Study On The Positioning Of Sounding Balloon Drifting In MM5

In order to analyze the impact of height-depending sounding balloon'~ drifting on mesoscale numerical model (MM5v37), objective analysis system of MM5 is improved using new sounding data with accurate position message at each pressure level observed by L-band radar system or wireless theodolite and provided by AOC of CMA.The temporal and spatial analysis results of sounding balloon drifting shows as follows: the frequency of latitudinal drifting is much higher than that of longitudinal drifting, and the drifting distance in winter and spring is much greater than that in summer and autumn. Except for Qinghai-Tibet Plateau, the phenomenon of drifting becomes obvious when the sounding balloon rises to about 500hPa and the drifting velocities are very fast from 500hPa to 100hPa. Besides, the drifting distance increases from southwest to northeast in China and have seasonal and areal variations which can demonstrate the seasonal and areal features of General Circulation in Asian and reflect the changes of the weather system to some extent.Through the simulations of precipitation of both strafiform clouds and convective clouds, we can conclude as follows: the positioning improves the initial fields. The temperature, pressure and wind fields change more in higher layers than in lower layers. That is consistent with the above-mentioned fact: the drifting distance of sounding balloon is greater in higher layers than in lower layers. Besides, the position correction will be better the analysis fields and is more sensitive to strong weather system; the center of vorticity and divergence has a better relation to the heavy precipitation field; the precision of each rainfall. grads has been improved obviously on both precipitation forms, especially on heavy rain and storm rain; for stratiform clouds, the precipitation results of low-resolution will be better on low rainfall grads, and high-resolution will perform better on high rain fall grads, and for convective clouds reverse, but that dose not mean the effect of MM5 model declining after adding sounding balloon drifting messages, there may be some relations to the microphysical schemes in MM5 and numerical evaluation methods and further case studies are needed.