SMALL-SCALE PLASMA INHOMOGENEITIES AND CORRELATED ELF EMISSIONS IN THE IONOSPHERE OVER AN EARTHQUAKE REGION

Cosmos-1809 satellite data on ELF emissions, plasma density, N-e and v ariations dN(e) in the ionosphere above the Spitak earthquake zone dur ing a period of enhanced aftershock activity are presented. The data s how that small-scale plasma inhomogeneities with dN(e)/N-e approximate to 3-8% and with a characteristic scale of 4-10 km along the orbit ar e excited on geomagnetic field tubes connected to the epicentral regio n, simultaneously with earthquake related ELF emissions. A generation mechanism for such inhomogeneities under the influence of seismic acti vity in terms of the dissipative instability of acoustic-gravity waves in the ionosphere is proposed. (C) 1997 Elsevier Science Ltd.