NP. Neap Range. The mean semidiurnal range of 

 tide when NEAP TIDES are occurring; the mean dif- 

 ference in height between neap high water and neap 

 low water. Sometimes called MEAN NEAP RANGE. (17) 



NPFSC . North Pacific Fur Seal Commission. 



NRC . National Research Council. 



NRL . Naval Research Laboratory. 



NSF. National Science Foundation. 



NSIA . National Security Industrial Association. 



NUCLEAR RESONANCE MAGNETOMETER . With this instru- 

 ment the measurement of the earth's magnetic field 

 depends on the magnetic moment of the atom. Hydro- 

 gen atoms are generally used, and these can be in 

 a compound such as water. Each hydrogen atom can 

 be looked upon as a tiny electromagnet whose 

 strength and direction are determined by the revo- 

 lution of the electron of the atom about its nuc- 

 leus. In a magnetic field, atoms of hydrogen have 

 a tendency to align themselves in opposition to the 

 field. If the direction of the field is suddenly 

 changed, there will be a moment pulling the atoms 

 toward the new direction. But each atom is a 

 midget gyroscope, and instead of shifting directly 

 to the new field direction, it will precess about 

 this direction. The frequency of this precession 

 will be a function only of the strength of the mag- 

 netic field. To measure the strength of the earth's 

 magnetic field, a bottle of water is subjected to 

 a strong magnetic field at right angles to the 

 earth's field. The voltage induced in a coil of 

 wire wrapped around the bottle is observed when the 

 auxiliary field is suddenly removed. This voltage 

 will have a frequency of alternation of the order 

 of 2,000 cycles per sec, its exact value depending 



on the strength of the earth's field. The time of 

 2,000 cycles of this voltage can be measured using 

 a 100-kc oscillator and a high-speed counter, 

 giving an accuracy of measurement of 1 part in 

 10^, or of the order of + 1/2 gamma. (35) 



NUMERICAL FORECASTING (MATHEMATICAL FORECASTING. 

 DYNAMIC FORECASTING. PHYSICAL FORECASTING. 

 NUMERICAL WEATHER PREDICTION.) The forecasting of 

 the behavior of atmospheric disturbances by the 

 numerical solution of the governing fundamental 

 equations of hydrodynamics, subject to observed 

 initial conditions. When applied to the cyclonic- 

 scale atmospheric disturbances in the form of a 

 dynamical model, these solutions form a method of 

 forecasting the behavior of the migratory pressure 

 systems of middle latitude. Numerical forecasting 

 is usually performed with the aid of high-speed 

 computing devices. (24) 



NUMERICAL WEATHER PREDICTION . (Abbreviated NWP.) 

 Same as NUMERICAL FORECASTING. (24) 



NUNATAK. An island of exposed rock standing above 

 a surrounding ice sheet. (17) 



NUN BUOY . A buoy the above water part of which is 

 in the shape of a cone or a truncated cone. (17) 



NUOS . Naval Underwater Ordnance Station. 



(IJS)NUSL . Navy Underwater Sound Laboratory. 



NWL . Naval Weapons Laboratory, Naval Facility, 

 Dahlgren, Virginia. 



NWPFC . Northwest Pacific Fisheries Commission. 



NWRC. National Weather Records Center. 



o 



OAS . Organization of American States . 



OBLIGATE AEROBES . Bacteria which use free oxygen 

 in respiration. (13) 



OBLIGATE ANAEROBES . Bacteria which function in the 

 total absence of free oxygen. (13) 



OCAS . Organization of Central American States. 



OCEAN CURRENT . 1. A movement of ocean water 

 characterized by regularity, either of a cyclic 

 nature, or more commonly as a continuous stream 

 flowing along a definable path. 



Three general classes, by cause, may be dis- 

 tinguished: (a) currents related to sea water 

 density gradients, comprising the various types of 

 gradient current; (b) wind-driven currents, which 

 are those directly produced by the stress exerted 

 by the wind upon the ocean surface; (c) currents 

 produced by long-wave motions. The latter are 

 principally tidal currents, but may include cur- 

 rents associated with INTERNAL WAVES, TSUNAMIS, 

 and SEICHES. The major ocean currents are of 

 continuous, stream-flow character, and are of 

 first-order importance in the maintenance of the 

 earth's thermodynamic balance. (24) 



2. A current constituting part of 

 the general oceanic circulation. A periodic cur- 

 rent is one having a velocity which changes cycli- 



cally at somewhat regular intervals, as a tidal 

 current. A seasonal current is one which has large 

 changes in velocity due to seasonal winds. A 

 permanent current is one which continues with rela- 

 tively little periodic or seasonal change. A DRIFT 

 CURRENT is any broad, shallow, slow-moving ocean 

 current. A STREAM CURRENT is a relatively narrow, 

 deep, fast-moving ocean current. (17) 



OCEAN FLOOR . See FLOOR. 



"OCEANEERING" . A term which has been used in the 

 technical literature to identify OCEAN ENGINEERING. 



OCEAN ENGINEERING . Ocean Engineering is the en- 

 gineering concerned with the development of new 

 equipment concepts and the methodical improvement 

 of techniques which enable man to successfully 

 operate beneath the surface of the ocean in order 

 to develop and exploit its many resources. 



OCEANIC . Of or pertaining to the ocean. (17) 

 OCEANIC ANTICYCLONE. See SUBTROPICAL HIGH. 



OCEANIC HIGH . See SUBTROPICAL HIGH. 



OCEANICITY (OCEANITY) . The degree to which a point 

 on the earth's surface is in all respects subject 

 to the influence of the sea; the opposite of con- 

 tinentality. Oceanicity usually refers to climate 

 and its effects. One measure for this characteris- 

 tic is the ratio of the frequencies of maritime to 

 continental types of air mass. (24) 



OCEANITY. See OCEANICITY. 



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