bluuebunny/crossref_metadata_2025_split huggingface dataset:
Daily and Hourly Surface PM2.5 Estimation From Satellite AOD
Authors: Zhang Hai , Kondragunta Shobha 
Published: February 2021

AbstractNational Oceanic and Atmospheric Administration (NOAA) and United States Environmental Protection Agency (USEPA) have been deriving surface particulate matter with a median diameter of 2.5 µm or less (PM2.5) from satellite aerosol optical depth (AOD) over Continental United States (CONUS) using a climatological PM2.5‐AOD regression relation. However, because PM2.5‐AOD relation can change over time, this method can have large errors when the relation deviates from the climatological values. In this work, the geographically weighted regression (GWR) model is used to estimate surface PM2.5 from AOD. The parameters of the regression model are derived dynamically in a daily or hourly manner using surface PM2.5 measurements and AOD from satellite. The method is evaluated using Visible Infrared Imaging Radiometer Suite (VIIRS) AOD and Advanced Baseline Imager (ABI) AOD to estimate daily and hourly PM2.5 over CONUS, and Advanced Himawari Imager AOD to estimate hourly PM2.5 over Taiwan. The algorithm performs much better than using simple climatological relationships. The estimated daily PM2.5 from VIIRS AOD has a cross validation (CV) R2 of 0.59 with surface measured PM2.5, bias of 0.09 µg/m3 and Root mean square error (RMSE) of 5.66 µg/m3. The hourly PM2.5 estimates from ABI AOD has a CV R2 of 0.44, bias of 0.04 µg/m3, and RMSE of 4.53 µg/m3. The algorithm will run in near‐real‐time at NOAA to provide air quality community PM2.5 estimates over CONUS.
Late Cretaceous Ridge Reorganization, Microplate Formation, and the Evolution of the Rio Grande Rise – Walvis Ridge Hot Spot Twins, South Atlantic Ocean
Authors: Sager William W. , Thoram Sriharsha , Engfer Daniel W. , Koppers Anthony A. P. , Class Cornelia 
Published: February 2021

AbstractRio Grande Rise (RGR) and Walvis Ridge (WR) are South Atlantic large igneous provinces (LIPs), formed on the South American and African plates, respectively, mainly by volcanism from a hot spot erupting at the Mid‐Atlantic Ridge (MAR) during the Late Cretaceous. Both display morphologic complexities that imply their tectonic evolution is incompletely understood. We studied bathymetry, gravity, and vertical gravity gradient maps derived from satellite altimetry to trace faults providing indications of seafloor spreading directions and changes. We also examined magnetic anomalies for time constraint and reflection seismic data for structural information. Abyssal hill fabric and magnetic anomaly data indicate that the area between RGR and WR was anomalous between anomalies C34 (83.6 Ma) and C30 (66.4 Ma) owing to reorganization of a right‐lateral transform on the MAR. This event began ∼92 Ma as the transform shifted south to form multiple, short‐offset right‐lateral transforms, with the reorganization extending through anomaly C34 and ending before anomaly C30. Anomalous spacing of magnetic anomalies and discordant fault fabric indicate that a microplate formed with a core of Cretaceous Quiet Zone seafloor. As the MAR jumped eastward, this microplate was captured by the South American plate and now resides mostly in a basin between the main RGR plateau and a related ridge to the east (East Rio Grande Rise). The microplate is ringed by igneous massifs, implying a link with volcanism. The results presented here indicate that these two LIPs had a complex Late Cretaceous history that belies simple hot spot models.
A Multiyear Constraint on Ammonia Emissions and Deposition Within the US Corn Belt
Authors: Hu Cheng , Griffis Timothy J. , Frie Alexander , Baker John M. , Wood Jeffrey D. , Millet Dylan B. , Yu Zhongjie , Yu Xueying , Czarnetzki Alan C. 
Published: February 2021

