Acoustic Radar Studies of Rain Microphysics

S. G. Bradley Physics Department, University of Auckland, Auckland, New Zealand

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Abstract

Raindrop size distributions are obtained from the Doppler frequency spectrum of an acoustic radar. Number concentrations of 12 drop diameters with a minimum diameter 0.14 cm are obtained and averaged over 3–15 min at 20-m range gates from 20 to 220 m. The last three range gates are used to estimate rain intensity–dependent background noise, which is dynamically subtracted from the signals. Multifrequency sounding is also used.

Intercomparisons with the vertical rain intensity profile from an X-band radar and with drop size distributions from an impact disdrometer show general agreement between instruments and demonstrate the usefulness of the acoustic profiler in giving vertical continuity below the range of electromagnetic radars. Temporal variations in raindrop size distributions are found to have an essentially flat spectrum for periodicities shorter than 12 min, although the step response to a sudden change in rainfall rate is a function of drop size. Principal component analysis applied to a time series of drop spectra shows that nearly all the variation is at the large-drop end. The utility of the acoustic radar is demonstrated for examining the microphysics of rain through time-dependent changes.

Corresponding author address: Dr. S. G. Bradley, Physics Dept., University of Auckland, Private Bag 92019, Auckland, New Zealand.

Email: s.bradley@auckland.ac.nz

Abstract

Raindrop size distributions are obtained from the Doppler frequency spectrum of an acoustic radar. Number concentrations of 12 drop diameters with a minimum diameter 0.14 cm are obtained and averaged over 3–15 min at 20-m range gates from 20 to 220 m. The last three range gates are used to estimate rain intensity–dependent background noise, which is dynamically subtracted from the signals. Multifrequency sounding is also used.

Intercomparisons with the vertical rain intensity profile from an X-band radar and with drop size distributions from an impact disdrometer show general agreement between instruments and demonstrate the usefulness of the acoustic profiler in giving vertical continuity below the range of electromagnetic radars. Temporal variations in raindrop size distributions are found to have an essentially flat spectrum for periodicities shorter than 12 min, although the step response to a sudden change in rainfall rate is a function of drop size. Principal component analysis applied to a time series of drop spectra shows that nearly all the variation is at the large-drop end. The utility of the acoustic radar is demonstrated for examining the microphysics of rain through time-dependent changes.

Corresponding author address: Dr. S. G. Bradley, Physics Dept., University of Auckland, Private Bag 92019, Auckland, New Zealand.

Email: s.bradley@auckland.ac.nz

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  • Beard, K. V., 1976: Terminal velocity and shape of cloud and precipitation drops aloft. J. Atmos. Sci.,33, 851–864.

    • Crossref
    • Export Citation
  • Bergeron, T., 1965: On the low-level redistribution of atmospheric water caused by orography. Proc. Int. Conf. Cloud Physics (suppl.), Tokyo, Japan, 96–100.

  • Bradley, S. G., and C. D. Stow, 1977: The effect of raindrop interactions on observed drop size distributions. J. Appl. Meteor.,16, 1206–1213.

    • Crossref
    • Export Citation
  • ———, and K. R. George, 1994: The use of a small acoustic wind profiler from a sea-going platform. Int. J. Remote Sens.,15, 237–244.

    • Crossref
    • Export Citation
  • ———, W. R. Gray, L. D. Pigott, A. W. Seed, C. D. Stow, and G. L. Austin, 1995: Rainfall redistribution over low hills due to flow perturbation. J. Hydrol., in press.

  • Coulter, R. L., and T. J. Martin, 1989: Minisodar measurements in rain. J. Atmos. Oceanic Technol.,6, 369–377.

    • Crossref
    • Export Citation
  • Dore, A. J., T. W. Choularton, D. Fowler, and R. Storeton-West, 1990: Field measurements of wet deposition in an extended region of complex topography. Quart. J. Roy. Meteor. Soc.,116, 1193–1212.

    • Crossref
    • Export Citation
  • Fabry, F., 1994: Observations and uses of high resolution radar data from precipitation. Ph.D. dissertation, McGill University, 134 pp.

  • Hill, F. F., K. A. Browning, and M. J. Bader, 1981: Radar and raingauge observations of orographic rain over south Wales. Quart. J. Roy. Meteor. Soc.,107, 643–670.

    • Crossref
    • Export Citation
  • Little, C. G., 1972: On the detectability of fog, cloud, rain and snow by acoustic echo-sounding methods. J. Atmos. Sci.,29, 748–755.

    • Crossref
    • Export Citation
  • Marshall, J. S., and W. M. K. Palmer, 1948: The distribution of raindrops with size. J. Meteor.,5, 165–166.

    • Crossref
    • Export Citation
  • Neff, W. D., and R. L. Coulter, 1986: Acoustic remote sensing. Probing the Atmospheric Boundary Layer, D. H. Lenschow, Ed., Amer. Meteor. Soc., 201–239.

    • Crossref
    • Export Citation
  • Presendorfer, R. W., and C. D. Mobley, 1988: Principal Component Analysis in Meteorology and Oceanography. Elsevier, 425 pp.

  • Shamanaeva, L. G., 1988: Acoustic sounding of rain intensity. J. Acoust. Soc. Amer.,84, 713–718.

    • Crossref
    • Export Citation
  • Ulbrich, C. W., 1983: Natural variations in the analytical form of the raindrop size distribution. J. Climate Appl. Meteor.,22, 1764–1775.

    • Crossref
    • Export Citation
  • Wratt, D. S., and Coauthors, 1996: The New Zealand Southern Alps Experiment. Bull. Amer. Meteor. Soc.,77, 683–692.

    • Crossref
    • Export Citation
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