Feed aggregator

SummaryWe develop a new method for estimating the autocorrelation function (ACF) from segmented data with the assumption of stochastic stationarity. The ACF of a signal is represented as the summation of the cross terms of sub-segments of arbitrary length. To successfully remove undesired transients in the data, this method introduces a correction for the amplitude bias associated with the removal of sub-segments, based on the comparison between the expected stationary signal and the measured signal. The method reconstructs and accesses later lag times, provides finer frequency resolution, obtains a better signal-to-noise ratio, which enables the extraction of detailed temporal or spectral structures from noisy data sets. As an application, we successfully retrieved a spectrum of the Earth’s seismic hum on the vertical component with fine frequency resolution and compared it to synthetic autocorrelation for spatially isotropic and homogeneous excitation by random shear traction at the ocean bottom and random pressure at the Earth’s surface. Although both models can explain the observed fundamental spheroidal modes, shear traction is better at explaining the observed overtones above 3 mHz. From 2 to 3 mHz, the pressure source also contributes to the excitation of the overtones, and the shear traction becomes dominant again below 2 mHz. This new method is anticipated to be effective in extracting valuable information from rare records within the context of extraterrestrial seismology.

SummaryNortheast China, with its complicated regional tectonic evolution, situated within the eastern Central Asian Orogenic Belt, is a key region for understanding lithospheric deformation and mantle dynamics. However, the ongoing debate surrounding its lithospheric structure and evolutionary processes remains, largely attributed to data limitations and methodological constraints. In this study, we integrate topography, geoid height, surface heat flow, and Rayleigh wave phase velocity dispersion curves to conduct a detailed imaging of the lithospheric thermal and compositional structure in Northeast China. We find a significant east-west gradient in lithospheric thickness, ranging from approximately 60 km in the east to 140 km in the west, and a compositional transition in the lithospheric mantle from fertile peridotite in the east to refractory peridotite in the west. By integrating analyses of upper mantle anisotropy and the spatiotemporal distribution of Mesozoic basalts, we argue that the lithospheric delamination and mantle upwelling may have combined to cause the lithospheric thinning in the region. This study highlights the significance of joint inversion of multiple datasets and integrated multidisciplinary analysis.

SummaryTraditional methods for measuring geopotential difference using optical fiber frequency transfer or satellite-based time-frequency transfer, based on general relativity, require the use of two clocks and the calibration of these clocks. Here we present a simplified clock transportation experiment using a single hydrogen clock to measure the geopotential difference between two time-frequency stations, separated by 129 km with a height difference of 1,245 m, by GNSS precise point positioning time-frequency transfer. Taking the reference clock of International GNSS Service (IGS) time as a ‘bridge’, we extract the gravity frequency shift between the two stations by comparing the fractional frequency differences between the hydrogen clock and the ‘bridge’ before and after clock transportation. The determined geopotential difference between the two stations is 12075.9$\pm $118.5 m²/s², which closely aligns with the value computed by the EIGEN-6C4 global gravity field model, with a difference of -78.7 m²/s². These results validate the feasibility of geopotential difference measurements with a single clock and highlight several advantages compared to the dual-clock method: elimination of inter-clock calibration, low operational complexity and equipment cost, high data utilization efficiency but similar precision of geopotential difference measurement. Furthermore, this method can be extended to other similar techniques to measure geopotential differences, provided that they enable users to connect to a stable time-frequency reference.

