bluuebunny/crossref_metadata_2025_split huggingface dataset:
Annual Sediment Transport Dynamics in the Narayani Basin, Central Nepal: Assessing the Impacts of Erosion Processes in the Annual Sediment Budget
Authors: Morin Guillaume P. , Lavé Jérôme , France‐Lanord Christian , Rigaudier Thomas , Gajurel Ananta Prassad , Sinha Rajiv 
Published: August 2018

AbstractIdentifying the roles of erosional processes in the denudation of mountain ranges requires a better understanding of erosional sensitivity to climatic, topographic, or lithologic controls. We analyzed erosion in the Narayani River basin (draining central Nepal and presenting contrasted lithologic and geochemical signatures in its outcropping rocks and a wide variety of erosional processes and climatic conditions) to assess the relative contributions of erosion processes to the annual sediment export. By combining acoustic Doppler current profiler measurements with depth profiles and daily surface samplings of the suspended load, we propose a simplified model to precisely calculate sediment fluxes at the basin outlet. We estimate an equivalent erosion rate of
mm/year for the year 2010, similar to the average value of
mm/year estimated from 15 years of records and long‐term (~ky) denudation rates of 1.7 mm/year derived from cosmogenic nuclides. The stability of erosion is attributed to efficient buffering behavior and spatial integration in the drainage system. Strong relations between rainfall events and the sediment export suggest that the system is mainly supply limited. Combining physical calculation of sediment fluxes with grain size analyses and geochemical tracers (hydroxyl isotopic compositions, carbonate contents, and total organic carbon content), we estimate that glacial and soil erosion do not contribute more than 10% and a few percentage, respectively, to the total budget and are only detectable during premonsoon and early monsoon periods. During the monsoon, erosion by landslides and mass wasting events overwhelms the sediment budget, confirming the dominant role of these erosional processes in active mountain chains.
CloudNet: Ground‐Based Cloud Classification With Deep Convolutional Neural Network
Authors: Zhang Jinglin , Liu Pu , Zhang Feng , Song Qianqian 
Published: August 2018

AbstractClouds have an enormous influence on the Earth's energy balance, climate, and weather. Cloud types have different cloud radiative effects, which is an essential indicator of the cloud effect on radiation. Therefore, identifying the cloud type is important in meteorology. In this letter, we propose a new convolutional neural network model, called CloudNet, for accurate ground‐based meteorological cloud classification. We build a ground‐based cloud data set, called Cirrus Cumulus Stratus Nimbus, which consists of 11 categories under meteorological standards. The total number of cloud images is three times that of the previous database. In particular, it is the first time that contrails, a type of cloud generated by human activity, have been taken into account in the ground‐based cloud classification, making the Cirrus Cumulus Stratus Nimbus data set more discriminative and comprehensive than existing ground‐based cloud databases. The evaluation of a large number of experiments demonstrates that the proposed CloudNet model could achieve good performance in meteorological cloud classification.
Investigation of Acoustic Waves in the Ionosphere Generated by a Deep Convection System Using Distributed Networks of GPS Receivers and Numerical Modeling
Authors: Azeem Irfan , Walterscheid Richard L. , Crowley Geoff 
Published: August 2018

AbstractAcoustic waves generated in the lower atmosphere may become an important source of variability in the upper atmosphere. Although excited with small amplitudes compared to gravity waves, they are minimally subjected to viscous dissipation and may reach large amplitudes at F region altitudes. We present total electron content data from a dense network of ground‐based GPS receivers during an outbreak of severe weather over Kansas on 26 May 2016. The results show annular traveling ionospheric disturbances (TIDs) propagating radially outward from the center of the storm. The TID characteristics were consistent with acoustic waves in the infrasonic range. We have modeled the disturbance by including a heat source representing latent heat release from a large thunderstorm. The modeled disturbance at ionospheric altitudes resembles the TIDs in terms of phase speed, frequency, and horizontal wavelength. We conclude that the observed TIDs were caused by an acoustic wave generated by deep convection.
Saturn's Plasma Density Depletions Along Magnetic Field Lines Connected to the Main Rings
Authors: Farrell W. M. , Hadid L. Z. , Morooka M. W. , Kurth W. S. , Wahlund J.‐E. , MacDowall R. J. , Sulaiman A. H. , Persoon A. M. , Gurnett D. A. 
Published: August 2018

