global-scale winds courtesy: u. of alaska 02.23.2010 general circulation > global wind systems...

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