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Science, Volume 385, Issue 6709, August 2024.

Science, Volume 385, Issue 6709, August 2024.

Performance evaluation of an online monitor based on X-ray fluorescence for detecting elemental concentrations in ambient particulate matter
Ivonne Trebs, Céline Lett, Andreas Krein, Erika Matsumoto Kawaguchi, and Jürgen Junk
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-134,2024
Preprint under review for AMT (discussion: open, 0 comments)
This study explores the effectiveness of the Horiba PX-375 monitor for analyzing the elemental composition of airborne particulate matter (PM). Understanding this composition of PM is important for identifying its sources, assessing potential health risks, and developing strategies to reduce air pollution. The PX-375 monitor proved to be a valuable tool for ongoing air quality monitoring studies and could be particularly useful as pollution levels and sources change in the future.

HSW-V v1.0: localized injections of interactive volcanic aerosols and their climate impacts in a simple general circulation model
Joseph P. Hollowed, Christiane Jablonowski, Hunter Y. Brown, Benjamin R. Hillman, Diana L. Bull, and Joseph L. Hart
Geosci. Model Dev., 17, 5913–5938, https://doi.org/10.5194/gmd-17-5913-2024, 2024
Large volcanic eruptions deposit material in the upper atmosphere, which is capable of altering temperature and wind patterns of Earth's atmosphere for subsequent years. This research describes a new method of simulating these effects in an idealized, efficient atmospheric model. A volcanic eruption of sulfur dioxide is described with a simplified set of physical rules, which eventually cools the planetary surface. This model has been designed as a test bed for climate attribution studies.

Risk-informed representative earthquake scenarios for Valparaíso and Viña del Mar, Chile
Hugo Rosero-Velásquez, Mauricio Monsalve, Juan Camilo Gómez Zapata, Elisa Ferrario, Alan Poulos, Juan Carlos de la Llera, and Daniel Straub
Nat. Hazards Earth Syst. Sci., 24, 2667–2687, https://doi.org/10.5194/nhess-24-2667-2024, 2024
Seismic risk management uses reference earthquake scenarios, but the criteria for selecting them do not always consider consequences for exposed assets. Hence, we adopt a definition of representative scenarios associated with a return period and loss level to select such scenarios among a large set of possible earthquakes. We identify the scenarios for the residential-building stock and power supply in Valparaíso and Viña del Mar, Chile. The selected scenarios depend on the exposed assets.

The effect of slab touchdown on anticrack arrest in propagation saw tests
Philipp L. Rosendahl, Johannes Schneider, Grégoire Bobillier, Florian Rheinschmidt, Bastian Bergfeld, Alec van Herwijnen, and Philipp Weißgraeber
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-122,2024
Preprint under review for NHESS (discussion: open, 0 comments)
Our research investigates the role of anticracks in snowpacks and their impact on avalanche formation, focusing on anticracks due to weak layer collapse. We discovered that slab touchdown on the snow below the weak layer decreases the energy available for crack propagation, potentially leading to a stop of crack propagation. This underscores the importance of mechanical interactions in snowpack stability. Our work offers new insights for enhancing avalanche prediction and mitigation strategies.

Abstract

The earliest Asian summer monsoon onset (SMO) occurs in the Bay of Bengal (BoB), heralding the coming of the rainy season. In late April or early May, the strong sea surface temperature (SST) diurnal variation accompanied by ocean surface warming triggers the SMO. However, this observed diurnal cycle intensity cannot be reasonably simulated by state-of-the-art climate models, resulting in a spurious delayed SMO. To address this issue, the SST diurnal cycle parameterized by a diagnostic sublayer scheme was incorporated into a climate model named FIO-ESM v2.0. The large diurnal amplitude of SST contributes to surface warming and changes atmospheric circulation. Consequently, the high-pressure anomaly at high levels and an inverted trough at low levels promote more convective activity, triggering an earlier SMO. Our findings improve the ability of climate models in simulating the evolution of the Asian monsoon system.

