Trade Cumulus Dynamics in a Lagrangian view, revealing hidden order

Non-precipitating marine trade cumulus (TrCu) fields often appear sparse and disorganized, suggesting weak cloud–cloud interaction and localized plume-triggered formation. But is it really the case?

Unlike stratocumulus decks, for which clouds continuously trace boundary-layer circulation, TrCu clouds are intermittent and short-lived, so instantaneous cloud snapshots undersample the underlying dynamics. Using large-eddy simulations, we show that when cloud core locations are corrected for advection in a Lagrangian frame and accumulated over several hours, a persistent cellular convective “machinery” emerges beneath the apparent disorder. These steady convective cells are long-lived and form the dynamical backbone of the cloud field. Cloud formation repeatedly initiates along their updraft walls, so the recovered cellular pattern predicts where clouds recur despite strong intermittency aloft. This reframes sparse trade cumulus as a deterministic organization imposed from below and provides a physically grounded route toward organization-aware parameterizations.