General Circulation and Climate Zones

Martin VisbeckDEES, Lamont-Doherty Earth Observatory

visbeck@ldeo.columbia.edu

Outline

Introduction- Climate zones

The surface wind circulation - Climate Belts

The sea level pressure distribution - Monsoons

The upper troposphere

The subtropical jet stream (thermal wind relation)

The Hadley circulation

Middle latitude weather systems (baroclinic instability)

Climate zones and rainfall

General Circulationtake away ideas and understanding

Understand how the global atmospheric circulation relates to the distribution of solar heating over the globe.

Learn about the components of the global circulation:

the mean meridional circulation, trade winds and westerlies, jet streams and weather belts.

Note the effect of mountains and land-ocean distribution on the global circulation.

Learn about climate zones and the global distribution of temperature and rainfall.

Climate Zones

Moist Tropical Climate

Dry Climate

Moist Climate & Mild Winters

Moist Climate & Severe Winters

Polar Climate

Highland Climate

Climate Zones

Moist Tropical Climate

Dry Climate

Moist Climate & Mild Winters

Moist Climate & Severe Winters

Polar Climate

Highland Climate

Climate Zones

Moist Tropical Climate

Dry Climate

Moist Climate & Mild Winters

Moist Climate & Severe Winters

Polar Climate

Highland Climate

Climate Zones

Moist Tropical Climate

Dry Climate

Moist Climate & Mild Winters

Moist Climate & Severe Winters

Polar Climate

Highland Climate

Climate Zones

Moist Tropical Climate

Dry Climate

Moist Climate & Mild Winters

Moist Climate & Severe Winters

Polar Climate

Highland Climate

Climate Zones

Moist Tropical Climate

Dry Climate

Moist Climate & Mild Winters

Moist Climate & Severe Winters

Polar Climate

Highland Climate

General CirculationThe surface wind circulation - climate belts

Hurricanes "move"to the west.... why?

General CirculationThe surface wind circulation - climate belts

Weather systems "move"to the east.... why?

General CirculationThe surface Temperature

Surface air temperature: Warm Equator, cold Polar regions Is this in radiative balance?

General CirculationThe surface wind circulation - climate belts

Atmospheric motion is driven by the uneven horizontal distribution of pressure and thus net incoming radiation. On a global scale, the most outstanding part of this uneven distribution is its latitudinal dependence.

General CirculationThe surface energy balance

I ~ T4Atmosphere/Ocean Heat Transport

General CirculationThe surface wind circulation - climate belts

As we have discussed earlier, atmospheric motion is driven by the uneven horizontal distribution of net incoming radiation. On a global scale, the most outstanding part of this uneven distribution is its latitudinal dependence.

The atmosphere (and oceans) respond to this imbalance by attempting to move heat from the tropics and subtropics, where insolation surpasses the infrared terrestrial radiation going out to space, to the middle and high latitudes, where there is a net radiative loss of heat. Convection, the vertical process of heat transport, and advection, the horizontal process of heat and moisture transport, work together to accomplish this goal.

General CirculationThe surface energy balance

How is the planet transporting this heat from the equator to the pole?

Atmosphere/Ocean Heat Transport

General CirculationLarge scale energy transport

A non rotating planet might have a circulation like this.

What will the Coriolis force do?

General CirculationThe large scale wind system

A slow rotating planet might have a circulation like this.

What will the Coriolis force do?

General CirculationThe surface energy balance

What will the Coriolis force do?

A three cell structure emerges:

Hadley Cell

Mid-L. Cell

Polar Cell

General CirculationThe surface wind and pressure

Why is there a High at the "Horse Latitudes"

at about 30° latitude?

General CirculationThe tropical circulation

Convection in the ITCZ

Sinking near 30 N/S causes the high pressure

General CirculationThe surface wind and pressure

Why is there a Low at about 60° latitude?

Polar Cell

General CirculationThe surface wind and pressure

Given the High / Low pressure distribution what would a frictional balance look like?

General CirculationThe surface wind and pressure

Given the High / Low pressure distribution what would a geostrophic balance look like?

General CirculationThe surface wind and pressure

Polar Easterlies

Westerlies

Trade Winds

ITCZ (Low)

Subtropical High

Subpolar Low

General CirculationThe surface pressure

NorthernWinter (January)

High over Land, Low over Ocean

General CirculationThe surface pressure

Northern Summer (July)

High over Ocean, Low over Land

Monsoon

Seasonal cycle of heating produces the monsoon winds akin to the daily occurring sea-breeze.

General CirculationThe surface wind and pressure

Lets look at the upper level flow...

500 and 300 hPa level.

General CirculationAtmospheric Heat transport

Two direct cellsHadley & Polar

One indirect cellMid-Latitude (storms)

Poleward Heat Transport by Weather Systems

General CirculationThe seasonal cycle revisited

Strong Temperature contrast in high latitudes

Strong over Land...why?

General CirculationClimate Zones

What will the Coriolis force do?

A three cell structure emerges:

Hadley Cell

Mid-L. Cell

Polar Cell

General CirculationClimate Zones Evaporation - Precipitation

Evaporation: where air is subsiding

Precipitation: where air is rising

Climate Zones

Moist Tropical Climate

Dry Climate

Moist Climate & Mild Winters

Moist Climate & Severe Winters

Polar Climate

Highland Climate