Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Author's personal copy Atmospheric Research 98 (2010) 426–437 Contents lists available at ScienceDirect Atmospheric Research j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / a t m o s Comparison of advection and steam fogs: From direct observation over the sea Ki-Young Heo a, Kyung-Ja Ha a,⁎, Larry Mahrt b, Jae-Seol Shim c a b c Division of Earth Environmental System, College of Natural Science, Pusan National University, Busan, South Korea College of Oceanic and Atmospheric Science, Oregon State University Corvallis, Oregon, USA Coastal Disaster Prevention Research Division, Korea Ocean Research & Development Institute, Ansan, South Korea a r t i c l e i n f o Article history: Received 26 April 2010 Received in revised form 4 August 2010 Accepted 4 August 2010 Keywords: Sea fog Advection fog Steam fog a b s t r a c t 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 −200 W m−2 of latent heat flux and −70 W 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, 360 W m−2 of latent heat flux and 150 W 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. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Sea fog is defined as a phenomenon with horizontal visibility reduced by condensation to less than 1 km near the surface over the ocean (Roach, 1994). Sea fog causes transportation problems including automobile accidents, aircraft takeoff and landing problems, and marine accidents due to poor visibility. In addition, sea fog is one of the immediate causes of property damage, public health and financial losses (Forthun et al., 2006). Understanding the characteristics of sea fog is hence an important societal issue. Fog processes involve droplet microphysics, aerosol chemistry, radiation, turbulence, large/small-scale dynamics, and surface conditions (Gultepe et al., 2007). Often, sea fog consists of mesoscale (tens of kilometres) spatial structure ⁎ Corresponding author. Tel.: +82 51 5102177; fax: +82 51 5151689. E-mail address: [email protected] (K.-J. Ha). 0169-8095/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.atmosres.2010.08.004 and time scales of hours. It is difficult to predict the formation and dissipation of fog using numerical weather forecast models because of lack of vertical and horizontal resolution and lack of quantitative understanding of the physical processes as turbulent mixing, radiation divergence, and microphysics (Pagowski et al., 2004; van der Velde et al., 2010). In addition, model skill in forecasting sea fog strongly depends on the correct initialization of the atmospheric state (Rémy and Bergot, 2009) as well as the correct oceanic thermal conditions (Heo and Ha, 2010). Fog processes involve droplet microphysics, aerosol chemistry, radiation, turbulence, large/small-scale dynamics, and surface conditions (Gultepe et al., 2007). Atmospheric aerosol concentrations play an important role of fog formation under both undersaturated and slightly supersaturated conditions (Pruppacher and Klett, 1997). Previous studies showed the role of air quality in the fog formation. For instance, Vautard et al. (2009) showed the trends in mist and haze have been correlated to atmospheric aerosol trends. The Author's personal copy K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 427 Fig. 1. Location of Ieodo Ocean Research Station (IORS). Gray shading indicates bathymetry. The IORS is constructed on the underwater rock Ieodo in the East China Sea (125.18°E, 32.12°N). The contours represent bathymetries of −40 m, −100 m and −200 m. The bathymetry around the IORS is about −40 m. decline in air pollution was shown to be linked to the visibility increase: the temporal and spatial patterns of fog and mist declines are strongly correlated with emission reductions. Witiw and Baars (2003) presented that some evidence points to increasing air pollution as a possible reason for fog increase. In addition, van Oldenborgh and van Ulden (2003) showed that the decrease in the number of fog and mist days is spatially and temporally correlated with the decrease in SO2 emissions. They also showed that the correlations are also statistically significant for dense fog. In Korea, it has been reported that the occurrence of sea fog in the southwestern sea or the Yellow Sea is maximum in July, mainly due to air–sea temperature differences, as the result of warm air advection over a cold pool (Cho et al., 2000; Fu et al., 2006). This advection-type fog is generally considered to be a typical sea fog in the middle latitudes under stable conditions associated with cold sea surfaces (Klein and