bluuebunny/crossref_metadata_2025 huggingface dataset:
A top–down, multidisciplinary study of the structure and function of the pack-ice ecosystem in the eastern Ross Sea, Antarctica
Authors: Ackley S.F. , Bengtson J.L. , Boveng P. , Castellini M. , Daly K.L. , Jacobs S. , Kooyman G.L. , Laake J. , Quetin L. , Ross R. , Siniff D.B. , Stewart B.S. , Stirling I. , Torres J. , Yochem P.K.
Published: April 2019

We used a top–down, multidisciplinary approach to examine the physical and biological environment of the pack ice of the eastern Ross Sea (approximately 125–170°W) during the austral summer of 1999/2000 from RVIB Nathaniel B. Palmer and its ship-based helicopters. The approach focused on pack-ice seals while incorporating studies of biotic and abiotic factors that may influence the distribution and abundances of these apex predators in the Ross Sea to yield a holistic understanding of the structure and function of this complex, large marine ecosystem. This research represented the US component of the international Antarctic Pack Ice Seal (APIS) program, which was designed to document the circumpolar distribution and abundance of Antarctic pack-ice seals. The eastern Ross Sea is one of the two major areas in the Southern Ocean where substantial pack ice exists throughout summer. We found that vast multi-year ice floes (>20 km diameter) and smaller floes north of the shore-fast ice front provide a unique habitat for seals and penguins (apex predators) to forage and haul out while molting in late summer. Farther north, more Ross seals were observed than in any previous surveys in the circumpolar pack ice, perhaps because they are attracted to the area in summer to molt on large stable first-year ice floes. Extensive fast ice along the coastline and drifting pack ice in the shelf–slope boundary zone provided haul-out areas for seals and penguins with access to feeding in the coastal shelf region. Distributions of potential prey for seals and penguins varied over the study area, as determined by nets, acoustics, and diving surveys. Antarctic krill (Euphausia superba) were found throughout the survey region, overlapping the distributions of two smaller species, Thysanoëssa macrura (primarily off-shelf) and E. crystallorophias (primarily found on-shelf). In some locations, E. superba occurred at high densities underneath ice floes, where they foraged on the sea-ice microbial community. Two general fish communities, oceanic and shelf, were distinguished. Off-shelf fishes were members of the classic oceanic midwater fish fauna, whereas on-shelf fishes were Antarctic endemics. The abundance of pelagic fishes was relatively low throughout the study area compared with other Southern Ocean ecosystems. In contrast, benthic fish biomass and diversity on-shelf were high (41 species, 6 families). Hydroacoustic analyses indicated that densities of potential prey were highest in the coastal shelf region where large aggregations of euphausiids (primarily E. crystallorophias) and individual juvenile Antarctic silverfish (Pleuragramma antarcticum) occurred.
Use of vegetation types by Svalbard reindeer from Arctic winter to spring
Authors: Lindner Elke
Published: April 2019

Svalbard reindeer were examined for their dependency on seasonal changes from January to May and their choice of certain vegetation types. Snow characteristics and accumulation appear to be the main factors for the changing use of vegetation types from open plains and wetland in January and February to slopes and areas with ridge and heath vegetation in April and May. The results confirm other studies of the grazing behaviour of reindeer and caribou on the Norwegian mainland and in North America.
Carl von Ditmar, 1822–92: a geologist in Kamchatka
Authors: Tammiksaar Erki
Published: April 2019

From 1851 to 1855, the Baltic-German geologist Carl von Ditmar explored and made scientific observations of Kamchatka. This area had first been scientifically investigated by Georg Wilhelm Steller and Stepan Petrovich Krasheninnikov in the 1730s and 1740s. However, until the last decade of the nineteenth century, little was added to the studies by Steller and Krasheninnikov, despite almost all of the Russian circumnavigations having gone through Kamchatka. It was only in 1890 that Ditmar's detailed investigation of the natural history and peoples of the Kamchatka peninsula was published. Although Ditmar remains little known to the broader public, his investigations are still used by those investigating Kamchatka.
Obituary
Authors: Hattersley-Smith Geoffrey
Published: April 2019

André Roch, the great Swiss mountaineer, Alpine guide, and ski instructor, died in Geneva on 19 November 2002, aged 96.
Interaction of fluvial and gravitational processes in Laagkolldalen, Nathorst Land, central Spitsbergen, Svalbard
Authors: Stange Rolf
Published: April 2019

At three localities in Svalbard, there are unusual geomorphological features, where solifluidal sediment bodies were at first eroded at the bottom and not at the top, as should normally be expected. It is suggested that the thermoerosion of the refrozen solifluidal sediment is caused by water running down the valleys or gullies it blocks. Thermoerosion affects the lower part of the frozen sediment, whereas the upper part remains frozen, thus creating a bridge-like feature and, consequently, subsurface drainage over shorter distances. As all three localities have a similar lithology in common, this seems to be a significant factor.
Obituary
Authors: Hattersley-Smith Geoffrey
Published: April 2019

