The long-term observational data of sunshine duration(SD) and diffuse radiation percentage(defined as diffuse solar radiation/total solar radiation, DRP) on sunny days during 1960–2005 were analyzed in 7 urban agglomerations and the whole of China. The results show that the sunny sunshine duration(SSD) has decreased significantly except at a few stations over northwestern China in the past 46 years. An obvious decrease of the SSD is found in eastern China, with the trend coefficients lower than-0.8. Accompanied by the SSD decline, the sunny diffuse radiation percentage(SDRP) in most stations shows obvious increasing trends during the 46 years. The averaged SDRP over China has increased 2.33%per decade, while the averaged SSD shows a decrease of-0.13 hr/day per decade. The correlation coefficient between SDRP and SSD is-0.88. SSD decreased over urban agglomerations(small to large city clusters) in the past 46 years, especially in large cities and medium cities, due to the strong anthropogenic activities and air pollution represented by aerosol option depth(AOD) and tropospheric column NO2(Tro NO2). On the regional scale, SSD has an opposite trend from SDRP during 1960 to 2005, and the variation trends of regional mean values of SSD and SDRP in southeastern China are more pronounced than those in northwestern China.
This study discusses the sensitivity of convective parameterization schemes(CPSs) in the Regional Climate Model(version 4.3)(Reg CM4.3) over East/South Asia. The simulations using different CPSs in Reg CM are compared to discover a suitable scheme for this region, as the performance of different schemes is greatly influenced by region and seasonality. Over Southeast China and the Bay of Bengal, the Grell scheme exhibits the lowest RMSEs of summer precipitation compared to observed data. Moreover, the Emanuel over land and Grell over ocean(ELGO) scheme enhances the simulation, in comparison with any single CPS(Grell/Emanuel) over Western Ghats, Sri Lanka, and Southeast India. Over the Huang–Huai–Hai Plain(3H) and Tibetan Plateau(TP) regions of China, the Tiedtke scheme simulates the more reasonable summer precipitation with high correlation coefficient and comparable amplitude. Especially, it reproduces a minimum convective precipitation bias of 8 mm d-1and the lowest RMSEs throughout the year over East/South Asia. Furthermore, for seasonal variation of precipitation, the Tiedtke scheme results are closer to the observed data over the 3H and TP regions. However, none of the CPSs is able to simulate the seasonal variation over North Pakistan(NP). In comparison with previous research, the results of this study support the Grell scheme over South Asia. However, the Tiedtke scheme shows superiority for the 3H, TP and NP regions. The thicker PBL, less surface latent heat flux, the unique ability of deep convection and the entrainment process in the Tiedtke scheme are responsible for reducing the wet bias.
