Experimental evidences of pre-seismic effects in the Earth's ionosphere as a reason for neutral density and temperature measurements onboard microsatellites

Abstract

Complexity of the seismic activity requires a wide number of control parameters to be used from ground-based and orbital observations to examine ionosphere-thermosphere-lithosphere coupling processes. At present, it is commonly accepted that some of the processes addressed to the ionospheric plasma response of the seismic activity include electromagnetic ULF/VLF emissions, ion density irregularities, ion drift velocity and ion composition changes, night time airglow emissions, stimulated high energy particle precipitation etc. In the present paper, experimental data from the Neutral Atmospheric Composition Spectrometer (NACS) onboard Dynamics Explorer-B (DE-B) satellite are used. In a selected case, we have observed increased neutral He concentration at 830 km altitude, preceding Guam earthquake at 0605UT on 4 January 1982 with M=6.1 magnitude of the main shock. At the maximum of the He enhancement, He density is of about 55% higher than the observed mean value over the same latitudes from the few lateral orbits before and after the earthquake. A possible explanation of such an enhancement of He is addressed to some increase of the exospheric temperature over the earthquake zone. The existence of strong geomagnetic field control to the ionospheric seismic effects could be a serious problem when we are interested of local effects over the earthquake epicentre. As an example, electromagnetic emissions associated with seismic activity often registered in a broad area around the epicentre could be observed at distant conjugate regions along the geomagnetic field line. Under the same reason, ionospheric plasma density or temperature perturbations due to Earth's seismic activity could be observed far from the earthquake epicentre. In this sense, we suggest in situ satellite measurements of the neutral composition and temperature near/and above the F-peak to be used as a new opportunity in search of additional sensitive key parameters to examine the seismic effects in the preparatory phase of a certain earthquake. It is obvious that combined ionospheric plasma and neutral gas measurements carried out onboard the satellite enlarge significantly investigation opportunities of the microsatellite platform.