So can we assume that the exceptional conditions reported by Larry Kaiser
were
related to this Flare on 5 feb.if so there is a delay of one week between
the
event and the change in propagation! is this unique or has it been observed
before?
The MDE (or shortwave blackout) is caused by particles (from the sun) that
travel at much slower speed than light. Delays of 24h and more between the
(visual) occurence of a flare and MDE are common.
Usually SIDs appear to be associated with increased D layer absorbtion and
consequent radio blackouts.Perhaps there is another mechanism in the
recovery
of the ionosphere from such an event which results in the dramatic
improvement
in propagation noted by Larry.
Increased D-layer absorption is causing the 'blackout' on HF. Some theories
say that under extreme conditions the ionisation of the D-layer can be that
strong that it will reflect LF (and eventually MF) instead of absorb it.
I remind an article in CQ-DL (somewhere in the 80's) that handles about
this and it even mentioned QSO's between Germany and Malta (abt. 2000km) at
noon (during summer) on 1.8MHz during a strong MDE.
In the past I have noted increased signalstrengths (on 136kHz) from
northern Europe (OH and SM) whan the A-index was high. At the same time
signalstrengths from southern Europe (I) was hardly affected.
73, Rik ON7YD
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