Hartmann, 1993). These dense, widespread, and long-duration fogs may begin to extend toward the coast with sufficient advection of warmer moist air (Croft et al., 1997). In contrast, steam fog in the Yellow Sea is associated with cold air advection. It tends to be observed in March and April and results from advection of cold dry air over a relatively warm ocean. In recent years, some costly or even catastrophic events in Korea have been caused by dense sea fog. For instance, the number of sea fog-related ship crashes is 193 Table 1 Meteorological instruments used in the study. Sensor Manufacturing company Model Observation elements Range Accuracy Wind monitor-MA RM YOUNG 05106 Temperature and humidity sensor VAISALA HMP45A Optical precipitation sensor 3D sonic anemometer VAISALA Campbell scientific, Inc. PWD-21 CSAT3 Wind direction Wind speed Temperature Humidity Visibility Wind (ux, uy) (uz) 360° 0—60 m s−1 −40–+ 60 °C 0.8–100% 10–20,000 m ± 30 m s−1 ±8 cm s−1 ± 2° ± 0.3 m s−1 ± 0.2 °C ± 2–±3% ± 10–± 15% b± 4 cm s−1 b±2 cm s−1 Author's personal copy 428 K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 during the period from 2004 to 2008, and over 50% of those occurred in the Yellow Sea. In addition, more than 20 flights were cancelled in every year at the Incheon Airport which is major airport in Korea located in the Yellow Sea. Fog formation is determined not only by the meteorological conditions, but also by the oceanic conditions through surface fluxes (He and Weisberg 2002, 2003; Virmani and Weisberg 2003). The previous studies have suggested that physical processes important for sea fog formation include the turbulent transfer of heat and moisture and the cooling of air masses that travel over colder waters. However, few studies on the physical mechanisms of the formation and evolution of sea fog have been conducted from direct observations over the open sea. The Ieodo Ocean Research Station (IORS) data, which is introduced in Section 2, has been especially useful in formulating the synopsis for fog formation at the ocean surface with measurements of sea temperature, wind, air temperature, humidity, turbulent heat and momentum flux as well as visibility. This study focuses on the comparison of physical mechanisms between advection and steam fogs over the Yellow Sea with the goal of better understanding the formation, evolution and dissipation of the fogs using direct observations of turbulent fluxes from IORS. In Section 2, a description of IORS and instruments is summarized. Each fog Fig. 2. Time evolution of wind speed (solid line), wind direction (wind barbs), humidity (dashed line), air temperature (dashed dot line), sea temperature (thick solid line) and fog (shaded area, visibility b 1 km) for advection fog event (a) during 60 h from 03 UTC 1 to 15 UTC 3 June 2005 and (b) during 36 h 00 UTC 11 to 12 UTC 12 May 2005. Author's personal copy K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 429 event is illustrated and discussed in Section 3. Finally, we present our conclusions for the physical explanation of the sea fog formation, evolution and dissipation. 2. Measurement 2.1. Measurement site The Ieodo Ocean Research Station (IORS), which was constructed by the Korean government in 2003 in order to observe the oceanic environment of East Asia, is an integrated meteorological and oceanographic observation site. It is constructed on the Ieodo underwater rock which is located in the East China Sea (32.12oN, 125.17oE) about 149 km to the southeast of Jeju Island (Fig. 1) while most ocean platforms are constructed near the coastal region for convenient management (Johansson et al., 2001). The structure is of a fixed jacket type installed at a depth of 40 m. The facility includes meteorological and oceanographic instruments. The IORS has provided the oceanic–atmospheric measurement for studying air–sea interaction due to the open-sea location. Studies conducted at IORS have investigated various timeseries of atmospheric components; analyzed meteorological flux data (Oh et al., 2010a,b); and validated remotely-sensed satellite data (Heo et al., 2008). 