中国夏季夜雨的空间分布特征

夜雨作为降水日变化中的特殊现象,是一种独特的气候资源。论文借助2 046 个经质量控制的自动气象站逐小时降水资料分析中国夏季夜雨空间分布特征,并比较分析不同典型夜雨区和非典型夜雨区的降水日变化特征。结果表明:中国夜雨现象站点多且分布较广。降水峰值时间多出现在下午和后半夜,其中东部多发生在下午,西部多发生在后半夜;夜雨现象最明显的区域是青藏高原、四川盆地、云贵高原,此外在山脉及附近区域也普遍存在,北方和西部最明显;而夜雨现象不明显的区域在长江中下游以南区域;中国大部分地区夜间的降水前半夜少于后半夜,而青藏高原东部、四川盆地大部分地区呈现前半夜多于后半夜。地形对降水日变化的主要影响为双日波特征,降水峰值不仅出现在下午,也出现在后半夜;其次,波动性更大。山区夜雨的成因与独特地形的热力差异引起的山谷风环流有关,而下午的峰值与太阳辐射加热大气引起的热对流有关;高原夜雨与山区不同,可能与夏季对流性的积状云比较多有关。

Spatial Distribution of Night Rainfall in Summer over China

Diurnal variability of rainfall is an important aspect of regional climates to fully understand the climate systems. When precipitation occurs regularly during particular time periods of the day the atmospheric system usually is characterized by conditions and physical processes that suggest strong convection during the favored periods. As one of the special characteristics of daily variation in precipitation, night rainfall is an unique and valuable agricultural climate resource. In this paper, the hourly precipitation data for 2046 automatic weather stations all over China from 2005 to 2007 provided by the National Meteorological Information Center was used to study the diurnal variations of precipitation in summer (from June to August) during 2005 to 2007. The temporal and spatial distribution of the night rainfall in summer over China was analyzed. Differences in diurnal variation of precipitation between the typical and the atypical rainfall regions were also compared. Results showed that the night rainfall occurred widely over China. The precipitation peaked mostly at afternoon (eastern China) and midnight (western China). The night rainfall appeared most obviously in the Tibetan Plateau, the Sichuan Basin, the Yunnan-Guizhou Plateau as well as the mountains and surrounding areas in the northern part and western part of China. The percentage of the hourly average precipitation in the nighttime for most parts of the Tibetan Plateau and the Sichuan Basin reached 60%, even up to 80% for individual stations. The percentage for most parts of the Yunnan-Guizhou Plateau was above 50%. However the night rainfall occurred rarely in areas south of the middle-lower Yangtze River. The percentage of the hourly average precipitation in the nighttime for such areas was mostly below 40%, especially only 20% for many areas of Guangdong and Hainan provinces. Nine typical regions were selected to further study the diurnal variation of precipitation in the night rainfall area. The precipitation occurred frequently in late night than in early night over most parts of China, except eastern part of the Tibetan Plateau and the Sichuan Basin. The diurnal variation of precipitation was also affected by topography. The precipitation peaked both at afternoon and night. Night rainfall in mountainous areas was related to mountain-valley wind circulation caused by thermal contrast, while precipitation peaked at afternoon due to thermal convection caused by solar radiation. The difference of night rainfall between plateaus and mountains may be related to large amount of cumulus cloud in summer.