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Abstract

Electromagnetic ion cyclotron (EMIC) waves are a key plasma mode affecting radiation belt dynamics. These waves are important for relativistic electron losses through scattering and precipitation into Earth's ionosphere. Although theoretical models of such resonant scattering predict a low-energy cut-off of ∼1 MeV for precipitating electrons, observations from low-altitude spacecraft often show simultaneous relativistic and sub-relativistic electron precipitation associated with EMIC waves. Recently, nonresonant electron scattering by EMIC waves has been proposed as a possible solution to the above discrepancy. We employ this model and a large database of EMIC waves to develop a universal treatment of electron interactions with EMIC waves, including nonresonant effects. We use the Green's function approach to generalize EMIC diffusion rates foregoing the need to modify existing codes or recompute empirical wave databases. Comparison with observations from the electron losses and fields investigation mission demonstrates the efficacy of the proposed method for explaining sub-relativistic electron losses by EMIC waves.

Abstract

Neuromorphic sensors have inherently-fast speeds and low data rates, which potentially make them ideal for the observation of transient sources, such as lightning and sprites. Particularly, for remote observations. In this article, we report the first observations of sprites from the ground with a neuromorphic sensor. These observations are accompanied by measurements with established instruments such as low-light level and high-frame rate cameras. We determine that neuromorphic sensors can capture sprites and determine their duration to an accuracy of roughly 6 ms. Average sprite durations were found to be 55 ms within our data set. We have also ascertained that sprites may be too dim for the neuromorphic sensors to resolve the internal spatiotemporal dynamics, at least without the aid of intensifiers.

Abstract

We perform a comprehensive investigation of the statistical distribution of outer belt electron acceleration events over energies from 300 keV to ∼10 MeV regardless of storm activity using 6-years of observations from Van Allen Probes. We find that the statistical properties of acceleration events are consistent with the characteristic energies of combined local acceleration by chorus waves and inward radial diffusion. While electron acceleration events frequently occur both at <2 MeV at L < 4.0 and at multi-MeV at L > 4.5, significant acceleration events are confined to L > ∼4.0. By performing superposed epoch analysis of acceleration events during storm and non/weak storm events and comparing their geomagnetic conditions, we reveal the strong correlation (>0.8) between accumulated impacts of substorms as measured by time-integrated AL (Int(AL)) and the upper flux limit of electron acceleration. While intense storms can provide favorable conditions for efficient acceleration, they are not necessarily required to produce large maximum fluxes.

Abstract

Several seismic tomographic studies have been carried out to outline the intricate interplay between tectonics and magma uprising at Etna volcano. Most of these studies assume a seismically isotropic crust. Here we employ a novel methodology that accounts for the anisotropic structure of the crust. Anisotropy patterns are consistent with the Etna structural trends, unveiling the depth extent of fault segments. A high-velocity volume, deepening toward the northwest, identifies the subducting foreland units that appear to confine a low-velocity anomaly, interpreted as the expression of magmatic fluids within the crust. A discontinuity, likely tectonic in origin, affects the subducting units and allows magma transfer from depth to the surface. This structural configuration may explain the presence of such a very active basaltic strato-volcano within an atypical collisional geodynamic context.

Abstract

Over recent decades, the southeastern United States (Southeast) has become increasingly well represented by the terrestrial climate proxy record. However, while the paleo proxy records capture the region's hydroclimatic history over the last several centuries, the understanding of near surface air temperature variability is confined to the comparatively shorter observational period (1895-present). Here, we detail the application of blue intensity (BI) methods on a network of tree-ring collections and examine their utility for producing robust paleotemperature estimates. Results indicate that maximum latewood BI (LWBI) chronologies exhibit positive and temporally stable correlations (r = 0.28–0.54, p < 0.01) with summer maximum temperatures. As such, we use a network of LWBI chronologies to reconstruct August-September average maximum temperatures for the Southeast spanning the period 1760–2010 CE. Our work demonstrates the utility of applying novel dendrochronological techniques to improve the understanding of the multi-centennial temperature history of the Southeast.

