The Influence of Shear on Deep Convection Initiation. Part II: Simulations

Journal Article · 31 May 2022 · Journal of the Atmospheric Sciences

DOI: https://doi.org/10.1175/JAS-D-21-0144.1 · OSTI ID:1870928

Peters, John M. ^[1]; Morrison, Hugh ^[2]; Nelson, T. Connor ^[3]; Marquis, James N. ^[4]; Mulholland, Jake P. ^[1]; Nowotarski, Christopher J. ^[5]

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1. a Department of Meteorology, Naval Postgraduate School, Monterey, California
2. b National Center for Atmospheric Research, Boulder, Colorado
3. c Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, Colorado
4. d Pacific Northwest National Laboratory, Richland, Washington
5. e Department of Atmospheric Science, Texas A&M University, College Station, Texas

Abstract This study evaluates a hypothesis for the role of vertical wind shear in deep convection initiation (DCI) that was introduced in Part I by examining behavior of a series of numerical simulations. The hypothesis states, “Initial moist updrafts that exceed a width and shear threshold will ‘root’ within a progressively deeper steering current with time, increase their low-level cloud-relative flow and inflow, widen, and subsequently reduce their susceptibility to entrainment-driven dilution, evolving toward a quasi-steady self-sustaining state.” A theoretical model that embodied key elements of the hypothesis was developed in Part I, and the behavior of this model was explored within a multidimensional environmental parameter space. Remarkably similar behavior is evident in the simulations studied here to that of the theoretical model, both in terms of the temporal evolution of DCI and in the sensitivity of DCI to environmental parameters. Notably, both the simulations and theoretical model experience a bifurcation in outcomes, whereby nascent clouds that are narrower than a given initial radius R ₀ threshold quickly decay and those above the R ₀ threshold undergo DCI. An important assumption in the theoretical model, which states that the cloud-relative flow of the background environment V _CR determines cloud radius R , is scrutinized in the simulations. It is shown that storm-induced inflow is small relative to V _CR beyond a few kilometers from the updraft edge, and V _CR therefore plays a predominant role in transporting conditionally unstable air to the updraft. Thus, the critical role of V _CR in determining R is validated.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-76RL01830; SC0020104
• OSTI ID: 1870928
• Report Number(s): PNNL-SA-162701
• Journal Information: Journal of the Atmospheric Sciences, Journal Name: Journal of the Atmospheric Sciences Journal Issue: 6 Vol. 79; ISSN 0022-4928
• Publisher: American Meteorological SocietyCopyright Statement
• Country of Publication: United States
• Language: English