06/12/2017

Estimation of Depolarization Ratio Using Modern Dual-polarization Weather Radars

New technique may provide better information about updrafts, ice, and hail within convective clouds.

The Science

Depolarization ratio (DR) was historically the first polarimetric radar variable measured by dual-polarization weather radars. Depolarization ratio can provide information about particle phase (water or ice) and shape. However, this important variable is not measured by modern radars with simultaneous transmission/reception of orthogonally polarized waves, although they do measure other polarimetric variables. A new technique allowing for estimating depolarization ratio on a fleet of scanning dual-polarization ARM radars is suggested.

The Impact

This technique, if implemented on a fleet of scanning dual-polarization radars, such as those maintained by the DOE ARM scientific user facility and used in DOE’s Atmospheric System Research program, will greatly enhance their utility for microphysical characterization of clouds and precipitation.

Summary

A special signal-processing routine combined with the use of a high-power phase shifter makes it possible to measure depolarization without compromising measurements of other polarimetric variables. The feasibility of the recommended approach has been demonstrated using observations with S, C, and X-band dual-polarization weather radars. Among potential applications, four major challenging practical tasks can be addressed using depolarization ratio measurements: 1) identification and quantification of deep convective updrafts, 2) detection of hail and determination of its size above the melting layer, 3) discrimination between various habits of ice aloft, and 4) identification and quantification of riming processes associated with the presence of super-cooled cloud water.

Principal Investigator(s)

Alexander Ryzkhov
National Severe Storms Laboratory
[email protected]

Funding

Funding for some of the authors was provided by NOAA/Office of Oceanic and Atmospheric Research under NOAA – University of Oklahoma Cooperative Agreement NA11OAR4320072, U.S. Department of Commerce. Sergey Matrosov was sponsored in part by the US Department of Energy Atmospheric System Program under award number DE-SC0013306. Research based on the Bonn X-band radar was carried out in the framework of the Hans-Ertel-Centre for Weather Research (http://www.herz-tb1.uni-bonn.de/) funded by the BMVBS (Federal Ministry of Transport, Building and Urban Development) and the SFB/TR 32 (Transregional Collaborative Research Centre 32, http://www.tr32.de/) funded by the DFG (German Research Foundation)

References

Ryzhkov, A., S. Matrosov, V. Melnikov, D. Zrnic, P. Zhang, Q. Cao, M. Knight, C. Simmer, and S. Troemel. “Estimation of Depolarization Ratio Using Weather Radars with Simultaneous Transmission/Reception.” Journal of Applied Meteorology and Climatology 12 July (2017). DOI:10.1175/JAMC-D-16-0098.1