What is Trough (meteorology)?
[[Image:Trough.jpg|thumb|250px|Representation of alternating troughs and ridges in upper-level [[Westerlies]] for the [[Northern Hemisphere]], with regions of convergence and divergence labeled.]] A '''trough''' is an elongated area of comparatively low [[atmospheric pressure]], usually in association with [[weather fronts]]. Convective cells may form in the surrounding area of troughs and give birth to a [[tropical cyclone]]. Some tropical or subtropical areas, such as the Philippines or south China are greatly affected by convection cells along a trough. In the mid-latitude westerlies, troughs and ridges often exchange with each other, especially when upper-level winds are in a high-amplitude pattern. For a trough in the westerlies, the region just west of the trough axis is typically an area of convergent winds and descending air - and hence high pressure - while the region just east of the trough axis is an area of fast, divergent winds and low pressure. Tropical waves are a type of trough in easterly currents, a cyclonic northward deflection of the trade winds. {{weather-stub}} [[Category:Meteorology]] [[fi:Matalan sola]]