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Outdoor Glossary: O

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O1
Lunar diurnal constituent. See K1. Speed = T - 2s + h = 13.943,035,6 per solar hour.

obliquity factor
A factor in an expression for a constituent tide (or tidal current) involving the angle of the inclination of the Moon's orbit to the plane of the Earth's Equator.

obliquity of the ecliptic
The angle which the ecliptic makes with the plane of the Earth's Equator. Its value is approximately 23.45.

obliquity of the Moon's orbit
The angle which the Moon's orbit makes with the plane of the Earth's Equator. Its value varies from 18.3 to 28.6, depending upon the longitude of the Moon's ascending node; the smaller value corresponding to a longitude of 180 and the larger one, to a longitude of 0.

occiput
Rear portion of crown. Synonym(s): hindhead.

Ocean
The great body of salt water which occupies two-thirds of the surface of the Earth, or one of its major subdivisions.

ocean current
A nontidal current constituting a part of the general oceanic circulation.

oceanography
The science of all aspects of the oceans, in spite of its etymology. The term, oceanography, however, implies the interrelationships of the various marine sciences of which it is composed. This connotation has arisen through the historical development of marine research in which it has been found that a true understanding of the oceans is best achieved through investigations based on the realization that water, its organic and inorganic contents, motions, and boundaries are mutally related and interdependent.

offshore
(1) In beach terminology, the comparatively flat zone of variable width, extending from the SHOREFACE to the edge of the CONTINENTAL SHELF. It is continually submerged. (2) The direction seaward from the shore. (3) The zone beyond the nearshore zone where sediment motion induced by waves alone effectively ceases and where the influence of the sea bed on wave action is small in comparison with the effect of wind. (4) The BREAKER ZONE directly seaward of the LOW TIDE line.

offshore breakwater
A BREAKWATER built towards the seaward limit of the LITTORAL ZONE, parallel (or nearly parallel) to the shore.

offshore currents
(1) Currents outside the surf zone. (2) Any current flowing away from the shore.

offshore wind
A wind blowing seaward from the land in the coastal area.

old growth
Old forests often containing several canopy layers, variety in tree sizes and species, decadent old trees, and standing and dead woody material.

onshore
A direction landward from the sea.

onshore current
Any current flowing towards the shore.

onshore wind
A wind blowing landward from the sea.

OO1
Lunar diurnal, second-order, constituent. Speed = T + 2s + h = 16.139,101,7 per solar hour.

open sea
Same as HIGH SEAS.

operculum
Swollen structure in pigeons overarching the nostril.

opposable
describes the position of the thumb relative to the fingers. An opposable thumb allows raccoons to grasp and manipulate small objects.

opposing winds
A wind blowing in the opposite direction to that in which the waves are travelling.

ordinary
With respect to tides, the use of this nontechnical word has, for the most part, been determined to be synonymous with mean. Thus, ordinary high (low) water is the equivalent of mean high (low) water. The use of ordinary in tidal terms is discouraged.

ordinary high water mark (OHWM)
(SMP) That mark that will be found by examining the bed and banks and ascertaining where the presence and action of waters are so common and usual, and so long continued in all ordinary years, as to mark upon the soil a character distinct from that of the abutting upland, in respect to vegitation as that condition exists on June 1, 1971, as it may naturally change thereafter, or as it may change thereafter in accordance with permits issued by a local government or the department

ordinary tide
This expression is not used in a technical sense by the U.S. Coast and Geodetic Survey, but the word "ordinary" when applied to tides, may be taken as the equivalent of the word "mean". Thus "ordinary HIGH WATER LINE" may be assumed to be the same as "mean high water line".

organic soil
Soil at least partly derived from living matter, such as decayed plant material.

orifice
See stilling well and protective well.

orthophotograph
A photograph prepared from a perspective photograph by removing distortions and displacements of points caused by tilt, relief, and perspective.

orthophotomap
A map made by assembling a number of orthophotographs into a single, composite picture.

ORV
Off-road vehicles, such as motor cycles, 4-wheel drive vehicles, and 4-wheelers.

oscillation
A periodic motion backward and forward. To vibrate or vary above and below a mean value.

outcrop
A surface exposure of bare rock, not covered by soil or vegetation.

outer primaries
Group of primaries farthest from the body.

outer secondaries
Group of secondaries farthest from the body.

outer tail feathers
Part of the tail farthest from the center.

outer wing
Alula and primaries.

outfall
(1) The vent of a river, drain, etc. (2) A structure extending into a body of water for the purpose of discharging sewage, storm runoff or cooling water.

outflanking
EROSION behind or around the inner end of a GROIN or BULKHEAD, usually causing failure of the structure.

overfalls
Breaking waves caused by a conflict of currents, or by the wind moving against the current.

overfishing
To fish to the detriment of (a fishing ground) or to the depletion of (a kind of organism); to fish until all the fish are gone

overmature timber
Trees that have attained full development, particularly in height, and are declining in vigor, health, and soundness.

oversplash
The water that splashes over the top of a BREAKWATER, seawall, etc.

overstory
The upper canopy layer; the plants below comprise the understory.

overtide
A harmonic tidal (or tidal current) constituent with a speed that is an exact multiple of the speed of one of the fundamental constituents derived from the development of the tide-producing force. The presence of overtides is usually attributed to shallow water conditions. The overtides usually considered in tidal work are the harmonics of the principal lunar and solar semi diurnal constituents M2 and S2, and are designated by the symbols M4, M6, M8, S4, S6, etc. The magnitudes of these harmonics relative to those of the fundamental constituents are usually greater in the tidal current than in the tide.

overtopping
Water carried over the top of a COASTAL DEFENSE due to wave run-up or surge action exceeding the crest height.

overwash
(1) The part of the UPRUSH that runs over the crest of a BERM or structure and does not flow directly back to the ocean or lake. (2) The effect of waves overtopping a COASTAL DEFENSE, often carrying sediment landwards which is then lost to the beach system.

oyashio
A current setting southwestward along the Siberian, Kamchatka, and Kuril Islands coasts in the Bering Sea and North Pacific Ocean.

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