Magnetospheric response to the IMF: substorms

We review the evidence for the control of magnetospheric substorms by the interplanetary magnetic field (IMF). Early statistical results, as well as recent correlation studies, are cited to show the strong degree of control exerted by the IMF over substorms as measured by auroral electrojet (AE, AL) parameters. Recent case studies and linear prediction filtering methods reveal quite clearly that substorms have both a 'driven' and an 'unloading' aspect. The driven component has a response time of 10 - 20 min, while the unloading time scale is - 1 hr. ISEE-3 deep-magnetotail results and recent Dynamics Explorer polar imaging data are related in this paper to these two separate facets of the substorm sequence. Dimensional analysis studies have delineated which solar wind-magnetosphere coupling formalisms are physically tenable and which give the best representation of the empirical data. The review concludes with a discussion of the total magnetospheric energy output parameter, UT, and some of the problems inherent in its calculation. It is shown that as presently formulated, UT cannot be meaningfully compared to solar wind input parameters by the usual correlation methods. (author)