Investigating Microphysical and Dynamical Processes Controlling Convective Cloud Characteristics and Lifecycle Within Different Aerosol and Ambient Environments

Abstract

Deep convective clouds are found throughout the tropics and midlatitudes, vary in structure from isolated to highly organized systems, and play a vital role in the Earth’s energy and water budgets and climate system. Convective cloud systems are composed of individual convective cells, with small spatial (<1 km to a few tens of km) and temporal (minutes to hours) scales, that control formation and maintenance mechanisms of deep convective systems. Despite the importance of convective cell lifecycles in weather and climate, they remain poorly understood, difficult to measure, and are challenging to accurately represent in our numerical weather prediction models. This is likely due to the complexities of microphysical and dynamical processes that change rapidly, interact with each other, and are influenced by aerosols and atmospheric environments. Our recent model intercomparison study from aerosol sensitivity experiments of deep convection has also revealed large variability in modeled precipitation as a function of both storm morphology and model type and demonstrated indirect effects of aerosols on the updraft dynamics in mixed and cold phases. We will need deeper assessment of the lifecycle of convective cells to enhance our understanding of the processes leading to variability in these clouds.

The following three science questions of the proposed study continue to focus on the processes dictating convective cell lifecycles:

• (SQ1) How do the fundamental characteristics of convective cells evolve throughout the convective lifecycle?;
• (SQ2) How does aerosol loading impact the microphysical and dynamical processes of convective cells and the resulting cell characteristics over the cell lifecycle?; and
• (SQ3) How does variability in the ambient environment impact the characteristics of convective cell evolution and modulate the aerosol effects?

These SQs will be addressed through the use of dense observations of convective cell lifecycle and aerosols around the Houston area collected during the TRacking Aerosol Convection Interactions ExpeRiment (TRACER). We will focus on rapid evolution of cell characteristics and interactions between cloud processes and aerosols, using the frequent vertical scans from radar measurements and cloud-system resolving models that highlight a synergistic model observation framework from the TRACER model intercomparison products. The observational and modeling analysis will be extended to northwestern Alabama with data from the ARM deployment at the Bankhead National Forest (BNF). Each science question has two associated objectives. SQ1 is investigated by characterizing convective cells as a function of cell lifetime using radar observations during TRACER and characterizing the convective cells by identifying the predominant microphysical and dynamical processes as a function of cell lifetime using high-resolution cloud-resolving model simulations. SQ2 is addressed by investigating the cell characteristics and lifecycle within different aerosol environments using the TRACER data and quantifying the changes in warm, mixed, and ice phase cloud characteristics, the associated microphysical processes, and their feedbacks to vertical air motion, associated with aerosol changes, using the model simulations of selected TRACER case study events. Finally, SQ3 is clarified by investigating how the environmental factors influence the cell characteristics and aerosol impacts on cell evolution using TRACER and BNF observations and investigating how the environmental factors influence the cell characteristics and aerosol impacts on microphysical and dynamical evolution, using TRACER and BNF high resolution cloud resolving model simulations.

It is expected that the cell characteristics revealed in this study and the proposed analysis techniques may be broadly applicable toward convective clouds in other regions in the world. This will further lead to improvement of convective parameterizations in regional/global models and the evaluation of aerosol-cloud processes in cloud-resolving models and provide preliminary measurements and analysis for evaluation and optimization of the future satellite radar missions.