Abstract
Relativistic electron fluxes in the outer radiation belt exhibit significant variability during geomagnetic storms and substorms. This study investigates rapid relativistic electron enhancements (REE) in the outer radiation belt throughout the entire Van Allen Probes (RBSP) era from October 2012 to October 2019. Utilizing RBSP measurements, we identify 182 rapid REE events characterized by a factor of greater than two increase in relativistic electron fluxes within a half RBSP orbit (approximately 4.5 hr) at L = 4.5–5.5. Approximately 76% of rapid REE events occur during geomagnetic storms. Rapid REEs during storms are concentrated within the 12-hr period preceding and the 24-hr period following the end of the storm's main phase. Intense REE are more likely found in storm's main phase compared to moderate REE. Sub-relativistic and relativistic electron injections are commonly observed during rapid REE. Substorm activities (AL/AE, MPB index) and convection (AU index) are more intense before and during REE, in contrast to the intervals following REEs. The intensity of rapid REE correlates with the strength of substorms and convection. This comprehensive survey suggests that rapid REEs in the outer radiation belt are likely associated with, but not strictly tied to, geomagnetic storms. Enhanced convection and substorm appear to create favorable conditions for rapid REE. These substorms and enhanced convection are likely linked to favorable solar wind conditions for REEs, as documented in previous studies.
Abstract
The generation of medium-scale traveling ionospheric disturbances (MSTIDs) in the mid-latitude F region ionosphere, particularly in the presence of sporadic E (Es) layers or geomagnetically conjugate features, has been the focus of extensive investigation using both observational and numerical modeling approaches. Recent observations have revealed the occurrence of nighttime MSTIDs over the continental US during storm conditions even without invoking the Es instability. While this phenomenon is considered to be electrified and likely associated with the Perkins instability, the influences of storm-enhanced density (SED), electric fields, and winds on the excitation of nighttime MSTIDs remain a complicated issue and require further quantitative analysis. In this study, we develop a two-dimensional numerical model of the nighttime ionospheric electrodynamics at midlatitudes using the ionospheric ion continuity equation and the electric field Poisson equation to investigate the characteristics of MSTIDs in the SED base region during storm conditions. We demonstrate that the magnetic inclination effect can explain the lower latitude preference of the MSTIDs during magnetic storms, while the development of MSTIDs is primarily influenced by intense storm electric fields under the background ionospheric condition of large density gradients associated with SED. However, the impact of neutral winds on the MSTIDs growth varies, depending on their specific direction determined by the strongly dynamic spatiotemporal variation of the thermosphere and ionosphere during storms. Therefore, the MSTIDs stormtime scenario results from a combination of multiple important factors.
Abstract
The ionospheres of Jupiter's icy moons have been observed by in situ plasma measurements and radio science. However, their spatial structures have not yet been fully characterized. To address this, we developed a new ray tracing method for modeling the radio occultation of the ionospheres using Jovian auroral radio sources. Applying our method to Jovian auroral radio observations with the Galileo spacecraft, we derived the electron density of the ionosphere of Ganymede and Callisto. For Ganymede's ionosphere, we found that the maximum electron density on the surface was 76.5–288.5 cm−3 in the open magnetic field line regions and 5.0–20.5 cm−3 in the closed magnetic field line region during the Galileo Ganymede 01 flyby. The difference in the electron density distribution was correlated with the accessibility of Jovian magnetospheric plasma to the atmosphere and surface of the moons. These results indicated that electron-impact ionization of the Ganymede exosphere and sputtering of the surface water ice were effective for the producing Ganymede's ionosphere. For Callisto's ionosphere, we found that the densities were approximately 350 and 12.5 cm−3 on the night side hemisphere during Callisto 09 and 30 flybys, respectively. These results combined with previous observations indicated that atmospheric production through sublimation controlled the ionospheric density of Callisto. This method is also applicable to upcoming Jovian radio observation data from the Jupiter Icy Moon Explorer, JUICE.
SummaryReducing the gap between geophysical inversion and geological interpretation can be achieved by integrating geological modelling into geophysical inversion. For this, we use a generalised, iterative level-set gravity inversion scheme in which geological units are deformed automatically. During the inversion process, a regularisation term is defined using automated geological modelling to account for geological data and principles. This provides model-dependent geological constraints and encourages geological realism throughout inversion. To alleviate the dependence on the starting model and consider the possibility of features unseen by direct observations, an automated geophysical data-driven method is proposed to insert new rock units in the model. Uncertainty quantification is achieved through the null space shuttle algorithm, which is used to generate a series of alternative models that are consistent with geophysical data. This methodology is applied to assess the uncertainties of a pre-existing 3D crustal-scale geological model of the Western Pyrenean orogeny (France, Spain). The area is characterized by a positive gravity anomaly generally attributed to the presence of a shallow mantle body. The impact of variations in shape and density of key crustal and mantle features is investigated. Different scenarios are explored in 3D space to produce a range of viable, relatively simple crustal scale models of the area. This application demonstrates the capability and potential of this approach to evaluate alternative interpretations of geophysical data. The results show the plausibility of scenarios with a shorter subducted Iberian lower crust and a denser Axial Zone than in the pre-existing model.