Abstract

Volcanic aerosols reduce global mean precipitation in the years after major eruptions, yet the mechanisms that produce this response have not been rigorously identified. Volcanic aerosols alter the atmosphere's energy balance, with precipitation changes being one pathway by which the atmosphere acts to return toward equilibrium. By examining the atmosphere's energy budget in climate model simulations using radiative kernels, we explain the global precipitation reduction as largely a consequence of Earth's surface cooling in response to volcanic aerosols reflecting incoming sunlight. These aerosols also directly add energy to the atmosphere by absorbing outgoing longwave radiation, which is a major cause of precipitation decline in the first post-eruption year. We additionally identify factors limiting the post-eruption precipitation decline, and provide evidence that our results are robust across climate models.

Abstract

Atmospheric rivers (ARs) are known to produce both beneficial and extreme rainfall, leading to natural hazards in Chile. Motivated to understand moisture transport during AR events, this study performs a moisture budget analysis along 50 zonally elongated ARs reaching the western coast of South America. We identify the convergence of moist air masses of tropical/subtropical origin along the AR as the primary source of vertically integrated water vapor (IWV). Over the open ocean, moisture convergence is nearly balanced by precipitation. The advection of moisture along the AR, although smaller compared to mass convergence, significantly increases toward the landfalling region. The near conservation of IWV over the open ocean, observed by tracking a Lagrangian atmospheric column along the ARs, is the explanation behind the seemingly tropical origin of ARs in time-lapse visualizations of IWV.

Abstract

Benthic δ18O stacks are the benchmarks by which paleoceanographic data are stratigraphically aligned and compared. However, a recent study found that between 1.8 and 1.9 million years ago (Ma) several Ceara Rise records differed substantially from the widely used LR04 global stack. Here, we use new Bayesian stacking software to construct regional stacks and demonstrate a geographical divergence in benthic δ18O features from 1.8 to 1.9 Ma. The pattern of isotopic stage features observed in the Ceara Rise is widespread throughout the Atlantic and differs notably from Pacific records. We propose that this regional difference in isotopic stages may be the result of relatively strong precession forcing and weaker obliquity forcing between 1.8 and 1.9 Ma. In accordance with the Antiphase Hypothesis, our results highlight a period of apparent sensitivity to regional precession forcing that is masked during most of the 41-Kyr world due to the amplitude modulation of obliquity forcing.

Abstract

Efforts to predict long-term changes in continental runoff at both global and basin scales generally remain ambiguous. Here we use a global runoff reconstruction and a Bayesian statistical method to narrow uncertainties in runoff projections from the latest generation of global climate models. Three representative tropical river basins are used to illustrate the application and showcase the potential for substantial reduction in modeling uncertainty. Yet, results are fairly sensitive to the selected reconstruction thus highlighting the need for reliable and homogeneized gridded runoff data sets or river discharge measurements. Moreover, climate models do not account for water withdrawals, whose effect on observed runoff should also be removed in order to detect and attribute the hydrological effect of climate change. Finally, and more importantly, most models fail at capturing the observed recent decrease in runoff ratio, which may highlight either model deficiencies or increasing water derivation over the selected river basins.

Abstract

Contrasting the extensive research on summer atmospheric rivers (ARs) in the Antarctic Peninsula (AP), winter AR impacts are less understood. This study examines a unique warming event from 1 to 3 July 2023, using in situ winter observations and ERA5 reanalysis. On 2 July, Frei station experienced an extreme warm event with a temperature of 2.7°C and a significant rise in the freezing level, coinciding with winter rainfall. A pressure dipole pattern over the AP, with contrasting circulations over Bellingshausen and Weddell Seas, facilitated an AR, carrying warm, humid air initially from South America/Atlantic and then the southeast Pacific. This shift resulted in anomalous water stable isotope composition in precipitation. Trends suggest a strengthening winter pressure dipole, associated with increased AR frequency and higher temperatures in northern AP. These findings highlight the importance of winter observations in exploring AR impacts, bridging knowledge gaps about winter AR behaviors.

