Abstrakt
Frequency-time spectrograms of electromagnetic waves observed in the inner magnetosphere in the frequency range of about 1-8 kHz are sometimes formed by several nearly horizontal and almost equidistant intense lines. Such events are called magnetospheric line radiation (MLR).
We use a list of 1230 MLR events identified in all the data measured by the low-altitude satellite Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) during the duration of the mission (2004-2010). We compare the occurrence of MLR events with solar wind parameters and geomagnetic indices using a superposed epoch analysis.
It is found that MLR events occur more often after periods of enhanced geomagnetic activity, being statistically related to specific solar wind parameters. Moreover, the length of the analyzed time interval allows us to investigate the influence of the solar cycle and the season of the year.
The events occur more often during the northern winter and spring than during the northern summer. As for the spatial distribution of the events, they occur less frequently at geomagnetic longitudes of the South Atlantic Anomaly.
We analyze energy spectra of electrons precipitating in this area at the times of MLR events, and we derive energy-latitude plots of electron flux variations related to the MLR occurrence. Finally, we perform a detailed wave analysis of two MLR events for which high-resolution multicomponent data are available.
The events are right-handed and nearly circularly polarized, propagating at oblique wave normal angles from larger radial distances and larger geomagnetic latitudes.