SummaryThe 2022 Har Lake earthquake sequence, which began in January 2022 and lasted for ∼70 days, jolted the Har Lake area, which is located in the western Qilian Shan, northeastern Tibetan Plateau. Two Mw>5.5 earthquakes occurred during the earthquake sequence, among which the March 25 Mw5.8 event is considered the largest event recorded in the area. However, determining the seismogenic faults of the earthquake sequence, as well as the detailed rupture features, is difficult due to the lack of geological data and near-field seismological observations. In this study, we use Sentinel-1 synthetic aperture radar (SAR) data to obtain the coseismic deformation field, identify possible ruptured faults and associated fault geometries, and further estimate detailed coseismic slip models of the two Mw>5.5 earthquakes. The results show that the January 23 Mw5.6 earthquake (Earthquake A) occurred on a N15°W-trending dextral-slip fault with a dip angle of ∼61°. For the March 25 Mw5.8 earthquake (Earthquake B), the interferometric synthetic aperture radar (InSAR) data can be described by either an ∼N–S-trending dextral-slip fault or an ∼E–W-trending sinistral-slip fault. The ∼N–S-trending fault better describes the aftershock distribution, while the ∼E–W-trending model is more consistent with the regional geological setting. We suggest that the complex coseismic ruptures in the multiple-fault system are driven by widespread NE–SW-trending compression in the western Qilian Shan. This study demonstrates the importance of integrating geodetic and seismological observations to capture the full complexity of moderate earthquakes and further suggests potential seismic hazards in the Har Lake area.
SummaryClay minerals are extensively used in a wide range of applications. In particular, clay-bearing formations are considered as suitable radioactive waste repository. Electrical resistivity tomography is an appropriate tool to monitor the properties of clay-bearing locations. However, an inherent drawback of a conventional resistivity survey is its ambiguity in distinguishing between the effects of groundwater salinity, clay content, and porosity. A discrimination can be achieved on the basis of the induced polarization method that provides a complex conductivity. The main purpose of this study is the investigation of the complex conductivity of clay samples with a special focus on the contribution of surface conductivity produced by an excess of ions in the electrical double layer coating the solid particles. Six clay mixtures were selected that include an almost pure kaolinite sample, a sample consisting of a mixture of kaolinite, illite, and smectite, a crushed saponite breccia, a Ca-bentonite sample, and two illite clay samples. Besides the enriched kaolinite, the other samples are natural geomaterials that contain more than 40 weight per cent clay minerals. The mineralogical compositions of the samples were determined by quantitative X-ray diffraction analysis. The clay powder was mixed with a varying volume of sodium chloride solution to get plastic state clay samples with varying water content. The samples were investigated by the spectral induced polarization method in a frequency range between 1 mHz and 1 kHz. The resulting complex conductivity spectra indicate a decrease of the real part of the electrical conductivity with rising water content for the illite, bentonite and saponite breccia samples. The overall conductivity of these clay samples is dominated by their surface conductivity. In contrast, the electrical conductivity of kaolinite and kaolinite-illite mixture does not show any significant changes with the water content. For all samples, the imaginary part of electrical conductivity increases at low water content. The real part of the surface conductivity indicates a linear dependence on the volumetric clay content. The slope of this linear relationship can be used to distinguish the types of clay. The ratio between imaginary conductivity and surface conductivity, which decreases with increasing clay content, proves to be a suitable parameter that characterizes the connectivity of clay aggregates in the sample. The surface conductivity of the pure kaolinite sample has been determined in an additional multi-salinity experiment. The resulting surface conductivity is in good agreement with the experiment of varying water content. The multi-salinity experiment has shown that the resulting petrophysical parameters depend on the procedure of sample packing, which may lead to anisotropy. The effect of anisotropy is attributed to the alignment of the plate-like kaolinite particles in the course of the packing and consolidation procedure.
Every day, women are working on frontier science in Earth's unforgiving polar environments. Our study, published today in PLOS Climate, investigated what their experiences are actually like.
