global-scale winds courtesy: u. of alaska 02.23.2010 general circulation > global wind systems...
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Global-scale WindsCourtesy: U. of Alaska
02.23.2010
General Circulation
> Global wind systems General circulation 1-cell, 3-cell models, comparison to real world
> Semi-permanent pressure features
> Jet streams
Scales of Motion - Hierarchy
Small turbulenteddies
ThunderstormsTornadoes
WaterspoutsDust devils
Land/sea breezeMtn/Valley breeze
ChinookSanta Ana
HurricanesTopical storms
Weather MapHighs and LowsWeather fronts
Longwaves
secondsto
minutes
minutesto
hours
hoursto
days
daysto
weeks
microscale
mesoscale
synopticscale
planetaryscale
Atmospheric General Circulation
+ Large-scale, hemispheric flow + DRIVING FORCE??+ Average wind patterns across globe
+ Interrupted by highs and lowsmoving through
UNEQUAL HEATINGOF THE EARTH
THERMAL IMBALANCE
WARM
COLD
COLD
Atmospheric General CirculationUNEQUAL HEATING OF THE EARTH
THERMAL IMBALANCE
WARM
COLD
COLD
Net GAIN
Net LOSS
Net LOSS
Energy Imbalance Driver of Atmospheric Circulation
Models of Atmospheric CirculationSingle-cell ModelAssume1) aqua planet2) sun over equator 3) non-rotating earth
WARM
COLD
COLD
Single-cell ModelAssume1) aqua planet2) sun over equator 3) non-rotating earth
Result>excessive heating at equator
>thermally-driven convection cell
>pole-ward flow aloft equator-ward flow sfc
>termed, Hadley cell
Models of Atmospheric Circulation
pressure
low
high
The Atmosphere, 8th edition, Lutgens and Tarbuck, 8th edition, 2001
Three-cell ModelAssume1) aqua planet2) sun over equator 3) non-rotating earth3) non-rotating earth
Result>excessive heating at equator
>thermally-driven convection cells
>deflection of winds
>Hadley cell Ferrel cell Polar cell
Models of Atmospheric Circulation
The Atmosphere, 8th edition, Lutgens and Tarbuck, 8th edition, 2001
Atmospheric Circulation Models vs Reality
The Atmosphere, 8th edition, Lutgens and Tarbuck, 8th edition, 2001
Idealized winds Actual winds
Atmospheric Circulation Models vs Reality
Idealized winds
Actual winds Why the difference?1) land-water distribution2) seasonality
unequal heating/cooling rates
Atmospheric Circulation
Some Features of Note:Equatorial
•ITCZ (Intertropical Convergence Zone)
•Equatorial low
•Area of low wind speed Doldrums (weak PG)
Atmospheric Circulation
Some Features of Note:Subtropics
•Trade winds
•Horse latitudesweak winds
•Subtropical highwarm and dryDesert areas of the world
Atmospheric Circulation
Some Features of Note:Midlatitudes, Polar
•Prevailing westerlies
•Polar front and areas of low pressure
•Polar easterlies
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH winter
Persistent Circulation Patterns NH winter
Sea level pressure and prevailing winds
> subtropical highs
Persistent Circulation Patterns NH winter
Sea level pressure and prevailing winds
> 2 major subpolar lows: near polar front, storm track
Persistent Circulation Patterns NH winter
Sea level pressure and prevailing winds
> subpolar highs: shallow, thermally induced
Persistent Circulation Patterns NH winter
Sea level pressure and prevailing winds
> subpolar trough in SH: high winds and seas, roaring 40s
Persistent Circulation Patterns NH winter
Sea level pressure and prevailing winds
> ITCZ displaced south
Persistent Circulation Patterns NH summer
Sea level pressure and prevailing winds
> ITCZ displaced north
Persistent Circulation Patterns NH summer
Sea level pressure and prevailing winds
> Subtropical highs move north
Persistent Circulation Patterns NH summer
Sea level pressure and prevailing winds
> Thermal lows develop over land
Persistent Circulation Patterns NH summer
Sea level pressure and prevailing winds
> Weak Icelandic Low remains, Aleutian Low disappears
Persistent Circulation Patterns NH summer
Sea level pressure and prevailing winds
> Asian Monsoon season
Seasonal Circulation Patterns
Sea level pressure and prevailing winds
winter summer
Subpolar lows disappearSubtropical highs remainZone of max heating shifts northWeak equator - pole temp gradient
Strong thermal imbalanceStrong pressure gradientStrong windsStrong equator - pole temp gradient
Thermal Imbalance is the Driver
Seasonal Circulation Animation
Sea level pressure and windsUniversity of Oregon
Thermal Imbalance is the Driver
L
H
General Circulation and Precipitation
Wet
Wet
Wet
Dry
Dry
Dry
DryWet Dry
Wet Dry
Wet Dry
Wet Dry
seasonally
General Circulation and Precipitation
Precipitation (mm)University of Oregon
Dry
Wet
Jet Streams
• Fast-moving rivers of air
• High altitudes (~ 35000 ft) near tropopause
• Long, shallow, narrow moving west to east
• First observed during WW II
• Suspected earlier from ground observations of fast-moving cirrus
Jet Streams
• Mark boundary between surface air masses
• Shows ridges, troughs, eddies
• Changes in space and time
Jet Streams
• Seasonality
• Note the speeddifferences
• Surface temperature differences
• Tend to steer storm tracks
Jet Streams
Jet Streaks
Jet Stream and Jet Travel