bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future
Authors: Noble T. L. , Rohling E. J. , Aitken A. R. A. , Bostock H. C. , Chase Z. , Gomez N. , Jong L. M. , King M. A. , Mackintosh A. N. , McCormack F. S. , McKay R. M. , Menviel L. , Phipps S. J. , Weber M. E. , Fogwill C. J. , Gayen B. , Golledge N. R. , Gwyther D. E. , Hogg A. McC. , Martos Y. M. , Pena‐Molino B. , Roberts J. , van de Flierdt T. , Williams T. 
Published: August 2020

AbstractThe Antarctic Ice Sheet (AIS) is out of equilibrium with the current anthropogenic‐enhanced climate forcing. Paleoenvironmental records and ice sheet models reveal that the AIS has been tightly coupled to the climate system during the past and indicate the potential for accelerated and sustained Antarctic ice mass loss into the future. Modern observations by contrast suggest that the AIS has only just started to respond to climate change in recent decades. The maximum projected sea level contribution from Antarctica to 2100 has increased significantly since the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report, although estimates continue to evolve with new observational and theoretical advances. This review brings together recent literature highlighting the progress made on the known processes and feedbacks that influence the stability of the AIS. Reducing the uncertainty in the magnitude and timing of the future sea level response to AIS change requires a multidisciplinary approach that integrates knowledge of the interactions between the ice sheet, solid Earth, atmosphere, and ocean systems and across time scales of days to millennia. We start by reviewing the processes affecting AIS mass change, from atmospheric and oceanic processes acting on short time scales (days to decades), through to ice processes acting on intermediate time scales (decades to centuries) and the response to solid Earth interactions over longer time scales (decades to millennia). We then review the evidence of AIS changes from the Pliocene to the present and consider the projections of global sea level rise and their consequences. We highlight priority research areas required to improve our understanding of the processes and feedbacks governing AIS change.
Impact of Scenario Selection on Robustness
Authors: McPhail C. , Maier H. R. , Westra S. , Kwakkel J. H. , van der Linden L. 
Published: August 2020

AbstractMultiple plausible future scenarios are being used increasingly in preference to a single deterministic or probabilistic prediction of the future in the long‐term planning of water resources systems. These scenarios enable the determination of the robustness of a system—the consideration of performance across a range of plausible futures—and allow an assessment of which possible future system configurations result in a greater level of robustness. There are many approaches to selecting scenarios, and previous studies have observed that the choice of scenarios might affect the estimated robustness of the system. However, these observations have been anecdotal and qualitative. This paper develops a systematic, quantitative methodology for exploring the influence of scenario selection on the robustness and the ranking of decision alternatives. The methodology is illustrated on the Lake Problem. The quantitative results obtained confirm the qualitative observations of previous works, showing that the selection of scenarios is important, as it has a large influence on the robustness value calculated for each decision alternative. However, we show that it has a relatively small influence on how those decision alternatives are ranked. This implies that despite the difference in robustness values, similar decision outcomes will be reached in this case study, regardless of the basis on which the scenarios are obtained. It is also revealed that the impact of the scenarios on the robustness values is due to complex interactions with the system model and robustness metrics.
Random Forest Model of Ultralow‐Frequency Magnetospheric Wave Power
Authors: Bentley S. N. , Stout J. R. , Bloch T. E. , Watt C. E. J. 
Published: August 2020

