Evaluating different techniques for constraining lower atmospheric variability in an upper atmosphere general circulation model: A case study during the 2010 sudden stratospheric warming

We analyze the effects specified dynamics (SD) and 4D Tendency nudging have on accurately reproducing the middle and upper atmospheric variability induced by the 2010 sudden stratospheric warming (SSW) event in the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM). TIME-GCM numerical experiments were performed using constrained middle atmospheric winds and temperatures from a high-altitude version of the Navy Global Environmental Model to compare the previously implemented SD scheme, with the newly implemented 4D Tendency scheme.

Model comparisons focused on zonal mean winds, composition, planetary waves, and tides in the thermosphere-ionosphere system. Through 4D Tendency nudging we reveal that coupling coefficients of the one-way SD coupling approach between the TIME-GCM and observed SSW conditions were too strong. Prior implementations produced unusually strong vertical shears in the zonal mean winds in the mesosphere and lower thermosphere (MLT), where the model is free running.