After a brief review of magnetospheric and interplanetary phenomena for intervals with enhanced solar wind-magnetosphere interaction, an attempt is made to define a geomagnetic storm as an interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads, through a substantial energization in the magnetosphere-ionosphere system, to an intensified ring current sufficiently strong to exceed some key threshold of the quantifying storm time Dst index. The associated storm/substorm relationship problem is also reviewed. Although the physics of this relationship does not seem to be fully understood at this time, basic and fairly well established mechanisms of this relationship are presented and discussed. Finally, toward the advancement of geomagnetic storm research, some recommendations are given concerning future improvements in monitoring existing geomagnetic indices as well as the solar wind near Earth. knowledge of magnetospheric physics using spacecraft, as compared to older epochs when most of that knowledge had to come from ground observations. In addition, past attempts to formulate definitions for storms were restricted only to the near-Earth environment, the ionosphere and magnetosphere. However, with the subsequent accumulation of information obtained in the interplanetary medium, critical aspects of these definitions now involve diverse findings related to the solar wind dynamics [e.g., Burton et al., 1975; Gonzalez and Tsurutani, 1987; Tsurutani and Gonzalez, 1987]. Motivated by an interest in trying to find unifying concepts about the geomagnetic storm and the longstanding problem of storm/substorm relationship, the authors of this review paper met at the National Institute for Space Research of Brazil (INPE), at Sho Jos6 dos Campos, Sho Paulo, during the interval of November 5-8, 1991. The results obtained in this meeting, together with further elaboration, are presented in this paper in the following sequence.Section 2 is devoted to historical aspects of geomagnetic storm research, as based on ionospheric and magnetospheric parameters. In section 3 the interplanetary origin of storms is addressed. A brief review follows on solar wind-magnetosphere coupling, particularly applied to storm intervals. Then, for completeness, the seasonal and solar cycle distribution of storms is briefly considered. Section 4 reviews basic aspects of the storm/substorm relationship problem. In section 5, a discussion about additional mechanisms that contribute to ring current intensification as well as about basic mechanisms for ring current decay is given. A brief review on the relationship of Dst to other geomagnetic indices follows. Section 6 gives summary concepts on geomagnetic storms and on their relationship to substorms. A definition for a geomagnetic storm is suggested. Finally, in section 7 recommendations con-5771 5772 GONZALEZ ET AL.: REVIEW PAPER cerning future improvements in monitoring existing geomagnetic indices as well as the solar wind near the Earth are provided...
