas species in these emissions are usually water (H2O), Carbon Dioxide (CO2), and Sulfur Dioxide (SO2). SO2 monitoring methods are widespread, using COSPEC, mini-DOAS, SO2 cameras, and space-borne SO2 data. However, since H2O and SO2 are frequently scrubbed out by near-surface processes, they may be obscured unless the magma is already near the surface. SO2 is most useful for volcanoes that erupt frequently and have a dry chimney for easy gas escape. CO2 is more difficult to measure remotely than SO2} because the atmospheric background concentration of CO2 is so much higher than for SO2. Nevertheless, CO2 is important because it is the first gas to exsolve from magma (together with helium), and it is minimally affected by scrubbing and other near-surface processes. CO2 monitoring has been attempted by ground-based CO2 flux monitoring and by crater plume CO2 measurements using ground-based open-path FTIR and airborne closed-path IR measurements. In this study, we assess data acquired by JAXA’s GOSAT satellite for detection and eventually quantification of volcanic CO2 emissions. Two strategies are being investigated: (1) standard scheduled observation points, (2) repeat targeted observation requests of known centers of strong volcanic emissions. With a field of view of 10 km, GOSAT has the potential to provide spatially integrated data for entire volcanic edifices. Adverse factors include: Complex terrain, orographic clouds, emission plumes of water vapor and ash, and unknown CO2 dispersion behavior. Globally, over 80 active volcanoes are located within 50 km of a GOSAT standard observation point, but these points are usually rejected by the standard L2 SWIR CO2 algorithm because of cloud brightness. Repeat observation requests have a great potential to detect volcanic anomalies because they can target the actual points of emissions. We present comparisons of these two approaches, and comparisons to available SO2 data from the Ozone Monitoring Instrument (OMI).

Schwandner, F. M.; Carn, S. A.; Head, E. M.; Newhall, C. G.

2010-12-01

368

Numerical modeling of Asian dust emission and transport with adjoint inversion using LIDAR network observations  

Directory of Open Access Journals (Sweden)

Full Text Available A four-dimensional variational (4D-Var data assimilation system for a regional dust model (RAMS/CFORS-4DVAR; RC4 is applied to a heavy dust event which occurred between 20 March and 4 April 2007 over eastern Asia. The vertical profiles of the dust extinction coefficients derived from NIES LIDAR observation network are directly assimilated. We conduct two experiments to evaluate impacts of selections of observation sites: Experiment A uses five Japanese observation sites located only downwind of dust source regions; the other Experiment B uses these sites together with two other sites near source regions (China and Korea. Validations using various observation data (e.g., PM10 concentration, MODIS AOT, OMI Aerosol Index, and the dust extinction coefficient derived by space-based LIDAR NASA/CALIPSO are demonstrated. The modeled dust extinction coefficients are improved considerably through the assimilation. Assimilation results of Experiment A are consistent with those of Experiment B, indicating that observations of Experiment A can capture the dust event correctly and include sufficient information for dust emission inversion. Time series of dust AOT calculated by modeled and LIDAR dust extinction coefficients show good agreement. At Seoul, Matsue, and Toyama, assimilation reduces the root mean square errors of dust AOT by 31–32%. Vertical profiles of the dust layer observed by CALIPSO are also compared with assimilation results. The dense dust layer was trapped between ?=280–300 K and elevated higher toward the north; the model reproduces those characteristics well. The modeled dust AOT along the orbit paths agrees well with the CALIPSO dust AOT, OMI AI, and the coarse mode AOT retrieved from MODIS; especially the modeled dust AOT and the MODIS coarse mode AOT are consistent quantitatively. Assimilation results increase dust emissions over the Gobi Desert and Mongolia considerably; especially between 29 and 30 March, emission flux is increased by about 2–3 times. The heavy dust event is caused by the heavy dust uplift flux over the Gobi Desert and Mongolia during those days. We obtain the total optimized dust emissions of 57.9 Tg (Experiment A; 57.8% larger than before assimilation and 56.3 Tg (Experiment B; 53.4% larger.

