LONG WAVE 



long wave — In oceanography, same as shallow 

 water wave. (5) 



long-wave radiation — See infrared radiation. 



looming — An apparent elevation of distant ter- 

 restrial objects caused by abnormal atmospheric 

 refraction. Because of looming, objects below 

 the horizon are sometimes visible. The opposite 

 is sinking. (68) 



loop— 1. That part of a standing wave or 

 clapotis where the vertical motion is greatest 

 and the hoi'izontal velocities are least. Loops 

 (sometimes called antinodes) are associated with 

 clapotis and with seiche action resulting from 

 resonant wave reflections in a harbor or bay. 

 (61) 



2. A pattern of field observations. Such a 

 pattern is useful in correcting for drift in grav- 

 ity meter observations. 



loop bar — A bar formed by the junction of the 

 ends of two spits on the mainland side of an 

 offshore island undergoing wave erosion. 



loose ice — See broken ice. 



loose pack ice — Broken ice which is easily nav- 

 igable. (59) 



Loran — A long-range electronic navigation sys- 

 tem which uses the time divergence of pulse- 

 type transmission from two or more fixed sta- 

 tions. (This term is derived from the words 

 "?ong-range navigation.") (63) 



lough — See loch. 



love wave — (or Q wave). A transverse wave 

 propagated along the boundary or two elastic 

 media, both of which have rigidity; that is, 

 both media must be capable of propagating 

 transverse waves. A surface seismic wave in 

 which the particles of an elastic medium, vibrate 

 transverse to the direction of the wave's travel, 

 with no vertical component. (35) 



low — 1. A cyclone, or area of low atmospheric 

 pressure. (68) 



2. A submarine depression of any size or 

 shape; also called a bathymetric low. 



low energy environment — A region character- 

 ized by a general lack of wave or current motion, 

 permitting the settling and accumulation of very 

 fine-grained sediment (silt and clay). (2) 



lower high water — (abbreviated LHTW). The 

 lower of two high waters of any tidal day where 

 the tide exhibits mixed characteristics. See 

 mixed tide. 



lower high water interval — (abbreviated 

 LHWI). The interval of time between the 

 transit (upper or lower) of the moon over the 

 local or Greenwich meridian and the next lower 

 high water. This expression is used when there 

 is considerable diurnal inequality. See luni- 

 tidal interval. (68) 



lower low water — (abbreviated LLW). The 

 lower of two low waters of any tidal day where 

 the tide exhibits mixed characteristics. See 

 mixed tide. 



lower low water datum — An approximation of 

 mean lower low water that has been adopted 

 as a standard datum for a specific area although 

 it may differ slightly from a later determination. 



lower low water interval — (abbreviated LLWI) . 

 The interval of time between the transit (upper 

 or lower) of the moon over the local or Green- 

 wich meridian and the next lower low water. 

 This expression is used when there is consider- 

 able diurnal inequality. See lunitidal inter- 

 val. (68) 



lower transit — See transit. 



lowest low water — (or loioest normal loxo xoater) . 

 A plane of reference whose distance below mean 

 sea level corresponds with the mean level of 

 lowest low water of any normal tide. 



lowest low water springs — A plane of reference 

 approximating the mean level of lowest low 

 water during" syzygy (spring tides). 



lowest normal low water — See lowest low water. 



low tide — See low water. 



low velocity layer — Any layer in which the veloc- 

 ity of compressional wave propagation is lower 

 than in the adjacent layers. Such a layer can 

 act as an efficient channel for the propagation 

 of elastic waves for great distances. (2) 



low water — (abbreviated LW; or law tide). The 

 lowest limit of the surface water level reached 

 by the lowering tide. Low water is caused by 

 the astronomic tide-producing forces and/or 

 the effects of meteorological conditions. 



low water datum — An approximation of mean 

 low water which has been adopted as a standard 

 datum for a specific area although it may differ 

 slightly from a later determination. 



low water equinoctial springs — Low water 

 springs near the times of the equinoxes. 



low water full and change — The average inter- 

 val of time between the transit (upper or lower) 

 of the full or new moon and the next low water. 

 (68) 



low water inequality — See diurnal inequality. 



low water interval — (abbreviated LWI). See 

 lunitidal interval. 



low water line — The intersection of the plane of 

 low water with the shore ; it varies daily with 

 changing Imiar phases and meteorological con- 

 ditions. 



low water lunitidal interval — See lunitidal in- 

 terval. 



low water neaps — See mean low water neaps. 



low water of ordinary spring tides — (abbrevi- 

 ated LWOST). A tidal datum appearing in 

 some British publications, based on low water 

 of ordinary spring tides. (61) 



low water quadrature — See mean low water 

 neaps. 



low water springs — See mean low water springs. 



low water stand — The condition at low tide when 

 there is no change in the height of the water 

 level. A similar condition at high tide is called 

 high water stand. (68) 



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