Air current

Horizontal currents

A difference in air pressure causes an air displacement and generates the wind. The Coriolis force deflects the air movement to the right in the northern hemisphere and the left in the southern one, which makes the winds parallel to the isobars on an elevation in pressure card. It is also referred as the geostrophic wind.

Pressure differences depend, in turn, on the average temperature in the air column. As the sun does not heat the Earth evenly, there is a temperature difference between the poles and the equator, creating air masses with more or less homogeneous temperature with latitude. Differences in atmospheric pressure are also at the origin of the general atmospheric circulation while the air masses are separated by ribbons where temperature changes rapidly. These are the fronts. Along these areas, higher winds aloft form. These horizontal jets (jet streams) can reach speeds of several hundred kilometers per hour and can span thousands of kilometers in length, but are narrow, having tens or hundreds of kilometers of width.

On the surface, the friction due to the terrain and other obstacles (buildings, trees, etc.) may contribute to a slowdown and/or a wind deflection. Thus, a more turbulent wind in the atmospheric boundary layer. This wind can be channeled through narrows, like valleys. The wind will also be raised along the slopes of the mountains to give local air currents.