Evolutionary Characteristics And Structural Asymmetry Of The Double Eye Wall In Tropical Cyclones

Concentric eyewalls(CEs)are common phenomenon in the development of strong tropical cyclones(TCs).The CEs is often accompanied with eyewall replacement cycles(ERC),which leads to dramatic changes in the TC central pressure and wind size.In this paper,we use a combination of aircraft observation and active/passive multi-satellite datasets to study the vortex evolution of CEs and the asymmetric structure of CEs in sea surface wind field and precipitation structure to validate the physical mechanism of CEs.The study contents and conclusions are as followed:In the first section,768 radial legs of 12 hurricanes in Atlantic basin were used to research the vortex evolution of CEs.It is concluded that the CE structure tilted outward with height from the bottom to the top while the outer eyewall tilted more than the inner eyewall.Combining the active and passive microwave remote sensing observation dataset,we revealed that the abnormal intensity changes of Hurricane Irma(2017)was due to the strong convection at the end of the spiral rainband which generated a new outer eyewall at last,so-called third eyewall,which inhibits the development of the second eyewall.Hence,Irma didn't reintensify at last.In the second section,we analyzed the asymmetric structure of CEs by combining high-resolution SAR-derived surface wind field and GPM precipitation dataset.It is illustrated that TC intensity was weakened when the CEs structure appeared on the left of TC moving direction and enhanced when the CEs appeared on the right.In addition,the outer eyewall formed mainly in the right-front quadrant with the direction of TC movement,due to a wind velocity vector superposition from rotational velocity and movement velocity.In the individual analysis of the precipitation structure of Hurricanes Irma and Jose based on GPM DPR,it is found that the inner eyewall was driven by convective precipitation and the outer eyewall was affected by stratocumulus precipitation.The precipitation structure shows that the height of the outer eyewall is concentrated below 5 km,The vertical structure of the outer eyewall of Hurricane Jose was not coherent from the radar observations,which showed a strong echo in the upper and the sea-surface level and a weak echo in the middle.This phenomenon validates the previous proposal that the asymmetric stratus cloud precipitation mechanism is the physical mechanism for the formation of the binocular wall.