bluuebunny/crossref_metadata_2025_split huggingface dataset:
Food consumption estimates of Barents Sea harp seals
Authors: Nilssen Kjell T , Pedersen Ole-Petter , Folkow Lars P , Haug Tore 
Published: July 2014

The consumption of various prey species, required by the Barents Sea harp seal (Phoca groenlandica) stock in order to cover their energy demands, has been estimated by combining data on the energy density of prey species and on seasonal variations in the energy expenditure and body condition of the seals. Data on diet composition and body condition were collected in the period 1990-1996 by sampling harp seals during different seasons, in various areas of the Barents Sea. All diet composition data were based on reconstructed prey biomass, and adjustments were made for differences in digestibility of crustaceans and fish. The number of seals representing different age and sex groups were calculated for the entire population, and the monthly food requirements were estimated. In 1998, the total Barents Sea harp seal stock was estimated to comprise 2.22 million seals based on a mean production of 301,000 pups. After adjustments for a pup mortality of 30% its total annual food consumption was estimated to be in the range of 3.35-5.05 million tonnes (depending on choice of input parameters). Assuming that there are seasonal changes in basal metabolic rate associated withchanges in body mass, and that the field metabolic rate of the seals corresponded to two times their predicted basal metabolic rate, the annual food consumption of the Barents Sea harp seal stock was estimated. If capelin (Mallolus villosus) was assumed to be abundant, the annual total consumption was estimated to be 3.35 million tonnes, of which 1,223,800 tonnes were crustaceans, 807,800 tonneswere capelin, 605,300 tonnes were polar cod (Boreogadus saida), 212,400 tonnes were herring (Clupea harengus), 100,500 tonnes were cod (Gadus morhua) and 404,200 tonnes were "other fish". A very low capelin stock in the Barents Sea (as it was in the period 1993-1996) led to switches in seal diet composition, with increased consumption of polar cod (from ca. 16%-18 % to ca. 23%-25 % oftotal consumption), other gadoids (dominated by cod, but also including haddock (Melanogrammus aeglefinus) and saithe (Pollachius virens)), herring, and "other fish". Using the same set of assumptions as in the previous estimate, the total consumption would have been 3.47 million tonnes, divided between various prey species as follows (in tonnes): polar cod 876,000, codfish (cod, saithe and haddock) 359,700, "other fish" 618,800, herring 392,500, and crustaceans 1,204,200. Overall, the largest quantities of food were estimated to be consumed in the period June-September.In 1999, the total Barents Sea harp seal stock size was estimated to be 2.18 (95% CI, 1.79 to 2.58) million animals, which would give an annual food consumption in the range of 2,69 - 3.96 million tonnes (based on upper and lower 95% confidence limits and adjusted for a pup mortality rate of 0.3) if capelin is assumed to be abundant.
Direct and indirect effects of minke whale abundance on cod and herring fisheries: A scenario experiment for the Greater Barents Sea
Authors: Schweder Tore , Hagen Gro S , Hatlebakk Einar 
Published: July 2014

To study the pattern of interaction between minke whale (Balaenoptera acutorostrata) abundance and the main fisheries in the Greater Barents Sea, a simulation experiment was carried out. The population model involves 4 species interconnected in a food web: cod (Gadus morhua), capelin (Mallotus villosus), herring (Clupea harengus) and minke whales. Minke whales are preying on cod, capelin andherring; cod are preying on (young) cod, capelin and herring; herring in the Barents Sea are preying on capelin; while capelin is a bottom prey in the model. The consumption function for minke whales is non-linear in available prey abundance, and is estimated from stomach content data and prey abundance data. The model is dynamic, with a time step of one month, and there are two areas: the BarentsSea and the Norwegian Sea. Minke whale abundances are kept on fixed levels, while recruitment in fish is stochastic.Cod and herring fisheries are managed by quotas targeting fixed fishing mortalities, while capelin is managed with a view to allow the cod to have enough food and leaving a sufficient spawning stock of capelin. The model is simulated over a period of 100 years for a number of fixed levels of minke whaleabundance, and simulated catches of cod, herring and capelin are recorded.The experiment showed interactions between whale abundance and fish catches to be mainly linear. For cod catches, both the direct effect of whales consuming cod, and the indirect effect due to whales competing with cod for food and otherwise altering the ecosystem, are linear and of equal importance. The net effect on the herring fishery is of the same magnitude as the net effect on the cod fishery, witheach extra whale reducing the catches of both species by some 5 tonnes. These conclusions are conditional on the model and its parameterisation.
Global MHD modeling of ionospheric convection and field‐aligned currents associated with IMF By triggered theta auroras
Authors: Watanabe Masakazu , Sakito Shintaro , Tanaka Takashi , Shinagawa Hiroyuki , Murata Ken T. 
Published: July 2014

