On the Use of Radar Depolarization Ratios for Estimating Shapes of Ice Hydrometeors in Winter Clouds

Sergey Y. Matrosov Cooperative Institute for Research in the Environmental Sciences, University of Colorado, and NOAA/Environmental Technology Laboratory, Boulder, Colorado

Search for other papers by Sergey Y. Matrosov in
Current site
Google Scholar
PubMed
Close
,
Roger F. Reinking NOAA/Environmental Technology Laboratory, Boulder, Colorado

Search for other papers by Roger F. Reinking in
Current site
Google Scholar
PubMed
Close
,
Robert A. Kropfli NOAA/Environmental Technology Laboratory, Boulder, Colorado

Search for other papers by Robert A. Kropfli in
Current site
Google Scholar
PubMed
Close
,
Brooks E. Martner NOAA/Environmental Technology Laboratory, Boulder, Colorado

Search for other papers by Brooks E. Martner in
Current site
Google Scholar
PubMed
Close
, and
B. W. Bartram NOAA/Environmental Technology Laboratory, Boulder, Colorado

Search for other papers by B. W. Bartram in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

An approach is suggested to relate measurements of radar depolarization ratios and aspect ratios of predominant hydrometeors in nonprecipitating and weakly precipitating layers of winter clouds. The trends of elevation angle dependencies of depolarization ratios are first used to distinguish between columnar-type and plate-type particles. For the established particle type, values of depolarization ratios observed at certain elevation angles, for which the influence of particle orientation is minimal, are then used to estimate aspect ratios when information on particle effective bulk density is assumed or inferred from other measurements. The use of different polarizations, including circular, slant-45° linear, and two elliptical polarizations, is discussed. These two elliptical polarizations are quasi-circular and quasi-linear slant-45° linear, and both are currently achievable with the National Oceanic and Atmospheric Administration Environmental Technology Laboratory’s Ka-band radar. In comparison with the true circular and slant-45° linear polarizations, the discussed elliptical polarizations provide a stronger signal in the “weak” radar receiver channel; however, it is at the expense of diminished dynamic range of depolarization ratio variations. For depolarization measurements at the radar elevation angles that do not show much sensitivity to particle orientations, the available quasi-circular polarization provides a better depolarization contrast between nonspherical and spherical particles than does the available quasi-linear slant-45°polarization. The use of the proposed approach is illustrated with the experimental data collected during a recent field experiment. It is shown that it allows successful differentiation among pristine planar crystals, rimed planar crystals, long columns, blocky columns, and graupel. When a reasonable assumption about particle bulk density is made, quantitative estimates of particle aspect ratios from radar depolarization data are in good agreement with in situ observations. Uncertainties of particle aspect ratios estimated from depolarization measurements due to 0.1 g cm−3 variations in the assumed bulk density are about 0.1.

Corresponding author address: Dr. Sergey Y. Matrosov, R/E/ET6, 325 Broadway, Boulder, CO 80303.

smatrosov@etl.noaa.gov

Abstract

An approach is suggested to relate measurements of radar depolarization ratios and aspect ratios of predominant hydrometeors in nonprecipitating and weakly precipitating layers of winter clouds. The trends of elevation angle dependencies of depolarization ratios are first used to distinguish between columnar-type and plate-type particles. For the established particle type, values of depolarization ratios observed at certain elevation angles, for which the influence of particle orientation is minimal, are then used to estimate aspect ratios when information on particle effective bulk density is assumed or inferred from other measurements. The use of different polarizations, including circular, slant-45° linear, and two elliptical polarizations, is discussed. These two elliptical polarizations are quasi-circular and quasi-linear slant-45° linear, and both are currently achievable with the National Oceanic and Atmospheric Administration Environmental Technology Laboratory’s Ka-band radar. In comparison with the true circular and slant-45° linear polarizations, the discussed elliptical polarizations provide a stronger signal in the “weak” radar receiver channel; however, it is at the expense of diminished dynamic range of depolarization ratio variations. For depolarization measurements at the radar elevation angles that do not show much sensitivity to particle orientations, the available quasi-circular polarization provides a better depolarization contrast between nonspherical and spherical particles than does the available quasi-linear slant-45°polarization. The use of the proposed approach is illustrated with the experimental data collected during a recent field experiment. It is shown that it allows successful differentiation among pristine planar crystals, rimed planar crystals, long columns, blocky columns, and graupel. When a reasonable assumption about particle bulk density is made, quantitative estimates of particle aspect ratios from radar depolarization data are in good agreement with in situ observations. Uncertainties of particle aspect ratios estimated from depolarization measurements due to 0.1 g cm−3 variations in the assumed bulk density are about 0.1.

