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)– ‘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• 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