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A deformation of the solid earth in response to the gravitational tidal forces of the Sun and Moon. The largest effect is the semi-diurnal deformation nearly in phase with the transit of the Moon – its amplitude is less than 20 cm.
Intense low-pressure systems that happen on average several times a year off the east coast of Australia – in particular, southern Queensland, New South Wales and eastern Victoria.
The tidal phase during which the water level is falling, or the tidal current is flowing seaward (ebb current). Opposite to flood.
Describes the radio signal that appears on a radar display when it's reflected by precipitation such as rain or hail.
Dynamic biological community of interacting plant, animal and micro-organisms and their physical environment.
Small disturbance in the wind that can cause turbulence.
Movement of water in wind-driven currents. This process brings colder water to the coastline.
Refers to the extensive warming of the central and eastern Pacific Ocean that leads to a major shift in weather patterns across the Pacific Ocean and neighbouring countries. In Australia (particularly eastern Australia), drier and warmer-than-average conditions are more likely in El Niño events.
Climate driver in the Pacific Ocean that swings between 3 phases: El Niño, neutral and La Niña. Southern Oscillation is the changes in atmospheric pressure (and hence in climate) linked to the El Niño warming.
In relation to water, electrical conductivity is the capacity of the water to transmit a flow of electricity. It's a common measure of water salinity.
The distance between mean sea level and a point on the earth’s surface.
Used in at least two different ways in tidal work – as a synonym for phase lag, and for a period of time (usually a nodal cycle) over which a mean is calculated as the basis for a tidal datum.
The geographic circle at 0° latitude on the earth’s surface.
Zone of relatively low pressure along the equator, including across northern Australia.
The height at which a rising parcel of air will become equal in temperature to that of the environment, at which point it is no longer buoyant and thus will cease to rise in the atmosphere without forcing.
Theoretical model under which waters, uniformly covering the face of the Earth, respond instantly to the tide-producing forces of the Moon and Sun and form an equilibrium under action of these forces.
Friction, inertia, irregular distribution of the land masses are all disregarded under this theory, but the model provides an important theoretical basis for tidal science.
The hypothetical tide which would be produced by the lunar and solar gravitational forces under the equilibrium theory in the absence of any other ocean dynamics or terrestrial constraints.
The time when the sun crosses the equator, when night and day are of equal length. This is around 21 March (autumn equinox) and 22 September (spring equinox).
Global changes of sea level taking place over many years. Sometimes associated with ocean volume changes or with globally synchronous changes.
However, such ocean surface displacements are now understood to be spatially irregular.
Changing from liquid to vapour.
When assessing and accounting for water resources, evaporation refers to the movement of water from the land surface (mainly liquid) to the atmosphere (water vapour). Land surface water available for evaporation includes surface water, soil water, water within vegetation, and water on vegetation and paved surfaces.
Total amount of water moved from the land surface to the atmosphere through evaporation and plant transpiration.
Plant transpiration describes how water moves through a plant and evaporates from exposed parts such as leaves and stems.
One of many deviations in the Moon's orbit caused by changes in the solar gravitational potential during the course of orbit, which produces evectional constituents. See also variation.
The measure of energy received per unit area.
Area of clear skies that develops in the centre of a tropical cyclone. It usually comes with light winds and no rain.
Organised band of cumulonimbus clouds that surrounds the eye of a tropical cyclone.