Ring current ion composition during solar minimum and rising solar activity: Polar/CAMMICE/MICS results

This paper shows statistical results of the ring current ion composition an d its variability as a function of solar cycle and magnetospheric activity for 3 < L < 8. Spin-averaged energetic particle (1-200 keV) measurements fr om Polar are combined with geomagnetic indices as well as solar wind and in terplanetary observations from the Wind spacecraft during a period from Sep tember 1996 to March 1999. The statistics are performed both for time-avera ged values for all periods as well as for peak flux values during geomagnet ic storms (defined as Dst < -50 nT) that occurred during this period. The a verage O+ energy density increases by about a factor of 5 during the rising phase of the solar cycle from the minimum values in 1996, while the averag e values of H+ and He show variability but no consistently increasing trend . The O+ flux is small (below 10%) compared with the hydrogen flux, and the average energy density ranges from a few percent at solar minimum to simil ar to 10% at high solar activity time in early 1999. The O+ flux is typical ly smaller than the He+ flux, reaching comparable values only during the la tter part of the period when the solar activity increased. Analogously, the energy densities of O+ and He+ are about equal during 1996 and 1997, where as the O+ energy density is about twice the He+ energy density during the h igher solar activity period in 1998 and early 1999.