AbstractThe US Corn Belt is a global hotspot of atmospheric ammonia (NH3), a gas known to adversely impact the environment and human health. We combine hourly tall tower (100 m) measurements and bi‐weekly, spatially distributed, ground‐based observations from the Ammonia Monitoring Network with the US National Emissions Inventory (NEI) and WRF‐Chem simulations to constrain NH3 emissions from April to September 2017–2019. We show that: (1) NH3 emissions peaked from May to July and were 1.6–1.7 times the annual NEI average; (2) average growing season NH3 emissions from agricultural lands were remarkably similar across years (3.27–3.64 nmol m−2 s−1), yet showed substantial episodic variability driven by meteorology and land management; (3) dry deposition was 40% of gross emissions from agricultural lands and exceeded 100% of gross emissions in natural lands. Our findings provide an important benchmark for evaluating future NH3 emissions and mitigation efforts.
Iron Regulation of North Atlantic Eddy Phytoplankton Productivity
Authors: Browning Thomas J. , Al‐Hashem Ali A. , Hopwood Mark J. , Engel Anja , Belkin Igor M. , Wakefield Ewan D. , Fischer Tim , Achterberg Eric P. 
Published: February 2021

AbstractCyclonic ocean eddies drive upwelling of deep waters enhanced in nutrients, which can elevate phytoplankton productivity. At mid‐latitudes in the North Atlantic, satellite images show enhanced chlorophyll‐a associated with eddies. However, surface macronutrient concentrations are often not fully depleted in this region, implying enhanced macronutrient supply is not the primary control. We conducted high resolution sampling through two mid‐latitude Atlantic eddies in late spring, located 800 and 350 km east of the Newfoundland Grand Banks. Waters outside of both eddies had unused residual macronutrients, low dissolved iron, and iron‐stressed phytoplankton. Inside both eddies, plankton biomass was higher and macronutrient concentrations lower. However, full macronutrient drawdown and an absence of iron stress were only present in the eddy nearer the continental shelf. From these two examples, iron supply and proximity to shelf iron sources appear to be important factors regulating productivity and macronutrient utilization in mid‐latitude North Atlantic cyclonic eddies.
Observations of the Channel Illuminations During Dark Periods in Long Positive Sparks
Authors: Zhao Xiangen , Liu Xiaopeng , Yang Yongchao , Wang Xiankang , Liu Yang , He Junjia 
Published: February 2021

AbstractNo observations show evidence of ionization in long air gap discharge during dark periods. However, for the first time, weak channel illuminations are observed during the so‐called dark periods in this paper. The length of these faint bright channels is almost constant during each dark period and is nearly equal to that of the remaining low‐density channels created by the previous discharge. The phenomenon, that is, the dark period is not really dark, is more likely to occur at the time when there is a greater change rate of the applied voltage. These findings are based on the high‐speed direct imaging and Schlieren photography together, in which the former is used to visualize the bright channels and the latter to detect the low‐density area.
Local Time and Longitudinal Differences in the Occurrence Frequency of Ionospheric EMIC Waves During Magnetic Storm Periods
Authors: Wang Hui , He Yang Fan , Lühr Hermann , Zhang Jichun 
Published: February 2021

AbstractThe spatial and temporal distributions of ionospheric electromagnetic ion cyclotron (EMIC) waves during magnetic storms from 2014 to 2018 were studied using Swarm observations. Ionospheric EMIC waves preferably occurred during storms and their recovery phases at subauroral regions within an average magnetic latitude of 40–55°. There were more wave events during more intense and longer period storms. However, the correlation between event number and storm duration was not good. This might be due to the effect of heavy oxygen ions on EMIC wave generation and the loss of ring current high‐energy ions by the EMIC waves. There are obvious magnetic local time (MLT) differences in the peak occurrence frequency of EMIC waves during storm phases. The enhanced solar wind dynamic pressure was favorable for duskside EMIC waves. With an increased substorm activity, the wave occurrence rate peak shifted from the morning side to the dusk‐premidnight sector. During the recovery phase of a storm, EMIC waves in the 12–24 MLT sector appeared preferably in the earlier part than those in the 00–12 MLT sector. This shift in local time is related to the eastward rotation of the plasmaspheric plume toward morning during the late storm recovery phase and its overlap with the ring current. Highest occurrence frequency of the storm time EMIC waves could be found in the South Atlantic Anomaly region, which might be related to the drift shell splitting and the wave propagation effect in the weak magnetic field region.
Modeling Magma System Evolution During 2006–2007 Volcanic Unrest of Atka Volcanic Center, Alaska
Authors: Zhan Yan , Gregg Patricia M. , Lu Zhong 
Published: February 2021

