The coupling between shallow trade wind cumulus clouds and sub-cloud processes is not well understood and remains one of the roadblocks to improving our climate modelling capability. As model resolution increases, the steady-state assumption adopted in conventional convection schemes no longer holds and the knowledge about the evolution of clouds is necessary to improve the parameterization. Observations have provided evidence of sub-cloud coherent updrafts being the roots of shallow clouds, but it is currently not practical to continuously detect how the shallow clouds evolve alongside the sub-cloud coherent structures. In this study, we develop a novel approach to detect cloud-subcloud coupling during the cloud life cycle and analyse a large eddy simulation of marine shallow cumulus based on the BOMEX campaign. Our results demonstrate how the activity of sub-cloud coherent updrafts (SCUs) affect the evolution of shallow cloud properties during their life cycles, from triggering to development, and through to dissipation. Most clouds (~80%) are related to SCUs during their lifetime but not every SCU (~20% for short-lived ones) leads to cloud formation. The fastest growing SCUs in a relatively moist region are most likely to initiate clouds. The evolution of cloud base mass-flux depends on cloud lifetime. Compared with short-lived clouds, longer lived clouds have longer periods of development, even normalized by the full lifetime, and tend to increase their cloud base mass-flux to a stronger maximum. This is consistent with the evolution of mass flux near the top of SCU, indicating that the development of clouds is closely related to the sub-cloud activity. When the SCUs decay and detach from the lifting condensation level, the corresponding cloud base starts to rise, signifying the start of cloud dissipation, during which the cloud top lowers to approach the rising cloud base. Previous studies have described similar conceptual pieces of this relationship but here we provide a continuous framework to cover all the stages of cloud-subcloud coupling. Our study takes a step forward to demonstrate how the sub-cloud coherent structures interact with the shallow clouds. The comprehensive physical picture of the whole cloud life cycle uncovered in this study provides useful insights to improve the representation of cloud evolution in convection parameterizations with an explicit treatment of the cloud life cycle in the future.

cloud life cycle,shallow cumulus clouds;,sub-cloud coherent updrafts;