Download circulation - El Camino College

CIRCULATION
Global Wind Circulation
Winds generated by…
Pressure differences due to…
• Unequal heating of Earth’s surface
Winds blow to balance inequalities…
Air Pressure…
• Surface Temperature differences
Wind patterns seasonally migrate N & S…
Latitudes of maximum Solar Radiation
Global Wind Circulation
Equator – Low
Poles – High
Without Land
or Rotation…
Surface…
• Poles Æ
Equator
Aloft…
• Equator Æ
Poles
Hadley (1735)
Global Wind Circulation
Air Aloft…
Some Æ Poles
Most Subsides…
• 30° Latitude
Global Wind Circulation
3-Cell Model
(1920s)
Hadley Cell
• 0-30°
Mid-Latitude
• 30-60°
Polar
• 60-90°
Global Wind – ITC
Equator
Intense Sunlight
• Warm Air Rises
“Equatorial Low”
• AKA – InterTropical
Convergence Zone
(ITCZ)
Weak Winds
• = Doldrums
Clouds & Rain (Daily)
Global Wind – STH
30° Latitude
Air Aloft flows from Equator
Æ 30° Latitude
Pile-up Aloft at 30°
Air Sinks…
• Coriolis stronger…
– Earth’s Rotation
• Radiation Cooling…
– Air Density Increases
Global Wind – STH
30° Latitude
Creates High Pressure
Sub-Tropical High
• AKA “Horse Latitudes”
Weak Winds
Clear Skies & Dry Air
Global Wind – Trade Winds
Trade Winds
Surface Air pile-up at
30° Latitude
• Air Diverges
Sub-Tropical High Æ
Equatorial Low
• Northeast Trades
• Southeast Trades
Global Wind – Trade Winds
Trade Winds
Strong reliable Winds
Æ Equator
• Sailing Ships…
– Exploration
– Trade
Winds Converge at
Equator…
• Air Rises…
Global Wind – Hadley Cells
Between...
Equator
30° Latitude
Both N & S…
Antitrade
Winds Aloft
Global Wind – Westerlies
Westerlies
Sub-Tropical High Æ
60° Latitude
• More deflection due
to Rotation
– Stronger Coriolis
Not continuous…
• Series of Mid-Latitude
Cyclonic Storms
migrating…
Global Wind – Polar
Polar High
Cold, Dense Air Sinks
Wind blows away from
High at Poles
• “Polar Easterlies”
– Weak Winds
Global Wind – Polar
60° Latitude
Convergence of…
• Polar Easterlies
• Westerlies
Polar Front
Air Rises
• Low Pressure
• Cold & Rain, Snow
AKA “Subpolar Low”
Global Wind Circulation
Polar High
Polar Easterlies
Polar Front
Subpolar Low
Westerlies
ST High
Horse…
Trade Winds
Equatorial Low
Doldrums
ITCZ
Idealized Circulation
Only ideal for…
Subpolar Low in
So. Hemisphere
ITCZ
Changes…
Seasons
Land in No.
Hemisphere
• Monsoons
Pressure Cells
Pressure Cells in
No. Hemisphere
ST High
• Hawaiian
– AKA “Pacific”
• Azores
Subpolar Low
• Aleutian
• Icelandic
Sub-Tropical Highs
30°N Latitude…
Hawaiian & Azores
Trade Winds
30° Latitude Æ Equator
From East
• NE Trades in No. Hemisphere
Trade Winds & Rain
Leeward side
SW & Dryer
Windward side
NE & Wet
Intertropical Convergence
ITCZ – Equatorial Low
Bends Poleward over Land
Straddles Equator
Satellite – ITC & STH
ITCZ (Low)
Clouds…
• Equator
ST High
Clear…
• Sahara
• SW Africa
Westerlies
30° Æ 60° Latitude
From West
• Europe
Polar Highs
North Pole
South Pole
Antarctica
Polar Easterlies
Poles Æ 60° Latitude
From Northeast
Global Wind Circulation
Idealized Winds & Pressure
Composite by Latitude
Westerlies
Westerlies strong Aloft – Balance…
Pressure Gradient Æ Pole
Coriolis Force Æ Equator
Jet Streams
High Speed
Winds Aloft
120-240 mph
Due to steep
Temperature
Gradient
between…
• Surface
• Aloft
Jet Streams
Polar Jet Stream
Polar Front
Strongest
in Winter
Subtropical
Jet Stream
Subtropical
High
Weak in
Summer
Jet Streams
Polar Jet Stream
Center of Storms…
• Polar Easterlies
• Westerlies
Subtropical Jet
Not Permanent
Weaker
Polar Jet Stream
Changes seasonally…
North in Summer
• 35 mph
South in Winter
• 75 mph
Rossby Waves
Waves in Polar
Jet Stream
Fastest flow…
• “Core”
Stronger dip
Southward in
Winter
• Cold Polar Air
Æ South
• Cyclonic Storms
Polar Jet Stream
Jet Stream Core – January
Wind & Ocean Currents
Winds drive Ocean Currents
High Pressure at 30° drives Trade Winds
• Trade Winds drive Equatorial Currents
ST Highs & Trade Winds
30° Latitude Highs…
NE & SE Trades
Wind & Ocean Currents
Equatorial Currents hit Land Masses…
Circulate Clockwise in Northern Hemisphere
• Counterclockwise in Southern Hemisphere
Wind & Ocean Currents
North
Atlantic
Ocean
Equatorial
Current Æ
Gulf Stream
Wind & Ocean Currents
North Atlantic Ocean
Gulf Stream Æ North Atlantic Current (Warm)
• È Canaries (Cold) Æ Equatorial Current
Wind & Ocean Currents
Equatorial current
Other Currents…
Warm – Flows West
Warm on West side
Cold on East side
Wind & Ocean Currents
Northern
Hemisphere
Southern
Hemisphere
Wind & Ocean Currents
Affects Weather…
North Atlantic Current warms Europe
• Above normal for High Latitude
Wind & Ocean Currents
Cold Currents cool Air Æ Fog
West Coast Deserts
• Atacama (Peru)
• Baja CA
• Namib (SW Africa)
Wind & Ocean Currents
Upwelling in Cold Currents…
Coriolis deflects Water from Coasts
• Deeper Cold water rises to replace it
Wind & Ocean Currents
Maintain Earth’s Heat Balance…
Redistribute Excess from Equator Æ Poles
• Remedy Deficit at Poles
Wind & Ocean Currents
Heat Transfer for Earth’s Heat Balance…
¼ from Ocean
¾ from Wind
El Niño
Normally very strong Equatorial Current
Build-up of Warm Water & Pressure in West
Reverses with counter-current in December
El Niño
Normally Cold Peru Current...
