The Computation And Study Of Global Background Winds In The Middle Atmosphere

The knowledge of special and temporal distribution of stratospheric and mesospheric(about 12-110km, (Andrews D.G.,et al,1987)) wind fields are important to study the chemistry and dynamics, especially the waves in middle atmosphere; likewise, wind fields are also very important parts of the wind mode. In the past,scientists used to observe wind fields in mesosphere and low thermosphere with meteor radar,MF radar,MST radar and the optical technique such as lidar and FPI. These instruments could measure the wind in a fixed location continuously, and are usually of good resolution and precision. But they are not usually mounted in the symmetric locations, and the height range they can measure is comparatively narrow, so obvious errors will occur in the atmospheric mode built on the data obtained from the ground-based observatory that are rarely distributed.This article tries to derive the middle atmospheric wind from the data of MLS onboard the Aura satellite, i.e. the temperature,density and pressure of middle atmosphere, including the global background wind with a time resolution of a single day and the zonal mean zonal wind, as will help us to obtain accurate middle atmospheric data, to understand the variation of middle atmosphere associated with time and space, as well as to provide accurate middle atmospheric background wind for the wave studies.Firstly, the partial differential equation is derived from the basic equation series of atmospheric dynamics according to the characteristic of middle atmosphere and some rational hypothesises and abbreviations. The partial differential equation is nearly the same as the usual geostropic equation(balanced by pressure gradient force and Coriolis force),but is added by the term of curvature acceleration. As a result, the wind fields will be more accurate especially near the pole. If the proper sizes and weighs of the window rectangles are chosen, nonmigrating tides will be almost smoothed out.Comparisons of the derived Aura wind with WuHan meteor radar and Australian Adelaide observatory are used to validate it. The comparison results prove that Aura wind is in good agreement with WuHan meteor radar and Australian Adelaide observatory. Variations of wind associated with height are in good agreement with the observed results. The difference of zonal wind from directly observed wind data is no more than 20m/s,and the relative difference is less than 18%.The meridional wind velocity is of the same amount with the observed wind, and it is no more than 20m/s,and their difference is less than 10m/s. Comparative result suggests that, Aura wind is in better agreement with the observed wind below 80km than that above 80km,this is due to the effect of NLTE, which will be discussed in this article particularly.At last, the variations of derived Aura wind associated with time and space are studied in this article. It shows that west wind prevails in northern hemisphere in January,February,November and December, while east wind prevails in southern hemisphere; east wind prevails in northern hemisphere in May,June,July and Augest, while west wind prevails in southern hemisphere; in March,April,September and November, the wind velocity is small, less than 30m/s,in these seasons the wind direction will shift. All these results are in good agreement with the wind mode such as HWM-93 and the directly detected wind.It is found in the studies of the wind variation associated with height that, west wind prevails in both northern and southern hemisphere near 12km,and wind velocity decreases from 12km to 20km.But in higher altitude, the difference of wind direction in northern and southern hemisphere become obvious, and wind velocity become greater. The largest wind velocity amounts to more than 60 or 70m/s.Both in winter and in summer, the largest wind is of the same amount, and the largest wind velocity appears in middle latitude. All the attributes that wind's variation associated with height is in agreement with the popular wind mode and observed results.Above all, this article seeks the way to derive the global background wind from temperature,density and pressure obtained from Aura. Both the comparison with directly detected wind data form observatory and the analysis of atmospheric attributes prove that the method is right. So, a new way to obtain middle atmospheric wind is found for the studies of middle atmosphere, and we can offer plenty of middle atmospheric wind data of more validity for further studies.