AbstractUsing numerical magnetohydrodynamic simulations, we investigate the evolution of ionospheric convection and field‐aligned currents (FACs) when θ auroras are formed in response to interplanetary magnetic field (IMF) By transitions. When the polarity of IMF By switches abruptly during northward IMF periods, the crossbar of the θ aurora is isolated from the flankside auroral oval and drifts into the polar cap. This drift motion is involved in a large round cell associated with new IMF By, with sunward convection residing only on the dayside tip of the crossbar. There exists an IMF By‐controlled large‐scale FAC system on the crossbar. When the θ aurora is drifting duskward (dawnward), the FACs are located on the dawnside (duskside) boundary of the crossbar adjacent to the “new” lobe. In contrast, the magnetospheric source region of the crossbar FAC system is located on the duskside (dawnside) boundary of the protruded plasma sheet adjacent to the “old” lobe. In the source region, plasma thermal pressure feeds the electromagnetic energy of FACs, and these processes can be interpreted as coupling of slow mode and Alfvén mode disturbances. In the ionosphere, the crossbar‐associated FACs close with part of the region 1 currents associated with the new crescent cell. The magnetospheric source of that part of the region 1 FACs is located on the plasma sheet boundary and the magnetopause both adjacent to the new lobe. Dynamo processes in the old‐lobe side and the new‐lobe side work together to drive the ionospheric drift motion of the crossbar.
Interhemispheric field‐aligned currents: Simulation results
Authors: Lyatskaya Sonya , Khazanov George V. , Zesta Eftyhia 
Published: July 2014

AbstractWe present simulation results of the 3‐D magnetosphere‐ionosphere current system including the Region 1 and Region 2 field‐aligned currents, ionospheric currents, and interhemispheric field‐aligned currents flowing between the northern and southern conjugate ionospheres in the case of asymmetry in ionospheric conductivities in two hemispheres. The model shows that the interhemispheric currents can be an important part of the global 3‐D current system in high‐latitude ionosphere, especially during summer‐winter months, when in winter ionosphere they can be comparable and even exceed both Region 1 and Region 2 currents. An important feature of these interhemispheric currents is that they link together processes in two hemispheres, so that the currents observed in one hemisphere can provide us with information about the currents in the opposite hemisphere. Although the interhemispheric currents might play a notable role in the total 3‐D current system, they have not been sufficiently studied yet. The study of the contribution from the interhemispheric currents into the total 3‐D current system allows us to improve understanding and forecasting of geomagnetic, auroral, and ionospheric disturbances in two hemispheres.
Variability of sea‐ice in the northern Weddell Sea during the 20th century
Authors: Murphy E. J. , Clarke A. , Abram N. J. , Turner J. 
Published: July 2014

AbstractThe record of winter fast‐ice in the South Orkney Islands, northern Weddell Sea, Antarctica, is over a century long and provides the longest observational record of sea‐ice variability in the Southern Hemisphere. Here we present analyses of the series of fast‐ice formation and breakout dates from 1903 to 2008. We show that over the satellite era (post‐1979), the timing of both final autumn formation and complete spring breakout of fast‐ice is representative of the regional sea‐ice concentrations (SIC) in the northern Weddell Sea, and associated with atmospheric conditions in the Amundsen Sea region to the west of the Antarctic Peninsula. Variation in the fast‐ice breakout date is influenced by the intensity of the westerly/north‐westerly winds associated with the Southern Annular Mode (SAM). In contrast, the date of ice formation displays correlations with regional oceanic and sea‐ice conditions over the previous 18 months, which indicate a preconditioning during the previous summer and winter, and exhibits variability associated with variation in tropical Pacific sea‐surface temperature (i.e., the El Niño‐Southern Oscillation, ENSO). A reduction in fast‐ice duration at the South Orkney Islands around the 1950s was associated with both later formation and earlier breakout. However, there were marked changes in variability (with periodicities of 3–5, 7–9, and 20 years) in each of the series and in their relationships with ENSO and SAM, indicating the need for caution in interpreting changes in ice conditions based on shorter‐term satellite series.
Physics‐controlled thickness of shear zones caused by viscous heating: Implications for crustal shear localization
Authors: Duretz T. , Schmalholz S. M. , Podladchikov Y. Y. , Yuen D. A. 
Published: July 2014