Becomes Warm with El Niño
• Lose Fishing
Southern Oscillation
Normally…
W Pacific – Warm Water, Rainy & Low Pressure
E Pacific – Cool Water, Dry & High Pressure
Southern Oscillation
El Niño reversal…
W Pacific – Cool Water, Dry & High Pressure
E Pacific – Warm Water, Rainy & Low Pressure
El Niño
Late year reversal becomes long-lasting…
Irregularly ~ 3-7 years
Affects climate outside region
El Niño
Affects Subtropical & Westerly Jet Streams
Wetter in Peru
Dryer in Australia & Indonesia
El Niño
Affects U.S.A. weather…
Wetter Winter in NW & SE
Warmer Winter in NE
Less Hurricanes
El Niño & La Niña
El Niño…
Warmer
ocean at
Equator
La Niña…
Colder
ocean at
Equator
• Above
average
El Niño & La Niña
ENSO Index – El Niño/Southern Oscillation
Cycles between El Niño & La Niña
El Niño
La Niña
La Niña
La Niña affects U.S.A. weather…
Cool & Snowy in NW
Cold Winters in Great Plains
Dry in SW & SE
More Hurricanes
Season Changes
Seasons shift Solar
Radiation…
Pressure Cells…
• Migrate N & S
• Strengthen
& weaken
other cells
Season Changes
Season Changes
InterTropical Convergence Zone (ITCZ)…
Ç North in July
È South in January
January Surface Pressure
Pressure Cells È South
ITCZ Low
Subpolar Lows…
Pacific & Azores Highs
Aleutian & Icelandic
July Surface Pressure
Pressure Cells…
ITCZ Low Ç North
Azores High Æ Bermuda High
Aleutian & Icelandic Lows disappear
California Seasons
Summer
Winter
Monsoons
= Seasonal Winds
Due to changes…
• Temperature
• Pressure
Asia – Interior
Winter Monsoon
Summer Monsoon
Monsoons
Winter
Monsoon
Cold in Siberia
Subsiding Air
• High Pressure
Wind from
Land Æ Sea
• North È
South
DRY
Monsoons
Summer
Monsoon
Hot on Land
• Rising Air
• Low Pressure
Wind from
Sea Æ Land
• North
South Ç
Monsoons
Summer
Monsoon
Moist Air from
Sea Æ Land
Orographic
Lifting up mtns
ITCZ Ç North
• Low Pressure
WET – RAINY
Monsoons – South Asia
Wet Summer
Cherrapunjee,
India
1,042” Rain
in 1 year
Dry Winter
Monsoons – East Asia
World Monsoon Areas
½ World’s Population
South Asia
Eurasia
Southeast Asia
Monsoon – SW USA
Summer
Heat…
Air Rises
Low
Pressure
Moist Air…
Gulf of
California
Monsoon – SW USA
Rainy Summer
July, August
• Tucson, AZ
World Zonal Precipitation
Sea Level Precipitation…
Matches Air Pressure zones
• Differential Solar Radiation
– Latitude & Seasons
World Zonal Precipitation
4 Major Zones:
Polar High
• Dry
Subpolar Low
• Wet – (Westerlies)
Subtropical High
• Dry
ITCZ
• Wet
World Zonal Precipitation
Transitional Latitudes
for Solar Seasons
Between ITCZ &
Subtropical High
• Summer Wet
• Winter Dry
World Zonal Precipitation
Transitional Latitudes
for Solar Seasons
Between Subtropical
High & Subpolar Low
• Summer Dry
• Winter Wet
Subtropical Highs
East Coasts
Wet – Warm ocean
West Coasts
Dry – Sinking Air
Hypothetical Continent
Hypothetical Continent
Northern
Hemisphere
Continent
Precipitation at
Sea Level if no
Topography
• 7 Regions
Annual Precipitation
Annual Precipitation
Wet Regions
0-10° Latitude
Patterns of Precipitation
Wet Regions
10-25° Latitude
East Coasts
• Trade
Winds
Patterns of Precipitation
Wet Regions
25-40° Latitude
East Coasts
• Warm
Ocean
Currents
Patterns of Precipitation
Wet Regions
40-60° Latitude
West Coasts
• Westerly
Winds
Patterns of Precipitation
Dry Regions
20-30° Latitude
• Subtropical High
Patterns of Precipitation
Dry Regions
20-30° Latitude
West Coasts
• Subtropical
High
Patterns of Precipitation
Dry Regions
Rainshadow
areas
Patterns of Precipitation
Dry Regions
Polar Areas…
• Polar High
Precipitation Variability
Wet areas – Less Variability between years
Dry areas – More Variability between years