Updated HF Propagation Charts from the UK

I have just updated my short-path propagation charts from the UK with the latest predicted smoothed sunspot numbers.

It takes about half a day to do - it took longer this time as I was using a new, faster laptop, but couldn't remember the log-in details for my server!

Anyway. they are done now. They are updated up to January 2027. Interestingly, the predicted smoothed sunspot numbers range from 120 for February 2026 to 96 for January 2027. These come from the Space Weather Prediction Centre in the US and are SIDC figures.

So it looks like we will have another good year of HF propagation, before the numbers star to slide further in late 2027. 

I still recommend both Proppy and VOACAP.com if you want detailed HF forecasts, or if you want to do long-path predictions. But for casual use my charts are fine, and produced using VOACAP.

Autumn 2022 HF popagation charts updated

 

I have just updated my propagation charts for October, November and December 2022 with new sunspot numbers. 

I will update the Spring 2023 charts when we get a little closer as they are likely to change as we head towards the maximum of solar cycle 25. 

Anyway, it is nice to see some good predictions of DX on 10 metres and if the past two weeks are anything to go by they are pretty spot on with very loud signals from the USA. 

ARRL's W1AW's CW practice files were romping in the other day on 28.0675MHz Nice to see 10 metres doing what it does best! 

Click here for the charts or use the link on the right-hand side.

HF propagation charts updated for 2021

I've now updated my propagation prediction charts for 2021 with the predicted smoothed sunspot numbers from NOAA/NASA.

So that's a chart for every hour, for every band and for every month, or more than 2,300 charts in total! The process is fairly automated, but it still fairly tedious and takes about a day to do.

The charts are useful as a quick guide to what parts of the world may be workable and which aren't. If you want more accurate charts then the ITURHFPROP-based predtest.uk or the VOACAP-based voacap.com websites are better.

I may need to update them as the year progresses as we get a better idea of how Solar Cycle 25 pans out. At the moment it isn't looking too good. December 2020 saw a sprinkling of SS25 sunspots with a corresponding rise in HF activity. But since January is has been pretty dire really with long periods of no spots 

Anyway, to avoid confusion, I have updated form February onwards. This means that January is actually for 2022. 

The charts are produced using Hamcap which is a VOACAP-based application and they are for short-path only.

VHF propagation video released on YouTube

As a result of the success of our HF Propagation video on YouTube, which has had 2,000 views in two months, the Propagation Studies Committee has now launched a 20-minute VHF propagation video as well.

The video was originally produced for club presentations, but with Covid-19 and the lockdown, it wasn't getting much use.

So if you have never heard what an auroral contact sounds like, for example, now's your chance!

See https://www.youtube.com/watch?v=5Yo4IFn6AAY&t=8s

Steve G0KYA
Chairman, RSGB Propagation Studies Committee

Range of HF propagation tools launched

There is now a range of online propagation tools available from the RSGB's Propagation Studies Committee, including Proppy for RadCom, VOACAP for RadCom, Predtest and Propquest. All very popular according to the feedback.

We highlighted these at the recent Newark Hamfest.

RSGB has now set up quicklinks to each of the tools, which will make it easier in the GB2RS audio bulletin. These are: 

Propquest
Shows real-time critical frequency and MUFs over various path lengths. Excellent tool for HF users.
See www.rsgb.org/propquest

Predtest
Designed by Gwyn G4FKH, calculates the probability of propagation over different paths and for different modes. Includes point-to-point and animated displays.
See www.rsgb.org/predtest

VOACap for RadCom
Shows the probability of propagation to 28 different locations around the world – the same locations used in the RadCom predictions. Can be tweaked for your particular station including mode, gain and power.
See www.rsgb.org/voacap

Proppy for RadCom
Uses the latest ITURHFPPROP tool to calculate the probability of propagation to the same 28 locations used in RadCom.
See www.rsgb.org/proppy

HF propagation charts updated

I have just updated my HF short-path propagation prediction charts for the UK (accessed via a link on the right).

I had to update them with the latest smoothed sunspot numbers for the next 12 months.

This is a little depressing as after May 2019 the predicted SSN falls to "one" and stays like that for the rest of the year! Sunspot minimum is currently thought to be later this year, but could spill over into 2020.

