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Source: AGU Advances

Imagine the catastrophic winds of a category 5 hurricane. Now, imagine even faster winds of more than 100 meters per second, encircling the planet and whipping clouds across the sky, with no end in sight. This scenario would be astonishing on Earth, but it’s business as usual on Venus, where the atmosphere at cloud level rotates about 60 times faster than the planet itself—a phenomenon known as superrotation. In contrast, Earth’s cloud-level atmosphere rotates at about the same speed as the planet’s surface.

Prior research has explored the mechanisms driving atmospheric superrotation on Venus, but the details remain murky. New evidence from Lai et al. suggests that a once-daily atmospheric tidal cycle, fueled by heat from the Sun, contributes much more to the planet’s extreme winds than previously thought.

Rapid atmospheric rotation often occurs on rocky planets that, like Venus, are located relatively close to their stars and rotate very slowly. On Venus, one full rotation takes 243 Earth days. Meanwhile, the atmosphere races around the planet in a mere 4 Earth days.

To better understand this superrotation, the researchers analyzed data collected between 2006 and 2022 by the European Space Agency’s Venus Express satellite and the Japan Aerospace Exploration Agency’s Akatsuki satellite, which both studied Venus’s atmosphere by detecting how it bends radio waves. The research team also simulated superrotation using a numerical model of Venus’s atmosphere.

The analysis focused specifically on thermal tides—one of several atmospheric processes, alongside meridional circulation and planetary waves, whose interactions have previously been shown to sustain Venus’s superrotation by transporting momentum. Thermal tides are patterns of air movement that occur when sunlight heats air on the dayside of a planet. Venusian thermal tides can be broken into two major components: diurnal tides, which follow a cyclical pattern repeating once per Venusian day, and semidiurnal tides, which have two cycles per day.

Earlier research suggested that semidiurnal tides are the main thermal tide component involved in superrotation. However, this study—which includes the first analysis of thermal tides in Venus’s southern hemisphere—found that diurnal tides play a primary role in transporting momentum toward the tops of Venus’s thick clouds, suggesting diurnal tides are major contributors to the rapid winds.

Though the researchers note that further clarification of the contributions of diurnal tides is needed, the work sheds new light on Venus’s extreme winds and could aid meteorological research on other slowly rotating planets. (AGU Advances, https://doi.org/10.1029/2025AV001880, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), Key driver of extreme winds on Venus identified, Eos, 106, https://doi.org/10.1029/2025EO250436. Published on 19 November 2025. Text © 2025. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

A new tool aims to do for heat waves what Saffir and Simpson did for hurricanes.

CalHeatScore, an online mapping tool developed by the California Office of Environmental Health Hazard Assessment, ranks heat wave risk on a straightforward scale of 0 to 4. And just like the Saffir-Simpson scale for hurricane strength, CalHeatScore delivers its warnings days in advance. It’s designed to help Californians prepare for heat emergencies and uses socioeconomic factors to tailor information for each individual zip code.

“[CalHeatScore] gives you a warning for your community that reflects the characteristics of your community.”

“It gives you a warning for your community that reflects the characteristics of your community,” explained John Molitor, an environmental data scientist at Oregon State University who helped build the tool.

The hyperlocal method provides meteorologists, emergency managers, and the public with a shared understanding of risk during California’s extreme heat. Molitor and his colleagues will share their work at AGU’s Annual Meeting 2025 in New Orleans on 16 December.

Scorching in Sacramento

CalHeatScore was born during a heat wave. Legislators had been pushing for a warning system for months, and the bill was finally approved in September 2022 during a 10-day heat wave that broke 1,500 temperature records across California. The heat wave caused 395 excess deaths in the state, 4 times the toll of California’s deadliest wildfire, according to the Los Angeles Times.

The tool—officially dubbed the California Communities Extreme Heat Scoring System and launched in December 2024—was designed to prevent future heat deaths by providing a streamlined and site-specific warning system. It includes targeted public health information, like community heat risk and the locations of the nearest public cooling centers.

Building a Model

CalHeatScore draws from a range of data sources, recognizing that heat risk is more than just temperature.

First, developers established a baseline using temperature data and emergency room visits from 2008 to 2018, looking specifically for diagnoses that increase with heat. The current operational model uses zip codes as a proxy for socioeconomic data, while a second-stage model will add specific population data to pinpoint communities of concern.

