Microphysical properties of clouds over Eureka, Canada between 2006 and 2009

Few measurements have been made of the microphysical properties of Arctic clouds despite their importance to the surface energy budget. Long-term measurements at surface observation sites are important not only because they yield valuable information on the variation of atmospheric properties, but also because they serve as validation data for retrievals from satellite instruments. In this study, cloud microphysical properties over the Canadian Network for the Detection of Arctic Change (CANDAC) site at Eureka, Nunavut (80° N 86° W) are reported at high temporal resolution (about 10 minutes) from March 2006 through April 2009. The Mixed-phase Cloud Retrieval Algorithm (MIXCRA) is used to retrieve ice fraction (cloud particle phase), effective radii of ice and water particles, and cloud optical depth. Cloud temperature and ice and liquid water paths are also retrieved. MIXCRA uses an assimilation of spectral infrared radiances, a cloud mask from lidar and radar data, precipitable water vapor from a microwave radiometer, and radiosonde profiles. A conservative optical depth threshold of 0.25 was used to ensure that the instruments were viewing clouds. Additional screening was applied, which ultimately yielded nearly 300,000 cloudy cases for analysis. Monthly averages of the retrieved properties allow an examination of seasonal cycles and interannual variability. Liquid water clouds occur frequently in summer, while ice-only clouds dominate in winter. Mixed-phase clouds occur in all months with a frequency ranging from 20 to 40%. Ice fraction appears to have some dependence on temperature. Monthly size distributions of liquid water droplets and ice crystals are sometimes bi-modal. Comparisons to cloud properties during the SHEBA experiment will be shown.