Abstract
VARIATIONS IN THE RELATION OF THE BAROMETRIC GRADIENT TO THE FORCE OF THE WIND.—In a very suggestive paper recently communicated to the Meteorological Society of London, Mr. Clement Ley shows that the mean velocity of the wind corresponding to each barometric gradient is much higher in summer than in winter, and that this is the case at all stations examined, with all winds, with all lengths of radius of isobaric curvature, and with all values of actual barometric pressure. The diurnal and seasonal variation in the relation of the gradient to the force of the wind is unquestionably one of the fundamental questions of meteorological research, and we hope Mr. Ley will soon again return to its discussion, with ampler data for a more satisfactory handling of the subject than he has yet had before him. That the mean diurnal oscillations of the barometer cannot be neglected in the inquiry is very evident. Thus, while in June at 8 A.M. the barometer at Kew is 0.015 inch above the daily average, on the coast at Falmouth it is only 0.001 inch; but while at 3 P.M. it is 0.015 inch below the average at Kew, it is still 0.001 inch above the average at Falmouth. Crossing to the Continent and contrasting Helder on the coast with Namur inland, it is seen that hi June at 8 A.M. the barometer at Helder is 0.004 inch under the average, while at Namur it is 0.008 inch above it, but at 3 P.M. it is at Helder 0.007 inch above, whereas at Namur it is 0.011 inch below the average. An interesting part of the paper is that descriptive of the mean diurnal variations in the velocity of the wind, in which, among other interesting features, it is pointed out that at the coast stations, the mean horary curve in summer approximates in type to the winter curve at the Inland stations, the diurnal maximum being about 2 P.M. In, connection with this it is interesting to note that while at Valentia and Falmouth the anemometric maximum occurs in summer about 2 P.M., the barometric minimum does not occur till from three to four hours later. The point might be even still more strikingly put by a reference to the observations made at Pola, near the head of the Adriatic Sea, where during June, July, and August, 1876, the anemometric maximum occurred from 10 A.M. to noon, and the barometric maximum from 11 A.M. to 1 P.M. The two maxima are thus all but contemporaneous, a result directly opposed to the view generally entertained that in such cases the barometric maxima are contemporaneous with the anemometric minima. London presents very considerable facilities for the working out of this question in its two well-equipped observatories at Greenwich and Kew, and in the number of meteorological stations situated within a radius of fifty miles, in connection with the Meteorological Office, Mr. Glaisher, and the London Meteorological Society. Observations made at these stations at 9 A.M., 3, and 9 P.M., would render possible the drawing of the isobarics over the south-east of England, with an approach to correctness sufficient to give the barometric gradients for Greenwich and Kew as may meet the requirements of the problem. Isobarics drawn from the Daily Telegraphic Reports alone, while sufficient in a first tentative inquiry, are, owing to the great distances between the stations, necessarily very hypothetical, and therefore much too rough for any satisfactory investigation of this important subject.
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Meteorological Notes . Nature 16, 50–51 (1877). https://doi.org/10.1038/016050a0
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DOI: https://doi.org/10.1038/016050a0