A Comparative Study on the Summer Raindrop Size Distribution Among Areas over the Central and Eastern Qinghai-Xizang （Tibetan） Plateau and the Western Sichuan Basin

Abstract

To promote the understanding of precipitation microphysical characteristics and differences in the central and eastern Qinghai-Xizang （Tibetan） Plateau and the Sichuan Basin， disdrometer measurements collected at Naqu， Yushu， Linzhi， Batang， Luding， and Chengdu from July to August 2019 and 2020 are utilized to comprehensively investigate the characteristics and differences of raindrop size distributions （RSDs） among the six different areas.Meanwhile， local empirical relations between the Gamma shape parameter and slope parameter and between the reflectivity factor and rain rate are proposed and compared.The results show that RSDs in the basin and adjacent areas （Chengdu and Luding） are generally wider and have higher number concentrations of medium-to-large raindrops （diameter ≥1.0 mm） than those in the plateau areas （Naqu， Yushu， Linzhi， and Batang） due to the contribution of more strong convective precipitation.In contrast， RSDs in the plateau areas are narrower and possess higher number concentrations of small raindrops （diameter <1.0 mm） due to more occurrences of stratiform and weak-convective precipitation.RSDs gradually become wider with higher number concentrations as the increase of rainfall intensity both in the six observation areas.The RSD differences among the six observation areas can also change with the rain rate.Specifically， when the rain rate exceeds 0.1 mm·h-1， the increase of the number concentration of small raindrops with increasing rain rate is significantly greater in Naqu and Linzhi than in other areas， and can gradually exceed that in Chengdu.When the rain rate exceeds 5 mm·h-1， the differences in the number concentrations of medium-to-large raindrops between Chengdu and Luding and other plateau areas also gradually become larger.With the same shape parameters， the slope parameters in Chengdu and Luding are smaller than in other areas， indicating that they possess a slower decreasing rate of raindrop number concentration with increasing particle size than that in other plateau areas.Under the same radar echo intensities （reflectivity factor）， rain rates of stratiform precipitation in Naqu and Linzhi are greater than in other regions.The rain rate of convective precipitation in Linzhi is also greater than that in other areas when the radar echo is below 40 dBZ， but the rain rate of convective precipitation in Naqu can be smaller than that in other areas when the radar echo is greater than 40 dBZ.

Keywords

• qinghai-xizang （tibetan） plateau
• the sichuan basin
• raindrop size distribution
• precipitation microphysical properties