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Question about Type II Radio Emissions


KW2P
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I’m with you on this one.  I thought I understood the association pretty well until I couldn’t find an associated cme timestamp on the Cactus recent cmes to associate it with!!    I just scrolled down and I do see an M-2.36 flare which should account for this, however.   Solar ham is attributing it to a magnetic plage area 3558 I believe. Quite a surprise!   Edit here. Just one more thought.  I would expect the C. M And X levels to correspond fairly closely to the D-RAP absorption levels. It might be that the ionosphere is taking an unusually long time to recover in this instance is the only thing I can imagine. Strange indeed! 

Edited by hamateur 1953
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3 hours ago, KW2P said:

Here's another chance for me to show off the gaps in my knowledge. ūüôā

So I was thinking of doing some ham radio operating. I pulled up the flare page and the graph shows no significant flares. Good. Probably little or no blackout.

But I scrolled down and see there's a pretty strong blackout in progress: Type II radio emission. Here's where I'm confused. My understanding (apparently wrong) is that Type II radio emissions occur when a large/wide CME launches from the sun's "surface". This is early warning that a CME is coming in a couple of days. How does this affect us now? The CME just left the sun and is not here yet.

Blackouts are caused by excessively high UV/X-ray radiation. I'm not clear on how radio emissions or a CME that's en route can create a blackout. Reading about Type II radio emissions hasn't answered my questions.

/puzzled

 

Electromagnetic waves always travel at the same speed in a given medium (considering "vacuum" as a medium too, as it still has the properties that determine the propagation speed, in which the speed is commonly known as "the speed of light").

So the radio emission in question travels at that same speed; it is emitted as electrons are accelerated at the shock front of the CME in question.

I would think you already know this, so perhaps something else is unclear. If not and that clears it up, then great.

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I don’t know about @KW2P but until that recent M1.4 just hit us I have been puzzled over the increased d layer absorption.  It seemed too high to me given mid C level 10.7 flux.  Anyway we may get a nighttime E layer out of this which should make some folks amazed at our 50 mhz frequencies.    Penticton should be interesting today.  We were at 190 sfi last I looked. 

Edited by hamateur 1953
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1 hour ago, hamateur 1953 said:

I don’t know about @KW2P but until that recent M1.4 just hit us I have been puzzled over the increased d layer absorption.  It seemed too high to me given mid C level 10.7 flux.  Anyway we may get a nighttime E layer out of this which should make some folks amazed at our 50 mhz frequencies.    Penticton should be interesting today.  We were at 190 sfi last I looked. 

Well, I'm not a ham myself, so I don't pay that close attention to how much absorption there is or how well signals propagate, but it certainly sounds to me like a separate question, i.e. why D-layer absorption seems higher in general than it should be vs. why type II radio emissions reach us long before their associated CME.

I wouldn't really presume to know the answer to the former question; has it been more constant, or does it happen sporadically? If it happens sporadically, then I guess that's presumably an indication that it's tied to events we're seeing, but if it's been constant then my first guess would be increased levels of UV that aren't reflected in the X-ray flux, although I'm not sure what would cause that (and those are only my guesses, could certainly be some other explanation(s) for it). I would personally note that the X-ray flux has seemed relatively high lately on average, but I don't have any experience relating that to any specific levels of D-layer absorption.

Also, just out of curiosity I'm assuming you as hams want there to be more D-layer absorption as this generally means higher-frequency bands are opening up more, is that correct?

As for the Penticton flux for July 10 I just updated the data, and the adjusted 20:00 measurement reads 196.9, not bad at all.

Edited by Philalethes
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Actually we want less D layer absorption, generally speaking. So our signals may reach the higher E and F layers of our ionosphere. But as @KW2Pnoted the sun giveth and taketh away at times!  haha!! Btw solar soft seems to indicate that plage area 3358 was largely responsible for today’s unusually robust ionization.  As a further clarification for non hams. The higher the frequency in mhz we operate at, the less signal loss or attenuation we suffer.  Example: Our 40 meter band may be dead as disco, however our 10 meter band could conceivably be open worldwide.  Hopefully this helps.  Mike/Hagrid 

Edited by hamateur 1953
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8 hours ago, Philalethes said:

Electromagnetic waves always travel at the same speed in a given medium (considering "vacuum" as a medium too, as it still has the properties that determine the propagation speed, in which the speed is commonly known as "the speed of light").

