Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title><jats:p>We use the Magnetospheric Multiscale mission to observe a bi‐directional electron acceleration event in the electron foreshock upstream of Earth's quasi‐perpendicular collisionless bow shock. The acceleration region is associated with a decrease in wave activity, inconsistent with common electron acceleration mechanisms such as Diffusive Shock Acceleration and Stochastic Shock Drift Acceleration. We propose a two‐step acceleration process where an electron field‐aligned beam acts as a seed population further accelerated by a shrinking magnetic bottle process, with the shock acting as the magnetic mirror(s).</jats:p>

<jats:title>Abstract</jats:title><jats:p>Earth's upper mantle rheology controls lithosphere‐asthenosphere coupling and thus surface tectonics. Rock deformation experiments and seismic anisotropy measurements indicate that composite rheology (co‐existing diffusion and dislocation creep) occurs in the Earth's uppermost mantle, potentially affecting convection and surface tectonics. Here, we investigate how the spatio‐temporal distribution of dislocation creep in an otherwise diffusion‐creep‐controlled mantle impacts the planform of convection and the planetary tectonic regime as a function of the lithospheric yield strength in numerical models of mantle convection self‐generating plate‐like tectonics. The low upper‐mantle viscosities caused by zones of substantial dislocation creep produce contrasting effects on surface dynamics. For strong lithosphere (yield strength &gt; 35 MPa), the large lithosphere‐asthenosphere viscosity contrasts promote stagnant‐lid convection. In contrast, the increase of upper mantle convective vigor enhances plate mobility for lithospheric strength &lt;35 MPa. For the here‐used model assumptions, composite rheology does not facilitate the onset of plate‐like behavior at large lithospheric strength.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The development of hummocky topography is a poorly understood aspect of down‐wasting on debris‐covered glaciers that is often attributed to variable debris thickness. Thousands of enclosed depressions pit the hummocky topography. To better understand depression growth, we examined the size distribution and geometry of depressions on the Ngozumpa Glacier, in the Everest Region of Nepal. The depressions exhibited a power‐law size distribution, fractal perimeters, and power‐law depth‐area scaling, which suggest positive feedback growth. With a simple model, we showed that positive feedback growth produces similar power‐law size distributions. Based on these findings, we propose a “sinkhole” hypothesis for the development of depressions. Drainage into englacial sink points removes debris from the depressions and inhibits ponds from overflowing, thereby enabling positive feedback growth via incision, increased sub‐debris melt rates, and ice cliff retreat. By facilitating sustained depression growth, englacial drainage preconditions the ablation zone for the rapid growth of glacial lakes.</jats:p>

<jats:title>Abstract</jats:title><jats:p>In nearly all reservoirs, storage capacity is steadily lost due to trapping and accumulation of sediment. Despite critical importance to freshwater supplies, reservoir sedimentation rates are poorly understood due to sparse bathymetry survey data and challenges in modeling sedimentation sequestration. Here, we proposed a novel approach to estimate reservoir sedimentation rates and storage capacity losses using high‐resolution Sentinel‐2 satellites and daily in situ water levels. Validated on eight reservoirs across the central and western United States, the estimated reservoir bathymetry and sedimentation rates have a mean error of 4.08% and 0.05% yr<jats:sup>−1</jats:sup>, respectively. Estimated storage capacity losses to sediment vary among reservoirs, which overall agrees with the pattern from survey data. We also demonstrated the potential applications of the proposed approach to ungauged reservoirs by combining Sentinel‐2 with sub‐monthly water levels from recent satellite altimeters.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The 22 July 2020 Mw7.8 Simeonof earthquake was a deep megathrust event that ruptured along the Shumagin segment of the Alaska‐Aleutian subduction zone. This earthquake occurred ∼250 km from a seafloor geodetic GNSS‐Acoustic site IVB1, where we observed a velocity of 3.78 ± 1.15 cm/yr with the down‐going slab prior to the earthquake followed by 0.6 ± 0.7 eastward and −15.5 ± 0.8 cm northward coseismic offset. We computed a slip model of the coseismic rupture using the static offset at IVB1 alongside regional continuous GNSS and strong motion stations. The small static horizontal offset at the site precludes significantly shallower rupture than previously inferred from terrestrial observations, confirming that the Simeonof earthquake was a deep megathrust earthquake. The observed site velocity implies partial locking prior to the earthquake, implying significant shallow strain accumulation such that the small coseismic offset is unlikely to have relieved all of the accumulated strain since the last coseismic rupture.</jats:p>

