Editorial Type:
Article
Article Type:
Research Article

Cooling of Entrained Parcels in a Large-Eddy Simulation

Takanobu Yamaguchi Cooperative Institute for Research in Environmental Sciences, University of Colorado, and NOAA/Earth System Research Laboratory, Boulder, Colorado

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David A Randall Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

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Print Publication:
01 Mar 2012
DOI:
https://doi.org/10.1175/JAS-D-11-080.1
Page(s):
1118–1136
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Abstract

The relative importance, for cloud-top entrainment, of the cooling rates due to longwave radiation, evaporation, and mixing was assessed through analysis of the results produced by a Lagrangian parcel-tracking model (LPTM) incorporated into a large-eddy simulation model. The LPTM predicts each parcel’s trajectory over time, using the resolved velocity simulated by the host model. An LPTM makes it possible to identify entrained parcels; this is almost impossible to do in an observational study.

A nocturnal stratocumulus cloud was simulated over 4h using a 5-m horizontal grid spacing and a 2.5-m vertical grid spacing. At the start of the last hour of the simulation, over 40 million parcels were placed near the top of the inversion layer and then tracked. Parcel histories were analyzed to identify entrained parcels.

Entrainment occurs in cloud holes, which occur in dry regions of sinking air. Entrainment into the mixed layer is regulated by buoyancy, which requires parcels to be precooled in the inversion layer, prior to entrainment. A mixing fraction analysis was used to separate the cooling due to longwave radiation, evaporation, and mixing. Results show that radiative and evaporative cooling are of comparable importance, but that mixing is by far the dominant cooling mechanism. The radiative cooling rate is strongly inhomogeneous, and only weak radiative cooling is found in regions of entrainment. Therefore, the entrained parcels experience less than the horizontal-mean radiative cooling. Although radiative cooling maintains the boundary layer turbulence, its direct effect on buoyancy of entrained parcels is modest.

Corresponding author address: Takanobu Yamaguchi, NOAA/Earth System Research Laboratory (ESRL)/Chemical Science Division (R/CSD2), 325 Broadway, Boulder, CO 80305. E-mail: tak.yamaguchi@noaa.gov

Abstract

The relative importance, for cloud-top entrainment, of the cooling rates due to longwave radiation, evaporation, and mixing was assessed through analysis of the results produced by a Lagrangian parcel-tracking model (LPTM) incorporated into a large-eddy simulation model. The LPTM predicts each parcel’s trajectory over time, using the resolved velocity simulated by the host model. An LPTM makes it possible to identify entrained parcels; this is almost impossible to do in an observational study.

A nocturnal stratocumulus cloud was simulated over 4h using a 5-m horizontal grid spacing and a 2.5-m vertical grid spacing. At the start of the last hour of the simulation, over 40 million parcels were placed near the top of the inversion layer and then tracked. Parcel histories were analyzed to identify entrained parcels.

Entrainment occurs in cloud holes, which occur in dry regions of sinking air. Entrainment into the mixed layer is regulated by buoyancy, which requires parcels to be precooled in the inversion layer, prior to entrainment. A mixing fraction analysis was used to separate the cooling due to longwave radiation, evaporation, and mixing. Results show that radiative and evaporative cooling are of comparable importance, but that mixing is by far the dominant cooling mechanism. The radiative cooling rate is strongly inhomogeneous, and only weak radiative cooling is found in regions of entrainment. Therefore, the entrained parcels experience less than the horizontal-mean radiative cooling. Although radiative cooling maintains the boundary layer turbulence, its direct effect on buoyancy of entrained parcels is modest.

Corresponding author address: Takanobu Yamaguchi, NOAA/Earth System Research Laboratory (ESRL)/Chemical Science Division (R/CSD2), 325 Broadway, Boulder, CO 80305. E-mail: tak.yamaguchi@noaa.gov

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  • Ackerman, A. S., and Coauthors, 2009: Large-eddy simulations of a drizzling, stratocumulus-topped marine boundary layer. Mon. Wea. Rev., 137, 1083–1110.

    • Search Google Scholar
    • Export Citation

  • Albrecht, B. A., R. S. Penc, and W. H. Schubert, 1985: An observational study of cloud-topped mixed layers. J. Atmos. Sci., 42, 800–822.

    • Search Google Scholar
    • Export Citation

  • Bretherton, C. S., and Coauthors, 1999: An intercomparison of radiatively driven entrainment and turbulence in a smoke cloud, as simulated by different numerical models. Quart. J. Roy. Meteor. Soc., 125, 391–423.

    • Search Google Scholar
    • Export Citation

  • Bryan, G. H., J. C. Wyngaard, and J. M. Fritsch, 2003: Resolution requirements for the simulation of deep moist convection. Mon. Wea. Rev., 131, 2394–2416.

    • Search Google Scholar
    • Export Citation

  • Caldwell, P., and C. S. Bretherton, 2009: Large eddy simulation of the diurnal cycle in southeast Pacific stratocumulus. J. Atmos. Sci., 66, 432–449.

