Geomagnetic pulsations or micropulsations (1 mHz to 5 Hz)
The ULF waves of Magnetospheric science
Magnetospheric science defines ULF (Ultra Low Frequency) waves differently from ITU: waves with a frequency that is lower than that of the plasma (ion and electron plasma frequency)
Geomagnetic pulsations are categorized as follows:
Oscillations with quasisinusoidal waveform are called pulsations continuous (Pc). Those with waveforms that are more irregular are called pulsations irregular (Pi).
They are modelled with Magnetohydrodynamic (MHD) equations.
http://magbase.rssi.ru/REFMAN/SPPHTEXT/ulf.html (cites University of Oulu)
Excerpts from McPherron et al 2014
"Magnetic micropulsation is the name originally given to low frequency oscillations of the Earth’s magnetic field. The name represents the manner in which these oscillations were discovered through observation of the end of a very long compass needle with a microscope."
"How are ULF waves created? ULF waves are created by a variety of processes in a magnetized plasma. Plasma is the name given to highly ionized gases threaded by a magnetic field. When the collision frequency in a plasma is sufficiently low, the charged particles simply gyrate around the magnetic field and travel along it. Any force that moves the charged particles also moves the magnetic field and vice versa. In this situation the field and plasma are "frozen together". This concept enabled Hannes Alfvén to describe a simple process that creates a low frequency wave that propagates along a magnetic field line. He received the Nobel Prize for this discovery and the wave he described is now called the Alfvén wave. Alfvén’s model for wave generation is summarized in Figure 3."
"Gyro resonance (or cyclotron resonance) applies to the situation where a circularly polarized wave and a charged particle rotate (gyrate) about the magnetic field at the same frequency. Because the electric field of the wave and the particle velocity maintain a constant angle with respect to each other, the field is able to exert a force on the charge for a long interval. This allows energy transfer to occur (Brice, 1964). In which direction the energy flows depends on the relative angle. In the magnetosphere cyclotron resonance between a left circularly polarized wave and protons is the mechanism that creates Pc 1 magnetic pulsations (0.5–5 Hz). This physical process is briefly described in the following paragraphs."
The British Geological Survey operates:
Similar more recent paper from the same group of authors indicating that daily Autonomic Nervous System (ANS) activity responds to changes in geomagnetic and solar activity:
HRV is used as an indicator of ANS function and dynamics
Note: Mood changes and fatigue may be associated to geomagnetic pulsations