File:Aerographer's Mate 3 and 2 (1976) (17758069790).jpg

Title: Aerographer's Mate 3 & 2
Identifier: aerographersmate00nava (find matches)
Year: 1976 (1970s)
Authors: Naval Education and Training Program Development Center; United States. Bureau of Naval Personnel
Subjects: United States. Navy; Meteorology; Oceanography
Publisher: Washington : U. S. Dept. of Defense, Navy Dept. , Naval Education and Training Support Command
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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Chapter 15 —METEOROLOGICAL ELEMENTS
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201.60 Figure 15-8. —Radiation fog. (2 to 5 knots) and clear skies are frequent. This permits maximum radiational cooling. ADVECTION FOG. — Advection fog is the name given to fog produced by air in motion or to fog formed in one place and transported to another. This type of fog is formed when warmer air is transported over colder land or water surfaces. Cooling from below takes place and gradually builds up a fog layer. The cooling rate depends on the wind speed and the difference between the air temperature and the tempera- ture of the surface over which the air travels. Advection fog can form only in regions where marked temperature contrasts exist within a short distance of each other, and only when the wind blows from the warm region toward the cold region. (See fig. 15-9.) It is easy to locate areas of temperature contrast on the weather map. They are usually found along coastlines or between snow-covered and bare ground. SEA FOG is always of the advection type and occurs when the wind brings moist warm air over a colder ocean current. The greater the difference between the air temperature and the ocean temperature, the deeper and denser the fog. Sea fog may occur during either the day or the night. Some wind is necessary, not only to provide some vertical mixing, but actually also to move the air to the place where It is cooled. Most advection fogs are found at speeds between 4 and 13 knots. Sea fogs have been maintained with wind speed as high as 26 knots. They exist at such speeds because of the lesser frictional effect over a water surface. Winds of equal speed produce less turbulence over water than over land. Sea fogs, which tend to persist for long periods of time, are quite deep and dense, Since the temperature of the ocean surface changes very little during the day, it is not surprising 359

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