Abstract

The Southeast Tropical Indian Ocean (SETIO), dominated by the Indian Ocean monsoon, is an important source region for strong mesoscale eddies. To date, the impacts of the Indian Ocean monsoon on mesoscale eddies have not been clarified. Here we report on the dipole response of mesoscale eddy formation to monsoon transition in the SETIO, using satellite and reanalysis data sets. During the summer monsoon season, anticyclonic eddies are mainly concentrated north of 12°S, while cyclonic eddies are south of 12°S. This situation reverses during the winter monsoon season. We attribute this dipole feature to the oceanic perturbations and current shear during the different monsoon periods. A geographical boundary along 12°S aligns with meridional changes in eddy potential energy, which delineates the generation and direction of the newly-formed eddies. The hot spot region, rich in eddy energy properties, tends to promote eddy formation and endurance during the monsoon periods.

Abstract

Soils are a major source of nitrogen oxides, which in the atmosphere help govern its oxidative capacity. Thus the response of soil nitric oxide (NO) emissions to forcings such as warming or forest loss has a meaningful impact on global atmospheric chemistry. We find that the soil emission rate of NO in Amazonia from a common inventory is biased low by at least an order of magnitude in comparison to tower-based observations. Accounting for this regional bias decreases the modeled global methane lifetime by 1.4%–2.6%. In comparison, a fully deforested Amazonia, representing a 37% decrease in global emissions of isoprene, decreases methane lifetime by at most 4.6%, highlighting the sensitive response of oxidation rates to changes in emissions of NO compared to those of terpenes. Our results demonstrate that improving our understanding of soil NO emissions will yield a more accurate representation of atmospheric oxidative capacity.

Abstract

Reliable pressure determination is crucial for high pressure and temperature experiments and meaningful interpretation of their geophysical implications. However, nearly all commonly-used pressure scales are secondary in nature, meaning their establishments rely on pre-existing primary shock-compression-based pressure scales, which due to their dynamic compression nature, large uncertainty in peak shock temperature estimation and electronic thermal pressure contribution can yield substantial (∼5%) uncertainties at 1 Mbar conditions. To overcome this intrinsic shortcoming, in this study a self-consistent primary pressure scale of KCl B2 phase was experimentally calibrated up to 85 GPa at ambient temperature using an approach through measuring the acoustic wave velocities and molar volume using Brillouin spectroscopy and Synchrotron X-ray diffraction. Best fitting of thermoelastic parameters based on our experimental results yields V 0 = 32.48 (9) cm3 mol−1, K T0 = 21.33 (70) GPa, K0′ ${{K}_{0}}^{\prime }$ = 4.836 (83), G 0 = 16.83 (237) GPa, G′ = 2.147 (115), γ 0 = 1.92 (11) and θ D0 = 251 (22) K. A KCl B2 phase primary pressure scale based on 3rd order Birch-Murnaghan equation of state (EOS) is established without relying on any external (shock compressed-based) pressure scales and further extended also to high temperatures in combination with thermal pressure effect calculated using Mie‒Grüneisen‒Debye model under quasi-harmonic approximation. Our newly established KCl B2 EOS thus enables accurate pressure determinations at simultaneously high pressure and temperature conditions up to Earth's core-mantle boundary and can serve as a benchmark for calibrating other secondary pressure scales.

