The Diagnostic Analysis Of Mesocale Vortexes Under Summer Monsoon

By using satellite data, the precipitation、the variation of wind direction and the feature of sea surface temperature over East Asia in summer were mainly analyzed. Started with the two characteristics of the seasonal inversion of monsoon direction and the seasonal alternation of dry-wet period, the following conclusions were obtained. In comparison of the three regions of Bay of Bengal, Indo-China Peninsula and the South China sea, Indo-China Peninsula is the area of earliest summer monsoon which in northwest-central was exploded on the24th pentad, but on the26th-28th pentad in southeast. Then is Bay of Bengal where the summer monsoon was occurred on24th pentad in southeast, and on the26th-28th pentad in northwest. The summer monsoon in the South China sea came finally on the28th pentad. The sea surface temperature rise earlier than the precipitation and the variation of wind direction, which means the rising sea surface temperature strengthened the convective activities and having a great influence on the occurrence of the summer monsoon. Satellite proved the measured data with high resolution, so that we can get the more accurate result by more effective measurement of meteorological elements.There are two of synoptic systems in MCS of eastern China and Western Pacific region:MCV and MAV. They were found both existed in MCS from the statistic analysis after the occurrence of the summer monsoon. Their spatial distribution were extremely similar in comparing both of the annual average ones, but the probability of MCV happening was higher than MAV. MCVs had an obvious monthly variation to the areas studied that with most widely distributed in June. Influenced by large-scale backgrounds like South Asian summer monsoon subtropical high、solar radiation,etc from May to October, the spatial distribution of MCVs developed first and then decreased. From the research of MCVs diurnal variation matching with the precipitation rate from May to October, the conclusion that MCVs on the ocean were more frequent than on land was drawn, and the emergence period of local MCVs in survey region were summarized as well. MCVs near the surface of the Sea of Japan and the northern South China was all-weather; on the ocean near land like around the Ryukyu Islands was active on morning; and on hilly area of southeast China preferred to occur at night. Whereas on land like North China Plain、around Changbai Mountains and Beijing-Tianjin-Tangshan(BTT) region MCVs were active on afternoon because of the effects of terrain、urban heat island, and so on. Noted that due to the specific geographical conditions or other factors, even in the same sort of MCVs, their duration and elevated levels were different from one another in different regions. Besides, this relative classification can only mean MCVs in one region were one type based, but not one type alone. The response to background system was primarily gravity model. The radius of MCVs on the ocean were greater than on land in general, while on Plains were greater than among mountainous and hilly areas, which illustrated that MCVs developed lager scale in the flat regional environment.Severe convective weather caused by the influence of tropical cyclone (TC) occurred in Jiangsu province was analyzed by various types of severe convective indices during10years (2001-2010). It was found, in such long time series, among all types of the severe convective weather accompanying with TC activities, the events of heavy precipitation typically occurred most frequently, followed by the severe thunderstorm weather. However, the thundered weather without rainfall is rarely happened, and no hail and tornadoes occurred actually. The statistical results also showed that there were21landing TCs basically influencing Jiangsu province during 10years and most of them were on the stage from TC to tropical depression (TD). The threshold of effectively convective indices of severe convective weather was lower than normal in general, which means that under the influence of TCs, it is more likely to cause convective instability, and the accumulation of instable energy ultimately lead severe convective weather.