ANOMALY IN THE LONG-DISTANCE 40-KHZ RADIO-WAVE PROPAGATION

Anomalous propagational characteristics (miday level greater than the midnight level) have been observed in the case of propagation of 40 kHz low frequency signal over a distance of 5100 km from Sanwa, Japan, to Calcutta. The anomaly is closely associated with geomagnetic storms. This is expected to be due to extra-ionization in the D-region caused by the precipitation of energetic charged particles. The storm after-effects have duration of one day in this low latitude path.