Northward IMF and Patterns of High-Latitude Precipitation and Field-Aligned Currents: The February 1986 Storm
AIR FORCE SYSTEMS COMMAND HANSCOM AFB MA GEOPHYSICS LAB
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On February 7, 1986, during a major geomagnetic storm the Bz component of the interplanetary magnetic field IMF turned strongly northward for several hours. Data from the Defense Meteorological Satellite Program F6 and F7 satellites and the HILAT satellite were used to study the evolution of the pattern of high-latitude precipitation and field-aligned currents in response to this change. Prior to the northward IMF period, the auroral zone was observed down to mid-latitudes and was very wide in latitude, and strong, large-scale region 1 region 2 currents were clearly present. Following the northward turning, the equatorward boundary of the auroral zone on the nightside contracted sharply poleward and polar cap arcs were observed. The strength of the region 1 region 2 currents decreased markedly and became immeasurably small at the time of the maximum contraction of the auroral oval. An NBZ current system was observed to grow and expand in the southern summer high latitude region over a period of more than 2 hours. When the IMF turned southward again, the pattern quickly reversed. The BPR contracted the CPS precipitation regions expanded the equatorward boundary of the auroral oval moved to lower latitudes the NBZ currents disappeared in less than 30 min and the region 1 region 2 currents reappeared. Again, the BPRCPS boundary did not move as rapidly and thus may indicate that the changes are due more to a reconfiguration within the magnetosphere than a change in the portion of the magnetosphere that is open or closed. Reprints.
- Atmospheric Physics