Partial ring current models for worldwide geomagnetic disturbances

Abstract

In recent years the longitudinal asymmetry of the ring current in the magnetosphere encircling the earth has been advocated to explain the geomagnetic field variation in middle and low latitudes. Direct observations of particles and magnetic field by means of satellites in the magnetosphere have given some supporting evidence for the existence of partial ring current in the magnetosphere. In this article a review is made of the analysis of low‐latitude geomagnetic variation during magnetic storms or substorms, and the contribution of the partial ring current system to low‐latitude geomagnetic variations is discussed. After examining the magnetic effect of each part of the partial ring current system, i.e., (1) the equatorial ring current in a limited longitude range, (2) the Birkeland (field aligned) current in the magnetosphere connecting the equatorial plane and the ionosphere, and (3) the current in the ionosphere, including an electrojet along the auroral zone or oval, we conclude that the main contribution to the longitudinal ΔH asymmetry in middle and low latitudes (H is the horizontal component of the geomagnetic field) comes primarily from the Birkeland current and neither from the partial ring current in the equatorial plane nor from the auroral electrojet. Therefore the models of partial ring current need to be modified so as not to overemphasize the ring‐form current closure in the equatorial plane. This article explains the reason for the above conclusions and gives some necessary considerations for interpreting the geomagnetic variations in low latitudes during magnetic storms and substorms and on quiet days.