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ABSTRACT
Visual cloud reports from land and ocean regions of the Arctic are analyzed for total cloud cover. Trends and interannual variations in surface cloud data are compared to those obtained from Advanced Very High Resolution Radiometer (AVHRR) and Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) satellite data. Over the Arctic as a whole, trends and interannual variations show little agreement with those from satellite data. The interannual variations from AVHRR are larger in the dark seasons than in the sunlit seasons (6% in winter, 2% in summer); however, in the surface observations, the interannual variations for all seasons are only 1%-2%. A large negative trend for winter found in the AVHRR data is not seen in the surface data. At smaller geographic scales, time series of surface- and satellite-observed cloud cover show some agreement except over sea ice during winter. During the winter months, time series of satellite-observed clouds in numerous grid boxes show variations that are strangely coherent throughout the entire Arctic.
1. Introduction
Arctic climate change has been among the most substantial of anywhere on earth in the past two decades. A companion paper, Eastman and Warren (2010, hereafter EWlO) has shown that cloud changes derived from surface observations (SURF) appear to be enhancing the warming seen in the Arctic. EWlO show an increasing trend in Arctic total cloud cover and a positive correlation between total cloud cover and surface air temperature in autumn, winter, and spring. Kay and Gettelman (2009) as well as EWlO suggest the presence of a positive cloud response to diminished sea ice extent during autumn. Significant trends in recent decades are observed in both Arctic sea ice and Arctic surface air temperature. Sea ice extent has shown a strong declining trend since the 1980s (Stroeve et al. 2008; NSIDC 2009a,b). Surface air temperature has been observed to increase at a rate of 0.5CC decade^sup -1^ by the International Arctic Buoy Programme (Rigor et al. 2000) and at a rate of 0.8°C decade^sup -1^ according to the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis (Kalnay et al. 1996). Given the relationships between clouds and both sea ice and surface temperature, it is likely that decadal trends in cloud cover are...