Other warning systems look at empirical distributions of heat, Molitor explained, but CalHeatScore looks for causal effects. The interdisciplinary team of physicians, health experts, and data scientists is specifically looking for drivers of heat impacts.

“People experience heat very differently through space and time,” Molitor said. A community with swimming pools and air-conditioning will experience a 100°F day different than a neighborhood of pavement and parking lots. Similarly, indoor office workers are protected from the heat in a way roofers, gardeners, and carpenters aren’t. By considering factors like age brackets and average income, CalHeatScore can determine the heat-related health risk for a community.

The platform’s clickable, searchable map is built on spatial modeling. “What happens in one zip code is going to be highly informed by what happens in nearby zip codes,” Molitor said. Multilevel modeling “is allowing us to take the data and drill down into all these little zip codes and come up with an appropriate heat warning system for each,” he said.

Decisionmaking Data

All that complexity results in a very simple scale. Heat risk is ranked 0 (low) through 4 (severe) and provided for the next 7 days.

That’s a useful approach, said Ashish Sharma, an atmospheric scientist at the University of Illinois Urbana-Champaign who was not involved in the project.

“If we look at decisionmaking, it’s binary. Either you act upon it, or you don’t,” he said. “Combining this information at the zip code level can really improve decisionmaking.”

But while the tool has a lot of strengths, the current map seems geared more for agencies and governments than the public, he noted. He hopes future iterations are more user-friendly.

To that end, the CalHeatScore team is exploring options to develop a mobile app. That would be a helpful addition, said Amy Cilimburg, the director of Climate Smart Missoula who’s also worked on local heat mapping. A phone app could allow a football coach on the sidelines or a daycare director on the playground to plan their week around the heat.

“There is a lot of utility and strength in a hyper-local map,” she said. The next test is making sure people know about the tool and start making decisions based on it.

Expanding the Map

The developers aim to expand awareness at the AGU Annual Meeting, sharing their work with an international audience. CalHeatScore is replicable. Any state or country with similar data could develop a 7-day warning system.

“What we have here is really advanced, and we’d like to be doing this for other jurisdictions.”

“What we have here is really advanced, and we’d like to be doing this for other jurisdictions,” said David Eisenman, a project principal investigator, professor of medicine, and codirector of the Center for Healthy Climate Solutions at the University of California, Los Angeles.

The blend of health outcomes, temperature levels, and demographic data is “a really unique approach,” Eisenman said.

CalHeatScore is built with health outcomes and heat vulnerability in mind. When the next heat wave rolls through California, residents will have a new way to communicate and tolerate the temperature.

—J. Besl (@j_besl, @jbesl.bsky.social), Science Writer

20 November 2025: This article has been updated to correct the role of David Eisenman.

Citation: Besl, J. (2025), New tool maps the overlap of heat and health in California, Eos, 106, https://doi.org/10.1029/2025EO250432. Published on 19 November 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

US budget cuts risk creating blind spots in Earth monitoring systems that would imperil weather forecasting and climate research for years to come, the deputy chair of a key UN-backed climate monitoring body warned in an AFP interview.

Beryllium-7 is a radioactive isotope of beryllium produced by cosmic rays in the atmosphere. A Japanese research team has explored, over space and time, how the beryllium-7 is transported from the atmosphere to Earth's surface. Their goal was to better understand the mechanisms of atmospheric mixing on Earth. Their research is published in the Journal of Geophysical Research: Atmospheres on October 14, 2025.

SummaryAccurate quantification of natural gas hydrate is essential for resource potential and climate impact assessment. Archie’s empirical equations are commonly used to quantify hydrates from electrical resistivity measurements. One dominant Archie equation parameters, i.e. saturation parameter (n), is generally assumed to be constant for different hydrate saturation range for a given reservoir. However, n actually varies with hydrate saturation and morphology, and the exact relationship between n and hydrate saturation or morphology still remains poorly understood, leading to great uncertainties in resistivity-derived saturations. Here we investigate the effect of hydrate saturation and dominant hydrate morphologies on n using well logs from four sites in both fine and coarse-grained sediments: two sites with fluid-displacing hydrate (site W11 from the third Guangzhou Marine Geologic Survey; and Mallik 5L-38 well in the Mackenzie Delta) and two sites with fracture-filling hydrate (site 10 from Indian National Gas Hydrate Program Expedition 01; and site W08 from the second Guangzhou Marine Geologic Survey). We calculated n value using Archie’s law with hydrate saturation determined from velocity. Our results demonstrate a clear negative relationship between hydrate content and n value. Moreover, n estimates from two fracture-filling sites show greater variability compared to fluid-displacing sites. At a fracture-filling hydrate site, site 10, various trends between n and hydrate saturation are possibly caused by the distint gas compositions of hydrate. Our results demonstrate that significant effects of hydrate morphology and saturation on n that are site specific, and can be used to enhance the accuracy of gas hydrate quantification.

