Dynamic instabilities of simulated hurricane-like vortices and their impacts on the core structure of hurricanes. Part II: Moist experiments

The energy flows of a simulated moist hurricane-like vortex are analyzed to examine the processes that change the intensity and structure of tropical cyclones. The moist vortex used in this study is initially axisymmetric on an f plane and is placed on a uniform surface - an ocean with constant sea surface temperature of 29°C. Two simulations are performed using the following different environmental flows: one in a calm environment and the other in weak environmental vertical shear. The differences between the intensities and structures of the two simulated vortices are discussed in terms of energy flows. While the structure and intensity of the vortex without shear are relatively steady, those of the vortex with shear experience dramatic changes. The sheared vortex shows delayed weakening, persistent wavenumber 1 asymmetry with maximum rainfall on the downshear left side, and top-down breakdown. In both vortices barotropic energy conversion is stronger than baroclinic energy conversion. However, baroclinic processes in the upper levels of the sheared vortex play an important role in weakening the vortex. The energy flow diagram and the cross section of energy conversion terms show the existence of multiple baroclinic eddy life cycles at the upper levels of the sheared vortex. The activity of the baroclinic eddies continues until ventilation of the upper-level warm-core structure is sufficient to weaken the sheared vortex. © 2008 American Meteorological Society.