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The Victorian origins of ‘space weather’

Thank you Stormwatchers for all your hard work drawing Storm Fronts! While you continue to help us improve space weather forecasts, here is an article on the history of space weather (which includes solar storms) written by Lee Macdonald, a science historian.

 


The Victorian origins of ‘space weather’

Lee Macdonald

Today we take it for granted that activity on the Sun causes colourful displays of the aurora (the ‘northern lights’ in the northern hemisphere; the ‘southern lights’ south of the equator) and, in extreme cases, power cuts and disruptions to satellite communications. We now know that the Sun triggers these phenomena through its magnetic field and the stream of subatomic particles it emits, called the ‘solar wind’ – which in turn affects Earth’s magnetic field. We call the state of the solar wind and magnetic activity in the solar system ‘space weather’. Aurorae do not just take place on Earth: they can occur on any planet that has both a magnetic field and an atmosphere. They have been photographed in the atmospheres of Jupiter, Saturn, Uranus and Neptune; more recently, spacecraft have imaged them in the skies of Mars.

We strongly associate pictures of aurorae on other planets, as well as terms like ‘space weather’ and ‘solar wind’, very much with the space age. However, the possibility of detecting aurorae on other planets – and, by implication, the existence of the Sun’s influence throughout the solar system – was first suggested by two British astronomers working in the mid-nineteenth century: Balfour Stewart (1828-1887) and Edward Sabine (1788-1883).

A correlation between aurorae and the Earth’s magnetic field had been known since the eighteenth century, when Anders Celsius (best known for the Celsius temperature scale) and Olof Hiorter noticed frequent and wild oscillations in the direction of magnetic north during an auroral display. In the 1830s, the astronomer and scientific polymath John Herschel (1792-1871) undertook a systematic study of sunspots while on a four-year observing expedition at the Cape of Good Hope in South Africa. In 1837, he noticed a peak in both sunspot and auroral activity and thought that it would be worth investigating whether a correlation between these two phenomena applied more generally. Six years later, German apothecary and astronomer Heinrich Schwabe discovered that the number of sunspots waxed and waned in a ten-year cycle. Then, in 1852, Sabine discovered a similar periodicity in the Earth’s magnetic field and noticed that it coincided exactly with Schwabe’s sunspot cycle. Herschel saw this discovery as confirmation of a link between sunspots and aurorae, and he now suggested that the ‘red clouds’ seen during a solar eclipse (now known as solar prominences) might be ‘reposing auroral masses’.

In response to Sabine’s discovery, the British Association for the Advancement of Science (BAAS) set up a solar telescope and a suite of magnetic instruments in the Association’s observatory at Kew, to further investigate this correlation. The solar telescope, known as the Kew ‘photoheliograph’, took pictures of the Sun every clear day so that sunspot activity could be compared with the magnetic readings. (See separate article and associated video on the ConSciCom web pages about Elizabeth Beckley’s role in solar photography at Kew: https://conscicom.org/2017/03/09/work-peculiarly-fitting-to-a-lady-elizabeth-beckley-and-the-early-years-of-solar-photography/)

In 1859, Balfour Stewart became superintendent of Kew Observatory. On 1 September that year, just two months after Stewart took up his post, the astronomers Richard Carrington and Richard Hodgson independently noticed a pair of bright lights appear above a large sunspot group, only to disappear a few minutes later. The timing of this explosion on the Sun, now known to have been a solar flare, coincided exactly with a jump in the traces produced by the magnetic instruments at Kew, and triggered Stewart’s interest in connections between solar activity and terrestrial magnetism.

In the early 1860s, Stewart and Sabine engaged in a lively correspondence on the nature of the newly-discovered Sun-Earth connections. In an August 1862 letter to Sabine, Stewart revived (without acknowledgement) Herschel’s 1852 assertion that the red clouds seen during eclipses might be aurorae on the Sun. In his reply to Stewart, Sabine took the speculation further, suggesting that the solar ‘aurorae’ triggered aurorae on Earth and wondered whether ‘all the planets participate in such appearances, though we may never attain to their observation’. Stewart, in turn, suggested a variety of observational evidence in favour of the red solar clouds being aurorae, including the fact that, as with sunspots, their greatest frequency coincided with periods of magnetic disturbance on Earth. As to Sabine’s suggestion that aurorae might occur on all the planets, Stewart wondered whether ‘perhaps Mr De La Rue could photograph one [of the planets] during an Aurora and ascertain this’.

