Suppression of light precipitation by air pollution：A comparison between observations in South China and the Tibetan Plateau

Precipitation and visibility (surrogate for aerosol loading) records at the 10 weather stations in the Tibetan Plateau and South China were examined with the span of 32 years (1980—2011). It was shown that the values of visibility were high in the Tibetan Plateau and low in South China. The light rainfall decreased at the 3 stations in South China (Nanning, Beihai and Baise) while the other 7 stations ( 2 in South China and 5 in the Tibetan Plateau) showed little fluctuation. A significant positive correlation was observed between the visibility at 20:00 BT and the light rainfall during the following 24 hours in the stations Nanning, Beihai and Baise with the other 7 stations having no significant correlation, which might suggest that the decrease trends of the light rainfall were caused by air pollution suppressing precipitation. The quantitative analysis showed that for each reduction of 1 kilometer of the visibility at 20:00 BT, the light rainfall of the following 24 hours would decrease by 0.019, 0.028 and 0.027 mm in the stations Nanning, Beihai and Baise, respectively. The correlation coefficients were significantly positive between the visibility at 20:00 BT and the normalization convective available potential energy (NCAPE) of the following 24 hours, which was consistent with the phenomenon of air pollution suppressing light rainfall. It was also observed that the response of NCAPE to the invigoration effect of visibility/aerosol had 2 peaks for each day.