A team of geoscientists have analyzed the composition of rocks in the Eifel, a volcanic region encompassing parts of western Germany, Belgium and Luxembourg. They discovered that it differs depending on the region.
Terrestrial water bodies (WBs), including lakes, ponds, and reservoirs, are pivotal components of Earth's hydrological and biogeochemical systems, offering vital ecosystem services. Yet, conventional studies often overlook small water bodies or overstate their prevalence. This is particularly true for regions like the Qinghai-Xizang Plateau, which is home to numerous alpine lakes. In these areas, human impact is minimal, and the number of small water bodies is increasing due to glacier melting.
By testing core samples, an international team of geoscientists and geologists has found evidence that much of what is now West Antarctica was a river delta or estuary 34 to 44 million years ago. Their findings are published in the journal Science Advances.
California's earthquake early-warning system is getting a seismic upgrade, one that will allow residents to receive more timely alerts about shaking from an incoming megaquake.
Abstract
To ensure the robustness of both civilian and military infrastructure, it is important to protect electric power grids, smart grids, and other electrotechnologies from known and possibly as-of-yet unknown space weather hazards. Space weather can generate intense geoelectric fields at the surface of the Earth, as well as large voltage gradients across long distances of the Earth. These voltage gradients can lead to geomagnetically induced currents (GICs), which are known to produce hazards to electric power grids. The finite-difference time-domain (FDTD) method is a powerful and versatile method that has already been applied to the study of geoelectric fields. The advantages of FDTD over other methods are that it can account for more geometrical complexities and realistic time waveforms and that it directly solves for geoelectric fields. Snell's Law predicts that any electromagnetic waves incident on the ground should essentially propagate straight downwards into the low resistivity ground. For this reason, vertical FDTD grid resolutions of 1/3 of a skin depth were usually chosen, while the horizontal grid resolution was relaxed. We find, however, that there is another important consideration for choosing an FDTD grid resolution applied to real-world scenarios: localized field variations due to currents generated by ground features. It turns out the grid resolution requirements are much stricter when taking this physics into account.
Humanity is ignoring major planetary vital signs as atmospheric carbon dioxide levels soar to all-time highs and Earth records its 12th consecutive month of record-breaking heat, international climate officials warned this week.
Addressing class imbalance in soil movement predictions
Praveen Kumar, Priyanka Priyanka, Kala Venkata Uday, and Varun Dutt
Nat. Hazards Earth Syst. Sci., 24, 1913–1928, https://doi.org/10.5194/nhess-24-1913-2024, 2024
Our study focuses on predicting soil movement to mitigate landslide risks. We develop machine learning models with oversampling techniques to address the class imbalance in monitoring data. The dynamic ensemble model with K-means SMOTE (synthetic minority oversampling technique) achieves high precision, high recall, and a high F1 score. Our findings highlight the potential of these models with oversampling techniques to improve soil movement predictions in landslide-prone areas.
Regional modelling of extreme sea levels induced by hurricanes
Alisée A. Chaigneau, Melisa Menéndez, Marta Ramírez-Pérez, and Alexandra Toimil
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-100,2024
Preprint under review for NHESS (discussion: open, 0 comments)
Tropical cyclones drive extreme sea levels, causing large storm surges due to low atmospheric pressure and strong winds. This study explores factors affecting the numerical modelling of storm surges induced by hurricanes in the tropical Atlantic. Two ocean models are compared and used for sensitivity experiments. ERA5 atmospheric reanalysis forcing generally improves storm surge estimates compared to parametric wind models. Including ocean circulations reduces errors in storm surge estimates.
Author(s): Qianyi Ma, Jiaxin Liu, Zhuo Pan, Xuezhi Wu, Huangang Lu, Zhenan Wang, Yuhui Xia, Yuekai Chen, Kyle G. Miller, Xinlu Xu, and Xueqing Yan
Collision between relativistic electron sheets and counterpropagating laser pulses is recognized as a promising way to produce intense attosecond x rays through coherent Thomson backscattering (TBS). In a double-layer scheme, the electrons in an ultrathin solid foil are first pushed out by an intens…
[Phys. Rev. E 109, 065205] Published Thu Jun 06, 2024
Author(s): Amin Barzegar, Firas Hamze, Christopher Amey, and Jonathan Machta
Annealing algorithms such as simulated annealing and population annealing are widely used both for sampling the Gibbs distribution and solving optimization problems (i.e., finding ground states). For both statistical mechanics and optimization, additional parameters beyond temperature are often need…
[Phys. Rev. E 109, 065301] Published Thu Jun 06, 2024