Warren De La Rue (1815-1889) was then Britain’s leading pioneer of astronomical photography. He was instrumental in designing the Kew photoheliograph and was famous for his photographs of the Moon. Neither De La Rue’s nor anyone else’s photographic technology was then capable of photographing aurorae on other planets, but since 1979 spacecraft, including the Hubble Space Telescope, have photographed aurorae around the poles of Mars, Jupiter, Saturn, Uranus and Neptune (though scientists believe that Jupiter’s aurorae are due primarily to the interaction of the planet’s magnetic field with its volcanic satellite Io rather than the solar wind).

Saturn_Aurora_HST_1998Figure 1. Aurora around the southern pole of Saturn, photographed with the Hubble Space Telescope. Image courtesy J. T. Trauger (Jet Propulsion Laboratory) and NASA.

Although Sabine and Stewart’s prediction had to wait more than a century to be vindicated, their logic was correct: something emanating from the Sun was influencing the entire solar system at the same time. We now know that this ‘solar wind’ is made up of charged subatomic particles that become tangled in planetary magnetic fields and cause their atmospheres to glow with auroral light. What, however, could these two visionaries have had in mind in 1862, when the smallest particle known to exist was the hydrogen atom?

Stewart’s work makes it clear that he believed solar emissions travelled through an invisible, all-pervading medium called the ‘ether’. In the mid-nineteenth century, with the rise of the wave theory of light, such a medium had become a popular way of explaining how light travelled through space. In the forefront of this ether physics was Stewart’s contemporary and fellow Scot, James Clerk Maxwell (1831-1879), whose electromagnetic theory described mathematically how light is an electrical and magnetic wave that propagates through this hypothetical ether. The ether was needed in the wave theory of light, because as a wave, light needed something to propagate through, just as sound requires air in which to travel.

Moreover Stewart, a staunch Christian believer, saw the ether as a convenient way of explaining the newly-discovered law of the conservation of energy without compromising the religious doctrine that the universe would one day come to an end. The ether provided a repository into which all the energy in the universe would eventually be dissipated, leaving the universe ultimately devoid of light and heat.

Stewart believed that as the planets changed their positions relative to the Sun, they moved through this ether and drew energy out of the Sun, causing magnetic effects that gave rise to sunspots and, as a consequence, aurorae. According to Stewart, the ether meant that the Sun and planets were tightly bound to one another, so that the motion of one body would have an effect on the others. Over the 1860s and 1870s, he used the solar results at Kew to develop some increasingly elaborate theories that attempted to correlate the positions of planets in their orbits with variations in sunspot activity. At the same time, he built experiments to find evidence for the ether, by measuring the heating of a disc spinning rapidly in a vacuum, eliminating friction with the air as a source of heat.

Link here:- https://www.nasa.gov/feature/goddard/comet-encke-a-solar-windsock-observed-by-nasa-s-stereo to a movie taken in 2007 by the STEREO A spacecraft, showing the tail of Comet Encke being buffeted by the solar wind – thought by Balfour Stewart and his contemporaries to be due to the ether. Image courtesy NASA/STEREO.

Both these approaches had inconclusive results. Stewart claimed to have detected heating in his spinning disc experiments, though modern scientists believe that this was due to the less-than-perfect vacuum attainable with the equipment of the mid-nineteenth century. After 1905, the ether theory gradually became discredited by Albert Einstein’s special theory of relativity. This painted a new picture of how light waves travel through space, dispensing with the notion of an ether.

However, the story of Balfour Stewart’s researches into solar-terrestrial physics has one ironic twist. In 1870, Stewart left Kew to become professor of ‘natural philosophy’ (now called physics) at Owens College in Manchester (now the University of Manchester). One of his students at Manchester was a young Joseph John (‘J. J.’) Thomson, who in 1897 would discover the electron – the first of the subatomic particles now known to make up the solar wind.

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Welcome to Solar Stormwatch!

Hi! I’m Shannon. I first became involved with Stormwatch about a year ago, analysing the results of an original Solar Stormwatch activity; Track-it-back, and I’m now excited to be starting a PhD, studying space weather at the University of Reading, looking at solar storms.

cme

Image: a solar storm or coronal mass ejection (NASA)

 So, what are solar storms, and why do we care about them?

Solar storms, also known as coronal mass ejections (CMEs), are huge clouds of solar material emitted from the Sun. These are part of the phenomenon we call ‘space weather’. If these reach the Earth, they can cause geomagnetic storms with severe consequences, such as damage to power transformers leading to wide-spread, long-term power outages. Other impacts include increased radiation exposure for astronauts and passengers on commercial flights, damage to satellites, and reduced accuracy of GPS systems.

