W-band (95 GHz) Radar Attenuation in Tropical Stratiform Ice Anvils

Abstract : Attenuation of W-band (95 GHz) radar signal by atmospheric ice particles has long been neglected in cloud microphysics studies. In this work, 95 GHz airborne multi-beam cloud radar observations in tropical stratiform ice anvils are used to estimate vertical profiles of 95 GHz attenuation. Two techniques are developed and compared, using very different assumptions. The first technique examines statistical reflectivity differences between repeated aircraft passes through the same cloud mass at different altitudes. The second technique exploits reflectivity differences between two different path lengths through the same cloud, using the multi-beam capabilities of the cloud radar. Using the first technique, the two-way attenuation coefficient produced by stratiform ice particles ranges between 1 and 1.6 dB km−1 for reflectivities between 13 and 18 dBZ, with an expected increase of attenuation with reflectivity. Using the second technique, the multi-beam results confirm these high attenuation coefficient values and expand the reflectivity range, with typical attenuation coefficient values of up to 3-4 dB km−1 for reflectivities of 20 dBZ. The potential impact of attenuation on precipitating ice cloud microphysics retrievals is quantified using vertical profiles of mean and 99th percentile of ice water content derived from non-corrected and attenuation-corrected reflectivities. A large impact is found on the 99th percentile of ice water content, which increases by 0.3 – 0.4 gm−3 up to 11 km height. Finally, T-matrix calculations of attenuation constrained by measured particle size distributions, ice crystal mass – size and projected area – size relationships are found to largely underestimate cloud radar attenuation estimates.
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Submitted on : Saturday, June 8, 2019 - 2:01:34 PM
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Alain Protat, Surendra Rauniyar, Julien Delanoë, Emmanuel Fontaine, Alfons Schwarzenboeck. W-band (95 GHz) Radar Attenuation in Tropical Stratiform Ice Anvils. Journal of Atmospheric and Oceanic Technology, American Meteorological Society, 2019, (in press). ⟨10.1175/JTECH-D-18-0154.1⟩. ⟨insu-02151487⟩



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