Evaluation of Simulated Drop Size Distributions and Microphysical Processes Using Polarimetric Radar Observations for Landfalling Typhoon Matmo (2014)

Abstract

AbstractThe Morrison (Morr), Thompson (Thom), Thompson aerosol‐aware (ThomA), and WRF double‐moment 6‐class (WDM6) microphysics schemes within the WRF model are used to simulate landfalling Typhoon Matmo (2014) and evaluated against polarimetric radar observations in terms of raindrop size distribution (RSD) and microphysical processes. Focus is placed on the inner rainband convection. Only ThomA is able to reproduce observed RSD characteristics having even smaller mean raindrop sizes and larger number concentrations than those of typical maritime convection, when measured in terms of mass‐weighted mean diameter and normalized RSD intercept parameter. The diagnoses of microphysical transfer terms show that warm rain processes are dominant in all experiments. The accretion and autoconversion processes dominate the production of rainwater content and raindrop number concentration, respectively. Examinations of vertical profiles of hydrometeor masses and number concentrations as well as rainwater‐related microphysical transfer rates suggest that raindrop total number concentration NTr near the freezing level, mainly produced by the autoconversion process, plays an important role in determining the near‐surface RSD characteristics. Morr and Thom assume fixed values of cloud droplet number concentration NTc that are much larger than those predicted by ThomA, leading to much smaller NTr near the freezing level produced by the autoconversion process. Sensitivity experiments using much reduced NTc substantially increase predicted NTr, mainly through invigoration of autoconversion. These results indicate that adequately predicting NTc is very important for capturing the right RSD characteristics for landfalling typhoons over East China where Typhoon Matmo is one of the representative examples.