Synoptic Charts

Question 1

Low air pressure cells:

Answer 1

Low pressure cell’s air flows anticlockwise in the northern hemisphere and clockwise in the Southern Hemisphere. They are often associated with unstable weather conditions: cloudy skies, rain and relatively strong winds. Air pressure decreases towards the centre of the pressure system.

Question 2

High pressure systems and cells:

Answer 2

High pressure systems are areas of stable atmosphere conditions: gentle winds, clear skies and little chance of rain. Air pressure increases towards the centre of the pressure system. Air flow out from the high pressure system in an anticlockwise direction.

Question 3

Cold fronts

Answer 3

Cold fronts occur when a mass of cold, dense air pushes it under a mass of warm air, forcing it to rise. As the warm air rises, it cools and condensation takes place. Lower temperatures are experienced once the front has passed.

Question 4

Warm fronts

Answer 4

Warm fronts occur when a warm parcel of air over takes a colder, denser parcel of air. As with a cold front, rain often results as air rises. However, rainfall resulting from the passage of a warm front tends to last for a longer period of time and to be less intense than that resulting from a cold front. Warm fronts are not common in Australia.

Question 5

Rain

Answer 5

Areas that have received rainfall are shown by diagonal lines.

Question 6

Wind direction

Answer 6

Wind direction and strength for selected locations are shown using lines with small barbs or tails. With the help of a legend we can determine wind speed. Winds are named after the direction from which they blow. A southerly, for example, blows from the south. Winds are strongest where isobars are close together. It is useful to know that winds occur when air moves from areas of high pressure to areas of low pressure.

Question 7

Isobars

Answer 7

Isobars are lines that join places of equal atmospheric pressure. Air pressure is measured in hectopascals (hPa). Isobars are usually drawn at intervals of 2 hPa. Isobars are also known as isohytes.

Question 8

Air pressure

Answer 8

Air pressure is the weight of the air pressing down on the earth’s surface. If air is warmed, it expands, rises and creates a low pressure area on the earths surface. If air is cooled, it contracts, descends and creates an area of high pressure on the earths surface. Areas of high and low pressure determine much of the earths weather.

Question 9

High and Low pressure cells

Answer 9

Most high and low pressure areas move from west to east across Australia.