Feed aggregator

Abstract

The understanding of the velocity structure and basement morphology within the basin is crucial for seismic hazard mitigation and the study of basin evolution. To explore the intricate structure of the Binchuan Basin in western Yunnan, China, we deployed a linear dense array in the northern region of the Binchuan Basin, with inter-station distance ranging from 50 to 100 m. We propose a novel receiver function processing workflow. Initially, we extracted coherent receiver functions based on the dense array, followed by a inversion of basement morphology, S-wave velocities, and sedimentary layer's average V p /V s ratio jointly with frequency-dependent teleseismic apparent shear velocity and receiver function waveforms. The results show that S-wave velocity anomalies correspond to the unconsolidated sediments. The thickness of the sedimentary layer ranges from ∼0.5 to ∼0.75 km. The basement morphology suggests the basin is controlled by normal faults. Additionally, intra-basin faults displayed higher fault displacement to length ratios (∼0.27) than most isolated normal faults (10−3–10−1), which may result from accumulated fault displacement due to interactions between fault segments. These results emphasize the significant role of N–S trending intra-basin faults in basin evolution, suggesting that micro-block rotations and transitional movements within the Northwestern Yunnan Rift Zone are primary mechanisms shaping the Binchuan Basin. We further proposed a multi-stage model for the evolution of the Binchuan Basin. The robustness testing validates that the proposed processing flow is an effective approach to comprehensively image the basin velocity structure and the basement morphology.

Abstract

This study uses a unique combination of geostationary and low-Earth orbiting satellite-based lightning and precipitation observations, respectively, to examine the evolution of deep convection during the tropical cyclone (TC) lifecycle. The study spans the 2018–2021 Atlantic Basin hurricane seasons and is unique as it provides the first known analysis of total lightning (intra-cloud and cloud-to-ground) observed in TCs through their extratropical transition and post-tropical cyclone (PTC) phases. We consider the TC lifecycle stage, geographic location (e.g., land, coast, and ocean), shear strength, and quadrant relative to the storm motion and environmental shear vectors. Total lightning maxima are found in the forward right quadrant relative to storm motion and downshear of the TC center, consistent with previous studies using mainly cloud-to-ground lightning. Increasing environmental shear focuses the lightning maxima to the downshear right quadrant with respect to the shear vector in tropical storm phases. Vertical profiles of radar reflectivity from the Global Precipitation Measurement mission show that super-electrically active convective precipitation features (>75 flashes) within the PTC phase of TCs have deeper mixed phase depths and higher reflectivity at −10°C than other phases, indicating the presence of more intense convection. Differences in the net convective behavior observed throughout TC evolution manifest in both the TC-scale frequency of lightning-producing cells and the intensity variations amongst individual convective cells. The combination of continuous lightning observations and precipitation snapshots improves our understanding of convective-scale processes in TCs, especially in PTC phases, as they traverse the tropics and mid-latitudes.

Abstract

Earth possesses a Poincaré mode called Free Core Nutation (FCN) due to the misalignment of the rotation axes of the mantle and fluid outer core. FCN is the primary signal in the observations of Celestial Pole Offsets (CPO) and maintained by geophysical mechanisms that are yet to be understood. Earlier studies suggested an origin in Atmospheric Angular Momentum (AAM)—and to a lesser degree Oceanic Angular Momentum (OAM)—but discrepancies between these geophysical excitations and the geodetic (CPO-based) excitation were too large to reach definite conclusions. Here we use newly calculated, 3-hourly AAM and OAM series for the 1994–2022 period, in conjunction with the latest CPO series from the International Earth Rotation and Reference Systems Service (IERS 20 C04 series), to demonstrate a markedly lower power ratio (∼ ${\sim} $4.6) of geophysical over geodetic excitation at the FCN frequency compared to previous works (ratio ∼ ${\sim} $10). Among all excitation sources, the AAM pressure term exhibits the highest coherence (0.56) and correlation (0.48) with the geodetic excitation, whereas the coherence with OAM is smaller by a factor of 3. Similar analyses using existing angular momentum series give comparable, albeit smaller coherence and correlation results. We attribute the relevant AAM pressure term signal to Northern Hemispheric landmasses and further show consistent temporal variations in the amplitude of geophysical and geodetic excitations around the FCN band. Our results thus corroborate evidence for large-scale atmospheric mass redistribution to be the main cause of continuous FCN excitation.