James Edward Butler Futtit Farrington, known to friends and expedition colleagues by his nickname ‘Fram,’ died at Lisburn, Co. Antrim, on 4 October 2002, aged 94. He was one of a handful of surviving holders of the Polar Medal in Bronze, abolished after 1941. He should also have received the Polar Medal in Silver, but the medal was denied him during his lifetime through a technicality; it has, however, since been awarded to him after his death.
Travels with mules: Antarctica 1912
Authors: Savours Ann
Published: April 2019

Seven pack mules were taken from India to the Antarctic in 1912. Their preparations for the voyage and for use in exploration are described. The names of the animals and of their leaders are recorded from the account of their expedition from winter quarters to find the last camp of Scott's Polar Party.
THINKING CONSTITUTIONALLY: THE PROBLEM OF DELIBERATIVE DEMOCRACY
Authors: Elkin Stephen L.
Published: April 2019

A variety of arguments have been advanced that deliberation should be
at the center of any good political regime in which there is popular
self-government. Deliberation is to be the basis for lawmaking, that
is, for the making of the collectivity's binding decisions. Thus,
John Rawls says, “[O]f course, actual constitutions
should be designed as far as possible to make the same determinations
as the ideal legislative procedure.” This procedure, in turn, is
defined as having laws that result from “rational legislators
… who are conscientious, trying to follow the principles of
justice as their standard.” These legislators “are not to
take a narrow or group-interested standpoint.” Joshua Cohen
broadly agrees with Rawls and characterizes Rawls's view as one
that argues for a democratic politics that is built around public
deliberation. Cohen says (agreeing with Rawls) that “an ideal
pluralist scheme, in which democratic politics consists of fair
bargaining among groups each of which pursues its particular or
sectional interest, is unsuited to a just society.” John Dryzek
shares these views and comments that the “essence of democratic
legitimacy should be sought … in the ability of all individuals
subject to a collective decision to engage in authentic deliberation
about that decision.” Others have argued along similar lines,
including James Bohman, Amy Gutmann and Dennis Thompson, David
Gauthier, and Jurgen Habermas.
POLICY IMPLICATIONS OF ZERO DISCOUNTING: AN EXPLORATION IN POLITICS
AND MORALITY
Authors: Cowen Tyler
Published: April 2019

What are our political obligations to future generations? How does
morality suggest that we weight current interests against future interests?
Do politics or markets place greater weight upon interests in the very distant
future? How should we discount future costs and benefits?
MR. PINOCCHIO GOES TO WASHINGTON: LYING IN POLITICS
Authors: Weissberg Robert
Published: April 2019

A more provocative subject than “lying in politics”
is difficult to imagine. Everybody, from the proverbial “Joe
Sixpack” to ivory-tower philosophers, can wax eloquently on the subject,
if only because easy-to-find, shocking (and occasionally sexually
“juicy”) examples abound. If moral outrage were judged an
essential vitamin, then condemning dishonesty undoubtedly guarantees a daily
megadose. Unfortunately, at least for those who crave self-indulgent outrage,
the anti-lying case is less than 100 percent compelling. It is a quagmire of
the first order, if only because those who cherish frankness also usually
confess to lying. Hannah Arendt once suggested that lies are a necessary and
justifiable tool of the statesman's trade. Formulating damnation criteria
invites mind-boggling paradoxes, and strident defenders of
truth-telling, with scant exception, admit that falsehoods are
“sometimes” permitted for “good” reasons. And
what might be these “good reasons”? Who can say for sure?
Centuries of erudite scholarship on this point might be encapsulated as
“Lying to me is bad, but I can consent to deceiving others for
noble purposes, as artfully decided by myself.”
POLITICAL MORALITY AS CONVENTION
Authors: Barry Norman
Published: April 2019

A remarkable feature of contemporary political discourse is the
dominance of morality. One legacy of logical positivism (which was
dominant from the mid-1930s until the end of the 1960s) and analytical
(or linguistic) philosophy was the reluctance of political theorists
during the twentieth century to engage in substantive argument about
appropriate social ends or individual rights and values. Philosophers
were content to describe the linguistic framework within which related
political proposals were discussed without offering any proposals
themselves. It was felt that the philosopher was not especially
qualified to give political advice or make any recommendations. The
technical political theorist was properly confined to the
second level of inquiry, that is, explanation of the meaning
of concepts, not the first level, which was concerned with
questions of how we ought to live, or issues of public policy.
Economists and sociologists might have the technical skills appropriate
for inquiries into public policy, but as to the big
questions—such as the ends and purposes of man and
society—almost anybody could make pronouncements. The important
point was that reason was incapable of adjudicating between
rival versions of the good life.
GOD'S IMAGE AND EGALITARIAN POLITICS
Authors: Fletcher George P.
Published: April 2019

These days, American politicians are loath to cite biblical passages
for fear of being charged with breaching the wall between church and
state. There was a time when a presidential candidate could claim that
a certain monetary policy would “crucify us on a cross of
gold.” This kind of rhetoric is now taboo. America's
national leaders even avoid quoting the religious phrases from the
Declaration of Independence, particularly its references to the
“Creator” or “Nature's God.” Although in
the past some of the greatest American political oratory—Abraham
Lincoln at Gettysburg (1863) or Martin Luther King, Jr., at the Lincoln
Memorial (1963)—relied unashamedly on biblical sources and
imagery, it is no longer considered acceptable to argue publicly in the
language of either the Hebrew or Christian Bibles. However religious
American society might still be today, political rhetoric is noticeably
nonreligious.
Constitutional and Institutional Developments
Authors: Rydberg Åsa
Published: April 2019

