1.2 ATMOSPHERIC CIRCULATION

• Atmospheric circulation: global-scale movement of the layer of air surrounding the Earth.

• Hot air rises (low density)

• Cold air falls (high density)

• Air warmed at the equator rises and moves toward the poles. Cold air from the poles is more dense and moves toward the equator = CONVECTION

CORIOLIS EFFECT• Similar to ocean currents, the coriolis effect

causes wind to deviate to the right in the northern hemisphere and to the left in the southern hemisphere.

PREVAILING WINDS• Major atmospheric currents that blow in a

given direction according to global patterns of movement.

AIR MASSES

• Air Mass: A large expanse of the atmosphere with relatively uniform temperature and humidity.

• When two air masses meet they do not mix together, cold dense air will slide beneath the light warm air.

• The line where two air masses meet is called a front.

COLD FRONT

• Advancing cold air meets warm air.

• The warm air rises rapidly and cools into thick cumulus cloud.

• A cold front results in wind and heavy rain.

WARM FRONT• Advancing warm air meets cold air

• The warm air rises and cools gradually and thin light nimbostratus clouds are formed.

• Warm fronts result in long lasting cloudy weather. and showers.

VERTICAL AIR MASS MOVEMENT – ANTICYCLONES, DEPRESSIONS, CYCLONES

ANTICYCLONES

• Anticyclone (“H”): an area of atmospheric circulation revolving around a high-pressure center. The air turns clockwise in the Northern Hemisphere.

• Sinking air particles prevent cloud-forming movements, the sky is clear and the weather is stable.

COLD AIR SUBSIDING:

ANTICYCLONE (“H”)

DEPRESSIONS

• Depression (“L”): an area of atmospheric circulation revolving around a low-pressure centre. The air turns counter clockwise in the northern hemisphere and clockwise in the southern hemisphere.

• Violent winds, tropical storms, floods, landslides etc.

WARM AIR RISING:DEPRESSION (“L”)

CYCLONES

• Depressions that form in tropical areas that result in violent winds revolving around an area of low pressure.