bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct Evidence for Throat Aurora Being the Ionospheric Signature of Magnetopause Transient and Reflecting Localized Magnetopause Indentations
Authors: Han De‐Sheng , Liu J.‐J. , Chen X.‐C. , Xu T. , Li B. , Hu Z.‐J. , Hu H.‐Q. , Yang H.‐G. , Fuselier S. A. , Pollock C. J. 
Published: March 2018

AbstractMagnetopause transients, observing as brief entries into the magnetosheath by satellites, are commonly observed in the vicinity of the magnetopause and have been explained by several possible mechanisms. However, satellite observations alone are insufficient to determine the dynamics and context of transients. Throat auroras are characterized as north‐south aligned discrete auroral forms extending from the equatorward edge of the discrete auroral oval that are only observed near dayside convection throat region and have been suggested as the ionospheric signature of localized magnetopause indentations. Using coordinated observations from the Magnetospheric Multiscale Mission (MMS) and ground‐based all‐sky imagers, we show apparent one‐to‐one correspondences between transients observed by MMS near the subsolar magnetopause and throat auroras observed on the ground. The correspondence is valid not only for typical throat aurora with larger spatial scale but also for these with tiny scales. We even notice that the transient durations observed by satellite are approximately proportional to the width (east‐west extension) of the throat aurora. These results provide direct evidence that throat auroras are ground signatures for the magnetopause transients. With the aid of auroral observations, we suggest that these transients reflect localized magnetopause indentations but are not produced by motion of the entire magnetopause. We also found that most transients observed here are associated with earthward flow enhancements, which indicates that high‐speed jets in the magnetosheath could be a driver for producing these transients.
Detailed Regression Model of Plasma Sheet By
Authors: Petrukovich A. A. , Lukin A. S. 
Published: March 2018

AbstractIn a statistical model plasma sheet By primarily depends on interplanetary magnetic field (IMF)
and geodipole tilt τ. With 11 years of Geotail measurements we investigate a role of several other parameters with a linear regression model. Optimal averaging window of IMF input, maximizing correlation and regression coefficients, is found to be 2.25 hr. Influence of IMF
and local Bz on IMF penetration (regression with regard to
) and the deviations from the predefined warp deformation are at the level 5–10% relative to the primary model coefficients. The IMF penetration beyond 25 RE is somewhat larger for northward IMF, while closer to the Earth it becomes somewhat larger for southward IMF. These smaller effects turned out to be rather uneven across the tail, making reliable quantification and physical interpretation not always possible. The major reasons of difficulties are uneven coverage and internal correlations in the input space (
–τ–
) due to combination of spacecraft orbit and neutral sheet dynamics, effects of coordinate transformations, etc. In particular, origins of extremely large IMF
penetration (order of 30–50% above the average one) for some years and tail locations remain not fully clear. A larger multispacecraft data set covering all seasons in all spatial zones is necessary to further advance in this study.
Rarefaction of the Very Slow (<350 km/s) Solar Wind in Cycle 24 Compared With Cycle 23
Authors: Tokumaru Munetoshi , Shimoyama Tomoya , Fujiki Ken'ichi , Hakamada Kazuyuki 
Published: March 2018

AbstractWe investigate long‐term variation of the very slow solar wind (VSSW), whose speed is less than 350 km/s, during the period between 1997 and 2015, that is, Cycles 23 and 24, using interplanetary scintillation measurements, which enable determination of the global distribution of the flow speed and the electron density fluctuation level ΔNe. We find that the occurrence rate of VSSW increases in the maximum phase of the solar cycle, and it was mostly associated with high ΔNe in Cycle 23. However, the VSSW is found to be more associated with low ΔNe in Cycle 24. This fact is consistent with an increased occurrence of the low‐density VSSW observed in situ in Cycle 24. These facts, which are considered to be a manifestation of weak solar activity in this cycle, suggest that the VSSW has become significantly rarefied in recent years. We identify the source region of the VSSW on the photosphere using a potential field analysis and examine the magnetic field properties of the VSSW source. We find that the low‐ΔNe VSSW is associated with a smaller expansion factor and possibly a slightly weaker photospheric field strength than the high‐ΔNe VSSW. The results obtained here may suggest that more open magnetic field areas producing the VSSW in Cycle 24 are formed in the quiet Sun region, which is associated with a lower mass flux supply into the corona, than those in Cycle 23.
Energy Balance From a Mantle Pseudotachylyte, Balmuccia, Italy
Authors: Ferrand Thomas P. , Labrousse Loïc , Eloy Grégoire , Fabbri Olivier , Hilairet Nadège , Schubnel Alexandre 
Published: March 2018

