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Last night a pronounced fading pattern
occured on my VLF dual-loop grabber. It was apparently caused by an area of
fairly localized lightning activity, which passed over Nuernberg around
20 UT, and continued moving northward during the night.
df6nm.bplaced.net/VLF/pictures/vlfwide_Blitzortung_140523_0400.png shows a colour-DF spectrogram, including an insert
from the Blitzortung.org archive covering Germany from 22 to 04
UT. While the storm activity receded from about 200 to 500 km
distance, the spectral maxima moved upwards, and their spacing
increased from about 2 to 3 kHz. This would be consistent
with superposition of groundwave and variable elevation angle
skywave: When the source moves away, skywave becomes less steep,
associated with a smaller geometrical delay difference and further spaced
spectral features.
All the best,
Markus (DF6NM)
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