Could the Full Moon Excite a Low-Frequency Perturbation on the Earth's Magnetic Field?

Both ground based magnetometers and ionospheric radars at Earth have frequently detected Ultra Low Frequency (ULF) fluctuations at discrete frequencies extending below one mHz-range. Many dayside solar wind drivers have been convincingly demonstrated as driver mechanism. In this paper we investigate and propose an additional, nightside generation mechanism of a low frequency magnetic field fluctuation. We propose that the Moon may excite a magnetic field perturbation of the order of 1 nT at discrete frequencies when it travels through the Earth’s magnetotail $\approx$ 4-5 days every month. Our theoretical prediction is supported by simulations and a case study of ARTEMIS magnetic field measurements at the lunar orbit in the Earth’s magnetotail. ARTEMIS detects peaks in magnetic field fluctuation power at frequencies of 0.37 to 0.47 mHz that are not present in the solar wind.