K. Yumimoto

2007-11-01

369

Particle precipitation induced by short-duration VLF waves in the magnetosphere  

International Nuclear Information System (INIS)

An extension of a previous test particle simulation model (Inan et al.,1978) of the gyroresonance wave-particle interaction in the magnetosphere is used to compute the detailed time variation of the precipitated energy flux induced by monochromatic short-duration VLF waves. The resulting precipitation pulse is found to have a characteristic shape dependent on the L value, a cold plasma density wave frequency, and duration, as well as the energetic particle distribution function. The role of these variables in determining the temporal variation and the magnitude of the precipitated flux is discussed for a wide range of typical magnetospheric parameters. As an example, a 400-ms wave pulse with a frequency of 6.825 kHz (equatorial half-gyrofrequency) at L = 4 and for a cold plasma density of 400 el/cc produces a 3.5-s long precipitation pulse as observed at 1000 km, with the flux reaching its peak value at approximately 3.8 s after the injection of the wave at the same point. Our findings indicate that if the predicted temporal variations can be observed, the results may be used to diagnose some of the details of the energetic particle distribution in the magnetosphere. The magnitude of the precipitated flux is a function of the trapped particle distribution. For example, for typical trapped electron distribution interacting with a 5 kHz wave of 1 pT intensity at L = 4 the peak precipitated energy flux is found to be 5 x 10-3 ergs/cm2 s. The predict3 ergs/cm2 s. The predicted fluxes for typical parameters are 102--103 times larger than typical background precipitation levels at these latitudes and would be detectable with presently available instruments

370

Response of the mid-latitude D-region ionosphere to the total solar eclipse of 22 July 2009 studied using VLF signals in South Korean peninsula  

Science.gov (United States)

In this paper, we analyze VLF signals received at Busan to study the the D-region changes linked with the solar eclipse event of 22 July 2009 for very short (?390 km) transmitter-receiver great circle path (TRGCP) during local noon time 00:36-03:13 UT (09:36-12:13 KST). The eclipse crossed south of Busan with a maximum obscuration of ?84%. Observations clearly show a reduction of ?6.2 dB in the VLF signal strength at the time of maximum solar obscuration (84% at 01:53 UT) as compared to those observed on the control days. Estimated values of change in Wait ionospheric parameters: reflection height (h?) in km and inverse scale height parameter (?) in km-1 from Long Wave Propagation Capability (LWPC) model during the maximum eclipse phase as compared to unperturbed ionosphere are 7 km and 0.055 km-1, respectively. Moreover, the D-region electron density estimated from model computation shows 95% depletion in electron density at the height of ?71 km. The reflection height is found to increase by ?7 km in the D-region during the eclipse as compared to those on the control days, implying a depletion in the Lyman-? flux by a factor of ?7. The present observations are discussed in the light of current understanding on the solar eclipse induced D-region dynamics.

Phanikumar, D. V.; Kwak, Y.-S.; Patra, A. K.; Maurya, A. K.; Singh, Rajesh; Park, S.-M.

2014-09-01

371

Search for extended gamma ray emission in Markarian 421 using VERITAS observations  

CERN Document Server

Very high energy (VHE: >100 GeV) gamma rays coming from AGN can pair-produce on the intergalactic background light generating an electromagnetic cascade. If the Intergalactic Magnetic Field (IGMF) is sufficiently strong, this cascade may result in an extended isotropic emission of photons around the source, or halo. Using VERITAS observations of the blazar Markarian 421, we search for extended emission by comparing the source angular distribution (${\\theta}^2$) from a quiescent period with one coming from a flare period, which can be considered as halo-free. ${\\chi}^2$ test showed no significant statistical differences between the samples, suggesting that the effect is either non-existent or too weak to be detected. We calculated upper limits for the extended flux considering different angle ranges, the most stringent being <8% of the Crab Nebulae flux (C.U), in the range $0\\deg \\leq {\\theta} \\leq 0.1\\deg$ .

,

2014-01-01

372

First Observation of Beta-Delayed Three-Proton Emission in 45Fe  

Energy Technology Data Exchange (ETDEWEB)

The decay of extremely neutron deficient 45Fe has been studied by means of a new type of a gaseous detector in which a technique of digital imaging was used to record tracks of charged particles. The + decay channels accompanied by proton emission were clearly identified. In addition to -delayed one-proton and -delayed two-proton decays, -delayed three-proton emission was recorded which represents the first direct and unambiguous observation of this decay channel. The branching ratio for the decay of 45Fe and the corresponding partial half-life are found to be 0.30 0.04 and T1/2( ) = 8.7 1.3 ms, respectively.

