Analysis and Application of the Relationship between Cumulonimbus (Cb) Cloud Features and Precipitation Based on FY-2C Image

Yu Liu,Zhao-Liang Li,Chun-Xiang Shi,Du-Gang Xi

doi:10.3390/atmos5020211

Abstract

Although cumulonimbus (Cb) clouds are the main source of precipitation in south China, the relationship between Cb cloud characteristics and precipitation remains unclear. Accordingly, the primary objective of this study was to thoroughly analyze the relationship between Cb cloud features and precipitation both at the pixel and cloud patch scale, and then to apply it in precipitation estimation in the Huaihe River Basin using China’s first operational geostationary meteorological satellite, FengYun-2C (FY-2C), and the hourly precipitation data of 286 gauges from 2007. First, 31 Cb parameters (14 parameters of three pixel features and 17 parameters of four cloud patch features) were extracted based on a Cb tracking method using an artificial neural network (ANN) cloud classification as a pre-processing procedure to identify homogeneous Cb patches. Then, the relationship between Cb cloud properties and precipitation was analyzed and applied in a look-up table algorithm to estimate precipitation. The results were as follows: (1) Precipitation increases first and then declines with increasing values for cold cloud and time evolution parameters, and heavy precipitation may occur not only near the convective center, but also on the front of the Cb clouds on the pixel scale. (2) As for the cloud patch scale, precipitation is typically associated with cold cloud and rough cloud surfaces, whereas the coldest and roughest cloud surfaces do not correspond to the strongest rain. Moreover, rainfall has no obvious relationship with the cloud motion features and varies significantly over different life stages. The involvement of mergers and splits of minor Cb patches is crucial for precipitation processes. (3) The correlation coefficients of the estimated rain rate and gauge rain can reach 0.62 in the cross-validation period and 0.51 in the testing period, which indicates the feasibility of the further application of the relationship in precipitation estimation.

Highlights

Cumulonimbus (Cb) clouds, which are intense convective clouds, are often associated with heavy precipitation in the tropics and at the mid-latitudes
The relationship between precipitation and Cb features was determined at the pixel and cloud patch scales
The results show that deviations in the cloud gravity center and geometric center have almost the same influence on precipitation and that heavy precipitation may occur in the convective center with deviation of the convective cloud center (DCC) = 0, and on the front of convective clouds with high DCC

Summary

Introduction

Cumulonimbus (Cb) clouds, which are intense convective clouds, are often associated with heavy precipitation in the tropics and at the mid-latitudes. Determining the statistical relationship between precipitation and Cb clouds is essential for improving the rainfall estimation algorithms from satellite imagery. Based on the spatial scales from which cloud features are computed, the analysis of the relationship between cloud features and precipitation can be classified into three categories: pixel-based, window-based and patch-based [1]. A wide variety of studies have been performed to detect the relationship between cloud features and rainfall at the pixel scale. Lu and Wu [3] analyzed the precipitation characteristics considering cloud top temperature, temperature gradients and the occurrence of overshooting cloud tops. Those investigations demonstrated that rain usually increases progressively as the cloud-top temperature decreases [4].

Objectives

Methods

Results

Conclusion