The structure of the mesosphere during sudden stratospheric warmings in a global circulation model

[1] Mesospheric coolings and wind reversals during sudden stratospheric warmings are studied in a 570 day permanent January simulation with the Kuhlungsborn Mechanistic Circulation Model (KMCM). The model is run at a high resolution in combination with an advanced parameterization of turbulence, allowing for an explicit description of gravity-wave effects. Self-generated major sudden stratospheric warmings are quantified with benchmark tests of Charlton and Polvani (2007) and are found to be nearly realistic. Extension of the tests into the mesosphere gives rise to a benchmark diagram for the entire middle atmosphere, showing that the mesospheric cooling is robust while the mesospheric wind response is variable. The same features appear in a composite constructed from five stratospheric warming events. The zonal-mean structures indicate an old stratopause descending with about 6 km per day during about 5 days before the central date. About 10 days after the central date, an elevated new stratopause develops in the upper mesosphere and subsequently progresses downward, which is driven by westward gravity waves. Temporal characteristics are deduced from 7 day smoothed daily time series from representative stratospheric and mesospheric zonal-mean quantities. A correlation analysis shows that the temperature signals are anticorrelated, while the wind signals are uncorrelated. The begin, peak, and end times of the events are diagnosed with two objective methods. Both methods reveal nearly equal-time appearance of stratospheric warming and wind deceleration (within 2 days), followed by mesospheric cooling with a delay of less than 5 days. This rules out mesospheric precursors of sudden stratospheric warmings in our simulation.