• Ackerman, A. S., , M. P. Kirkpatrick, , D. E. Stevens, , and O. B. Toon, 2004: The impact of humidity above stratiform clouds on indirect aerosol forcing. Nature, 432 , 10141017.

    • Search Google Scholar
    • Export Citation
  • Austin, P., , Y. Wang, , R. Pincus, , and V. Kujala, 1995: Precipitation in stratocumulus clouds: Observations and modeling results. J. Atmos. Sci., 52 , 23292352.

    • Search Google Scholar
    • Export Citation
  • Baker, M. B., 1993: Variability in concentrations of cloud condensation nuclei in the marine cloud-topped boundary layer. Tellus, 45B , 458472.

    • Search Google Scholar
    • Export Citation
  • Baumgardner, D., , B. Baker, , and K. Weaver, 1993: A technique for measurement of cloud structure on centimeter scales. J. Atmos. Oceanic Technol., 10 , 557565.

    • Search Google Scholar
    • Export Citation
  • Beard, K. V., , and H. T. Ochs, 1993: Warm-rain initiation: An overview of microphysical mechanisms. J. Appl. Meteor., 32 , 608625.

  • Beheng, K. D., 1994: A parameterization of warm cloud microphysical conversion processes. Atmos. Res., 33 , 193206.

  • Beheng, K. D., , and G. Doms, 1986: A general formulation of collection rates of cloud and raindrops using the kinetic equation and comparison with parameterizations. Beitr. Phys. Atmos., 59 , 6684.

    • Search Google Scholar
    • Export Citation
  • Berry, E. X., , and R. L. Reinhardt, 1974: An analysis of cloud drop growth by collection. Part II: Single initial distributions. J. Atmos. Sci., 31 , 18251831.

    • Search Google Scholar
    • Export Citation
  • Bott, A., 1998: A flux method for the numerical solution of the stochastic collection equation. J. Atmos. Sci., 55 , 22842293.

  • Bretherton, C. S., and Coauthors, 2004: The EPIC 2001 stratocumulus study. Bull. Amer. Meteor. Soc., 85 , 967977.

  • Brown, P. R. A., , G. Richardson, , and R. Wood, 2004: The sensitivity of large-eddy simulations to the parameterization of drizzle. Proc. 14th ICCP Conf. on Clouds and Precipitation, Bologna, Italy, ICCP, CD-ROM, 174.

  • Comstock, K., , S. Yuter, , and R. Wood, 2004: Reflectivity and rain rate in and below drizzling stratocumulus. Quart. J. Roy. Meteor. Soc., 130 , 28912919.

    • Search Google Scholar
    • Export Citation
  • Davis, M. H., 1972: Collisions of small droplets: Gas kinetic effects. J. Atmos. Sci., 29 , 911915.

  • Feingold, G., , and Z. Levin, 1986: The lognormal fit to raindrop spectra from frontal convective clouds in Israel. J. Climate Appl. Meteor., 25 , 13461363.

    • Search Google Scholar
    • Export Citation
  • Frisch, A. S., , C. W. Fairall, , and J. B. Snider, 1995: Measurement of cloud and drizzle parameters during ASTEX with a Kα band Doppler radar and a microwave radiometer. J. Atmos. Sci., 52 , 27882799.

    • Search Google Scholar
    • Export Citation
  • Golovin, A. M., 1963: The solution of the coagulation equation from cloud droplets in a rising air current. Izv. Akad. Nauk. SSSR Ser. Geofiz., 5 , 783791.

    • Search Google Scholar
    • Export Citation
  • Hall, W. D., 1980: A detailed microphysical model within a two-dimensional dynamic framework: Model description and preliminary results. J. Atmos. Sci., 37 , 24862507.

    • Search Google Scholar
    • Export Citation
  • Hobbs, P. V., 1993: Aerosol–Cloud–Climate Interactions. Academic Press, 235 pp.

  • Hudson, J. G., , and S. S. Yum, 2001: Maritime–continental drizzle contrasts in small cumuli. J. Atmos. Sci., 58 , 915926.

  • Jonas, P. R., 1972: The collision efficiency of small drops. Quart. J. Roy. Meteor. Soc., 98 , 681683.

  • Jones, A., , D. L. Roberts, , M. J. Woodage, , and C. E. Johnson, 2001: Indirect aerosol forcing in a climate model with an interactive sulphur cycle. Hadley Centre Tech. Note HCTN-25, Meteorological Office, 34 pp.

  • Kessler, E., 1969: On the Distribution and Continuity of Water Substance in Atmospheric Circulations, Meteor. Monogr., No. 32, Amer. Meteor. Soc., 84 pp.

  • Khairoutdinov, M., , and Y. Kogan, 2000: A new cloud physics parameterization in a large-eddy simulation model of marine stratocumulus. J. Atmos. Sci., 57 , 229243.

