Transcript Chapter 7: Air Circulation

Chapter 7
Circulation of the Atmosphere
The Atmosphere 9e
Lutgens & Tarbuck
Power Point by Michael C. LoPresto
Microscale
Atmospheric Circulation
Scales
Scale
Distance
Time scale
Examples
Macroscale
Planetary
Synoptic
1000 – 40,000 km Weeks or more Westerlies
100 – 500 km
Days to weeks Hurricanes
Mesoscale
1 – 100 km
Minutes to
hours
Thunderstorm
s, Land-sea
breeze
Microscale
< 1km
Seconds to
minutes
Gusts, dust
devils
Mesoscale Sea Breeze (occurs in afternoon)
Mesoscale Land Breeze (occurs in early morning)
Valley Breeze (afternoon)
Mountain Breeze (early morning)
Other Common, Named
Mesoscale Winds
• Chinook – warm winter wind that
descends off mountains (Foehn in Alps;
Santa Ana in So. Cal.)
• Katabatic – cold, powerful winter wind
that descends off glaciers (mistral in
Alps)
Macroscale: Global Circulation
Oversimplifie
d global
model
(why is it
wrong?)
Best Model
for Global
Circulation
Idealized & Actual Prevailing Global Winds
Seasonal Pressure and Wind Patterns
January Average Global Pressure and Winds
July Average Global Pressure and Winds
Monsoons
• Seasonal wind (and precipitation)
events on large continents
– Cooling of land during winter creates high
pressure, pushes air offshore (cold dry
winds)
– Heating of land during summer creates low
pressure, sucks air inland (warm wet
winds)
Winter Monsoon Circulation
L
Summer Monsoon Circulation
North American
Monsoon
L
The Westerlies and the Jet Stream
Jet Stream
Jet Stream
300 mb Equal-Pressure Surface 4.15.05
300 mb Equal-Pressure Surface 4.15.05
Rossby Waves
Meridional and Zonal Flow
Ocean Currents
El Nino/Southern Oscillation
Effects of El Nino
ENSO
El Nino Winter Surface Air
Pressure Anomaly
low
high
low
La Nina Winter Surface Air
Pressure Anomaly
high
1997 ENSO Movie
http://www.noaanews.noaa.gov/stories/s997.htm
http://www.cdc.noaa.gov/ENSO/
http://www.cdc.noaa.gov/map/clim/sst_olr/el_nino_anim.shtml
http://www.cdc.noaa.gov/map/clim/sst_olr/old_sst/sst_9798_anim.shtml
http://www.cdc.noaa.gov/ENSO/Compare/
1982-1983 ENSO Movie
Average Tropical Pacific Sea Surface
Temperature
Sea Surface Temperature March 2002
ENSO Rainfall in North America
El Nino Winter Precipitation
Rate Anomaly
La Nina Winter Precipitation
Rate Anomaly
Current ENSO conditions: Equatorial Pacific
sea surface temperatures (top) and
temperature anomalies (bottom)
Drought
Flooding, erosion
Drought
Utah: On average, ENSO years are normal, but
some ENSO years have brought severe flooding
Worldwide ENSO Effects
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