By far the most exciting VHF propagation mode in my opinion is Sporadic-E which can magically appear for a limited time and allow long distance (DX) VHF radio contacts to be made, often at high signal strengths by even the most modest radio stations.

Sporadic-E propagation, also known as ES propagation, is a type of atmospheric phenomenon that occurs in the VHF (Very High Frequency) bands of the radio spectrum. It affects frequencies typically ranging from 28 MHz to 220 MHz, which include several amateur radio VHF bands and the FM broadcast band of 87-108 MHz.

Sporadic-E (abbreviation Es) enhanced VHF radio propagation is just that, sporadic yet present most days for several hours at a time during daylight hours on 50 MHz usually most years between May to August in the Northern hemisphere, peaking in June sometimes with rare short duration openings supporting radio signal reflections on frequencies as high as 144 MHz, and with daily timings over several years showing the greatest chance of Es being present between 11:00-12:00 UTC and 16:00-18:00 UTC. Sporadic-E is observed on 144 MHz less than 10% as often as on 50 MHz.

For many years there have also recorded a much weaker and shorter Sporadic-E season around the Winter solstice (21st December) when the intensity of the sun's solar radiation is at its maximum over the winter months. I have only ever worked it a few times.

However in 2020/2021 things changed quite noticeably from previously recorded years, the usual Es season didn't end in August, but carried on throughout September, October, November, December and into January 2021 with at least 3 large European wide Sporadic-E openings each month on 50 MHz workable even from here in the far North of England. I don't know if this is because many more Radio Amateurs are using the weak signal data mode FT8 and are able now to detect and work Es openings in a way that wasn't previously possible with CW and SSB and/or is it because so many people are at home monitoring the VHF bands due to Covid-19 lockdowns. Or is some unexplained physical change in the atmosphere.

Excellent Sporadic-E 144 MHz events occurred in 1989, 2006, 2009, 2010, 2011, 2017, 2020, 2021 and 2022 which have been at both maximum and minimum points in the 11 year sun solar cycle, which demonstrates that the peak of the solar cycle is not a factor required for Sporadic-E to occur, however solar flares and CME can both be triggers. For an excellent evaluation summary of 144 MHz Sporadic-E from 2001 to the present day I highly recommend viewing the MMMonVHF website which shows you all the data collated and broken down into time, day, month, year, quantity and Es cloud positions.

Another characteristic supported by my own live monitoring over 40 years and extensive collected data from DXcluster spots since 2001, in the Northern hemisphere for European propagation, is that the vast majority of Sporadic-E reflection areas or clouds seem to occur mostly over the Bay of Biscay, Switzerland and the Balkans. Here in the UK it is probable on most days in Summer to work Italy and Spain easily on 50 MHz, it is much rarer perhaps 5-10% of Es days for the reflecting Es cloud to be situated over the North Sea allowing communication from the UK to Scandinavia, however when this does occur it is in this very marked direction. Even rarer openings occur in the direction of Iceland from the UK, but several triple hop Sporadic-Es clouds do reasonably often open paths from the UK to the USA on 50 MHz.

Sporadic-E (Es) occurs in the Ionosphere at heights of between 90-130 km (110 km average) altitude and appears to concern strong areas of non-uniform and patchy plasma metallic ion and electron density irregularities that cause VHF radio waves to be reflected back to Earth by forward scatter. The metallic ions necessary are deposited in the Ionosphere by daily meteor activity (heating and ablation) even in the absence of major shower or meteor storm activity, the primary metal types being iron (Fe) and Magnesium (Mg). The total metal ion density determining whether or not the Es layer can support VHF signal forward scatter or not. The winds and electric fields at these altitudes act to compress the ions into thin layers of around 4 km in depth.

There are minimum distances for each band for propagation via Sporadic-E, lesser distances seen would be impossible by this propagation mode as the required MUF would be simply too high and must therefore be by another mechanism such as Aircraft Scatter or Tropo scatter etc. The minimum distances by VHF band are shown below.

50 MHz minimum Es distance 800 km (exceptionally down to 400 km, but usually around 800 km)

70 MHz minimum Es distance 1000 km (exceptionally down to 400 km, but usually around 1000 km)

144 MHz minimum Es distance 1400 km

The minimum distances are important because if the angle of incidence is too high and acute the MUF will not support the reflection and the VHF radio waves will simply pass through the Sporadic-E cloud layer and not be reflected. The higher the frequency the shallower the angle of incidence needs to be.

