Quarterdiurnal tide in the middle atmosphere (QuarTA)

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The dynamics of the mesosphere and lower thermosphere (MLT) is strongly determined by solar tides and their variability. One of the tidal components is the quarterdiurnal tide (QTD), which has occasionally been reported in ionospheric sporadic E parameters and radar and few satellite observations. While the diurnal, semidiurnal, and also terdiurnal tidal components have been analyzed more frequently, the QDT hast attained much less attention, mainly owing to its smaller amplitudes, which makes observations more difficult. To fill this gap, within QuarTA the QDT and its forcing mechanisms will be analyzed in detail. The characteristics of the tide in MLT dynamics will be analyzed using meteor radar winds, in particular making use of the long-term data set at Collm, Germany, in combination with other Northern Hemisphere radar observations. The global structure of the QDT will be analyzed in sporadic E occurrence rates obtained from GPS radio occultations complemented by ionosonde observations. These observations will be interpreted by wind shear observed by radar and obtained from numerical modelling. To get insight into the forcing mechanisms of the QDT, we shall use a mechanistic circulation model of the middle atmosphere, which includes nonlinear interaction processes as well as radiative forcing. In sensitivity experiments, the different forcing mechanisms will be turned off both separately and in combination. Within QuarTA, from combining local and global observations with numerical modelling, we therefore expect to get more insight into the global structure of the QDT as well as into its forcing processes, which have not yet been analyzed in sufficient detail.