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H. J. S. Fernando, I. Gultepe, C. Dorman, E. Pardyjak, Q. Wang, S. W Hoch, D. Richter, E. Creegan, S. Gaberšek, T. Bullock, C. Hocut, R. Chang, D. Alappattu, R. Dimitrova, D. Flagg, A. Grachev, R. Krishnamurthy, D. K. Singh, I. Lozovatsky, B. Nagare, A. Sharma, S. Wagh, C. Wainwright, M. Wroblewski, R. Yamaguchi, S. Bardoel, R. S. Coppersmith, N. Chisholm, E. Gonzalez, N. Gunawardena, O. Hyde, T. Morrison, A. Olson, A. Perelet, W. Perrie, S. Wang, and B. Wauer

“There it is, fog, atmospheric moisture still uncertain in destination, not quite weather and not altogether mood, yet partaking of both.” —Hal Borland Fog is a collection of suspended water droplets or ice crystals near the Earth’s surface that causes horizontal near-surface visibility to drop below 1 km ( Myers 1968 ; WMO 1992 ). Different from clouds, fog forms near the surface and hence dynamic, microphysical, physicochemical, thermodynamic, surface, and environmental processes that

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I. Gultepe, T. Kuhn, M. Pavolonis, C. Calvert, J. Gurka, A. J. Heymsfield, P. S. K. Liu, B. Zhou, R. Ware, B. Ferrier, J. Milbrandt, and B. Bernstein

Increased understanding of ice fog microphysics can improve frost and ice fog prediction using forecast models and remote-sensing retrievals, thereby reducing potential hazards to aviation. Ice fog occurs usually at temperatures less than −15°C because of direct deposition of water vapor into ice nuclei. It significantly affects aviation and transportation in northern latitudes because ice fog causes low visibilities and ice crystal accumulation on the surface of structures. Ice fog may also be

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Robert Spirig, Roland Vogt, Jarl Are Larsen, Christian Feigenwinter, Andreas Wicki, Joel Franceschi, Eberhard Parlow, Bianca Adler, Norbert Kalthoff, Jan Cermak, Hendrik Andersen, Julia Fuchs, Andreas Bott, Maike Hacker, Niklas Wagner, Gillian Maggs-Kölling, Theo Wassenaar, and Mary Seely

Fog life cycles in the central Namib Desert have been studied during the NaFoLiCA intensive observation period, which is described together with initial analyses of the extensive dataset. Fog as a meteorological phenomenon is associated with low visibility, high relative humidity/cold air, and danger for car/air traffic. However, in one of the driest regions on Earth—the Namib Desert—fog instead represents a major source of water for plants and animals. Figure 1 illustrates this striking

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J. D. Price, S. Lane, I. A. Boutle, D. K. E. Smith, T. Bergot, C. Lac, L. Duconge, J. McGregor, A. Kerr-Munslow, M. Pickering, and R. Clark

A collaborative field and modeling study used a small system of valleys as a natural laboratory to study the formation and evolution of fog. Atmospheric fog can have a high impact on human activity, particularly transport ( Gultepe et al. 2007 ). Delays due to poor visibility can be extensive and costly. Agarwal et al. (2005) estimated that fog causes a decrease in vehicle speed of 6%–12% and a reduction in traffic capacity of 10%–12% on freeways in Iowa. Figures for the impact of fog on

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V. J. Oliver and M. B. Oliver

Visibilities of 100 to 200 miles over large areas are reported by pilots flying in the Arctic winter of interior Alaska. However, when the airport is reached, they find ice fog and visibility near zero. This condition is described and reasons are presented for ice fog formation and persistence in the vicinity of towns while other areas equally cold remain fog free.

