bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamics of Fast Ice off the Northeast Coast of Greenland (79°N) Over a Full Year (2012–2013)
Authors: Wang Caixin , Negrel Jean , Gerland Sebastian , Divine Dmitry V. , Dodd Paul , Granskog Mats A. 
Published: June 2020

AbstractNorske Øer Ice Barrier (NØIB) is a vast region of fast ice off northeast Greenland. To understand its thermodynamics, an ice mass balance buoy (IMB) was deployed in late August 2012. The IMB operated for a full year, providing unique year‐round observations of air, snow, ice, and upper ocean. Here, we examine atmospheric conditions and snow and sea ice evolution, derive the ocean heat flux at the deployment site, and investigate the effect of snow on the sea ice mass balance. Although an extremely low surface air temperature of −52°C was recorded at the IMB site, the sum of freezing‐degree days (4,848 K·d) is similar to that in the central Arctic. The maximum snow depth 0.73 m (on 29 May 2013, when ice was 2.19 m thick) is thicker than typically observed on level Arctic landfast ice and drift ice, and thick snow appears common in this region. Ocean heat flux was large in autumn and early winter (>7 W m−2), attributed in part to local solar heating of surface waters in summer and advected ocean heat later in the year. The combination of high ocean heat flux and thick snow resulted in a net loss of ice at the ice bottom over the year. A one‐dimensional sea ice model suggests that the thick snow cover limits bottom ice growth significantly. The heavy snow load could potentially have contributed 0.29 m snow ice; however, we cannot unambiguously prove this happened.
Modeling the Dielectric Properties of Minerals From Crystals to Bulk Powders for Improved Interpretation of Asteroid Radar Observations
Authors: Hickson D. C. , Boivin A. L. , Tsai C. A. , Daly M. G. , Ghent R. R. 
Published: June 2020

AbstractPlanetary radar has provided a growing number of data sets on the inner planets and near‐Earth and main belt asteroid populations in the solar system. Physical interpretation of radar data for inference of surface properties requires constraints on the constitutive parameters of the material making up a given surface. In this study, the complex permittivity of seven minerals as a function of frequency and porosity is measured using the coaxial transmission line method to determine the mixing equation that best describes the relationship between the real part of the complex permittivity of single mineral crystals and granular mineral powders. We find the Looyenga‐Landau‐Lifshitz and Bruggeman symmetric mixing equations to describe our experimental results with the highest accuracy. The variation in the real part of the permittivity of solid mineral crystals between different minerals is shown to depend on the grain density and the chemical composition of the minerals. These mixing relationships are incorporated into an asteroid radar model and used to calculate the porosity in the near‐surface of seven asteroids visited by robotic spacecraft using Earth‐based radar observations. The results of the asteroid radar model support the presence of significant porosity in the boulders on the surface of asteroid 101955 Bennu. This research highlights the ability of radar to measure the porosity on asteroid surfaces and provides theoretical and experimental justification for the inversion of permittivity to bulk density assumed by the asteroid radar model.
Investigation of Water Interactions With Apollo Lunar Regolith Grains
Authors: Jones Brant M. , Aleksandrov Aleksandr , Dyar M. Darby , Hibbitts Charles A. , Orlando Thomas M. 
Published: June 2020

AbstractDesorption activation energies of chemisorbed water on Apollo lunar Samples 14163 and 10084 were determined by temperature program desorption (TPD) experiments conducted under ultrahigh vacuum conditions. Desorption at the grain/vacuum interface and desorption/transport of water though the porous medium with readsorption were found to reproduce the experimental TPD signal. Signal from the grain/vacuum interface yielded desorption activation energies and site probability distributions. Highland sample 14163 exhibited a broad distribution of binding site energies peaking at 60 kJ mol−1, while mare sample 10084 exhibited a narrower distribution of binding site energies peaking at 65 kJ mol−1. The highland sample adsorbed approximately 30% more water than the more space weathered and mature mare sample, suggesting maturity may not be a good predictor of the degree of molecular water uptake on lunar regolith. Water desorption from the lunar surface over a typical lunar day was simulated with the measured coverage‐dependent activation energies of the mare and highland samples. The resulting desorption profile of water through a lunar temperature cycle is in general agreement with Lunar Reconnaissance Orbiter (LRO) Lyman‐α Mapping Project (LAMP) spacecraft‐based observations of trends for both highland and mare assuming ~1% submonolayer coverage and that photon stimulated desorption is neglected.
Fault Structure and Origin of Compressional Tectonic Features Within the Smooth Plains on Mercury
Authors: Peterson Georgia A. , Johnson Catherine L. , Byrne Paul K. , Phillips Roger J. 
Published: June 2020