AbstractWe report on a set of clear and abrupt decreases in the high‐frequency boundary of whistler mode emissions detected by Cassini at high latitudes (about ±40°) during the low‐altitude proximal flybys of Saturn. These abrupt decreases or dropouts have start and stop locations that correspond to L shells at the edges of the A and B rings. Langmuir probe measurements can confirm, in some cases, that the abrupt decrease in the high‐frequency whistler mode boundary is associated with a corresponding abrupt electron density dropout over evacuated field lines connected to the A and B rings. Wideband data also reveal electron plasma oscillations and whistler mode cutoffs consistent with a low‐density plasma in the region. The observation of the electron density dropout along ring‐connecting field lines suggests that strong ambipolar forces are operating, drawing cold ionospheric ions outward to fill the flux tubes. There is an analog with the refilling of flux tubes in the terrestrial plasmasphere. We suggest that the ring‐connected electron density dropouts observed between 1.1 and 1.3 Rs are connected to the low‐density ring plasma cavity observed overtop the A and B rings during the 2004 Saturn orbital insertion pass.
An Improved Prediction of Indian Summer Monsoon Onset From State‐of‐the‐Art Dynamic Model Using Physics‐Guided Data‐Driven Approach
Authors: Sahana A. S. , Ghosh Subimal 
Published: August 2018

AbstractPrediction of Indian Summer Monsoon onset, which marks the beginning of the South Asian monsoon, has significant implications on monsoon characteristics and subsequent nationwide agricultural planning. Here we make the most skillful prediction of monsoon onset with a physics‐guided data‐driven model integrated with the operational monsoon prediction by Coupled Forecast System version 2. Drivers of the variability of onset, which are well simulated by Coupled Forecast System version 2, viz., tropical Pacific sea surface temperature, reversal of tropospheric temperature gradient and strengthening of westerlies over AS during the early summer are identified as potential predictors. Data‐driven method, Least Absolute Shrinkage and Selection Operator, makes the final selection of predictors for the linear regression model of onset. We obtain an improved correlation of 0.6 between simulated and observed onset dates with the proposed integrated statistical dynamical model as compared to 0.44 obtained with the operational dynamic monsoon prediction model.
Overturning the Mediterranean Thermohaline Circulation
Authors: Waldman Robin , Brüggemann Nils , Bosse Anthony , Spall Michael , Somot Samuel , Sevault Florence 
Published: August 2018

AbstractFor more than five decades, the Mediterranean Sea has been identified as a region of so‐called thermohaline circulation, namely, of basin‐scale overturning driven by surface heat and freshwater exchanges. The commonly accepted view is that of an interaction of zonal and meridional conveyor belts that sink at intermediate or deep convection sites. However, the connection between convection and sinking in the overturning circulation remains unclear. Here we use a multidecadal eddy‐permitting numerical simulation and glider transport measurements to diagnose the location and physical drivers of this sinking. We find that most of the net sinking occurs within 50 km of the boundary, away from open sea convection sites. Vorticity dynamics provides the physical rationale for this sinking near topography: only dissipation at the boundary is able to balance the vortex stretching induced by any net sinking, which is hence prevented in the open ocean. These findings corroborate previous idealized studies and conceptually replace the historical offshore conveyor belts by boundary sinking rings. They challenge the respective roles of convection and sinking in shaping the oceanic overturning circulation and confirm the key role of boundary currents in ventilating the interior ocean.
The Role of Waves, Shelf Slope, and Sediment Characteristics on the Development of Erosional Chenier Plains
Authors: Nardin William , Fagherazzi Sergio 
Published: August 2018

AbstractCheniers are sandy ridges parallel to the coast separated by muddy deposits. Here we explore the development of erosional chenier plains, which form by winnowing during storms, through dimensional analysis and numerical results from the morphodynamic model Delft3D‐SWAN. Our results highlight that wave energy and inner‐shelf slope play an important role in the formation of erosional chenier plains. We further show that different sediment characteristics and wave climates lead to three alternative coastal landscapes: sandy strandplains, mudflats, or the more complex erosional chenier plains. Low inner‐shelf slopes are the most favorable for mudflat and chenier plain formation, while high slopes decrease the likelihood of mudflat development and preservation, favoring the formation of strandplains. The present study shows that erosional cheniers can form only when there is enough sediment availability to counteract wave action and for a specific range of shelf slopes.
Impact of Parametrized Nonorographic Gravity Wave Drag on Stratosphere‐Troposphere Coupling in the Northern and Southern Hemispheres
Authors: Polichtchouk Inna , Shepherd Theodore G. , Byrne Nicholas J. 
Published: August 2018

