Absorption of decimetre radio waves in the Earth's high-latitude ionosphere during a geomagnetic storm in June 2015

Abstract

We have analyzed the radio occultation (RO) results of ∼100 sounding sessions of the high-latitude (>65°N) lower ionosphere of the Earth's northern hemisphere, which were carried out on 22-23 June 2015 at the GPS-frequency of 1545.42 MHz (L1 band) in the FORMOSAT-3/COSMIC experiment. Coronal plasma ejections that reached the Earth in this period provoked a class G4 magnetic storm (strong geomagnetic storm with planetary Kp-index equal to 8), which in turn caused significant ionospheric fluctuations of radio waves on the sounding paths: navigation (GPS) satellites - low-orbit (FORMOSAT-3/COSMIC) satellites. For the first time, the analysis of FORMOSAT-3/COSMIC radio frequency measurements revealed the absorption of L1 radio waves in the lower high-latitude ionosphere of the Earth. The absorption value is ∼3 dB in the range of 60-90 km and in some cases reaches ∼10 dB at altitudes from 90 to 95 km. It is shown that it is possible to obtain the absorption coefficient of GPS-frequency radio waves in the Earth's ionosphere at these altitudes from experimental data of FORMOSAT-3/COSMIC.