Regional Climate Effects of Internally and Externally Mixed Aerosols over China

A regional climate model is employed to simulate the aerosols （dust, sulfate, black carbon, and organic carbon） and their direct effect on the climate over China. The emphasis is on the direct radiative forcing due to the change in mixing state of aerosols. The results show that direct radiative forcing is significantly different between externally and internally mixed aerosols. At the top of the atmosphere （TOA）, the radiative forcing of externally mixed aerosols is larger than that of internally mixed ones, especially in the Tarim desert region where the difference is about 0.7 W m-2. At the surface, however, the situation becomes opposite, especially in the Sichuan basin where the difference is about 1.4 W m-2. Nonetheless, either externally or internally mixed aerosols in China can result in a significant cooling effect, except for the warming in South China in winter and the slight warming in North China in February. The cooling effect induced by externally mixed aerosols is weaker than that induced by internally mixed aerosols, and this is more obvious in spring and winter than in summer and autumn. In spring and summer, the inhibiting effect of externally mixed aerosols on precipitation is less than that of internally mixed aerosols, whereas in autumn and winter the difference is not obvious.

Comparison of Aerosol Effects on Simulated Spring and Summer Hailstorm Clouds

Numerical simulations are carried out to investigate the effect of cloud condensation nuclei（CCN） concentrations on microphysical processes and precipitation characteristics of hailstorms. Two hailstorm cases are simulated, a spring case and a summer case, in a semiarid region of northern China, with the Regional Atmospheric Modeling System. The results are used to investigate the differences and similarities of the CCN effects between spring and summer hailstorms. The similarities are：（1） The total hydrometeor mixing ratio decreases, while the total ice-phase mixing ratio enhances, with increasing CCN concentration;（2） Enhancement of the CCN concentration results in the production of a greater amount of small-sized hydrometeor particles, but a lessening of large-sized hydrometeor particles;（3） As the CCN concentration increases, the supercooled cloud water and rainwater make a lesser contribution to hail, while the ice-phase hydrometeors take on active roles in the growth of hail;（4） When the CCN concentration increases, the amount of total precipitation lessens,while the role played by liquid-phase rainfall in the amount of total precipitation reduces, relatively, compared to that of icephase precipitation. The differences between the two storms include：（1） An increase in the CCN concentration tends to reduce pristine ice mixing ratios in the spring case but enhance them in the summer case;（2） Ice-phase hydrometeor particles contribute more to hail growth in the spring case, while liquid water contributes more in the summer case;（3） An increase in the CCN concentration has different effects on surface hail precipitation in different seasons.