So the radio emission in question travels at that same speed; it is emitted as electrons are accelerated at the shock front of the CME in question.

I would think you already know this, so perhaps something else is unclear. If not and that clears it up, then great.

Haha, yes I do know that.

As I described in the original post, my understanding is that Type II radio emissions are given off / generated by a CME as it's lifting off the surface of the sun. So Type II emissions give us days of advance warning that a CME has been launched.

The radio waves arrive at Earth in 8 minutes. The CME arrives several days later. Radio waves do not ionize the atmosphere. So I'm puzzled how the blackout graphic seems to explain the blackout (which is overionization of the D Layer) as caused by radio emissions. This isn't possible.

/p

 

3 hours ago, hamateur 1953 said:

Actually we want less D layer absorption, generally speaking. So our signals may reach the higher E and F layers of our ionosphere. But as @KW2Pnoted the sun giveth and taketh away at times!  haha!! Btw solar soft seems to indicate that plage area 3358 was largely responsible for today’s unusually robust ionization.  As a further clarification for non hams. The higher the frequency in mhz we operate at, the less signal loss or attenuation we suffer.  Example: Our 40 meter band may be dead as disco, however our 10 meter band could conceivably be open worldwide.  Hopefully this helps.  Mike/Hagrid 

Yes. Well said.

I'm cobbling together a little writeup on propagation I'll post over in the ham radio section that goes into a little more detail and hopefully explains what is probably confusing to non-radio people. Such as:

Solar radiation (UV/X-ray) is low, and hams are not happy.

Radiation increases and we're happy.

Big blast of UV radiation from a flare and we're not happy.

What's going on here?  Stay tuned.

EDIT: I wrote up a little blurb on the basic basics of propagation here: https://community.spaceweatherlive.com/topic/2882-basics-of-shortwave-radio-propagation/

 

Edited by KW2P
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A solar radio emission is more like an active jammer in terms of how it disrupts radio communications. These emissions appear as active signals in certain frequency bands for some time.  Normal radio signals that occupy those bands may be overwhelmed by the solar radio emissions.

The radiation blackouts from flares (R1, R2, R3) are more related to the increased radio absorption from too much ionization of the D layer, stopping radios from reaching E and F layers to refract signals for skywave propagation.

For hams, ionization is a Goldilocks scenario - not too cold, not too hot.  It has to be just right.  Not too little, and not too much ionization is best.

And hams don't like the sunspots in particular, but we like the flux that is associated with the sunspots.

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6 minutes ago, Drax Spacex said:

A solar radio emission is more like an active jammer in terms of how it disrupts radio communications. These emissions appear as active signals in certain frequency bands for some time.  Normal radio signals that occupy those bands may be overwhelmed by the solar radio emissions.

The radiation blackouts from flares (R1, R2, R3) are more related to the increased radio absorption from too much ionization of the D layer, stopping radios from reaching E and F layers to refract signals for skywave propagation.

For hams, ionization is a Goldilocks scenario - not too cold, not too hot.  It has to be just right.  Not too little, and not too much ionization is best.

And hams don't like the sunspots in particular, but we like the flux that is associated with the sunspots.

I marked your post as a solution.  I was aware of solar and ionospheric noise and sometimes listen for it if I happen to catch a flare at the start. You can sometimes hear the band go quiet and the character of the noise change. Normal atmospheric noise from distant thunderstorms, etc. gets quieted and replaced with the rushing sound of radio signals direct from the sun. Kind of cool.

So it sounds like you're saying that Type II radio emissions are a kind of jamming. What still puzzles me is why does the graphical representation of a blackout look the same as for a flare?  A flare induced blackout results in absorption that affects higher and higher frequencies as the ionization of the D-layer increases. It seems that "jamming" would have a very different frequency curve.

It's this graphic here I'm referring to: latest.png

The graph at the right side has the same shape for a flare and a Type II. Seems it ought to be different.

Hmm.

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1 hour ago, KW2P said:

So it sounds like you're saying that Type II radio emissions are a kind of jamming. What still puzzles me is why does the graphical representation of a blackout look the same as for a flare? 

