Isentropic analysis of hurricane circulation

Hurricanes, as many other atmospheric flows, are associated with turbulent motions over a wide range of scales. Here we propose to adapt a new technique based on the isentropic analysis of convective motions to study the circulation in hurricane simulations. The proposed approach differentiates the air masses in terms of the equivalent potential temperature. In doing so, one separates the rising air parcels at high entropy from the subsiding air at low entropy. This also filters out oscillatory motions associated with gravity waves and isolate the overturning motions associated with convection and the meso-scale circulation. One of the key benefits of this technique is that it allows to unambiguously determine the thermodynamic properties of the hurricane inflow and outflow, as well as the thermodynamic transformation of the air parcels within the storm. Hence, we expect that it can provide an important insight into how far the environmental air can penetrate into a hurricane, and how this may impact storm intensity under various conditions.

We analyze idealized hurricane simulations from the the Weather Research and Forecasting (WRF 2.2) model on the 1000km by 1000km domain at 1km horizontal resolution. To average the calculated parameters we choose 12 hours of the most steady, axisymmetric circulation. We determine the  characteristics of this steady state to compare it with the transient features.  The approach is well-suited for analysis of simulated convection without requiring specifics of the models. This is advantageous in diagnostics of the convective transport in increasingly complex numerical models. The isentropic streamfunction could be used as an intermediary diagnostic for comparison between high resolution cloud resolving models and single column models.