Generation of perturbation electric field suitable for triggering of equatorial spread-F by gravity waves in the E-region and zonal winds in the F-region

Abstract

A new mechanism for the generation of perturbation electric fields which can produce irregularities in the electron density in the F-region, which in turn can act as seed irregularities suitable for the growth of equatorial spread-F is described. The mechanism involves (i) gravity wave winds in the E-region producing electron density irregularities which in turn make the flux tube integrated Pedersen and Hall conductivities non-uniform in this region, (ii) eastward winds in the base of F-region and in the intermediate region which give rise to downward electric fields through dynamo action, (iii) these downward electric fields transport the plasma from 130 km region into the lower E-region and thus enhance the Hall conductivity in the E-region, (iv)the eastward electric fields transport the ionization upwards, thereby decreasing the conductivity in the region between 130 km and the base of the F-region, and, (v) the zonal currents, driven by the electrojet fields and the F-region dynamo fields while flowing in the non-uniformly conducting E-region give rise to the required perturbation electric fields. Using realistic values of various parameters, the amplitudes of perturbations in the vertical plasma drift velocities was found to be as large as 6.5 ms^-1. This amplitude is much larger than 1.3 ms^-1 required to produce 5% perturbation in the electron density near the base of the F-region normally used in the simulation of the equatorial spread-F.