bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interactions between land use change and carbon cycle feedbacks
Authors: Mahowald Natalie M. , Randerson James T. , Lindsay Keith , Munoz Ernesto , Doney Scott C. , Lawrence Peter , Schlunegger Sarah , Ward Daniel S. , Lawrence David , Hoffman Forrest M. 
Published: December 2016

AbstractUsing the Community Earth System Model, we explore the role of human land use and land cover change (LULCC) in modifying the terrestrial carbon budget in simulations forced by Representative Concentration Pathway 8.5, extended to year 2300. Overall, conversion of land (e.g., from forest to croplands via deforestation) results in a model‐estimated, cumulative carbon loss of 490 Pg C between 1850 and 2300, larger than the 230 Pg C loss of carbon caused by climate change over this same interval. The LULCC carbon loss is a combination of a direct loss at the time of conversion and an indirect loss from the reduction of potential terrestrial carbon sinks. Approximately 40% of the carbon loss associated with LULCC in the simulations arises from direct human modification of the land surface; the remaining 60% is an indirect consequence of the loss of potential natural carbon sinks. Because of the multicentury carbon cycle legacy of current land use decisions, a globally averaged amplification factor of 2.6 must be applied to 2015 land use carbon losses to adjust for indirect effects. This estimate is 30% higher when considering the carbon cycle evolution after 2100. Most of the terrestrial uptake of anthropogenic carbon in the model occurs from the influence of rising atmospheric CO2 on photosynthesis in trees, and thus, model‐projected carbon feedbacks are especially sensitive to deforestation.
Global variability and changes in ocean total alkalinity from Aquarius satellite data
Authors: Fine Rana A. , Willey Debra A. , Millero Frank J. 
Published: December 2016

AbstractThis work demonstrates how large‐scale Aquarius satellite salinity data have provided an unprecedented opportunity when combined with total alkalinity (TA) equations as a function of salinity and temperature to examine global changes in the CO2 system. Alkalinity is a gauge on the ability of seawater to neutralize acids. TA correlates strongly with salinity. Spatial variability in alkalinity and salinity exceed temporal variability. Northern Hemisphere has more spatial variability in TA and salinity, while less variability in Southern Ocean TA is due to less salinity variability and upwelling of waters enriched in alkalinity. For the first time it is shown that TA in subtropical regions has increased as compared with climatological data; this is reflective of large‐scale changes in the global water cycle. Thus, as temperature and salinity increase in subtropical regions, the resultant increase in TA and ocean acidification is reinforcing that from oceanic uptake of atmospheric CO2.
New insights into magma plumbing along rift systems from detailed observations of eruptive behavior at Axial volcano
Authors: Sigmundsson Freysteinn 
Published: December 2016

AbstractThe magma reservoir in geophysical volcano plumbing models is often modeled as a simple geometric volume, filled with magma of uniform properties. However, the constraints on reservoir size and magma properties in volcano roots are typically indirect and poor. Axial Seamount, a volcano at a depth of about 1500 m on the Juan de Fuca mid‐oceanic ridge in the Pacific Ocean, has both high‐resolution seismic images of its subsurface magma and detailed results from monitoring of its most recent eruption and associated seismicity and ground deformation. The 2015 eruption at Axial Seamount is the best monitored submarine eruption so far because of observations made possible by the Ocean Observatories Initiative, and seismic imaging of magma at this volcano is better than in most other environments because of advanced analysis of extensive seismic reflection profiling at sea and the relatively simple volcano structure. This allows new understanding compared to findings from earlier observations from monitored rifting episodes on land. Geophysical magma plumbing models, in general, may need to allow for more complexities, namely, spatial heterogeneities in magma composition, melt content, and location of major volume changes within a single magma dominated crustal volume during eruptions.
Directional gravity wave momentum fluxes in the stratosphere derived from high‐resolution AIRS temperature data
Authors: Ern M. , Hoffmann L. , Preusse P. 
Published: December 2016

