Abstract
Herein, we analyze the variations in the ionosphere for the period of two weeks before the M6.7 earthquake in India on 3 January 2016. The earthquake occurred after a series of magnetic substorms on 31 December 2015 and 1 January 2016. The relative total electron content (TEC) disturbances have been estimated using global TEC maps and calculated numerically using the 3D global first-principle Upper Atmosphere Model (UAM) for the whole period including the days before, during, and after the substorms. Numerical simulations were repeated with the seismogenic vertical electric currents switched on at the earthquake epicenter. The UAM calculations have reproduced the general behavior of the ionosphere after the main phase of the geomagnetic storm on 1 January 2016 in the form of negative TEC disturbances propagating from high latitudes, being especially strong in the Southern (summer condition) Hemisphere. It was shown that the local ionospheric effects of seismic origin can be identified in the background of the global geomagnetic disturbances. The seismo-ionospheric effects are visible in the nighttime regions with the additional negative TEC disturbances extending from the eastern side of the epicenter meridian to the western side, both in the observations and in the UAM simulations. It was found that the vertical electric field and corresponding westward component of the electromagnetic [E × B] drift played a decisive role in the formation of the ionospheric precursors of this earthquake.
Highlights
In the paper by Namgaladze et al (2013) [1], the total electron content (TEC) variations before strong earthquakes (EQs), modeled with the global upper atmosphere model (UAM), were considered for geomagnetically quiet conditions
The numerical calculations were carried out taking into account seismogenic currents as well as discounting them; this was to distinguish the effects of the seismogenic electric currents from the effects of magnetic activity, but this is not related with the earthquake preparation
This study presents the numerical calculations related to the low latitude ionosphere effects created by the vertical electric currents of seismic origin under high geomagnetic activity
Summary
In the paper by Namgaladze et al (2013) [1], the total electron content (TEC) variations before strong earthquakes (EQs), modeled with the global upper atmosphere model (UAM), were considered for geomagnetically quiet conditions. The main features of the EQ preparation effects in TECs are the locality, connections with the tectonic faults, weak mobility, and small occupied areas [1] in comparison with the ionospheric effects of the geomagnetic storms and substorms. The latter are usually global, connected with the auroral precipitations and electric fields related to the solar wind, and propagate equatorwards from the auroral zones, sometimes in the form of Travelling Ionosphere Disturbances (TIDs) due to the Acoustic. Gravity Waves (AGW) (Brunelli and Namdaladze, 1988) [2] Their duration can range from several hours for substorms to several days for storms
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