These charts are meant as a rough guide. Other tools that are available are:

1. The VOACAP RadCom prediction tool - this replicates the locations found in the monthly RSGB publication, but lets you choose your own mode, power and antennas to give more accuracy.

2. The Predtest.uk tool - this tool, developed by Gwyn Williams G4FKH, uses the latest ITURHFPROP prediction engine to let you produce point-to-point or area propagation predictions, again with full control over the input parameters.

3. Propquest - this is a near real-time tool, developed by Jim G3YLA, that shows the critical frequency and extrapolated maximum usable frequencies available over different path lengths. The critical frequency (the frequency at which a radio wave launched vertically stills gets returned to Earth) is derived from ionosonde data, mainly from Chilton and Fairford.

It should be your first port of call to see what conditions are like. In the summer it also has predictions for Sporadic E, courtesy of Jim.

Steve G0KYA
RSGB PSC Chairman

Predicting space weather – and how to get it wrong!

Space weather prediction is an inexact science. We still don’t fully understand the Sun or how it works.

This means that predicting what HF radio conditions are going to be like over the next seven days can be challenging – especially when you have to produce the forecast a couple of days before it is published.

This week was a perfect example of how to get it wrong!

I prepare the HF part of the RSGB’s GB2RS Propagation Prediction forecast on Thursday afternoon. Jim G3YLA looks at VHF and Sporadic E, before it is sent to John G4BAO who adds some more info on any microwave propagation such as rain scatter and also adds the EME report.

I then edit it, add my HF predictions and send it to RSGB HQ so it can be collated, published and sent to GB2RS readers on Friday.

Sunspots on Thursday 23rd August 2018.

At that point this week the Sun looked fairly innocuous with one tiny sunspot group, a solar flux index of 70 and a sunspot number of 15, representing one sunspot group with five tiny spots.

There were no obvious coronal holes and NOAA predicted the K index would likely be two all week due to a lack of geomagnetic disturbances. The US Air Force agreed.

So far so good!

At 04:45UTC on Monday 20th NOAA had reported:

“Region 2719 (S06, L=133, class/area Bxo/010 on 19 Aug)
developed in the SE quadrant on 19 Aug. No significant flare events
occurred from either region. Other activity included a filament
eruption centered near S11W04 observed lifting off the solar disk at
approximately 19/0538 UTC. An associated coronal mass ejection was
observed off the SW limb in SOHO/LASCO C2 imagery at 19/0812 UTC.
WSA/Enlil modelling of the event suggested the ejecta was primarily
directed westward of the Sun-Earth line and is not expected to cause
any significant effects.”

So the CME wasn’t earth-directed so shouldn’t be a problem – bear with me!

The NOAA report for Monday 20th August said there were no events.
The NOAA report for Tuesday 21st August said there was an RSP (a sweep-frequency radio burst) at 18:46UTC observed at Palahua, Hawaii, USA
The NOAA report for Wednesday 22nd August said there were no events.
The NOAA report for Thursday 23rd August said that at 20:23UTC on Thursday evening the older region 2719 emitted an an “A class” X-ray solar flare. “A class” flares are the weakest and it was after sunset in the UK so didn’t have any major impact for us according to the ionosonde data.

But there were further A class flares on Friday 24th August, which were at 12:47-12:50 UTC, 21:54-21:58 UTC and 21:57-22:01 UTC.

The Chilton and Fairford Ionosondes in the UK show Friday’s flare’s effect at 12:47 as there is a gap in the data.

You can see this at Jim G3YLA’s Propquest site at: http://www.propquest.co.uk/graphs.php?type=archive

But by Saturday 25th August a new large sunspot
group had appeared.

By Friday another new sunspot group (2720) had emerged, which grew rapidly and by Saturday it was quite large. Sunspot AR2720 is not only large, but also strange. Its magnetic polarity is reversed. The North and South ends of its magnetic field are backwards compared to the norm for sunspots in decaying Solar Cycle 24.

So could AR2720 be from the next solar cycle, Solar Cycle 25? We’ve already had one reverse polarity sunspot which has been attributed to Cycle 25, but that was last year. This is going to be discussed over the coming weeks.

Action on Friday 24th August continued.

