九章講壇第六期——暨空間科學先導專項前沿報告

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Abstract

Recent emphasis on dipolarization fronts (DFs) has led to the impressionDFs play a significant role in bringing magnetic flux to the innermagnetosphere during substorms. In this work, we investigate the amount ofmagnetic flux transport associated with DFs by examining the frozen-in fieldline condition (FIC) for previously reported DF events. A study of 18 DF casesshows that the FIC does not hold for 17 cases when the ratio of |[Ey+ (V×B)y]/(V×B)y| exceeds0.5, i.e., the mismatch ofEyand –(V×B)yexceeds 50%; this criterion is applied only when the electric field magnitudeexceeds 0.5 mV/m to eliminate times of low-level electric fluctuations.Furthermore, the peak magnetic flux transport rate for DFs in which FIC holdsis found to be in the range of ~8 – 42 kWb/s/REwhile theaccumulated flux transport within the DF intervals to be ~0.1 – 2.8 MWb/RE.Assuming a dawn-dusk dimension of 3REfor a DF, theaccumulated magnetic flux transport is ~0.3 - 8 MWb, which amounts to ~0.1 –2.2 % of what is needed to account for magnetic flux increase in the near-Earthdipolarization during substorms. This result casts doubt on the idea that DFsplay a significant role in substorm dipolarization.

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