Atmospheric circulation

Global Heat budget

• Excess at the equator• Deficit at the poles• Therefore all air and

ocean currents transport heat pole wards

A non-rotating earth•Convection Cells: This is the term used to describe the process of warm air rising, travelling laterally, cooling and sinking and returning to the source region along the surface.•If there was no land on earth, we would have two big convection cells, one in each hemisphere•Remember, air moves from hot to cold and high to low pressure•Convection cells would operate from the equator (heat surplus) to the poles(net deficit) with air flowing upwards at the equator, cooling at the top of the troposphere and descending when cool at the poles.

The three cells

• Unfortunately it is not that simple! The earth is split into three cells in each hemisphere

Coriolis

• This is the effect of the earth spinning.

• It affects all large bodies of liquid or gas, ie water and air

• Remember the earth spins anticlockwise if you were looking down on the North Pole, as in from west to east

• Therefore along the equator, major currents flow from east to west.

Hadley cells

• The helical circulation patterns of which the Trade Winds form the surface expression; the north–south component of this helical circulation is known as the Hadley circulation; the two ‘Hadley cells’ can be seen on either side of the Equator

Global Circulation

Air pressure systems

The ITCZ

• This stands for the Inter Tropical Convergence Zone

• It is the junction near the equator where the two Hadley cells land based currents meet

• It’s position changes with regards to season

changing conditions over continent and ocean in a monsoon climate

(a) Northern winter: dry, cooled air subsides over the continent, which is a region of high surface pressure; winds blow off the continent picking up moisture from the much warmer ocean and eventually moist air rises at the Intertropical Convergence Zone, causing abundant rain. (b) Northern summer: land is now much warmer than the ocean, so the region of low surface pressure corresponding to the ITCZ and its zone of rain has moved northwards towards the interior of the continent.

Orographic Rainfall

The Daisy World Hypothesis

• http://library.thinkquest.org/C003763/flash/gaia1.htm