AbstractSurface deformation and seismicity provide critical information to understand the dynamics of volcanic unrest. During 2006–2007, >80 mm/yr uplift was observed by interferometric synthetic aperture radar (InSAR) at the central Atka volcanic center, Alaska, coinciding with an increasing seismicity rate. On November 25, 2006, a phreatic eruption occurred at the Korovin volcanic vent, 5‐km north of the central Atka, following the drainage of its crater lake a month prior to the eruption. The InSAR data are assimilated into three‐dimensional finite element models using the Ensemble Kalman Filter to investigate: (1) the pressure source creating the surface deformation; (2) the triggering of the volcano‐tectonic (VT) earthquakes in the Atka volcanic center; and (3) the triggering of the phreatic eruption at Korovin. The models show that the pressure source required to create the surface deformation is a NE‐tilted, oblate ellipsoid, which rotated from steep to gentle dipping from June to November 2006 before the eruption. The modeled dilatancy in a pre‐existing weak zone, coinciding with the Amlia‐Amukta fault, driven by the pressure source has a spatial and temporal correlation with the evolution of the VT earthquakes during the unrest. The fault dilatancy may have increased the connected porosity and permeability of the fault zone allowing fluid injection which triggered the observed seismicity. In addition, the dilatated fault may have increased the fluid capacity of the fault zone by ∼105 m3, causing the discharge of the crater lake at Korovin. Consequently, the phreatic eruption of the Korovin volcano may have been triggered.
Effects of Porosity and Water Saturation on the Yield Surface of Upper Cretaceous Reservoir Chalks From the Danish North Sea
Authors: Amour F. , Christensen H. F. , Hajiabadi M. R. , Nick H. M. 
Published: February 2021

AbstractThe locus and shape of the yield surface of chalk in the stress space represent key input parameters in geomechanical models, as it dictates the onset and amount of plastic deformation. The study aims at reconstructing for the first time the initial end cap and shear failure line of intact reservoir chalk in plots of mean‐deviatoric stress versus porosity. One hundred and thirty‐seven stress‐strain measurements describe the effects of initial porosity between 30% and 45% and initial water saturation on the yield surface in order to cover a wide spectrum of reservoir rocks. The physico‐chemical processes taking place at pore collapse under oil‐ and water‐saturated conditions are discussed. The experimental data collected from previous works quantify the hardening and softening effects observed with decreasing porosity and increasing water saturation. The results also indicate that the stress interval characterizing the elastic to elasto‐plastic transition zone and the curvature of the end cap are dependent on porosity and quartz content. These observed trends suggest changes in the sequence of local failures acting in the rock matrix at the onset of compaction. Comparisons with previous studies suggest that the water weakening effect differs between outcrop and reservoir chalk likely due to a change in mineralogy. A yield function is proposed to build the yield surface and to capture the porosity‐dependent change in the shape of end cap and the water weakening effect. The outcomes provide key input data describing the mechanical behavior and properties of chalk under laboratory conditions required for compaction simulation studies.
New Evidence for the Fluctuation Characteristics of Intradecadal Periodic Signals in Length‐Of‐Day Variation
Authors: Ding Hao , An Yachong , Shen Wenbin 
Published: February 2021

AbstractThe intradecadal fluctuations in the length‐of‐day variation (∆LOD) are considered likely to play an important role in core motions. Two intradecadal oscillations, with ∼5.9 and ∼8.5 years periods (referred to as SYO and EYO, respectively), have been detected in previous studies. However, whether the SYO and the EYO have exhibited stable damping trends since 1962 and whether geomagnetic jerks are possible excitation sources for the SYO/EYO are still debated. In this study, based on different methods and different ∆LOD records with different time spans, we showed robust evidence to prove that the SYO and the EYO have had no stable damping trends since 1962. We also found that there may be a ∼7.6 years signal, but given that its average amplitude is too small, further confirmations are needed in the future. After confirming that the jerks have no special consistency with the peaks/valleys of the EYO/SYO, we further used a deconvolution process and confirmed that the geomagnetic jerks seem to be related to sudden changes in the SYO/EYO time series and their excitation series. Thus we finally suggest that jerks are possible excitation sources of the SYO/EYO. After using a deconvolution process, we estimate that the periodPand quality factorQof the SYO and the EYO are [P = 5.85 ± 0.06 years,Q ≥ 180] and [P = 8.45 ± 0.17 years,Q ≥ 350], respectively.
High‐Pressure Deformation of Iron–Nickel–Silicon Alloys and Implications for Earth’s Inner Core
Authors: Brennan Matthew C. , Fischer Rebecca A. , Couper Samantha , Miyagi Lowell , Antonangeli Daniele , Morard Guillaume 
Published: February 2021

