Characteristics and Source of Unexpected Modes Observed in the Low Frequency Seismic Spectrum

The initial observations of the continuous excitation of Earth's normal modes were first presented a decade ago. While significant research by multiple groups has been directed at the source of the continuous excitation since these discovery papers, the proposed sources do not explain the observations. We present more detailed multitaper analysis of seismic data recorded by the IRIS Global Seismic Network, laser strainmeter data from PFO, and coherence estimated between this data and the interplanetary magnetic field measured at ACE. Our analysis shows: 1. Coherence and phase relations between the North and East components of seismic velocity are largely aligned with the geomagnetic field. This also occurs in data from laser strainmeters, excluding simple magnetic coupling to the instruments. 2. The temporal dependence of the hum exhibits a strong diurnal dependence aligned with geomagnetic activity. The lunar component is usually weaker or absent, so forcing by nonlinear interactions of ocean waves seems improbable. 3. The horizontal seismic velocity is coherent with the interplanetary magnetic field measured by the ACE spacecraft at the first Lagrange point and with magnetic fields measured on GOES and similar sources. We conclude that "Earth's hum comes from the Sun".