2-COMPONENT AURORAL ELECTROJET - IMPORTANCE FOR SUBSTORM STUDIES

This paper attempts to synthesize the diverse number of observations o f electric fields and currents in the high-latitude ionosphere during substorms. By demonstrating that there are often spatial shifts among regions of high ionospheric conductivity, large electric fields and in tense currents in the auroral electrojet, it is shown that substorm ti me variations of the current patterns over the entire polar region con sist of two basic components. The first is related to the two-cell con vection pattern and the second to the westward electrojet in the dark sector, which is in turn related to the three-dimensional wedge curren t system. These two components result from the relative strength of el ectric fields and conductivities in the intensification of the auroral electrojet and are identified as the signatures for directly driven a nd the unloading components in solar wind-magnetosphere interactions. We contend that disturbed intervals do not necessitate the presence of substorm expansion-phase activity and that the vast number of earlier complex results concerning the auroral electrojet carl be ascertained from the high degree of variability of the two components, depending on substorm events, substorm phases, and their own spatial/temporal sc ale sizes. It is demonstrated that several major issues that have rema ined controversial are now accounted for reasonably well in terms of t his two-component electrojet model. We also predict specific features of the substorm auroral electrojet that have not yet been observed.