2.2. Instrumentation The instruments installed at IORS are as follows (Table 1); Wind monitor-MA (RM YOUNG) and HMP45A (Vaisala), which measure wind direction, wind speed, temperature and humidity at a height of 43 m above sea surface. A PWD-21 (Vaisala), installed at 33 m above sea surface, is used to observe visibility. The turbulent fluxes have been observed by an open path eddy covariance (OPEC) system composed of sonic anemometer (CSAT3, Campbell Scientific Inc., USA) and an open path infrared gas analyzer (IGRA: LI-7500, LiCor Inc., USA). The sonic anemometer is installed on the boom of the pillar under the deck at the heights of 16 m and 12 m from mean sea level. The installed direction of sonic anemometer was alternated between the northwestern (NW) and the southeastern (SE) according to season to measure prevailing wind. The recording speed of the fast-response data is 10 Hz. The characteristics of the sonic anemometer and the IRGA were well documented in previous experiments (Foken et al., 1997). The observations started 11 February 2004 and continue until present. Unfortunately, the moisture flux data became erratic after fog formation apparently due to condensation on the windows of the fast-response moisture sensor. Horizontal and vertical velocities, temperature and moisture fluctuations are recorded at a frequency of 10 Hz and covariances are averaged over 30 min time periods. In order to obtain the turbulent flux data from the IORS, Oh et al. (2010) investigated the effect of atmospheric and oceanic conditions on the errors in the fast-response data and evaluated different characteristics of tilt correction methods. They mentioned that the removal of the turbulent fluxes data generally depend on wind speed, relative humidity, significant wave height, visibility, and stability. According to this study, most of the turbulent flux data are removed under any foggy condition. To compare the turbulent fluxes between advec- Fig. 3. Specific humidity (q) and saturated specific humidity (qs, solid line) as functions of air temperature during (a) from 03 UTC 1 to 15 UTC 3 June 2005 and (b) from 00 UTC 11 to 12 UTC 12 May 2005 for advection fog events. tion and steam fogs, the general quality control methods could not be used. In general, the fluxes could be made less noisy by more averaging. The tendencies (time derivatives) could be made less noisy by computing over a 1 h period or even maybe a 3 h period. However, we could not combine into one or several hour period due to the short duration of fogs except for the first advection fog case. The meteorological data except for turbulent fluxes measured every 10 mins are collected to analyze the variation of ambient conditions associated with foggy conditions. 3. Result and discussion 3.1. Fog cases The occurrence of sea fog over the Yellow Sea tends to increase in frequency from April to July, and in August it rapidly Author's personal copy 430 K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 Author's personal copy K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 decreases (Cho et al., 2000; Zhang et al., 2009). The Yellow Sea is a favored place for sea fog because of its relatively cold water and location adjacent to the warm Kuroshio Current (Gao et al., 2007; Lewis et al., 2004). The seasonal increase of frequency of advection fogs over the Yellow Sea from June to July arises primarily from strong warm air advection over the cooler water, which is mainly due to the persistent southerly flow. Gao et al. (2007) emphasized the importance of southerly winds for the formation of advection fogs. The IORS data capture a persistent period of advection fog from 1 to 3 June 2005 (AF1) and on 11 May 2005 (AF2). We also examine steam fog cases on 6 April 2004 (SF1) and on 28 February 2006 (SF2) which appear to be due to a decrease in air temperature following an abrupt change in wind direction, wind speed and relative humidity. Unfortunately, we have only the sea temperature at 10 m depth and cannot estimate the exact air–sea surface temperature difference. In the case of SF2, the data of turbulent fluxes cannot be analyzed due to many errors and missing values. 3.2. Advection fog Fig. 2(a) shows the time evolution of wind direction, wind speed, relative humidity, air temperature, sea temperature (10-m depth) and visibility during the advection fog event from 1600 UTC 1 June to 0230 UTC 3 June 2005. Cooling of the air temperature caused by the cooler water, moisture advection and evaporation from the ocean increases the relative humidity. The air temperature decreases due to cooling of moist air by radiative flux divergence, cooling due to turbulent flux divergence, and cold air advection (Ha and Mahrt, 2003). While the air temperature decreases only slightly with time at a fixed point, stronger cooling occurs in a Lagrangian framework following the flow. The downward heat flux prior to fog formation is approximately 20 W m−2. The southerly wind speed decreases from 15 m s−1 to less than 5 m s−1 at the fog onset time. When the wind speed increases slightly and the wind direction changes