Improving ionospheric predictability requires accurate simulation of the mesospheric polar vortex

Abstract

SynopsisThe mesospheric polar vortex (MPV) plays a critical role in coupling the atmosphere-ionosphere system, so its accurate simulation is imperative for robust predictions of the thermosphere and ionosphere. While the stratospheric polar vortex is widely understood and characterized, the mesospheric polar vortex is much less well-known and observed, a short-coming that must be addressed to improve predictability of the ionosphere. The winter MPV facilitates top-down coupling via the communication of high energy particle precipitation effects from the thermosphere down to the stratosphere, though the details of this mechanism are poorly understood. Coupling from the bottom-up involves gravity waves (GWs), planetary waves (PWs), and tidal interactions that are distinctly different and important during weak vs. strong vortex states, and yet remain poorly understood as well. Moreover, generation and modulation of GWs by the large wind shears at the vortex edge contribute to the generation of traveling atmospheric disturbances (TADs) and traveling ionospheric disturbances (TIDs). Unfortunately, representation of the MPV is generally not accurate in state-of-the-art general circulation models (GCMs), even when compared to the limited observational data available. Models substantially underestimate eastward momentum at the top of the MPV, which limits the ability to predict upward effects in the thermosphere. The zonal wind bias responsible for this missing momentum in models has been attributed to deficiencies in the treatment of GWs and to an inaccurate representation of the high-latitude dynamics. Such deficiencies limit the use of these models to study the role of the MPV in the transport of constituents and in wave-mean flow interactions, and to elucidate the mechanisms by which the atmosphere-ionosphere system is interconnected. In the coming decade, simulations of the MPV must be improved. This can be accomplished by constraining the model temperature and wind fields in the mesosphere and lower thermosphere (MLT) with a more extensive suite of satellite and ground-based observations. In addition, improvements to current model GW parameterizations are required to more accurately simulate the processes that govern the generation, propagation, and dissipation of GWs.