Non-zonal Structures of Mesosphere/lower Thermosphere Dynamics at Middle Latitudes (NOSTHEM)

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During NOSTHEM, longitudinal differences of mean winds, tidal parameters, and planetary and gravity waves in the mesosphere/lower thermosphere (MLT) will be analyzed and interpreted. The influence of these differences on the representativeness of single sites for describing zonal means of winds and wave parameters will be quantified. This will allow us to quantitatively estimate the uncertainty of mean climatology, long-term trends, and measures of interannual variability observed at single sites. The contribution of non-zonal structures to mean circulation and its variability will be determined. Hemispheric analyses of lower and middle atmosphere waves and circulation parameters will be used to analyze the role of these in establishing longitudinal differences. This will then resolve the question whether there is a significant difference between the mid-latitude MLT wind regimes in Western and Eastern Europe, and which are the underlying processes leading to these differences.The NOSTHEM project will make use of the two very similar VHF meteor radar observations at similar latitude, but with a 36° difference in longitude in order to specify quantitatively the influence of non-zonal structures on mean circulation, waves and tides. In order to obtain a comprehensive picture of non-zonal structures in the MLT dynamics, the concurrent observations of winds and temperatures using VHF radars at Collm and Kazan will be completed by numerical modelling using a circulation model of the middle atmosphere, satellite observations, and reanalyses.Main goals of NOSTHEM are (1) a quantitative description of similarities and differences of MLT circulation parameters at two longitudes, (2) an extrapolation of this analysis to the full hemispheric view based on satellite observations and modelling, and (3) a quantitative estimation of the role of waves in the specific characteristic of circulation parameters at single sites. As a final goal, we shall explain longitudinal differences through their underlying processes, and also provide guidelines for the interpretation of both mean climatology and trend analyses made at single sites in terms of their representativeness for hemispheric dynamics.The research within NOSTHEM will be performed jointly by Universität Leipzig, Institute for Meteorology, Leipzig, Germany, and the Department of Radiophysics, Institute of Physics, Kazan Federal University, Russian Federation.