Abstract
Shear strain localization refers to the phenomenon of accumulation of material deformation in narrow slip zones. Many materials exhibit strain localization under different spatial and temporal scales, particularly rocks, metals, soils, and concrete. In the Earth's crust, irreversible deformation can occur in brittle as well as in ductile regimes. Modeling of shear zones is essential in the geodynamic framework. Numerical modeling of strain localization remains challenging due to the non-linearity and multi-scale nature of the problem. We develop a numerical approach based on graphical processing units (GPU) to resolve the strain localization in two and three dimensions of a (visco)-hypoelastic-perfectly plastic medium. Our approach allows modeling both the compressible and incompressible visco-elasto-plastic flows. In contrast to symmetric shear bands frequently observed in the literature, we demonstrate that using sufficiently small strain or strain rate increments, a non-symmetric strain localization pattern is resolved in two- and three-dimensions, highlighting the importance of high spatial and temporal resolution. We show that elasto-plastic and visco-plastic models yield similar strain localization patterns for material properties relevant to applications in geodynamics. We achieve fast computations using three-dimensional high-resolution models involving more than 1.3 billion degrees of freedom. We propose a new physics-based approach explaining spontaneous stress drops in a deforming medium.
Joint research led by Professor An Zhisheng from the Institute of Earth Environment of the Chinese Academy of Sciences has revealed the pivotal role of the growth of the Antarctic ice sheet and associated Southern Hemisphere sea ice expansion in triggering the mid-Pleistocene climate transition (MPT). It has also shown how asymmetric polar ice sheet evolution affects global climate.
Rocks recently exposed to the sky after being covered with prehistoric ice show that tropical glaciers have shrunk to their smallest size in more than 11,700 years, revealing the tropics have already warmed past limits last seen earlier in the Holocene age, researchers from Boston College report in the journal Science.
Abstract
The long-standing “energy crisis” at the giant planets refers to the anomalous heating of planetary thermospheres compared to the available energy from solar irradiance. The coupling between planetary magnetospheres and their upper atmospheres is thought to address these crises, though the sources and pathways of energy transport have not been fully explored at each system. In particular, the total available energy from the upstream solar wind at each planet has not been comprehensively quantified. Here we apply recently developed models of energy conversion by magnetic reconnection and the Kelvin-Helmholtz instability to each of the Giant Planets, providing estimates of the average external energy inputs for each system between 1985 and 2020. We find that external energy associated with solar-wind-magnetospheric coupling significantly exceeds that from solar extreme ultraviolet photons. While internal energy sources are known to dominate at Jupiter and Saturn, external sources may be significant at Uranus and Neptune.
Time-resolved measurements of the densities of individual frozen hydrometeors and fresh snowfall
Dhiraj K. Singh, Eric R. Pardyjak, and Timothy J. Garrett
Atmos. Meas. Tech., 17, 4581–4598, https://doi.org/10.5194/amt-17-4581-2024, 2024
Accurate measurements of the properties of snowflakes are challenging to make. We present a new technique for the real-time measurement of the density of freshly fallen individual snowflakes. A new thermal-imaging instrument, the Differential Emissivity Imaging Disdrometer (DEID), is shown to be capable of providing accurate estimates of individual snowflake and bulk snow hydrometeor density. The method exploits the rate of heat transfer during the melting of a snowflake on a hotplate.
Synergy of active and passive airborne observations for heating rates calculation during the AEROCLO-SA field campaign in Namibia
Mégane Ventura, Fabien Waquet, Isabelle Chiapello, Gérard Brogniez, Frédéric Parol, Frédérique Auriol, Rodrigue Loisil, Cyril Delegove, Luc Blarel, Oleg Dubovik, Marc Mallet, Cyrille Flamant, and Paola Formenti
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-121,2024
Preprint under review for AMT (discussion: open, 0 comments)
Biomass burning aerosols (BBA) from Central Africa, are transported above stratocumulus clouds. The absorption of solar energy by aerosols induce warming, altering the clouds dynamics. We developed an approach that combines polarimeter and lidar to quantify it. This methodology is assessed during the AEROCLO-SA campaign. To validate it, we used flux measurements acquired during aircraft loop descents. Major perspective is the generalization of this method to the global level.
