S
Remote sensing of the ocean surface height by satellite-mounted microwave radar.
Techniques have been developed for extracting the tidal constants for the larger constituents from the satellite data, despite its sampling interval being about twenty times longer than the semi-diurnal period.
It provides an accurate global ocean database of tidal constants, which was previously restricted to areas close to coastal tide gauges and to numerical models constrained over wide areas of the ocean surface.
To add something to the point where no more can be absorbed, dissolved, or retained. In meteorology, it is used when discussing the amount of water vapor in a volume of air.
The line on a thermodynamic diagram that depicts the change in temperature of a saturated air parcel as it rises or falls and undergoes cooling or heating due to adiabatic expansion or compression.
The rate of change in temperature of a saturated air parcel as it adiabatically ascends or descends through the atmosphere. The rate varies, from approximately 1.5 to 3°C per 1,000 feet, e.g., the more water vapour present in a rising parcel of air, the greater the condensation, and thus the greater is the latent heat released, reducing the rate of cooling.
Used to describe an amount of cloud covering the sky of three or four oktas (eighths). In aviation forecasts and reports it is coded as SCT.
Breeze blowing from the sea towards land, due to the relative warmth of the land.
A type of advection fog that forms when warm moist air advects over water with a cooler temperature, and the consequent cooling of that air to below its dewpoint by the underlying cooler water.
Water temperature close to the surface of the sea. It's usually measured 1–20 m below the sea surface.
See Wind waves.
The discontinuity in temperature and humidity that marks the leading edge of the intrusion of cool and moist maritime air associated with a sea-breeze.
In Australia, the seasons are:
- Spring – September, October, November
- Summer – December, January, February (the hottest months)
- Autumn – March, April, May
- Winter – June, July, August (the coldest months)
While some people and countries use the equinoxes and solstices to define the start of each season, it's a better fit to Australia's temperatures to use 1 March, 1 June, 1 September and 1 December. Defining each season as a set of three whole calendar months is also useful for presenting climate-based statistics.
In tide tables, a port for which predictions are required, but for which predictions from the nearest standard port must be used (with suitable corrections). Used when insufficient data for a reliable harmonic analysis is available.
Also called a subordinate port.
Height and direction of the swell with the second-highest energy.
A standing wave in an enclosed or semi-enclosed body of water set off by weather, seismicity, or incident ocean waves.
Seiches are primarily a resonance phenomenon, whose wavelength and period are determined by the geometry. A characteristic feature is the existence of nodes – points of minimum water level disturbance, but greatest horizontal currents – and antinodes, where the reverse occurs.
Relating to earthquakes.
The description of the tide-generating potential was simplified in several ways, two of which were by ignoring the continuous re-distribution of mass that occurs as the water moves in response to the tidal forces, and by ignoring the warping of the elastic solid earth surface as the water level varies. These effects are commonly combined into the term 'self-attraction and loading' (SAL).
A tide, having a period or cycle of approximately one-half of a tidal day.
The direction towards which the current or tidal stream is flowing.
The Bureau defines a severe thunderstorm as one with winds of 48 knots or greater, or hail of diameter 2 cm or larger, or tornadoes or flash floods.
Weather with the potential to affect safety and wellbeing or cause damage to property and infrastructure.
Precipitation, often short-lived (but may last up to an hour) and heavy, falling from convective clouds. They usually begin and end suddenly and occur over localised areas. In aviation forecasts and reports it is coded as SH.
Rain that usually begins and ends suddenly. Showers are relatively short-lived but may last half an hour – often, but not always, separated by blue sky. For terms describing showers in forecasts see:
Combined height of the sea and the swell that mariners experience on open waters. Refers to the average wave height of the highest third of the waves.
Also known as combined sea and swell, or total wave height.
Understanding what's going on in the environment – what it means now and in future for a particular task. Often used in relation to emergency management.
