AOSC 200 Lesson 5 Observing the Atmosphere There

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 Microwavelengths

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 • • • 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. 21 a

Fig. 5. 21 b

Plot of boundary layer winds from the Fort Meade, MD wind profiler during a high ozone episode 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