SummaryFull-waveform inversion (FWI) is a method that utilizes seismic data to invert the physical parameters of subsurface media by minimizing the difference between simulated and observed waveforms. Due to its ill-posed nature, FWI is susceptible to getting trapped in local minima. Consequently, various research efforts have attempted to combine neural networks with FWI to stabilize the inversion process. This study presents a bidirectional physics-constrained full waveform inversion (BP-FWI) framework that leverages transfer learning by pre-training on simple initial models and utilizing the results. Additionally, it employs FWI gradients to co-optimize both the neural network and the adaptive residual learning module under bidirectional physics constraints. By eliminating the reliance on a large amount of manually constructed synthetic datasets, the proposed training strategy addresses the challenge of data dependency. Furthermore, through the joint optimization strategy guided by bidirectional constraints, the neural network is able to focus on integrating physically-informed prior knowledge into global stratigraphic representations, while the adaptive residual learning module specializes in learning residual mappings from the network’s output, thereby capturing subtle inter-layer velocity variations in local geological structures. Evaluating the method on two benchmark models under various conditions, including absent low-frequency data, noise interference, non-uniform receiver configurations, and differing initial models, along with corresponding ablation experiments, consistently demonstrates the superiority of the proposed approach.

For decades, scientists have been baffled by two enormous, enigmatic structures buried deep inside Earth with features so vast and unusual that they defy conventional models of planetary evolution.

Water levels are creeping upward on shorelines across the world, and decision-making systems are not keeping up. One barrier to including sea level rise projections in adaptation plans is limited information on the full range of possible outcomes.

Source: Earth’s Future

Water levels are creeping upward on shorelines across the world, and decisionmaking systems are not keeping up. One barrier to including sea level rise projections in adaptation plans is limited information on the full range of possible outcomes.

Substantial scientific uncertainty exists around how quickly ice sheets could collapse. This uncertainty means high-end sea level rise projections have been particularly tough for coastal planners to incorporate into their risk assessments for critical infrastructure such as nuclear power plants. In the United Kingdom, current official guidance states that planners should consider a worst-case scenario of 1.9 meters of sea level rise by 2100, but recent scientific evidence suggests that worse scenarios are plausible. Given the broad range and large uncertainty surrounding high-end projections, new tools for decisionmakers are sorely needed.

Weeks et al. present a new decisionmaking framework that includes a “decision-game” approach. This decision-game approach involves a time-step based progression through a plausible sea level rise scenario, allowing participants to prime long-term thinking skills, analyze impacts of previous decisions, and test their strategies for adaptation. The new framework, coproduced by the United Kingdom’s Met Office and Environment Agency, also incorporates scientific advances that have taken place since the last major update to high-end sea level rise projections in 2009.

To test their framework, the researchers held a decision-gaming workshop that was attended by consultants, coastal risk management experts, and climate change advisers. The researchers presented a hypothetical U.K. coastal city to the participants and gradually revealed the local sea level change over the 21st century and beyond for a high-end scenario. Participants held nuanced discussions and gained a deep understanding of the ramifications that their adaptation planning decisions would have over time, the researchers report. With widespread deployment, the framework could help coastal communities build resilience against rising waters. The researchers also note that the approach could be adapted to help make decisions about managing other climate hazards in various regions. (Earth’s Future, https://doi.org/10.1029/2025EF006086, 2025)

—Saima May Sidik (@saimamay.bsky.social), Science Writer

Citation: Sidik, S. M. (2025), A new way for coastal planners to explore the costs of rising seas, Eos, 106, https://doi.org/10.1029/2025EO250375. Published on 18 November 2025. Text © 2025. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

About 1.5 million years ago, the mid-depth waters of the tropical Pacific Ocean suddenly grew cooler. The change came rapidly, and it spread across thousands of kilometers.

Before then, Earth’s climate had been relatively stable. Cycles of ice ages and interglacial periods had already begun, but they were shorter, and the tropical Pacific remained warm. Its surface temperature barely changed even as polar ice advanced and retreated.

So how did the waters suddenly become cold?

