Cloud-Radiation Feedback Facilitates the Secondary Eyewall Formation of Tropical Cyclones

Secondary eyewall formation (SEF) is a common phenomenon of intense tropical cyclones (TC), which significantly influences the intensity and size of TCs. However, forecasting SEF remains a challenge since SEF is dominated by internal dynamical processes but is highly sensitive to environmental forcings. This study probes into the influences of cloud-radiation feedback (CRF) on SEF with a set of idealized simulations and it turns out that CRF is critical to SEF. The key mechanism lies in an upper-level anomalous radiative warming associated with CRF in the outer-core region, which facilitates the development of outer rainbands (ORBs) as well as the stratiform precipitation of ORBs. The broader stratiform precipitation area and stronger stratiform heating profile of ORBs provide favorable conditions for triggering the following convective updrafts associated with SEF at the radially inward side. The results presented in this study highlight the importance of CRF in SEF and imply that the precipitation characteristics of rainbands is an important pathway for CRF affecting the intensity and structure of TCs.