AbstractEarth’s inner core exhibits strong seismic anisotropy, often attributed to the alignment of hexagonal close‐packed iron (hcp‐Fe) alloy crystallites with the Earth’s poles. How this alignment developed depends on material properties of the alloy and is important to our understanding of the core’s crystallization history and active geodynamical forcing. Previous studies suggested that hcp‐Fe is weak under deep Earth conditions but did not investigate the effects of the lighter elements known to be part of the inner core alloy. Here, we present results from radial X‐ray diffraction experiments in a diamond anvil cell that constrain the strength and deformation properties of iron‐nickel‐silicon (Fe–Ni–Si) alloys up to 60 GPa. We also show the results of laser heating to 1650 K to evaluate the effect of temperature. Observed alloy textures suggest different relative activities of the various hcp deformation mechanisms compared to pure Fe, but these textures could still account for the theorized polar alignment. Fe–Ni–Si alloys are mechanically stronger than Fe and Fe–Ni; extrapolated to inner core conditions, Si‐bearing alloys may be more than an order of magnitude stronger. This enhanced strength proportionally reduces the effectivity of dislocation creep as a deformation mechanism, which may suggest that texture developed during crystallization rather than as the result of postsolidification plastic flow.
Regional‐Scale, Sector‐Specific Evaluation of Global CO2 Inversion Models Using Aircraft Data From the ACT‐America Project
Authors: Gaudet B. J. , Davis K. J. , Pal S. , Jacobson A. R. , Schuh A. , Lauvaux T. , Feng S. , Browell E. V. 
Published: February 2021

AbstractWe use 148 airborne vertical profiles of CO2 for frontal cases from the summer 2016 Atmospheric Carbon and Transport—America (ACT‐America) campaign to evaluate the skill of 10 global CO2 in situ inversion models from the version 7 Orbiting Carbon Observatory–2 (OCO‐2) Model Intercomparison Project (MIP). Model errors (model posterior—observed CO2 dry air mole fractions) were categorized by region (Mid‐Atlantic, Midwest, and South), frontal sector (warm or cold), and transport model (predominantly Tracer Model 5 (TM5) and Goddard Earth Observing System—Chemistry [GEOS‐Chem]). All inversions assimilated the same CO2 observations. Overall, the median inversion profiles reproduce the general structures of the observations (enhanced/depleted low‐level CO2 in warm/cold sectors), but 1) they underestimate the magnitude of the warm/cold sector mole fraction difference, and 2) the spread among individual inversions can be quite large (>5 ppm). Uniquely in the Mid‐Atlantic, inversion biases segregated according to atmospheric transport model, where TM5 inversions biases were −3 to −4 ppm in warm sectors, while those of GEOS‐Chem were +2 to +3 ppm in cold sectors. The large spread among the mean posterior CO2 profiles is not explained by the different atmospheric transport models. These results show that the inversion systems themselves are the dominant cause of this spread, and that the aircraft campaign data are clearly able to identify these large biases. Future controlled experiments should identify which inversions best reproduce mid‐latitude CO2 mole fractions, and how inversion system components are linked to system performance.
Constraining Martian Regolith and Vortex Parameters From Combined Seismic and Meteorological Measurements
Authors: Murdoch N. , Spiga A. , Lorenz R. , Garcia R. F. , Perrin C. , Widmer‐Schnidrig R. , Rodriguez S. , Compaire N. , Warner N. H. , Mimoun D. , Banfield D. , Lognonné P. , Banerdt W. B. 
Published: February 2021

AbstractThe InSight mission landed on Mars in November 2018 and has since observed multiple convective vortices with both the high performance barometer and the low‐noise seismometer SEIS that has unprecedented sensitivity. Here, we present a new method that uses the simultaneous pressure and seismic measurements of convective vortices to place constraints on the elastic properties of the Martian subsurface and the Martian vortex properties, while also allowing a reconstruction of the convective vortex trajectories. From data filtered in the (0.02–0.3 Hz) frequency band, we estimate that the mean value ofη(η = E/[1 − ν2], whereEis the Young's modulus andνis the Poisson's ratio) of the Martian ground in the region around SEIS is 239 ± 140 MPa. In addition, we suggest that the previously reported paucity of vortex seismic observations to the west of InSight may be due to the fact that the ground is harder to the west than to the east, consistent with geomorphological surface interpretations.
Relationship Between Leaf Maximum Carboxylation Rate and Chlorophyll Content Preserved Across 13 Species
Authors: Qian X. , Liu L. , Croft H. , Chen J. 
Published: February 2021

