PERSISTENCE 



persistence — 1. In general, the tendency for the 

 occurrence of a specific event to be more proba- 

 ble, at a given time, if that same event has oc- 

 curred in the immediately preceding time period. 

 2. (also called constancy, steadiness). With 

 respect to the long term nature of the wind at 

 a given location, the ratio of the magnitude of 

 the mean wind vector to the average speed of 

 the wind without regard to direction. 

 (5) 



persistency — See constancy of the current. 



Peru Current — (also called Humboldt Current). 

 The cold ocean current flowing north along the 

 coasts of Chile and Peru. The Peru Current 

 originates from the West Wind Drift in the 

 subantarctic Pacific Ocean. The northern limit 

 of the current can be placed a little south of the 

 Equator, where the flow turns toward the west, 

 joining the South Equatorial Current. 



Petersen grab — A type of bottom sampler con- 

 sisting of two hinged semicylindrical buckets 

 held apart by a cocking device. On striking 

 the bottom the locking device is released so that, 

 on hauling, the buckets revolve and come to- 

 gether, enclosing a sample of the bottom. 



Phaeocystis — A genus of brown, unicellular, and 

 colonial, marine phytoplankton of the class 

 Chrysophyceae. Colonies are surrounded by 

 large gelatinous sheaths. This alga appears in 

 vast concentrations at times, especially m neritic 

 parts of the North Atlantic, coloring the water 

 brown and imparting an offensive odor to it. 

 Plankton nets towed through such masses are 

 clogged rapidly. Herring reportedly avoid 

 these concentrations. 



plantom bottom — See "deep scattering layer. 



pharyngeal teeth — Specialized dentition on vari- 

 ous gill arch elements in fishes ; in some species 

 these teeth are used in sound production. 



phase — The state of aggregation of a substance, 

 for example, solid (ice), liquid (water), or gas 

 (vapor). (5) 



phase angle — The angular measure along a simple 

 harmonic wave. (5) 



phase difference — See epoch. 



phase inequality — 1. Variations in the tide or 

 tidal currents associated with changes in the 

 phase of the moon. At new and full moon 

 (springs) the tide-producing forces of the sun 

 and moon act in conjunction, resulting in greater 

 than average tide and tidal currents. At first 

 and last quarters of the moon (neaps) the tide- 

 producing forces oppose each other result in 

 smaller than average tide and tidal currents. 

 (See fimire for tide cycle.) 



2. See spring tide, neap tides, tidal cur- 

 rents. 

 (50) 



phase lag — See epoch. 



phase reduction — A processing of high and low 

 water observations to obtain quantities such as 

 spring and neap tide ranges and tidal currents. 



which are associated with the changing phase 

 of the moon. 



phase speed — See wave velocity. 



phase velocity — Velocity, measured over a short 

 time period, at which a particular wave crest 

 is propagated through water or rock media. 

 (35) 



phasor — The complex quantity measuring an 

 impedance. It may be computed as the quotient 

 of two other complex quantities, which are also 

 called phasors, and which are derived from 

 sinusoidally varying magnitudes of the stimu- 

 lus and the response in question. (28) 



phi grade scale — A logarithmic transformation 

 of the Wentworth grade scale for size classifica- 

 tions of sediment grains based on the negative 

 logarithm to the base 2 of the particle diameter. 



Phi 

 Grade 

 Scale 



-8 



-7 



-6 



-5 



-4 



-3 



-2 



-1 







4-1 



+2 



+S 



-1-4 



+ 5 



-1-6 



-1-7 



-1-8 



-t-9 



-t-10 



-hll 



-1-12 



>-H2 



Modified 



Grades 



(Millimeters) 



>256. 



128. 0\ 

 64.0/ 

 32. 0] 

 16. 1 

 8. Of 

 4. Oj 

 2.0 

 1.0 

 0.5 

 0.25 

 0. 125 

 0. 0625 

 0. 0313 

 0. 0156 

 0. 0078 

 0. 0039 

 0. 00195 

 0. 00098 

 0. 00049 

 0. 00024 



<0. 00024 



Wentworth 

 Sediment Class 



Boulders, Rock. 

 Cobbles 



Pebbles- 



•Gravel 



Granules 



Very Coarse 



Coarse 



Medium ^Sand 



Fine 



Very Fine 



isilt 



^Clay 



Colloids. 



Phleger corer — A gravity sampling tube used to 

 obtain 1%-inch diameter samples up to 4 feet 

 long. The sampler consists of a tailfiji assembly 

 with attached weight, a core barrel with a 

 plastic liner inside it, a core cutter, and a core 

 catcher. When fully rigged, the corer weighs 

 about 100 pounds. 



pholad — See rock borer. 



phosphate phosphorus — An ionic form of phos- 

 phorus occurring in nature; an essential nutrient 

 for marine organisms. Estimates of primary 

 productivity have been made by determining 

 phosphate concentrations in a water column dur- 

 ing different seasons. 



phosphor — See scintillator. 



phosphorescence — 1. The production of light 

 without sensible heat. 



2. Emission of electromagnetic radiation by 

 a substance as a result of previous absorption of 

 radiation of shorter wavelength. In contrast 

 to fluorescence, the emission may continue for 

 a considerable time after cessation of the exist- 

 ing irradiation. 



122 



