“…In this case, the field line ( L = 1.235) is so close to the
surface at the magnetic equator that the edge of the wavefront and the Poynting flux of the L1 mode is tangent to the
surface, which makes MLAT = 20° a critical magnetic latitude of the power line. The L1 mode transformed from the R1 mode of PLE generated by the power lines at higher magnetic latitudes may be guided along the field lines after crossing the
surface and get absorbed through ion cyclotron resonance (e.g., Gurnett & Brice,
1966; Shklyar & Kuzichev,
2014) before reaching the magnetic equator.…”