Oceanic and Radiative Controls of Global Tropical Cyclone Potential Intensity

The moored maximum potential intensity (MMPI) provides a measure of tropical cyclone (TC) potential intensity (PI) on par with Emanuel’s maximum potential intensity (EMPI), but with explicit representation of ocean dynamics on PI. This additional degree of freedom makes MMPI adjustable to suit different assumptions about the nature of TC interaction with the ocean. Rather than using tropical cyclone heat potential (TCHP), which is the ocean heat content (OHC) in excess of 26°C, the total OHC could be used. Additionally, the depth of integration can be chosen based on different assumptions. Here, OHC is integrated to 100m based on recent research showing that TCs tend to mix and hence interact with OHC over this depth. A detailed analysis of the oceanic influences on PI is presented with special focus on the controls of PI trends. Connections between trends in the MMPI budget terms, observed maximum intensity, and rapid intensification of landfalling storms are explored. OHC and sea surface temperature (SST) exert control on PI in different ways, with OHC contributing to the individual oceanic heat fluxes and SST influencing the sign of the trend. Changes in advection (horizontal and vertical) and OHC tendency, which we regard as “storage” of heat in the ocean, control how changes in OHC manifest in PI. The sign of the trend depends on the relative rates of increase of SST and tropopause temperature and to a lesser extent on local trends in 10m wind speed. The magnitude of PI depends heavily on the oceanic and radiative heat fluxes at the ocean surface, with different budget terms dominating in different regions. PI is increasing over most of the world ocean during the 27-year study period from 1994 through 2020, especially poleward of 30° as temperature and OHC dynamics trends intensify in those regions. This coincides with increases in TC intensity, TC persistence, and cyclogenesis at those latitudes, and the advent of so-called “category 6” storms and Mediterranean TC-like storms (“medicanes”).