_{Plot shows the horizontal profile of (first row) column relative humidity and (second row) ocean surface temperature anomaly. Data are produced using cloud resolving model, SAM.}

The interaction between the ocean and atmosphere is a complex and dynamic process that has a significant impact on cloud formation and behavior, as well as the atmospheric boundary layer. The exchange of heat, moisture, and momentum between these two systems plays a critical role in shaping weather patterns, ocean currents, and climate. For example, the temperature of the ocean can affect the stability of the air above it, which in turn can influence the development of clouds and precipitation. In addition, the ocean serves as a major source of water vapor and energy for the atmosphere, which can have a significant impact on the structure, moisture content and behavior of clouds. Understanding these interactions between the ocean and atmosphere is essential for accurately predicting weather and climate, as well as for managing and mitigating the impacts of climate change.

Cloud and precipitation processes can also impact the ocean, creating ocean surface temperature anomalies that can persist for several hours and have a significant impact on the evolution of atmospheric boundary layer and clouds locally. For example, rain and evaporative cooling can cause a decrease in sea surface temperature and creating local negative anomalies. These anomalies can impact the stability of the air above the ocean and influence the formation and behavior of clouds. In turn, changes in the cloud and precipitation patterns can lead to further oceanic anomalies, creating a feedback loop between the two systems. Understanding these feedbacks between the ocean and atmosphere is critical for predicting and mitigating the impacts of climate change.

During my PhD, I focused on studying the interaction between the ocean surface and atmosphere, specifically how sea surface temperature (SST) anomalies affect the organization of convection using cloud-resolving simulations. One of my studies showed that a warm SST anomaly, also known as a hot spot, can significantly accelerate the organization of convection by generating a local circulation that creates convergence of moisture towards the hot spot, making it a favorable environment for future convection and precipitation. The strength of the large-scale circulation is determined by the hot spot’s fractional area and its temperature anomaly.

In another work I investigated the feedbacks between interactive SST and the self-aggregation of deep convective clouds. I found that the interactive SST decelerates the aggregation and that the deceleration is larger with a shallower ocean slab. However, the driest columns eventually have a negative SST anomaly, which strengthens the diverging shallow circulation and favors aggregation. This diverging circulation out of dry regions is well correlated with the aggregation speed and can be linked to a positive surface pressure anomaly, which itself is the consequence of SST anomalies and boundary layer radiative cooling. These findings highlight the complex and interconnected nature of ocean-atmosphere interactions and how they impact cloud formation and organization. Figure above shows the column relative humidity and SST anomaly in an coupled ocean-atmosphere set-up.

One question that has not received enough attention is whether the small-scale ocean anomalies that form due to rain evaporation and cold pool propagation need to be parameterized. Although these small anomalies may not have a significant impact on the ocean, they play a crucial role on the formation of shallow circulation, evolution and emergence of sub-grid-scale cloud structure, as well as the atmospheric boundary layer process. This would be an interesting avenue to explore!

Papers:
S. Shamekh, C. Muller, J.-P. Duvel, F. D’Andrea; JAS(2020); “How Do Ocean Warm Anomalies Favor the Aggregation of Deep Convective Clouds?“

S. Shamekh, C. Muller, J.-P. Duvel, F. D’Andrea; JAMES(2020); “Self-Aggregation of Convective Clouds With Interactive Sea Surface Temperature”

C. Muller et al, ARFM(2022); “Spontaneous aggregation of convective storms“