Transcript AOSC200_summer_lect5

AOSC 200
Lesson 5
Observing the Atmosphere
• There are several instruments that are used to
measure the basic atmospheric variables/
• Temperature – Thermometer
– Mercury
– Resistance
• Pressure – Barometer
• Humidity – psychrometer, dew point hygrometer
• Wind Speed - Anemometer
• Wind Direction – Wind vane
• Precipitation – Rain Gauge
Max-min Thermometer
Temperature Measurement
• Max-Min thermometer
• Resistance thermometer
• Remote measurement by observing thermal
IR emissions.
• Clinical thermometer
Fig. 5-3, p. 130
Humidity Measurements
• Dew-point hygrometer.
• Uses a laser beam and a mirror. The mirror is
cooled down, and when dew is formed on the
mirror, the laser beam is scattered.
• Wet-bulb psychrometer. Two thermometers, one
wrapped with a wet cloth. Air is passed over both,
the wet bulb will show a lower temperature.
Relative humidity obtained from pre-calculated
tables.
• Remote measurements using Microwave
wavelengths
Mercury Barometer
Fig. 5-4, p. 131
Pressure Measurement
• Mercury barometer – long tube sealed at
one end and filled with mercury, with open
end immersed in a bath of mercury. Closed
end has vacuum above mercury column.
Height of column measures the pressure.
• Aneroid barometer – ‘without liquid’. Spiral
thin wall cell which twists as the pressure
changes. Not as accurate as the mercury
barometer
• Electronic – transistors whose resistance is
sensitive to pressure.
Fig. 5.4
Wing Gauge
Wind Measurement
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Anemometers measure wind speed
Wind vanes measure wind direction
Combination measures wind velocity
Cup anemometers
Propellers
From space one can observe the speed with
which clouds move
Rain Gauge
Tipping Rain Gauge
Fig. 5-12, p. 139
Radar Observations
• RAdio Detection And Ranging
• Pulse of radio waves is sent out from transmitter.
Time it takes for the pulse to return gives the
distance to the cloud/precipitation.
• The amount of the pulse that is scattered can be
used to tell how much rain is falling.
• Doppler effect
• Doppler RADAR can detect wind speed
• Wind profiler
Fig. 5.19
Fig. 5.21a
Fig. 5.21b
Plot of boundary layer winds from the Fort Meade, MD
wind profiler during a high ozone episode
LLJ
LLJ
LLJ
Geosynchronous Orbit
Fig. 5-13, p. 140
Sun-synchronous (polar) orbit
Satellite Observations
• Two principle orbits are used
• Sun-synchronous, aka polar orbiter, LEO
• 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 – orbits around the earth always
above the equator. Orbital period is 24 hours, i.e.
it stays above the same point on the ground.
Visible image from the GOES Satellite Aug 7, 2000
Fig. 5.14
IR image from the GOES satellite, Aug 2, 2000
Fig. 5.15
Water vapor image, August 7, 2000
Fig. 5.17
Fig. 5.22