Properties of Arctic Clouds from Multiple Atmospheric Observatories

Understanding how cloud properties vary across the Arctic is important for determining how the atmosphere influences the surface energy balance and the cryosphere (snow cover and sea ice). High-quality, surface-based measurements from multiple locations in the Arctic are now available for studying how cloud properties vary both spatially and temporally. Measurements from Atqasuk and Barrow, Alaska, Eureka, Canada, NyÅlesund, Norway, Summit, Greenland, and the SHEBA Ice Station are used to derive macrophysical (e.g., cloud occurrence fraction, vertical distribution) and microphysical properties (e.g., phase, optical depth, particle size) of Arctic clouds. At most locations, arctic clouds occur less frequently in winter and most frequently in late summer and fall. Interannual variability in cloud fraction is usually less than 15% for any given month at any location and typically less than 3% for annual cloud fractions. Low-level clouds occur most often above these locations. Large differences in monthly average longwave cloud radiative forcing at the surface are seen between Barrow and Eureka with higher values at Barrow.