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

Very Low Frequency (VLF) disturbances in the ionospheric electric field observed by DEMETER satellite prior to three different earthquakes that occurred during the years 2008–2009 have been presented. The electromagnetic wave data has been analyzed for 5 few days before the earthquake with special attention to the variation in spectral characteristics and non-linear effects using the statistical and wavelet based techniques. Results indicate that the earthquake preparation process may disturb the ionospheric plasma and these disturbances can reach the non-linear stage leading to the strong variations in the electromagnetic field and plasma parameters. The 10 enhancement in statistical parameters shows the coherent structure and intermittent phenomenon which is the signature of turbulence. The characteristics features of VLF disturbances have further been studied using the wavelet and bispectral analysis tools which provide useful information on the plasma turbulence

Study of Ionospheric Variability during the Storm of January, 2005 using GPS and DEMETER Satellite Measurements

The dual frequency Global Positioning System (GPS) receiver provides an opportunity to determine Total Electron Content (TEC) over the crest of equatorial ionization anomaly region Bhopal by taking advantage of the dispersive nature of the ionospheric medium. The TEC values observed for the geomagnetic storm of the January 2005 is used in this paper to discuss the behaviour of ionospheric total electron content (TEC) during geomagnetically disturbed period. Variation of TEC is studied in correlation with the geomagnetic index Dst and southward component of interplanetary magnetic field Bz. The TEC variability is found to vary between with the maximum negative excursion of Dst index during the geomagnetic storms days. Positive phase is observed. Maximum TEC variability is observed during the recovery phase of the storms. Electron and ion density measurements from the DEMETER satellite are compared with the TEC measurements. The study of storm time TEC behaviour is very important due to recent increase in satellite-based navigation applications. Keywords: Ionosphere, geomagnetic storms, GPS, DEMETER, TE

Response of low latitude ionosphere to the space weather event of November 2012 in the Asian Sector

49-56Ionospheric response to geomagnetic storms is determined by the efficiency of the solar wind-magnetosphere-ionosphere coupling that underlies the transfer of tremendous amount of mass and energy. A study was carried out to see the response of the equatorial and low latitude ionosphere to the moderate geomagnetic storm of 14 November 2012. This study was carried out using vertical total electron content (VTEC) measured by Global Positioning System (GPS) receivers along the ~ 115°-121°E longitude. The GPS TEC observations showed pronounced positive storm effects in the Asian sector (~115°-121°E) during the main phase of the storm, for the low latitude and crest of anomaly stations. During the main phase of the storm, the interplanetary electric field (IEF) penetrated to the equatorial ionosphere and caused significant density changes in the equatorial ionization anomaly (EIA) region. The eastward prompt penetration electric field, associated with southward interplanetary magnetic field (IMF) augmented the normal daytime eastward dynamo electric field, resulting in intensification of equatorial ionization anomaly (EIA) and VTEC enhancements observed over the anomaly crest stations. Results showed that EIA region was significantly affected during geomagnetic storms in comparison to the low latitude ionosphere

Effect of upflowing field-aligned electron beams on the electron cyclotron waves in the auroral region

The role of low density upflowing field-aligned electron beams (FEBs) on the growth rate of the electron cyclotron waves at the frequencies ω r 1.5 keV) have been found to have significant effect on the growth rate. Analysis has revealed that it is mainly the T ‖b which inhibits the growth rate (magnitude) and the range of frequency (bandwidth) of the instability mainly in the higher frequency spectrum. The inhibition in the growth rate and bandwidth increases with increase in T ‖b. The FEBs with less E b (giving drift velocity) reduce growth rate more than the beams with larger E b. The inhibition of growth rate increases with the increase in the ratio ω e/Ωe indicating that the beams are more effective at higher altitudes

Daytime very low frequency (VLF) emissions observed at Maitri station, Antarctica

The present paper deals with the study of naturally occurring Very Low Frequency (VLF) radio waves at Indian Antarctic Station, Maitri (70° 46'S, 11° 44'E) on the basis of routine continuous observation made during day time. From the detail analysis of daytime data on the basis of continuous observation made at the ground station, we have presented a few of VLF phenomena such as rising types of emissions - discrete and periodic emissions. These recent observations at Maitri, Antarctica may reveal propagational characteristic for the various VLF emissions generated during daytime

Initial results of VLF emissions observations on the ground station at Maitri, Antarctica

The ground based VLF database from Indian Antarctic station Maitri (70°46¢ S, 11° 44¢ E, L ~ 4.6) has been searched for very low frequency (VLF) emissions during January-February of the years 1998 and 1999. The VLF recording system was successfully installed during the XVII Indian Scientific Expedition to Antarctica (ISEA) 1997-98. The spectrograms of analysed data have revealed the common occurrence of various emission events like chorus rising emissions, emission of rising type, falling emission of hook type and multiple emissions. Also the observed emissions (periodic and quasi-periodic) are found to be risers and fallers triggered from the top of hiss band

Ionospheric variations observed by the DEMETER satellite in the mid-latitude region during strong earthquakes

International audienceThe French micro-satellite DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) was launched on June 29, 2004. The orbit of DEMETER is polar, circular with an altitude of 710 km. The main scientific objective of this mission is to study the ionospheric perturbations, which may be linked to seismic activity. To achieve this, the payload of DEMETER allows the measurement of some important plasma parameters (ion composition, electron density, temperature and energetic particles). This paper presents examples of electron and ion density irregularities simultaneously observed for three earthquakes that occurred in the mid-latitude region. The DEMETER in situ measurements show the presence of electron and ion density irregularities near the epicenter of these earthquakes. These perturbations were recorded by the ISL (Langmuir Probe) and IAP (thermal plasma analyzer) experiments onboard DEMETER. The repetitiveness of the perturbations close to the epicenters is shown for these three events