Portugal - Atlas do Ambiente I.1 - Insolação

Summary

In the Portuguese meteorological literature, insolation means «sunshine duration» however be it known by «solar radiation» in the English speaking countries. Sunshine is a very important climatic element as far as human activities and behaviour of ecosvystems are concerned. The «sunshine duration» is expressed either in hours or in percentage. Sunshine duration is generally measured by sunshine recorders, the Campbell-Stokes being the most used one. However, the method followed does not provide the true duration of the period, or periods of bright sunshine. The Sunshine Duration Chart was based on climatological normals of reference for the 1931-1960 period; and it took into account not only the network of 30 climatological stations running for a whole period of 30 years, but also other 26 stations running for periods greater than 15 but less than 30 vears. The Chart shows that the minimum values of bright sunshine occur in the highlands of Minho (1800 hours per year), and the highest values (3000 hours or more per year) in the coast of Algarve eastwards of Praia da Rocha, in the Setúbal peninsula, in the Costa do Estoril (between Lisbon and Cascais), and in the Alentejo border with Spain. The sunshine duration in Portugal is much higher than its average value for Europe, only being exceeded by a few small areas of the Mediterranean coastlands. 6