Weather and Climate basics Charles Darwin Climate Symposium 14 October 2011
Joel Lisonbee NT 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 • Air has mass • Gravity pulls air down AIR 1m
• Air Pressure is the force exerted by the column of air directly above you. •Measured by a barometer
ma
1m
•In millibars (mb) •Hecto Pascals (hPa) 1m
•Sometimes inches of mercury
Side note: air pressure and altitude • If air pressure is weight of air above you • Then less air above you means lower air pressure
Air pressure (cont.)
AIR
AIR
AIR
AIR
Convergence
AIR
AIR
L
H
Divergence
Air Pressure
Pressure lines (isobars) on a weather chart
L
Air flow around Low pressure system
L
Hot Air Rises‌Cold Air Sinks
Atmospheric layers
– Troposphere • 6.5 °C/km
– Dry air parcel • 9.8 °C/km
% of atmosphere above that level
• Temperature change with height
Convection
H
L
Sea Surface Temperature (SST): The temperature of the ocean surface
H
North/South Circulation
•Over Simplified model •Other Complications include: •Spinning planet •Tilted axis •Land masses/oceans •Water vapour
Global Circulation • Forces from Earth’s rotation create: – 6 circulation cells – Bands of high and low pressure – Easterly and westerly winds
L H
H L L
L
H H
East/West circulation
Winds are named for the direction they came from:
H
West wind / westerlies
L
East wind / easterlies
H
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 Australia www.bom.gov.au/climate/change/
www.climatechangeaustralia.gov .au