Geos 114
Introduction to Meteorology
Definitions
• Meteorology
– Study of the atmosphere & the processes that causes
weather
• Weather
– State of the atmosphere at a particular place & time.
Described by T, Humidity, Ppt., Wind speed
• Climate
– Average values of weather conditions at some place
for at least 30 years beginning with the first year of a
decade (i.e. 1971-2000; average annual and monthly
temp, ppt). Tabulation of extreme events during time
of record i.e. high/low T, greatests snowfall, most
intense rainfall)
• Climatology
– Study of climate, control, spatial and temporal
variability
Climatic Zones
• Tropic Humid (A)
• Dry Climates (B)
– Steppe (BS) and desert (BW)
• Subtropical Climates (C)- Mediterranean
• Snow Forest Climates (D)- temperate
continental (i.e. northeast US)
• Polar Climates (E)- poleward of arctic & antarctic
circles
• Highland Climates (H)- mountanous terrain
every 300 meters of altitude is equivalent to
500km of latitude.
Climatic Zones
Sources of Weather Info
• Weather Radio
– Low Power VHF High Band FM
– Constant weather information
– Repeat messages every 4-6 minutes
– Transmits all other sorts of emergencies
• Cable & Broadcast TV
– The Weather Channel
• WWW
NOAA Weather Radio
The Weather Channel
Intro to Weather Systems & Maps
• ASOS: Automated Surface Observing
System (installed at airports) records
24hrs/day
– Temp., humidity, dew point, wind speed &
direction, Pressure
ASOS
Pressure Systems
• Pressure: weight per unit area of a column of air
stretching from the earth’s surface up to through the
atmosphere
• Highs (anticyclones)
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‘H’ on a map
Fair weather systems
Cold or cool, dry air (NW Canada)
Hot, mild, dry air (from land further south)
Clockwise, outward spiral
• Lows (cyclones)
– ‘L’ on a map
– Stormy weather systems
– Counterclockwise, inward spiral
• Highs and lows move with prevailing winds (eastward in
North America)
Pressure Systems
H
L
Air Masses
• Large uniform air mass (temperature and
humidity) associated with high pressure system
• Cold air masses form at high latitudes
• Humid air masses over maritime surfaces
• Dry air masses over arid/semi arid regions
• Cold & Dry
• Cold & Humid
• Warm & Dry
• Warm & Humid
Fronts
• Narrow band between 2 air masses that
differ in T, humidity, or both
• Fronts form where air masses collide
– Ppt & cloudiness
• Fronts:
– Stationary
– Cold
– Warm
Fronts
Fronts
Vocabulary
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Max. T (oF; oC)
Min. T
Dew Point
Relative Humidity (%)
Ppt. amount
Air pressure (29.92 inches, 760 millimeters Hg; millibars
(mb) 1013.25mb at sea level)
Wind direction; speed
Sky cover (no clouds; few (1/8-2/8 cloud cover);
scattered (3/8-4/8); broken clouds (5/8-7/8); overcast
(completely cloud covered))
Weather watch- NWS possibility of hazard
Weather warning- NWS imminent hazard
Weather Satellites
• GOES (geostationary operational
environmental satellite)
– 36,000km (22,300mi); equatorial, eastward
motion, same view 75oW, 135oW
• POES (polar-orbiting operational
environmental satellite)
– N-S orbit 800-1000km above surface
• Measure visible radiation that is scattered
or reflected and infrared
GOES
Weather Radar & Doppler
• Complements satellite data
• Microwave radiation
• Emits pulses that are reflected by rain, snow,
hail which appear as blotches known as echoes
• Doppler determines velocity of targets moving
towards or away from unit depending on
frequency bet. Outgoing & returning signal
• Monitor circulation of air within a storm system
and provide advance warning of severe weather
Doppler Radar
Sky Watching
• Clouds- aggregates of water droplets or
ice crystals or both
• Fog- ground contact cloud reduces
visibility to less than 1000m
• Stratiform- horizontal layers, gentle rising
of air over broad region ahead of a warm
front
• Cumuliform- puffy, vigorous ascent of
warm air ahead of a cold front
Clouds
• Fair weather cumulus clouds
• Storm cumulonimbus clouds produce
lightning & thunder
• Clouds at different altitudes may move
horizontally in different directions and
speeds
Cloud Types