Comments on "An evaluation of hurricane superintensity in axisymmetric numerical models" by Rapha\"el Rousseau-Rizzi and Kerry Emanuel

TL;DR

This paper critiques and revises a recent theoretical derivation of maximum hurricane velocity, emphasizing the importance of kinetic energy changes and water lifting power, leading to a modified velocity estimate independent of sensible heat flux.

Contribution

It identifies missing terms in the previous derivation and provides a revised formula for hurricane maximum velocity considering kinetic energy and water lifting effects.

Findings

The original derivation neglected kinetic energy in the outflow.

Proper accounting for water lifting alters the velocity estimate.

The revised formula shows velocity independence from sensible heat flux.

Abstract

In a recent paper Rousseau-Rizzi and Emanuel (2019) presented a derivation of an upper limit on maximum hurricane velocity at the surface. This derivation was based on a consideration of an infinitely narrow (differential) Carnot cycle with the warmer isotherm at the point of the maximum wind velocity. Here we show that this derivation neglected a significant term describing the kinetic energy change in the outflow. Additionally, we highlight the importance of a proper accounting for the power needed to lift liquid water. Finally, we provide a revision to the formula for surface fluxes of heat and momentum showing that, if we accept the assumptions adopted by Rousseau-Rizzi and Emanuel (2019), the resulting velocity estimate does not depend on the flux of sensible heat.