上海地区通风指数的应用研究

Application of the ventilation index in Shanghai

利用2013—2014年上海地区的风廓线资料及NCEP再分析资料,计算研究了上海地区通风指数的变化情况,并结合实际天气情况和预报经验,对常用通风指数公式进行本地化修正.通过分析修正前后的通风指数与颗粒物浓度的关系发现,修正后通风指数的时间变化特征与PM_(2.5)浓度的时间变化有显著的负相关关系,且经过修正的通风指数对于PM_(2.5)浓度变化的指示意义更强;研究其在典型污染个例中的应用情况发现,修正后的通风指数低时,对应的PM_(2.5)浓度值高,说明修正后的通风指数能较好地反映出边界层内大气对污染物的扩散和输送作用;另外,与未修正的通风指数对比发现,修正后的通风指数降低了原通风指数的数值,对污染的指示意义更强,尤其表现在上海地区受冷空气影响时,修正后的通风指数较原通风指数降低明显,能更好地反映出大气对上游地区污染物的输送作用.由此可见,经过修正后的通风指数更适用于本地化的预报服务,这也为上海地区的空气质量预报和霾预报提供了一个新的参考指标.

In this work,we have modified the ventilation index based on analysis of local weather conditions of Shanghai using wind profiler and NCEP reanalysis data（ 1° ×1°）. Experiences gained through daily forecasting have also been taken into account while modifying the ventilation index. Comparing the modified and the original ventilation index,we found the following features. First,the modified ventilation index shows stronger inverse correlation with PM（2.5） concentration,and it can better reflect the temporal variation of PM（2.5） concentration compared with the original index. Study of the typical pollution episode also shows substantially lower values of the modified ventilation index at higher PM（2.5） concentrations,reflecting suppressed transport and mixing in the boundary layer. Lastly,compared to the original one,value of the modified ventilation index is substantially lower when Shanghai is affected by the pass of cold front. Therefore,it can better reflect the transport of upwind pollutants during front passage. In summary,the modified ventilation index is more applicable for the local air quality forecasting in Shanghai,and it can be used as a new reference index for air quality and haze forecast of the city.