Sporadic-E Radio Propagation

[KW2P]

It was suggested to start a topic to discuss theories surrounding Sporadic-E radio wave propagation.

A quick review of what we're talking about here.

Shortwave radio signals can travel long distances. 8,000 miles is not unusual. Under lucky conditions, signals can travel all the way around the world. How is this possible on a spherical planet when radio waves travel in a straight line and ought to simply radiate off into space?  Such long distances are possible because the F-Layer of the ionosphere at a height of about 200 miles (originally called the Heaviside Layer) reflects radio waves. So the idea is to aim your radio waves generally at the horizon so they reach the ionosphere about 1,200 miles away, reflect, and reach the ground as much as 2500 miles away, where they can be received by a suitable antenna. These waves might then reflect from the ground or the sea and make another hop of up to 2,500 miles. This is conventional shortwave radio that can reach around the world.

But experimenters long ago soon discovered that radio waves occasionally were reflected by a layer much closer to the ground, the E-Layer at 60 to 70 miles altitude. For decades this phenomenon was observed and taken advantage of by ham radio enthusiasts including myself. It also caused occasional problems with television broadcast signals being received hundreds of miles away. In one case, Italians were picking up English TV broadcasts. But what caused this was a big mystery. Ham radio enthusists studied the phenomenon, kept careful records and discovered that reflective regions seemed like clouds that would slowly drift over a period of hours from one region of the U.S. to another. What on Earth is going on? There were lots of theories. Was it related to thunderstorms?  For a while it seemed to be and this was the dominant explanation.

It was also observed that Sporadic-E (Es) is seasonal. In the Northern Hemisphere, there is a peak in Es activity around June and July and a smaller peak around December. What's this about?

Around 1970, researchers made a connection between wind shear 60 miles up and Sporadic-E clouds. The puzzle was starting to come together. But what was reflecting the radio waves?

In 2012 came a paper that may have solved the problem. The paper proposed the idea that microscopic metal particles left behind by meteors passing through the atmosphere were somehow gathered into clouds and moved around by wind shear. Now we have a reflective substance that might be correct. The seasonal behaviors also seem to be explained by wind shear patterns combined with meteor activity, which is also seasonal.

This paper exists in several forms. This one is probably the most digestible: A Model for Sporadic E: Meteors+ Wind Shear+Lorentz Force

Work remains to be done. Some theories suggest that solar activity also plays a part so researchers are looking for connections between Es and Cycle 25.

Lastly, I'm no expert on this topic. I'm am interested user of Es propagation.

 

 

[TrueMayItBe]

Fascinating stuff! I loved learning all throughout your post, and I'd have to say - in my inexpertise, I agree with the 2012 paper, suggesting a collection of meteorite particles as the true cause to the radio waves reflective element(s) at around 60 miles.

 

Wind shear and all -

 

 

My Many Thanks for the Well-Put-Together Read,

Best,

-SJW

[Drax Spacex]

 

I do wonder if a cloud of metal particles alone is sufficient to enable RF refraction or if ionization is required.   Project Needles was supposed to test this, but the results are unknown.

Es seems to have a lot in common with meteor scatter (aka meteor burst or MB) RF propagation mode.  They occur at about the same altitude, both short-lived (though meteor scatter is quite short-lived - only lasting on the order of seconds per meteor).  Meteor scatter has been investigated as a viable operational mode of RF propagation:  https://apps.dtic.mil/sti/citations/ADA271604.

That paper describes the importance of "coherent scatter" which diminshes as the meteor tail spreads out and the sweet-spot value range for "electron density" to support a viable MB radio link.

A tantalizing quote from this paper:  "The Antarctic test of MB terminals demonstrated a persistent non-meteoric propagation mechanism, possibly sporadic E, which dominated link performance. Although this phenomena masked most, if not all, meteor trail-scatter events, it demonstrated nearly continuous VHF connectivity at a range of about 1400 km."

 

[hamateur 1953]

United Parcel Systems actually used ( perhaps still does ) meteor scatter propagation to reliably track their shipments. So evidently they placed a lot of faith in the reliability of apparently random events.  I believe they got 220-222 mhz of our former allocation. Well guess we could have told them it wouldn’t have worked well for voice!  Data bursts perhaps.  was reallocated last year to our railroads. 

Edited March 21 by hamateur 1953
updated after checking current status.

[KW2P]

34 minutes ago, hamateur 1953 said:

United Parcel Systems actually used ( perhaps still does ) meteor scatter propagation to reliably track their shipments. So evidently they placed a lot of faith in the reliability of apparently random events.  I believe they got 220-222 mhz of our former allocation. Well guess we could have told them it wouldn’t have worked well for voice!  Data bursts perhaps.  was reallocated last year to our railroads. 

That seems do-able. We hams operate under narrow bandwidth restrictions and artificial data rate limitations. UPS or rail companies could use a 30 kHz bandwidth and much higher data rate to achieve good performance -- a ping/response time of a small fraction of a second.

