A Cloud-Resolving Simulation of Hurricane Bob (1991): Storm Structure and Eyewall Buoyancy

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Abstract
A numerical simulation of Hurricane Bob (1991) is conducted using the Pennsylvania State University–National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5) with a horizontal grid spacing of 1.3 km on the finest nested mesh. The model produces a realistic hurricane that intensifies slowly during the period of finescale simulation. The time-averaged structure is characterized by a wavenumber-1 asymmetry with maximum low-level vertical motions and near-surface inflow in the left-front quadrant relative to the nearly aligned storm motion and mean wind shear vectors and strong outflow just above the boundary layer collocated with the updrafts. Instantaneous distributions of radial flow, vertical motion, and precipitation are strongly modified by a wavenumber-2 asymmetry that rotates cyclonically around the center at about half the speed of the mean tangential winds, consistent with the theory for vortex Rossby waves. The time-mean asymmetric vertical motion is comprised of smal... Abstract A numerical simulation of Hurricane Bob (1991) is conducted using the Pennsylvania State University–National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5) with a horizontal grid spacing of 1.3 km on the finest nested mesh. The model produces a realistic hurricane that intensifies slowly during the period of finescale simulation. The time-averaged structure is characterized by a wavenumber-1 asymmetry with maximum low-level vertical motions and near-surface inflow in the left-front quadrant relative to the nearly aligned storm motion and mean wind shear vectors and strong outflow just above the boundary layer collocated with the updrafts. Instantaneous distributions of radial flow, vertical motion, and precipitation are strongly modified by a wavenumber-2 asymmetry that rotates cyclonically around the center at about half the speed of the mean tangential winds, consistent with the theory for vortex Rossby waves. The time-mean asymmetric vertical motion is comprised of smal...