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Untangling Dynamical and Microphysical Controls of Convective Updraft Vertical Velocity: Insights from a Lagrangian Perspective

Active Dates 9/1/2023-8/31/2026
Program Area Atmospheric System Research
Project Description
Convective systems are a fundamental component of the Earth system through their role in transporting heat, moisture, aerosols, and momentum. The characteristics and intensity of convection are fundamentally linked to the vertical velocity within clouds. High vertical velocity generates high supersaturation inside clouds, allowing a more significant fraction of cloud condensation nuclei to be activated into cloud droplets. Strong vertical velocities also enhance ice particle growth and are an important feature of hail- and lightning-generating severe weather. It is therefore of utmost importance to understand the controlling factors of convective vertical motions.

Despite decades of research into convective systems, many aspects regarding updraft vertical velocity remain poorly understood, including how it is controlled by different interactions (e.g., dynamics-microphysics, dynamics-environment, and dynamics-boundary layer interactions). This incomplete knowledge limits our ability to forecast deep convection adequately and faithfully represent its effects in large-scale models, undermining models’ credibility for future climate projections. Our limited understanding is first due to lacking observational constraints, where reliable measurements of updraft properties and environment are sparse, making validation of theories or model results difficult. The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Tracking Aerosol Convection Interactions Experiment (TRACER) field campaign, during which convective systems and their associated dynamical and microphysical properties were extensively sampled over Houston, Texas provides a great solution to the observation issue. The other long-standing obstacle is that, in highly coupled convective systems, too many factors interfere with updraft dynamics-microphysics feedback and cloud-environment interactions, making causal inferences difficult. We thus propose to adopt novel Lagrangian modeling and analysis techniques to decouple the multivariant confounding and find clear causal links behind those interactions. With this approach, we aim to answer the following essential questions:

Q1. What mechanisms (warm-phase, cold-phase, change in relative humidity) primarily drive the aerosol-related convective invigoration (updraft dynamics-microphysics interaction)?

Q2. How is convective invigoration influenced by other processes, such as entrainment mixing (updraft dynamics-environment interaction)?

Q3. How do environmental and boundary layer processes such as the sea breeze affect the convective initiation and cloud base updraft velocity variability (updraft dynamics-boundary layer interaction)?

We will address our science questions by extensively using ARM TRACER observations, and analyze the interactions that affect updraft velocity primarily through the lens of a Lagrangian perspective. We will use idealized large eddy simulation (LES) simulations, combined with a newly developed Lagrangian cloud microphysics scheme (Super-droplet Method, SDM) to quantify entrainment mixing in a novel way, extensively explore microphysical and dynamical processes behind convective invigoration, and determine how entrainment affects invigoration in the same framework. We will also use Lagrangian particle tracking capacity to quantify the influence of sea breeze on cloud base updraft velocity, both dynamically and thermodynamically, and determine the role this circulation has in initialing convection and contributing to cloud base updraft velocity variability.

Our proposed work will carve out a new path to disentangle the roles of interfering factors in complex interactions. Following this path, we expect to sort out the dynamical and microphysical controls on updraft velocity in convective systems and build up a novel observation-modeling-analysis pipeline, shedding light on the design of convection and cloud microphysics schemes for next-generation climate models. This framework can significantly help understand and predict weather and extreme events in Houston and can be generalized to other coastal cities where the world’s most dense population resides.
Award Recipient(s)
  • University Corporation for Atmospheric Research (PI: Tian, Yang)