AbstractIn order to reduce uncertainties in modeling the stratospheric circulation, global observations of gravity wave momentum flux (GWMF) vectors are required for comparison with distributions of resolved and parametrized GWMF in global models. For the first time, we derive GWMF vectors globally from data of a nadir‐viewing satellite instrument: we apply a 3‐D method to an Atmospheric Infrared Sounder (AIRS) temperature data set that was optimized for gravity wave (GW) analysis. For January 2009, the resulting distributions of GW amplitudes and of net GWMF highlight the importance of GWs in the polar vortex and the summertime subtropics. Net GWMF is preferentially directed opposite to the background wind, and, interestingly, it is dominated by large‐amplitude GWs of relatively long horizontal wavelength. For convective GW sources, these large horizontal scales are in contradiction with traditional thoughts. However, the observational filter effect needs to be kept in mind when interpreting the results.
Scientific considerations for future spectroscopic measurements from space of activity on the Sun
Authors: Holman Gordon D. 
Published: December 2016

AbstractHigh‐resolution UV and X‐ray spectroscopy are important to understanding the origin and evolution of magnetic energy release in the solar atmosphere, as well as the subsequent evolution of heated plasma and accelerated particles. Electromagnetic radiation is observed from plasma heated to temperatures ranging from about 10 kK to above 10 MK, from accelerated electrons emitting photons primarily at X‐ray energies, and from ions emitting in γ rays. These observations require space‐based instruments sensitive to emissions at wavelengths shorter than the near UV. This article reviews some recent observations with emphasis on solar eruptive events, the models that describe them, and the measurements they indicate are needed for substantial progress in the future. Specific examples are discussed demonstrating that imaging spectroscopy with a cadence of seconds or better is needed to follow, understand, and predict the evolution of solar activity. Critical to substantial progress is the combination of a judicious choice of UV, EUV, and soft X‐ray imaging spectroscopy sensitive to the evolution of this thermal plasma combined with hard X‐ray imaging spectroscopy sensitive to suprathermal electrons. The major challenge will be to conceive instruments that, within the bounds of possible technologies and funding, have the flexibility and field of view to obtain spectroscopic observations where and when events occur while providing an optimum balance of dynamic range, spectral resolution and range, and spatial resolution.
Ionospheric signatures of gravity waves produced by the 2004 Sumatra and 2011 Tohoku tsunamis: A modeling study
Authors: Yu Yonghui , Wang Wenqing , Hickey Michael P. 
Published: December 2016

AbstractIonospheric fluctuations inferred from observations of total electron content have previously been attributed to tsunamis and have confirmed the strong coupling between Earth's ocean and ionosphere via atmospheric gravity waves (AGWs). To further advance our understanding of this wave coupling process we employ a linear full‐wave model and a nonlinear time‐dependent model to examine the ionospheric response to the AGW perturbations induced by the 2004 Sumatra and the 2011 Tohoku tsunamis. In the 2004 case, our modeling analyses reveal that one component of the propagating AGWs becomes dynamically unstable in the E‐region ionosphere at a range exceeding 2000 km in a direction 340° clockwise from north. Another component becomes convectively unstable in the E‐region ionosphere at a range exceeding 700 km in a direction 250° clockwise from north. In the 2011 case, a significant enhancement in the ionospheric disturbance occurs in a direction northwest from the epicenter about 1 h following the tsunami onset, in general agreement with observations. Our simulations also indicate that the AGW propagating toward the southeast is responsible for a traveling ionospheric disturbance that remains of an observable amplitude for over 4 h during which time it propagates horizontally almost 4000 km.
Nonlinear dynamics of electrons interacting with oblique whistler mode chorus in the magnetosphere
Authors: Hsieh Yi‐Kai , Omura Yoshiharu 
Published: December 2016

