The Energetics of the Lagrangian Evolution of Tropical Convective Systems

Abstract

Convective lifecycle is often conceptualized to progress from congestus to deep convection and develop further to stratiform anvil clouds, accompanied by a systematic change in the vertical structure of vertical motion. This archetype scenario has been developed largely from the Eulerian viewpoint, and has yet to be explored whether or not the same lifecycle emerges itself in a moving system tracked in the Lagrangian manner. To address this question, Lagrangian tracking is applied to tropical convective systems in combination with a thermodynamic budget analysis forced by satellite-retrieved precipitation and radiation. A new method is devised to characterize the vertical motion profiles in terms of the column import or export of moisture and moist static energy (MSE). The Bottom-heavy, Mid-heavy, and Top-heavy regimes are identified for every one-square-degree grid pixel accompanying tracked precipitation systems, making use of the diagnosed column export/import of moisture and MSE. Major findings are as follows. The Lagrangian evolution of convective systems is dominated by a state of dynamic equilibrium among different convective regimes rather than a monotonic progress from one regime to the next. The transition from the Bottom-heavy to Mid-heavy regimes is fed with intensifying precipitation presumably owing to a negative gross moist stability (GMS) of the Bottom-heavy regime, whereas the transition from the Mid-heavy to Top-heavy regimes dissipates the system. The Bottom-heavy to Mid-heavy transition takes a relaxation time of about 5 h in the equilibrating processes, whereas the relaxation time is estimated as roughly 20 h concerning the Mid-heavy to Top-heavy transition.