Vertical Retrieval of AOD using SEVIRI data, Case Study: European Continent
Maryam Pashayi, Mehran Satari, and Mehdi Momeni Shahraki
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-105,2024
Preprint under review for AMT (discussion: open, 0 comments)
Our study estimates the SEVIRI AOD profile across Europe with 3 km spatial and 15-minute temporal resolution. Using machine learning models trained on 2017–2019 SEVIRI data and validated with 2020 CALIOP data, we found that RF performs best at higher altitudes, with wind speed and direction playing a crucial role in improving accuracy. Validation with EARLINET data confirms strong agreement with XGB.
The UK needs coordinated plans to stop a rush for air conditioning as temperatures rise, experts say.
To experience a volcanic eruption is to witness nature's raw power. If you would like to see one for yourself, Iceland is a great location for it. Since 2021, seven eruptions have taken place along the Reykjanes Peninsula, close to Reykjavík.
Surprise floods: the role of our imagination in preparing for disasters
Joy Ommer, Jessica Neumann, Milan Kalas, Sophie Blackburn, and Hannah L. Cloke
Nat. Hazards Earth Syst. Sci., 24, 2633–2646, https://doi.org/10.5194/nhess-24-2633-2024, 2024
What’s the worst that could happen? Recent floods are often claimed to be beyond our imagination. Imagination is the picturing of a situation in our mind and the emotions that we connect with this situation. But why is this important for disasters? This survey found that when we cannot imagine a devastating flood, we are not preparing in advance. Severe-weather forecasts and warnings need to advance in order to trigger our imagination of what might happen and enable us to start preparing.
Soil liquefaction that results in infrastructure damage has long been a point of contention for urban planners and engineers. Accurately predicting the soil liquefaction risk of a region could help overcome this challenge.
Complex topography of glacier surfaces under accelerating global warming presents unprecedented challenges to traditional methods of glaciological observation due to intense fragmentation and differential melting.
Abstract
Climate feedbacks over the historical period (here defined as 1850–2014) have been investigated in large ensembles of historical and single forcing experiments (hist-ghg, hist-aer, and hist-nat), with 47 members for each experiment. Across the historical ensemble with all forcings, a range in estimated Effective Climate Sensitivity (EffCS) between approximately 3–6 K is found, a considerable spread stemming solely from initial condition uncertainty. The spread in EffCS is associated with varying Sea Surface Temperature (SST) patterns seen across the ensemble due to their influence on different feedback processes. For example, the level of polar amplification is strongly correlated with the amount of sea ice melt per degree of global warming. This mechanism is related to the large spread in shortwave clear-sky feedbacks and is the main contributor to the different forcing efficacies seen across the different forcing agents, although in HadGEM3-GC3.1-LL these differences in forcing efficacy are shown to be small. The spread in other feedbacks is also investigated, with the level of tropical SST warming strongly correlated with the longwave clear-sky feedbacks, and the local surface-air-temperatures well correlated with the spread in cloud radiative effect feedbacks. The metrics used to understand the spread in feedbacks can also help to explain the disparity between feedbacks seen in the historical experiment simulations and modeled estimate of the feedbacks seen in the real world derived from an atmosphere-only experiment prescribed with observed SSTs (termed amip-piForcing).
Abstract
Zonal extensions of the Western Pacific subtropical high (WPSH) strongly modulate extreme rainfall activity and tropical cyclone (TC) landfall over the Western North Pacific (WNP) region. These zonal extensions are primarily forced on seasonal timescales by inter-basin zonal sea surface temperature (SST) gradients. However, despite the presence of large-scale zonal SST gradients, the WPSH response to SSTs varies from year to year. In this study, we force the atmosphere-only NCAR Community Earth System Model version 2 simulations with two real-world SST patterns, both featuring the large-scale zonal SST gradient characteristic of decaying El Niño-developing La Niña summers. For each of these patterns, we performed four experimental sets that tested the relative contributions of the tropical Indian Ocean, Pacific, and Atlantic basin SSTs to simulated westward extensions over the WNP during June–August. Our results indicate that the subtle differences between the two SST anomaly patterns belie two different mechanisms forcing the WPSH's westward extensions. In one SST anomaly pattern, extratropical North Pacific SST forcing suppresses the tropical Pacific zonal SST gradient forcing, resulting in tropical Atlantic and Indian Ocean SSTs being the dominant driver. The second SST anomaly pattern drives a similar westward extension as the first pattern, but the underlying SST gradient driving the WPSH points to intra-basin forcing mechanisms originating in the Pacific. The results of this study have implications for understanding and predicting the impact of the WPSH's zonal variability on tropical cyclones and extreme rainfall over the WNP.
