Relative Timing of Nightside and Dayside Plasmapause Motion: Two Events in June 2001

Abstract

We examine the relative timing of dayside and nightside plasmapause motion following southward interplanetary magnetic field turnings on 2 and 9 June 2001. For both events the delay between the dayside and nightside plasmapause response is less than the temporal resolution of Imager for Magnetopause-to-Aurora Global Exploration extreme ultraviolet observations (10 min). Our result thus establishes a possible upper limit (<= 10 min) on the day-to-night onset delay. From analysis of the extreme ultraviolet-observed plasmapause motion we find on 2 June the time-averaged plasmapause E field was (in mV/m) 0.61 near noon magnetic local time, 0.35 near midnight magnetic local time, and 0.44 overall. The normalized plasmapause speed data (both dayside and nightside) are fitted to the curve (0.09 +/- 0.05)L-3, consistent with a spatially uniform and time-constant dawn-dusk penetration E field that is 9% of the solar wind field. On 9 June the time-averaged E field values (mV/m) were 0.24 (dayside), 0.28 (nightside), and 0.26 (overall); the plasmapause motion was consistent with a penetration E field 10% of the solar wind field. Plasmasphere erosion is a fundamental element of the dynamic magnetospheric response to solar wind driving. This study yields an important observational constraint on the day-to-night timing of the plasmapause response. The result also has implications for the two main models for the cause of erosion (convection and interchange).