Bolei Yang, William R. Boos , Ji Nie

In real-world observations, long-lived tropical mesoscale convective clusters (TMCCs) often exhibit quasi-periodic oscillations. Previous studies have suggested that these oscillations can be induced by external forcings. However, many idealized simulations provided evidence that TMCCs can display quasi-periodic behavior even without external forcings. Through this study, it is demonstrated that all TMCCs possess an inherent internal oscillation, and the physics behind is a convectively coupled inertia-gravity oscillation. When deep convection within a TMCC decays, the stratiform heating within the system triggers an inertia-gravity oscillation. This oscillation induces upward motion at lower levels of the disturbance, which facilitates the recovery of low-level buoyancy and initiates new convection. Notably, in this oscillation, diabatic heating serves not only as a consequence of the preceding oscillation but also as the source for the subsequent oscillation. The internal oscillation acts as a fundamental component in the life cycle of long-lived TMCCs, providing clearer physical intuition for understanding the variation of TMCCs in real-world scenarios.