An Automated Procedure For Determining Quiet Daily Geomagnetic Variations

We present a new automated procedure for determination of the undisturbed daily variations of the magnetic field observed by ground based magnetometers. The method determines the quiet day variations in two steps: 1) A determination of the yearly trend. and 2) a determination of the daily variations. Both steps utilizes a sliding window and bins data according to magnitude and a typical value is determined. The window size is adjusted according to the variability of the data. The technique is validated by the use of data from published quiet days and our automated quiet day curve. The full-width-at-half-max (FWHM) of this difference strongly depends on the magnetic latitude. We find that below 60 degrees magnetic latitude the FWHM for the N/E/Z component is ~15/8/7 nT respectively. This paper explains the method, discusses the validation and shows results from individual stations as well as the statistics from >150 stations.