Those maps are only for D-region absorption from X-ray emissions and proton events, not for radio emissions. 
I don't think there is a map for solar radio emissions.


There are two types of this map. One represents the absorption of a particular frequency in dB (on 5, 10, 15, 20, 25 and 30 MHz), and the one you are showing is the highest frequency which is absorbed by 1 dB.
https://www.swpc.noaa.gov/products/d-region-absorption-predictions-d-rap

Another misconception is that radio emissions always result in an ICME.
Radio emissions are produced by the interaction of a CME with the corona. That can also happen if the CME is not powerful enough to leave the gravitational field of the sun.

Edited by helios
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10 hours ago, KW2P said:

Haha, yes I do know that.

As I described in the original post, my understanding is that Type II radio emissions are given off / generated by a CME as it's lifting off the surface of the sun. So Type II emissions give us days of advance warning that a CME has been launched.

The radio waves arrive at Earth in 8 minutes. The CME arrives several days later. Radio waves do not ionize the atmosphere. So I'm puzzled how the blackout graphic seems to explain the blackout (which is overionization of the D Layer) as caused by radio emissions. This isn't possible.

/p

 

Yes. Well said.

I'm cobbling together a little writeup on propagation I'll post over in the ham radio section that goes into a little more detail and hopefully explains what is probably confusing to non-radio people. Such as:

Solar radiation (UV/X-ray) is low, and hams are not happy.

Radiation increases and we're happy.

Big blast of UV radiation from a flare and we're not happy.

What's going on here?  Stay tuned.

EDIT: I wrote up a little blurb on the basic basics of propagation here: https://community.spaceweatherlive.com/topic/2882-basics-of-shortwave-radio-propagation/

 

A coronal mass ejection (CME) shock wave and a radio burst shock wave are not the same thing.
A coronal mass ejection (CME) is a massive release of plasma and magnetic field from the Sun's corona. It is typically associated with solar flares and can eject billions of tons of solar material into space. When a CME travels through the interplanetary medium, it creates a shock wave called a "CME shock wave." This shock wave can cause disturbances in the solar wind and interact with the Earth's magnetosphere, potentially leading to geomagnetic storms and auroras.
On the other hand, a radio burst shock wave refers to a phenomenon associated with solar radio bursts. Solar radio bursts are intense bursts of radio waves emitted by the Sun, typically caused by energetic processes such as solar flares or coronal mass ejections. When a solar radio burst occurs, it can produce a shock wave with the acceleration of electrons which propagates through the solar atmosphere and affects the surrounding plasma.
While both CME shock waves and radio burst shock waves originate from solar activity, they have different causes and characteristics. CME shock waves are associated with the physical ejection of solar material, while radio burst shock waves are related to the emission of intense radio waves during solar flares.
Also of note is that whilst radio waves travel at or near light speed shock waves associated with radio bursts and CMEs travel through the interplanetary medium more slowly.

N.

Edited by Newbie
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1 hour ago, KW2P said:

So it sounds like you're saying that Type II radio emissions are a kind of jamming. What still puzzles me is why does the graphical representation of a blackout look the same as for a flare?  A flare induced blackout results in absorption that affects higher and higher frequencies as the ionization of the D-layer increases. It seems that "jamming" would have a very different frequency curve.

It's this graphic here I'm referring to: latest.png

The graph at the right side has the same shape for a flare and a Type II. Seems it ought to be different.

Hmm.

The image above is from D-Region Absorption Prediction (D-RAP) model.  It does not include terrestrial or solar radio emissions as an input.  X-Ray flux and solar energetic particles (SEP) are the inputs to this model.

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5 hours ago, hamateur 1953 said:

Actually we want less D layer absorption, generally speaking. So our signals may reach the higher E and F layers of our ionosphere.

Oh, I see, so the extra ionization that leads to the formation of the D-layer isn't actually necessary for the upper layers to form then, I take it. I was thinking the D-layer was a "necessary evil" of sorts that ends up being present whenever there are good conditions for high-frequency bands. Correct me if I'm wrong.

Does that mean there's a "sweet spot" for the flux when it comes to ham radio, a level that you don't really want to go beyond because it leads to more D-layer absorption?

