Figure 7

Sensitivity to the data treatment of the amplitude and phase of periodic signals. Amplitude and phase obtained for annual (right) and semiannual (left) periodic signals for the X component at Sitka (57°N, 225°E, four top panels) and Tucson (32°N, 249°E, four bottom panels), for different data selection (OMM constructed from night only data or from all-hours values) and window lengths δ t. The phase of the periodic signal (originally in radians) is translated into the date at which occurs the first maximum of the annual (or semiannual) fit to the data (for each epoch, a phase of zero would correspond to January 1).