Concentric Eyewalls and Tropical Cyclone Vortex-scale Structure Characteristics

More than half of major TCs form concentric eyewalls (CEs) at least once in their life cycle. There have been few studies on the vortex-scale structure characteristics of these TCs. This study investigates the relationship between secondary eyewall size and the TC vortex-scale structural features prior to the formation of CE, utilizing satellite data, high-resolution reanalysis data and best-track dataset. The results show that there is a significant positive correlation between the secondary eyewall size and the strength of outer-core circulation and TC size. The stronger the outer-core circulation is and the larger the TC size is, the larger the secondary eyewall size is. Furthermore, the differences in vortex-scale structure between the major TCs that do not form obvious CE structure and the TCs that form CE structure are compared and analyzed. The strength of outer-core circulation in TCs without obvious CE structure is much weaker and the corresponding TC size is smaller. The results of this study demonstrate that TC needs to reach certain size as well as a certain intensity to form CE structure.