By decision of the Judges at the Nineteenth plenary session of the International Criminal Tribunal for the former Yugoslavia (ICTY) one new rule was adopted and 16 rules of the Rules of Procedure and Evidence were amended. The new rule concerns affidavit evidence. The rule regarding amendments of the rules was changed so that an amendment shall enter into force seven days after the day of issue of an official Tribunal document containing the amendment, instead of immediately after the issuance. The rules on contempt of the Tribunal and false testimony under solemn declaration were made stricter as they were both amended to allow for a Chamber to impose substantially longer terms of imprisonment on persons who have been found guilty of such offences.
Case Analysis: Reviewing the Case of Dražen Erdemović: Unchartered Waters at the International Criminal Tribunal for the former Yugoslavia
Authors: Linton Suzannah
Published: April 2019

Dražen Erdemović was one of the first people to appear in proceedings before the International Criminal Tribunal for the former Yugoslavia, as a potential witness in the Rule 61 proceedings against Radovan Karadžić and Ratko Mladić. The proceedings involving his own actions have now been completed. The case of Dražen Erdemović opened a Pandora's box of complex legal and moral issues. In this article, the ground-breaking case is examined in its entirety, with an emphasis on the novel issues that arose at each stage. It provides an overview of the procedural and substantive issues, and considers the implications that the case has had upon the development of international law and the proceedings at the International Tribunal. Finally, this article considers the case of Dražen Erdemović in the context of the International Tribunal's mandate to bring peace and reconciliation to the former Yugoslavia.
Mechanisms of control in activating and deploying lexical knowledge
Authors: CARR THOMAS H.
Published: April 2019

David Green's excellent paper “Mental control of the bilingual lexico-semantic system” raises three fundamental questions. My goal is to suggest elaborations on his answers that might make the arguments stronger and more comprehensive.
Not by words alone: Comments on a proposal for the control of access to bilingual language representations
Authors: KROLL JUDITH F. , MICHAEL ERICA
Published: April 2019

Green makes the critical observation that models of lexical and semantic representation in bilingual memory fail to specify a mechanism that would enable the bilingual speaker to act. Under the conditions typical of most experimental research, bilinguals are asked to perform a well-defined task, such as word or picture naming, lexical decision, or translation. The question Green raises is how is it that the bilingual effectively performs one of these tasks rather than another? And within a given task such as word translation, how does the individual manage to produce words in one language and suppress the other? The goal of Green's proposal is to provide a preliminary account of the control apparatus that a bilingual would need to possess in order to perform effectively in this environment. An adequate model of these control mechanisms will presumably allow us to understand not only how bilinguals perform simple laboratory tasks, but also how they manage to engage the appropriate language during normal discourse, including code-switching with other bilingual speakers.
Mental control, language tags, and language nodes in bilingual lexical processing
Authors: LI PING
Published: April 2019

In this paper Green proposes an inhibitory control (IC) model of bilingual lexical processing. At the core of Green's arguments is the notion of “mental control,” formulated in terms of inhibition, control schemas, and a supervisory attentional system. The very notion of control, it seems, suggests some sort of intentional, exogenous force at work (e.g., the supervisory attentional system). Presumably mental control differs from automatic processes (Schneider & Shiffrin, 1977), yet in the IC model there is no precise computational specification of how the various parameters of the control system actually interact to determine automatic bilingual processes. In a computational view, the IC model has quite some symbolic AI flavor (e.g., with goal-oriented decision boxes and control schemas), but it also attempts to integrate activation-based accounts (e.g., interactive activation mechanisms). Again, because the model remains at a rather conceptual level as presented, it is difficult to determine how successful it will be in combining symbolic and connectionist approaches in understanding bilingual processing.
Mental control and language selection
Authors: SCHREUDER ROBERT , HERMANS DAAN
Published: April 2019

A surprisingly large part of the population of the world is at least bilingual. The question as to how people are able to control their language system is an important one and has been a topic for highly active research in recent years. Until now, models have been quite simplistic, but Green places his model in a wider framework of attention and control, drawing our attention to the fact that the mechanisms involved in language control share basic properties with the systems in other cognitive domains. Green introduces the (not language-specific) supervisory attentional system in combination with language task schemas which make it possible to adapt to the situation in which the bilingual system is functioning. Models of bilingual processing should be able to explain how lexical processing is affected by, among others, task demands (see also Dijkstra, van Jaarsveld, and ten Brinke, 1998). By adding a general mechanism of attentional control that is independently motivated by general cognitive mechanisms, Green has enriched his previous model considerably. In what follows we will first make some general remarks about the model Green proposes. In the second part we will discuss some recent results from our group that nicely tie in with some of the basic properties of the model outlined by Green.
The IC model and code-switching
Authors: TREFFERS-DALLER JEANINE
Published: April 2019

