Vertical Distributions of Raindrops and Z‐R Relationships Using Microrain Radar and 2‐D‐Video Distrometer Measurements During the Integrative Monsoon Frontal Rainfall Experiment (IMFRE)

Lingli Zhou,Liang Leng,Bin Wang,Xiquan Dong,Zhikang Fu,Chunguang Cui,Baike Xi

doi:10.1029/2019jd031108

Abstract

AbstractThe vertical characteristics of raindrop size distributions (DSD) and Z‐R relationships for monsoon frontal rainfall have been investigated using the co‐located two‐dimensional video disdrometer and micro rain radar at the Xianning surface site, and the S‐band weather radar at the Wuhan radar site during the Integrative Monsoon Frontal Rainfall Experiment (IMFRE). In this study, a total of 1,896 rain samples (1‐min resolution) were collected and classified into three categories of convective rain (CR), stratiform rain (SR), and light rain (LR), and their corresponding rain microphysical properties were explored. The LR category is dominated by the evaporation of smaller raindrops and the break‐up processes of larger raindrops, resulting in decreasing trends in radar reflectivity and rain rate as the raindrops fall. The SR category undergoes a competition of break‐up and coalescence processes, with weak increases in radar reflectivity and rain rate. Whereas, for the CR category, the coalescence process is dominant on the falling path of raindrops, especially below 1 km, leading to sharp increases in radar reflectivity and rain rate. The microrain radar data at height of 200 m is quantitatively compared with the two‐dimensional video disdrometer data, and a good agreement is found between them. Further, the number concentrations of raindrops are negatively correlated with the diameters of raindrops and discrepant significantly at different heights among the three rain categories. The height‐dependent Z‐R relationships found for LR, SR, and CR categories will provide insightful information for improving radar rainfall estimate of monsoon frontal rainfall over central China in the future.

Highlights

Heavy rainfall and flooding events over central China during the monsoon season from June to July, often triggered by the multiscale monsoon frontal systems, have caused economic losses up to billions of dollars and more than thousands of deaths in the past decades (Cui et al, 2015; Ding & Chan, 2005)
The quantitative precipitation estimate (QPE) products generated from ground‐based single‐pol operational weather radars, even with appropriate Z‐R relationships, cannot accurately represent the surface rainfall information because the measured radar reflectivity is obtained at increasing height with increasing range
Some studies suggested that the coalescence and break‐up processes are important factors to govern the temporal and vertical evolutions of the DSDs (Mcfarquhar & List, 1993; Prat et al, 2012), whereas other studies demonstrated that these two processes are less critical for the lower RRs (Barthes & Mallet, 2013; List et al, 1987; Prat & Barros, 2007)

Summary

Introduction

Heavy rainfall and flooding events over central China during the monsoon season from June to July, often triggered by the multiscale monsoon frontal systems, have caused economic losses up to billions of dollars and more than thousands of deaths in the past decades (Cui et al, 2015; Ding & Chan, 2005). It is necessary to investigate the characteristics of monsoon frontal rainfall through integrated observations with high spatial and temporal resolutions. Chandrasekar et al (2003) noted that the DSD significantly impacted the radar quantitative precipitation estimate (QPE) by determining a particular Z‐R relationship, a conventional technique for converting radar reflectivity into RR. The QPE products generated from ground‐based single‐pol operational weather radars, even with appropriate Z‐R relationships, cannot accurately represent the surface rainfall information because the measured radar reflectivity is obtained at increasing height with increasing range.

Objectives

Results

Conclusion