    • Search Google Scholar
    • Export Citation

  • Cheng, A., and K.-M. Xu, 2009: A PDF-based microphysics parameterization for simulation of drizzling boundary layer clouds. J. Atmos. Sci., 66, 2317–2334.

    • Search Google Scholar
    • Export Citation

  • Cheng, A., K.-M. Xu, and B. Stevens, 2010: Effects of resolution on the simulation of boundary-layer clouds and the partition of kinetic energy to subgrid scales. J. Adv. Model. Earth Syst., 2 (3), doi:10.3894/JAMES.2010.2.3.

    • Search Google Scholar
    • Export Citation

  • Deardorff, J. W., 1980: Cloud top entrainment instability. J. Atmos. Sci., 37, 131–147.

  • de Roode, S., and Q. Wang, 2007: Do stratocumulus clouds detrain? FIRE I data revisited. Bound.-Layer Meteor., 122, 479–491.

  • Feingold, G., I. Koren, H. Wang, H. Xue, and W. A. Brewer, 2010: Precipitation-generated oscillations in open cellular cloud fields. Nature, 466, 849–852.

    • Search Google Scholar
    • Export Citation

  • Gerber, H., G. Frick, S. P. Malinowski, J. L. Brenguier, and F. Burnet, 2005: Holes and entrainment in stratocumulus. J. Atmos. Sci., 62, 443–459.

    • Search Google Scholar
    • Export Citation

  • Harrington, J. Y., G. Feingold, and W. R. Cotton, 2000: Radiative impacts on the growth of a population of drops within simulated summertime arctic stratus. J. Atmos. Sci., 57, 766–785.

    • Search Google Scholar
    • Export Citation

  • Heus, T., G. van Dijk, H. J. J. Jonker, and H. E. A. Van den Akker, 2008: Mixing in shallow cumulus clouds studied by Lagrangian particle tracking. J. Atmos. Sci., 65, 2581–2597.

    • Search Google Scholar
    • Export Citation

  • Hill, A. A., G. Feingold, and H. Jiang, 2009: The influence of entrainment and mixing assumption on aerosol–cloud interactions in marine stratocumulus. J. Atmos. Sci., 66, 1450–1464.

    • Search Google Scholar
    • Export Citation

  • Khairoutdinov, M. F., and D. A. Randall, 2003: Cloud resolving modeling of the ARM summer 1997 IOP: Model formulation, results, uncertainties, and sensitivities. J. Atmos. Sci., 60, 607–625.

    • Search Google Scholar
    • Export Citation

  • Khairoutdinov, M. F., S. K. Krueger, C.-H. Moeng, P. A. Bogenschutz, and D. A. Randall, 2009: Large-eddy simulation of maritime deep tropical convection. J. Adv. Model. Earth Syst., 1 (15), doi:10.3894/JAMES.2009.1.15.

    • Search Google Scholar
    • Export Citation

  • Krueger, S. K., G. T. McLean, and Q. Fu, 1995: Numerical simulation of the stratus-to-cumulus transition in the subtropical marine boundary layer. Part II: Boundary-layer circulation. J. Atmos. Sci., 52, 2851–2868.

    • Search Google Scholar
    • Export Citation

  • Kuo, H.-C., and W. H. Schubert, 1988: Stability of cloud-topped boundary layers. Quart. J. Roy. Meteor. Soc., 114, 887–916.

  • Kurowski, M. J., S. P. Malinowski, and W. W. Grabowski, 2009: A numerical investigation of entrainment and transport within a stratocumulus-topped boundary layer. Quart. J. Roy. Meteor. Soc., 135, 77–92.

    • Search Google Scholar
    • Export Citation

  • Leonard, B. P., 1991: The ULTIMATE conservative difference scheme applied to unsteady one-dimensional advection. Comput. Methods Appl. Mech. Eng., 88, 17–74.

    • Search Google Scholar
    • Export Citation

  • Lilly, D. K., 1968: Models of cloud-topped mixed layers under a strong inversion. Quart. J. Roy. Meteor. Soc., 94, 292–309.

  • Lin, C., and A. Arakawa, 1997: The macroscopic entrainment processes of simulated cumulus ensemble. Part I: Entrainment sources. J. Atmos. Sci., 54, 1027–1043.

    • Search Google Scholar
    • Export Citation

  • Lock, A. P., 2009: Factors influencing cloud area at the capping inversion for shallow cumulus clouds. Quart. J. Roy. Meteor. Soc., 135, 941–952.

    • Search Google Scholar
    • Export Citation

  • Mlawer, E. J., S. J. Taubman, P. D. Brown, M. J. Iacono, and S. A. Clough, 1997: Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave. J. Geophys. Res., 102 (D14), 16 663–16 682.

    • Search Google Scholar
    • Export Citation

  • Moeng, C.-H., and Coauthors, 1996: Simulation of a stratocumulus-topped planetary boundary layer: Intercomparison among different numerical codes. Bull. Amer. Meteor. Soc., 77, 261–278.

