Survey of magnetospheric line radiation events observed by the DEMETER spacecraft

[1] Magnetospheric line radiation (MLR) events are electromagnetic waves in the frequency range between about 1 and 8 kHz that, when presented as a frequency-time spectrogram, take the form of nearly parallel and clearly defined lines, which sometimes drift slightly in frequency. They have been observed both by satellites and ground-based instruments, but their origin is still unclear. We present a survey of these MLR waves observed by the DEMETER spacecraft (at an altitude of about 700 km). Three years of VLF Survey mode data were manually searched for MLR events, creating the largest event satellite database of about 650 events, which was then used to investigate the wave properties and geographical occurrence. Finally, the most favorable geomagnetic conditions (Kp and Dst indices) for the occurrence of MLR events have been found. It is shown that MLR events occur mostly at L > 2 (upper limit is given by a limitation of the spacecraft), they occur primarily inside the plasmasphere, and there is a lower number of events occurring over the Atlantic Ocean than elsewhere on the globe. The MLR events occur more often during the day and usually during, or after, periods of higher magnetic activity. Their frequencies usually lay between about 2 and 6 kHz, with the total frequency bandwidth of an observation being below 2 kHz in the majority of cases. Moreover, it is shown that the longitudinal dimensions of the MLR events can be as large as 100° and they can last for up to a few hours. Finally, we discuss a possibility that MLR events may be triggered by power line harmonic radiation (PLHR) and we report an event supporting this hypothesis.