2 hours ago, Drax Spacex said:

 

I do wonder if a cloud of metal particles alone is sufficient to enable RF refraction or if ionization is required.   Project Needles was supposed to test this, but the results are unknown.

Es seems to have a lot in common with meteor scatter (aka meteor burst or MB) RF propagation mode.  They occur at about the same altitude, both short-lived (though meteor scatter is quite short-lived - only lasting on the order of seconds per meteor).  Meteor scatter has been investigated as a viable operational mode of RF propagation:  https://apps.dtic.mil/sti/citations/ADA271604.

That paper describes the importance of "coherent scatter" which diminshes as the meteor tail spreads out and the sweet-spot value range for "electron density" to support a viable MB radio link.

A tantalizing quote from this paper:  "The Antarctic test of MB terminals demonstrated a persistent non-meteoric propagation mechanism, possibly sporadic E, which dominated link performance. Although this phenomena masked most, if not all, meteor trail-scatter events, it demonstrated nearly continuous VHF connectivity at a range of about 1400 km."

 

Hmm, it sounds like they discovered something interesting like near-continuous Sporadic-E at the poles.

As far as ionization, I don't know. We know that intense UV can ionize the D-Layer, which is the cause of blackouts. And while Sporadic-E is more likely to occur during the day, it also occurs at night when there's no source of ionization.

[hamateur 1953]

Fascinating Drax. They were also using our maximum input power at 1kw around 48 mhz just below our six meter band. I remember once talking with naval station NPG out of san francisco he refused to divulge his input power 🤣🤣🤣

2 hours ago, Drax Spacex said:

 

I do wonder if a cloud of metal particles alone is sufficient to enable RF refraction or if ionization is required.   Project Needles was supposed to test this, but the results are unknown.

Es seems to have a lot in common with meteor scatter (aka meteor burst or MB) RF propagation mode.  They occur at about the same altitude, both short-lived (though meteor scatter is quite short-lived - only lasting on the order of seconds per meteor).  Meteor scatter has been investigated as a viable operational mode of RF propagation:  https://apps.dtic.mil/sti/citations/ADA271604.

That paper describes the importance of "coherent scatter" which diminshes as the meteor tail spreads out and the sweet-spot value range for "electron density" to support a viable MB radio link.

A tantalizing quote from this paper:  "The Antarctic test of MB terminals demonstrated a persistent non-meteoric propagation mechanism, possibly sporadic E, which dominated link performance. Although this phenomena masked most, if not all, meteor trail-scatter events, it demonstrated nearly continuous VHF connectivity at a range of about 1400 km."

 

 

Edited March 21 by hamateur 1953

[hamateur 1953]

Last year I think it was I corresponded with a fellow ham living in the arctic giving him kudos for an excellent article on ionosondes. In CQ magazine. He asserted the complete lack of an ionosphere at his latitude. Not particularly surprising to me although Id bet in summer months he probably sees some f2. Hence the idea of anything refractive in the antarctic would surprise many hams! 

[Marcel de Bont]

@KW2P I am thinking about moving this topic to the HAM radio forum. This topic seems perfectly fit for that forum and it would be nice to get some discussions over there as well and perhaps attract new HAM radio users to use that forum. Agreed?

[KW2P]

5 hours ago, Marcel de Bont said:

@KW2P I am thinking about moving this topic to the HAM radio forum. This topic seems perfectly fit for that forum and it would be nice to get some discussions over there as well and perhaps attract new HAM radio users to use that forum. Agreed?

Yes, sounds like a good idea to me!

[Drax Spacex]

A good Sporadic E discussion and videos from an Australian (VK) amateur radio ham https://3fs.net.au/sporadic-e-propagation/

[hamateur 1953]

Deal me in too Marcel. no problem. 

[hamateur 1953]

Well ok then @KW2P you have the floor.  Occurs at night when no ionization is present??   I will bite. Perhaps you intended to type “ should have been present”. I will refrain from putting words in your mouth, however, as that would be unconscionable. What say OM?  ( hamspeak for fellow old guy) 

[KW2P]

1 hour ago, hamateur 1953 said:

Well ok then @KW2P you have the floor.  Occurs at night when no ionization is present??   I will bite. Perhaps you intended to type “ should have been present”. I will refrain from putting words in your mouth, however, as that would be unconscionable. What say OM?  ( hamspeak for fellow old guy) 

I should have said "no source of ionization" is present. It's night, no UV or soft X-rays.  And yet, Es can crop up in the middle of the night. Which argues in favor of the meteorite particles.

That's not to say there's no effect from ionization during the day. Es is more common during the day than at night so maybe there is more than one mechanism in play at once.

[hamateur 1953]

Yes Im in full agreement with ya on that indeed. Although personally I’ve only witnessed Auroral Es when the source was well known to me even fifty yrs ago.  

41 minutes ago, KW2P said:

I should have said "no source of ionization" is present. It's night, no UV or soft X-rays.  And yet, Es can crop up in the middle of the night. Which argues in favor of the meteorite particles.

That's not to say there's no effect from ionization during the day. Es is more common during the day than at night so maybe there is more than one mechanism in play at once.

