bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proton Ring Evolution and Its Effect on Magnetosonic Wave Excitation: Particle‐In‐Cell Simulation and Linear Theory
Authors: Ouyang Zhihai , Yuan Zhigang , Yu Xiongdong , Yao Fei 
Published: June 2021

AbstractIn this letter, we used one‐dimensional (1‐D) particle‐in‐cell (PIC) simulations as well as linear theory to investigate the relationship between proton ring evolution and fast magnetosonic (MS) wave excitation. Simulations demonstrate that most of the ring protons can be scattered toward lower energies via MS waves excited by the initial proton ring distribution, leading to the increase of the proton ring speed corresponding to the maximum phase space density. These protons with a higher ring speed can further excite MS waves at a lower frequency. As a result, a new “double ring” distribution is found to be formed through scattering of higher energy protons by the lower frequency MS waves. The letter demonstrates the detailed evolution process of proton ring distribution and its effect on the excitation of MS waves.
Do Existing Theories Explain Seasonal to Multi‐Decadal Changes in Glacier Basal Sliding Speed?
Authors: Gimbert F. , Gilbert A. , Gagliardini O. , Vincent C. , Moreau L. 
Published: June 2021

AbstractTheoretical descriptions of ice‐bed friction beneath glaciers and ice sheets are key to predict changes in sea level. Applicability of these theories at the natural landscape scale and over long periods has however not been tested. Here we test hard bed friction laws by analyzing a unique data set of in‐situ basal sliding measurements collected over three decades under an Alpine glacier enduring large changes in geometry. We report many observational features that are in striking agreement with theoretical predictions. However, we also observe an undocumented behavior where the basal stress state stabilizes near Iken's limit under meltwater input, which suggests the basal effective pressure is primarily set by bed shear stress rather than by water input and drainage specifics as commonly thought. As a result, long‐term changes in year‐averaged sliding velocities follow a simple power law scaling with bed shear stress as opposed to more complex pressure‐dependent relationships.
Delayed Collapse of the North Pacific Intermediate Water After the Glacial Termination
Authors: Zhao Debo , Wan Shiming , Lu Zhengyao , Zhai Lina , Feng Xuguang , Shi Xuefa , Li Anchun 
Published: June 2021

AbstractCarbon release from the North Pacific in glacial‐interglacial cycles has been mainly linked to the North Pacific Intermediate Water (NPIW) formation and associated carbon/nutrient water upwelling and biological productivity changes. However, relationship between NPIW and atmospheric CO2 change in the early interglacial remains unclear. Here we report a high‐resolution sediment record of NPIW evolution based on paleo‐redox changes in the Western North Pacific during the last 400 ka. Our proxy and model results reveal a delayed collapse of NPIW after the glacial termination was coeval with decreased salinity of intermediate water and increased net rainfall in the North Pacific. Such weakened NPIW formation in the North Pacific probably make a contribution to maintain high atmospheric CO2 concentrations through weakened intermediate‐to‐deep ocean stratification and reduced subsurface biological pump net efficiency, countering the return to more stratified conditions in the Southern Ocean, which should drive down atmospheric CO2 during the early interglacial.
Assessing Biases and Climate Implications of the Diurnal Precipitation Cycle in Climate Models
Authors: Christopoulos Costa , Schneider Tapio 
Published: June 2021

AbstractThe diurnal cycle is a common benchmark for evaluating the performance of weather and climate models on short timescales. For decades, capturing the timing of peak precipitation during the day has remained a challenge for climate models. In this study, the phase and amplitude of the diurnal precipitation cycle in Coupled Model Intercomparison Project (CMIP) models are compared to satellite data. While some improvements align CMIP6 models closer to satellite observations, significant biases in the timing of peak precipitation remain, especially over land. Notably, precipitation over land in CMIP6 models still occurs ∼5.4 h too early; the diurnal cycle amplitude is ∼0.81 mm day−1 too small over the oceans. Further, the diurnal phase of oceanic precipitation correlates weakly with the equilibrium climate sensitivity in CMIP6 models: models with a later precipitation peak over oceans tend to exhibit a higher climate sensitivity. However, it is unclear whether this relationship is robust.
Sea Surface Height Anomalies of the Arctic Ocean From ICESat‐2: A First Examination and Comparisons With CryoSat‐2
Authors: Bagnardi M. , Kurtz N. T. , Petty A. A. , Kwok R. 
Published: June 2021

