Summing up the sunshine


THE sunniest place in the world is the eastern part of the Sahara desert with 4,300 hours of sunshine every year - 97 per cent of the possible total. Many regions in the lower latitudes, however, regularly experience more than 3,000 hours a year, and not unnaturally perhaps, in such places the sun tends to dominate the daily lives of the inhabitants.

In the 16th century, for example, when the Spaniards roughly intruded on the Aztecs and the Incas of Central and South America, they found civilisations where it was believed that the sun fought a daily battle against the night; to win this recurring struggle the sun had to be nourished with frequent sacrifices of human hearts and blood. And the ancient Egyptians were even more imaginative in their traditions: they believed that every morning a celestial cow gave birth to a golden calf that was the sun, and that every evening "the woman of the sky" opened up her mouth to swallow him. In both cases, the locals built massive temples befitting the sun's status as their premier god.

In Europe, however, sunshine has always been more scarce. The number of hours of sunshine experienced every year decreases from just under 3,000 hours in Greece and southern Spain to 1,000 hours or less in the far north, with areas that enjoy the classical Mediterranean climate having in excess of 2,000 hours per year. For astronomical reasons, the difference between north and south is most marked during the winter months, the seasonal ration varying from more than 450 hours in the Mediterranean to less than 70 hours in the vicinity of the Arctic circle.

It is no surprise that Ireland takes its place among the nations less endowed in this respect. We muster an annual average of less than 1,200 hours in parts of Ulster, and a maximum of about 1,700 hours in the extreme southeast. May and June are our sunniest months, and December the month in which we experience the least.

The long term records for European sunshine show some variation over the decades. There was a gradual rise in the average number of hours sunshine in central and western Europe during the first half of this century, so that the sunniest decades, the 1940s and 1950s, were about 5 per cent sunnier than the longterm average. There has been a gradual decline since then, and our annual ration nowadays is close to what it was some 90 years ago. Not unexpectedly, this latterday fall in sunshine has been accompanied by a corresponding increase in the average amount of cloud, much of the extra, we suspect, comprising the high cirrus type cloud whose origins can be traced to condensation trails from aircraft.