Statistics of substorm occurence in storm and non-storm periods

We have investigated similarities and differences between substorms occurring in stormtime and those in less disturbed periods, using data from the MICS instrument on CRRES to investigate composition changes in ring current ions in the energy range 70-400 keV/e. A statistical study shows that while substorms show some size and composition dependence on Dst, the strongest effect is that substorm injected energetic ion composition reflects the background population at energisation. These results are supported by a superposed epoch analysis which shows that the composition of storm time injections is similar to the set of all (storm and quiet time) oxygen rich injections. Moreover, these injections which have a high initial oxygen background, which is the condition that pertains in storms. We conclude that, during solar maximum when these measurements were made, substorms are not directly responsible for the injection of oxygen ions into the ring current.