*5.35*ln(394/337) = 0.8 Wm-2
Observational constraints on Arctic Ocean clouds and radiative fluxes during the early 21st century
Jennifer E. Kay, Tristan L'Ecuyer
Abstract: Arctic Ocean observations are combined to create a cloud and radiation climatology for the early 21st century (March 2000 - February 2011). Data sources include: observed top-of-atmosphere (TOA) radiative fluxes (CERES-EBAF), active (CloudSat, CALIPSO) and passive (MODIS) satellite cloud fraction observations, and observationally constrained radiative flux and cloud forcing calculations (CERES-EBAF, 2B-FLXHR-LIDAR).Uncertainty in flux calculations is dominated by cloud uncertainty, not surface albedo uncertainty. The climatology exposes large geographic, seasonal, and inter-annual variability in the influence of clouds on radiative fluxes but, on average, Arctic Ocean clouds warm the surface (+10 Wm-2, 2B-FLXHR-LIDAR) and cool the TOA (−12 Wm-2, CERES-EBAF, 2B-FLXHR-LIDAR).Shortwave TOA cloud cooling and longwave TOA cloud warming are stronger in 2B-FLXHR-LIDAR than in CERES-EBAF, but these two differences compensate each other yielding similar net TOA values. During the early 21st century, summer TOA albedo decreases are consistent with sea ice loss, but are unrelated to summer cloud trends that are statistically insignificant. In contrast, both sea ice variability and cloud variability contribute to inter-annual variability in summer shortwave radiative fluxes. Summer 2007 had the largest persistent cloud, radiation, and sea ice anomalies in the climatology. During that summer, positive net shortwave radiation anomalies exceeded 20 Wm-2 over much of Arctic Ocean. This enhanced shortwave absorption resulted primarily from cloud reductions during early summer, and sea ice loss during late summer. In summary, the observations show that while cloud variability influences absorbed shortwave radiation variability, there is no summer cloud trend affecting summer absorbed shortwave radiation.