Trough (meteorology)

Encyclopedia : T : TR : TRO : Trough (meteorology)

This article is about the meteorological phenomenon. For other uses, see Trough (disambiguation).

A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts.

In United States, a trough may be marked as a brown dashed line. If it is not marked, troughs may still be identified as an extension of isobars away from a low pressure center. The weather charts in some countries or regions mark troughs by a line. In Hong Kong[link] or Fiji[link], it is represented by a bold line extended from a low pressure center [link] or between two low pressure centers [link]; in Macau[link], it is a dotted line.

Sometimes, a trough may be a region between two high pressure centers and there is not a low pressure center. In this case, it is still represented by a line between the two high pressure centers.

If a trough forms in the mid-latitudes, a temperature difference between two sides of the trough usually exists in the form of a weather front. A weather front is usually less convective than a trough in the tropics or subtropics (such as a tropical wave). Sometimes, collapsed frontal systems will degenerate into troughs.

Convective cells may develop in the vicinity of troughs and give birth to a tropical cyclone. Some tropical or subtropical regions 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 alternate, 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.

Trough (meteorology)

See also