THE DIAGNOSIS OF SYMMETRIC INSTABILITY OF THE "93.5" BLACK STORM

WANG Wen;CHENG Lin-sheng

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Plateau Meteorology ›› 1999, Vol. 18 ›› Issue (2) : 127-137.

THE DIAGNOSIS OF SYMMETRIC INSTABILITY OF THE "93.5" BLACK STORM

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Abstract

With the criteria of linear and non-linear symmetric instability,the mechanism of a black storm occurred in the Northwest China from 4 to 6 May 1993("93.5") is diagnosed by using three time level output data of a MM4 model which well simulated the developing structure and evolution of the "93.5" black storm.The results show that the location of maximum of the wet bulb potential vorticity is corresponding to that of squall line and from the vertical cross section chart of pseudo angular momentum and potential equivalent temperature (M-θe) it can be seen that the region where the slope of θe surface is more vertical than the M is also consistant to the movement of the black storm.The linear conditional symmetric instability is a possible explanation for the squall line.The Lagrangian parcel theory is applied to diagnose the "93.5" black storm and it is shown that the positive σ2 or negative fq (∂lnθ/∂z)-1 and the cusp catastrophe are corresponding to the developement and movement of the squall line,limited comparison lends some support to the hypothesis that non-linear CSI can be a dominant formative mechanism of the black storm,though more sophisticated studies are required.

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Black storm / Linear and non-linea / Symmetric instabilit

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WANG Wen , CHENG Lin-sheng. THE DIAGNOSIS OF SYMMETRIC INSTABILITY OF THE "93.5" BLACK STORM. Plateau Meteorology. 1999, 18(2): 127-137

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