Debunking a Pillar of Ionospheric Science, and Building a New One: Episode I

Dear reader, I’m excited to try this non-traditional strategy, the thing they call a blog (honestly!), to tell you about my research into the foundations of ionospheric physics. But I suppose I should first tell you who is talking. After listening to Joan Baez sing at my elementary school, protesting the war in San Francisco with my mother, climbing over a fence because she was scared of the batons, swimming naked in a river with my entire 8th grade class, shocking the head of the math department at Palo Alto High School, working as a carpenter, out of a Volkswagen Bug, having my Fiat pulled out of a ditch by the man who made the first computer mouse (Figure 2 below) in his garage, designing my own religion, seeing people die who shouldn’t have died, working as a microwave engineer, marrying a much more conservative Chinese woman, having it work out, earning a Ph.D. in quantum gravity, and becoming the father of two hims, each amazing in their own way, I found myself trying to break into the field of ionospheric physics as a compromise approach to earning a living— at that same research lab where that wooden computer mouse arrived the next morning for testing (SRI International, where I have worked for 23 years).

Although I didn’t have time to worry about it back then, I noticed that while the magnetospheric people were all about MHD waves, there was no talk of what became of these waves when they entered the ionosphere. In the ionosphere, it was all about electrostatic theory, which made things very simple and easy. After spending a little while looking for an explanation, I quickly gave up. Quite a few years passed before I realized that I might actually be able to bridge this gap. My 2016 paper got great reviews, but was met with a deafening silence. My second paper did not get great reviews. I suspect a few of those referees had to be rushed directly to the hospital. Thank you to those few who supported me! But since I am given confidence by my rigorous education in physics and mathematics, and since the negative reviews were just sour grapes, it’s blogs away. You might now notice a slight change in tone.

The interaction of the magnetosphere with the ionosphere and atmosphere involves electromagnetic energy incident from the magnetosphere (for example as shown in Figure 1 on top left), which is output from an empirical Poynting flux model made from FAST satellite data (Cosgrove et al., 2014). The energy is dissipated by means of currents that flow through the ionospheric conductance, which arises because of the high rate of collisions with the neutral atmosphere, so that the currents cause heating and acceleration of the atmosphere. Various effects flow from this, with a particularly notable one being disruption of satellite orbits. Thus, it is important that we understand the physics that gives rise to the ionospheric conductance, which forms the inner boundary for magnetospheric modelling.

The ionospheric conductance has heretofore been calculated using a form of electrostatic theory that is very close to the textbook theory, where all time derivatives are set to zero and what remains of the equations of motion are applied to a boundary value problem. But since electrostatic theory is not valid in all cases, it is important to ask if we can show that it is valid for this ionospheric application, or, if not, to derive an electromagnetic calculation that can replace it.

The transition between electromagnetics and electrostatics is addressed in the transmission line theory of electrical engineering. Consider the simple “lumped element” circuit shown in the top panel of Figure 3, consisting of a switched harmonic source with internal resistance, driving a capacitor. In order to be properly causal, this circuit is generally analyzed by taking the Laplace transform in time, which provides a solution as a sum of steady-state and transient terms. In many cases we are only interested in the steady-state part, which leaves the usual idea of a capacitive admittance operating in a harmonic circuit (Yin = iω0C, a positive imaginary number).

The terminology “lumped element” indicates that we are considering the capacitor to be very small, so that it doesn’t matter where the electrical connections are made to the parallel plates, and we can assume that the capacitor energizes everywhere all-at-once. But in reality when the switch is flipped, there is an electromagnetic signal that enters the capacitor on the side with the electrical leads, and then propagates across to the other edges, and bounces around until a steady state is reached. And depending on the size of the capacitor, there may be a portion of a wavelength inside the capacitor. When this happens the lumped element (electrostatic) analysis is too idealized to be of use.

