Magnetic Flux For The Substorm Current System And Dipolarization Fronts

Abstract:

Recent emphasis on dipolarization fronts (DFs) has led to the impression DFs play a significant role in bringing magnetic flux to the inner magnetosphere for the substorm current system. In this work, we investigate the amount of magnetic flux transport associated with DFs by examining the frozen-in field line condition (FIC) for previously reported DF events. A study of 18 DF cases shows that the FIC does not hold for 17 cases when the ratio of |[E_y + (V×B)_y]/(V×B)_y| exceeds 0.5, i.e., the mismatch of E_y and –(V×B)_y exceeds 50%. Furthermore, the peak magnetic flux transport rate for DFs in which FIC holds is found to be in the range of ~8 – 42 kWb/s/R_E while the accumulated flux transport within the DF intervals to be ~0.1 – 2.8 MWb/R_E. Assuming a dawn-dusk dimension of 3 R_E for a DF, the accumulated 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-Earth dipolarization for the substorm current system. This result casts doubt on the idea that DFs play a significant role in substorm dipolarization and the substorm current system.