Hurricane's maximum potential intensity and surface heat fluxes

The concept of Maximum Potential Intensity (PI) relates the maximum velocity of tropical storms to environmental parameters. Since its original formulation by Emanuel (1986), two major modifications were made resulting in a considerable range of predicted PI values. First, dissipative heating was suggested to increase maximum velocity by up to 20%. Second, the power expended to lift water (the gravitational power of precipitation) was recently suggested to reduce maximum velocities by 10-30%. Here we re-derive the PI concept separating its dynamic and thermodynamic assumptions. First, we show that there is no ambiguity from dissipative heating: irrespective of whether thermal dissipation occurs or not, the PI concept uniquely relates maximum velocity to the latent heat flux (not the total oceanic heat flux as in the original formulation). Our revised velocity estimate is independent of sensible heat flux. Second, we clarify that accounting for the gravitational power of precipitation has little impact on PI. Third, we demonstrate that a key feature of the PI concept is that the negative work of the pressure gradient in the upper atmosphere consumes all the kinetic energy generated in the boundary layer. This dynamic constraint is independent of thermodynamic assumptions such as isothermal heat input from the ocean, and thus can apply to diverse circulation patterns. Finally, we show that the maximum kinetic energy per unit volume in the PI concept is approximately equal to the partial pressure of water vapor at the surface.