“Take physics, study physics” — A conversation with Prof. Earle R. Williams

- What brought you to Hungary, and what kind of scientific connections do you have here?

- I’ve been coming here for nearly 30 years. I first met Gabriella in 1996, in Boulder, Colorado — by coincidence, we were both just beginning to measure the Earth’s Schumann resonances. That coincidence became the framework for many collaborations. I like to measure the duration of our relationship in solar cycles: one solar cycle is 11 years, and we’re now finishing the third. I should also acknowledge the Hungarian Academy of Sciences, which supported two visiting-scientist positions that allowed me to come here for extended periods to exchange with colleagues on many topics of mutual interest.

- What are the most exciting developments in your field right now?

- The most exciting development for me is our ability to independently monitor two different lightning populations in the three major “chimneys” of global lightning activity: the American chimney, the African chimney, and the Maritime Continent chimney in the western Pacific. The two lightning populations are the ordinary lightning flashes that dominate the Schumann resonance „background” signal, and the large and energetic Q-burst flashes that can singlehandedly „ring” the Schumann resonances to levels larger than all the other lightning flashes combined, for hundreds of milliseconds.

Lightning over continents is roughly 20 times more prevalent than over oceans, so these three regions dominate the global signal. Using Schumann resonance methods, we can now tell on any given day which chimney is dominant — Africa or America or the Maritime Continent — and that matters for understanding global atmospheric circulation. Lightning is also very sensitive to vertical motion in moist convection, which is notoriously hard to measure by other means. The ascending air over these chimneys produces descending, dry air elsewhere — like the Sahara Desert.

- Why should ordinary people care about Schumann resonances?

- Because they help us understand how the atmosphere and ionosphere changes over time. Climate change is real, global warming is happening right before our eyes, and many independent datasets confirm this. We want to know how lightning responds to that change. On short timescales, lightning tentatively increases with air temperature. But the fundamental question of what happens to global lightning in a warmer world is still open.

There’s also the aerosol question: continued fossil fuel use increases both CO₂ and atmospheric aerosols, and more aerosols may mean more lightning. We have some evidence that global lightning decreased slightly during the pandemic of 2020 because of the global diminishment of aerosol, linked with the reduction in global consumption of fossil fuel.

- How do you actually measure these phenomena?

- That’s precisely the strength of the Hungarian collaboration. Gabriella has been very disciplined in maintaining long-running measurements at the Nagycenk Observatory, and we have been less conscientious in Rhode Island. Comparing these two records has been scientifically essential. Gabriella’s focus on Schumann resonance frequencies — as opposed to our focus on amplitudes — has yielded its own important results on the dynamics of the lightning source regions, including evidence that lightning distribution responds to the solar cycle.

- How does the solar cycle affect lightning?

- The sunspot cycle goes up and down roughly every 11 years — we don’t fully understand what sets this time scale, it’s an outstanding problem in solar physics, but it’s very consistent. Gabriella found strong evidence that lightning responds to it: not so much a change in total lightning, but a shift in its geographic distribution. This finding is consistent with the idea that galactic cosmic rays can initiate lightning discharges. A recent paper by Xuan-Min Shao suggests that every lightning flash is initiated by a cosmic ray shower, which is consistent with the global findings.

- You mentioned thunderstorms as particle accelerators — can you explain?

- Thunderstorms can accelerate electrons to megavolt energies and produce gamma rays — gamma-ray glows and bursts. If you’re in the wrong place at the wrong time, you can receive a substantial dose of gamma radiation. The connection between this phenomenon and the global electric circuit and Schumann resonances is not yet well studied, but there’s little doubt a connection exists. Gamma-ray glows cause ionization and changes in the electrical conductivity of air over the chimneys, which will affect the global circuit; this is on our list for further work.

- What are the biggest unanswered questions in this field?

- One is the ambiguity of lightning’s response to temperature over long timescales. We don’t have Schumann records over centuries — only a few decades. There’s a long-standing meteorological observation called “Thunder Day,” where observers worldwide have recorded whether thunder was heard on a given day and running for more than 100 years. Preliminary analyses suggest increasing thunder days in many regions, but we don’t yet know whether that’s a global-warming signal or an observational artifact. Another big question is why global warming affects different regions so differently — the northern hemisphere is warming faster than the tropics, and thunder-day trends vary in ways we don’t yet understand.

 Another big puzzlement at present is a mystery lightning source: a signature in Schumann resonances in the early UT hours in Africa that resembles lightning but which lacks any optical counterpart in space-based lightning detection. The equatorial electrojet is being examined as a possible explanation, with kind assistance from István Lemperger.

- How do you estimate the relative contributions of the three chimneys?

We now have two complementary approaches: long-term station records at high latitude and geophysical inversion, which uses data from multiple stations to estimate each chimney’s daily strength. Tamás Bozóki and Ernő Prácser have been instrumental in developing the inversion methods. The best validation of the inversion method came from the 2022 Tonga eruption: the intense lightning concentrated at one location (the volcano) produced a clear spike-up in Schumann resonances, and our inversion method located it accurately. Machine learning could help further with the global meteorological analysis — chimney rankings vary day to day, contrary to conventional wisdom in atmospheric electricity, and AI could help identify what regional weather patterns are associated with specific rankings in chimney strength.

- What advice would you give to young scientists interested in this field?

- We need fresh talent. My main recommendation: train in physics first. Many of the key problems in this field — energetic particles from thunderstorms, gamma-ray processes — are fundamentally physics problems. A strong physics background is transferable to meteorology and geophysics, but the reverse is more difficult. As for getting involved internationally: visiting MIT as post-docs is possible through fellowships such as Fulbright. Getting in as a graduate student is very competitive, but MIT has a strong geophysics program for those who make it. Take physics, learn physics.

- What are the prospects for future cooperation?

- The global electric circuit is naturally suited to international collaboration — everyone can measure it, and comparing station observations is essential. One current project in Italy involves the DC global circuit: the Schumann resonance is the AC circuit, but the quasi-steady voltage between the Earth’s surface and the ionosphere constitutes a DC circuit that is much harder to measure locally because of local noise. We’re testing a large collector — a 14 km long unenergized power line near Milan — as an atmospheric current sensor. If we can stabilize the system and protect the electronic circuits from the effect of lightning, we could monitor daily variations in the DC circuit and learn how thunderstorms and electrified shower clouds couple to the ionosphere. Globally representative measurements of the DC global circuit from a single location are traditionally far more difficult than Schumann resonances.

 The broader vision: with better station networks, improved inversion tools, satellite lightning data from instruments like NASA’s GLM and EUMETSAT’s MTG, and AI, we can make the most of these inexpensive, planetary-scale measurements. I’d also like to see free data sharing among Schumann stations. There are only about 15–20 active worldwide, and they’re not yet well networked, but still operating individually.