Weather and Climate INCOMPLETE


Weather and Climate

Weather - The day to day changes in the atmosphere (Short-term)

e.g - temperature, cloud cover, precipitation, wind speed

Climate - The average weather conditions over a longer period of time - 30 years (Long-term)

e.g. - average measurements of temeprature, precipitation etc

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Atmospheric Layers

Atmosphere - The gaseous envelope that surrounds a celestial body (planet)

Atmospheric pressure decreases - It is caused by the density of air around you - Lack of living organisms and material means the air is less dense - As the altitude increases, the atmospheric pressure decreases


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Composition of the Atmosphere

Main Elements - 99%                                 

Nitrogen - 78%

Oxygen - 21%

Trace Elements - 1%

Argon, Carbon Dioxide, Neon

Helium, Methane, Nitrous Oxide

Xenon, Ozone, Nitrogen Dioxide

Iodine, Carbon Monoxide, Ammonia, Water Vapour

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The troposphere extends from the Earth's surface to about 12km up (0-7 miles above sea level)

  • The highest temperatures are found here - Solar radiation heats the Earth
  • The temeprature decrease with altitude - The Earth's surface warms the troposphere - The further away frrom the surface, the cooler it gets
  • There is a lot of turbulence (air movement) - Warm air rises through the layer and cool air sinks
  • Most weather processes happen here
  • The troposphere has lots of clouds - There is a lot of water vapour that has evaporated from the Earth's surface
  • Wind speeds increase the higher you go in this layer - Less frictional drag

The tropopause is the boundary between the troposphere and the startosphere.

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The stratosphere extends from around 12km up to about 50km up (7-30 miles above sea level)

  • Temperature increases with altitude - The ozone layer is found in the lower stratosphere which absorbs solar radiation which warms the upper stratosphere
  • The atmopshere is thinner - Lower pressure and lack of water vapour
  • Wind speeds increase with height
  • The stratosphere has little to no turbulence and there aren't many clouds

The stratopause is the boundary between the stratosphere and mesophere

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The mesophere extends from 50km to 85-90km up above the Earth's surface (30-51miles above sea level)

  • Temperature decreases with altitude - The mesophere is warmed by the stratosphere below - The further away, the cooler it gets
  • Strong winds up to 3,000km/h
  • No water vapour or dust to absorb radiation

The mesopause is the boundary between the mesophere and thermosphere

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The thermosphere extends from 85-90km to around 100km up  (51-90 miles above sea level)

  • Temperature increases with altitude - Small amounts of oxygen in this layer absorb solar radiation, warming the thermosphere
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Atmospheric Heat Budget

The atmospheric heat budget is the balance between the incoming and outgoing solar radiation

The Earth recieves energy from the sun in the form of shortwave solar radiation (Insolation)

This means that the Earth's surface (except the polar regions) has a net gain in energy.

The atmosphere has a net defecit in energy - The Earth is recieving the atmosphere's energy

This means that due to this difference in energy, heat is transferred from the surface of the Earth to the atmosphere by radiation, conduction and heat

About 50% of insolation is absorbed by the surface of the Earth and is then released as long wave radiation (e.g. infrared or heat energy). This radiation heats up the troposphere

The other 50% of incoming solar radiation is split in three ways:

25% is reflected back into space by the air and clouds in the atmosphere

20% is absorbed by the air and clouds in the atmosphere

5% is reflected back into space by the Earth's surface

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Atmospheric Heat Budget

Equator/Tropical Latitudes

  • The sun's rays are more concentrated - The midday sun is high in the sky throughout the year - Intense heating
  • The sun's rays have less atmosphere to pass through - Less energy is lost through absorption and relection by the atmosphere
  • In tropical rainforest areas, dense vegetation absorbs radiation - Low albedo effect

Poles/High Lattitudes

  • The sun's rays are less concentrated - The sun's angle is much lower, so the rays of energy are spread out over a larger area - Less intense heating
  • The Earth's curved shape - The planet's surface slopes away from the sun (Poles especially) - Less intense heating
  • In polar areas, the snow and ice cover reflect much more of the solar radiation - Higher albedo effect

