Paper#: 86
Poster #: 7
Session Name: Poster Session 1
Room: East Ballroom
Day: Tuesday
Time: 10:10 a.m.-Noon
Abstract Title: Solar Wind Control of the High-Latitude Propagation of the Substorm Electrojet
PresentSurname: Despirak, I.
All Authors: I. Despirak, A. Lubchich, A. Yahnin
Abstract : During the expansion phase of substorm the westward electrojet propagates poleward following the auroral expansion. Sometimes the electrojet propagates from the auroral zone up to very high latitudes (CGLat >75-80). Previous studies showed that this is possible under high-speed solar wind conditions. This report is devoted to further investigation of the conditions under which the substorms can propagate to very high latitudes. On the basis of data from the Wind satellite and ground-based geomagnetic station network IMAGE we analyzed more than 570 substorm events during 1995-1996 and showed that, in addition to the high solar wind velocity, the duration and value of negative Bz- component of interplanetary magnetic field are important parameters for the high-latitude propagation of the electrojet. In average, under high-speed (>500 km/s) solar wind the appearance of substorm electrojet at high latitudes is preceded by a ~1.5-hour interval of negative Bz, while substorms developing inside the auroral zone are preceded by only a ~30-minute interval of negative Bz. In other words, we found the correlation between the appearance of substorm at high latitude and solar wind electric field (Ey = -V*Bz) integrated for a 1.5-hour interval. The probability of observation of the substorm at higher latitude increases as the duskward solar wind electric field increases. These findings suggest a simple explanation in terms of reconnection model. Since Ey is a measure of the reconnection rate at dayside magnetopause, the longer interval of large Ey the large supply of the magnetic energy is stored in the tail lobes, which may be released in the magnetosphere-ionosphere system in form of the intense substorm. According to the reconnection model, the substorms are the result of the reconnection at the near-Earth neutral line (NENL), and the auroral bulge area is proportional to the reconnected surplus of the tail-lobe magnetic flux. Evidently, the large supply of the magnetic flux should associate with the large-scale auroral bulge, and, in particular, with high-latitude location of its poleward edge and related westward electrojet.