Abstract
We investigate the role of depleted flux tubes in both large‐scale configurations and transient reconfigurations during the 13 March 2009 steady magnetospheric convection (SMC) event. A series of numerical simulations with different plasma boundary conditions were carried out using the Rice Convection Model with an equilibrated magnetic field model (RCM‐E) in order to examine what kind of local‐time‐dependent entropy distribution could best reproduce the observed overall configurations during this SMC event. The results are summarized as follows: (1) the simulation with data‐driven boundary conditions (called D run) produces a depleted plasma sheet over all the local times and yields the best overall agreement with multipoint observations of THEMIS and GOES spacecraft in the plasma sheet and the inner magnetosphere. (2) The simulation with empirical model boundary conditions (called E run) predicts an overstretched magnetic field and larger plasma pressure than observations. (3) The simulations with a persistent low‐entropy flow channel around the midnight sector during the entire SMC interval result in plasma pressure distribution as large as the E run in the inner edge of the plasma sheet. Our simulation indicates that at least for this event, the pressure‐balance inconsistency is avoided during a strong earthward convection interval only when the entire plasma sheet earthward of 20 RE is supplied with low‐entropy plasma. Further simulations show that the earthward transport of plasma sheet bubbles in the background of D run, which mimics the overall configuration best, tends to cause smaller magnetic field dipolarization and produce smaller magnitudes of flows than bubble injections in the background of E run. The results are consistent with the fact that although there are transient flow bursts during SMCs, none of them are accompanied by significant large‐scale reconfigurations in the near‐Earth plasma sheet.
Published Version
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