Comparisons of bin and bulk microphysics schemes in simulations of topographic winter precipitation with radar and radiometer measurements

• Published in: Quarterly journal of the Royal Meteorological Society Vol. 144; no. 715; pp. 1926 - 1946
• Main Authors: Han, Mei, Braun, Scott A., Matsui, Toshihisa, Iguchi, Takamichi
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-07-2018; Wiley Subscription Services, Inc
• Subjects: Brightness temperature; clouds; Educational institutions; graupel; hydrometeor mass spectra; Hydrometeors; Ice nuclei; Mass; Mass spectra; Microphysics; microwave remote sensing; Microwave scattering; Precipitation; Precipitation processes; PSDs; Radar; Radar reflectivity; Radiative transfer; Radiative transfer models; Radiometers; Rainfall; Reflectance; Satellite data; Satellites; Simulators; Snow; Spectra; Surface radiation temperature; Topography; Weather forecasting; Winter; Winter precipitation; WRF
• ISSN: 0035-9009; 1477-870X
• DOI: 10.1002/qj.3393

The Hebrew University Cloud Model (HUCM) bin scheme and the Thompson bulk scheme in the Weather Research and Forecasting (WRF) model are compared to assess biases often found in simulated brightness temperature and radar reflectivity. Compared to our preceding study that evaluated several bulk schemes in the WRF model, the current study obtains a reduction of the bias from excessive microwave scattering by precipitation ice for both HUCM bin and the Thompson bulk microphysics schemes for a topographic winter precipitation event associated with an atmospheric river. The Thompson particle size distributions (PSDs) and snow particle density assumption are implemented into the Goddard Satellite Data Simulator Unit (G‐SDSU) and have produced improvements. Despite the greater sophistication of the bin scheme in representing cloud and precipitation processes, the simulation with the Thompson bulk scheme is generally in better agreement with observations for this winter event.
The explicitly resolved hydrometeor PSDs in HUCM enable analysis of mass spectra variations in response to changes in microphysics assumptions. Two HUCM sensitivity runs tested the enhancement of snow particle breakup and the influence of ice nuclei (IN) concentration. Higher IN concentration resulted in increased snow mass and broadened the spectrum toward small‐size particles. Modified snow mass spectra and resultant changes in graupel contributed to modifications in scattering and reflectivity simulations. The article demonstrates the bin scheme's capability to provide a new means to improve our understanding of uncertainties in mesoscale weather models and radiative transfer models.
This study assesses biases often found in simulated brightness temperature and radar reflectivity in mesoscale models. It obtains a reduced bias of excessive microwave scattering by precipitation ice in simulations with both HUCM bin and Thompson bulk schemes for a topographic winter precipitation event. Despite greater sophistication of the bin scheme, the simulation with Thompson bulk scheme is generally in better agreement with observations for this case. Tests with enhanced snow breakup and higher IN concentration with the bin scheme modified snow mass spectra and graupel, which is reflected in scattering and reflectivity calculations. The article also demonstrates the bin scheme's capability of providing a new means to improve our understanding of uncertainties in mesoscale weather models and radiative transfer models.