SummaryShale gas extraction could produce underground stress perturbation and local seismicity, which could put a threat human casualty. The Weiyuan area in the Sichuan province, China, underwent massive gas production and a significant increase of earthquake since 2015. In this study, we focus on human-induced subsurface hydrofracturing, calculate cumulative underground Coulomb-stress changes using a 3D numerical model, and probe the main cause of recent seismic activity in the Weiyuan area based on continuous regional stress/displacement loading. The simulation reveals the regional extent of positive Coulomb stress change with fractures matches the distribution of the moderate and micro seismicity in the past ten years. Background regional tectonic stress in the vicinity of the active fault likely resulted in earthquake preparation within and around the active faults; hydraulic fracturing changes mainly the displacement and stress pattern in the vicinity of the fracturing wells, and enhanced fracturing intensity (fracture volume-to-model volume ratio (θ), causes more obvious difference; faults may be locked prior to fracturing, and even small fracturing intensity may trigger the earthquakes near faults and fracturing wells; the seismic risk will be significantly increased near the two faults and fracturing wells in the next 50 years.

Forests play a central role in the global carbon cycle as trees store carbon in their trunks, branches, roots and leaves. However, climate change and human activities can change the ability of forests to absorb carbon and the annual changes in these carbon stocks are highly variable in space and time around the globe. That's why having continuous observations of the evolution of forest biomass over a long period is important for monitoring this essential climate variable.

After a massive earthquake off the coast of Kamchatka, a peninsula in the far east of Russia, on July 30, 2025, the world watched as the resultant tsunami spread from the epicenter and across the Pacific Ocean at the speed of a jet plane.

Forests cover about 40% of the EU's land area. Between 1990 and 2022, they absorbed around 10% of the continent's man-made carbon emissions. However, the carbon dioxide absorption capacity of forests, also known as carbon sinks, is becoming increasingly weaker.

Source: Journal of Geophysical Research: Planets

Spectacular aurorae dance and shimmer nearly continuously at Jupiter’s poles. These grand displays are driven by energetic particles that are funneled toward the poles within Jupiter’s vast magnetosphere, or the area of space affected by the planet’s magnetic field. These particles then stream down toward the Jovian surface, setting atmospheric molecules aglow. Jupiter’s aurorae occur mainly at ultraviolet wavelengths and are hundreds of times more energetic than Earth’s.

Sometimes, Jupiter’s aurorae grow much brighter for hours or days at a time. Potential causes may involve the solar wind’s influence on the magnetosphere or the dynamics of energetic particles spewed into space by Jupiter’s volcanic moon Io. However, clarifying the solar wind’s role in any one brightening event would require taking simultaneous measurements of Jupiter’s magnetosphere and aurorae and their relationship with the solar wind—a difficult undertaking.

Recently, NASA’s Juno mission has made such simultaneous measurements possible. Giles et al. used data collected by the Jupiter-orbiting spacecraft to study how the gas giant’s ultraviolet aurorae responded when its magnetosphere was temporarily but dramatically compressed to a smaller size on 6 and 7 December 2022. Compression events happen from time to time and are normal, but this one was stronger than almost any previously observed.

Data from two of Juno’s onboard instruments—the Jovian Auroral Distributions Experiment (JADE) and Waves—suggest that as Juno neared Jupiter in its elliptical orbit on 6 December, the spacecraft was overtaken by the outer edge of the shrinking magnetosphere before later reentering it closer to Jupiter.

Additional data from modeling efforts suggest that just as sometimes seen with Earth’s magnetosphere, the extreme compression was caused by a sudden intensification of the solar wind that exerted a powerful squeeze on Jupiter’s magnetosphere.

This squeeze coincided with a major spike in ultraviolet auroral emissions. Another of Juno’s instruments, its ultraviolet spectrograph, measured the aurora’s peak power at this time to be 12 terawatts—6 times its baseline power level.

Given the coincident timing of these rare events, the researchers concluded that the powerful auroral display was likely triggered by the major solar wind shock compressing the magnetosphere. Further research could clarify the mechanisms by which compression can boost the aurora and explore additional processes that could trigger brightening events. (Journal of Geophysical Research: Planets, https://doi.org/10.1029/2025JE009012, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), A solar wind squeeze may have strengthened Jovian aurorae, Eos, 106, https://doi.org/10.1029/2025EO250281. Published on 1 August 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.

