The position and height of auroral absorption deduced from VLF phase measurements

Abstract

The main findings from VLF measurements during auroral absorption are as follows: The geographical extent of auroral absorption seems to be at least a factor of two larger than found by HF riometers. The VLF reflection layer is markedly depressed during auroral disturbances. At night large and rapid fluctuations in the reflection layer may occur simultaneously over distances of more than 500–1000 km. During day-time the depressed VLF reflection layer seems to be relatively homogeneous over the same distances.