AbstractModels of magnetospheric ultralow‐frequency (ULF) waves can be used to study wave phenomena and to calculate the effect of these waves on the energization and transport of radiation belt electrons. We present a decision tree ensemble (i.e., a random forest) model of ground‐based ULF wave power spectral density driven by solar wind speed vsw, north‐south component of the interplanetary magnetic field Bz, and variance of proton number density var(Np). This model corresponds to four radial locations in the magnetosphere (roughly L ∼ 4.21 to 7.94) and spans 1–15 mHz, with hourly magnetic local time resolution. The decision tree ensembles are easier to use than the previous model generation; they have better coverage, perform better at predicting power, and have reduced error due to intelligently chosen bins in parameter space. We outline the difficulties in extracting physics from parameterized models and demonstrate a hypothesis testing framework to iteratively explore finer driving processes. We confirm a regime change for ULF driving about Bz = 0. We posit that ULF wave power directly driven by magnetopause perturbations corresponds to a latitude‐dependent dawn‐dusk asymmetry, which we see with increasing speed. Model uncertainty identifies where the underlying physics is not fully captured; we find that power due to substorms is less well characterized by Bz > 0, with an effect that is seen globally and not just near midnight. The largest uncertainty is seen for the smallest amounts of solar wind driving, suggesting that internal magnetospheric properties may play a significant role in ULF wave occurrence.
Climate Change Dominated Long‐Term Soil Carbon Losses of Inner Mongolian Grasslands
Authors: Xin Xiaoping , Jin Dongyan , Ge Yong , Wang Jianghao , Chen Jiquan , Qi Jiaguo , Chu Housen , Shao Changliang , Murray Philip J. , Zhao Ruixue , Qin Qi , Tang Huajun 
Published: August 2020

AbstractSoil organic carbon (SOC) is the most critical component of global carbon cycle in grassland ecosystems. There has been growing interest in understanding SOC dynamics and driving forces of grassland biomes at various temporal and spatial scales. Up to now, estimates of long‐term and large‐scale changes in SOC of grassland biomes have been mostly based on modeling approaches and manipulative experiments, rather than direct measurements. During 2007–2011, we repeated 141 soil profiles of the sampling in 1963–1964 (up to 1‐m depth) to quantify the long‐term changes of SOC storage in the major grassland types of Inner Mongolia in order to tease apart the relative contributions of climate change and grazing. We found that SOC decreased in all soil types, except in the eolian sandy soils, from 1963 to 2007, with an average reduction rate of 1.8 kg C m−2 (~22.9% or 0.52% year−1) in the grassland biome of Inner Mongolia. We quantitatively clustered the soils into four groups using principal component analysis (PCA) and detected clear spatial dependency of the changes on climate and grazing. The climate change was responsible for 15.3–34.9% of the total SOC variations, whereas grazing intensity accounted for <9.5% of the changes. Our findings indicated that climate change, rather than grazing, was the primary forcing for the changes in SOC of Inner Mongolia grasslands. We presume that other driving forces, such as changes in nongrazing‐resultant wind erosion and atmospheric nitrogen deposition, might have played a role albeit their effects need to be further examined.
Plasma Waves Causing Relativistic Electron Precipitation Events at International Space Station: Lessons From Conjunction Observations With Arase Satellite
Authors: Kataoka Ryuho , Asaoka Yoichi , Torii Shoji , Nakahira Satoshi , Ueno Haruka , Miyake Shoko , Miyoshi Yoshizumi , Kurita Satoshi , Shoji Masafumi , Kasahara Yoshiya , Ozaki Mitsunori , Matsuda Shoya , Matsuoka Ayako , Kasaba Yasumasa , Shinohara Iku , Hosokawa Keisuke , Uchida Herbert Akihito , Murase Kiyoka , Tanaka Yoshimasa 
Published: August 2020

AbstractWe report three different types of relativistic electron precipitation (REP) events observed at International Space Station (ISS), associated with electromagnetic ion cyclotron (EMIC) waves or whistler mode waves as observed by the Arase satellite at conjugate locations near the magnetic equator. Three different detectors installed on the ISS were complementarily used; CALET/CHD as the detector of precipitating MeV electrons, MAXI/RBM as the detector of sub‐MeV electrons from horizontal and vertical directions, and SEDA‐AP/SDOM to quantitatively measure the energy spectrum. The REP event on 21 August 2017 shows a quasiperiodic intensity variation at ~1 Hz which corresponds to variations of the EMIC waves at the Arase altitudes. The REP event on 24 April 2017 shows rapid and irregular intensity variation which corresponds to the amplitude variation of chorus waves, while the REP events on 26 October 2017 shows a smooth quasiperiodic time variation at ~0.2 Hz which corresponds to the amplitude variation of “electrostatic” whistler mode waves. This study clearly demonstrates that the time variation of REP events at ISS are caused by various types of plasma waves near the magnetic equator.
The Physical Mechanisms for the Sunrise Enhancement of Equatorial Ionospheric Upward Vertical Drifts
Authors: Chen Junjie , Wang Wenbin , Lei Jiuhou , Dang Tong 
Published: August 2020