from south to north, the supply of water vapor by advection becomes insufficient to maintain the fog. To identify the cause of the increase in relative humidity, Fig. 3 shows the variation of specific humidity (q) and air temperature (Ta) before, during and after the fog events. Before the advection fog events, the values of Ta and q are increasing towards saturation due to advection of warm and moist air while those are located under a saturation line. When saturation is almost reached during the advection fogs, more liquid water is being produced while Ta and q change with the saturation line and the fog is intensifying. The Ta and q are temporally decreased during the fog. These temporal decreases appear to parallel with saturation line. After the AF1, the liquid water is decreasing with increasing Ta and fixed q due to a change in wind direction which results in the restriction on the moisture supply. After the AF2, the liquid water is being maintained with stationary state Ta and q. The dissipation of the fog is related to the 431 decrease in the air–sea temperature difference in this case (shown in Fig. 2b). To recognize the variation of surface fluxes and their relation to the evolution of advection fog, the observed data of turbulent fluxes are analyzed before, during, and after the weather event. In the case of AF1 shown in Fig. 4, an important feature of the turbulent heat fluxes is a fluctuation from positive to negative latent and sensible heat fluxes prior to the advection fog formation, which is apparently due to condensation in the stable surface layer and evaporation from the ocean in the neutral surface layer. The negative latent heat fluxes ranging from −200 W m−2 to 0 W m−2 are maintained during the fog event (Figs. 4a and b), which suggests that southerly wind supplies moisture to initiate and maintain the fog event, and atmospheric cooling contributes to condensation shown in Fig. 3(a). The negative sensible heat fluxes ranging from 0 to −60 W m−2, which imply turbulent transport of sensible heat from atmosphere to ocean, initiate and maintain cooling and condensation before and during the advection fog with stable stratification (Figs. 4c and d). Upward fluxes of fog droplets occur when the sensible heat flux is strongly negative. The fog begins to dissipate when latent and sensible heat fluxes converge to near zero and atmospheric stability tends to be neutral conditions. An effect of turbulence for vertical momentum flux was examined by friction velocity (u*) calculated with perturbation of u, v, w. Stable stratification develops from cooling of the lower air, and then, the sensible heat flux is downward from atmosphere to ocean and the evaporated water is confined to a thin layer. The dense fog occurs during the stable and neutral stratification which limits downward mixing of dryer air. Therefore, the advection fog is characterized by longduration, which lasts for more than 30 h in this case. Advection fog can be persistent since the synoptic situation, which originally created this fog, does not change very fast. Advection fog will be dissipated through the passage of a front, a change of air mass, increasing wind speed and change in wind direction. In this case, the fog is dissipated through an increasing wind speed. Fig. 5 shows the variation of surface fluxes and their relation to the evolution of AF2, with different behavioral patterns compared to AF1. Prior to the fog formation, there are few changes in the latent heat flux despite of the steadily increasing Ta and q (Fig. 3b) by the southerly wind. The rapid decrease in Ta just before the fog formation shown in Figs. 2(b) and 3(b) saturates the lower atmosphere and consequently rapidly decreases the latent heat flux from 0 to −90 W m−2. The negative sensible heat flux ranging from 0 to −70 W m−2 during the fog is in the stable and neutral atmospheric conditions, which induces the upward fluxes of fog droplets. Sensible and latent heat fluxes modified by the air–sea interaction determine the evolution of the advection fogs together with the modification of the low-level atmospheric stability. The relatively short duration in the AF2 resulted from the strong turbulence caused by sudden change in wind direction. Fig. 4. Latent heat flux (W m−2) as a function of (a) wind speed and (b) specific humidity (q, g/kg). Sensible heat flux (W m−2) as a function of (c) wind speed and (d) z/L. (e) friction velocity (m s−1) as a function of wind speed. Filled diamonds, circles and filled triangles are indicated before, during, and after advection fog event from 03 UTC 1 to 15 UTC 3 June 