As global temperatures continue to rise, India is grappling with increasingly severe heat waves. As early as April, many Indian cities, including New Delhi, the capital, have experienced record temperatures above 115 degrees Fahrenheit.
Ancient ocean temperatures are most commonly reconstructed by analyzing the ratio of different oxygen atoms in the calcium carbonate remains of fossils. However, this presents many challenges, including a combination of biological processes known as "vital effects" which are very noticeable in corals and can affect the data.
Abstract
In this study, a variable-resolution version of the Community Earth System Model (VR-CESM) with mesh refinement (∼0.125°) over East Asia is used to simulate the regional climate in this region. For the evaluation of model performance and sensitivity to model resolution, the simulated near-surface temperature and precipitation are compared with observations and simulation results from a globally quasi-uniform (∼1°) CESM (UN-CESM). Results show that VR-CESM better simulates the spatial patterns and seasonal variations of mean temperature and precipitation than UN-CESM over China. For extreme events, VR-CESM improves the simulation of the occurrence frequency of wintertime daily minimum temperature and heavy precipitation. In regions with complex terrains, VR-CESM better resolves the topographic forcing and captures the observed fine-scale spatial patterns of temperature and precipitation, although precipitation is still overestimated. For East Asian summer monsoon precipitation, both UN-CESM and VR-CESM tend to overestimate (underestimate) the precipitation over northern (southern) China, which is associated with too strong meridional water vapor transport in the models and biases in the large-scale circulation in the middle and upper troposphere. Different from previous studies with different physics parameterizations and refined domains, as the model resolution increases, simulated monsoon precipitation evolution is not obviously improved, and convective precipitation intensity decreases over eastern China. Despite this, our results indicate that VR-CESM simulates regional climate, topographical forcing, and large-scale circulations over East Asia reasonably well, and thus it can be applied for the future climate projection in the region.
Recent decades have seen rapid warming in the Arctic, known as Arctic amplification, which has impacted the Arctic's cryosphere and ecosystems and influenced global weather and climate through changes in atmospheric circulation.
Abstract
In rivers worldwide, multiple scales of dunes coexist. It is unknown how the larger, primary dunes interact with secondary bedforms that are superimposed. We test the hypothesis that streamwise variability in the sediment flux inferred from the downstream migration of secondary bedforms explains migration of the host dune, based on bathymetric data from a lowland, sand-bedded river. Results indicate that transport estimated from secondary bedform migration increases along the host dune stoss, eroding the stoss slope. When the superimposed bedforms disintegrate at the primary lee slopes, results indicate that all sediment transport associated to secondary bedform migration is arrested in the lee of the host dune, explaining migration of the host dune. When secondary dunes persist however, only part of the sediments transport linked to secondary dunes contributes to the migration of the host dune. This study gives novel insight into the fundamental mechanisms controlling the kinematics of compound dunes.
Abstract
Influenced by climate change, numerous lakes in permafrost regions are draining, showing significant spatial variability. This study focuses on St. Lawrence Island, where over the last two decades, 771 of 3,271 lakes have drained—a rate around 40 times higher than across the entire northern permafrost region. The surge in lake drainage began in 2018, coinciding with record low sea ice extent in the Bering Sea and unprecedented bird mortalities. Using satellite imagery and machine learning methods, we analyzed drainage events to identify the climatic drivers and potential climate thresholds affecting the island's lake ecosystems. Our findings indicate that autumn peak temperatures above 6°C more than triple the drainage probability, and warming-induced permafrost thawing may be the direct driver of lake drainage. This research highlights the vulnerability of Arctic lake ecosystems to climate change and assists in developing predictive models for permafrost response, crucial for mitigating impacts on Arctic communities.