To understand how this effect can be accommodated, consider the case of a capacitor that is long and thin, with the leads attached at the near end. Assuming that the signal cannot leak out and radiate away, this long and thin structure is a transmission line that is open-circuited at the far end. The signal propagates from the electrical leads to the far end where it reflects back, and then continues bouncing back and forth until a steady state is reached. Assuming there is only one propagating electromagnetic mode, the steady-state amounts to a superposition of two oppositely propagating waves, which are phased so that the current is zero at the open-circuited end.

From this description can be derived the well known formula for the steady-state input admittance seen by the source, which may be found, for example, in equation 3.88 from Collin (1966), and setting the load admittance to zero,where l is the length of the transmission line, Y0 is the characteristic admittance of the wave mode, and kz is the wavevector in the direction along the line (i.e., in the “parallel” or z direction). A schematic for the circuit with the open-circuited transmission line replacing the lumped-element capacitor is shown in the middle panel of Figure 3.

Since Y0 is usually a real number, the formula (1) provides that when the transmission line is short and the waves are not too lossy (i.e., kz is strongly real), then it does in fact function as a capacitor with admittance iY0kzl. But as the line gets longer the tangent function causes an oscillation between capacitive and inductive behavior, with near singularities where real(kz)l is a multiple of 90°. The singularities arise when the electric field of the reflected wave cancels that of the incident wave, where wave dissipation makes the cancelation imperfect, and is reflected in the imaginary part of kz. The famous “Smith chart” provides a graphical representation for lossless transmission lines that was a staple of microwave laboratories in the days before computers were widely available, which, by the way, was really not very long ago (bottom panel of Figure 3).

The ionosphere is not long and thin like this hypothetical capacitor. The capacitor was made thin to ensure that we do not question the coherence of the excitation produced by the electrical connections at the end. But as long as we stipulate that the excitation is coherent the capacitor can be made very wide, with electrical connections spread along its width. For example, the electrical connections could be phased so that they excite a simple plane wave, with some chosen transverse wavelength. In fact, assuming this very-wide geometry actually removes an approximation that we had swept under the rug, which is that to properly analyze the thin capacitor we should form a wavepacket in the transverse direction. If the capacitor is very wide, like, for example, the ionosphere, then there is no such approximation, and we can analyze one transverse wavelength at a time.

Thus, consider the gedankenexperiment shown in Figure 4, where the ionosphere is simplified to be a uniform slab of collisional plasma, with empty space below. The middle panel of Figure 3 is now the electromagnetic equivalent circuit for this simplified version of magnetosphere-ionosphere coupling, with the ionosphere represented by the open-circuited transmission line. The downward looking input admittance for an incident plane wave is given by the same transmission line formula (1), where Y0 and kz depend on the frequency and transverse wavelength of the plane wave.

The real part of the input admittance is, of course, the ionospheric conductance. We can compare the input admittance to the well known electrostatic approximation, which is the field line integrated conductivity, σPl, where σP is the (zero frequency) Pedersen conductivity. Doing this we derive some preliminary criteria for electrostatic theory,  where kz = 2π/λz − i/ldz, λz is the wavelength, and ldz is the dissipation scale length for the propagating electromagnetic mode.

To my knowledge, the last of the three criteria (2) was first derived by Cosgrove (2016), who named iY0kz the wave-Pedersen conductivity, since it replaces the usual (zero-frequency) Pedersen conductivity in an electromagnetic calculation of ionospheric conductance. Cosgrove (2016) also found that Y0 is strongly imaginary, while kz is strongly real, so that iY0kz is in fact strongly real, as expected for the ionospheric admittance. An important corollary comes from the tangent function dependence (1), which suggests the unexpected possibility that the ionospheric conductance could contain (near) singularities and change sign, if the parallel wavelength is ever comparable to the thickness of the ionosphere.

Does this ever happen? Does iY0kz equal σP? Is there really only one propagating electromagnetic mode in the ionosphere? What happens when the ionosphere is vertically inhomogeneous? Stay tuned for the next episode. But I’ll give you a hint, the answer is not boring, just ask those referees who are recovering in the hospital— on second thought, don’t ask them (Cosgrove, 2022).

