ALEUTIAN LOW 



2. The expression "aid to navigation" should 

 not be confused witli "navigational aid," a bi'oad 

 expression covering any instrument, device, 

 chart, metliod, etc. intended to assist in the navi- 

 gation of a craft. (68) 



air bladder — (also called stoini hladder, gas tlad- 

 der) . A membranous sac of atmospheric gases 

 lying in tlie body cavity between the vertebral 

 column and the alimentary tract of certain 

 fishes. It serves a hydrostatic function in most 

 fishes that possess it ; in some it participates in 

 sound production. 



airborne expendable bathythermograph — A 

 buoyant canister which is ejected into the water 

 from an aircraft to provide measurements of 

 water temperature with depth. The tempera- 

 ture information is transmitted to the aircraft. 

 Tlie instnunent is designed to measure the tem- 

 perature from the surface to 1,000 feet with an 

 accuracy of ±5 percent in depth and a tempera- 

 ture accuracy of ±0.5°F within the range of 

 28° to 90°F. 



airborne oceanography — The use of airborne 

 platforms such as aircraft and helicopters to 

 study physical parameters of the ocean. 



airborne radiation thermometer — An infrared- 

 sensing device which measures the sea surface 

 temperature from an aircraft. 



airborne sea and swell recorder — A frequency 

 modulated continuous wave radar system used to 

 measure wave height from an aircraft. 



air embolism — (also called traumntic air ein- 

 ioUsm). The blocking of an artery by an air 

 bubble. A serious potential injury among 

 divers or personnel escaping from submarines. 

 It is caused by an expansion of air inside the 

 lungs, which increases when the breath is held 

 during ascent. Lung tissues rupture, air is 

 forced into the capillaries of the lung, and the 

 resulting air bubbles are carried to the heart 

 and into the arterial system. 



airglow — (also called night-sky light, femumient 

 aurora^. The quasi-steady radiant emission 

 from the upper atmosphere over middle and low 

 latitudes; as distinguished from the sporadic 

 emission of auroras which occur over high lati- 

 tudes. Airglow is not to be confused with air- 

 light. (5) . . . 



airlight — In determinations of visual range, light 

 from sun and sky which is scattered into the eyes 

 of an observer by atmospheric suspensoids (and, 

 to slight extent, by air molecules) lying in the 

 observer's cone of vision. That is, airlight 

 reaches the eye in the same manner that diffuse 

 sky radiation reaches the earth's surface. Air- 

 light is not to be confused with airglow. (5) 



air mass — A widespread body of air, the proper- 

 ties of which can be identified as (a) having been 

 established while that air was situated over a 

 particular region of the earth's surface (air- 

 mass source region), and (b) undergoing spe- 

 cific modifications while in transit away from 



the source region. An air mass is often defined 

 as a widespread body of air that is approxi- 

 mately homogeneous in its horizontal extent, 

 particularly with reference to temperature and 

 moisture distribution; in addition, the vertical 

 temperature and moisture variations are ap- 

 proximately the same over its horizontal extent. 

 The stagnation or long-continued motion of 

 air over a source region permits the vertical tem- 

 perature and moisture distribution of the air to 

 reach relative equilibrium with the underlying 

 surface. (5) 



air-mass source region — An extensive area of the 

 earth's surface over which bodies of air fre- 

 quently remain for a sufficient time to acquire 

 characteristic temperature and moisture proper- 

 ties imparted by that surface. Air so modified 

 becomes identifiable as a distinct air mass. (5) 



aktological — Refers to nearshore shallow water 

 areas, environment, sediments, or life. (2) 



Alaska Current — A current that flows northwest- 

 ward and westward along the coasts of Canada 

 and Alaska to the Aleutian Islands. 



It contains water from the North Pacific Cur- 

 rent, and has the character of a warm current ; 

 it therefore exercises an influence on climatic 

 conditions of the region similar, but on a smaller 

 scale, to that which the North Atlantic and 

 Norway Currents exercise on the climates of 

 northwestern Europe. 



albedo — The ratio of the amount of electromag- 

 netic radiation reflected by a body to the 

 amount incident upon it, commonly expressed as 

 a percentage. The albedo is to be distmguished 

 from the reflectivity, which refers to one spe- 

 cific wavelength (monochromatic radiation). 

 (6) 



In the oceans the albedo of the water's sur- 

 face (direct solar radiation) ranges from about 

 6 to 11 percent between 40°]Sr and 40°S; the 

 reflectivity for diffuse sky radiation is some- 

 what larger. 



Alberta low — A low pressure area centered on the 

 eastern slope of the Canadian Rockies in the 

 province of Alberta, Canada. 



Formerly, it was thought that such lows ac- 

 tually originated (more or less independently) 

 over this location. It is now recognized that de- 

 pressions moving inland from tTie Pacific are 

 the actual parent systems. Alberta lows appear 

 as these systems enhance, or are enhanced by, the 

 dynamic trough that is atypical, almost semi- 

 permanent, feature of this region. (5) 



Aleutian Current — A current setting southwest- 

 ward along the south coasts of the Aleutian 

 Islands. 



Aleutian low — The low pressure center located 

 near the Aleutian Islands on mean charts of sea 

 level pressure. It represents one of the main 

 centers of action in the atmospheric circula- 

 tion of the Northern Hemisphere. 



