The Importance of Electric Field in Formation of Sporadic E (Es) at the Equatorial Region

Abstract

It has been shown analytically and by appropriate numerical methods that the formation and localization of sporadic E (Es) in the equatorial area can be determined by the height profiles of the ion vertical drift velocity and its divergence. In this case, the existence of a minimum negative value (maximum convergence rate) in the divergence profile, when ions converge vertically into the Es layer, is significantly determined by both the neutral wind velocity and the zonal and vertical components of the electric field. 

 In the equatorial region, with a constant westward electric field, the maximum vertical convergence rate of ions is in the region of the height where the ion-neutral collisional  () and ion cyclotron () frequencies are equal. In case of the constant upwards or downwards electric field, this rate is located at approximately 0.9H (where H is a neutral scale) above or below the region where , respectively. The vertical convergence of the ions developed in these regions and the formation of the Es layer can take place against the background of their upward or downward drift. It localizis in the node of this drift velocity, or in the regions where this velocity disappears. Such predicted formation and behavior of Es layers are demonstrated by numerical methods.    

The effect of the zonal and vertical components of the electric field, as well as the wind velocity determined by the HWM14 data, on the processes of ion convergence/divergence development is shown. In these cases, the ion convergence/divergence process induced by the electric field can affect both the formation and disruption (depletion) of the Es layer formed by neutral wind, as well as can also form an additional layer.