Abstract

Powerful lightning strikes generate broadband electromagnetic signals. At Extremely Low Frequencies (ELF), the signal partly leaks into the ionosphere and produces whistlers that can be detected by satellites. Indeed, the satellites of the European Space Agency (ESA) Swarm Earth Explorer mission can detect those signals during 250 Hz burst-mode acquisition campaigns of their Absolute Scalar Magnetometers (ASM). The dispersion of these whistlers depends on their propagation path and the distribution of ionization in the ionosphere crossed along that path. In this paper, we introduce a technique to derive a new measure of ionosphere electron content, the Total square-Root Electron Content (TREC), using the arrival times of two frequencies of the whistler signal. We validate this approach by using data from ionosondes and from in situ measurements of the electron density at Swarm location. This technique brings new opportunities for sounding the ionosphere in regions poorly observed by other techniques.

Abstract

The tropical arm of Atlantic Multidecadal Variability (AMV) influences climate worldwide, yet the mechanisms generating it remain unclear. Here, we examine experiments with sea surface temperature (SST)-restoring in the extratropical North Atlantic in multiple models and use mixed-layer heat budgets to elucidate the important mechanisms. Our results demonstrate that the tropical AMV is driven by wind-mixed-layer-SST feedback. The evolution has two phases with tropical AMV SST anomalies growing from April to October and decaying from November to March. The amplitude of the growth phase surpasses that of the decay phase, resulting in overall tropical Atlantic warming during positive AMV phases. During summer, positive SST anomalies in the extratropics weaken the trade winds, resulting in a shallower mixed-layer with reduced heat capacity. Subsequent absorption of climatological shortwave radiation in this shallower mixed-layer then causes SSTs to warm, generating the tropical AMV. Importantly, anomalous surface heat-fluxes make modest contributions to tropical AMV in these experiments.

Abstract

In this work, we present a metastable helium lidar system for the measurements of metastable helium He(23S) density in the thermosphere and lower exosphere. This lidar system consists of a high power 1,083 nm pulsed laser, a 1 m aperture laser beam expander, six 1 m aperture receiving telescopes and a superconducting nanowire single-photon detector (SNSPD). This system realizes metastable helium density detection up to 1,000 km. Daily rapid variation of metastable helium density within several hours was measured with a height resolution of 50 km for the first time. It demonstrates the capability of ground-based lidar for continuous height-resolved detection of the atmospheric metastable helium in the height range of 200–1,000 km. This is a promising tool to help study the coupling of neutral and ionized atmosphere in this height range and further providing observation basis for space weather prediction.

Abstract

The closure of an ancient ocean basin via oceanic arc-continent collision has two subduction styles with opposite polarities, which may proceed via subduction polarity reversal (SPR) or a subduction zone jump (SZJ). Interpreting the geometry or kinematic evolution of ancient collisional zones, especially the original subduction polarity, can be challenging. Here we used 2D thermo-mechanical modeling to investigate the dynamic evolution process of SPR versus SZJ. Our modeling predicts different structural, topographic, magmatic, and basin histories for SPR and SZJ, which can be compared against, and help interpret, the geologic record past sites of oceanic closure during collisional orogens. Our results match geologic observations of past collisions in Kamchatka, eastern Russia, and the Banda Arc, eastern Indonesia, and thus our results can help effectively decode the evolutionary history of past arc-continent collisions.

Abstract

To better understand and improve the prediction of the seasonal surface temperature (TS) across the United States, we employed convolutional neural network (CNN) models trained on the Community Earth System Model Version 2 Large Ensemble (CESM2 LENS). We used lagged sea surface temperatures (SST) over the tropical Pacific region, containing the information of the El Niño Southern Oscillation (ENSO), as input for the CNN models. ENSO is the principal driver of variability in seasonal US surface temperatures (TSUS) and employing CNN models allows for spatiotemporal aspects of ENSO to be analyzed to make seasonal TSUS predictions. For predicting TSUS, the CNN models exhibited significantly improved skill over standard statistical multilinear regression (MLR) models and dynamical forecasts across most regions in the US, for lead times ranging from 1 to 6 months. Furthermore, we employed the CNN models to predict seasonal TSUS during extreme ENSO events. For these events, the CNN models outperformed the MLR models in predicting the effects on seasonal TSUS, suggesting that the CNN models are able to capture the ENSO-TSUS teleconnection more effectively. Results from a heatmap analysis demonstrate that the CNN models utilize spatial features of ENSO rather than solely the magnitude of the ENSO events, indicating that the improved skill of seasonal TSUS is due to analyzing spatial variation in ENSO events. The proposed CNN model demonstrates a promising improvement in prediction skill compared to existing methods, suggesting a potential path forward for enhancing TSUS forecast skill from subseasonal to seasonal timescales.

