What are emic waves?

Electromagnetic Ion Cyclotron, or EMIC, waves are oscillations in Earth’s magnetic field at or near the same gyrating (going in circles) near or at the same frequency as ions, molecules that have lost or gained an electron, resulting in a net electric charge. 

EMIC waves are caused by charged particles (ions) that propagate in unstable distributions along Earth’s magnetic field lines. One small perturbation can cause the ions to oscillate, which then creates a wave. EMIC waves have been observed more often when there is higher geomagnetic activity taking place (e.g. in a more disturbed magnetosphere/magnetic field), but are also present during time of lower activity. Studies have also found that EMIC waves tend to occur more frequently as a solar phase descends.