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An issue of considerable interest is the so-called multicellular thunderstorm system, as opposed to supercells, which are often presumed to be unicellular. A form of multicellular convection that has already been simulated extensively is the squall line. The typical method for simulating this form of deep line-oriented convection has been to release a number of laterally-aligned IB's. After the initial storms develop, their outflows merge, producing a line of convection resembling a squall line. Squall lines are not the only type of multicellular convection observed, however. In isolated multicell storms, a succession of updrafts is typical.  1, fiche 1, Anglais, - multicellular%20thunderstorm%20system

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Thunderstorms are often classified into a spectrum based on their cell structure: single cells, multicellular storms, and supercells. The type of storm depends on the instability and relative wind conditions at different layers of the atmosphere (shear). The "single-cell" (unicell) thunderstorm is [a] three-stage situation ... usually lasting about 30 minutes from the start of significant precipitation. A severe unicell storm is often referred to as a pulse thunderstorm. ... In a multicell thunderstorm, several thunderstorm cells merge into a larger system. The cloud becomes divided into updraft and downdraft regions separated by a gust front. The gust front may extend for several miles ahead of the storm, bringing with it increases in wind speed and atmospheric pressure, decreases in temperature, and shifts in wind direction. The storm itself will have different portions sequentually going through the various thunderstorm stages. In many cases the immature cells develop along a line known as a "flanking line," resulting in what is known as a line multicell.  6, fiche 1, Anglais, - multicellular%20thunderstorm%20system

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storm system: Often refers to "thunderstorm system" (in French: "système orageux"), which is a frequent type of storm system but not the only one; an elliptic form which can be used when there is no risk of ambiguity.  3, fiche 1, Anglais, - multicellular%20thunderstorm%20system

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