Quantifying the IT effect of upward propagating tides with TIEGCM-ICON

The vertical coupling of the lower and upper atmosphere via atmospheric solar tides is very variable and affects the thermosphere and ionosphere system. In this study, we use Ionospheric Connection (ICON) explorer data from 220-270 Day of Year, 2020 when large changes in the migrating semidiurnal tide (SW2) and the zonal and diurnal mean (ZM) zonal wind occurred within 8 days. We use the ICON Level4 product, the thermosphere-ionosphere-electrodynamics general circulation model (TIEGCM) driven by tides fitted to ICON observations via the Hough Mode Extension (HME) method. The effect of the upward propagating tides is isolated by examining the difference between two TIEGCM simulations with and without tidal HME forcing at the model lower boundary.

The simulations reveal strong changes in the latitudinal structure of the solar SW2 and the ZM zonal wind at 250 km. These SW2 changes are associated with the prevalence of antisymmetric HMEs after DOY 232. Similar variations to SW2 are captured in the migrating diurnal, terdiurnal and quaddiurnal tides at 250 km. The strong dynamical changes decrease the zonal and diurnal mean O/N2 by roughly 10% and the NmF2 by approximately 15-20%. These changes are stronger than general seasonal behavior and highlight the effect of rapid SW2 changes on the upper thermosphere and ionosphere as captured by TIEGCM-ICON.