Miernik, K. [University of Warsaw; Dominik, Wojciech [Warsaw University; Janas, Z. [University of Warsaw; Pfutzner, M. [University of Warsaw; Bingham, C. R. [University of Tennessee, Knoxville (UTK); Czyrkowski, Henryk [Warsaw University; Cwiok, Mikolaj [Warsaw University; Darby, Iain [University of Tennessee, Knoxville (UTK); Djbrowski, R. [University of Warsaw; Ginter, T. N. [Michigan State University, East Lansing; Grzywacz, R. [University of Tennessee, Knoxville (UTK); Karny, M. [University of Warsaw; Korgul, A. [University of Warsaw; Kusmierz, W. [University of Warsaw; Liddick, Sean [University of Tennessee, Knoxville (UTK); Rajabali, Mustafa [University of Tennessee, Knoxville (UTK); Rykaczewski, Krzysztof Piotr [ORNL; Stolz, A. [Michigan State University, East Lansing

2007-01-01

373

First observation of ?-delayed three-proton emission in 45Fe  

International Nuclear Information System (INIS)

The decay of extremely neutron deficient 45Fe has been studied by means of a new type of a gaseous detector in which a technique of digital imaging was used to record tracks of charged particles. The ?+ decay channels accompanied by proton emission were clearly identified. In addition to ?-delayed one-proton and ?-delayed two-proton decays, ?-delayed three-proton emission was recorded which represents the first direct and unambiguous observation of this decay channel. The branching ratio for the ? decay of 45Fe and the corresponding partial half-life are found to be 0.30±0.04 and T1/2(?)=8.7±1.3 ms, respectively

374

Relations between observable parameters of collisionally broadened emission lines of rotating stars: a useful plot  

International Nuclear Information System (INIS)

This paper emphasizes the importance of spectroscopy techniques and the need of additional assumptions in analyzing stellar spectra, when experimental data are mapped in terms of a few parameters. Collisionally broadened profiles of emission lines originated in circumstellar material surrounding rotating stars are analyzed. Theoretical relationships between the ratio of the central flux intensity to the equivalent width of the emission line Fij,0/Wij, and the half-width at half of the maximum HWHMij are found. The plane (HWHMij, Fij,0/Wij) shows general trends of the measurements and imposes bounds to the plasma parameters and the rotation velocities of the stars. With some educated guesses, it can be inferred whether the circumstellar material is spherically distributed or has a disc-like structure. As an example, an observational evaluation is made from data of gamma Cass. (paper)

375

Energetic Neutral Atom Emissions From Venus: VEX Observations and Theoretical Modeling  

Science.gov (United States)

Venus has almost no intrinsic magnetic field to shield itself from its surrounding environment. The solar wind thus directly interacts with the planetary ionosphere and atmosphere. One of the by-products of this close encounter is the production of energetic neutral atom (ENA) emissions. Theoretical studies have shown that significant amount of ENAs are emanated from the planet. The launch of the Venus Express (VEX) in 2005 provided the first light ever of the Venus ENA emissions. The observed ENA flux level and structure are in pretty good agreement with the theoretical studies. In this paper, we present VEX ENA data and the comparison with numerical simulations. We seek to understand the solar wind interaction with the planet and the impacts on its atmospheres.

Fok, M.-C.; Galli, A.; Tanaka, T.; Moore, T. E.; Wurz, P.; Holmstrom, M.

2007-01-01

376

Cassini and Wind Stereoscopic Observations of Jovian Non-Thermal Radio Emissions  

Science.gov (United States)

During two intervals in 1999, simultaneous observations of Jupiter's decametric and hectometric radio emissions were made with the Cassini radio and plasma wave instrument (RPWS) and the radio and plasma wave instrument (WAVES) on the Wind spacecraft in Earth orbit. During January, the Jovian longitude difference between the two spacecraft was about 5 deg, whereas for the August-September Earth flyby of Cassini, the angle ranged from 0 deg to about 2.5 deg. With these separations, the instantaneous widths of the walls of the hollow conical radiation beams of some of the decametric arcs were measured suggesting that the typical width is approximately 2 deg. The conical beams seem to move at Io's revolution rate rather than with Jupiter's rotation rate. Additionally, some of the non-arc emissions have very narrow and quite peculiar beamwidths.

Kaiser, Michael L.; Kurth, W. S.; Hospodarsky, G. B.; Gurnett, D. A.; Zarka, P.