Abstract

We investigate the absolute momentum flux (AMF) and vertical wind variance ρw′2‾ $\left(\rho \overline{{w}^{\prime 2}}\right)$ of gravity waves (GWs) along with intermittencies in the upper troposphere and lower stratosphere (UTLS) during 2017–2022 using the Middle Atmosphere Alomar Radar System at Andøya, Norway (69.30°N, 16.04°E). We categorized the AMF and ρw′2‾ $\rho \overline{{w}^{\prime 2}}$ into different period ranges (30 min–2 hr, 2–6 hr, 6–13 hr, 13 hr–1 day, and 30 min–1 day) to study the significance of short- and long-period waves. The selection of these period bands was based on the boundary conditions of the available spectra: 30 min (Nyquist frequency), 13 hr (inertial period), and 1 day (based on our interest in maximum long-period oscillations). Through the investigation of the AMF and ρw′2‾ $\rho \overline{{w}^{\prime 2}}$, we wish to determine in detail the GW characteristics at northern polar latitudes. Furthermore, it is crucial to assess the intermittency as it considerably influences and alters the GW attributes. Our novel results indicate for both AMF and ρw′2‾ $\rho \overline{{w}^{\prime 2}}$: (a) seasonal variation with minima during summer (May–September); (b) higher magnitude in the upper troposphere (<9.00 km) than the lower stratosphere; (c) short-period components (30 min–2 hr, 2–6 hr) are more intermittent in the entire UTLS; and (d) the long-period components (6–13 hr, 13 hr–1 day) demonstrate lower (higher) intermittency in the upper troposphere (lower stratosphere) in summer implying a plausible wave-filtering mechanism.

Abstract

Earth experienced the strongest geomagnetic storm in 20 years over 10–13 May 2024. The Ap and Dst geomagnetic indices were 273 and −291.94 nT on 11 May. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics satellite observed significant enhancement in thermospheric infrared emission at 15, 5.3, 4.3, and 1.27 μm. On 11 May the daily global power radiated by nitric oxide (NO) at 5.3 μm was 1.41 TW and by carbon dioxide (CO2) at 15 μm was 1.35 TW. These are the largest single day power values observed by SABER in 22 years and the first time the daily power radiated by NO exceeded that of CO2. The total infrared power (above background) radiated during the storm was 2.64 TW (2.28 × 1017 J). Significant enhancement in limb radiance observed at 4.3 μm (to 250 km tangent height) is likely indicative of NO + formation during the storm.

Abstract

The Tibetan Plateau (TP) is suffering from a substantial decline in terrestrial water storage (TWS) in exorheic basins, threatening water resources that are critical for ∼2 billion people downstream. TWS changes are commonly estimated using gravity satellites through observations of the total terrestrial mass storage (TMS) change, with an implicit assumption of a negligible contribution from sediment transport. Through long-term (2002–2017) sediment flux observations in seven headwater basins on the TP, we reveal that the gravity satellite-derived TMS has decreased at a rate of 3.85 ± 0.23 Gt yr−1 in the seven basins, of which 0.35 ± 0.04 Gt yr−1 is contributed by sediment transport. Neglecting this contribution leads to an overestimation of the TWS loss by 10.1 ± 1.3%, equivalent to the annual water demand of an additional 0.62 million people in the surrounding nations. Regionally, the overestimation is surprisingly high in the Indus River and Yarkant River basins, reaching up to 50.8%–77.6%.

