bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Geothermal Heat Flux Map of Antarctica Empirically Constrained by Seismic Structure
Authors: Shen Weisen , Wiens Douglas A. , Lloyd Andrew J. , Nyblade Andrew A. 
Published: June 2020

AbstractThe geothermal heat flux (GHF) is an important boundary condition for modeling the movement of the Antarctic ice sheet but is difficult to measure systematically at a continental scale. Earlier GHF maps suffer from low resolution and possibly biased assumptions in tectonism and crustal heat generation, resulting in significant uncertainty. We present a new GHF map for Antarctica constructed by empirically relating the upper mantle structure to known GHF in the continental United States. The new map, compared with previously seismologically determined one, has improved resolution and lower uncertainties. New features in this map include high GHF in the southern Transantarctic Mountains where warmer uppermost mantle is introduced by lithospheric removal and in the Thwaites Glacier region. Additionally, a modest GHF in the central West Antarctic Rift system near the Siple Coast and an absence of large‐scale regions with GHF greater than 90 mW/m2 are found.
Rapid Cooling and Increased Storminess Triggered by Freshwater in the North Atlantic
Authors: Oltmanns M. , Karstensen J. , Moore G. W. K. , Josey S. A. 
Published: June 2020

AbstractRecent winters have been unique due to the rapid and extreme cooling of the subpolar North Atlantic. Here, we present a novel view on its causes and consequences. Combining in‐situ observations with remote sensing and atmospheric reanalysis data, we show that increased freshening of the subpolar region gives rise to a faster surface cooling in fall and winter. Large freshwater events, in particular, result in pronounced cold anomalies with sharp temperature gradients that promote an enhanced storminess. The storms reinforce the cooling by driving stronger heat losses and modulating the surface flow. Consistent with this mechanism, past freshwater events have been followed by cold anomalies in winter of approximately −2°C and increases in the North Atlantic Oscillation index of up to ∼0.6 within 3 years. We expect that future freshwater discharges into the North Atlantic will amplify the cold anomaly and trigger an enhanced wintertime storminess with far‐reaching climatic implications.
Effects of Lateral Entrainment Mixing With Entrained Aerosols on Cloud Microphysics
Authors: Chen Jingyi , Liu Yangang , Zhang Minghua 
Published: June 2020

AbstractThe effects of entrained environment air and aerosols on cloud properties remain a critical yet understudied topic. This study first introduces a new entraining cloud parcel model considering entrained aerosols. With entrained aerosols represented by a newly introduced parameter, the impacts of entrainment rate and entrained aerosols on cloud microphysical properties are investigated. The results show that the relationships between entrainment rate and cloud microphysical properties are highly nonlinear when the entrained aerosols vary. With the lateral entrainment mixing, a new phenomenon is revealed that the height of maximum parcel supersaturation cannot be reached when the entrainment rate is beyond a certain critical value. This new critical entrainment rate is different from the critical entrainment rate defined by Barahona and Nenes (2007, https://doi.org/10.1029/2007JD008473), beyond which clouds cannot form. This finding has important implications for developing parameterization of droplet activation, which is based primarily on the assumption of the existence of maximum supersaturation.
Critical Fluid Injection Volumes for Uncontrolled Fracture Ascent
Authors: Davis Timothy , Rivalta Eleonora , Dahm Torsten 
Published: June 2020

AbstractHydrofracturing is a routine industrial technique whose safety depends on fractures remaining confined within the target rock volume. Both observations and theoretical models show that, if the fluid volume is larger than a critical value, pockets of fluid can propagate large distances in the Earth's crust in a self‐sustained, uncontrolled manner. Existing models for such critical volumes are unsatisfactory; most are two‐dimensional and depend on poorly constrained parameters (typically the fracture length). Here we derive both analytically and numerically in three‐dimensional scale‐independent critical volumes as a function of only rock and fluid properties. We apply our model to gas, water, and magma injections in laboratory, industrial, and natural settings, showing that our critical volumes are consistent with observations and can be used as conservative estimates. We discuss competing mechanisms promoting fracture arrest, whose quantitative study could help to assess more comprehensively the safety of hydrofracturing operations.
Parallel Electrostatic Waves Associated With Turbulent Plasma Mixing in the Kelvin‐Helmholtz Instability
Authors: Wilder F. D. , Schwartz S. J. , Ergun R. E. , Eriksson S. , Ahmadi N. , Chasapis A. , Newman D. L. , Burch J. L. , Torbert R. B. , Strangeway R. J. , Giles B. L. 
Published: June 2020

