The Impact of Lower Atmospheric Forecast Errors on Ionospheric Conditions During Geomagnetic Storms using WACCM-X 2.2

Accurate space weather forecasting critically depends on understanding the influence of internal atmospheric dynamics on the ionosphere during geomagnetic storms. We investigate this by conducting two sets of simulations with the Whole Atmospheric Community Climate Model with Thermosphere and Ionosphere Expansion (WACCM-X 2.2) for the geomagnetic storms of 5-6 April 2010 and 17-18 March 2013. In our analysis run, lower atmospheric dynamics are constrained using the Modern-Era Retrospective Analysis for Research and Applications version 2 data throughout the experiment. Subsequent forecast runs are conducted in free-running mode, each is initiated from initial conditions derived from the analysis run 20, 10, 5, 2, and 1 day prior to the onset of each storm. Our findings reveal that initial Total Electron Content (TEC) biases begin in the equatorial region and extend to higher latitudes as forecast duration increases. Significant deviations in the amplitudes of semi-diurnal migrating (SW2) and non-migrating diurnal (DE3) tides in the equatorial E-region occur within 1–2 days of forecasting. These tidal deviations impact vertical plasma drift in the equatorial F-region, leading to TEC biases. Additionally, biases in the zonal-mean zonal winds in the mesosphere and lower thermosphere (MLT) at mid-to-high latitudes influence the amplitude of SW2 and DE3 tides. These wind biases correlate with forecast errors in resolved wave forcing and parameterized gravity wave drag, highlighting that inaccuracies in wave forcing processes are a major source of forecast errors in the ionosphere-thermosphere system.