Fundamental Properties of the Atmosphere

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Fundamental Properties of the Atmosphere
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• Meteorology is the study of the atmosphere and
  atmospheric phenomena as well as the interaction
  of the atmosphere with the Earths surface,
  oceans and human activities.

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Atmospheric Composition

• Gases individual molecules moving above the
  Earths surface
• Aerosols tiny suspended solid particles or
  liquid droplets (e.g. haze)
• Clouds composed of a mixture of liquid droplets
  and ice crystals (and they also contain aerosols
  and gases).

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Main Gases in Earths Atmosphere

• Nitrogen (N2) - 78 by volume
• Oxygen (O2) 21 by volume
• Argon (Ar) - 1 by volume
• Carbon dioxide (CO2)
• Water vapor (H2O)
• Neon (Ne)
• Helium (He)

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Gases in Earths Atmosphere (Cont.)

• Methane (CH4)
• Hydrogen (H2)
• Nitrous oxide (N2O)
• Ozone (O3)
• Xenon (Xe)

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Fundamental Properties and Units

• 1. Mass the quantity of matter
• Unit kilogram (kg)
• Symbol m
• 2. Length the distance between two points
• Unit meter (m)
• Symbol depends on coordinate
• system (eg. dx)

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Fundamental Properties and Units (Cont.)

• 3. Volume the amount of space occupied
• by a solid, liquid or gas.
• Unit cubic meter (m3)
• Symbol - V

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Fundamental Properties and Units (Cont.)

• 4. Density mass divided by volume
• Units kilograms per cubic meter
• (kg m-3)
• Symbol ?
• ? m/V

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Fundamental Properties and Units (Cont.)

• 5. Velocity (speed) distance traveled
• divided by the elapsed time
• Units meters per second (m s-1)
• Symbol V
• V dx/dt

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Fundamental Properties and Units (Cont.)

• Note The National Weather Service reports and
  plots wind speed in knots (kt).
• 1 kt 0.515 m s-1

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Fundamental Properties and Units (Cont.)

• 6. Acceleration the change in velocity
• divided by the elapsed time
• Units meters per second squared
• (m s-2)
• Symbol a
• a dV/dt

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Fundamental Properties and Units (Cont.)

• 7. Force mass multiplied by acceleration
• Units kilogram meter per second
• squared (also called a Newton)
• (kg m s-2 N)
• Symbol F
• F ma

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Fundamental Properties and Units (Cont.)

• The fundamental forces determine the motion of
  air in the Earths atmosphere.
• The pressure gradient force
• The gravitational force
• The frictional force

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Fundamental Properties and Units (Cont.)

• 8. Pressure is the force exerted on a
• surface divided by the area of the surface.
• Units kilograms per meter per second
• squared (Pascal)
• (kg m-1 s-2 Pa)
• Symbol - p

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Fundamental Properties and Units (Cont.)

• p F/A
• where A is the area of the surface

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Fundamental Properties and Units (Cont.)

• On surface and upper level maps the U.S. National
  Weather Service (NWS) reports pressures in
  millibars (mb).
• 1 mb 100 Pa 1 hPa (hectoPascal)

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Fundamental Properties and Units (Cont.)

• In reports for the public the NWS and media often
  report the sea level pressure in units of inches
  of mercury.
• The sea level pressure is the pressure that a
  weather station on the surface of the Earth would
  measure if the station was located at sea level.

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Fundamental Properties and Units (Cont.)

• 33.865 mb 1.0 inch of mercury
• 3386.5 Pa 1.0 inch of mercury

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Fundamental Properties and Units (Cont.)

• Barometer is an instrument designed to measure
  the pressure exerted by the air.
• The NWS used to use mercury in glass barometers
  to measure pressure.

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Mercury in glass barometer
This end of the tube is open
Fill the tube with mercury
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Mercury in glass barometer
Some but not all of the mercury runs out of the
tube. Approximately 30 inches of mercury remains
in the tube if the barometer is near sea level.
The force exerted by the air keeps all of the
mercury from running out of the tube.
Upend the tube and stick the open end into a
container of mercury
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Mercury in glass barometer
The pressure increases which forces more mercury
into the tube and we have a rising barometer
When a high pressure system moves over the
barometer there is more force pressing down on
the container of mercury
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Fundamental Properties and Units (Cont.)

• Standard Sea Level Pressure
• 101325 Pa 1013.25 mb 29.92 inches
• of mercury

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Fundamental Properties and Units (Cont.)

• 9. Work is done when a force of
• of magnitude, f, displaces a mass, m,
• across a distance, dx.
• The work done is equal to the
• magnitude of the force multiplied by
• the distance.

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Fundamental Properties and Units (Cont.)

• Units kilograms meters squared per
• second squared (equal to a
• Joule) (kg m2 s-2 J)
• Symbol W
• W fdx

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Fundamental Properties and Units (Cont.)

• Work represents the energy expended to displace
  the mass, m, the distance, dx.
• 9. Energy is the stored capacity to do work.
• Energy has the same units of work.
• Units (kg m2 s-2 J)
• Symbol - E