Lesson 2Lesson 2

General General CirculationCirculation

Specification: Major climate controls

Quick RecapQuick Recap Last lesson we learnt that uneven heating Last lesson we learnt that uneven heating

across the earth led to movement of air.across the earth led to movement of air.

Uneven heating is caused by a number of Uneven heating is caused by a number of factors eg seasons, surface coverage etc.factors eg seasons, surface coverage etc.

Movement of air occurs both horizontally Movement of air occurs both horizontally and vertically. (Notes from HW on this).and vertically. (Notes from HW on this).

Air moves in mysterious Air moves in mysterious ways!ways!

Golden rules:Golden rules: Air ALWAYS moves from an Air ALWAYS moves from an

area of HIGH pressure to an area of HIGH pressure to an area of LOW pressure. area of LOW pressure. (Filling (Filling up a void of lower air pressure) up a void of lower air pressure)

The greater the differences in The greater the differences in pressure, the faster the wind will pressure, the faster the wind will blow.blow.

Cold air holds less moisture.Cold air holds less moisture.

Basic Basic CirculationCirculation

Cold polar air moves

towards the warm

equator.

Hot tropical air moves

towards the cold poles.

Remember the differences in the heat supply.

Remember air moves both horizontally and vertically within the confines of the atmosphere.

Movements… Movements… at the equatorat the equator

Once air starts moving from hot and cold places, a more complicated circulation pattern is revealed.

The effects of pressure play an important part in pushing or pulling air, not to mention the spin of the earth.At the equator due to intense heating, the air lifts up freely (convection). This results in buoyant air spreading out so there is less air at the surface – ie LOW PRESSURE.

This movement vertically encourages cloud growth – rain – hence tropical rainforests are found under areas of low pressure.

Movements… Movements… at the polesat the poles

At the polar regions the air is very stable – dry and cold. This encourages the air to sink, creating HIGHER pressure at the surface.

High pressure at the surface is found at regular locations across the globe. Under these conditions, different biomes are found – typically deserts. EG

The North & South pole are both under high pressure – Cold deserts

The Sahara and Kalahari deserts are both under high pressure – Hot deserts

(Desert = Less than 250mm rain per annum)

Coriolis Coriolis The Coriolis force deflects air to the right The Coriolis force deflects air to the right in the Northern hemisphere (and to the in the Northern hemisphere (and to the left in the Southern hemisphere) left in the Southern hemisphere) when when viewed along the line of motionviewed along the line of motion. . This is due to the spin of the Earth, it is This is due to the spin of the Earth, it is this force that provides the surface winds this force that provides the surface winds with their directions, otherwise they with their directions, otherwise they would flow simply direct North South.would flow simply direct North South.

http://www-tc.pbs.org/wgbh/nova/elnino/anatomy/images/coriolis.gif

Polar Cell

Ferrell Cell

Hadley Cell

Its all mixed up!So far then, we know that air moves from high to low pressure areas (Fig A).

•Air doesn’t simply move from the equator to the poles and vice versa (Fig A).•The spin of the Earth (Coriolis Force) affects direction of winds.•There are three large cells that act to transfer heat in the Northern & Southern Hemispheres – Polar, Ferrell and Hadley (Fig B.)

A

B

Source areas of high and low pressure follow a known pattern.

Tri Cell Tri Cell This model shows what we expect to happen when air moves. It flows from High to Low in each cell, transferring heat energy as it moves.

Its all twisted! ~ Planetary Surface Its all twisted! ~ Planetary Surface WindsWinds

Collaborative SummaryCollaborative SummaryUsing these words / terms, complete a Using these words / terms, complete a summary of your understanding from today’s summary of your understanding from today’s lesson. lesson. Share with your neighbour and add something Share with your neighbour and add something extra to your partner’s work to develop it.extra to your partner’s work to develop it.

CoriolisCoriolisSurface windsSurface windsHigh pressureHigh pressureLow pressureLow pressureConvergingConvergingDivergingDiverging