A Method for Retrieving Vertical Air Velocities in Convective Clouds over the Tibetan Plateau from TIPEX-III Cloud Radar Doppler Spectra

Jiafeng Zheng,Keyun Zhu,Binyun Wang,Jingya Wu,Liping Liu

doi:10.3390/rs9090964

Abstract

In the summertime, convective cells occur frequently over the Tibetan Plateau (TP) because of the large dynamic and thermal effects of the landmass. Measurements of vertical air velocity in convective cloud are useful for advancing our understanding of the dynamic and microphysical mechanisms of clouds and can be used to improve the parameterization of current numerical models. This paper presents a technique for retrieving high-resolution vertical air velocities in convective clouds over the TP through the use of Doppler spectra from vertically pointing Ka-band cloud radar. The method was based on the development of a “small-particle-traced” idea and its associated data processing, and it used three modes of radar. Spectral broadening corrections, uncertainty estimations, and results merging were used to ensure accurate results. Qualitative analysis of two typical convective cases showed that the retrievals were reliable and agreed with the expected results inferred from other radar measurements. A quantitative retrieval of vertical air motion from a ground-based optical disdrometer was used to compare with the radar-derived result. This comparison illustrated that, while the data trends from the two methods of retrieval were in agreement while identifying the updrafts and downdrafts, the cloud radar had a much higher resolution and was able to reveal the small-scale variations in vertical air motion.

Highlights

The Tibetan Plateau (TP) is the largest and highest plateau on our planet, with an average altitude of over 4000 m and a complicated terrain
An alternating variation was observed in radar-measured Z, mean Doppler velocity (MV), and σv across the cumuli, indicating that inhomogeneous ω and microscopic properties were being generated in the interior of the clouds, a feature that is strikingly similar to aircraft observations from previous studies [35]
The derived vertical air velocities show updrafts that occur in the middle of cumulous cells with the cores corresponding to positive MV and downdrafts located on both sides

Summary

Introduction

The Tibetan Plateau (TP) is the largest and highest plateau on our planet, with an average altitude of over 4000 m and a complicated terrain. Vertical air motion over the TP is stronger than over other areas because of significant ground heating, leading to the frequent occurrence of convective cells. Several early investigations suggested that convective clouds over the TP account for approximately 60% of the total cloud amount, with convective cell occurrence rates. 1.5 times higher than over other regions of China. There may be up to 300 convective cells on the plateau per day [6,7]. These convective cells can move eastwards to central and eastern China and cause severe weather [8,9]. The specific natural environment on the TP results in unique cloud and precipitation properties, especially when compared to low-altitude regions [10,11], and can prominently limit the simulation capabilities of numerical

Methods

Results

Discussion

Conclusion