Some characteristics of the ionospheric irregularities associated with E_sq layers

Abstract

Spaced fading records at Thumba for times when E_sq disappears following large changes in the geomagnetic H component are studied. The results for the periods when E_sq is present are known to show fast fading, westward drift, and highly elongated ground diffraction patterns with a small semiminor axis. During periods when there is no E_sq the fadings are found to be very slow, the drift direction is reversed to the east, and the ground diffraction pattern becomes almost isotropic with a large semiminor axis, whose alignment is a few degrees off the magnetic N-S direction. The characteristics of the fading and those of the ground diffraction pattern when E_sq disappears are similar to the characteristics usually obtained at latitudes well away from the equator. The E_sq is thus suggested to be a superposition of additional irregularities over the normal E region irregularities (similar to those in the E region at nonequatorial latitudes). Close dependence of the direction of the electric field with the occurrence of E_sq favors the conclusion that E_sq is due to the cross-field instability created by the action of the H field with the Hall polarization field and the plasma density gradient.