R
Acronym for RAdio Detection And Ranging. An electronic instrument used to detect distant objects and measure their range by detecting scattered or reflected radio energy.
The process by which energy is propagated through any medium by virtue of the wave motion in that medium. Electromagnetic radiation, which emits heat and light, is one form.
Fog that forms when radiational cooling at the earth’s surface lowers the temperature of the air near the ground to, or below, its dew-point. RAIN Precipitation in the form of liquid water droplets greater than 0.5 mm diameter. In aviation forecasts and reports it is coded as RA.
The cooling of the earth’s surface and the adjacent air which occurs at night when the earth’s surface suffers a net loss of heat due to outgoing radiation being greater than incoming radiation.
A quasi-periodic rise and fall of sea level caused by meteorological variability. Also known as meteorological tides.
Condensed moisture from the atmosphere falling as liquid water drops greater than 0.5 mm in diameter.
Compared to showers, rain is steadier and normally falls from stratiform (layer) cloud.
For terms describing rain in forecasts see:
Precipitation in the form of liquid water droplets greater than 0.5 mm diameter. Rain precipitation is generally steady and widespread and normally falls from stratiform (layer) cloud. In aviation forecasts and reports it is coded as RA.
Day when rainfall of at least 0.2 mm is recorded.
Total liquid from precipitation or condensation from the atmosphere, measured in a rain gauge.
See Chance of any rain.
Likely rainfall is the amount of rain with a 50% chance of happening during the day.
This is used as the lower value of the possible rainfall range in town forecasts.
Possible higher rainfall is the amount of rain with a 25% chance of happening during the day. There is also a 75% chance there won't be this much rain.
This is used as the higher value of the possible rainfall range in town forecasts.
Possible rainfall range is part of town forecasts. It describes the expected rainfall range for the day.
The rainfall range highlights the variability of certain types of rain. On showery or thunderstorm days where rain is more 'hit and miss', the possible rainfall range may be quite large (for example, 5–30 mm). When steady rainfall is expected over a wide area, the range may be smaller (for example, 10–15 mm).
The difference between the maximum and minimum water levels during a typical tidal cycle.
A criterion used in tidal analysis, which requires that only constituents which are separated by at least one complete period from their neighbouring constituents over the length of data available should be included in the harmonic analysis of a given time series. See also synodic period.
A tidal stream which flows alternately in approximately opposite directions with slack water at each reversal of direction. Encountered mainly in straits and channels. Also known as a reversing stream. See also streams.
Total amount of electromagnetic energy emitted from the sun that is reflected from the ground and irradiates a specified unit horizontal surface from underneath.
Irradiance emitted from the sun that is reflected from the ground and irradiates a specified unit horizontal surface from underneath.
The clockwise or western rotational direction of the lunar nodes around the ecliptic. This is opposite to that of most other rotations and orbits of the solar system.
The ratio of the vapour pressure to the saturation vapour pressure with respect to water. Also known as the ratio of the existing amount of water vapour to that which could be held by a parcel of air. It is usually expressed as a percentage.
Amount of moisture in the air. It's a percentage of the maximum moisture the air could hold at that temperature.
Height of sea level above land at a particular location or point of reference. For example, a coastal benchmark.
The difference between the observed sea level and the tidal prediction for a given location.
Residuals are most commonly due to weather related effects, limitations of the harmonic model, harbour seiches and errors in measurement or data processing. All of which leave recognisable imprints in the data.
In relation to radar, it is the ability to read two distinct targets separately. The clearer the resolution, the nearer the two objects can be to each other and still be distinguishable.
A result of the large amplitudes. Occurs when the frequency of a force is equal to the natural oscillation frequency of a system.
Tidal resonance occurs when the natural period of an ocean or sea is close to the period of a tide-producing force.
The representation of observed tidal variations as frequency-dependent amplitude and phase responses to the forcing functions, usually the gravitational and radiational tide-producing forces.
Elongated area of high pressure. On a weather map it shows as rounded isobars extending outwards from a high pressure system and has a ridge line.
Ice formed by the rapid freezing of supercooled water droplets when they contact an exposed object, such as an aircraft frame, forming a white and opaque granular deposit of ice.
A narrow shearing current flowing offshore through the surf zone. Sometimes (misleadingly) called a rip tide. Rips are a part of a circulation cell forced by surface wave transport, and have little to do with tides.
A low-level, horizontal, tube-shaped cloud. Usually associated with a thunderstorm gust front, where the roll cloud is completely detached from the base of the cumulonimbus cloud. It will sometimes form with a cold front.
A tidal stream that flows continually with the direction of flow changing through all points of the compass during a tidal cycle. Usually found offshore where there are no restricting barriers.
This natural tendency of tidal flows (they become rectilinear only when restricted) is due to the Coriolis force. See also streams.
A cloud formation found in the lee of a mountain or similar barrier. The air rotates around a horizontal axis parallel to the barrier, causing a hazard to aircraft.
The maximum distance at which the runway, or lights or markers delineating it, can be seen from a position above a specified point on its centerline.