The Mid-Tail Configuration Under Prolonged Northward IMF: An Event Study With ARTEMIS Observation and Global MHD Simulations

Abstract:

The magnetotail configuration is strongly controlled by the IMF orientation, but the solar wind-magnetosphere coupling and the resulting plasma and magnetic field structures in the mi-tail, particularly under northward IMF, are not well understood. In this study, we present ARTEMIS observations of the mid-tail magnetosphere (X ~ –60 R_E) during a prolonged northward IMF period (> 48 hr, starting from ~22 UT on Feb 12 2014). The two ARTEMIS probes (separated by ~3 R_E) were on the duskside plasma sheet (|B| < ~6 nT for most of the time) moving from Y ~22 to 2 R_E. ARTEMIS observed the low latitude boundary layer (LLBL) extending from the flank inward to Y ~5 R_E with hot (a few keV) plasma sheet ions mixed with cold (several hundreds of eV) tailward-moving plasma. The appearance of the cold plasma is more quasi-periodic (a few minutes) near the flank, suggesting a likely association between the LLBL formation and Kelvin-Helmholtz/surface waves. The magnetic field strength fluctuates substantially and can go down to as small as < 1 nT, suggesting fluctuations in the current sheet thickness that might result from current sheet flapping motion. To evaluate these likely physical processes, we are currently determining the temporal changes of the plasma and magnetic field spatial structures using the two probe measurements and comparing these observations with results from different global MHD simulation runs conducted at NASA Community Coordinated Modeling Center, including LFM, Open GGCM, and BATS-R-US.