Abstract:

Based on the monthly precipitation and evaporation data from 139 meteorological stations in the southeast side of the Tibetan Plateau and NCEP reanalysis data with 2.5°×2.5° spatial resolution, the characteristics of dry and wet season and its causes in the southeast side of the Tibetan Plateau were analyzed by diagnosing the seasonal water vapor flux, distribution of total atmospheric precipitable water and water vapor divergence. The results showed that there were the southwest water vapor transports in four seasons in the southeast side of the Tibetan Plateau, and that in winter and spring were still strong. However, the water vapor divergence existed over the southeast side of the Tibetan Plateau in four seasons, especially it was stronger and broader in winter and spring, which wasn’t conducive to the occurrence and sustaining of precipitation. Meanwhile, the atmospheric column in the southeast side of the Tibetan Plateau was shorter than that in the surrounding area under the influence of plateau topography, which led to the total atmospheric precipitable water less than the surrounding area, and the seasonal variation of total atmospheric precipitable water was obvious, that in winter and spring was only 1/3 to 1/2  of the summer. Therefore, the seasonal drought in the southeast side of the Tibetan Plateau was subject to the less total atmospheric precipitable water and stronger and boarder water vapor divergence in winter and spring.

Key words: dry season, wet season, water vapor transport, total atmospheric precipitable water,  water vapor divergence

摘要：

利用台站降水、蒸发资料和NCEP再分析资料，通过季节水汽输送、大气可降水量分布、水汽辐合辐散诊断对西南水汽通道上青藏高原东南侧干、湿季气候特征及成因进行了分析。结果显示，四季青藏高原东南侧均存在西南水汽输送，即使冬、春季也有较强盛的水汽输送，但其上空四季均维持有水汽辐散场，不利于降水发生和维持，尤其冬、春季强度更强、范围更广。同时，受低纬高原地形影响，这一地区大气气柱短，导致青藏高原东南侧大气可降水量比周边地区明显偏少，且存在明显的季节变化，冬、春季大气可降水量仅为夏季的1/3～1/2。可见，青藏高原东南侧季节性干旱受冬、春季大气可降水量的减少和其上空更强更广的水汽辐散场共同影响所致。

关键词: 干季, 湿季, 水汽输送, 大气可降水量, 辐合辐散