Ring current energy injection rate and solar wind-magnetosphere energy coupling

Abstract

Assuming that the formation of the ring current belt is a direct consequence of an enhanced convection of plasma sheet protons, the expression for the energy injection rate U R is formulated as a function of the cross-tail potential drop φ CT for a simple electric field-magnetic field model. It is shown that an approximate expression for U R thus formulated consists of two parts: (i) the first part U R1 , which is linearly proportional to φ CT , is supplied by the corotation electric field and (ii) the second part U R>2 , which is proportional to φ 2 CT , is supplied by the solar wind energy input to the magnetosphere. The second part U R2 dominates the ring current energy input when the cross-tail potential drop φ CT is greater than ∼ 95 keV, namely during disturbed periods. An important finding is that the second part U R2 of the ring current energy input is shown to be proportional to the solar wind-magnetosphere energy coupling function ϵ, recovering the observationally established relationship. Therefore, the present study verifies that an enhanced convection is the cause of the ring current formation.