AbstractIn the Balmuccia massif (NW Italy), a pseudotachylyte vein network (N068 trending) in a spinel lherzolite is interpreted as the product of frictional melting during a single Mw > 6 earthquake. The subvertical fault underwent a metric dextral coseismic displacement, raking 60°SW. The average width of the main slip surface is ~ 5 mm. A dense network of thin (20–200 μm) injection and ultramylonite‐like veins decorates the fault walls. In the injection veins, Raman microspectrometry mapping reveals pockets of still preserved amorphous silicate, containing ≈ 1% of structurally bound H2O. In the ultramylonite‐like veins, electron backscattered diffraction mapping reveals that ultrafine (0.2–2 μm) olivine grains exhibit a strong fabric with (010) planes parallel to shearing, consistent with temperatures above 1250°C during deformation and suggesting fast recrystallization from the frictional melt. The veins also exhibit pyroxene and recrystallized spinel, which proves that the earthquake occurred at a minimum depth of 40 km. The energy balance demonstrates that complete fault lubrication must have occurred during coseismic sliding (i.e., dynamic friction coefficient ≪ 0.1). Because of the low viscosity of slightly hydrated ultramafic liquids (≈ 1 Pa·s), we argue that lubrication was only transient, as the melt could rapidly flow into tensile fractures, which led to rapid cooling and promoted strength recovery and sliding arrest. Combined together, our observations suggest that this pseudotachylyte is the frozen record of a deep (>40 km) earthquake of 6 < Mw < 7. Its focal mechanism is deduced from the crystal preferred orientation due to late coseismic creep in ultramylonite‐like veins and deciphered by electron backscattered diffraction.
Characterizing Afterslip and Ground Displacement Rate Increase Following the 2014 Iquique‐Pisagua Mw 8.1 Earthquake, Northern Chile
Authors: Hoffmann Felix , Metzger Sabrina , Moreno Marcos , Deng Zhiguo , Sippl Christian , Ortega‐Culaciati Francisco , Oncken Onno 
Published: March 2018

AbstractThe 2014 Iquique‐Pisagua Mw 8.1 earthquake ruptured only parts of the 1877 Northern Chile‐Southern Peru seismic gap. Here we present a comprehensive analysis of 152 continuous and campaign Global Positioning System time series that captured more than a decade of interseismic loading prior to the event and 2 years of afterslip. In high spatiotemporal resolution, our data document upper plate response not only at the coseismically affected latitudes but also at the adjacent Loa plate segment to the south. Using a combination of elastic and viscoelastic half‐space models of different stages of the seismic cycle, we found that the highly coupled, former seismic gap contains a narrow low coupling zone at 21°S latitude. Just after the 2014 earthquake, this zone acts as a barrier impeding afterslip to continue southward. Possible reasons for this impediment could involve crustal heterogeneities or coupling discontinuities at the plate interface. After 2 years, afterslip cumulates to a maximum of ~89 cm and becomes negligible. Global Positioning System observations south of the inferred seismotectonic barrier reveal a deformation rate increase in the second year after the event. Our slip models suggest that this could be caused by a downdip coupling increase, perhaps bringing the highly coupled southern Loa segment closer to failure. Taken together, our results reveal (1) the interaction between different areas undergoing stress release and stress buildup in a major seismic gap, (2) constraints for the temporal variation of coupling degree in different stages of the seismic cycle, and (3) the influence of large earthquakes at adjacent segments.
Calibrating Dense Spatial Arrays for Amplitude Statics and Orientation Errors
Authors: Langston Charles A. 
Published: March 2018

