Weak and Frequent Monsoon Precipitation over the Tibetan Plateau
Weak and Frequent Monsoon Precipitation over the Tibetan Plateau
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DOI：
10.2151/jmsj.79.419
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发表时间：
2001-03
影响因子：
3.1
通讯作者：
K. Ueno;H. Fujii;Hiroyuki Yamada;Liping Liu
中科院分区：
文献类型：
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作者：
K. Ueno;H. Fujii;Hiroyuki Yamada;Liping Liu
利用GAME-Tibet国际项目1998年5 ~ 9月在青藏高原那曲盆地（海拔4500-5000 m）密集观测的降水资料，分析了该地区降水的时空尺度、类型和强度及其时间变化。根据降水量和GMS/IR对流指数的变化，确定了6月中旬至9月上旬为季风期。流域平均季风降水量为336毫米，大部分降水以雨或冰雹的形式提供。降雪可能性为50%的最低海拔估计在海拔5000米左右。亚洲季风区6 ~ 8月逐日降水资料显示，青藏高原降水频繁，但强度较弱。在那曲盆地，季风季节降水量大于0. 25 mm/d的天数比例为87%，平均小时降水强度为1. 27 mm/h。降水量昼夜差异不明显，降水强度日变化明显，白天有小于1 mm/h的弱降水，夜间有大于3 mm/h的强降水。大部分事件与高原天气尺度云区的通过有关。白天的事件包括孤立的对流回波与一个小的空间尺度，夜间的事件包括广泛的层状回波。根据这些观测结果，讨论了白天强降水频繁的概念机制。
This study analyzed the temporal and spatial scales, types, and intensity of precipitation with their temporal variability by using the precipitation data, intensively observed as part of the GAME-Tibet international project, at the Naqu basin (4500-5000 m) in the Tibetan Plateau from May to September, 1998. The monsoon period at the basin was defined from the middle of June to the beginning of September by the precipitation and GMS/IR convective index variation. Basin averaged monsoon precipitation was 336 mm, and most of the precipitation were provided as rain or hail. The lowest altitude for a 50 % possibility of snowfall was estimated at almost around 5000 m above sea level. Daily precipitation data records from June to August in the the Asian monsoon region highlighted frequent precipitation with weak intensity in the Tibetan Plateau. In the Naqu basin, the percentage of days with precipitation of more than 0.25 mm/d was 87 % during the monsoon season, and the average hourly precipitation intensity was 1.27 mm/h. Difference in the accumulated precipitation amount between daytime and nighttime was not obvious, but the clear diurnal change existed in the precipitation intensity, i.e., weak precipitation events below 1 mm/h in the daytime and rather heavy precipitation events above 3 mm/h at night. Most of the events are associated with the passing of synoptic (plateau) scale cloud area over the plateau. The daytime events consisted of isolated convective echoes with a small spatial scale, the nighttime events consisted of widespread stratiform echoes. According to these observational results, conceptual mechanisms underlying the daytime frequent precipitation with weak intensity are discussed.