Abstract

Secondary organic aerosol (SOA) formed through the atmospheric transformation of organic vapors constitutes a significant portion of fine particulate matter or PM2.5. While recent laboratory studies underscore the importance of intermediate-volatility organic compounds (IVOCs) as key precursors to SOA, field observations that recognize the role of both volatile organic compounds (VOCs) and IVOCs in SOA formation remain scarce. In this study, we conducted concurrent measurements of VOCs and IVOCs in ambient air at urban and suburban sites in Guangzhou during a PM2.5 pollution event in winter 2021. The results reveal that between 12:00–15:00 local time, the photochemically adjusted initial concentrations of VOCs at both sites were approximately 7 times higher than that of IVOCs. However, the SOA formation potential (SOAFP) of primary hydrocarbon IVOCs exceeded that of VOCs by over 3–4 times. Receptor modeling results further indicated that while ship emissions contributed to less than 10% of the C2–C22 primary hydrocarbons concentration (VOCs + primary carbonaceous IVOCs), they accounted for the most significant source (approximately 40%) of SOA formation. This study highlights the substantial role of IVOCs in SOA formation and emphasizes the importance of future PM2.5 pollution control measures targeting major IVOCs contributors, such as ship emissions in harbor cities.

Abstract

We investigated the crustal radial anisotropy in the eastern South China Block (ESCB) with the F-J multimodal ambient noise tomography. Well corresponding to widespread mid-crustal low-velocity zones in the VSV ${V}_{SV}$ model, a pronounced mid-crustal channel of positive radial anisotropy is revealed. In the Cathaysia Block, it may origin from sub-horizontally aligned quartz induced by extension and correspond to the phase transition of α $\alpha $ to β $\beta $ quartz. In other areas, while, it may be relevant to other well-aligned minerals. This positive mid-crustal radial anisotropy channel not only provides the solid evidence for dominative extensional deformation since late Mesozoic, but also may indicate an important detachment surface, contributing much to the early Mesozoic magmatism in the ESCB.

No abstract is available for this article.

Abstract

The properties of the first kilometers of the Martian atmospheric Planetary Boundary Layer have until now been measured by only a few instruments and probes. InSight offers an opportunity to investigate this region through seismoacoustics. On six occasions, its seismometers recorded short low-frequency waveforms, with clear dispersion between 0.4 and 4 Hz. These signals are the air-to-ground coupling of impact-generated infrasound, which propagated in an low-altitude atmospheric waveguide. Their group velocity depends on the structure of effective sound speed in the boundary layer. Here, we conduct a Bayesian inversion of effective sound speed up to 2,000 m altitude using the group velocity measured for events S0981c, S0986c and S1034a. The inverted effective sound speed profiles are in good agreement with estimates provided by the Mars Climate Database. Differences between inverted and modeled profiles can be attributed to a local wind variation in the impact→station direction, of amplitude smaller than 2 m/s.

Abstract

Nitrogen (N) is extremely depleted in the bulk silicate Earth (BSE). However, whether the silicate magma ocean was as N-poor as the present-day BSE is unknown. We performed multi-anvil experiments at 20 GPa and 1,673−2,073 K to determine the dihedral angle of Fe−Ni−N alloy melt in ringwoodite matrix to investigate whether percolation of Fe-rich alloy melt in the solid mantle can explain N depletion in the BSE. The dihedral angles ranged from 112° to 137°, surpassing the wetting boundary. Our experiments suggest that N removal from the mantle by percolation of Fe-rich alloy melt to the Earth's core is unlikely. Therefore, besides N loss to space during planetesimal and planetary differentiation, as well as its segregation into the Earth core, the stranded Fe-rich metal in the deep mantle could be a hidden N reservoir, contributing to the anomalous depletion of N in the observable BSE.

