The broadly latitudinal bands of high and low atmospheric pressure that girdle the Earth, set up by the unequal heating of the surface and by the rotation of the Earth, and which govern the planetary wind system.
- Four main belts in each hemisphere, from the equator poleward: the equatorial low (doldrums), the subtropical high (horse latitudes, near 30°), the subpolar low (near 60°), and the polar high.
- The equatorial low and the polar high are thermally induced (heating and cooling); the subtropical high and subpolar low are dynamically induced (by descending and converging air and the Earth's rotation).
- At the equatorial low (doldrums) air rises, giving calm and heavy convectional rain; at the subtropical high (horse latitudes) air descends, giving clear, dry conditions and the great deserts.
- The belts shift seasonally, following the apparent migration of the overhead Sun north and south, which is central to the monsoon and to seasonal rainfall.
- Winds blow from high-pressure belts toward low-pressure belts, giving the trade winds, westerlies, and polar easterlies.
The names and approximate latitudes of the belts, the thermal versus dynamic origin, and the link of the subtropical high to deserts and of the equatorial low to rain are standard climatology items.
Equatorial low (rising air, rain) versus subtropical high (sinking air, deserts); thermally induced (equatorial low, polar high) versus dynamically induced (subtropical high, subpolar low); pressure belts (latitudinal) versus winds (which blow between them).
Equatorial low, subtropical high, subpolar low, and polar high belts drive the planetary winds; the subtropical high makes the great deserts.