A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts. diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure above any area in the Earths atmosphere caused by the weight of air. ... A guide to the symbols for weather fronts that may be found on a weather map: 1. ...

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. A guide to the symbols for weather fronts that may be found on a weather map: 1. ... Tropical waves, also known as easterly waves, are elongated areas of relatively low air pressure, oriented north to south, causing areas of cloudiness and thunderstorms. ...

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. Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004. ...

The weather charts in some countries or regions mark troughs by a line. In Hong Kong or Fiji, it is represented by a bold line extended from a low pressure center [1] or between two low pressure centers [2]; in Macau, 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.

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. A pressure system is a region of the Earths atmosphere where air pressure is unusually high or low. ...

See also

• Geopotential height
• Ridge (meteorology)