1981—2014年四川不同强度霾时空特征及气候成因研究

Spatial-temporal characteristics of haze days with different intensities in Sichuan during 1981—2014 and their climate causes

利用四川156个气象观测站1981—2014年霾日观测资料,对区域内不同强度霾日的时空分布特征及变化趋势进行分析.结果发现:不同强度霾日数呈现轻霾和重霾显著上升、中霾下降的趋势,20世纪90年代后霾日整体偏多,其中,秋、冬季发生频率偏高,12月和1月是多发时段;不同强度年均霾日高值区集中在盆地中部、东部地区,低值区主要位于盆地西南地区,并呈现盆地中北部霾日逐年减少,盆地南部逐年增多的变化趋势.结合季节特征探讨霾日形成机理发现,春、夏季欧亚中高纬度呈现两槽一脊的环流形势,印缅槽较强,利于降水,盆地相对湿度为85%以上,高原东侧上升气流较明显,大气对流层中下层为"上冷下暖"的递减层结,利于大气污染排放物垂直交换及其对外扩散;秋、冬季高纬度以纬向环流为主,经向环流偏弱,冷空气被阻挡在盆地以北以西区域,盆地东部为下沉气流,850 h Pa以下的偏东气流使东部污染物向西蔓延,青藏高原以东地区上空为显著的"上暖下冷"逆温层结,相对湿度为80%左右,地面气温增加,相对湿度下降,使霾不易向雾转换,加重霾日高频状况的发生.

The spatial and temporal characteristics and the variation trend of the number of haze days with different intensities in Sichuan during 1981-- 2014 were studied by using the haze observation data of 156 stations. The results showed that the number of days with light haze and heavy haze events exhibited a significant rising trend, while moderate haze event showed a downward trend, especially after the 1990s. Autumn and winter had the most frequent haze events, especially in December and January. High number of haze days with different intensities was mainly concentrated in the central and eastern parts of Sichuan Basin, while the number was relatively low in southwest part. In terms of the long-term change trend, the central and nortbern parts showed a decreasing trend, as compared with increasing trend over the southern part. Investigation of haze formation mechanisms implied that in spring and summer, the circulations of two-through and one-ridge change at 500 hPa in middle-high latitude regions of Eurasia. The positive anomalies of the water vapor transport from Bay of Bengal were stronger. The relative humidity of the basin was higher than 85%. The updraft on the east side of the Tibetan Plateau was prominent. Lower troposphere exhibited a ＂high-altitude cold low-altitude warm＂ pattern, which was conducive to the vertical exchange and external diffusion of the pollutants. In autumn and winter, zonal circulation was stronger, while the meridional circulation was weaker in high latitudes. The cold air tended to be blocked in the west and north of Sichuan basin. The sinking airflow on the east side of the Tibet Plateau is notable, favoring pollutants dispersion across the basin. Inversion layer was developed in the lower troposphere, and aggravated the occurrence of haze days.