Global-scale Winds Courtesy: U. of Alaska 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 turbulent eddies Thunderstorms Tornadoes Waterspouts Dust devils Land/sea breeze Mtn/Valley breeze Chinook Santa Ana Hurricanes Topical storms Weather Map Highs and Lows Weather fronts Longwaves seconds to minutes minutes to hours hours to days days to weeks microscale mesoscale synoptic scale planetary scale

Atmospheric General Circulation + Large-scale, hemispheric flow + DRIVING FORCE?? + Average wind patterns across globe + Interrupted by highs and lows moving through UNEQUAL HEATING OF THE EARTH THERMAL IMBALANCE WARM COLD

Atmospheric General Circulation UNEQUAL HEATING OF THE EARTH THERMAL IMBALANCE WARM COLD Net GAIN Net LOSS Energy Imbalance Driver of Atmospheric Circulation

Models of Atmospheric Circulation Single-cell Model Assume 1) aqua planet 2) sun over equator 3) non-rotating earth WARM COLD

Single-cell Model Assume 1) aqua planet 2) 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

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 windsActual winds

Atmospheric Circulation Models vs Reality Idealized winds Actual winds Why the difference? 1) land-water distribution 2) 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 latitudes weak winds Subtropical high warm and dry Desert 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

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 disappear Subtropical highs remain Zone of max heating shifts north Weak equator - pole temp gradient Strong thermal imbalance Strong pressure gradient Strong winds Strong equator - pole temp gradient Thermal Imbalance is the Driver

Seasonal Circulation Animation Sea level pressure and winds University of Oregon Thermal Imbalance is the Driver L H

General Circulation and Precipitation Wet Dry WetDry WetDry WetDry WetDry seasonally

General Circulation and Precipitation Precipitation (mm) University of Oregon Dry Wet

Jet Streams Fast-moving rivers of air High altitudes (~ 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 speed differences Surface temperature differences Tend to steer storm tracks

Jet Streams

Jet Streaks

Jet Stream and Jet Travel