Summary Points

High Pressure Cells

• Highest pressure in the centre
• Anti-clockwise direction
• Isobars are elongated in an east west direction
• Isobars are widely spaced
• Associated with clear sky

Low Pressure Cells

• Lowest pressure in the centre
• Moves in an clockwise direction
• Associated with rising and cooling air and therefore rain
• Possibility of cloud cover
• Isobars closer together therefore giving stronger winds.
• More common in southern Australia in winter.
• In tropical regions they develop into tropical cyclones under hot moist conditions.

Cold Front

• Boundary zone between two air masses
• Air masses of different temperature and moisture characteristics do not mix
• Cold air move more vigorously and force their way beneath warm air causing the warm air to rise.
• Rising and cooling air gives rise to cloud and the possibility of rain
  Cold front occurs you experience–temp decrease, pressure decrease, winds increase, winds change direction, cloud increases, chance of rain increases
• Occurs more often in winter–rainfall to mid latitudes.
• They bring the cool change in summer.

Air Masses

An air mass is a thick and extensive portion of the troposphere having uniform temperature and humidity, characteristics derived from its source region.

Weather Maps (Synoptic Charts)

High pressure systems in southern and eastern Australia bring warm to hot northerly, westerly or northwesterly winds from the inland areas.

• Low-pressure systems in southern and eastern Australia bring cool and moist southerly winds from the southern ocean and Tasman Sea.
• Low-pressure cells with rising and cooling air are responsible for much of the rain.
• As cold fronts pass over southern and eastern Australia they bring the following conditions; a fall in temp, a fall in air pressure, an increase in cloud cover, possibility of rain, change in wind direction from the north to the south, increase in wind strength.
• In summer the position of the high pressure cells are frequently over the Great Australian Bight. Low pressure cells over the centre of Australia–due to the strong heating of the earth surface and intense low-pressure cells off the northwest and northeast coasts may develop into tropical cyclones.
• In winter southern Australia cold fronts pass over more frequently. High pressure over the centre of Australia. Rainfall is common over the southern part of Australia.

Wind Direction

• Air revolves anti-clockwise outwards around a high(anticyclone)
• Air moves clockwise inwards around a low (cyclone)
• Winds are approximately parallel to the isobars
• Winds are named by the direction which they below.

Terms

• Fine: No rain or other precipitation
• Fog: Suspension of fine water droplets reducing visibility
• Mist: Similar to fog but greater visibility
• Smog: Smoke induced fog
• Drizzle: Uniform precipitation in fine droplets
• Rain: Steady and fails from status clouds
• Showers: Often short lived and heavy rain periods