expressed: in cycles per second, as a percentage 

 of the pass-band center frequency, or as the dif- 

 ference between the upper and lower cutoffs in 

 octaves. (9) 



NOMINAL PASS-BAND CENTER FREXjUENCY . The nominal 

 pass-band center frequency is the geometric mean of 

 the nominal cutoff frequencies. If the lower and 

 upper cutoff frequencies of a filter are 200 and 

 800 cycles per second respectively, the center 

 frequency will be 400 cycles per second. (9) 



NOMSS . National Operational Meteorological Satel- 

 lite System operated by the U. S. Weather Bureau. 

 Its mission is to continuously observe worldwide 

 weather conditions and to process, analyse and 

 catalog the data obtained for use in weather ser- 

 vices and research. 



NONLINEAR DAMPING . Nonlinear damping is damping 

 due to a damping force that is not proportional to 

 velocity. (2) 



KONTIDAL CURRENT . A current that is due to causes 

 other than the tide-producing force. Classed as 

 nontidal are the permanent ocean currents such as 

 the GULF STREAM and the EQUATORIAL CURRENTS, which 

 are a part of the general ocean circulation, the 

 fresh-water discharge of a river, and temporary 

 currents caused by the wind. These currents lack 

 the periodicity which characterizes the tidal 

 currents. (14) 



NORC. National Oceanographic Research Center. 



NORMAL ICE LIMIT. See AVERAGE LIMIT OF ICE. 



NORMALIZED AMPLITUDE . The response along the axis 

 of the major lobe plotted with a value of unity 

 (or db). (7) 



NORMALLY DISPERSIVE . Waves which travel faster as 

 their wavelengths increase. A characteristic of 

 gravity waves . 



often masked by shallow and variable wind-driven 

 surface movements so that they are sometimes 

 called the North Atlantic drift. 



Along the mid-Atlantic ridge the North Atlan- 

 tic current is divided into two major branches; 

 the northern branch flows between latitudes 50°N 

 and 52"^ separated from the Labrador current by 

 the cold wall. The other branch flows approximate- 

 ly in latitude 45°N and carries undiluted Gulf 

 Stream water. Of these branches the northern 

 continues mainly toward the east-northeast and 

 divides, part flowing into the Norwegian Sea and 

 part turning toward the north and northwest even- 

 tually giving rise to the IRMINGER CURRENT. (24) 



NORTH CAPE CURRENT . An Arctic Ocean current flow- 

 ing northeastward and eastward around northern 

 Norway, and curving into the Barents Sea. The 

 North Cape current is the continuation of the 

 northeastern branch of the NORWEGIAN CURRENT. (17) 



NORTHEAST DRIFT CURRENT . A North Atlantic Ocean 

 current flowing northeastward toward the Norwegian 

 Sea, gradually widening and, south of Iceland, 

 branching and continuing as the IRMINGER CURRENT 

 and the NORWEGIAN CURRENT. The northeast drift 

 current is the northern branch of the NORTH ATLAN- 

 TIC CURRENT. (17) 



NORTH EQUATORIAL CURRENT . In the Atlantic the 

 north Equatorial current originates to the north- 

 ward of the Cape Verde Islands and flows almost 

 due west at an average speed of about 0.7 knots. 

 In the western part of the Atlantic Ocean the 

 north Equatorial current joins the branch of the 

 SOUTH EQUATORIAL CURRENT which has crossed the 

 Equator and turns northward . It terminates in 

 the current through the Yucatan Channel and the 

 ANTILLES CURRENT. The continuation of these cur- 

 rents represents the beginning of the GULF STREAM 

 system which dominates the circulation of a great 

 part of the North Atlantic Ocean. In the Pacific 

 the beginning of the north Equatorial current is 

 found where the waters of the EQUATORIAL COUNTER- 

 CURRENT turns to the north off Central America. 

 The volume transport is periodically increased 

 along its path by water added from the north by 

 such currents as the CALIFORNIA CURRENT. At about 

 150 degrees West longitude the volume transport 

 above a depth of 1000 m is about 45 million m /sec, 

 and this value is approximately equal to the maxi- 

 mum transport of the corresponding current in the 

 Atlantic Ocean. (12, 13) 



NORMAL MODE OF VIBRATION . A normal mode of vibra- 

 tion is a mode of free vibration of an undamped 

 system. In general, any composite motion of the 

 system is analyzable into a summation of its nor- 

 mal modes . (2) 



NORMAL WATER (COPENHAGEN WATER. STANDARD SEA WATER. 

 EAU DE MER NORMALE) . A standard sea-water prepara- 

 tion, the chlorinity of which lies between 19.30 

 and 19.50 per mille (0/00) and has been determined 

 to within + 0.001 per mille. 



Normal water is used as a convenient compari- 

 son standard for chlorinity measurements of sea 

 water samples by titration. It is prepared by the 

 Hydrographical Laboratories, Copenhagen, Denmark. 

 (24) 



NORMAL WINTER. 



Refers to normal ice season, that 



is, the average ice conditions based on a number 

 of recorded winters in a given area. 



NORTH ATLANTIC CURRENT . A continuation of the 

 GULF STREAM, originating at about 40°N latitude 

 and 50°W longitude, comprising all the easterly 

 and northerly currents of the North Atlantic 

 originating in the region east of the Grand Banks. 

 The branches of the North Atlantic current are 



NORTH PACIFIC CURRENT . A Pacific Ocean current 

 flowing eastward and southeastward from a point 

 between the Aleutian and Hawaiian Islands toward 

 the west coast of North America, gradually widen- 

 ing and the greater part curving southward, a small 

 part nearest the California coast merging with the 

 southern branch of the ALEUTIAN CURRENT to continue 

 southeastward as the CALIFORNIA CURRENT. The North 

 Pacific current is the continuation of the KUROSHIO, 

 and forms the northern and northeastern part of the 

 general clockwise oceanic circulation of the North 

 Pacific Ocean. (17) 



NORWEGIAN CURRENT . Part of the northern branch of 

 the NORTH ATLANTIC CURRENT, which flows northward 

 along the coast of Norway, The water of the Nor- 

 wegian current eventually enters the Arctic Ocean, 

 from which the main discharge is via the EAST GREEN- 

 LAND CURRENT. (24) 



NORWESTLANT . Northwest Atlantic (Project). 



NOTOCHORD . The elastic cellular axial support 

 formed ventral to the nerve cord in the early em- 

 bryo of all chordates ; either surrounded or sup- 

 planted by the vertebrae in most vertebrates. (19) 



NOTS . Naval Ordnance Test Station, U. S. Navy, 

 China Lake, California. 



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