Earth Magnetism and Rock Physics

GeoSciences Column: Don’t throw out that diary – medieval journals reveal the secret of lightning

GeoSciences Column: Don’t throw out that diary – medieval journals reveal the secret of lightning

When 17th century Japanese princess Shinanomiya Tsuneko took note of an afternoon storm in her diary one humid Kyoto summer, she could not have imagined her observations would one day help resolve a longstanding scientific conundrum. Statistical analysis of her journals has revealed a link between lightning strikes and the solar wind – proving that your teenage diary could contain good science, as well as bad poetry.

The mystery of lightning

Lightning has amazed and alarmed weather-watchers since time immemorial. So it may come as a surprise that we still have little idea what sets off one of nature’s most thrilling spectacles.

Any school child will tell you lightning is caused by a difference in electrical charge. Up- and downdrafts cause molecules of air and water to bump against each other, exchanging electrons. When the potential difference is big enough, all those separated charges comes rushing back in one big torrent, superheating the air and turning it into glowing plasma – that’s what we call lightning.

So far, so sensible. But there’s a problem. Air is an insulator – and a very good one at that. To get the current flowing, charged particles need some sort of bridge to travel across. And it’s this bridge that has vexed lightning scientists – fulminologists – for decades.

The most prominent theory points the finger at cosmic rays – heavy, fast-moving particles that impact the Earth from space. Packing energy roughly equivalent to a fast-bowled cricket ball into one tiny atom-sized package, a cosmic ray can shred electrons from their nuclei with ease. The spectacular Northern Lights reveal the effect this can have on the atmosphere: columns of ionised air, perfect conductors for charges to travel along.

Most cosmic rays originate in deep space, hurled at close to the speed of light from distant supernovae. The extreme heat of the sun’s surface also sends more than a few our way – the so-called ‘solar wind’ – but because these particles are more sluggish than galactic cosmic rays, researchers at first doubted they could have much effect on the atmosphere. Lightning’s time in the sun was yet to come.

27 days of summer

Anyone who has lived a year in Japan will be familiar with the country’s long, sultry summers – and its famously methodical Met Agency. It’s a good place to go looking for lightning.

Inspired by some tantalising work out of the UK, Hiroko Miyahara and colleagues across Japan went sifting through their own Met data for patterns that might suggest a connection between solar weather and lightning strikes. They had their eye out for one pattern in particular – the 27-day cycle caused by the sun’s rotation. This is just short enough that the solar wind streaming from any given region of the sun is fairly constant, limiting the impact of solar variability on the data. It’s also short enough to fit comfortably within one season, which helped the authors compare apples with apples over long timespans.

Armed with the appropriate controls, and a clever method they developed for counting lightning strikes that smooths over patchy observations, Miyahara and the team got stuck into the data for Japan circa 1989–2015. Early in 2017, in a paper published in Annales Geophysicae, they presented their results. The 27-day signal stood out to four standard deviations: a smoking-gun proof that solar weather and lightning strikes are connected.

But how is the relatively sluggish solar wind able to influence lightning strikes? The key, according to Miyahara, is the effect the solar wind has on the Earth’s magnetic field – sometimes bolstering and sometimes weakening it, allowing the more potent galactic cosmic rays to wreak their mayhem.

A window into the past

Of course, the 27-day cycle is only the shortest of the major solar cycles. It is well known that the intensity of the sun varies on an 11-year cycle, related to convection rates in the solar plasma. Less understood are the much longer centurial and millennial cycles. The sun passed through one such cycle between the late Middle Ages and now. The so-called Little Ice Age, coinciding with a phase of low sunspot activity known as the Maunder Minimum, precipitated agricultural collapse and even wars across the world – and solar physicists believe we may be due for another such minimum in the near future, if it hasn’t begun already.

Understanding these cycles is a matter of no small importance. Unfortunately, pre-modern data is often scattered and unreliable, hampering investigations. A creative approach is called for – one that blends the disciplines of the human historian and the natural historian. And this is exactly what Miyahara and the team attempted next.

Shinanomiya Tsuneko was born in Kyoto 1642 – just before the Maunder Minimum. A daughter of the Emperor, Shinanomiya became a much-respected lady of the Imperial Court, whose goings-on she meticulously recorded in one of the era’s great diaries. Luckily for Miyhara and his colleagues in the present day, Shinanomiya was also a lover of the weather, carefully noting her observations of all things meteorological – especially lightning.

Figure and text from Miyahara et al, 2017b: “a) Group sunspot numbers around the latter half of the Maunder Minimum. b) Solar cycles reconstructed from the carbon-14 content in tree rings. The red and blue shading denotes the periods of solar maxima and minima, respectively, used in the analyses. c) Periodicity of lightning events during the solar maxima shown in panel (b). The red dashed lines denote 2 and 3 SD during the solar maxima, and the red shaded bar indicates the 27–30-day period. d) Same as in panel c) but for solar minima.”

