Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Adiabatic Parcel Simulations

Grabowski, Wojciech W.; Abade, Gustavo C.

doi:10.1175/JAS-D-17-0043.1

Title: Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Adiabatic Parcel Simulations

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Abstract

Abstract This paper investigates spectral broadening of droplet size distributions through a mechanism referred to as the eddy hopping. The key idea, suggested a quarter century ago, is that droplets arriving at a given location within a turbulent cloud follow different trajectories and thus experience different growth histories and that this leads to a significant spectral broadening. In this study, the adiabatic parcel model with superdroplets is used to contrast droplet growth with and without turbulence. Turbulence inside the parcel is described by two parameters: (i) the dissipation rate of the turbulent kinetic energy ε and (ii) the linear extent of the parcel L. As expected, an adiabatic parcel without turbulence produces extremely narrow droplet spectra. In the turbulent parcel, a stochastic scheme is used to account for vertical velocity fluctuations that lead to local supersaturation fluctuations for each superdroplet. These fluctuations mimic the impact of droplets hopping turbulent eddies in a natural cloud. For L smaller than a few meters, noticeable spectral broadening is possible only for strong turbulence—say, ε > 100 cm2 s−3. For L typical for grid lengths of large-eddy simulation (LES) models (say, L between 10 and 100 m), the impact is significant even with relativelymore »« less

Authors:

Grabowski, Wojciech W. ^[1]; Abade, Gustavo C. ^[2]

National Center for Atmospheric Research,a Boulder, Colorado, and Institute of Geophysics, Faculty of Physics, University of Warsaw, Warsaw, Poland
Institute of Geophysics, Faculty of Physics, University of Warsaw, Warsaw, Poland

Publication Date:: Mon Apr 24 00:00:00 EDT 2017

Sponsoring Org.:: USDOE

OSTI Identifier:: 1352726

Grant/Contract Number:: SC0016476

Resource Type:: Published Article

Journal Name:: Journal of the Atmospheric Sciences

Additional Journal Information:: Journal Name: Journal of the Atmospheric Sciences Journal Volume: 74 Journal Issue: 5; Journal ID: ISSN 0022-4928

Publisher:: American Meteorological Society

Country of Publication:: United States

Language:: English

Citation Formats


                    Grabowski, Wojciech W., and Abade, Gustavo C. Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Adiabatic Parcel Simulations.  United States: N. p., 2017. 
Web.  doi:10.1175/JAS-D-17-0043.1.

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                    Grabowski, Wojciech W., & Abade, Gustavo C. Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Adiabatic Parcel Simulations.  United States.  https://doi.org/10.1175/JAS-D-17-0043.1

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                    Grabowski, Wojciech W., and Abade, Gustavo C. Mon .  
"Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Adiabatic Parcel Simulations".  United States.  https://doi.org/10.1175/JAS-D-17-0043.1.

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@article{osti_1352726,

  title        = {Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Adiabatic Parcel Simulations},

  author       = {Grabowski, Wojciech W. and Abade, Gustavo C.},

  abstractNote = {Abstract This paper investigates spectral broadening of droplet size distributions through a mechanism referred to as the eddy hopping. The key idea, suggested a quarter century ago, is that droplets arriving at a given location within a turbulent cloud follow different trajectories and thus experience different growth histories and that this leads to a significant spectral broadening. In this study, the adiabatic parcel model with superdroplets is used to contrast droplet growth with and without turbulence. Turbulence inside the parcel is described by two parameters: (i) the dissipation rate of the turbulent kinetic energy ε and (ii) the linear extent of the parcel L. As expected, an adiabatic parcel without turbulence produces extremely narrow droplet spectra. In the turbulent parcel, a stochastic scheme is used to account for vertical velocity fluctuations that lead to local supersaturation fluctuations for each superdroplet. These fluctuations mimic the impact of droplets hopping turbulent eddies in a natural cloud. For L smaller than a few meters, noticeable spectral broadening is possible only for strong turbulence—say, ε > 100 cm2 s−3. For L typical for grid lengths of large-eddy simulation (LES) models (say, L between 10 and 100 m), the impact is significant even with relatively modest turbulence intensities. The impact increases with both L and ε. The representation of eddy hopping developed in this paper can be included in a straightforward way in the subgrid-scale scheme of a Lagrangian LES cloud model and may lead to a significant acceleration of simulated rain development through collision–coalescence.},

  doi          = {10.1175/JAS-D-17-0043.1},

  journal      = {Journal of the Atmospheric Sciences},

  number       = 5,

  volume       = 74,

  place        = {United States},

  year         = {Mon Apr 24 00:00:00 EDT 2017},

  month        = {Mon Apr 24 00:00:00 EDT 2017}

}

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