AbstractSatellite and incoherent scatter radar observations have shown frequently a strong enhancement of upward vertical E × B drifts in the equatorial ionospheric F region near sunrise. Previous studies suggested that this enhancement is associated with the local equatorial wind dynamo, the same process used to explain the prereversal enhancement after sunset. However, this hypothesis has never been tested in a first‐principles way. In this study, we explore the physical mechanisms responsible for the sunrise enhancement of equatorial upward vertical drifts using the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. The model well reproduces the sunrise enhancement of upward vertical drifts observed at Jicamarca on 10 June 2004. The simulation results show that large eastward zonal electric fields occur around sunrise at all latitudes but with a peak at middle latitudes. Further numerical experiments reveal that the equatorial sunrise enhancement at solar minimum is primarily driven by the E region zonal wind dynamo at middle latitudes rather than by the local dynamo effect in the equatorial region. Specifically, the intensity of the equatorial eastward electric field near sunrise is determined by the magnitudes of westward wind and its longitudinal gradient at middle latitudes and the declination of the dawn termination.
Observations of Anomalous Charge Structures in Supercell Thunderstorms in the Southeastern United States
Authors: Stough Sarah M. , Carey Lawrence D. 
Published: August 2020

AbstractAnomalous thunderstorm charge structures (ACSs), characterized by a dominant layer of positive charge in the lower mixed‐phase region, are uncommon and rarely reported outside of the Great Plains region of the United States. This study documents the kinematics, precipitation microphysics, and charge structures of two supercell thunderstorms exhibiting ACSs that were observed in the Southeastern United States. Ground‐based three‐dimensional total lightning observations, polarimetric Doppler radar observations, and environmental model analysis of these supercells presented the opportunity to evaluate conceptual models of ACS development and characteristics in an atypical parameter space. In both anomalous storms, prominent layers of positive charge were located in lower to middle mixed‐phase regions (−10°C to −30°C) of updrafts and were spatially associated with riming hydrometeor types. Simultaneously, negative charge regions were identified above the primary positive charge layers in the upper mixed‐phase and glaciated region of updrafts, collocated with graupel and small ice hydrometeors. While coarse charge structure observations were consistent with noninductive charging‐based models of anomalous storms, charge structure complexities were also observed that suggested variability in cloud microphysical conditions. Analysis of the environments in which these storms formed indicated that several parameters thought to increase mixed‐phase liquid water content in favor of anomalous charging were inconsistent with those documented in the Great Plains region. However, environmental humidity metrics were most comparable. Comparisons between these and other documented anomalous storms identified similarities in kinematic structure and microphysical conditions while motivating ongoing study of the environmental parameter space supportive of ACSs.
The Unique Characteristics and Potential Mechanisms of the MJO‐QBO Relationship
Authors: Sakaeda Naoko , Dias Juliana , Kiladis George N. 
Published: August 2020

