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The Glossary of Meteorology defines a monsoon trough simply: A line in a weather map showing the locations of minimum sea level pressure in a monsoon region. [1] Several regions worldwide qualify as a monsoon region: western Mexico, the far western north Pacific Ocean and north Indian Ocean near southeast Asia, the far western south Pacific Ocean near Australia, central South America, and occasionally near the west coast of Africa. Monsoon troughs are associated with the axis of the Intertropical Convergence Zone (ITCZ) as well as with waves within the monsoon regime itself. These symbols, showing various weather fronts, might be found on a weather map. ...
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The thunderstorms of the Intertropical Convergence Zone form a line across the eastern Pacific Ocean. ...
The ITCZ, or InterTropical Convergence Zone, is a belt of low pressure girdling the globe at the equator. ...
August position of the ITCZ in the Pacific Ocean
February position of the ITCZ in the Pacific Ocean Image File history File links Size of this preview: 800 × 420 pixelsFull resolution (900 × 473 pixel, file size: 142 KB, MIME type: image/jpeg) U.S. Navy, Naval Research Lab http://www. ...
Image File history File links Size of this preview: 800 × 420 pixelsFull resolution (900 × 473 pixel, file size: 142 KB, MIME type: image/jpeg) U.S. Navy, Naval Research Lab http://www. ...
Image File history File links Size of this preview: 800 × 420 pixelsFull resolution (900 × 473 pixel, file size: 145 KB, MIME type: image/jpeg) U.S. Navy, Naval Research Lab http://www. ...
Image File history File links Size of this preview: 800 × 420 pixelsFull resolution (900 × 473 pixel, file size: 145 KB, MIME type: image/jpeg) U.S. Navy, Naval Research Lab http://www. ...
Movement
Monsoon troughing reaches its zenith in latitude during the late summer when the wintertime surface ridge in the opposite hemisphere is the strongest and the ITCZ reaches as far as the 40th parallel in the Northern Hemisphere in August. Likewise, in the Southern Hemisphere, it is at its greatest extent in February. [2] On the charts on the left and right, the areas of convergence in the streamline field mark the climatological position of the monsoon trough associated with the ITCZ for those respective months.
Monsoon Depression near Bangladesh Image File history File links MonsoonDepression2004091600. ...
Image File history File links MonsoonDepression2004091600. ...
Effect of wind surges Increases in the relative vorticity of a monsoon trough is normally a product of increased wind convergence. Wind surges can lead to this increase in convergence. A strengthening or equatorward movement in the subtropical ridge can cause a strengthening of a monsoon trough as a wind surge moves southward towards its location. As fronts move through the subtropics of one hemisphere during their winter, wind surges can cross the equator in oceanic regions and enhance a monsoon trough in the other hemisphere's summer. A key way of detecting whether a wind surge has reached a monsoon trough is the formation of a burst of thunderstorms within the feature. Vorticity is a mathematical concept used in fluid dynamics. ...
A surface weather analysis for the United States on October 21, 2006. ...
Embedded depressions If a circulation forms within the monsoon trough it is able to compete with the neighboring thermal low over the continent, a wind surge will occur at its periphery. Such a circulation which is broad in nature within a monsoon trough is known as a monsoon depression. Monsoon depressions are generally asymmetric, and tend to have their strongest winds on their eastern periphery. [3]
Role in tropical cyclogenesis Worldwide, the monsoon trough is the main genesis region for tropical cyclones. [4] Vorticity-rich low level environments lead to a better than average chance of tropical cyclone formation.[3] This is because a pre-existing near-surface disturbance with sufficient vorticity and convergence is one of the six requirements for tropical cyclogenesis. [5] The monsoon trough is one such area of strong low-level vorticity. There appears to be a 15-25 day cycle in thunderstorm activity associated with the monsoon trough, which is roughly half the wavelength of the Madden-Julian Oscillation, or MJO. [6] This mirrors tropical cyclone genesis near these features, as genesis clusters in 2-3 weeks of activity followed by 2-3 weeks of inactivity. [4] Indeed, tropical cyclones can form in outbreaks around these features under special circumstances, tending to follow the next cyclone to its north and west. [7] This is different than the Atlantic Ocean, where tropical cyclones mainly form from tropical waves which move offshore Africa. Eastern Pacific Ocean tropical cyclone formation shows a hybrid of these two mechanisms. Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ...
Vorticity is a mathematical concept used in fluid dynamics. ...
Global Tropical Cyclone Tracks Cyclogenesis is the technical term describing the development or strengthening of a surface low pressure system, or cyclone, in the atmosphere. ...
5-day running mean of MJO. Note how it moves eastward with time. ...
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Whenever the ITCZ-related trough on the eastern side of the summertime Asian monsoon is in its normal orientation, tropical cyclones along its periphery will move with a westward motion. If it is reverse oriented, tropical cyclones will move more poleward. Tropical cyclone tracks with S shapes tend to be associated with reverse-oriented monsoon troughs. [8] The South Pacific convergence zone and South American convergence zones are generally reverse oriented. [2] Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ...
The South Pacific Convergence Zone (SPCZ) is a band of low-level convergence, cloudiness and precipitation extending from the west Pacific warm pool south-eastwards towards French Polynesia. ...
See also Global Tropical Cyclone Tracks Cyclogenesis is the technical term describing the development or strengthening of a surface low pressure system, or cyclone, in the atmosphere. ...
Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ...
References
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