Download Chap 7 global winds

Global Winds
Scales of atmospheric motion. A) tiny micro scale
motions
B) Are part of the larger mesoscale motions
Wave clouds, called billow clouds, forming
in a region of wind shear.
Fig. 7-CO, p.166
C) which are part of the much larger synoptic scale
motions
Fig. 7-1, p.168
Smaller scale motions not visible at large scales
FIGURE 7.2 Under stable conditions, air flowing past
a mountain range can create eddies many
kilometers downwind from the mountain itself.
Table 7-1, p.168
Wind
Shear
Formation of clear air turbulence (CAT) along a
boundary of increasing wind speed shear.
Side view… with top layer of air moving over layer
below
p.171a
Fig. 7-2, p.170
Wind
Shear
Turbulent eddies downwind of a
mountain chain produce Kelvin
Helmholtz waves. The visible clouds that
form are called billow clouds.
p.171b
Thermal Circulations produced by the
heating and cooling of
the atmosphere near
the ground.
H = high pressure
L = low pressure
isobaric surfaces =
surfaces of constant
pressure.
Fig. 7-3, p.172
Isobars all lie parallel here, so…
…no horizontal variation in P or T and no pressure
gradient or wind
Fig. 7-3a, p.172
Sea breeze and
land breeze
(a) At the surface, a
sea breeze blows
from the water onto
the land
Air aloft moves to the north and “piles up”..which reduces
surface air P to the south and raises it to the north…
PGF is established from N=>S, thus wind blows N=>S
Fig. 7-3c, p.172
FIGURE 7.5 Surface heating and lifting of air along a
sea breeze combine to form thunderstorms almost
daily during the summer in southern Florida.
Fig. 7-5, p.174
(b) land breeze
blows from land out
over water
Note: pressure at the
surface changes more
rapidly with the sea
breeze. (stronger pressure
gradient force and higher
winds)
Fig. 7-4, p.173
FIGURE 7.6 Changing annual wind flow patterns
associated with the winter and summer Asian
monsoon. By defn, “monsoons” change direction
seasonally.
Fig. 7-6, p.174
FIGURE 7.7 Enhanced
infrared satellite (IR)
image
heavy arrows show
strong monsoonal
circulation
Showers and
thunderstorms
(yellow and red)
forming over the
southwestern section
of the United States,
July, 2001.
Katabatic Winds
• drainage winds
• •bora
Katabatic winds are quite fierce in parts of Antarctica,
with hurricanehurricane-force wind speeds.
Fig. 7-7, p.175
FIGURE 7.8 Valley breezes blow uphill during the
day; mountain breezes blow downhill at night. (The
L’s and H’s represent pressure, whereas the purple
lines represent surfaces of constant pressure.)
Fig. 7-8, p.176
FIGURE 7.9 As mountain slopes warm during the
day, air rises and often condenses into cumuliform
clouds, such as these. The Grand Tetons.
Fig. 7-9, p.176
Chinook (Foehn) Winds
• Chinook winds
• 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.
Fig. 7-14, p. 180
FIGURE 7.11 A chinook wall cloud forming over the
Colorado Rockies (viewed from the plains).
Fig. 7-11, p.179
Cities near the warm air–cold air boundary can
experience sharp temperature changes, if cold air
should rock up and down like water in a bowl.
p.178
FIGURE 7.12 Surface
weather map showing
Santa Ana conditions in
January in California.
Max temperatures for
this particular day
given in °F. Note down
slope winds blowing
into southern
California raise
temperatures into the
upper 80s
Fig. 7-12, p.179
FIGURE 7.13 Formation of a dust devil. On a hot, dry day, the
atmosphere next to the ground becomes unstable. As the heated
air rises, wind blowing past an obstruction twists the rising air,
forming a rotating column, or dust devil. Air from the sides rushes
into the rising column, lifting sand, dust, leaves, or any other loose
material from the surface.
Fig. 7-13, p.180
FIGURE 7.14 A dust
devil forming on a clear,
hot summer day just
south of Phoenix,
Arizona.
Fig. 7-14, p.180
FIGURE 7.15 Diagram (a) shows the general circulation of air
on a non rotating earth uniformly covered with water and with
the sun directly above the equator. (Vertical air motions are
highly exaggerated in the vertical.) Diagram (b) shows the
names that apply to the different regions of the world and
their approximate latitudes.
Fig. 7-15, p.182
Fig. 7-15a, p.182
FIGURE 7.16 Diagram (a) shows the idealized wind and
surface-pressure distribution over a uniformly watercovered rotating earth. Diagram (b) gives the names of
surface winds and pressure systems over a uniformly
water-covered rotating earth.
