Convergence (meteorology)
The convergence in Météorologie indicates an area of the atmosphere where flows of air of various directions meet to create an accumulation of mass which possibly leads to a vertical movement from where the formation of Nuage S and Précipitation S. One distinguishes convergence from broad scale, known as synoptic, which gives weather systems the such hollow barometric, the depression S and the Cyclone S; and convergence with small scales which will give clouds isolated like the Cumulus or clouds of Orage. The reverse of convergence is the divergence.
Principle
See also: atmospheric primitive Equations
From the mathematical point of view, the convergence of mass of the air can be calculated starting from the equations which govern the atmosphere. These equations comprise terms of convergence and divergence which connects the variation of pressure and temperature by the compression of these parameters in a more restricted zone.
Synoptic
See also: Cyclogénèse
The atmospheric Circulation is the result of the differences in pressures which one finds around the Ground. Those are created by the difference in received energy of the Sun, according to the latitude, and the rotation of planet. Close to the Ecuador, the general circulation of the Alizé S gives two zones of rather stable convergence is the Zone of intertropical convergence and the Zone of convergence of the southern Pacific giving a low relative pressure in these areas.
Méso-scale
To more small scales, the drain of the winds by topography or a differential warming between two zones having different reflective properties can lead to a convergence. One thus notes mechanical convergences as in the area of Seattle where one finds in the arm of the sea of Puget Sound a convergence of the winds on low level downstream from the Olympiques mountains. This is due to the fact that the winds of west must pass on each side of the mountains what creates a lower pressure downstream from the flow of air towards which the two branches of circulation must converge. Typical thermal convergences meet along the zone between general flow and that of the breeze of sea, between flow between the sunny and cloudy zones, etc
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