The research seeks to advance our understanding of internal dynamics in governing Tropical Cyclone (TC) intensification and improve forecasting skills for rapid change of TC intensity. The results and products of this project can be immediately implemented in operational models for TC prediction, disseminated to the broader TC modeling community, and used in Principal Investigator (PI)'s course teaching in TC theories and applications. The project supports a postdoctoral researcher. The educational goal of the project is to train and educate the next generation of scientists with the engagement of postdoctoral researcher and graduate/undergraduate students.The conventional view of Tropical Cyclone (TC) intensification regards the absolute angular momentum as a materially conserved quantity above the friction layer. This study seeks to demonstrate that the eddy process associated with eyewall and rainband convection serves as a sole forcing for the azimuthal-mean angular momentum conservation. It is this forcing that provides an ultimate mechanism for triggering and driving Rapid Intensification (RI) of TCs that cannot be explained by the classic TC intensification theories. At the current resolution of operational models, the PIs demonstrate that the sub-grid scale (SGS) forcing above the PBL associated with convection poses an important bearing on TC intensification, especially RI. How to generate a realistic SGS forcing aloft in the TC inner-core region is a new challenge in turbulent mixing parameterization that has not been previously explored. The most important features of this EAGER project are: (1) advance our understanding of the role of eddy forcing associated with eyewall and rainband convection in modulating intensity change of TCs and (2) develop physically robust parameterization to represent sub-grid scale forcing associated with convection above the PBL in numerical models used for TC prediction.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.