Linking Marine Fog Variability in Atlantic Canada to Changes in Large-Scale Atmospheric and Marine Features

The sea surface temperature (SST) front in the North Pacific (NP) has a potential to modulate the atmospheric boundary layer and cloud properties within it. We investigated the impact of the SST gradient along with the Oyashio Extension on low‐level cloud properties during summertime based on a Weather Research and Forecasting (WRF) numerical simulation. To reveal the SST gradient impact, we conducted two experiments with different boundary conditions from July to August for 3 years from 2014 to 2016: the first with 0.25° daily SST data (CTL experiment) and the second with spatially smoothed SST without SST frontal characteristics (SMO experiment). The period mean cloud water mixing ratio of marine fog on the northern flank of the front in the CTL experiment was larger than that in the SMO experiment by about 20% of the mean value. The SST front affected not only the mean state but also the synoptic variability of the marine fog, and the magnitude of the effects depended on the meridional wind across the SST front. We found two competing physical processes modulating the marine fog on the northern flank. First, a local cold SST anomaly reduced the saturated water vapor pressure near the surface, which is favorable for fog formation (SST anomaly effect). Second, warm temperature advection from southern to northern flanks suppressed the fog formation, and the suppression was effective when the horizontal gradient of SST anomaly was large (SST frontal effect). Our results indicated the importance of the SST gradient in summertime Oyashio Extension for the marine fog formation.

In this study, the changes in the occurrence of marine fog over the summer North Pacific in warmer sea surface temperature (SST) or increased CO2 climates were investigated based on atmospheric model simulations by using the fifth phase of the Climate Model Intercomparison Project (CMIP5) multimodel data. Initially, the marine fog representation in CMIP5 multimodels was briefly evaluated globally. We found that the simulated marine fog occurrence was represented relatively well in boreal summer but poorly in other seasons. The results indicated that the changes in the North Pacific high‐pressure system accompanied by changes in horizontal wind patterns control the changes in marine fog occurrence in the North Pacific. The magnitude of contrasting pair changes in marine fog occurrence in the western and eastern North Pacific are primarily determined by the magnitude of changes in the North Pacific high‐pressure system. Global‐scale changes in the vertical profiles of the atmosphere (stability changes) can also affect the marine fog changes. These changes in marine fog over the North Pacific were consistent among most CMIP5 models.

In this paper, we propose a new method of numerical differentiation to determine the height of the top layer of the atmospheric boundary layer. In this method, a regularization technique is used to convert the problem of calculating the differential of the curve of the corners into the problem of finding the minimum value of the objective function. The two-parameter model function method is used to select the regularization parameters. Finally, the maximum gradient method is used to determine the top height of the boundary layer. Firstly, the effectiveness of the new method is validated through two numerical experiments. The experimental results show that as the noise of the occultation data increases, the fluctuation of the height of the boundary layer top obtained by the difference method and the numerical differentiation method combined with the L curve scheme increases. And the height obtained by the two-parameter model function method is very stable, which shows that the new method can filter the noise well, thereby retaining the main information about the profile. Then, based on the COSMIC angle data in January, April, July and October 2007－2011, the new method is used to analyze the seasonal characteristics of the height of the global oceanic and atmospheric boundary layer, compared with the seasonal distribution obtained by “zbalmax” with the occultation data. The results show that the seasonal distribution characteristics of the two data are very consistent: the height of the boundary layer is higher in the area where the sea surface temperature is higher than that in the surrounding sea area; on the contrary, the height of the boundary layer top is lower. In the sea area where the warm current passes, the height of the boundary layer is higher; in the sea area where the cold current passes, the height of the boundary layer is lower.

This study focuses on the physical processes in marine fog and its impact on optical attenuation using measurements from Sable Island during the 2022 FATIMA Grand Banks field campaign. The analyses used the water‐droplet size distribution from a fog monitor (FM‐120) and the meteorological optical range (MOR) measured by a present weather sensor (PWD22) as primary data sources, augmented by frequent radiosonde launches collocated with other FATIMA instruments. Analyses of the frequent radiosonde launches revealed the presence of fog associated with frequent frontal passages throughout the intensive measurement period. Based on the 35 days of microphysics measurements, we also identified and analyzed nine reduced visibility events (RVEs) when the mean MOR was less than 1 km. Furthermore, the data were categorized based on the weather code to characterize the observed hydrometeor further into clear, mist, fog, and precipitation categories. This study shows evidence of persistent stable thermal stratification in the fog layer, often accompanied with low‐level jets in or above the fog layer. The droplet spectra in fog indicated a bimodal distribution below the droplet size of 50 m. Our results also show a consistent power‐law relationship between visibility and fog liquid water content for pure marine advection fog events, which are different from coastal fog, only. In particular, a power‐law fit seems to resemble closely the theoretical relationship given by previous studies of the marine fog.

