Chapter 5 - Ring current development

Abstract

This chapter describes the properties of ring current source populations as well as transport processes that lead to ring current formation. During geomagnetic activity, the ring current intensity is highly sensitive to variations in the plasma source populations and to the processes that transport the plasma to form the ring current. The major source of electrons and ions to the ring current is the plasma sheet. In the plasma sheet, ions such as H+, O+, He+, and N+ that originate from the solar wind and/or the ionosphere comingle, and their spectral distributions vary with solar and magnetic activity. The bulk properties of plasma sheet particles have been analyzed from several observational studies and a few empirical models of bulk plasma sheet properties have been developed. The charged particles from the plasma sheet gyrate, bounce, and drift within the dynamic inner magnetospheric electric and magnetic fields. Although the particle and fields system is electrodynamic, charged particles of different energies (∼1 keV to several hundreds of keV) respond differently to electric and magnetic field variations on slower (∼ 30 min to several hours) and more rapid (∼1 to 10’s min) time scales. The concepts of convective and diffusive transport with regard to ring current formation are described. Field variations can be localized and transient, particularly during substorms, and may lead to localized and bursty injection of particles in the inner plasma sheet to the inner magnetosphere. Such transport processes and their effects on the formation of the ring current are described.