The Hurricane Intensity Issue

Abstract

The intensity issue of hurricanes is addressed in this paper using the angular momentum budget of a hurricane in storm-relative cylindrical coordinates and a scale-interaction approach. In the angular momentum budget in storm-relative coordinates, a large outer angular momentum of the hurricane is depleted continually along inflowing trajectories. This depletion occurs via surface and planetary boundary layer friction, model diffusion, and “cloud torques”; the latter is a principal contributor to the diminution of outer angular momentum. The eventual angular momentum of the parcel near the storm center determines the storm’s final intensity. The scale-interaction approach is the familiar energetics in the wavenumber domain where the eddy and zonal kinetic energy on the hurricane scale offer some insights on its intensity. Here, however, these are cast in storm-centered local cylindrical coordinates as a point of reference. The wavenumbers include azimuthally averaged wavenumber 0, principal hurricane-scale asymmetries (wavenumbers 1 and 2, determined from datasets) and other scales. The main questions asked here relate to the role of the individual cloud scales in supplying energy to the scales of the hurricane, thus contributing to its intensity. A principal finding is that cloud scales carry most of their variance, via organized convection, directly on the scales of the hurricane. The generation of available potential energy and the transformation of eddy kinetic energy from the cloud scale are in fact directly passed on to the hurricane scale by the vertical overturning processes on the hurricane scale. Less of the kinetic energy is generated on the scales of individual clouds that are of the order of a few kilometers. The other major components of the energetics are the kinetic-to-kinetic energy exchange and available potential-to-available potential energy exchange among different scales. These occur via triad interaction and were noted to be essentially downscale transfer, that is, a cascading process. It is the balance among these processes that seems to dictate the final intensity.

Assimilation of radial velocity and reflectivity data from coastal WSR‐88D radars using an ensemble Kalman filter for the analysis and forecast of landfalling hurricaneIke(2008)

“…Many efforts have been made to identify the factors affecting intensity prediction (Anthes, 1982;Emanuel, 2005;Krishnamurti et al, 2005;Rogers et al, 2006;Li and Pu, 2009;Khain et al, 2010). These factors include surface heat and moisture fluxes, sea-surface temperature and environmental wind shear.…”

Impact of local data assimilation on tropical cyclone predictions over the Bay of Bengal using the ARW model

“…With the advent of high-performance computing, advanced highresolution mesoscale models are employed to simulate the above processes for better prediction of tropical cyclones (e.g. Chen et al, 1995;Liu et al, 1997;Kurihara et al, 1998;Aberson, 2001;Wang, 2001;Krishnamurti, 2005;Braun et al, 2006;Fierro et al, 2009;Smith and Thomsen, 2010;Nolan et al, 2009;Gentry and Lackmann, 2010;among others).…”

The Use of a Vortex Insertion Technique to Simulate the Extratropical Transition of Hurricane Michael (2000)

“…Note that the variability among the members of the ensemble is not enough to explain the rapid intensification period observed between 15 and 18 h (in terms of MSLP). This is not a surprise since it is well known that numerical models have difficulty forecasting sudden changes in the intensity of tropical cyclones, given that the processes governing these changes occur at scales unresolved by the model (Krishnamurti et al 2005).…”