Glossary


S

The terms and definitions found in the glossary relate to the science of meteorology.

For descriptions and definitions of words used in the Bureau's forecasts and warnings, please refer to Weather Words.

SALR
The Saturated Adiabatic Lapse Rate (SALR) is the rate at which the temperature of a parcel of air saturated with water vapour changes as the parcel ascends or descends.
The SALR is often taken as 1.5 degree Celsius per 1000ft, although the actual figure varies according to the amount of water vapour present.
SCO
Stands for Seasonal Climate Outlook. These are outlooks of rainfall and temperature for three months ahead and are updated every month. See http://www.bom.gov.au/climate/ahead/
Sea and Swell, Combined
Also known as total wave height, or significant wave height. Combined sea and swell describes the combined height of the sea and the swell that mariners experience on open waters. The height of the Combined sea and swell refers to the average wave height of the highest one third of the waves. A lookup table has been developed to outline how the Combined sea and swell is calculated.
Sea and Swell
  • Peak Wave Period: Period in seconds between the swells of the primary swell component. The larger the time difference, the greater the amount of energy associated with the swells.
  • Primary Swell: Height and direction of the swell with the highest energy component. This is sometimes referred to as the dominant swell.
  • Sea waves: waves generated by the wind blowing at the time, and in the recent past, in the area of observation.
  • Secondary Swell: Height and direction of the swell with the second highest energy component.
  • Swell Period: See Peak Wave Period.
  • Swell waves: waves which have travelled into the area of observation after having been generated by previous winds in other areas. These waves may travel thousands of kilometres from their origin before dying away. There may be swell present even if the wind is calm and there are no 'sea' waves.
  • Wave period: the average time interval between passages of successive crests (or troughs) of waves.
  • Wave Height: Generally taken as the height difference between the wave crest and the preceding trough.
  • Wave Length: The mean horizontal distance between successive crests (or troughs) of a wave pattern.

See the Sea and Swell tables for detailed of sea and swell scales.

See the Second Swell page for more information about Secondary Swell.
Sea breeze
A local onshore wind. Cooler air from over the sea flows onto the shore to replace the warm air rising over the land. On sunny days the land heats up more quickly, and to a greater extent, than the sea. The air in contact with the land warms and expands and the resulting changes in the pressure and temperature differences and distributions cause the sea breeze circulation. At night, when the land cools more quickly, and to a greater extent, than the sea, the reverse land breeze circulation is set up.
Seasons
In Australia, the seasons are defined by grouping the calendar months in the following way:
  • Spring - the three transition months September, October and November.
  • Summer - the three hottest months December, January and February.
  • Autumn - the transition months March, April and May.
  • Winter - the three coldest months June, July and August.
These definitions reflect the lag in heating and cooling as the sun appears to move southward and northward across the equator. They are also useful for compiling and presenting climate-based statistics on time scales such as months and seasons.
Showers
Precipitation, often short-lived (but may last half an hour) and heavy, falling from convective clouds. Usually begin and end suddenly.
Sleet
Generally refers to a mixture of rain and snow or falling snow that is melting into rain.
Smog
Smog (contraction for 'smoke fog') is a fog in which smoke or other forms of atmospheric pollutant have an important part in causing the fog to thicken, and have unpleasant and dangerous physiological effects.
Snow
Precipitation of ice crystals, most of which are branched (sometimes star shaped).
Southern Oscillation Index (SOI)
The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.

Click here for more information
Spring
The three transition months September, October and November (for the southern hemisphere).
Squall
A squall comprises a rather sudden increase of the mean wind speed which lasts for several minutes at least before the mean wind returns to near its previous value. A squall may include many gusts.
SST(s)
Stands for Sea Surface Temperature(s), also SSTA(s) - Sea Surface Temperature Anomalies. Anomalies in the surface temperature are associated with changes in the heat exchange between atmosphere and ocean, or changes in ocean currents or upwelling, and these changes can drive large changes in rainfall and atmospheric circulation patterns. SSTAs are therefore often strongly related to the development and maintenance of unusual climate patterns, such as ENSO.
Storm Force Wind Warning
A Storm Force Wind Warning is a statement which warns of winds averaging from 48 knots and up to 63 knots in coastal waters and high seas areas.
Stratosphere
Layer of the atmosphere between about 10 and 50 kilometres above the ground.
Stratus cloud
Low cloud forming a uniform layer.
Strong Wind Warning
A Strong Wind Warning is a statement which warns of winds averaging from 26 knots and up to 33 knots in coastal waters.
Summer
The three hottest months December, January and February (for the southern hemisphere).
Sunshine
Direct radiation from the sun, as opposed to the shading of a location by clouds or by other obstructions.
Supercell
A persistent, single, intense updraught and downdraught coexisting in a thunderstorm.
Synoptic chart
Chart showing lines of equal pressure (isobars), corrected to mean sea level (MSL), over a broad area (eg Australia). Based on the synoptic observations taken simultaneously every 3 hours by weather observers and Automatic Weather Stations across Australia.
Synoptic scale
A horizontal length scale that corresponds to the size of the large-scale features of the lower atmosphere (ie the highs and lows over mid-latitude regions).