On the Factors Modulating the Stratocumulus to Cumulus Transitions

Irina Sandu Max Planck Institute for Meteorology, Hamburg, Germany, and European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom

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Bjorn Stevens Max Planck Institute for Meteorology, Hamburg, Germany

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Abstract

Large-eddy simulation (LES) is used to explore the role of various processes in regulating the stratocumulus to cumulus transition (SCT). Simulations are based on a composite case derived from a Lagrangian analysis of 2 yr of data from the northeastern Pacific. The simulations reproduce well the observed transition from a compact stratocumulus layer to more broken fields of cumulus, simply as a response to increasing sea surface temperatures (SSTs) along the transition. In so doing they support earlier theoretical work that argued that the SCT was a response of boundary layer circulations to increased forcing by surface latent heat fluxes. Although the basic features of the SCT imposed by the increase in SST are robust, a variety of other factors affect the detailed character of the SCT. For example, enhanced precipitation or increased downwelling longwave radiative fluxes can accelerate the reduction in cloud cover that accompanies the SCT, while a gradual decrease in the large-scale divergence can make changes in cloud cover that accompany the SCT relatively more modest. The simulations also demonstrate that the pace of the SCT is mainly set by the strength of the temperature inversion capping the initial stratocumulus-topped boundary layer.

Corresponding author address: Irina Sandu, ECMWF, Shinfield Park, Reading RG2 9AX, United Kingdom. E-mail: irina.sandu@ecmwf.int

Abstract

Large-eddy simulation (LES) is used to explore the role of various processes in regulating the stratocumulus to cumulus transition (SCT). Simulations are based on a composite case derived from a Lagrangian analysis of 2 yr of data from the northeastern Pacific. The simulations reproduce well the observed transition from a compact stratocumulus layer to more broken fields of cumulus, simply as a response to increasing sea surface temperatures (SSTs) along the transition. In so doing they support earlier theoretical work that argued that the SCT was a response of boundary layer circulations to increased forcing by surface latent heat fluxes. Although the basic features of the SCT imposed by the increase in SST are robust, a variety of other factors affect the detailed character of the SCT. For example, enhanced precipitation or increased downwelling longwave radiative fluxes can accelerate the reduction in cloud cover that accompanies the SCT, while a gradual decrease in the large-scale divergence can make changes in cloud cover that accompany the SCT relatively more modest. The simulations also demonstrate that the pace of the SCT is mainly set by the strength of the temperature inversion capping the initial stratocumulus-topped boundary layer.

Corresponding author address: Irina Sandu, ECMWF, Shinfield Park, Reading RG2 9AX, United Kingdom. E-mail: irina.sandu@ecmwf.int
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  • Albrecht, B. A., C. S. Bretherton, D. W. Johnson, W. H. Schubert, and A. S. Frisch, 1995: The Atlantic Stratocumulus Transition Experiment—ASTEX. Bull. Amer. Meteor. Soc., 76, 889904.

    • Search Google Scholar
    • Export Citation
  • Bretherton, C. S., 1992: A conceptual model of the stratocumulus-trade-cumulus transition in the subtropical oceans. Proc. 11th Int. Conf. on Clouds and Precipitation, Montreal, QC, Canada, ICCP, 374–377.

    • Search Google Scholar
    • Export Citation
  • Bretherton, C. S., and R. Pincus, 1995: Cloudiness and marine boundary layer dynamics in the ASTEX Lagrangian experiments. Part I: Synoptic setting and vertical structure. J. Atmos. Sci., 52, 27072723.

    • Search Google Scholar
    • Export Citation
  • Bretherton, C. S., and M. C. Wyant, 1997: Moisture transport, lower-troposphere stability, and decoupling of cloud-topped boundary layers. J. Atmos. Sci., 54, 148167.

    • Search Google Scholar
    • Export Citation
  • Bretherton, C. S., S. K. Krueger, M. C. Wyant, P. Bechtold, E. van Meijgaard, B. Stevens, and J. Teixeira, 1999: A GCSS boundary-layer cloud model intercomparison study of the first ASTEX Lagrangian experiment. Bound.-Layer Meteor., 93, 341380.

    • Search Google Scholar
    • Export Citation
  • De Roode, S., and P. Duynkerke, 1997: Observed Lagrangian transition of stratocumulus into cumulus during ASTEX: Mean state and turbulence structure. J. Atmos. Sci., 54, 21572173.

    • 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 I: Boundary-layer structure. J. Atmos. Sci., 52, 28392850.

    • Search Google Scholar
    • Export Citation
  • Liou, K.-N., Q. Fu, and T. Ackerman, 1988: A simple formulation of the delta-four-stream approximation for radiative transfer parameterizations. J. Atmos. Sci., 45, 19401948.

