The large outer eyewall of long-lived concentric eyewall tropical cyclones

In this study, we used 1997-2004 passive microwave satellite imagery over both western North Pacific (WNP) and Atlantic (ATL) basins to examine the long-lived concentric eyewall (CE) tropical cyclones (TCs). The observations reveal that 23% (15%) of the total CE TC belongs to the long-lived category in WNP (ATL) in which the CE TC maintained its CEs structure for more than 20 h in the satellite data. In addition, we found these long-lived CE TCs often possess large moats and wide outer eyewalls. Satellite data shows a high correlation between the width of outer eyewall and the cloud liquid water content, indicating that the long-lived CE TCs may be with large diabatic heating in the wide outer eyewall.

We conducted in a framework of balanced vortex, for the CE TC with large moat and wide outer eyewall such as Typhoon Winnie (1997), to assess their dynamic energy efficiency of heat in generating the kinetic energy. Our results indicate that, with the fixed heating in the outer eyewall region, the system dynamic efficiency decreased by 40% when the moat size increased from 100 km to 200 km. On the other hand, the system efficiency can increase by 50% when the outer eyewall width increased from 100 km to 160 km. Our energy diagnoses indicate that large moat and wide outer eyewall play significant but opposite roles in generating the TC kinetic energy, which is crucial to the life time of CE TC.