From 02:00UTC a series of solar flares were recorded, mainly from the new region 2720. These were B-class solar flares.

By the early hours of Sunday morning, 26th August the K index had started to climb, peaking at Kp7 at 03:00 and 06:0UTC. The bands on Sunday were lousy with a lack of signals across the board in the UK as the ionosphere collapsed. The 14.100MHz IARU beacons were all inaudible.

The Kp index hit 7 in the early hours of Sunday
26th August 2018.

A sweep with my SDRPlay receiver and SDRUno software saw very few signals on 20m at all and virtually nothing higher in frequency. There were a few weak and watery CW signals from Germany on 40m.

So what was the cause?

NOAA now says there had been an earth-directed coronal mass ejection on Monday 20th August that no-one seemed to comment on at the time. NOAA’s own records don’t show any solar flares on Monday August 20th – see (ftp://ftp.swpc.noaa.gov/pub/indices/events/20180820events.txt)

So was it this CME or the one on the 19th that is now reported as causing the high-speed solar wind stream that brought about the Kp7 event and auroral conditions? The experts seem to think so – now!

Or was it a CME as a result of the solar flares on Friday 24th August? That to me would seem more likely and fit in with the roughly two-day solar wind transit time to Earth.

SpaceWeather.com described it as a “surprise geomagnetic storm” and I think that’s a pretty apt description as no-one predicted it.

If that is the case there is no way I could have known about it when I filed the copy to RSGB on Friday morning. This report predicted quiet geomagnetic conditions for the week commending Sunday 26th August – I don’t think so somehow!

Oh, the joys of space weather and HF radio propagation forecasting!

IBP propagation predictions for the UK for May 2018

Propagation predictions for the International Beacon Chain
for the UK, May 2018.

In an effort to try to make HF propagation predictions more accurate I have been playing with a different method of producing them using the ITURHFPROP software.

Previously I had been calculating the field strength of each beacon and then converting that to an S point level. It was pointed out that this isn't the best way and that calculating the signal strength in dBm and then converting it would be better.

They are based on 100W to a dipole at 10m - we know that the IBP chain use a Cushcraft R5 antenna.

I then hit the problem as to what antenna gain do you use. This may sound simplistic, but in fact it isn't as the actual gain off a dipole will depend upon its height, its orientation and the required take-off angle.

Now, the take-off angle will depend upon what ionospheric mode is dominant at that point in time. That is, is it one F-layer hop, two F-layer hops or a combination of E and F-layer hops.

After a lot of thought and discussion I settled on setting the gain at both ends at 0dBi, which appears to give reasonable results - setting it at 2.15dBi gave over-optimistic results

Anyway, attached is the plot of predictions for the beacon chain for May 2018. I'll check to see how accurate it is and adjust the input files accordingly. The ultimate goal is to the transfer these settings to other HF predictions.

If anyone wants to report on whether they find these accurate or not please let me know. They are median predictions, which means some days may be better, some days worse.

Just click on the chart to enlarge it.

IBP beacon predictions for UK using ITURHFPROP

Over Christmas and the New Year I got better acquainted with the ITURHFPROP propagation prediction software.

This is the software that Gwyn G4FKH uses to produce the monthly HF predictions for RSGB’s RadCom magazine and which was produced by the ITU.

Gwyn adapted it to produce a graphical output, which can be found at www.predtest.uk

But I was intrigued to see if I could use it to produce some predictions for the worldwide International Beacon Project (IBP) chain that runs on 14, 18, 21, 24 and 28MHz. I won’t go into too many details here about the IBP network as you can find all you would want to know at http://www.ncdxf.org/beacon/

The good news is that as they all use the same power output (100W max.) and the same antenna (pretty much a unity gain or +2.15dBi antenna) it should be fairly easy to model what the expected signal strength should be here in the UK.

ITURHFPROP runs in Windows and uses an input file with all the parameters needed, such as your QTH lat. and long., the transmitter’s lat. and long., required SNR, bandwidth, smoothed sunspot number, power etc etc.

You then run it from the command line and it creates an output file.

I ended up creating input files for each of the beacons, and a spreadsheet that can take each of the output Field Strength (dB(1uV/m)) figures and convert them into S units.

