bluuebunny/crossref_metadata_2025 huggingface dataset:
Impacts of climate change and urban heat island on mortality risk: summer average vs. extreme heat events
Authors: Huang Wan Ting Katty , Manoli Gabriele , Braithwaite Isobel , Charlton-Perez Andrew , Sarran Christophe , Sun Ting
Published: March 2022

Climate change is expected to increase heat-related mortality risks. However, mortality risks associated with cold weather, which can also occur during summertime, are expected to decrease. The overall impact of temperature changes on summer average risk may therefore evolve differently than the risk associated with heat extremes. A similar, though less pronounced, picture can also be painted for the impact of urban heat island on mortality risk. In two separate studies, we highlight the differing impacts of warming on summer mean versus extreme heat-related mortality risk. Factors such as the local climate and vulnerability to heat play a role in mediating the net summer average impact, while a clear enhancement of risk during extreme heat events is expected in association with both climate change and urban heat island effects. These findings provide a more comprehensive picture of the potential impact of climate change and urbanisation on summer temperature-related mortality risks, which may be relevant for adaptation and mitigation strategies.
Magnetosphere simulations with ideal MHD, Hall MHD and the MHD with Adaptively Embedded Particle-in-Cell (MHD-AEPIC) models
Authors: Toth Gabor , Wang Xiantong , Chen Yuxi
Published: March 2022

The Magnetohydrodynamic with Embedded Particle-In-Cell (MHD-EPIC) model has been developed and applied successfully to Earth, Mercury, Mars and Ganymede magnetosphere simulations. While MHD-EPIC is many orders of magnitude faster than a fully kinetic global model, it can become prohibitively slow if the potential region of interest where kinetic phenomena, such as magnetic reconnection, can occur is large. This is due to the fact that the PIC domain in MHD-EPIC is restricted to a set of static Cartesian boxes. For example, a very large PIC box would be needed to accommodate the flapping motion of the magnetotail current sheet during a geomagnetic storm simulation. To tackle this problem, we have developed a new MHD with Adaptively Embedded Particle-In-Cell (MHD-AEPIC) model. MHD-AEPIC inherits all numerical algorithms from MHD-EPIC and incorporates a new adaptive PIC model, the Flexible Kinetic Simulator (FLEKS). FLEKS allows the PIC cells to be activated and deactivated during a simulation. The coupling between the MHD model and the adaptive PIC grid has been developed and implemented into the Space Weather Modeling Framework. We have also developed physics-based criteria to identify potential reconnection sites, which makes the adaptation fully automatic. In this work, we apply the new MHD-AEPIC model to a geomagnetic storm simulation and demonstrate how adaptation makes this simulation feasible. We compare MHD-AEPIC, Hall MHD and ideal MHD simulation results with each other and with observations ranging from electron scales to global scales. In particular, we demonstrate that MHD-AEPIC is capable of reproducing electron-scale physics in a global simulation.
Spatio-temporal variations in rock wall temperature in Norway post the Little Ice Age 
Authors: Czekirda Justyna , Etzelmüller Bernd , Westermann Sebastian , Isaksen Ketil , Magnin Florence
Published: March 2022

Warming-induced permafrost degradation is believed to be responsible for the increasing number of rock-slope instabilities, such as rockfalls or rock avalanches, over the past few decades. Relationship between permafrost degradation and geomorphological activity, is nevertheless, hard to establish because often little is known about the permafrost distribution in steep slopes. In the present study, we assess spatio-temporal changes in rock wall temperature in Norway post the Little Ice Age, using the two-dimensional ground heat flux model CryoGrid 2D. We create transects across the monitored rock walls in the Western Norway, in the high alpine range of Jotunheimen and in the Northern Norway.

               Our results demonstrate that rock wall temperature at 20 m depth increased by an average of 0.2 °C decade-1 since the 1980s. Therefore, if atmospheric warming rates remain similar, rock wall permafrost currently at -1 °C at 20 m depth could degrade completely at this depth by 2070. Furthermore, we show how rock wall temperature is influenced by: (1) rock wall geometry, (2) rock wall size, (3) magnitude of surface offsets due to the incoming shortwave solar radiation, (4) snow conditions above and below rock walls, (5) blockfield-covered plateaus or glaciers in their vicinity. Multi-dimensional thermal effects are smaller in Norway than in the European Alps due to the dissimilarities in mountain geometry and smaller differences in ground surface temperature between various mountainsides. Rock walls with large surface offsets arising from solar radiation might be warmer than plateaus above or talus slopes below, thus ground heat flux in such rock walls is directed towards colder plateaus or talus slopes. Furthermore, thermal conditions in blockfield-covered plateaus have impact on rock wall temperature and lead to larger warming rates at 20 m depth, whereas large glaciers decrease warming rates at the same depth. Therefore, a potential glaciers retreat would likely increase ground warming rates in the nearby parts of rock walls.  
Origins of sea level variability in tide gauges along the U.S. Atlantic coast
Authors: Abele Anrijs , Royston Sam , Bamber Jonathan
Published: March 2022

Being a ‘hotspot’ of sea level rise and a densely populated area, the Atlantic coast of U.S. is a site of scientific interest with high societal significance. Coincidentally, this area also hosts a number of long-span tide gauges and other high quality in-situ observations. The advent of dedicated coastal processing and synthetic aperture radar (SAR) altimeters has provided more reliable, higher resolution observations to enable better understanding of how sea level on the shelf is linked to the open ocean. To further constrain the sea level reconstructions and future sea level projections in the coastal regions, better understanding of processes affecting sea level is needed. The aim of this study is to understand the sources of variability in VLM-corrected sea level measured by tide gauges and geocentric sea level, and the differences between them.

