Abstract: Based on observational data of atmospheric visibility from 53 meteorological stations in Liaoning province from 1961 to 2014,the spatiotemporal distribution of the number of fog days was analyzed.The inter-annual and inter-decadal variations of fog days in different regions according to the rotated empirical orthogonal function (REOF) method were investigated for understanding the regional characteristics of fog days on multi-time scales.The results show that the number of fog days has a low-high-low-high zonal distribution from the west to the east in Liaoning province in recent 54 years.Annual mean number of fog days in Liaoning province can be divided into six regions,including the western-central region,the eastern mountainous region,the southern-central region,the western region,the southern coastal region,and the northern region.The annual number of fog days has an increasing trend in the southern coastal region,the western-central region and the northern region,while the number of fog days decreases in the eastern mountainous region and the southern-central region,however,the fog days in the western region do not change obviously.The variation of fog days is significantly different from different regions.The annual mean fog days in the western-central region,the eastern region,the southern-central region,the western region and the southern coastal region have very strong inter-decadal variability,however,those in the north region has obvious inter-annual variability.The inter-annual variability of annual mean fog days in the western-central region and the southern-central region has a declining trend,but that in the other four regions is in an increasing stage.The inter-decadal variability of annual mean fog days is in a decline stage in the western-central region,the eastern region and the western region,however,it is in an increasing stage in the other regions.

Key words: Fog days, Rotated empirical orthogonal function(REOF), Sub-region, Wavelet analysis