The height of the Sporadic-E cloud relative to the Earth's curvature is also important. It has been established that Sporadic-E clouds gradually descend as time goes by during the day, before eventually disappearing some time after sunset, exceptionally lasting until midnight.

The generally accepted Sporadic-E heights are between 90-130 km (110km average)

Research and published papers indicate that it is the daily ablation of thousands of metallic meteors from all directions that are required, rather than just intense meteor showers from single radiants. During the Summer months there is approximately three times more metallic meteorite deposition than in the winter months.

Sporadic-E occurs most notably on the VHF 28 MHz, 50 MHz, 70 MHz and 144 MHz amateur radio bands where the ionized E layer of the atmosphere at around 110 km altitude reflects forward scatter VHF radio signals back to Earth, rather than them normally travelling straight through the atmosphere into space, with received radio signals being extremely strong.

Monitor the VHF amateur radio bands and beacons and if Es signals are exceptionally strong on a lower band such as 50 MHz and at the lower end of the single hop distance range (<500 km) this can be a good indicator that Es will be supporting even higher frequencies, so consider listening up on the 70 MHz or 144 MHz bands too. If travelling in your car away from your shack try monitoring 87.6 MHz FM on your analogue vehicle radio to see if you can hear Es broadcast station signals from outside the UK (Tip from Dave Edwards G7RAU, thanks!)

Long distances on 50 MHz can be worked via Sporadic-E clouds at altitudes between 90-130km above the Earth's surface. Most of the rarer multi hop Sporadic-E events appear to occur between a maximum of up to three separate clouds. 

Some extensive 144 MHz very long distance Propagation Studies in Germany by Dr. Volker Grassmann DF5AI and Udo Langenohl DK5YA include their theorised possibility of VHF signal reflections from one Sporadic-E cloud hitting the ground and being reflected back up to a second Sporadic-E cloud, where there are either large bodies of water, such as lakes or rivers and even the theorised possibility of ground reflections from railway track metal lines.

A separate paper discusses Thunderstorm effects on Sporadic-E propagation at 144 MHz. Click on images below and open in new tab to read their research papers.

Single hop Sporadic-E 800-2400 km where the path is Earth-Cloud-Earth (exceptionally down to 400 km when MUF is near maximum)

Double-hop Sporadic-E up to 4800 km where the path is Earth-Cloud-Cloud-Earth

Triple-hop Sporadic-E up to around 7200 km where the path is Earth-Cloud-Cloud-Cloud-Earth.

(N.B. Triple hop Sporadic-E has been observed on 50 MHz, 90 MHz (extremely rare from Europe to USA only recorded once), but never seen on 144 MHz

With the advent of special weak signal data modes many more observations of the triple hop Sporadic-E are being observed on 50 MHz, seemingly favours the path from Europe to North America.

Very rare quadruple hop Sporadic-E (4xEs) on 50 MHz has been observed on a daylight path from Japan to Europe in July 2023 after a M5.8 magnitude solar flare with SFI 214

Distances for VHF radio signals in excess of 7200 km are extremely rare via Sporadic-E alone, as the chances of more than three sporadic and random Es clouds all being in the perfect positions at the same time. Look for Sporadic-E propagation joining up with another Propagation mechanism such as Trans Equatorial Propagation (TEP), Meteor Scatter or via F2 propagation. F2 propagation supporting 50 MHz occurs only near or during, the 11 year average, Solar Cycle maximum when the F-layer supports refraction (bending) of signals at 50 MHz from that much higher altitude layer, ranging in height from 200-500km, back to Earth where they may bounce from the ground/sea back to the F-Layer again. This is how it is possible to work Australia from the UK on 50 MHz.

With any long distance 50 MHz propagation the polarisation of the transmitted VHF signal may be changed from horizontal to vertical, or vice versa, after it is reflected or refracted by a single or multiple Sporadic-E clouds, indeed the signal should not be thought of a like a narrow laser beam striking a mirror, but should be likened to a much wider car headlight striking a corrugated shiny tin roof, with the reflected light or radio signal scattered in multiple different forward directions. This can lead to the VHF radio signal having differently polarised mixed components, or the same polarisation, which can become out of phase and create an unusual twisted 'barbers pole' effect visible on the spectrum screen of SDR receivers.