Fog constitutes a thick, opaque blanket of air hugging Earth’s surface, laden with small water droplets or ice crystals. Fog disrupts transportation, poses security threats, disorients human perception, and impacts communications and ecosystems. Collusion of atmospheric, terrestrial, and hydrologic processes produces fog droplets that pullulate over hygroscopic aerosols that act as condensation nuclei. Marine fog is particularly complex, since underlying dynamic, thermodynamic, and (bio)physicochemical processes span fifteen decades of spatial scales, from megameter-sized synoptic weather systems to nanometer-scale bioaerosols. This paper overviews the first international field campaign [Fog and Turbulence Interactions in the Marine Atmosphere-Grand Banks campaign (Fatima-GB)] of the project dubbed Fatima conducted during 1–31 July 2022 in the Grand Banks region of the North Atlantic. Therein, weather systems and commingling cold and warm oceanic waters provide entrée for fog genesis. Measurement platforms included an islet southwest of Nova Scotia (Sable Island), a research vessel (Atlantic Condor), an offshore oil platform, and autonomous surface vehicles. The instrument array comprised of extant remote and in situ sensors augmented by novel sensing systems prototyped and deployed in marine fog to penetrate the smallest scales of turbulence, examine aerosols, and quantify radiation budget. The comprehensive dataset so gathered, together with satellite and reanalysis products, mesoscale model, and large-eddy simulations, demonstrated that the long-held hypotheses of marine fog formation by warm air advection over colder water and in areas of enhanced (shelf) turbulence need to be revisited. The study also elicited new phenomena, for example, the fog shadow (clearings of fog downstream of islands).

Observations show that the northeast Pacific (NEP) is a fog-prone area in winter compared with the northwest and central Pacific where fog rarely occurs in winter. By synthesizing observations and reanalysis results from 1979 to 2019, this study investigates the atmospheric circulation and marine atmospheric boundary layer structure associated with marine fog over the NEP in winter. Composite analysis shows that the eastern flank of the Aleutian low and the northwestern flank of the Pacific subtropical high jointly contribute to a northward air flow over the NEP. Under such conditions, warm and moist air flows through a cooler sea surface and facilitates the formation of advection-cooling fog. The air near the sea surface in foggy areas is cooled by the downward sensible heat flux. The smaller upward latent heat flux (∼10 W m−2) compared to the surrounding area (>60 W m−2) demonstrates that the moisture originates from the advection instead of local evaporation. The lower (at 925 to 875 hPa) and stronger (up to 0.08 K hPa−1) inversion layer, compared with cloudy cases and the turbulence in the lower atmosphere (below 975 hPa), also promotes fog formation and evolution. Approximately 68% of all fog cases (42242) show positive differences between surface air temperature (SAT) and sea surface temperature (SST), while 32% are negative, during southerly winds. Composite analysis of the latter shows lower specific humidity above the inversion bottom compared to the former. Dry air enhances longwave radiative cooling from the fog top, favoring cooling of the fog layer, gradually causing SAT to fall below SST.

The present study investigates reasons of interdecadal changes in the relationship between the western North Pacific (WNP) tropical cyclone (TC) genesis and tropical Indian Ocean (TIO) and tropical North Atlantic Ocean (TNA) sea surface temperature (SST) in early‐1990s. It is found that the above interdecadal changes are related to changes in the coherence of TIO and TNA SST variations with equatorial central‐eastern Pacific Ocean (EPO) SST variations. During 1970s through mid‐1980s, TIO and TNA SSTs tend to vary in phase with EPO SST on both interannual and interdecadal time scales. The combined effects of TIO and EPO SST anomalies induce opposite environment and TC changes in southeastern and northwestern WNP, leading to a weak correlation of basin‐wide WNP TC and TIO SST. Similarly, TNA and EPO SST anomalies induce opposite environment and TC changes in northeastern and southeastern WNP and thus basin‐wide WNP TC‐TNA SST correlation is weak. During late 1990s through early 2000s, TIO and EPO SST variations have a weak coherence due to their opposite relations on interannual and interdecadal time scales. TIO SST anomalies alone induce anomalous circulation over most WNP so that basin‐wide WNP TC‐TIO SST relationship is strong. The interannual and interdecadal SST variations remain coherent in TNA and EPO but with a switch of sign in their relationship in early 1990s. TNA and EPO SST anomalies induce same environment and TC changes in northeastern and southeastern WNP, and thus, basin‐wide WNP TC‐TNA SST relationship is strong. Numerical model experiments validate the importance of coherent regional SST anomalies.