AbstractWe perform test particle simulations for relativistic electrons interacting with a whistler mode chorus packet propagating at oblique angles. By confirming that the energy transport of oblique lower band chorus is nearly along the ambient magnetic field, we apply the gyroaveraging method in calculating equations of motion of electrons. We trace evolution of a delta function of relativistic electrons in a phase space of kinetic energy and equatorial pitch angle and obtain numerical Green's functions of the chorus wave‐particle interactions. Examining the Green's functions in a wide range of kinetic energies, we find that Landau resonance can accelerate MeV electrons efficiently and that higher nth resonances such as n =− 1 and n = 2 also contribute to acceleration of electrons at high equatorial pitch angles (∼70°) and high energies (∼2 MeV). We investigate the rate of energy gain of the cyclotron resonance acceleration and the Landau resonance acceleration and find that the perpendicular component of wave electric field dominates both accelerations for MeV electrons. Furthermore, the proximity between the parallel components of Vp and Vg of oblique whistler mode waves and the nonlinear trapping condition make the interaction time of Landau resonance much longer than that of n = 1 cyclotron resonance, resulting in efficient acceleration of MeV electrons.
On the governing dynamics of the VHF radar echoes from the mesosphere and collision‐dominated lower E region over Gadanki (13.5°N, 79.2°E)
Authors: Selvaraj D. , Patra A. K. , Sathishkumar S. , Kishore Kumar K. , Narayana Rao D. 
Published: December 2016

AbstractIn the present communication, the role of neutral dynamical processes in governing the morphology and seasonal variations of daytime VHF radar echoes from the mesosphere and the collision‐dominated lower E region is discussed. While the seasonal variations of mesospheric echo occurrence show semiannual variation with their maxima in the equinoxes, the occurrence of E region echoes shows strong annual variation peaking in the summer with two secondary maxima identical to semiannual variation of the mesospheric echoes. The occurrence rates of the E region echoes, however, display year‐to‐year variability. Semiannual variations in the occurrence of low‐latitude mesospheric echoes are closely linked with similar variations in the occurrences of temperature inversion, large wind shear, tides, and gravity wave activities in the same height region. In the case of E region echoes, the summer maximum and equinoctial secondary maxima are found to be linked with similar variations in wind and wind shear, Es activity, tidal, and gravity wave activities. Further, the summer maximum is found to be strongly correlated with that of meteor flux and nonmigrating diurnal tide. This finding is significant given the fact that such wind field in the presence of metallic ions could form both Es and field‐aligned irregularities. The present results show that tides and gravity waves are the most important dynamical factors governing the morphology and seasonal variations of the mesospheric as well as lower E region echoes observed over Gadanki. These results are discussed in the light of current understanding on the dynamical coupling of the mesosphere and lower E region through tides and gravity waves.
Creating space plasma from the ground
Authors: Carlson H. C. , Djuth F. T. , Zhang L. D. 
Published: December 2016

AbstractWe have performed an experiment to compare as directly as realizable the ionization production rate by HF radio wave energy versus by solar EUV. We take advantage of the commonality that ionization production by both ground‐based high‐power HF radio waves and by solar EUV is driven by primary and secondary suprathermal electrons near and above ~20 eV. Incoherent scatter radar (ISR) plasma‐line amplitudes are used as a measure of suprathermal electron fluxes for ISR wavelengths near those for 430 MHz and are indeed a clean measure of such for those fluxes sufficiently weak to have negligible self‐damping. We present data from an HF heating experiment on November 2015 at Arecibo, which even more directly confirm the only prior midlatitude estimate, of order 10% efficiency for conversion of HF energy to ionospheric ionization. We note the theoretical maximum possible is ~1/3, while ~1% or less reduces the question to near practical irrelevance. Our measurements explicitly confirm the prediction that radio‐frequency production of artificial ionospheres can be practicable, even at midlatitudes. Furthermore, that this midlatitude efficiency is comparable to efficiencies measured at high latitudes (which include enhancements unique to high latitudes including magnetic zenith effect, gyrofrequency multiples, and double resonances) requires reexamination of current theoretical thinking about soft‐electron acceleration processes in weakly magnetized plasmas. The implications are that electron acceleration by any of a variety of processes may be a fundamental underpinning to energy redistribution in space plasmas.
Crustal structure and origin of the Eggvin Bank west of Jan Mayen, NE Atlantic
Authors: Tan Pingchuan , Breivik Asbjørn Johan , Trønnes Reidar G. , Mjelde Rolf , Azuma Ryosuke , Eide Sigurd 
Published: December 2016

