A Multi-Model, Multi-Scheme Evaluation of Scale-Aware Convective Parameterization for Gray-Zone Tropical Cyclone Simulation over the South China Sea

Abstract

Gray-zone tropical cyclone (TC) simulations, in which convection is partially resolved and partially parameterized at grid spacings of approximately 3 to 15 km, are sensitive to how grid spacing changes across adaptive meshes. This study evaluates three scale-aware convective parameterization schemes (CPS), the Grell-Freitas (GF), Multi-Scale Kain-Fritsch (MSKF), and New Tiedtke (NTDK), across regional (WRF) and global (Model for Prediction Across Scales, MPAS; ClusterTech Platform for Atmospheric Simulation, CPAS) models for TC simulation over the South China Sea. Twenty-seven simulations spanning three TC cases (Category 2 to 5 intensity, including single-TC and binary interaction scenarios) are verified against observations. While domain-averaged precipitation differs by only 10 to 20% across models, the Convective Rain Ratio (CRR, the fraction of total precipitation produced by the CPS) shows that models achieve similar rainfall through different convective partitioning. Across the 27 simulations, CPS choice accounts for 44% of CRR variance, compared with 29% for the model framework and 16% for the selected TC case. CRR differences are largest in the gray zone, ranging from 30% to over 90% across schemes. Both global models exhibit mid-level drying relative to WRF regardless of CPS choice. This deficit may partly reflect differences in large-scale moisture constraints between regional and global model frameworks. CPAS’s adaptive mesh partially restores outer rainband precipitation relative to MPAS but introduces discontinuities where grid spacing changes sharply. Identical CPS produce different CRR patterns across models, differing by more than 20% for individual TC cases. Current scale-aware CPS adjust their behavior based on local grid spacing, but do not account for how rapidly that spacing changes across the mesh. Future schemes should explicitly account for local gradients in grid spacing.