Relationship between eyewall slopes, inner-core structures, and intensities of TCs

On the basis of a one-year simulation using a high-resolution nonhydrostatic global circulation model with a 7-km horizontal grid spacing, the relationships between eyewall slopes, inner-core structures, and intensities of tropical cyclones (TCs) are investigated.

The results show that stronger TCs generally have warm core maxima at higher levels as their intensities are stronger. In order to clarify how the warm core structures are related to TC intensities, the vortex structure and the extent of thermal wind balance is investigated. By gradually introducing simplifications, we found that the warm core structures can be well captured only using the tangential wind field within the inner core region with the ambient temperature profile.

Based on a balanced model, we propose a hypothesis which gives an explanation for the relationship between TC intensity and eyewall slope which is an indicator of inner-core structure of TC. It suggests that as eyewall slopes approach to upright (horizontal), TC intensities increase (decrease). The result of the analysis using the simulation data is consistent with the proposed model. These results suggest that eyewall slopes are useful to diagnose TC intensities.