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FRANK S. SECHRIST and JOHN A. DUTTON

Abstract

A new Lagrangian method of determining energy conversion rates for individual cyclones is developed and applied to the rapidly deepening storm of Nov. 29–30, 1963.

It is shown that 12-hr average conversion rates can be determined for arbitrary volumes of the atmosphere that move with the velocity of the mean wind. The method is straightforward, relatively easy to apply, and eliminates the necessity of evaluating boundary flux terms and other quantities that are difficult to measure accurately.

The new Lagrangian method has the advantage of providing vertical profiles of the conversion rates that exhibit revealing temporal changes. It appears that the storm initially acquired kinetic energy in the lowest layers southwest of the center. Later, the largest kinetic energy increases occurred south of the center at intermediate levels. By the time the storm reached maturity, the largest increases were taking place at high levels northeast of the storm while kinetic energy decreases occurred below.

Finally, 36-hr isentropic trajectories are used to trace parcels backward in time for the purpose of determining the source regions of air characterized by large values of kinetic energy. The results of this analysis indicate that a preexisting source of kinetic energy associated with the jet maximum northwest of the storm provided part of the storm's energy; the remainder was generated locally as ascending air parcels accelerated northeastward from the nearly barotropic region in the warm sector of the cyclone.

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