Sea Fog Research Articles

A Numerical Study of Sea-Fog Formation over Cold Sea Surface Using a One-Dimensional Turbulence Model Coupled with the Weather Research and Forecasting Model

The formation mechanism of a cold sea-fog case observed over the Yellow Sea near the western coastal area of the Korean Peninsula is investigated using numerical simulation with a one-dimensional turbulence model coupled with a three-dimensional regional model. The simulation was carried out using both Eulerian and Lagrangian approaches; both approaches produced sea fog in a manner consistent with observation. For the selected cold sea-fog case, the model results suggested the following: as warm and moist air flows over a cold sea surface, the lower part of the air column is modified by the turbulent exchange of heat and moisture and the diurnal variation in radiation. The modified boundary-layer structure represents a typical stable thermally internal boundary layer. Within the stable thermally internal boundary layer, the air temperature is decreased by radiative cooling and turbulent heat exchange but the moisture loss due to the downward vapour flux in the lowest part of the air column is compensated by moisture advection and therefore the dewpoint temperature does not decrease as rapidly as does the air temperature. Eventually water vapour saturation is achieved and the cold sea fog forms in the thermal internal boundary layer.

Sea fog separating from the lee slope of a 40 metre hill on Siu Kau Yi Chau Island, Hong Kong

WeatherVolume 67, Issue 2 p. E1-E1 Inside Cover Photograph Sea fog separating from the lee slope of a 40 metre hill on Siu Kau Yi Chau Island, Hong Kong First published: 25 January 2012 https://doi.org/10.1002/wea.1900Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume67, Issue2February 2012Pages E1-E1 RelatedInformation

Fog Detection over China’s Adjacent Sea Area by using the MTSAT Geostationary Satellite Data

AbstractA fog threshold method for the detection of sea fog from Multi-function Transport Satellite (MTSAT-1R) infrared (IR) channel data is presented. This method uses principle component analysis (PCA), texture analysis, and threshold detection to extract sea fog information. A heavy sea fog episode that occurred over China's adjacent sea area during 7-8 April 2008 was detected, indicating that the fog threshold method can effectively detect sea fog areas nearly 24 hours a day. MTSAT-1R data from March 2006, June 2007, and April 2008 were processed using the fog threshold method, and sea fog coverage information was compared with the meteorological observation report data from ships. The hit rate, miss rate, and false alarm rate of sea fog detection were 66.1%, 27.3%, and 33.9%, respectively. The results show that the fog threshold method can detect the formation, evolution, and dissipation of sea fog events over period of time and that the method has superior temporal and spatial resolution relative to...

Tidewater glacier fluctuations in central East Greenland coastal and fjord regions (1980s–2005)

AbstractSummer 2000/01 ASTER and Landsat 7 scenes and semi-automated digitization were used to compile a glacier inventory for local glaciers of the Geikie Plateau region, central East Greenland. Of the 332 glaciers (41 591 km2), 120 are tidewater-terminating and drain 90% of the glacierized area. Differencing the 2000/01 tidewater margins from the 1980s GEUS map database ice polygons (113 glaciers) and from 2004/05 ASTER tidewater margins (78 glaciers) shows a cumulative tidewater terminus width decrease from 196 km to 183 km between the 1980s and 2000s, with a corresponding areal loss of ~31 km2 and an effective length change of –14.3 km. Between 2000/01 and 2004/05, areal loss was 26 km2. Average margin retreat rate increased two- to threefold, from 1.7–2.1km2 a–1 (1980s– 2000) to 3.9–5.7km2 a–1 (2000–05). Advances are negligible, apart from two surges, of which one was previously undetected. Coastal, ‘outer’ fjord-terminating, glaciers have two to three times larger areal and effective length retreat rates than ‘inner’ fjord-terminating glaciers. We investigate possible causes and hypothesize that, in addition to ocean temperature and sea ice, changes in sea fog may affect coastal-terminating more than inner fjord-terminating glaciers.

