Spontaneous-adjustment emission of inertia-gravity waves by unsteady vortical motion in the hurricane core



Spontaneous-adjustment emission of inertia-gravity waves (IGWs) from unsteady vortical motion in the hurricane core is further examined. An idealized divergent barotropic model simulation is conducted in an unforced framework using a highly asymmetric potential vorticity (PV) field, consisting of an offset monopole embedded in an elliptically shaped ring, which is motivated by concentric eyewalls that were observed in the inner core of hurricane Ivan (2004). The simulation proceeds in two phases. The first phase is marked primarily by inner-core potential vorticity (PV) mixing and rearrangement as the monopole interacts with the ring, however axisymmetrization does not occur. This leads to a second phase characterized by a prolonged (lasting at least 36 h) period of spontaneous-adjustment emission of IGWs to the environment. During the spontaneous-adjustment phase, unsteady vortical motion acts as an IGW source, constraining the frequency and radial wavenumber of the waves. Diagnostics of this simulation reveal two important conclusions. First, the spontaneous radiation of IGWs is insignificant for vortex intensification or decay; rather, PV mixing in the early portion was more important. Secondly, using a non-divergent barotropic model simulation of the same configuration and idealized simulations, we demonstrate that non-axisymmetrization in this case-study is caused primarily by PV (Rossby wave) dynamics, with the Rossby-IGW instability only playing a minor role. These results support the existence of a slow quasi-manifold with exponentially small fuzziness at small Froude and large Rossby numbers. Copyright © 2010 Royal Meteorological Society