I then created a batch file that runs all of the predictions for each of the beacons in one go. With an I5 processor this takes less than about 15 seconds.

The spreadsheet then formats these so that I can produce the chart you see on the page. This may sound long-winded, but it really doesn’t take long. I’m sure someone with Python programming skills could automate the whole thing, but I wanted to make sure it worked first before going any further.

The end result has proved to be quite accurate and shows that at this point in the sunspot cycle we can’t expect miracles in terms of hearing the distant beacons. While some are audible on 14 and 18MHz, generally we are not hearing much above that.

In the UK, what have been audible quite regularly this month on 14.100MHz are RR90 (Novosibirsk, Siberia), CS3B (Madeira), 4U1UN (New York) and occasionally 4X6TU (Tel Aviv).

It also shows what the effect of an elevated K index can be as this generally means the beacons are less audible (if there at all) as the MUF declines. We have been suffering from the adverse effects of coronal holes recently and that isn't going to end any time soon.

You can see the predicted MUF over different path lengths in near real-time using the graphed ionosonde data for the UK at http://www.convectiveweather.co.uk/ionosphere/graphs.php?type=live

This was produced by fellow RSGB Propagation Studies Committee member Jim G3YLA and his colleagues at Weatherquest in Norwich.

I’ve posted the predictions here to see if they are of interest to anyone. If they are I’ll update them monthly.

To view the January IBP prediction chart full size just click here.

Propagation prediction maps updated until June 2018

I have now updated my propagation maps with the latest predicted smoothed sunspot numbers for the period up until the end of June 2018.

You can access them using this link.

The sunspot numbers continue to fall as we head towards sunspot minimum sometime around 2019.

If you use the charts look for about 60-70% reliability for SSB (yellow or hotter) and perhaps 40-50% for CW or PSK (green). For FT8 you may be able to work stations where the reliability is down to 20-30% (blue).

Of course, these are a guide and if you want to try making charts for your own station I recommend the online software at either voacap.com or www.predtest.uk/

HF Propagation at Sunspot Minimum

The effects of coronal holes are likely to continue for a
couple of years.

This weekend I’ll be giving a talk at the RSGB conference on “HF Propagation at Sunspot Minimum.”

This will show that we can expect the minimum to be around late 2019 or 2020. It is hard to be precise, as the minimum is something you can define after the event, not before or during!

What I will say is that we can probably expect the effects of solar coronal holes to continue, at least until we are well into the minimum.

Geomagnetic storms can cause problems on HF, although they can also bring short-lived ionospheric enhancements so they are a double-edged sword.

For example, on Tuesday 10th October the bands were open to DX all the way up to 12 metres. But as the solar wind from the coronal hole hit on Wednesday, apart from a short-lived ionospheric enhancement the MUFs took a dive.

By Thursday (12th) lunchtime, 20m was struggling to fully open and 17m was showing very little activity indeed. But by Thursday afternoon, and with a K of 5,  I had worked Saudi Arabia on 10m SSB.

This shows that at sunspot minimum with a solar flux index of just 66, quiet geomagnetic conditions may be better than stormy ones. So look for a K index in three 0-2 range, not 5-7! But then again, when solar plasma first hits the earth we may get some short-lived enhancements right up to 10m, so a high initial K index can work for us.

For those who weren't at the lecture, I showed that monthly average maximum useable frequencies will decline with the sunspot number. This doesn't mean there won't be F2-layer openings on 21MHz and higher, just that they won't be as reliable or as long lasting.

Other than that I encourage people to play with a propagation program to get an idea of what might be possible.

My suggestions are:

Windows based

VOAProp

HAMcap

W6ELProp (when installing, right click and run as administrator on Windows 10)

VOACAP


Online

VOACAP.com

Predtest.uk


Other sources of info I mention are:

Solarham.com

NOAA – Space Weather Prediction Centre

Real-time F2 critical frequency display (this will soon move to Propquest.co.uk)

Smoothed Sunspot Numbers

Latest extreme UV image of the sun from the Solar Dynamics Observatory spacecraft (shows coronal holes)

Lastly, I talk about the difficulties of predicting openings with FT8. One suggestion is to use VOACAP and set the required SNR to a figure of -20dB or so. It is usually set to about 24-31dB for CW and 45 for SSB. This is still experimental (as some SNR figures are quoted as dB per Hz, while others are quoted in a 2500Hz bandwidth), so you might have to play with it. VOACAP’s settings are critical and it is worth reading the notes on the VOACAP website and also the “Top 10 mistakes in using VOACAP”.