In his contribution Green proposes a very interesting model of bilingual speech processing, the inhibitory control (IC) model. The model's aim is to account for the way in which bilinguals control their two language systems. Although the model was not developed to account for code-switching, the author explicitly goes into implications of his model for code-switching and this makes it very relevant for linguists working in that field. Until now, psycholinguistic aspects of code-switching have received far less attention in the literature than the syntactic aspects of code-switching. The model therefore offers an excellent starting point for incorporating insights from psycholinguistics into code-switching research and vice versa.
Assessment of the Representation of West African Storm Lifecycles in Convection‐Permitting Simulations
Authors: Crook Julia , Klein Cornelia , Folwell Sonja , Taylor Christopher M. , Parker Douglas J. , Stratton Rachel , Stein Thorwald
Published: April 2019

Convection‐permitting models perform better at representing the diurnal cycle and the intermittency of convective rainfall over land than parameterized‐convection models. However, most of the previous model assessments have been from an Eulerian point of view, while key impacts of the rainfall depend on a storm‐relative perspective of the system lifecycle. Here a storm‐tracking algorithm is used to generate storm‐centered Lagrangian lifecycle statistics of precipitation over West Africa from regional climate model simulations and observations. Two versions of the Met Office Unified Model with and without convection parameterization at 4‐, 12‐, and 25‐km resolution were analyzed. In both of the parameterized‐convection simulations, storm lifetimes are too short compared to observations, and storms have no preferred propagation direction; the diurnal cycle of initiations and dissipations and the spatial distribution of storms are also inaccurate. The storms in the convection‐permitting simulations have more realistic diurnal cycles and lifetimes but are not as large as the largest observed storms. The convection‐permitting model storms propagate in the correct direction, although not as fast as observed storms, and they have a much improved spatial distribution. The rainfall rate of convection‐permitting storms is likely too intense compared to observations. The improved representation of the statistics of organized convective lifecycles shows that convection‐permitting models provide better simulation of a number of aspects of high‐impact weather, which are critical to climate impacts in this important geographic region, providing the high rainfall rates can be taken into account.
Multidimensional Feature Explorer for Unbalanced Spatiotemporal Data
Authors: Li Dongshuang , Gao Hong , Luo Wen , Yu Zhaoyuan , Yuan Linwang
Published: April 2019

Feature analysis of weak nonlinear signals from geographic spatiotemporal data has received increasing attention. Most existing signal processing methods cannot effectively perform comprehensive feature analysis because of the multiple dimensions and unbalance of spatiotemporal data. We developed a divide–aggregate–explore method for the feature analysis of spatiotemporal data. In our method, strategies for dividing different dimensions are defined for multidimensional analysis, and the tensor–block structure is adopted to reorganize the original data and distinguish differences in dimensions. Then, information‐based data aggregation is used to weaken the impact of dimensional unbalance. Case studies based on climatic reanalysis field data released by the National Oceanic and Atmospheric Administration showed that the proposed method can effectively extract weak propagation signals such as the El Niño–Southern Oscillation and El Niño–Southern Oscillation Modoki. Our method can also reveal more detailed evolutionary characteristics of complex coupling systems in different dimensions compared with classical feature detection methods such as principal component analysis and tensor decomposition.
Isotopic Fractionation in Photolysis of Ozone in the Hartley and Chappuis Bands
Authors: Huang Chao‐Hui , Bhattacharya S. K. , Hsieh Zhi‐Ming , Chen Yu‐Jung , Yih Tai‐Sone , Liang Mao‐Chang
Published: April 2019

The isotopic enhancement of atmospheric ozone (O3) is mainly determined by two processes of formation and photolytic decomposition. The formation is known to be associated with isotopic fractionation which can be as high as 120‰ relative to the parent oxygen. Photolysis‐induced isotopic fractionation in O3, however, is not known accurately. Absorption cross sections of various ozone species have been calculated by Zero Point Energy‐based model and quantum mechanical wave packet model. But their predictions pertaining to isotopic fractionations have not been verified experimentally. In the present work, we performed irradiation experiments of O3 at several wavelengths in the Hartley and Chappuis bands and determined the dissociative isotopic fractionation factors by a Rayleigh distillation model. In laboratory conditions, photolysis of ozone produces reactive atomic and/or molecular oxygen which influence the dissociative process through secondary chemistry. The complex interplay of primary photolysis and secondary chemistry was tracked by a kinetic model, and isotopic fractionation factors associated with photolysis alone were derived within a range of uncertainties. The fractionations are found to depend on the photon wavelength and deviate significantly at some wavelengths from the predicted values. For example, at 254 nm the zero point energy‐based models predict lower photolysis rate coefficients for the lighter isotopic species; the present data show about 50‰ higher values.
Response of Ionospheric Profile Parameters to Equatorial Electrojet Over Peruvian Station
Authors: Bello S. A. , Abdullah M. , Hamid N. S. A. , Reinisch B. W. , Yoshikawa A. , Fujimoto A.
Published: April 2019