AbstractThe Kelvin‐Helmholtz Instability (KHI) is thought to be an important driver of mass and momentum transfer from the solar wind to the Earth's magnetosphere. We present observations from NASA's Magnetospheric Multiscale mission of ion acoustic‐like waves associated with turbulence during the KHI interval on 8 September 2015. These parallel electrostatic waves are nonlinear, can have amplitudes in excess of 100 mV/m, and may be associated with a field‐aligned potential drop. We perform a survey of all vortices in the 8 September 2015 event, investigating the occurrence of electrostatic waves below the ion plasma frequency. We find that they tend to occur in the turbulent region in the middle of the KHI vortices, independent of the presence of compressed or intermittent currents. This suggests that the waves occur in the presence of plasma mixing in the vortex region and that they may play a part in the overall turbulent dissipation process.
Quantifying Fluid‐Wettable Effective Pore Space in the Utica and Bakken Oil Shale Formations
Authors: Zhang Yuxiang , Hu Qinhong , Barber Troy J. , Bleuel Markus , Anovitz Lawrence M. , Littrell Kenneth 
Published: June 2020

AbstractCombined (ultra‐) small angle neutron scattering measurements [(U)SANS] and a contrast matching technique were employed to quantify the porosity and pore size distribution from 1 nm to 10 μm and to differentiate accessible (open) pores and inaccessible (closed) pores with respect to organophilic and hydrophilic fluids for two Utica and two Bakken shale samples. The results indicate that around 40–70% of the pores in the Utica oil shales (mixed carbonate mudstone) are accessible to oil, and 34–37% of the pore surfaces are water‐wet. In contrast, the Bakken oil shales (mixed siliceous mudstone and carbonate/siliceous mudstone), which have high total organic carbon contents, have a higher proportion of isolated pore space that is not preferentially wet by oil or water, with less than 36% of the pores accessible to both fluids. In addition, for both formations, pores less than 3 nm in diameter are not oil accessible (organic matter related) but water accessible (clay tactoids related).
Disproving the Bodélé Depression as the Primary Source of Dust Fertilizing the Amazon Rainforest
Authors: Yu Yan , Kalashnikova Olga V. , Garay Michael J. , Lee Huikyo , Notaro Michael , Campbell James R. , Marquis Jared , Ginoux Paul , Okin Gregory S. 
Published: June 2020

AbstractMotivated by the ongoing debates about the relative contribution of specific North African dust sources to the transatlantic dust transport to the Amazon Basin, the current study integrates a suite of satellite observations into a novel trajectory analysis framework to investigate dust transport from the leading two North African dust sources, namely, the Bodélé depression and El Djouf. In particular, this approach provides observation‐constrained quantification of the dust's dry and wet deposition along its transport pathways and is validated against multiple satellite observations. The current large ensemble trajectory simulations identify favorable transport pathways from the El Djouf across the Atlantic Ocean with respect to seasonal rain belts. The limited potential for long‐range transport of dust from the Bodélé depression is attributed to the currently identified extensive near‐source dust removal primarily by dry and wet deposition during boreal winter and summer, respectively.
Mechanisms Underlying Recent Arctic Atlantification
Authors: Asbjørnsen Helene , Årthun Marius , Skagseth Øystein , Eldevik Tor 
Published: June 2020

