FLOOD AXIS 



feet, and are considered to be the result of ex- 

 treme pressure ice formation. 



flood axis — The average direction of the tidal 

 current at strength of flood. 



flood current — The tidal current associated with 

 the increase in the height of a tide. Flood cur- 

 rents generally set toward the shore, or in the 

 direction of the tide progression. Erroneously 

 called flood tide. {See figure for current 

 curve.) 



flood interval — The interval between the transit 

 of the moon over the meridian of a place and 

 the time of the strength of the following flood 

 tidal current. (50) 



flood strength — The flood tidal current at time 

 of maximum speed, usually associated with the 

 lunar tide phase and/or minimum river dis- 

 charge at springs near perigee. {See figure for 

 current curve.) 



flood tide — See rising tide, flood current. 



flora — The plant population of a particular loca- 

 tion, region, or period. 



florescence — The rapid reproduction of plankton. 

 See plankton bloom. 



Florida Current — A fast current with speeds of 

 2 to 5 knots that sets through the Straits of 

 Florida to a point north of Grand Bahama 

 Island where it joins the Antilles Current to 

 form the Gulf Stream. 



The Florida Current is traced to the Yucatan 

 Channel where the greater part of the water 

 flowing through that channel turns clockwise 

 into the Straits of Florida. 



flotsam — See jettison. 



flow — The combination of tidal and nontidal cur- 

 rent which represents the actual water move- 

 ment. 



flowmeter — 1. A device employing propellers, 

 savonious rotors and/or pressure sensors to 

 measure water movement, such as currents, 

 stream flow, etc. 



2. A special type device employing a pro- 

 peller-counting mechanism (which must be prop- 

 erly calibrated) is used to measure the amount 

 of water passing through a plankton net or 

 other sampling device. 



flow noise — The noise produced by water move- 

 ment past the transducer or hydrophone array 

 housing, and th.& noise produced by breaking 

 waves against the hull of a moving ship. 



fluctuation — 1. The variations of water level 

 height from mean sea level that are not due to 

 tide-producing forces and are not included in 

 the predicted heights of the tide. 



2. The change in average amplitudes of suc- 

 cessive pulses; sound pulses that are projected 

 with the same amplitude at intervals of a few 

 seconds will, after transmission, differ from each 

 other in amplitude. 



fluorescence — 1. The emission of electromag- 

 netic radiation by a substance as the result of an 



absorption of energy from some other radiation, 

 either electromagnetic or corpuscular, and char- 

 acterized by the fact that it occurs only so long 

 as the stimulus responsible for it is maintained. 

 The continued emission of light after the absorp- 

 tion of radiation has ceased is called phosphor- 

 escence. 



2. The electromagnetic X-radiation so pro- 

 duced. 



3. In X-rays, characteristic X-radiation emit- 

 ted as a result of absorption of X-rays of higher 

 frequency. 



4. /See phosphorescence. 



flushing time — The time required to remove or 

 reduce to a permissible concentration any dis- 

 solved or suspended contaminant in an estuary 

 or harbor. 



fluviomarine — Deposits carried into the sea from 

 the land, re-sorted and redistributed by waves 

 and currents, and mixed with the remains of 

 marine animals. 



flux — (or transport). Tlie rate of flow of a 

 quantity, as for example, heat flux. 



flux-gate magnetometer — An instrument de- 

 signed to measure the earth's magnetic field. 



The flux-gate magnetometer, also known as 

 the saturable reactor, makes use of a ferromagnet 

 element of such high permeability that the 

 earth's field can induce a magnetization that is 

 a substantial proportion of the saturation value. 

 If this field is superimposed upon a cyclic field 

 induced by sufficiently large alternating current 

 in a coil around the magnet, the resulting field 

 will saturate the core. The phase of each en- 

 ergizing cycle at which saturation is reached 

 gives a measure of the earth's ambient field. 

 (35) 



fluxmeter — An instrument for measuring the in- 

 tensity of a magnetic field. (68) 



fluxoturbidite — Strata deposited from turbidity 

 currents later disturbed by sliding or 

 slumping. (2) 



flying bar — A looped bank or spit f onned on the 

 landward side of an island which i-emains after 

 the island itself has been eroded to below sea 

 level by wave attack. (2) 



flying squid — See sea arrow. 



foam line — The front of a wave as it advances 

 shoreward after it has broken. (61) {See 

 figure for breaker.) 



focus — In seismology, the source of a given set 

 of elastic waves. The true center of an earth- 

 quake, within which the strain energy is first 

 converted to elastic wave energy. (2) 



fog — A hydrometer consists of a visible aggregate 

 of minute water droplets suspended in the at- 

 mosphere near the earth's surface. According 

 to international definition, fog reduces visibility 

 below one kilometer (0.62 statute mile). (5) 



64 



