bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continent‐scale strike‐slip on a low‐angle fault beneath New Zealand's Southern Alps: Implications for crustal thickening in oblique collision zones
Authors: Lamb Simon , Smith Euan , Stern Tim , Warren‐Smith Emily 
Published: August 2015

AbstractNew Zealand's Southern Alps lie adjacent to the continent‐scale dextral strike‐slip Alpine Fault, on the boundary between the Pacific and Australian plates. We show with a simple 2‐D model of crustal balancing that the observed crustal root and erosion (expressed as equivalent crustal shortening) is up to twice that predicted by the orthogonal plate convergence since ∼11 Ma, and even since ∼23 Ma when the Alpine Fault formed. We consider two explanations for this, involving a strong component of motion along the length of the plate‐boundary zone. Geophysical data indicate that the Alpine Fault has a listric geometry, flattening at mid crustal levels, and has accommodated sideways underthrusting of Australian plate crust beneath Pacific plate crust. The geometry of the crustal root, together with plate reconstructions, requires the underthrust crust to be the hyperextended part of an asymmetric rift system which formed over 500 km farther south during the Eocene—the narrow remnant part today forms the western margin of the Campbell Plateau. At ∼10 Ma, the hyperextended margin underwent shallow subduction in the Puysegur subduction zone, and then was dragged over 300 km along the length of the Southern Alps beneath a low‐angle (<20°) section of the Alpine Fault. We speculate that prior to 10 Ma, more distributed lower crustal shortening and thickening occurred beneath the Southern Alps, accommodating southward extrusion of continental crust in the northern part of the plate boundary zone, providing a mechanism for clockwise rotation of the Hikurangi margin.
High effusion rates of the Cordón Caulle 2011–2012 eruption (Southern Andes) and their relation with the quasi‐harmonic tremor
Authors: Bertin D. , Lara L. E. , Basualto D. , Amigo Á. , Cardona C. , Franco L. , Gil F. , Lazo J. 
Published: August 2015

AbstractHigh effusion rates of intermediate‐to‐high‐silica lavas seem to be less uncommon than previously thought, in particular during their initial eruptive stages. In this study, we report satellite‐based time‐averaged discharge rates for the 2011–2012 effusive phase at Cordón Caulle, which are well correlated with the evolution of the quasi‐harmonic tremor, the most significant seismic signal after the initial explosive stage. Such a correspondence could become a key method for detection of the onset of effusive phases, especially in remote and/or very cloudy areas, supplying an additional tool for effective warnings and near‐real‐time hazard appraisal.
Overlap statistics of shallow boundary layer clouds: Comparing ground‐based observations with large‐eddy simulations
Authors: Corbetta G. , Orlandi E. , Heus T. , Neggers R. , Crewell S. 
Published: August 2015

AbstractHigh‐resolution ground‐based measurements are used to assess the realism of fine‐scale numerical simulations of shallow cumulus cloud fields. The overlap statistics of cumuli as produced by large‐eddy simulations (LES) are confronted with Cloudnet data sets at the Jülich Observatory for Cloud Evolution. The Cloudnet pixel is small enough to detect cumuliform cloud overlap. Cloud fraction masks are derived for five different cases, using gridded time‐height data sets at various temporal and vertical resolutions. The overlap ratio (R), i.e., the ratio between cloud fraction by volume and by area, is studied as a function of the vertical resolution. Good agreement is found between R derived from observations and simulations. An inverse linear function is found to best describe the observed overlap behavior, confirming previous LES results. Simulated and observed decorrelation lengths are smaller (∼300 m) than previously reported (>1 km). A similar diurnal variation in the overlap efficiency is found in observations and simulations.
Lightning leader altitude progression in terrestrial gamma‐ray flashes
Authors: Cummer Steven A. , Lyu Fanchao , Briggs Michael S. , Fitzpatrick Gerard , Roberts Oliver J. , Dwyer Joseph R. 
Published: August 2015

