Документ взят из кэша поисковой машины. Адрес оригинального документа : http://star.arm.ac.uk/~ambn/abstract344.html Дата изменения: Wed Sep 27 15:12:10 2000 Дата индексирования: Tue Oct 2 00:01:42 2012 Кодировка: Поисковые слова: m 5

We analyse the records of sunshine hours obtained since the late 19th century from four stations geographically distributed throughout Ireland. A gradual decrease in sunshine hours has occured at all four sites since records begun, with a slight recovery between 1950 and 1970 which roughly coincided with a temporary reversal in the upward trend in mean air temperature. We interpret the overall fall in sunshine duration as due to increasing cloud factors resulting from increased evaporation rates over the Atlantic as sea-surface temperatures have risen. We have confirmed a strong negative correlation between sunshine factors from ground-based observations and satellite-based cloud factors over Ireland. In addition, we find that cloud factors over Ireland correlate well with cloud factors over large oceanic areas such as the North Atlantic and mid-high latitudes generally. Thus cloud factors (and similarly sunshine factors) from regions on the boundaries of large oceans which lie in the direction of the prevailing wind, could be useful in determining the long-term changes in cloud factors over more extended areas. Knowledge of such long term variability in the Earth's cloud cover is important input information for modelling past climate change. We have tried to assess the importance of cosmic rays as a link between solar activity and climate from a study of the ISCCP-D2 satellite cloud factors and Irish Sunshine data. Whilst our results confirm the strong correlation between total cloud factor and cosmic rays over non-tropical oceans between 1984 and 1991 previously reported, we find that this correlation breaks down in the subsequent period 1991-94. We have looked for indirect evidence of cloud formation by cosmic rays from the variation in the sunshine factor following forbush decreases. Here again, our data show no significant effect, though this may be due in part at least to the small amplitude of the cosmic ray flux change and the large scatter in the sunshine data. A study of the variation of the sunshine factor during the solar cycle showed a conspicuous peak at seven years after sunspot minimum (three years after maximum) for the four Irish sites and in most seasons. However, in view of the geographical proximity of the Irish stations and the possibly linked behaviour from season to season through the North Atlantic Oscillation, there is no strong evidence to tie such effects to the cosmic ray flux.