The National Observatory of Athens is the first research Institution created in Greece (1842). Atmospheric measurements at the Athens center (Thission station) have been performed since the late 19th century and the station has been recognized by the World Meteorological Organization among other 60 centennial stations worldwide, for its uninterrupted operation spanning more than 100 years. This is the oldest climatic station in Greece and of the oldest in the Eastern Mediterranean.
Solar radiation related measurements were performed since 1900. These 113-year long measurements (1900-2012) are presented in this work. Surface solar radiation (SSR) variability is presented showing small changes in SSR from 1900 to 1953, with a maximum decrease of 2.9% per decade in SSR when taking in to account the 1910-1940 period. For the 1955-1980 period, a -2% change per decade has been observed, that matches but it is in the lower limit, compared with various European long-term SSR measurement (solar dimming) related studies. For the 1980-2012 period we have calculated a positive change (+1.5% per decade) which is also in the lower limit of the reported positive (brightening period) changes in SSR around Europe. Comparing the 30-year periods (1954-1983 and 1983-2012) we have found a difference of 4.5%. Most of the observed changes in SSR after 1954 can be attributed partly to cloudiness and mostly to aerosol load changes.
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