What Limits the Secondary Eyewall Formation in Intense Tropical Cyclones

Favorable environmental conditions and possible intrinsic mechanisms for the secondary eyewall formation (SEF) in tropical cyclones have been suggested and investigated extensively in the past few decades. In the western North Pacific, satellite data reported that a substantial portion of the intense typhoons exhibited the concentric eyewall structure. The rest of the intense typhoons had either a single eyewall throughout their lifetime or concentric eyewalls that were not sampled by the imaging swath of satellites. Alternatively, it is of interest to explore why an intense typhoon does not experience SEF. The Advanced Research WRF (Weather Research and Forecasting) model is used to reproduce numerical simulations of typhoons of interest. The external conditions and internal dynamics during the intensifying stage of the storms, which do not undergo SEF, are investigated and compared with the possible pathways to SEF proposed in the literature. This study also aims to design proper thought experiments to examine if SEF could be triggered by prescribed momentum or heating forcings.