AbstractThe impact of parametrized nonorographic gravity wave drag (NOGWD) on the stratosphere‐troposphere dynamical coupling in atmospheric models is relatively unexplored. Using the European Centre for Medium‐Range Weather Forecasts Integrated Forecast System, we find that changes in NOGWD strength have a substantial impact on the tropospheric eddy‐driven jet (EDJ) in both hemispheres, but the sense of the impact is opposite in the two hemispheres. In the Northern Hemisphere the impact occurs via changes in the amplitude and persistence of stratospheric anomalies. In the Southern Hemisphere it occurs instead via differences in the sensitivity of the EDJ to a given stratospheric anomaly, arising from changes in the seasonal cycle leading up to the polar vortex breakdown. Increasing NOGWD eliminates the springtime phase of the Southern Hemisphere tropospheric semiannual oscillation, resulting in a more equatorward annual‐mean EDJ and showing that the semiannual oscillation cannot be explained entirely from tropospheric mechanisms.
Dipole Types of Autumn Precipitation Variability Over the Subtropical East Asia‐Western Pacific Modulated by Shifting ENSO
Authors: Hu Chundi , Chen Dake , Huang Gang , Yang Song 
Published: August 2018

AbstractRecent autumns have exhibited two dipole types of precipitation variability (DIPO1 and DIPO2) over the subtropical East Asia‐western Pacific (SEAWP). Meanwhile, El Niño–Southern Oscillation (ENSO) has undergone significant mode shift, exhibiting as the eastern Pacific or central Pacific ENSO (EPSO or CPSO). Whether there was any physical linkage between the two remains unclear. Here we demonstrate for the first time that interannual variations of DIPO1 and DIPO2 are closely linked to EPSO and CPSO, respectively. Shifting ENSO modulates the patterns of SEAWP precipitation dipole mainly via changing the path of tropospheric moisture transport and the location of anomalous water vapor convergence/divergence due to different low‐level cyclone/anticyclone activities induced by EPSO or CPSO. Further analysis shows that the interdecadal variability of SEAWP precipitation is also linked to the La Niña‐like climate shift in 1998. Hence, our study provides some new insight into the ongoing hot debate on the shifting ENSO and increasing autumn drought in southeastern China.
Great Expectations: Plans and Predictions for New Horizons Encounter With Kuiper Belt Object 2014 MU69 (“Ultima Thule”)
Authors: Moore Jeffrey M. , McKinnon William B. , Cruikshank Dale P. , Gladstone G. Randall , Spencer John R. , Stern S. Alan , Weaver Harold A. , Singer Kelsi N. , Showalter Mark R. , Grundy William M. , Beyer Ross A. , White Oliver L. , Binzel Richard P. , Buie Marc W. , Buratti Bonnie J. , Cheng Andrew F. , Howett Carly , Olkin Cathy B. , Parker Alex H. , Porter Simon B. , Schenk Paul M. , Throop Henry B. , Verbiscer Anne J. , Young Leslie A. , Benecchi Susan D. , Bray Veronica J. , Chavez Carrie L. , Dhingra Rajani D. , Howard Alan D. , Lauer Tod R. , Lisse C. M. , Robbins Stuart J. , Runyon Kirby D. , Umurhan Orkan M. 
Published: August 2018

AbstractThe New Horizons encounter with the cold classical Kuiper Belt object 2014 MU69 (informally named “Ultima Thule,” hereafter Ultima) on 1 January 2019 will be the first time a spacecraft has ever closely observed one of the free‐orbiting small denizens of the Kuiper Belt. Related to but not thought to have formed in the same region of the solar system as the comets that been explored so far, it will also be the most distant, and most primitive body yet visited by spacecraft. In this letter we begin with a brief overview of cold classical Kuiper Belt objects, of which Ultima is a prime example. We give a short preview of our encounter plans. We note what is currently known about Ultima from Earth‐based observations. We then review our expectations and capabilities to evaluate Ultima's composition, surface geology, structure, near space environment, small moons, rings, and the search for activity.
MMS Observations of Harmonic Electromagnetic Ion Cyclotron Waves
Authors: Usanova M. E. , Ahmadi N. , Malaspina D. M. , Ergun R. E. , Trattner K. J. , Reece Q. , Leonard T. , Fuselier S. A. , Torbert R. B. , Russell C. T. , Burch J. L. 
Published: August 2018