“We’re usually interested in the mid-depth waters—not the surface, not the deep ocean—because that’s where the music is.”

A new study published in Communications Earth and Environment suggests that the cold water came from the Southern Ocean and traveled northward through ocean tunnels into the tropics. An ocean tunnel, the research explains, describes a “channel for water masses that connects different oceanic and consequently, atmospheric regions.”

“We’re usually interested in the mid-depth waters—not the surface, not the deep ocean—because that’s where the music is,” said Jacek Raddatz, a climate scientist at GEOMAR Helmholtz Centre for Ocean Research Kiel, in Germany, and first author of the study.

“The Pacific is the largest ocean and important for global circulation and climate,” he continued. “That’s why we focused our study on the tropical Pacific.”

Tunnels of Colder, Fresher Water

The researchers analyzed tests of planktonic foraminifera (forams) recovered from a sediment core drilled from the Manihiki Plateau, a submerged ridge in the tropical South Pacific. The plateau is located at the eastern edge of the Western Pacific Warm Pool, the region with the highest ocean temperatures in the world.

The team measured magnesium-to-calcium ratios and oxygen isotope values in tests of two species of forams. One species lived near the surface, and the other lived about 400 meters down. With those values, the scientists reconstructed past temperatures and salinity spanning a period from about 2.5 million to 1 million years ago.

“At the Manihiki Plateau, we see that around 1.5 million years ago, there’s a drop in both temperature and salinity,” said Raddatz.

This timing matched a major growth of Antarctic ice.

The new research indicates cold Antarctic water traveled northward through the Pacific’s mid-depths as a pulse, a process known as ocean tunneling.

“Cold water forms off places like Chile, Peru, and California and slowly sinks. It moves toward the equator beneath the surface,” explained Matt Luongo, a climate scientist and postdoctoral researcher at the University of Washington, in Seattle. He was not involved in the study. “If that water becomes cooler or fresher, then maybe…10 to 20 years later, the equator ends up bringing up cooler water too. That’s basically how ocean tunneling connects distant parts of the ocean.”

Raddatz and his fellow researchers also examined how the cooling was related to Earth’s orbital cycles: eccentricity, or the shape of Earth’s orbit; obliquity, or the angle at which Earth’s axis is tilted with respect to its orbital plane; and precession, or the direction Earth’s axis is pointed.

They found a consistent pattern. “We see the same increase in obliquity-related signals in Antarctic ice volume, in midlatitude temperature reconstructions, and in our salinity record,” Raddatz said. “That led us to conclude that they’re all connected through the same mechanism.”

Raddatz and his colleagues think the cooling may have been an early step toward the period when Earth’s ice ages grew longer and more intense. “We think this might be a first step that led, maybe, to the Mid-Pleistocene Transition.”

Interesting, but Not Definitive

Luongo agreed the study shows that South Pacific waters did chill out and freshen up about 1.5 million years ago and that the source of these changes came from the Southern Hemisphere. The research is “interesting, because it helps explain why the thermocline in the equatorial Pacific is so cold and fresh,” he said.

But he also cautioned against directly linking the changes to Antarctic ice growth. “It’s suggestive of the ice sheet, the wiggles match, but it also could be something else,” said Luongo. “There are a lot of things that can cause freshening of the waters.”

Raddatz and his colleagues plan to extend their work to other ocean basins. They want to add nutrient and carbon measurements to build a fuller picture of how mid-depth waters evolve. “If we understand these variations,” he said, “we can also explain the growth and decline of biodiversity hot spots in the deep sea.”

—Larissa G. Capella (@CapellaLarissa), Science Writer

Citation: Capella, L. G. (2025), Ocean tunneling may have set off an ancient Pacific cooldown, Eos, 106, https://doi.org/10.1029/2025EO250428. Published on 18 November 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Source: Journal of Geophysical Research: Biogeosciences

This is an authorized translation of an Eos article. 本文是Eos文章的授权翻译。

氮是全球环境的重要组成部分，影响着农业、气候、人类健康和生态系统。氮循环的作用已经得到了更广泛的认识，然而用于预测全球环境变化的地球系统模型（ESM）仍然没有将其完全纳入考量。

Kou-Giesbrecht主张在ESM中交互式地纳入完整的氮循环，以解释氮在陆地、海洋和大气之间复杂且相互关联的流动方式。氮直到最近才被纳入一些ESM的陆地模型中，并且仅仅作为初级生产力的限制因素。

