AOSC 200

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AOSC 200

• Lectures 8, 9, 10, 11

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Precipitation

• Raindrops grow by two processes
• (1) collision-coalescence warm clouds.
• (2) Bergeron process cold clouds

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(No Transcript)
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Airflow Over a Mountain
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How do we observe the atmosphere?

• Direct Methods
• Temperature
• Mercury thermometer, resistance thermometer
• Pressure
• Barometer mercury and aneroid
• Humidity
• Psychrometer (RH), dew point hygrometer
• Wind
• Anemometer (wind speed)
• Precipitation
• Rain Gauge

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Satellite Observations

• Two principle orbits are used
• Sun-synchronous, aka polar orbiter, LEO (Low
  Earth Orbit) 850 km.
• Orbits in the sun-earth plane, crosses over the
  poles. NOAA LEO cross the equator at 2.00 pm and
  2.00 am each day. Each orbit takes about 90
  minutes
• Geosynchronous, GEO (Geostationary) orbits
  around the earth always above the equator
  36,000km. Orbital period is 24 hours, i.e. it
  stays above the same point on the ground.

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Doppler Effect
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Newtons Laws

• First Law (Law of Inertia) A body at rest
  tends to stay at rest while a body in motion
  tends to stay in motion, traveling at a constant
  speed and in a straight line, until acted upon by
  an outside force
• Second Law (Law of Momentum) A force exerted on
  an object (including a parcel of water or gas) of
  a given mass causes the object to accelerate in
  the direction of the applied force and in
  proportion to the force divided by the objects
  mass.
• Fma

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Forces that Move the Air

• Gravitational Force
• Directed toward the center of the earth
• Approximately equal mass times g (9.8m/s)
• Pressure Gradient Force
• Always directed from High pressure to Low
• Expressed as a force per unit mass

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CORIOLIS EFFECT

• WEATHER MAP SHOWS THAT WINDS GO AROUND A LOW
  PRESSURE AREA, NOT ACROSS THE ISOBARS.
• THIS DEVIATION IS A RESULT OF THE EARTH'S
  ROTATION AND HAS BEEN NAMED THE CORIOLIS EFFECT
  (CORIOLIS FORCE)
• THIS FORCE ALWAYS ACTS AT RIGHT ANGLES TO THE
  DIRECTION OF MOTION.

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Centrifugal Force
Fig. 6.11
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Geostrophic Flow

• Balance between Pressure Gradient Force and
  Coriolis Force
• Flow is at a constant velocity, parallel to
  isobars
• Usually applies to winds aloft where friction is
  negligable

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Fig. 6-15, p. 172
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Surface Winds

• Balance between Pressure Gradient Force, Coriolis
  Force and Friction
• Causes surface winds to cross isobars toward Low
  pressure

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Land/Sea Breeze

• Caused by different heating rates over land and
  water
• Daytime wind from the ocean onto the land
• Night wind from land out over ocean