Statistical methods for research on diurnal variations

Abstract

It is explained that research on the variability of the diurnal variations is necessary, because the usual method of discussing the average variations alone leads one to overlook characteristic features of the phenomenon. The use of harmonic dials for this purpose is described, and the formulae for numerical and graphical work are given. The use of the two‐dimensional standard deviation and of the probable ellipse for estimating the accuracy of average diurnal variations is explained. The procedure is applied to the diurnal variation of declination on quiet days at Huancayo observatory in southern summer, and the results are discussed. The variability is surprisingly large and affects both amplitudes and phases of the sine‐waves. Some days with particularly large and small amplitudes are picked out. Preliminary results of similar calculations for Watheroo Observatory are summarized, among others the remarkable dial for the 24‐hourly wave in horizontal intensity, which indicates that the focus of the diurnal atmospheric current‐system passes on some days north, on other days south of Watheroo. Some remarks on future work are added.