The Variation Of Sea Fog With Cold Air In The East China Sea And Yellow Sea And The Study Of Forecast Method

Firstly,in this paper, the climate characteristics, meteorological and ocean conditions of sea fog with cold air are studied based on the observation data. The results show that the sea fog with cold air mainly occurs in winter and spring with about 15% of the total number of sea fog and more than half of them are heavy fog processes. Most of cold air processes in which the sea fog forms are weak with less than 4℃reduction of air temperature within a day and less than 8 m/s of wind speed. The relative humidity of air to form fog at daytime is different from that at night. Sea fog occurs at night almost under the situation that air is at or near saturation point, however there is no such strict restriction at daytime. Although the favorable temperature difference between the surface air and sea surface to form fog is from–2℃to 2℃, the sea fog with cold air still takes up 13 % which is higher than that of the general sea fog when the difference exceeds–2℃. The inversion and near isothermal of air near surface almost always appear over the East China Sea when sea fog occurs under the cold air, but this condition is rarely seen in the northern Yellow Sea. Take the Small Yangshan Island station as an example where more sea fog processes occur with cold air, the continuation time for most of the sea fog is less than 2 hours and about 19 % of the sea fog processes persist longer than 4 hours. When sea fog occurs with cold air, the visibility over coastal land nearby is better because of unfavorable conditions for fog there.Secondly,the WRF model is used to stimulate the fog process under the infuence of cold air,which can reappear in the modeling on some degree although the fog area simulated is smaller and the visibility is larger than observations.The visibility is mainly affected by the mixing ratio of cloud water. Generally the fog area with less then 500m visibility is, within the area with more then 0.1g/kg for mixing ratio of cloud water.Finally , the Characteristics of different grade of sea fog are statistically analyzed based on Surface observation data from nine coastal and island stations are used along Yellow Sea and East China Sea coast. And the favorable sea and atmospheric conditions to form sea fog are studied by quantity. The conditions with no sea fog are determined and the sea fog forecasting equations are established. In the end, sea fog forecasting with three grades is carried on by use of output from atmospheric-circulation model, such as the air temperature, wind speed and its direction, relative humidity of air, sea surface temperature etc. The results show that the sea fog objective forecast method has high skill for sea fog forecast over large area, especially in the sea fog season during February and April in 2007 although there is some weakness in some aspects.In the whole the skill for sea fog forecast over Yellow Sea is higher than over East China Sea. The objective forecast system can run automatically from data input to output of results with high stability during past year.