Atmospheric circulation

Atmospheric circulation is the large-scale movement of air driven by uneven heating and pressure differences, then shaped by planetary rotation and terrain. It transports heat, moisture, and momentum around a planet.

Hadley cell: A tropical circulation cell in which air rises near the equator, flows poleward aloft, descends in the subtropics, and returns near the surface. It carries heat from the tropics toward subtropical latitudes.
Geostrophic wind: A wind whose pressure-gradient force is balanced by the Coriolis effect, flowing approximately parallel to isobars. It approximates much of the free-atmosphere flow away from the equator.
Trade winds: Persistent tropical easterly winds that blow toward the equatorial low-pressure belt from the subtropics. They are the surface return flow of the Hadley circulation.
General circulation model: A numerical model that simulates large-scale atmospheric or oceanic circulation using physical equations on a three-dimensional grid. Models test how circulation responds to heating, rotation, and changing climate conditions.
Coriolis effect: The apparent deflection of moving objects in a rotating reference frame, directed rightward in the Northern Hemisphere and leftward in the Southern Hemisphere. Earth’s rotation deflects large-scale winds and helps organize circulation into rotating patterns.
Geostrophic balance: The approximate balance between the pressure-gradient force and the Coriolis effect in large-scale atmospheric motion. This balance shapes the winds that connect pressure patterns to circulation.
Westerlies: Prevailing midlatitude winds that generally blow from west to east in both hemispheres. They carry weather systems through the midlatitude circulation.
Hadley circulation: The thermally driven tropical overturning circulation that transports energy and angular momentum between the equator and subtropics. The real Hadley circulation varies with season and longitude, unlike a fixed idealized cell.
Pressure-gradient force: The force per unit mass that accelerates air from regions of higher pressure toward regions of lower pressure. Pressure differences provide the direct force that starts much atmospheric motion.
Atmospheric convection: The vertical transport of heat by buoyant air rising and denser air sinking. Convection drives rising branches of circulation where the atmosphere is heated.

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