Corresponding author address: Dr. Sergey Y. Matrosov, R/E/ET6, 325 Broadway, Boulder, CO 80303.

smatrosov@etl.noaa.gov

Save
  • Aydin, K., and C. Tang, 1997: Millimeter wave radar scattering from model ice crystal distributions. IEEE Trans. Geosci. Remote Sens.,35, 140–146.

  • Bohren, C. F., and D. R. Huffman, 1983: Absorption and Scattering of Light by Small Particles. John Wiley and Sons, 530 pp.

  • Dungey, C. E., and C. F. Bohren, 1993: Backscattering by nonspherical hydrometeors as calculated by the coupled-dipole method: An application in radar meteorology. J. Atmos. Oceanic Technol.,10, 526–532.

  • Heymsfield, A. J., 1972: Ice crystal terminal velocities. J. Atmos. Sci.,29, 1348–1357.

  • Heymsfield, A. J., 1982: A comparative study of the rates of development of potential graupel and hail embryos in High Plains storms. J. Atmos. Sci.,39, 2867–2897.

  • Holt, A. R., 1984: Some factors affecting the remote sensing of rain by polarization diversity radar in 3- to 35-GHz frequency range. Radio Sci.,47, 1399–1421.

  • Kropfli, R. A., and R. D. Kelly, 1996: Meteorological research applications of mm-wave radar. Meteor. Atmos. Phys.,59, 105–121.

  • Matrosov, S. Y., 1991: Theoretical study of radar polarization parameters obtained from cirrus clouds. J. Atmos. Sci.,48, 1062–1070.

  • Matrosov, S. Y., and R. A. Kropfli, 1993: Cirrus cloud studies with elliptically polarized Ka-band radar signals. A suggested approach. J. Atmos. Oceanic Technol.,10, 684–692.

  • Matrosov, S. Y., R. F. Reinking, R. A. Kropfli, and B. W. Bartram, 1996: Estimation of ice hydrometeor types and shapes from radar polarization measurements. J. Atmos. Oceanic Technol.,13, 85–96.

  • Oguchi, T., 1983: Electromagnetic wave propagation and scattering in rain and other hydrometeors. Proc. IEEE,71, 1029–1078.

  • Pruppacher, H. R., and J. D. Klett, 1978: Microphysics of Clouds and Precipitation. D. Reidel, 714 pp.

  • Reinking, R. F., S. Y. Matrosov, R. T. Bruintjes, and B. E. Martner, 1997a: Identification of hydrometeors with elliptical and linear polarization Ka-band radar. J. Appl. Meteor.,36, 323–339.

  • Reinking, R. F., S. Y. Matrosov, B. E. Martner, and R. A. Kropfli, 1997b: Differentiation of freezing drizzle from ice hydrometeors and freezing rain with dual-polarization radar. J. Aircraft,34, 778–784.

  • Sassen, K., 1980: Remote sensing of planar ice crystal fall attitudes. J. Meteor. Soc. Japan,58, 422–429.

  • Shurcliff, W. A., 1962: Polarized Light. Harvard University Press, 208 pp.

  • Torlashi, E., and A. R. Holt, 1999: A comparison of different polarization schemes for the radar sensing of precipitation. Radio Sci.,33, 1335–1352.

  • Vivekanandan, J., D. S. Zrnić, S. M. Ellis, R. Oye, A. V. Ryzhkov, and J. Straka, 1999: Cloud microphysical retrieval using S-band dual-polarization radar measurements. Bull. Amer. Meteor. Soc.,80, 381–388.

  • Zrnić, D. S., and A. V. Ryzhkov, 1999: Polarimetry for weather surveillance radars. Bull. Amer. Meteor. Soc.,80, 389–406.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 370 95 4
PDF Downloads 217 79 8