The Impact of Spectral Nudging on Dynamical Downscaling of Regional Cliamte Model over CORDEX-East Asia

Abstract

Regional Climate Models (RCMs), including the RegCM4, are good tools for producing added climate information at a small scale (e.g., extreme precipitation) that the Global Circulation Model (GCM) cannot resolve. However, the results of RCM simulations forced by GCM have errors and uncertainties. To reduce these drawbacks, the Spectral Nudging Technique (SNT) has been applied as an alternative method for boundary conditions. To understand the impact of the SNT on the dynamical downscaling of RCM, in this study, we conducted the sensitivity experiments to the SNT using the RegCM4 forced by the United Kingdom Earth System Model (UKESM). The SNT studies in RegCM4 are considerably meaningful in the CORDEX East Asian region due to the insufficiency of previous studies. We focused on the impact of the SNT on mean and extreme precipitation. The sensitivity experiment showed that the SNT could improve the simulations of mean and extreme precipitation compared with GCM and RCM without the SNT. The impact of the SNT was significant in JJA as well as DJF, especially on extreme precipitation. Additionally, we analyzed the synoptic field related to mean and extreme precipitation to examine why the SNT improved the simulation of the RegCM4.