 

[hamateur 1953]

How about a four hour analog tv signal witnessed one sunny day in late june channel 2  from KDIX Dickinson ND? Of course analog TV ran higher power.  numerous other examples exist. We didn’t have analog 2 in seattle and were a bit surprised to find KDIX all of a sudden. 🤣

[KW2P]

4 hours ago, hamateur 1953 said:

How about a four hour analog tv signal witnessed one sunny day in late june channel 2  from KDIX Dickinson ND? Of course analog TV ran higher power.  numerous other examples exist. We didn’t have analog 2 in seattle and were a bit surprised to find KDIX all of a sudden. 🤣

Yes, these things happened on low-band VHF TV. People were puzzled. Under extreme Es conditions propagation up to the 3 meter band has occurred so FM broadcast signals have been picked up far outside their intended service area.

[helios]

On 3/24/2023 at 7:17 AM, KW2P said:

I should have said "no source of ionization" is present. It's night, no UV or soft X-rays.  And yet, Es can crop up in the middle of the night. Which argues in favor of the meteorite particles.

It should be said though that ionized particles can be long-living and transported from other parts of the planet.
https://acp.copernicus.org/articles/21/4219/2021/

[hamateur 1953]

Great discussion @KW2P !! 

[hamateur 1953]

That paper was well worth the read for me anyway, because it dispelled a misconception I’d held for some time regarding the apparent coincidence of meteoric activity and sporadic E. Although as @KW2P noted many mechanisms may still be at play here.  

4 hours ago, helios said:

It should be said though that ionized particles can be long-living and transported from other parts of the planet.
https://acp.copernicus.org/articles/21/4219/2021/

 

[KW2P]

On 3/25/2023 at 4:26 AM, helios said:

It should be said though that ionized particles can be long-living and transported from other parts of the planet.
https://acp.copernicus.org/articles/21/4219/2021/

Great article. Finally got time to read it.

One thing that's clear is we shouldn't feel badly that it's taken 90 years to get close to an answer, and we still don't have it all. It's complicated.

As a ham radio guy I would someday like to have accurate forecasts of Es conditions, but that's still off in the future.

After reading the article I'm a bit puzzled about why the repeated reference to "metal ions".  Metals are conductive because the electrons in the outer shell are loosely bound and free to move. As a result, metals are easily ionized. But metals reflect radio waves regardless. It doesn't matter whether they're ionized or not. Why doesn't the article just say "metallic particles"?

[Drax Spacex]

3 hours ago, KW2P said:

After reading the article I'm a bit puzzled about why the repeated reference to "metal ions".  Metals are conductive because the electrons in the outer shell are loosely bound and free to move. As a result, metals are easily ionized. But metals reflect radio waves regardless. It doesn't matter whether they're ionized or not. Why doesn't the article just say "metallic particles"?

I think radio propagation using the ionosphere requires ions and free electrons (ionized charged particles) for refraction.  I suspect neutral metallic particles could scatter radio waves, but probably lacks the regular arrangement and spacing of a plasma that interacts sympathetically with the frequency of a radio EM wave to refract them.  Smooth boundaries of a conductive material can reflect radio waves (including ocean salt waters below for long distance multiple hop skywave propagation).

Another posit on the cause of Es can be found here.  It's another twist on the wind shear explanation, and sounds similar to how a tornado is formed.  I'm not quoting the text because it's copyrighted, but search for "sporadic" in the following page.  https://www.britannica.com/science/ionosphere-and-magnetosphere/Ionospheric-variations

[KW2P]

22 hours ago, Drax Spacex said:

I think radio propagation using the ionosphere requires ions and free electrons (ionized charged particles) for refraction.  I suspect neutral metallic particles could scatter radio waves, but probably lacks the regular arrangement and spacing of a plasma that interacts sympathetically with the frequency of a radio EM wave to refract them.  Smooth boundaries of a conductive material can reflect radio waves (including ocean salt waters below for long distance multiple hop skywave propagation).

Another posit on the cause of Es can be found here.  It's another twist on the wind shear explanation, and sounds similar to how a tornado is formed.  I'm not quoting the text because it's copyrighted, but search for "sporadic" in the following page.  https://www.britannica.com/science/ionosphere-and-magnetosphere/Ionospheric-variations

Thanks for posting. The whole article is a pretty good condensation of the whole ionosphere / radio propagation topic.  I was a bit surprised that the article frames the metal ion theory as fact when many still consider it an unproven hypothesis. Encyclopedia article authors sometimes do that. It is nevertheless a good article to read and a good intro to the whole field.

[Drax Spacex]

1 hour ago, KW2P said:

Thanks for posting. The whole article is a pretty good condensation of the whole ionosphere / radio propagation topic.  I was a bit surprised that the article frames the metal ion theory as fact when many still consider it an unproven hypothesis. Encyclopedia article authors sometimes do that. It is nevertheless a good article to read and a good intro to the whole field.

Agreed.  It's often a challenge to sort out between what is fact and what is assertion; between what is theoretical and what has been empirically observed and confirmed.