Development of a Regional Air-Sea Coupled Model and its Application Over CORDEX-EA Domain

Abstract:

A regional air-sea coupled model coupled through OASIS3.0 was developed for CORDEX East Asia. The regional air-sea coupled model, named as FROALS, was composed of a regional climate model RegCM3 as its atmospheric component, a global climate ocean model (LICOM) as its oceanic component. The performance of regional atmospheric model over CORDEX EA was firstly optimized by tuning seven parameters, using the multiple very fast simulated annealing approach. The performance of FROALS in the simulation of Asian summer monsoon during 1989-2010 was assessed by using the metrics developed by the CLIVAR Asian–Australian Monsoon Panel (AAMP) Diagnostics Task Team. Results indicated that FROALS exhibited good performance in simulating the climatology of Asian summer monsoon. The simulated JJA mean SST biases were weaker than those in CMIP5 multi-model ensemble mean (MMEM). The skill of FROALS approached that of CMIP5 MMEM in terms of the annual cycle of Asian summer monsoon. The model also well captured the spatial pattern of the intraseasonal variability variance and extreme climate indices of Asian summer monsoon despite with larger amplitude.

Then driven by the historical simulation and future climate projection from a global climate system model, dynamical downscaling has been conducted at the uniformly horizontal resolution of 50 km. The impacts of regional air-sea coupling on the simulation of East Asian summer monsoon rainfall have been investigated with comparisons to the corresponding standalone regional climate model (RCM) simulations. The added value of FROALS with respect to the driving global climate was evident in terms of both climatology and interannual variability of summer rainfall over eastern China, contributing from both the high horizontal resolution and the reasonably simulated moisture fluxes convergence. Compared with the standalone RCM simulation, the spatial pattern of the simulated low level monsoon flow over East Asian-western North Pacific was improved in the FROALS due to the inclusion of regional air-sea coupling. The impact of regional air-sea coupling in future climate change downscaling is investigated.