AbstractAccurately resolving spatio‐temporal variations in sea surface height across the polar oceans is key to improving our understanding of ocean circulation variability and change. Here, we examine the first 2 years (2018–2020) of Arctic Ocean sea surface height anomalies (SSHA) from the photon‐counting laser altimeter onboard NASA's Ice, Cloud, and land Elevation Satellite‐2 (ICESat‐2). ICESat‐2 SSHA estimates are compared to estimates from ESA's CryoSat‐2 mission, including semisynchronous along‐track measurements from the recent CRYO2ICE orbit alignment campaign. There are documented residual centimeter‐scale range biases between the ICESat‐2 beams (in release‐003 data) and we opted for a single‐beam approach in our comparisons. We find good agreement in the along‐track estimates (spatial correlation coefficient >0.8 and mean differences <0.03 m) as well as in the gridded monthly SSHA estimates (temporal correlation coefficient of 0.76 and a mean difference of 0.01 m) from the two altimeters, suggesting ICESat‐2 adds to the CryoSat‐2 SSHA estimates.
Air‐Sea Interaction in the Western Tropical Pacific and its Impact on Asymmetry of the Ningaloo Niño/Niña
Authors: Kusunoki Hidehiro , Kido Shoichiro , Tozuka Tomoki 
Published: June 2021

AbstractNingaloo Niño/Niña is the dominant interannual sea surface temperature (SST) variability off Western Australia with the former typically stronger than the latter. Although a recent study suggested that oceanic teleconnections from the Pacific partly contribute to the amplitude asymmetry, this seems counterintuitive as La Niña, which often induces the Ningaloo Niño, is generally weaker than El Niño. Here, mechanisms of the amplitude asymmetry in the oceanic teleconnection are investigated by analyzing reanalysis data and conducting ocean model simulations. Sensitivity experiments using a linear continuously stratified model reveal that stronger easterly wind anomalies in the western equatorial Pacific contribute to the stronger oceanic teleconnection during the Ningaloo Niño. Furthermore, a mixed layer heat budget analysis with a regional ocean model shows that negatively skewed SST anomalies in the central equatorial Pacific related to the skewed wind anomalies in the western equatorial Pacific, are mainly induced by vertical advection/diffusion and entrainment.
Intermittent Reduction in Ocean Heat Transport Into the Getz Ice Shelf Cavity During Strong Wind Events
Authors: Steiger Nadine , Darelius Elin , Wåhlin Anna K. , Assmann Karen M. 
Published: June 2021

AbstractThe flow of warm water toward the western Getz Ice Shelf along the Siple Trough, West Antarctica, is intermittently disrupted during short events of Winter Water deepening. Here we show, using mooring records, that these 5–10 days‐long events reduced the heat transport toward the ice shelf cavity by 25% in the winter of 2016. The events coincide with strong easterly winds and polynya opening in the region, but the Winter Water deepening is controlled by non‐local coastal Ekman downwelling rather than polynya‐related surface fluxes. The thermocline depth anomalies are forced by Ekman downwelling at the northern coast of Siple Island and propagate to the ice front as a coastal trapped wave. During the events, the flow at depth does no longer continue along isobaths into the ice shelf cavity but aligns with the ice front.
Measuring Fault Zone and Host Rock Hydraulic Properties Using Tidal Responses
Authors: Guo H. , Brodsky E. E. , Goebel T. H. W. , Cladouhos T. T. 
Published: June 2021

