Feed aggregator

Abstract

Crustal deformation and hydrothermal percolation related to the India-Asia collision have caused extensive remagnetization of the Tethyan Himalaya Terrane (THT). The present work identified three phases of regional remagnetization during 62.3–50.0 Ma for the east-central THT. Consequently, a model of three-stage India-Asia collision was proposed. The east-central THT first collided with the southward migrated southern margin of the Lhasa Terrane (LT) at 5.4 ± 0.9°N during 62.3–60.9 Ma. Subsequently, the THT continuously moved northward and pushed the southern margin of the LT back to its original position prior to the initiation of fore-arc and back-arc extension on both sides of the Gangdese magmatic arc. Since the final suturing of the THT with Asia at ∼10°N during 59.8–58.0 Ma, the east-central THT remained stationary until India collided with it at 10.9 ± 5.1°N at ∼50.0 Ma.

Abstract

Climatic impacts of historical volcanism are principally tied to the eruption size, while observation versus model discrepancies have been commonly attributed to the uncertainties in paleo-reconstruction or malpresentation of volcanic aerosols in models. Here we present convergent evidence for significant compensation effect of ocean latent heat (LH) in balancing the tropical volcanic-induced heat loss, by introducing an effective perturbation ratio which is found to decrease with increasing eruption magnitude. Four LH compensation hot spots overlapping with the trade wind regions are identified, together with three western boundary currents regions with intensified LH loss. Comparison between the 1258 Samalas and 1452 Unidentified eruptions suggests considerable modulation of the concurring El Nino-Southern Oscillation on LH anomaly, which is further verified by CESM large ensemble sensitivity experiments. This study depicts how the interplay between the ocean and the atmosphere could contribute to the overall resilience of the climate system in the face of volcanic disturbances.

Abstract

There is ample evidence for ice layers and lenses within glacial firn. The standard model for ice layer formation localizes the refreezing by perching of meltwater on pre-existing discontinuities. Here we argue that even extreme melting events provide insufficient flux for this mechanism. Using a thermomechanical model we demonstrate a different mechanism of ice layer formation. After a melting event when the drying front catches up with the wetting front and arrests melt percolation, conductive heat loss freezes the remaining melt in place to form an ice layer. This model reproduces the depth of a new ice layer at the Dye-2 site in Greenland. It provides a deeper insight into the interpretation of firn stratigraphy and past climate variability. It also improves the simulation of firn densification processes, a key source of uncertainty in assessing and attributing ice sheet mass balance based on satellite altimetry and gravimetry data.

Abstract

Understanding the coupling between rock permeability, pore pressure, and fluid flow is crucial, as fluids play an important role in the Earth's crustal dynamics. We measured the distribution of fluid pressure during fluid-flow experiments on two typical crustal lithologies, granite and basalt. Our results demonstrate that the pore-pressure distribution transitions from a linear to a non-linear profile as the imposed pore-pressure gradient is increased (from 2.5 to 60 MPa) across the specimen. This non-linearity results from the effective pressure dependence of permeability, for which two analytical formulations were considered: an empirical exponential and a new micromechanics-based model. In both cases, the non-linearity of pore pressure distribution is predicted. Using a compilation of permeability versus Terzaghi's effective pressure data for granites and basalts, we show that our micromechanics-based model has the potential to predict the pore pressure distribution over the range of effective pressures expected within the brittle crust.

Abstract

Carbon dioxide is a key gas to monitor at volcanoes because its concentration and isotopic signature can indicate changes to magma supply and degassing behavior prior to eruptions, yet carbon isotopic fluctuations at volcanic summits are not well constrained. Here we present δ13C results measured from plume samples collected at Stromboli volcano, Italy, by Uncrewed Aerial Systems (UAS). We found contrasting volcanic δ13C signatures in 2018 during quiescence (−0.36 ± 0.59‰) versus 10 days before the 3 July 2019 paroxysm (−5.01 ± 0.56‰). Prior to the eruption, an influx of CO2-rich magma began degassing at deep levels (∼100 MPa) in an open-system fashion, causing strong isotopic fractionation and maintaining high CO2/St ratios in the gas. This influx occurred between 10 days and several months prior to the event, meaning that isotopic changes in the gas could be detected weeks to months before unrest.