2005. Author's personal copy 432 K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 Fig. 5. Same as Fig. 4 except for advection fog event from 00 UTC 11 to 12 UTC 12 May 2005. Author's personal copy K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 433 Fig. 6. Time evolution of wind speed (solid line, m s−1) and friction velocity (dashed line, m s−1) (a) during 60 h from 03 UTC 1 to 15 UTC 3 June 2005 (AF1) and (b) during 36 h 00 UTC 11 to 12 UTC 12 May 2005 (AF2). Fig. 6 shows the time evolution of wind speed and u* during the advection fog events. A near collapse of turbulence and downward momentum flux results from a decrease of wind speed just prior to the fog onset. The termination of the fog is associated with increasing wind speed and increasing downward momentum flux, which corresponds to a negative latent heat flux that does not exceed −100 W m−2. The u* before the advection fogs behave apparently different from that during and after the fogs. Stable atmospheric conditions before the advection fogs lead to the weak u*. The time evolutions of u* show that the momentum flux does not govern the dissipation of advection fogs. The wind speed seems to be modulated by mesoscale motions with a period a few hours, which also appears in the vertical motion field. Under a weak large-scale flow, mesoscale motions lead to a meandering of the wind direction, and the generation of turbulence by unresolved mesoscale motions becomes important (Mahrt, 2007). Such mesoscale motions appear to determine the exact time of onset and dissipation of fog. 3.3. Steam fog Steam fog develops from flow of cold air over warmer water, but is normally of limited spatial extent. The warmer water generates turbulence, mixing, and significant upward heat flux. Moisture mixes upward where the air saturates, condenses, and forms fog (Lundquist and Bourcy, 2000). Fig. 7 depicts the time evolution of wind direction, wind speed, relative humidity, air temperature, sea temperature and visibility during the steam fog events. When compared to advection fog, the steam fogs are characterized by stronger wind speed and shorter duration. Prior to formation of the fogs, southerly flow leads to a slight increase of air temperature. A sudden change in wind direction from south to north is observed at the time of the fog formation. The northerly wind decreases the air temperature to values 9 °C and 7 °C in SF1 and SF2, respectively, below the 10-m sea temperature, which increases the relative humidity of the air up to 95% due to evaporation from the warmer ocean. Author's personal copy 434 K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 Fig. 7. Same as Fig. 2 except for steam fog event (a) during 48 h from 00 UTC 6 to 12 UTC 7 April 2004 and (b) during 36 h from 00 UTC 28 to 12 UTC 29 February 2006, respectively. In the case of steam fog events, the increase in q (SF1) and the decrease in Ta (SF2) are observed at the time of steam fog formation as a result of evaporation from the sea (Fig. 8a and b). Prior to the formation of the steam fogs, high Ta and low q conditions are maintained in the atmosphere, and Ta and q are gradually close to saturation. The increase in q is dominant at the time of steam fog formation in SF1 and SF2, and the variation of Ta and q are decreasing on the saturation line. The decrease in Ta and the evaporation from the ocean are persisted for hours, which continues to produce the liquid water. In spite of the decrease in Ta, the fog is dissipated by the decrease in q due to reduction of evaporation. Fig. 9 shows the scatter diagram of the surface fluxes, which is the same as Fig. 4, but for the steam fog case (SF1). Because steam fog is formed by the advection of cold air over warmer water, unstable stratification develops due to surface heating. Prior to the fog formation, the change from stable to unstable stratifications contributes to evaporation (Fig. 9b and d), and decreasing wind speed suppresses upward momentum flux (Fig. 9e). And then, there is oscillation between positive and negative sensible heat flux (Fig. 9c). The negative latent heat flux before the steam fog indicates that the moisture accompanied by southerly winds begins to saturate. During this period, the sensible heat flux is main form of energy transfer from the ocean because there is negative latent heat flux. During the fog event, latent heat flux increases with the decrease in q, which moistens a fog layer. The positive latent heat flux ranging from 70 to 360 W m−2 Author's personal copy K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 435 wind shear. The fog is dissipated