AbstractThe major physiographic “smooth plains” units on Mercury are dominantly composed of volcanic deposits that have been deformed by horizontal compressive stresses. An open issue is whether these features formed by stresses induced by global contraction, bending stresses due to volcanic loading, or some combination of both. In this study, we model the surface expression of 12 shortening structures within several smooth plains units across Mercury to determine the geometries of the underlying faults. We implement an elastic dislocation model, using both listric and planar fault geometries, to place estimates on the depth of faulting for each feature. We show that a majority of smooth plains shortening structures penetrate the lithosphere to depths greater than 15 km. Thrust faults of this scale have not previously been recognized within the planet's smooth plains units and require a large horizontal stresses to form, which is best explained if this stress arises from global contraction. Further, our results suggest that the observed relief and length contrast between features in the smooth plains units and older intercrater plains units can be explained by interior layering of, and/or a shallower brittle‐ductile transition underlying, the smooth plains units.
Influence of Calcium Perchlorate on Organics Under SAM‐Like Pyrolysis Conditions: Constraints on the Nature of Martian Organics
Authors: Millan M. , Szopa C. , Buch A. , Summons R. E. , Navarro‐Gonzalez R. , Mahaffy P. R. , Johnson S. S. 
Published: June 2020

AbstractMost of the organics detected on Mars so far are aliphatic and aromatic organo‐chlorine compounds. The smallest were first identified by the thermal treatment of the solid samples by Viking in 1976; although at the time, they were attributed to contamination. Since 2012, a larger variety of structures have been identified by the Sample Analysis at Mars experiment aboard the Curiosity rover. Evidence suggests that the chlorohydrocarbons formed during pyrolysis of sedimentary materials. Laboratory experiments show that heating of samples containing oxychlorines, such as chlorates (ClO3−) and perchlorates (ClO4−), along with organic matter present at Mars' surface is the logical source of these compounds. Nevertheless, this discovery of indigenous organic matter in the Mars regolith raises important questions: How do the oxychlorines influence the pyrolysis of organics? What are the organics precursors of the organo‐chlorinated molecules detected on Mars? Is there a way to identify the parent molecules in a sample after pyrolysis? This paper presents the results of systematic laboratory experiments of the products formed during the pyrolysis of organic compounds from three chemical families—polycyclic aromatic hydrocarbons, amino acids, and carboxylic acids—in presence of calcium perchlorates. Results show that the polycyclic aromatic hydrocarbon parent molecules and most of the carboxylic acids are still detectable after pyrolysis in presence of calcium perchlorate and that the degradation and/or evolution of all parent molecules mostly depends on their chemical nature. In addition, we demonstrate that the chlorohydrocarbons detected on Mars by the Sample Analysis at Mars instrument could come from the three chemical families studied.
Arctic Amplification of Global Warming Strengthened by Sunlight Oxidation of Permafrost Carbon to CO2
Authors: Bowen J. C. , Ward C. P. , Kling G. W. , Cory R. M. 
Published: June 2020

AbstractOnce thawed, up to 15% of the ∼1,000 Pg of organic carbon (C) in arctic permafrost soils may be oxidized to carbon dioxide (CO2) by 2,100, amplifying climate change. However, predictions of this amplification strength ignore the oxidation of permafrost C to CO2 in surface waters (photomineralization). We characterized the wavelength dependence of permafrost dissolved organic carbon (DOC) photomineralization and demonstrate that iron catalyzes photomineralization of old DOC (4,000–6,300 a BP) derived from soil lignin and tannin. Rates of CO2 production from photomineralization of permafrost DOC are twofold higher than for modern DOC. Given that model predictions of future net loss of ecosystem C from thawing permafrost do not include the loss of CO2 to the atmosphere from DOC photomineralization, current predictions of an average of 208 Pg C loss by 2,299 may be too low by ~14%.
Dilatory and Downward Development of 3‐m Scale Irregularities in the Funnel‐Like Region of a Rapidly Rising Equatorial Plasma Bubble
Authors: Tulasi Ram S. , Ajith K. K. , Yokoyama T. , Yamamoto M. , Hozumi K. , Shiokawa K. , Otsuka Y. , Li G. 
Published: June 2020