5 hours ago, hamateur 1953 said:

The higher the frequency in mhz we operate at, the less signal loss or attenuation we suffer.  Example: Our 40 meter band may be dead as disco, however our 10 meter band could conceivably be open worldwide.

Yeah, that much I'd gathered, and that makes sense. My thinking was that the conditions where using the higher-frequency bands inevitably come with more D-layer absorption that is primarily bad for the low-frequency bands, but that this is still desirable because the higher-frequency bands are so much better to use anyway, but I'm sure I haven't got the entire story right (especially considering how Solar flares clearly cause radio blackouts). Great to hear from the first-hand experience of hams on the matter, ionospheric physics and its relation to Solar activity and ham radio is very interesting.

4 hours ago, KW2P said:

As I described in the original post, my understanding is that Type II radio emissions are given off / generated by a CME as it's lifting off the surface of the sun. So Type II emissions give us days of advance warning that a CME has been launched.

The radio waves arrive at Earth in 8 minutes. The CME arrives several days later. Radio waves do not ionize the atmosphere. So I'm puzzled how the blackout graphic seems to explain the blackout (which is overionization of the D Layer) as caused by radio emissions. This isn't possible.

Well, first thing to note is that the radio emission will continue for as long as electrons are accelerated along the shock front of the CME, which leads to the radio emission continuing for a while after the CME is launched as it moves through the corona. As electrons will be accelerated less and less during this process, this leads to the frequency of the emission lowering over time (I read that this is rarely exactly correct in reality due to various irregularities in the corona, but you can typically see it as a general rule, at least so it seems from looking at radio spectrograms).

Secondly, the blackout in this case would not be caused by ionization of the ionosphere, but by directly interfering with the radio frequencies typically used in radio communication, i.e. by decreasing the signal-to-noise ratio directly. Maybe this is the part that was confusing you.

Going through the posts sequentially I see Drax has already mentioned this now, so hopefully that part is cleared up!

As for the map, I believe helios is correct, and that it's somewhat confusing to have the notice about a blackout right above it without it actually being part of the map. I could be wrong, though, as it could be a combination; seen alone I agree that such a radio emission would essentially be seen as a single color in such a map, but if ionization from e.g. a flare is present simultaneously, and this attenuates higher frequencies sufficiently (more than 1 dB), then it wouldn't readily be seen on the map itself (but would likely crop up in the graphic of attenuation at specific frequencies as increased attenuation at the specific frequency the radio emission were currently at).

That being said, it does say "absorption", which leads me to believe that it isn't really accounting for radio emissions. They are quite short-lived anyway, and from what I've seen tend to move past the frequencies in question rather fast, so my guess is that they wouldn't necessarily be as great of a nuisance to hams as the other types of blackouts.

Edited by Philalethes
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Lots of good input here!  Thank you to Newbie, Helios, Drax, et al.

All the above put together fully answers my question. Very helpful. Now I must do some more studying.

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8 hours ago, Philalethes said:

Oh, I see, so the extra ionization that leads to the formation of the D-layer isn't actually necessary for the upper layers to form then, I take it. I was thinking the D-layer was a "necessary evil" of sorts that ends up being present whenever there are good conditions for high-frequency bands. Correct me if I'm wrong.

Does that mean there's a "sweet spot" for the flux when it comes to ham radio, a level that you don't really want to go beyond because it leads to more D-layer absorption?

 

Hmm. The thing I wrote about propagation basics does leave this question open.

Regarding the sweet spot question, there may be such a sweet spot but SFI never goes high enough to discover it. Even Cycle 19 didn't reach an SFI high enough to affect the D-layer. It takes the extreme output of a flare to strengthen the D-layer.

Does that answer the question?

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2 hours ago, KW2P said:

Hmm. The thing I wrote about propagation basics does leave this question open.

Regarding the sweet spot question, there may be such a sweet spot but SFI never goes high enough to discover it. Even Cycle 19 didn't reach an SFI high enough to affect the D-layer. It takes the extreme output of a flare to strengthen the D-layer.

Does that answer the question?

Definitely; and your post about the basics really filled in the rest of what I was wondering about too. The difference in how the F- and D-layers build up really explains a lot.

