The spatial distribution, radiative forcing, and climatic effects of tropospheric ozone in China during summer were investigated by using the regional climate model RegCM4. The results revealed that the tropospheric ozone column concentration was high in East China, Central China, North China, and the Sichuan basin during summer. The increase in tropospheric ozone levels since the industrialization era produced clear-sky shortwave and clear-sky longwave radiative forcing of 0.18 and 0.71 W m(-2), respectively, which increased the average surface air temperature by 0.06 K and the average precipitation by 0.22 mm day(-1) over eastern China during summer. In addition, tropospheric ozone increased the land-sea thermal contrast, leading to an enhancement of East Asian summer monsoon circulation over southern China and a weakening over northern China. The notable increase in surface air temperature in northwestern China, East China, and North China could be attributed to the absorption of longwave radiation by ozone, negative cloud amount anomaly, and corresponding positive shortwave radiation anomaly. There was a substantial increase in precipitation in the middle and lower reaches of the Yangtze River. It was related to the enhanced upward motion and the increased water vapor brought by strengthened southerly winds in the lower troposphere.

Mineral aerosols scatter and absorb incident solar radiation in the atmosphere, and play an important role in the regional climate of High Mountain Asia (the domain includes the Himalayas, Tibetan Plateau, Pamir, Hindu-kush, Karakorum and Tienshan Mountains). Dust deposition on snow/ice can also change the surface albedo, resulting in perturbations in the surface radiation balance. However, most studies that have made quantitative assessments of the climatic effect of mineral aerosols over the High Mountain Asia region did not consider the impact of dust on snow/ice at the surface. In this study, a regional climate model coupled with an aerosol-snow/ice feedback module was used to investigate the emission, distribution, and deposition of dust and the climatic effects of aerosols over High Mountain Asia. Two sets of simulations driven by a reanalysis boundary condition were performed, i.e., with and without dust-climate feedback. Results indicated that the model captured the spatial and temporal features of the climatology and aerosol optical depth (ADD). High dust emission fluxes were simulated in the interior of the Tibetan Plateau (TP) and the Yarlung Tsangpo Valley in March-April-May (MAM), with a decreasing trend during 1990-2009. Dry deposition was controlled by the topography, and its spatial and seasonal features agreed well with the dust emission fluxes. The maximum wet deposition occurred in the western (southern and central) TP in MAM (JJA). A positive surface radiative forcing was induced by dust, including aerosol-snow/ice feedback, resulting in 2-m temperature increases of 0.1-0.5 degrees C over the western TP and Kunlun Mountains in MAM. Mineral dust also caused a decrease of 5-25 mm in the snow water equivalent (SWE) over the western TP, Himalayas, and Pamir Mountains in DJF and MAM. The long-term regional mean radiative forcing via dust deposition on snow showed an rising trend during 1990-2009, which suggested the contribution of aerosols surface radiative effects induced by snow darkening was increased since 1990. (C) 2016 Elsevier B.V. All rights reserved.

The different spatial distributions of aerosol-induced direct radiative forcing and climatic effects in a weak (2003) and a strong (2006) East Asian summer monsoon (EASM) circulation were simulated using a high-resolution regional climate model (RegCM3). Results showed that the atmospheric circulations of summer monsoon have direct relations with transport of aerosols and their climatic effects. Both the top-of-the-atmosphere (TOA) and the surface-negative radiative forcing of aerosols were stronger in weak EASM circulations. The main difference in aerosol-induced negative forcing in two summers varied between 2 and 14 W m(-2) from the Sichuan Basin to North China, where a maximum in aerosol-induced negative forcing was also noticed in the EASM-dominated areas. The spatial difference in the simulated aerosol optical depth (AOD) in two summers generally showed the similar pictures. Surface cooling effects induced by aerosols were spatially more uniform in weak EASM circulations and cooler by about 1-4.5 degrees C. A preliminary analysis here indicated that a weaker low-level wind speed not conducive to the transport and diffusion of aerosols could make more contributions to the differences in the two circulations.

The authors used a high-resolution regional climate model (RegCM3) coupled with a chemistry/aerosol module to simulate East Asian climate in 2006 and to test the climatic impacts of aerosols on regional-scale climate. The direct radiative forcing and climatic effects of aerosols (dust, sulfate, black carbon, and organic carbon) were discussed. The results indicated that aerosols generally produced negative radiative forcing at the top-of-the-atmosphere (TOA) over most areas of East Asia. The radiative forcing induced by aerosols exhibited significant seasonal and regional variations, with the strongest forcing occurring in summer. The aerosol feed-backs on surface air temperature and precipitation were clear. Surface cooling dominated features over the East Asian continental areas, which varied in the approximate range of -0.5 to -2 degrees C with the maximum up to -3 degrees C in summer over the deserts of West China. The aerosols induced complicated variations of precipitation. Except in summer, the rainfall generally varied in the range of -1 to 1 mm d(-1) over most areas of China.