Long-term study of the summer wind variability in the mesosphere and lower thermosphere over nearly two decades at middle and high latitudes

<p>Winds at the mesosphere and lower thermosphere have been measured by partial reflection radars and specular meteor radars for almost two decades (2004-2022) over Germany and Norway (i.e., middle and high latitudes, respectively). Continuous wind measurements during the mentioned period are important to understand their long-term behavior. The zonal mean wind climatology displays an eastward wind during the winter months and a westward summer jet below ~85km at middle latitudes (~90km at high latitudes). Above the mentioned height, an eastward wind jet is observed. In the meridional wind component, the southward summer wind displays amplitudes between 4 and 5 times less intense than the westward jet. We studied the intensity of the summer wind components, the long-term variability and the possible connection to external forcing (i.e. El Ni&#241;o-Southern Oscillation, and quasi-biennial oscillation, solar activity and geomagnetic activity). Analyzing the summer winds for low and high geomagnetic activity classified with the Ap index, there is a significant difference between both cases suggesting disturbances in the wind due to high geomagnetic activity. The long-term study shows significant trends at middle latitudes in the monthly summer values of the westward summer jet. As a consequence of the increase in the westward wind, a decrease in the southward component is observed at the same latitudes. While at high latitudes the eastward jet shows a decreasing velocity during July.</p>