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1 Laboratory of Meteorology 2 Foundation for Research and Technology-Hellas 3 Department of Physics 4 Department of General Applied Science 5 Department of Electrical Engineering

Abstract : The monthly mean shortwave SW radiation budget at the Earth-s surface SRB was computed on 2.5-degree longitude-latitude resolution for the 17-year period from 1984 to 2000, using a radiative transfer model accounting for the key physical parameters that determine the surface SRB, and long-term climatological data from the International Satellite Cloud Climatology Project ISCCP-D2. The model input data were supplemented by data from the National Centers for Environmental Prediction ? National Center for Atmospheric Research NCEP-NCAR and European Center for Medium Range Weather Forecasts ECMWF Global Reanalysis projects, and other global data bases such as TIROS Operational Vertical Sounder TOVS and Global Aerosol Data Set GADS. The model surface radiative fluxes were validated against surface measurements from 22 stations of the Baseline Surface Radiation Network BSRN covering the years 1992?2000, and from 700 stations of the Global Energy Balance Archive GEBA, covering the period 1984?2000. The model is in very good agreement with BSRN and GEBA, with a negative bias of 14 and 6.5 Wm-2, respectively. The model is able to reproduce interesting features of the seasonal and geographical variation of the surface SW fluxes at global scale, which is not possible with surface measurements. Based on the 17-year average model results, the global mean SW downward surface radiation DSR is equal to 171.6 Wm?2, whereas the net downward or absorbed surface SW radiation is equal to 149.4 Wm?2, values that correspond to 50.2 and 43.7% of the incoming SW radiation at the top of the Earth-s atmosphere. These values involve a long-term surface albedo equal to 12.9%. Significant increasing trends in DSR and net DSR fluxes were found, equal to 4.1 and 3.7 Wm?2, respectively, over the 1984?2000 period equivalent to 2.4 and 2.2 Wm?2 per decade, indicating an increasing surface solar radiative heating. This surface SW radiative heating is primarily attributed to clouds, especially low-level, and secondarily to other parameters such as total precipitable water. The surface solar heating occurs mainly in the period starting from the early 1990s, in contrast to the commonly reported decreasing trend in DSR through the late 1980s, found also in our study. The computed global mean DSR and net DSR flux anomalies were found to range within ±8 and ±6 Wm?2, respectively, with signals from El Niño and La Niña events, and the Pinatubo eruption, whereas significant positive anomalies have occurred in the period 1992?2000.





Author: N. Hatzianastassiou - C. Matsoukas - A. Fotiadi - K. G. Pavlakis - E. Drakakis - D. Hatzidimitriou - I. Vardavas -

Source: https://hal.archives-ouvertes.fr/



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