AbstractWe evaluate the parameters that control the thickness of ductile shear zones that are generated by viscous heating. We employ two‐dimensional thermomechanical numerical models to simulate shear zone development under compression. Results show that the shear zone thickness is essentially independent on the numerical resolution and the initial size of a weak inclusion that triggers shear localization. A simple scaling law is derived which predicts the thickness with six physical parameters: far‐field stress and strain rate, thermal conductivity (both constant and temperature dependent), initial temperature, activation energy, and stress exponent. The scaling law is confirmed by numerical simulations for a wide range of parameters. For crustal deformation conditions typical temperature increase ranges between 50°C and 200°C, and the predicted thickness is between 1 km and 7 km. These thicknesses agree with natural crustal and lithospheric shear zones suggesting that shear heating is a process controlling crustal shear zone formation.
The scale of the magnetotail reconnecting current sheet in the presence of O+
Authors: Liu Y. H. , Kistler L. M. , Mouikis C. G. , Roytershteyn V. , Karimabadi H. 
Published: July 2014

AbstractThe reconnection current layer thickness is expected to scale with either the ion inertial length or the ion gyroradius. Both of these quantities scale with the mass of the ions present. During geomagnetically disturbed times, the reconnection layer in the magnetotail can contain a significant amount of O+. Using Cluster multi‐spacecraft measurements, we have studied nine reconnection events in the magnetotail plasmasheet, to determine whether the reconnecting current sheet thickness scales with the ion gyroradius or the ion inertial length, and whether the amount of O+ in the plasma sheet has an effect on the current layer thickness. We find that the thickness is equal to the H+ gyroradius, even when the plasma sheet has a high O+ content. This result is in contrast to Hall MHD expectations and likely results from the multiscale nature of the current sheet.
Nonlinear evolution of ion acoustic solitary waves in space plasmas: Fluid and particle‐in‐cell simulations
Authors: Kakad Bharati , Kakad Amar , Omura Yoshiharu 
Published: July 2014

AbstractSpacecraft observations revealed the presence of electrostatic solitary waves (ESWs) in various regions of the Earth's magnetosphere. Over the years, many researchers have attempted to model these observations in terms of electron/ion acoustic solitary waves by using nonlinear fluid theory/simulations. The ESW structures predicted by fluid models can be inadequate due to its inability in handling kinetic effects. To provide clear view on the application of the fluid and kinetic treatments in modeling the ESWs, we perform both fluid and particle‐in‐cell (PIC) simulations of ion acoustic solitary waves (IASWs) and estimate the quantitative differences in their characteristics like speed, amplitude, and width. We find that the number of trapped electrons in the wave potential is higher for the IASW, which are generated by large‐amplitude initial density perturbation (IDP). The present fluid and PIC simulation results are in close agreement for small amplitude IDPs, whereas for large IDPs they show discrepancy in the amplitude, width, and speed of the IASW, which is attributed to negligence of kinetic effects in the former approach. The speed of IASW in the fluid simulations increases with the increase of IASW amplitude, while the reverse tendency is seen in the PIC simulation. The present study suggests that the fluid treatment is appropriate when the magnitude of phase velocity of IASW is less than the ion acoustic (IA) speed obtained from their linear dispersion relation, whereas when it exceeds IA speed, it is necessary to include the kinetic effects in the model.
Aspect angle dependence of naturally enhanced ion acoustic lines
Authors: Akbari H. , Semeter J. L. 
Published: July 2014

