Variations in Tropical Cyclone Genesis Factors in Simulations of the Holocene Epoch
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The thermodynamic factors related to tropical cyclone genesis are examined in several simulations of the middle part of the Holocene epoch when the precession of Earth's orbit altered the seasonal distribution of solar radiation and inone transient simulation of the millennium preceding the industrial era. The thermodynamic properties most crucial for genesis display a broad stability across both periods, although both orbital variations during the mid-Holocene (MH) 6000years ago (6ka) and volcanic eruptions in the transient simulation have detectable effects. It is shown that the distribution of top-of-the-atmosphere radiation 6ka altered the Northern Hemisphere seasonal cycle of the potential intensity of tropical cyclones in addition to slightly increasing the difference between middle tropospheric and boundary layer entropy, a parameter thathas been related to the incubation period required for genesis. The Southern Hemisphere, which receivesmore solar radiation during its storm season today than it did 6ka, displays slightly more favorable thermodynamic properties during theMHthan in the preindustrial era control. Surface temperatures over the ocean in both hemispheres respond to radiation anomalies more slowly than those in upper levels, altering the thermal stability. Volcanism produces a sharp but transient temperature response in the last-millennium simulation that strongly reduces potential intensity during the seasons immediately following a major eruption. Here, too, the differentialvertical temperature response is key: temperatures in the lower and middle troposphere cool, while those nearthe tropopause rise. Aside from these deviations, there is no substantial variation in thermodynamic properties over the 1000-yr simulation. © 2012 American Meteorological Society.
author list (cited authors)
Korty, R. L., Camargo, S. J., & Galewsky, J.