Tuesday, 25 January 2011
Washington State Convention Center
In recent years, several studies have shown decreasing trends in surface-observed total cloud amount since the 1950s over much of China, with the largest decrease beginning in the late 1970s. Where visibility has not likely been affected by increasing anthropogenic aerosol loading (western and parts of northern China), these studies seem to indicate that in fact cloud amount has decreased, largely driven by more frequent observations of totally clear sky. The true nature of changes in cloud amount where visibility has been decreasing (much of eastern China) is likely more complicated, related to the challenge of observers detecting certain cloud types - especially higher, optically thinner clouds - and possibly inflating the frequency of observed "clear sky". To better evaluate and understand natural and anthropogenic influences on the surface-observed cloud amount record from China, we will examine a suite of additional variables whose records extend generally back to the early 1970s or early 1980s, and thereby overlap the period of greatest decreases in cloud amount. These variables include surface-observed cloud type, satellite-observed cloud amount and cloud type, and cloud area fraction from climate model runs of the Climate of the 20th Century (20C3M) experiment. We examine variables at both the regional and grid-box scales, and, where possible, for individual stations.
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