AbstractAn iterative procedure is designed to calibrate dense arrays of three‐component seismic instruments for station amplitude statics and horizontal component orientation errors. Station amplitude statics refers to differences in sensor and digitizer gains and amplification effects due to local site and installation conditions. Amplitude statics and orientation errors can seriously affect computation of the wavefield gradient tensor that is the basis of seismic strain and rotation computations as well as analysis of wave field attributes through wave gradiometry since wave spatial gradients rely on first‐order differences of the wavefield between sensors in an array. The technique is based on the assumption of a common wave field observed over a small array using teleseismic earthquake observations. In situ calibration of the broad band, 800‐m aperture array at Pinyon Flat, California, achieves relative amplitude precision for vertical components of the array from 0.16% to 0.25% and horizontal components from 0.16% to 0.61%. Relative sensor orientations can be determined to a precision better than 0.35°. Comparison of horizontal strains computed from array observations of a regional M4.9 earthquake and strains from the Gladwin Tensor borehole strain meter at Pinyon Flat shows excellent correspondence over the frequency band of 0.05 to 2 Hz. Agreement of borehole measured strains and seismic array strains for regional/local seismic events gives confidence that a borehole strain meter and single, three‐component, colocated seismometer can be used as a “point array” for deducing wavefield attributes from wave gradiometry.
Seasonal Evolution of Ocean Heat Supply and Freshwater Discharge From a Rapidly Retreating Tidewater Glacier: Jorge Montt, Patagonia
Authors: Moffat Carlos , Tapia Fabian J. , Nittrouer Charles A. , Hallet Bernard , Bown Francisca , Boldt Love Katherine , Iturra Claudio 
Published: March 2018

AbstractProglacial fjords are critical conduits for the exchange of heat and freshwater between the ocean and land ice, and their dynamics heavily modulate the rate of retreat of tidewater glaciers. Here the magnitude, spatial structure, and seasonal evolution of the ocean forcing on the proglacial fjord off a rapidly retreating glacier (Jorge Montt, Patagonia) are characterized using data from multiple shipboard surveys from 2010 to 2016, a multiyear mooring array, and a weather station. The melting of the glacier is forced by relatively warm (8–11°C) waters entering the fjord over a shallow (45 m deep) sill ≈20 km from the terminus. This warm subsurface water is renewed every summer from the surface layer of Gulf of Penas., is transported along the 100‐km long Baker Channel, and reaches the proglacial fjord in the late austral summer to early fall, where it remains relatively warm until late austral spring. Analysis of the freshwater fractions in the fjord reveals that the total freshwater content has a strong seasonal signal with maximum fractional values in the summer, mostly explained by the seasonality of subglacial discharge from the glacier. The submarine melting fraction has no strong seasonal signal, but is a first‐order contributor to the freshwater content of the fjord in winter. This seasonal evolution is consistent with idealized theories of meltwater production, and suggests that the seasonal supply of heat is critical to sustain a high mean temperature for melting, but does not directly control the melting rate variability.
Submesoscale Mixing on Initial Dilution of Radionuclides Released From the Fukushima Daiichi Nuclear Power Plant
Authors: Kamidaira Yuki , Uchiyama Yusuke , Kawamura Hideyuki , Kobayashi Takuya , Furuno Akiko 
Published: March 2018

