The Sensitivity of Cumulus Congestus Lifecycles and Behavior to Static Stability and Aerosol Loading within the CAMP2Ex Environment

Cumulus congestus clouds have been recognized as an important tropical convective cloud mode for over 20 years. These clouds benefit from and contribute to environmental heat and moisture preconditioning in the context of upscale convective growth. Each of the 3 tropical convective modes are bounded by a stable layer in the tropical-mean thermodynamic profile, and congestus are impacted by both the freezing and trade wind stable layers. Beyond environmental thermodynamics, the aerosol properties of the bulk environment also impact congestus. Aerosol effects on cloud droplet concentrations are well-known to result in more numerous, smaller cloud droplets when aerosol loading is higher, with the few aerosol studies on congestus showing warm-phase dynamical enhancement due to aerosol indirect effects. However, the relative impacts of simultaneously perturbing low-level thermodynamics and aerosols, and the effects of each on different stages of congestus evolution, have not yet been explored. Our research goal is, thus, to examine the lifecycles of congestus, and determine how the cloud properties at different stages in their evolution differ as both environmental stability and aerosol concentrations are perturbed. Our goal is addressed using a suite of large eddy simulations and observations of congestus in a variety of thermodynamic and aerosol conditions that were collected around the Philippines during the recent NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex). The simulations are conducted using the Regional Atmospheric Modeling System (RAMS) with initial thermodynamic and aerosol environments similar to those observed in CAMP2Ex. These data are used with a modified version of the Tracking and Object-Based Analysis of Clouds (tobac) tool to objectively identify, track, and classify congestus clouds at different stages in their evolution. The 3 convective modes are then grouped by morphological similarities, and congestus characteristics such as longevity, dynamical structure, and microphysical properties are contrasted in the context of stability and aerosol impacts. Results indicate a stronger aerosol impact, and that moderate stability and aerosol favor congestus longevity and glaciation, whereas higher values of each suppress these qualities.