Abstract:By using NCEP daily reanalysis data and surface weather data of 7 counties in Ningbo over 2001-2012, and Lamb Jenkinson objective classification method and statistical method, we analyzed the regular pattern of regional haze events in Ningbo and corresponding atmospheric circulation characteristics. The results show that the regional haze in Ningbo has a seasonal distribution feature, and winter is the period with most frequent haze, while in summer haze is the least. There are about 15 times on annual average. Jumpily increasing of the regional haze in 2011 and 2012 is closely related to atmospheric circulation. The circulation for regional haze is divided into four types: Type A, Type AN, Type AS and Type C, accounting for 65.9%, 12.3%, 6.7% and 4.7% respectively. Type A mainly occurs in autumn and winter with stable and straight circulation. Type AN occurs in winter with significantly increasing meridional circulation. Type AS occurs in spring and autumn during the changing intervals of cold air and warm air. Type C occurs in spring and summer with significantly strengthened western Pacific high pressure and weak low pressure ambient field on the ground. Cyclonic circulation at 500 hPa, west airflow and gentle breeze at 850 hPa in eastern coast are helpful for the occurrence of regional haze in Ningbo. On the contrary, anticyclonic circulation at 500 hPa and strong partial south airflow at 850 hPa suppress the haze. When Type A circulation occurs with weak cold air or static and stable air condition, the probability of continuous haze days and severe haze event increases.