AbstractRecent warming and reduced sea ice concentrations in the Atlantic sector of the Arctic Ocean are the main signatures of ongoing Arctic “Atlantification.” The mechanisms driving the warming trends are nevertheless still debated, particularly regarding the relative importance of oceanic and atmospheric heat fluxes. Here, heat budgets along main Atlantic water pathways through the Barents Sea and Fram Strait are constructed to investigate the mechanisms of Atlantification during 1993–2014. The largest warming trends occur south of the winter ice edge, with ocean advection as the main driver. Warming in the marginal ice zone is mainly due to low surface heat loss from the 1990s to the mid‐2000s. In the ice‐covered northwestern Barents Sea, ocean advection and air‐sea heat fluxes act in concert to drive a gradual warming of the upper ocean. Despite a weakened stratification, no evidence is found of vertical oceanic temperature fluxes driving this upper‐ocean warming.
Prominent Daytime TEC Enhancements Under the Quiescent Condition of January 2017
Authors: Huang Fuqing , Lei Jiuhou , Zhang Ruilong , Li Na , Gu Shengyang , Yu You , Liu Libo , Owolabi Charles , Ning Baiqi , Li Guozhu , Zhong Jiahao , Dang Tong , Ren Dexin , Yi Wen , Luan Xiaoli , Xue Xianghui , Yu Tao , Li Faquan , Dou Xiankang , Yoshikawa Akimasa 
Published: June 2020

AbstractIt is well known that the ionospheric electron densities in the F‐region usually undergo day‐to‐day variability with the magnitude of ~20–35%, associated with the solar as well as geomagnetic activities and the meteorological forcing from the lower atmosphere. In this study, we reported remarkable enhancements in the total electron content (TEC) from the Beidou geostationary (GEO) satellites during the quiescent geophysical condition of January 2017 prior to the arrival of the sudden stratosphere warming (SSW). The daytime TEC around the equatorial ionization anomaly region increased by 75–160% and lasted for several days. The equatorial electrojet and Sq current in the ionospheric E‐region at low and middle latitudes showed the corresponding increase during the TEC enhancement interval. The possible contributions from the variations of solar EUV flux and geomagnetic activity are ruled out. Our further analysis showed that the diurnal tides in the temperature from Sounding of the Atmosphere using Broadband Emission Radiometry and the solar and lunar semidiurnal tides of neutral winds from two radars over China became strong during this period of interest. These results suggest that the lower atmospheric tidal forcing could contribute to the great and long‐duration TEC enhancement in the ionosphere even though the SSW had not happened yet.
Universal Scaling of Thin Current Sheets
Authors: Zelenyi L. M. , Malova H. V. , Grigorenko E. E. , Popov V. Yu , Dubinin E. M. 
Published: June 2020

AbstractThin current sheets (TCSs) with thicknesses about ion Larmor radii are widespread in space. It is important to describe their equilibrium structure allowing them to store and then explosively release the accumulated free energy. When ions are moving along quasi‐adiabatic trajectories while magnetized electrons follow guiding center drift orbits, TCSs can be described within the framework of a hybrid approach. The thickness of the embedded electron sheet remains uncertain because of the scale‐free character of electron motion. In this work, we propose a novel analytical model of the multilayer TCS that provides a universal expression describing the inner (embedded) electron sheet in dependence of TCS characteristics. An unusual property of the embedded electron layer revealed in this analysis is the nonlinear profile of the magnetic field in the inner layer: B(z) ~ z1/3, which conforms excellently with MAVEN observations of 43 TCSs in the Martian magnetotail.
The Contribution of Sprite Streamers to the Chemical Composition of the Mesosphere‐Lower Thermosphere
Authors: Pérez‐Invernón F. J. , Malagón‐Romero A. , Gordillo‐Vázquez F. J. , Luque A. 
Published: June 2020

AbstractSprites are mesospheric filamentary discharges that liberate and accelerate large quantities of electrons. They produce local enhancements of some chemical species and fast (millisecond) optical emissions. In this work, we couple a self‐consistent 2‐D model of sprites with an extensive chemical scheme to calculate the injection of chemical species by one sprite streamer in the mesosphere 0.85 ms after its onset. The N, NO, and N2O injections per streamer are about 1021 atoms, 6 × 1019 molecules, and 1018 molecules, respectively. According to our results, longer simulations are necessary to determine the role of sprites in the concentration of N2O in the mesosphere. We also calculate the contribution of sprite glows to space‐based photometers of the Atmosphere‐Space Interactions Monitor and the Tool for the Analysis of RAdiations from lightNIngs and Sprites.
Aeolian Creep Transport: Theory and Experiment
Authors: Wang Peng , Zhang Jie , Dun Hongchao , Herrmann Hans J. , Huang Ning 
Published: June 2020

