High Resolution Simulations of the Chemistry and Dynamics of the Mesosphere and Lower Thermosphere During the 2018‐2019 Sudden Stratosphere Warming

The 2018–2019 sudden stratospheric warming (SSW) is simulated using a high‐resolution whole atmosphere model that includes interactive chemistry and constrained meteorology. The simulations are performed using a high‐resolution (∼0.25) configuration of the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) with the meteorology constrained up to ∼10 hPa using ECMWF Reanalysis v5 (ERA5). The high‐resolution WACCM‐X simulations are compared to satellite and ground‐based observations as well as two whole atmosphere data assimilation systems. Based on these comparisons, the high‐resolution WACCM‐X simulations are shown to alleviate two long‐standing biases in low‐resolution (∼2) WACCM‐X: a westward wind bias in the mesosphere and lower thermosphere (MLT) at wintertime high‐latitudes, and insufficient downward transport of nitric oxide (NO) following SSWs. The high‐resolution simulations are also able to capture much of the day‐to‐day variability in MLT winds seen in meteor radar observations. The simulations represent the first meteorologically constrained high‐resolution whole atmosphere simulations with fully interactive chemistry, and demonstrate that high‐resolution whole atmosphere model simulations can significantly improve representation of dynamical and chemical variability in the middle and upper atmosphere during SSWs.