A thermodynamic diagram with a skewed temperature scale on the horizontal axis and a logarithmic scale of pressure on the vertical axis. It is used to plot radiosonde soundings which give a vertical profile of air temperature and dew point temperature through the atmosphere. Forecasters use it to evaluate and forecast air parcel behaviour. Some values that can be determined are the Convective Condensation Level, the Lifting Condensation Level, and the Level of Free Convection.
The state of a tidal stream when its speed is or nearly zero. Especially the moment when the reversing stream changes its direction. Also known as slack tide or slack. See also streams.
A mixture of rain and snow, or falling snow that is melting into rain.
Fog or haze thickened by smoke or other forms of atmospheric pollution. Can be hazardous to health.
Small particles produced by combustion that are suspended in the air (a transition to haze may occur when the smoke particles have travelled great distance and when the larger particles have settled out, the remaining haze particles become widely scattered through the atmosphere). In aviation observations and forecasts it is coded as FU.
Precipitation of ice crystals, most of which are branched (sometimes star-shaped).
Snow that falls for a short period, usually starting and ending suddenly. Typically, it falls from clouds formed by convection.
The water in the spaces between soil particles.
If all the spaces are occupied by air, the soil is completely dry. If they're all filled with water, the soil is saturated.
The time when the sun is at its furthest from the equator and the tilt in the Earth's axis lines up most with the direction of the sun. This means there is the greatest difference between daylight and night-time hours. These times mark the longest (around 22 December) and shortest (around 21 June) days in the southern hemisphere. They're known as the summer and winter solstices.
Tides occurring near the times of summer and winter solstice, when the sun is overhead at the Tropic of Cancer or Capricorn.
Calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin. It's used to gauge the strength of El Niño and La Niña events and their potential effect on the Australian region.
A classification of tidal constituents according to their period. The principle species are semidiurnal, diurnal, and long period.
The rate of change in the phase of a constituent expressed in degrees per hour. The speed is equal to 360° divided by the constituent period expressed in hours.
The rate at which a stream or current flows. Usually expressed in knots or metres per second.
One of the 4 seasons of the year. In the southern hemisphere it's September, October and November.
See tidal plane.
The tides of increased range, or tidal streams of increased speed, occurring semi-monthly near the times of full moon and new moon. See also fortnightly tides.
A sudden strong wind or storm that is usually intense but short-lived.
Extended narrow region (or line) of gusty winds. Often these come with thunderstorms and rain, but a squall line can also happen when skies are clear. It's generally part of a cold front or thunderstorm environment.
A luminous and sometimes audible electric discharge that occurs from objects, especially pointed ones, when the local electrical field (voltage) attains a strength of near 1000 volts per centimetre. It often occurs during the latter phases of a violent thunderstorm. It typically appears on the extremities of aircraft, lightning rods and steeples.
A state of the atmosphere in which a lifted air parcel will sink to its equilibrium level once the lifting mechanism ceases, due to the air parcel being denser (cooler) than the surrounding air.
The condition at high or low water when there is no perceptible change in the height of tide for a period of time. Sometimes called platform tide. See also streams.
A mathematical model of the atmosphere which is standardised so that predictable calculations can be made.
In the context of tide tables, a port for which sufficient data is available in order for a set of official predictions to be produced. Also known as a primary port, especially in North America.
An atmospheric wave that is stationary with respect to the earth’s surface.
Any water information in the aquifer framework used by a State.
Any water information in a State's National Groundwater Information System (NGIS) database.
Fog that forms when when cool air, passing over warm water, reaches its saturation point due to water evaporating from the warm water into the cooler air. Fog rising in the convection currents above the water give rise to a steaming appearance.
A well that is connected to the sea through a small opening which filters out any high frequency waves while admitting the long period tidal (and other) level variations. Used by some types of tide gauges to measure sea level, traditionally via a float or some other means.
See Thunderstorm.
Abnormal rise in sea level above the normal tide levels. These powerful ocean movements are caused by strong winds piling water up against the coast as a cyclone approaches.