In Quebec, the Atlantic Provinces, and adjacent offshore areas almost all systems are represented. Gas and/or oil shows have been reported from Ordovician, Devonian, Carboniferous, late Mesozoic, and Tertiary rocks. The only commercial production of oil and gas is from a fluviolacustrine sequence in the lower Carboniferous near Moncton, New Brunswick. In recent years the search for petroleum has expanded to include the Gulf of St. Lawrence, most of the continental shelf, and part of the slope. Offshore geophysical surveys indicate sedimentary thicknesses of 20,000 ft on the outer Labrador shelf, 24,000 ft in the Gulf of St. Lawrence, 20,000 ft on the Scotian shelf, and 18,000 ft on the Grand Banks of Newfoundland. On the Scotian shelf, shallow drillholes, grab samples, and a 15,106-ft well indicate the presence of Quaternary, Tertiary, and Cretaceous sedimentary strata. On Grand Banks, two holes penetrated Tertiary and Cretaceous strata. One well was abandoned in salt at 4,834 ft and the other at 5,250 ft in siltstone. From 1963 to 1969 the petroleum industry has conducted more than 150 crew-months of geologic and geophysical offshore exploration in Eastern Canada.

Changes in marine fog in a warmer climate are investigated through simulations using the atmospheric component of a global climate model, with both observed and perturbed sea surface temperature forcing. Global changes in marine fog occurrence in different seasons are compared. We show that the changes in marine fog occurrence correspond well to changes in horizontal temperature advection near the surface in a warmer climate. Therefore, the changes in marine fog can be well explained by large‐scale circulation changes. Regarding changes in the characteristics of marine fog, we show that the in‐cloud liquid water content of marine fog is consistently increased in a warmer climate, for a given horizontal surface temperature advection. It is also confirmed that the contribution of changes in marine fog to cloud feedback is not negligible, but is small.

The possible influence of Atlantic sea surface temperature (SST) on winter haze days in China at interannual and decadal time scales is investigated using the observed haze-day data from 329 meteorological stations, National Centers for Environmental Prediction-National Centers for Atmospheric Research (NCEP-NCAR) reanalysis, and a SST dataset for 1978–2012. Wintertime haze days in China show robust interannual variations and significant increases over time. The SST anomalies over the North Atlantic from summer to the following winter exhibit a significant in-phase relationship with winter haze days on both decadal and interannual time scales, whereas the anomalous negative-positive SSTs from north to south over the South Atlantic from autumn to the following winter show a significant positive relationship with winter haze days on the interannual time scale. The anomalous warm SST over the North Atlantic, i.e., the positive phase of the Atlantic multidecadal oscillation (AMO), corresponds to the positive phase of the Arctic oscillation (AO). This result implies that a stable mean flow and strong westerly anomalies exist over north China. The anomalous dipole pattern in the South Atlantic results in the abnormal southerly airflow in the troposphere over eastern China. Neither the westerly anomalies over north China nor the southerly anomalies over eastern China, which are associated with the North Atlantic and South Atlantic SST anomalies, respectively, are conducive to occurrences of cold air. Consequently, the weakened cold airflow from north of eastern China suppresses the dispersion of pollutants over China and results in above-normal haze days.

Rapid formation of a deep layer of fog and clouds extending to a height of 2 km was observed over Sable Island off Nova Scotia on 13–14 July 2019. This fog and cloud event was dominantly caused by the rapid intrusion of a trough from a cyclone over NE Canada. The trough quickly moved from SW–W to E–NE and encroached on the coastal waters of Nova Scotia. Due to the warm front in the trough, the air temperature increased up to 4 km in height with increased stability, while the sea‐level pressure at Sable Island dropped by 11 hPa within 12 hours. The moderate to strong winds turned counterclockwise from the N to the SE, converging with the SE winds maintained by the ridge located to the east. There was no indication of an advection‐type fog mechanism because the surface air temperature was not adjusted to the colder sea‐surface temperature that could have resulted in saturation of the surface air. The leading portion of a massive cloud band in the trough passing over Sable Island included precipitation before fog formation. The rain that evaporated in the unsaturated and warm subcloud layer effectively reduced the air temperature and significantly increased the wet‐bulb temperature in this layer. The cloud extended into the moist subcloud layer, while fog formed at 1400 UTC 13 July and lasted until 2327 UTC 13 July (with two brief periods of mist lasting less than two hours). The development of this deep layer of fog and cloud in the NW Atlantic was caused by evolving synoptic conditions through the simultaneous effects of a rapid trough intrusion over coastal waters with a massive cloud band, induced precipitation causing cloud deepening into the subcloud layer, and surface wind convergence forcing vertical mixing in a stable marine boundary layer.

