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Geophysical Research Letters


Reverse polarity, or South-then-North (SN) bipolar, traveling compression regions (SN TCRs) are often observed in the Earth's magnetotail lobes. These events have been interpreted as either slowly earthward propagating "proto-plasmoids" during extremely quiet geomagnetic conditions, or due to pressure pulses in the solar wind or magnetosheath compressing the magnetotail. This study presents a survey of 21 IMP 8 observations of SN TCRs and the corresponding solar wind pressure conditions as measured by WIND. We found that solar wind or magnetosheath pressure pulses nicely explain most (17), though not all, of the SN TCR observations. Therefore, it appears that both explanations previously given are needed to explain SN TCRs. We also found that most of these events occurred during northward Interplanetary Magnetic Field (IMF) conditions. This suggests that the magnetotail may respond differently to solar wind dynamic pressure pulses for different orientations of the IMF.



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