Solar flares and sporadic E

[VK2ZRH]

on 3 Jun 2007, the logger displayed the following posts:

03Jun 07:18 VK2ZZY M5 flare just occurred - watch for dx in next few days!

03Jun 09:02 VK36 Flares affect F not Es fwiw.

03Jun 11:55 VK6KXW Not so steve this is from the reknown nature url .... http://www.nature.com/nature/journal/v1 ... 047a0.html

03Jun 11:56 VK6KXW Also http://www.nature.com/nature/journal/v1 ... 690a0.html

Preliminary comments:
1/ Google is not always your friend
2/ Nature isn't the 'fount of all knowledge'
3/ E-layer ionisation is not the same as sporadic E (Es) ionisation

First of all, the effects of solar flares on the ionosphere are complex, but well known. For a little refresher, go to the IPS radio & Space Services website at http://www.ips.gov.au/Educational/5/3 and read Introduction to HF Radio Propagation.

Flares will enhance E-layer ionisation on the sunlit side of the Earth. But not to the extent that VHF propagation is possible. That link to the Nature article by Bazzard makes that clear!

Sporadic E ionisation results from wind shears (a monumentally complex subject) in the E-region (90-160 km) gathering and compressing long-lived metallic ions (chiefly iron and magnesium) into thin 'sheets' or 'clouds'. The ionisation in these sheets can reach densities (and density gradients) sufficiently high to refract/reflect VHF.

A fond belief dwells among some radio amateurs that solar flares are, or must be, responsible for the sporadic E that supports VHF (even upper-HF)
propagation. After all, sporadic E propagation often appears suddenly, with strong signals, in a seemingly explosive burst. Despite decades of research, the 'chain of causality' for this has never been established.

Solar flares are transient brightenings of the Sun's chromosphere ('colour sphere', from the red glow of ionised hydrogen) that may last for a few
minutes to a few hours (see www,ips.gov.au/Educational/2/5). Solar flares pump out enormous amounts of energy across the visible, UV and RF spectrum.

There's been a lot of scientific research on solar-terrestrial relations over the past 80 years, a monumental quantum of that on solar-ionospheric
relations. Much has been explained. And much of that has raised many more questions that need explaining. Some people are working on it. And among all of that, a considerable volume of work has been carried out on the relationships between various solar phenomena and sporadic E (Es).

Having trawled through a host of scientific and technical papers over recent years on the subject of Es, I vaguely noticed that, somewhere along the continuum of research, the interest in solar flares and sporadic E dropped off, pretty much from around 35 years ago. I remember losing
interest in the subject myself around the mid-1970s, although I was still keenly interested in Es.

I think I've found the reason: a 1971 paper by a couple of Russian authors that put the kybosh on solar flare production of Es. Here's the abstract. Make of it what you will.

"The Sporadic E Layer and Chromospheric Flares"

O. Ovezcel 'Dyyev and M.B. Ostanina

Ashkhabad, Izvestiya Akademii Nauk Kurkmenskoy SSR. Seriya
Fiziko-Tekhnicheskikh.

Khimicheskikh i Geologicheskikh Nauk, No. 3, 48-52, 1971.

Optical observations of solar flares were made for determining the dependence of Es on chromospheric flares.

Information was used on optical flares published in the solar data bulletins together with ionospheric data for Ashkhabad station. The authors took into account all flares of importance 1-3+. This was supplemented by data on radio bursts with lambda = 10 cm on the basis of measurements at Ottawa and on the basis of Es data for Washington.

In order to clarify whether a flare causes an effect in the Es layer the authors examined the 15-minute values of the limiting reflection frequency foEs before, during and after a flare. This made it possible to determine whether the particular flare is accompanied by an increase in foEs and after what time from flare occurrence this foEs increase is observed. The foEs values were examined for the day after flare onset. As intense Es cases the authors used those cases when the foEs values increased in comparison with the ordinary diurnal variation by not less than 2-3 Mc/sec.

During 1962 and 1964 a total of 140 optical flares was studied, together with about 100 radio bursts with lambda = 10 cm. Among the 140 optical
flares 74 were accompanied by an foEs increase; in 65 cases there was no increase in Es intensity after a flare. Most (up to 3/4) of the flares not
accompanied by an effect in Es were in the autumn and winter months. On the other hand, study of all cases of observation of intense Es revealed
many cases of Es with a marked increase in foEs without any correlation with chromospheric flares (most of these cases were in the summer months).

Thus, this entire analysis revealed that in 45% of the cases flares are not accompanied by an effect in Es, particularly in the autumn and winter months; vice versa, there are cases of the appearance of intense Es, most frequently in summer, without correlation with flares.

This suggests that the coincidence of an increase in Es intensity, that is, an increase in foEs with the observed solar flares, is a random
phenomenon. PEs values for different time intervals after chromospheric flares do not exceed the monthly PEs values for all frequencies, that is, it can be assumed that there is a random coincidence between a sudden foEs increase and flares. It is concluded that chromospheric flares can exert a definite effect on the sporadic E layer only under minimum solar activity conditions.

End of abstract.

Posted in the interests of dispelling persistent myths.

73, Roger Harrison VK2ZRH

---------------------------

[VK6KXW]

Hi Roger,

A most interesting and unexpected message you have posted to the forum.
At last some meaningful debate for all to sink their teeth into.
But I am puzzled [ possible other readers are too] by one part of your argument that doesn't jell with me from the very dated 1971 Russian authors, namely they state ......

