Letter: Keeping a check on rainy days of the week

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Sir: George Nicholson's rainfall figures (Letters, 22 July) show that Sundays are driest by almost the same amount that Thursdays are wettest. The daily mean value is 134.13; the Sunday departure from this is 8.96 and the Thursday departure is 9.03 (all in inches of rain). Both values correspond to about 1.8 standard deviations, differences which would be considered barely significant in terms of most meteorological data.

Since it seems highly improbable that natural processes which induce rainfall are related to the days of the week, I suggest that Mr Nicholson seeks an interpretation in terms of manmade effects. The low Sunday value may be a clue that the working week could have a bearing on it. Summarising the rainfall over 39 years may obscure trends that a more detailed study would reveal. It might be worthwhile to look at public holidays; the possible effects of seasons could also be examined. In addition, he might consider whether there are local industrial sources of discharges to air which could conceivably affect the rainfall at his point of measurement.

Yours faithfully,




23 July