AbstractPrevious studies have shown that Madden‐Julian oscillation (MJO) convective activity increases when quasi‐biennial oscillation (QBO) easterlies appear in the lower stratosphere, and that this relationship is seen only during boreal winter. However, the physical mechanism behind this relationship is not fully understood. Building upon previous literature on the MJO‐QBO relationship, this study first tests whether the relationship between the QBO and MJO extends to other modes of organized tropical convection. Our analysis shows that the QBO does not have any significant relationship with other modes of variability such as convectively coupled equatorial waves (CCEWs). An extended analysis for periods prior to 1979 also shows that the boreal winter QBO‐MJO relationship substantially weakens prior to 1979. These results imply that, in addition to the seasonal dependence, any proposed mechanisms for the relationship between the QBO and MJO must be able to explain the uniqueness of this relationship with respect to other CCEWs, as well as the reason for its strengthening after 1979. Among the analyzed modes of tropical convection, the MJO is the most sensitive to the modulation of high cloud fraction and associated radiative feedback by the QBO and this sensitivity may weaken prior to 1979. These results indicate that the strong top‐heaviness of vertical motion and cloud‐radiative feedback associated with the MJO are important to explain its unique relationship with the QBO.
Mediterranean Overflow Over the Last 250 kyr: Freshwater Forcing From the Tropics to the Ice Sheets
Authors: Sierro Francisco J. , Hodell David A. , Andersen Nils , Azibeiro Lucia A. , Jimenez‐Espejo Francisco J. , Bahr André , Flores Jose Abel , Ausin Blanca , Rogerson Mike , Lozano‐Luz Rocio , Lebreiro Susana M. , Hernandez‐Molina Francisco Javier 
Published: August 2020

AbstractTo investigate past changes in the Mediterranean Overflow Water (MOW) to the Atlantic, we analyzed the strength of the MOW and benthic δ13C along the last 250 kyr at Integrated Ocean Drilling Program (IODP) Site U1389 in the Gulf of Cadiz, near the Strait of Gibraltar. Both the strength of the MOW and the benthic δ13C were mainly driven by precession‐controlled fluctuations in the Mediterranean hydrologic budget. Reduced/enhanced Nile discharge and lower/higher Mediterranean annual rainfall at precession maxima/minima resulted in higher/lower MOW strengths at Gibraltar and stronger/weaker Mediterranean overturning circulation. At millennial scale, the higher heat and freshwater loss to the atmosphere during Greenland stadials increased buoyancy loss in the eastern Mediterranean. This enhanced the density gradient with Atlantic water, resulting in a higher MOW velocity in the Gulf of Cadiz. Unlike non‐Heinrich stadials, a lower‐amplitude increase in velocity was seen during Heinrich stadials (HSs), and a significant drop in velocity was recorded in the middle phase. This weak MOW was especially recognized in Termination I and II during HS1 and HS11. These lower velocities at the depth of Site U1389 were triggered by MOW deepening due to the lower densities of Atlantic intermediate water caused by freshwater released from the Laurentide and Eurasian ice sheets. The intrusion of salt and heat at deeper depths in the Atlantic during HSs and its shoaling at the end could have contributed to drive the changes in the Atlantic Meridional Overturning Circulation during Terminations.
New Timing and Depth Constraints for the Catalina Metamorphic Core Complex, Southeast Arizona
Authors: Ducea Mihai N. , Triantafyllou Antoine , Krcmaric Jordan 
Published: August 2020

AbstractThe Santa Catalina‐Tortolita‐Rincon Mountains of Southeast Arizona are a classic metamorphic core complex (MCC) and represent footwall exposures of crustal rocks exhumed by a detachment system. This study presents new evidence for the formation of the majority of ductile deformation during the Eocene (~46 Ma), synchronous with the emplacement of the regionally significant Wilderness Sills Suite (57–45 Ma). The evidence is provided by Eocene U‐Pb ages of syn‐ to late kinematic dikes emplaced in the principal ductile mylonitic fabric of the Catalina forerange, earlier than the brittle normal fault system and the formation of Tucson basin beginning with the latest Oligocene. Well‐documented shear sense indicators may not reflect extension at that time (Eocene), but more likely the direction of crustal flow now rotated during later extension. Muscovite‐plagioclase Rb‐Sr isochron ages of three mylonitic rocks are all clustered around 34 Ma, which is inferred to be the last age when these rocks were being deformed under ductile conditions following the emplacement of the Wilderness Sills Suite and various related dikes. Biotite‐plagioclase Rb‐Sr ages on the same rocks demonstrate that the section cooled below ~300°C at 25–26 Ma during the development of normal faulting. Normal faulting was synchronous with the emplacement of the Catalina Intrusive Suite. New U‐Pb age results for Catalina Intrusive Suite indicate a combined mean age of 24.9 Ma. Chemical compositions of hornblende‐plagioclase pairs were obtained on six Catalina Intrusive Suite samples; depth estimates for the emplacement of the Catalina Intrusive Suite average of about 6 km. These results suggest that the exposed Catalina ductile detachment system was at about 5 km beneath the surface at 25 Ma. These new data bring new light into the development of this core complex and suggest that the similarity in orientations of principal ductile and brittle fabrics at the Catalina MCC locality are coincidental. Neither was the principal ductile fabric developed during the low‐angle normal faulting of the latest Oligocene nor was this exposed section a midcrustal one at that time. Transient, pluton emplacement‐enhanced, and extension‐related ductile deformation at shallow crustal levels operated locally at ~25 Ma but that does not account for the development of the majority of the Catalina MCC mylonites.
Transport and Retention of Sulfidized Silver Nanoparticles in Porous Media: The Role of Air‐Water Interfaces, Flow Velocity, and Natural Organic Matter
Authors: Leuther Frederic , Köhne John Maximilian , Metreveli George , Vogel Hans‐Jörg 
Published: August 2020

