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How to use A index effectively
[from a hcdx list discussion in 1998]

Question: Has anyone come up with any good theory on what conditions are likely to be like regarding the A Index or the K Index?

Mauno Ritola, Finland: I think that the lower the K and A-index is the better, but they have to low for some days before the conditions really improve.
But stratospheric warmings can spoil everything. I think it was in 1987 we had low A and K for a long time and yet nothing special was heard from North America.
In the 80's I also experienced A index going up to 15 and it spoiled nothing maybe because it came back so quickly to 1 the next day.
I think that when there is some very slight activity in the geom. field, the K-index given every three hours doesn't give a full picture of the thing. It may show 0 and there still is activity and the results are poor.
It should be a kind of average of measurements maybe each half hour. These are my humble thoughts just from experience of about 25 years and to talk about this in English is even more difficult!
A real theory on these things would be really interesting.

J.D. Stephens, USA: TA reception can be enhanced with a K index of 4 (although the lower the value the better).
Checking the OH2BUA web page for a summary of the geomagnetic conditions for January 5th, 1998, the A index varied between 3 and 5, and the K index between 0 and 2.
These values indicate it's definitely quiet enough to allow some TAs to cross the pond, although at least for those like you and I who aren't located on the U.S. East Cast, increased probability of reception should be from more or less mid-latitude countries (such as Spain, Portugal, Canaries, Italy, Saudi Arabia, etc. Incidentally, enhanced reception of Saudi Arabia-1521 has been reported here in the U.S. during the last few days.
By the way, the aforementioned website also shows that the geomagnetic indices dropped throughout the night to a current January 6th value of A=2, and K=1.

Paul Ormandy, New Zealand: I don't think the A index alone is a good indicator of reception as one of the best ever W Coast NA openings I've heard was when the A index was nigh on 100!
And I would agree that sometimes when the A index is low, reception can be poor.
NZ DXer Peter Chambers monitored various indicies and concluded that we couldn't hear Argentina, Brazil, Uruguay, Paraguay unless the A index was over 14. As for the K index, I've never been able to make any conclusions in respect to K index variations.

David Onley, Australia: As Paul Ormandy, I don't think the A index alone is a good indicator of reception.
I've had similar observations and it's one of the hardest things to predict/monitor.. I've had great reception during major storming.. I suppose it depends on where you are & what effect the storm has had on the circuits..
I'm not sure if too much scientific research has ever been done in this area.
As far as knowing what conditions are like.. the bottom line is to just turn the set on & see.. I've never been one to pay too much attention to the reports..
However.. getting back to what I first mentioned.. It would be mighty interesting to know on average what solar conditions are like when we have good East/West & Nth/Sth paths open with above average signals.

Hermod Pedersen, Sweden: All of this also affects signals coming from Latin America.
When NA signals are depressed by aurora, life becomes more easy for signals coming in a more southernly path.
This is even more enhanced in the tropical bands. When a storm hits the atmosphere, lots of signals on the Northern hemisphere is blocked out, leaving a more clean path to signals from regions around the Equator.
Thus signals from central Africa and Peru/Bolivia get an extra boost during stormy conditions - that is, if it is not too stormy, when all signals are affected unfavourable.

Karel Honzik, Czech Republic: I heard and read several times that signals from south become better because the signals from northern latitudes disappear during the storm (here in the northern hemisphere), but I do not think it is so.
The signals simply "gain power" and are much stronger than usual. It happens of course also on channels where is no interference from "northern" stations.
There is a theory of a "positive phase of the storm" which starts just before the storm starts. This theory was supported by the development we could monitor on August 27, 1998.
Excellent signals especially from Latin America have been observed on several places in Europe during the night of Aug 26/27 (UTC), just before the storm started at around 0400 UTC.
The whole development depends very much on many aspects and it is very difficult to make predictions. I am quite interested in this area. Many of my predictions already failed, especially when I alerted my DX-friends in
advance. Quite a number of predictions was OK, mostly when my friends were not sitting at their receivers because they expected the prediction to fail again :-)
My experience: excellent conditions usually do not repeat the next day/night.

Jean Burnell, Canada: Karel Honzik recently pointed out that there are two main schools of thought regarding how radio propagation is affected in solar storms.
The first is that northern propagation is adversely affected so equatorial signals just appear to be enhanced, i.e., northern signals are eliminated.
The second hypothesis is that, as Karel says, "The signals simply 'gain power' and are much stronger than usual."
Actually, I think that both phenomena operate, at least at MW frequencies.
During the past evenings I've noticed what I've always seen during times of high solar activity...signals from northern Europe and North America are very much attenuated, and signals from equatorial regions are enhanced.
There are certain beacon signals that can be used to illustrate this enhancement. These are stations on unique frequencies for which the idea that they are covered up by northern stations cannot apply. For me, examples of such stations are Kara, Togo, which is now on 1502.68 kHz,the Voice of Nevis on 895 kHz, and Radio Grenada on 535 kHz.
The first of these is not usually detectable except as a very faint heterodyne against 1503 kHz, but at 2253 UTC on 26 August I had this on a simple loop antenna with SINPO 34433.
On the other hand, it is true that northern signals are very much attenuated, because in the past few days I have barely been able to hear any signals from Europe (except Spain!). In contrast, during "quiet" conditions stations like TalkRadio on 1089 kHz, NRK on 1314 kHz and BBC on 909 kHz are easily receivable here in St. John's, even on a car radio.

Gert Nilsson, Sweden: I think we have to consider the difference of signal path when we discuss the importance of A-Index.
The A-index is a good instrument to decide adsorption of signals passing the auroral zone. In the northern part of Scandinavia almost every transatlantic signal passes through this zone and very high A-index means almost no signals at all.
On the other hand long periods with very low solar activity and low A-index seems to favor signals from Canada. A small disturbance makes signals further south to come through. A good transatlantic period very often ends with a very good peak towards the southern parts of the US, Mexico and later exceptional signals from South America.
On the 30th of December 1997 there was a disturbance reaching earth around 03.00 UTC with a peak for signals from California and in the morning you could here Colombians on every channel well after sunrise! Signals from Brazil, Argentina and Uruguay are often heard when A-index is rather high.
When A-index is very high I often have good reception of Africa and southern Europe here 500 kilometers north of Stockholm as the powerhouses in Russia and northern Europe are much weaker.
I always check Jan Alvestad Internet page Solar Activity Report at http://dxlc.com/solar/
I think it is an excellent source of information. It should be a good choice also for DX-ers in North America wanting to receive stations in northern Europe and the Far East.

Nick Hall-Patch, Canada: There have been a number of articles written over the years regarding geomagnetic conditions and MW reception.
Try the National Radio Club reprints by Gordon Nelson, particularly articles P1, P6 and P7.
The club offers a number of propagation and other articles . A listing is available from National Radio Club Publications Center, P.O. Box 164, Mannsville, NY 13661-0164 U.S.A. for U.S. postage suitable for your location (they likely take IRC's and US$ bills)
US$1 will get you a list of reprints from IRCA Reprints c/o Steve Ratzlaff, 1885 E Bayshore Rd Sp 90, E Palo Alto CA 94303. Articles T26, T32, and T54 will be of interest particularly once you've read Nelson's early articles.
Stratospheric warming was covered in QST February 1997, page 76. The author is interested in amateur bands, so realize that stratwarms have a greater effect the lower you go in frequency (i.e. MW). The author refers to some seminal earlier work on the subject.
Geomagnetic upsets have the most effect on trans auroral paths, many of which are between Europe and North America, home to many DXers. It does seem that western North America to Australasia paths which are away from the auroral zone benefit from increased geomagnetic activity.
But don't paths from Australia to southern Africa cross the southern auroral zone?
Have Aussies and Zedders observed what high A-indices do to those signals?
Hope this helps some folks.


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