To reduce the impacts of solar storms, we need to be able to accurately predict if and when a storm will hit the Earth. Therefore, we want to learn as much as we can about the nature and evolution of these storms.

During my PhD, I intend to work on improving solar storm forecasts, and I’m hoping that through Solar Stormwatch, we can create a dataset of tracked solar storms to help me achieve this. To this end, we have created a new Stormwatch activity; Storm Front. In Storm Front we would like you to help us track solar storms as they travel away from the Sun by tracing the outlines of storms in images from the wide-angle cameras on the STEREO spacecraft.

interface

Image: the Storm Front interface

I will use the storm fronts that you trace to create a dataset which tracks solar storms as they move away from the Sun. The Sun constantly emits solar material out into space – the solar wind, and this dataset will allow me to study the interaction between the solar wind and these storms, and examine how the solar wind distorts the shape of solar storms. This will hopefully allow forecasts of solar storms with greater accuracy.

solwind

Image: visualisation of the solar wind (NASA)

Check back here for updates on the project, but in the meantime, feel free to ask us any questions you might have on the ‘Talk’ page… Thanks for reading, look forward to hearing from you!

Creating a Solar Stormwatch Catalogue from YOUR clicks.

Hello, I’m Luke and I work with Chris Scott (formerly Davis!) at the University of Reading as a postdoctoral research assistant. Recently I’ve been doing some work with the large amount of Trace-it data that has been generated over the last few years. We thought it was a good time to update everyone on the work we have been doing.

The short story is that we have turned the roughly 40000 time-elongation (t-e) profiles generated by Trace-it into a catalogue of CMEs seen by Heliospheric Imager (HI) instruments aboard STEREO-A (STA) and STEREO-B (STB). The Solar Stormwatch catalogue provides profiles of the CME fronts in the remarkable field-of-view (FOV) of the HI instruments. The HI FOV covers regions of the inner heliosphere not accessible to the coronagraph instruments that are more commonly used to build CME catalogues. Therefore the Solar Stormwatch catalogue should allow us to study the structure and dynamics of CME fronts in a way not previously possible using other presently available CME catalogues. This has been written up into a paper which is currently under review for publication in the journal Space Weather. So, first things first, thank you to everyone that has contributed to Solar Stormwatch. I think that we have produced a useful catalogue of CMEs, which will hopefully be of use to the wider space weather community – this wouldn’t have been possible without all of the contributors to Solar Stormwatch.

Let’s begin with a quick review of the raw data produced by Trace-it. Trace-it analysed J-maps made from HI1 and HI2 images, for both STA and STB, over 18 distinct position angles separated by 5 degrees, except for one position angle, which was centered on the ecliptic plane.

The J-maps covered a time span of January-2007 to February-2010. As of a few months ago, the Trace-it results consisted of database of 38171 t-e profiles, 22007 from STA and 16164 from STB, generated by 4599 Solar Stormwatch users.

If elongation angles and position angles are unfamiliar to anyone reading this, Figure 1 shows an image from HI1A, over which contours of constant position angle (in blue) and constant elongation angle (in red) have been overlaid, to make these coordinates clear.

Figure 1

Figure 1. An example of a differenced image from the HI1A camera, overlaid with contours of

constant PA (in blue) and constant elongation angle (in red). The elongation and PA contours

are in 5◦ increments. A CME is visible to the right of the image, between 5◦ and 10◦ elongation

and with maximum extent in PA between 65◦ and 135

To separate the t-e profiles into groups which represent individual CMEs we looked for periods when many t-e profiles were clustered in a short space of time. To do this, we counted how many t-e profiles began in a 7-hour window, for every hour covering the data set, and whenever the count of profiles was higher than a threshold of 22 counts we defined that as an event. This happens whenever lots of us have seen features over multiple position angles but at similar times. Figure 2 shows an example of this. Panel A) shows a STA J-map, at PA=110 degrees, overlaid with the t-e profiles generated by the Solar Stormwatchers as red dots, whilst the blue dots mark the earliest occurring point in each profile. In this instance, this position angle was tracked 11 times by 8 different Solar Stormwatchers. Panel B) shows the count of these profiles as a function of time, using the 7 hour sliding window. Note that this count is done over every position angle, whereas the J-map shows the t-e profiles at one position angle only. There is a well defined maximum in the count, which we use to define the onset of this event and identify the t-e profiles that describe it. The thresholds we picked are arbitrary but sensible, we could have used different ones and had similar results – for anyone interested in how we picked these numbers, we go into a bit more detail in the paper.

