The impact of two land‐surface schemes on the characteristics of summer precipitation over East Asia from the RegCM4 simulations

Abstract

This study evaluates the performance of the regional climate model RegCM4, which incorporates the Biosphere-Atmosphere Transfer Scheme (BATS) and Community Land Model (CLM3) land-surface schemes, in simulating the summer precipitation over East Asia. The characteristics of summer precipitation are analysed in terms of mean amount, frequency and intensity of daily precipitation. The results show that the simulation of the summer precipitation is significantly sensitive to the choices of the land-surface schemes. Despite several deficiencies, the simulation of daily precipitation with CLM3 exhibits superior performance to that with BATS. The BATS simulation tends to systematically overestimate both precipitation frequency and intensity, and hence total precipitation across the whole domain. On the other hand, the CLM3 simulation substantially reduces the wet biases produced in the BATS simulation. The difference in performance between the two simulations mainly results from convective precipitation rather than large-scale precipitation. Since excessive convective precipitation tends to suppress large-scale precipitation, the BATS simulation also exhibits a limitation in properly simulating the ratio of convective and large-scale precipitation. Such behaviour can be explained by the influence of soil moisture on convective precipitation. Persistently wetter soil moisture in the BATS land-surface scheme can modulate the partitioning of surface heat fluxes inadequately, leading to overestimation of latent heat flux and underestimation of sensible heat flux over South China, in particular. Consequently, it affects the thermodynamic structure (as described by the stability indices), which in turn affects the atmospheric stability to determine the convective activity. The CLM3 simulation generates a more realistic representation of equivalent potential temperature, convective available potential energy and convective inhibition, and thus improves the characteristics of daily precipitation.

Evaluating the impacts of cumulus, land surface and ocean surface schemes on summertime rainfall simulations over East-to-southeast Asia and the western north Pacific by RegCM4

“…Furthermore, an additional model experiment with GAS plus BATS over land, and Emanuel plus Zeng2 over the ocean, also gives BIAS of 34.7 % over land (results not shown in the table). These results suggest that BATS is inclined to largely overestimate the latent heat flux over land, which is consistent with previous studies (see, e.g., Steiner et al 2005Steiner et al , 2009Diro et al 2012;Kang et al 2014). These studies all attributed the overestimation of latent heat flux to the more moist soil layers in the land surface model, which was also discovered during the course of this study (figure not shown).…”

“…Based on a number of test runs, it was found that the use of the Emanuel scheme, CLM and Zeng2 generally gives the best performance in simulating the summertime circulation over East-to-southeast Asia and the western north Pacific region, in agreement with previous studies (see, e.g., Im et al 2008;Huang and Chan 2014;Kang et al 2014). To further evaluate the effects of different physics on the modelsimulated climate, totally seven combinations were tested in this study (Table 1), including the basic one of using Emanuel, CLM and Zeng2 (i.e., experiment E-C-Z2).…”

“…2b, e) indicates that the BATS model overestimates rainfall over land, while CLM gives more realistic rainfall over Indochina and coastal eastern China. The superiority of CLM to the BATS land surface model is supported by earlier studies (Dai et al 2003;Kang et al 2014). Based on results from the E-C-Z2, E-C-Z1 and E-C-B runs using different ocean surface schemes (Fig.…”

“…Surface latent heat flux parameterizations over land, as well as those over the ocean, are also very important because they control the quantity of moisture entering into atmosphere from the Earth's surface (Wang et al 1996;Chen and Avissar 1994;Wang et al 2003;Li et al 2012). It is obvious that one needs to test the sensitivity of precipitation in RegCM4 to different physics, in order to select the best combination of schemes for realistic regional rainfall and climate simulations (see, e.g., Huang et al 2013;Kang et al 2014).…”

Performance of cumulus parameterization schemes in the simulation of Indian Summer Monsoon using RegCM4

“…Although spin-ups of regional models vary in the range of 10 days to one month (Wang et. al, 2003;Martínez et al, 2006;Zhong et al, 2006;Kang et al, 2014) and even longer for climate scale simulation, one month is sufficient for a seasonal scale (five months) simulation to achieve dynamical equilibrium of the model internal physics and lateral boundary conditions, as mentioned in the earlier literature. It is reported in an earlier study by Anthes et al (1989) that regional models reach the equilibrium stage around 2-3 days.…”