Relationship Between Air Pollution Events in Autumn and Winter in Chongqing and the Classification of Synoptic Situation Based on Self-Organizing Maps
In order to understand the circulation characteristics of air pollution events in autumn and winter in Chongqing, this paper uses NCEP reanalysis data to classify the surface sea level pressure fields of air pollution events by using the self-organizing map (SOM) algorithm. Then by means of subjective comparative analysis, three types of typical surface pressure fields are summarized: uniform pressure pattern, low pressure pattern and the bottom pattern of high pressure. Among them, the uniform pressure pattern is divided into two types: one is the uniform pressure pattern between two cold fronts and the other is in the weak high pressure. The bottom pattern of high pressure can be divided into three types according to the center position of cold high pressure, including north high pressure type, northwest high pressure type and northeast high pressure type. By comparative analysis, it is found that the concentration of air pollutants on the bottom pattern of high pressure is the highest, thus the air pollution is the most serious. The analysis by using conventional observation data and L-band radiosonde data shows that all kinds of pollution weather patterns are characterized by high static wind frequency on the surface, low horizontal wind speed near the surface, high probability of inversion, stable atmospheric stratification and low height of atmospheric boundary layer. Based on the large-scale synoptic circulation, dynamic and thermal conditions and backward trajectory simulation, the causes for the three types of typical pollution weather processes are investigated, and the results would provide a reference for air pollution potential forecast and concentration prediction in Chongqing.