Some really good image examples of this twisted 'barbers pole' out of phase signal effect, which is particularly, or only evident, on double hop Sporadic-E, have been kindly provided to me by Paul Logan from Fermanagh, Northern Ireland, who is a very active and well known Broadcast FM DXer on Twitter @FMDXIreland as observed by him in the frequency band of 87-108 MHz. The twisted 'barbers pole' out of phase signals at 2800-3000 km distances, shown in the images below, stand out as clearly different from the single hop Sporadic-E distance stations signals, that do not have the twisted barbers pole effect visible.

Whilst on the subject of FM DX in Band II between 87-108 MHz the fantastic website of FMList has a visual mapping system showing in real-time DX spot paths via Sporadic-E, which reveal readily Es skip 'doughnuts', with the missing centres being the approximate location of the Es clouds. As can be seen in the image below, dated 17th June 2023 at 1000 UTC, where two separate simultaneous Sporadic-E clouds can be visually observed.

Single hop Sporadic-E is routine, double hop considerably rarer and triple hop rarer still, as all the clouds must perfectly align and be at the right heights and with sufficiently high MUF to support such high VHF frequencies.

Triple hop Sporadic-E signals in Band II VHF frequencies 87-108 MHz are extremely rare

On 26th June 2009 Paul Logan from Lisnaskea, Northern Ireland IO64GG had triple hop Sporadic-E reception on the Broadcast FM band from eight US States and one Canadian province. The most distant signal received was that of WVAS radio in Montgomery, Alabama, USA on 90.7 MHz at a distance of 6456 km (4012 miles). The reception was recorded and later confirmed by WVAS newsreader Marcus Hyles.

On 5th July 2022 Bryce Foster (K4NBF) Co-host of the VHF DX podcast received a triple hop Sporadic-E FM signal on 87.8 MHz from Portugal to Cape Cod, USA

I have found strong Sporadic-E stations within 87-108 MHz can be heard and received here in the UK from Spain, often accompanied by openings on the Amateur Radio 70 MHz band, but sometimes without any 70 MHz Amateur Radio stations being heard. I can only put this down to the transmitter powers of the FM Broadcast stations being often measured in many kW and therefore with many magnitudes higher ERP than from Amateur Radio stations.

This also used to be the case when the old Band 1 TV transmitters 47-68 MHz were heard easily in the UK from Spain, before any openings were received on the Amateur Radio 50 MHz band due to the difference in ERP levels. This was via Meteor Scatter or Sporadic-E. Unfortunately the Band 1 TV transmitters in Spain have all since closed down.

On 144 MHz the distances for single hop Es contacts appear to all be in the range of between 1400-2400 km with rarer double hop Es extending this to a recorded maximum of 3600 km. Longer distances can be found online, however they all appear to be via Tropospheric Ducting + Sporadic-E (TRDES), analysis of the Callsigns/locators show them all to have an extensive over water path (Sea) and intense Tropospheric Ducting was reported at the time to be the main Propagation mechanism.

No triple hop Sporadic-Es has ever been recorded for frequencies as high as 144 MHz, the highest frequency this has been observed has been 90.7 MHz. The angle the radio signal hits the Sporadic-E cloud needs to be shallow enough to permit reflection, depending on the MUF value, otherwise if too steep or not supported by the MUF it will not be reflected and instead pass straight through the Es cloud and off into space.

The exact multi hop mechanism for each signal may not be readily identifiable and may be signals reflecting off a single Es cloud layer or multiple separate Sporadic-E clouds and/or various mixtures of Cloud and the Earth (TBC) with potential reflections from water offering significantly less attenuation than from land. It has also been suggested that metal train tracks might also permit ground reflections, as well as bodies of water such as lakes and rivers or the Sea.

It is also theorised and pretty much correlated that the Es cloud layers are not uniform and flat, but may have parts or all tilted at times at up to 45 degrees where they often have an irregular wavy surface, like corrugated metal sheeting (see image below).  This can slightly complicate understanding the precise Sporadic-E hop mechanism being observed on 50 MHz with the theory being of many instances where two cloud Es formations exist, the Es layers being tilted towards each other.

