Download
1 / 15
150 likes | 155 Vues
Lesson 3. General Circulation. Quick Recap. Last lesson we learnt that uneven heating across the earth led to movement of air. Uneven heating is caused by a number of factors eg seasons, surface coverage etc. Movement of air occurs both horizontally and vertically.
E N D
Lesson 3 General Circulation
Quick Recap • Last lesson we learnt that uneven heating across the earth led to movement of air. • Uneven heating is caused by a number of factors eg seasons, surface coverage etc. • Movement of air occurs both horizontally and vertically.
Air moves in mysterious ways! Golden rules: • Air ALWAYS moves from an area of HIGH pressure to an area of LOW pressure. (Filling up a void of lower air pressure) • The greater the differences in pressure, the faster the wind will blow. • Cold air holds less moisture.
Basic Circulation Hot tropical air moves towards the cold poles. Cold polar air moves towards the warm equator. Remember the differences in the heat supply. Remember air moves both horizontally and vertically within the confines of the atmosphere.
Movements… at 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… at 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)
http://www-tc.pbs.org/wgbh/nova/elnino/anatomy/images/coriolis.gifhttp://www-tc.pbs.org/wgbh/nova/elnino/anatomy/images/coriolis.gif Coriolis The Coriolis force deflects air to the right in the Northern hemisphere (and to the left in the Southern hemisphere) when viewed along the line of motion. This is due to the spin of the Earth, it is this force that provides the surface winds with their directions, otherwise they would flow simply direct North South.
Coriolis videos • http://www.youtube.com/watch?v=aeY9tY9vKgs&NR=1&feature=endscreen • http://www.youtube.com/watch?v=Kk7sXkzmtp0&feature=related
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). A Source areas of high and low pressure follow a known pattern. B • 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.)
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.
Collaborative Summary Using these words / terms, complete a summary of your understanding from today’s lesson. Share with your neighbour and add something extra to your partner’s work to develop it. • Coriolis • Surface winds • High pressure • Low pressure • Converging • Diverging
Homework 1 Study the next slide which shows the average annual global distribution of insolation at the Earth’s surface. Describe and comment on the distribution shown. (7 marks) 2 With the aid of a diagram, describe the structure of the atmosphere. (8 marks)
