Abstract: Based on the observational data of heavy fog in Anshan area from 1951 to 2014,the spatial and temporal characteristics of heavy fog were analyzed using a linear trend method and a polynomial trend method.The results show that the annual and seasonal numbers of fog days from 1951 to 2014 are larger in the southeastern region of Anshan,but smaller in the northwestern and central regions.The heavy fog days in different regions have different seasonal variations.Heavy fog events occur frequently in summer and autumn (from June to October) in the southeastern mountainous region,while they occur mostly in late autumn and winter (from November to January) in the other regions.Heavy fog days have a decreasing trend in the central region of Anshan,a weakly increasing trend in the western region,and a clear increasing trend in the southeastern region.The longest duration time of regional heavy fog events in Anshan is 7 d.It is seldom to have a heavy fog occurring in the whole region.Such events occurred only eight times from the record.The heavy fog events in Anshan show distinct regional feature due to the topographic effect.It seldom occurs in the plain regions,but frequently appears in mountainous regions and lasts longer.The duration time of heavy fog events in Anshan is about 1-2 h,and their starting time is usually around 05:00-06:00,08:00,and 20:00,mostly lasting for 20-21 h.Due to the inter-decadal variability of heave fog days in Anshan from 1961 to 2010,the number of fog days increases in the southeastern mountainous region and decreases in the central region.Since 1990s,it has decreased significantly in the central region,but increased in the northeastern region,which shows great regional difference.Meanwhile,the feedback of human activities to climate and environment is probably another reason for the variation of heavy fogs in Anshan.

Key words: Heavy fog, Topography, Regional feature, Human activity