![]() Physical processes important for sea fog formation include the turbulent transfer of heat and moisture, the cooling of air masses that travel over colder waters near Newfoundland ( Taylor 1915, 1917) and along the east coast of Scotland as well as in the neighboring North Sea ( Lamb 1943), and radiative cooling at the top of the fog or stratus layer ( Lamb 1943 Filonczuk et al. ![]() 2000) and near CST at the east tip of SDP ( Wang 1983) ( Fig. 2004), contributing to a high frequency of sea fog occurrence and a prolonged fog season along the Korean coast of the Yellow Sea ( Cho et al. Tidal mixing cools shelf regions ( Su and Su 1996 Ma et al. Sea fog formation via stratus lowering is found in the cool season (November–April) when SST is warmer than the surface air off the California coast ( Koračin et al. The steady northwesterly flow off the California coast, along with the upwelling and cold SSTs in response to the winds, are responsible for fog formation in the warm season (May–October) when the greatest frequency of sea fog occurs ( Byers 1930 Sverdrup and Fleming 1941 Sverdrup et al. Mechanisms involved in the seasonal variations of the frequency of sea fog occurrences have been studied elsewhere. 1), corroborates the importance of warm/moist advection for Yellow Sea fog formation. ![]() The fact that fog days are several times more frequent on the southern (upwind) than northern (downwind) coast of SDP, such as at CD, YT, and PL ( Fig. The prevailing surface winds are south-southeasterlies at speeds from 2 to 10 m s −1 near the southern coast of SDP, advecting warm/moist air from the south ( Wang 1983 Diao 1992 Zhang et al. Longer-duration fog events are generally found from June to July, with the longest at 10 days for a 23-yr period from 1977 to 1989 ( Diao 1992). During the fog season, 65%∼87% of the fog observations report visibility of less than 200 m at Qianliyan (QL) and Xiaomaidao (XM), with the average duration of sea fog events lasting about 2 days ( Diao 1992). The fog season is typically from April to July along the southern coast of Shandong Peninsula (SDP) when the sea surface temperature (SST) is lower than the surface air temperature (SAT) ( Figs. Sea fog in the Yellow and East China Seas belongs generally to the type of fog known as advection fog, which forms as warm/moist air passes over colder water ( Wang 1983). Stations on the northwest (NW) Yellow Sea coast typically record more than 50 foggy days a year while the maximum of over 80 days is found at Chengshantou (CST) station in the northern Yellow Sea. Figure 1 shows the number of fog days as a function of calendar month based on 30 yr of station observations. The Yellow Sea experiences heavy fog over a significant fraction of the year. Sea fog often causes shipwrecks and disrupts transportation and other socioeconomic activities over the ocean and in coastal regions. Back trajectories for foggy and fog-free air masses support the results from the climatological analysis. The August wind shift over the Yellow Sea is part of a large-scale change in the East Asian–western Pacific monsoons, characterized by enhanced convection over the subtropical northwest Pacific and the resultant teleconnection into the midlatitudes, the latter known as the western Pacific–Japan pattern. The retreat of Yellow Sea fog is associated with a shift in the prevailing winds from southerly to easterly from July to August. The lack of such warm/moist advection on the east flank of the anticyclone leads to a gradual increase in fog occurrence on the Korean coast. The southerlies on the west flank of this anticyclone advect warm and humid air from the south, causing the abrupt fog onset on the Chinese coast. The land–sea differential warming also leads to the formation of a shallow anticyclone over the cool Yellow and northern East China Seas in April. The prevailing west-southwesterlies at 925 hPa advect warm continental air to form an inversion over the western Yellow Sea. In April, the land warms up much faster than the ocean. The land–sea contrast is the key to these changes. From March to April over the northwestern Yellow Sea, a temperature inversion forms in a layer 100–350 m above the sea surface, and the prevailing surface winds switch from northwesterly to southerly, both changes that are favorable for advection fog. This study investigates the mechanisms for such steplike evolution that is inexplicable from the gradual change in solar radiation. The Yellow Sea fog season is characterized by an abrupt onset in April in the southern coast of Shandong Peninsula and an abrupt, basin-wide termination in August. Sea fog is frequently observed over the Yellow Sea, with an average of 50 fog days on the Chinese coast during April–July.
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