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/