by the increasing in wind speed and wind shear in spite of the large air–sea temperature difference, in which case increased downward mixing of dryer air eliminates the fog. 4. Discussion and conclusion Fig. 8. Same as Fig. 3 except for steam fog events, (a) 00 UTC 6 to 12 UTC 7 April 2004 and (b) 00 UTC 28 to 12 UTC 29 February 2006. shows that evaporation and fog droplets are increased with sharp variation of air temperature shown in Fig. 7(a). The sensible heat flux oscillates between −200 W m−2 and 150 W m−2 while the atmospheric stability changes unstable to stable conditions. The dissipation of steam fog starts when the wind increases while the surface heat and momentum fluxes decrease. During the fog event, the wind speed gradually increases and the persistent northerly wind maintains lower air temperature. During the steam fog event, the wind speed temporarily decreases, but the momentum flux increases due to buoyancy generation of turbulence (Fig. 10). This mixing apparently restricts steam fog through convective mixing of dry air downward to the surface. Although atmospheric conditions maintain a constant air–sea temperature difference and Ta after the steam fog, the decrease in q shown in Fig. 8a seems to be caused by the increase in wind speed and Advection and steam fogs are frequently observed in the Yellow Sea from March to July. Meteorological data and ocean data obtained from the Ieodo Ocean Research Station (IORS), which is located in East China Sea, have been used to study the mechanisms of advection and steam fogs over the ocean. The results of air–sea coupling indicate that the mechanisms of the formation, evolution and dissipation are different for advection and steam fogs. The transport of warm moist air by southerly flow over the cooler ocean surface forms stable stratification. The negative latent heat fluxes ranging from −200 W m−2 to 0 W m−2 are maintained during the fog event when the air cools below its dew point. Weakening winds and collapsing turbulence seem to contribute to the onset of advection fog events. The negative sensible heat fluxes ranging from 0 to −70 W m−2 induce the upward fluxes of fog droplets in the stable and neutral atmospheric conditions. Turbulent heat fluxes modified by the air–sea interaction determine the evolution of the advection fogs together with the modification of the low-level atmospheric stability that confines the water vapor to a thin layer before and during the fog events. The increasing stable stratification limits downward mixing of dryer air and produces a dense and long-duration advection fog in defect of turbulence. Steam fog develops from cold air advection over a warmer ocean surface, but is normally of limited spatial extent. Steam fog occurs as warm air is replaced by cold air due to a rapid change in the wind direction from north to south, leading to a negative air–sea temperature difference. Before the change in the wind direction, relative humidity increases due to advection or/and evaporation. The positive latent heat flux as much as 360 W m−2 implies that evaporation and fog droplets are increased with sharp decrease in air temperature. And then, the sensible heat flux oscillates between −200 W m−2 and 150 W m−2 while the atmospheric stability changes unstable to stable conditions. The increase in wind speed and wind shear, and consequent downward transport of dryer air lead to dissipation of the steam fog in spite of the large air–sea temperature difference. Acknowledgments This work was supported by grant of the “Eco-Technopia 21 Project” by the Korean Ministry of Environment and Korean Ocean Research & Development Institute as "Construction of ocean research stations and their application studies". Larry Mahrt was partly supported by Grant N000140810409 from the U.S. Office of Naval Research. This work was also supported by the second stage of the Brain Korea 21 Project. The authors are very grateful to reviewers for their constructive criticism and helpful discussions. Author's personal copy 436 K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 Fig. 9. Same as Fig. 4 except for steam fog event from 00 UTC 6 to 12 UTC 7 April 2004. Author's personal copy K.-Y. Heo et al. / Atmospheric Research 98 (2010) 426–437 437 Fig. 10. Time evolution of wind speed (solid line, m s−1) and friction velocity (dashed line, m s−1) during 48 h from 00 UTC 6 to 12 UTC 7 April 2004 (SF1). References Cho, Y.K., Kim, M.O., Kim, B.C., 2000. Sea fog around the Korean Peninsula. J. Appl. Meteorol. 