what is the global circulation system?
- The movement of air across the planet occurs in a specific pattern, to keep the earths temperature in balance. The whole system is driven by the equator, which is the hottest part of the Earth.
- Air rises at the equator, leading to low pressure and rainfall. When the air reaches the edge of the atmosphere, it cannot go any further and so it travels to the north and south.
- The air becomes colder and denser, and falls, creating high pressure and dry conditions at around 30° north and south of the equator. Large cells of air are created in this way.
what kinds of climatic zones are there
- a hot wet climate around the equator as warm air rises where the hadley cells meet
- a hot dry climate as air sinks where the harley and ferrell cells meet, that’s why there’s deserts around the tropics
- unsettled weather at around 60° N and S as cool air mixes w warm air where the polar and ferrell cells meet, including the wet mild climate in the uk
explain the belts of pressure
- air cools and sinks at the polar cells, creating a belt of high pressure and a cold dry climate
- at about 60° N and S at the ferrell cell, cold polar air mixes w warmer air and rises, creating a belt of low pressure
- cool air sinks at the harley cell, creating a belt of high pressure, as the air sinks, it becomes warmer and drier
- warm air rises, creating a belt of low pressure. as the air rises it cools, clouds form in the inter tropical convergence zone, then release precipitation. above the itcz, the air separates and moves to higher latitudes.
what is insolation?
the sun radiates energy in heat and light, only some of the radiation reaches earth
why does the equator have the potential to be the hottest part of the world, and why are the poles so cold?
the suns rays are strongest there, the suns rays hit earth at an angle at the poles which result in the lower temperatures
what are some factors affecting temperatures around the world?
- albedo effect
- cloud cover
- winds - surface winds move heat around the world
- ocean currents - water if fluid, ocean currents move heat easily, eg the uk is warmer rhan other countries at the same latitude bc it’s warmed by the north atlantic drift, which is a warm ocean current originating in the carribean
- land and sea - on land i solar ion is concentrated on the surface, at sea it reaches deeper because water is transparent. water is slower to warm up than land, but it stays warm for longer
- altitude - higher up air pressure is lower which makes temperatures colder
what is the albedo effect?
how much a surface reflects or absorbs the suns rays, eg polar ice has a high albedo as it reflects more heat and it makes the poles colder, the oceans and rainforests have a low albedo, and absorb more heat
what is cloud cover
clouds reflecting the suns rays, although potential indo latino is stronger at the equator, thick clouds reduce the temperature, i dilation is acc stronger close to the tropics which are largely free from cloud cover
what is wind?
the movement of air from an area of high pressure to one of low pressure, the greater the difference in pressure, the stronger the wind
- winds at ground level are slowed by friction
what kinds of wind are there
- trade winds
- katabatic winds
- jet streams
what are trade winds?
winds that blow from high pressure belts to low pressure belts
- trading ships used them to sail around the world
what are katabatic winds?
caused by air flowing downhill
- in antarctica large ice sheets sloping gently into the sea contribute to wind speeds of it wr 320km/h
what are jet streams?
winds high in the atmosphere called jet streams are very strong as there’s little to slow them down
- mf everest has jet streams
what are tornadoes
very strong rotating winds
- much smaller than tropical storms and can occur over both land and sea, can be extremely hazardous and can reach 400km/h
how do you measure wind speed and direction?
by anemometers, which are used to measure wind speed by counting the number of times they rotate in a minute
- wind speed and direction in a location can be shown by using a rose chart
- wind speed is measured using the beaufort scale, ranging from 0 (calm) to 12 (hurricane)
what is precipitation?
when warm air rises, it carries water vapour, and as it rises the air cools and the water vapour condenses to form clouds. eventually the clouds release precipitation which falls to earth as rain sleet snow or hail
what are the patterns of rain around the world?
areas of low pressure have rising air and high levels of precipitation
areas of high pressure have descending air and low precipitation
on a global scale rain falls heavily in a band around the equator, but the tropics are much drier
on a regional scale, the coasts of continents can be particularly wet
on a local scale, precipitation is influenced by altitude
what kinds of rainfall are there?
- conventional rainfall
- frontal rainfall
- relief rainfall
what is conventional rainfall
strong sunshine warms up the ground and air above it
pockets of warm air rise as convection currents
at high altitudes, the air cools and its water vapour condenses to form clouds
when rain falls it can be heavy, sometimes thunderstorms, this type of rain is significant at the equator where temperatures are high
what is frontal rainfall
when warm air meets cool air it’s called a front, the warm air rises over the cool air and clouds are formed
- eventually there’s steady rain
- frontal rainfall is common in the uk because it’s situated where the arm air from the tropics meets cool air from the north pole
what is relief rainfall?
when wind gets to mountains the warm air is forced to rise, leading to cooling, condensation and precipitation on the windward side of the mountain
when the air descends on the leeward side it will be dry, creating a rain shadow
in the uk mountains like the pennines tend to be wetter on their western sides and drier on the east
