Atmospheric Circulation (Ch. 8) Ocean & Atmosphere are intertwined Gases & waters freely exchanged Wind Weather Climate
Atmospheric Structure Consists of Layers Separated by Temperature Stratosphere: Temperature with altitude Little circulation Injections of volcanic eruptions Troposphere: Temperature with elevation Where weather occurs Temperature with altitude 30+ mi. above earth (ozone layer) 11-30 miles (clouded layer) 0-11 mi
Composition and Properties of Air Transparent, odorless gases & water vapor (up to ~4% of volume) Condenses as Precipitation Dust particles, pollution 78.1% 20.9% Dry Air Compostion Other gases (0.9%)
Atmospheric Circulation Earth-Sun Dynamics Solar Energy (light) converted to heat energy Uneven Heating 1. Earth is a sphere Radiation (heat) varies with latitude 2. Earth is tilted on its axis Radiation varies with season
Light passes through more atmosphere: light absorption
Solar Radiation Varies with Latitude Greatest at Equator(direct rays) As move toward poles (oblique) Reflection (albedo) Weak near equator Strong near poles (ice cover) direct oblique
Wind & Ocean Currents distribute heat Poles: Lose more heat than gain (reflection) Equator: Gains more heat than loses
Northern Hemisphere Seasons Earth s Tilt Causes Uneven solar Heating - Seasons
Earth is tilted on its axis 23.5 As Earth rotates around sun (365 days) One pole or other is closer to sun: Seasons Tilt toward sun at Summer Solstice (June 21-North) At poles = 24 hrs. day Tilt away from sun at Winter Solstice (21 Dec N.) At Poles = 24 hr. Night Equator has little seasonal variation in temp.
Winds on a Non-rotating Earth Would Be Simple: Warm air rises at equator Cools as it rises & water vapor condenses as rain Surface winds blow from equator to poles Dry, cool air, then sinks at the poles
Warm Air Rises, Cool Air Falls = Convection Current
Coriolis Effect Eastward rotation of Earth on its axis 15 /hr Deflects moving objects (air, water) away from initial course Earth spins faster at Equator (0 ) 1700 km/hr Than at higher latitudes 1260 km/h at 43 Air masses move in curved path (deflected) instead of straight
Coriolis Effect: Earth s Rotation deflects moving objects (air, airplane, ocean currents) Deflected: Clockwise (North. Hemis.) Counterclockwise (South) No Deflection at Equator to 5º Wider disc spins faster Both disks must rotate 15 /1 Hr. or Earth would rip itself apart!
Hemispherical wind cells get divided into 6 smaller latitudinal systems Air rises Air falls Air rises Air falls Air rises
Trades (0-30 latitude): from East to West Westerlies (30-60 latitude): from West to East Rain! Polar Easterlies (60-90 latitude): from East to West
Monsoons Summer (Rainy): Land warms, air rises Draws cooler, moist air from ocean Winter (Dry): Cool continental air drawn towards ocean
Southern Arizona Summer Monsoon Gulf of California Cold, dense air rushes to "fill the gap" caused by the rising warm air
Coastal Areas (Land & Sea Breezes) Occurs daily Sunset: winds shift (breezy) Day: warm land air rises Replaced by cool sea air onshore wind Night: Land cools (faster than sea) Warmer sea air rises Replaced by cool land air Offshore wind
Hurricanes (Typhoons) Form from equatorial trade winds (blow E to W) Begin in warm water: >26 C (79 F) Moist, low pressure Convergence of rotating wind Storm becomes hurricane at wind speed: 119km (74 mi) Dissipate over land or cold water
Move westward with Trade winds Form at 10º-25º N & S Latitude
Where Do Hurricanes Occur? Sea surface temps. for North. Hemisphere Summer: Yellow, orange, & red = H 2 O warm enough to sustain hurricanes (>26 C)
Hot, humid tropical air rises, drops moisture as it cools Heat Energy released when water vapor converted to liquid heat energy drives the cyclone (2.4 trillion kw hours of power/day)
Storm Surges Elevated Seawater Driven by Hurricane As high as 12 m (40 Ft)
Storm surge: onshore rush of water caused by high winds pushing on ocean's surface Wind causes water to pile up above sea level Shoreline bathymetry can have added effect Particularly damaging if occurs at high tide Combines effects of surge & tide
Biloxi, Mississippi 9 m (30 ft.) Hurricane Katrina (2005): Greatest recorded storm surge (USA) = 9 meters (30 feet) high
Hurricane Katrina 23-31 Aug. 2005 Max wind -175 mph Most destructive U.S. storm Gulf Port, MS
Cat. 3 (125 mph): MS/LA border Cat. 4 (140 mph): Plaquemines Parish, LA
Inland flooding causes most hurricanerelated deaths
New Orleans: Built on an Estuary Levees cut-off Mississippi River sediment supply Sinking below sea level London St. Canal
Are Hurricanes getting more frequent or stronger? Hurricanes only form over oceans w/ surface temps. > 26 C Average ocean-surface temps. have risen ~0.5 C since 1970 Raising the temp. above 26 C may : Number of storms Storm length Maximum strength Proportion that are strong