AbstractHarmonically related electromagnetic ion cyclotron waves with the fundamental frequency near the double oxygen cyclotron frequency were observed by the MMS spacecraft on 18–20 May 2016. The wave activity lasted for three days, detected by the spacecraft on their consecutive inbound passages through the Earth's plasma sheet boundary layer. The waves were seen in both magnetic and electric fields, formed by over 10 higher order harmonics. Simultaneous ion flux measurements show the presence of ion ring distributions suggesting the energy source for the observed waves. The ion cyclotron harmonics were observed together with broadband waves extending from ~Hz to ~kHz frequency range, ion and electron phase space holes, and chorus waves. During some intervals, there is a clear modulation of chorus wave packets at the ion cyclotron fundamental harmonic frequency. These observations are particularly interesting since they suggest cross‐frequency and cross‐species coupling between processes happening on ion and electron scales.
Faults and Non‐Double‐Couple Components for Induced Earthquakes
Authors: Wang Ruijia , Gu Yu Jeffrey , Schultz Ryan , Chen Yunfeng 
Published: August 2018

AbstractFocal mechanisms of induced earthquakes reflect anthropogenic contributions to preexisting geological features and fault slippages. In this paper, we examine fault‐related (double‐couple (DC)) and possibly fluid‐related (non‐double‐couple (non‐DC)) mechanisms of induced earthquakes (M2–6) at regional scales. We systematically compare well‐resolved focal mechanisms of 33 events in the Western Canada Sedimentary Basin, among which 12 were induced by hydraulic fracturing and one by secondary recovery. Most of the seismicity is dominated by strike‐slip/thrust faulting regimes, whereas limited (but consistent) non‐DC components are obtained from injection‐induced seismicity in central Alberta. We interpret the persistent compensated‐linear‐vector‐dipole components (M2.1–3.8) as reflecting fracture growth and/or noncoplanar faults slippages during hydraulic‐fracturing stimulations. We further expand the moment tensor decomposition analysis to four representative classes of induced seismicity globally and find that the overall contribution of non‐DC components is comparable between induced and tectonic earthquakes.
Improved Reanalysis and Prediction of Atmospheric Fields Over the Southern Ocean Using Campaign‐Based Radiosonde Observations
Authors: Sato Kazutoshi , Inoue Jun , Alexander Simon P. , McFarquhar Greg , Yamazaki Akira 
Published: August 2018

AbstractThis study investigated the impact of radiosonde observations from the Southern Ocean obtained by the Australian R/V Aurora Australis on the ALERA2 experimental ensemble reanalysis data set and ensemble forecast experiment. An observing system experiment (OSE) that included additional ship‐launched radiosonde data captured the atmospheric structure over the Southern Ocean. ALERA2 without additional radiosondes had positive temperature biases exceeding 7 °C in the upper troposphere when low‐pressure cyclonic systems passed over the ship. The spread in the upper level was reduced by 15% in the OSE, which propagated downstream from the ship's position because of the sparse observing network over southern high latitudes. Comparison of two 63‐member ensemble forecast experiments initialized by ALERA2 and the OSE revealed that prediction of midlatitude cyclone tracks was improved by the realistic representation of upper‐level troughs in the OSE forecast. This confirms that additional radiosondes over the Southern Ocean reduce uncertainty and error in midlatitude cyclone forecasts.
The Bagnold Dunes in Southern Summer: Active Sediment Transport on Mars Observed by the Curiosity Rover
Authors: Baker Mariah M. , Lapotre Mathieu G. A. , Minitti Michelle E. , Newman Claire E. , Sullivan Robert , Weitz Catherine M. , Rubin David M. , Vasavada Ashwin R. , Bridges Nathan T. , Lewis Kevin W. 
Published: August 2018

