10/29/2023 0 Comments Sea fog weatherSeveral studies have evaluated the turbulence in sea fog indirectly. 2012), the west coast of the Korean Peninsula ( Kim and Yum 2012), and the northwest Pacific ( Tachibana et al. Sea fog with these two types of boundary layer characteristics also appears in the Yellow Sea, the East China Sea ( Wang 1985 Huang and Zhou 2006 Zhang et al. When a stratus layer forms anterior to the fog, a combination of buoyancy and radiative cooling lowers the cloud to the sea surface, transforming the cloud to fog ( Pilié et al. The fog forms initially by contact of warm air with cold sea, but then is maintained mainly by radiation from fog top, which depresses the fog temperature below SST ( Findlater et al. It is also similar to the sea fog on the Scottish coast, known as the Haar, which has been studied by Lamb (1943) and Findlater et al. West Coast, the latter of which was studied initially by Petterssen (1938), Emmons and Montgomery (1947), and Leipper (1948). In contrast, the defining characteristic of cold advection fog is having the value of SAT be continuously less than SST.Ĭold advection fog off the coast of southern China is similar to the sea fog on the U.S. The fog is then maintained by strong advection of warm, moist air over the cold sea surface. Taylor (1917) pointed out the formation mechanism, which was then later confirmed by Byers (1930) and Lamb (1943). Warm advection fog forms by the transport of heat via eddy diffusion (mechanical turbulence) from the upper warm saturated air to the sea surface and thereby cools the air adjacent to the sea. We use this feature as its defining characteristic. The former case is called warm advection fog here, which has the typical feature that the surface air temperature (SAT) exceeds the sea surface temperature (SST). He showed that both warm air passing over a cold sea and cold air blowing over a warm sea can form sea fog. But of these, only advection fog is common off the coast of southern China, so we focus on advection fog here.Īdvection fog was first studied by Taylor (1917). (2004) describe four main types: advection fog, thermal buoyancy fog, radiative cooling fog, and steam fog. And the type of fog is generally based on the primary formation mechanism ( Gultepe et al. Such small-scale characteristics depend on the fog type. In particular, the role of small-scale turbulence in fog needs to be clarified ( Lewis et al. However, improvement of sea-fog forecasting will require better observations of fog. The present study seeks to improve our knowledge of sea fog in this unique area. For example, fog characteristics over the South China Sea are quite unique in many aspects including the formation, seasonal aspect, and extremely large fog-layer depths, but this area has seen relatively little study. West Coast and China’s Yellow Sea because sea-fog characteristics differ by area ( Koračin et al. Most studies of sea fog focus on particular areas such as the U.S. Sea-fog forecasting under different synoptic and mesoscale conditions is crucial for commerce and travel, yet still a complicated problem worldwide. 5) Low-level vertical advection is important for both fogs, but has a larger influence on fog development in the warm advection fog case. However, the sensible and latent heat flux differ between the cases: in the cold advection fog case, the sensible and latent heat fluxes are roughly upward, averaging 2.58 and 26.75 W m −2, respectively however, in the warm advection fog case, the sensible and latent heat flux are mostly downward, averaging −6.98 and −6.22 W m −2, respectively. 4) The momentum fluxes of both fog cases are below 0.04 kg m −1 s −2. 3) Turbulence near the sea surface is mainly thermally driven for cold advection fog, but mechanically driven for warm advection fog. 2) For warm advection fog, two layers of low cloud can merge to form deep fog, with the depth exceeding 1000 m, when strong advection of warm moist air produces active thermal-turbulence mixing above the thermal-turbulence interface. These findings include the following: 1) For cold advection fog, the top can extend above the inversion base, but formation of an overlaying cloud causes the fog to dissipate. The measurement data come from two sites: one on the coast and one at sea. This study analyzes measurements of the small-scale turbulence, together with the boundary layer structure and the synoptic and mesoscale conditions over the life cycle of a cold advection fog event and a warm advection fog event, both off the coast of southern China. Small-scale turbulence has an essential role in sea-fog formation and evolution, but is not completely understood.
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