AbstractThe magnetic aspect angle dependence of naturally enhanced ion acoustic lines (NEIALs) is investigated using two multibeam experiments with the 450 MHz electronically steerable Poker Flat Incoherent Scatter Radar. In each experiment, dynamics in the accompanying auroral activity suggest that the source of free energy for the instability is equally present, in a statistical sense, in a wide portion of sky. Yet strong variations in backscattered power are observed when radar beam direction is altered by only 1°. In our observations, the strongest scattered power appears in the magnetic‐zenith direction and weakens with increasing angle between the radar beam and the magnetic lines of force. NEIALs occurring above the F region peak are observed to disappear almost completely at aspect angles as small as 2°. The results are somewhat surprising since previous experiments have detected NEIALs at aspect angles up to 15°. It is shown that during dynamic geophysical conditions, such as the substorm intervals studied in this report, more than one of the generation mechanisms proposed to explain NEIALs may be operating simultaneously. The different mechanisms result in different spectral morphologies and different degrees of sensitivity to the magnetic aspect angle.
Nonadiabatic heating in magnetic reconnection
Authors: Ma Xuanye , Otto Antonius 
Published: July 2014

AbstractPlasma transport process as a fundamental problem in magnetospheric physics is often associated with strong nonadiabatic heating. At the magnetopause, observations show an increase of specific entropy (i.e., S = p/ργ) by 2 orders of magnitude from the magnetosheath into the magnetosphere. In the near‐Earth magnetotail, particle injection requires strongly entropy depleted plasma bubbles, and their evolution can be strongly modified in the presence of nonadiabatic heating. In this study, one of the critical plasma transport mechanisms, magnetic reconnection, is investigated as a nonadiabatic process in the framework of MHD. It is important to examine whether magnetic reconnection can provide sufficient nonadiabatic heating to explain the observed plasma properties and to identify plasma conditions that allow such strong nonadiabatic heating. We demonstrate that the entropy can indeed strongly increase associated with magnetic reconnection provided that the plasma beta (i.e., the ratio of thermal to magnetic energy density) is low in the inflow region of reconnection.
Testing pulse density distribution for terrestrial gamma ray flashes
Authors: Abukhaled Marwan , Allen Edward , Guessoum Nidhal 
Published: July 2014

AbstractMaximum likelihood fits for the time profiles of 51 terrestrial gamma ray flashes (from Compton Gamma Ray Observatory/Burst and Transient Source Experiment and Fermi Gamma‐Ray Space Telescope/Gamma‐Ray Burst Monitor) were calculated for five proposed probability densities. A lognormal distribution, which had been used by other researchers, was compared with piecewise Gaussian, piecewise exponential, inverse Gaussian, and Ornstein‐Uhlenbeck probability density functions. The piecewise Gaussian and piecewise exponential distributions are justified physically through assuming exponential growth and decay of the electron avalanches which result in the gamma ray bursts and are therefore highly relevant in this context. However, identifying the electron avalanche phenomenon as a form of stochastic exit time process, the inverse Gaussian and Ornstein‐Uhlenbeck are reasonable alternatives. Results of the maximum likelihood calculations indicate that the five probability densities fit the gamma ray pulse data equally well. By this comparison, our aim is to indicate to terrestrial gamma ray flash researchers these other at least equally valid distribution functions, which may give insights into the physical processes that the electrons (and the positrons) undergo in the gamma ray flashes.
First U.S.‐China joint ground‐based Fabry‐Perot interferometer observations of longitudinal variations in the thermospheric winds
Authors: Wu Qian , Yuan Wei , Xu Jiyao , Huang Cong , Zhang Xiaoxin , Wang Jing‐song , Li Tao 
Published: July 2014