We are using along-track geocentric sea level anomaly from Sentinel-3A SAR altimeter, sea level anomalies from high resolution ocean model, VLM correction from GNSS stations, and hourly total water level measurements from a set of 16 tide gauges along the Atlantic coast of the U.S. By developing a statistical model for sea level at tide gauges and geocentric sea level on the shelf, the differences in variability are partitioned. Finally, these differences are compared to change in climatic variables to provide a discussion about the geophysical origins of observed variability differences.
The influence of accretionary orogenesis on rift dynamics
Authors: Erdős Zoltán , Buiter Susanne , Tetreault Joya
Published: March 2022

The Wilson Cycle of closing and opening of oceans is often schematically portrayed with ‘empty’ oceanic basins. However, bathymetric and geophysical observations outline anomalous topographic features, such as microcontinents and oceanic plateaus, that can be accreted when oceans close in subduction. This implies that numerous rifted margins have formed in regions characterized by the presence of previously accreted continental terranes. The main factors controlling where and how such continental rifts localize in relation to the inherited compressional structures is yet to be explored properly. Potential factors that can influence the evolution and structural style of a rift in such a tectonic setting include the thermo-tectonic age of the accretionary orogen, the number and type (size, rheology) of accreted terranes, the nature of terrane boundaries, as well as the velocity of rifting.

We use 2D finite-element thermo-mechanical models to investigate how the number and size of accreted terranes as well as the duration of tectonic quiescence between orogenesis and extension (i.e., the amount of time available for the thermal re-equilibration of the thickened lithosphere) affect the style of continental rifting. Our results can further understanding of how rifted margins formed after accretionary orogenesis are influenced by the compressional stage such as the Norwegian rifted margin, where the late-Paleozoic to Mesozoic rifting occurred after the early Paleozoic Caledonian orogeny.

We test two hypotheses. According to our first hypothesis, the location of the rift is dependent on the age of the accretion. If extension directly follows accretion, we expect the thick lithosphere of the orogen to be strong in a brittle sense, causing extension to localise adjacent to the orogen. In contrast, if the onset of extension happens after a period of tectonic quiescence, the accretionary orogen has time to heat up and viscously weaken, allowing it to localize deformation more efficiently. We test this hypothesis by varying the amount of time available for thermal re-equilibration.

Secondly, we hypothesize that the degree to which the compressional structures such as terrane boundaries in the accretionary stack reactivate depends on the size and complexity of the accreted assembly (through the number and size of the accreted terrains) as well as the strength of shear zones. We test this hypothesis by varying the number of terranes accreted prior to rifting.

Our preliminary results show that the subduction interface is reactivated in an extensional regime, but without a period of quiescence the reactivation is temporary and rifting occurs in the unthickened foreland basin area.
A Joint Point-source Moment Tensor and a Single Force Inversion Within Hierarchical Bayesian Inference for Revealing the Source Mechanism of Underground Nuclear Explosions
Authors: Hu Jinyin , Phạm Thanh-Son , Tkalčić Hrvoje
Published: March 2022

A seismic moment tensor (MT) consisting of 6 independent components is widely used to parameterise a seismic point-source by assuming no net torque. However, there are well-documented seismic sources for which net torques are significant, and single force (SF) components are necessary to describe the physics of the problem, e.g., the collapse of cavities, landslides, and glacier earthquakes. Therefore, combining MT and SF components can explore a broader range of source representation in seismic source inversion. In addition, rigorous uncertainty estimate has been a leading-edge topic in seismic source inversion. A complete uncertainty treatment should consider both data noise involved in the acquisition process and theoretical error primarily due to imperfect knowledge of Earth structure. Recent advancements jointly treating data noise and theoretical errors have been made for the MT representation within the hierarchical Bayesian framework, where noise is treated as a free parameter. However, to our best knowledge, a decomposition of the seismic source to MT and SF, including a rigorous treatment of uncertainty, remains an unaddressed problem. Here, we propose a joint inversion scheme of MT and SF within the hierarchical Bayesian framework that accounts for both data and structural (theory) uncertainties. Several carefully designed synthetic experiments modelling underground explosions demonstrate the feasibility of this method. Our current focus is on practical applications. We are hopeful that our approach will provide further insights into the physics of seismic sources for underground nuclear explosions, thus helping verify compliance with the CTBT.
The Diurnal Evolution of Controls on Trade Wind Mesoscale Morphologies
Authors: McCoy Isabel L. , Zuidema Paquita , Baidar Sunil , Vial Jessica , Schulz Hauke , Brewer Alan
Published: March 2022

The diurnal cycle in trade wind cloudiness has been observed to be driven by the diurnal cycle in the relative frequency of occurrence of mesoscale morphologies (i.e., Vial et al. 2021). These morphologies have been grouped based on their distinct appearance and cloud size into four categories, from small to large sizes: Sugar, Gravel, Flowers, and Fish. The diurnal cycle in cloudiness is associated with a late afternoon maximum in the smallest (Sugar) clouds which give way to clouds of larger size and vertical extent (Gravel, then Flowers) throughout the night. A remaining question is how sub-cloud dynamics evolve diurnally to facilitate this diurnal cycle in cloud morphology and thus cloudiness.

