Winds and shears in the mesosphere and lower thermosphere: Results from four decades of chemical release wind measurements

Since 1958, over 400 chemical tracer measurements have been made of the wind profiles in the upper mesosphere and lower thermosphere. The measurements cover a wide range of latitudes, longitudes, seasons, and local times. The results from the analysis of the data set show that a wind maximum in the altitude range between 100 and 110 km is a consistent feature of the observations at midlatitudes and low latitudes. The wind speed associated with the maximum exceeds 100 m s −1 in over 60% of the observations. Large shears are found, especially on the bottomside of the wind maximum, and the observed shears are often large enough to be either unstable or approaching instability. The wind maximum and shear features are characteristics of the overall data set and are not tied to particular observation sites, particular seasons, or special conditions.