Earth Sciences 2240F/G Lecture Notes - Lecture 4: Ionosphere, Thermosphere, Jet Stream
11 Jun 2018
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The Physics and Chemistry of Air and Water
2.0 Atmosphere
• present atmosphere compromised of several layers
• have own physical, chemical and temperature characteristics
• bottom up these layers are:
o troposphere: surface to about 12 km
o stratosphere: up to 50 km
o mesosphere: up to 80 km
o thermosphere: up to 500-700 km
▪ thermosphere is sometimes called the ionosphere
▪ but, ionosphere is any electrified region of the upper
atmosphere
▪ at 80 km, gas of atmosphere is so thin that free
electrons can exist for short periods of time before they
are captured by a nearby positive ion
▪ existence of charged particles at this altitude and
above, signals the beginning of the ionosphere region
• Troposphere:
o Contains ~80% of the mass of the atmosphere
o Thickest near equator (close to 18 km) and thinnest near the
poles (~8km)
o Rise in thickness occurs mid-latitude, exerts a fundamental
control on global weather patterns
o Main layer of atmospheric circulation
• Tropopause:
o Boundary between the troposphere and stratosphere
o Surface of equal pressure
o Marked by jet streams (narrow zones of swift high-altitude
winds)
• Stratosphere:
o Zone above the weather
o Temperature gradually climbs with height
o Contains the ozone-enriched layer
• Mesophere:
o Layer where incoming asteroids or meteroids first begin to
burn
o Because of lack of ozone, temperature drops within it (about -
85C)
• Thermosphere:
o Air is very thin and highly responsive to solar radiation,
varying velocity of solar winds affects it
o During solar flares, velocity of solar winds is greatly
enhanced, and temperature can rise to 1225 C and then fall
to as low as 225 C
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The Physics and Chemistry of Air and Water
o Dramatic temperature changes occur because there are few
molecules to absorb and distribute heat
o Northern Lights are produced in thermosphere by ionization
processes as an extraordinarily strong flux of electrons
streams in from the sun
• Only gaseous species able to escape from Earth’s gravity field are:
hydrogen and helium, neon with an atomic weight of 20 does not
escape, and the lightest of the major atmospheric gases have
similar molecular weights 17-ammonia, 18- water and 16-methane
o Thus quanitity of volatile or potentially volatile material in
whole earth is assumed not to have changed since earliest
times, except for loss of hydrogen and helium
2.1 Origin of the Atmosphere
• Mars, Earth and Venus originally has identical atmospheric
compositions
• All three planets also had liquid water, inherited from comet and
asteroid impacts
• Venus:
o Early days of differentiation, solar radiation readily penetrated
the clouds of Venus to warm the planet’s surface
o As solar output increased and the surface heated, and as
more CO2 from volcanoes entered the atmosphere (thus
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The Physics and Chemistry of Air and Water
increasing pressure), liquid surface water was probably
evaporated
o Atmosphere became so thick that radiation could not be
reflected back into space from the surface and greenhouse
simply got stronger and atmosphere got thicker
o Finally equilibrium reached where atmosphere was so thick
that is reflected most of the in-coming solar radiation, thus
keeping the whole planet at about 464 C constantly
• Mars:
o Evidence of surface water at early stage
o Still surface and subsurface ice and recent evidence of liquid
water coming to surface
o Proximity to asteroid belt left it exposed to a somewhat
higher flux of impacts than earth, result was gradual erosion
of mars’ atmosphere
o As planet cooled, volcanism decreased, with greenhouse
gases gone, and temperature dropped, liquid water became
impossible
o Solar radiation broke down water molecules, hydrogen
escaped and oxygen was combined with surface soils
o Today, atmosphere very thin, surface temperatures change
dramatically every day
• Comets and carbonaceous chondrites ( a type of meteorite)
contributed the elements of the volatiles of earth, mars and venus
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Document Summary
The physics and chemistry of air and water. The physics and chemistry of air and water in the days of accretion and the following periods of heavy bombardment: once volcanism became an active process, the atmosphere and hydrosphere were maintained by degassing of the interiors. A hot day in mile high denver just as a storm is moving in, i. e. a low pressure center. The physics and chemistry of air and water: air"s density is highest at, low elevation, when temperature is low, and when pressure is high, ex. The physics and chemistry of air and water: winds are deflected by the coriolis force (right in northern. The physics and chemistry of air and water acquires its characteristics before sinking and travelling along paths called deep ocean currents. Atlantic is a giant vertical circulation cell linked to the deeper circulation of the ocean: large volume of salty water, cools and sinks to depths below.
