Hurricane's Maximum Potential Intensity and the Gravitational Power of Precipitation

Abstract

The concept of Maximum Potential Intensity (MPI) is widely used in tropical cyclone research to estimate the minimum central pressure and the maximum velocity of tropical storms from environmental parameters. The MPI pressure derives from consideration of an idealized thermodynamic cycle, while the MPI velocity additionally requires information about real-time power and heat flows within the storm. Recently MPI velocity was proposed to be a substantial overestimate (by 10-30 percent) presumably neglecting the power needed to lift precipitating water (the gravitational power of precipitation). This conclusion did not involve a theoretical analysis of the MPI concept but was based on observed hurricane rainfall to estimate gravitational power of precipitation. However, since the MPI pressure estimate does explicitly account for lifting water, and the MPI velocity derives from this pressure, the question arises whether a correction to MPI velocity is required. Here we represent and examine the MPI derivations in their most general form and show that although a correction to MPI velocity is justified, it is an order of magnitude or so smaller than originally proposed. We show that the neglect of gravitational power of precipitation in the MPI velocity estimate was caused by the incomplete formulation of the general relationship between pressure work and dissipation of kinetic energy, taken per unit time and integrated over the storm. We highlight the importance of an internally consistent framework to estimate both storm energy and power and provide some perspectives for further investigating the role of moisture.