Analysis of Characteristics of Low Vortex Precipitation in the Tibetan Plateau from 1979 to 2015

In order to study long-term precipitation characteristics of the Tibetan Plateau vortex, statistical analysis of precipitation characteristics associated with the Tibetan Plateau vortex over the past 37 years has been conducted based on the dataset of the Tibetan Plateau vortex from 1979 to 2015. Precipitation areas as well as daily precipitation amount observed at weather stations in the Tibetan Plateau are also used. The results show that annual vortex precipitation exhibits an upward trend. The precipitation center is located at Naqu of the Tibetan Plateau, and decreases eastward. The precipitation is largely comprised of summer low vortex precipitation, while both summer precipitation and annual precipitation have a significant positive correlation with total precipitation. The vortex precipitation is declining at Anduo station, whereas its average contribution to annual total is as high as 33%. The vortex precipitation generally shows an upward trend at Naqu and Toto River stations with the increasing rates of 0.21 mm/a and 0.65 mm/a, respectively. The correlation coefficient between low vortex frequency and low vortex precipitation is 0.66 at Naqu area however, the percentage of precipitation accounted for by the vortex precipitation in the Toto River shows a decreasing trend. The low vortex precipitation in the Tibetan Plateau is dominated by light rainfall, while moderate rainfall is the main contributor to total vortex rainfall. The trend analysis shows that the largest increase center of the Tibetan Plateau vortex precipitation is located in northern Qinghai, where the increasing rate reaches 0.88 mm/a, and the second largest center is located along the Yarlung Zangbo River in southwestern Tibet. At the same time, light rainfall induced by the low vortex basically increases in the whole region with the center located in northeastern Tibet and southwestern Qinghai. The upward trend of moderate rainfall is mainly found in southwestern Tibet, Qinghai region and western Sichuan. An obvious rising center is located in southern Qinghai with an increasing rate of up to 0.67mm/a, and the downward trend is mainly distributed in northeastern Tibet.