A comparison of the effects of CIR- and CME-induced geomagnetic activity on thermospheric densities and spacecraft orbits: Statistical studies

Enhanced energy input from the magnetosphere to the upper atmosphere during geomagnetic storms has a profound effect on thermospheric density and consequently near-Earth satellite orbit decay. These geomagnetic storms are caused by two different processes. The first is coronal mass ejections (CMEs) and the second is corotating interaction regions (CIRs). CME-driven storms are characterized by large maximum energy input but relatively short duration, whereas CIR-driven storms have relatively small maximum energy input but are of a considerably longer duration. In this paper we carried out a statistical study to assess the relative importance of each kind of storm to satellite orbital decay. The results demonstrate that CIR storms have a slightly larger effect on total orbital decay than CME storms do in a statistical sense. During the declining phase and the minimum years of a solar cycle, CIR storms occur frequently and quasiperiodically. These storms have a large effect on thermospheric densities and satellite orbits because of their relatively long duration. Thus, it is important to fully understand their behavior and impact.