AbstractPore pressure diffusion along faults influences induced seismicity and rupture mechanics. In situ hydraulic diffusivity measurements along faults are rare and generally lower than inferred from seismicity migration. Here we use the tidal response of deep geothermal boreholes to measure fault diffusivity and permeability. Initial interpretations of the observation with a homogeneous confined aquifer model result in diffusivities of 10−3–10−1 m2/s. However, this model mixes signals from both the conduit and the host rock. We develop a model for tidal response with a fault passing through the aquifer based on the fault‐guided fracture network and solve for hydraulic properties in both the fault and the host rock. The resulting fault permeability is 2 × 10−14–7 × 10−14 m2 (90% confidence interval[CI]) and fault diffusivity is 0.08–0.33 m2/s (90% CI), which is 2 orders of magnitude higher than the host rock diffusivity in some wells, thus highlighting the role of faults as fluid conduits.
The Importance of the Representation of DMS Oxidation in Global Chemistry‐Climate Simulations
Authors: Hoffmann Erik Hans , Heinold Bernd , Kubin Anne , Tegen Ina , Herrmann Hartmut 
Published: June 2021

AbstractThe oxidation of dimethyl sulfide (DMS) is key for the natural sulfate aerosol formation and its climate impact. Multiphase chemistry is an important oxidation pathway but neglected in current chemistry‐climate models. Here, the DMS chemistry in the aerosol‐chemistry‐climate model ECHAM‐HAMMOZ is extended to include multiphase methane sulfonic acid (MSA) formation in deliquesced aerosol particles, parameterized by reactive uptake. First simulations agree well with observed gas‐phase MSA concentrations. The implemented formation pathways are quantified to contribute up to 60% to the sulfate aerosol burden over the Southern Ocean and Arctic/Antarctic regions. While globally the impact on the aerosol radiative forcing almost levels off, a significantly more positive solar radiative forcing of up to +0.1 W m−2 is computed in the Arctic (>60°N). The findings imply the need of both further laboratory and model studies on the atmospheric multiphase oxidation of DMS.
A Process‐Oriented Diagnostic to Assess Precipitation‐Thermodynamic Relations and Application to CMIP6 Models
Authors: Ahmed Fiaz , Neelin J. David 
Published: June 2021

AbstractA process‐oriented diagnostic (POD) is introduced to measure the thermodynamic sensitivity of convection in climate models. The physical basis for this POD is the observed tropical precipitation‐buoyancy relationship. Fast timescale precipitation and thermodynamic profiles over oceans are POD inputs; these are used to evaluate model precipitation sensitivities to lower‐tropospheric measures of subsaturation (SUBSATL) and undilute conditional instability. The POD is used to diagnose 24 coupled model inter‐comparison project phase six (CMIP6) models. Half the diagnosed models exhibit SUBSATL sensitivity close to observed, while six models are excessively sensitive. Parameter perturbation experiments with the Community Atmospheric Model (CAM5) support the physical basis for the POD. Increasing entrainment increases the CAM5 precipitation SUBSATL sensitivity. Switching off the convective scheme or modifying the convective trigger to be oversensitive to moisture reproduces the excessive SUBSATL sensitivity seen among CMIP6 models. Models with excessive SUBSATL sensitivities have precipitating mean states closer to grid‐scale saturation and likely support more grid‐scale convection.
Effects of Climate Model Mean‐State Bias on Blocking Underestimation
Authors: Kleiner Ned , Chan Pak Wah , Wang Lei , Ma Ding , Kuang Zhiming 
Published: June 2021

AbstractIn discussions of extreme weather trends, the subject of atmospheric blocking remains an open question, in part because of the inability of climate models to accurately reproduce blocking frequency patterns for the current climate. A number of factors have been proposed to explain this failure, including specific problems with model physics and inadequate resolution. In this paper, we show that, in the case of the National Center for Atmospheric Research Community Atmosphere Model (NCAR CAM), its underestimation of blocking frequency is caused by its mean state bias and that correcting that bias increases blocking frequency estimates over Europe and decreases the root‐mean‐square error versus reanalysis from 0.015 to 0.011.
Contrasting Responses of Idealised and Realistic Simulations of Shallow Cumuli to Aerosol Perturbations
Authors: Spill George , Stier Philip , Field Paul R. , Dagan Guy 
Published: June 2021