AbstractThe equatorial plasma bubbles, once developed, grow nonlinearly into topside ionosphere, and simultaneous secondary instabilities lead to the development of shorter scale irregularities. The altitudinal growth and generation of smaller scale irregularities determine the spatio‐temporal occurrence and the intensity of ionospheric scintillations at wide spectrum of radio waves and have significant implications on the GNSS/Satellite Based Augmentation Systems. In this letter, we present a unique equatorial plasma bubble observation from equatorial atmosphere radar that provides hitherto undisclosed evidence for the smaller (3‐m) scale irregularities initially developing at higher altitudes and subsequently developing to lower altitudes in a narrow funnel‐like structure. The responsible mechanisms for early development of shorter scale irregularities in the topside and their subsequent development at lower altitudes are discussed in light of difference between the time scales of altitudinal growth and cascading rate of secondary instabilities through high‐resolution bubble model simulations.
Stress‐Dependent b Value Variations in a Heterogeneous Rate‐and‐State Fault Model
Authors: Dublanchet P. 
Published: June 2020

AbstractThe magnitudes of earthquakes are known to follow a power law distribution referred to as the Gutenberg‐Richter empirical law. Seismological observations and laboratory experiments suggest a decrease of the decay exponent (b value) with differential stress. The physical mechanism controlling this decrease, however, remains unclear. The present study is dedicated to the origin of relative b value variations with stress obtained in a 2‐D rate‐and‐state planar fault model considering a population of asperities with size‐dependent fracture energy. The simulations show that both b value in the intermediate magnitude range and mainshock magnitude increase with normal stress. Analytical relationships are derived, showing that the increase of b value is related to the decrease of critical nucleation length with normal stress, enhancing the productivity of small‐magnitude events and partial ruptures. The theoretical formulas also show how the increase of mainshock magnitude is a consequence of normal stress dependence of stress drop.
The Insulating Effect of Methane Clathrate Crust on Titan's Thermal Evolution
Authors: Kalousová Klára , Sotin Christophe 
Published: June 2020

AbstractSaturn's largest moon Titan is unique for its dense, methane‐rich atmosphere, with ongoing complex organics chemistry, and the hydrocarbon lakes and seas on its frigid surface. Titan also harbors a subsurface water ocean, and its ice shell is likely capped by a thick crust of low‐conductivity methane clathrates that are very stable under Titan's surface conditions. Here, we investigate the effect of this insulating clathrate crust on convection in the ice shell. Without the clathrate crust, convection occurs below a stagnant lid that is a few tens of kilometers thick and limits the exchange between the surface and the deep ocean. We show that a 5–10 km thick clathrate crust reduces the stagnant lid thickness about threefold thus increasing the potential for the ocean‐surface exchange. Moreover, the insulating effect of clathrates dramatically decreases the amount of extracted heat thus limiting the freezing rate of Titan's ocean.
Antarctic Surface Mass Balance: Natural Variability, Noise, and Detecting New Trends
Authors: King Matt A. , Watson Christopher S. 
Published: June 2020

AbstractThe emergence of new, statistically robust trends in Antarctic surface mass balance (SMB) requires an understanding of the underlying SMB variability (noise). We show that simple white or AR[1] noise models do not adequately represent the variability of SMB in both the RACMO2.3p2 SMB model output (1979–2017) and composite ice core records (1800–2010), underestimating low‐frequency variability. By testing a range of noise models, we find that a Generalized Gauss Markov (GGM) model better approximates the noise around a linear trend. The general preference for GGM noise applies over spatial scales from the total ice sheet down to individual drainage basins. Over the longest timescales considered, trend uncertainties are 1.3–2.3 times larger using a GGM model compared to using an AR1 model at the ice sheet scale. Overall, our results suggest that larger trends or longer periods are required before new SMB trends can be robustly separated from background noise.
Factors Affecting the 2019 Atlantic Hurricane Season and the Role of the Indian Ocean Dipole
Authors: Wood Kimberly M. , Klotzbach Philip J. , Collins Jennifer M. , Caron Louis‐Philippe , Truchelut Ryan E. , Schreck Carl J. 
Published: June 2020