This two cloud Es formation appears to account for 50 MHz signals in the distance range of 2400-3200 km i.e. more than a single hop maximum (2400 km), but much less than for double-hop (4800 km). The signal path being Earth-Cloud-Cloud-Earth.

Noctilucent clouds at around 85km altitude - Photo by Jan Koeman, Kloetinge, the Netherlands, July 2009

In the two Es cloud formation path live example shown below, captured at 18:12 UTC on 17th July 2018, I was hearing the station of SV1NZX in KM17 square via Sporadic-E on 50 MHz at a very strong signal level, my station G0ISW in IO84 square being 2741 km in distance away and therefore well beyond the maximum single hop distance of 2400 km.

Looking at the live MUF mapping software display there were two significant Es cloud areas in place (circled in red) on the path, both at a similar distance from our stations, therefore it appears that the signal was being reflected from these separate Es clouds at the same time, with both Es clouds layers probably being slightly tilted towards each other with wavy irregular cloud surfaces, the path being Earth-Cloud-Cloud-Earth.

Be aware though that in multi hop Sporadic-E propagation of two (2xEs) or three (3xEs) clouds, they are unlikely to be evenly spread apart between the transmitting and receiving stations, one cloud may be very close, the other/s very far away or any combination, as well as differing altitudes.

Sporadic-E on 144 MHz defies any specific direct correlation with AGW, wind shear and thunder storms. In the example below at 17:53 UTC on 23rd July 2018 there is a pronounced Es reflecting layer shown over the Balkans and their mountain ranges, but checks on live wind charts show no jet stream or other significant wind activity anywhere near and also no lightning whatsoever.

After sunset the ionised Es layer usually fades until it can no longer support VHF signals being reflected from it, probably due to no longer receiving solar radiation, however on rare occasions Sporadic-E VHF propagation has been known to occur even up to local midnight.

From observations in Europe, over the past 30 years, Sporadic-E clouds are randomly generated signal reflecting areas, which vary in size depending on the frequency band they can support  i.e. 50 MHz Sporadic-E clouds are usually significantly larger and can often be around 500 x 500 km (5 x 5 grid squares) in size, whereas on 144 MHz they may often only be 50-100 km in size i.e. a single grid square, unless a very significant and much rarer large opening event. The usual small reflecting area on 144 MHz means fewer stations will be ideally located to benefit from using it. Some stations will enjoy the enhanced long distances being worked and others will miss it entirely if not in the right place at the right time.

In the image below we can see that there was one locator square where the 50 MHz Sporadic-E signal paths were crossing in JO22, no mountains nearby.

In the images below white lines show the paths on 50 MHz, grey lines are 70 MHz and red lines are 144 MHz.

On 144 MHz the Sporadic-E layers in Summer have been observed to move slowly from East to West and sometimes correlate with intense thunder storms, but not always. Note the correlation between this very significant 144 MHz Sporadic-E opening reflection zone, shown below on 12th July 2018, and the live map of lightning strikes at the same time in the same area. The 144 MHz opening on the border of Poland with Ukraine shown below lasted just over 1 hour and despite much similar lightning visible in Norway no such Sporadic-E opening occurred there. However later in the week further extensive thunder storms were present and no Sporadic-E was observed anywhere in Europe, all the necessary combination of ingredients not being present.

In addition whilst 50 MHz Sporadic-E band openings can last most of the day, 144 MHz openings can be very short lived and occur much less frequently, only being available for a few days each year and for much less time, sometimes only as little as a few minutes or an hour and almost always in June.

From my own observations 144 MHz Sporadic-E reflecting areas do sometimes, but not always, coincide with intense thunder storms and due to the height of the Es reflecting layer being between 90-130 km I theorised a link with the then little known electrical Sprite phenomenon perhaps, possibly generating Atmospheric Gravity Waves (AGW) and causing wind shear at 90 km altitude and higher.

Image credit https://en.wikipedia.org/w/index.php?curid=4262250

Abestrobi Own work CC BY-SA 3.0

The higher the frequency the more intense the Sporadic-E ionised layer has to be to support forward scatter propagation via it, at 144 MHz in particular it can be frustrating to see the small reflecting area favour radio amateurs in a particular geographic area reasonably close, but in your own location nothing is heard and vice versa. Sometimes the reflecting areas at the centre of the lines connecting the QSOs converge over a particular area each year, the Bay of Biscay near France is one such area. Often the reflecting layer/cloud moves over hours in a East to West direction. Using the Live-MUF mapping software it is very easy in real time to observe these events.