Radiosonde Observation of Sea Fog and Meso-Anticyclone over the Sea of Okhotsk

Radiosonde Observation of Sea Fog and Meso-Anticyclone over the Sea of Okhotsk

Characteristics of the boundary layer structure of sea fog on the coast of Southern China

Using boundary layer data with regard to sea fog observed at the Science Experiment Base for Marine Meteorology at Bohe, Guangdong Province, the structure of the atmospheric boundary layer and the characteristics of the tops of the fog and the clouds were analyzed. In addition, the effects of advection, radiation, and turbulence during sea fog were also investigated. According to the stability definition of saturated, wet air, the gradient of the potential pseudo-equivalent temperature equal to zero was defined as the thermal turbulence interface. There is evidence to suggest that two layers of turbulence exist in sea fog. Thermal turbulence produced by long-wave radiation is prevalent above the thermal turbulence interface, whereas mechanical turbulence aroused by wind shear is predominant below the interface. The height of the thermal turbulence interface was observed between 180 m and 380 m. Three important factors are closely related to the development of the top of the sea fog: (1) the horizontal advection of the water vapor, (2) the long-wave radiation of the fog top, and (3) the movement of the vertical turbulence. Formation, development, and dissipation are the three possible phases of the evolution of the boundary-layer structure during the sea fog season. In addition, the thermal turbulence interface is the most significant turbulence interface during the formation and development periods; it is maintained after sea fog rises into the stratus layer.

A Comparison Study Between Spring and Summer Fogs in the Yellow Sea-Observations and Mechanisms

New observations from buoys and soundings reveal the discrepancies in air–sea interface and in vertical structures between spring (April to May) and summer (July) fogs in the Yellow Sea. Spring fogs are shallow with a robust temperature inversion, dry layer and cold phase (surface air temperature or SAT is lower than sea surface temperature or SST); summer fogs are deep with weaker stability, indistinct fog top and warm phase (SAT > SST). Along with numerical simulations, conceptual models for the mechanisms of temperature inversion are suggested. The land–sea contrast is responsible for the robust temperature inversion in spring, and the deep southerlies derived from the east Asian summer monsoon and the adiabatic sinking from the western Pacific subtropical high contributes to the weaker inversion in summer. The dry layer above the sea fog top intensifies the longwave radiative cooling effect to lead to the cold phase in spring fogs. The radiative cooling is weaker in summer fogs resulting in SAT > SST.

Large-Scale Environmental Influences on the Onset, Maintenance, and Dissipation of Six Sea Fog Cases over the Yellow Sea

Sea fog is typically formed and developed under a set of favorable environmental conditions, which are associated with the station pressure changes, sea level pressure, winds, temperature, water vapor supply, and sea surface temperature. Understanding of these environmental factors during the evolution of a sea fog episode is crucial for forecasting the occurrence and severity of sea fogs over the ocean and adjacent coastal areas. In this study, the large-scale environment variability of six fog events over the Yellow Sea was investigated. It was realized in the present study that the northwest Pacific Ocean high (NPH) is vital to fog formation over the Yellow Sea. In our study, six fog cases can be basically divided into two types: (1) pressure-weakening type, (2) pressure-strengthening type. The former type happened in spring and the latter type in summer. Prevailing southerly winds, accompanied with the well-positioned NPH, may supply a large amount of warm water vapor for the fog formation and maintenance. The intensity of the air temperature inversion is stronger in summer cases than that in spring ones. The wind direction change from south to north and the unstable lower atmosphere may lead to fog’s dissipation. This study may provide a comprehensive understanding of sea fog’s onset, maintenance, and dissipation over the Yellow Sea.

Marine Boundary Layer Structure for the Sea Fog Formation off the West Coast of the Korean Peninsula

Marine boundary layer (MBL) structure for the formation of sea fogs off the west coast of the Korean Peninsula are examined for the investigation period from January 2002 to August 2006, using the meteorological data measured at a buoy and the vertical sounding data measured at an island in this region. There is the total of 3,294 vertical soundings during the investigation period. Based on these vertical soundings, the MBL structure is classified as convective boundary layer (CBL; when inversion exists aloft but at altitudes lower than 3 km, 1,618 soundings), stable boundary layer (SBL; when inversion base is at the surface, 655 soundings) or near-neutral boundary layer (NNBL; when there is no inversion or inversion base is higher than 3 km altitude, 1,021 soundings). Under the CBL condition, the most frequently formed lower level cloud is stratocumulus but fogs do form in spring and summer months mostly as warm sea fogs [TSST (=T–SST) 0) are the most frequently found lower level clouds. The effects of turbulence, advection and radiation on sea fog formation vary with turbulence strength, represented by bulk Richardson number, Rb. For cold sea fog cases, in the highly turbulent regime (Rb 0.30) regimes, the effects of turbulence decrease dramatically and so do the advection effects but radiative cooling is still strong, again making it the crucial reason for the successful formation of cold sea fogs. On the other hand, the turbulent moisture supply from the warmer sea surface is the crucial factor for the formation of warm sea fogs while turbulent warming and radiative cooling largely cancel each other out and the advection effects are negligibly small.

