Posted by
Stephen W. Kercel on
Dec 19, 2006; 9:51pm
URL: http://elecraft.85.s1.nabble.com/OT-K-index-2-But-Bands-Deader-Than-Doornail-tp442135p442136.html
Jeff:
It is a perfectly reasonable topic, and one I've been wondering about myself.
Since Thanksgiving, we've had astoundingly bad conditions with lots
of flares and storms.
There are three mechanisms of disruption indicated on the NOAA Web
site, radio blackouts due to X-rays which are mostly felt on the
sunlit side of the Earth and dissipate in a matter of hours, "solar
storms" which are bursts of heavy particles (protons, as I recall),
and the solar wind (a stream of electrons).
As I understand the numbers, K is a "near real time" (reported every
3 hours) indication of disruption of propagation due to the
geomagnetic fluctuations caused by fluctuations in the solar wind.
With each value of K there is an associated value of a, with a pseudo
logarithmic relationship between K and a, such that k=1 => a=3, and
k=9 => a=400. A is the average of the last 8 a values, and thus is an
indication of the cumulative effect of the solar wind on the
geomagnetic field over the past 24 hours.
It is important to realize that A and K are statistical measures that
correctly describe propagation most of the time, but not always.
A=9 is not low. It is usually an indication of "marginal but somewhat
useful" conditions.
My guess is that when the atmosphere takes a series of severe hits,
as has happened over the past week, it takes much more than 24 hours
(suggested by formula for the A index) for the atmosphere to "heal"
itself, irrespective of the low A and K values currently being reported.
It is my observation over recent months that once we've had a
geomagnetic storm it requires two continuous days of both K and A <=
2 before one sees the return of good conditions.
The problem is aggravated by the low sunspot numbers, and consequent
low MUFs. I've noticed that most nights lately from New England, one
hears practically nothing from Europe on 40 m (although one can hear
Caribbean stations running European pileups). The reason is that the
MUF between NE and EU most nights is about 6 MHz. 40 is dead but 80
(in between storms) can be very lively.
Anyway, given the low MUFs, most HF bands are dead much of the time,
and 80 is only usable when the noise (partly induced by geomagnetic
activity) dies down.
I'd be curious what other list members know about this.
73,
Steve Kercel
AA4AK
At 03:53 PM 12/19/2006, Jeff wrote:
>My apologies for going off-topic, but I'm learning to interpret the various
>solar parameters, such as the A- and K-indexes, and I'm a bit confused. The
>K-index is only 2 at 2045 UTC on Dec. 19, but I can't hear ANY CW signals on
>any band, which, until recent weeks, was a very unusual state of affairs.
>The A-index is 9, which I believe is also relatively low. Shouldn't I be
>hearing at least a couple of signals, or is it just that everyone is still
>at work?
>
>Thanks & Happy Holidays,
>Jeff
>WB5GWB
>Long Island, NY
>
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