On the Enhancement of Dayside Cusp Field Aligned Current: Case Study of Cluster Observation.

Abstract:

On 23^rd September 2014, the fleet of Cluster spacecraft penetrated Energetic Electron Wall at the noon and observed field aligned current indicated by a bipolar structure of Ba component in MFA coordinate. The FAC locates in cusp according to the polarity of bipolar and main particle energy. The amplitude of the bipolar structure kept increasing and the its region also enhanced consecutively as observed by the spacecraft one by one. The enhancement of bipolar structure happened after IMF magnetic field turned to northward from southward and DP increased from 1.4 to 2.0 nPa sharply. Meanwhile AE increased from 150 nT to 300 nT slowly. Therefor this phenomenon is concluded as the cusp current enhanced as the development of substorm. Furthermore, calculation presents that the electron current appears to be a triple sheet while the proton current is a double sheet, and electrons contribute more than protons to the current and its enhancement. The energy spectrum of proton also shows energy dispersion and pitch angle dispersion which may result from time of flight effect.