Arctic and subarctic soils store a significant proportion of Earth’s carbon. But rising temperatures could drain these soils of nitrogen—a key nutrient. The loss could reduce plant growth, limiting the soils’ ability to store carbon and amplifying global warming, according to a new study.

High-latitude soils store vast amounts of carbon because cold temperatures slow microbial activity. Though plants produce organic matter through photosynthesis, microorganisms can’t consume it fast enough, leading to its accumulation over time. Scientists have long worried that a warmer Arctic would accelerate microbial activity, releasing stored carbon into the atmosphere as carbon dioxide (CO2). But they also hoped that warmer temperatures would stimulate plant growth, which would reabsorb some of the carbon and partially offset these emissions.

The new research shows that the latter scenario is very unlikely because warming causes soils to lose nitrogen, a loss that could inhibit plant growth.

“We didn’t expect to see nitrogen loss.”

The findings come from a decade-long experiment in a subarctic grassland near Hveragerði, Iceland. In 2008, a powerful earthquake altered geothermal water flows in the region, turning previously average patches of soil into naturally heated zones with temperature gradients ranging from 0.5°C to 40°C above previous levels. The event created a unique natural laboratory for observing how ecosystems respond to long-term warming.

Using stable nitrogen-15 isotopes to trace nutrient flows in the landscape, the researchers found that for every degree Celsius of warming, soils lost between 1.7% and 2.6% of their nitrogen. The greatest losses occurred during winter and early spring, when microbes remained active but plants were dormant. During this time, nitrogen-containing compounds such as ammonium and nitrate were released into the soil, but with plants unable to absorb them, they were lost by either leaching into groundwater or escaping into the atmosphere as nitrous oxide, a greenhouse gas nearly 300 times more potent than CO2.

The findings were published in a paper in Global Change Biology.

“We didn’t expect to see nitrogen loss,” said Sara Marañón, a soil scientist at the Centre for Ecological Research and Forestry Applications in Spain and the study’s first author. “The soil’s mechanisms to store nitrogen are breaking down.”

A Leaner, Faster Ecosystem

The researchers also found that warming weakened the very mechanisms that help soils retain nitrogen. In warmer plots, microbial biomass and the density of fine roots—both key to nitrogen storage—were much lower than in cooler plots. Though microbes were less abundant, their metabolism was faster, releasing more CO2 per unit of biomass. Meanwhile, plants struggled to adapt, lagging behind in both growth and nutrient uptake.

“Microbial communities are able to adapt and reach a new equilibrium with faster activity rates,” Marañón said. “But plants can’t keep up.”

“This is a not-so-optimistic message.”

Heightened microbial metabolism initially results in greater consumption of the nitrogen and carbon available in the soil. After 5 or 10 years, however, the system appears to reach a new equilibrium, with reduced levels of organic matter and lower fertility. That shift suggests that warming soils may transition to a permanently less fertile state, making it harder for vegetation to recover and leading to irreversible carbon loss.

Scientists have traditionally thought that as organic matter decays faster in a warmer climate, the nitrogen it contains will become more available, leading to increased productivity, said Erik Verbruggen, a soil ecologist at the University of Antwerp in Belgium who was not involved in the study. “This paper shows that actually, this is not happening.”

Instead, nitrogen is being leached out of the soil during the spring, making it unavailable for increased biomass production. “This is a not-so-optimistic message,” Verbruggen said.

An Underestimated Source of Greenhouse Gases

With Arctic regions warming faster than the global average, this disruption to the nutrient cycle could soon become more apparent. Nitrogen and carbon loss from cold-region soils may represent a significant and previously underestimated source of greenhouse gas emissions—one that current climate models have yet to fully incorporate.

The researchers periodically returned to the warm grassland near Hveragerði, Iceland, to measure nitrogen. Credit: Sara Marañón

The researchers plan to explore the early phases of soil warming by transplanting bits of normal soils into heated areas and also to investigate how different soil types respond to heat. Marañón noted that the Icelandic soils in the study are volcanic in origin and very rich in minerals, unlike organic peat soils common in other Artic regions.

