Observational Evidence and Formation Mechanism of Low?Density Cells in the Upper Thermosphere on September 8, 2017

The low-density cell structure in the high-latitude thermosphere is referred to as density depletion with respect adjacent area. Based on Gravity Recovery and Climate Experiment (GRACE) accelerometer data during September 2017 geomagnetic storms, thermospheric mass at about 350 km are estimated further investigated especially regions. At least two kinds of cells over Southern Hemisphere (SH) observed along GRACE orbit. To understand structures SH by GRACE, we investigate underlying physical mechanism based thermosphere-ionosphere numerical simulations using Thermosphere-Ionosphere Electrodynamic General Circulation Model Global Ionosphere Thermosphere Model. According simulation results, formation attributed storm-time vertical advection horizontal velocity divergence driven auroral ion convection. critical height observable shown be not less than km. meridional spatial scale approximately or slightly larger 1,500 Three cells, including dawn sector one night were 1 hour after direction interplanetary magnetic field BY component reversed. occurrence essential included empirical model storm time.