| Fog is always regarded as a kind of "cloud" microphysical process happened in the atmospheric boundary layer in the numerical simulation, studies have shown that aerosol is one of key factor that influences the occurrence and development of fog. This paper attempts to use WRF-Chem (Weather Research and Forecasting Model Coupled with Chemistry) model, to carry out comparative studies of aerosol effect on sea/land fog, in order to deepen the understanding of aerosol effect and improve fog prediction ability.One large-scale sea fog over the Yellow Sea occurred in March 2006, and one land fog over the north of China occurred in November 2009, are chosen to be studied in this paper. First, we acquire the evolution of fogs by the MTS AT (Multi-functional Transport Satellite) satellite-derived data, and analyze the weather situations and stratification characteristics when the fog occurred using FNL data which is offered by NECP (National Centers for Environmental Prediction). Second, a good initial filed is provided by cycling-3DVAR that assimilates many routine and non-routine data, and a series of numerical experiments which use appropriate aerosol direct radiation effect and indirect nuclear effect schemes are designed and carried out. At last, we analyze the mechanism of aerosol effect on sea/land fog in detail.The results illustrate that:1) Aerosol direct radiative effect has an impact on fog concentration and fog top height by increasing long wave radiation, such as the average fog top height of sea fog has increased 10.7 m, while this direct effect is too feeble to bring significant changes in fog area, the scoring(POD、FAR、Bias and ETS) improvement rate of twice fog process is less than 6%.2) Aerosol particle can influence Twoemy effect and Albrecht effect by altering cloud droplet concentration, the sensitive experiments on cloud droplet concentration tell us appropriate number for sea/land fog is 108-109kg-1. Increased cloud droplet concentration prompts sea fog average concentration by 0.6 g·kg-1 to 1.8 g·kg-1.3) Twomey effect hinders solar radiation reaching the ground (average radiation flux decreases 39.4%), which leads the inter turbulence intensity of land fog to weaken 29.5%, so it is suitable for the land fog to maintain and develop after the sun rises. For the sea fog, although average solar radiation flux has weakened 17.4%, the higher sea specific heat make turbulence intensity just decrease 3.9%. As a result, change of sea fog area is very small, and maximum score improvement rate is only 6.8%.4) Albrecht effect can reduce precipitation in fog. Besides, it extends the cloud life cycle and cloud albedo, which will bring sea/land fog area some degree of change. For example, the ETS scoring of land fog improves 9.9%, while it is less than the improvement rate of Twomey effect (65.3%); the response of se fog area is very weak for Albrecht effect (ETS score reduces 0.5%)... |
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