“Arctic soils also include permafrost in places like northern Russia and parts of Scandinavia, and they are the largest carbon reservoirs in the world’s soil,” Verbruggen said. The soils analyzed in this research, on the other hand, were shallow grassland soils. “They are not necessarily representative of all Arctic soils.”

Still, Verbruggen added, the study’s findings highlight the delicate balance between productivity and nutrient loss in these systems.

Soil’s abundant carbon reserves make it a major risk if mismanaged, Marañón said. “But it can also become a potential ally and compensate for CO2 emissions.”

—Javier Barbuzano (@javibar.bsky.social), Science Writer

Citation: Barbuzano, J. (2025), As the Arctic warms, soils lose key nutrients, Eos, 106, https://doi.org/10.1029/2025EO250282. Published on 1 August 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.

Author(s): L. Ansia, P. Velarde, M. Fajardo, and G. O. Williams

Nonthermal photoionized plasmas are now established in the laboratory and require models that treat the atomic processes and electron distribution self-consistently. We investigate the effects of inelastic thermalization in iron under intense x-ray irradiation using the atomic model BigBarT, suited …

[Phys. Rev. E 112, 025201] Published Fri Aug 01, 2025

Author(s): H. P. Le, E. V. Marley, and H. A. Scott

Electron distributions in laser-produced plasmas will be driven toward a super-Gaussian distribution due to inverse bremsstrahlung absorption [Langdon, Phys. Rev. Lett. 44, 575 (1980)]. Both theoretical and experimental evidence suggest that fundamental plasma properties are altered by the super-Gau…

[Phys. Rev. E 112, 025202] Published Fri Aug 01, 2025

Terrestrial plants drove an increase in global photosynthesis between 2003 and 2021, a trend partially offset by a weak decline in photosynthesis—the process of using sunlight to make food—among marine algae, according to a study published in Nature Climate Change.

SummaryIn this study, we compare the usability of a simplified microtremor-based empirical method and a conventional microtremor method based on an inversion analysis of a subsurface velocity structure model for constructing a map of average S-wave velocity (AVS) values. In the simplified (empirical) method, the phase velocities of Rayleigh waves, which can be obtained by processing a microtremor array, at wavelengths of 13, 25, and 40 m are regarded as AVS values from the ground surface to depths of 10, 20, and 30 m (${\overline {Vs} }_{10},{\overline {Vs} }_{20},\ {\rm{and}}\ {\overline {Vs} }_{30}$), respectively. Microtremor array surveys were conducted at 173 observation points within a 15 km × 17 km area east of Aso caldera, Kyushu, Japan (target area). AVS values are obtained by applying the empirical method to the phase velocities obtained at each observation point. The AVS values at an observation point (located near the centre of the target area) with velocity logging data are verified by a comparison with those based on the velocity logging data (i.e. overestimations by 6 per cent at maximum). It is found that for the entire target area, the spatial distribution of the obtained AVS values is consistent with the geological distribution. The AVS values within areas of the Aso-3 ignimbrite are 30–40 per cent larger than those within areas of thick soil and tephra on the strongly consolidated Aso-4 ignimbrite. In addition, the AVS values of the Aso-3 deposits are more than 10 per cent larger than those of the Aso-4 deposits and about 10 per cent smaller than those of geological units older than the Aso-3 deposits. We also apply a conventional (i.e. inversion) method to the phase velocity data at each observation point to obtain a one-dimensional S-wave velocity (Vs) structure model from which we deduce AVS values. The deduced AVS values at the velocity logging point are underestimated by -8 per cent, with differences from the AVS values obtained using the empirical method reaching 13 per cent. The average systematic difference between the two methods is 15 per cent, as determined from a statistical analysis. None the less, a strong correlation is found between the methods, with an average correlation coefficient of 0.94, with no evidence showing that either method is more accurate. The empirical method can be used to construct an AVS map if overestimation is carefully considered. This analysis also reveals that the average maximum survey depths of the one-dimensional Vs structures based on the inversion method are only 23±10 m, making them often insufficient to map ${\overline {Vs} }_{20}$ and ${\overline {Vs} }_{30}$ (the ratios of the available to total numbers of data points are only 60 and 21 per cent, respectively). In contrast, the empirical method can determine ${\overline {Vs} }_{10},{\overline {Vs} }_{20},\ \ {\rm{and}}\ {\overline {Vs} }_{30}$ at more than 80 per cent of all sites. The construction of AVS maps using the empirical method is effective in terms of the simplicity and reliability of planning, observational efficiency, and simplicity of data processing, which support a practical and objective approach to seismic assessments.