We examine the daily evolution of trade wind mesoscale morphologies with in situ observations from the 2020 joint campaign, EUREC4A (Elucidating the Role of Clouds–Circulation Coupling in Climate) and ATOMIC (Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign), that took place in January and February in the Northwest tropical Atlantic. Measurements from the Ronald H. Brown research vessel allow us to analyze differences in the daily evolution of boundary layer structure and dynamics between morphologies. We decompose Doppler lidar-derived mass fluxes into their vertical velocity and cloud fraction contributions and examine their effect on diurnal cloud evolution as well as their relationship to environmental controls such as surface wind speeds, energy and moisture fluxes, stability, and near-surface air properties. Relationships between environmental controls and morphologies are further extended with the long-term recorded observations at the nearby moored NTAS (Northwest Tropical Atlantic Station) buoy.
 Dynamics Insight of  Internal Tide Radiation in the Kuroshio 
Authors: Xu Zhenhua
Published: March 2022

Ocean circulation strongly influences how internal tides radiate and break and stimulates the spatial inhomogeneity and temporal variation of internal tidal mixing. Qualitative and quantitative characterizations of interactions between internal tides and general circulation are critical to multi-scale circulation dynamics. Based on significant progress in regional circulation simulation, we obtain an observation-supported internal tide energy field around Luzon Strait by deterministically resolving the dynamics of the radiating paths of the internal tide energy. These paths are created when the known most powerful internal tide of Luzon Strait interacts with the Kuroshio Current. We found that the radiating tidal pattern, local dissipation efficiency, and energy field respond differently to the leaping, looping, and leaking Kuroshio paths within Luzon Strait. Our new insights into the dynamics and our clarifying the controlling refraction mechanism within the general circulation create the potential for internal tides to be represented better in climate models. 
Using K-Means Clustering to Compare Adjoint Waveform Tomography Models of California and Nevada
Authors: Doody Claire , Rodgers Arthur , Boehm Christian , Afanasiev Michael , Krischer Lion , Chiang Andrea , Simmons Nathan
Published: March 2022

Full waveform inversion models by adjoint methods represent the most detailed seismic tomography models currently available for waveform simulations. However, the influence of starting models on final inversion results is rarely studied due to computational expense. To study this influence, we present three adjoint waveform tomography models of California and Nevada using three different starting models:  the SPiRaL global model (Simmons et al., 2021), the CSEM_NA model (Krischer et al., 2018), and the WUS256 model (Rodgers et al., 2021). Each model uses the same dataset of 103 events between magnitudes 4.5 and 6.5 that occurred from January 1, 2000 to October 31st, 2020. For each event, 175-475 stations record data, creating dense path coverage over California. The model iterations are computed using Salvus. We begin by  running iterations for each starting model at three period bands: 30-100 seconds, 25-100 seconds, and 20-100 seconds. For each period band, we run iterations until the average misfit for all events is no longer reduced; over all period bands, we run more than 55 iterations and see misfit reductions of up to 40% in some period bands. Each model shows velocity anomalies of up to 20%, but the difference in VS values between the models can be significant. Most of these differences seem to correlate with small-scale differences in the starting models. To test whether these differences between the models could affect the interpretation of their results, we utilize k-means clustering to analyze the similarities in large-scale structure in all three models (e.g. Lekic and Romanowicz, 2011). We separate each model into a crustal layer (0-30km depth) and uppermost mantle layer (30-150km), then run a k-means clustering algorithm on absolute Vs wavespeeds and anisotropy [(Vsh/Vsv)^2] separately. We show that regardless of the differences seen on visual inspection, all three models can resolve tectonic-scale structures equally.

 

This work was supported by LLNL Laboratory Directed Research and Development project 20-ERD-008. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-830615.
Sensitivity to spatial and temporal resolution in the performance of a parsimonious hydrological model for quantifying water balance partitioning in dryland regions.
Authors: Quichimbo E. Andres , Singer Michael Bliss , Michaelides Katerina , Rosolem Rafael , Cuthbert Mark
Published: March 2022