AbstractThe 2019 Atlantic hurricane season exhibited above‐average Accumulated Cyclone Energy—60% of which was produced by Hurricanes Dorian and Lorenzo. Most tropical cyclone (TC) activity was concentrated in a ~6‐week period from late August to early October. During the early part of the season, relatively TC‐unfavorable conditions persisted in the main development region (MDR). The MDR environment became largely favorable in September, followed by an abrupt shift back to less conducive conditions in October coincident with a strongly positive Indian Ocean Dipole (IOD). The IOD produced an El Niño‐like teleconnection pattern observed through 200‐hPa velocity potential anomalies. In the subtropical Atlantic, above‐average sea surface temperatures persisted for much of the season, which may have contributed to increased activity at higher latitudes. Given the neutral El Niño‐Southern Oscillation conditions during the 2019 hurricane season, our study highlights the need for further analysis of IOD impacts on Atlantic TC activity.
Spring Barrier to the MJO Eastward Propagation
Authors: Li Kuiping , Yu Weidong , Yang Yang , Feng Lin , Liu Shouhua , Li Lili 
Published: June 2020

AbstractThe Maritime Continent (MC) often exerts barrier effect on the eastward propagation of the Madden‐Julian Oscillation (MJO), and the strongest (weakest) effect occurs in spring (winter). After passing over the MC, the MJO slightly weakens by approximately 10% in winter and it sharply decays by more than 50% in spring. The physics for this spring barrier are understood from the perspective of the frictionally coupled Kelvin‐Rossby wave theory. In spring, the abrupt reduction in the boundary layer moisture convergence that occurs at the MC causes the decoupling of the Kelvin‐Rossby wave packet associated with the MJO: Kelvin waves emit from the major convection, while Rossby wave component rapidly decays in the Indian Ocean. An intermediate atmospheric model involving both the fundamental dynamics of the frictionally coupled Kelvin‐Rossby wave theory and the mean states confirms that the spring barrier is determined primarily by the mean surface moisture, particularly by its zonal distribution.
Krill Hotspot Formation and Phenology in the California Current Ecosystem
Authors: Fiechter Jerome , Santora Jarrod A. , Chavez Francisco , Northcott Devon , Messié Monique 
Published: June 2020

AbstractIn the California Current Ecosystem, krill represent a key link between primary production and higher trophic level species owing to their central position in the food web and tendency to form dense aggregations. However, the strongly advective circulation associated with coastal upwelling may decouple the timing, occurrence, and persistence of krill hotspots from phytoplankton biomass and nutrient sources. Results from a coupled physical‐biological model provide insights into fundamental mechanisms controlling the phenology of krill hotspots in the California Current Ecosystem, and their sensitivity to alongshore changes in coastal upwelling intensity. The simulation indicates that dynamics controlling krill hotspot formation, intensity, and persistence on seasonal and interannual timescales are strongly heterogeneous and related to alongshore variations in upwelling‐favorable winds, primary production, and ocean currents. Furthermore, regions promoting persistent krill hotspot formation coincide with increased observed abundance of top predators, indicating that the model resolves important ecosystem complexity and function.
Assessing Global and Local Radiative Feedbacks Based on AGCM Simulations for 1980–2014/2017
Authors: Zhang Rudong , Wang Hailong , Fu Qiang , Rasch Philip J. 
Published: June 2020

