Image, polar, and geosynchronous observations of substorm and ring current ion injection

The geomagnetic storm of October 4-6, 2000 provides an exceptionally good opportunity to examine the role of substorms during the storm because of the relatively moderate solar wind driving and because of the excellent set of satellite observations. We show that the entire day of October 4 was characterized a sequence of substorms and a gradual build-up of the storm-time ring current. We examined one of those substorms in some detail showing that it had the expected signatures of a magnetospheric substorm. ENA observations and in situ measurements show that the substorms clearly do provide a mechanism for transporting energetic ions from the magnetotail to the inner magnetosphere. Substorm injections do not, however, provide the only mechanism. As other studies have suggested, the evidence from this storm shows that the presence of a quasi-steady convection electric field plays an additional important role. This is seen through the comparison of Dst which decreases slowly and smoothly over nearly 10 hours with geosynchronous particle injections which occur impulsively at roughly 2-hour intervals producing a "sawtooth" injection profile. Further evidence comes from ENA observations that show both impulsive injection during substorms and continued intensification and eastward expansion in response to convection electric fields. We also investigate the transport and symmetry of the ring current particles. We find that, even more than 10-hours into the storm when Dst had decreased below -100 nT and at least five clear substorm injections had occurred, the ring current remained highly asymmetric with essentially no ENA emissions from the dawn-to-noon sector. We also find that Dst, SYM-H, and ASY-H all respond approximately equally in spite of the fact that there is apparently no symmetric component to the ring current until later in the storm.