AbstractThe Eggvin Bank, located between the Jan Mayen Island and Greenland, is an unusually shallow area containing several submarine volcanic peaks, confined by two transforms on the Northern Kolbeinsey Ridge (NKR). We represent P and S wave velocity models for the Eggvin Bank based on an Ocean Bottom Seismometer profile collected in 2011, showing igneous crustal thickness variations from 8 km to 13 km. A 2–5 km increase is associated with two separate 20–30 km wide segments under the main seamounts. The oceanic crust has three layers: upper crust (L2A: 2.8–4.8 km/s), middle crust (L2B: 5.5–6.5 km/s), and lower crust (L3: 6.7–7.35 km/s). Both the thick layer 2(A/B) and the high ratio of layer 2(A/B) thickness to total crustal thickness indicate that secondary, intraplate magmatism built the seamounts of the Eggvin Bank. The seamount in the north where the crust is thickest has a flat top indicating subaerial exposure but is deeper than those with rounded tops in the south and is therefore probably older. Comparing lower crustal seismic velocity with crustal thickness also indicates that the degree of mantle melting may be higher in the north than in the south. An enriched mantle source presently feeds the NKR magmatism and probably influenced the Eggvin Bank development also at earlier times. To what extent the Eggvin Bank has been influenced by the Iceland plume is uncertain, both an enriched mantle component and elevated mantle temperature may have played a role at different times and locations.
Anthropogenic and natural ground deformation in the Hengill geothermal area, Iceland
Authors: Juncu D. , Árnadóttir Th. , Hooper A. , Gunnarsson G. 
Published: December 2016

AbstractWe investigate crustal deformation due to the extraction of water and steam from a high‐enthalpy geothermal reservoir; a common occurrence, yet not well understood. The cause of this deformation can be a change in pressure or in temperature in the reservoir, both of which can be caused by extraction or injection of geothermal fluids. Our study area, the Hengill mountains in SW Iceland, is an active volcanic center and a plate triple junction that hosts two power plants producing geothermal energy. This combination of natural and anthropogenic processes causes a complex displacement field at the surface. We analyze geodetic data—Global Navigation Satellite System and Interferometric Synthetic Aperture Radar—to obtain the surface velocity field, which we then simulate using an inverse modeling approach. We focus on the deformation around the geothermal power plants but need to model the regional tectonic and volcanic deformation as well, because the signals are overlapping. We find that plate motion and a deep contracting body can explain the broad scale signal in the area. Local deformation near the two power plants, Hellisheidi and Nesjavellir, can be explained by extraction of geothermal fluids. We estimate reservoirs extending from 0.6 to 3.0 km depth at Hellisheidi, and 1.0 to 3.0 km depth at Nesjavellir for observed pressure decrease rates of 0.25 MPa/yr and 0.1 MPa/yr, respectively. We find that the main cause for the subsidence in the geothermal area is the observed pressure drawdown.
Links between atmosphere, ocean, and cryosphere from two decades of microseism observations on the Antarctic Peninsula
Authors: Anthony Robert E. , Aster Richard C. , McGrath Daniel 
Published: December 2016

The lack of landmasses, climatological low pressure, and strong circumpolar westerly winds between the latitudes of 50°S to 65°S produce exceptional storm‐driven wave conditions in the Southern Ocean. This combination makes the Antarctic Peninsula one of Earth's most notable regions of high‐amplitude wave activity and thus, ocean‐swell‐driven microseism noise in both the primary (direct wave‐coastal region interactions) and secondary (direct ocean floor forcing due to interacting wave trains) period bands. Microseism observations are examined across 23 years (1993–2015) from Palmer Station (PMSA), on the west coast of the Antarctic Peninsula, and from East Falkland Island (EFI). These records provide a spatially integrative measure of both Southern Ocean wave amplitudes and the interactions between ocean waves and the solid Earth in the presence of sea ice, which can reduce wave coupling with the continental shelf. We utilize a spatiotemporal correlation‐based approach to illuminate how the distribution of sea ice influences seasonal microseism power. We characterize primary and secondary microseism power due to variations in sea ice and find that primary microseism energy is both more sensitive to sea ice and more capable of propagating across ocean basins than secondary microseism energy. During positive phases of the Southern Annular Mode, sea ice is reduced in the Bellingshausen Sea and overall storm activity in the Drake Passage increases, thus strongly increasing microseism power levels.
Modeling geomagnetically induced currents
Authors: Boteler D. H. , Pirjola R. J. 
Published: December 2016

