The Effect of Sub-Auroral Polarization Streams on Ionosphere and Thermosphere: Non-Hydrostatic Simulations

Abstract:

Simulations with the Global Ionosphere-Thermosphere Model (GITM) revealed new aspects of the effects of sub-auroral polarization streams (SAPS) on thermosphere-ionosphere system: (1) Traveling atmospheric disturbances (TAD) could be induced by the sudden variation of the location and strength of SAPS. Abrupt frictional heating resulted in internal gravity waves (IGW), which propagated equatorward with ~10 mins period at the speed of 830 m/s. The perturbations in vertical and meridional wind could surpass the magnitude of 100 m/s. (2) Traveling ionospheric disturbances (TID) were also induced through ion-neutral coupling processes. At middle latitudes, the ions were generally controlled by ion-neutral collisions and the pressure gradient built by the redistribution of plasma. The disturbance in integrated electron content (IEC) from 100 km to 600 km altitude was ~0.3 TECu, which could be observable in GPS-TEC data. (3) The changes in horizontal neutral wind show a two-cell pattern. In the northern hemisphere, the wind flew in a clockwise circle to the north of SAPS channel, while anti-clockwise to the south. This two-cell pattern was the combined result of ion-drag, Coriolis force and pressure gradient. (4) It was confirmed that the westward zonal wind induced by SAPS could be directed poleward by Coriolis force, which could be the cause of the reported poleward wind surge during the St. Patrick day storm in 2015. However, a more complicated scenario was proposed based on the simulations. The sudden decrease of Joule heating within the auroral oval could result in the northward wind surge, which was also enhanced under the action of either Coriolis force or pressure gradient induced by SAPS.