Dryland regions cover around one-third of the global land surface and are naturally prone to water scarcity. Drylands typically experience highly variable precipitation, both spatially and temporally, with potential evapotranspiration (PET) greatly exceeding annual rates of precipitation. However, our ability to accurately quantify the key components of the water partitioning in these regions is hampered by the scarcity of data and the highly dynamic nature of the hydrological processes. In this context, assessing the ability of models to represent the key hydrological processes at different spatial and temporal scales is of key importance to enhance our understanding and quantification of the water balance in dryland regions. Here, we have assessed the impact of the model grid size and the temporal scale of climatic forcing in combination with variations in model structure in the description and representation of key hydrological processes that influence the water partitioning in dryland regions. The analysis was performed in the Walnut Gulch Experimental Watershed where a dense network of hydrological measurements is readily available for model evaluation. We show that our parsimonious model, DRYP, can describe well the water partitioning across a range of different temporal and spatial scales. However, we find that sub-daily time steps of precipitation and PET, combined with a fine spatial resolution of less than or equal to 1km grid size, are needed for robust quantification of the water partitioning, which is also very sensitive to the choice of infiltration model. The results highlight the important role of channel losses through the streambed of ephemeral streams (~7% of the precipitation), and the impact of the underlying alluvial riparian area in the partitioning of water fluxes between riparian vegetation evapotranspiration (~60 % of transmission losses) and the production of focused groundwater recharge (~3 % of the precipitation). These results have important implications for the potential for improving the performance of large scale models in dryland regions by indicating the appropriate temporal and spatial scales required for the proper representation of dryland hydrological processes.
Olivine and enstatite formation during seismic faulting in serpentinite: an experimental approach
Authors: Wu Wei-Hsin , Kuo Li-Wei , Smith Steven A. F. , Tarling Matthew S.
Published: March 2022

Olivine and enstatite, formed by dehydroxylation of serpentine, have been naturally and experimentally documented as evidence of paleo-earthquake rupture propagation within natural serpentinite-bearing slip zones. To investigate the rheological and textural evolution during dehydroxylation of serpentinite, we performed rotary-shear friction experiments on water-saturated serpentinite powders using drained and undrained conditions (where drained conditions allow for excess fluid pressure to escape the gouge holder). Using a purpose-built gouge sample holder containing a thermocouple 1.5 mm from the eventual principal slip zone (PSZ), the experiments were performed at a seismic slip rate (1 m/s) and 10 MPa normal stress. Mechanical results show that in undrained experiments, the apparent friction coefficient (μ) initially reaches a peak value of ~0.21-0.24, followed by dramatic weakening to a steady-state value of 0.12-0.09, associated with gouge compaction, while the temperature at the thermocouple steadily increased reaching a maximum of ~180°C. In drained experiments, a plateau-like friction coefficient with a value of ~0.42 was reached, associated with gouge compaction at a steady temperature of ~250°C at the thermocouple, followed by a drop to a steady-state value of ~0.19, associated with gouge dilation at a temperature of ~450°C. The friction coefficient then gradually increased, reaching a value of ~0.3 (i.e. restrengthening) with gouge compaction and a max. temperature at the thermocouple of ~635°C by the end of the experiment. The PSZ of the products were examined by scanning electron microscope, in-situ synchrotron X-ray diffraction, and focused ion beam transmission electron microscope. Microanalysis showed no mineral phase changes in undrained experiments, which we interpret to indicate that fluid vaporization and pressurization buffered the temperature to below that required for serpentinite dehydroxylation. However, the PSZ in drained experiments contains well-developed aggregates of nanometric, rounded to polygonal forsterite + enstatite, which provide evidence for serpentinite dehydroxylation at temperatures of >600°C within the PSZ. Our observations indicate that fluid drainage facilitates a significant temperature increase within the gouge layer at seismic slip rates. We conclude that dehydroxylation of natural serpentinite gouges may occur under relatively dry conditions or when co-seismic permeability increases (e.g. due to fracturing) allow for efficient fluid drainage and decrease the efficiency of thermal pressurization.
Diffusion creep of a Na-Ca-amphibole-bearing blueschist
Authors: Tokle Leif , Hufford Lonnie , Morales Luiz , Madonna Claudio , Behr Whitney
Published: March 2022

Blueschists are a major constituent rock type along the subduction zone interface and therefore critical to our understanding of subduction zone dynamics. Previous experimental work on natural blueschists focus on either seismic anisotropy or on the process of eclogization of a blueschist aggregate; however, little is known about the mechanical properties of blueschist rocks. We have conducted a suite of general shear deformation experiments in the Griggs apparatus to constrain the rheology of a blueschist aggregate. The sample material derives from a natural blueschist that was crushed into a powder. The powder consists of ~55% sodic amphibole, ~30% epidote, ~8% quartz, ~5% titanite, ~2% ilmenite, and <1% mica. Deformation experiments were conducted at 1.0 GPa confining pressure, temperatures of 650, 675, 700, and 750°C, and no water added. All of the deformation experiments were strain rate stepping experiments with either 4 or 5 strain rate steps per experiment with strain rates ranging from ~2.7e-5 to 5.2e-7 s-1. Based on the mechanical data we determine a stress exponent of 1.9 +/- 0.3. Microstructural and EDS analysis shows the initial Na-amphibole grains transform into a fine-grained aggregate of new Na-Ca-amphibole with lower Na and Si and higher Fe and Ca plus albite and ilmenite. The fine-grained aggregates accommodate the majority of the strain while epidote deforms by rigid body rotation or brittle deformation. Based on both the mechanical and microstructural observations, we interpret the fine-grained aggregates to be deforming by diffusion creep. Additional analyses will be conducted to constrain the grain size to develop flow law parameters to estimate the rheology of the subduction zone interface.
A Control Simulation Experiment for August 2014 Severe Rainfall Event Using a Regional Model
Authors: Maejima Yasumitsu , Miyoshi Takemasa
Published: March 2022