氮的作用远不止于植物生长，它还是一种强效温室气体，也是臭氧形成和气溶胶成分的重要驱动因素。野火会释放氮氧化物和氨，导致颗粒物浓度升高；海洋微生物既吸收氮也释放氮。氮向海洋的输出会影响海洋初级生产力，也影响海洋氮的排放，而海水中过量的氮会导致富营养化，即营养物质过剩，从而引发有害藻类大量繁殖。

尽管氮循环在全球范围内都非常重要，但ESM中的许多氮循环组成部分即使被包括在内，也不是完全交互的，有些甚至根本没有被纳入模型；相反，它们只是作为静态输入提供给模型。作者认为，在陆地、海洋和大气之间动态模拟氮循环，将大大缩小我们对地球气候和环境近期演变的认知差距。

为了实现这一目标，我们需要更多的观测数据来更好地建立陆地氮循环的基准模型，并开展实验操作，为氮相关过程提供经验约束。作者指出，这些进展有助于我们理解并实现《科伦坡可持续氮管理宣言》的目标，即到2030年将氮废弃物减少一半，这样每年可以节省1000亿美元，并有助于减缓气候变化，改善生物多样性、粮食安全和公共卫生。(Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2025JG009209, 2025)

—科学撰稿人Nathaniel Scharping (@nathanielscharp)

This translation was made by Wiley. 本文翻译由Wiley提供。

Read this article on WeChat. 在微信上阅读本文。

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The massive 2018 eruption of Kīlauea Volcano on Hawai'i Island lasted for months, destroyed neighborhoods, and was associated with 60,000 earthquakes.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Journal of Geophysical Research: Solid Earth

Giant dyke swarms are networks of long, sheet-like cracks in Earth’s crust that carry molten rock (magma) sideways for hundreds of kilometers. In a new study, Foschi and Cartwright [2025] use shallow, laterally injected sills—thin, horizontal sheets of solidified magma—as natural pressure gauges to reconstruct magma pressure along a 660 kilometers dyke from the Mull volcanic center.

The authors run large Monte Carlo simulations (many randomized model runs) to account for uncertainty and find that magma pressure remained high enough that eruption at the surface should have been possible in many places. Despite that, the dykes did not erupt, and the paper shows the classic ideas of neutral buoyancy (where magma stops rising because it becomes the same density as the surrounding rock) or simple mechanical blockage do not explain this. Instead, field evidence and the pressure reconstructions point to near‑surface cooling by groundwater: when hot magma meets cold water or wet sediment it cools, becomes more viscous (thicker), and stalls before reaching the surface.

This finding matters because it changes how we think about long‑range magma transport and eruption risk: strong subsurface cooling can prevent eruptions even when subsurface pressures are high. The sill‑piezometer approach also offers a practical method for constraining magma pressure in other volcanic systems, improving models of where and how magma moves underground.

Citation: Foschi, M., & Cartwright, J. A. (2025). Constraints on magma pressure distribution during long range lateral propagation of giant radial dyke swarms. Journal of Geophysical Research: Solid Earth, 130, e2025JB031995. https://doi.org/10.1029/2025JB031995

—Nikolai Bagdassarov, Associate Editor, JGR: Solid Earth

Text © 2025. The authors. CC BY-NC-ND 3.0
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In light of the ongoing fifteen-year megadrought in Chile, an international team of researchers, including Francesca Pellicciotti from the Institute of Science and Technology Austria (ISTA), addressed a bold future scenario. Their findings: by the end of the century, the considerably worn-out glaciers will not be able to buffer a similar megadrought. They call for coordinated global climate policies to develop effective water management strategies. The results are published in Communications Earth & Environment.

Researchers at the University of California, Irvine and NASA's Jet Propulsion Laboratory have identified stormlike circulation patterns beneath the Antarctic ice shelves that are causing aggressive melting, with major implications for global sea level rise projections.

The weather patterns that produced some of Europe's most extreme heat waves over the past three decades could prove far more lethal if they strike in today's hotter climate, pushing weekly deaths toward levels seen during the COVID pandemic, according to a study in Nature Climate Change.

An international team of scientists, including a senior researcher at Heriot-Watt University in Edinburgh, Scotland, has uncovered new evidence of ancient wildfires that reshapes our understanding of Earth's turbulent Early Triassic epoch, about 250 million years ago.