AbstractWe examine radiative feedbacks based on short‐term climate variability by analyzing atmospheric general circulation model (AGCM) simulations, including Atmospheric Model Intercomparison Project within CMIP phase 6 (AMIP6) with known effective radiative forcing (ERF) for 1980–2014 and one with zero ERF for 1980–2017. We first verify the Kernel‐Gregory feedback calculation by showing that both clear‐sky radiative fluxes and all‐sky radiative feedbacks from the kernel method agree with model simulations. We find that global‐mean net feedback for 1980–2017/2014 is −2 W m−2 K−1, about twice the feedback estimated for long‐term warming (4 × CO2) experiments. This difference is mainly caused by a near‐zero global‐mean net cloud feedback for 1980–2017/2014. We show that the lapse rate feedback for 1980–2017/2014 is the largest contributor to the amplified temperature change over the three poles (Arctic, Antarctic, and Tibetan Plateau), followed by surface albedo feedback and Planck feedback deviation from its global mean. Except for a higher surface albedo feedback in Antarctic, other feedbacks are similar between Arctic and Antarctic.
Improving AI System Awareness of Geoscience Knowledge: Symbiotic Integration of Physical Approaches and Deep Learning
Authors: Jiang Shijie , Zheng Yi , Solomatine Dimitri 
Published: June 2020

AbstractModeling dynamic geophysical phenomena is at the core of Earth and environmental studies. The geoscientific community relying mainly on physical representations may want to consider much deeper adoption of artificial intelligence (AI) instruments in the context of AI's global success and emergence of big Earth data. A new perspective of using hybrid physics‐AI approaches is a grand vision, but actualizing such approaches remains an open question in geoscience. This study develops a general approach to improving AI geoscientific awareness, wherein physical approaches such as temporal dynamic geoscientific models are included as special recurrent neural layers in a deep learning architecture. The illustrative case of runoff modeling across the conterminous United States demonstrates that the physics‐aware DL model has enhanced prediction accuracy, robust transferability, and good intelligence for inferring unobserved processes. This study represents a firm step toward realizing the vision of tackling Earth system challenges by physics‐AI integration.
Seasonally Modulated Stratospheric Aerosol Geoengineering Alters the Climate Outcomes
Authors: Visioni Daniele , MacMartin Douglas G. , Kravitz Ben , Richter Jadwiga H. , Tilmes Simone , Mills Michael J. 
Published: June 2020

AbstractBy reflecting some incoming solar radiation, stratospheric aerosol intervention using SO2 would reduce global mean temperature. Previous research has shown that multiple injection latitudes can be used to maintain not only global mean temperature, but also interhemispheric and equator‐to‐pole temperature gradients. However, the regional climate response depends not only on where the SO2 is injected, but also on when. We show here that even with these same objectives and same choices of latitudes, injecting in only one season instead of continuously throughout the year results in significant differences in regional climate, for instance in the magnitude of precipitation changes over India. The differential outcomes highlight the potential for underlying trade‐offs, with different choices regarding deployment leading to a different distribution of benefits or harms. This aspect of climate engineering should be considered in developing governance and emphasizes the need for a deeper understanding of the mechanisms underlying the regional responses.
Puzzling Haze Events in China During the Coronavirus (COVID‐19) Shutdown
Authors: Chang Yunhua , Huang Ru‐Jin , Ge Xinlei , Huang Xiangpeng , Hu Jianlin , Duan Yusen , Zou Zhong , Liu Xuejun , Lehmann Moritz F. 
Published: June 2020

AbstractIt is a puzzle as to why more severe haze formed during the New Year Holiday in 2020 (NYH‐20), when China was in an unprecedented state of shutdown to contain the coronavirus (COVID‐19) outbreak, than in 2019 (NYH‐19). We performed a comprehensive measurement and modeling analysis of the aerosol chemistry and physics at multiple sites in China (mainly in Shanghai) before, during, and after NYH‐19 and NYH‐20. Much higher secondary aerosol fraction in PM2.5 were observed during NYH‐20 (73%) than during NYH‐19 (59%). During NYH‐20, PM2.5 levels correlated significantly with the oxidation ratio of nitrogen (r2 = 0.77, p < 0.01), and aged particles from northern China were found to impede atmospheric new particle formation and growth in Shanghai. A markedly enhanced efficiency of nitrate aerosol formation was observed along the transport pathways during NYH‐20, despite the overall low atmospheric NO2 levels.