JP1.11 Barotropic Instability in the Caribbean and the Tropical East Pacific

Monday, 8 June 2009
Stowe Room (Stoweflake Resort and Confernce Center)
Saska Gjorgjievska, New Mexico Tech, Socorro, NM; and D. Raymond

The Charney-Stern instability condition says that the regions with background potential vorticity (PV) field such that the meridional PV gradient on isentropic surfaces changes sign are potentially unstable. Disturbances that occur in these regions may grow. We investigate two such regions, the Caribbean and the tropical East Pacific. We ask whether barotropic instability in these regions is strong enough to generate easterly waves. Correlation between the PV gradient and cyclogenesis in these regions is found (Molinari at al. 1996) .

Here real data have been used to calculate background PV fields for the potentionally unstable regions. The PV profiles are then input into a simple shallow water model and the resulting solutions are analyzed. The results show that instabilities can indeed be generated, but their growth rates are very small. That raises a question: Is the PV sign reversal the first order cause for easterly wave genesis in these regions, or is something else more important?

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