Studies on Pre-sc Polar Ionosphere and HF Radio Propagation over Polar Paths
II. Pre-sc Increase of WWV 20 and 25Mc/s Field Intensity and of f0F2 in High Latitudes
1965 Volume 17 Issue 1 Pages 45-57
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1965 Volume 17 Issue 1 Pages 45-57
Storm-time variations of WWVV 25, 20, 15, 10, 5, and 2.5Mc/s, and of the average deviations of f0F2 from the monthly median are examined for fifty geomagnetic storms during August 1957-February 1959. Abnormal increases of field intensity of WWV 20 and 25Mc/s, and of Δf0F2 occur from about 18 hours before a geomagnetic storm sudden commencement. Such field intensity increases have not statistically been found below 15Mc/s. The abnormal increases of field intensity at 20 and 25Mc/s may be interpreted as being due to a decrease in deviative absorption associated with an increase in f0F2 for the penetration frequency near 20-25Mc/s. The low latitude boundary of the pre-sc increase of f0F2 lies around 57°. 0N in geomagnetic latitude. A pre-sc increase of Δf0F2 in high latitudes is also found for geomagnetic storms associated with PCA during August 1957-February 1959.
