Coupling between the solar wind and the magnetosphere: CDAW 6

Abstract

Interplanetary conditions (VBs V²Bs ε) are derived from ISEE 3 and IMP 8 field and plasma data for the two Coordinated Data Analysis Workshop (CDAW 6) intervals of study and are compared with various aspects of geomagnetic activity (AE, UT, derived Joule heating, electric potential, westward, eastward and total electrojet currents). The March 22 (day 81), 1979, interval contains two distinct periods of geomagnetic activity, both highly correlated with interplanetary features. The start of the first active interval is caused by a southward turning of the interplanetary magnetic field (IMF) associated with the passage of a heliospheric current sheet. The start of the second interval is related to a second IMF southward turning. The geomagnetic activity intensifies when the second crossing of the current sheet, and a ram pressure increase of 4 to 6, impinges on the magnetosphere. Because the interplanetary parameters VBs, V²Bs and ε decrease across the discontinuity, it is concluded that either additional energy is injected into the magnetosphere from the conversion of ram energy into magnetospheric substorm energy or some feature associated with current sheet crossing “triggers” the release of previously stored magnetosphere/magnetotail energy. It is not possible at this time to distinguish between these two possibilities. For day 81, VBs, V²Bs and ε were highly correlated with AL, AE, westward and equivalent currents with coefficients ranging from ∼0.75 to 0.90. The interplanetary parameters were significantly less correlated with geomagnetic activity in the second interval (days 90–91, 1979), with all correlation coefficients being less than 0.6. Several possible explanations for the latter result are (1) the scale of Alfvénic fluctuations was small in comparison to the size of the magnetosphere and the “upstream” spacecraft did not get an accurate indication of the solar wind impinging on the magnetosphere, or (2) during some periods of high and continuous activity, substorms are due to internal magnetospheric processes and occur randomly, independent of the interplanetary drivers.