The role of interactive SST in the cloud‐resolving simulations of aggregated convection

This study investigates the role of interactive sea surface temperature (SST) in the early development of aggregated convection using a vector vorticity equation cloud-resolving model coupled to a slab ocean. The simulations are initialized by a mock Walker circulation driven by initial SST gradient in the elongated x axis, with an average of 300 K and sinusoidal variation of amplitude ranging from 1.5 to 3 K. According to large-scale perturbation strength, which is caused by SST variation, the results can be divided into two groups. Under weak perturbation, convection-SST feedback efficiently eliminates SST gradient and moisture anomaly. The large-scale environment is homogenized within 2 days. Even though SST in the group with stronger perturbation undergoes a similar process, significant moist static energy (MSE) advection in the boundary produces enough moisture difference to introduce virtual temperature effect and aggregation is triggered. Once dry zone starts to expand, radiative and convective effects regenerate SST gradient, which intensifies circulation and accelerates the process. We further show that the evolution of aggregation or not is captured by the trend of MSE-EIS (estimated inversion strength) variance. The results highlight the boundary layer processes on the formation of aggregated convection in the tropics. Plain Language Summary In an idealized numerical simulation of deep convection over the tropical region, the clouds can sometimes develop into a large organized moist patch surrounded by dry air. This process is called convective aggregation and is believed to have profound implication for the climate system. In this study, the authors investigate the development of convective aggregation when the air-sea exchanges of energy are considered. In this scenario, the deep clouds can block the solar radiation and cools the sea surface temperature, prohibiting the develop of convection. On the other hand, it can heat the ocean when there are no clouds, promoting further development of convection. The authors showed that when the above process dominates, there will be no convective aggregation. They showed that it is necessary to focus on the atmosphere stability near the surface over the regions of no clouds for the convective aggregation.