Es Path Symmetry

I've been wanting to write about a visual phenomenon I often see on the FM List Visual Logbooks during Es openings. The problem I have in demonstrating this is that you really need to see this particular display live, as it happens, as the Visual Logbook will quickly fill up with additional propagation paths and the general effect becomes fuzzy and lost as the propagation path moves.

Now, I expect this phenomenon is already widely understood in amateur radio circles. It's just that I have never come across it before and, even after asking a few ham operators, not one of them said they were aware of this effect.

What is it? Well, I can only describe it as a symmetrical propagational pattern, maybe there's even a circular pattern in this too, as you will hopefully see. The best way I can demonstrate this pattern is to show you graphics of the early stages of a few Es openings from this summer. Let's start with a fairly obvious one - yesterday's Es opening:

Note the central region in this propagation 'spread' which covers a circular-ish effect in southern Spain. There is a main band of propagation. Note also the two outer flanks. It's probably not so easy to see the circle, but you should see a kind of elliptical effect. Bear with me on this as it's not so clear once the propagation path has moved around, as it did today, but you can see this effect better with just a few minutes of Es, and also thanks to having a broadband SDR receiver which lets you see this pattern more readily.


Moving on to 2015-06-20:



Another example of symmetry. Even a circle again.


Then 2015-06-14:




And hopefully still as obvious, this more prolonged opening:



This time the opening was fairly stable and you can see two broad paths of reception, with two flanks at either side.Again, roughly symmetrical


There are many better examples of this, but the clarity is lost as the opening continues and the symmetry is buried under an ever-increasing mass of lines. As I say, you really need to take a snapshot over just a few minutes - five or less, then the effect is much, much clearer. I cannot separate the time slots on the daily FM List logbooks, hence using these four images which offer the best examples I could find, but I do see this very pattern with virtually all Es openings.

What does it tell us though? It certainly doesn't say that the areas between the lines, where nothing was received, don't have any radio stations. That's clearly not the case at all.

Perhaps it's possible to get a good idea of the shape of an Es cloud from this.

Hopefully this is of interest - and it's probably something which is already understood, or is SDR technology now showing us something we haven't previously been able to see?