CII. Directional observations of atmospherics—1916–1920

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Abstract
13,000 bearings of atmospherics; taken between 1916 and 1920, at six British coastal direction-finding stations, spread over 7½° in latitude and 9° in longitude, are analysed statistically. Diurnal and seasonal variations of the apparent direction of arrival of atmospherics are established, the sense of both variations being counter-clockwise with increasing solar altitude. The mean direction of arrival is about 140° E. of N., the mean diurnal range and mean seasonal range are both of the order of 30°, both ranges decrease with increasing latitude. The distribution is skew, the mean being displaced clockwise from the mode (1) in the afternoon, (2) in summer, and (3) in low latitudes, counter-clockwise (1) at other times of the day, (2) in winter, and (3) in high latitudes. Observations in daylight give a mean displaced 26° counter-clockwise from the mean for dark hour observations. Observations between noon and midnight have a mean 15° counter-clockwise from that for observations between midnight and noon. “P.M.” observations show particularly marked skewness, evidently due to the sunset midnight period. The scattering from the mean or mode for the group, measured by the standard deviation, is great (l) between sunrise and noon, (2) in daylight, (3) A.M., (4) in summer, (5) in low latitudes and small, (1) between sunset and midnight, (2) in darkness, (3) P.M., (4) in spring, (5) in high latitudes. Fourier analysis of monthly means and modes gives non-periodic terms between 130° and 150° , variations of twelve-monthly period with amplitudes between 4° and 40°, this amplitude being great in the S.E., small in the N.W., the maximum deviation from mean occurring early in the W., late in the E., and on the mean about one month after the solstices. The variation of six-monthly period follows a similar longitude-phase law. The scattering reaches its maximum about one month after the summer solstice, is less in high latitudes, and its annual range is greater in the S.E. than in the N.W. These results are tested in the case of a seventh station in S.E. England.

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