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doi: 10.1002/qj.49707532403pmid: N/A
An attempt has been made to measure the angle between wind direction and isobar at three heights, 3,000 ft, 700 mb (10,000 ft approximately), and 500 mb (18,000 ft approximately), at six‐hourly intervals, above Liverpool, during January and February 1946. On many occasions the isobars (or contours of an isobaric surface) were not sufficiently well defined to permit of measurement, on others, wind observations were not available; in all, the following number of measurements were made:— 3,000 ft 119 700 mb 167 500 mb 186 The isobars or contours were drawn, in each case, without reference to any wind observations. The accuracy of determination of the direction of the wind and of the isobars was considered in each case, and though the exact accuracy is in some doubt, it is considered that many of the deviations of the wind direction from the isobars which were found, were significant. The means of these deviations were (reckoned positive across the isobar from high to low pressure):— At 3,000 ft 7° 700 mb 1.5° 500 mb 0.1° The deviations measured at 3,000 ft were probably not typical, for it seems likely that, even at 3,000 ft the mountains have an appreciable effect on the wind direction. Analysis of the deviations showed no correlation with the stability of the air. An attempt was made to correlate the deviations at 700 and 500 mb with the general weather situation and development with some apparent success. It was found that, at both levels, there was a negative deviation on the boundary of an anticyclone, i.e. inflow to the anticyclone. Also, that at 500 mb and less markedly at 700 mb, deviations were positive ahead of a trough in the upper air, to the top of the wedge, and negative behind the trough. On one occasion the observed deviations agreed with general expectations from significant features of the general situation. The geostrophic wind was also measured at 3,000 ft, from the surface isobars, due allowance being made for height and excluding all cases of marked horizontal temperature gradients in the vicinity. The mean value of the moduli of the vector deviations of the wind from the geostrophic was found to be 9.1 kt, and the root mean.
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