Abstract
Abstract. Two model experiments, namely a control (CTL) experiment without aerosol–radiation feedbacks and a experiment with online aerosol–radiation (RAD) interactions, were designed to study the radiative feedback on regional radiation budgets, planetary boundary layer (PBL) meteorology and haze formation due to aerosols during haze episodes over Jing–Jin–Ji, China, and its near surroundings (3JNS region of China: Beijing, Tianjin, Hebei, East Shanxi, West Shandong and North Henan) with a two-way atmospheric chemical transport model. The impact of aerosols on solar radiation reaching Earth's surface, outgoing long-wave emission at the top of the atmosphere, air temperature, PBL turbulence diffusion, PBL height, wind speeds, air pressure pattern and PM2.5 has been studied focusing on a haze episode during the period from 7 to 11 July 2008. The results show that the mean solar radiation flux that reaches the ground decreases by about 15% in 3JNS and 20 to 25%in the region with the highest aerosol optical depth during the haze episode. The fact that aerosol cools the PBL atmosphere but warms the atmosphere above it leads to a more stable atmospheric stratification over the region, which causes a decrease in turbulence diffusion of about 52% and a decrease in the PBL height of about 33%. This consequently forms a positive feedback on the particle concentration within the PBL and the surface as well as the haze formation. Additionally, aerosol direct radiative forcing (DRF) increases PBL wind speed by about 9% and weakens the subtropical high by about 14 hPa, which aids the collapse of haze pollution and results in a negative feedback to the haze episode. The synthetic impacts from the two opposite feedbacks result in about a 14% increase in surface PM2.5. However, the persistence time of both high PM2.5 and haze pollution is not affected by the aerosol DRF. On the contrary over offshore China, aerosols heat the PBL atmosphere and cause unstable atmospheric stratification, but the impact and its feedback on the planetary boundary layer height, turbulence diffusion and wind is weak, with the exception of the evident impacts on the subtropical high.
Highlights
Aerosol direct radiative forcing (DRF) arises from the reforming of the Earth-atmosphere radiation budget by the absorption and scattering of solar radiation and the absorption and the emission of thermal radiation
These results suggest that the suppression of diffusion turbulence by aerosol DRF is both certain and significant over the middle and eastern Chinese mainland with its high pollutants while, in contrast, impact over the sea region is small and can be negligible during haze episodes
A detailed discussion is summarized as follows: Solar radiation flux reaching the ground is decreased by about 15 % in 3JNS and by 20–25 % in the region with the highest Aerosol optical depth (AOD)
Summary
Aerosol direct radiative forcing (DRF) arises from the reforming of the Earth-atmosphere radiation budget by the absorption and scattering of solar radiation and the absorption and the emission of thermal radiation The aerosol optical properties are used as input parameters in a radiative transfer scheme where the radiative heating rates are fed back to the online dynamic frame of the GRAPES/CUACE This allows us to evaluate aerosol DRF and its impact on the local radiation budget and the PBL meteorological features including air temperature, heating/cooling profile rates, wind intensity, planetary boundary layer height (PBLH), turbulence diffusion and air pressure pattern over 3JNS
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