AbstractThe sulfidation and aging of silver nanoparticles (Ag‐NPs) with natural organic matter (NOM) are major transformation processes along their pathway in wastewater treatment plants and surface waters. Although soils appear to be a sink for disposed Ag‐NPs, the impact of variable saturation on the transport and retention behavior in porous media is still not fully understood. We studied the behavior of sulfidized silver nanoparticles (S‐Ag‐NPs, 1 mg L−1) in saturated and unsaturated sand columns regarding the effects of (i) the presence of NOM (5 mg L−1) in the aquatic phase on retention, transport, and remobilization of S‐Ag‐NPs and (ii) the distribution and quantity of air‐water and solid‐water interfaces for different flow velocities determined via X‐ray microtomography (X‐ray μCT). Unsaturated transport experiments were conducted under controlled conditions with unit gradients in water potential and constant water content along the flow direction for each applied flux. It was shown that (i) NOM in S‐Ag‐NP dispersion highly increased the NP‐mobility; (ii) differences between saturated and unsaturated transport were increasing with decreasing flux and, consequently, decreasing water contents; (iii) both, solid‐water and air‐water interfaces were involved in retention of S‐Ag‐NPs aged by NOM. Using numerical model simulations and X‐ray μCT of flow experiments, the breakthrough of Ag‐NP could be explained by a disproportional increase in air‐water interfaces and an increasing attachment efficiency with decreasing water content and flow velocity.
An Analytical Method to Calculate Groundwater Released From an Aquitard Undergoing Nonlinear Consolidation
Authors: Luo Huan , Li Zhaofeng , Luo Maolin , Zhang Qiang , Illman Walter A. 
Published: August 2020

AbstractThe estimation of groundwater released from aquitards is important for the groundwater resource management. In this study, a governing equation of drawdown variation within the aquitard, which undergoes nonlinear consolidation, was obtained based on the consolidation theory of Gibson et al. (1967, https://doi.org/10.1680/geot.1967.17.3.261). Then, analytical solutions of drawdown variations within an aquitard were derived for a single aquifer underlying an aquitard, as well as for the case when there are aquifers above and below an aquitard. Drawdown solutions were obtained for both the cases when there was a sudden hydraulic head decline in the confined aquifer(s). The characteristics of the groundwater dynamics and water balance in the aquitard have been analyzed with the analytical solution. A laboratory experiment was conducted to verify the analytical solution, and a type‐curve fitting method was presented to calculate the aquitard's hydraulic parameters. Our study revealed that the cumulative water released from the aquitard predicted by Gibson's theory (1967) is less than that obtained through Terzaghi's theory (1943). Groundwater released from the aquitard increases with increasing compression index, aquitard thickness, and drawdown of the adjacent aquifer, and with decreasing initial void ratio and initial effective stress. The time for the drawdown to reach steady state increases with increasing compression index, initial void ratio, and aquitard thickness, and with decreasing initial effective stress and hydraulic conductivity.