Solar and HF Propagation Update

I haven’t written about the state of the sun and propagation recently (apart from my weekly HF contribution to the RSGB’s GB2RS report).

So, it seemed like a good idea to publish an update.

It is now July 2017 and the sun is completely spotless. The solar flux index (SFI) is 72 and the sunspot number is zero (as you might expect).

Given that the SFI never goes below around 65-66 this shows just how spotless the sun actually is. And current predictions are that we will hit sunspot minimum in 2019-2020.

As the Solar Influences Data Center (SIDC) says “As the current solar cycle 24 gradually gives way to the new solar cycle 25, several consecutive days and even weeks without sunspots will become the norm.

“The previous minimum surprised scientists and solar observers by being the deepest in nearly 90 years. Will the upcoming solar cycle minimum show as many spotless days, or will solar cycle 25 take off much faster than expected?”

For this we will have to wait and see.

The first sunspot of solar cycle 25 has already been spotted (December 2016). Its high latitude (23°) and reverse polarity showed that it definitely belonged to the next sunspot cycle.

But don’t get too excited as sunspot cycles usually overlap, by up to four years. This again, might put the solar minimum into 2019/2020.

The sun with coronal holes on 5th July 2017.

Meanwhile, we are still suffering the effects of a series of coronal holes (CHs). These are areas of the sun with “open” magnetic fields that allow the solar wind to pour out. If Earth-facing these can result in an increased K index, an initial propagation enhancement, and then probably reduced MUFs, noisy bands and possible aurora.

CHs are a feature of a declining solar cycle, but should eventually subside a little. The best way to predict their effects is to look at the sun in extreme ultraviolet light using the SDO spacecraft and look for dark patches. If a CH is on or near the sun’s equator and earth-facing we might expect the impact of the solar wind in perhaps two days, although this can vary depending upon its speed.

So at the moment the low SFI means that, other than sporadic E openings, we can’t expect the maximum useable frequency over 3,000km to climb much above 14 or perhaps 18MHz.

So if you want F2 layer DX concentrate on 30, 20 and 17 metres.

In the Northern hemisphere we are in the summer doldrums with lower MUFs during the day, but higher MUFs (than winter) in the evening and night.

This is due to a change in the ionospheric chemistry with a shift towards more diatomic species and fewer monatomic ones. These are harder to ionise as they are more tightly bonded, hence the lower levels of ionisation.

One quick tip. Don’t write off 20m and 30m in the late evening – they might still surprise you with some DX.

Playing with the propagation prediction system at Predtest, which uses the ITURHFPROP engine and is managed by Gwyn G4FKH, will give you some idea of what band may be open to where.

What we can say is that good DX paths, such as transatlantic and far eastern, will return in the Autumn, perhaps late September – but the lower HF bands, 30, 20 and sometimes 17m will still be the “money bands” for DX.

A Predtest prediction for 20m at 21:00UTC in July 2017 for the UK. the smoothed sunspot number being used is 18.

HF and solar conditions continue to decline

I've now updated my hourly HF propagation charts for the UK for the next three months.

The charts, with real time solar information, can be found at http://www.infotechcomms.co.uk/propcharts/
You can definitely see the effects of the current poor solar conditions. As the charts are produced by VOACAP it is suggested we use the smoothed sunspot number (SSN) for the calculations.

In January 2016 the SSN was 44.8, but this month it is just 29.2. In fact, the actual daily sunspot number is even lower than this at around zero to 11 with a solar flux index in the low 70s.

Given that at sunspot minimum we wouldn't expect the solar flux index to drop below 66 you can see that we are very close to the kind of conditions we can expect over the next few years.

NASA says the current sunspot cycle is the smallest since cycle 14, which had a maximum smoothed sunspot number of 107.2 in February of 1906.

The current prediction for sunspot cycle 24 (this one) gives a smoothed sunspot number maximum of about 101 in late 2013.