Abstract

We present a physical mechanism for generating ∼GeV ions in the Jovian radiation belts. The mechanism is called relativistic turning acceleration (RTA) and involves a special form of nonlinear wave trapping by electromagnetic ion cyclotron (EMIC) waves. Necessary conditions for RTA include a near-equatorial source of EMIC waves, strong wave amplitudes (of the order of a few percent of the background magnetic field strength), and a source of ions of sufficiently high energy. RTA occurs when a fraction of equator-ward moving ions encounters pole-ward moving waves, and, in so doing, becomes entrapped and undergoes a turning motion. The trapped ions then move poleward in the same direction as the waves and eventually become detrapped, but during the turning motion the ions undergo significant acceleration. We rigorously verify this process by providing the theory of nonlinear interactions between relativistic protons and coherent EMIC waves. The RTA process has been previously established for the analogous whistler mode wave-electron interaction. We carry out particle simulations for protons at R = 2R J (where R J  = Jovian radius) interacting with EMIC waves of amplitude B w  = 0.02B 0eq (where B 0eq  = background magnetic field strength at the equator). We confirm that a large portion of test protons experience RTA and that some protons of critical energy 240 MeV can be accelerated to 10 GeV in a period of 5 s. The nonlinear acceleration process is crucially controlled by the trapping condition 0 < S < 1 where S is the inhomogeneity factor.

Abstract

The paper presents the effects of the storm-time prompt penetration electric fields (PPEF) and traveling atmospheric disturbances (TADs) on the total electron content (TEC), foF2 and hmF2 in the American sector (north and south) during the geomagnetic storm on 23–24 April 2023. The data show a poleward shift of the Equatorial Ionization Anomaly (EIA) crests to 18°N and 20°S in the evening of 23 April (attributed to eastward PPEF) and the EIA crests remaining almost in the same latitudes after the PPEF reversed westward. The thermospheric neutral wind velocity, foF2, hmF2, and TEC variations show that TADs from the northern and southern high latitudes propagating equatorward and crossing the equator after midnight on 23 April. The meridional keograms of ΔTEC show the TAD structures in the north/south propagated with phase velocity 470/485 m/s, wave length 4,095/4,016 km and period 2.42/2.30 hr, respectively. The interactions of the TADs also appear to modify the wind velocities in low latitudes. The eastward PPEF and equatorward TADs also favored the development of a clear/not so clear F3 layer in northern/southern regions of the equator.

SummaryUsing forward mantle convection models starting at 140 Ma, and assimilating plate reconstructions as surface velocity boundary condition, we predict present-day mantle structure and compare them with tomography models, using geoid as an additional constraint. We explore a wide model parameter space, such as different values of Clapeyron slope and density change across 660 km, density and viscosity of the thermochemical piles at the core-mantle boundary (CMB), internal heat generation rate, and model initiation age. We also investigate the effects of different strengths of a weak layer below 660 km and weaker asthenosphere and slabs. Our results suggest that slab structures at different subduction zones are sensitive to the viscosity of the asthenosphere, strength of slabs, values of Clapeyron slope and the density and viscosity of the thermochemical piles, while different internal heat generation rates do not affect the slab structures. We find that with a moderately weak asthenosphere (1020 Pas) and strong slabs, the predicted slab structures are consistent with the tomography models, and the observed geoid is also matched well. Moreover, our models successfully reproduce the degree-2 structure of the lower mantle beneath Africa and the Pacific, also known as Large Low Shear Velocity provinces (LLSVPs). A moderate Clapeyron slope of -2.5 MPa/K at 660 km aids in slab stagnation while higher values result in massive slab accumulation at that depth, ultimately leading to slab avalanches. We also find that the convective patterns in the thermal and thermochemical cases with slightly denser LLSVPs are similar, although the geoid amplitudes are lower for the latter. However, with more dense LLSVPs, the slabs cannot perturb them and no plumes are generated. Plumes arise as thermal instabilities from the edges of the LLSVPs, when cold and viscous slabs perturb them. While our predicted plume locations are consistent with the observed hotspot locations, matching the plume structures in tomography models is difficult. These plumes are essential in fitting the finer features of the observed geoid. In longer-duration models, more voluminous subducted material reaches the CMB, which tends to erode the LLSVPs significantly, and yields a poor fit to the observed geoid. Our results suggest that with the presence of a thin, moderately weak layer below 660 km, a slightly dense LLSVP, and Clapeyron slope of -2.5 MPa/K, the velocity anomalies in seismic tomography and the long-wavelength geoid can be matched well. One of the limitations of our models is that the assimilated plate motion history may be too short to overcome arbitrary initial conditions effects. Also, assimilated true plate velocities in our models may not represent the true convective vigor of the Earth.

