Statistical Characteristics of Raindrop Size Distribution in Monsoon Season over South China Sea

Ying Pang,Sheng Chen,Asi Zhang,Chaoying Huang

doi:10.3390/rs13152878

Abstract

The South China Sea (SCS) is the largest and southernmost sea in China. Water vapor from the SCS is the primary source of precipitation over coastal areas during the summer monsoon season and may cause the uneven distribution of rainfall in southern China. Deep insight into the spatial variability of raindrop size distribution (DSD) is essential for understanding precipitation microphysics, since DSD contains abundant information about rainfall microphysics processes. However, compared to the studies of DSDs over mainland China, very little is known about DSDs over Chinese ocean areas, especially over the South China Sea (SCS). This study investigated the statistical characteristics of the DSD in summer monsoon seasons using the second-generation Particle Size and Velocity (Parsivel2) installed on the scientific research vessel that measured the size and velocity of raindrops over the SCS. In this study, the characteristics of precipitation over the SCS for daytime and nighttime rains were analyzed for different precipitation systems and upon different rain rates. It was found that: (1) rain events were more frequent during the late evening to early morning; (2) more than 78.2% of the raindrops’ diameters were less than 2 mm, and the average value of mass-weighted mean diameter Dm (1.46 mm) of the SCS is similar to that over land in the southern China; (3) the stratiform precipitation features a relatively high concentration of medium to large-sized rain drops compared to other regions; (4) the DSD in the SCS agreed with a three-parameter gamma distribution for the small raindrop diameter. Furthermore, a possible factor for significant DSD variability in the ocean compared with the coast and large islands is also discussed.

Highlights

Precipitation plays a critical role in the hydrological cycle and the Earth’s climate system
The data were divided into two periods, which belonged to either the daytime type (BJT 06:00 to 18:00) or nighttime type (BJT 18:00 to 06:00) according to the definitions of daytime and nighttime by Yang et al [46] based on the local mean sunrise and sunset time in summer
After analyzing the navigation information of the Shenkuo, we found that the precipitation mainly occurred on the open ocean far away from the coastline or large island

Summary

Introduction

Precipitation plays a critical role in the hydrological cycle and the Earth’s climate system. Raindrop size distribution (DSD) is helpful in understanding the characteristics of microphysical processes, such as coalescence and breakup processes [1]. The accurate detection of the DSD is important for many fields [2]. The DSD describes precipitation microphysics characteristics at raindrop scale and provides detailed information that is relevant to large-scale precipitation processes [3]. It is useful for optimizing the short term weather forecasting through developing microphysical parameterization schemes in numerical weather prediction models and can be used to improve quantitative precipitation estimation (QPE) [4]. The DSDs in various regions have received an increasing amount of attention

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Conclusion