An Investigation of Equivalent Potential Temperature as a Measure of Tropical Cyclone Intensity.
Technical note 1957-1975,
FLEET WEATHER CENTRAL/JOINT TYPHOON WARNING CENTER FPO SAN FRANCISCO 96630
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Several investigators of tropical and mid-latitude sounding data have attempted to differentiate between the disturbed and the undisturbed states of the atmosphere. One parameter, which has been used to approximate the total energy of a parcel of air, and thus distinguish between these two states, is the equivalent potential temperature Theta epsilon. Radiosonde data from Clark Air Base in the Republic of the Philippines and tropical cyclone dropsonde data have been analyzed for Theta epsilon. It is shown that a mid-tropospheric minimum in total energy vanishes as a tropical cyclone approaches Clark Air Base, with subsequent increases in Theta epsilon extending through 400 mb. From an analysis of dropsonde data obtained in tropical cyclone centers, large values as well as rapid increases in Theta epsilon were observed for tropical cyclones which deepened explosively. Since these changes in Theta epsilon are not the product of synoptic scale motions nor horizontal advective processes, it is proposed that they result from the direct mechanical lifting of heat and moisture in the form of convective hot towers. A procedure for forecasting explosive deepening is postulated. Author