The next sunspot minimum is currently predicted to occur around 2019-2020.

The solar maximum for cycle 25 is predicted to be around 2025, possibly with a monthly smoothed maximum sunspot number of around 60-65. If true, this is almost down to Dalton Minimum levels.

What we are seeing is that the ionosphere is currently struggling to regularly open up to DX at frequencies much higher than about 18MHz. Around the UK we are even finding 40m (7MHz) closing to inter-G contacts by early afternoon, if it opens at all.

This means that 80m (3.5MHz) and 60m (5MHz) are coming into their own, although both are struggling with inter-G contacts by late afternoon.

A succession of coronal holes and their associated high-speed solar wind streams are also causing disruption to the ionosphere. While these are typical of this point in the sunspot cycle they are generally not helping DX at all.

This week's high K indices have been caused by such a hole, although the solar wind has mostly had a north-facing Bz field, which is less likely to couple with the Earth's magnetic field, and we have't seen the very high K indices that indicate severe auroral conditions.

Lastly, readers might be interested in a new HF propagation tool based on the ITU's ITURHFPROP software and developed by Gwyn G4FKH. The URL is http://www.predtest.uk

The 'Area Coverage' predictions have been available for some time, but a new Point-to-Point prediction tool is now available. Clicking on the link starts the process, when the form is filled out a series of plots are available depicting propagation between the required Tx. and Rx. sites.

New features include various colour schemes for the plots allowing users with colour preferences to make the best viewing choice for themselves.

Steve G0KYA

Working Santa's elves in Lapland, Christmas 2016

Every week I produce the HF propagation report for the RSGB's GB2RS news. This week I thought I would do something a little different. If you have children or grandchildren they might find it interesting. I worked them on 20m SSB on the 14th and they were LOUD! Here is the report:

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

This week we have a slightly different approach to the HF propagation news. We want to help you and your family contact Santa's elves in Lapland, Finland.

The station Oscar Foxtrot Nine X-ray (OF9X) is once again on the air this Christmas from Santa Claus land in the Arctic Circle.

Twelve elves are operating OF9X (that is, “Old-Father-Nine-Christmas”) from the city of Oulu in Finland for the entire month of December

To work the elves at OF9X, the best starting point is the DX cluster or reverse beacon network to see where they are operating. They have been spotted on many bands and modes over the past week.

The HF predictions suggest seventeen or twenty metres (18MHz or 14MHz) both give a good possibility of a contact with a probability of greater than 90% during the hours of daylight. Even 15m may be possible around midday.

Forty metres (7MHz) should also give a high probability for the whole 24 hours, while 80m and 160m may also be open during the hours of darkness in the UK.

But get in quick, NOAA is predicting unsettled geomagnetic conditions from December 19^th to the 23^rd due to a recurrent coronal hole.

New book: Radio Propagation Explained

Blog readers might be interested to know that I have a new book out. “Radio Propagation Explained” is based on Ian Poole's excellent “Radio Propagation Principles and Practice”, (published in 2004) but has been updated throughout.

It is bang up to date with the current amateur radio allocations in the UK and has new chapters on propagation prediction software, web resources and propagation on the LF and MF bands.

While I was at it I added a lot more information about Sporadic E, tropospheric propagation and the Sun and its impact on the ionosphere and HF.

As such the Radio Society of Great Britain felt it made more sense to give it a new title to avoid confusion with people who already owned the original book.

Giles Read at RSGB reviewed it and wrote : ”It's not an expensive book, yet it's worth its weight in gold – highly recommended.”

The other good news is that the price has been kept low – the RSGB member price is £11.04 and non-members pay £12.99.

It can be bought from the RSGB if you are in UK/Europe, or as a Kindle version on Amazon.com and Amazon.co.uk

GB2RS Propagation Presentation

On Sunday 9th October I'm giving a talk at the RSGB Convention on how we prepare the weekly RSGB GB2RS Propagation report.

This looks at HF, VHF, moonbounce, aurora, rain scatter and much more.

To save people hurriedly scribbling down all the URLs in the presentation I have turned it into a PDF for download with all the URLs hyperlinked.

I'm not sure if this is of too much use if you haven't seen the presentation, but it does show all the resources that are used each week.