The response of the ionospheric bottomside electron density profile parameters of the F2 layer, namely, the maximum electron density (NmF2), the maximum height of F2 layer (hmF2), and bottomside thickness (B0) parameter to the equatorial electrojet (EEJ) current is examined for a Peruvian location at the Jicamarca station (12 °S, 76.9 °W) in the South American sector. The results of the analysis show that both hmF2 and B0 increase for ~2 h before sunrise and exhibit a postsunset peak during the equinoctial and summer months. The increase in the peak height, hmF2, is observed to terminate before midday, while B0 continued to increase throughout the daytime. The apparent midday and postnoon peaks in NmF2 occur in all the seasons under study. It was demonstrated that a relationship exists between EEJ and the profile parameters hmF2 and B0 during low and moderate solar conditions. Conversely, the correlation coefficient between EEJ and NmF2 is statistically significant only during solar minimum conditions but correlates poorly, if at all, with EEJ during moderate solar activity.
Shorting Factor In‐Flight Calibration for the Van Allen Probes DC Electric Field Measurements in the Earth's Plasmasphere
Authors: Lejosne Solène , Mozer F. S.
Published: April 2019

Satellite‐based direct electric field measurements deliver crucial information for space science studies. Yet they require meticulous design and calibration. In‐flight calibration of double‐probe instruments is usually presented in the most common case of tenuous plasmas, where the presence of an electrostatic structure surrounding the charged spacecraft alters the geophysical electric field measurements. To account for this effect and the uncertainty in the boom length, the measured electric field is multiplied by a parameter called the shorting factor (sf). In the plasmasphere, the Debye length is very small in comparison with spacecraft dimension, and there is no shorting of the electric field measurements (sf = 1). However, the electric field induced by spacecraft motion greatly exceeds any geophysical electric field of interest in the plasmasphere. Thus, the highest level of accuracy in calibration is required. The objective of this work is to discuss the accuracy of the setting sf = 1 and therefore to examine the accuracy of Van Allen Probes electric field measurements below L = 2. We introduce a method to determine the shorting factor near perigee. It relies on the idea that the value of the geophysical electric field measured in the Earth's rotating frame of reference is independent of whether the spacecraft is approaching perigee or past perigee, that is, it is independent of spacecraft velocity. We obtain that sf = 0.994 ± 0.001. The resulting margins of errors in individual electric drift measurements are of the order of ±0.1% of spacecraft velocity (a few meters per second).
Recent Reoccurrence of Large Open‐Ocean Polynya on the Maud Rise Seamount
Authors: Jena B. , Ravichandran M. , Turner J.
Published: April 2019

Satellite observations have shown that the largest and most prolonged Maud Rise open‐ocean polynya since the 1970s appeared on 14 September 2017 (~9.3 × 103 km2) within the seasonal sea‐ice cover which expanded maximum on 1 December 2017 (~298.1 × 103 km2) and existed for 79 days. Record negative anomalies of sea‐ice concentration were observed in and around the polynya. The occurrence of the polynya was associated with a large cyclonic eddy and negative wind stress curl that facilitated melting of sea‐ice. Concurrently, a region of positive sea level pressure anomalies extended over the entire northern Weddell Sea accompanied by record low negative anomalies (deep depressions) over the southwest Weddell Sea and the Maud Rise. The atmospheric circulation anomalies advected moist‐warm air from the midlatitudes, resulted a record atmospheric warming (~11.5 °C) in the Maud Rise that favored this rare event as one of the largest open‐ocean polynyas.
Impacts of Multiscale FACs on the Ionosphere‐Thermosphere System: GITM Simulation
Authors: Zhu Qingyu , Deng Yue , Richmond Arthur , McGranaghan Ryan M. , Maute Astrid
Published: April 2019

In this study, field‐aligned currents (FACs) and ionospheric electric fields on different spatial scales are investigated through the analysis of FAC data from the Swarm satellites and electric field data from the Dynamic Explorer 2, respectively, from all seasons and under all solar wind conditions and varying levels of solar activity. Distributions of the average and variable components of FAC and electric field are the main focuses of this study, where the FAC variability is represented by the standard deviation of FAC in each magnetic latitude/magnetic local time bin and electric field variability is represented by the square root of the sum of squares of standard deviations of magnetic eastward and equatorward components of the electric field. We found that the mean patterns of the FAC and electric field are mainly contributed by the large‐scale (wavelength: ⩾500 km) FAC and electric field. Unlike the average, in addition to the large scale, variabilities of FAC and electric field are not negligible on mesoscale (wavelength: 100–500 km) and small scale (wavelength: 8–100 km), while the FAC variability shows a different scale dependence from the electric field variability. Specifically, for decreasing scale sizes, the FAC variability increases while the electric field variability decreases, suggesting that the strong FACs on small scale and mesoscale do not necessarily correspond to strong ionospheric electric fields on those scales. Further, FAC variabilities on large scale and mesoscale are included into the Global Ionosphere Thermosphere Model (GITM) and the corresponding impacts on Joule heating have been assessed. It was found that, for the conditions studied here, the large‐scale FAC variability may significantly increase the Joule heating (~160% globally) and that the enhancement due to the mesoscale FAC variability is not negligible (~36% globally).
Oscillatory Flows in the Magnetotail Plasma Sheet: Cluster Observations of the Distribution Function
Authors: De Spiegeleer A. , Hamrin M. , Gunell H. , Volwerk M. , Andersson L. , Karlsson T. , Pitkänen T. , Mouikis C. G. , Nilsson H. , Kistler L. M.
Published: April 2019