Abstract

The asthenosphere is commonly defined as an upper mantle zone with low velocities and high attenuation of seismic waves, and high electrical conductivity. These observations are usually explained by the presence of partial melt, or by a sharp contrast in the water content of the upper mantle. Low viscosity asthenosphere is an essential ingredient of functioning plate tectonics. We argue that a substantial component of asthenospheric weakening is dynamic, caused by dislocation creep at the base of tectonic plates. Numerical simulations of subduction show that dynamic weakening scales with the surface velocity both below the subducting and the overriding plate, and that the viscosity decrease reaches up to two orders of magnitude. The resulting scaling law is employed in an apriori estimate of the lateral viscosity variations (LVV) below Earth's oceans. The obtained LVV help in explaining some of the long-standing as well as recent problems in mantle viscosity inversions.

Abstract

The study investigates the rapid intensification (RI) of tropical cyclones (TCs) in the Northwestern Pacific. We found that rapid changes in the maximum wind speed (V max ) and the minimum central pressure (P min ) are not always concurrent. RI cases can be categorized into three types: (a) RIv, only V max strengthens rapidly; (b) RIp, only P min decreases rapidly; (c) RIpv, rapid changes in V max and P min occur concurrently. At the onset of RI, RIv-type TCs exhibit the weakest intensity and the smallest size, with deep convection concentrated in the inner-core region; RIp-type TCs are characterized by the strongest cyclone intensity and the largest outer-core size, with strong convection covering the inner- and outer-core regions; RIpv-type TCs show moderate intensity, size, and convection distribution. For RIpv, significant strengthening of wind profile is concentrated in the inner-core region, while for RIp it is more prominent in the outer-core.

Evaluating post-wildfire debris-flow rainfall thresholds and volume models at the 2020 Grizzly Creek Fire in Glenwood Canyon, Colorado, USA
Francis K. Rengers, Samuel Bower, Andrew Knapp, Jason W. Kean, Danielle W. vonLembke, Matthew A. Thomas, Jaime Kostelnik, Katherine R. Barnhart, Matthew Bethel, Joseph E. Gartner, Madeline Hille, Dennis M. Staley, Justin K. Anderson, Elizabeth K. Roberts, Stephen B. DeLong, Belize Lane, Paxton Ridgway, and Brendan P. Murphy
Nat. Hazards Earth Syst. Sci., 24, 2093–2114, https://doi.org/10.5194/nhess-24-2093-2024, 2024
Every year the U.S. Geological Survey produces 50–100 postfire debris-flow hazard assessments using models for debris-flow likelihood and volume. To refine these models they must be tested with datasets that clearly document rainfall, debris-flow response, and debris-flow volume. These datasets are difficult to obtain, but this study developed and analyzed a postfire dataset with more than 100 postfire storm responses over a 2-year period. We also proposed ways to improve these models.

Simulations of the collection of mesospheric dust particles with a rocket instrument
Adrien Pineau, Henriette Trollvik, Herman Greaker, Sveinung Olsen, Yngve Eilertsen, and Ingrid Mann
Atmos. Meas. Tech., 17, 3843–3861, https://doi.org/10.5194/amt-17-3843-2024, 2024
The mesosphere, part of the upper atmosphere, contains small solid dust particles, mostly made up of material from interplanetary space. We are preparing an experiment to collect such particles during a rocket flight. A new instrument has been designed and numerical simulations have been performed to investigate the airflow nearby as well as its dust collection efficiency. The collected dust particles will be further analyzed in the laboratory in order to study their chemical composition.