DRIFT CARD 



drift card — A card such as is used in a drift bottle, 

 encased in a buoyant, waterproof envelope and 

 released in the same manner as a drift bottle. 



Cheaper and lighter than bottles, drift cards 

 are especially suited to dropping in large quanti- 

 ties from aircraft, and it is supposed that the 

 card, having less freeboard than a bottle, is less 

 affected by wind. 8ee drift bottle. (5) 



drift current — (sometimes called ocean current). 

 1. A wide, slow-moving ocean current princi- 

 pally caused by winds. Example are the exten- 

 sion of the North Atlantic Current (the North 

 Atlantic Drift) and the West Wind Drift. 

 See wind-driven current. 



2. The current determined from the differ- 

 ences between dead reckoning and a naviga- 

 tional fix. 



3. A current defined by assuming that the 

 wind stress is balanced by the sum of the corio- 

 lis and frictional forces. 



drift ice — ( or -floating ice ) . Any sea ice that has 

 drifted from its place of origin. The term is 

 used in a wide sense to include any area of sea 

 ice, other than fast ice, no matter what form it 

 takes or how disposed. See close pack ice. 

 (5) 



drift ice foot — See ramp. 



drif tmeter — (or drift sight) . An instrument for 

 measuring drift angle. See Geomagnetic 

 Electrokinetograph. (68) 



drift sight — See drif tmeter. 



drift station — A scientific station established on 

 the ice of the Arctic Ocean. Most drift stations 

 are based on ice floes, although two American 

 stations (T-3 and AELIS II) have been on ice 

 islands. 



U.S.S.R. stations are numbered consecutively 

 from NP-1 (NP for North Pole) and are some- 

 times referred to as "SP" for the Eussian 

 "Severnyy Polyus" (North Pole) . 



Drift Station Bravo— /See T-3. 



drogue — ( or parachute drogue ) . A current meas- 

 uring assembly consisting of a weighted para- 

 chute and an attached surface buoy. The 

 parachute can be placed at any desired depth 

 and current speed and direction determined by 

 tracking and timing of the surface buoy. 



drown — To submerge land beneath water either 

 through a rise in the level of the water or by 

 sinking of the land. ( 2 ) 



drowned river mouth — See estuary. 



drydock iceberg — See valley iceberg. 



dry organic matter — Dry plankton less ash after 

 ignition. The most reliable and the preferred 

 weighing method in determining the biomass. 



dry plankton — Plankton dried to a constant 

 weight by a specified method. See dried 

 weight. 



dry weight— See dried weight. 



duct — A layer in the ocean or atmosphere where 

 refraction and, probably, reflection result in 



the trapping of electromagnetic waves, or sound 

 waves. 



ducting — The trapping of sound or electromag- 

 netic waves within a layer, resulting in extended 

 ranges. 



dugong — An aquatic herbivorous mammal, some- 

 times referred to as a sea cow, of the order Si- 

 renia allied to the manatee, but with a bilobate 

 tail like that of a whale. 



duir.ped deposit — The accumulation of sediment 

 deposited more rapidly than waves and currents 

 are able to redistribute it. ( 2 ) 



dumping ground — A sea area within which ma- 

 terial dredged from other areas is deposited. 

 See spoil ground. 



duration — 1. The interval of time of the rising or 

 falling tide, or the length of time of flood or 

 ebb tidal currents. 



2. In wave forecasting, the length of time the 

 wind blows in essentially the same direction over 

 the fetch. (61) 



dynamic calculations — The procedure based on 

 the summation of dynamic depth intervals from 

 the surface of the ocean to any specified level; 

 dynamic differences between stations are de- 

 rived and consequently the relative speed and 

 direction of currents at different levels. 



dynamic depth — See dynamic height. 



dynamic height — (or geodynamic height). The 

 amount of work done when a water particle of 

 unit mass is moved vertically from one level to 

 another; the dimensions are those of potential 

 energy per unit mass. 



dynamic height anomaly^ (also called aawmaly 

 of geopotential difference) . In oceanography, 

 the excess of the actual geopotential difference, 

 between two given isobaric surfaces, over the 

 geopotential difference in a homogeneous water 

 column of salinity 35 per mille ( 7oo ) and 

 temperature 0°C. 



The dynamic height anomaly between two 

 isobaric surfaces is the product of the mean 

 specific volume anomaly and the difference 

 in pressure (in decibars) ; the latter is assumed 

 to equal the difference in depth in meters. (5) 

 See geostrophic current. 



dynamic meter — (or geodynamic meter). The 

 standard unit of dynamic height expressed as 

 10 square meters per second per second. Its 

 inclusion in the hydrostatic equation elimi- 

 nates the factor of gravity acceleration in 

 dynamic calculations. 



dynamic oceanography — The study of ocean- 

 ographic motions as solutions of the funda- 

 mental equations of hydrodynamics or other sys- 

 tems of equations appropriate to special 

 situations. 



The restrictions of this definition suflS.ce to 

 distinguish dynamic oceanography from other 

 fields, for example, physical oceanography or 

 synoptic oceanography, such distinctions being 



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