Correlation Study of Plasmasheet Ions with Solar Wind and Geomagnetic Conditions

Abstract

AbstractObservations obtained from CIS/CODIF and RAPID instrument onboard Cluster are used to investigate the temporal behavior of H+ and O+ ions in the storm time plasmasheet and the relationship between plasmasheet ions and solar wind conditions. It is found that: (1) The number density of O+ ions (0~40 keV) is quite low before SSC, and increases slowly as Dst decreases, reaching its peak value at the vicinity of Dst minimum. The density of H+ ions enhances greatly shortly before SSC, and decreases sharply after SSC. It keeps at a relatively low level during the whole main phase and recovery phase. Fluxes of energetic H+ and O+ ions enhance greatly after SSC and reach their maximum values before their low energy counterparts. It is implied that ions injected into ring current at early storm time are mainly H+ ions and only at later times could O+ ions significantly affect the ring current. (2) During geomagnetic active times, solar wind pressure, density and electric field are positively correlated with simultaneous H+ and O+ number density in the plasmasheet. The dependence of H+ number density on solar wind parameters is stronger under northward IMF (Interplanetary Magnetic Field), while O+ number density favors southward IMF. During geomagnetic quiet times, there is no clear evidence for a correlation between solar wind conditions and ions in the plasmasheet.