Shinanomiya’s diary is one of five Miyahara and the team consulted to build a continuous database of lightning activity covering an astonishing 100 years of Kyoto summers. Priestly diaries, temple records, and the family annals of the Nijo clan were all cross-referenced to produce the data set, which preserves a fascinating slice of Earth weather during the sun’s last Grand Minimum.
Analysis of this medieval data revealed the same 27-day cycle in lightning activity observed in more recent times – proof of the influence of the solar wind on lightning frequency. The strength of this signal proved to be greatest at the high points of the sun’s 11-year decadal sunspot cycle. And the signal was almost completely absent between 1668 and 1715 – the era of the Maunder Minimum, when sunspot numbers are known to have collapsed.

Put together, the data provide the strongest proof yet that solar weather can enhance – and diminish – the occurrence of lightning.

Lightning strikes twice

Miyahara and the team now hope to expand their dataset beyond the period 1668 – 1767. With a little luck – and a lot of digging around in dusty old archives – it may be possible to build a record of lightning activity around Japan from before the Maunder Minimum all the way up to the present day. A record like this, covering a grand cycle of solar activity from minimum to maximum and, perhaps soon, back to a minimum again, would help us to calibrate the lightning record, providing a powerful new proxy for solar activity past and future. It may even help us to predict the famously unpredictable – lightning strikes injure or kill a mind-boggling 24,000 people a year.

As for the rest of us, the work of Miyahara and his colleagues should prompt us to look up at the sky a little more often – and note down what we see. Who knows? Three hundred years from now, it could be your diary that sets off a climate revolution – though it may be best to edit out the embarrassing details first.

by Rohan S. Byrne, PhD student, University of Melbourne


Miyahara, H., Higuchi, C., Terasawa, T., Kataoka, R., Sato, M., and Takahashi, Y.: Solar 27-day rotational period detected in wide-area lightning activity in Japan, Ann. Geophys., 35, 583-588,, 2017a.

Miyahara, H., Aono, Y., and Kataoka, R.: Searching for the 27-day solar rotational cycle in lightning events recorded in old diaries in Kyoto from the 17th to 18th century, Ann. Geophys., 35, 1195-1200,, 2017b.

Imaggeo on Mondays: A spectacular view of moss-covered rocks

Imaggeo on Mondays: A spectacular view of moss-covered rocks

Geology has shaped the rugged landscape of the Isle of Skye – the largest island of Scotland’s Inner Hebrides archipelago. From the very old Precambrian rocks (approximately 2.8 billion years old) in the south of the island, through to the mighty glaciers which covered much of Scotland as recently as 14,700 years ago, the modestly-sized island provides a snap-shot through Earth’s dynamic history.

A far cry from its modern cold, foggy and drizzly weather, back in the Jurassic age (250 million years ago, or so), the island was part of hot and dry desert. Over time, the sea encroached the low-lying plain, depositing sands and muds, and later sandstones, as well as thin limestones and shales across the island. The best examples of these rocks are found on the western side of the island, on the Strathaird Peninsula, but they can also be found on northern and eastern coastal stretches too.

Fast-forward to the Tertiary period (approximately 60 million years ago) and the landscape changed dramatically. The calm tropical waters had made way for explosive eruptions, which vented lavas from crack’s in the Earth’s crust. The lavas blanketed large areas of the north of the island, covering the sediments deposited back in the Jurassic.

Long after the surface explosive activity ended, the cracks in the Earth’s crust continued to serves as pathways for molten magma to move below the surface. In the norther part of the island, the lava travelled sideways, pushing its way between the layers of Jurassic sedimentary rocks. The black lavas, layered between the lighter coloured limestones and sandstones (as pictured above), are in stark contrast with the present-day moss-covered cliffs.

The most spectacular examples of this layering of volcanic units atop sedimentary rocks can be seen not far from where this photograph was taken, at Kilt Rocks, in south Staffin. Visitors to the area can also enjoy Mealt waterfall, where water from Mealt Loch (the Scottish word for lake) tumbles spectacularly into the Sound of Raasay.

Marius Ulm, who captured today’s featured image, is a civil/coastal engineer meaning a totally different aspect of the geology captured his attention:

“From a coastal engineering point of view, what is interesting is the missing moss-cover at the cliff’s toe. There is a line which marks the transition where the rocks stop being covered by moss also indicates how high water regularly rises due to tides. It tells us the tidal range (difference between low and high water) reaches up to 5 m in this area.”

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at


Five top tips to apply for small grants

Five top tips to apply for small grants

Stephanie Zihms, the ECS Representative for the EMRP Division (and incoming Union Level Representative) has applied for a range of small scale grants (<£15,000, ca. 16,965€). At this year’s General Assembly, she was one of two speakers at the ‘How to write a research grant’ short course, where she shared  insights from her successes and failures. In today’s post she tells us about the top five lessons she learnt in the process of applying for funds.

