Warm Core Structures in a Global High-Resolution Nonhydrostatic Modelwithout Cumulus Parameterization

Abstract:

Although the existence of the warm core has long been recognized, the relative frequency of the heights of warm cores and the relationship between heights and intensities are unclear owing to lack of observations.

This study investigate the relationship between warm core structures and intensities of tropical cyclones (TCs) on the basis of a one-year simulation using a high-resolution global nonhydrostatic model (the Nonhydrostatic Icosahedral Atmospheric Model; NICAM) with a 7-km horizontal grid spacing. The analysis with the data comprising 4,728 samples of 85 TCs reveals a clear relationship between warm core heights and intensities for relatively strong TCs. It is also found that warm core heights tend to ascend as TCs intensify after TCs reach sufficient intensities, and the warm core heights tend to descend as TCs decay.

In addition, a diagnosis using the thermal wind balance equation clarified what aspects of vortex structures are significant for warm core structures. The result shows that warm core structures can be well captured from only within the inner core tangential wind field and the ambient temperature profile. This suggests that the warm core heights, the heights of large baroclinicity, can be inferred from shapes of angular momentum surfaces. Comparison between warm core heights and slope of eyewall inner edge reveals warm core height increases as the slope decreases for sufficiently strong TCs.