Solar wind control of auroral zone geomagnetic activity, Geophys

Abstract. An empirical analysis of solar wind-magneto-sphere energy coupling functions is reported. Using the tech-nique of linear prediction filtering with 2.5 minute data, we examine the relationship of auroral zone geomagnetic activity to solar wind power input functions which depend on the solar wind quantities VB 2, VBs, or V2Bs. In this analysis a least squares prediction filter or impulse response function which relates a solar wind power function to an auroral zone geomagnetic index is designed directly from the data. We find that the computed impulse response functions have the characteristics of a low pass filter with a time delay which may be dependent on the strength of the energy input. While the AL index is reasonably well related to the solar wind energy functions, the AU index shows a substantially poorer relationship. In addition, high frequency variations of the auroral indices and some substorm expansions are not predictable with solar wind information alone, suggesting that internal magnetospheric processes partially control the AL index. We also find that the e parameter which depends on VB • ' in the solar wind has a poorer relationship to auroral zone geomagnetic activity than a power parameter having a VB, solar wind dependence