【作者】 杨程；

【导师】 王元； 江静；

【作者基本信息】 南京大学 ， 气象学， 2013， 博士

【摘要】 本文首先使用卫星资料对东亚地区夏季的降水、风向变化以及海温特征作诊断分析；同时对经典螺旋度作改进提出第三类热成风螺旋度用以讨论夏季风的爆发进程。两者共同研究结果显示孟加拉湾、中南半岛、南海这三个地区中,夏季风最先于第24候在孟加拉湾东南部爆发,之后在第25-26候于孟加拉湾西北和中南半岛地区爆发,南海地区夏季风在第28候爆发。海温的上升比降水和风向变化略早,说明海表温度上升引起对流活动的加强,对夏季风的爆发有重要影响。通过对研究区域SGV’的诊断分析,发现夏季风背景下区域内潜在对流活动呈增加的趋势。卫星资料提供了高水平分辨率的实测资料,能够更直接有效的测量各气象要素,得到更精确的结果。在夏季风爆发之后,对中国东部和西太平洋地区MCS中的两类天气系统MCV和MAV作统计分析,发现MCV和MAV都存在于MCS中。对比两者多年年平均空间分布可知,它们的空间分布非常类似,但MCV发生的概率比MAV高。在研究区域内MCV的月变化特征明显,其中以6月份分布范围最广。由于从5月到10月,受到南亚夏季风、副热带高压、和太阳辐射等大尺度背景场的影响,MCV空间分布存在一个明显的加强减弱的过程。通过对MCV日变化特征的分析,匹配5月-10月的降水率。总结出研究区域内局地MCV发生的日变化特征。同时分析发现海洋上MCV发生的频率高于陆地。日本海附近洋面以及南海北部洋面属于全天候MCV。靠近陆地的洋面如琉球群岛附近属于清晨活跃型MCV。中国东南丘陵地区属于夜发型MCV。而陆地上如华北平原、长白山附近以及京津唐地区由于受到地形、城市热岛效应等作用,属于午后活跃型MCV。需要注意的是,即使在同一类MCV中,不同的地区由于具体的地理环境等因素,使得MCV的持续时间和活跃程度也各不相同。另外,这种分类是相对的,只能说某地区的MCV是以某一类为主,而不能说某地区就只有某一类的MCV。各区域内对背景系统的响应主要以重力模式为主。洋面上的MCV半径总体看来大于陆地上。平原地区的MCV半径大于山地丘陵地区。说明MCV在平坦的局地环境下容易发展到较大的尺度。由于热带气旋是夏季造成各类强对流天气的重要系统之一,因此对多年来热带气旋中的MCV和MAV发生情况进行普查,发现热带气旋中的MCV和MAV同时出现的概率最高。据此选取2012年11号热带气旋“海葵”,具体分析它在登陆前后内部的涡旋演变过程。考虑到热带气旋中MCV的重要影响,对2001年至2010年在江苏地区受热带气旋影响造成的各类强对流天气进行天气分析。发现各类强对流天气中,短时强降水天气发生的频率最高；其次是雷雨大风天气；一般雷暴天气很少发生；龙卷和冰雹天气从未发生。地理位置越往南的区域越容易受到热带气旋的影响,这种影响主要以热带气旋前部外围云系为主。统计结果表明在研究年份内共有21个热带气旋影响江苏地区,其中13个热带气旋造成的短时强降水天气事件多于三次,且多数影响热带气旋都处于向热低压减弱的阶段。在这个阶段热带气旋中心气压逐渐升高、中心风速偏弱,但由于移速较慢以及地面摩擦作用仍会造成相关区域各种强对流天气的发生。短时强降水天气发生时,热带气旋离相关区域多数都在400km范围以上,这是因为强对流天气的发生不仅需要水汽和不稳定条件,还受到局地环境等因素的影响。所以强对流天气的发生与热带气旋和影响区域之间的距离并没有必然的联系。使用强对流指数分析了受热带气旋影响下短时强降水天气的发生情况,归纳出热带气旋影响下对流指数阈值。总体来看,各类指数的阈值在热带气旋影响下都偏低,即由于热带气旋的作用更容易造成对流不稳定、能量堆积最终导致各类强对流天气现象发生。更多还原

【Abstract】 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.更多还原