Hi
I think this recently published paper on space hurricanes might at least to
some extent explain why on some nights with seemingly promising Solar
indices (low Solar wind speed and density, Bz component positive),
trans-polar propagation just does not happen on topband:
https://www.nature.com/articles/s41467-021-21459-y
In short, as I (non-scientist) read it - during the periods of low speeds
and density of Solar wind, positive Bz component and dominant By component,
scientists have observed space hurricanes which bring down into ionosphere
lots of electrons/energy , which is comparable to the amounts observed
during Solar storms.
Quote:
*"The space hurricane opens a rapid energy transfer channel from space to
the ionosphere and thermosphere, and would be expected to lead to important
space weather effects like increased satellite drag, disturbances in High
Frequency (HF) radio communications, and increased errors in
over-the-horizon radar location, satellite navigation, and communication
system*s"
73
Agris/YL2VW
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