AbstractShallow clouds remain greatly significant in improving our understanding of the atmosphere. Using the Met Office Unified Model, we compare highly idealised simulations of shallow cumuli with those using more realistic domains, with open lateral boundaries and varying large‐scale forcing. We find that the realistic simulations are more capable of representing the cloud field on large spatial scales, and appear to limit the aerosol perturbations leading to impacts on the thermodynamic conditions. Aerosol perturbations lead to changes in the cloud vertical structure, and thermodynamic evolution of the idealised simulations; a central feature of behavior seen previously in idealised simulations. Modelling approaches with open boundaries and time‐varying forcing may allow for improved representation of shallow clouds in the atmosphere, and greater understanding of how they may respond to perturbations.
Impact of Microphysics on Tropical Precipitation Extremes in a Global Storm‐Resolving Model
Authors: Bao Jiawei , Windmiller Julia M. 
Published: June 2021

AbstractThe impact of microphysics on tropical precipitation extremes is explored with a global storm‐resolving model by modifying the terminal velocity of raindrops. Depending on the time scales, precipitation extremes respond differently. Hourly extremes are influenced dynamically through the microphysical modulation on the convective updraft speed, as a faster terminal velocity of raindrops increases the updraft speed by reducing the total condensates in the atmosphere which increases the updraft buoyancy. However, the response of daily precipitation extremes is more sensitive to the microphysical impact on convective organization. By being more organized with decreasing terminal velocity, daily precipitation extremes are enhanced due to increased precipitation efficiency and intensified updrafts. Thus, the results suggest that microphysics, despite often occurring at small spatial scales, can influence the circulation at larger scales, and the microphysical imprint across different time scales plays an important role in regulating tropical precipitation extremes.
The Characteristics of Three‐Belt Structure of Sub‐MeV Electrons in the Radiation Belts
Authors: Li Yu‐Xuan , Yue Chao , Hao Yi‐Xin , Zong Qiu‐Gang , Zhou Xu‐Zhi , Fu Sui‐Yan , Chen Xing‐Ran , Zhao Xing‐Xin 
Published: June 2021

AbstractAfter the launch of Van Allen Probes, the three‐belt structures of ultra‐relativistic electrons are discovered. In this study, we investigate the three‐belt structures of sub‐MeV electrons, which may form under different mechanism compared with those of ultra‐relativistic electrons and are worth in‐depth analysis. Based on the differential flux data from Magnetic Electron Ion Spectrometer onboard Radiation Belt Storm Probes‐B satellite, we find 54 events, in which two comparable peaks of sub‐MeV electron fluxes and a slot appear where there should be the outer radiation belt. Through the statistical analysis, the three‐belt structures of sub‐MeV electrons are found to be closely related to symmetric H‐component (SYM‐H) and Auroral Electrojet (AE) indices. The 2‐day SYM‐H minimum and AE maximum before the event have a linear trend with the remnant belt and the “second slot” locations. The L‐values of the remnant belt and the “second slot” of different energy electrons decrease as energy increases in general and show interesting characteristics during their temporal evolution. Moreover, the lifetime of the remnant belt of different energy electrons increases as energy increases. We find similarities and differences between sub‐MeV and ultra‐relativistic electrons three‐belt events, which provides a new perspective in three‐belt structure study.
Using Fractals to Describe Ecologically Relevant Patterns in Distributions of Large Rocks in Streams
Authors: Dwyer G. K. , Cummings C. R. , Rice S. P. , Lancaster Jill , Downes Barbara J. , Slater L. , Lester Rebecca E. 
Published: June 2021