AbstractRadio emissions continue to provide insight into the production of terrestrial gamma ray flashes (TGFs) by thunderstorms, including the critical question of the conditions under which they are generated. We have identified several TGF‐associated lightning radio emissions in which the altitudes of in‐cloud lightning leader pulses that precede and follow the TGF can be measured. We combine these with high absolute timing accuracy TGF observations from the Fermi satellite to determine the development of the lightning channel before, during, and after the TGF production. All of these TGFs were produced several milliseconds after the leader had initiated and when the leaders reached 1–2 km in length. After the TGFs, the leaders all continued to ascend for several more kilometers with no dramatic change in their characteristics, although they all exhibited high average velocities of 0.8–1.0 × 106 m/s. Implications in the context of TGF models are discussed. These results paint the first clear picture of the lightning processes that occur before, during, and after TGF production.
Ross ice shelf vibrations
Authors: Bromirski P. D. , Diez A. , Gerstoft P. , Stephen R. A. , Bolmer T. , Wiens D. A. , Aster R. C. , Nyblade A. 
Published: August 2015

AbstractBroadband seismic stations were deployed across the Ross Ice Shelf (RIS) in November 2014 to study ocean gravity wave‐induced vibrations. Initial data from three stations 100 km from the RIS front and within 10 km of each other show both dispersed infragravity (IG) wave and ocean swell‐generated signals resulting from waves that originate in the North Pacific. Spectral levels from 0.001 to 10 Hz have the highest accelerations in the IG band (0.0025–0.03 Hz). Polarization analyses indicate complex frequency‐dependent particle motions, with energy in several frequency bands having distinctly different propagation characteristics. The dominant IG band signals exhibit predominantly horizontal propagation from the north. Particle motion analyses indicate retrograde elliptical particle motions in the IG band, consistent with these signals propagating as Rayleigh‐Lamb (flexural) waves in the ice shelf/water cavity system that are excited by ocean wave interactions nearer the shelf front.
TES observations of the interannual variability of PAN over Northern Eurasia and the relationship to springtime fires
Authors: Zhu Liye , Fischer Emily V. , Payne Vivienne H. , Worden John R. , Jiang Zhe 
Published: August 2015

AbstractPeroxyacetyl nitrate (PAN) plays an important role in atmospheric chemistry through its impact on remote oxidant and nitrogen budgets. PAN is formed rapidly in boreal fire plumes through the oxidation of short‐lived volatile organic compounds in the presence of nitrogen oxide radicals. Here we present new satellite observations of PAN from the Tropospheric Emission Spectrometer (TES) over northern Eurasia for April 2006–2010. We observe large interannual variability in TES PAN observations, and we show that fires are one source of this variability using (1) Moderate Resolution Imaging Spectroradiometer Mean Fire Radiative Power observations and (2) Hybrid Single‐Particle Lagrangian Integrated Trajectory backward trajectories. We also show that cold springtime temperatures and enhanced vertical mixing in the lower free troposphere over northeastern Eurasia likely played a role in the detection of PAN from TES in April 2006 in this region.
Atmospheric response to the North Pacific enabled by daily sea surface temperature variability
Authors: Zhou Guidi , Latif Mojib , Greatbatch Richard J. , Park Wonsun 
Published: August 2015

AbstractOcean‐atmosphere interactions play a key role in climate variability on a wide range of timescales from seasonal to decadal and longer. The extratropical oceans are thought to exert noticeable feedbacks on the atmosphere especially on decadal and longer timescales, yet the large‐scale atmospheric response to anomalous extratropical sea surface temperature (SST) is still under debate. Here we show, by means of dedicated high‐resolution atmospheric model experiments, that sufficient daily variability in the extratropical background SST needs to be resolved to force a statistically significant large‐scale atmospheric response to decadal North Pacific SST anomalies associated with the Pacific Decadal Oscillation, which is consistent with observations. The large‐scale response is mediated by atmospheric eddies. This implies that daily extratropical SST fluctuations must be simulated by the ocean components and resolved by the atmospheric components of global climate models to enable realistic simulation of decadal North Pacific sector climate variability.
Dynamical and thermodynamical modulations on future changes of landfalling atmospheric rivers over western North America
Authors: Gao Yang , Lu Jian , Leung L. Ruby , Yang Qing , Hagos Samson , Qian Yun 
Published: August 2015