AbstractOrbiter‐based observations have demonstrated that active aeolian environments are ubiquitous across Mars. Here we examine one such environment, the Bagnold Dune Field in Gale crater, with repeat imaging campaigns conducted from Curiosity during southern summer. Images reveal widespread migration of aeolian impact ripples (up to 2.8 cm/sol), which is in stark contrast to the inactivity of similar bedforms during southern winter. The winds responsible for steady southwestward migration of ripples are consistent with predictions of regional‐scale flows that enter the crater from the north and interact with the topography of Mount Sharp but are not fully representative of all dune‐forming winds. Inferred friction speeds of 1.5 m/s needed to explain mobilization of bedforms are likely not being achieved, and thus, a majority of sediment transport may be taking place at subthreshold conditions. This hypothesis is further supported by sand flux estimates that suggest a low saltation flux environment within the dune field.
Perpendicular Current Reduction Caused by Cold Ions of Ionospheric Origin in Magnetic Reconnection at the Magnetopause: Particle‐in‐Cell Simulations and Spacecraft Observations
Authors: Toledo‐Redondo Sergio , Dargent Jérémy , Aunai Nicolas , Lavraud Benoit , André Mats , Li Wenya , Giles Barbara , Lindqvist Per‐Arne , Ergun Robert E. , Russell Christopher T. , Burch James L. 
Published: August 2018

AbstractCold ions of ionospheric origin are present throughout the Earth's magnetosphere, including the dayside magnetopause, where they modify the properties of magnetic reconnection, a major coupling mechanism at work between the magnetosheath and the magnetosphere. We present Magnetospheric MultiScale (MMS) spacecraft observations of the reconnecting magnetopause with different amounts of cold ions and show that their presence reduces the Hall term in the Ohm's law. Then, we compare two particle‐in‐cell simulations, with and without cold ions on the magnetospheric side. The cold ions remain magnetized inside the magnetospheric separatrix region, leading to the reduction of the perpendicular currents associated with the Hall effect. Moreover, this reduction is proportional to the relative number density of cold ions. And finally, the Hall electric field peak is reduced along the magnetospheric separatrix owing to cold ions. This should have an effect on energy conversion by reconnection from electromagnetic fields to kinetic energy of the particles.
Interaction Between Moderate Earthquakes and Volcanic Eruptions: Analyses of Global Data Catalog
Authors: Nishimura Takeshi 
Published: August 2018

AbstractThe interaction between earthquakes and volcanic eruptions is investigated by analyzing a modern seismic data catalog of centroid moment tensor solutions and eruption records summarized by the Smithsonian Institution. To determine the average features of the interactions, the numbers of earthquakes that occurred before and after the initiation of each eruption with a volcanic explosivity index of larger than or equal to 2 are analyzed. The results show that moderate earthquakes, which have moment magnitudes of 5 to 6 (Mw 5–6), are activated within a horizontal distance of 50 km from volcanoes for about 0.3 years after the initiation of an eruption. About 13% of volcanic eruptions are accompanied by moderate earthquakes. The occurrence possibility of earthquakes every 0.1 years for 0.3 years after an eruption is about 5 times larger than normal. No significant dependence on the tectonic settings and major rock types is recognized.
Radar Altimetry as a Robust Tool for Monitoring the Active Lava Lake at Erebus Volcano, Antarctica
Authors: Peters N. J. , Oppenheimer C. , Brennan P. , Lok L. B. , Ash M. , Kyle P. 
Published: August 2018

AbstractThe level of lava within a volcanic conduit reflects the overpressure within a connected magma reservoir. Continuous monitoring of lava level can therefore provide critical insights into volcanic processes and aid hazard assessment. However, accurate measurements of lava level are not easy to make, partly owing to the often dense fumes that hinder optical techniques. Here we present the first radar instrument designed for the purpose of monitoring lava level and report on its successful operation at Erebus volcano, Antarctica. We describe the hardware and data‐processing steps followed to extract a time series of lava lake level, demonstrating that we can readily resolve ∼1 m cyclic variations in lake level that have previously been recognized at Erebus volcano. The performance of the radar (continuous, automated data collection in temperatures of around −30 °C) indicates the suitability of this approach for sustained automated measurements at Erebus and other volcanoes with lava lakes.