Quiet-time low latitude ionospheric electrodynamics in the non-hydrostatic Global Ionosphere–Thermosphere Model

Abstract

Recently the University of Michigan's Global Ionosphere–Thermosphere Model (GITM) has been equipped with new potential dynamo solver. GITM explicitly solves the full three-dimensional dynamo equations of the thermosphere and ionosphere self-consistently with realistic forcing. Unlike the other coupled global ionospheric models, GITM relaxes the hydrostatic assumption. It includes the IGRF magnetic field with the modified APEX coordinate system, set for the date of the simulation. The model runs are initiated with MSIS model for the neutral atmosphere and with IRI model values for the ionospheric charged particles, but eventually computes these quantities self consistently. The model is also updated to include lower boundary tidal forcing. During geomagnetic quiet conditions, the poleward boundary of the ionospheric dynamo in the model is fixed at ±70° geomagnetic latitude. Two-dimensional electrostatic potential patterns are constructed assuming the equipotential field lines. The model is run for 10 days to ensure quasi-equilibrium state. The GITM simulations reproduce the stronger dynamo processes near dusk during solar maximum. The seasonal dependence is investigated during spring equinox, June and December solstices. GITM results indicate a weaker evening pre-reversal enhancement (PRE) during winter and a stronger PRE during equinoctial months. It is found that the time of PRE occurrence in the Philippine sector is independent of the solar activity and season. Also the seasonal effects are prominent near dawn and dusk sectors. The morning reversal of the vertical drifts occurs late during March and the evening reversals are late during month of December. The effects of different lower boundary tidal inputs have been studied, which reveal the significance of E-region wind dynamo in determining F-region plasma drifts. The model is capable of capturing the salient features of the low to mid-latitude ionosphere, and should be a helpful tool for the investigation of the upper atmosphere and ionosphere.