Abstract

The effect of modified equator-to-pole temperature gradients on the jet stream by low-level polar warming and upper-level tropical warming is not fully understood. We perform aquaplanet simulations to quantify the impact of different sea surface temperature distributions on jet stream strength, large wave amplitudes and extreme waviness. The responses to warming in the waviness metrics Sinuosity Index and Local Wave Activity are sensitive to the latitude range over which they are calculated. Therefore, we use a latitude range that accurately represents the position of the jet. The uniform warming scenario strengthens the jet and reduces large wave amplitudes. Reductions in meridional temperature gradients lead to weakened mid-latitudinal jet strength and show significant decreases in large wave amplitudes and jet stream waviness. These findings contradict the mechanism that weakened jet streams increase wave amplitudes and extreme jet stream waviness. We conclude that weakened jet streams do not necessarily become wavier.

Abstract

The growing demand for advanced wireless communication, high-resolution imaging, and innovative medical applications in the Terahertz (THz) frequency range has driven remarkable developments in meta-surface-based antennas. This comprehensive review delves into the cutting-edge advancements, novel designs, and practical applications of meta-surfaces in the THz spectrum. The review begins by exploring the materials employed in meta-surfaces and their crucial role in achieving efficient THz operation. It delves into the realm of polarization diversity, revealing innovative approaches to harnessing the potential of meta-surfaces for polarization control and conversion. A key area of focus is beam-steering technology, with a thorough investigation into beam-steering techniques that have significant implications for enhancing wireless communication, high-resolution imaging, and the internet of things. The paper highlights the potential of these techniques in addressing real-world challenges and advancing THz technology. Furthermore, this review provides an in-depth examination of the innovative antenna designs tailored for THz applications, shedding light on their characteristics and benefits. It also explores the exciting possibilities of THz technology within the medical field, including precise bio sensing and cancer cell detection.

No abstract is available for this article.

No abstract is available for this article.

Abstract

During geomagnetic storms, the capabilities of current climate models in predicting ionospheric behavior are notably limited. A data assimilation tool, Estimating Model Parameters Reverse Engineering (EMPIRE), implements a Kalman filter to ingest electric density rate correcting the background electric potential and neutral wind. For the baseline setup, or case (1), EMPIRE ingests electron density global map output from the Ionospheric Data Assimilation 4-Dimensional (IDA4D) algorithm. In this work, a new augmentation method is evaluated in which ion drift measurements are also assimilated into EMPIRE. The ion drift measurements used in the new augmentation method are obtained from Super Dual Auroral Radar Network (SuperDARN) sites in the mid-to-high latitude region of the northern hemisphere. Cases (2) and (3) are set up for evaluating the impacts from ingesting different types of observations: SuperDARN fit and grid data, respectively. Six independent data sources are used as validation data sets to compare outcomes with or without ingesting ion drifts. One is the vector ion velocities derived from the Millstone Hill Incoherent Scatter Radar (MHISR) and a second is the vertical drift from Arecibo site. The other four are SuperDARN ion velocity grid data from Saskatoon, Kapuskasing, Christmas Valley West, and Hokkaido East. Results show improvements in performance at mid-latitudes by augmenting electron density rates with 3D spatially distributed line-of-sight ion drift measurements, with negligible improvements to low and high latitude estimations. The lack of improvement at high-latitudes is attributed to the increase in EMPIRE ion drift error poleward of 60° magnetic.