    • Search Google Scholar
    • Export Citation

  • Moeng, C.-H., P. P. Sullivan, M. F. Khairoutdinov, and D. A. Randall, 2010: A mixed scheme for subgrid-scale fluxes in cloud-resolving models. J. Atmos. Sci., 67, 3692–3705.

    • Search Google Scholar
    • Export Citation

  • Monin, A. S., and A. M. Obukhov, 1954: Basic laws of turbulent mixing in the atmosphere near the ground. Tr. Akad. Nauk SSSR, 24, 163–187.

    • Search Google Scholar
    • Export Citation

  • Randall, D. A., 1976: The interaction of the planetary boundary layer with large-scale circulations. Ph.D. dissertation, University of California, Los Angeles, 247 pp.

    • Search Google Scholar
    • Export Citation

  • Randall, D. A., 1980: Conditional instability of the first kind upside-down. J. Atmos. Sci., 37, 125–130.

  • Randall, D. A., and W. H. Schubert, 2004: Dreams of a stratocumulus sleeper. Atmospheric Turbulence and Mesoscale Meteorology, E. Fedorovich, R. Rotunno, and B. Stevens, Eds., Cambridge University Press, 71–94.

    • Search Google Scholar
    • Export Citation

  • Randall, D. A., and Coauthors, 2007: Climate models and their evaluation. Climate Change 2007: The Physical Science Basis, S. Solomon et al., Eds., Cambridge University Press, 589–662.

    • Search Google Scholar
    • Export Citation

  • Savic-Jovcic, V., and B. Stevens, 2008: The structure and mesoscale organization of precipitating stratocumulus. J. Atmos. Sci., 65, 1587–1605.

    • Search Google Scholar
    • Export Citation

  • Schubert, W. H., J. S. Wakefield, E. J. Steiner, and S. K. Cox, 1979: Marine stratocumulus convection. Part I: Governing equations and horizontally homogeneous solutions. J. Atmos. Sci., 36, 1286–1307.

    • Search Google Scholar
    • Export Citation

  • Shao, Q., D. A. Randall, C. H. Moeng, and R. E. Dickinson, 1997: A method to determine the amounts of cloud-top radiative and evaporative cooling in a stratocumulus-topped boundary layer. Quart. J. Roy. Meteor. Soc., 123, 2187–2213.

    • Search Google Scholar
    • Export Citation

  • Siebesma, A. P., and Coauthors, 2003: A large eddy simulation intercomparison study of shallow cumulus convection. J. Atmos. Sci., 60, 1201–1219.

    • Search Google Scholar
    • Export Citation

  • Siems, S. T., C. S. Bretherton, M. B. Baker, S. Shy, and R. E. Breidenthal, 1990: Buoyancy reversal and cloud-top entrainment instability. Quart. J. Roy. Meteor. Soc., 116, 705–739.

    • Search Google Scholar
    • Export Citation

  • Stevens, B., and Coauthors, 2005: Evaluation of large-eddy simulations via observations of nocturnal marine stratocumulus. Mon. Wea. Rev., 133, 1443–1462.

    • Search Google Scholar
    • Export Citation

  • vanZanten, M. C., and P. G. Duynkerke, 2002: Radiative and evaporative cooling in the entrainment zone of stratocumulus—The role of longwave radiative cooling above cloud top. Bound.-Layer Meteor., 102, 253–280.

    • Search Google Scholar
    • Export Citation

  • Wang, H., and G. Feingold, 2009: Modeling mesoscale cellular structures and drizzle in marine stratocumulus. Part I: Impact of drizzle on the formation and evolution of open cells. J. Atmos. Sci., 66, 3237–3256.

    • Search Google Scholar
    • Export Citation

  • Weil, J. C., P. P. Sullivan, and C.-H. Moeng, 2004: The use of large-eddy simulations in Lagrangian particle dispersion models. J. Atmos. Sci., 61, 2877–2887.

    • Search Google Scholar
    • Export Citation

  • Xu, K.-M., and D. A. Randall, 1995: Impact of interactive radiative transfer on the macroscopic behavior of cumulus ensembles. Part I: Radiation parameterization and sensitivity tests. J. Atmos. Sci., 52, 785–799.

    • Search Google Scholar
    • Export Citation

  • Yamaguchi, T., 2010: Cloud-top entrainment analyzed with a Lagrangian parcel tracking model in large-eddy simulations. Ph.D. dissertation, Department of Atmospheric Science, Colorado State University, 115 pp.

    • Search Google Scholar
    • Export Citation

  • Yamaguchi, T., and D. A. Randall, 2008: Large-eddy simulation of evaporatively driven entrainment in cloud-topped mixed layers. J. Atmos. Sci., 65, 1481–1504.

    • Search Google Scholar
    • Export Citation

  • Yamaguchi, T., D. A. Randall, and M. F. Khairoutdinov, 2011: Cloud modeling tests of the ULTIMATE-MACHO scalar advection scheme. Mon. Wea. Rev., 139, 3248–3264.

    • Search Google Scholar
    • Export Citation

  • Zalesak, S. T., 1979: Fully multidimensional flux-corrected transport algorithms for fluids. J. Comput. Phys., 31, 335–362.

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