SummaryIn this study we obtain 35 903 high-quality P-wave receiver functions from 1737 teleseismic events recorded at 120 dense broadband TanluArray temporary stations deployed in and around the Tanlu fault zone (TLFZ). After station azimuth and sediment correction are made, a detailed Moho depth distribution is obtained by CCP stacking. Our results show a sharp change in the Moho depth across the TLFZ from the west to east, which well corresponds to the surface geological structure. The deepest Moho (38.0 ∼ 40.0 km) occurs beneath the Dabie orogenic belt and the Sulu orogenic belt. The Moho beneath the Luxi uplift, Jiangnan orogenic belt and Jiaodong uplift is deeper (36.0 ∼ 37.0 km), whereas the Subei basin and the southern basin of the South Yellow Sea have a shallow Moho (28.0 ∼ 30.0 km). There is an obvious Moho uplift near Weifang, which corresponds to the Changle ancient volcano on the surface and may be a channel for upwelling of hot mantle material. The Moho is unclear under the fault zone near Tancheng, which is speculated to be a channel for upwelling of hot mantle material. It may be related to upwelling of hot and wet flows in the big mantle wedge above the subducted Pacific slab that is stagnant in the mantle transition zone beneath East Asia, which is a possible cause of the 1668 M8.5 Tancheng earthquake.

A new study shows that natural dust particles swirling in from faraway deserts can trigger freezing of clouds in Earth's Northern Hemisphere. This subtle mechanism influences how much sunlight clouds reflect and how they produce rain and snow—with major implications for climate projections.

Around 800 million years ago, during the Tonian period, the Yangtze Block in South China experienced significant tectonic activity, in which the ancient supercontinent Rodinia broke off from the area that is now South China. This created the Yangtze Block plate, which then collided with the China Ocean Plate, causing an area of subduction—where the oceanic plate slides under the lighter continental plate. This process is known to result in the creation of a string of volcanoes on the surface.

Algal growth is accelerating in lakes across Canada, including those far from human development, and a new study shows that climate change is the primary driver.

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

Lakes that form on top of glaciers on Earth (called supraglacial lakes) have been observed to drain downwards when a fracture forms.  The fracture may further propagate through a process called hydrofracturing, where additional pressure is caused by the weight of the overlying water. 

Europa is a moon of Jupiter with a subsurface ocean under an outer icy lithosphere that is likely tens of kilometers thick. Taking this glacial lake analogy to Europa, Law [2025] investigates whether this process was likely to play a role in perched water bodies in Europa’s icy shell. The perched water bodies, those formed inside of the ice shell, could be created through either convective upwellings in Europa’s icy shell or through an impact to the surface. 

Illustration of scenarios discussed for perched water bodies and how they may evolve over time. Upper row: possible evolution of a perched water body that formed through convection or other in-shell processes. The collapse of the shell above the water may enable downward hydrofacturing by weakening the shell above. Lower panel: possible evolution of a perched water body that formed as a result of an impact, as an alternative way to weaken the upper shell. Credit: Law [2025], Figure 1

The author concludes that downward hydrofracture and drainage of liquid water from perched water bodies on Europa are possible if the overlying ice lithosphere is thin or mechanically weak. Such a condition might occur if there is a perched water body below a broken-up region of crust (called chaos regions on Europa) or shortly after an impact crater forms. 