Figure 2

This gives us groups of t-e profiles for each CME – 113 from STA and 80 from STB. However, we had to do a bit of quality control, as it is not good enough just to have to t-e profiles that start at similar times – they could come from coincident but unrelated solar transients that are widely separated in position angle. So we used another set of rules to exclude any t-e profiles which look like they may belong to a different solar transient. This process is detailed more in the paper, but the result of it is that we have to discard 6 events that we are too unsure about, 3 each from STA and STB. This leaves us with 110 events from STA and 77 from STB.

At this point, we have defined sets of t-e profiles which we think robustly identify CMEs seen by the Solar Stormwatchers. The next step is to average these profiles along each position angle the event was observed. An example of this averaging is shown in Figure 3. The black dots show the t-e profiles generated by the Solar Stormwatchers for one event and along one PA, which includes 13 t-e profiles, generated by 9 different Solar Stormwatchers. The red-dots and red-lines show the average profile and the uncertainty in the average profile.

Figure 3

Figure 3. An example of an average t-e profile, for CME number 59 from STA, tracked along a PA of 110 degrees. The black dots show the individual t-e profiles and the red dots mark the consensus profile while the two red lines indicate the uncertainty in the mean time coordinates.

Now we can turn this around and overlay the average t-e profiles for each position angle back onto the original differenced images that made the J-maps they were tracked in. Figure 4 shows a movie of the evolution of an event through the HI1A field-of-view. The yellow lines mark the maximum extent of PAs that the J-maps used by Stormwatch cover, whilst the regions bounded in red mark the locations where the consensus profiles (like figure 3) suggest the CME front should be. The width of the bounded region arises from the uncertainty in the consensus profile at that position angle, so that wider regions mean we are less sure where the CME front is.

Figure 4

Figure 4. This movie shows a sequence of HI1A differenced images in which a CME can be seen to enter and propagate across the HI1A field-of-view. The yellow lines mark the outer limits of the position angles of the J-maps analysed by Trace-it. The red lines mark the location of the CME front, and are calculated from the averaged t-e profiles (see Figure 3) along each position angle the event was tracked.

We are in the process of making this CME catalogue available in an easily usable form so that the rest of the space weather community can get involved and hopefully start using it for some research. In November we will be taking this work to the European Space Weather Week conference in Belgium, to present this work to other researchers. In the meantime, we have some plans for some things we would like to do with the Solar Stormwatch catalogue, which we will update you with when there is more to say.

Thanks!

Solar wind causes sparks to fly

You may have noticed a bit of a splash in the press last Thursday, when I and my co-authors at the University of Reading had a study published showing that the solar wind appears to affect lightning rates over Europe. If you are interested, you can download the paper here;

Environmental Research Letters, Solar wind modulation of lightning;

or, if you don’t fancy wading through a scientific paper, you can see me trying to explain it without waving my arms around too much in a short video, here;

And, if neither of those approaches appeals, you can read on for a short summary of the work (I’m assuming you’re interested otherwise you wouldn’t have chosen to read this blog, right?).

It’s long been thought that cosmic rays (very energetic particles generated throughout the galaxy, accelerated on shock-fronts created by supernova explosions) could be responsible for causing electrically charged clouds to discharge to ground in the form of lightning. As the cosmic rays fall through the atmosphere, the argument goes, they ionise the air, free electrons get accelerated further by the electric field present in the cloud and a runaway breakdown of air results, ending in a lightning flash.

What does the Sun have to do with this? Well, the Sun is an active star with an eleven year solar cycle. The solar wind drags the solar magnetic field into space where it shields the Earth from some of the cosmic rays. When the Sun is active, the solar magnetic field around Earth is stronger and we see fewer cosmic rays reaching the ground. There is also evidence that there is less lighting at these times. So that’s the long-term view, but what happens over shorter timescales?

While you can use solar storms, or Coronal Mass Ejections (CMEs) as they are known, with their enhanced magnetic fields, to look for short-term enhancements of the interplanetary magnetic field, relatively few events travel Earthwards to make a statistical survey conclusive. Instead, we looked at fast solar wind streams. While these produce a smaller depletion in cosmic ray flux (around 1%) compared with CMEs (around 10%) they co-rotate with the Sun and so wash past Earth at regular intervals. We were expecting therefore to see a reduction in lighting but instead we saw that the lightning rates went up (there is a moral here; never try to anticipate the result of an experiment!). The answer, we think, lies with ‘solar energetic particles’ that are accelerated ahead of the solar wind stream, like surfers on a huge wave. While these do not reach the energies of cosmic rays, it is likely that they nevertheless are able to penetrate the Earth’s atmosphere to the height of thunder clouds where they presumably do a similar job to that thought to be done by cosmic rays in initiating lightning.

