Glossary |
Select a letter from the index given below,
to be shown those glossary items which begin with the same letter.
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A |
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Advection |
The sideways movement of air in the lower atmosphere due to the differences
in air pressure (commonly called wind). Process of transfer of
air mass properties by the velocity field of the atmosphere. |
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Air |
The mixture of gases and particles that make up our atmosphere. |
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Amounts |
Amounts shows the quantity of the element requested.
For example, choosing the amounts column under
Rainfall Maps
will give a rainfall map of how much rainfall (in millimetres) has fallen
for the time period and area chosen.
If you choose deciles, this gives an element a ranking, thus
demonstrating how it compares with the surrounds. For example, a decile rainfall
map will show whether the rainfall is above average, average or below average
for the time period and area you have already chosen. |
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Analogue |
A past situation, which resembles the current situation, is called an analogue,
which can then be used as a guide for what is to come. For example, by finding similar
SOI patterns
to the current year, we can then examine rainfall patterns from that time
to use as a guide as to what will happen this year. The Bureau of Meteorology's
Seasonal Climate Outlook includes a listing of several analogue years
in which the SOI behaved similarly to the current year. |
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Anemometer |
A device used to measure wind speed. |
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Anomaly |
The departure of an element from its long-period
average value for the location concerned. For example, if the maximum
temperature for June in Melbourne was 1 degree Celsius higher than the
long-term average for this month, the anomaly would be +1 degrees Celsius.
The current international standard is to use the 30 year average from
1961 to 1990 as the long-term average. |
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Anticyclones |
Atmospheric circulations that rotate anti-clockwise in the southern
hemisphere. Anticyclones are areas of higher pressure and are generally
associated with lighter winds and fine and settled conditions. |
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The Apparent Temperature (AT) - Heat Index |
The apparent temperature (AT), invented in the late 1970s, was designed to measure thermal sensation in indoor conditions. It was extended in the early 1980s to include the effect of sun and wind. Only the modification due to wind is taken into account on this site. The AT index used by the Bureau is based on a mathematical model of an adult, walking outdoors, in the shade. The AT is defined as; the temperature, at the reference humidity level, producing the same amount of discomfort as that experienced under the current ambient temperature and humidity.
The Apparent Temperature is available for each state and territory:
NSW and ACT: www.bom.gov.au/products/IDN65179.shtml
Victoria: www.bom.gov.au/products/IDV65079.shtml
Queensland: www.bom.gov.au/products/IDQ65214.shtml
Western Australia: www.bom.gov.au/products/IDW65100.shtml
South Australia: www.bom.gov.au/products/IDS65004.shtml
Tasmania: www.bom.gov.au/products/IDT65050.shtml
Northern Territory: www.bom.gov.au/products/IDD65155.shtml
Antarctica: www.bom.gov.au/products/IDT65024.shtml
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Atmosphere |
The mixture of gases surrounding a planet. |
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Australian Height Datum (AHD) |
In 1971 the mean sea level for 1966-1968 was assigned
the value of zero on the Australian Height Datum at
thirty tide gauges around the coast of the Australian continent. The
resulting datum surface, with minor modifications in two metropolitan
areas, has been termed the Australian Height Datum (AHD) and was adopted
by the National Mapping Council as the datum to which all vertical
control for mapping is to be referred. Elevations quoted using this
datum are normally followed with the acronym (AHD). See
http://www.ga.gov.au/nmd/geodesy/datums/ahd.jsp for further information. |
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Autumn |
One of the four seasons of the year. The transition months March, April
and May (southern hemisphere). |
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AWS |
Automatic Weather Station. |
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