Environmental Influences on Hurricane Intensification

Robert T. Merrill Department of Atmospheric Science, Colorado State University, Fort Collins, Fort Collins, Colorado

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Abstract

Although driven by internal processes, hurricanes are also regulated by conditions in their oceanic and atmospheric surroundings. Sea surface temperature determines an upper bound on the intensity of hurricanes, but most never reach this potential, apparently because of adverse atmospheric conditions.

Winds measured by satellite cloud tracking, commercial aircraft, and rawinsondes are composited using a rotated coordinate system designed to preserve the asymmetries in the upper-tropospheric environment. Composites of upper-tropospheric environmental flows for intensifying and nonintensifying hurricanes for a five-year period are compared. Nonintensifying composites indicate stronger mean environmental flow relative to the hurricane motion, unidirectional flow over and near the hurricane center, and slightly weaker radial outflow and/or more pronounced anticyclonic flow surrounding the center in the upper troposphere.

Abstract

Although driven by internal processes, hurricanes are also regulated by conditions in their oceanic and atmospheric surroundings. Sea surface temperature determines an upper bound on the intensity of hurricanes, but most never reach this potential, apparently because of adverse atmospheric conditions.

Winds measured by satellite cloud tracking, commercial aircraft, and rawinsondes are composited using a rotated coordinate system designed to preserve the asymmetries in the upper-tropospheric environment. Composites of upper-tropospheric environmental flows for intensifying and nonintensifying hurricanes for a five-year period are compared. Nonintensifying composites indicate stronger mean environmental flow relative to the hurricane motion, unidirectional flow over and near the hurricane center, and slightly weaker radial outflow and/or more pronounced anticyclonic flow surrounding the center in the upper troposphere.

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