Atmospheric Circulation
the weather is constantly changing because the winds are always moving
All planets with atmospheres have winds depending on how much energy they receive from the sun
The Earth has bands of steady winds
atmospheric circulation is the basis for our everyday weather
there are many factors affecting weather & they keep changing
Global Heat Budget
the sun provides all of the energy leading to changes in our weather
without Solar energy, the air that surrounds the Earth would remain still
The sun's energy reaches the Earth's surface unevenly and this causes the atmosphere to move as wind
at the equator, sunlight hits the earth directly
Towards the poles the sunlight hits the surface at an angle and there is less heating because it is spread over a larger area
also at this lower angle, more sunlight is reflected from the oceans and ice
clouds also affect the sun's energy as they shade the earth and keep our atmosphere cool
about 30% of solar radiation is reflected back into space
the air in our atmosphere is warm which stops the shadows from becoming too cold
the sunlight warms the surface of the earth which then radiates at the infrared wavelength up into the atmosphere
some is absorbed by water vapour and other gases
eventually all of the radiation goes back into space but the greenhouse gases slow it down
The greenhouse effect
Convection
Our atmosphere tends to be hotter near the ground as the warm surface heats it
the warm air then rises and warms the atmosphere
when water evaporates it takes energy into the atmosphere- this is released when the vapour condenses to form clouds.
where this happens we get a pocket of low pressure and air flows inward to replace the rising air
when air cools, it gains mass and sinks, causing a high pressure cell, and air flows outwards from this
On earth, air flowing from high to low pressure zones is wind
Coriolis effect
Because of Earth's rotation, no wind can travel over a long distance in a straight line
winds coming from the poles are deflected and end up spinning around the polar regions- Antarctica is the windiest place on Earth and the equator is relatively still and calm
different parts of the Earth's surface are travelling at different speeds- at the equator surface and air are moving at 1600kph ,30'-1400kph ,60'- 800kph ,at poles- 0kph
Storms
at 60' latitude, westerly winds meet the cold polar easterly winds and this creates a belt of storms at a collision zone known as the polar front
the relatively warm moist westerly air rises above the cold polar air, making storms
on earth we have seasons because the axis is tilted at an angle of 23.5'
the pressure belts appear to move north and south seasonally