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Interannual Variations of Arctic Cloud Types: Relationships with Sea Ice and Comparisons with Satellite Observations Ryan Eastman Stephen Warren University of Washington Department of Atmospheric Sciences Changes in Arctic Climate What is the role of cloud cover in Arctic climate change? What is the Cloud Radiative Effect (CRE) in the Arctic? CRE depends on season, cloud type CRE – whether clouds warm or cool the surface Longwave (IR) effect dominates during autumn, winter and spring − Shortwave effect dominates during summer − Due to a higher sun and no snow on top of sea ice Shupe & Intrieri (2003), using SHEBA data, conclude that phase, temperature, and height all have a strong impact on CRE − Due to low sun angles and a high surface albedo Water clouds are warmer, usually thicker, and stronger emitters Effects of cloud changes depend on the type of cloud and the season of the change Cloud Detection Satellite looking down Surface looking up Cloud Data Synoptic surface observations from land (1971-2007) and ocean (1954-2008) − Including observations taken from stations drifting on sea ice Observations taken daily every three or six hours − Nighttime observations thrown out if insufficient moonlight − Stations specifically chosen to include nighttime obs Total cloud cover and nine cloud types: − High cloud (cirriform) − Middle Clouds: Altocumulus, Altostratus, Nimbostratus − Low Clouds: Cumulonimbus, Cumulus, Stratus, Stratocumulus, fog Arctic Stations Observations per Year (Hundreds) From ships and stations Using These Data... Compiled an Arctic cloud climatology for 60° to 90° North For this presentation: − Study a sub-dataset over only the Arctic ocean Cloud trends over the Arctic ocean Correlations of cloud cover with Arctic sea ice extent and surface air temperature Cloud anomalies in years with high/low ice minima − Compare with other available Arctic cloud data Correlations with Sept. Sea Ice Extent Correlations with Sept. Sea Ice Extent Less September ice observed after cloudy spring − Cloud forcing More autumn clouds occur when less ice is present − Cloud response Correlations with Sept. Sea Ice Extent Summer nimbostratus clouds show a positive correlation with September sea ice extent Correlation with Surface Air Temperature Superposed Epochs Determine the years with greatest and least September sea ice extent for the period 1979 to 2007 Calculate the average percent cloud cover for each cloud type for the 5 highest and 5 lowest ice years Superposed Epochs Results Low clouds more prevalent during the autumn of a low ice September Suggests cloud response to sea-ice retreat − Less September ice ⇓ More autumn cloud cover Arctic Ocean Cloud Study Results Cloud changes of recent decades appear to enhance Arctic Warming − − − During winter positive cloud trends may contribute to warm temperatures In Summer negative trends in precipitating clouds are associated with less ice in September During spring and autumn positive cloud trends are likely acting to enhance warming and reduce sea ice Autumn clouds increase after a low-ice September, as also shown by Kay and Gettelman This work has been submitted to Journal of Climate Comparison of Cloud Detection Methods Satellite Data Surface Observations APP-x and Surface TOVS and Surface Observations, 60° to 90°N Observations, Ocean Only Individual Boxes During DJF Interannual variations in satellite data in all 10° grid boxes are coherent throughout the Arctic − Individual boxes plotted as gray lines, Arctic mean is thick line Surface observations do not show this tendency Acknowledgments Robert Wood, Cecilia Bitz, Mike Wallace, Axel Schweiger, Xuanji Wang, and Jeff Key for helpful feedback and discussion Carole Hahn, Xuanji Wang, Jeff Key, and Axel Schweiger for making data available NSF's Climate Dynamics Program & NOAA's Climate Change Data and Detection program