Plasma dynamics in Earth's magnetotail is often studied using moments of the distribution function, which results in losing information on the kinetic properties of the plasma. To better understand oscillatory flows observed in the midtail plasma sheet, we investigate two events, one in each hemisphere, in the transition region between the central plasma sheet and the lobes using the 2‐D ion distribution function from the Cluster 4 spacecraft. In this case study, the oscillatory flows are a manifestation of repeated ion flux enhancements with pitch angle changing from 0° to 180° in the Northern Hemisphere and from 180° to 0° in the Southern Hemisphere. Similar pitch angle signatures are observed seven times in about 80 min for the Southern Hemisphere event and three times in about 80 min for the Northern Hemisphere event. The ion flux enhancements observed for both events are slightly shifted in time between different energy channels, indicating a possible time‐of‐flight effect from which we estimate that the source of particle is located ∼5–25RE and ∼40–107RE tailward of the spacecraft for the Southern and Northern Hemisphere event, respectively. Using a test particle simulation, we obtain ∼21–46 RE for the Southern Hemisphere event and tailward of X∼ − 65RE (outside the validity region of the model) for the Northern Hemisphere event. We discuss possible sources that could cause the enhancements of ion flux.
Characteristics of Energetic Electron Precipitation Estimated from Simulated Bremsstrahlung X‐ray Distributions
Authors: Xu Wei , Marshall Robert A.
Published: April 2019

Determination of the fluxes and spectra of energetic particle precipitation into the Earth's atmosphere is of critical importance for radiation belt dynamics, magnetosphere‐ionosphere coupling, as well as atmospheric chemistry. To improve the assessments of precipitating electrons using X‐ray measurements requires deeper understanding of bremsstrahlung production, transport, and redistribution throughout the atmosphere. Here we use first‐principles Monte Carlo models to explore relativistic electron precipitation events from the perspective of bremsstrahlung X‐rays. The spatial distribution of X‐rays is quantified from the ground level up to satellite altitudes. We then simulate X‐ray images that would be captured using an ideal camera and calculate the energy spectra of X‐rays originating from monoenergetic beams of precipitating electrons. Moreover, we show how these impulse responses to monoenergetic beams can be used to reconstruct the precipitating source using an inversion technique. Modeling results show that space‐borne measurements of backscattered X‐rays provide a promising method to estimate precipitation spatial size, fluxes, and spectra.
Two‐Dimensional Maps of In Situ Ionospheric Plasma Flow Data Near Auroral Arcs Using Auroral Imagery
Authors: Clayton Robert , Lynch Kristina , Zettergren Matt , Burleigh Meghan , Conde Mark , Grubbs Guy , Hampton Don , Hysell David , Lessard Marc , Michell Robert , Reimer Ashton , Roberts T. Maximillian , Samara Marilia , Varney Roger
Published: April 2019

Some existing auroral data products are insufficient for ionospheric simulation input on subkilometer spatial scales and high (second) time resolution near the boundaries of arc structures. Ideally, two‐dimensional data maps of the relevant parameters over these small scales would provide models with constraining inputs. Available in situ data have the time and spatial resolution for small‐scale features but only provide a 1‐D cut through the structure. Ground‐based data can provide 2‐D maps but have lower resolution in time and space than is required to accurately interpret the small‐scale structure near an arc. This paper provides a method to construct two‐dimensional maps of auroral parameters from the combination of one‐dimensional in situ data cuts with two‐dimensional ground‐based (and time dependent) camera imagery. Arc boundaries for each image are defined, and the available 1‐D ionospheric flow data are replicated into many 1‐D cuts at different points along the arc, yielding an irregularly sampled 2‐D flow map. These mapped data are fitted to a regular grid via a divergence minimization routine to generate a regularly sampled flow field that is enforced as divergence free. Comparison of the generated 2‐D data maps to available information from camera inversions and other data products is shown, as are assumptions made through the replication process and alternative strategies. Reconstructed flow maps are shown to maintain the small‐scale features near arc boundaries while increasing the dimensionality to 2‐D and to follow the time evolution of the arc structure by comparisons to imagery. The average electric field magnitudes per unit area of the reconstructed and divergence‐minimized flow fields are also calculated and compared between different data sources.
An Alternative Origin of High Vp/Vs Anomalies in Slow Slip Regions: Experimental Constraints From the Elastic Wave Velocity Evolution of Highly Fractured Rock
Authors: Nishimura K. , Uehara S. , Mizoguchi K.
Published: April 2019

