Chapter Notes: Atmosphere and Climate
Introduction
Looking up at the sky, we see clouds, sunshine, and feel breeze - all results of the atmosphere, the blanket
of air surrounding the Earth.
The atmosphere is held around the Earth by gravity (the force of attraction Earth's mass exerts on nearby
objects) and is a mixture of gases vital for survival of all living beings.
Functions of the atmosphere:
• Shields us from harmful solar radiation, including ultraviolet rays.
• Regulates Earth's temperature by trapping some of the Sun's energy, preventing it from escaping into
space.
• Influences weather and climate systems - temperature, humidity, and air pressure.
Composition of the Atmosphere
The atmosphere is a mixture of various gases:
• Nitrogen (78%) and Oxygen (21%) are the two most abundant and essential gases.
• Other gases present in smaller quantities: carbon dioxide (0.04%), argon (0.93%), helium, neon,
krypton, xenon, ozone, hydrogen (together "Others" ~0.03%).
• Also contains water vapour (varies between 0.1% to 0.4%, important for cloud formation and
precipitation) and tiny dust particles.
• Composition varies with altitude.
, Structure of the Atmosphere
The atmosphere has a layered structure, defined by changes in temperature and density with increasing
altitude. Air density is highest near Earth's surface and decreases with altitude.
Layer Extent Key Facts
Troposphere Up to ~12 km Most important layer; temperature decreases with altitude;
(average) nearly all weather phenomena (rainfall, fog, hail) occur here.
Stratosphere Up to ~50 km Free of clouds/weather disturbances - ideal for flying
aeroplanes; contains the ozone layer, which absorbs harmful
UV radiation; separated from the mesosphere by the
stratopause.
Mesosphere Up to ~80 km Temperature decreases with altitude; most meteorites entering
the atmosphere burn up here.
Thermosphere 80 km to 700 km Temperature rises rapidly with altitude (absorbs X-rays and UV
radiation); reflects radio waves; contains the ionosphere; site of
auroras.
Exosphere Uppermost layer Very thin air; light gases like helium and hydrogen escape into
space.
Introduction
Looking up at the sky, we see clouds, sunshine, and feel breeze - all results of the atmosphere, the blanket
of air surrounding the Earth.
The atmosphere is held around the Earth by gravity (the force of attraction Earth's mass exerts on nearby
objects) and is a mixture of gases vital for survival of all living beings.
Functions of the atmosphere:
• Shields us from harmful solar radiation, including ultraviolet rays.
• Regulates Earth's temperature by trapping some of the Sun's energy, preventing it from escaping into
space.
• Influences weather and climate systems - temperature, humidity, and air pressure.
Composition of the Atmosphere
The atmosphere is a mixture of various gases:
• Nitrogen (78%) and Oxygen (21%) are the two most abundant and essential gases.
• Other gases present in smaller quantities: carbon dioxide (0.04%), argon (0.93%), helium, neon,
krypton, xenon, ozone, hydrogen (together "Others" ~0.03%).
• Also contains water vapour (varies between 0.1% to 0.4%, important for cloud formation and
precipitation) and tiny dust particles.
• Composition varies with altitude.
, Structure of the Atmosphere
The atmosphere has a layered structure, defined by changes in temperature and density with increasing
altitude. Air density is highest near Earth's surface and decreases with altitude.
Layer Extent Key Facts
Troposphere Up to ~12 km Most important layer; temperature decreases with altitude;
(average) nearly all weather phenomena (rainfall, fog, hail) occur here.
Stratosphere Up to ~50 km Free of clouds/weather disturbances - ideal for flying
aeroplanes; contains the ozone layer, which absorbs harmful
UV radiation; separated from the mesosphere by the
stratopause.
Mesosphere Up to ~80 km Temperature decreases with altitude; most meteorites entering
the atmosphere burn up here.
Thermosphere 80 km to 700 km Temperature rises rapidly with altitude (absorbs X-rays and UV
radiation); reflects radio waves; contains the ionosphere; site of
auroras.
Exosphere Uppermost layer Very thin air; light gases like helium and hydrogen escape into
space.