    • Search Google Scholar
    • Export Citation
  • Lock, A., 2009: Factors influencing cloud area at the capping inversion for shallow cumulus clouds. Quart. J. Roy. Meteor. Soc., 135, 941952.

    • Search Google Scholar
    • Export Citation
  • Lu, M. L., and J. H. Seinfeld, 2005: Study of the aerosol indirect effect by large-eddy simulation of marine stratocumulus. J. Atmos. Sci., 62, 39093932.

    • Search Google Scholar
    • Export Citation
  • Mellado, J., 2010: The evaporatively driven cloud-top mixing layer. J. Fluid Mech., 660, 536.

  • Moeng, C.-H., 2000: Entrainment rate, cloud fraction, and liquid water path of PBL stratocumulus clouds. J. Atmos. Sci., 57, 36273643.

    • Search Google Scholar
    • Export Citation
  • Pincus, R., and B. Stevens, 2009: Monte Carlo spectral integration: A consistent approximation for radiative transfer in large eddy simulations. J. Adv. Model. Earth Syst., 1 (1), doi:10.3894/JAMES.2009.1.1.

    • Search Google Scholar
    • Export Citation
  • Pincus, R., M. Baker, and C. Bretherton, 1997: What controls stratocumulus radiation properties? Lagrangian observations of cloud evolution. J. Atmos. Sci., 54, 22152236.

    • Search Google Scholar
    • Export Citation
  • Sandu, I., J. L. Brenguier, O. Geoffroy, O. Thouron, and V. Masson, 2008: Aerosol impacts on the diurnal cycle of marine stratocumulus. J. Atmos. Sci., 65, 27052718.

    • Search Google Scholar
    • Export Citation
  • Sandu, I., B. Stevens, and R. Pincus, 2010: On the transitions in marine boundary layer cloudiness. Atmos. Chem. Phys., 10, 23772391.

    • Search Google Scholar
    • Export Citation
  • Seifert, A., and K. Beheng, 2001: A double-moment parameterization for simulating autoconversion, accretion and self-collection. Atmos. Res., 59–60, 265281.

    • Search Google Scholar
    • Export Citation
  • Simmons, A., S. Uppala, D. Dee, and S. Kobayashi, 2007: Era-Interim: New ECMWF reanalysis products from 1989 onwards. ECMWF Newsletter, No. 110, ECMWF, Reading, United Kingdom, 25–35. [Available online at http://www.ecmwf.int/publications/newsletters/pdf/110_rev.pdf.]

    • Search Google Scholar
    • Export Citation
  • Stevens, B., 2000: Cloud transitions and decoupling in shear-free stratocumulus-topped boundary layers. Geophys. Res. Lett., 27, 25572560.

    • Search Google Scholar
    • Export Citation
  • Stevens, B., 2007: On the growth of layers of non-precipitating cumulus convection. J. Atmos. Sci., 64, 29162931.

  • Stevens, B., and A. Seifert, 2008: Understanding macrophysical outcomes of microphysical choices in simulations of shallow cumulus convection. J. Meteor. Soc. Japan, 86, 143162.

    • Search Google Scholar
    • Export Citation
  • Stevens, B., G. Feingold, W. C. Cotton, and R. L. Walko, 1996: Elements of the microphysical structure of numerically simulated nonprecipitating stratocumulus. J. Atmos. Sci., 53, 9801006.

    • Search Google Scholar
    • Export Citation
  • Stevens, B., W. C. Cotton, G. Feingold, and C.-H. Moeng, 1998: Large-eddy simulations strongly precipitating, shallow, stratocumulus-topped boundary layers. J. Atmos. Sci., 55, 36163638.

    • 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, 14431462.

    • Search Google Scholar
    • Export Citation
  • Stevens, B., A. Beljaars, S. Bordoni, C. Holloway, M. Koehler, S. Krueger, V. Savic-Jovcic, and Y. Zhang, 2007: On the structure of the lower troposphere in the summertime stratocumulus regime of the northeast Pacific. Mon. Wea. Rev., 135, 9851005.

    • Search Google Scholar
    • Export Citation
  • vanZanten, M. C., and Coauthors, 2011: Controls on precipitation and cloudiness in simulations of trade-wind cumulus as observed during RICO. J. Adv. Model. Earth Syst., 3, M06001, doi:10.1029/2011MS000056.

    • Search Google Scholar
    • Export Citation
  • Wang, S., B. Albrecht, and P. Minnis, 1993: A regional simulation of marine boundary-layer clouds. J. Atmos. Sci., 50, 40224043.

  • Wyant, M., C. Bretherton, H. Rand, and D. Stevens, 1997: Numerical simulations and a conceptual model of the subtropical marine stratocumulus to trade cumulus. J. Atmos. Sci., 54, 168192.

    • Search Google Scholar
    • Export Citation
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