南方两次相似降雪(雨)过程的对比研究

2006年2月中旬和下旬,长江三角洲一带分别发生降雪和降雨过程,预报过程中对降水形态的预报存在失误。通过对这两次过程的比较分析,期望为今后的预报中区分南方地区的固态降水和液态降水提供一定参考。得出以下一些主要结论:降雪过程高空槽前以偏西气流为主,环流较平;降水过程,槽前西南气流强盛,偏南分量明显。南方大雪的产生须由东北风回流产生的冷平流在华东一带形成冷中心,而北到西北风产生的冷平流降温往往因为降水与降温不同步,无法形成大雪。降雪过程开始前,850hPa附近存在干层,而降雨过程则是中低层都湿。逆温层和700～800hPa的温度对降水形态有重要影响。降雪过程结束时高层先变干,而降雨过程结束时是中层先变干。降雪过程,上空大气中冰雪区集中,含雪量和冰晶含量大值中心与降雪带位置相对应。降雨过程含雪量下界抬高,含雪量和冰晶含量大值中心落后于降雨带,并且南压过程中快速减弱,冰雪区分散。

Comparison Study of Two Similar Rain and Snow Processes in South China

In middle ten-days and last ten-days of February in 2006, there were tow precipitation processes in Changjiang delta, i.e. snow and rain respectively, but the forecast of precipitation type was wrong. A comparison of these two processed shows that in the snow process, there was west wind in the front of trough and the circulation was flat, whereas in the rain process, there was southwest wind in the front of trough. Snow would happen only if the cold advection, which was resulted from the northeast return current, generated a cold center over east China. However the north and northwest wind decreased the air temperature, but no precipitation would happen atthe same time, .so there would be no snow in this case. Before snowing the air at 850 hPa was dry and before raining the air at low-middle levels was wet. The temperatures at 700-800 hPa and in the inversion layer were important to the precipitation type. At the end of snow process the air in high level become dry first, whereas at the end of rain process the air in middle level become dry fist. In snow process the snow and ice crystals were centralized in the high level, and the center of snow content was at 600-700 hPa. In rain process, the lower boundary of snow content lifted up and its center was in a level above 600 hPa. The center of snow content weakened very fast when it moved down northwards.