Sea fog in the English Channel

WeatherVolume 66, Issue 4 p. 103-106 Research Article Sea fog in the English Channel Bernard Burton, Corresponding Author Bernard Burton b.j.burton@btinternet.com Wokingham, Berkshire27 Cantley Crescent, Wokingham, RG41 1NUSearch for more papers by this author Bernard Burton, Corresponding Author Bernard Burton b.j.burton@btinternet.com Wokingham, Berkshire27 Cantley Crescent, Wokingham, RG41 1NUSearch for more papers by this author First published: 28 March 2011 https://doi.org/10.1002/wea.651Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume66, Issue4April 2011Pages 103-106 RelatedInformation

Biogeochemical implications of increased mineral particle concentrations in surface waters of the northwestern North Pacific during an Asian dust event

[1] Simultaneous observations were made in the marine atmospheric boundary layer and surface ocean during spring 2007 to investigate potential impacts of Asian dust on a semi-pelagic region of the northwestern North Pacific. The results suggest that mineral dust aerosols were scavenged by sea fog, and their deposition to the ocean increased the particle concentration in surface seawater. The atmospheric input of mineral dust to the ocean surface from this event was calculated to be 40 to 680 mg m−2 event−1. A general relationship for the solubility of iron from dust particles led to an estimate of 20 to 330 μg m−2 for the amount of bio-available iron delivered during the dust event. This input of bio-available iron is comparable to total dissolved iron added during an iron fertilization experiment in the northwestern North Pacific in which an enhancement of primary production was observed.

The Formation of a Surface Anticyclone over the Yellow and East China Seas in Spring

A surface anticyclone develops in April over the Yellow-East China Seas. The Yellow-East China Sea anticyclone (YESA) is confined in the marine atmospheric boundary layer but highly influential during the onset of sea fog season along the Chinese coast. This paper investigates the mechanism for YESA formation using atmospheric reanalysis, satellite observations and model experiments. Our analysis indicates that YESA is composed of three parts: (1) the westerlies to the north are the surface extension of the westerly wind jet; (2) the southerlies on the Chinese coast are due to the thermal wind between the warm continent and cool Yellow-East China Seas; (3) the northeasterlies to the south are due to the thermal wind between the cool East China Sea and warm Kuroshio Current. The regional atmospheric model successfully simulates the YESA under realistic boundary conditions. In an experiment where the Bohai-Yellow Seas are replaced with flat land, the surface anticyclone is pushed south and forms offshore along the new land-sea boundary, consistent with the thermal high mechanism over the cool sea surface temperature.

Comparison of advection and steam fogs: From direct observation over the sea

Sea fog occurs frequently over the Yellow Sea in spring and summer, which causes costly or even catastrophic events including property damage, marine accidents, public health and financial losses. Case studies of advection and steam fogs using direct observation over the sea are constructed to better understand their formation, evolution and dissipation. A southerly wind supplies moisture to initiate advection fog events (AFs). Approximately −100 to −200W m−2 of latent heat flux and −70W m−2 of sensible heat flux during mature AFs are characterized with stable stratification which maintains dense fog by limiting downward mixing of dryer air. Steam fogs (SFs) develop from flow of cold air over warmer water, but are normally of limited persistence. During the SFs, a northerly wind decreases the air temperature below the sea surface temperature, which increases the relative humidity through evaporation from the warmer ocean. During mature SF, 360W m−2 of latent heat flux and 150W m−2 of sensible heat flux are characterized with neutral and unstable atmospheric conditions. The increase in wind speed and wind shear mixes dry air downward to the surface and limits the duration of the SF.

