Weather and Climate basics Charles Darwin Climate Symposium 14 October 2011 Joel Lisonbee NT Climate...
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Transcript of Weather and Climate basics Charles Darwin Climate Symposium 14 October 2011 Joel Lisonbee NT Climate...
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
L
AIR
AIR
Air pressure (cont.)
AIR
AIR
AIRA
IR
H
DivergenceConvergence
Air Pressure
Pressure lines (isobars) on a weather chart
L
Air flow around Low pressure system
L
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
L
L
L L
H
H
H
H
L HH
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/