Understanding the mechanism of episodic slow slip events at the deep part of subduction zones is important for seismic hazard mitigation and understanding fault mechanics. It has been thought that highly pressurized fluids play an important role in the occurrence, of which one of the evidences are observations of high Vp/Vs (ratio of P wave to S wave velocity) anomalies in the source regions, combined with laboratory measurements of Vp/Vs for intact rocks. However, it remains unclear whether “high Vp/Vs ratios” straightforwardly mean “high pore pressure conditions” for highly damaged fault rocks constituting subduction plate boundary faults. Here we examined the degree of damage of seafloor metabasalt in the Shimanto accretionary complex at the Nankai trough, a limited proxy of oceanic crust going down to the deep slow slip region while being subjected to successive subduction megathrust faulting. We investigated the pressure dependencies of Vp/Vs for dolerite specimens damaged by thermal stressing, simulating in situ damage conditions. We found that the more intense the rock damage, the higher the Vp/Vs ratio. An extrapolation of our results to the slow slip depth under hydrostatic condition indicates that for rocks with a fracture density >1.5 mm−1 (comparable to the fracture densities of ancient oceanic crust), Vp/Vs > 1.85, as observed at the Nankai trough, can be achieved even when the pore pressure is hydrostatic. We suggest that the contribution of not only fluid pressurization but also progressive fracturing of the plate interface on the emergence of slow slip events could be considered.
Primary and Secondary Red Bed Magnetization Constrained by Fluvial Intraclasts
Authors: Swanson‐Hysell Nicholas L. , Fairchild Luke M. , Slotznick Sarah P.
Published: April 2019

The magnetization of hematite‐bearing sedimentary rocks provides critical records of geomagnetic reversals and paleogeography. However, the timing of hematite remanent magnetization acquisition is typically difficult to constrain. While detrital hematite in sediment can lead to a primary depositional remanent magnetization, alteration of minerals through interaction with oxygen can lead to the postdepositional formation of hematite. In this study, we use exceptionally preserved fluvial sediments within the 1.1‐billion‐year‐old Freda Formation to gain insight into the timing of hematite remanence acquisition and its magnetic properties. This deposit contains siltstone intraclasts that were eroded from a coexisting lithofacies and redeposited within channel sandstone. Thermal demagnetization, petrography, and rock magnetic experiments on these clasts reveal two generations of hematite. One population of hematite demagnetized at the highest unblocking temperatures and records directions that rotated along with the clasts. This component is a primary detrital remanent magnetization. The other component is removed at lower unblocking temperatures and has a consistent direction throughout the intraclasts. This component is held by finer‐grained hematite that grew and acquired a chemical remanent magnetization following deposition resulting in a population that includes superparamagnetic nanoparticles in addition to remanence‐carrying grains. The data support the interpretation that magnetizations of hematite‐bearing sedimentary rocks held by >400‐nm grains that unblock close to the Néel temperature are more likely to record magnetization from the time of deposition. This primary magnetization can be successfully isolated from cooccurring authigenic hematite through high‐resolution thermal demagnetization.
Deep Seismic Structure Across the Southernmost Mariana Trench: Implications for Arc Rifting and Plate Hydration
Authors: Wan Kuiyuan , Lin Jian , Xia Shaohong , Sun Jinlong , Xu Min , Yang Hongfeng , Zhou Zhiyuan , Zeng Xin , Cao Jinghe , Xu Huilong
Published: April 2019

The southernmost Mariana margin lacks a mature island arc and thus differs significantly from the central‐north Mariana and Izu‐Bonin margins. This paper presents a new P wave velocity model of the crust and uppermost mantle structure based on a 349‐km‐long profile of wide‐angle reflection/refraction data. The active source seismic experiment was conducted from the subducting Pacific plate to the overriding Philippine plate, passing through the Challenger Deep. The subducting plate has an average crustal thickness of ~6.0 km with Vp of 7.0 ± 0.2 km/s at the base of the crust and low values of only 5.5–6.9 km/s near the trench axis. The uppermost mantle of the subducting plate is characterized by low velocities of 7.0–7.3 km/s. The overriding plate has a maximum crustal thickness of ~18 km beneath the forearc with Vp of ~7.4 km/s at the crustal bottom and 7.5–7.8 km/s in the uppermost mantle. A zone of slight velocity reduction is imaged beneath the Southwest Mariana Rift that is undergoing active rifting. The observed significant velocity reduction in a near‐trench crustal zone of ~20–30 km in the subducting plate is interpreted as a result of faulting‐induced porosity changes and fracture‐filling fluids. The velocity reduction in the uppermost mantle of both subducting and overriding plates is interpreted as mantle serpentinization with fluid sources from dehydration of the subducting plate and/or fluid penetration along faults.
Hydraulic and Poroelastic Rock Properties From Oscillating Pore Pressure Experiments
Authors: Hasanov Azar K. , Dugan Brandon , Batzle Michael L. , Prasad Manika
Published: April 2019

