Transcript Document
Chapter 7:
Atmospheric
Circulations
Scales of atmospheric motions
Eddies - big and small
Local wind systems
Global winds
Global wind patterns and the oceans
Scales of Atmospheric
Motions
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
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
isobars and density
differences
thermal circulations
Sea and Land Breezes
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
Monsoon wind system
India and eastern Asian monsoon
other monsoons
Fig. 7-10, p. 178
Mountain and Valley Breezes
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
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
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
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
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
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
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
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
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
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
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
Upwelling is strongest
when wind is parallel
to the coastline
El Niño and the Southern
Oscillation
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
North Atlantic Oscillation
Arctic Oscillation: pressure difference between
Arctic and regions to its south
Pacific Decadal Oscillation
Fig. 7-36, p. 199