Means and Trends of Shortwave Irradiance at the Surface Estimated from Global Energy Balance Archive Data

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Means and trends of shortwave irradiance at the earth’s surface are calculated from pyranometer measurements stored in the Global Energy Balance Archive (GEBA) database. The GEBA database contains the most comprehensive set of shortwave irradiance monthly means. The relative random error of measurement is approximately 5% of a monthly mean in general and approximately 2% of a yearly mean. The shortwave irradiance yearly means are analyzed in a 2.5° × 2.5° grid. In average example grid cells in Europe (no large altitude differences, no coasts), the difference of shortwave irradiance yearly means measured at different stations (station effect) is less than 5% of the cell mean, and the interannual variability is approximately 4% of the cell mean. On most continents, shortwave irradiance decreases significantly in large regions, and significant positive trends are observed only in four small regions.