AbstractThis study examines future changes of landfalling atmospheric rivers (ARs) over western North America using outputs from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The result reveals a strikingly large increase of AR days by the end of the 21st century in the RCP8.5 scenario, with fractional increases between 50% and 600%, depending on the seasons and landfall locations. These increases are predominantly controlled by the super‐Clausius‐Clapeyron rate of increase of atmospheric water vapor with warming, while changes of winds that transport moisture in the ARs, or dynamical effect, mostly counter the thermodynamical effect of increasing water vapor, limiting the increase of AR events in the future. The consistent negative effect of wind changes on AR days during spring and fall can be linked to the robust poleward shift of the subtropical jet in the North Pacific basin.
Magnetic meridional winds in the thermosphere obtained from Global Assimilation of Ionospheric Measurements (GAIM) model
Authors: Lomidze Levan , Scherliess Ludger , Schunk Robert W. 
Published: August 2015

AbstractThermospheric neutral winds play an important part in the dynamics of ionospheric plasma and represent one of the key inputs for ionospheric physics‐based models. Yet wind measurements are scarce and generally lack global coverage and continuity. To help mitigate this shortcoming, a data assimilation model was used to estimate neutral winds in the low‐ and middle‐latitude thermosphere. Seasonal global maps of NmF2 and hmF2 were generated from Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultation measurements for geomagnetically quiet and low solar flux conditions. The maps were assimilated into the Utah State University Global Assimilation of Ionospheric Measurements–Full Physics (GAIM‐FP) model. GAIM‐FP, which uses the physics‐based ionosphere‐plasmasphere model (IPM) and employs an ensemble Kalman filter technique, significantly improved the agreement between the modeled and measured NmF2 and hmF2 globally compared to the IPM. Global quiet time magnetic meridional winds were derived for December and June solstices and March equinox. The morphology of the derived winds was analyzed and validated by comparing with ground‐based measurements and with wind values from the empirical horizontal wind model. GAIM‐FP‐estimated winds were shown to be in good agreement with the wind observations. Furthermore, the sensitivity of the derived winds to uncertain parameters, including the O+‐O collision frequency, neutral composition, number of radio occultations, and data errors, was investigated. The uncertainties were found to have only small effects on the derived winds. The results of this work indicate that thermospheric wind estimation from GAIM‐FP is a valuable tool for wind specification over regions where limited or no wind measurements exist.
Cusp dynamics under northward IMF using three‐dimensional global particle‐in‐cell simulations
Authors: Cai D. , Esmaeili A. , Lembège B. , Nishikawa K‐I 
Published: August 2015

AbstractThe interaction of the solar wind with the terrestrial magnetosphere is analyzed with the help of three‐dimensional (3‐D) global, full‐electromagnetic particle‐in‐cell (PIC) simulations, in the configuration where the interplanetary magnetic field (IMF) is steadily northward. The present study is mainly focused on the cusp region and associated particle momenta dynamics. Within the present context and to the best of our knowledge, this work represents the first numerical simulation for analyzing the cusp dynamics using a fully self‐consistent 3‐D kinetic and electromagnetic approach. The main goals of the study are the following: (i) to retrieve the main known features of the cusp to validate the use of 3‐D PIC “global” simulations, (ii) to compare with previous results obtained with 3‐D MHD simulations, (iii) to create an updated global view of the cusp based on use of 3‐D PIC simulation, which cannot be obtained from a MHD approach, and (iv) to compare with statistical results from the Cluster mission. In particular, the stagnant exterior cusp (SEC) identified in previous statistical analysis of experimental data is retrieved, and it is possible to more precisely define the edges of the SEC region. In addition, we will focus on cusp features recently observed by the Cluster mission, for example, the Alfvén Transition Layer or ATL and on the features not reproduced by either MHD or the hybrid approach, which have been used to characterize the outer edges of the cusp more clearly.
Physics‐based reconstruction of the 3‐D density distribution in the entire quiet time plasmasphere from measurements along a single pass of an orbiter
Authors: Kotova G. A. , Verigin M. I. , Bezrukikh V. V. 
Published: August 2015

