Characteristics of nighttime West-to-East VLF waves propagation using the South America VLF Network (SAVNET)

We present the monitoring of ~ 4 years of daily VLF amplitude curves using two parallel propagation paths from the South America VLF Network (SAVNET). During this period, the time of occurrence (Terminator Times) of deep amplitude minima were measured. We discuss typical properties of West-to-East VLF subionospheric propagation like the seasonal effect on the temporal evolution of Terminator Times, the fact that they are simultaneously detected on parallel propagation paths, and the derivation of the undisturbed nighttime ionospheric height. The method known as the terminator time method is also a promising way of looking for possible seismic-electromagnetic effects.