Abstract
Abstract. A meteor radar in the UK (near 52° N) has been used to measure the mean winds of the mesosphere/lower-thermosphere (MLT) region over the period 1988–2000. The seasonal course and interannual variability is characterised and comparisons are made with a number of models. Annual mean wind trends were found to be + 0.37 ms-1 yr-1 for the zonal component and + 0.157 ms-1 yr-1 for the meridional component. Seasonal means revealed significant trends in the case of meridional winds in spring ( + 0.38 ms-1 yr-1) and autumn ( + 0.29 ms-1 yr-1), and zonal winds in summer ( + 0.48 ms-1 yr-1) and autumn ( + 0.38 ms-1 yr-1). Significant correlation coefficients, R, between the sunspot number and seasonal mean wind are found in four instances. In the case of the summer zonal winds, R = + 0.732; for the winter meridional winds, R = - 0.677; for the winter zonal winds, R = - 0.472; and for the autumn zonal winds R = + 0.508.Key words. Meteorology and atmospheric dynamics (climatology; general circulation; middle atmospheric dynamics)
Highlights
The general circulation of the mesosphere/lowerthermosphere (MLT) region is profoundly influenced by the deposition of momentum by waves ascending from lower heights
This momentum transfer leads to departures from the purely zonal geostrophic flow predicted by the consideration of radiative equilibrium alone
The consequent adiabatic heating and cooling caused by these vertical motions forces the temperature structure away from the radiative equilibrium state and results in non-radiative equilibrium zonal winds
Summary
The general circulation of the mesosphere/lowerthermosphere (MLT) region is profoundly influenced by the deposition of momentum by waves ascending from lower heights. The mean winds of the MLT region have been measured by a wide variety of techniques, there have been comparatively few studies of sufficient duration to allow investigation of the variability and trends in the mean winds on decadal and longer time scales. Such studies are important because theoretical work indicates that the circulation of the MLT region may be influenced by long-term anthropogenic climate change and the 11-year solar cycle
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