Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

Journal Article · Fri Jun 09 04:00:00 EDT 2017 · Atmospheric Measurement Techniques (Online)

DOI:https://doi.org/10.5194/amt-10-2129-2017· OSTI ID:1374609

Blanchard, Yann ^[1]; Royer, Alain ^[2]; O'Neill, Norman T. ^[2]; Turner, David D. ^[3]; Eloranta, Edwin W. ^[4]

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1. University of Sherbrooke, Quebec (Canada). Center for Remote Sensing Applications and Research; Universite de Sherbrooke, Quebec, Canada
2. University of Sherbrooke, Quebec (Canada). Center for Remote Sensing Applications and Research
3. Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado (United States). Global Systems Division
4. Univ. of Wisconsin, Madison, WI (United States). Space Science and Engineering Center

Multiband downwelling thermal measurements of zenith sky radiance, along with cloud boundary heights, 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 semitransparent 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 downwelling thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, cloud geometric thickness and cloud base altitude. A lookup table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to a maximum value 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 over 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 high spectral resolution downwelling IR radiance measurements between 8 and 21µm was also performed. It confirms the robustness of the optical depth retrieval and the fact that the broadband thermal radiometer retrieval was sensitive to small particle (TIC1) sizes.

• Research Organization: University of Oklahoma, Norman, OK (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: SC0008830
• OSTI ID: 1374609
• Journal Information: Atmospheric Measurement Techniques (Online), Journal Name: Atmospheric Measurement Techniques (Online) Journal Issue: 6 Vol. 10; ISSN 1867-8548
• Publisher: European Geosciences Union
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES