THE Monthly Weather Bulletin is an essential vade mecum for the serious weather buff. It is a slender booklet of some 20 pages, published, as its name suggests, 12 times every year by the Meteorological Service, and available on subscription for a modest fee. Each issue provides the reader with a regular and up to date assortment of facts, figures and information about the weather of the month concerned, with graphs, tables and convenient summaries. A recent issue, for example, provides an interesting assessment of the glorious summer of 1995.
It is not easy to find an objective way of measuring the "goodness" of a summer to encapsulate the entire season in a single number in such a way that the better ones can be identified for fond remembrance, and the poorer examples reviled without injustice. After all, a warm summer that is unpleasantly wet and dull is no less mediocre than a bright one characterised by chilly winds. One way of taking all these diverse factors into account is to use the "Poulter Index".
The Poulter Index, named after a certain Dr Poulter who devised it, is based on the reasonable assumption that the character of a particular summer depends mainly on three specific variables: temperature, rainfall, and sunshine. Other features such as cloudiness, windiness, or the frequency or absence of thunderstorms - are assumed to be related to these elements, and in any event they are known to have a much smaller impact on our collective memory.
The score assigned to each summer is calculated by a special formula carefully devised to give due weight to each of these three elements. The good summer of 1976, for example, had a Poulter Index in the Irish midlands of 405, awhile that of 1985, probably the worst in recent years, scored a miserable 249. The average Irish summer scores about 335 on Poulter's scale.
So, viewed from the distant, dark perspective of a chilly January, was summer 1995 really as good as we remember it? Was it, taken for all and all, the best we ever had - or has mid winter added a glow of false enchantment to the memory?
The vital statistics confirm our best impressions. Summer 1995 at Birr and Dublin scored 433 and 443 respectively on the Poulter scale, making it the highest scoring summer for a century or more at those places. In the southwest 1995 was less spectacular: the summer at Valentia Observatory scored 425, but even that was the highest figure there for 40 years. By contrast, as if we need reminding, the summers of 1993 and 1994 were mediocre, achieving Poulter Indices in the region of 300.