AbstractAeolian sand transport drives geophysical phenomena, such as bedform evolution and desertification. Creep plays a crucial, yet poorly understood, role in this process. We present a model for aeolian creep, making quantitative predictions for creep fluxes, which we verify experimentally. We discover that the creep transport rate scales like the Shields number to the power 5/2, clearly different from the laws known for saltation. We derive this 5/2 power scaling law from our theory and confirm it with meticulous wind tunnel experiments. We calculate the creep flux and layer thickness in steady state exactly and for the first time study the relaxation of the flux toward saturation, obtaining an analytic expression for the relaxation time.
Temperature Proxies as a Solution to Biased Sampling of Lake Methane Emissions
Authors: Jansen Joachim , Thornton Brett F. , Wik Martin , MacIntyre Sally , Crill Patrick M. 
Published: June 2020

AbstractLake emissions of the climate forcing trace gas methane (CH4) are spatiotemporally variable, but biases in flux measurements arising from undersampling are poorly quantified. We use a multiyear data set (2009–2017) of ice‐free CH4 emissions from three subarctic lakes obtained with bubble traps (n = 14,677), floating chambers (n = 1,306), and surface concentrations plus a gas transfer model (n = 535) to quantify these biases and evaluate corrections. Sampling primarily in warmer summer months, as is common, overestimates the ice‐free season flux by a factor 1.4–1.8. Temperature proxies based on Arrhenius functions that closely fit measured fluxes (R2 ≥ 0.93) enable gap filling the colder months of the ice‐free season and reduce sampling bias. Ebullition (activation energy 1.36 eV) expressed greater temperature sensitivity than diffusion (1.00 eV). Resolving seasonal and interannual variability in fluxes with proxies requires ∼135 sampling days for ebullition, and 22 and 14 days for diffusion via models and chambers, respectively.
Elevation Changes of the Fennoscandian Ice Sheet Interior During the Last Deglaciation
Authors: Lane T. P. , Paasche Ø. , Kvisvik B. , Adamson K. R. , Rodés Á. , Patton H. , Gomez N. , Gheorghiu D. , Bakke J. , Hubbard A. 
Published: June 2020

AbstractThe dynamics and paleo‐glaciology of ice sheet interiors during the last deglaciation are poorly constrained, hindering ice sheet model reconstructions. We provide direct evidence of Fennoscandian Ice Sheet (FIS) interior behavior during deglaciation through surface exposure dating. Our results demonstrate early thinning of the FIS, prior to the Younger Dryas (YD, 12.8–11.7 ka). Interior thinning in central Norway was concurrent with retreat along the coastline, exposing ice‐free mountainous tracts, potentially as early as 20–15 ka. The FIS then formed moraines in these ice‐free tracts during the YD. This is contrary to current hypotheses advocating a landscape fully covered by cold, inactive ice during this period. Present empirical and model reconstructions fail to capture rapid interior downwastage, increasing uncertainties in ice sheet volume estimates and sea level contributions.
Experimental Determination of the Conditions Associated With “Zebra Stripe” Pattern Generation in the Earth's Inner Radiation Belt and Slot Region
Authors: Lejosne Solène , Mozer Forrest S. 
Published: June 2020

AbstractThe “zebra stripes” are peaks and valleys commonly present in the spectrograms of energetic particles trapped in the Earth's inner belt and slot region. Several theories have been proposed over the years to explain their generation, structure, and evolution. Yet, the plausibility of various theories has not been tested due to a historical lack of ground truth, including in situ electric field measurements. In this work, we leverage the new visibility offered by the database of Van Allen Probes electric drift measurements to reveal the conditions associated with the generation of zebra stripe patterns. Energetic electron fluxes by the Radiation Belt Storm Probes Ion Composition Experiment between 1 January 2013 and 31 December 2015 are systematically analyzed to determine 370 start times associated with the generation of zebra stripes. Statistical analyses of these events reveal that the zebra stripes are usually created during substorm onset, a time at which prompt penetration electric fields are present in the plasmasphere. All the pieces of experimental evidence collected are consistent with a scenario in which the prompt penetration electric field associated with substorm onset leads to a sudden perturbation of the trapped particle drift motion. Subsequent drift echoes constitute the zebra stripes. This study exemplifies how the analysis of trapped particle dynamics in the inner belt and slot region provides complementary information on the dynamics of plasmaspheric electric fields. It is the first time that the signature of prompt penetration electric fields is detected in near‐equatorial electric field measurements below L = 3.
Observational Validation of Cutoff Models as Boundaries of Solar Proton Event Impact Area
Authors: Heino Erkka , Partamies Noora 
Published: June 2020