Temporal and spatial characteristics of fog occurrence over the Korean Peninsula

In this study, fogs are classified based on the spatial and temporal characteristics over South Korea using the visibility data and the empirical orthogonal function (EOF) and wavelet analyses. With fog defined in terms of visibility (<1 km), the EOF analysis is performed to extract spatial distribution characteristics via dimension reduction, whereas the space‐time wavelet expansion is applied to the EOF time series to specify the fog characteristics in the space of time versus scale (i.e., period in this study). The first EOF mode occupies 48.9% of total variance and shows the fog distribution covering almost entire areas of South Korea with one sign (+), except at the eastern coast and western part of the southern coast. The wavelet analysis reveals that this fog occurs based on meteorological conditions of various scales from daily to seasonal, thus classified as mixed fog. The second EOF mode, which occupies 19.5% of total variance, shows distinct separation of spatial distribution of fog, with a negative (−) sign in winter over northwestern coastal/inland, western coastal, and south central mountain areas of South Korea and a positive (+) sign in other seasons elsewhere. With cycles of 1–2 weeks and 1–2 months being dominant in the wavelet analysis, this fog is considered to be strongly affected by synoptic scale weather systems and monsoon. Fog over the positive area is mostly affected by monsoon and/or cyclonic frontal systems, thus classified as frontal fog, whereas that over the negative area is affected by the cold‐core anticyclones moving over warm sea surface in winter or by radiative cooling, thus classified as steam fog (coastal/sea) or radiation fog (inland), respectively. The mountain area may have upslope fog because of orographic lifting. The third EOF mode, occupying 6.7% of total variance, depicts distinct spatial separation of fog distribution around the coastal areas with a negative (−) sign and in the inland areas with a positive (+) sign. The former, with a dominant 1–2 week cycle, is classified as sea fog affected by migratory anticyclones and monsoon in late spring and summer, while the latter, with a dominant diurnal variation, represents radiation fog under clear sky in autumn. It turns out that the combined EOF and wavelet analyses are useful to assess the detailed spatial and temporal characteristics of various types of fog occurrence in South Korea.

The characteristics of sea fog with different airflow over the Huanghai Sea in boreal spring

Using the observations from ICOADS datasets and contemporaneous NCEP/NCAR reanalysis datasets during 1960–2002, the study classifies the airflows in favor of sea fog over the Huanghai (Yellow) Sea in boreal spring (April–May) with the method of trajectory analysis, and analyzes the changes of proportions of warm and cold sea fogs along different paths of airflow. According to the heat balance equation, we investigate the relationships between the marine meteorological conditions and the proportion of warm and cold sea fog along different airflow paths. The major results are summarized as follows. (1) Sea fogs over the Huanghai Sea in spring are not only warm fog but also cold fog. The proportion of warm fog only accounts for 44% in April, while increases as high as 57% in May. (2) Four primary airflow paths leading to spring sea fog are identified. They are originated from the northwest, east, southeast and southwest of the Huanghai Sea, respectively. The occurrence ratios of the warm sea fog along the east and southeast airflow paths are high of 55% and 70%, while these along the southwest and northwest airflow paths are merely 17.9% and 50%. (3) The key physical processes governing the warm/cold sea fog are heat advection transport, longwave radiation cooling at fog top, solar shortwave warming and latent heat flux between airsea interfaces. (4) The characteristics of sea fog along the four airflow paths relate closely to the conditions of water vapor advection, and the vertical distribution of relative humidity.

Local meteorological and synoptic characteristics of fogs formed over Incheon international airport in the west coast of Korea

Fogs observed over Incheon international airport (IIA) in the west coast of Korea from January 2002 to August 2006 are classified into categories of coastal fog, cold sea fog, and warm sea fog based on the areal extent of the fogs and the difference between the air temperature (T) and the SST, i.e., cold sea fog if TSST = T−SST > 0°C and warm sea fog if TSST SST). Increases of Td are significant during the warm sea fog periods (1.4°C), implying that efficient moisture supply is essential to warm sea fog formation. Four major synoptic patterns are identified in association with the observed fogs. The most frequent is a north Pacific high that accounts for 38% of cases. Surface or upper inversions are present in 77%, 69%, and 81% of the fog periods for coastal, cold, and warm sea fogs, respectively.