An abnormal rise in sea level over and above the normal (astronomical) tide levels. It can be thought of as the change in the water level due to the presence of a storm.
These powerful ocean movements are caused by strong winds piling water up against the coast as a cyclone or other low pressure system approaches.
Tide that combines storm surge with normal tide levels.
The water level that results from the combination of the storm surge and the normal (astronomical) tide.
The high water mark on a shoreline, typified by the presence of flotsam and jetsam (types of marine debris associated with vessels).
Cloud that forms in a flattish layer rather than developing height.
Cloud that forms in the lower levels of the atmosphere in a relatively flat layer, with some taller, more clumpy areas. It can produce drizzle.
The boundary zone between the stratosphere and the mesosphere. In the stratosphere the temperature increases with height, with the stratopause being the point of maximum temperature, prior to a decrease in temperature in the mesosphere.
The layer of the atmosphere located between the troposphere and the mesosphere. It is characterized by an increase in temperature with height and an absence of convective clouds and associated turbulence.
Low cloud forming a uniform layer.
Flow of water in streams, rivers and other channels. Also called 'flow'.
Also known as tidal currents. Sometimes used to refer exclusively to the tidal currents along the main directions of ebb and flood.
The set of the current is the direction in which it flows. On the incoming tide, the streams are said to be in flood and the outgoing streams are in ebb. The stand of the tide occurs near high and low water when the water level is unchanging.
Tidal streams which flow back and forth along a line are rectilinear, whereas those that follow an elliptical circuit (due to the Coriolis force) are rotary. See also rotary flow.
Wind blowing at speeds of 40–50 km/h.
An area where 2 tectonic plates meet and move towards each other. One slides underneath the other and moves down into the Earth. The resulting undersea earthquakes are the main cause of tsunamis.
The process of ice changing directly into water vapour.
A descending motion of air in the atmosphere, usually with the implication that it extends over a broad area such as occurs with a high pressure system.
A band of relatively strong winds found between 20 and 40° latitude in the middle and upper troposphere. Jet streams form near boundaries of adjacent air masses with significant differences in temperature.
One of the 4 seasons of the year. In the southern hemisphere it's the 3 hottest months – December, January and February.
Times of day when sun protection is recommended (when the UV index is 3 and above).
Little chance of the sun being hidden by cloud.
Cloud expected to cover up to 15% of the sky for most the day.
A day can be called sunny though more than half the sky is covered in cirrus cloud. Cirrus clouds are often thin and wispy, allowing enough sunlight through to produce shadows.
Persistent, single, intense, rotating updraught and downdraught coexisting in a thunderstorm. It can bring violent winds (sometimes tornadoes), heavy rain and hail.
When the temperature of a liquid falls below its freezing point, without it becoming a solid.
Wind speed and direction measured at 10 m above the Earth's surface. In the marine environment, surface wind generates waves locally. Strong surface winds that come with intense storms can cause large swell waves.
See Peak wave period.
Waves which have travelled from the area where they were caused (for example, by storm activity and wind). They may travel thousands of kilometres from their origin before dying away. There can be swell waves even if the wind is calm and there are no sea waves.
The minimum length of data necessary to separate a pair of constituents according to the Rayleigh criterion.
The average period of the revolution of the Moon around the Earth with respect to the Sun or the average interval between corresponding phases of the Moon. The synodical month is 29.5305888 mean solar days long. Also known as lunation or lunar month.
Chart showing lines of equal pressure (isobars), corrected to mean sea level, over a broad area (for example, Australia). They're based on the observations taken every 3 hours by weather observers and automatic weather stations. Also called weather maps.
Used to describe weather features in the lower atmosphere that range in size from several hundred to several thousand kilometres across. For example, it's often used about high and low pressure systems over mid-latitude regions.
The condition whereby the Sun, Earth and Moon are in alignment. See also quadrature.