Fig. 7-16, p.183
Fig. 7-15b, p.182
Fig. 7-21, p. 185
Global Wind Patterns and
the Oceans
FIGURE 7.17 Average sea-level pressure distribution and surface wind-flow patterns for
January (a) and for July (b). The heavy dashed line represents the position of the ITCZ
Fig. 7-17a, p.184
(intertropical convergence zone).
The General Circulation and
Precipitation Patterns
• major controls
• ITCZ, midlatitude storms, polar front
• Most of the world’
world’s
thunderstorms are found
along the ITCZ.
FIGURE 7.17 Average sea-level pressure distribution and surface wind-flow patterns for
January (a) and for July (b). The heavy dashed line represents the position of the ITCZ
Fig. 7-17b, p.185
(intertropical convergence zone).
FIGURE 7.19 During the summer, the Pacific high moves
northward. Sinking air along its eastern (over California) margin
produces a strong subsidence inversion, which causes relatively
dry weather to prevail. Along the western margin of the Bermuda
high, southerly winds bring in humid air, which rises, condenses,
Fig. 7-19, p.187
and produces abundant rainfall.
FIGURE 7.20 Average annual precipitation for Los Angeles,
Fig. 7-20, p.187
California, and Atlanta, Georgia.
Westerly Winds and the Jet
Stream
• jet streams
• subtropical jet stream
• polar front jet stream
FIGURE 7.22 Average position of the polar front jet
stream and the subtropical jet stream, with respect
to a model of the general circulation in winter. Both
jet streams are flowing into the page, away from the
viewer, which would be from west to east. Fig. 7-22, p.188
Position of the polar jet stream and the subtropical jet stream at the 300mb level during the morning of March 10, 1998. Solid gray lines are lines of
equal wind speed (isotachs) in knots. Heavy lines show the position of the jet
streams. Heavy blue lines show where the jet stream directs cold air southward,
while heavy red arrows show where the jet stream directs warm air northward.
Fig. 7-23, p.189
Upwelling of
cold water!
…upwelling depends on the wind…
…and the Coroilis force.
FIGURE 7.25 Average sea surface temperatures (°F) along the
Fig. 7-25, p.191
west coast of the United States during August.
FIGURE 7.26 As winds blow parallel to the west coast of
North America, surface water is transported to the right
(out to sea).Cold water moves up from below (blue arrows)
Fig. 7-26, p.191
to replace the surface water.
Coriolis effect bends the
northerly wind to the
right and out to sea
…the net effect is that a
shallow layer of sfc
water heads at right
angles to the sfc wind
and head seaward...
…thus allowing the
cold water to rise!
Fig. 7-26a, p.191
Fig. 7-26b, p.191
usual: high P over SE
Pacific and low P over
Indonesia =>easterly
trade winds…
=upwelling & cool H2O
in E Pacific; warm
H2O to west.
Strong trades=La Nina
Atmos. P dec over Pacific
…trades weaken…or
reverse!
…countercurrent, warm
H2O=> west
Note thermocline changes
El Nino!
Fig. 7-27, p.193
Fig. 7-27b, p.193
Fig. 7-28a, p.194
Fig. 7-27a, p.193
FIGURE 7.28 (a) Average sea
surface temperature departures
from normal as measured by
satellite. During El Niño
conditions upwelling is greatly
diminished and warmer than
normal water (deep red color),
extends from the coast of South
America westward, across the
Pacific.(b) During La Niña
conditions, strong trade winds
promote upwelling, and cooler
than normal water(dark blue
color) extends over the eastern
and central Pacific.
(NOAA/PHEL/TAO)
Fig. 7-28, p.194
Fig. 7-28b, p.194
FIGURE 7.29 Regions of climatic abnormalities=>A strong ENSO event may trigger a response
in nearly all areas shown; a weak event in only some areas. Note that the months in black type
indicate months during ENSO; months in red type indicate the following year.(After NOAA
Fig. 7-29, p.195
Climatic Prediction Center.)
Aleutian low
strengthens =
more Pacific
storms into AK
and Calif.
FIGURE 7.30 Typical winter sea surface temperature departure from
normal in °C during the Pacific Decadal Oscillation’s warm phase (a)
and cool phase (b). (Source: JISAO, University of Washington, obtained
via the http://www.jisao.washington.edu/pdo/ Used with permission of
N. Mantua.)
Fig. 7-30, p.196
Winters cooler and
wetter in NW N.
Amer.; wetter in
Great Lakes;
warmer and drier
in southern US.
Drier in the Great
Lakes; cooler and
wetter in southern
US
PDO-warm phase-warm surface water off west coast of
NA—cooler than normal in central north Pacific Fig. 7-30a, p.196
PDO-cold phase-cooler than average surface waters off
west coast of NA; warmer than aver. in N. Cent. Pacific.
Fig. 7-30b, p.196