Science, Volume 385, Issue 6708, August 2024.

Science, Volume 385, Issue 6708, August 2024.

Abstract

This study provides the design and demonstration of a Ku/K band horn-fed linear polarization (LP) to circular polarization (CP) converter using a reflectarray antenna based on the holographic technique and the generalized law of total reflection without any iterative algorithms. The proposed hologram performs wide-range frequency beam scanning with minimum gain losses and cross-polarization levels. It comprises 2,500 diagonal slotted octagonal subwavelength metasurfaces with a periodicity of 0.266λ 0 = 4 mm at 20 GHz as the center frequency. Two equations are defined to compute Y 11 of the proposed unit cell regarding its dimensions for TE(0,0) and TM(0,0) Floquet modes. They significantly simplify the coding procedure and reduce the computational time for synthesizing the hologram. The antenna is simulated using the CST software from 14 to 25 GHz. As a confirmation, a prototype is manufactured and measured at 16, 18, 20, 22, and 24 GHz to verify its performance. The simulated and measured results are well-matched. The presented hologram achieves 40% 1.8-dB axial ratio (AR) bandwidth (16–25 GHz), 40% 3.3-dB gain bandwidth (16–24 GHz), and above 30% 2-dB gain bandwidth (16–22 GHz). Moreover, the antenna can perform beam scanning from 42° to 24° by changing the frequency from 16 to 24 GHz with peak gain values greater than 20.33 dBi. The LHCP pencil beams are at least 24° off-broadside, so the proposed hologram avoids the feed blockage. These achievements make the hologram one of the best candidates for satellite communications, radar applications, short-range communication, and point-to-point communication.

Abstract

Forecasting landslide inundation upon catastrophic failure is crucial for reducing casualties, yet it remains a long-standing challenge owing to the complex nature of landslides. Recent global studies indicate that catastrophic hillslope failures are commonly preceded by a period of precursory creep, motivating a novel scheme to foresee their hazard. Here, we showcase an approach to hindcast landslide inundation by linking satellite-captured precursory displacements to modeling of consequent granular-fluid flows. We present its application to the 2021 Chunchi, Ecuador landslide, which failed catastrophically and evolved into a mobile debris flow after four months of precursory creep, destroying 68 homes along its lengthy flow path. Underpinned by uncertainty quantification and in situ validations, we highlight the feasibility and potential of forecasting landslide inundation damage using observable precursors. This forecast approach is broadly applicable for flow hazards initiated from geomaterial failures.

Abstract

Climate change is creating a new era of infectious disease crises, further exacerbated by extreme weather. However, the relationship between extreme weather and infectious disease remain unclear. Here, we provide a new quantitative study on the impact of cold wave on COVID-19 as an example. We found that during cold waves, extreme cold temperatures coupled with rapid aerosol transport accelerated COVID-19 outbreaks. It directly increased the number of COVID-19 cases in Beijing by 28.1% in the winter of year 2022. More urgently, cold temperatures led to a higher risk of death during infectious disease outbreaks, with a 7.07% increase in confirmed deaths and a 16.61% increase in excess mortality. Our findings emphasize the urgent need to promote a synergistic policy for responding to infectious diseases during cold wave disasters in order to minimize the risk of death among the elderly and those with underlying diseases.

Science, Volume 385, Issue 6710, Page 790-795, August 2024.

Science, Volume 385, Issue 6708, Page 503-503, August 2024.

Science, Volume 385, Issue 6708, Page 502-502, August 2024.

Science, Volume 385, Issue 6708, Page 522-528, August 2024.

Science, Volume 385, Issue 6708, Page 566-572, August 2024.

Science, Volume 385, Issue 6708, Page 549-553, August 2024.

Science, Volume 385, Issue 6708, Page 554-560, August 2024.

Science, Volume 385, Issue 6708, Page 533-538, August 2024.

Science, Volume 385, Issue 6708, Page 544-549, August 2024.

Science, Volume 385, Issue 6708, Page 528-532, August 2024.