If I understand it right, as long as there's enough ionization in the F-layer (or sporadic E is present), you essentially get a corresponding upper limit on the frequency, whereas the more abrupt ionization of the D-layer seen from flares will set a lower limit on the frequency depending on the strength of the flare (and possibly other conditions, just trying to simplify; and of course there will be different levels of attenuation at different frequencies in general).

So in other words, in certain cases, if the flux has been high for a long time, opening up bands that border on or are fully inside the VHF part of the spectrum (i.e. 6 meters/50 MHz and shorter/higher), then you could generally speaking use those VHF bands even during the blackouts of certain strong flares, as long as they're not strong enough to match the F-layer ionization with the sudden increase in D-layer ionization (but raising the range of possible wavelengths to use in the process).

Feel free to provide any further corrections or clarifications if any of that is either incorrect or oversimplified, but at least I think I understand it a lot better now.

Would also be cool to see some data on how the different fluxes and flares tend to set the different limits, although I assume there will always be some variability there that's not possible to fully account for. I'm sure there are lots papers and articles about it if I dig around a bit.

Edited by Philalethes
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1 hour ago, Philalethes said:

So in other words, in certain cases, if the flux has been high for a long time, opening up bands that border on or are fully inside the VHF part of the spectrum (i.e. 6 meters/50 MHz and shorter/higher), then you could generally speaking use those VHF bands even during the blackouts of certain strong flares, as long as they're not strong enough to match the F-layer ionization with the sudden increase in D-layer ionization (but raising the range of possible wavelengths to use in the process).

Yes, yes, and yes. You've got it. All that you said is correct.

And you extrapolated correctly. If the SFI is high enough for long enough (very rare) like it was at the peak of Cycle 19, the F-layer becomes so strongly ionized that F propagation extends up to and a little beyond the 6 meter VHF band (50 MHz). Yes, during Cycle 19, the 6 meter band opened worldwide, 24 hours a day. Unbelievable. I was too young to appreciate it at the time and I don't expect it in my lifetime, but we know it's possible.

= = =

I left out as much as I could from the propagation thingus I wrote. Too much information isn't good. I wanted to focus on the mainstay of worldwide shortwave communication, so the F and D layers. Before satellites came along, shortwave broadcasting, radio teletype, radio fascimile, all on shortwave, was how information and news got around the world. In 1960, a photo from Berlin appearing on the front page of a Los Angeles newspaper got there via shortwave radio.

I dismissed the E layer because it's only of interest to hobbyists like me. I skipped what the E-layer is useful for. Many of us, myself included, pursue Es propagation as a sub-hobby. The reason for this pursuit is that Sporadic E provides long-distance propagation on bands that are normally closed during most of the sunspot cycle: 12, 10, and 6 meters. The E-layer does not reflect frequencies below about 22 MHz. I believe I've seen Es on the 15 meter band (21 MHz) but others say that's not possible.

In any case, Sporadic E is the only way to get beyond line-of-sight on 12 (24 MHz) and 10 meters (28 MHz) except during solar max. (You could bounce signals off the moon, but that's another sub-hobby.)

Six meters (50 MHz) is classed as a VHF band, not HF (shortwave) which implies line-of-sight only. But it reflects well from the E-layer. So when there's a strong blackout, many of us head to 6 meters and hope for an E cloud to appear somewhere in range that we can bounce signals off of.

So if, for example, an E cloud forms over the State of Kentucky, then hams in roughly a 1,000 mile circle around that cloud can communicate via the 6 meter band. Sometimes there will be more than one cloud allowing double hops. So West Virginia to California is technically possible on 10 meters even during solar minimum via Sporadic E. It takes patience and persistence and that's part of the fun. (Ham radio is an egalitarian hobby. Everyone faces the same challenge and the only thing standing in your way is yourself.)

By observing propagation over a period of hours it becomes clear that there are reflective clouds that drift slowly. Nowadays with computers and many hams logging every contact on the Internet in real time, real-time maps can be drawn and it's immediately obvious that there are reflective clouds that drift.

Sporadic E clouds can appear at any time. They appear most frequently in June and July (now) and there's another smaller peak in December.

Because of wind shear aloft, Sporadic E is much more common at the equator, almost a daily thing. Communication along the equator via Es is commonplace. Also, transequatorial or transeq. is common. The southern states of the U.S. can communicate with South America on 10 and 12 meters almost on a daily basis, regardless of the solar cycle.

