H 



haar — A wet sea fog which sometimes invades 

 eastern Scotland and parts of eastern England, 

 especially during siunmer. (68) 



hachures — 1. Short lines on topographic or 

 nautical charts to indicate the slope of the 

 ground or submarine bottom. They usually 

 follow the direction of the slope. (68) See 

 contour. 



2. Inward pointing short lines or "ticks" 

 around the circumference of a closed contour 

 indicating a depression or a minimum. (60) 



hadal — ( also called superocennic deep ) . Pertain- 

 ing to the greatest depths of the ocean. {See 

 figure for classification of marine environ- 

 ments.) 



half-life — The average time, ^>^, required for the 

 decaj' of one-half the atoms of a sample of a 

 radioactive substance. Each radionuclide has 

 an unique half-life, which is related to its dis- 

 integration constant. A, and mean life, t, as 

 follows : 



?'j^ = l?22A=0.693A= 0.693 t. 

 »S'ee radioactive half-life. (41) 



half-meter plankton net — A qualitative type 

 filtering net with a half-meter opening tapering 

 to a detachable bucket of a few inches diameter. 

 The net is usually some gi-ade of silk bolting 

 cloth numbered 0000 to 25 depending upon the 

 number of meshes per linear inch. 



half tide — The condition or time of the tide when 

 at the level midway between any given high tide 

 and the following or preceding low tide. (68) 



half-tide level — See mean tide level. 



halmyrolysis — Chemical rearrangement and re- 

 placement, and weathering which occurs in sedi- 

 ment or rocks on the sea floor. (2) 



halobolite — See nodules. 



halocline — A well-defined vertical gradient of 

 salinity which is usually positive. 



halogen — Any of four elements (chlorine, bro- 

 mine, iodine, and fluorine) found as ions in sea 

 water. 



halogenic deposits — Marine salt deposits. (2) 



Halosphaera — A genus of gi'een, single-celled 

 marine phytoplankton of the class Xantho- 

 phyceae. The genus occurs in both warm and 

 temperate waters and also has been reported to 

 be very abundant at times in antarctic waters. 



harbor — An area of water affording natural or 

 artificial protection for ships. 



Harbor Analog System — See Nearshore Envi- 

 ronmental Analog Prediction System. 



harbor area — The area of the water surface in a 

 harbor or port, measured at a given datum. 



harbor oscillation — (or harbor surging). The 

 nontidal vertical water movement in a harbor or 

 bay. Usually the vertical motions are low, but 

 when oscillations are excited by a tsunami or 

 storm surge they may be quite large. Variable 

 winds, air oscillations, or surf beat also may 

 cause oscillations. See seiche. 



harbor surging — See harbor oscillation. 



harbor volume — The volumetric water content of 

 a harbor or port measured at a given datum. 



hard bottom — The sea floor not covered by uncon- 

 solidated sediment. (2) 



Hardy continuous plankton recorder — (or 

 Hardy recorder). A plankton sampler de- 

 signed to collect specimens of plankton during 

 normal passage of a ship. The device consists 

 of a towed container enclosing a continuously 

 moving strip of silk gauze (about 60 meshes per 

 inch) which filters and stores the plankton pass- 

 ing into the orifice of the container. Knowing 

 the speed of travel of the gauze and the course 

 and speed of the ship, it is then possible to deter- 

 mine the distribution of plankton along the 

 ship's route. 



Hardy recorder — See Hardy continuous plank- 

 ton recorder. 



harmonic — A sinusoidal quantity having a fre- 

 quency that is an integral multiple of the fre- 

 quency of a periodic quantity to wliich it is 

 related. (6) 



harmonic analysis — (or harmonic reduction). 

 1. A statistical method for determining the 

 amplitude and period of certain harmonic or 

 wave components in a set of data with the aid of 

 Fourier series. (5) 



2. The method by which the observed tide or 

 tidal current at any place is separated into 

 elementary harmonic constituents. (50) 



harmonic analyzer — A machine designed to re- 

 solve a periodic curve into its harmonic con- 

 stituents. (50) 



harmonic constant — The amplitude and epoch of 

 any harmonic constituent of the tide or tidal 

 current at any locality. ( 50 ) See constituent. 



harmonic constituent — See constituent. 



harmonic function — 1. Any solution of the La- 

 place equation. ( 5 ) 



2. In tide and tidal current predictions, a 

 quantity that varies as the cosine of an angle that 

 increases uniformly with time. (68) 



207-109 o— 66- 



75 