Knowledge of hydraulic and poroelastic properties is essential for simulating fluid flow in porous media. Accurate constraints on these properties have impacts on production forecasts and economics. In this paper we document an improvement of the oscillating pore pressure experiment by simultaneously measuring hydraulic and poroelastic properties of reservoir rocks. Measurements were carried out for four conventional reservoir rock quality samples at oscillation frequencies of 0.025–1 Hz and effective pressures of 3.5–62 MPa. Estimated permeability values decreased with increasing effective pressure and increased sharply above a frequency range of 0.3–0.4 Hz. We established that hydraulically measured storage capacities are overestimated by almost an order of magnitude when compared to elastically derived ones. Biot coefficient was estimated both from hydraulic and strain measurements, and comparison of two data sets reveals high uncertainty of the hydraulic specific storage measurements. We documented grain crushing and pore collapse event in a dolostone sample, observed as a permanent and drastic decrease of permeability and bulk modulus. We validated our method by detecting irreversible microstructural changes independently by hydraulic, elastic, X‐ray microtomography (μCT) and nuclear magnetic resonance (NMR) measurements. Our approach can be used to constrain and to improve the estimation of specific storage and thus leads to better model inputs and forecasts.
Spatial Scales of Turbulent Flow Structures Associated With Interacting Barchan Dunes
Authors: Bristow N. R. , Blois G. , Best J. L. , Christensen K. T.
Published: April 2019

The spatial coherence of turbulent flow structures throughout the flow field associated with a collision between a smaller upstream barchan laterally offset from a larger downstream barchan is investigated using inhomogeneous, two‐point correlation coefficients of fluctuating streamwise velocity, from which the distribution, size, and orientation of the large‐scale motions in the flow are analyzed. Measurements were made with fixed‐bed models in a refractive‐index‐matched flume environment allowing uninhibited optical access where the flow field is captured using particle‐image velocimetry in both streamwise‐wall‐normal and streamwise‐spanwise planes. The shear layer of a barchan produces flow structures of smaller length scale, yet still on the order of the barchan height, and stronger positive streamwise fluctuations near the bed as compared to the incoming boundary layer, and these effects prevail far downstream. Analysis of the orientations of the flow structures suggests secondary flow motions induced by the barchan horns, and interdune flow modification through collision stages indicates changing flow interaction regimes with decreasing interdune separation. The combination of enhanced positive streamwise fluctuations near the bed and significant spatial coherence indicates that for a field‐scale barchan of sufficient size, the coherence of flow structures produced in its wake is of comparable scale to the characteristic drag length associated with aeolian transport. As length scales nominally scale with barchan height, the morphodynamics of collisions between barchans of disparate size can be partially explained through this paradigm of flow structure coherence.
Carbon Uptake in Surface Water Food Webs Fed by Palaeogroundwater
Authors: Mazumder Debashish , Saintilan Neil , Hollins Suzanne , Meredith Karina , Jacobsen Geraldine , Kobayashi Tsuyoshi , Wen Li
Published: April 2019

The use of 14C to elucidate sources of carbon within freshwater aquatic ecosystems is challenging the assumption that modern autochthonous carbon dominates energy flows. We measured the uptake of old carbon through several trophic levels of a wetland fed by groundwater of the Great Artesian Basin, Australia, the largest artesian basin in the world. Stable isotopes (δ13C and δ15N) and radiocarbon (14C) were used to quantify food chain links and connection between groundwater and surface water food webs. Our results suggest that old groundwater was the dominant carbon source even at the highest trophic levels, with predatory fish returning apparent carbon ages of up to 11 ka. Stable isotope analysis (δ13C and δ15N) identified trophic links between fish, aquatic insects, and algae with smaller contributions from particulate organic matter to the food webs. As natural mound springs and associated wetlands are the only source of reliable water during dry periods over vast areas of the western Great Artesian Basin, the result has potential implications for the interpretation of archaeological artifacts associated with indigenous passage within the interior.
A Ca. 2.8‐Ga Plume‐Induced Intraoceanic Arc System in the Eastern North China Craton
Authors: Gao Lei , Liu Shuwen , Zhang Bo , Sun Guozheng , Hu Yalu , Guo Rongrong
Published: April 2019

The conversion of Archean tectonic regimes from mantle plume to plate tectonic and the mechanism of subduction initiation are two crucial issues in the current Earth sciences. A typical komatiite‐tholeiite sequence consisting of ~2,850–2,800‐Ma komatiites and ~2,780–2,710‐Ma basaltic and andesitic to dacitic volcanic rocks is well preserved in the Archean Western Shandong terrane of the eastern North China Craton. These volcanic rocks were derived from the partial melting of a depleted mantle source with subsequent fractional crystallization, a metasomatized subarc mantle wedge, and a descending oceanic slab. Structural and kinematic observations suggest that the Qixingtai‐Yanlinguan‐Panchegou granite‐greenstone belt experienced ~2.85–2.80‐Ga extensional deformation (D1) by upwelling of a mantle plume and NE‐SW‐oriented shortening (D2) during ~2.78–2.71 Ga. The petrogenesis of the Mesoarchean to early Neoarchean metamorphosed volcanic rock series and regional deformation indicate that a plume‐induced self‐sustaining intraoceanic arc system with SW‐dipping subduction polarity operated ~2.8 Ga, followed by the evolution from initial to mature subduction. An increasing pull caused by the descending slab generated gravitational instability in the surrounding oceanic lithosphere and formation of a new initial subduction zone adjacent to the preexisting arc system. Similar to the process in the Western Shandong terrane, plume activity generally culminated in subduction events in many other Archean greenstone belts, revealing that plume‐arc interaction may have been a crucial mechanism for global Archean tectonic regime conversion from mantle plume to initial plate subduction in the crust of the early Earth.