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of one of the fundamental constituents derived from the
current-induced draw-down (Bernoulli effect) error in
development of the tide-producing force. The presence of
water level measurements.
overtides is usually attributed to shallow water conditions.
pelorus An instrument formerly used on a vessel in
The overtides usually considered in tidal work are the
connection with a current line and current pole to obtain
harmonics of the principal lunar and solar semidiurnal
the set of the current. In its simplest form, it was a disk
constituents M2 and S2, and are designated by the symbols
about 8 inches in diameter and graduated clockwise for
M4, M6, M8, S4, S6, etc. The magnitudes of these harmonics
every 5° or 10° . It was mounted rigidly on the vessel,
relative to those of the fundamental constituents are
usually with the 0° mark forward and the diameter through
usually greater in the tidal current than in the tide.
this mark parallel with the keel. Bearings were then related
Oyashio A current setting southwestward along the
to the vessel's compass and converted to true.
Siberian, Kamchatka, and Kuril Islands coasts in the Bering
perigean tides or tidal currents Tides of
Sea and North Pacific Ocean.
increased range or tidal currents of increased speed
occurring monthly as the result of the Moon being in
P
perigee. The perigean range (Pn) of tide is the average
p Rate of change (as of January 1, 1900) in mean
range occurring at the time of perigean tides and is most
longitude of lunar perigee.
conveniently computed from the harmonic constants. It is
p = 0.004,641,83° per solar hour.
larger than the mean range where the type of tide is either
19
semidiurnal or mixed, and is of no practical significance mariners, the U.S. Coast Guard, and other marine interests
where the type of tide is predominantly diurnal. in voice or digital form. First introduced in Tampa Bay.
perigee The point in the orbit of the Moon or a potential, tide-producing Tendency for particles
man-made satellite nearest to the Earth. The point in the on the Earth to change their positions as a result of the
orbit of a satellite nearest to its companion body. gravitational interactions between the Sun, Moon, and
perihelion The point in the orbit of the Earth (or Earth. Although gravitational attraction varies inversely as
other planet, etc.) nearest to the Sun. the square of the distance of the tide producing body, the
period Interval required for the completion of a resulting potential varies inversely as the cube of the
recurring event, such as the revolution of a celestial body distance.
or the time between two consecutive like phases of the tide predicting machine See tide predicting machine.
or tidal current. A period may be expressed in angular pressure gauge A water level gauge that is operated
measure as 360°. The word also is used to express any by the change in pressure at the bottom of a body of water
specified duration of time. due to the rise and fall of the water level. See gas purged
permanent current A current that runs con- pressure gauge.
tinuously and is independent of tides and other temporary pressure gradient force, horizontal The horizontal
causes. Permanent currents include the general surface component of the product of the specific volume and the
circulation of the oceans. rate of decrease in pressure with distance.
Peru Current A South Pacific Ocean current set- pressure sensor A pressure transducer sensing de-
ting northward along the west coast of South America. It vice for water level measurement. A relative transducer is
has sometimes been called the Humboldt Current because vented to the atmosphere and pressure readings are made
an early record of its temperature was taken by the German relative to atmospheric pressure. An absolute transducer
scientist Alexander von Humboldt in 1802. It has also been measures the pressure at its location. The readings are then
called the Peruvian or Chilean Current. The name corrected for barometric pressure taken at the surface.
Corriente de Peru was adopted by a resolution of the primary control tide station A tide station at
Ibero-American Oceanographic Conference at its which continuous observations have been made over a
Madrid-Malaga meeting in April 1935. minimum of 19 years. Its purpose is to provide data for
phase (1) Any recurring aspect of a periodic phe- computing accepted values of the harmonic and
nomenon, such as new Moon, high water, flood strength, nonharmonic constants essential to tide predictions and to
etc. (2) A particular instant of a periodic function the determination of tidal datums for charting and for
expressed in angular measure and reckoned from the time coastal and marine boundaries. The data series from this [ Pobierz całość w formacie PDF ]

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