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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amt-2016-371
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
14 Nov 2016
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Measurement Techniques (AMT) and is expected to appear here in due course.
Thin ice clouds in the Arctic: Cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry
Yann Blanchard1, Alain Royer1, Norman T. O'Neill1, David D. Turner2, and Edwin W. Eloranta3 1Centre d’Applications et de Recherches en Télédétection, Université de Sherbrooke, Sherbrooke, Québec, Canada
2Global Systems Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA
3Space Science and Engineering Center, University of Wisconsin, Madison, Wisconsin, USA
Abstract. Multi-band thermal measurements of zenith sky radiance, along with height profile information, were used in a retrieval algorithm, to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian high-Arctic. Ground-based thermal infrared (IR) radiances for 150 semi-transparent ice clouds cases were acquired at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80° N, 86° W). We analyzed and quantified the sensitivity of thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, thickness and bottom altitude. A look up table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to values of 2.6 and to separate thin ice clouds into two classes: 1) TIC1 clouds characterized by small crystals (effective particle diameter ≤ 30 μm), and 2) TIC2 clouds characterized by large ice crystals (effective particle diameter > 30 μm). The retrieval technique was validated using data from the Arctic High Spectral Resolution Lidar (AHSRL) and Millimeter Wave Cloud Radar (MMCR). Inversions were performed across three polar winters and results showed a significant correlation (R2 = 0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of TIC1 and TIC2 clouds. A partial validation relative to an algorithm based on infrared radiance measurements at high spectral resolution between 8 and 21 μm was also carried out. It confirms the robustness of the optical depth retrieval and the fact that the radiometer retrieval was sensitive to small particle (TIC1) sizes.

Citation: Blanchard, Y., Royer, A., O'Neill, N. T., Turner, D. D., and Eloranta, E. W.: Thin ice clouds in the Arctic: Cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-371, in review, 2016.
Yann Blanchard et al.
Yann Blanchard et al.

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Short summary
Multi-band thermal measurements of zenith sky radiance were used in a retrieval algorithm, to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian high-Arctic. The retrieval technique was validated using a synergy lidar and radar data. Inversions were performed across three polar winters and results showed a significant correlation (R2 = 0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of thin ice clouds.
Multi-band thermal measurements of zenith sky radiance were used in a retrieval algorithm, to...
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