Transcript WINDS

LOCAL, REGIONAL AND GLOBAL SCALE WINDS,
EL NIÑO AND SOUTHERN OSCILLATION (ENSO)
LOCAL SCALE WINDS
 Sea Breeze-Land Breeze Circulation
 Due to temperature differences between coastal and
inland regions
 For southern California, the most likely time for SeaBreeze is Summer, late afternoon:
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Warmer regions inland set up conditions to build thermal low
air pressure
Cooler water along coastal regions sets up conditions to build
thermal high air pressure
Air always moves from areas of higher pressure to areas of
lower pressure.
Sea Breeze Circulation
Afternoon warming of valley floors,
produces thermals of warm rising air –
Thermal Low develops over valleys.
Over the ocean, cooler water produces
a Thermal High with cool sinking air.
Result: Cool, moist air flows onshore
toward valleys in late afternoons.
Effects: Decrease in temperature and
an increase in relative humidity.
Locally, sea breeze from Santa Monica
Bay flows onshore and makes its way
into the surrounding Los Angeles
Basin, even into the San Fernando
Valley
Land Breeze Circulation
 During night, radiational cooling in the local valleys
lifts warmer air away from valley flo0rs creating an
inversion layer in the atmosphere
 Valley regions are cooler at the surface producing a
thermal high pressure.
 C0astal areas are slightly warmer than adjacent valleys,
producing a thermal low pressure.
 Time for the greatest difference in temperatures is
close to sunrise, setting up conditions for a land
breeze, as air is moved offshore from valleys to coast.
Land Breeze Circulation
Differences in temperature
between adjacent valleys and
coastal area set up conditions
for offshore flow of air
Mountain and Valley Breezes
Similar to the land and sea breeze in its diurnal cycle are the valley and mountain
breezes.
Valley breezes occur in the day because air along mountain slopes is heated more
intensely than air at the same elevation over a valley floor.
Rapid radiational heat loss in the evening reverses the process to produce a
mountain breeze.
Santa Ana Winds
 Santa Ana Winds are warm, dry, high velocity winds
that flow into southern California.
 The winds usually begin in late summer-early fall and
extend to December; typically ending with the arrival
of the winter rainy season.
 The source region for the winds is northeast of
southern California near Utah.
 In the late summer-early summer, a large high
pressure system (The Great Basin High) develops near
the area of Utah, western United States.
Santa Ana Winds
 Average elevation in Utah is ~5000 feet, while average elevation in
southern California is ~ 500 feet : a 4500 foot difference.
 Descending air is heated by compression (dry rate of heating at
100C/1000 meters or 5.50 F/1000 feet).
 250 F added to the air temperature as it descends from the high
towards southern California
 Warmed air is funneled between Sierra Nevada on west and Wasatch
Mountains to the East.
 Air flows over Mojave Desert – lowering specific humidity.
 Acceleration of the air occurs two ways:
 Funneling through the canyons of the Transverse Ranges
 Flowing downslope the Transverse Ranges under gravity
Great Basin High
forming near Utah,
producing conditions
for development of
Santa Ana Winds in
southern California.
Note the isobaric
pressure near Utah,
compared to southern
California.
Temperatures near
Utah are in the mid-50s
F, while temperatures in
southern California are
in the high 80s F.
Santa Ana Winds: Hot, Dry and High
Velocity
Santa Ana Winds and Fire Season in
southern California
Recent Fires in southern California
CONTINENTAL SCALE WINDS:
MONSOONS
 Monsoon - from Arabic word “mausim” – means “
changing wind directions with a change in season”.
 Monsoon are associated with heavy precipitation.
 There are monsoons in many areas of the world,
including western United States.
 Arizona, for example, receives most of its annual
precipitation during its summer monsoonal season
 Most described are the monsoons in southern Asia –
India.
 India has two monsoons: Winter and Summer
Winter Monsoon in India
 During the winter, the Asian landmass becomes very
cold, producing a large high pressure system over most
of the southern Asian region.
 This high pressure rotates air clockwise, out from the
center; pushing the cool, relatively dry air off the
subcontinent.
 The warmer waters of the Indian Ocean produce a
relatively weak low pressure system.
Winter Monsoon in India
Summer Monsoons in India
 In summer, the Asian continental landmass heats up
producing very large thermal Low air pressure systems
 Over the relatively cooler Indian Ocean, a thermal
high pressure develops
 The large continental Low draws in the cool, high
humidity air from the Indian Ocean.
 The cool humid air is lifted along the Himalayan
Mountains, producing massive amounts of
precipitation in the northern regions of India
Summer Monsoons in India
East Asian Monsoons
Bangladesh
Summer Monsoon, India
UPWELLING AND OCEAN CURRENTS
 Cold ocean currents flow almost parallel to the west
coast of large continents
 California Current, North America
 Humboldt (Peru) Current, South America
 Benguela Current, Africa
 The Earth's rotation and strong seasonal winds push
the surface water away from the western coast of North
America, South America and Africa.
 Upwelling of the nutrient rich water occurs on the
western edge of the continental shelf replacing the
warmer waters.
 The abundant marine life within the Galapagos Archipelago thrives
in these nutrient rich waters.
UPWELLING PROCESS
Peru
Humboldt Current
Upwelling along west coast of
South America:
Humboldt Current flows north along west coast of South America. Coriolis Force
pulls the surface water away from coastline, allowing upwelling of nutrient-rich
deep and cold water.
El Niño
 El Niño originally referred to the warm ocean current
that appears along the Pacific coast of South America
each year around Christmas
 El Niño is an atmospheric and oceanic disturbance in
the tropical Pacific Ocean.
 The name was given by Peruvian fishermen owing to the
timing of the appearance of this disturbance.
 During an El Niño event the following events occur:
 Dwindling of trade winds
 Changes in barometric pressure across the Pacific
 Sea surface temperature anomalies are recorded
 Rainfall patterns are disrupted
El Niño and the Humboldt Current
 The Humboldt Current is a northward flowing current
along the west side of South America
 Coriolis Force and surface winds act to pull surface
water away from the coast – creating Upwelling along
the west coast of South America
 Upwelling promotes:
 Plankton growth as they follow the cold water pulled up
from depth
 Anchovies follow the plankton – major food source
 Sea birds follow the anchovies
 Guano is deposited on local islands by the sea birds
Normal Conditions in tropical
Pacific
El Niño in tropical Pacific
El Niño and Peruvian Fishing Industry
 During an El Niño, the fishing industry in Peru
experiences a strong decline
 Peru’s fishing industry accounts for a significant
portion of Peru’s economy
 World’s foremost producer and exporter of fishmeal
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Fishmeal a major component of all animal feed globally
In historic El Niño events, cost of animal feed increased
around the world due to the collapse of Peruvian fishing
 1972-73 El Niño
 Anchovy catch reduced from 10.3 million metric tons
(1971) to 4.6 million metric tons (1972)
 1982-83 El Niño
 Anchovy catch reduced by 50% from 1981 catch
El Niño and Upwelling
El Niño-Southern
Oscillation Events
“Walker Cycle”
El Niño – Southern Oscillation
Events (ENSO)
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Upwelling along Peruvian coast ceases
Trade winds weaken
Weak equatorial eastward current develops
Moisture and temperature patterns alter as air pressure
systems ‘flip-flop’ :
Normal high pressure near Peru moves toward western
Pacific creating droughts in Australia
• Normal low pressure near mid-Pacific moves toward Peru,
creating records storms, floods and landslides
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