<jats:title>Abstract</jats:title><jats:p>During recent decades, both greenhouse gases (GHGs) and anthropogenic aerosols (AAs) drove major changes in the Earth's energy imbalance. However, their respective fingerprints in changes to ocean heat content (OHC) have been difficult to isolate and detect when global or hemispheric averages are used. Based on a pattern recognition analysis, we show that AAs drive an interhemispheric asymmetry within the 20°‐35° latitude band in historical OHC change due to the southward shift of the atmospheric and ocean circulation system. This forced pattern is distinct from the GHG‐induced pattern, which dominates the asymmetry in higher latitudes. Moreover, it is found that this significant aerosol‐forced OHC trend pattern can only be captured in analyzed periods of 20 years or longer and including 1975–1990. Using these distinct spatiotemporal characteristics, we show that the fingerprint of aerosol climate forcing in ocean observations can be distinguished from both the stronger GHG‐induced signals and internal variability.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Shear thinning and brittle failure of silicate melt control the dynamics of volcanic eruptions, but their molecular‐scale origin is still unclear. Here, we conducted tension and compression experiments on silicate melts, using time‐resolved X‐ray diffraction. Our experiments revealed that the intermediate‐range ordering of silicate structures, that is, the ring size formed by the SiO<jats:sub>4</jats:sub> tetrahedra, demonstrated elastic and anisotropic dilation under tension and shrinkage under compression in the non‐Newtonian regime. In contrast, there were no significant changes in short‐range ordering, such as Si–O and Si–Si distances. Based on these findings, we inferred that shear thinning observed under high stress originates from the formation of anisotropically deformed large and small rings in silicate structures that are energetically unfavorable and unstable. Brittle failure occurred under high‐stress conditions, in both tension and compression. We propose a stress criterion as a necessary and sufficient condition for magma failure, rather than a strain rate criterion.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Oceanic lee waves play an important role in dissipating wind‐driven ocean circulations and powering turbulent diapycnal mixing. Here we investigate impacts of the greenhouse warming on global energy conversion into lee waves using a linear theory of lee wave generation and output from a high‐resolution (0.1° for the ocean) coupled global climate model. The global energy conversion rate into lee waves under the historical (1930s) climate condition is estimated to be 193.0 ± 3.0 GW. Under the high carbon emission scenario, this conversion rate is projected to decrease by about 20% by the end of 21st century, due to weakened bottom large‐scale mean flows, mesoscale eddies and stratification. The decrease of the conversion rate is widespread and particularly pronounced in the Gulf Stream and Drake Passage.</jats:p>

<jats:title>Abstract</jats:title><jats:p>We show that the return‐point memory of cyclic macroscopic trajectories enables the derivation of a thermodynamic framework for quasistatically driven dissipative systems with multiple metastable states. We use this framework to sort out and quantify the energy dissipated in quasistatic fluid‐fluid displacements in disordered media. Numerical computations of imbibition–drainage cycles in a quasi‐2D medium with gap thickness modulations (imperfect Hele‐Shaw cell) show that energy dissipation in quasistatic displacements is due to abrupt changes in the fluid‐fluid configuration between consecutive metastable states (Haines jumps), and its dependence on microstructure and gravity. The relative importance of viscous dissipation is deduced from comparison with quasistatic experiments.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The 2022 heatwave in China featured record‐shattering high temperatures, raising questions about its origin and possible link to global warming. Here we show that the maximum temperature anomalies over Central China reached 13.1°C in the summer of 2022, which is ∼4.2σ above the 1981–2010 mean with a return period of tens of thousands of years. Our results suggested that the persistent high‐pressure anomaly and associated extreme heatwave likely resulted mainly from internal variability, although anthropogenic warming has increased the probability of such extreme heatwaves. We also estimate that the 2022‐like heatwave becomes six to seven times more likely under persistent high‐pressure conditions when compared to stochastic circulation states. Due to a shift toward warmer mean temperatures and a flattening of the probability distribution function, such rare extreme heatwaves are projected to become much more common at a global warming level of 4°C, occurring once about every 8.5 years.</jats:p>