Swarm is the fourth Earth Explorer mission of the European Space Agency (ESA), launched on 23 November 2013. The mission provides an opportunity for better knowledge of the near-Earth electromagnetic environment. This study presents an initial attempt to derive an ultra low-frequency (ULF) wave index from low-Earth orbit satellite data. The technique can be potentially used to define a new product from the mission, the Swarm ULF wave index, which would be suitable for space weather applications.

Based on the methods of critical fluctuations and natural time, we have shown that the fracture-induced MHz electromagnetic emissions recorded by two stations in our network prior to two recent significant earthquakes that occurred in Cephalonia present criticality characteristics, implying that they emerge from a system in critical state.

Our study demonstrates a remarkable association between the earthward penetration of ULF waves and radiation belt electron enhancements during four magnetic storms that occurred in 2001. In the past, ULF waves had been observed at unusual depths during rare superstorms. But ULF wave activity, reaching magnetic shells as low as 2, was also observed during relatively intense storms when it played a key role in diffusing electrons radially inward and thereby accelerating them to higher energies.