Kinetic energy budgets of moving systems: Case studies for an extratropical cyclone and hurricane Celia, 1970

Abstract

Kinetic energy budgets of an extratropical cyclone and Hurricane Celia, 1970 are examined in moving coordinates. This represents a first attempt to diagnose the energy budgets of moving systems using the method suggested by Vincent & Chang (1973).

Both systems are studied during three stages of their life histories over the United States. The extratropical cyclone is investigated for a 36-hour period during which it develops in the lee of the Rockies, matures and occludes as it moves rapidly eastward toward the Atlantic Ocean. Hurricane Celia is investigated for a 48-hour period after landfall, as it traverses southern Texas into New Mexico. This consists of a 12-hour mature stage, a 12-hour rapidly decaying stage and a subsequent 24-hour slowly decaying stage when the storm dissipates.

Generally speaking, the major findings are: (1) boundary fluxes of kinetic energy are important in maintaining the energy budget of the extratropical cyclone except during its occluded stage, whereas, they are practically negligible during all stages of Hurricane Celia's life cycle; (2) upward transport of kinetic energy in the extratropical cyclone produces vertical divergence in the troposphere and convergence in the stratosphere, while for Celia a vertical transport occurs away from the layer of maximum kinetic energy (∼ 500 mb) with the energy being transported into the stratosphere and toward the surface; (3) generation takes place in the lower troposphere with a somewhat larger destruction aloft for the extratropical cyclone, whereas, generation occurs in all layers for Celia; (4) dissipation, calculated as the residual in the energy budget, represents an energy loss during all stages for both storms except in the upper levels during the developing state of the extratropical cyclone.

Sensitivity analyses were performed on the original data to evaluate the effect of random errors on kinetic energy budget calculations. The combined effect of random errors ranging between ±10 degrees for wind direction, ±20% for wind speed, and ±0.5% for geopotential height, occasionally cause certain terms in the budget to vary by almost a factor of two; however, the trend in the results and subsequent scientific interpretations remain essentially the same as those using original data.