1999-01-01

377

Probing the lower ionospheric perturbations associated with earthquakes by means of subionospheric VLF/LF propagation  

Science.gov (United States)

There have been reports for many years that the ionosphere is very sensitive to seismic effects, and the detection of ionospheric perturbations associated with earthquakes (EQs) attracts a lot of attention as a very promising candidate for short-term EQ prediction. In this review we present a possible use of VLF/LF (very low frequency (3-30 kHz)/low frequency (30-300 kHz)) radio sounding of seismo-ionospheric perturbations. In order to avoid the overlapping with my own previous reviews, we first show some pioneering results for the Kobe EQ and we try to present the latest results including the statistical evidence on the correlation between the VLF/LF propagation anomalies (ionospheric perturbations) and EQs (especially with large magnitude and with shallow depth), medium-distance (6-8 Mm) propagation anomalies, the fluctuation spectra of subionospheric VLF/LF data (the effect of atmospheric gravity waves, the effect of Earth's tides, etc.), and the mechanism of lithosphere-atmosphere-ionosphere coupling. Finally, we indicate the present situation of this kind of VLF/LF activities going on in different parts of the globe and we suggest the importance of international collaboration in this seismo-electromagnetic study.

Hayakawa, Masashi

2011-12-01

378

Unusual Fluctuations of the Nighttime VLF Signal Amplitude before Seismic Events  

Science.gov (United States)

We present the results of an analysis of yearlong (2007) monitoring of nighttime data of the VLF signal amplitude. We use the VLF signals, transmitted from the Indian Navy station VTX (latitude 8.43° N, longitude 77.73° E) at 18.2 kHz and received at the Indian Centre for Space Physics, Kolkata (latitude 22.5° N, 87.5° E). We analyzed this data to find out the correlation between night time amplitude fluctuation and seismic events. We found, analyzing individual earthquakes (with magnitudes greater than 5) as well as from statistical analysis (of all the events with effective magnitudes greater than 3.5), that nighttime fluctuation of the signal amplitude has the highest probability to be beyond the 2? levels about three days prior to the seismic events. Recently an earthquake of magnitude 7.4 occurred at Southwestern Pakistan (latitude 28.9° N, longitude 64° E). We analyze the nighttime VLF signals for two weeks around this earthquake day to see if there were any precursory effects of this earthquake. We find that the amplitude of the nighttime VLF signals anomalously fluctuated four days before this earthquake. Thus, the nighttime fluctuation could be considered as a precursor to enhanced seismic activities.

Ray, Suman; Chakrabarti, Sandip Kumar; Sasmal, Sudipta; Mondal, Sushanta Kumar

2012-07-01

379

Propagation of LF/VLF radio waves below a nonuniform ionosphere  

International Nuclear Information System (INIS)

A simple approach to LF/VLF field calculations for a non-uniform, isotropic ionosphere is developed. The theory introduces two modifications to the standard wave hop theory: namely the use of local reflection coefficients and the use of an average reflection height for the path integrals. Sample calculations, including a comparison with measured results, are presented. (author)

380

Correlation between night time VLF amplitude fluctuations and seismic events in Indian sub-continent  

Science.gov (United States)

We present the results of an analysis of yearlong (2007) monitoring of night time data of the VLF signal amplitude. We use the VLF signals, transmitted from the Indian Navy station VTX (latitude 8.43(°) N, longitude 77.73(°) E) at 18.2 kHz and received at the Indian Centre for Space Physics, Kolkata (latitude 22.5(°) N, 87.5(°) E). We analyzed this data to find out the correlation between night time amplitude fluctuation and seismic events. We found, analyzing individual earthquakes (with magnitudes >5) as well as from statistical analysis (of all the events with effective magnitudes greater than 3.5), that night time fluctuation of the signal amplitude has the highest probability to be beyond the 2? levels about three days prior to the seismic events. Recently an earthquake of magnitude 7.4 occurred at South-western Pakistan (latitude 28.9(°) N, 64(°) E). We analyze the night time VLF signals for two weeks around this earthquake day to see if there were any precursory effects of this earthquake. We find that the amplitude of the night time VLF signals anomalously fluctuated four days before this earthquake. Thus, the night time fluctuation could be considered as a precursor to enhanced seismic activities.