SummaryA comprehensive full-waveform inversion model of the seismic velocity, covering nearly the entire tectonic domain of the western Pacific (FWP24) is developed using an optimized many-core version of SPECFEM3D_GLOBE on the New Generation Sunway supercomputer. Taking the global adjoint tomography model GLAD-M25 as the initial model, the three-component seismograms from 1 228 earthquakes recorded at 3 687 stations are employed in iterative gradient-based inversions for three period bands: 40-100 s, 17-40 s, and 10-60 s. A total of 36 iterations are carried out using the conjugate gradient method to update the velocities of horizontally and vertically polarized P-waves and S-waves (Vph, Vpv, Vsh, and Vsv) in the FWP24 model. This process systematically reduces the phase difference between the synthetic and observed seismograms within the phase measurements. Compared with existing region inversion results, the FWP24 model realizes a wider, more continuous, and higher-resolution inversion range, including all subduction zones in the western Pacific (e.g. Kurile-Japan, Izu-Bonin-Mariana, New-Britain-Solomon, New-Hebrides, and Tonga-Kermadec). Furthermore, compared to the initial model, FWP24 reveals more detailed structures particularly in oceanic regions around the Philippine Sea Plate, the Caroline Sea Plate and the Ontong-Java Plateau by applying more seismic data.

SummaryThe ratio R of shear-wave to compressional-wave velocity variations (dlnVs/dlnVp) is a useful physical parameter to study the thermochemical properties of the Earth’s interior. Several approaches have been employed to estimate R (or its inverse 1/R), but they either assume the same local resolution in models of dlnVs and dlnVp or assume the same ray paths for S- and P-phases, while excluding valuable data and overlooking uncertainties. We overcome these issues by characterizing both dlnVs and dlnVp through the Backus-Gilbert based SOLA method to obtain R including its uncertainties. This approach enables us to ensure that dlnVs and dlnVp share the same local resolution, making it possible to compute their ratio through division. In addition, SOLA provides uncertainties on dlnVs and dlnVp, which we propagate into our estimates of R using the Hinkley distribution for dlnVs/dlnVp. When resembling a Gaussian, the Hinkley distribution provides Gaussian uncertainties for R, enabling us to interpret tomographic features as for instance in terms of slab morphology or partial melt with greater confidence. To illustrate our new approach, we use a data set of P- and S-phase onset-time residuals from ISC to infer the velocity anomalies and the ratio R (or 1/R) in South-East Asia between 100 and 800 km depth. As the SOLA method is driven by data uncertainties, we reassess the provided ISC uncertainties using a statistical approach before developing models of dlnVs and dlnVp with their uncertainties. Based on our quantitative model estimates, we argue that a large velocity anomaly below the Sumatra slab, with a value of R over 2.5, is resolved given our data and their uncertainties. However, in contrast to previous work, we do not find evidence for a slab hole under Java. Our proposed approach to obtain R with uncertainties using the Hinkley distribution can be applied to a large range of tomographic imaging settings.

SummaryWe investigate the effect of statistically non-stationary turbulence in the Earth’s outer core on the effective turbulent electromotive force generated by the convectively driven flow of liquid iron and the evolution characteristics of the geomagnetic field. The non-stationarity means that interactions of distinct waves are crucial, and the effect of beat induces a slow time variation of the large-scale electromotive force. This provides an attractive and fairly simple physical mechanism for the random appearance of short-lived geomagnetic excursions and reversals separating long periods of relatively stable field, through non-synchronized evolution of the amplifying α-effect and turbulent diffusion. This implies rare and random appearance of simultaneous suppression of the α-effect and enhancement of diffusion which leads to a sudden magnetic energy drop, i.e. an excursion. The turbulent field of what is termed MAR waves (Magnetic-Archemedean-Rossby) is analysed. The dispersion relation and structure of such waves involving the joint effect of the Lorentz, buoyancy, and Coriolis forces together with curvature of the core-mantle boundary are obtained and utilized for estimation of the non-stationary electromotive force in the core. The solutions for the large-scale dipole possess an Earth-like behaviour, magnitude, and timescales, and the physical mechanism of the process, including identification of two dynamically important parameters, is discussed. Similar ideas concerning the dynamics of waves within the so-called Stratified Ocean at the top of the Core (SOC) were considered in the recent work Mizerski (2025). The SOC is an important but thin, strongly stratified layer near the core-mantle boundary, and here, the possibility of global non-equilibrium dynamo mechanisms is analysed. It is possible that the surface and bulk mechanisms coexist in the core, both adding to the complexity of the observed picture of reversal occurrences.