AbstractThis study developed a submesoscale eddy‐resolving oceanic dispersal modeling system comprising a double‐nested oceanic downscaling model and an offline oceanic radionuclide dispersion model. This was used to investigate the influences of submesoscale coherent structures (SCSs) and associated ageostrophic secondary circulations (ASCs) on the three‐dimensional (3‐D) dispersal of dissolved cesium‐137 (137Cs) released from the Fukushima Daiichi Nuclear Power Plant (FNPP1). Extensive model‐data comparison demonstrated that the innermost high‐resolution model, with a lateral grid resolution of 1 km, could successfully reproduce transient mesoscale oceanic structures, the Kuroshio path and stratification, and spatiotemporal variations of 137Cs concentrations. Using an accompanying mesoscale eddy‐resolving model (grid resolution: 10 km) as a guide, we showed that submesoscale dynamics are important for improved representation of both the eddy field and the resultant 3‐D dispersal of 137Cs, with the temporal variability of surface 137Cs near the FNPP1 being equivalent to that in the coarse‐resolution model. According to energy conversion and spectral analyses, SCSs and ASCs occur most intensively on the submesoscale, primarily because of shear instability. However, baroclinic instability serves as a secondary mechanism. SCSs have prominent seasonality, reflected by intensification in the colder months, which is when the FNPP1 accident occurred. Analysis of the vertical flux of 137Cs was performed by decomposition of the variables into eddy, mesoscale, and submesoscale components using frequency and wave number filters. It revealed that 42.7% of the FNPP1‐derived 137Cs was transported downward below the mixed layer by eddies with the major contribution being from ASCs induced by submesoscale eddies.
Wind Stress Mediated Variability of the Filchner Trough Overflow, Weddell Sea
Authors: Daae K. , Darelius E. , Fer I. , Østerhus S. , Ryan S. 
Published: March 2018

AbstractThe Filchner Trough (FT) is a key site for exchange of water masses between the Weddell Sea continental shelf and the deep ocean. Cold and dense Ice Shelf Water (ISW), a precursor for Antarctic Bottom Water, flows north along the FT and overflows the Filchner Sill. Although access of warm water to the Weddell Sea continental shelf is limited due to the presence of the Antarctic Slope Front, southward transport of warm water is facilitated through the FT. We use moored current meters from the Filchner Sill region to show that the monthly scale variability of the ISW overflow is connected to the variability of the alongslope wind stress upstream. Periods with significant correlation between the wind and ISW overflow are characterized by (I) wind directed along the continental slope, (II) high ISW overflow speed, and (III) high variability in the 16–64 day period band for wind and current. We propose that a recirculation of the slope current, associated with the Antarctic Slope Front, may occur in the FT during periods of strong wind forcing, and that such recirculation could explain the correlation between the wind stress and the ISW overflow. We further show that an increased wind stress along the continental slope leads to increased current speed within the slope current and the Antarctic Coastal Current, with possible implications for the on‐shore heat transport.
Climate Change Projected to Exacerbate Impacts of Coastal Eutrophication in the Northern Gulf of Mexico
Authors: Laurent Arnaud , Fennel Katja , Ko Dong S. , Lehrter John 
Published: March 2018

AbstractThe continental shelf in the northern Gulf of Mexico experiences expansive seasonal hypoxic conditions and eutrophication‐driven acidification in bottom waters. Rising surface ocean temperatures, freshwater and nutrient inputs, and atmospheric CO2 will further exacerbate these conditions. Using a high‐resolution, regional circulation‐biogeochemical model, we simulated the spatiotemporal dynamics of oxygen and inorganic carbon in the northern Gulf of Mexico under present and a projected future (2100) climate state. Results indicate a modest expansion of the hypoxic zone, but more severe hypoxia and greater exposure to prolonged hypoxic conditions. The main drivers underlying these changes are a reduction in oxygen solubility (accounting for 60–74% of the change) and increased stratification (accounting for less than 40%). pH is projected to decrease across the shelf with lowest values in hypoxic waters where aragonite saturation will approach the saturation limit. In the model simulations, acidification is primarily driven by atmospheric and offshore CO2 levels, while the enhancement in stratification only accounts for 7% or less of the total change in pH. Decreased buffering capacity and increased stratification in the future will enhance respiration‐induced acidification (i.e., a decrease in bottom water pH by respired CO2), which will amplify the climate‐induced acidification. According to the model, the magnitude of future changes varies significantly from year to year. The largest effects are simulated in years with large freshwater discharge and upwelling‐favorable winds.
Microbial Community Responses to Modern Environmental and Past Climatic Conditions in Omongwa Pan, Western Kalahari: A Paired 16S rRNA Gene Profiling and Lipid Biomarker Approach
Authors: Genderjahn S. , Alawi M. , Wagner D. , Schüller I. , Wanke A. , Mangelsdorf K. 
Published: March 2018

