The Height of F-Layer Irregularities in the Arctic Ionosphere

Abstract

Results and interpretations of oblique incidence soundings of the arctic ionosphere are presented. Anomalous echoes are found to be prevalent in high latitudes in contrast to lower latitudes where 2F groundscatter predominates. One of the echoes seen regularly at College, Alaska has been identified as direct F-layer (IF) backscatter. The observations of the IF echo provide direct evidence of the presence of irregularities in the F-layer between heights of 350 and 600 km. The IF echoes are recorded regularly at night and occasionally during the day in disturbed periods. They appear to be associated with auroral ionization. Simultaneous reception of 2F echoes from the north and the south indicates that at times the reflecting layer is tilted. Tilt-angles in the vicinity of 2 to 3 degrees are found. The 2F echoes from the north usually connect to the extraordinary branch of the vertical incidence trace while the 2F echoes from the south appear to connect to the ordinary branch. The analysis of groundscattered (2F) echoes is extended from a plane to a spherical geometry, and it is shown that a geometrical extension of the plane earth theory is adequate. The observed range-frequency dependence differs only slightly from that predicted by the latter theory.