Publications and grants are an important aspect in academia and success in both areas necessary for career progression. Frustratingly, many grants are only available to researchers with open-ended or permanent contracts and since practice makes perfect you don’t want your first grant proposal to be for a million pounds, dollars or euros.

Instead, there are plenty of (often unknown) small scale grants available to fund anything from a trip to a conference through to a field campaign and to support some of your existing work. Applying for these gives you valuable insight when it comes to writing larger-scale grants and shows future employers you have a go-getting attitude.

  1. Start early – start small: Travel grants, internal support grants, field work grants – these all count and will help you get better at writing in a proposal style, learn the language of different panels and get used to the format of a proposal. You might also get a chance to learn how to budget and justify certain costs, a big aspect of proposal writing.
  2. Always ask for feedback: Not only on the grants you didn’t get but also on the ones you secured. It will tell you what the panel really liked about your proposal and you can highlight that even more next time.

    Some feedback from my successful Royal Academy of Engineering Newton Fund application. Credit: Stephanie Zihms

  3. Get training: See if your university or institution offers grant writing or academic writing courses – even if you’re not working on a proposal when you attend this training will come in handy when you do. You are also likely to make some good connections with people that will be able to help you when you do start applying.
  4. Get help: Either from colleagues, connections you made during a writing course, a specialised office within your university or even from the institution offering the grant. See if you can get previous applications that were successful to help you make sure you get the language right.
  5. Write, write, write: As an academic you will spend a lot of your time writing so it’s good to get lots of practice and make writing regularly a habit. I try and write for 1 hour every morning before I head to the office and I attend a weekly writing group on campus. Or join a virtual writing group via Twitter for example #AcWri or #AcWriMo for November – since it is Academic Writing Month.

    Set up for our weekly Hide & Write group. Credit: Stephanie Zihms

Do you have any top tips for securing your first grants? If so, we’d love to hear them and share them with the GeoLog community. Please share your experiences and suggestions in the comments below!

Stephanie’s full presentation can be downloaded here.

At the upcoming General Assembly, Stephanie will be delivering a workshop on how to apply for small scale grants. Full details will be available once the conference programme launches, so stay tuned to the EGU 2018 website for more.

By Stephanie Zihms, the ECS Representative for the EMRP Division (and incoming Union Level Representative)

EGU 2018 will take place from 08 to 13 April 2017 in Vienna, Austria. For more information on the General Assembly, see the EGU 2018 website and follow us on Twitter (#EGU18 is the official conference hashtag) and Facebook.

Imaggeo on Mondays: Magnetic interaction

Imaggeo on Mondays: Magnetic interaction

Space weather is a ubiquitous, but little known, natural hazard. Though not as tangible as a volcanic eruption, storm or tsunami wave, space weather has the potenital to cause huge economic losses across the globe. In Europe alone, the interaction of solar wind with our planet’s magnetosphere, ionosphere and thermosphere, could lead to disrutions to space-based telecommunications, broadcasting, weather services and navigation, as well as distributions of power and terrestrial communications.

The Sun’s magnetic field drives all solar activity, from coronal mass ejections (CMEs), to high-speed solar wind, and solar energetic particles. While not all solar activity impacts the Earth, when it does, it can cause a geomagnetic storm. The Earth’s magnetic field creates, the magnetosphere which protects us from most of the particles the Sun emits. But when a “CME or high-speed stream arrives at Earth it buffets the magnetosphere. If the arriving solar magnetic field is directed southward it interacts strongly with the oppositely oriented magnetic field of the Earth. The Earth’s magnetic field is then peeled open like an onion, allowing energetic solar wind particles to stream down the field lines to hit the atmosphere over the poles,” explains NASA.

Aurorae are the most visible effect of the sun’s activity on the Earth’s atmosphere. They usually occur 80 to 300 km above the Earth’s surface, but can extend laterally for thousands of kilometers. They most commonly occur at the Earth’s poles, meaning only those at very northern, or southern, latitudes get the chance to see them (at least regularly). However, they are a reminder of the Sun’snpower and the threat posed by space weather.

To bring aurora to those who haven’t seen them before, and raise awarness about space weather at the same time, Jean Lilensten, director of research at l’Institut de planétologie et d’astrophysique de Grenoble (IPAG) in France, created the Planeterrella; an experiment which includes two spheres, one acting as the Earth and the other acting as the Sun. It allows for auroral displays, and demonstrations of other phenomena which ocurr in the space environment, to be brought into classrooms and public outreach events.

Today’s featured image shows the Planeterrella and several space phenomena. The violet colors on the big sphere ( the “star” ) are due to N2+ (a nitrogen cation), while the redish light on the little one is due to nitrogen. Both colours are seen in actual aurorae on Earth. The red “bow” in the middle, between the two spheres, is a bow shock similar to the magnetopause between Earth and the Sun (of course not to scale). Finally, a direct magnetic reconnection between the two spheres can be seen at the bottom.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at