Evaluation of the performance of non-hydrostatic RegCM4 (RegCM4-NH) over China

Abstract

This study evaluates the performance of the latest version of non-hydrostatic RegCM4 (RegCM4-NH) customized over two vast urban agglomerations in China (i.e., the Pearl River Delta, PRD, and the Yangtze River Delta, YRD). The analysis focuses on how the dynamical core (hydrostatic versus non-hydrostatic) employed in the driving mother domain simulation can affect the regional characteristics of temperature and precipitation patterns in the PRD and YRD regions simulated by a 4 km resolution nested RegCM4-NH. In addition, we assess the sensitivity of the 4 km model results to the use of a convective parameterization scheme (CPS), since the 4 km grid size can be considered as a gray-zone resolution at which deep convection is partially resolved and may still need to be parameterized. For mean temperature, a reasonable performance is shown by all simulations, with the summer season mean bias mostly less than ±1°C when averaged over the PRD and YRD. However, the simulated daily temperature distribution is excessively peaked around the median value, indicating a large probability concentrated on a small temperature range. Although the higher resolution slightly ameliorates this deficiency, the effect of the dynamical core and CPS tends to be marginal. Conversely, precipitation behaves quite differently across simulations. The driving forcing from the non-hydrostatic mother domain simulation helps to reduce a severe dry bias seen over the PRD due to a reduction in convection inhibition. Use of the Emanuel CPS also tends to intensify localized precipitation events over mountainous regions in connection with stronger ascending motions over topographical features. The higher resolution also improves the phase of the diurnal cycle of precipitation, both with and without the use of the CPS. In general, the performance of RegCM4-NH over the PRD and YRD is found to be best when driven by a non-hydrostatic mother domain simulation and when turning on the Emanuel CPS.