Studies on Pre-SC Polar Ionosphere and HF Radio Propagation over Polar Paths I

Pre-SC Field Intensity Increase of WWV 20Mc/s Received at Hiraiso, Japan

Abstract

Storm-time variation of WWV 20Mc/s field intensity at Hiraiso is examined for about 50 geomagnetic storms during August 1957-February 1959. An abnormal increase of field intensity of WWV 20Mc/s appears from about 12 hours before a geomagnetic storm sudden commencement to a few hours after it. It is found that the storm-time variation of f₀F₂ deviation from the monthly median also shows pre-SC augmentations for the corresponding storm-time interval at Winnipeg and Fairbanks, which are located at approximate apexes of the Washington-Hiraiso 3 hops path. This close relation between these pre-SC phenomena suggests that the pre-SC intensity increase of HF polar path may be useful for the radio warning especially for periods of the solar minimum activity.