 

 

by Russell Bonner Cosgrove

 

 

 

References

Collin, R. E. (1966), Foundations for Microwave Engineering, McGraw-Hill.

Cosgrove, R. B. (2016), Does a localized plasma disturbance in the ionosphere evolve to electrostatic equilibrium? evidence to the contrary, J. Geophys. Res., 121, doi: https://doi.org/10.1002/2015JA021672.

Cosgrove, R. B. (2022), An electromagnetic calculation of ionospheric conductance that seems to override the field line integrated con- ductivity, Zenodo and ArXiv, doi: 10.48550/ARXIV.2211.10818, 10.5281/Zenodo.7416494.

Cosgrove, R. B., H. Bahcivan, S. Chen, R. J. Strangeway, J. Ortega, M. Alhassan, Y. Xu, M. V. Welie, J. Rehberger, S. Musielak, and N. Cahill (2014), Empirical model of poynting flux derived from fast data and a cusp signature, J. Geophys. Res., 119, 411–430, doi: https://doi.org/10.1002/2013JA019105.

Space magnetometry from Swarm and beyond

The Swarm satellite mission is ESA's fourth Earth Explorer in space since late 2013. As we prepare to
celebrate 10 years of successful operations (and looking forward to many years more!), the Swarm community met 10-12 October 2023 in sunny Frascati, Italy, for the thirteenth Data Quality Workshop to compare notes and plan for the future of the mission to explore Earth's magnetic field.

With the foremost minds in satellite magnetometry gathered in one room, and expertise ranging from geophysics, space instrumentation and operations to software engineering, this regular meeting is always exciting. Swarm's primary three spacecraft (https://visuals.earth.esa.int/satellites/swarm), as well as other contributing spacecraft, continue to provide invaluable measurements that probe many phenomena, from the flow of material in Earth's core to electric currents above the atmosphere driven by solar activity. We have been able to improve the data quality (i.e. improved calibration and error correction) year-on-year and continue to evolve and grow the large portfolio of data products and services which have enabled scientists to publish over 500 research papers so far, as well as providing critical input to many applications, from navigation and mineral exploration to space weather prediction.

There are two new advances in the data delivery worth mentioning here. Firstly, there is the implementation of a new "FAST" processing chain, which makes data available within a few hours (subject to down-linking constraints imposed by the satellite orbits and ground station locations). This makes it possible to use Swarm for same-day space weather monitoring. The second point is in connection with the VirES data access and exploitation platform which radically increases the accessibility of the data. We are building new capabilities in the on-demand processing of data through the SwarmPAL software, where scientists contribute algorithms and tooling that are made more flexible and coherent through the adoption of a common framework.

The growing opportunities don't stop there though. On 13th October, some of us from the Swarm workshop travelled on to the Royal Astronomical Society, London, for another meeting showing some of the first results from the newly launched Macau Science Satellite (MSS-1). This new mission offers highly complementary data to Swarm and we expect new research analysing the joint dataset over the coming years. With the growing number of operators of high-precision magnetometers in space, the need to collaborate and coordinate is more important than ever.

For more news about Swarm, click here.

---

Ashley Smith is a postdoctoral researcher at the University of Edinburgh, working as part of the Swarm DISC (Data, Innovation, and Science Cluster). He is passionate about computing technologies and open source software and his research interests include geomagnetic field modelling and space weather. He can be contacted by email at ashley.smith@ed.ac.uk.