There’s loads more work to do in order to fully understand where these particles end up and how they influence lightning but if we can understand this effect, there is the tantalising possibility that we could use our observations of solar wind streams from space to forecast the severity of lightning events several weeks in advance. With around 24,000 lightning associated deaths occurring worldwide every year, anything we can do to predict the severity of lightning in advance has to be useful, doesn’t it?

While all this has been going on, we have been analysing the Stormwatch data too, and it’s been very informative. More on these results soon.

Thanks again for your enthusiasm and time, keep clicking! (don’t forget Trace It!)

Chris.

Calling All Stormwatchers : BBC 2 documentary needs your help!!

‘Here Comes The Sun’ is special one-off documentary for BBC 2 investigating the nature of the Sun during this period of heightened solar activity – the solar maximum. The presenters, Kate Humble and Helen Czerski, along with a team of experts will explore how the Sun works, how its secrets could power our future and what the current behaviour of the Sun means for us. One strand of the programme will focus on Space Weather Prediction: examining the fundamental mechanisms that cause solar storms, the impact they may have on the Earth’s infrastructure, and how scientists are working to predict this type of solar behaviour, which is why they are looking for your help…!

The team are coming to film at the Rutherford Appleton Laboratory (RAL), in Oxford, on the 28th of February and 1st March and are looking to recruit a group of around 20 UK-based Stormwatchers to come to RAL and be part of this programme! It is a wonderful opportunity to bring the Solar Stormwatch project into the public eye and illustrate the important job of every single Stormwatcher. It will be great fun and a good excuse to get together with other fellow Stormwatchers!

This is a great opportunity and we are hoping this exposure on a national level will encourage more people to get involved!!

If you are interested please do not hesitate to contact Fay Finlay for more information. Fay.Finlay@bbc.co.uk or 0141 422 6991.

See your data analysis like never before!

Attention Stormwatchers!

Remember all that data analysis you’ve been doing for us? All those storms you’ve tracked in both archive and real time data have now been used to create an animation of what the Sun has been up to over the first three years of the STEREO mission. Over the summer, a student of mine, Amy Skelt, wrote a program to enable us to view your data analysis in a unique way. By taking all your CME tracking information and combining it with my analysis of smaller solar wind features, we can now create animations showing the activity of the solar wind throughout the first three years of the STEREO mission. Just in time for Christmas I’ve used Amy’s software to create a movie of the entire Stormwatch analysis so far. You can view the movie here;

It’s incredible! You can now see the constant stream of solar wind material as it erupts into space and even the spirals created as the various sources of solar wind rotate with the Sun. And when a solar storm erupts, you can see which planets are in the firing line!

We’ve had to make some assumptions about the rate at which the solar storms expand and so any differences between this movie and the real world will help us understand how realistic our assumptions are. Amy made the software very flexible so that you can view the solar system from a fixed point (as in the attached movie), from above or even from a moving object. You can even go for a ride on comet Encke and see how it fares as it rides the solar wind!

As usual, many, many thanks for your time and efforts so far. In the New Year my group and I at the University of Reading will be using your data analysis to investigate what we have learned so far about using STEREO HI data to make real-time forecasts. Working with the UK Met Office, we will ultimately be applying what we learn to improving the operational space weather forecasting model that they will be running. In the current climate, there is much talk of ‘impact’. I can confidently say that you are helping us with our impact. Both metaphorically and literally!

I hope that those of you that are about to celebrate Christmas have a wonderful holiday.

See you in the New Year for more Solar Storming!

Chris.

Solar Stormwatch Community Poster

SSW_thumb

As part of the Zooniverse’s Advent Calendar we’ve been producing massive, author posters, built up of the names of the people who take part in our various projects. Solar Stormwatch’s community poster is Day 14 of our calendar and features an image not from STEREO but from NASA’s Solar Dynamics Observatory (SDO).

This image was taken about 17:50 UT on December 6th this year. The prominence seen in this image is nearly a million kilometers across! Although the entire Earth would be just a few pixels tall on this image, the 25,000 volunteers who gave their permission to have their names published by the project are found written larger than this in 12pt font!

You can download the image in a large 5000-pixel size (22 MB) or in a smaller 3000-pixel size (8 MB).