MEANS AND TRENDS OF SHORTWAVE IRRADIANCE AT THE SURFACE ESTIMATED FROM GLOBAL ENERGY-BALANCE ARCHIVE DATA

Means and trends of shortwave irradiance at the earth's surface are ca lculated from pyranometer measurements stored in the Global Energy Bal ance Archive (GEBA) database. The GEBA database contains the most comp rehensive set of shortwave irradiance monthly means. The relative rand om error of measurement is approximately 5% of a monthly mean in gener al and approximately 2% of a yearly mean. The shortwave irradiance yea rly means are analyzed in a 2.5 degrees X 2.5 degrees grid. In average example grid cells in Europe (no large altitude differences, no coast s), the difference of shortwave irradiance yearly means measured at di fferent stations (station effect) is less than 5% of the cell mean, an d the interannual variability is approximately 4% of the cell mean. On most continents, shortwave irradiance decreases significantly in larg e regions, and significant positive trends are observed only in four s mall regions.