---

Instabilities of the Earth’s magnetic field over multi-millennial timescales

Earth’s magnetic field varies over a wide range of time scales. The very long multi-millennial scales are associated with variations of the internal core field. The short timescales, annual and shorter, are related to field contributions generated by current systems in the ionosphere and magnetosphere. The most dramatic changes occur at the longest periods, namely geomagnetic reversals and excursions. They represent a significant decrease in the field intensity, with reversals having a complete polarity flip and longer duration in contrast to excursions. While the reversals are global events, the excursions can be of global and regional nature. For the latter, only part of the Earth is affected with very low intensity and transitional directions. The last geomagnetic reversal, Matuyama-Brunhes, happened 780,000 years ago, and the last global excursion, the Laschamps excursion, occurred 41,000 years ago. These events are studied with indirect measurements, paleomagnetic data from sedimentary cores and volcanic rocks. Global data compilations enable us to reconstruct the field’s spatial and temporal variations and to better understand the core processes responsible for these variations.

Magnetic field lines during a period of high dipole moment, for example 1900 AD (top) and the Laschamps geomagnetic excursion, 41,000 years ago (bottom). The figures show the dipole-dominated structure at stable periods and very complex, multipolar structure of the magnetic field in transitional epochs. The color maps represent the radial field component at the Earth’s surface. The blue lines are pointing inward and red lines in an outward direction.

Credit: Maximilian Schanner, GFZ Potsdam, 2022. https://sec23.git-pages.gfz-potsdam.de/korte/pymagglobal-3d-fieldlines/

doi: 10.5880/GFZ.2.3.2020.005

While the current configuration of the geomagnetic field can be approximated with a dipole (having two poles, magnetic north and south pole), during geomagnetic excursions, the dipole is not a dominant component. The figures present the magnetic field lines of a dipole vs. non-dipole-dominated field, where the former is characteristic of the present-day and the latter of the Laschamps excursion. Over very long time scales, tens of thousands to millions of years, the field closely approximates a geocentric axial dipole. This hypothesis allows using the paleomagnetic data for reconstructing plate tectonics.

Direct observations indicate that the magnitude of the Earth's magnetic axial dipole has decreased since 1840, and predictions of geomagnetic secular variation show that it will likely continue to decrease over the following decades. A weakened geomagnetic field may lead to numerous hazards like satellite outages, disturbances in communications and navigation, and induced currents in pipelines and transmission lines. The following questions come naturally:

Will the geomagnetic field go through an excursion or a reversal in the future? Most probably yes, considering the dynamic nature of the field and the frequency variations of these transitional events.

Is the geomagnetic field heading towards an excursion or reversal now? Probably not, based on analyses of available paleomagnetic field models covering the past 10,000 and 100,000 years and the fact that the field at present seems to be clearly stronger than the long-term average.

Can we predict such events? No, this remains an open question because it is hard to foresee the long-term changes. The geomagnetic field intensity needs to decay further for several centuries to recognize and distinguish a future transitional event from normal secular variation.

Sanja Panovska is a postdoctoral researcher at the Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences. Her primary research focus is reconstructing the long-term evolution of the geomagnetic field based on paleomagnetic data over different timescales from the Holocene, to 100,000 years and over the Earth’s geological history. She is also involved in studies on productions of cosmogenic isotopes, paleomagnetosphere and paleoaurora.

'Geoscience Connections' on YouTube!

The joint IAGA-IASPEI proposal awarded by IUGG consists of a documentary, web series and short movies about the science and the scientists of the 8 different IUGG associations and the connections between them.

While the documentary and web series will be released later on, the short movies of the scientists and early career researchers from the different associations are now being released on IUGG and IAGA YouTube channels!

Every Tuesday and Friday, a video will be published which would include an introduction about the researcher followed by a description of the science they do. The videos, less than 5 minutes in length, have been aimed at the general public and early career researchers. For some weeks, an additional video about science outreach will also be made available.

Have a look here and head over to our YouTube for more!

Keep a look out at our social media channels for upcoming videos.

Imposter syndrome in research

Imposter syndrome is the inability to accept that your accomplishments are a result of your hard work and abilities. Or in other words, you are a researcher.

Here are some of the simplest tests to check if you have the syndrome-

    1) You think you don't know any/many things but have become good at pretending that you do.

