Distinguishing between Warm and Stratiform Rain Using Polarimetric Radar Measurements

Sergey Y Matrosov

doi:10.3390/rs13020214

Abstract

Modeled statistical differential reflectivity–reflectivity (i.e., ZDR–Ze) correspondences for no bright-band warm rain and stratiform bright-band rain are evaluated using measurements from an operational polarimetric weather radar and independent information about rain types from a vertically pointing profiler. It is shown that these relations generally fit observational data satisfactorily. Due to a relative abundance of smaller drops, ZDR values for warm rain are, on average, smaller than those for stratiform rain of the same reflectivity by a factor of about two (in the logarithmic scale). A ZDR–Ze relation, representing a mean of such relations for warm and stratiform rains, can be utilized to distinguish between warm and stratiform rain types using polarimetric radar measurements. When a mean offset of observational ZDR data is accounted for and reflectivities are greater than 16 dBZ, about 70% of stratiform rains and approximately similar amounts of warm rains are classified correctly using the mean ZDR–Ze relation when applied to averaged data. Since rain rate estimators for warm rain are quite different from other common rain types, identifying and treating warm rain as a separate precipitation category can lead to better quantitative precipitation estimations.

Highlights

Warm rain is formed mostly by the coalescence of cloud water droplets into rain drops taking place primarily in the atmosphere with temperatures above 0 ◦ C
The atmospheric layer where snowflake melting takes place is usually manifested by the reflectivity enhancement, which is known as the radar bright band, so stratiform rain is sometimes called bright-band (BB) rain, and warm rain is referred to as non-bright band (NBB) rain [3]
This is an important result, especially given the fact that the theoretical relations were obtained using drops size distribution (DSD) observed during the Hydrometeorology Testbed (HMT) Southeastern (HMT-SE) United States deployment, but the radar variables were observed by the radar near the U.S West Coast. 6This of 10 fact indicates that a potential polarimetric radar-based differentiation between these rain types could have a rather general applicability

Summary

Introduction

Warm rain is formed mostly by the coalescence of cloud water droplets into rain drops taking place primarily in the atmosphere with temperatures above 0 ◦ C (i.e., the freezing level temperature). Due to differing drops size distribution (DSD) shapes, warm NBB and stratiform BB rains are characterized by distinctly different average relations between equivalent radar reflectivity factor (hereafter just reflectivity, Ze ) and rain rate, R (i.e., Ze = aRb relations) [3,6]. Such relations are often utilized for operational radar-based QPE using the multi-radar multi sensor (MRMS) approach [7]. Of particular interest was assessing the efficacy of differentiating between these rain types using observational data, which have measurement uncertainties and, possibly, biases

Data and Methods

Results

Differences in Ze –R Estimators for Warm and Stratiform Rains

Findings

Conclusions