    • Search Google Scholar
    • Export Citation
  • Liu, Y., , and P. H. Daum, 2004: Parameterization of the autoconversion process. Part I: Analytical formulation of the Kessler-type parameterizations. J. Atmos. Sci., 61 , 15391548.

    • Search Google Scholar
    • Export Citation
  • Liu, Y., , P. H. Daum, , and R. McGraw, 2004: An analytical expression for predicting the critical radius in the autoconversion parameterization. Geophys. Res. Lett., 31 .L06121, doi:10.1029/2003GL019117.

    • Search Google Scholar
    • Export Citation
  • Menon, S., and Coauthors, 2003: Evaluating aerosol/cloud/radiation process parameterizations with single-column models and Second Aerosol Characterization Experiment (ACE-2) cloudy column observations. J. Geophys. Res., 108 .4762, doi:10.1029/2003JD003902.

    • Search Google Scholar
    • Export Citation
  • Pawlowska, H., , and J-L. Brenguier, 2003: An observational study of drizzle formation in stratocumulus clouds for general circulation model (GCM) parameterizations. J. Geophys. Res., 108 .8630, doi:10.1029/2002JD002679.

    • Search Google Scholar
    • Export Citation
  • Pincus, R., , and S. A. Klein, 2000: Unresolved spatial variability and microphysical process rates in large scale models. J. Geophys. Res., 105 , 2705927066.

    • Search Google Scholar
    • Export Citation
  • Pruppacher, H. R., , and J. D. Klett, 1997: Microphysics of Clouds and Precipitation. Kuwer Academic Publishers, 976 pp.

  • Rotstayn, L. D., 1997: A physically based scheme for the treatment of stratiform clouds and precipitation in large-scale models. I: Description and evaluation of the microphysical processes. Quart. J. Roy. Meteor. Soc., 123 , 12271282.

    • Search Google Scholar
    • Export Citation
  • Rotstayn, L. D., 2000: On the “tuning” of autoconversion parameterizations in climate models. J. Geophys. Res., 105 , 1549515507.

  • Rotstayn, L. D., , and Y. Liu, 2005: A smaller global estimate of the second aerosol effect. Geophys. Res. Lett., 32 .L05708, doi:10.1029/2004GL021922.

    • Search Google Scholar
    • Export Citation
  • Stephens, G. L., and Coauthors, 2002: The CloudSat mission and the EOS constellation: A new dimension of space-based observations of clouds and precipitation. Bull. Amer. Meteor. Soc., 83 , 17711790.

    • Search Google Scholar
    • Export Citation
  • Stevens, B., , R. L. Walko, , W. R. Cotton, , and G. Feingold, 1996: The spurious production of cloud-edge supersaturations by Eulerian models. Mon. Wea. Rev., 124 , 10341041.

    • Search Google Scholar
    • Export Citation
  • Stout, G. E., , and E. A. Mueller, 1968: Survey of relationships between rainfall rate and radar reflectivity in the measurement of precipitation. J. Appl. Meteor., 7 , 465474.

    • Search Google Scholar
    • Export Citation
  • Tripoli, G. J., , and W. R. Cotton, 1980: A numerical investigation of several factors contributing to the observed variable density of deep convection over south Florida. J. Appl. Meteor., 19 , 10371063.

    • Search Google Scholar
    • Export Citation
  • Tzivion, S., , G. Feingold, , and Z. Levin, 1987: An efficient numerical solution to the stochastic collection equation. J. Atmos. Sci., 44 , 31393149.

    • Search Google Scholar
    • Export Citation
  • vanZanten, M. C., , B. Stevens, , G. Vali, , and D. Lenschow, 2005: Observations of drizzle in nocturnal marine stratocumulus. J. Atmos. Sci., 62 , 88106.

    • Search Google Scholar
    • Export Citation
  • Wilson, D. R., , and S. P. Ballard, 1999: A microphysically based precipitation scheme for the UK Meteorological Office unified model. Quart. J. Roy. Meteor. Soc., 125 , 16071636.

    • Search Google Scholar
    • Export Citation
  • Wood, R., 2000: Parametrization of the effect of drizzle upon the droplet effective radius in stratocumulus clouds. Quart. J. Roy. Meteor. Soc., 126 , 33093324.

    • Search Google Scholar
    • Export Citation
  • Wood, R., 2005: Drizzle in stratiform boundary layer clouds. Part I: Vertical and horizontal structure. J. Atmos. Sci., 62 , 30113033.

    • Search Google Scholar
    • Export Citation
  • Wood, R., , and P. Blossey, 2005: Comments on “Parameterization of the autoconversion process. Part I: Analytical formulation of the Kessler-type parameterizations.”. J. Atmos. Sci., 62 , 30033006.

