TYPHOON 



is visibly conspicuous, but all waters contain 

 some suspended matter and therefore are turbid. 



turbidity current — (or density cwrent^ mud floiu, 

 .suspension current) . A highly turbid, relatively 

 dense current carrying large quantities of clay, 

 silt, and sand in suspension which flows down 

 a submarine slope througli less dense sea water. 



turbulence — A state of fluid flow in which the in- 

 stantaneous velocities exhibit irregular and ap- 

 parently random fluctuations, so that in prac- 

 tice only statistical properties can be recognized 

 and subjected to analysis. These fluctuations 

 often constitute major deformations of the flow 

 and are capable of transporting momentum, en- 

 ergy, and suspended matter at rates far in excess 

 of the rate of transport, by molecular ditfusion 

 and conduction in a nonturbulent or laminar 

 flow. (5) 



turbulent diffusion — See eddy diffusion. 



turbulent flow — A flow characterized bj' irregu- 

 lar, random velocity fluctuations. 



turn of the tide — See change of tide. 



turnover rate — Usually, the net primary produc- 

 tion per unit primary standing crop (phyto- 

 plankton) under natural light conditions, or 

 more specifically, the production divided by the 

 standing stock (biomass). 



turret ice — See ropak. 



turtlegrass — See seagrass. 



tusk shell — See tooth shell. 



two-year ice — A Russian term for young polar 

 ice. 



tychoplankton — Plankton consisting of animals 

 and plants which have temporarily migrated or 

 have been carried into the plankton fi-om their 

 normal benthic habitat. 



Tyler standard grade scale — A scale for sizing 

 particles based on the square root of 2 used as 

 specifications for sieve mesh. Alternate class 

 limits closely approximate the class limits on the 

 Udden grade scale, and the intermediate limits 

 are the geometric means of the ITdden scale 

 values : O.'SO, 0.71, 1.00, 1.41, 2.00. (2) 



Tyndall flowers — Small water-filled cavities, 

 often of basically hexagonal shape, which appear 

 in the interior of ice masses upon which liglit is 

 falling. Their formation results from the melt- 

 ing ice by radiative absorption at points of de- 

 fect in the ice lattice. (5) 



type of tide — The characteristic feature of the 

 tide (tidal current) determined from the com- 

 bination of its diurnal and semidiurnal com- 



ponents. Tides are classified as semidiurnal, 

 mixed, and diurnal, but there are no sharply de- 

 fined limits separating the groups. 



DAYS 





TYPES OF TIDE CURVES 



typhon — See typhoon. 



typhoon — (also spelled typhon). A severe tropi- 

 cal cyclone in the western Pacific. (5) 



207-109 O - 66 - 12 



171 