Sometimes on 144 MHz there may be correlation with Es reflecting areas and thunder storms generating extensive lightning activity (another theory), but by no means do they coincide every time. On the morning of 3rd May 2016 there was a clear 50 MHz Es reflecting layer centred over the Baltic states, but no wind shear or AGW from mountains, nor any thunder storm lightning activity found using live data, so the required ingredients were much simpler.

In June 1989, during a particularly intense radio Es event on 144 MHz, I observed the distant DX stations heard to slowly all shift SW over the course of two hours, in a direction not associated with the jet stream, but consistent with the Earth's rotation in relation to the Sun.

If we consider the 'wind shear' theory formulated in the 1960's by Whitehead (1961) and Axford (1963) in which vertical shears in the horizontal wind form thin layers (several kilometres thick) from metallic ionisation through ion-neutral collisional coupling and acting in the presence of the Earths magnetic field and through the Lorentz force. The original metallic ions thought to be present from meteoric origin.

Wind shear from the Jet Stream at altitudes of between 9-16 km above ground level over mountains has been suggested to have an association with Sporadic Es, part of the so called 'wind shear' theory. Using the live wind chart below and setting the wind height altitude to 500 hPA  (11 km) should allow observations and comparisons to be conducted in real-time with Sporadic Es cluster maps to support or discount any such correlation, with wind effects.

(Right click on image below and select o'pen link in new tab' for current live jet stream map)

Noctilucent clouds do prove that there are wind effects present at very high 90 km altitudes caused by Atmospheric Gravity Waves (AGW), their non uniform composition can be likened to the theorised irregularity of Sporadic-E clouds.

Noctilucent clouds at around 85km altitude - Photo by Jan Koeman, Kloetinge, the Netherlands, July 2009

How are there wind effects and potential 'wind shear' at 90 km altitude required for Sporadic-E? Well, Atmospheric Gravity Waves (AGW) required to form Noctilucent clouds and other wind effects at these high altitudes can be generated by either violent intense thunderstorms or wind flow over high mountain ranges, which cause vertical displacement of the air flow with the AGWs forming when buoyancy pushes air up and gravity later pulls it back down.

The AGW can be likened to a corrugated tin roof effect being placed on the original horizontal air flow and these uneven waves of air then travel to high altitudes and new waves form underneath so a sequence of waves will be formed. AGW are medium scale waves with the horizontal wavelength ranging from several tens to several thousands of kilometres and a vertical wavelength of several kilometres. Using radar measurement AGW have been observed to reach heights of around 85-88 km, the same height as Noctilucent clouds. The AGW can even penetrate up to the Ionosphere where they trigger ionospheric irregularities and add to the recipe for Sporadic-E likelihood.

The generally accepted height of the Sporadic Es reflecting layer is around 90-130 km, which is very significantly higher than the jet stream altitude of 11 km. Although annual the intensity of Es events varies by year and had been very poor compared with the 1980's and 1990's, despite peaks and troughs of the solar cycle. In 2017 and since it has mostly been much better.

There is a definite connection with the radiation intensity of the Sun due to the primary seasonal Summer nature of the event in the Northern hemisphere. Also the Es events tend to mostly occur during daylight hours at VHF. A 3-6 day cycle pattern of building up to a Es peak also seems quite prevalent where generated by jet stream wind shear, possibly an electric ion charge/discharge cycle period perhaps, it does seem strange to see very active Sporadic-E one day and absolutely nothing the next day despite Solar conditions appearing unchanged. Fair weather return currents can dissipate Sporadic-E clouds

Significant solar flares and thunderstorms can help generate Sporadic-E clouds in a much shorter time frame than by Jet Stream winds alone.

The Earth has a Global Electric Circuit (right click on image below for video explanation) with lots of variables daily impacting upon it at Ionospheric altitudes, many of these factors will contribute to whether or not VHF radio signals can be propagated over vastly longer distances than normal on any given day.