Albedo Effect - The measure of how much of the sun's energy is reflected back to space

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Factors affecting Solar Radiation

There are 4 main factors that affect how much solar radiation the atmosphere recieves:

1) Solar Constant - The amount of solar radiation we get from the sun. It varies slightly with the sun's activity. When the sun is more active, the Earth recieves more solar radiation

2) Earth's distance from the Sun - The distance changes as it orbits. When the Earth is closer to the sun, it recieves more solar radiation

3) Length of Day and Night - This varies with the seasons (due to the Earth's tilt) which are more noticeable at higher altitudes. In winter there are fewer hours of daylight  - less solar radiation

4) Altitude/Angle of the sun varies with latitude:

  • Near the equator, the sun is higher in the sky and incoming solar radiation is (more) concentrated over a smaller surface area. The rays have a shorter distance to travel.
  • Near the poles, the sun is lower in the sky and incoming solar radiation is (less) concentrated over a larger surface area. The rays have a longer distance to travel and they don't all reach the surface
  • There is less solar radiation at higher altitudes
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Higher Latitudes/Altitudes

Higher Latitudes are colder because:

  • They recieve less solar radiation - The sun is lower in the sky
  • They recieve less solar radiation - Fewer hours of daylight in winter

Higher Altitudes are colder because:

  • The Earth's surface heats the atmosphere through conduction - The temperature is higher closer to the heat source and decreases away from it
  • Air pressure decreases with altitude - There are fewer air molecules and they move more slowly - They create less heat, which means lower temperatures
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Effects of Seasonality

Seasonality - The seasonal shift in the trace of the sun on the Earth's surface during its orbit

Our Winter

North - Deficit

South - Surplus

Equator - Surplus

Our Summer

North - Surplus

South - Deficit

Equator - Surplus

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Tri-Cellular Model


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Winds are large scale movements of air caused by differences in air pressure

The differences in air pressure are caused by differences in atmospheric heating between the equator and the poles

Winds are part of global atmospheric circulation cells. These cells have a body of warm rising air which creates an area of low pressure and a body of cool falling air which creates an area of high pressure

Winds move FROM the areas of high pressure TO the areas of low pressure

There are three main types of global atmospheric circulation cells - Hadley, Ferrel and Polar Cells

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Hadley Cell

  • These cells operate between the equator and 30 degrees north of the equator, and 30 degrees south of the equator
  • They produce winds in the form of tropical easterlies
  • Air rises at the equator (an area of low pressure) and travels towards the poles before falling back down to earth around the sub tropics (30 degrees north/south) due to the cooling of the air and the loss of moisture. This causes high pressure at these regions
  • The air travels back to the equator, whilst being warmed by the Earth's surface and collecting moisture. This causes it to then rise again when it reaches the equator.
  • The air rises about 10-15km into the atmosphere
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Ferrel Cell

  • These cells operate between 30 and 60 degrees north of the equator and 30-60 degrees south of the equator
  • The air flows eastward towards the poles along the ground
  • The air flows FROM high pressure TO low pressure
  • When the air reaches 60 degrees north or south, it rises due to the air warming and gaining moisture over land
  • This causes an area of low pressure
  • As the air rises it travels back round to 30 degrees north/south and cools and loses moisture before reaching the 30 degrees mark - causing high pressure
  • In this cell, the winds are south-westerlies and are warm
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Polar Cell

  • The cell operates between 60 degrees north of the north pole and so on
  • Cold dense air moves along the Earth's surface and becomes warmer, wetter and less dense until the air reaches so many degrees north or south when it is now warmer and starts to rise. This causes low pressure
  • The cell reaches a maximum height of 7.5km in the atmosphere. It then moves towards the poles as the air cools and condenses before it starts to sink around the poles, causing high pressure
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Wind Movement

1) At the equator, the sun warms the Earth which transfers heat to the air above, causing it to rise. Rising air creates low pressure, clouds and rain. This zone of low pressure and rising air is called the Intertropical Convergence Zone (ITCZ)

2) As the air rises it cools and moves 30 degrees North and South of the Equator

3) 30 degrees north and south of the equator, the cool air sinks, creating high pressure. Sub tropical jet streams are found here (fast moving currents of air)

4) The cool air reaches the ground surface and moves as surface winds either back to the equator or towards the poles:

Surface winds blowing towards the equator are called trade winds. They blow from the SE in the southern hemisphere and from the NE in the northern hemisphere. At the equator, these trade winds meet in the ITCZ and are heated by solar radiation. This causes them to rise, condense and form clouds.