Torrential rainfall is a threat in the modern society. To predict severe weather, convection resolving numerical weather prediction (NWP) is effective. This study explores a Control Simulation Experiment (CSE) aimed at controlling precipitation amount and locations to potentially prevent catastorphic disasters by simulating different scenarios of interventions of small perturbations taking advantage of the chaotic nature of dynamics. In this study, we perform a CSE using a regional model SCALE-RM for a severe rainfall event which caused catastrophic landslides and 77 fatalities in Hiroshima, Japan on August 19 and 20, 2014.

We perform a 1-km-mesh, hourly-update, 50-member observing system simulation experiment (OSSE) for this rainfall event initialized at 0000 UTC August 18. This provides the initial conditions for a 6-hour ensemble forecast initilaized at 1500 UTC Augest 19. To create small perturbations to change the nature run, we take the differences of all model variables between an ensemble member having the heaviest rain and another ensemble member having the weakest rain. Moreover, we normalize the perturbations so that the maximum wind speed is 0.1 m s-1. In this preliminary CSE, we try to control the heavy rainfall by giving the perturbations to the nature run in the OSSE at each time step from 1500 UTC to 1600 UTC on August 19, although the perturbations for all variables at all grid points are something beyond human’s engineering capability. In the nature run, 6-hour accumulated rainfall amount from 1500 UTC to 2100 UTC reaches 210 mm at the peak grid point. By contrast, the rainfall amount decreases to 118 mm in the CSE. We plan to apply limitations to the perturbations.
Seismogenesis in granite under brittle-plastic transition condition
Authors: Kim Jae Hoon , Ree Jin-Han
Published: March 2022

Most of earthquakes occur below 10-km depth in the Korean Peninsula. For example, the focal depth of the Mw 5.5 Gyeongju Earthquake in 2016, the largest instrumental earthquake in South Korea since scientific earthquake monitoring started in 1978, is about 14 km with hypocentral basement rocks of granitoid and temperature of 370°C (thus, brittle-plastic transition condition). A study on ancient granitoid shear zones with the similar temperature condition will aid in understanding the seismogenesis in the brittle- plastic transition regime. The Yecheon shear zone is an NE- to NNE-striking right-lateral shear zone cross-cutting Mesozoic granitoid belt in South Korea. The deformation temperature of the main shear zone was estimated to be about 350 ℃. In the southeastern margin of the shear zone, protomylonites change gradually into mylonites and then abruptly into ultramylonites toward southeast. Quartz and feldspar grains both of protomylonite and mylonite deform by dislocation creep and brittle fracturing, respectively. Greenish ultramylonite consists of quartz-, feldspar-, muscovite- and epidote-rich layers within matrix of quartz, muscovite and epidote. The protomylonite commonly displays a composite S-C foliation. The deflecting S-foliation of mylonite toward ultramylonite is sharply truncated by the boundary between mylonite and ultramylonite. Thin (several mm to several cm) greenish layers occur in protomylonite subparallel to mylonitic foliation or cross-cutting the foliation at a low angle. They also show injection structure with flow banding and cataclastic deformation along the protomylonite boundary. The greenish layer consists of fragments of protomylonite and matrix of very fine-grained quartz, feldspar, muscovite and epidote. Epidote grains of ultramylonite and greenish layers replace phengitic mica, biotite and plagioclase and show graphic texture. Together with epidote formation, chloritization of biotite and albitization of K-feldspar are prominent in the greenish layers. The growth of hydrothermal minerals including epidote and chlorite within the greenish layers and shear band along the C-foliation indicates fluid circulation in the layers. We interpret the greenish layers were generated during seismic events in fluid-rich conditions and thus seismic event may be caused by pore pressure build up. Once the greenish layers develop, deformation was localized along the layers due to much reduced grain size in interseismic periods, and the greenish layers became ultramylonite with further grain-size reduction.
Recent progress on developments of the magnetohydrostatic extrapolation
Authors: Zhu Xiaoshuai , Wiegelmann Thomas , Inhester Bernd
Published: March 2022

The magnetohydrostatic (MHS) extrapolation is developed to model the three-dimensional magnetic fields and plasma of the solar atmosphere with the measured vector magnetogram used as boundary condition. It differs from the nonlinear force-free field (NLFFF) extrapolation in that it takes into account plasma forces include pressure gradient and gravity. In this presentation, I will report the recent progress in two aspects on developments of the MHS extrapolation. The first one is the development of a preprocessing method to deal with the non-MHS vector magetograms. The reason of doing this is that there are a small number of the vector magnetograms which are not consistent with the MHS equilibria. The second aspect is the combination of the MHS extrapolation and the NLFFF extrapolation to improve the efficiency of the computation.
Drivers for seasonal variability in sea level around the China seas
Authors: Qu Ying , Jevrejeva Svetlana , Williams Joanne , Moore John
Published: March 2022

