Atmosphere-Ionosphere (A-I) Coupling as Viewed by ICON: Day-to-Day Variability Due to Planetary Wave (PW)-Tide Interactions

Coincident Ionospheric Connections Explorer (ICON) measurements of neutral winds, plasma drifts and total ion densities (:=Ne, electron density) are analyzed during January 1-21, 2020 to reveal the relationship between neutral winds and ionospheric variability on a day-to-day basis. Atmosphere-ionosphere (A-I) connectivity inevitably involves a spectrum of planetary waves (PWs), tides and secondary waves due to wave-wave nonlinear interactions. To provide a definitive attribution of dynamical origins, the current study focuses on a time interval when the longitudinal wave-4 component of the E-region winds is dominated by the eastward-propagating diurnal tide with zonal wavenumber s = -3 (DE3). DE3 is identified in winds and ionospheric parameters through its characteristic dependence on local solar time and longitude as ICON's orbit precesses. Superimposed on this trend are large variations in low-latitude DE3 wave-4 zonal winds (±40 ms-1) and topside F-region equatorial vertical drifts at periods consistent with 2-days and 6-days PWs, and a ~3-day ultra-fast Kelvin wave (UFKW), coexisting during this time interval; the DE3 winds, dynamo electric fields, and drifts are modulated by these waves. Wave-4 variability in Ne is of order 25%-35%, but the origins are more complex, likely additionally reflecting transport by ~20-25 ms-1 wave-4 in-situ winds containing strong signatures of DE3 interactions with ambient diurnal Sun-synchronous winds and ion drag. These results are the first to show a direct link between day-to-day wave-4 variability in contemporaneously measured E-region neutral winds and F-region ionospheric drifts and electron densities.

Thermosphere-Ionosphere-Electrodynamics General Circulation Model for the Ionospheric Connection Explorer: TIEGCM-ICON

The NASA Ionospheric Connection explorer (ICON) will study the coupling between the thermosphere and ionosphere at low- and mid-latitudes by measuring the key parameters. The ICON mission will also employ numerical modeling to support the interpretation of the observations, and examine the importance of different vertical coupling mechanisms by conducting numerical experiments. One of these models is the Thermosphere-Ionosphere-Electrodynamics General Circulation Model-ICON (TIEGCM-ICON) which will be driven by tidal perturbations derived from ICON observations using the Hough Mode Extension method (HME) and at high latitude by ion convection and auroral particle precipitation patterns from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE). The TIEGCM-ICON will simulate the thermosphere-ionosphere (TI) system during the period of the ICON mission. In this report the TIEGCM-ICON is introduced, and the focus is on examining the effect of the lower boundary on the TI-system to provide some guidance for interpreting future ICON model results.