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1 hour ago, KW2P said:

Yes, yes, and yes. You've got it. All that you said is correct.

And you extrapolated correctly. If the SFI is high enough for long enough (very rare) like it was at the peak of Cycle 19, the F-layer becomes so strongly ionized that F propagation extends up to and a little beyond the 6 meter VHF band (50 MHz). Yes, during Cycle 19, the 6 meter band opened worldwide, 24 hours a day. Unbelievable. I was too young to appreciate it at the time and I don't expect it in my lifetime, but we know it's possible.

= = =

I left out as much as I could from the propagation thingus I wrote. Too much information isn't good. I wanted to focus on the mainstay of worldwide shortwave communication, so the F and D layers. Before satellites came along, shortwave broadcasting, radio teletype, radio fascimile, all on shortwave, was how information and news got around the world. In 1960, a photo from Berlin appearing on the front page of a Los Angeles newspaper got there via shortwave radio.

I dismissed the E layer because it's only of interest to hobbyists like me. I skipped what the E-layer is useful for. Many of us, myself included, pursue Es propagation as a sub-hobby. The reason for this pursuit is that Sporadic E provides long-distance propagation on bands that are normally closed during most of the sunspot cycle: 12, 10, and 6 meters. The E-layer does not reflect frequencies below about 22 MHz. I believe I've seen Es on the 15 meter band (21 MHz) but others say that's not possible.

In any case, Sporadic E is the only way to get beyond line-of-sight on 12 (24 MHz) and 10 meters (28 MHz) except during solar max. (You could bounce signals off the moon, but that's another sub-hobby.)

Six meters (50 MHz) is classed as a VHF band, not HF (shortwave) which implies line-of-sight only. But it reflects well from the E-layer. So when there's a strong blackout, many of us head to 6 meters and hope for an E cloud to appear somewhere in range that we can bounce signals off of.

So if, for example, an E cloud forms over the State of Kentucky, then hams in roughly a 1,000 mile circle around that cloud can communicate via the 6 meter band. Sometimes there will be more than one cloud allowing double hops. So West Virginia to California is technically possible on 10 meters even during solar minimum via Sporadic E. It takes patience and persistence and that's part of the fun. (Ham radio is an egalitarian hobby. Everyone faces the same challenge and the only thing standing in your way is yourself.)

By observing propagation over a period of hours it becomes clear that there are reflective clouds that drift slowly. Nowadays with computers and many hams logging every contact on the Internet in real time, real-time maps can be drawn and it's immediately obvious that there are reflective clouds that drift.

Sporadic E clouds can appear at any time. They appear most frequently in June and July (now) and there's another smaller peak in December.

Because of wind shear aloft, Sporadic E is much more common at the equator, almost a daily thing. Communication along the equator via Es is commonplace. Also, transequatorial or transeq. is common. The southern states of the U.S. can communicate with South America on 10 and 12 meters almost on a daily basis, regardless of the solar cycle.

Glad to see that I'm not off-track there. And all that further information is also very interesting, first-hand accounts about how things work in practice in particular are definitely valuable! Will be interesting to see in the future if some cycle beats out SC19 and manages to open up further VHF bands, if it's not in too many decades or centuries.

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7 minutes ago, Philalethes said:

Glad to see that I'm not off-track there. And all that further information is also very interesting, first-hand accounts about how things work in practice in particular are definitely valuable! Will be interesting to see in the future if some cycle beats out SC19 and manages to open up further VHF bands, if it's not in too many decades or centuries.

From the start of the current cycle my intuition was that it would be a big one. I secretly hoped it would be a replay of Cycle 19. Thus far, Cycle 25 has delivered on that hope. Whether it continues on its  furious track is unknown.

But back to propagation...  The blackout has been going on all day now with almost constant flaring. This strengthened the D layer causing the blackout but the sustained radiation for hours will gradually affect the F layer too.

On a day like today, I patiently wait for sundown. The D layer will disappear and the sustained radiation may have pumped up the F layer somewhat, making for a night of excellent radio conditions.

I just checked the numbers and, wow, the SFI is the highest I've seen in over 20 years: 213. This is higher than any level reached during the previous cycle. Propagation tonight should be great. (And Cycle 25 is still just getting started. It could stall out but at present we're on track for a repeat of Cycle 19. Fingers crossed.)

