The response of the middle atmosphere temperature to short term solar UV radiation related to the 27-day period of the sun has been studied by Rayleigh Lidar at mid-latitude in the height range 30--90 km. Among the 9 sequences, each of 3 to 4 months duration, which corresponds to clear solar signature, two types of behavior have been found: either the temperature response is positively correlated with the solar UV flux in the whole height range, or the response reverses abruptly from positive to negative within the height interval 40--60 km. It is important to notice that this second type of behavior is observed as well in summer or in winter, i.e., even in the absence of planetary wave activity, but has only been seen during the Westward phase of the QBO.

If such a change of the temperature is confirmed to be solar induced, this response to change in the UV flux is clearly different from the one we observed for the 11-year solar cycle. Therefore the 27-day signature of atmospheric structure should not be used as a proxy for the 11-year variation. ¿ American Geophysical Union 1992