    2) Somebody said you don't deserve it and it stayed with you. 50 others said the opposite but you think they are just being nice or don't know anything.

    3) You are reading this.

"Piled Higher and Deeper" by Jorge Cham
www.phdcomics.com

If it has been established that you are an imposter in your eyes, I have a few things to say.

    1) Talk to your peers. Most often others are thinking the same thing but nobody has the courage to speak it out loud or discuss.

    2) But keep in mind, nobody has been through what you have been through. Sure, everybody has had their own struggles but that doesn't make their or your struggle more or less difficult. Your thoughts can differ and thats okay.

    3) Feelings can't be measured. Feelings are different for different people for different things. They can also be similar but don't try to find a way to normalise them.

    4) You need to accept the advice you give others.

    5) Reach out. To anyone or everyone. You might end up helping someone else when you were just looking for it yourself.

At the end of the day, it's okay to have imposter syndrome if its not affecting you strongly. Sometimes, it helps you to do better. But if its consuming your thoughts too much, ask for help. Especially for early career researchers, it would be great if mentors and supervisors could make sure the student is comfortable being themselves and can ask for help whenever needed, personally or professionally.

Shout out in the comments if you would like to read more such thoughts and blogs from researchers at different levels of their careers. Or if you'd like to ask or reach out for support.

---

Shivangi Sharan is a postdoctoral research associate at Imperial College London, working on prioritising the research that will be carried out using the JUICE magnetometer data. Previously, she has worked on the interior of Mars and Jupiter using their magnetic observations. She is an active member of the IAGA Blog Team and can be contacted via e-mail here.

---

Oscillating relic magnetic field in the Sun can explain solar long-term evolution and systematic hemispheric asymmetry

Sun is a magnetic star whose magnetic field is generated in the upper third of solar interior by the motion of charged particles called solar plasma. Upward transport of hot plasma and differential rotation form a system of electric currents that produce magnetic fields. This is called the solar dynamo mechanism. Magnetic fields can be seen on the solar surface, occasionally even by naked eye, as sunspots, whose variable occurrence has been followed during several hundred years. Sunspots vax and vane according to a roughly 11-year cycle, commonly called the sunspot cycle. However, the height and length of sunspot cycles also vary in a roughly 100-year cyclicity called the Gleissberg cycle. The maximum of the last Gleissberg cycle was during cycle 19 (in the late 1950s), which is the highest solar cycle so far. This activity has declined now and, since cycle 24, solar activity is on a much lower level.

The heights of the past solar cycles have alternated so that an odd cycle is higher than the previous even cycle. This is called the Gnevyshev-Ohl (G-O) rule according to its finders. Since cycle properties vary randomly in dynamo models, this systematic alternation of cycle heights cannot be explained by dynamo theory. On the other hand, a relic or fossil magnetic field prevailing in the solar interior from the times of solar system formation can, together with the dynamo mechanism, naturally explain the G-O rule. Relic electric currents producing a relic magnetic field can exist during billions of years because currents weaken very slowly in the Sun due to high electric conductivity. Relic currents must flow in the direction of solar rotation in order to agree with the G-O rule. This creates a relic magnetic field which is northward oriented.

Solar northern and southern hemispheres depict very often somewhat different levels of activity. It was recently shown (Mursula, 2023) that solar hemispheres are systematically asymmetric so that maximum activity is stronger in the northern than southern hemisphere in odd cycles, while it is stronger in the southern hemisphere in even cycles. Again, such a systematic alternation cannot be explained by the dynamo alone. However, it can be explained by a relic magnetic field which is shifted slightly northward from the solar equator (see Figure). It was also found there that cycle height and asymmetry are correlated. Cycle 19 was not only the highest but also most strongly dominated by activity of the northern hemisphere. The relic field had its largest shift to the north during this cycle. Accordingly, the Gleissberg cycle can be explained as an excursion of the location of the relic field to the north (or south) and back to the solar equator during a roughly 100-year oscillation. A full oscillation of relic consists of two Gleissberg cycles, with one shift to the north and one to the south. This also gives a new interpretation for the 210-year Suess/deVries cycle as the full relic oscillation cycle and connects Gleissberg cyclicity and Suess/deVries cyclicity under the same new paradigm of an oscillating relic field.