AbstractHigh energy protons accelerated during solar proton events (SPEs) can access the Earth's middle atmosphere at high and middle latitudes causing large‐scale ionization and chemical changes. In this study, we have compared the performance of two cutoff latitude models that predict the limit of the SPE impact area in the atmosphere during 73 SPEs from 1997 to 2010. We use observations from 13 riometer stations and the D Region Absorption Prediction (DRAP) model to test the performance of the two cutoff latitude models by Dmitriev et al. (2010, https://doi.org/10.1029/2010JA015380) and Nesse Tyssøy and Stadsnes (2015, https://doi.org/10.1002/2014JA020508). We find similar performance from the two cutoff latitude models with respect to observations, but the Dmitriev et al. (2010, https://doi.org/10.1029/2010JA015380) model performs slightly better when observations are contrasted with the DRAP model results. The better performing model is also continuous with magnetic local time and particle energy, making it more suited for future use in climate model proton forcing. SPE forcing is currently included in climate models with a single static cutoff latitude limit at 60° geomagnetic latitude. In reality, the area that the solar protons can access is not static but varies with particle rigidity and geomagnetic conditions. We estimate that the SPE impact area is overestimated 90% of the time by this single static cutoff limit and the average overestimation of the impact area is about 15–25% for protons with energies <32 MeV.
Particle‐in‐Cell Simulations of Characteristics of Rising‐Tone Chorus Waves in the Inner Magnetosphere
Authors: Ke Yangguang , Lu Quanming , Gao Xinliang , Wang Xueyi , Chen Lunjin , Wang Shaojie , Wang Shui 
Published: June 2020

AbstractWhistler mode chorus waves in the Earth's inner magnetosphere are usually composed of discrete elements, and each element can be characterized by the following properties: the amplitude, the duration, the frequency span, and the frequency chirping rate. Using a one‐dimensional (1‐D) particle‐in‐cell (PIC) simulation code, we study the dependence of these properties of a rising‐tone chorus on the number density nheq/nc0 and temperature anisotropy AT of energetic electrons at the magnetic equator. The whistler waves are first excited around the magnetic equator by anisotropic energetic electrons and then develop into a rising‐tone chorus when they leave away from the equator. During the propagation toward the pole, the rising‐tone chorus with nearly constant frequency span first enhances and then decays. Its frequency chirping rate declines in the early stage and then gradually increases. Meanwhile, the chorus duration is quite the opposite due to propagation effect. Over a suitable range of nheq/nc0 to generate rising‐tone chorus, the frequency chirping rate of the excited rising‐tone chorus first increases and then saturates, while its saturated amplitude, duration, and frequency span have a rising tendency with the increasing nheq/nc0. As for AT, the frequency chirping rate of the generated rising‐tone chorus is increasing with the increase of AT that is consistent with prediction of nonlinear theory, while the duration is just the opposite. Our simulation study can give a further understanding of the generation and propagation of rising‐tone chorus waves.
ECTACI: European Climatology and Trend Atlas of Climate Indices (1979–2017)
Authors: Peña‐Angulo D. , Reig‐Gracia F. , Domínguez‐Castro F. , Revuelto J. , Aguilar E. , van der Schrier G. , Vicente‐Serrano S. M. 
Published: June 2020

AbstractA fundamental key to understanding climate change and its implications is the availability of databases with wide spatial coverage, over a long period of time, with constant updates and high spatial resolution. This study describes a newly gridded data set and its map viewer “European Climatology and Trend Atlas of Climate Indices” (ECTACI), which contains four statistical parameters (climatology, coefficient of variation, slope, and significant trend) from 125 standard climate indices for the whole Europe at 0.25° grid intervals from 1979 to 2017 at various temporal scales (monthly, seasonal, and annual). In addition, this study shows, for the first time, the general trends of a wide variety of updated standard climate indices at seasonal and annual scales for the whole of Europe, which could be a useful tool for climate analysis and its impact on different sectors and socioeconomic activities. The data set and ECTACI map viewer are available for free (http://ECTACI.csic.es/).