Atmospheric Circulations

Meteorology 10 - Weather and ClimateFall 2008CHAPTER 7

FOCUS: air circulation patterns on Earth

Chapter 7: Atmospheric Circulations

• Scales of atmospheric motions• Eddies - big and small• Local wind systems• Global winds• Global wind patterns and the oceans

Scales of Atmospheric Motions

Scales of Atmospheric Motions

• scales of motion

• microscale

• synoptic scale

• planetary scale

• Lots of important weather events occur Lots of important weather events occur on microscales, like evaporation of on microscales, like evaporation of liquid water molecules from the liquid water molecules from the earth’s surface.earth’s surface.

Eddies - Big and Small

Eddies - Big and Small

• eddy

• rotor

• wind shear

• turbulence

• Wind shear can sometimes be observed by watching theWind shear can sometimes be observed by watching themovement of clouds at different altitudes.movement of clouds at different altitudes.

Local Wind Systems

Thermal Circulations

• isobars and density

• differences

• thermal circulations

Fig. 7-4, p. 172

Stepped Art

Sea and Land Breezes

• sea breeze

• land breeze

• sea breeze front

• Florida sea breezes

• Sea and land breezes Sea and land breezes also occur near the also occur near the shores of large shores of large lakes, such as the lakes, such as the Great Lakes.Great Lakes.

Fig. 7-5, p. 174

Stepped Art

Seasonally Changing Winds - the Monsoon

• Monsoon wind system

• Asian monsoon

• other monsoons

Mountain and Valley Breezes

• valley breeze

• mountain breeze• The nighttime mountain breeze is sometimes calledThe nighttime mountain breeze is sometimes calledgravity winds or drainage winds, because gravitygravity winds or drainage winds, because gravitycauses the cold air to ‘drain’ downhill.causes the cold air to ‘drain’ downhill.

Katabatic Winds

• drainage winds

• bora• Katabatic winds are quite fierce in parts of Antarctica, Katabatic winds are quite fierce in parts of Antarctica, with hurricane-force wind speeds. with hurricane-force wind speeds.

Chinook (Foehn) Winds

• Chinook winds

• compressional heating

• chinook wall cloud

• In Boulder, Colorado, along the eastern flank of the In Boulder, Colorado, along the eastern flank of the Rocky Mountains, chinook winds are so common thatRocky Mountains, chinook winds are so common thatmany houses have sliding wooden shutters to protectmany houses have sliding wooden shutters to protecttheir windows from windblown debris.their windows from windblown debris.

Fig. 7-14, p. 180

Santa Ana Winds

• Santa Ana wind

• compressional heating

• wildfires

• Many Southern Many Southern California California residents residents regularly hose regularly hose downdowntheir roofs to their roofs to prevent fires prevent fires during Santa Ana during Santa Ana wind season.wind season.

Desert Winds

• dust storms

• dust devils

Global Winds

General Circulation of the Atmosphere

• cause: unequal heating of the earth’s surface

• effect: atmospheric heat transport

• Ocean currents also transport heat from the equator toOcean currents also transport heat from the equator tothe poles and back.the poles and back.

Sun’s energy is not distributed evenly over Earth

Tropics - more incoming radiation (red) than outgoing radiation (blue)Energy must be transported poleward

Fig. 7-29, p. 193

Stepped Art

Single-cell Model• basic assumptions

• Hadley cell

• why the single-cell model is wrong

• One of the world’s One of the world’s premier atmospheric premier atmospheric science research science research facilities,the facilities,the Hadley Hadley Centre for Climate Centre for Climate Research, is named Research, is named after after George Hadley.George Hadley.

Three-cell Model

• model for a rotating earth• Hadley cell• doldrums• subtropical highs• trade winds• intertropical convergence

zone• westerlies• polar front• polar easterlies

• Many global circulation terms,Many global circulation terms,including ‘trade winds’ and including ‘trade winds’ and ‘doldrums’, were named by ‘doldrums’, were named by mariners who were well acquaintedmariners who were well acquaintedwith wind patterns.with wind patterns.

Fig. 7-21, p. 185

Average Surface Winds and Pressure: The Real World

• semipermanent highs and lows

• Bermuda high & Pacific high

• Icelandic low & Aleutian low

• Siberian high

• The Bermuda High frequently brings The Bermuda High frequently brings hot, muggy weather to the eastern hot, muggy weather to the eastern US.US.

Fig. 7-22a, p. 188

Fig. 7-22b, p. 189

The General Circulation and Precipitation Patterns

• major controls

• ITCZ, midlatitude

storms, polar front

• Most of the Most of the world’s world’s thunderstorms are thunderstorms are found along the found along the ITCZ.ITCZ.

Westerly Winds and the Jet Stream

• jet streams

• subtropical jet stream

• polar front jet stream

Wind in the upper troposphere: Jet Streams

Subtropical Jet - Coriolis turning of Hadley cellMid-Latitude Jet – results from a steep temperature gradient

Global Wind Patterns and the Oceans

Winds and Upwelling

• upwelling

• wind flow parallel to the coastline• Upwelling frequently occurs Upwelling frequently occurs along the coast of along the coast of California.California.

El Niño and the Southern Oscillation

• El Niño events

• Southern Oscillation

• La Niña

• teleconnections

• ENSO is an example of a global-ENSO is an example of a global-scale weather phenomenon.scale weather phenomenon.

Fig. 7-32, p. 196

Fig. 7-33, p. 197

Fig. 7-34, p. 197

Other Atmosphere-Ocean Interactions

• North Atlantic Oscillation

• Arctic Oscillation

• Pacific Decadal Oscillation• Other atmosphere-ocean interactions may very well beOther atmosphere-ocean interactions may very well bediscovered in the coming years.discovered in the coming years.

Jet Streams

Jet Streams