Scale-dependence of tropical oceanic deep convective systems’ cloud shield morphology to environmental conditions

In the tropics, a significant portion of precipitation originates from deep convective systems (DCS), which are composed of convective cells organized in both space and time. These systems are characterized by upper-level cloud shields made up of high-altitude, ice-topped clouds that form cohesive and recognizable structures, easily identifiable in satellite imagery. These cloud shields vary widely in spatial and temporal scales, ranging from a few dozen to millions of square kilometers and lasting from a few hours to several days. Due to their ubiquity over tropical oceans, these cloud shields play a critical role in the Earth's radiation budget and influence related climatic feedbacks. However, their potential morphological changes in response to climate change remain poorly understood.

In this study, we analyze the sensitivity of the cloud shield morphology to environmental conditions using a comprehensive dataset spanning nine years of satellite observations over the entire tropical ocean. By combining this dataset with the recent ECMWF reanalysis, we build robust statistics to explore the relationship between cloud shield morphology and environmental factors. Our focus is on a specific dimension of this complex problem: investigating how the thermodynamic and dynamic environment influences the morphology of the cloud shield. This work advances previous studies by encompassing the full spectrum of deep convective systems (DCS), rather than focusing solely on mesoscale convective systems (MCS). Moreover, we emphasize the cloud shield characteristics of these systems, going beyond the traditional focus on precipitation features morphology. Multilinear regression between DCS morphology and environment is used in a 2D phase space linked to the life cycle of the systems, namely the time to reach the maximum extension and the associated maximum area.

In this presentation, we will show that dynamical drivers exert stronger morphological control than the thermodynamic factors. The result reveals an overwhelming role for wind shear over a deep tropospheric layer in explaining the scale dependence of cloud shield morphology. In particular, the variability of the shield growth rate is very well explained by deep layer shear. The depth of the systems is also strongly related to dynamics and secondly to water vapor loading. These results feed the debate on the relative role of deep- vs. low-level shear in influencing deep convection.