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Reddy C.D.,Indian Institute of Geomagnetism
Geodesy and Geodynamics

The lithosphere and the atmosphere/ionosphere, continuously exchange energy through various coupling mechanisms. Earthquake creates waves of energy, e.g. direct shock acoustic waves (SAWs) and Rayleigh wave induced acoustic waves (RAWs). In the event of an earthquake occurring beneath the sea, atmospheric gravity waves (AGWs) are also generated. If the earthquake is large enough (Mw > 6), SAWs, RAWs and AGWs induce detectable ionospheric plasma perturbations. Inferring the seismological information from these seismo-ionospheric manifestations is the subject that pertains to ionospheric seismology. Both ground and satellite based advanced radio techniques are being used in monitoring ionospheric plasma perturbations. In this study, seismo-ionospheric anomalies and implications from recent GNSS observations in India and South-East Asia are discussed, mainly pertaining to the following. (1) From the ionospheric plasma response to 2015 Nepal earthquake, the estimated group velocity for Andaman and Indian shield regions are 2100 ms-1 and 3900 ms-1 respectively and validated from ground measurements. (2) Atmospheric acoustic resonance at 4.0 mHz and a train of wave packet of TEC variation resulting from the beat phenomenon observed at the site 'umlh' and (3) GNSS-based tsunami warning which is going to be promising tool in augmenting the existing tsunami warning systems. © 2016 Institute of Seismology, China Earthquake Administration. Source

Tsurutani B.T.,Jet Propulsion Laboratory | Lakhina G.S.,Indian Institute of Geomagnetism
Geophysical Research Letters

A "perfect" interplanetary coronal mass ejection could create a magnetic storm with intensity up to the saturation limit (Dst ∼ -2500 nT), a value greater than the Carrington storm. Many of the other space weather effects will not be limited by saturation effects, however. The interplanetary shock would arrive at Earth within ∼12 h with a magnetosonic Mach number ∼45. The shock impingement onto the magnetosphere will create a sudden impulse of ∼234 nT, the magnetic pulse duration in the magnetosphere will be ∼22 s with a dB/dt of ∼30 nT s-1, and the magnetospheric electric field associated with the dB/dt ∼1.9 V m-1, creating a new relativistic electron radiation belt. The magnetopause location of 4 R E from the Earth's surface will allow expose of orbiting satellites to extreme levels of flare and ICME shock-accelerated particle radiation. The results of our calculations are compared with current observational records. Comments are made concerning further data analysis and numerical modeling needed for the field of space weather. ©2014. American Geophysical Union. All Rights Reserved. Source

Sathishkumar S.,Indian Institute of Geomagnetism | Sridharan S.,National Atmospheric Research Laboratory
Journal of Geophysical Research: Space Physics

Mesospheric wind observations by the medium frequency radar and geomagnetic field observations at Tirunelveli (8.7°N, 77.8°E, 1.75°N dip angle) are used to study the relative importance of solar and lunar influences in the variabilities of mesospheric tides and equatorial electrojet (EEJ) strength during the unprecedented major stratospheric sudden warming (SSW) of 2009. It is observed that the afternoon reversal in the EEJ, popularly known as counter electrojet, occurs consecutively for several days during the SSW event, when there is an enhancement of solar semidiurnal tide in both zonal wind at 90 km and EEJ strength over Tirunelveli. Although the amplitude of lunar tides also shows enhancement, it is much less than that of solar. The diurnal tidal amplitude in zonal wind and EEJ strength also shows large enhancement just before the onset of SSW. However, solar semidiurnal tide dominates diurnal tide during the SSW. The diurnal tidal phase in zonal wind shifts to a few hours earlier during the SSW. The lunar semidiurnal tidal phase shifts to later hours in both zonal wind and EEJ strength. The main observation of the present study is that the large semidiurnal tide observed during the SSW 2009 is mostly solar driven and only partly lunar driven, although tidal planetary wave interaction also may play a vital role. Although a similar behavior is noticed during the SSW 2006 also, the large lunar semidiurnal tide observed in the EEJ strength without having large lunar semidiurnal tide in the underlying mesospheric winds needs further investigation. © 2012. American Geophysical Union. All Rights Reserved. Source

In the present paper, for the first time, an attempt has been made to study the seasonal, altitudinal, diurnal and latitudinal variation of low latitude electron density obtained using COSMIC radiooccultation (RO) measurements over Indian longitudes during the deep solar minimum year 2008. The seasonal variation shows enhanced electron densities at vernal and autumn equinoxes compared to winter and summer seasons. The observations also suggest a shift in the time and altitude at which the peak of the electron density occurs in different seasons. An important finding is that there exists an equinoctial asymmetry in the electron density with respect to altitude and latitude, where the electron density is higher at vernal equinox compared to autumn equinox. The latitudinal and seasonal variationof peak electron density (NmF2) during 10:00-14:00 hrs LT indicate enhanced equatorial ionization anomaly (EIA) on either side of the magnetic equator at both vernal and autumn equinoxes compared to theother seasons. Seasonal variation of equatorial electrojet (EEJ) strength obtained from geomagnetic H-field variations also shows strong EEJ at vernal and autumn equinoxes indicating that EEJ strength indeed partly controls the EIA development. Further, the results indicate that NmF2 over the northern EIA crest region is correlated well with solar flux. Source

Tsurutani B.T.,Jet Propulsion Laboratory | Lakhina G.S.,Indian Institute of Geomagnetism | Verkhoglyadova O.P.,Jet Propulsion Laboratory
Journal of Geophysical Research: Space Physics

The fundamental features of ∼0.1-0.2 s duration ∼0.5 s spaced ionospheric electron precipitation "microbursts," ∼5 to 15 s microburst "trains," and 5-15 s electron precipitation pulsations are reviewed in light of similar temporal structures of electromagnetic whistler mode "chorus" waves detected in the outer magnetosphere. Past observations of microbursts point to extremely rapid (ms timescale) wave-particle interactions, probably between lower band chorus subelements (durations of ∼10 to 100 ms) and energetic ∼10 to 100 keV electrons. A recent theory explaining such rapid interaction rates observed in microbursts is briefly reviewed. Arguments are given why ∼5-15 s X-ray (and optical) pulsations are also associated with chorus scattering of energetic electrons. Comments about relativistic (E > 1 MeV) microbursts are also provided. There are, however, many other unsolved problems of outer zone energetic electron precipitation. The authors will attempt to indicate several of these for the interested reader. Finally, an appendix is provided for a brief review of two-frequency chorus and some current problems with that topic. ©2013. American Geophysical Union. All Rights Reserved. Source

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