Raindrop Size Distribution Measurements at High Altitudes in the Northeastern Tibetan Plateau during Summer

Abstract

Characteristics of raindrop size distribution during summer are studied by using the data from six Parsivel disdrometers located in the northeastern Tibetan Plateau. The analysis focuses on convective and stratiform precipitation at high altitudes from 2434 m to 4202 m. The results show that the contribution of stratiform and convective precipitation with rain rate between 1 ⩽R<5 mm h⁻¹ to the total precipitation increases with altitude, and the raindrop scale and number concentration of convective precipitation is larger than that for stratiform precipitation. The droplet size spectra of both stratiform and convective precipitation shows a single peak with a peak particle size between 0.31–0.50 mm, and they have essentially the same peak particle size and number concentration at the same altitude. The maximum spectral widths of stratiform clouds are between 4 mm and 5 mm, while those of convective clouds range from 4 mm to 8 mm. The Gamma distribution is more suitable than the Marshall-Palmer distribution in terms of the actual raindrop spectrum distribution. The stratiform precipitation particles are smaller with higher number concentration, while the opposite is true for the convective precipitation particles. The convective precipitation particles drop faster than stratiform precipitation particles when the particle size exceeds 2 mm, and the falling velocity of raindrops after standard curve fitting is underestimated during the observation period. Moreover, conventional radar estimation methods would underestimate the precipitation in the Northeastern Tibetan Plateau.

摘 要

利用位于青藏高原东北部的 6 个 Parsivel 激光雨滴谱仪资料, 研究 2434 m 至4202 m 的对流性质降水和层状性质降水夏季雨滴大小的分布特征. 结果表明: 在两种降水类型中, 范围在1≤R<5 mm h⁻¹ 的雨强 (R) 对总降水量的贡献随海拔升高而增大. 对流降水的雨滴尺度和数量浓度均大于层状降水. 层状降水和对流降水的雨滴谱均为单峰, 峰值粒径在 0.31 ~ 0.50 mm 之间, 且在同一高度具有基本相同的峰值粒径和数量浓度. 层状降水雨滴谱的最大谱宽在 4 ~ 5 mm 之间, 对流降水雨滴谱的最大谱宽在 4 ~ 8 mm 之间. Gamma 分布比 Marshall-Palmer 分布更适合实际雨滴谱分布. 层状降水雨滴较小, 数量浓度较高,而对流降水雨滴则相反. 当雨滴粒径超过 2 mm 时, 对流降水雨滴的下降速度比层状降水快, 且下落速度标准曲线拟合将低估观测期间实际雨滴的下降速度. 此外, 传统的雷达估算方法会低估青藏高原东北部地区的降水量.