If hydrofracturing is possible, this may provide a means to transport melt from near the surface of Europa to deeper parts of the icy crust, or potentially all the way to the subsurface ocean.  The movement of melt and other elements or minerals carried with it may affect the habitability of Europa by bringing nutrients and chemical disequilibria to the subsurface ocean.

Citation: Law, R. (2025). Rapid hydrofracture of icy moon shells: Insights from glaciology. Journal of Geophysical Research: Planets, 130, e2024JE008403. https://doi.org/10.1029/2024JE008403

—Kelsi Singer, Associate Editor, JGR: Planets

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.

body {background-color: #D2D1D5;} Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.

515 miles—roughly the distance from Washington, D.C. to Detroit, one-third the length of the Colorado River, and now, the longest lightning bolt ever recorded.

That’s right: A new analysis of satellite data has revealed that a 22 October 2017 storm over the U.S. Midwest created a lightning bolt that reached 829 kilometers (515 miles), from eastern Texas to nearly Kansas City. The record-setting bolt lasted about 7 seconds. 

The record was certified by the World Meteorological Organization (WMO), the weather agency of the United Nations, and entered into their World Weather and Climate Extremes Archive.

Researchers discovered the lightning bolt while analyzing lightning detection data from NOAA’s GOES-16 satellite. They published their findings in the Bulletin of the American Meteorological Society today. 

Imagery from the GOES-16 satellite shows the record-breaking lightning bolt. Red circles mark positively charged subsidiary branches of lightning, and blue circles mark negatively charged subsidiary branches. Credit: World Meteorological Organization, American Meteorological Society, Peterson et al. 2025, https://doi.org/10.1175/BAMS-D-25-0037.1

The 515-mile-long bolt is considered a megaflash, which refers to lightning that reaches at least 100 kilometers (62 miles). Megaflashes extend through the clouds, initiating hundreds of cloud-to-ground bolts along the way. The flash from the 2017 storm created more than 116 cloud-to-ground offshoots seen in the above map as blue and red dots.

 
Related

•  Read the report in the Bulletin of the American Meteorological Society
•  WMO Certifies Megaflash Lightning Record in U.S.A.
•  Longest Lightning “Mega-Flash” Sets a Shocking New Record
 

Less than 1% of storms create megaflash lightning; most flashes reach less than 16 kilometers (10 miles). 

Still, most people don’t realize how far from a storm lightning can strike. “The storm that produces a lightning strike doesn’t have to be over top of you,” Randy Cerveny, a geographer at Arizona State University and coauthor of the new report, said in a press release. 

Historically, scientists have detected lightning using ground-based networks that estimate location and speed based on the time it takes radio signals emitted by lightning to reach antennas. Satellite-based lightning detectors are a relatively recent addition to atmospheric scientists’ toolkit, and allow researchers to detect lightning continuously on continent-scale distances.

The previous record certified by the WMO was a flash over the southern United States and the Gulf of Mexico measured by satellite sensors to be 768 kilometers (477 miles) long. 

“It is likely that even greater extremes still exist, and that we will be able to observe them as additional high-quality lightning measurements accumulate over time,” Cerveny said.

—Grace van Deelen (@gvd.bsky.social), Staff Writer

These updates are made possible through information from the scientific community. Do you have a story idea about science or scientists? We’re listening! Send us a tip at eos@agu.org. 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.

Every day, as the sun sets, billions of small animals make their way from the depths of the ocean to the surface to feed. As the next day begins, these zooplankton swim back down. It's the largest synchronous migration on the planet, responsible for carrying vast amounts of carbon from the ocean surface to the deep.