Weather and Climate basics
Charles Darwin Climate Symposium14 October 2011
Joel LisonbeeNT Climate Services Centre
Bureau of Meteorology
Weather and Climate basics
Goal: To explain and define basic weather and climate terms
• Weather: “The state of the atmosphere…the short-term (minutes to days) variations in the atmosphere” AMS Glossary of Meteorology
• Climate: “The slowly varying aspects of the atmosphere-hydrosphere-land surface system” AMS Glossary of Meteorology
– Often taken as a 30 year average
Air Pressure
• Force = mass X acceleration, F=ma
• Pressure: net force per unit area, P=F/A
1 m
1 m
ma
• Air has mass
• Gravity pulls air down
• Air Pressure is the force exerted by the column of air directly above you.
•Measured by a barometer
•In millibars (mb)
•Hecto Pascals (hPa)
•Sometimes inches of mercury1 m
AIR
Side note: air pressure and altitude
• If air pressure is weight of air above you
• Then less air above you means lower air pressure
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AIR
AIR
Air pressure (cont.)
AIR
AIR
AIRA
IR
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DivergenceConvergence
Air Pressure
Pressure lines (isobars) on a weather chart
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Air flow around Low pressure system
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Hot Air Rises…Cold Air Sinks
Atmospheric layers%
of atmosphere above that level
• Temperature change with height
– Troposphere• 6.5 °C/km
– Dry air parcel• 9.8 °C/km
L HH
Sea Surface Temperature (SST): The temperature of the ocean surface
Convection
•Over Simplified model•Other Complications include:
•Spinning planet•Tilted axis•Land masses/oceans•Water vapour
North/South Circulation
Global Circulation
• Forces from Earth’s rotation create: – 6 circulation
cells– Bands of high
and low pressure
– Easterly and westerly winds
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H
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H
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East/West circulation
Winds are named for the direction they came from:
West wind / westerlies East wind / easterlies
Walker Circulation
• Walker Circulation: a patterns of rising and sinking motion in the Tropics which creates east/west circulation
climatology average conditions and anomalies
• Climate: “The slowly varying aspects of the atmosphere-hydrosphere-land surface system” AMS Glossary of Meteorology
– Often taken as a 30 year average
• Climate variability: “any variations of the atmosphere/ocean system around a mean state” AMS Glossary of Meteorology
• Climate Change: “Any systematic change in the long-term statistics of climate elements sustained over several decades or longer” AMS Glossary of Meteorology
Mean climate and anomaly
Measured
Expected
Anomalies
Mean Climate and anomaly
Climatology: mean, average, or expected
conditions
Negative Anomaly
Positive Anomaly
Climate Variability
• Example: El Niño/La Niña– Seasonal SST
Changes in the Pacific
– Seasonal to annual effects
– Drought or Flood?• Australia or Pacific
Islands
Climate Change: Trends in past climate
Climate Change in Australiawww.climatechangeaustralia.gov.auwww.bom.gov.au/climate/change/