Trying to estimate the length of the Sporadic E (Es) season and calculate the "lag".

I have recently been criticising some others for taking a few bits of evidence related to amateur radio and then building that up into a theory of Sporadic E. In my view this does not have credibility.

I am about to do something similar so this needs some qualification. I have been looking through my log book. This is obviously limited by loads of factors, but it still might be worth a look. There are 13859 entries in there, not the five data points which one of the other theorists used. Not that I have made 13859 contacts since I arrived at this location in 2009. Oh no, there are more than that. I am not legally required to log all my contacts, and a lot of local ones were not logged. That was in the olden days when there were local stations to work.

None of the missed log entries should matter for this purpose, as I have been very careful to log all my Es contacts. However, this is an early warning that we need to be aware of the many possible areas of bias in the data.

OK, I looked at the Es contacts at GM4FVM on 50MHz from 2011 to 2023. I arbitrarily excluded contacts from early December through to February to exclude "Winter Es" or "Christmas Es" or whatever you want to call that. This first measure was for the length of the season between the first contact and the last, not counting how many contacts resulted in any day or week. This method does not identify the peak of the season in terms of contacts, nor log periods with specific openings such as mini-seasonal paths to Japan or links to TEP. However, every Es contact in the log counted for this purpose including those specific ones. The data was aggregated up from activity days into activity weeks to make the maths practical.

I expected that the "lag" means that Es started later in the year and ended later in the year than a strict correspondence to the Midsummer Day (by which I mean 21 June -ish). I had expected to find that the seasons tend to be roughly the same length each year, just all shifted towards the end of the year.

Sporadic E contacts at GM4FVM 2011 to 2023 (1)

As usual, click if you wish to see an enlarged version of the images.

First of all, you can see the lag. It is about 4 weeks in the first period rising to about 5.5 weeks later. Es starts later than the Spring Equinox and now ends after the Autumn Equinox. So the data (as far as it goes) backs up my initial hunch.

Secondly, and unexpectedly, the Es season appears to be getting longer. The data seemed to fall into three distinct periods. That averages fell very close in each year within each four year period, and then there was a sharp step up to the later period each time. There were three distinct periods standing out from the statistics.

I really doubt that the period of enhanced propagation really is getting longer. I reckon it just looks like that. This finding took me back into my log for some explanation of what is happening. During the 2011 to 2014 period I was mostly using SSB ("pre data period"). During 2015 to 2018 I was using mostly PSK, JT65 and some JT9. Although FT8 was appearing not many people were using it (so this was the "PSK+JT period"). During 2019 to 2023 FT8 was in full swing and lots of people were using it ("FT8 period").

I may be wrong here, but I think that what appears to be a longer season is largely down to me switching from SSB via PSK and JT into FT8. During the SSB period I had to search out stations as they were spread throughout the band. During the PSK+JT period it was either the same spread (PSK) or I was using modes with long periods (JT65) or few followers (JT9). The sensitivity would have been higher than with SSB, but those modes did not have wide acceptance. Then during the FT8 period lots of stations appeared on the same frequency and the mode was even more sensitive. This is my theory about this; just my idea.

Working stations on Es on 50MHz has become easier over those years. More people are doing it, and that also contributes to what looks like a longer season. I doubt if the propagation has changed even though it looks like it has. It is easier to work people now because while at the start of my time on 6m stations had to have transverters, and build their own antennas, these days they have ready made equipment. Data modes have become much easier to use, computers have become cheaper and faster. Also we no longer need lossy data interfaces but we can now pass digital audio in our radios via USB plugs. As it gets easier, more stations come on looking for DX, and the season appears to extend as marginal propagation gets exploited.

Now that I had the basic information that it is indeed shifted to later in the year, I started thinking about the "shape" of the season. It feels to me that once the main season starts, usually about 4 weeks after the first contact, it suddenly bursts forth and reaches a quick peak, and then subsides gradually until the end.

So how to find where the peak is? My data measured so far is just contacts spread over time. It does not show when the main burst of activity happens. I could only do this on 50MHz by going over every contact individually - which I might do some day but not right now. There are thousands of them. So what might measure the timing of the peak? It dawned on me that my 2m Es contacts usually only happen at the peak.

I make the usual pre-condition that these are just my own data, and sometimes I am away, not watching 2m, or something similar. I spent a lot of my early years here thinking that 2m Es was rarely possible from this far north. Would there be enough data? Well, just like on 6m, the spread of data modes has provided me with a lot more data than I thought I had - 31 data points. There are bound to be fewer as these probably represent the peak of the Es propagation each year.

I then calculated those days from first to last contact and put them on the same graph:-

Sporadic E contacts at GM4FVM 2011 to 2023 (2)

The 2m contacts were almost symmetrically spaced on either side of midsummer. Unlike the 6m contacts where the lag was at least 4 weeks, the lag at 2m was almost zero (less than 12 hours) and not statistically significant.

This suggests to me that my second hunch that the Es peak comes in a rush towards the start of the season is also right at this station. However, just as on 6m, my figures just show when the 2m contacts happened not how big the opening might be on that day. Such figures on the "bigness" of an opening can be very misleading, as openings to my west are never big because there is just the Atlantic Ocean in that direction. 2m Es openings almost never include multi-hop Es, or not from here anyway, and nor have I noted them linking to TEP (not YET!!!). So the subjective quality of an opening is not something that I have tried to measure. But still, if the 2m contacts do indeed represent the peak of Es propagation then the peak here does not appear to lag behind the midsummer like the rest of the season does.

Now I want to go further into speculation. What might the shape of the Es season look like if I could work out the "bigness" of openings? Well, here is the FVM conjecture. I suggest that it looks like a gamma graph something like this one:-

Gamma distribution.

With apologies to whoever drew this, I cannot give an attribution as I cannot find where it came from via the internet. Let me know if it is yours; meanwhile I will try to find a better one. I am using it as x along the bottom axis looks like months of the Es season, and f(x) could be the "FVM-Es-bigness scale" [now you are getting carried away Jim].

Anyway, if this is roughly the shape of the season it would fit with the pre-data mode earlier years simply sampling the top part of the graph, say above f(x) = 0.3, and then as we got more sensitive modes and more activity we are sampling further down the vertical axis and finding the tail on the right. Thus the lag seems to be getting later and the season longer, which is what I found. 

Warning: This is just one guy's log history. It is not very reliable. I could do more and better statistical analysis but that would expose the unreliability of using any amateur's data. So it is not scientific, and no ham survey ever will be. Despite this I think it does provide something to think about.

When I was at college there was a lot of enthusiasm for using "qualitative" data. That is not gold standard statistically but it does show trends. What I have tried to do here is show what I have found in a qualitative way. It is up to you whether you believe it or not. For me, however, it has "face validity". It seems to explain what I have been seeing over the years.

First thing I can see is that the lag on 6m pretty well rules out Es linking into TEP in the Spring from here, but would suggest that is more likely in the Autumn. A quick check suggests in my case that Es linking is at least 9 times more likely to happen in Autumn. Secondly, I had better not rely on the lag to look for 2m Es contacts later in the year, as they seem to be equally spaced around midsummer. I will miss them if I wait. And thirdly, whatever the reason, it is worth hanging on looking for 6m Es right into the tail of the season, certainly in October and even later.

This works for me, and I hope it sheds some light on the Es season in some way for others.

73 Jim

GM4FVM