Globally variable ocean and atmospheric dynamics lead to spatially complex seasonal cycles in sea level. The China Seas, that is the Bohai, Yellow, East China and the South China seas, is a region with strong seasonal amplitudes, and straddles the transition between tropical and temperature zones, monsoonal and westerlies, shelf and deep ocean zones. Here we investigate the drivers for seasonal variability in sea level from tide gauge records, satellite altimetry along with output from the NEMO (Nucleus for European Modeling of the Ocean) model including sea surface height and ocean bottom pressure along with meteorological data in the China Seas. The seasonal cycle accounts for 37% - 94% of sea level variability in 81 tide gauge records, ranging from 18 to 59 cm. We divided the seasonal cycles into four types: 1) an asymmetric sinusoid; 2) a clearly defined peak on a flat background; 3) a relatively flat signal; 4) a symmetric co-sinusoid. Type 1 is found in northern China and Taiwan, Korea, Japan and The Philippines where Inverse Barometer (IB) effects dominates seasonality along with a steric contribution. The seasonal monsoon associated with barotropic response and freshwater exchange play important roles in type 2, (eastern and southern Chinese coasts), type 3 (East Malaysia) and type 4 (Vietnam and Gulf of Thailand). IB corrected seasonal cycle amplitudes are larger in continental shelf areas than the deep ocean, with a maximum in the Gulf of Thailand, and NEMO underestimates the seasonal amplitude along the coast by nearly 50%.
QBO wind influence on MJO-induced temperature anomalies in the upper troposphere and lower stratosphere in an idealized model
Authors: Lim Yuna , Son Seok-Woo
Published: March 2022

The dynamical mechanism by which the quasi-biennial oscillation (QBO) might influence the temperature anomaly, associated with the Madden-Julian oscillation (MJO), in the equatorial upper troposphere and lower stratosphere (UTLS) is examined by conducting a series of initial-value experiments using a dry primitive equation model. The observed temperature response to the MJO convection becomes colder and more in-phase with the convection during easterly QBO (EQBO) than westerly QBO (WQBO) phases. This QBO-dependent MJO temperature anomaly in the UTLS is qualitatively reproduced by model experiments in which EQBO or WQBO background state is artificially imposed above 250 hPa while leaving the troposphere unaltered. As in the observations, the cold anomaly in the UTLS becomes strengthened and steepened with EQBO-like background state than WQBO-like one. It turns out that the QBO zonal wind, instead of temperature, plays a major role in determining the UTLS temperature anomaly by modulating wave energy dispersion.
Modeling the evolution of central Asian drylands during the Cenozoic
Authors: Zhang Ran , Zhang Zhongshi , Jiang Dabang , Ramstein Gilles , Dupont-Nivet Guillaume , Li Xiangyu
Published: March 2022

The evolution of central Asian drylands during the Cenozoic is a hot topic in paleoclimate research, but the underlying mechanism remains unclear. Here, we investigate this topic with climate modeling based on six key geological periods. Our results indicate that central Asian drylands have existed since the early Eocene, after which they move northward and become narrower. Although changed land–sea distribution and decreased atmospheric CO2 concentration promote the aridification of drylands, they only slightly affect the latitudinal distribution of drylands. By comparison, the growth of Asian high-topography areas, especially the Tibetan Plateau (TP), makes central Asian drylands move northward, concentrate in narrow latitudinal bands, and increase in intensity. Good model-data qualitative agreement is obtained for stepwise aridification in midlatitude inland Asia north of ~40°N, and the uplifted main and northern TP by the early Miocene likely forced drylands to change in this region.
Influence of rainfall patterns on sediment yield in flood couplets of a check dam on the Chinese Loess Plateau
Authors: Yin Minfeng , Zhang Jiaqiong
Published: March 2022

Check dam plays a crucial role in controlling soil erosion on the Loess Plateau and reducing sediment loads in the Yellow River. Moreover, sediment deposition in check dams also provides valuable information for understanding of soil erosion on the Loess Plateau. Study on the influence of rainfall patterns on sediment yield in small catchments scale is significant for the reasonable arrangement of soil and water conservation measures, particularly for complex environments such as the wind-water erosion crisscross region. This study estimated sediment yield trapped by the check dam in Laoyeman catchment based on deposited flood couplets formed in erosion rainfall events during the period 1978-2010. All erosive rainfall were divided into three rainfall patterns according to the precipitation, rainfall duration and rainfall erosivity, and the correspondence analysis between sediment yield and rainfall pattern was analyzed. Results showed that there were 1.1´105 t sediment deposited in the dam filed during the trapping history of the check dam as a whole. It has three obvious change stages, which had sediment yield of 4.53´104 t during 1978-1988, 4.48´104 t during 1988-1997, and 1.68´104 t during 1997-2010, respectively. The stage 1989-1997 had the fastest annual deposition rate of 4.98×103 t·year-1, 20.9% and 286% faster than stage 1978-1988 and stage 1998-2010. For similar rainfall pattern in these three stages, sediment yield and the characteristic of flood couplet change were closely related to both rainfall erosivity and land use types. This was also approved by the significant decrease of sediment yield on condition of similar rainfall pattern in a decade before and after the implementation of Grain for Green project indicated that this project made a great contribution to the control of soil erosion on the Loess Plateau. The impact of rainfall pattern on sediment yield indicated that the largest sediment yield is initiated under short duration and high intensity rainfall events, while the sediment in the reservoir area is mainly deposited under the rainfall pattern of moderate precipitation, erosivity and duration. That is the reason for the wettest year (1995) had relatively low sediment deposition, while the year (1982) had strong rainfall erosivity had the maximum annual sediment yield (1.68´104 t).
Local and remote forcing of sea-level variation off the northeast US coast
Authors: Lee Tong , Wang Ou , Piecuch Christopher , Fukumori Ichiro , Fenty Ian , Frederikse Thomas , Menemenlis Dimitris , Ponte Rui , Zhang Hong
Published: March 2022