AbstractDue to a lack of well‐preserved terrestrial climate archives, paleoclimate studies are sparse in southwestern Africa. Because there are no perennial lacustrine systems in this region, this study relies on a saline pan as an archive for climate information in the western Kalahari (Namibia). Molecular biological and biogeochemical analyses were combined to examine the response of indigenous microbial communities to modern and past climate‐induced environmental conditions. The 16S rRNA gene high‐throughput sequencing was applied to sediment samples from Omongwa pan to characterize the modern microbial diversity. Highest diversity of microorganisms, dominated by the extreme halophilic archaeon Halobacteria and by the bacterial phylum Gemmatimonadetes, was detected in the near‐surface sediments of Omongwa pan. In deeper sections abundance and diversity significantly decreases and Bacillus, known to form spores, become dominant. Lipid biomarkers for living and past microbial life were analyzed to track the influence of climate variation on the abundance of microbial communities from the Last Glacial Maximum to Holocene time. Since water is an inevitable requirement for microbial life, in this dry region the abundance of past microbial biomarkers was evaluated to conclude on periods of increased paleoprecipitation in the past. The data point to a period of increased humidity in the western Kalahari during the Last Glacial to Holocene transition indicating a southward shift of the Intertropical Convergence Zone during this period. Comparison with results from a southwestern Kalahari pan suggests complex displacements of the regional atmospheric systems since the Last Glacial Maximum.
Estimating Convection Parameters in the GFDL CM2.1 Model Using Ensemble Data Assimilation
Authors: Li Shan , Zhang Shaoqing , Liu Zhengyu , Lu Lv , Zhu Jiang , Zhang Xuefeng , Wu Xinrong , Zhao Ming , Vecchi Gabriel A. , Zhang Rong‐Hua , Lin Xiaopei 
Published: March 2018

AbstractParametric uncertainty in convection parameterization is one major source of model errors that cause model climate drift. Convection parameter tuning has been widely studied in atmospheric models to help mitigate the problem. However, in a fully coupled general circulation model (CGCM), convection parameters which impact the ocean as well as the climate simulation may have different optimal values. This study explores the possibility of estimating convection parameters with an ensemble coupled data assimilation method in a CGCM. Impacts of the convection parameter estimation on climate analysis and forecast are analyzed. In a twin experiment framework, five convection parameters in the GFDL coupled model CM2.1 are estimated individually and simultaneously under both perfect and imperfect model regimes. Results show that the ensemble data assimilation method can help reduce the bias in convection parameters. With estimated convection parameters, the analyses and forecasts for both the atmosphere and the ocean are generally improved. It is also found that information in low latitudes is relatively more important for estimating convection parameters. This study further suggests that when important parameters in appropriate physical parameterizations are identified, incorporating their estimation into traditional ensemble data assimilation procedure could improve the final analysis and climate prediction.
Numerical Solutions of the Mean‐Value Theorem: New Methods for Downward Continuation of Potential Fields
Authors: Zhang Chong , Lü Qingtian , Yan Jiayong , Qi Guang 
Published: March 2018

AbstractDownward continuation can enhance small‐scale sources and improve resolution. Nevertheless, the common methods have disadvantages in obtaining optimal results because of divergence and instability. We derive the mean‐value theorem for potential fields, which could be the theoretical basis of some data processing and interpretation. Based on numerical solutions of the mean‐value theorem, we present the convergent and stable downward continuation methods by using the first‐order vertical derivatives and their upward continuation. By applying one of our methods to both the synthetic and real cases, we show that our method is stable, convergent and accurate. Meanwhile, compared with the fast Fourier transform Taylor series method and the integrated second vertical derivative Taylor series method, our process has very little boundary effect and is still stable in noise. We find that the characters of the fading anomalies emerge properly in our downward continuation with respect to the original fields at the lower heights.