AbstractMeasuring the physical complexity of habitats or ecological resources is often achieved using system‐specific methods that make comparisons across ecosystems difficult. One measure that is applicable across multiple ecosystems and scales is the fractal dimension, which has the benefit of generality as well as potential scale independence. This study evaluated the use of box‐counting and entropy fractal dimensions for characterizing the complexity of emergent rock distributions in six streams across Scotland and Australia. Emergent rocks (ER) are important hydraulic features and ecological resources, including as oviposition sites for aquatic insects and cover for fish. We completed fractal analysis on counts of ER in 5‐m segments along longitudinal stretches of the six streams. All six streams exhibited fractal behavior (self‐similarity), suggesting that fractals can be used to measure the complexity of longitudinal ER distributions in a way that is scale independent. Entropy was a superior measure due to its ability to differentiate among the six streams whereas box‐counting could not. Together, field results and numerical simulations showed that fractal dimensions of emergent rock distributions were related to stream geomorphology. Well‐developed bedforms, like alternating pools and riffles had better organized emergent rocks because large bed materials were more likely to be emergent in topographic highs. Streams with coarser bed materials had more chaotic arrangements of emergent rocks because this increased the general abundance of emergent rocks, making differentiation between topographic highs and lows less distinctive. Fractal dimensions, therefore, can measure the complexity of river systems in a way that is relevant to geomorphological and ecological processes.
Assessing secondhand and thirdhand tobacco smoke exposure in Canadian infants using questionnaires, biomarkers, and machine learning
Authors: Parks Jaclyn , McLean Kathleen E. , McCandless Lawrence , de Souza Russell J. , Brook Jeffrey R. , Scott James , Turvey Stuart E. , Mandhane Piush J. , Becker Allan B. , Azad Meghan B. , Moraes Theo J. , Lefebvre Diana L. , Sears Malcolm R. , Subbarao Padmaja , Takaro Tim K. 
Published: June 2021

Abstract
Background
As smoking prevalence has decreased in Canada, particularly during pregnancy and around children, and technological improvements have lowered detection limits, the use of traditional tobacco smoke biomarkers in infant populations requires re-evaluation.

Objective
We evaluated concentrations of urinary nicotine biomarkers, cotinine and trans-3’-hydroxycotinine (3HC), and questionnaire responses. We used machine learning and prediction modeling to understand sources of tobacco smoke exposure for infants from the CHILD Cohort Study.

Methods
Multivariable linear regression models, chosen through a combination of conceptual and data-driven strategies including random forest regression, assessed the ability of questionnaires to predict variation in urinary cotinine and 3HC concentrations of 2017 3-month-old infants.

Results
Although only 2% of mothers reported smoking prior to and throughout their pregnancy, cotinine and 3HC were detected in 76 and 89% of the infants’ urine (n = 2017). Questionnaire-based models explained 31 and 41% of the variance in cotinine and 3HC levels, respectively. Observed concentrations suggest 0.25 and 0.50 ng/mL as cut-points in cotinine and 3HC to characterize SHS exposure. This cut-point suggests that 23.5% of infants had moderate or regular smoke exposure.

Significance
Though most people make efforts to reduce exposure to their infants, parents do not appear to consider the pervasiveness and persistence of secondhand and thirdhand smoke. More than half of the variation in urinary cotinine and 3HC in infants could not be predicted with modeling. The pervasiveness of thirdhand smoke, the potential for dermal and oral routes of nicotine exposure, along with changes in public perceptions of smoking exposure and risk warrant further exploration.
Erythropoietin monotherapy for neuroprotection after neonatal encephalopathy in low-to-middle income countries: a systematic review and meta-analysis
Authors: Ivain Phoebe , Montaldo Paolo , Khan Aamir , Elagovan Ramyia , Burgod Constance , Morales Maria Moreno , Pant Stuti , Thayyil Sudhin 
Published: June 2021

AbstractObjectiveWe examined whether erythropoietin monotherapy improves neurodevelopmental outcomes in near-term and term infants with neonatal encephalopathy (NE) in low-middle income countries (LMICs).MethodsWe searched Pubmed, Embase, and Web of Science databases to identify studies that used erythropoietin (1500–12,500 units/kg/dose) or a derivative to treat NE.ResultsFive studies, with a total of 348 infants in LMICs, were retrieved. However, only three of the five studies met the primary outcome of death or neuro-disability at 18 months of age or later. Erythropoietin reduced the risk of death (during the neonatal period and at follow-up) or neuro-disability at 18 months or later (p < 0.05). Death or neuro-disability occurred in 27.6% of the erythropoietin group and 49.7% of the comparison group (risk ratio 0.56 (95% CI: 0.42–0.75)).ConclusionThe pooled data suggest that erythropoietin monotherapy may improve outcomes after NE in LMICs where therapeutic hypothermia is not available.