The relative contributions of local and remote wind stress and air-sea buoyancy forcing to sea-level variations along the East Coast of the United States are not well quantified, hindering the understanding of sea-level predictability there. Here, we use an adjoint sensitivity analysis together with an Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate to establish the causality of interannual sea-level variations near the Nantucket island, the approximate geographic center of the northeast US coast where sea-level fluctuations are coherent. Wind forcing explains 68% of the Nantucket interannual sea-level variance, while wind and buoyancy forcing together explain 97% of the variance. Wind stress contribution is near-local, primarily from the New England shelf northeast of Nantucket. We disprove a previous hypothesis about Labrador Sea wind stress being an important driver of Nantucket sea-level variations and another hypothesis suggesting local wind stress being a secondary driver. Buoyancy forcing, as important as wind stress in some years, includes local contributions as well as remote contributions from the subpolar North Atlantic that influence Nantucket sea level a few years later. Our rigorous adjoint-based analysis corroborates previous correlation-based studies that sea-level variations in the subpolar gyre and the northeast US coast can both be influenced by subpolar buoyancy forcing. Forward forcing perturbation experiments further indicate remote buoyancy forcing affects Nantucket sea level mostly through slow advective processes, although waves can cause rapid Nantucket sea level response within a few weeks. Our results quantifying the spatial distribution of forcing contributions to Nantucket sea-level variations are also useful for the development of machine-learning models for predicting sea-level variation off the northeast US coast.
Link Between the Landslides and the Generated Seismic Signals: Dynamic Inversion and Numerical Simulation
Authors: Cui Yifei
Published: March 2022

The high-speed landslide may result in varying degrees of damage to downstream, such as dammed lake and subsequent dam failure and outburst flood. Nowadays, the seismic station is able to records the seismic signals of the entire process of landslide, provides valuable data for understanding the landslide process. Meanwhile, numerical simulation can also simulate the entire landslide process. However, it is seriously affected by variability of input parameters. To tackle the scientific challenge, we comprehensively analyzed the 2018 Baige landslide by firstly performing a joint time-frequency domain transform of the seismic signal using short-time fourier transform. We then reconstruct the land slide force history using empirical Green’s function. We used the constructed landslide force history inversion to calibrate the numerical input parameters using Discrete Element Method. Finally, we use the calibrated parameters to construct the whole process of landslide numerically. This study provides a potential way that improves the rationality and reliability of the landslide reconstruction using multi-method joint analysis.
High concentrations of environmentally persistent free radicals in fire derived pyrogenic organic matter
Authors: Sigmund Gabriel , Santin Nuno Cristina , Pignitter Marc , Tepe Nathalie , Doerr Stefan Helmut , Hofmann Thilo
Published: March 2022

Fire derived pyrogenic organic matter / charcoal is a source of environmentally persistent free radicals, which are precursors of potentially harmful reactive oxygen species. We analyzed charcoal samples from ten wildfires, including crown as well as surface fires in boreal, temperate, subtropical and tropical climate regions. Concentrations of environmentally persistent free radicals in these samples were orders of magnitude higher than those found in soils or other “background” matrices, as measured via electron spin resonance spectroscopy. The highest concentrations were measured in woody charcoals that were highly carbonized. We also found that environmentally persistent free radicals remained unexpectedly stable in the field for at least 5 years.

More details can be found in our recently published article: https://www.nature.com/articles/s43247-021-00138-2
Relationship between seismic swarms and episodic inflations at Akutan Volcano in Alaska
Authors: Song Zilin , Tan Yen Joe
Published: March 2022

