Ionosphere and Thermosphere Observations in the Context of Whole Atmosphere Modelling

Modelling the whole atmosphere from the surface to the ionosphere allows us to better forecast and understand our weather and climate. It is a scientific and computational challenge to model this complex system numerically with its many drivers and feedback loops. Recent efforts to improve whole atmosphere models include raising the altitude to incorporate improved representations of the ionosphere and thermosphere. The Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X) is one of the most comprehensive numerical models, spanning the range of altitude from the Earth’s surface to the upper thermosphere (~700 km). WACCM-X can model the global ionosphere and thermosphere, whilst providing coupling between atmosphere layers through chemical, physical and dynamical processes. Using WACCM-X, we can explore the implications of this coupling for the climate and for the near space environment. 

The high-latitude ionosphere-thermosphere behaves dynamically during geomagnetically active times due to time-varying solar wind driving and internal magnetospheric dynamics. We present high- and mid-latitude observations from the Super Dual Auroral Radar Network, Incoherent Scatter Radars and Fabry-Perot Interferometers which observe the ionosphere-thermosphere system. We investigate observed plasma flows, which respond directly to solar wind driving, alongside WACCM-X model simulations which are nudged to a meteorological reanalysis dataset in the troposphere and stratosphere during a variety of solar storm conditions. We discuss these in the context of time-varying dynamics due to solar wind driving and investigate the expansion of the high-latitude convection to lower latitudes during geomagnetic storms. Our results show that the latitudinal expansion is not yet fully captured in WACCM-X and we discuss how this may be mitigated. We further show that during a geomagnetic storm, the differences between the WACCM-X ionospheric data and the observations by SuperDARN at high- to mid-latitudes may vary by up to ~20 kV for the electrostatic potential during a geomagnetic storm. This translates to an electric field difference of 25 mV/m and differences in the plasma drift velocities in excess of ~800 m/s.