Myriametric radio emissions—radio emissions with wavelengths of 10 to 100 kilometers—coming from Earth’s magnetosphere have been observed previously. Now, a new type of myriametric radio emission known as a terrestrial myriametric radio burst (TMRB) has been reported.
Fung et al. report simultaneous detection of a TMRB by the widely separated Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) and Geotail satellites on 19 August 2001. The radio burst occurred over a period of about an hour and a half and had a frequency range of about 12 to 50 kilohertz. The authors found that the TMRB was beamed directly from a discrete source and had a fan beam radiation pattern.
They compared their observations to characteristics of known types of terrestrial myriametric radio (TMR) emissions and found that the timing, frequency range, and spectral characteristics of the TMRB emission are distinct from the known types of TMR. In addition, no other TMRB events were similarly identified during the period from 2001 to 2005 when both satellites were operating, leading the authors to suggest that such events are rare because their identification requires multiple spacecraft to be in the right observing locations during the time of the burst, which depends on a particular combination of solar wind and magnetospheric conditions. They suggest that the TMRB was likely caused by magnetic reconnection (breaking and rejoining of magnetic field lines) at high latitude in the dayside of Earth’s magnetosphere due to a northward orientation of the interplanetary magnetic field (the magnetic field carried outward from the Sun by the solar wind).
