Climatic Characters Of Sea Fog Formation Of The Huanghai And Analysis Of Visibility

The sea fog is one of the severe weather over the sea and coastal areas. Horizontal and vertical visibility is very low in fog, which affects safety of navigation and flight and causes the catastrophic accident. Spring and summer is the foggy season which is usually between April and July on Huanghai. The averaged foggy days are more and more from April to July. That is to say, the averaged foggy days are the most in July. It's been pointed that the fog is advective fog on Huanghai. The circulation and synoptic background is the conditions of formatting fog. Thus by analyzing the NCEP/NCAR reanalysis monthly means data and using the numerical modeling, this paper studies the most important climoatic backgrounds of sea fog formation, including the circulation, vapor transport condition, SST and the net longwave radiation, and their relationships in spring and summer. These researches will help us understanding the macro-scale conditions of formatting sea fog and forecasting short-range climate more accuratelyBy using composed and case study, the climoatic background of sea fog formation of the Huanghai in spring (April) and summer (July) has been analyzed, which include circulation, vapor transport condition, SST and the net longwave radiation. The results show that : (1) In spring, the vapor required isn't afforded by local atmosphere but by tropic atmosphere. The warm and moist air is offered by appropriate macroscale circulation from tropic. Compared with circulation, vapor and its transport condition, SST isn't important. Otheirwise sea fog would feedback to the net long wave radiation; (2) In summer, the number of foggy days is decided by the intension of summer monsoon. As well as in spring, the vapor of formatting fog comes from tropic atmosphere in summer, not offering by local atmosphere. The transport of vapor depends on the lower tropospheric jet. SST condition which is as important as the circulation condition plays great role in process of sea fog and vapor condensation, which is very different with in spring; (3) The results of the numericalmodel indicates that the advective transport of vapor is an very important factor in fog formation on Huanghai.The visibility is the important factor affecting the safety of navigation and flight transport, while the lower visibility not only influences the traffic, but also is very dangerous. In coastal area, the lower visibility brought by sea fog is the major weather factor, which can cause the traffic accidents. The research studies the different time-scales variations of visibility can improve the forecast of visibility. The paper analyzes hourly diurnal meteorological visibility data, relative humidity data and wind velocity in Xiamen airport from 2000 to 2002 with statistical method and wavelet analysis method, and found that the visibility of Xiamen airport has distinct daily, seasonal, intraseasonal and quasi-rwo-week variations. Daily variation shows that visibility is the lowest in the morning and evening while reaches the peak on afternoon. The visibility has the annual variation, which is the lowest between March and May and the best in summer. The season when the visibility is the worst is the foggy period in Xiamen. Besides these oscillations, visibility has the remarkable intraseasonal variation (30~60 days) and quasi-two-week variation (10~20 days), which have quasi-two-year period in both summer and winter. This interannual variation relates to interannual oscillation of the East Asia monsoon.Since the existing observing means limited, it's difficult for the study of visibility on sea. But with the development of the satellite remote sensing, the variation of visibility on sea could be analyzed by different channels data of satellite, which is one of the work of this paper. It can be succeeded in fitting visibility using the first and fifth channel data of NOAA16.