Large scale structure of the stratosphere and the lower mesosphere (20–60 km) over the northern hemisphere during the MAP/WINE campaign
Résumé
All available temperature and wind measurements from radiosondes, rockets, satellites and lidar over the northern hemisphere have been used to construct large scale patterns of the temperature and circulation fields up to 60 km during the period 1 December 1983 to 1 March 1984. Main sources of information for the height range above 30 km are the uppermost spectral channel of the Stratospheric Sounding Unit (SSU) on-board the NOAA satellites and the meteorological rocket soundings. Rocket launches are generally scheduled on a weekly basis over the northern hemisphere, and the large scale patterns were derived for those days on which these measurements are available.
The method used to retrieve temperature fields from the satellite measured radiances contains several steps.
(a) First, estimated fields for the temperature at 7 pressure levels were constructed; in the lower middle stratosphere 50, 30 and 10 mbar level analyses by the stratospheric group Berlin were taken; at 5, 1, 0.4 and 0.2 mbar regressed temperature fields from the SSU radiances were updated by all in situ temperature measurements (the multiple regression coefficients have been derived for the period of MAP/WINE).
(b) Stratopause height fields were estimated by means of the temperature profiles provided by the Solar Mesosphere Explorer (SME) and rocket soundings. (c) With the input of (a) and (b) and the a priori assumption that the temperature maximum is situated at the stratopause height, a solution of the radiation transfer equation is possible for the measured SSU radiances with a time and space dependent stratopause.
The computed temperature fields are added hydrostatically to the 10 mbar height analysis, so that geopotential heights, geostrophic winds and temperatures at pressure levels up to 60 km become available once a week for dynamical computations.
The circulation will be described in terms of planetary waves and zonal means. The interaction of the waves with the mean flow, resulting in a breakdown of the westerly circulation at the end of February, will be discussed.
The remarkable changes at high latitudes over northern Europe are shown to be connected with processes at middle and low latitudes.