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H. Appleman

Studies carried out in Alaska and Canada have shown that fog is a relatively rare phenomenon at temperatures between 0° and − 30°F, with a minimum frequency between − 20° and −30°. At still lower temperatures, however, the frequency of fog increases rapidly. This effect is noted only in the immediate vicinity of inhabited areas, such as towns and airfields. The reason for the sudden increase in fog frequency at these temperatures, and the rarity or lack of fog at the higher temperatures, has not been heretofore explained. In a recent study on aircraft condensation trails, it was shown that if the temperature is sufficiently low (between − 20 and − 40°F, depending on the relative humidity), the burning of hydrocarbon fuels, such as would occur in towns and at airfields, easily results in supersaturation of the air and a “surface contrail” or ice fog. At higher temperatures, on the other hand, combustion actually reduces the relative humidity of the atmosphere, hindering the formation of fog. In this paper it is shown that low-temperature (ice) fogs form as a result of the combustion process, and curves are presented showing the temperature-dew-point relationship necessary for the formation of such fogs.

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Dale F. Leipper

Weather forecasts and warnings are the most important services provided by the meteorological profession. The effective development of forecasting methods rests upon comprehensive knowledge of the phenomena to be forecast. To help provide such knowledge, this review includes a chronological summary of pertinent information concerning fog on the U.S. west coast. There is increasing evidence that periods of dense fog at National Weather Service west coast stations fall within a 5- to 15-day sequence of synoptic events. Further, such sequences may be divided into four distinct phases: initial conditions, fog formation, fog development and extension, and stratus. A separate article will review West Coast fog forecasting approaches and present resulting methods.

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I. Gultepe, G. Pearson, J. A. Milbrandt, B. Hansen, S. Platnick, P. Taylor, M. Gordon, J. P. Oakley, and S. G. Cober

The main purpose of this work is to describe a major field project on fog and summarize the preliminary results. Three field phases of the Fog Remote Sensing and Modeling (FRAM) project were conducted over the following two regions of Canada: 1) the Center for Atmospheric Research Experiments (CARE), in Toronto, Ontario (FRAM-C), during the winter of 2005/06, and 2) Lunenburg, Nova Scotia (FRAM-L), during June 2006 and June 2007. Fog conditions observed during FRAM-C were continental in nature, while those conditions observed during FRAM-L were of marine origin. The main objectives of the project were to attain 1) a better description of fog environments, 2) the development of microphysical parameterizations for model applications, 3) the development of remote sensing methods for fog nowcasting/forecasting, 4) an understanding of issues related to instrument capabilities and improvement of the analysis, and 5) an integration of model data with observations to predict and detect fog areas and particle phase. During the project phases, various measurements at the surface, including droplet and aerosol spectra, ice crystal number concentration, visibility, 3D turbulent wind components, radiative fluxes, precipitation, liquid water content profiles, and cloud ceiling, were collected together with satellite measurements. These observations will be studied to better forecast/nowcast fog events in association with results obtained from numerical forecast models. It is suggested that improved scientific understanding of fog will lead to better forecasting/nowcasting skills, benefiting the aviation, land transportation, and shipping communities.

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Thomas E. Jermin

Summary

The statistics of fog and low ceilings at Pendleton are discussed in relation to the topographic situation, prevailing winds, type of fog process, etc. The explanations require careful attention to topography. Nov. to Jan. is the foggy season; radiation, prefrontal, and advection are the chief types, but postfrontal and upslope fog also occur. Typical situations for each are illustrated. The forecasting by use of Brunt's radiation equation or the methods of George has not yet been satisfactorily worked out; some forecasting rules are cited however.

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Elmer Robinson and Gordon B. Bell Jr.

Wiresonde temperature soundings were taken during two winters at Eielson Air Force Base, near Fairbanks, Alaska, as part of an ice fog investigation. Correlations were found between the depths of the visible fog layers and the steep portions of the temperature inversions.

The steep portions of the temperature inversions were usually confined to the lowest 100 feet of the atmosphere. The frequency of occurrence of strong surface inversions was less than had previously been expected for an arctic continental area with temperatures in the vicinity of −40C. This is attributed to the modifying effect of the ice fog, which was usually present in the observation area at temperatures below −30C.

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