The Dynamic Response of the Westward Auroral Electrojet and Polar CAP Currents to Solar Wind-Magnetosphere Coupling

We present results of studies using high-time resolution data to determine the response of magnetospheric currents to coupling with the solar wind. In the first study, we apply the concept of dimensional analysis to the problem of solar wind-magnetosphere coupling in order to find the dependence of the coupling rate on solar wind variables. We find that energy input to the magnetosphere and as represented by the AE indices occurs at a rate proportional to p^{1over6}EG( theta) where p is the solar wind dynamic pressure, E is the solar wind motional electric field, and G(theta) is a "leaky" gating function which expresses coupling rate dependence on the interplanetary magnetic field (IMF) orientation. In the second study, we determine the temporal relationship between the solar wind motional electric field (VB_ {rm s}) and the westward auroral electrojet index, AL, by using the linear prediction technique. We find that the VB_{rm s} -AL response filters are composed of two response pulses. We hypothesize that the two response pulses each correspond to a different response mode of the magnetosphere. We suggest that one response pulse corresponds to AL index activity driven directly by solar wind-magnetosphere interaction while the other corresponds to activity driven by energy loading and unloading from the magnetotail. In the third chapter, we attempt to test the bimodal model for magnetospheric response by means of a simple computer analogue that is designed to mimic the behavior of the magnetosphere. Using linear prediction tests, we find that the model system is a reasonable representation of the actual magnetosphere. In the fourth study, we examine the AE indices to determine the accuracy of the index. The chapter focuses on known problems with the indices and attempts to address them by modifying the index generation scheme. We find that the index accuracy can be improved especially during quiet times and at substorm onset. In the fifth chapter, we extend our analysis by studying the PC index which measures Hall current flow across the polar cap. We find that the PC index response filter closely resembles the AL index filter, a result which suggests that both PC and AL are accurately quantifying the response of the magnetosphere. The differences between the PC and AL response filters suggest that the PC index responds primarily to dayside reconnection whereas the AL index responds more than PC to nightside reconnection. These results are mainly consistent with the bimodal response model of the magnetosphere.