Download - AOS 101
Background
• Observations allow meteorologists to assess the current state of the atmosphere
• Synchronized: taken at same time at every location
• Standardized: all measurements taken the same way
• Two main types: – SURFACE and UPPER AIR
Surface Observations
• Taken hourly at thousands of sites around the world
• Originally was manual, but now mostly automated
• Mostly at airports• Stations identified by four
letter code– KMSN = Madison– KORD = Chicago O’Hare
ASOS station
Upper Air Observations
• Radiosondes (weather balloons) measure the atmosphere aloft.
• Released twice daily at the same time globally.– 6 AM and 6 PM CST
• Can reach 90000 feet• 900 stations globally
– 72 in the continental U.S.
Radiosonde
Other data types
• Ships• Commercial
Aircraft (ACARS)• Satellite
• All this data goes into forecast models.
7 important measurements
• 1. Sky Cover– How much sky do clouds cover?– Partly cloudy, mostly cloudy, etc.
• 2. Current Weather– Is there precipitation falling? What type?– Is it foggy? Thunder?
3. Wind
• Speed– 1 mph = 0.869 kts = 0.447
m/s– Anemometer
• Direction– Measured from a direction– Either cardinal direction or degrees
• Examples: 0o = N, 225o=SW
– Wind vane
Cup anemometer
•4. Temperature– oF = (9/5 * oC) + 32; oC = (oF - 32) * 5/9 – Thermometer
•5. Air pressure– Units: hectopascals
(hPa), millibars (mb) or inches of mercury (“ Hg)
– hPa = mb– 1000 hPa = 29.53” Hg– Falling pressure = stormy
weather is on the way (usually).
– Barometer
Barometer
• 6. Dewpoint– Related to amount of moisture (water
vapor) in the air except in temperature units.
– The temperature to which the air must be cooled for condensation to take place• Example: Morning Dew
– If dewpoint is close to temperature (within 3o), expect fog, haze or precipitation.
• 7. Visibility– How far one can see horizontally.– Clear day visibility more than 10 miles– Fog or heavy snow can cause visibilities of
less than one mile
TT
ddvv ww
PPPappN
D
S
TT
ddvv ww
PPPappN
D
S• N = Sky Cover
– Quarters of sky that are cloud covered
TT
ddvv ww
PPPappN
D
S
TT
ddvv ww
PPPappN
D
S
• ww = current weather– Symbols
representing certain weather conditions
– Omitted if no current weather
RAIN
SNOW
DRIZZLE FRZ. DZ. SLEET
T’STORM FOG HAZE
TT
ddvv ww
PPPappN
D
S
TT
ddvv ww
PPPappN
D
S• D = Wind
direction – Line (wind barb)
drawn in direction wind is from.
TT
ddvv ww
PPPappN
D
S
TT
ddvv ww
PPPappN
D
S
• S = Wind speed (in knots)– Lines drawn at end of barb– Full line = 10 kts– Half line = 5 kts– Flag = 50 kts– Calm = circle around
station
TT
ddvv ww
PPPappN
D
S
TT
ddvv ww
PPPappN
D
S
• TT = Temperature– In Fahrenheit
TT
ddvv ww
PPPappN
D
S
TT
ddvv ww
PPPappN
D
S
• dd = Dewpoint– In Fahrenheit
TT
ddvv ww
PPPappN
D
S
TT
ddvv ww
PPPappN
D
S
• PPP = Pressure (in hPa)– If PPP>500, place a 9 in front of PPP and divide by
10, example 876 = 987.6 hPa– If PPP<500, place a 10 in front of PPP and divide
by 10, example 181 = 1018.1 hPa
• app = Pressure Tendency (in hPa)– Change in pressure over last 3 hours in tenths of
hPa (ALWAYS with a + or -), also a symbol describing how it has changed (see handout).
TT
ddvv ww
PPPappN
D
S
TT
ddvv ww
PPPappN
D
S • vv = Visibility (in miles)– can have a
fraction
• Several station models can be plotted on a map and analyzed to find fronts, high/low pressure systems, cold/warm areas, and areas of cloud cover…