39, 2473–2479. Croft, P.J., Pfost, R.L., Medlin, J.M., Johnson, G.A., 1997. Fog forecasting for the southern region: a conceptual model approach. Weather and Forecasting 12, 545–566. Foken, T., Weisensee, U., Krizel, H.-J., Thierman, V., 1997. Comparison of new type sonic anemometers. 12th Symposium on Boundary Layer and Turbulence. American Meteorological Society, pp. 356–357. Forthun, G.M., Johnson, M.B., Schmitz, W.G., Blume, J., Caldwell, R.J., 2006. Trends in fog frequency and duration in the southeast United States. Phys. Geogr. 27, 206–222. Fu, G., Guo, J., Xie, S.-P., Duan, Y., Zhang, M., 2006. Analysis and highresolution modeling of a dense sea fog event over the Yellow Sea. Atmos. Res. 81, 293–303. Gao, S., Lin, H., Shen, B., Fu, G., 2007. A heavy sea fog event over the Yellow Sea in March 2005: analysis and numerical modelling. Adv. Atmos. Sci. 24, 65–81. Gultepe, I., Tardif, R., Michaelides, S.C., Cermak, J., Bott, A., Bendix, J., Müller, M.D., Pagowski, M., Hansen, B., Ellrod, G., Jacobs, W., Toth, G., Cober, S.G., 2007. Fog research: a review of past achievements and future perspectives. Pure Appl. Geophys. 164, 1121–1159. Ha, K.-J., Mahrt, L., 2003. Radiative and turbulent fluxes in the nocturnal boundary layer. Tellus 55A, 317–327. He, R., Weisberg, R.H., 2002. West Florida shelf circulation and temperature budget for the 1999 spring transition. Cont. Shelf Res. 22, 719–748. He, R., Weisberg, R.H., 2003. West Florida shelf circulation and temperature budget for the 1998 fall transition. Cont. Shelf Res. 23, 777–800. Heo, K.-Y., Ha, K.-J., 2010. A coupled model study on formation and dissipation of sea fogs. Monthly Weather Review 138, 1186–1205. Heo, K.-Y., Kim, J.-H., Shim, J.-S., Ha, K.-J., Suh, A.-S., Oh, H.-M., Min, S.-Y., 2008. A remote sensed data combined method for sea fog detection. Korean Journal of Remote Sensing 24, 1–16 (in Korean with English abstract). Johansson, C., Smedman, A.-S., Hogstrom, U., Brasseur, J.G., Khanna, S., 2001. Critical test of the validity of Monin–Obukhov similarity during convective conditions. J. Atmos. Sci. 58, 1549–1566. Klein, S.A., Hartmann, D.L., 1993. The seasonal cycle of low stratiform cloud. J. Climate 6, 1587–1606. Lewis, J.M., Koračin, D., Redmond, K.T., 2004. Sea fog research in the United Kingdom and United States. Bull. Am. Meteorol. Soc. 85, 395–408. Lundquist, J.D., Bourcy, T.B., 2000. California and Oregon humidity and coastal fog. Proceedings, 14th Conference on Boundary Layers and Turbulence. Aspen, Colorado. Mahrt, L., 2007. Weak-wind mesoscale meandering in the nocturnal boundary layer. Bound-Layer Meteor. 7, 331–347. Oh, H.-M., Ha, K.-J., Heo, K.-Y., Kim, K.-E., Park, S.-J., Shim, J.-S., Mahrt, L., 2010a. On Drag Coefficient Parameterization with Post Processed Direct Fluxes Measurements over the Ocean. Asia-Pacific Journal of Atmospheric Sciences, under review. Oh, H.-M., Kim, K.-E., Ha, K.-J., Mahrt, L., Shim, J.-S., 2010b. Quality control and tilt correction effects on the turbulent fluxes observed at an ocean platform. Journal of Applied Meteorology and Climatology, under review. Pagowski, M., Gultepe, I., King, P., 2004. Analysis and modeling of an extremely dense fog event in southern Ontario. J. Appl. Meteorol. 43, 3–16. Pruppacher, H.R., Klett, J.D., 1997. Microphysics of Clouds and Precipitation. Kluwer Acdemic Publishers, Norwell. Rémy, S., Bergot, T., 2009. Assessing the impact of observations on a local numerical fog prediction system. Q. J. R. Meteorol. Soc. 135, 1248–1265. Roach, W.T., 1994. Back to basics: Fog: Part 1 — Definitions and basic physics. Weather 49, 411–415. van der Velde, I.R., Steeneveld, G.J., Wichers Schreur, B.G.J., Holtslag, A.A.M., 2010. Modeling and forecasting the onset and duration of severe radiation fog under frost conditions. Monthly Weather Review. doi:10.1175/2010MWR3427.1. van Oldenborgh, G.J., van Ulden, A.P., 2003. On the relationship between global warming, local warming in the Netherlands and changes in circulation in the 20th century. Int. J. Climatol. 23, 1711–1724. Vautard, R., Yiou, P., van Oldenborgh, G.J., 2009. Decline of fog, mist and haze in Europe over the past 30 years. Nat. Geosci. 2. doi:10.1038/ngeo414. Virmani, J.I., Weisberg, R.H., 2003. Features of the observed annual ocean– atmosphere flux variability on the West Florida shelf. J. Climate 16, 734–745. Witiw, M.R., Baars, J.A., 2003. Long term climatological changes in fog intensity and coverage. Proceedings of the AMS 14th Symposium on Global Change and Climate Variations, Long Beach, CA. Zhang, S.-P., Xie, S.-P., Liu, Q.-Y., Yang, Y.-Q., Wang, X.-G., Ren, Z.-P., 2009. Seasonal variations of Yellow Sea fog: observations and mechanisms. J. Climate 22, 6758–6772.