Between the tropical overturning of the Hadley cell and the cold circulation surrounding the poles lies the Ferrel cell. In a long-term average, surface air moves poleward from the subtropics, rises in the vicinity of the polar front, returns equatorward aloft, and descends near 30 degrees latitude. This places the cell roughly between 30 and 60 degrees in each hemisphere.
The neat loop is deceptive. Unlike the Hadley cell, the Ferrel cell is not primarily a thermally driven circulation with warm air rising at its hotter edge and cold air sinking at its colder edge. Its average motion runs in the opposite sense and is sustained largely by the storms and atmospheric waves that continually rearrange the midlatitudes.
A Thermally Indirect Cell
Near the surface, air moving poleward from subtropical high-pressure regions is deflected eastward by Earth’s rotation. This produces the prevailing westerlies that dominate much of the middle latitudes. Farther poleward, relatively warm air encounters colder air associated with the polar circulation. Their contrast establishes a sloping zone of strong horizontal temperature change.
The simplified model places rising motion near this boundary and an equatorward return flow higher in the troposphere. Air then sinks near the subtropical highs, completing the statistical loop. Because warmer air rises toward a colder region while cooler air is carried equatorward aloft, meteorologists describe the Ferrel circulation as thermally indirect.
Such a cell cannot maintain itself through differential heating alone. If the atmosphere were perfectly smooth and steady, friction and mixing would weaken its characteristic winds. Traveling low-pressure systems, high-pressure systems, and large meanders in the westerlies supply the necessary momentum and heat transport.
Storms Build the Average Circulation
Midlatitude cyclones grow where strong temperature gradients store potential energy. Their circulating winds move warm air poleward and cold air equatorward, reducing the contrast that helped them form. At the same time, these weather systems transport eastward momentum and modify the surrounding flow. When their effects are averaged across many events, a Ferrel-like overturning pattern emerges.
This means the cell visible in climate diagrams may be difficult to find on a daily weather map. A particular location may experience northward flow ahead of a low-pressure system, southward flow behind a cold front, or several days beneath a stationary high. Only after these alternating motions are combined over a wide area and long period does the prevailing pattern become clear.
Atmospheric scientists often describe these disturbances as eddies, a term that includes organized cyclones and anticyclones as well as broader wave motions. The Ferrel cell is sometimes called an eddy-driven circulation because these features do much of the work that sustains it.
Between Subtropical and Polar Air
The title “between air masses” describes the cell’s setting, but the atmosphere does not divide into permanent blocks. Maritime and continental surfaces produce air with different temperature and moisture characteristics, and weather systems continuously transform and mix those properties. The strongest boundary generally forms where the large-scale meridional temperature gradient is concentrated.
Above that region, a powerful band of westerly wind known as the polar-front jet often develops. The jet is not the upper arrow of the Ferrel cell in a simple mechanical sense. It arises from the horizontal temperature contrast and the resulting change of wind with altitude, while waves along it guide and intensify surface weather systems.
The subtropical side is linked to descending Hadley-cell air and the subtropical jet. The poleward side interacts with polar easterlies, cold outbreaks, and the polar-front storm track. The Ferrel cell thus occupies a transition zone where tropical energy and polar cold are repeatedly exchanged through moving weather systems.
Why Its Position Refuses to Stay Still
Storm tracks and jets migrate with the seasons, generally shifting toward the equator in winter and poleward in summer. Oceans and continents distort the bands, especially in the Northern Hemisphere, where major mountain ranges and strong land-temperature contrasts generate large stationary waves. The Southern Hemisphere’s broader ocean belt allows a more continuous westerly circulation, although it remains variable.
Week-to-week changes can be larger than the slow mean flow assigned to the cell. Blocking highs may redirect storms, while a highly meandering jet can carry subtropical air far poleward and polar air deep into lower latitudes. These events are not failures of the three-cell model; they are among the eddies from which its midlatitude average is constructed.
The Ferrel cell is therefore less a conveyor belt than a climate-scale summary of restless weather. It reveals the net direction of mass transport after many fronts, cyclones, anticyclones, and jet-stream waves have passed. Its existence depends on the very disturbances that a simple circulation diagram leaves out.