Left part of vertical line depicts the schematic operation of solar dynamo from solar minimum (plots of first column) to solar maximum (second column) by the action of differential rotation (depicted by capital omega). Minimum-time poloidal (vertical) magnetic field lines are transformed to maximum-time toroidal (horizontal) field lines. In the upper plots, poloidal lines are upward (so-called positive minimum), in the lower plots they are oriented downward. Right part of vertical line depicts how the existence of a northward oriented relic field (thick upward arrow) modifies the (pure) dynamo field. During a positive minimum (upper row), relic field and dynamo poloidal field are oriented in the same direction. As a result, the toroidal field due to relic (thick horizontal arrow) and dynamo toroidal field strengthen each other during th emaximum. This effect is stronger in the northern than southern hemisphere, leading to northern dominance in sunspot activity during odd maxima. In the negative minimum (lower row), relic and dynamo fields are opposite, which decreases the toroidal field in both hemispheres. However, the decrease is more effective in the northern hemisphere, which implies southern dominance during even maxima.

Oscillating relic magnetic field allows to make long-term forecasting for several cycles into the future, contrary to the one-cycle limit of pure dynamo theories. Cycle 25 will become slightly larger than cycle 24 because it is G-O favored but it will remain only moderately high because the relic shift is still quite small. Further on into the 21st century, cycle heights tend to increase since the relic shift is increasing, but cycle 26 is G-O disfavored and will remain still rather small. However, with increasing relic shift the G-O favored cycle 27 will already be a lot higher, maybe above 200 in annual sunspot numbers. Relic field will reach its maximum shift to the south in cycle 29, which will be the highest cycle in the 21st century, in analogy with cycle 19, which was the highest cycle of the 20th century. Thereafter, cycle heights will again start decreasing, with relic location returning to the solar equator. Cycle 29, as all odd cycles of the 21st century will be south-dominated, while even cycles will be north-dominated. Accordingly, the hemispheric dominance in the 21st century will alternate oppositely to that in the 20th century, because of the southern shift of the relic field.

Oscillating relic magnetic field will become the new paradigm of space climate, the study of long-term changes in the Sun and the solar-terrestrial environment, in the coming decades. Hopefully helioseismic methods and dynamo models amended by relic fields will soon be improved to allow them to possibly find more direct evidence for relic fields. Eventually, the above predictions on future cycles will test the new paradigm in the coming decades.

Kalevi Mursula is an active professor emeritus from the University of Oulu, Finland, where he was faculty professor for nearly 30 years and leader of the Center of Excellence of the Academy of Finland on space climate in 2014-2019. He is the originator of the concept of space climate and main organizer of a series of ten space climate symposia and schools in 2004-2023.

Carrington Event 1859 – Reconstructing Historical Space Weather Events

What is Space Weather and how does it affect us?

Space weather is the result of particles emitted by the Sun, termed the solar wind, interacting with the Earth's magnetic field. Large eruptions from the Sun, called Coronal Mass Ejections (CMEs), pose a hazard to the ground infrastructure, such as the high-voltage power network, in the form of Geomagnetically induced currents (GIC). GICs are excess currents in the power network that are created by the rapid variations of the magnetic field and in extreme cases have caused damage to transformers causing the power grid to temporarily shut down. These space weather events are the same natural phenomenon as those responsible for the Aurora becoming visible at mid-latitudes.

There are important questions about the hazard posed by space weather that are unanswered. These include:

• How big can geomagnetic storms be?

• How often do storms of this size occur?