A very lively start to the day at 0845 UTC on Sunday 28th May 2023 with a significant Sporadic-E opening on 144 MHz, MUF is already shortly afterwards 150 MHz. Looking at live Lightning strike map of Europe, there is no correlation observed this time. However there is very intense Meteor activity today believed originating from Comet 209P, which occurs every year between 24-31st May, see images below.

This Sporadic-E opening is staying frustratingly over central Poland at 1124 UTC and is now only up to 70 MHz, it has moved a little further West than earlier this morning. At 1305 UTC it still hasn't moved away from Poland and is getting weaker with just a few 50 MHz spots being shown. By 1650 UTC the Sporadic-E opening on 50 MHz largely gone and very little heard today here for the UK, surprising the Es didn't move or appear further West at all. Brief weak 50 MHz opening from UK to Scandinavia this evening

Sporadic-E + Tropospheric Ducting (TRDES)

Also in June 2019 Sporadic-E + marine Tropo Ducting allowed signals on the 144 MHz band to be received from D41CV in the Cape Verde Islands off the West Coast of Africa to be received by OE3NFC in Austria at a distance of 5107 km, the marine Tropo ducting path being from Cape Verde to Southern Spain where it joined the Sporadic-E path between Southern Spain and Austria.

The Sporadic-E cloud height is between 90-130km above the Earth, so this combined Propagation mechanism favours a shallow angle of reflection from the cloud down to the Sea surface, where it is then reflected from the water into the very much lower Tropo Ducting 'pipe' and then can travel considerably further. The height of the Tropo Ducting layer can vary from just above the Earth's surface to several km high. Surface based ducting typically forms over bodies of water and can be very close to that surface.

Sporadic-E + Trans Equatorial Propagation (TEPES)

An absolutely exceptional partial Sporadic-E contact occurred on the morning of 24th July 2018 between 0700-0800 UTC when the station of VK8AW (PH57) Darwin, Australia worked and was heard by stations in Europe on 50 MHz with the furthest station being G3TXF (IO71) in England at a distance of 14,118 km!

Previous theory and long established observations prior to 2018 stated there should be no F2 or Trans Equatorial Propagation (TEP) propagation except at solar maximum, but having communicated via e-mail with Gary Ashdown VK8AW it appears that his signals were reaching Southern Europe and the Middle East via Trans Equatorial Propagation (TEP) and were being further extended by widespread European Sporadic-E linking to it. Apparently 48-50 MHz signals are observed by VK8AW regularly from the Middle East and China and the new weak signal data mode FT8 is allowing two way radio communications, where they were previously almost unworkable or undetectable except at solar maximum in other modes such as SSB.

This mechanism of TEP + Sporadic-E propagation has been seen again on 50 MHz in Summer 2019 with many stations in Japan working Southern Europe and even UK stations on the South coast of England.

On 7th May 2023 there was another good example of Trans Equatorial Propagation (TEP) joining up with Sporadic-E on the 50 MHz band in the evening, allowing stations in Southern Europe and North America to work stations in South America, which would have been too far for Es alone.

Another good example of Trans Equatorial Propagation (TEP) joining up with Sporadic-E on the 50 MHz band on Saturday 13th May 2023, stations in Brazil workable here in Cumbria, NW England at around 1600 UTC

On Sunday 11th August 2024 a 144 MHz TEP contact using the Q65B data mode took place between S50C in JN76JG and V51WW in JH81OC at a distance of 7211 km. A fantastic result.

Highest recorded Sporadic-E MUF

The highest recorded Sporadic-E MUF that I can find so far online is 220MHz, where Bill Duval K5UGM (SK) and John Moore W5HUQ/4 broke through a 1500km path from Texas to Florida, USA on 14th June 1987

Intense Meteor Storm generated Sporadic-E propagation

When I participated in the fantastic Leonids November 2002 meteor storm event, with over 2300+ meteors per minute, the intensity was such that the whole 144 MHz band was wide open for many hours in the morning with the high signal strengths associated with Sporadic-E signals. The extreme rarity of this type of event makes it very special to witness, for me only once in my 40+ years of being a Radio Amateur.

I have also observed other meteor showers coinciding with Sporadic-E like openings, as happened in April 2017, April 2021, and April 2024 during the peak of the Lyrids meteor shower, no other mention of Sporadic-E by stations until May, but the signal strengths I observed were very high and prolonged again, for an hour or more.