Abstract

Antarctic warm extremes impact the cryosphere, with very warm extremes driving surface melt on ice shelves. Here, we analyze temperatures exceeding the 90th percentile and the associated circulation patterns and radiation anomalies. ERA5 reanalysis data show positive geopotential height anomalies related to the occurrence of warm extremes. The highest temperature during warm extremes appears on the western periphery of high-pressure systems, consistent with anticyclonic advection. Temperature anomalies during warm extremes are strongest in winter due to the transport of warm and moist air and a strong meridional temperature gradient. In summer, the weak meridional gradients of top-of-atmosphere downward solar radiation flux and surface air temperature contribute to weak temperature anomalies. Warm extremes are associated with positive longwave radiation anomalies in all seasons, but with negative shortwave radiation anomalies at the surface except during polar night. These relationships are verified by station observations. Our results confirm that Antarctic warm extremes are mostly driven by meridional advection of warm air, and suggest that these warm air masses are predominantly moist and cloudy.

Reliable water vapour isotopic composition measurements at low humidity using frequency-stabilised cavity ring-down spectroscopy
Mathieu Casado, Amaelle Landais, Tim Stoltmann, Justin Chaillot, Mathieu Daëron, Fréderic Prié, Baptiste Bordet, and Samir Kassi
Atmos. Meas. Tech., 17, 4599–4612, https://doi.org/10.5194/amt-17-4599-2024, 2024
Measuring water isotopic composition in Antarctica is difficult because of the extremely cold temperature in winter. Here, we designed a new infrared spectrometer able to measure the vapour isotopic composition during more than 95 % of the year in the coldest locations of Antarctica, whereas current commercial instruments are only able to measure during the warm summer months in the interior.

Abstract

We analyze low-altitude DEMETER spacecraft measurements obtained between 2006 and 2010, complemented by WWLLN lightning location data, to investigate the importance of lightning-generated whistlers for the energetic electron precipitation from the Van Allen radiation belts. We focus, in particular, on the United States region, where a significant seasonal variation in the occurrence of lightning has been observed. We show that both the precipitating electron fluxes and very low frequency wave intensities correlate well with the total lightning occurrence in the region. We further demonstrate that lightning-induced electron precipitation is more significant during periods of low geomagnetic activity compared to periods of high geomagnetic activity and during the nighttime than during the daytime. The energies of precipitating energetic electrons extend up to about 700 keV, roughly in agreement with the cyclotron resonance theory.

Abstract

The geometrical prediction of multiple hydraulic fractures fed from a single fluid source is a major challenge due to transient stress interference among fractures and nonlinear coupling between rock deformation and fluid flow. Here we find that the evolution of multiple hydraulic fractures under isotropic stresses is controlled by a dimensionless toughness, which measures the ratio of the energy dissipated in rock fracturing to that dissipated in viscous fluid flow. The existence of a relation between the dimensionless toughness and the dimensionless length of the arrested fractures is demonstrated by using a bifurcation analysis. The numerical results show that the fractures tend to grow simultaneously in the viscosity-dominated regime, and the scaling remains effective when the number of fractures varies. This study provides a quantitative and efficient tool for predicting the fracture pattern in engineered and natural fracture systems.

Abstract

Progress in locating the X-line on the magnetopause beyond the atypical due south interplanetary magnetic field (IMF) condition is hampered by the fact that the global plasma and field spatial distributions constraining where reconnection could develop on the magnetopause are poorly known. This work presents global maps of the magnetic shear, current density and reconnection rate, on the global dayside magnetopause, reconstructed from two decades of measurements from Cluster, Double Star, THEMIS and MMS missions. These maps, generated for various IMF and dipole tilt angles, offer a unique comparison point for models and observations. The magnetic shear obtained from vacuum magnetostatic draping is shown to be inconsistent with observed shear maps for IMF cone angles in 12.5° ± 2.5° ≤ |θ co | ≤ 45° ± 5°. Modeled maximum magnetic shear lines fail to incline toward the equator as the IMF clock angle increases, in contrast to those from observations and MHD models. Reconnection rate and current density maps are closer together than they are from the shear maps, but this similarity vanishes for increasingly radial IMF orientations. The X-lines maximizing the magnetic shear are the only ones to sharply turns toward and follow the anti-parallel ridge at high latitude. We show the behavior of X-lines with varying IMF clock and dipole tilt angles to be different as the IMF cone angle varies. Finally, we discuss a fundamental disagreement between X-lines maximizing a given quantity on the magnetopause and predictions of local X-line orientations.