Characteristics Of Sea Fog Frequency Over The Northern Pacific

In this thesis, the International Comprehensive Ocean-Atmosphere Data Set is utilized to investigate the time variation and space distribution of sea fog over the Northern Pacific and East Asian Sea. Meanwhile,we describe the patterns of meteorological and oceanographic environment conditions when sea fog occurs simultaneously. Based on two grid sizes (2°×2°over North Pacific, 1×1°over East Asian Sea), the'frequency-of-occurrence'is examined to display the frequency of sea fog monthly.The data derived from ICOADS in this article covers 100 years from 1909 to 2008. The heavy frequency of sea fog appears on middle and high latitude in North Pacific. From Hokkaido to the east of Kuril Islands, the great value beyond 40% in June and July, and the frequency in low latitude region is least. Great value zone moves with the seasonal variation. The Yellow Sea, East and south China Sea all influenced by sea fog, and the frequency shows a maximum in the northwest of yellow sea in June. In August, the value drops to 5%. In terms of time variation and space distribution, the fog season is delayed from south to north. In addition, several important routes are defined over North Pacific ocean and coastal waters of China. It is of practical significance to do some research on the seasonal and spatial variation of frequency along the routes.Corresponding to the synoptic observations, the relation between sea fog occurrence and meteorological factors is discussed in the vicinity of Kuril Islands and China Sea separately. When the visibility is less than 1000m, SW-S-SE wind dominated on the sea. The wind speed of Kuril Islands area is between 4.4m/s to 12.3m/s, and the air temperature continuously approach to dew-point temperature (DPT), sometimes even lower than DPT. It is indicated that atmospheric humidity is large when sea fog occurs. The temperature difference between air and sea surface is important physical conditions to influence the formation of sea fog. Through millions of reports from 1982 to 2008, the distribution of temperature difference (AT-SST) is given on the different scope. The frequency which represents air temperature higher (or lower) than sea surface temperature is discussed respectively. It is noticeable that in the vicinity of the Kuril Islands the value of AT-SST between -1℃to 3℃. Warm and cold current is major factors to influence the sea fog occurrence. The favorable condition of AT-SST for the formation of sea fog is between -1℃and 2℃in China Sea. In addition, complex and varied coastal terrains, islands as well as human activities all have an impact on the distribution of sea fog.