Inflow Layer Energetics of Hurricane Bonnie (1998) near Landfall

Abstract

Abstract On 26 August 1998, a NOAA WP-3D aircraft executed a curved track that mimics an inflow trajectory to the eyewall of Hurricane Bonnie. Global positioning system (GPS) sondes and airborne expendable bathythermographs jettisoned along the trajectory provide the observations to conduct an energy budget for the 1600-m-deep inflow to the eyewall. Surface fluxes are estimated via the bulk aerodynamic equations and the flux at the top of the inflow is solved as a residual. From 170- to 125-km radial distance from the circulation center the mean θe of the inflow remains constant despite combined sensible and latent surface fluxes in excess of 500 W m−2. Convective cells remove energy from the inflow boundary layer at a rate similar to the inputs from the sea. From 125 to 100 km, in the annulus adjacent to the eyewall, mean θe increases 4.5 K in response to higher surface fluxes and little loss through the inflow top. Energy balance may be achieved by either entrainment of higher θe through the top of the inflow layer, or by inclusion of just half the estimated heat from viscous dissipation. The authors infer that the secondary circulation of the eyewall inhibits convective cells from forming in this region and thus facilitates the rapid increase of energy in the inflow. The results support hypotheses that hurricane intensity appears to be strongly modulated by energy exchange in a meso-β region adjacent to and under the eyewall.