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 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 mercury 1 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 pressure (cont.) AIR 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

LHH 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

LHH East/West circulation Winds are named for the direction they came from: West wind / westerliesEast 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 Australia