HR: 10:20h
AN: A22A-01    [Abstracts]
TI: Interactions between climate and tropical cyclones
AU: * Webster, P J
EM: pjw@eas.gatech.edu
AF: Georgia Institute of Technology, Schools of Earth and Atmospheric Sciences & Environmental Engineering, Atlanta, GA 30308, United States
AB: For the last 50 years, there have been two major thrusts in tropical cyclone research: determining the state of the atmosphere and ocean that is suitable for the formation of tropical storms (the genesis criteria) and short-term forecasting of the track and intensity of storms. Efforts to forecast seasonal storm activity, especially in the North Atlantic Ocean, have been undertaken through empirical means and, more recently, using low-resolution climate models. Climate model results have been exceptionally encouraging suggesting that the tropical cyclogenesis factors are predictable and are part of the large scale tropical circulation. During the last few years, a spate of papers has noted the relationship between changes in sea-surface temperature (SST) and tropical cyclone intensity and frequency. A critical issue is determining to what degree the frequency of hurricanes, as well as their intensity distribution, will change in a warming world. We discuss recent research regarding the interactions of the climate system with tropical cyclones, including the role of climate in determining the genesis of tropical cyclones and the role of tropical cyclones in the heat balance of the planet. Specifically: (i) We re-examine the genesis criteria of tropical cyclones and add two new criteria based on the behavior of waves in a flow varying in longitude and the inertial instability of equatorial flow in a cross-equatorial pressure gradient environment. Tropical cyclones are seen to form where the stretching deformation is negative and where large-scale waves transform into tight smaller and highly energetic scale vortices. We also discuss the tendency for storms to develop and intensify where the near-equatorial flow is inertially unstable. (ii) Tropical cyclones act to cool the tropical oceans by > 1K/year by evaporation of ocean surface water and by entrainment mixing with cooler water from below the mixed layer. We suggest that tropical cyclones are important part of the heat budget of the planet and act as efficient ventilators of the tropical ocean, transporting heat polewards in both the ocean and the atmosphere. We discuss the mechanisms by which hurricanes efficiently transport mass and heat upwards and then polewards and how the vertically mixed heat in the oceans joins the annual cycle of ocean heat transport. We speculate that the near constancy of the global annual number of tropical cyclones is evidence that the heat transport of storms is governed by an integral constraint applying to the heat balance of the planet. With this information, we can speculate on the characteristics of tropical cyclones in a warmer world.
DE: 1218 Mass balance (0762, 1223, 1631, 1836, 1843, 3010, 3322, 4532)
DE: 1225 Global change from geodesy (1222, 1622, 1630, 1641, 1645, 4556)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly