I have been away again. This time to Poitiers in France
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| GM4FVM in the cafe in the Blossac gardens in Poitiers France (photo Mrs FVM). |
This photo does look a bit like one earlier this year in Vught in the Netherlands, though with a different Belgian tipple. Anyway, no radio on this trip. I note that once again, on my second visit to Montparnasse station in Paris, I was stopped and asked for a ticket by an RATP official. I am not sure if it is because of the way I look. Maybe they had intelligence that I might be a ticket dodger. Still, I suppose two visits separated by 35 years is a small sample. I must watch out for this again, as the Metro journey from Gare du Nord to Montparnasse is never easy at the best of times.
What follows has been revised on 12 October 2023 to include updated diagrams. It has been developed into a fuller article and this should appear on this blog later.
Back in Scotland now, on 28 September I worked Elivra, 6W/IV3FSG, in Senegal on 6m.
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| 50MHz contacts at GM4FVM on 28 September 2023 |
As usual, click the image to enlarge if necessary.
This contact reminds me of the one with TT8SN in Chad on 20 October 2022. This distances are similar - TT8SN is 5084km, while 6W/IV3FSG is 4766. Both are at the southern extreme on the Sahara desert. Both were happening at around the time of Trans Equatorial Propagation (TEP) further south into Africa. That posting can be found here.
At the time I pointed out that the propagation mode behind this contact to Chad was a mystery. Now after another one I feel a bit more certain as to how it happens.
In this recent case just before I worked 6W/IV3FSG I worked EA2AR and F5TMJ (LA3EQ had been worked 10 hours earlier). So there was Sporadic E towards the south of me. Later I heard V51WW in Namibia which was clearly TEP as he is on the other side of the Equator. I heard GM6NX working ZS6NK, so that is further evidence of crossing the Equator by TEP. Also, I could hear Spanish stations working V51JH and V51CO in Namibia. I was also hearing station in the same area when I worked TT8SN last year.
So that seems to sew it all up. There was Es from here to Spain, there was TEP from Spain across the equator to Africa, and presumably Es linking to TEP from Scotland to Africa. Es linking to TEP. Problem solved. That must be how I worked Senegal.
Erm... there is a flaw in this logic. Senegal is not across the Equator from Scotland. It is 14 degrees north of the Equator. Ah but, you say, that is the Geographic Equator. For this purpose we have to consider the Geomagnetic Equator, which is diverted north across Africa. True, but the diversion is not enough to put the Geomag Equator north of Senegal. From what I can see it passes just south of Senegal.
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| One of the many representations of the Geomag Equator on the internet |
None of these images on the internet are too clear. But I conclude that the Geomag Equator passes just south of Senegal, maybe about 12 degrees north of the Geographic Equator.
So if the signal from 6W/IV3FSG was an example of TEP propagation, it did not cross either of the Equators. There seems to be something in the expression "Trans Equatorial" which suggests to me a crossing of the Equator.
OK, having read various articles, especially those written by James Kennedy K6MIO/KH6, I think I have now got some sort of a grasp of this. Based on his ideas I have created a diagram showing the process.
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| Generalised representation of classic TEP (after K6MIO/KH6) |
However, K6MIO/KH6 does have an explanation of observed propagation effects which does explain both stations being on the same side of the Equator. In this case, I reckon "Trans Equatorial" refers to the effect in the ionosphere as shown by VK4YEH. This type of TEP is decidedly one sided.
K6MIO/KH6 describes the one sided effect as "Single-Lane F2" propagation. In his articles he shows diagrams of many TEP paths which are entirely in the north "Lane" reaching only north of the Geomag Equator. The paths he shows are mostly across the Pacific and several run generally south east to north west, but he also shows one running north east to south west . However, in the text he suggests that they can run north-south. The path to Senegal from me runs north east to south west at azimuth of 201 degrees.
James also says that the two stations must be within about 2000km of the same ionisation peak and if north-south they must be on opposite sides of the lane. Now I have done a little back of the envelope investigation of these figures in relation to my QSO. If indeed Senegal is close to the Geomag Equator (which the internet maps suggests it is) then it is far on the opposite side of the lane from Europe. James' article suggests that the skip points will be between 10 and 20 degrees from the Geomag Equator.
OK, assuming that TEP got the signal to Spain and Es carried it the rest of the way, my calculations suggest that the Senegal-Spain section would be about 3000km and the Spain-Scotland section would be about 1700km. These are both well within the potential of the two propagation modes. All the other conditions in the K6MIO/KH6 paper seems to be met. This looks like "Single-Lane F2" as described in the TEP articles.
K6MIO/KH6 has done proper scientific research and analysis, I have just read his articles. I am no earth scientist. I have used his ideas as the basis for a diagram which I think represents the situation on 28 September when I worked Elvira in Senegal.
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| 50MHz situation on 28 September 2023 |
I come to the conclusion that Single-Lane F2 is the method of propagation behind both of these contacts - partly by being convinced by K6MIO/KH6's scientific rigour - and partly by ruling out the alternative explanations.
Multi-hop Es looks very unlikely. I hate to write "never", but I cannot think of me ever seeing multi-hop Es at this time of year. Sure, there is Es all year, but outside the peak season (in my experience) it is single hop only. It would need to be three hops for this contact, two would not be enough. Add to that the time which was 19:30 local, and then multi-hop Es at this time of year seems extremely explanation. In July, maybe, but not in late September. Unless of course there is new type of multi-hop Es ....
Ordinary F-layer? I am pretty sure that the southern African stations were TEP and not F-layer propagation. There are a few signs of what might have been classic F-layer propagation but not enough to convince me that it has happened yet. Of course, TEP is F-layer propagation, but a very different type.
No, given that there was classic TEP and single-hop Es at the same time as this QSO this definitely looks like Es linking to "non-Trans-Equatorial-TEP" or to give it a better name "Single-Lane F2 associated with TEP".
I could say a lot more about Es linking and the distances involved in single-lane TEP, but I will not do it here. Let me just leave this as an idea. The idea is that when there is classic TEP around linking me in Scotland with the far south of Africa, there also seems to be [something] linking me with much further north in Africa. These shorter paths do not cross the equators. I believe that the [something] is single-lane TEP. In believing this I have thought about classic F-layer and multi-hop sporadic E propagation and rejected both as likely candidates.
OK, maybe [something] is another entirely new propagation method which just happens to occur when I hear other TEP. I doubt it.
Just because the path of a contact does not cross the equator does not mean we can rule out that it is caused by a trans-equatorial effect, such as TEP.
I see this type of propagation posted as TEP. The correct name in the articles is "Single-Lane F2" but as it is associated with TEP I doubt if anybody is going to change their idea of what to call it. So I will continue to post it as TEP for now as it is not classic F2 propagation either. Put another way, I do not believe that these contacts would have happened but for the TEP event which was noted at the same time.
Bit of a description dilemma there for now.
73 Jim
GM4FVM
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