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16 Jun 2009

GLOSSARY OF TERMS


40-day waves
also known 30-60-day waves, intra-seasonal oscillations, or Madden-Julian oscillations. Low pressure waves sweeping west-east across the top end of continent irregularly every 30-60 days (average 40 days), and triggering rainfall events.

Agistment
To 'Agist' is to take in and feed or pasture livestock for payment. Therefore 'Agistment' is the act of Agisting or the price paid for this service.

Anomalies
Anomalies deviations from the long-term mean.

Anticyclones
cells of high pressure associated with dry air, resulting in mainly cloud-free skies and little or no rainfall. Anticyclones move from west to east across Australia at 25o - 40oS.

Average
average rainfall is calculated by dividing the total by the number of entries, i.e. the arithmetic mean. (cf. median.)

Bush
A stretch of land covered with bushy vegetation or trees.

Bushman
One skilled in bushcraft.

Bush telegraph
An unofficial chain of communication by which information is conveyed and rumour spread, as by word of mouth.

Cell
a vertical circulation of the atmosphere in which warm air rises and cools, flows laterally at high levels, then descends. In the Hadley cell, air rises over the heat equator, flows toward the poles and descends after travelling about 25o of latitude.

CINRS
Climate Impacts and Natural Resource Sciences, part of the Queensland Department of Natural Resources and Mines

Coriolis
effect moving air or water is deflected horizontally because the speed of rotation of the Earth's surface is faster at low latitudes then at high latitudes. The Coriolis effect acts to the left in the southern hemisphere, imparting a clockwise swirl into an are of low pressure. There is little Coriolis effect within 7o of the equator.

Cyclones
depressions, or areas of low pressure, associated with rising warm air and clockwise air circulation (anticlockwise in northern hemisphere. A tropical cyclone is an intense depression fed by very warm (over 27oC) waters, and by latent heat energy release in condensation. The wind is given its swirl by the Coriolis effect.

Deciles
divide a set of recorded rainfalls (monthly, seasonal or annual) into ten groups. The lowest 10% of falls belong to decile range 1, the next lowest to decile range 2 and so on, up to the highest 10% of recorded falls, which belong to decile range 10. The top of decile range 5 is the median.

Droughts
or severe rainfall deficits, occur when a 12-month period receives less rain than in the driest 10% of calendar years. In eastern and northern Australia, they are often associated with strongly negative SOI values, commonly referred to as El Niño event or episode.

ENSO
(El Niño -Southern Oscillation) is a composite term referring to the whole suite of events associated with these negative SOI episodes.

El Niño
originally referred specifically to a warming of the sea off the coast of Peru, now more generally used for the unusual warming of a large area of the eastern equatorial Pacific Ocean. This is strongly linked to changes in the Walker Circulation and to negative phases of the Southern Oscillation.

Gyre
the anticlockwise (southern hemisphere) swirl of currents around an ocean basin, caused by the effect of the Coriolis force on prevailing winds.

ITCZ
the Intertropical Convergence Zone is where the moist south-east trade winds meet the north-east trades of the northern hemisphere. It is a zone of heavy rain and thunderstorms, and constitutes a main source of tropical rain.

Jackeroo
an apprentice station hand on a sheep or cattle property.

Kelpie
(our dog) .......The Clever Kelpie
A kelpie dog was being discussed in a country pub in Queensland. 'That there dog of mine's a bloody marvel,' said the proud bushman. 'He does just about everything. He brings in the cows, goes out after rabbits, gets the mail from the post-office, yards the sheep ...yes, he does just about everything.' 'Well,' said the stranger, 'if he's such a flaming marvel why don't you call him in and let me buy him a beer.' 'Now, fair go,mate,' said the bushman. 'That's one thing I won't allow. It would'nt be right, seeing as he's got to drive me home.'

La Niña
now used to refer to the opposite of an El Niño , or events associated with positive values of the SOI. (Also anti-ENSO).

Median
median rainfall is calculated by ranking totals from highest to lowest. The middle figure is the median. Annual rainfall averages and medians are usually close. Monthly averages may be well above the median in arid regions where the average is distorted by rare, but torrential, rainfall events. (cf. average).

Monsoon
the heavy summer rains in northern Australia, brought about by a moist inflow of air from the oceans to the northwest and northeast of Australia due to low pressure over the continent.

Probability
the chance of an event happening expressed as a percentage. A probability of 70% means the event can be expected to occur in 7 out of 10 years.

QCCA
Queensland Centre for Climate Applications, a joint Natural Resources & Mines / Primary Industries, Queensland Government initiative.

Rouseabout
A handyman on a station.

SOI
(Southern Oscillation Index) measures the strength of the Southern Oscillation; Troup's Index compares the difference in atmospheric pressure between Tahiti and Darwin.

SPOTA
Seasonal Pacific Ocean Temperature Analysis (pronunced 'spotter'), a forecast system (experimental) developed by Climate Impacts and Natural Resource Systems which provides long lead information on Queensland rainfall prospects.

Southern Oscillation
a see-saw of atmospheric pressure anomalies between the Indonesian region and the eastern tropical Pacific Ocean.

SST
sea surface temperature.

Swag
Bundle or roll carried across the shoulders or otherwise, and containing the personal belongings of a traveller through the bush.

Thermocline
narrow band of water where a strong temperature change occurs between the ocean's warm surface water and the deeper, cold layers.

Tropical-extratropical interactions
often significant rainfall-producing events in which moist airmasses from the tropics link up with weather systems from higher latitudes.

Troposphere
the layer of the Earth's atmosphere in which our weather occurs; about 20 km high at the equator, and 10-15 km high at mid-latitudes.

Tropopause
the upper limit of the troposphere.

Trade winds
south-east winds blowing across the southern Pacific and bringing moist unstable air into the ITCZ. These weaken in an El Niño (cause and effect).

Upwelling
upward movement of deep (abyssal), cold water to the surface.

Walker Circulation
the cellular flow of air in a vertical plane over the equatorial Pacific Ocean. Warm, moist air rises over the Indonesian region and tropical western Pacific within the ITCZ, releasing rain. The air then moves at high altitude (12 000 m) to the east and descends over the colder water of the eastern Pacific.