AbstractThe leaf maximum carboxylation rate (Vcmax) is a crucial parameter in determining the photosynthetic capacity of plants. Providing accurate estimates of leaf Vcmax, that cover large geographic areas and incorporate plant seasonality is central to correctly predicting carbon fluxes within the terrestrial global carbon cycle. Chlorophyll, as the main photon‐harvesting molecule in leaves, is closely linked to plant photosynthesis. However, how the nature of the relationship between the leaf maximum carboxylation rate (scaled to 25°C; Vcmax,25) and leaf chlorophyll content varies according to plant type is uncertain. In this study, we investigate whether a universal and stable relationship exists between leaf Vcmax,25 and leaf chlorophyll content across different plant types and verify it using field experiments. Measurements of leaf chlorophyll content (Chl) and CO2 response curves were made on 283 crop, shrub, tree, and vegetable leaves, across 13 species, in China and southern Ontario, Canada. A strong relationship was found between the leaf Vcmax,25 and chlorophyll content across different plant types (R2 = 0.65, p < 0.001). Cross‐validation showed that the model performs well, producing an RMSE value of 15.4 μmol m−2 s−1. The results confirm that leaf chlorophyll content can be a reliable proxy for estimating Vcmax,25, opening the door to accurate, spatially continuous estimates of Vcmax,25 at the global scale.
Loess‐Like Dust Appearance at 40 Ma in Central China
Authors: Meijer Niels , Dupont‐Nivet Guillaume , Barbolini Natasha , Woutersen Amber , Rohrmann Alexander , Zhang Yang , Liu Xiang‐Jun , Licht Alexis , Abels Hemmo A. , Hoorn Carina , Tjallingii Rik , Andermann Christoff , Dietze Michael , Nowaczyk Norbert 
Published: February 2021

AbstractAsian mineral dust has been studied extensively for its role in affecting regional‐to global‐scale climate and for its deposits, which enable reconstructing Asian atmospheric circulation in the past. However, the timing and origin of the dust deposits remain debated. Numerous loess records have been reported across the Asian continent with ages varying from the Miocene to the Eocene and linked to various mechanisms including global cooling, Tibetan Plateau uplift and retreat of the inland proto‐Paratethys Sea. Here, we study the Eocene terrestrial mudrocks of the Xining Basin in central China and use nonparametric end‐member analysis of grain‐size distributions to identify a loess‐like dust component appearing in the record at 40 Ma. This is coeval with the onset of high‐latitude orbital cycles and a shift to predominant steppe‐desert vegetation as recognized by previous studies in the same record. Furthermore, we derive wind directions from eolian dune deposits which suggest northwesterly winds, similar to the modern‐day winter monsoon which is driven by a high pressure system developing over Siberia. We propose that the observed shifts at 40 Ma reflect the onset of the Siberian High interacting with westerly derived moisture at obliquity timescales and promoting dust storms and aridification in central China. The timing suggests that the onset may have been triggered by increased continentality due to the retreating proto‐Paratethys Sea.
A Review on Different Techniques of Mutual Coupling Reduction Between Elements of Any MIMO Antenna. Part 1: DGSs and Parasitic Structures
Authors: Kumar Amit , Ansari Abdul Quaiyum , Kanaujia Binod Kumar , Kishor Jugul , Matekovits Ladislau 
Published: February 2021

AbstractThis two‐part article presents a review of different techniques of mutual coupling (MC) reduction. MC is a major issue when an array of antennas is densely packed. When the separation between the antennas is <λ0/2, i.e., half of the free‐space wavelength, the antenna parameters suffer from the surface wave, and the space wave coupling effect between the antenna elements. To reduce the MC influence, several techniques have been discussed in the scientific literature. This part of the review paper will discuss strategies: antenna placement and orientation approach, Defected Ground Structures (DGSs), slots/slits‐etching approach, protruding ground stub structures, and parasitic elements/structures. This article concludes with feasibility, applications, and comparison of the techniques mentioned above. Simultaneously, the applications and possibilities of the remaining methods are discussed in part two of the article.