Changes in cloudiness in the U.S. from surface observations

Cloudiness is an important climate variable for detection of climate change, understanding climate feedbacks, and evaluation of climate models. Since clouds are a major determinant of surface solar radiation, changes in cloud cover also have implications for future solar energy development. Current cloud datasets from satellites and human visual observations do not agree on some major aspects of long-term variability. Resolving these differences requires closer attention to data homogeneity issues. For surface-based observations, these issues are especially complex in the U.S. because of the effects of the introduction of ASOS in the early 1990s and have not yet been addressed thoroughly. Although earlier studies suggested that cloud cover had been increasing in the United States at least through the mid-1980s, there is reason to believe that this trend may have reversed. We will test this using a new analysis of U.S. cloud cover based on surface observations from the Integrated Surface Hourly database, and compare these results to satellite data and other related climatological information.