Transcript Document

Chapter 7:
Atmospheric
Circulations
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Scales of atmospheric motions
Eddies - big and small
Local wind systems
Global winds
Global wind patterns and the oceans
Scales of Atmospheric
Motions
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scales of motion
microscale
mesoscale
synoptic scale
planetary scale
• Lots of important weather events occur on microscales,
like evaporation of liquid water molecules from the
earth’s surface.
Fig. 7-2, p. 171
Eddies - Big and Small
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eddy
rotor
wind shear
turbulence
• Wind shear can sometimes be observed by watching the
movement of clouds at different altitudes.
•Kelvin Helmholtz waves
•Clear-air turbulence
•Billow clouds
Figure 1, p. 173
Local Wind Systems
Thermal Circulations
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isobars and density
differences
thermal circulations
Sea and Land Breezes
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sea breeze
land breeze
sea breeze front
Florida sea breezes
• Sea and land breezes also
occur near the shores of large
lakes, such as the Great
Lakes.
Fig. 7-6, p. 175
Seasonally Changing Winds the Monsoon
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Monsoon wind system
India and eastern Asian monsoon
other monsoons
Fig. 7-10, p. 178
Mountain and Valley Breezes
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valley breeze
mountain breeze
• The nighttime mountain breeze is sometimes called
gravity winds or drainage winds, because gravity
causes the cold air to ‘drain’ downhill.
Katabatic Winds
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Strong drainage winds: steep slope
• Katabatic winds are quite fierce in parts of Antarctica,
with hurricane-force wind speeds.
• Bora: a cold, gusty northeasterly wind along the Adriatic
coast in the former Yugoslavia
Chinook (Foehn) Winds
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Chinook winds—warm and dry
compressional heating
chinook wall cloud
• In Boulder, Colorado, along the eastern flank of the
Rocky Mountains, chinook winds are so common that
many houses have sliding wooden shutters to protect
their windows from windblown debris.
• It is called a Foehn along the leeward slopes of Alps.
Fig. 7-14, p. 180
Santa Ana Winds
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Santa Ana wind
compressional heating
wildfires
• Many Southern California residents
regularly hose down their roofs to prevent
fires during Santa Ana wind season.
• Difference between this and Chinook wind
Santa Ana: from elevated desert plateau;
Chinook: from cold plateau
Desert Winds
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dust and sand storms
dust devils – from surface
usually with a diameter of a few
meters and a height of <100 m
General Circulation of the
Atmosphere
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cause: unequal heating of the earth’s
surface
effect: atmospheric heat transport
• Ocean currents also transport heat from the equator to
the poles and back.
Single-cell Model
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basic assumptions: no rotation
Hadley cell
why is the single-cell model wrong?
• One of the world’s
premier atmospheric
science research
facilities,the Hadley
Centre for Climate
Research, is
named after
George Hadley.
Three-cell Model
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model for a rotating earth
Hadley cell
• Many global circulation terms,
doldrums
including ‘trade winds’ and
subtropical highs
‘doldrums’, were named by
trade winds
mariners who were well acquainted
with wind patterns.
intertropical
convergence zone
• Upper troposphere easterly is
westerlies
inconsistent with the observed
polar front
westerly
polar easterlies
Fig. 7-21, p. 185
Average Surface Winds and
Pressure: The Real World
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semipermanent highs and lows
Bermuda high & Pacific high
Icelandic low & Aleutian low
Siberian high
• The Bermuda High frequently brings hot, muggy
weather to the eastern US. in summer
• The ITCZ shifts toward the north in July (from
January)
Fig. 7-22a, p. 188
Fig. 7-22b, p. 189
The General Circulation and
Precipitation Patterns
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ITCZ, midlatitude
storms, polar front
• Most of the world’s
thunderstorms are found
along the ITCZ.
• Low rainfall over the
subtropical regions
Westerly Winds and the Jet
Stream
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jet streams
subtropical jet stream
polar front jet stream
Low-level jet stream over
the Central plains of the
U.S. (within 2 km above
surface), bringing moist
and warm air to form
nighttime thunderstorms
Global wind-driven ocean current
Fig. 7-29, p. 193
Winds and Upwelling
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Upwelling is strongest
when wind is parallel
to the coastline
El Niño and the Southern
Oscillation
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El Niño events
Southern Oscillation
La Niña
teleconnections
• ENSO is an example of a global-scale weather
phenomenon.
• Often Arizona has a wetter winter during El Nino
and a drier winter during La Nina;
• Usually northwestern U.S. has a drier winter during
El Nino and a wetter winter during La Nina.
Fig. 7-32, p. 196
Other Atmosphere-Ocean
Interactions
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North Atlantic Oscillation
Arctic Oscillation: pressure difference between
Arctic and regions to its south
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Pacific Decadal Oscillation
Fig. 7-36, p. 199