Impacts of Horizontal Resolution of the Lateral Boundary Conditions and Downscaling Method on the Performance of RegCM4.6 in Simulating the Surface Climate Over Central‐Eastern China

Abstract

This study investigated the impacts of horizontal resolution of lateral boundary condition (LBC) and downscaling method on the performance of RegCM4.6 in simulating the 2 m air temperature and precipitation over central eastern China. Two groups of experiments (direct downscaling experiments using LBC derived from the same reanalysis data but with different horizontal resolutions [0.75°, 1.5°, and 2.5°] and double‐nested downscaling experiment) with the model horizontal resolution of 20 km over central eastern China have been carried out. Results show that the direct downscaling experiments consistently outperform the double‐nested experiment to simulate the 2 m air temperature and precipitation over central eastern China, suggesting that adopting the direct downscaling method is appropriate to simulate the surface climate over central eastern China. Meanwhile, the direct downscaling experiments driven by the LBC derived from the reanalysis data with the horizontal resolution ranging from 0.75° to 2.5° display very comparable performance with a little better performance by adopting the LBC derived from the reanalysis data of much finer resolution. Further mechanism analysis indicates that much larger errors of LBC produced by the double‐nested downscaling method lead to the positive pressure biases and negative biases of water vapor convergence flux over Jianghuai Valley, which contribute to the much larger biases of precipitation and 2 m air temperature in the double‐nested downscaling experiment compared to the direct downscaling experiments. This study emphasizes that the direct downscaling method is superior to the double‐nested downscaling method for the simulations of 2 m air temperature and precipitation over central eastern China.

Influence of Direct-Downscaling and One-Way Nesting on Daily Mean Air Temperature of Egypt Using the RegCM4

“…Despite of the noted biases in DIR, it outperforms the NEST in comparison with the ERA5 particularly in the JJA and SON seasons in agreement with the results reported by Xu X, et al [11]. Therefore, DIR can be recommended for future studies concerning the impact of the climate change on the surface climate of Egypt following [18,19].…”

“…Xu X, et al [11] showed that direct downscaling considerably reduces the bias of the 2 m air temperature and precipitation compared to the two-way nesting technique over central eastern China. Further, the two-way nesting led to positive/negative biases of pressure/ water vapor convergence fl ux (relative to the direct downscaling) and eventually amplifying the biases of the 2 m air temperature and precipitation.…”

On the Sensitivity of Potential Evapotranspiration in Egypt to Different Dynamical Downscaling Options and Boundary Layer Schemes Using a High-Resolution Regional Climate Model

“…Additionally, the accuracy of the calculated PET is affected by the configuration of the regional climate model (e.g., the RegCM4) used for this purpose. The authors of [8] used the RegCM4 to conduct two experiments: (1) studying the influence of the direct down-scaling of ERA-Interim reanalysis with different horizontal grid spacings and (2) making a comparison between direct down-scaling and two-way nesting using ERA-Interim of 1.5 degrees on the near daily average air temperature and total surface precipitation. They claimed that the accuracy of the RegCM4 can be improved when direct down-scaling with an acceptable resolution is adopted.…”

“…For instance, the authors of [7] reported that high-resolution RCMs and improved physical parameterization could ensure a high capability to reproduce largescale atmospheric circulations. The authors of [8] also conducted experiments to constrain the mean air temperature and total surface precipitation concerning different reanalysis products using the RegCM4. They reported that direct downscaling to high-resolution ensures better performance than adopting a one-way nesting technique.…”

Influence of Topography and the Underlying Surface of the Bohai Sea on Wind and Gust Forecasts

“…The ground observations at China Meteorological Administration (CMA) are available at http://data.cma.cn/ en (Kang et al, 2022;Xu et al, 2022). The ECMWF HRES data set is available at https://apps.ecmwf.int/ archive-catalogue/?type=an%26class=od%26stream=o (Yu et al, 2021).…”