Characteristics of DSD Bulk Parameters: Implication for Radar Rain Retrieval

Liang Liao,Toshio Iguchi,Robert Meneghini,Ali Tokay

doi:10.3390/atmos11060670

Abstract

With the use of 213,456 one-minute measured data of droplet-size distribution (DSD) of rain collected during several National Aeronautics and Space Administration (NASA)-sponsored field campaigns, the relationships between rainfall rate R, mass-weighted diameter Dm and normalized intercept parameter Nw of the gamma DSD are studied. It is found, based on the simulations of the gamma DSD model, that R, Dm and Nw are closely interrelated, and that the ratio of R to Nw is solely a function of Dm, independent of the shape factor μ of the gamma distribution. Furthermore, the model-produced ratio agrees well with those from the DSD data. When a power-law equation is applied to fit the model data, we have: R = aN w D m b , where a = 1.588 × 10 − 4 , b = 4.706 . Analysis of two-parameter relationships such as R–Dm, Nw–R and Nw–Dm reveals that R and Dm are moderately correlated while Nw and Dm are negatively correlated. Nw and R, however, are uncorrelated. The gamma DSD model also reveals that variation of R–Dm relation is caused primarily by Nw. For the application of the Ku- and Ka-band dual-frequency radar for the retrieval of the DSD bulk parameters as well as the specific radar attenuations, the study is carried out to relate the dual-frequency radar reflectivity factors to the DSD and attenuation parameters.

Highlights

Observations of rain-drop size distributions (DSD) have been carried out for more than seven decades evolving from early use of rather primitive tools to the deployment nowadays of sophisticated advanced disdrometers
The R–Dm relation based on the DSD model agrees better with the nominal R–Dm relations adopted by the Dual-frequency Precipitation Radar (DPR) standard algorithm than the relation that is obtained by fitting directly to the data
The purpose of our study is to explore applications to the Ku- and Ka-band frequency radar, development of the full radar algorithm for the retrieval of rain profiles is beyond dual-frequency radar, development of the full radar algorithm for the retrieval of rain profiles is beyond the goal of this paper

Summary

Introduction

Observations of rain-drop size distributions (DSD) have been carried out for more than seven decades evolving from early use of rather primitive tools to the deployment nowadays of sophisticated advanced disdrometers. To effectively account for the changes in the DSD, a three-parameter gamma model has widely been used to represent actual raindrop size spectra for radar retrieval of rain microphysical and bulk properties [16,17,18,19,20]. 0.03 mm in m) despite the rms error in Nw (926 mm−1m−3), which, is still fractionally small as truth or true values while those that are derived from Equations (16)–(18) are referred to as the in view of Provided its large dynamic andscatter mean value ofthe. Nw the Equations (16–18) are based on the gamma DSD model with μ ranging from 0 to 10 rather than (right) versus their respective true values.

Rainfall

Two-dimensional

Because of large variations in exponents are denoted by ‘model’

Method

Summary and Conclusions