11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Tuesday, 4 June 2002
An annual cycle of Arctic cloud microphysics
Matthew D. Shupe, NOAA/ETL, Boulder, CO; and T. Uttal and S. Y. Matrosov
Poster PDF (2.2 MB)
An annual cycle of ground-based radar and radiometer cloud measurements from the Surface Heat Budget of the Arctic (SHEBA) Program were utilized to derive Arctic cloud microphysical and optical properties. A suite of microphysical retrieval techniques based on measurements from a 35-GHz cloud radar, a microwave radiometer, and a spectral IR radiometer were applied to clouds observed above the SHEBA ice camp in the Beaufort and Chukchi Seas during the time period of October 1997 to October 1998. All-liquid clouds were identified 14% of the time and were characterized by droplet effective radii of 7.3 Ám, liquid water contents of 0.085 g m-3, liquid water paths of 30-40 g m-2, liquid droplet concentrations of 50 cm-3, and SW optical depths of 6-9. Arctic liquid clouds are semi-adiabatic in nature, with droplet sizes and liquid water contents growing from cloud base up to a height of about 60% of the average cloud depth. The upper 40% of the average cloud generally shows a reduction in droplet sizes and water contents, however, the standard deviation of vertical profiles in this region is large, demonstrating a high variability in cloud-top mixing and/or the adiabatic nature of these clouds. Liquid cloud microphysics and SW optical depth all show seasonal variation with higher values in the summer. All-ice clouds were identified 31% of the time and were characterized by particle mean diameters of 80 Ám, ice water contents of about 0.009-0.012 g m-3, ice water paths of 25-30 g m-2, ice particle concentrations of 0.03-0.04 cm-3 and SW optical depths of 0.9-1.1. In general, profiles of ice water content and particle size show maxima at about 25% of the average cloud depth from the cloud base, following the general growth and sublimation of ice particles. Linear relationships between temperature and both mean and maximum retrieved ice particle sizes are observed for the range of -60 to -10 C. Ice water contents have an exponential relationship with temperature. The seasonal variation of ice-cloud parameters show larger particle sizes, ice water contents, ice water paths, and SW optical depths in the spring and summertime. Mixed-phase clouds were identified above the SHEBA ice camp 41% of the time. The ice component of these mixed-phase clouds was retrieved from the radar measurements, yielding mean values of 110 Ám, 0.022 g m-3, 45 g m-2, and 0.03 cm-3, respectively, for the same ice parameters as above. These values demonstrate that the mixed-phase clouds observed at SHEBA contained larger ice particles and water contents than the all-ice clouds, an observation that may be expected due to the difference in ice formation mechanisms between cirriform clouds and the ice in mixed-phase clouds.

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