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Seminar coordinator for Spring 2024 is Professor Deanna Hence: dhence@illinois.edu

Seminar - Luke Allen - Quantifying Entrainment and Dilution in Simulated Developing Thunderstorms

Event Type
Seminar/Symposium
Sponsor
Department of Atmospheric Sciences
Location
2079 Natural History Building
Date
Mar 31, 2020   3:30 pm  
Speaker
Like Allen
Contact
Joe Jeffries
E-Mail
jeffris2@illinois.edu
Phone
217-300-3024
Views
9

abstract:

Entrainment and mixing processes have long been known to occur in cumulus clouds, but remain poorly understood in many regards. These processes can reduce cloud liquid water content through evaporation, which can suppress buoyancy, precipitation output, and cloud vertical development. In particular, studies of deep convection and the transition from shallow to deep convection have not considered entrainment in great detail. Furthermore, the relationship between vertical wind shear, entrainment, and developing convection is not understood well. Recent work has shown that simulated storms entrain more in a strong-shear environment than one with no background wind; however, work by other investigators has indicated that entrainment is not the mechanism limiting convective growth in strong-shear environments. Here, idealized simulations of developing thunderstorms are conducted in a variety of wind shear environments with the goal of better understanding the role of entrainment in developing thunderstorms. The link between entrainment and dilution (i.e. reduction in cloud water content and/or buoyancy) is an important focus, as prior work often used dilution to imply entrainment. Rather than inferring entrainment from dilution, entrainment is directly calculated here as the mass flux across a cloud core surface defined by thresholds in vertical velocity and liquid water content. In general, more entrainment is found in simulations initialized with greater vertical wind shear. However, differences in dilution between simulations are less clear, implying that entrainment may not substantially affect storm development, but this requires further investigation.

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