AbstractThe data base of the Alpha‐3/Interball‐1 measurements was used for semiempirical 3‐D modeling of plasma distribution inside the plasmasphere for quiet (stationary) geomagnetic conditions. A 2‐D model describing the density distribution in the meridional plane is based on equations of the plasma distribution in the plasmasphere for the cases of thermal equilibrium and collisionless initial partial filling of plasmaspheric shells. This 2‐D model is then expanded into a 3‐D one using simple equations for the shape of the plasmapause and density behavior in the equatorial plane along the convection streamline. The model has six free parameters with clear physical meaning. This modeling approach can be applied for extrapolation of data from magnetospheric satellites with very different orbits into the entire plasmasphere.
Chorus intensity modulation driven by time‐varying field‐aligned low‐energy plasma
Authors: Nishimura Y. , Bortnik J. , Li W. , Liang J. , Thorne R. M. , Angelopoulos V. , Le Contel O. , Auster U. , Bonnell J. W. 
Published: August 2015

AbstractRecent studies have shown that chorus waves are responsible for scattering and precipitating the energetic electrons that drive the pulsating aurora. While some of the chorus intensity modulation events are correlated with <~100 eV electron density modulation, most of the chorus intensity modulation events in the postmidnight sector occur without apparent density changes. Although it is generally difficult to measure evolution of low‐energy (<~20 eV) electron fluxes due to constraints imposed by the spacecraft potential and electrostatic analyzer (ESA) energy range limit, we identified using Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite data that low‐energy ions of ~100 eV show density modulation that is correlated with chorus intensity modulation. Those low‐energy ions and electrons are field‐aligned with major peaks in 0° (for northern hemisphere winter event) and 180° (for northern hemisphere summer event) pitch angle, indicating that outflowing plasma from the sunlit hemisphere is the source of the low‐energy plasma density modulation near the equator. Plasma sheet plasma density, and ambient electric and magnetic fields do not show modulations that are correlated with the chorus intensity modulation. Assuming charge neutrality, the low‐energy ions can be used to represent cold plasma density in wave growth rate calculations, and the enhancements of the low‐energy plasma density are found to contribute most effectively to chorus linear growth rates. These results suggest that chorus intensity modulation is driven by a feedback process where outflowing plasma due to energetic electron precipitation increases the equatorial density that drives further electron precipitation.
Constraining the pickup ion abundance and temperature through the multifluid reconstruction of the Voyager 2 termination shock crossing
Authors: Zieger Bertalan , Opher Merav , Tóth Gábor , Decker Robert B. , Richardson John D. 
Published: August 2015

AbstractVoyager 2 observations revealed that the hot solar wind ions (the so‐called pickup ions) play a dominant role in the thermodynamics of the termination shock and the heliosheath. The number density and temperature of this hot population, however, have remained unknown, since the plasma instrument on board Voyager 2 can only detect the colder thermal ion component. Here we show that due to the multifluid nature of the plasma, the fast magnetosonic mode splits into a low‐frequency fast mode and a high‐frequency fast mode. The coupling between the two fast modes results in a quasi‐stationary nonlinear wave mode, the “oscilliton,” which creates a large‐amplitude trailing wave train downstream of the thermal ion shock. By fitting multifluid shock wave solutions to the shock structure observed by Voyager 2, we are able to constrain both the abundance and the temperature of the undetected pickup ions. In our three‐fluid model, we take into account the nonnegligible partial pressure of suprathermal energetic electrons (0.022–1.5 MeV) observed by the Low‐Energy Charged Particle Experiment instrument on board Voyager 2. The best fitting simulation suggests a pickup ion abundance of 20 ± 3%, an upstream pickup ion temperature of 13.4 ± 2 MK, and a hot electron population with an apparent temperature of ~0.83 MK. We conclude that the actual shock transition is a subcritical dispersive shock wave with low Mach number and high plasma β.
Frictional behavior of talc‐calcite mixtures
Authors: Giorgetti C. , Carpenter B. M. , Collettini C. 
Published: August 2015

