Fig. 1
From: Conjugate observations of power line harmonic radiation onboard DEMETER
Two typical PLHR events at the conjugate zones. a Frequency–time spectrograms of events A and B and their amplitude comparison. All PLHR lines are near 4150/4250/4350/4450 Hz and spaced by 100 Hz. The densities of the 4250 Hz and 4350 Hz lines in event B are stronger than those in event A. b Fluctuation of Ne. Dots are data measured by DEMETER, and they are fitted by a smoothing spline curve, where the red segment is the range of PLHR. The blue triangle represents the local peak of Ne. c Fluctuation of ∇Ne, where the blue triangle indicates ∇Ne = 0. d Variation in the SYM-H index during the occurrence of PLHR and three days before PLHR. The strongest value is only − 19 nT. Line in red represents event A and line in blue represents event B