On the origin of lower- and upper-frequency cutoffs on wedge-like spectrograms observed by DEMETER in the midlatitude ionosphere
2010
Abstract
We report observations of unusual lower and upper cutoff frequencies on VLF spectrograms recorded by the DEMETER satellite (orbiting at ∼700 km) during thunderstorm activity. The upper cutoff frequencies in the spectrograms under discussion vary rapidly.
On the contrary, the lower cutoff frequencies in the spectrograms are almost constant, so that the cutoffs cross at larger L. Between these cutoffs, which thus form a wedge, intense whistlers are observed, whereas only 0+ whistlers, and probably, ducted whistlers are present outside the cutoffs.