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A trough is an elongated region of relatively low atmospheric pressure without a closed isobaric contour that would define it as a low pressure area. Since low pressure implies a low height on a pressure surface, troughs and ridges refer to features in an identical sense as those on a topographic map. Troughs may be at the surface, or aloft, at ...
Airflow around troughs and ridges in upper troposphere. Given the direction of the winds around an anticyclonic circulation and the fact that weather systems move from west to east: [2] ahead of an upper-ridge, the airflow that comes from the polar regions and brings cold air.
When the zonal flow buckles, the atmosphere can flow in a more longitudinal (or meridional) direction, and thus the term "meridional flow" arises. Meridional flow patterns feature strong, amplified troughs of low pressure and ridges of high pressure, with more north–south flow in the general pattern than west-to-east flow. [10]
When this occurs over the tropics in concert with the Intertropical Convergence Zone, it is known as a monsoon trough. [7] Monsoon troughs reach their northerly extent in August and their southerly extent in February. [8] [9] [10] When a convective low acquires a well-defined circulation in the tropics it is termed a tropical cyclone. [6]
A col, also called saddle point or neutral point, is in meteorology, the point of intersection of a trough and a ridge in the pressure pattern of a weather map. It takes the form of a saddle where the air pressure is relatively higher than that of the low-pressure regions, but lower than that of the anticyclonic zones. [1]
The Hadley cell is a closed circulation loop which begins at the equator. There, moist air is warmed by the Earth's surface, decreases in density and rises. A similar air mass rising on the other side of the equator forces those rising air masses to move poleward. The rising air creates a low pressure zone near the equator.
A tropical upper tropospheric trough (TUTT), also known as the mid-oceanic trough, [1] is a trough situated in the upper-level (at about 200 hPa) tropics. Its formation is usually caused by the intrusion of energy and wind from the mid-latitudes into the tropics. It can also develop from the inverted trough adjacent to an upper level anticyclone.
Shortwave troughs are a cause of lift, or forcing, which is required for the development of thunderstorms and convection.Convection is very prevalent around shortwave troughs because not only do they provide forcing, but they are also associated with systems that provide other ingredients for the formation of thunderstorms, such as instability, wind shear, and helicity.