The long standing mystery of what exactly can generate Sporadic Es propagation continues, since it was first observed in the 1930's.

Anomalies investigated using multiple data sources for later analysis

On Sunday 2nd July 2023 at 1637 UTC I heard SV5DKL on 50.313 MHz FT8 via Sporadic-E at a distance of 3113km, so at double hop Es distance, but look at the map below where the Es clouds (centre of doughnuts) do not appear to line up for this and are showing the MUF ES for frequencies in the FM Broadcast band of at least 87.5 MHz. That must mean then that the MUF Es clouds supporting my 50 MHz reception must be in a different position or significantly larger in size i.e. more to the North of the doughnut holes Es reflecting areas seen below. We know that the higher the MUF frequency supported by any ES cloud, the smaller that cloud (doughnut hole) reflecting area will be and conversely the lower the frequency supported the larger the Es cloud area will be.

If we look instead at the map below from DXMAPS.com showing 50 MHz spots seen in the DX Cluster, for the same time period, we can potentially see two locations for the required double hop 50 MHz Es clouds, the first is possibly over Austria at the intersection of a few spot lines, the second over Bosnia & Herzegovina. That would make more sense, but is this correct? We need to see more data to confirm or not.

If we now look at the data image below, from PSKreporter.info, showing stations worked/heard by me G0ISW for the same time period, we can definitely see the  Sporadic-E path between me and SV5DKL, plus the similar double hop 2xEs path for me hearing another station shown in Israel. Interesting to see at least 3 stations I heard in Austria JN77/JN76, who all appear to be directly beneath where I had initially suspected the first Es cloud to be.

Therefore the first Es cloud cannot be directly over these stations in Austria, but must be earlier in the path, over Germany instead about locator squares JO30/JO40, at the midpoint between G0ISW and the three stations in Austria for what is clearly an Es single hop distance. The second ES cloud initial speculation location remains the same, somewhere over Bosnia, or further to the South East.

Unidentified Propagation analysis (UK to Japan 50 MHz) - since Solved

Here we see below at around 0819 UTC on Wednesday 12th July 2023 an opening on 50 MHz between the UK/Europe and Japan at distances of over 8600km. All areas are within daylight. The maximum triple hop Sporadic-E distance is 7200km, so could this have been Quadruple hop Es (4xES)?

We can discount Trans Equatorial Propagation (TEP) involvement, as all stations are well above the magnetic Equator.

The only other option for VHF at these distances would be F2 layer propagation, but still two years away from the expected 11 year peak of the solar cycle, in July 2025. F2 propagation for 50 MHz would then be expected, as previously seen, only over the Winter months, not Summer 2023.

Looking at the DX Cluster spots for 50 MHz there are very few single hop Sporadic-E spots showing within Europe so far. The SFI is at 214, unusually high indicating recent solar activity above the normal, the day before there was an M-Class 5.8 solar flare which generated a CME that hit Earth on 12th July 2023.

Conclusion is that this can only therefore be Quadruple hop Sporadic-E (4xES)triggered by the CME

Interestingly a short time later by 0900 UTC a significant Sporadic-E opening on 144 MHz had developed, centred over Ukraine, this supports Es clouds with clearly high enough MUF for 50 MHz being present earlier over the Europe to Japan path. Quadruple hop Sporadic-E (4xES) now looking more and more certain.

We can see from the MUF map below for Sporadic-E that there are Es clouds that would support 50 MHz signals over Europe, Ukraine, Russia, China and Japan. The lack of further reported MUF ES clouds in between may be accounted for by the scarcity of amateur radio stations within Siberia and Mongolia.

Quadruple hop 50 MHz Sporadic-E (x4 ES) UK to Japan path

We have seen this very rare event recently in 2023, after solar flares that generated CME, on entirely daylight paths between Europe and Japan on 50 MHz, however this morning Saturday 22nd July 2023 at 11.41 UTC we can see it is still possible after the sun has completely set in Japan. The solar flares with their extensive ionising radiation appear to be generating broad areas of Sporadic-E enhancement over huge distances, the latest flare was M 3.81 class on 19th July 2023 that generated CME's that hit on 21/22nd July 2023