Latitudinal and longitudinal variability of mesospheric winds and temperatures during stratospheric warming events

Continuous MF and meteor radar observations allow detailed studies of winds in the mesosphere and lower thermosphere (MLT) as well as temperatures around the mesopause. This height region is characterized by a strong variability in winter due to enhanced planetary wave activity and related stratospheric warming events, which are distinct coupling processes between lower, middle and upper atmosphere. Here the variability of mesospheric winds and temperatures is discussed in relation with major and minor stratospheric warmings as observed during winter 2005/06 in comparison with results during winter 1998/99. Our studies are based on MF radar wind measurements at Andenes (69 degrees N, 16 degrees E), Poker Flat (65 degrees N, 147 degrees W) and Juliusruh (55 degrees N, 13 degrees E) as well as on meteor radar observations of winds and temperatures at Resolute Bay (75 degrees N, 95 degrees W), Andenes (69 degrees N, 16 degrees E) and Kuhlungsborn (54 degrees N, 12 degrees E). Additionally, energy dissipation rates have been estimated from spectral width measurements using a 3 MHz Doppler radar near Andenes. Particular attention is directed to the changes of winds, turbulence and the gravity wave activity in the mesosphere in relation to the planetary wave activity in the stratosphere. Observations indicate an enhancement of planetary wave 1 activity in the rnesosphere at high latitudes during major stratospheric warmings. Daily mean temperatures derived from meteor decay times indicate that strong warming events are connected with a cooling of the 90 km region by about 10-20 K. The onset of these cooling processes and the reversals of the niesospheric circulation to easterly winds occur some days before the changes of the zonal circulation ill the stratosphere start indicating a downward propagation of the circulation disturbances from the MLT region to the stratosphere and troposphere during the stratospheric warming events. The short-term reversal of the mesospheric winds is followed by a period of strong westerly winds connected with enhanced turbulence rates and an increase of gravity wave activity in the altitude range 70-85 km. (c) 2007 Elsevier Ltd. All rights reserved.