AbstractUnderstanding the geomagnetic hazard to power systems requires the ability to model the geomagnetically induced currents (GIC) produced in a power network. This paper presents the developments in GIC modeling starting with an examination of fundamental questions about where the driving force for GIC is located. Then we outline the two main network modeling approaches that are mathematically equivalent and show an example for a simple circuit. Accurate modeling of the GIC produced during real space weather events requires including the appropriate system characteristics, magnetic source fields, and Earth conductivity structure. It is shown how multiple voltage levels can be included in GIC modeling and how the network configuration affects the GIC values. Magnetic source fields can be included by using “plane wave” or line current models or by using geomagnetic observatory data with an appropriate interpolation scheme. Earth conductivity structure can be represented by 1‐D, 2‐D, or 3‐D models that are used to calculate the transfer function between electric and magnetic fields at the Earth's surface. For 2‐D and 3‐D structures this will involve a tensor impedance function and electric fields that are not necessarily orthogonal to the magnetic field variations. It is now technically possible to include all these features in the modeling of GIC, and various software implementations are being developed to make these features more accessible for use in risk studies.
Investigation of representing hysteresis in macroscopic models of two‐phase flow in porous media using intermediate scale experimental data
Authors: Cihan Abdullah , Birkholzer Jens , Trevisan Luca , Gonzalez‐Nicolas Ana , Illangasekare Tissa 
Published: December 2016

AbstractIncorporating hysteresis into models is important to accurately capture the two phase flow behavior when porous media systems undergo cycles of drainage and imbibition such as in the cases of injection and post‐injection redistribution of CO2 during geological CO2 storage (GCS). In the traditional model of two‐phase flow, existing constitutive models that parameterize the hysteresis associated with these processes are generally based on the empirical relationships. This manuscript presents development and testing of mathematical hysteretic capillary pressure—saturation—relative permeability models with the objective of more accurately representing the redistribution of the fluids after injection. The constitutive models are developed by relating macroscopic variables to basic physics of two‐phase capillary displacements at pore‐scale and void space distribution properties. The modeling approach with the developed constitutive models with and without hysteresis as input is tested against some intermediate‐scale flow cell experiments to test the ability of the models to represent movement and capillary trapping of immiscible fluids under macroscopically homogeneous and heterogeneous conditions. The hysteretic two‐phase flow model predicted the overall plume migration and distribution during and post injection reasonably well and represented the postinjection behavior of the plume more accurately than the nonhysteretic models. Based on the results in this study, neglecting hysteresis in the constitutive models of the traditional two‐phase flow theory can seriously overpredict or underpredict the injected fluid distribution during post‐injection under both homogeneous and heterogeneous conditions, depending on the selected value of the residual saturation in the nonhysteretic models.
A Transition‐Metal‐Free and Base‐Mediated Carbene Insertion into Sulfur‐Sulfur and Selenium‐Selenium Bonds: An Easy Access to Thio‐ and Selenoacetals
Authors: Arunprasath Dhanarajan , Sekar Govindasamy 
Published: December 2016

AbstractA transition‐metal‐free and base‐mediated carbene insertion across sulfur‐sulfur and selenium‐selenium bonds has been developed by employing N‐tosylhydrazone as a stable and safe carbene precursor. The ylide formation from carbene followed by Stevens rearrangement are considered to be the key steps. This thiol and selenol‐free protocol delivers thioacetals and selenoacetals in good to excellent yields in short reaction time with good functional group tolerance. A one‐pot synthesis involving in situ generation of tosylhydrazone has also been demonstrated.magnified image