The physical mechanism by which the regions with increased or decreased total electron content, registered by measuring delays of GPS satellite signals before strong earthquakes, originate in the...

We identify two distinct electron populations associated with Alfvén waves in the Freja data set using the high time resolution state of the art electron detector. One of the populations, detected together with an Alfvén wave, is field‐aligned and can be seen as trapped within the wave. The other electron population is detected before the wave and consists of electrons which have left the wave at a point with a velocity higher than the local Alfvén speed. In the paper, the electrons leaving wave are modeled for different density profiles and are compared with the observed data. Depending on the density profile, the model can produce the same energy‐time and pitch angle‐time dispersion that is observed in the Freja data. The conclusion of the paper is that the Alfvén wave can explain the observed particle signatures. It is shown that the Alfvén wave acceleration can create electron signatures similar to inverted‐V structures. The density distribution along a flux tube has an important role in the type of particle signatures that can be detected at low altitudes.

The paper presents the results of studying anomalous variations in the total electron content (TEC) of the ionosphere as probable precursors of strong seismic events. The vertical drift of the F2...