Temporal and spatial variation of the ion composition in the ring current

A global view of the ring current ions is presented using data acquired by the instrument MICS onboard the CRRES satellite during solar maximum. The v ariations of differential intensities, energy spectra, radial profile of th e energetic particles and the origin of the magnetic local time (MLT) asymm etry of the ring current have been investigated in detail. O+ ions are an i mportant contributor to the storm time ring current. Its abundance in terms of number density increases with increasing geomagnetic activity as well a s its energy density. However, a saturation value for the energy density of O+ ions has been found. The low-energy H+ ions show a dramatic intensifica tion and a rapid decay. However, its density ratio during the storm maximum is almost constant. On the other hand, high-energy H+ ions first exhibit a flux decrease followed by a delayed increase. Its density ratio shows an a nti-correlation with the storm intensity. Both the positions of the maximum flux of O+ and He+ depend on storm activity: they move to lower altitudes in the early stage of a storm and move back to higher L-values during the r ecovery phase. Whereas the position of H+ and He++ show almost no dependenc e on the Dst index. The energy density distributions in radial distance and magnetic local time show drastic differences for different ion species. It demonstrates that the ring current asymmetry mainly comes from oxygen and helium ions, but not from protons. The outward motion of O+ around local no on may have some implications for oxygen bursts in the magnetosheath during IMF Bz negative conditions as observed by GEOTAIL.