Weather and climate and associated hazards

The structure of the atmosphere Part 1

Atmosphere divided into different layers due to major changes in temprature

The Troposphere

  • 0-12 km
  • Contains 75% of gasses in atmoshere
  • Most unstable layers - where our weather occurs
  • As height increases - Temprature decreases around 6.5 degrees celsius for every kilometer above the earth's surface

The Tropopause

A thin band located at the top of the troposphere that separates the troposphere from the stratosphere. 

The Stratosphere

  • 12-50km
  • Temprature fairly constant -60 degrees celsius in the lower part
  • Ozone absorbs ultraviolet radiation from the sun and this causes a temperature increase in the upper part of the layer

The Stratopause

Seperates the Stratosphere from the Mesosphere


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The structure of the atmosphere Part 2

The Mesosphere

  • 50-80 km 
  • This is the coldest region of the atmosphere as the temperature drops in this layer to about -100 degrees celsius

The Mesopause

Seperates Mesophere from Thermosphere

The Thermosphere

  • 80km +
  • The air is very thin. Meaning "heat sphere", the temperature is very high in this layer because ultraviolet radiation is absorbed and turned into heat by ozone and other gases elements. Temperatures often reach 2000 degrees celsius or more.
  • Ionosphere - This is the lower part of the thermosphere, extending from about 80 to 550 km. Gas particles absorb ultraviolet and X-ray radiation from the sun
  • Exosphere - the upper part of the thermosphere. It extends from about 550 km for thousands of kilometers. The air is very thin here
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The atmospheric heat budget

Insolation reaching the Earth's surface is concentrated in the tropics

In the tropical region there is a net heat gain. In contrast, the polar regions are said to have a net heat loss. The reason for this disparity is due to the altitude of the sun and latitude

In the tropics the altitude of the sun is highest and so insolation is more concentrated. In polar regions due to the low angle of the sun, insolation is spreadout over a larger area due to a lower angle

In addition due to this angle incoming electromagnetic radiation has to travel through more atmosphere. As a result, more radiation is absorbed or reflected back into space


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Atmospheic circulation Part 1

  • Due to irregular patterns of insolation absorbed at the Earth's surface the planet needs to transfer heat.
  • Heat transfers occur in a number of ways but can be broadly classified into two main types, atmospheric circulation and oceanic circulation.
  • Atmospheric circulation - involves vertical and horizontal air circulation and can be conceptually understood as a convection cell with vertical movements of air upwards and downwards and horizontal movements of air, more comminly known as surface winds
  • An area of high pressure is experiencing vertical air circulation downwards over a given area. Effectivley, a given parcel of air is being compressed by falling air above it and this causes surface winds to move away from high pressure.
  • Low pressure is experiencing the opposite, air is moving upwards within the parcel of air. Effectively this means that there is free space at the surface so winds rush in fill that space
  •  Due to the tricelluar model the globe has a distinct pattern of bands of low and high pressure.(



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Atmospheic circulation Part 2

This rising air is a direct result of the heating of air by the high altitude of the sun. As air is heated it vibrates and expands,. As it expands it becomes lighter and begins to rise. This convectional process of rising air over the ITCZ creates the familiar pattern of tropical rain. As air rises it cools adiabatically and condenses to produce towering cumulonimbus rain clouds. In addition, it forms an extended area of low pressure


Because the air has heated and remains warmer than the air around it, air continues to rise and as it rises it cools, untill it reaches the tropopause

At this point it can rise no further, because its temperature is now cold (approximately -50°C) and consistent with the temperature of the upper troposphere and tropopause around it. Due to continued rising air below it the cold air is forced to the south and north. As it moves away from the ITCZ it experiences radiationally cooling and begins to slowly sink. As the air sinks it warms and its relative humidity falls

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Atmospheic circulation Part 3

The resulting landforms of this sinking air are the great deserts located at 30 degrees north and south.

This convection cell is known as the Hadley Cell and through its circulation heat is transferred from the equator to the latitudes of 30°. From there, air is either returned back to the equator via trade winds or moved further north or south via the westerlies, where its forms part of the Ferrel Cell.

The trade winds and westerlies represent horizontal transfers of air and the direction is governed by two factors. Firstly, that surface winds move from bands of high pressure to bands of low pressure and secondly, that air is deflected by the rotation of the Earth. A deflection called the coriolis effect.


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Planetary surface winds

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