On the use of the LHR frequency determined from satellite VLF measurements for purposes of outer-ionosphere diagnostics

Values of the LHR frequency determined from satellite VLF measurements have been used for outer-ionosphere diagnostics together with independent measurements of one of the medium parameters. This proved that even the LHR frequency values alone can be used, at least to estimate the limiting values of electron concentration and effective ion mass in the vicinity of the satellite. The analysis of the well-known function describing the behavior of the LHR frequency in dependence on the plasma parameters of the outer ionosphere, also indicates that the principal factor determining its 'sensitivity' to changes of electron concentration is the relation between the electron gyrofrequency and electron plasma frequency. Consequently, the outer ionosphere has been divided into three regions with characteristic variations of the LHR frequency. It is shown that LHR frequency measurements can also be used to determine the 'low-latitude edge' of the through of light ions and electron concentration.