Abstract

In urban canyons, the reflections and obstructions of Global Navigation Satellite System (GNSS) signals frequently lead to significant errors in measurements, the number of which can be larger than that of the correct measurements. This leads to a severe degradation of GNSS performance in urban canyons. Various fault detection and exclusion (FDE) algorithms have been developed to cope with these outliers caused by multipath effects. Most of these FDE algorithms check the consistency among measurements. However, in urban canyons, their effectiveness is significantly compromised by the lack of fault-free measurements. There is an urgent need to develop new constraints for enhancing GNSS FDE performance. In recent years, the advent of Chip-Scale Atomic Clock (CSAC), known for their affordability and high frequency stability, offers a promising solution for accurately predicting receiver clock errors. Additionally, using city maps to establish height constraints is another way to increase redundancy. The purpose of this study is to improve the GNSS positioning accuracy in urban canyons with the aid of CSAC and city map data. A novel FDE algorithm is developed to search for positions through the constraints of height and receiver clock. Extensive tests were conducted in urban canyons to evaluate the performance of the system. Results showed that the positioning accuracy can be improved from tens of meters to less than 6 m.

Nature Geoscience, Published online: 10 September 2024; doi:10.1038/s41561-024-01509-y

Clinopyroxene offers clues about the inner workings of volcanic systems, as Teresa Ubide explains. Its ability to track where and when magma is stored may also help forecast eruptions.

Nature Geoscience, Published online: 10 September 2024; doi:10.1038/s41561-024-01544-9

Sand is an overlooked resource and is being depleted at an alarming rate. Improved management of sand extraction and consumption is imperative to protect sand resources and reduce the impacts of extraction.

Nature Geoscience, Published online: 10 September 2024; doi:10.1038/s41561-024-01531-0

Urgent need for greater earthquake resilience in continental Asia

Author(s): Andrey V. Zobnin, Andrey M. Lipaev, Roman A. Syrovatka, Alexandr D. Usachev, Vadim N. Naumkin, Oleg F. Petrov, Markus H. Thoma, Oleg V. Novitsky, and Sergey N. Ryzhikov

Fragmentation of a suspension of micron-sized plastic microparticles and their contraction into dense globules was experimentally obtained in a gas discharge plasma, when the plasma density was deliberately and abruptly increased. The globules took up spherical shapes 0.14–1.1 mm in diameters and co…

[Phys. Rev. E 110, 035203] Published Mon Sep 09, 2024

Abstract

The radio frequency interference (RFI) in global navigation satellite system (GNSS) signals has recently received much attention in the GNSS community because of frequent jamming issues. The carrier-to-noise density ratio (C/N0) is one of the common parameters to indicate the signal quality. In this work, we propose a real-time RFI analysis based on windowing and normalization of C/N0 observations. Specifically, the percentage of RFI values are analyzed based on the modified RFI detection. The steps to analyze the RFI levels (low, medium, high) are highlighted. In addition, we analyzed the occurrences of local RFI effects in areas surrounding the Suvarnabhumi International Airport as well as remote areas. We validate the modified RFI detection by using the GNSS reference stations at the urban, suburban, and outside the capital city in Thailand. The user positioning errors with the high (severe) RFI levels are investigated based on the single point positioning (SPP) and real-time kinematics (RTK). From the experimental simulations, the high RFI levels at the urban are higher than those at the suburban. As expected, the statistical analysis covering COVID-19 (2019 to 2023) shows that the high RFI levels in June 2023 (post COVID-19) are more than those in June 2020 and 2021 (lockdown COVID-19) by about twofold. Additionally, the SPP positioning errors with the medium/high RFI levels are clearly seen. There are more floating solutions in the RTK system in the year with more RFI presence.

Nature Geoscience, Published online: 09 September 2024; doi:10.1038/s41561-024-01511-4

Large-ensemble simulations suggest that strong regional trends in precipitation and temperature extremes will be common over the next two decades, even under stringent mitigation measures.