I'd say the only thing that could mess things up tonight is if the Kp index jumps up. I'm hoping it stays around 2 or goes even lower.

 

 

 

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@KW2P Re Blackouts.

Solar emissions can cause radio blackouts through a phenomenon known as solar radio bursts or solar radio storms the events being associated with solar flares and coronal mass ejections.

Solar flares release intense bursts of radiation across the electromagnetic spectrum, including radio waves. These bursts can interfere with the normal propagation of radio signals on Earth. When a solar flare occurs, it releases a surge of high-energy particles and electromagnetic radiation, including X-rays and extreme ultraviolet (EUV) rays.

The X-rays and EUV rays emitted during a solar flare can ionise the Earth's upper atmosphere. This ionisation disrupts the normal propagation of radio waves and can cause significant disturbances in the ionosphere.

This can affect radio signals in several ways:

Absorption: The ionized particles in the ionosphere can absorb radio waves, preventing them from reaching the Earth's surface or interfering with their quality and strength.

Scattering: The ionosphere can scatter radio waves in different directions, causing signal degradation or loss.

Refraction: The altered ionosphere can refract radio waves, redirecting them to areas where they may not be intended, resulting in poor communication.

Refraction is the bending of waves due to changes in the ionosphere's density and composition. The ionosphere consists of ionized gases, or plasma, which are created by solar radiation.

When radio waves reach the ionosphere, they can interact with the free electrons and ions present in the plasma. The ionosphere is composed of several distinct layers, such as the D, E, and F layers, each with varying electron density. Each layer is not homogeneous and there can be a ‚Äėlumpiness‚Äô to the local state of the ionosphere at any given moment.

One effect is change in velocity: The free electrons in the ionosphere can affect the velocity of the radio waves. As the waves pass through the ionosphere, the speed of the waves can change due to the varying electron density. This change in velocity leads to a change in the direction of the radio waves, causing them to bend or refract.

Another effect is frequency dependent bending: The degree of bending experienced by radio waves depends on their frequency. Higher frequencies tend to experience more bending than lower frequencies. This frequency-dependent refraction phenomenon is known as dispersion.

Reflection and transmission: Depending on the angle of incidence and the frequency of the radio waves, they can undergo different interactions in the ionosphere. Some of the waves may be reflected back to Earth, while others may be transmitted through the ionosphere and continue to propagate into space.

All of the above contribute to radio blackout.

Regards N.

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On 7/11/2023 at 3:47 PM, Philalethes said:

Glad to see that I'm not off-track there. And all that further information is also very interesting, first-hand accounts about how things work in practice in particular are definitely valuable! Will be interesting to see in the future if some cycle beats out SC19 and manages to open up further VHF bands, if it's not in too many decades or centuries.

lets all hope we make the 380 sfi attained by cycle 19 in 1957 58 winter. although 300 would probably be ok too!  Ha! 

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On 7/12/2023 at 12:17 AM, KW2P said:

(And Cycle 25 is still just getting started. It could stall out but at present we're on track for a repeat of Cycle 19. Fingers crossed.)

Sadly, I think that might be a bit optimistic.....

solar-cycle-comparison(7).jpeg.a3ab126f0e77726ddc379e8ab6c21c14.jpeg

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Perhaps, however from a hams perspective sfi is our bread and butter, so to speak. In terms of ssn I imagine without anything to back me up really, that we are about one year away from solar maximum. just sayin, Possibly what @KW2Pmeant was our solar flux was pushing over 200 this is very significant to us hams. 

Edited by hamateur 1953
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4 hours ago, hamateur 1953 said:

Perhaps, however from a hams perspective sfi is our bread and butter, so to speak. In terms of ssn I imagine without anything to back me up really, that we are about one year away from solar maximum. just sayin, Possibly what @KW2Pmeant was our solar flux was pushing over 200 this is very significant to us hams. 

SFI over 200 is great compared to where we've been.

Hope springs eternal, as the saying goes. I hope because what drives the surface features that matter to us is chaotic convection. No one understands enough about it to make firm predictions. And, we've only observed the sun for 25 cycles. This gives us an idea what's going on but not much more.

The Carrington Event happened during a solar minimum so nothing would surprise me.

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