Sixteen-day Atmospheric Planetary Wave in Variations in the Earth’s Magnetic Field According to Data from European Observatories

When studying the dynamics of the Earth’s atmosphere, it is of interest to examine the frequencies of geomagnetic field variations in the range of periods of a 16-day atmospheric planetary wave (from 14.5 to 18 days). This work analyzes the spectra of Earth’s magnetic field variations recorded between 2000 and 2023 at three European midlatitude magnetic observatories: the Belsk Observatory (Eastern Europe), the Furstenfeldbruck Observatory (Central Europe), and the Dourbes Observatory (Western Europe). Using the Lomb–Scargle periodogram method, harmonics associated with the modulation effects of long-period variations and tidal effects were identified in the spectrum in the range from 14.5 to 18 days. The analysis shows that the frequencies of geomagnetic variations are independent of the longitude of observations (the observatories are located at approximately the same latitude). Spectral harmonics caused by the modulation with a semiannual variation in the second harmonic of the sunspot cycle and a declination tidal were identified. For a tidal wave with a period of about two weeks, harmonics caused by the modulation effects of the 11-year solar cycle (Schwabe cycle), the fourth harmonic of the 22-year solar cycle, and annual and semiannual variations were identified. Harmonics with periods corresponding to the above modulation effects on a 16-day planetary wave are distinguished in the spectra. The spectral analysis results confirm the influence of processes observed in the neutral lower atmosphere on the dynamics of the upper atmosphere. The results can be used to develop atmospheric dynamics models.