27th Conference on Hurricanes and Tropical Meteorology


Global temperature redistribution by recurving tropical cyclones: A wildcard in midlatitude winter forecasting

Robert E. Hart, Florida State University, Tallahassee, FL

The existence of wind on Earth largely results from the gradient of temperature from the poles to the equator caused by varying incoming solar radiation with latitude. It has long been established, and more recently quantified, that this redistribution of temperature is accomplished through various means: oceanic currents, atmospheric currents, and latent heat release. Implied within the latter two is the role of tropical cyclones that move out of the tropics and poleward of the Hadley cell. It remains a curious wildcard within climate that although the pole to equator temperature gradient does not directly produce tropical cyclones, their very formation weakens this gradient if they leave the Hadley cell. Despite this understanding, the magnitude of this role has remained nebulous and qualitative. By examining the winter baroclinic activity following varying recurving tropical cyclone seasons, the role of recurving tropical cyclones in the redistribution of heat and moisture poleward is finally quantified. The results suggest that a recurving tropical cyclone, on average, weakens the mean pole-to-equator temperature gradient by approximately one percent. This decreases the necessary role of baroclinic activity in the winter season that follows, as the available potential energy has decreased. Accordingly, seasonal forecasting of winter climate anomalies of temperature and precipitation in the middle latitudes is possible when the hemispheric frequency of recurving tropical cyclones is well above or below normal. Unfortunately, with net tropical cyclone recurving frequency minimally predictable, some significant component of winter climate is necessarily unpredictable until the tropical season has nearly ended. This study suggests a unique view wherein tropical cyclones are integral to the variability and forcing of global climate, rather than incidental and solely responsive to other forcings, such as El Nino/La Nina.

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Session 3A, Extratropical Transition of Tropical Cyclones I
Monday, 24 April 2006, 1:30 PM-3:00 PM, Big Sur

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