Effects of Under-Resolved Convective Dynamics on the Evolution of a Squall Line

doi:10.1175/MWR-D-19-0187.1

Title: Effects of Under-Resolved Convective Dynamics on the Evolution of a Squall Line

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Abstract

Simulations of a squall line observed on 20 May 2011 during the Midlatitude Continental Convective Clouds Experiment (MC3E) using 750- and 250-m horizontal grid spacing are performed. The higher-resolution simulation has less upshear-tilted deep convection and a more elevated rear inflow jet than the coarser-resolution simulation in better agreement with radar observations. A stronger cold pool eventually develops in the 250-m run; however, the more elevated rear inflow counteracts the cold pool circulation to produce more upright convective cores relative to the 750-m run. The differing structure in the 750-m run produces excessive midlevel front-to-rear detrainment, reinforcing excessive latent cooling and rear inflow descent at the rear of the stratiform region in a positive feedback. The contrasting mesoscale circulations are connected to early stage deep convective draft differences in the two simulations. Convective downdraft condensate mass, latent cooling, and downward motion all increase with downdraft area similarly in both simulations. However, the 750-m run has a relatively greater number of wide and fewer narrow downdrafts than the 250-m run averaged to the same 750-m grid, a consequence of downdrafts being under-resolved in the 750-m run. Under-resolved downdrafts in the 750-m run are associated with under-resolved updrafts and transport mid–upper-level zonalmore »« less

Authors:

^[1]; Morrison, Hugh ^[2]; Zipser, Edward ^[3]

Pacific Northwest National Laboratory, Richland, Washington
National Center for Atmospheric Research, Boulder, Colorado
University of Utah, Salt Lake City, Utah

Publication Date:: 2020-01-01

Sponsoring Org.:: USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)

OSTI Identifier:: 1580005

Grant/Contract Number:: SC0008678; SC0016476

Resource Type:: Published Article

Journal Name:: Monthly Weather Review

Additional Journal Information:: Journal Name: Monthly Weather Review Journal Volume: 148 Journal Issue: 1; Journal ID: ISSN 0027-0644

Publisher:: American Meteorological Society

Country of Publication:: United States

Language:: English

Citation Formats


                    Varble, Adam, Morrison, Hugh, and Zipser, Edward. Effects of Under-Resolved Convective Dynamics on the Evolution of a Squall Line.  United States: N. p., 2020. 
        Web.  doi:10.1175/MWR-D-19-0187.1.

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                    Varble, Adam, Morrison, Hugh, & Zipser, Edward. Effects of Under-Resolved Convective Dynamics on the Evolution of a Squall Line.  United States.  doi:10.1175/MWR-D-19-0187.1.

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                    Varble, Adam, Morrison, Hugh, and Zipser, Edward. Wed .  
        "Effects of Under-Resolved Convective Dynamics on the Evolution of a Squall Line".  United States.  doi:10.1175/MWR-D-19-0187.1.

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@article{osti_1580005,

  title        = {Effects of Under-Resolved Convective Dynamics on the Evolution of a Squall Line},

  author       = {Varble, Adam and Morrison, Hugh and Zipser, Edward},

  abstractNote = {Simulations of a squall line observed on 20 May 2011 during the Midlatitude Continental Convective Clouds Experiment (MC3E) using 750- and 250-m horizontal grid spacing are performed. The higher-resolution simulation has less upshear-tilted deep convection and a more elevated rear inflow jet than the coarser-resolution simulation in better agreement with radar observations. A stronger cold pool eventually develops in the 250-m run; however, the more elevated rear inflow counteracts the cold pool circulation to produce more upright convective cores relative to the 750-m run. The differing structure in the 750-m run produces excessive midlevel front-to-rear detrainment, reinforcing excessive latent cooling and rear inflow descent at the rear of the stratiform region in a positive feedback. The contrasting mesoscale circulations are connected to early stage deep convective draft differences in the two simulations. Convective downdraft condensate mass, latent cooling, and downward motion all increase with downdraft area similarly in both simulations. However, the 750-m run has a relatively greater number of wide and fewer narrow downdrafts than the 250-m run averaged to the same 750-m grid, a consequence of downdrafts being under-resolved in the 750-m run. Under-resolved downdrafts in the 750-m run are associated with under-resolved updrafts and transport mid–upper-level zonal momentum downward to low levels too efficiently in the early stage deep convection. These results imply that under-resolved convective drafts in simulations may vertically transport air too efficiently and too far vertically, potentially biasing buoyancy and momentum distributions that impact mesoscale convective system evolution.},

  doi          = {10.1175/MWR-D-19-0187.1},

  journal      = {Monthly Weather Review},

  number       = 1,

  volume       = 148,

  place        = {United States},

  year         = {2020},

  month        = {1}

}

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