Zonal asymmetries in middle atmosphere temperatures Original Research Article

Zonal asymmetries are frequently seen in stratospheric temperature or trace gas fields as surf zones, streamers, filaments etc. They are also seen as very small-scale fluctuations, the intensity of which varies with longitude. Similar structures might be expected in the mesosphere as well, and several examples have recently been found. CRISTA 1 large-scale data are presented that indicate a surf zone in the middle mesosphere at the beginning of winter. Very small-scale data are shown from the CRISTA 2 mission. Mesospheric variability is found to be high at all altitudes, latitudes, and longitudes. There are considerable non-zonal structures in these fluctuations. (The duration of the Crista missions was about one week each.)Zonal asymmetries have been known for a long time from comparisons of ground stations measuring the same parameter in the mesosphere/lower thermosphere. As an example, upper mesosphere temperatures derived from OH∗ emissions are compared here for Wuppertal and Moscow (Zvenigorod), which are about 2000 km apart. A systematic and substantial difference in temperature is obtained, with higher temperatures at Wuppertal than at Moscow. The difference appears to follow the solar cycle: it is small at solar maximum and large (up to 28 K) at solar minimum. The reason for this surprising behavior is as yet unknown.