近海台风对中国东部夏季降水的贡献

Contribution of typhoon over coastal waters to summer rainfall in eastern China

目前汛期预测主要针对季风系统形成的降水,而对台风等热带系统的影响并未考虑,其主要原因是台风是一个剧烈的天气尺度过程,与短期气候预测尺度并不匹配,因而无法进行考虑.这也成为提升汛期预测技巧的一个制约因素.针对这样的问题,本文从气候的角度,提出一个能较为客观地衡量台风对夏季降水影响强弱的指数——台风影响指数.利用1960—2011年中国东部站点降水资料及中国气象局上海台风所整理的热带气旋资料,从月、季尺度对中国夏季台风影响强弱变化特征进行分析,探讨台风对东部地区夏季降水的贡献.结果表明:1)台风从6月至8月呈增强的趋势,6月份最弱,7月份居中,8月份最强;2)从台风降水及占总降水的比例分布来看,纬向呈东部高西部低,经向呈从东北地区至华南地区依次增大的趋势,长江以南地区台风降水量占夏季降水量的比重可达10%以上,7,8月份东南沿海地区的台风降水量最大可达100 mm以上,可达当月总降水量的40%;3)台风影响指数与夏季降水的相关表明,台风对中国东部降水的影响具有时、空差异性,6月份与华南地区呈负相关,7月份与东南沿海地区呈正相关,而与长江中下游地区呈负相关;8月份与华南、华北地区呈正相关、与长江中下游地区呈负相关.这主要是由台风、夏季风和西北太平洋副热带高压共同影响的.

Now, it is difficult to consider the typhoon rainfall in the short-term climate prediction. This is mainly because the typhoon is a strong synoptic scale system and it does not match the scale of the short-term climate forcast. It is a factor restricting the great improvement of forecast. By using station precipitation data in eastern China from 1960 to 2011 and CMA-STI Best track dataset for tropical cyclones over the western north pacific, we analyse the strength variation of typhoon influence from month and quarter scale in summer by determining the typhoon influence index, then discuss the contribution of typhoon rainfull to summer rainfall in eastern China. 1） On average, the typhoon is enhanced from June to August, it is weakest in June, and strongest in August. 2） From the distribution of typhoon rainfall and its proportion of the total precipitation in eastern China, totally, the tyhoon rainfall is higher in eastern region than in the western region on the same latitude, and it is higher in southern region than in the northern region on the same longitude. The ratio of typhoon rainfall to the total precipitation could reach up to 10% in the South of the Yangtze river region. The typhoon rainfall can also reach up to 100 mm in the southeast coastal area in July and August, which can amount to 40% of the total precipitation during the month. 3） The correlation of the typhoon influence index with summer precipitation shows that the typhoon＇s influences on the precipitation in eastern China are different spatiotemporally. The results indicate that the negative correlation is in southern part of Cllina in June, the positive correlation is the southeast coastal area in July, the positive correlation is in the south China in August, and the negative correlation is in the middle and lower reaches of the Yangtze river region, which are mainly due to the typhoon, summer moonsoon, and high pressure in the north-east pacific subtripics respectively.