Zonal and meridional

The terms zonal and meridional are used to describe directions on a globe. Zonal means "along a latitude circle" or "in the west–east direction"; while meridional means "along a longitude circle" (a.k.a. meridian) or "in the north–south direction".

These terms are often used in the atmospheric and earth sciences to describe global phenomena, such as "meridional wind flow", or "zonal 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.

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 (as in the Norma Jean album Meridional).

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