ATOC 181 Chapter Notes - Chapter 1: Radio Wave, Lapse Rate, Ionosphere

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Chapter 1 The Earth and its Atmosphere
Inward motion around low leads to rising motion, due to conservation of mass (results in cooling, condensation
and precipitation, thus lows are associated with stormy weather)
Atmosphere thin envelope of gases and tiny particles that surround Earth (essential for life, contains oxygen
and carbon dioxide for life-sustaining processes, supplies water and shields life from harmful UV radiation from
Sun)
99% of gases extend only 30 km above Earth’s surface
most weather occurs within the first 10-15 km
Nitrogen, oxygen, argon, water vapour, carbon dioxide (N and O experience little change, but CO2 and
others are increasing in concentration)
Most prevalent gas is N2
Clouds are not gas condensed vapour in the form of liquid droplets
Smog contains reactants of nitrogen and ozone
Ozone = primary component in photochemical smog
Majority of water on the planet is from outgassing
Air density is greatest at the surface and decreases as you go up
Atmospheric pressure always decreases with decreasing height
Early Atmosphere
Surface temp up to 110 degrees
Planet cooled water vapor condense to form clouds and rain, hence oceans
CO2 dissolved in rainwater
Life formed about 2 billion years ago and photosynthesis produced oxygen
Ozone shield formed
Radiosonde small instrument package carried aloft by helium balloons equipped with a radio transmitter,
measures temperature, air pressure, and humidity, giving soundings of these quantities
Troposphere temperature decreases with height (6.5 degrees/km), weather occurs in this layer, extends from
surface to about 12 km
Tropopause found at higher elevations at equator, lower towards poles
Stratosphere temperature is initially isothermal with height, then increases with height to about 50 km
Mesosphere temperature decreases with height, to about 80 km thermosphere; above 80 km, temperature
increases once again with height
3 regions of relative warmth: Earth’s surface, stratopause, and above 80 km
Ionosphere electrified region where ions and free electrons exist, plays a major role in radio communications,
D region reflects AM signals
Not really a layer but rather an electrified region within the upper atmosphere where fairly large
concentrations of ions and free electrons exist. Ions are atoms and molecules that have lost or gained one
or more electrons. Atoms lose electrons and become positively charged when they cannot absorb all of
the energy transferred to them by a colliding energetic particle or the sun’s energy
Radio wave propagation AM radio waves are long enough to interfere with ions in the suncharged D layer,
but at night the D layer is weak (due to less ion density), and the signal propagates further, requiring less power
Lower part of the ionosphere (D region) reflects standard AM radio waves back to Earth, but weakens
them through absorption. At night, the D region gradually disappears and AM radio waves are able to
penetrate higher into the ionosphere, into the E and F regions, where the waves are reflected back to
Earth.
Little absorption of radio waves in the higher reaches of the ionosphere and AM radio waves bounce
repeatedly from the ionosphere to the Earth’s surface and back to the ionosphere.
FM stations to not need to adjust because FM radio waves are shorter than AM waves and are able to
penetrate through the ionosphere without being reflected
Atmospheric pressure at any level represents the total mass of air above that level, and atmospheric
pressure always decreases with increasing height above the surface
The rate at which the air temperature decreases with height is called the lapse rate. A measured increase
in air temperature with height is called an inversion
Thermosphere has highest temp, mesosphere has coldest temp, troposphere contains familiar weather,
ozone gas found in stratosphere
Most abundant greenhouse gas = water vapour