You can download the PDF at:
http://www.infotechcomms.co.uk/downloads/GB2RS_Propagation.pdf

Coronal holes causing chaos on HF bands

Coronal holes appear as dark patches when
viewed in extreme UV light via the SDO spacecraft.

The past few months have seen very poor HF conditions with the higher bands often closed and maximum usable frequencies below 14MHz during daylight hours. This has been coupled with high K/A indices and aurora.

But what has been the cause?

HF conditions are generally worse in the summer months, with lower ionisation levels overall during daylight hours in the northern hemisphere.

This is believed to be due to a change in the chemical composition of the F layers of the ionosphere, with a predominance of molecular rather than atomic oxygen and nitrogen [1]. That is, atoms that are paired up have stronger bonds, which means it is harder for ionising radiation to liberate electrons. The actual process is quite complex and depends upon the ratios of [O]/[O2] and [O]/[N2]. The reaction is also temperature sensitive.

But over the past few months we had had an added problem – coronal holes (CHs) and coronal mass ejections (CMEs) from the sun.

A CH is an area on the sun where the corona is darker, colder, and has lower-density plasma than average. The magnetic field around a CH is also different – instead of returning to the surface, the magnetic field lines remain open and stretch out into space.

This can allow the charged solar wind to escape at high speeds, often up to 600-700 kilometres a second.

When a CH is positioned near the centre of the Earth-facing solar disk, especially when the “frozen in” magnetic field of the escaping plasma (Bz) points south, it can more easily couple with the earth's magnetic field.

The hot gasses can then flow to Earth as a solar wind high-speed stream (HSS), causing geomagnetic disturbances, including enhanced auroral activity and absorption at high latitudes. We can detect this geomagnetic storm as the Kp index rises to four or more.

Other effects can include a lowering of the critical frequency as the F layers are depleted causing the upper HF bands to close down. Higher noise levels may also be evident.

We can “see” CHs on the sun thanks to spacecraft. When viewed in the extreme ultraviolet light or X-ray spectrum they appear black due to their lower energy levels. The Solar Dynamics Observatory (SDO) has an X-ray imager called the Atmospheric Imaging Assembly (AIA) and its imagery can be found at www.solarham.net/latest_imagery/ – look for “AIA 211b W/ Coronal Holes”.

CHs can also be long lasting, their effects often being observed on several solar rotations (27 days) [2].

But the CH effects have also been augmented by CMEs. These are often linked to a solar flare and occur when the magnetic field within a sunspot breaks down allowing millions of tonnes of plasma to be ejected. This has similar effects to a CH as the plasma hits the earth, especially if the CME's magnetic field (Bz) is pointing south.

But why the sudden increase in CHs and CMEs recently?

Observation has shown that the sun is more unsettled after a peak in the sunspot cycle, with more frequent CMEs around solar maximum and CHs on the declining phase. The past few months have seen the decline of Cycle 24 – the least active in our lifetimes

In 2013 NASA spotted a CH that was at least 400,000 miles across – more than 50 Earths side by side [2]. And in March this year scientists saw one of the largest polar CH's they had observed in decades. It covered an estimated six- to eight-percent of the total solar surface [3].

CHs were first seen in images taken by astronauts on board NASA's Skylab space station in 1973 and 1974 [4]. So our data only go back two or three sunspot cycles, and we haven't got a lot to go on.

We know CHs can be long-lasting and we think they move closer and closer to the sun's poles near solar maximum.

But the best guess is that we will be stuck with CHs, CMEs and their effects for at least a few more years yet as we head towards sunspot minimum around 2020.


References:

1. “The Solar-terrestrial Environment”, J.K.Hargreaves.
2. www.nasa.gov/mission_pages/sunearth/news/gallery/20130618-coronalhole.html
3. www.nasa.gov/content/goddard/sdo-sees-two-coronal-holes
4. “The High-Latitude Ionosphere and it effects on Radio Propagation”, R.D.Hunsucker and J.K.Hargreaves.

Originally published in RSGB's RadCom magazine

Updated UK HF prediction charts

I've now updated my hourly UK HF Propagation Predictions maps for the rest of 2016.

You can view the charts using the link on the right or at infotechcomms.co.uk/propcharts/

These take into account the latest smoothed sunspot numbers from NOAA/NGDC.