AbstractFor the first time, three Fabry‐Perot interferometers from the U.S. (Boulder, 40°N, 105°W, 49°N magnetic latitude (MLAT)) and China (Xinglong: 40°N,115°E, 34°N, MLAT; Kelan: 39°N, 112°E, 33°N MLAT) were used to examine the longitudinal variations in the thermospheric winds due to the geomagnetic latitude differences between the American and Asian sectors. During a case of quiet geomagnetic condition, the meridional winds were very similar at the U.S. and Chinese stations. The meridional winds at Boulder reached most equatorward winds after midnight, whereas in China, the largest equatorward winds were found near midnight. The Boulder zonal winds turned westward earlier in the morning hours and had larger diurnal variations because of its higher magnetic latitude. During the case of low geomagnetic activity (Kp~2), the meridional winds were still similar in the U.S. and in China. Boulder zonal winds had much larger diurnal variation compared to the quiet condition (Kp~1). Thermosphere‐ionosphere‐electrodynamics general circulation model simulations show a very good agreement with observation for the meridional winds. The simulated zonal winds exhibit noticeable differences with observations, but the general tendencies in longitudinal variations with a larger diurnal variation near the auroral oval are correct. Simulations showed that the ion drift is not directly responsible for the longitudinal variations in the winds. The pressure gradient had more direct effect on the longitudinal changes in the winds. The simulation results also showed larger diurnal variations at higher geomagnetic latitudes due to the auroral oval heating. Nonmigrating tides were not observed in the two cases in October 2012.
The influence of IMF clock angle timescales on the morphology of ionospheric convection
Authors: Grocott A. , Milan S. E. 
Published: July 2014

AbstractWe exploit a database of high‐latitude ionospheric electric potential patterns, derived from radar observations of plasma convection in the Northern Hemisphere from the years 2000–2006, to investigate the timescales of interplanetary magnetic field (IMF) control of ionospheric convection and associated magnetospheric dynamics. We parameterize the convection observations by IMF clock angle, θ (the angle between geocentric solar magnetic (GSM) north and the projection of the IMF vector onto the GSM Y‐Z plane), and by an IMF timescale, τB (the length of time that a similar clock angle has been maintained prior to the convection observations being made). We find that the nature of the ionospheric convection changes with IMF clock angle, as expected from previous time‐averaged studies, and that for τB∼30 min, the convection patterns closely resemble their time‐averaged counterparts. However, as τB increases we find that the convection evolves away from the time‐averaged patterns to reveal modified characteristic flow features. We discuss these findings in terms of solar wind‐magnetosphere‐ionosphere coupling and consider their implications for understanding the time‐dependent nature of magnetospheric dynamics.
Experimental characterization of broadband electrostatic noise due to plasma compression
Authors: DuBois Ami M. , Thomas Edward , Amatucci William E. , Ganguli Gurudas 
Published: July 2014

AbstractFor a wide variety of laboratory and space plasma environments, theoretical predictions state that plasmas are unstable to inhomogeneous flows over a very broad frequency range. Such sheared flows are generated in the Earth's magnetosphere and intensify during active periods. Specifically, for a velocity shear oriented perpendicular to a uniform background magnetic field, the shear scale length (LE) compared to the ion gyroradius (ρi) determines the character of the shear‐driven instability that may prevail. An interpenetrating plasma configuration is used to create a transverse velocity shear profile in a magnetized plasma column, a condition similar to that found in the natural boundary layers. The continuous variation of ρi/LE and the associated transition of the instability regimes driven by the shear flow mechanism are demonstrated in a single laboratory experiment. Broadband wave emission correlated to increasing/decreasing stress (i.e., ρi/LE), a characteristic signature of a boundary layer crossing, is found under controlled and repeatable conditions. This result holds out the promise for understanding the cause and effect of the in situ observation of broadband electrostatic noise.
Body symmetry and physical strength in human males
Authors: Fink Bernhard , Weege Bettina , Manning John T. , Trivers Robert 
Published: July 2014

ObjectivesBody symmetry and physical strength in males have been related to aspects of mate “quality”—women seem to prefer men who display both “good genes” (as indexed by high symmetry/developmental health) and fighting ability (as indexed by physical strength). Here we show that fluctuating asymmetry (FA) of the body and physical strength are negatively correlated.MethodsBody FA (from 12 paired traits) and handgrip strength (HGS; a measure of muscular power and force) were measured in a sample of 69 heterosexual, right‐handed men (18–42 years).ResultsThere were positive correlations of body symmetry with HGS after controlling for the effect of body‐mass‐index.ConclusionsWe conclude that in males, body symmetry and physical strength are correlated such that symmetric individuals tend to develop higher strength, which may contribute to their success in inter‐ and intra‐sexual selection. Am. J. Hum. Biol. 26:697–700, 2014. © 2014 Wiley Periodicals, Inc.