Seismic swarms at volcanic regions are important manifestations of volcanic unrest. While they are often inferred to be related to fluid or magma movements, their underlying process remains an active research topic. In particular, quantifying the proportion of seismic swarms that are related to magma movement can potentially improve their utility for eruption forecasting. To better understand the relationship between seismic swarms and magma movement, we focus on the Akutan volcano where episodic inflations have been recorded every 2-3 years since 2002. We first applied template matching on continuous seismic waveforms between 2005-2017 to improve the earthquake catalog’s magnitude of completeness. We further classified the events as long-period (LP) or regular volcano-tectonic (VT) events based on their frequency content. After waveform-based double-difference relocation, we find that the VT and LP events are concentrated above and below the shallow magma reservoir respectively. We clustered the VT and LP events based on their spatiotemporal evolution and find that most clusters are swarm-like with no clear mainshock-aftershock sequences. Based on their temporal relation to the inflation episodes, we infer that the LP swarms are related to ascending magma into the shallow reservoir, which sometimes triggers VT swarms through stress transfer.
The influence of dune lee side shape on flow above bedforms
Authors: Lefebvre Alice , Cisneros Julia
Published: March 2022

Dunes which develop in large rivers, in tidally-constrained environments (estuaries and tidal channels) and in open marine areas (e.g. continental shelf) commonly have gentle lee sides, and more rarely steep lee sides close to the angle-of-repose (30°). Lee side angle has a strong influence on the interaction between dunes and flow: over steep lee side angles (> ca. 25°), the flow separates and a strong turbulent wake is formed. Over intermediate angles (ca. 15 to 25°), flow separation is reduced or intermittent and the wake is small and weak. Over angles less than ca. 15°, there is no flow separation and only little turbulence produced.

However, the lee side is rarely made of a straight line with a constant angle. Instead, it usually varies, with gentler and steeper portions. Recently, it has been demonstrated that dunes in big rivers have their maximum lee side angle situated close to the trough. On the other hand, the lee side of estuarine bedforms is situated close to the crest. The influence of the position of the steepest slope on flow properties above bedforms is currently unknown.

To characterise it, many numerical modelling experiments were carried out to simulate flow properties (Reynolds-averaged velocities and turbulence) over low and high-angle dunes, with their steepest slope varying between the crest and the trough. The results show that the position of the steep portion on the lee side has an influence on flow properties over dunes.
Maturity of worldwide glacier data sets – history and future ambitions
Authors: Gärtner-Roer Isabelle , Nussbaumer Samuel U. , Raup Bruce , Paul Frank , Welty Ethan , Windnagel Ann , Fetterer Florence , Zemp Michael
Published: March 2022

The creation and curation of environmental data present numerous challenges and rewards. In this study, we reflect on the maturity of freely available glacier data sets (inventories and changes), as well as on related demands by data providers, data users, and data repositories in-between. The amount of glacier data has increased significantly over the last two decades, especially as remote-sensing techniques have developed quickly. The portfolio of observed parameters has increased as well, which presents new challenges for international data centers, and fosters new expectations from users.

We assess the services of the Global Terrestrial Network for Glaciers (GTN-G) as the central organization for standardized data on glacier distribution and changes. Within GTN-G, different glacier data sets are consolidated under one umbrella, and the glaciological community supports this service by actively contributing their data sets and by providing strategic guidance via an Advisory Board. To assess each GTN-G data set, we present a maturity matrix and summarize achievements, challenges, and future ambitions.

Most challenges can only be overcome in a financially secure setting for data services and with the help of international standardization. Therefore, dedicated support and long-term commitment for certified data repositories build the basis for the successful democratization of data. In the field of glacier data, this balancing act has so far been successfully achieved through joint collaboration between data repositories, data providers, and data users. However, we also note an unequal allotment of funds for data creation and projects using the data, and data curation. Considering the importance of glacier data to answering numerous key societal questions (from water availability to global sea-level rise), this imbalance needs to be adjusted. In order to guarantee the continuation and success of GTN-G in the future, basic funding schemes, flexible adaptation measures, and regular evaluations are required.
Estimation of Earth rotation parameters from Lunar Laser Ranging data 
Authors: Biskupek Liliane , Singh Vishwa Vijay , Müller Jürgen , Zhang Mingyue
Published: March 2022

In addition to Very Long Baseline Interferometry (VLBI) the Earth rotation phase ∆UT1 can also be determined directly from Lunar Laser Ranging (LLR) data. With the other Earth Orientation Parameters (EOP) like terrestrial pole coordinates and nutation parameters, the determination of a full set of EOP is possible from LLR observations. In recent years LLR observations have been carried out with bigger telescopes (APOLLO) and at infrared wavelength (OCA, Wettzell). This resulted in a better distribution of LLR data over the lunar orbit and retro-reflectors with a higher accuracy. The aim of our recent study is to quantify, how much the EOP determination can be improved with the new high-accurate LLR data compared to previous years and if it can then be used to validate VLBI results. First, we focus on estimating ∆UT1 and terrestrial pole coordinates from different constellations such as single or multi-station data and for a different number of normal points per night. The accuracies of the results determined from the new LLR data (after 2000.0) have significantly improved, being less than 20 µs for ∆UT1, less than 2.5 mas for xp, and less than 3 mas for yp for nights selected from subsets of the LLR time series which have 10 and 15 normal points obtained per night. Second, we focus on the determination of corrections of the nutation coefficients to the MHB2000 model of the IERS Conventions 2010. Here we also see significant smaller correction values and accuracies with an improvement of one order of magnitude, that means accuracies better then 0.01 mas. Recent results will be presented and discussed.

This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC-2123 QuantumFrontiers – 390837967.