We continue to see a steady decline in sunspot activity as we fall away from the peak of solar cycle 24. Twelve months ago the solar flux index peaked at 163 in May. This month it has struggled to exceed 100 and is currently 94.

Coupled with this, we have suffered quite badly from the effects of plasma from solar coronal holes. These are areas of the sun with an open magnetic field that allows plasma to escape.

If these coronal holes are earth-facing the result can be an elevated K index as the plasma from the high-speed solar wind stream impacts the earth, especially if it has a negative or south-facing magnetic field, which couples more easily.

A high K index is usually a sign of poor HF conditions, with noisy bands and depressed maximum usable frequencies. Any path over the poles is also badly affected.

This can also lead to aurora, which while not being visible in the summer, can lead to openings on VHF.

The RSGB Propagation Studies Committee is also pleased to be able to present its latest HF propagation prediction tool, which is currently hosted at www.predtest.uk

This is still being developed and uses the newer ITURHFPROP software as its backend, rather than VOACAP.

We encourage amateurs to use the system, which can also be used for point-to-point predictions using a prototype tool called 'Proppy'.

Gwyn G4FKH, who is project manager for the new system, welcomes feedback. The goal is for the whole system to be moved to the RSGB website once finished.

Sporadic E season is under way

The Sporadic E (Es) season on 10m and 6m is well under way with lots of useful openings.

I was having a listen around 28MHz today and was struck by how many 10m beacons are audible when there doesn't appear to be any other activity on the band.

And they aren't high powered either. First I heard OK0EG on 28.2825MHz in the Czech Republic and a little late OY6BEC in the Faroes on 28.235MHz. Then a little later still I spotted a spike on the IC-756 Pro3's panadapter and it was F5ZWE near Toulouse on 28.2427MHz.

You can get a current list of 10m beacons, complied by Martin G3USF, at: http://www.keele.ac.uk/depts/por/28.htm

These are all running 10-15W and simple antennas, yet can reach S6-9 in the UK when the conditions are right.

We still don't completely understand Sporadic E, although the current thinking is that it is due to wind shear in the upper atmosphere that pushes ions together into clumps or clouds. The ions may come from meteors. Jim G3YLA, who is a professional meteorologist, is also looking at whether these winds, when they pass over mountain ranges, are forced upwards and create these "gravity waves" that force the ions together.

I also have a theory that solar flares can contribute to SOME of the ionisation on occasions, but mainly outside of the May-August period - there are plenty of instances of Es without any flare activity. I have some plots of Es in late April that correlate very well with solar flares.

Anyway, Jim posts some daily high-level wind charts in an attempt to understand what is happening. 

See http://forums.thersgb.org/index.php?forums/radio-propagation-questions/

Steve G0KYA

HF Propagation charts for the UK updated

I've now updated my propagation prediction charts for the UK through to April 2016.

See http://www.infotechcomms.co.uk/propcharts/

I've used the latest smoothed sunspot numbers from NOAA in the US. There is little point in updating them much further than four months as the SSNs change, and it takes me about three hours to do four month's worth of charts and upload them - that's a chart for every hour and for every band or 24 x 8=192 charts per month.

It is interesting to see how the solar cycle is falling away. In January 2015 the SSN was 62, now it is just 45. The coming months will see further falls.

This means that we will see fewer openings on 12m and 10m, but 15m should still open up at times. I worked the US Virgin islands on 15m CW this morning and it was open to the eastern seaboard of the US this afternoon so don't write it off.

The new
web based version of ITURHFPROP

The RSGB Propagation Studies Committee, of which I am the chair, is also working on a new online HF prediction system based on the ITU program ITURHFPROP.

This uses a different, but newer, ionospheric model to the VOACAP engine normally used, but the original ITURHFPROP software is not very easy to use.

But thanks to the work of Gwyn Williams (G4FKH), James Watson (HZ1JW) and Chris Behm we are getting closer to a web-based version. You can try the test model at http://www.predtest.uk/

Ultimately, it will have the ability to produce point to point predictions as well, just like VOACAP Online. But lets learn to walk before we run.

It will be interesting to compare the two models and Gwyn would welcome any feedback. His email details are on the web page for the new model