Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation
Russian Academy of Sciences
( founded in 1939 )
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Ionospheric plasma-wave interaction

Comparative analysis of spatial distribution of charged particle energy spectra and variations of wave spectra at auroral oval latitudes using APEX spacecraft data showed that several conditions should be fulfilled for LF AKR generation. These conditions are related both to the intensity and energy of precipitating ion and electron fluxes, and to albedo electrons and the ionospheric plasma parameters. The wideband HF emission was observed together with the LF AKR-type emission during the morning auroral oval crossing. At spacecraft apogee altitudes, in polar cap zone intense electron precipitations and an increase of plasma noise intensity at frequencies equal or below fHe were observed at the period when the IMF was nothward. These precipitations were accompanied by the horizontal currents crossing the polar cap, the so-called theta structure.

Yet in 1979 after the launch of Intercosmos-19 satellite the low frequency emission was discovered which was registered at auroral latitudes by topside sounder receiver and HF wideband AVCh-2 receiver. The more detailed analysis of the emission was made with the help of HF radiospectrometer onboard the APEX satellite in 1992. The main characteristic feature of the emission was that it frequency band exactly coincided with the one of AKR emission, i.e. 0.1 - 2 MHz. It was observed at auroral latitudes within the periods of increased auroral activity and was associated with the particle fluxes measured onboard the same satellite. The intriguing feature of the emission was that it was registered when the upwelling flux of energetic electrons was larger than the precipitating down one. Within the frame of the Data rescue project supported by the NASA grant the data of Cosmos 1809 satellite (1987) were re- analyzed with the help of new developed software permitting to use the AGC signal of the topside sounder receiver as the HF radiospectrometer data. This processing permitted to obtain the statistical distribution of the LF quasi AKR emission for the auroral latitudes of the Northern and Southern hemispheres. In general, the emission distribution fits well the auroral oval borders and coincides with the increased AE-index activity. But the interesting feature of the obtained distribution is that the emission is more or less uniformly allocated in local time domain. The possible physical mechanism of the observed emission is proposed. The different kind of wideband emission is observed within the cusp projection onto the ionosphere. The both kinds of emission permit to map the magnetospheric structures borders projection within the ionosphere.