The influence of lower atmosphere dynamics on MLT variability in the CMAT2 GCM using Newtonian Relaxation techniques

Abstract:

Recent research has established numerous links between dramatic meteorological events such as Sudden Stratospheric Warmings (SSWs), and variability in the upper atmosphere. In order to investigate the sensitivity of the MLT region to winds, waves, and tides generated in the troposphere and stratosphere, we have been developing techniques to drive UCL’s Coupled Middle Atmosphere and Thermosphere (CMAT2) GCM with a series of meteorological models and reanalyses.

Two such models are the UK Met Office’s Unified Model (UM), and the NRL NOGAPS-ALPHA reanalysis. In this study we couple these models with CMAT2 using Newtonian Relaxation in the overlapping lower/middle atmosphere regions. We demonstrate the variability imposed on the MLT region through a more realistic lower atmosphere representation when compared with the use of parameterised tidal and gravity wave schemes commonly used in GCMs. By running an ensemble of UM simulations, we show the sensitivity of the MLT region to different SSWs before, during, and after the onset of these events. Furthermore, we run the UM in forecast mode to investigate how migrating and non-migrating tides during both ‘quiet times’, and SSW events influence the behaviour of the MLT region.