Interaction of hurricane and cloud scales: contribution to hurricane intensity

The overwhelming amount of kinetic energy of tropical cyclones is contained within the azimuthal wave number zero, representing the symmetric flow, and azimuthal wave numbers one and two, representing the principal asymmetries. The spatial scale of the symmetric and asymmetric components of a hurricane's circulation is on the order of several hundreds of kilometers, while the individual cloud scales are on the order of a few kilometers. The clouds however are organized on the scale of the hurricane, i.e. at azimuthal wave numbers zero, one and two. The kinetic energy budget of hurricanes' wave numbers one and two is calculated using scale interaction approach. MM5 simulations of hurricanes Charley of 2004 and Katrina of 2005 are used to diagnose the kinetic energy interactions involving azimuthal wave numbers one and two, which represent the dominant asymmetries. We find that the wave-mean kinetic energy interactions and the potential to kinetic energy conversions are the dominant processes affecting the kinetic energy at wave numbers one and two. In an area-averaged sense the wave-mean interactions prevail. The wave-wave interactions are found to be large only in localized regions but their area-averaged contribution is found to be small. There appears to be a relationship between the kinetic energy tendency of wave numbers one and two and the hurricanes' intensification, particularly in the case of Katrina, which was a significantly stronger and larger storm with a much better defined asymmetric component.