Marine fog impacts human health, naval strategy, and biological productivity. Despite its importance, the skill of operational and global environmental models in forecasting marine fog and its optical properties remain limited due to our incomplete understanding of the physical processes that drive fog, particularly over its broad range of temporal and spatial scales. In this work, we present findings from a 71‐year climatological analysis covering a broad range of spatial and temporal scales of marine fog over Atlantic Canada and the Grand Banks of Newfoundland, Canada. Using International Comprehensive Ocean and Atmospheric Dataset observations from 1950 to 2020, European Centre for Medium‐range Weather Forecasts Reanalysis v5 products, and satellite imagery, we discuss fog formation in this region. Spatially, the Atlantic Canada continental shelf induces submesoscale ocean features along its rapid variation in bathymetry, which influence fog formation. Sharp sea‐surface temperature (SST) gradients and air–sea temperature differences coincide with the over‐the‐shelf fog maxima in summer (June, July, and August). The air–sea temperature differences show a clear signal that fog occurrence is higher with negative air–sea temperature differences (SST minus air temperature). This higher occurrence of fog is mainly isolated on the continental shelf, where colder SST typically exists. Satellite imagery of a fog event during the 2022 Fog and Turbulence Interactions in the Marine Atmosphere Multidisciplinary University Research Initiative campaign, funded by the Office of Naval Research, highlights the complicated interplay of shelf break dynamics and near‐surface atmospheric conditions. A fog bank is shown to form in the colder water regions over the shelf, outlining the shelf break and pointing to boundary‐layer and smaller‐scale processes that are driving fog formation. These observations are crucial in characterizing the spatial and temporal structure of the fog life cycle and provide a better understanding of fog occurrence in this region.

This book presents the history of marine fog research and applications, and discusses the physical processes leading to fog's formation, evolution, and dissipation. A special emphasis is on the challenges and advancements of fog observation and modeling as well as on efforts toward operational fog forecasting and linkages and feedbacks between marine fog and the environment.

The distribution, thickness, and mean grain size of surficial sediments on Sable Island Bank, Middle Bank, and Banquereau, Scotian Shelf, are used to re-evaluate interpretations made by others on mechanisms controlling long-term stability and net transport pathways of surface sand. A Holocene sand-ridge complex, the Sable Island Catena, extends 300 km across Sable Island Bank and Banquereau. This sand-ridge complex, which is up to 50 m thick, formed as a result of Holocene sediment transport on the outer banks and controls the modern-day distribution of bedforms and sediment size. A clockwise circulation of sand centred around Sable Island, which had been proposed as the mechanism maintaining the island, does not take place. Sand is transported from southwest to northeast across Sable Island Bank towards the Sable Island Catena; thereafter, sand is dispersed eastward. "Spillover" of sand from the banks to The Gully is not significant. Sand is trapped in depths less than 100 m. The processes proposed to have formed the Sable Island Catena are barotropic, storm-driven currents and associated sand transport and "fair-weather" dispersion of sand by strong, tidal flows or baroclinic currents, coupled with an abundant supply of sand-size sediment.

Sea‐surface temperature (SST) is a key driver for various interactions and feedbacks between components of the Earth System and can control local weather and climate. The formation of marine fog, for example, can be sensitive to small changes in SST at a scale of a few kilometres. As a contribution to understanding processes at the interface between air and sea, this article discusses results from a state‐of‐the‐art fully coupled regional atmosphere–land–ocean–wave prediction system for the UK at km scale. This study focuses on the impact of the changes in surface forcing resulting from coupling SST in the marine boundary layer and formation of summertime coastal fog over the North Sea.A study from July 2013 provided a good case to evaluate the role of SST in fog evolution. The benefit of an evolving SST in the coupled simulation is shown in capturing a warming trend in observed SST over the five‐day case study period, with a root‐mean‐square error (RMSE) against in situ observations of 1.1 K. In contrast, in uncoupled atmosphere‐only simulations, the initial‐condition SST is persisted for the duration of the case, as is more typical in current operational numerical weather prediction (NWP). In the uncoupled simulations, a cold bias develops over the modelling period and the RMSE against observed SST is 2.4 K.The impact of coupling is shown to propagate into the overlying marine boundary layer and therefore affect the formation of coastal fog. Increased heat flux from a relatively warmer sea surface in the coupled simulations led to near‐surface atmospheric instability, hampering stratus lowering and destroying the fog‐promoting inversion layer. This significantly reduced fog fractions in selected regions. The value of model coupling was assessed by comparing coupled and uncoupled simulations initialized at different times ahead of fog development.