Science / Tides and Currents Glossary

Phase Inequality: Variations in the tides or tidal currents due to changes in the phase of the Moon. At the times of new and full Moon the tide-producing forces of the Moon and Sun act in conjunction, causing . . . View Full Definition

Phase Reduction: A processing of observed high and low waters to obtain quantities depending upon the phase of the Moon, such as the spring and neap ranges of tide. At a former time this process was known as . . . View Full Definition

Physical Oceanographic Real Time System (PORTS): A national system of current, water level, and other oceanographical and meteorological sensors telemetering data in real-time to central locations for storage, processing, and dissemination . . . View Full Definition

Pressure Gauge: A water level gauge that is operated by the change in pressure at the bottom of a body of water due to the rise and fall of the water level. See gas purged pressure gauge.

Pressure Sensor: A pressure transducer sensing de-vice for water level measurement. A relative transducer is vented to the atmosphere and pressure readings are made relative to atmospheric pressure. An absol . . . View Full Definition

Primary Control Tide Station: A tide station at which continuous observations have been made over a minimum of 19 years. Its purpose is to provide data for computing accepted values of the harmonic and non-harmonic const . . . View Full Definition

Prime Meridian: The meridian of longitude which passes through the original site of the Royal Observatory in Greenwich, England and used as the origin of longitude. Also known as the Greenwich Meridian.

Priming Of Tide: The periodic acceleration in the time of occurrence of high and low waters due to changes in the relative positions of the Sun and Moon.

Progressive Wave: A wave that advances in distance along the sea surface or at some intermediate depth. Although the wave form itself travels significant distances, the water particles that make up the wave m . . . View Full Definition

Protective Well: A vertical pipe with a relatively large opening (intake) in the bottom. It is used with the air acoustic ranging sensor and electronic processing (filtering) technique to minimize the nonlin . . . View Full Definition

Pycnocline: A layer in which the density increases significantly (relative to the layers above and below) with depth.

QL: Larger lunar elliptic diurnal constituent. See M1. Speed = T – 3s + h + p = 13.398,660,9° per solar hour.

Quadrature Of Moon: Position of the Moon when its longitude differs by 90° from the longitude of the Sun. The corresponding phases are known as first quarter and last quarter.

R2: Smaller solar elliptic constituent. This constituent, with T2, modulates the amplitude and frequency of S2 for the effect of variation in the Earth's orbital speed due to its elliptical orbi . . . View Full Definition

Race: A very rapid current through a comparatively narrow channel.

Radiational Tide: Periodic variations in sea level primarily related to meteorological changes such as the semi daily (solar) cycle in barometric pressure, daily (solar) land and sea breezes, and seasonal (an . . . View Full Definition

Range Of Tide: The difference in height between consecutive high and low waters. The mean range is the difference in height between mean high water and mean low water. The great diurnal range or diurnal ra . . . View Full Definition

Real-Time: Pertains to a data collecting system that monitors an on-going process and disseminates measured values before they are expected to have changed significantly.

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