Fig. 6
From: A review of unusual VLF bursty-patches observed in Northern Finland for Earth, Planets and Space
Quasi-periodic VLF bursty-patches observed at KAN. Power spectrum density at KAN on 20 January 2021 from a 09:00 to 13:00 UT (10:30–14:30 MLT) and from b 10:35 to 10:45 UT, between 0 and 10 kHz. Dashed and dotted horizontal white lines show, respectively, the local equatorial 0.5 fce and fce for the L-shell of KAN. Long lasting quasi-periodic VLF bursty-patches are observed from ~ 09:30 UT between 4 and 9 kHz. In panel a they appear as vertical lines with a periodicity of a few minutes. A black shaped arrow is used to indicate the start and evolution of the emission envelope as a function of frequency. Panel b shows selected 10 min of the same emission at the timings indicated by the magenta line in panel (a). On panel b quasi-periodic features are clearly visible showing a periodicity of 1–2 min