14.5 Using Intensive Field Data for Evaluating Simulations of Mixed-Phase Clouds from WRF Cloud Microphysical Schemes

Friday, 13 July 2018: 9:30 AM
Regency D (Hyatt Regency Vancouver)
Aaron Naeger, Univ. of Alabama in Huntsville, Huntsville, AL; and B. A. Colle, N. Zhou, and A. L. Molthan

This study evaluates cloud microphysical schemes within the Weather Research and Forecasting (WRF) model system in simulating mixed-phase clouds during Global Precipitation Measurement (GPM) field campaigns supporting the NASA Precipitation Measurement Mission (PMM). An intensive suite of satellite, ground-based, and in situ instruments collected detailed measurements of mixed-phase clouds producing heavy precipitation during the GPM Cold Season Precipitation Experiment (GCPEX) from January – February 2012 in Ontario, Canada, and the Olympic Mountain Experiment (OLYMPEX) from November 2015 – February 2016. These robust datasets provide an opportunity to understand the various precipitation structures and associated microphysics in these vastly different environments, which can be effectively used for validating high resolution model simulations. Previous field experiments over the Pacific Northwest (e.g., IMPROVE) illustrated the importance of mountain gravity waves in modifying the precipitation distribution from cloud water generation and riming above the narrow windward ridges to enhanced snow generation aloft over the broader windward slope. Field measurements during GCPEX showed how the production of fast-falling rimed particles can promote an environment more suitable for frontal development and, consequently, lead to higher precipitation totals. Relatively large microphysical uncertainties and errors were associated with the ice and cloud water distributions during these field campaigns. This work aims to diagnose and improve these microphysical issues in the more advanced microphysical schemes within the Weather Research and Forecasting (WRF) model.

This talk will focus on the mixed-phase processes associated with stratiform and convective precipitation events during the OLYMPEX and GCPEX field campaigns. We evaluate the impact of ice microphysical processes (deposition, riming, and melting) on cloud water accretional growth and precipitation characteristics during these field events using surface gauges, ground radars (NPOL and DOW), in situ aircraft (Citation), and satellite sensor measurements (GMI and SSMIS). The WRF was nested down to 1-km grid spacing using the Global Forecast System (GFS) analyses for initial and boundary conditions for a relatively short 36-h simulation. Four unique bulk microphysical schemes were evaluated, including the predicted particle properties (P3) scheme, Thompson, YLin-Stony Brook, and Morrison schemes. We also conduct WRF simulations using the Hebrew University spectral bin microphysical (HUJI) scheme to help identify issues in the bulk parameterization schemes. Overall, larger depositional processes and riming production in the P3 scheme led to faster sedimentation rates of precipitating ice particles and enhanced precipitation totals, which were in better agreement with the observations compared to the other bulk schemes. The HUJI scheme generally overpredicted snow mass while underpredicting graupel/rime mass, which led to an underprediction in precipitation, which limited its use for improving the bulk microphysical schemes. Our model results highlight the importance of accurately representing microphysical processes in mixed-phase clouds for simulating precipitation in these different weather environments.

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