Ray, Suman; Chakrabarti, Sandip Kumar; Sasmal, Sudipta

381

In-situ stressing of rock: Observation of infrared emission prior to failure  

Science.gov (United States)

Blocks of igneous rocks such as anorthosite and granite subjected at one end to uniaxial stress have been shown to emit a small but distinct excess amount of infrared (IR) light (Freund, F. T., et al, JASTP, 71, 2009). This anomalous IR emission arises from the radiative de-excitation of electron vacancy defects, which, upon stress-activation, flow into the unstressed portion and recombine at the surface. This non-thermal IR emission occurs in the 8 ?m to 14 ?m wavelength region. Field experiments are performed by slowly stressing large boulders and monitoring the IR emission in situ with a Bruker EM27 Fourier Transform Infrared (FTIR) spectrometer. The boulders are prepared by drilling four blind holes into the rock, 50-100 cm deep, in an array roughly parallel to, and behind, the surface from where the IR emission is monitored. Any debris and water is blown out of the boreholes with compressed air, and the rock is given time to dry and relax from drilling-induced stresses. The holes are then filled with grout that expands upon curing, creating an increasing radial pressure of up to 5 × 103 t/m2. The experiments were carried out with two large granite boulders, one of about 30 t of hard (over 150 MPa) granite at the University of Arizona’s Henry "Hank" Grunstedt San Xavier Mining Laboratory, located in the copper mining district near Tucson, AZ and the other of about 7 t of weathered granite in the Sierra Nevada foothills near Oakhurst, CA. The Bruker EM27 FTIR spectrometer equipped with a 20 cm reflective telescope collects the IR emission from a safe distance at a rate of a full 4-16 µm spectrum every 30 sec. After recording baseline data, the grout was mixed with water and poured into the holes as IR emission was monitored continuously until the experiment was terminated after rock failure. The time of failure is noted whenever the first acoustic or visual cues are sensed from the boulder. The IR data shows that after a period of quiescence, pronounced non-thermal IR emission is observed within minutes of the rock failure.

Dahlgren, R.; Freund, F. T.; Momayez, M.; Bleier, T. E.; Dunson, C.; Joggerst, P.; Jones, K.; Wang, S.

2009-12-01

382

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

Directory of Open Access Journals (Sweden)

Full Text Available Methane emissions from natural wetlands and rice paddies constitute a large proportion of atmospheric methane, but the magnitude and year-to-year variation of these methane sources is still unpredictable. Here we describe and evaluate the integration of a methane biogeochemical model (CLM4Me; Riley et al., 2011 into the Community Land Model 4.0 (CLM4CN in order to better explain spatial and temporal variations in methane emissions. We test new functions for soil pH and redox potential that impact microbial methane production in soils. We also constrain aerenchyma in plants in always-inundated areas in order to better represent wetland vegetation. Satellite inundated fraction is explicitly prescribed in the model because there are large differences between simulated fractional inundation and satellite observations. A rice paddy module is also incorporated into the model, where the fraction of land used for rice production is explicitly prescribed. The model is evaluated at the site level with vegetation cover and water table prescribed from measurements. Explicit site level evaluations of simulated methane emissions are quite different than evaluating the grid cell averaged emissions against available measurements. Using a baseline set of parameter values, our model-estimated average global wetland emissions for the period 1993–2004 were 256 Tg CH4 yr?1, and rice paddy emissions in the year 2000 were 42 Tg CH4 yr?1. Tropical wetlands contributed 201 Tg CH4 yr?1, or 78 % of the global wetland flux. Northern latitude (>50 N systems contributed 12 Tg CH4 yr?1. We expect this latter number may be an underestimate due to the low high-latitude inundated area captured by satellites and unrealistically low high-latitude productivity and soil carbon predicted by CLM4. Sensitivity analysis showed a large range (150–346 Tg CH4 yr?1 in predicted global methane emissions. The large range was sensitive to: (1 the amount of methane transported through aerenchyma, (2 soil pH (± 100 Tg CH4 yr?1, and (3 redox inhibition (± 45 Tg CH4 yr?1.

L. Meng

2011-06-01

383

EMISSION HEIGHT AND TEMPERATURE DISTRIBUTION OF WHITE-LIGHT EMISSION OBSERVED BY HINODE/SOT FROM THE 2012 JANUARY 27 X-CLASS SOLAR FLARE  

International Nuclear Information System (INIS)

White-light emissions were observed from an X1.7 class solar flare on 2012 January 27, using three continuum bands (red, green, and blue) of the Solar Optical Telescope on board the Hinode satellite. This event occurred near the solar limb, and so differences in the locations of the various emissions are consistent with differences in heights above the photosphere of the various emission sources. Under this interpretation, our observations are consistent with the white-light emissions occurring at the lowest levels of where the Ca II H emission occurs. Moreover, the centers of the source regions of the red, green, and blue wavelengths of the white-light emissions are significantly displaced from each other, suggesting that those respective emissions are emanating from progressively lower heights in the solar atmosphere. The t