The vertical structure of tangential winds in tropical cyclones: theory, observations, and models

In this study, three-dimensional Doppler wind analyses of seven hurricanes on 21 different days are examined in an effort to gain some insight into the vertical structure of tropical cyclones. In particular, the decay of axisymmetric tangential winds both in the vertical direction and along sloping absolute angular momentum (M) surfaces are examined and compared to existing theoretical predictions. The slope of the Radius of Maximum Winds (RMW) is objectively determined and compared to the slope of the M surfaces. It is shown that while in most cases the observed vertical structure conforms to the expectations of theory, there is a subset of cases where M decreases upward along the RMW. Reasons for this behavior are investigated.

Two other longstanding “myths” of vertical structure are also reexamined: that the magnitude of the observed outward slope of the RMW with height varies directly with storm size, and inversely with intensity. It is demonstrated that the former is generally correct while the latter is apparently false. Comparisons with the idealized axisymmetric balance model of Emanuel (1995), and the analytical predictions of MPI theory upon which the model is based are shown to be consistent with these findings. Finally, the wind fields generated by high-resolution simulations are analyzed and compared to the observed hurricanes.