Surface winds blowing towards the poles are called westerlies. They blow from the NW in the southern hemisphere and from the SW in the northern hemisphere.

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Wind Movement cont.

5) 60 degrees north and south of the equator, the warmer surface winds meet the colder air from the poles. The warmer air is less dense than the cold air so it rises creating low pressure

6) Some of the air joins the Ferrel cell and moves back towards the equator, and the rest joins in the polar cell and moves towards the poles.

7) At the poles the cool air sinks, creating high pressure. The high pressure air is drawn back towards the equator in surface winds.

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Inter-Tropical Convergence Zone

  • The air flows along the surface of the Earth towards the equator which causes low pressure at the equator as the air begins to rise.
  • This area of low pressure is called the Inter-Tropical Convergence Zone (ITCZ)
  • It creates winds which turn westwards by the Coriolis effect


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Coriolis Effect

The Coriolis Effect causes a deflection in global wind patterns

Each point on the Earth's Surface rotates over 24 hours

The Earth's rotation and the tilt means that we experience the Coriolis Force

This deflects the direction of the wind (from high pressure to low pressure areas) to the right in the northern hemisphere and to the left in the southern hemisphere

This is why the wind around low and high pressure areas circulates in opposing directions in each hemisphere


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Jet Streams

Jet Streams - Fast flowing currents of air in the Earth's atmosphere

  • Meandering shape
  • Polar Jet Stream and Sub-Tropical Jet Stream
  • They are caused by the Earth's rotation and atmospheric heating
  • Located in the troposphere
  • The polar jet stream is stronger - it is closer to sea level
  • Speed of 100-300km per hour


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Ocean Currents

Ocean Currents - Large scale movements of water caused by differences in water density. The density of the water is dependent on the temeprature and salinity

  • Currents are affected by surface winds, the position of land masses and other currents.
  • They transfer heat energy from warmer to cooler regions. Warm ocean currents raise air temperature - warms the land nearby. Cool ocean currents lower air temperature - cools the land nearby
  • They form giant loops. They travel clockwise in the northern hemisphere and anticlockwise in the southern hemisphere. This is due to surface winds - trade winds push water west along the equator, westerlies push water east between 30 and 60 degrees North and South

The Gulf Stream carries warm water from the Caribbean Sea along the East Coast of America and across the Atlantic to Western Europe

The Gulf Stream keeps Western Europe much warmer than it would be without it

Water in the Gulf Stream cools in the northern hemisphere and becomes more dense. Some of this water sinks and is carried back to the Equator by the Canary Current, which cools the west coast of Africa

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Factors affecting Temperature

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Air Masses


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Air Masses

Air Masses - An area of air which has similar properties of temperature, and humidity. Air masses develop over areas of similar geographical characteristics such as polar ice caps and hot deserts

Tropical Maritime (TM)

  • Occurs during a warm sector of a depression
  • Very mild and wet with thick cloudcover in winter
  • No frost
  • Poor visibility
  • Warm in summer
  • Lower layers stable but upper layers aren't
  • Can give thunderstorms due to unstable layers
  • Winds are moderate
  • Very common over Britain
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Air Masses

Tropical Continental (TC)

  • Summer only when sub-tropical high pressures move north
  • Heat Waves
  • Very stable in lower layers (droughts)
  • Upper layers can be unstable (Thunderstorms)
  • Gentle winds come from the south

Polar Maritime (PM)

  • Very common over Britain
  • Cool conditions throughout the year
  • Warms over the Atlantic
  • Lower layers are unstable
  • Heavy showers over highland areas separated by sunny intervals
  • Cumuloform Clouds
  • Strong winds and gales
  • Good Visibility
  • Comes from the North West
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