DISTRIBUTION GRAPH 



distribution graph — In hydrology, a statistically 

 derived hydrograph for a storm of specified 

 duration, graphically representing the percent 

 of total direct runoff passing a point on a stream, 

 as a function of time. It is usually presented 

 as a histogram or table of percent runoff within 

 each of successive short time intervals. In prin- 

 ciple it is the same as the unit hydrograph; 

 both are used as tools in river forecasting and 

 for other purposes such as the comparison of 

 runoff characteristics of different drainage 

 areas. (5) 



diurnal — (or daily). 1. Daily, especially per- 

 taining to actions which are completed within 

 twenty-four hours and which recur every 

 twenty-four hours; thus, most reference is made 

 to diurnal cycles, variations, ranges, maximums, 

 etc. (5) 



2. Having a period or cycle of approximately 

 one lunar day (24.84 solar hours) : Certain 

 tides and tidal currents are said to be diurnal 

 when one high water and one low water, and 

 one flood and one ebb current, occur each 

 lunar day. 



diurnal constituent — Any tide constituent 

 whose period approximates that of a lunar day 

 (24.84 solar hours). See constituent. 



diurnal cooling — Heat lost by the surface of a 

 body of water during the night. This radia- 

 tional loss manifests itself in a small and tran- 

 sient positive gradient of temperature that is 

 observed near the surface in calm weather. See 

 diurnal heating. 



diurnal current — The type of tidal current hav- 

 ing only one flood and one ebb period in a tidal 

 day. (73) 



diurnal fluctuations — See diurnal. 



diurnal heating — Solar radiation absorbed by a 

 body of water during the daylight hours. This 

 short-wave radiation, by heating the upper layer 

 of the water, creates, in the absence of wind, a 

 small and transient surface thermocline. See 

 diurnal cooling. 



diurnal inequality — (also called daUy in- 

 equality). The difference in heights and dura- 

 tions of the two successive high waters or of 

 the two successive low waters of each day; 

 also, the difference in speed and direction of the 

 two flood currents or the two ebb currents of 

 each day. 



diurnal range — 1. The amount of variation be- 

 tween the maximum and minimum of any 

 element during 24 hours. 



2. Contracted form of great diurnal range. 



diurnal tide — A tide in which there is only one 

 high water and one low water each lunar day, 

 (5) {See figure for type of tide.) 



diurnal variation — See magnetic diurnal 

 variation. 



diurnal vertical migration — The daily vertical 

 movement of certain members of the plankton 

 and nekton. The movement usually is triggered 



by a change in light intensity, and influenced 

 by other factors such as temperature and 

 gravity. The migration generally is upward at 

 sunset and downward at sunrise. The rhythmic 

 movements of these organisms are thought to be 

 responsible for the typical movement of the 

 deep scattering layer. 



divergence — 1. A horizontal flow of water, in 

 different directions, from a common center or 

 zone; often associated with upwelling. 



2. In refraction phenomena, the increasing of 

 the distance between orthogonals in the direc- 

 tion of wave travel. Denotes an area of decreas- 

 ing wave height and energy concentra- 

 tion. (73) 



divergence loss — The part of the transmission 

 loss which is due to the spreading of sound 

 rays in accordance with the geometry of the 

 situation. For example, in the case of spherical 

 waves emitted by a point source, the sound 

 pressure at a point 20 yards distant from the 

 source will be only half as great as the sound 

 pressure 10 yards from the source. 



diving rule — See compression factor. 



diving saucer — A circular-shaped submersible 

 for undersea exploration. 



diving trim — The condition of a submarine which 

 is so compensated that completing the flooding 

 of the main ballast, safety, and bow buoyancy 

 tanks, will cause it to submerge with neutral 

 buoyancy and zero fore-and-aft trim. (64) 



division — See classification of organisms. 



doldrums — (also called equatorial calms). A 

 nautical term for the equatorial trough, with 

 special reference to the light and variable 

 nature of the winds. See equatorial air. (5) 



dolomite — A mineral or a rock composed of 

 the mineral CaMg{C0s).2; also called mag- 

 nesium limestone, which is deposited as dolomite 

 or produced later by substitution of magnesium 

 for some of the calcium. 



dolphin — 1. A member of the cetacean suborder 

 Odontoceti. The name is used interchangeably 

 with porpoise by some. More properly it is 

 given generally to the beaked members of the 

 family Delphinidae, except the larger members 

 which have been given the name "whale", such 

 as the killer whale and pilot whale. 



2. A pelagic fish of the genus Coryphaena 

 noted for its brilliant colors. 



3. A cluster of piles. (66) 



dome — (or kuppe). 1. This term is no longer 

 recommended by the ACUF for an elevation of 

 small area, rising with a steep angle to a depth 

 more than 200 meters (109 fathoms) below the 

 water surface. See seamount, knoll. 



2. A (acoustically transparent) transducer 

 enclosure, usually streamlined, used with echo- 

 ranging or listening devices to minimize turbu- 

 lence and cavitation noises arising from the 

 passage of the transducer through the water. 



50 



