Heat Transport and General Circulation

How the atmosphere and ocean move heat from the energy-rich tropics toward the poles, organizing the planet's wind belts and currents.

Definition

Meridional heat transport is the net poleward flux of energy carried by the atmosphere and ocean, and the general circulation is the planetary-scale system of winds and currents that, among other things, accomplishes this transport.

Scope

This topic covers the poleward transport of energy that compensates the latitudinal imbalance of radiation, and the circulation systems that accomplish it: the tropical Hadley cells, the mid-latitude eddies and jet streams, and the wind-driven and overturning ocean currents. It treats how much heat each component carries, how the partition between atmosphere and ocean varies with latitude, and how the general circulation sets the broad pattern of climate zones.

Core questions

• Why must the climate system transport heat poleward?
• How is the transport divided between the atmosphere and the ocean?
• What circulation systems carry the energy at different latitudes?
• How does heat transport shape the distribution of climate zones?

Key theories

Radiative imbalance and required transport

Because the tropics absorb more solar energy than they radiate while high latitudes radiate more than they absorb, the climate system must transport energy poleward, with the required total fixed by the radiation budget.

Partition between atmosphere and ocean

The atmosphere dominates poleward transport in mid-latitudes through eddies and the Hadley circulation, while the ocean carries a large share in the tropics through wind-driven and overturning currents.

Mechanisms

The surplus of absorbed solar energy in the tropics and the deficit at high latitudes create a temperature gradient that drives circulation. The Hadley cells carry energy out of the tropics, baroclinic eddies and jet streams transport it across mid-latitudes, and ocean currents move warm water poleward and cold water equatorward, together delivering the heat needed to balance the radiation deficit at high latitudes.

Clinical relevance

Heat transport determines the temperature contrast between equator and poles and the location of storm tracks and arid zones, so changes in it under warming reshape regional climate and weather extremes.

History

Understanding of the general circulation advanced from the Hadley and Ferrel conceptions of overturning cells to the mid-twentieth-century recognition, through the work of Starr, Lorenz, and others, that mid-latitude eddies dominate atmospheric heat transport; satellite radiation data and ocean observations later quantified the partition between atmosphere and ocean.

Debates

Atmosphere versus ocean share of tropical heat transport

The relative contribution of the ocean to poleward energy transport, especially in the tropics, has been refined as direct ocean measurements and radiation-budget residuals have improved.

Key figures

• Abraham Oort
• Kevin Trenberth
• Edward Lorenz
• Victor Starr

Seminal works

• peixotooort1992
• trenberthcaron2001

Frequently asked questions

Why does the climate need to transport heat?

The tropics absorb far more sunlight than they emit while the poles emit more than they absorb, so without poleward transport the tropics would keep warming and the poles cooling.

Does the ocean or the atmosphere carry more heat poleward?

The atmosphere carries most of the heat in mid- and high latitudes, while the ocean carries a comparable or larger share in the tropics.