Fig. 5b shows monthly averaged amplitude on VLF/LF radio signals for equinox months: April and October 2009. As for these two months, on the basis of comparing the curves for monthly average amplitude values during the period of 24 h, it is obvious that the shapes of these curves are similar to each other. There is a time difference when it comes to the moment of appearance and development of amplitude minima in April and October 2009.
On the basis of measured VLF/LF data our results for short paths, D