Abstract
Abstract. In the present study, three meteorological events of extreme deep moist convection, characteristic of south-eastern South America, are considered to conduct a systematic evaluation of the microphysical parameterizations available in the Weather Research and Forecasting (WRF) model by undertaking a direct comparison between satellite-based simulated and observed microwave radiances. A research radiative transfer model, the Atmospheric Radiative Transfer Simulator (ARTS), is coupled with the WRF model under three different microphysical parameterizations (WSM6, WDM6 and Thompson schemes). Microwave radiometry has shown a promising ability in the characterization of frozen hydrometeors. At high microwave frequencies, however, frozen hydrometeors significantly scatter radiation, and the relationship between radiation and hydrometeor populations becomes very complex. The main difficulty in microwave remote sensing of frozen hydrometeor characterization is correctly characterizing this scattering signal due to the complex and variable nature of the size, composition and shape of frozen hydrometeors. The present study further aims at improving the understanding of frozen hydrometeor optical properties characteristic of deep moist convection events in south-eastern South America. In the present study, bulk optical properties are computed by integrating the single-scattering properties of the Liu(2008) discrete dipole approximation (DDA) single-scattering database across the particle size distributions parameterized by the different WRF schemes in a consistent manner, introducing the equal mass approach. The equal mass approach consists of describing the optical properties of the WRF snow and graupel hydrometeors with the optical properties of habits in the DDA database whose dimensions might be different (Dmax′) but whose mass is conserved. The performance of the radiative transfer simulations is evaluated by comparing the simulations with the available coincident microwave observations up to 190 GHz (with observations from Tropical Rainfall Measuring Mission's (TRMM) Microwave Imager (TMI), Microwave Humidity Sounder (MHS) and Special Sensor Microwave Imager/Sounder (SSMI/S)) using the χ2 test. Good agreement is obtained with all observations provided special care is taken to represent the scattering properties of the snow and graupel species.
Highlights
The continental region east of the Andes, covering the south of Brazil, Paraguay, Uruguay and the north and centre of Argentina, is known for its large and intense mesoscale convective systems (MCSs) within which severe weather events develop
Since the simulation of passive microwave radiances requires good knowledge of the scattering properties of frozen hydrometeors, the present study further aims at improving the understanding of frozen hydrometeor optical properties and the characteristics of deep convection in the SESA region
While the particle size distribution of species is intrinsic to each Weather Research and Forecasting (WRF) microphysics scheme, cloud resolving models like WRF do not determine all of the parameters needed to determine the single-scattering properwww.atmos-meas-tech.net/10/3627/2017/
Summary
The continental region east of the Andes, covering the south of Brazil, Paraguay, Uruguay and the north and centre of Argentina (usually referred to as south-eastern South America, SESA), is known for its large and intense mesoscale convective systems (MCSs) within which severe weather events develop The description of cloud processes and the dynamical processes that result from numerical models need to be improved to more accurately describe key factors such as hydrometeor characteristics, latent heating profiles, radiative fluxes and forcing, entrainment and cloud updraft and downdraft properties This is important since, with the increase in computing power in recent years, the physical parameterizations in climate and numerical weather prediction (NWP) models have improved to incorporate microphysical processes, often at increasingly high resolution, resolving the dynamical interactions in convective systems. Meteorological events of extreme deep moist convection are considered to conduct a systematic evaluation of the micro-physical parameterizations available in the Weather Research and Forecasting (WRF) model. The following subsections describe the observations available during this meteorological event, the configuration used in the WRF model runs and its microphysics parameterizations and the radiative transfer model used
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