Zonal and meridional

A zonal region on the globe

The terms zonal and meridional are used to describe directions on a globe.

Zonal means "along a latitudinal circle" or "in the west–east direction." Zonal flow is a meteorological term regarding atmospheric circulation following a general flow pattern along latitudinal lines, as opposed to meridional flow along longitudinal lines. Zonal, in the context of physics, connotes a tendency of flux to conform to a pattern parallel to the equator of a sphere. Generally, zonal flow of the atmosphere brings a temperature contrast along the Earth's longitude. Extratropical cyclones in this environment tend to be weaker, moving faster and producing relatively little impact on local weather.

Meridional means "along a longitudinal circle" (a.k.a. meridian) or "in the north–south direction" . Meridional flow is a general air flow pattern from north to south, or from south to north, along the Earth's longitude lines (perpendicular to a zonal flow). Extratropical cyclones in this environment tend to be stronger and move slower. This pattern is responsible for most instances of extreme weather, as not only are storms stronger in this type of flow regime, but temperatures can reach extremes as well, producing heat waves and cold waves depending on the equator-ward or poleward direction of the flow.

These terms are often used in the atmospheric and earth sciences to describe global phenomena, such as "meridional wind", or "zonal average temperature". (Strictly speaking, zonal means more than simply a direction as it also implies a degree of localization in the meridional direction, so that the phenomenon in question is localized to a zone of the planet.)

"Meridional" is also used to describe the axis close to the chain orientation in a polymer fiber, while the term "equatorial" is used to describe the direction normal to the fiber axis.

For vector fields (such as wind velocity), the zonal component (or x-coordinate) is denoted as u, while the meridional component (or y-coordinate) is denoted as v.

Meridional meaning South

The word comes from Latin meri dies ("midday"), meaning the position of the Sun at that time. As the original Latin territory was in the Northern Hemisphere, this is still used with that sense in some Romance languages such as Portuguese (Banco Meridional, in Brazil), Spanish, French, Italian (as in Meridione) or even in English (as in the Norma Jean album Meridional).

The term meridional, sometimes abbreviated to "Mer.", was used in historical astronomy to indicate the southern direction on the celestial globe, together with septentrional ("Sep.") for northern, oriental ("Ori.") for eastern and occidental ("Occ.") for western.

See also

• Zonal and poloidal
• Zonal flow (plasma)
• Meridione