Impact of Microphysical Parameterizations on Simulated Hurricanes—Using Multi-Parameter Satellite Data to Determine the Particle Size Distributions that Produce Most Realistic Storms

Svetla Hristova-Veleva,Quoc Vu,Hui Su,Brian Knosp,F Joseph Turk,Bjorn Lambrigtsen,Ziad Haddad,Bryan W Stiles,Eun-Kyoung Seo,Alexandra Chau,Tsae-Pyng Shen,P Peggy Li

doi:10.3390/atmos12020154

Abstract

Understanding and forecasting hurricanes remains a challenge for the operational and research communities. To accurately predict the Tropical Cyclone (TC) evolution requires properly reflecting the storm’s inner core dynamics by using: (i) high-resolution models; (ii) realistic physical parameterizations. The microphysical processes and their representation in cloud-permitting models are of crucial importance. In particular, the assumed Particle Size Distribution (PSD) functions affect nearly all formulated microphysical processes and are among the most fundamental assumptions in the bulk microphysics schemes. This paper analyzes the impact of the PSD assumptions on simulated hurricanes and their synthetic radiometric signatures. It determines the most realistic, among the available set of assumptions, based on comparison to multi-parameter satellite observations. Here we simulated 2005′s category-5 Hurricane Rita using the cloud-permitting community Weather Research and Forecasting model (WRF) with two different microphysical schemes and with seven different modifications of the parametrized hydrometeor properties within one of the two schemes. We then used instrument simulators to produce satellite-like observations. The study consisted in evaluating the structure of the different simulated storms by comparing, for each storm, the calculated microwave signatures with actual satellite observations made by (a) the passive microwave radiometer that was carried by the Tropical Rainfall Measuring Mission (TRMM) satellite—the TRMM microwave imager TMI, (b) TRMM’s precipitation radar (PR) and (c) the ocean-wind-vector scatterometer carried by the QuikSCAT satellite. The analysis reveals that the different choices of microphysical parameters do produce significantly different microwave signatures, allowing an objective determination of a “best” parameter combination whose resulting signatures are collectively most consistent with the wind and precipitation observations obtained from the satellites. In particular, we find that assuming PSDs with larger number of smaller hydrometeors produces storms that compare best to observations.

Highlights

Improvement Project (HFIP) launched by NOAA (National Oceanic and AtmosphericAdministration) in collaboration with NASA (National Aeronautics and Space Administration), other agencies and institutions.Many factors determine a tropical cyclone’s genesis and evolution, such as the magnitude and direction of vertical shear of the environmental wind, upper oceanic temperature structure and low- and mid-level environmental relative humidity
We evaluate the model forecasts versus: (i) the radar reflectivity profiles collected by the precipitation radar (PR) onboard the Tropical Rainfall Measuring Mission (TRMM); and (ii) the brightness temperatures measured by the TRMM microwave radiometer (TMI)
We developed an ensemble of high-resolution simulations of Hurricane Rita (2005) using the Weather Research and Forecasting model (WRF) system and modifying the microphysical assumptions according to Table 1

Summary

Introduction

Improvement Project (HFIP) launched by NOAA (National Oceanic and AtmosphericAdministration) in collaboration with NASA (National Aeronautics and Space Administration), other agencies and institutions.Many factors determine a tropical cyclone’s genesis and evolution, such as the magnitude and direction of vertical shear of the environmental wind, upper oceanic temperature structure and low- and mid-level environmental relative humidity. Recalling [3] rain suppression, an elevated latent heat source and the associated modification of the storm’s depth will arguably alter the interaction with the ambient flow [4]. Regarding hurricanes, this is equivalent to modifying the storm’s steering level and, can result in storm track changes. The production of hydrometeors and the associated latent heat release are represented in numerical models with either convective parameterizations or microphysical parameterizations or both, depending on the resolution of the simulation. The microphysical parameterizations are best suited for model simulations with resolution ~1–3 km

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Conclusion