An observational and modeling study of a sea fog event over the Yellow Sea on 1 August 2003

A dense sea fog episode that occurred near the coastal city of Qingdao in the Shandong Peninsula of China on 1 August 2003 is investigated by using all of the available observational data and high-resolution modeling results from the Regional Atmospheric Modeling System (RAMS). This fog event reduced the horizontal visibility to be less than 60 m in some locations and caused several traffic accidents locally. In this paper, all of the available observational data, including visible satellite imagery of Geostationary Operational Environmental Satellite (GOES)-9 and MODerate-resolution Imaging Spectroradiometer (MODIS), objectively reanalyzed Final Analysis (FNL) data issued by the National Centers for Environmental Prediction (NCEP), sounding data at the Qingdao and Dalian stations, and the latest 4.4 version of the RAMS model, were employed to study this sea fog case. We begin with the analyses of the environmental conditions of the sea fog event, including the large-scale conditions, the difference between T2m (air temperature at 2 m altitude) and sea surface temperature (SST), and the atmospheric sounding profiles of the two stations. The characteristics of this sea fog event was documented by using visible satellite imagery of GOES-9 and MODIS. In order to better understand the fog formation mechanism, a high-resolution RAMS model of dimensions 4 km × 4 km was designed, which was initialized and validated by FNL data. A 54-h modeling period that started from 18 UTC 31 July 2003 reproduced the main characteristics of this sea fog event. The simulated lower visibility area agreed well with the sea fog area identified from the satellite imagery. It is shown that advection cooling effect plays a significant role in the fog formation.

A Coupled Model Study on the Formation and Dissipation of Sea Fogs

Abstract This study examined the impact of air–sea coupling using a coupled atmosphere–ocean modeling system consisting of the Coupled Ocean–Atmosphere Mesoscale Prediction System as the atmospheric component and the Regional Ocean Modeling System as the oceanic component. Numerical experiments for advection and steam fog events were carried out to clarify the modulation of the formation and dissipation of sea fogs by the air–sea temperature difference (air temperature minus sea surface temperature) and the atmospheric stability. The coupled simulation showed that advection fog is obviously controlled by low-level atmospheric stability and downward latent heat flux with oceanic cooling through air–sea coupling. In particular, air–sea coupling stabilizes the low-level atmosphere at the dissipation stage, and then suppresses vertical mixing, which retards the dissipation of advection fog. In the case of a steam fog event, the upward turbulent heat fluxes are increased significantly from the formation time to the mature time. A decrease in sea surface temperature cools the low-level atmosphere, which increases the condensation rate and low-level atmospheric stability, eventually retarding the dissipation of steam fog.

Mechanisms of Temporary Improvement and Rapid Changes in Visibility in Fogs

Environmental situations associated with temporary improvement or rapid changes in visibility in the presence of fog were analyzed to understand the mechanisms of these changes in visibility at Rokkasho Village, Aomori Prefecture, northeast Japan. This region is frequently affected by sea fogs. The profiles of liquid water content and drop size distribution in fogs were obtained by a direct photographic method using a tethered hot-air balloon. On the basis of the results, the temporary improvement in visibility on July 10, 2006 was attributed to convection-driven downward transport of air parcels with lower total water content than air parcels near the ground surface. The rapid changes in visibility at the same location on July 24 seemed to be related to mixing by Kelvin-Helmholtz waves. Mixing with an upper layer containing less water initially caused an improvement in visibility but subsequently, it led to the formation of a dense fog just above the ground surface in an area of upward flow. Settlement of fog drops from the dense fog above degraded the visibility in this area.

Seasonal Variations of Yellow Sea Fog: Observations and Mechanisms*

Abstract Sea fog is frequently observed over the Yellow Sea, with an average of 50 fog days on the Chinese coast during April–July. 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. This study investigates the mechanisms for such steplike evolution that is inexplicable from the gradual change in solar radiation. 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. The land–sea contrast is the key to these changes. In April, the land warms up much faster than the ocean. The prevailing west-southwesterlies at 925 hPa advect warm continental air to form an inversion over the western Yellow Sea. 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 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 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 retreat of Yellow Sea fog is associated with a shift in the prevailing winds from southerly to easterly from July to August. 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. Back trajectories for foggy and fog-free air masses support the results from the climatological analysis.