Characteristics of the Long‐Lived Concentric Eyewalls in Tropical Cyclones

Abstract

AbstractConcentric eyewalls (CEs) in tropical cyclones (TCs) in different basins were identified based on satellite imagery during 1997–2014. Their duration and structural parameters, including inner eyewall size, moat width, and outer eyewall width, were calculated. Differences in these parameters can best be distinguished by short‐lived and long‐lived CEs (i.e., CEs with durations shorter or longer than 20 h). A long‐lived CE tends to have a larger size, mainly contributed by a larger moat and a larger outer eyewall width. The inner eyewall size shows no significant difference between short‐lived and long‐lived CEs in the western North Pacific (WNP) but increases slightly and steadily with increasing CE durations in the Atlantic (ATL). Furthermore, the WNP has far more CEs than in ATL and in the eastern Pacific (EPAC) for all duration categories. Long‐lived CEs cover about 20% of all CEs and are associated with higher sea surface temperature and weaker vertical wind shear. In the WNP, the TC tracks associated with long‐lived CEs were with the less northward motion component. Furthermore, seven TCs with triple eyewalls in the WNP are identified during 1997–2014, with only one case in the EPAC and no ATL case. It is found that five cases of these triple eyewalls TC in the WNP evolved to long‐lived CEs. The results suggest that the CE internal dynamical process, the TC track during the CE period, and the environmental conditions are all critical to the CE size and duration.