Quote "It is concluded that chromospheric flares can exert
a definite effect on the sporadic E layer only under minimum
solar activity conditions" end of quote

If my memory is correct for a long while it seems, we have been rattling along the bottom of the current sunspot cycle.
In fact we have had numerous days of SF of 68 and SSN of Ø's.
To the readers that don't know a SSN of zero is a recognized measurement of nil sunspots being recorded on the face of the sun.

I now throw the forum open to all assembled.
No bricks please !


Posted in the interests of robust debate.

Peter L. Jackson
VK6KXW (ex-vk6zdy)

[VK4BKP]

3/ E-layer ionisation is not the same as sporadic E (Es) ionisation

....
A fond belief dwells among some radio amateurs that solar flares are, or must be, responsible for the sporadic E that supports VHF (even upper-HF)
propagation....

Was listening to 20 metres today with the more than usual activity being put down to solar flares. Also had a couple of beacons on 10m VK3RMH and VK5WI. Propagation never made it to 6m. At least not where I am. Would any of this have been related to the flares as some Hams were saying or would this have been the wind shear type?

[VK5BC]

Very interesting topic, wish I understood it better. My observations are that E's are certainly better during the bottom of the Sunspot cycle and this was observed & believed as far back as the 1960's.

As for activity following the recent flares I have not observed any E's on 10m or 6m but there was a small opening to Western USA yesterday on 10m, I worked one station in San Diego. There were some some strong state side signals on 15m & 40m yesterday but 20m, was quiet. Another interesting observation is that the noise level on 160m, 80m & 40m is the quietest it been here for a long time, infact the quietest I ever had on 160m.

It will be interesting observing conditions as the cycle progresses.

73 Brian
VK5BC

[VK2ZRH]

Kevin VK4BKP said:

Was listening to 20 metres today with the more than usual activity being put down to solar flares. Also had a couple of beacons on 10m VK3RMH and VK5WI. Propagation never made it to 6m. At least not where I am. Would any of this have been related to the flares as some Hams were saying or would this have been the wind shear type?

Well, from a look at the IPS ionogram viewer for the 4 hours before you made the post, either the F2 layer or Es would probably have supported the propagation you observed.

IPS issued the following warning:
IPS HF RADIO COMMUNICATIONS WARNING 07/14
ISSUED AT 03/2353Z JUNE 2007
BY THE AUSTRALIAN SPACE FORECAST CENTRE.

HF COMMS FADEOUTS EXPECTED DURING DAYLIGHT HOURS
FROM 04-06 JUNE 2007
IF COMMS DIFFICULTIES EXPERIENCED TRY A HIGHER FREQUENCY BAND

So - F-layer propagation conditions were most likely affected by the flares; the activity on the higher bands most likely resulted from flare-enhanced conditions.

Peter VK6XKW puzzled over "It is concluded that chromospheric flares can exert a definite effect on the sporadic E layer only under minimum solar activity conditions".

Firstly, Peter, just because the Russian paper was published in 1971 doesn't mean its relevancy has expired (as you said, pejoratively, very dated). Queensland professor J.D. Whitehead's 1961 paper on "The formation of the sporadic E layer in the temperate zones" remains relevant today despite more than 45 intervening years of research. Of the numerous papers I've sourced and read over the past 5 years, nothing new about solar flares and Es (note: NOT E's) has appeared (that I've been able to find).

That cryptic comment in the Russian paper's abstract is curious, to say the least. As I don't read Russian, don't know any translators of technical Russian (and an English translation seems to be unavailable), and no subsequent research into solar flares & Es has looked at this aspect, I can't throw any more light on it. Then again, we must all keep in mind that the focus of our interest is predominantly VHF propagation, while the focus of ionospheric researchers is predominantly the observable phenomena of ionospheric physics ~ the vast majority of sporadic E ionisation (as observed by ionosondes, satellites, ionospheric radar etc) does not support/influence terrestrial VHF propagation.

Let me put that into perspective with an example: between the spring equinox of 2005 (22 Sept 2005) and the autumnal equinox of 2006 (22 March 2006), a sporadic E layer with a penetration frequency (foEs) of at least 3 MHz formed over Brisbane and Sydney every day (for >5 minutes). I know, because I looked at each 5-minute ionogram and wrote down each incidence where foEs reached or exceeded 3 MHz. From fundamental ionospheric propagation geometry, these layers would have supported propagation up to ~18 MHz (or greater, where foEs exceeded 3 MHz).

Whether or not Es has some dependence on the Solar Cycle is a moot point. Over the years, some researchers have found (a) little correlation, (b) negative correlation (ie. greater incidence at solar minimum, lesser at maximum), (b) positive correlation and (d) a half-cycle variation. I should point out that these findings generally relate to a particular geographical location or region, not globally. Then again, at least one research paper I've read found that the maximum incidence of Es moved geographically to another region as the Solar Cycle progressed - so that, in a specific area/location the Es incidence declined as the solar maxima approached, but in an adjacent region the Es incidence increased. Because it is now known that Es is driven by complex wind systems in the mesosphere lower thermosphere (90-160 km) region, which are influenced by the tides, the seasons, the Earth's orbit, solar activity and the Solar Cycle, perhaps Es is a regular feature on a global scale, but we only experience it from a confined, 'local' perspective.

Brian VK5UBC observed: As for activity following the recent flares I have not observed any E's on 10m or 6m but there was a small opening to Western USA yesterday on 10m, I worked one station in San Diego. There were some some strong state side signals on 15m & 40m yesterday but 20m, was quiet. Another interesting observation is that the noise level on 160m, 80m & 40m is the quietest it been here for a long time, infact the quietest I ever had on 160m.

Hmm, that reads like 'typical' ionospheric variability to me (ie. there are differing explanations for the variety of conditions observed)!

Posted in the interest of further debate.

73, Roger Harrison VK2ZRH