GOES-East satellite view of the Americas with tropical cloud bands and midlatitude weather systems.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Cell depth enlarged. zonal-mean circulation, not individual weather systems.

Hadley and Polar cells are driven by rising warm air and sinking cold air; the Ferrel cell is sustained by heat and momentum transferred by weather systems.

How to read these results

Gold: tropical / polar surface easterlies · blue: midlatitude westerlies. The enlarged cloud belt follows the prescribed ITCZ; it is not observed cloud or a rainfall forecast. It is omitted at true scale.

Three-cell circulation

Locate the Hadley, Ferrel and polar cells and relate their circulation to broad patterns of winds and rainfall.

Drag to rotate. Hold Ctrl and scroll to zoom, or pinch on a touch screen.

Why it happens

Unequal solar heating and Earth’s rotation organise broad atmospheric circulation. Rising and sinking regions help explain the trade winds, westerlies and major pressure belts.

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GOES-East, 22 April 2014 at 11:45 UTC. Cloud belts reveal aspects of global circulation; a single image does not outline every atmospheric cell.

Try a comparison

Distinguish the eddy-driven Ferrel circulation from a thermally direct cell. Play the illustrative annual shift; explain why real ITCZ positions differ.

Reading the result

The three-cell pattern is an average framework; actual circulation shifts with seasons, continents and changing weather.

A common misunderstanding

The three atmospheric cells are fixed loops followed by individual air parcels.

The three-cell model describes broad averages of circulation across latitude. Real air moves through changing weather systems and mixes between regions. Continents, seasons and ocean conditions disturb the pattern, and the midlatitude Ferrel circulation is maintained largely by weather systems rather than a simple isolated convection loop.

Cases

Exam language

Hadley cell

The average tropical circulation in which air rises near the equatorial convergence zone, moves poleward aloft and descends in the subtropics. Near-surface return flow contributes to the trade winds. The real circulation shifts with seasons and continents.

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GOES-East cloud observations over the Americas, 22 April 2014. Tropical cloud bands and midlatitude systems provide evidence of atmospheric circulation. The three-cell pattern is a long-term zonal average, not three fixed cloud rings in this single image.

Ferrel cell

The mean midlatitude atmospheric circulation, with poleward near-surface flow and equatorward flow aloft. It is an indirect cell maintained largely by weather systems.

Polar cell

The average circulation in which cold air sinks near a pole and moves equatorward near the surface, returning poleward aloft. It forms part of a simplified global circulation model. Actual polar weather is less uniform than a single closed loop.

ITCZ

The intertropical convergence zone: a shifting belt where tropical trade winds meet and moist air often rises. Its position varies with season, oceans and land heating.

Trade winds

The prevailing tropical surface winds blowing towards the equatorial convergence zone. Earth’s rotation gives them an easterly component: they generally come from the northeast in the Northern Hemisphere and southeast in the Southern Hemisphere. Their position and strength vary seasonally.

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Terra MODIS, 27 May 2003. Northeasterly trade winds favour wetter, greener windward slopes; leeward slopes are drier. The bright ocean is sunglint.

Subtropical high

A region of relatively high atmospheric pressure commonly found near the poleward side of the Hadley circulation. Descending air tends to suppress cloud formation, helping explain many subtropical dry regions. Its position and strength vary with season and geography.

Thermal equator

A belt of the highest mean temperatures at a given season. It shifts with seasonal heating and geography and does not always coincide with the geographic equator or ITCZ.

Westerlies

The prevailing winds with a west-to-east component across much of the middle latitudes. They help steer many weather systems, although individual winds change as pressure systems move. Their average pattern reflects atmospheric circulation and Earth’s rotation.

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