• What is the series of events that can lead to the largest geomagnetic storms?

• What are the effects on modern technology?

  
  

What records do we have of historical geomagnetic storms?

The British Geological Survey (BGS) holds records for eight geomagnetic observatories operating in the UK going back to 1847. The digital era of geomagnetic observations began in the 1980s providing us with high-quality recordings of the Earth’s magnetic field but prior to this all data were recorded on photographic paper. The problem with the digital dataset is the dearth of very large geomagnetic storms. As shown in Figure 1, we have enjoyed an unusually quiescent era of solar activity since the 1960s.

Figure 1: Geomagnetic activity from 1880 to 2020, expressed by the daily Aa index. Figure produced as part of the British Geological Survey and the ESA Space Safety Programme (https://swe.bgs.ac.uk/bgs/indices.shtml?index=Aaindexdaily).

What is the Carrington Event?

These historical records contain some of the largest known geomagnetic storms including the famous Carrington event of 1st-2nd September 1859 – one of the large storms on record. The event and its lesser-known precursor were recorded at two rival observatories both operating in London at the time, Kew and Greenwich. This provides a great opportunity to cross-compare the two observatories only 20km apart.
The paper magnetograms provide a unique example of near-continuous measurements for the Carrington event and pre-cursor storm. We manually extracted the digital time series of Kew and Greenwich records of three components of vertical, horizontal and declination of magnetic field from 25-Aug to 05-Sep-1859 by digitizing the historic records. To assist with scaling the magnetograms into accurate time and magnetic units, we use published journal papers from the period to benchmark our interpretation and spot values recorded at Greenwich. This isn’t without its own problems, including:

• the poor quality of parts of the recorded traces

• overlap or missing traces

• Issues with instrumentation at the time of recording

• Lack of metadata to scale recorded traces to modern SI units of magnetic field.

Figure 2: Paper magnetograms recorded on photographic paper for observatories in London, UK. (a, b) Declination angle at Kew from 10:20UT 02-Sep-1859 to 12:05UT 05-Sep-1859 (c, d) Declination angle and Horizontal Force at Greenwich from 12:00UT 01-Sep-1859 to 12:00UT 03-Sep

Figure 3 shows the reconstructed time series of the magnetic field at both the Greenwich and Kew observatories. Reconstructing the days prior to the famous 1-2 September storms enables us to see the series of events that led to such an extreme geomagnetic storm. When storms occur in close succession, the first storm essentially clears the interplanetary space of solar wind and enables the subsequent storms to have greater impact on Earth. We can see evidence for a large storm during the 28th-30th storm for example. The period around August and September 1859 was unusually stormy compared to the modern era.

Figure 3: Digitized magnetograms of (a) horizontal magnetic field strength, (b) declination, (c) vertical magnetic field strength, at Kew (orange) and Greenwich (blue) observatories from 25- Aug to 05-Sep-1859. Highlighted green is the Carrington-observed flare at ~11:15-11:23 01 September 1859. Highlighted in grey are evidence for suspected earlier solar flares.

The analogue record is a rich and yet untapped source of information about geomagnetic activity in the past. With a more focussed effort and new digitisation tools, the community may be able to find better answers to the great unknowns of space weather hazards in future.

BGS Magnetograms: 
https://www.bgs.ac.uk/information-hub/scanned-records/magnetograms/

Authors:
E. Eaton¹, C. Beggan¹, E. Lawrence¹, E. Clarke¹, K. Matsumoto², H. Hayakawa^2
1British Geological Survey, ²Nagoya University

Eliot Eaton is a magnetotelluric field technician at the British Geological Survey, UK. His primary research focus is completing a magnetotelluric survey of England, Wales, and Southern Scotland to improve understanding of how geomagnetic storms influence the UK’s grounded infrastructure, such as the high-voltage power grid. During the COVID-19 pandemic, all fieldwork was postponed so he had the opportunity to dig into the historical geomagnetic archives of the UKs observatories.