    • Search Google Scholar
    • Export Citation
  • Yuter, S. E., , Y. L. Serra, , and R. A. Houze Jr., 2000: The 1997 Pan American climate studies tropical eastern Pacific process study. Part II: Stratocumulus region. Bull. Amer. Meteor. Soc., 81 , 483490.

    • Search Google Scholar
    • Export Citation
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Drizzle in Stratiform Boundary Layer Clouds. Part II: Microphysical Aspects

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  • 1 Met Office, Exeter, Devon, United Kingdom
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Abstract

This is the second of two observational papers examining drizzle in stratiform boundary layer clouds. Part I details the vertical and horizontal structure of cloud and drizzle parameters, including some bulk microphysical variables. In this paper, the focus is on the in situ size-resolved microphysical measurements, particularly of drizzle drops (r > 20 μm). Layer-averaged size distributions of drizzle drops within cloud are shown to be well represented using either a truncated exponential or a truncated lognormal size distribution. The size-resolved microphysical measurements are used to estimate autoconversion and accretion rates by integration of the stochastic collection equation (SCE). These rates are compared with a number of commonly used bulk parameterizations of warm rain formation. While parameterized accretion rates agree well with those derived from the SCE initialized with observed spectra, the autoconversion rates seriously disagree in some cases. These disagreements need to be addressed in order to bolster confidence in large-scale numerical model predictions of the aerosol second indirect effect. Cloud droplet coalescence removal rates and mass and number fall rate relationships used in the bulk microphysical schemes are also compared, revealing some potentially important discrepancies. The relative roles of autoconversion and accretion are estimated by examination of composite profiles from the 12 flights. Autoconversion, although necessary for the production of drizzle drops, is much less important than accretion throughout the lower 80% of the cloud layer in terms of the production of drizzle liquid water. The SCE calculations indicate that the autoconversion rate depends strongly upon the cloud droplet concentration Nd such that a doubling of Nd would lead to a reduction in autoconversion rate of between 2 and 4.

Radar reflectivity–precipitation rate (ZR) relationships suitable for radar use are derived and are shown to be significantly biased in some cases by the undersampling of large (r > 200 μm) drops with the 2D-C probe. A correction based upon the extrapolation to larger sizes using the exponential size distribution changes the ZR relationship, leading to the conclusion that consideration should be given to sampling issues when examining higher moments of the drop size distribution in drizzling stratiform boundary layer clouds.

Corresponding author address: Dr. Robert Wood, Dept. of Atmospheric Sciences, University of Washington, Box 351640, Seattle, WA 98102. Email: robwood@atmos.washington.edu

Abstract

This is the second of two observational papers examining drizzle in stratiform boundary layer clouds. Part I details the vertical and horizontal structure of cloud and drizzle parameters, including some bulk microphysical variables. In this paper, the focus is on the in situ size-resolved microphysical measurements, particularly of drizzle drops (r > 20 μm). Layer-averaged size distributions of drizzle drops within cloud are shown to be well represented using either a truncated exponential or a truncated lognormal size distribution. The size-resolved microphysical measurements are used to estimate autoconversion and accretion rates by integration of the stochastic collection equation (SCE). These rates are compared with a number of commonly used bulk parameterizations of warm rain formation. While parameterized accretion rates agree well with those derived from the SCE initialized with observed spectra, the autoconversion rates seriously disagree in some cases. These disagreements need to be addressed in order to bolster confidence in large-scale numerical model predictions of the aerosol second indirect effect. Cloud droplet coalescence removal rates and mass and number fall rate relationships used in the bulk microphysical schemes are also compared, revealing some potentially important discrepancies. The relative roles of autoconversion and accretion are estimated by examination of composite profiles from the 12 flights. Autoconversion, although necessary for the production of drizzle drops, is much less important than accretion throughout the lower 80% of the cloud layer in terms of the production of drizzle liquid water. The SCE calculations indicate that the autoconversion rate depends strongly upon the cloud droplet concentration Nd such that a doubling of Nd would lead to a reduction in autoconversion rate of between 2 and 4.

Radar reflectivity–precipitation rate (ZR) relationships suitable for radar use are derived and are shown to be significantly biased in some cases by the undersampling of large (r > 200 μm) drops with the 2D-C probe. A correction based upon the extrapolation to larger sizes using the exponential size distribution changes the ZR relationship, leading to the conclusion that consideration should be given to sampling issues when examining higher moments of the drop size distribution in drizzling stratiform boundary layer clouds.

Corresponding author address: Dr. Robert Wood, Dept. of Atmospheric Sciences, University of Washington, Box 351640, Seattle, WA 98102. Email: robwood@atmos.washington.edu

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