AbstractFaults involving phyllosilicates appear weak when compared to the laboratory‐derived strength of most crustal rocks. Among phyllosilicates, talc, with very low friction, is one of the weakest minerals involved in various tectonic settings. As the presence of talc has been recently documented in carbonate faults, we performed laboratory friction experiments to better constrain how various amounts of talc could alter these fault's frictional properties. We used a biaxial apparatus to systematically shear different mixtures of talc and calcite as powdered gouge at room temperature, normal stresses up to 50 MPa and under different pore fluid saturated conditions, i.e., CaCO3‐equilibrated water and silicone oil. We performed slide‐hold‐slide tests, 1–3000 s, to measure the amount of frictional healing and velocity‐stepping tests, 0.1–1000 µm/s, to evaluate frictional stability. We then analyzed microstructures developed during our experiments. Our results show that with the addition of 20% talc the calcite gouge undergoes a 70% reduction in steady state frictional strength, a complete reduction of frictional healing and a transition from velocity‐weakening to velocity‐strengthening behavior. Microstructural analysis shows that with increasing talc content, deformation mechanisms evolve from distributed cataclastic flow of the granular calcite to localized sliding along talc‐rich shear planes, resulting in a fully interconnected network of talc lamellae from 20% talc onward. Our observations indicate that in faults where talc and calcite are present, a low concentration of talc is enough to strongly modify the gouge's frictional properties and specifically to weaken the fault, reduce its ability to sustain future stress drops, and stabilize slip.
Momentum flux estimates accompanying multiscale gravity waves over Mount Cook, New Zealand, on 13 July 2014 during the DEEPWAVE campaign
Authors: Bossert Katrina , Fritts David C. , Pautet Pierre‐Dominique , Williams Bifford P. , Taylor Michael J. , Kaifler Bernd , Dörnbrack Andreas , Reid Iain M. , Murphy Damian J. , Spargo Andrew J. , MacKinnon Andrew D. 
Published: August 2015

AbstractObservations performed with a Rayleigh lidar and an Advanced Mesosphere Temperature Mapper aboard the National Science Foundation/National Center for Atmospheric Research Gulfstream V research aircraft on 13 July 2014 during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) measurement program revealed a large‐amplitude, multiscale gravity wave (GW) environment extending from ~20 to 90 km on flight tracks over Mount Cook, New Zealand. Data from four successive flight tracks are employed here to assess the characteristics and variability of the larger‐ and smaller‐scale GWs, including their spatial scales, amplitudes, phase speeds, and momentum fluxes. On each flight, a large‐scale mountain wave (MW) having a horizontal wavelength ~200–300 km was observed. Smaller‐scale GWs over the island appeared to correlate within the warmer phase of this large‐scale MW. This analysis reveals that momentum fluxes accompanying small‐scale MWs and propagating GWs significantly exceed those of the large‐scale MW and the mean values typical for these altitudes, with maxima for the various small‐scale events in the range ~20–105 m2 s−2.
Transboundary transport and deposition of Hg emission from springtime biomass burning in the Indo‐China Peninsula
Authors: Wang Xun , Zhang Hui , Lin Che‐Jen , Fu Xuewu , Zhang Yiping , Feng Xinbin 
Published: August 2015

AbstractBiomass burning from the Indo‐China Peninsula region is an important source of atmospheric mercury (Hg). We isolated 18 unique transport events over 2 years using observations of Hg and CO at a high‐altitude background site in southwestern China (Mount Ailao Observatory Station) to assess the transport and impact of Hg emissions from biomass burning. The quantity of Hg emission and the source regions were determined using ΔTGM/ΔCO slopes coupled with backward trajectory analysis and CO emission inventories. The slopes of ΔTGM/ΔCO appeared to be a useful chemical indicator for source identification. Industrial emission sources exhibited slopes in the range of 5.1–61.0 × 10−7 (parts per trillion by volume, pptv/pptv), in contrast to a slope of 2.0–6.0 × 10−7 for typical biomass burning. Transboundary transport of Hg from biomass burning led to episodically elevated atmospheric Hg concentrations during springtime. Hg emissions from biomass burning in the Indo‐China Peninsula region from 2001 to 2008 were estimated to be 11.4 ± 2.1 Mg yr−1, equivalent to 40% of annual anthropogenic emissions in the region. In addition, Hg emissions from biomass burning contained a substantial fraction of particulate bound Hg (PBM). Assuming that PBM readily deposits locally (within 50 km), the local Hg deposition caused by the PBM was estimated to be 2.2 ± 0.4 Mg yr−1, up to 1 order of magnitude higher than the PBM deposition caused by anthropogenic emissions during springtime in the region. The strong springtime emissions potentially pose a threat to the ecosystems of the Indo‐China Peninsula and southwest China.