bluuebunny/crossref_metadata_2025_split huggingface dataset:
Middle to Late Pleistocene Evolution of the Bengal Fan: Integrating Core and Seismic Observations for Chronostratigraphic Modeling of the IODP Expedition 354 8° North Transect
Authors: Reilly Brendan T. , Bergmann Fenna , Weber Michael E. , Stoner Joseph S. , Selkin Peter , Meynadier Laure , Schwenk Tilmann , Spiess Volkhard , France‐Lanord Christian 
Published: April 2020

AbstractWe investigate chronology and age uncertainty for the middle to upper Pleistocene lower Bengal Fan using a novel age‐depth modeling approach that factors lithostratigraphic, magnetostratigraphic, biostratigraphic, cyclostratigraphic, and seismic stratigraphic constraints, based on results from the International Ocean Discovery Program Expedition 354 Bengal Fan and analysis of the GeoB97‐020/027 seismic line. The initial chronostratigraphic framework is established using regionally extensive hemipelagic sediment units, and only age‐depth models of fan deposits that respect the superposition of channel‐levee systems between sites are accepted. In doing so, we reconstruct signals of regional sediment accumulation rate and lithogenic sediment input through the perspective of a two‐dimensional ~320 km transect at 8°N that are consistent with more distal and more ambiguous regional records. This chronology allows us to discuss the depositional history of the middle to upper Pleistocene lower Bengal Fan within the context of sea level, climate, and tectonic controls. We hypothesize, based on the timing of accumulation rate changes, that progradation and intensification of the Bengal Fan's channel‐levee system at 8°N was largely driven by increases in sea level amplitude during this time. However, it is also possible this progradation was influenced by changes in Pleistocene climate and increased Himalayan erosion rates, driving greater sediment flux to the fan.
Neural Network Repair of Lossy Compression Artifacts in the September 2015 to March 2016 Duration of the MMS/FPI Data Set
Authors: da Silva Daniel , Barrie A. , Gershman D. , Elkington S. , Dorelli J. , Giles B. , Patterson W. 
Published: April 2020

AbstractDuring the September 2015 to March 2016 duration (sometimes referred to as Phase 1A) of the Magnetospheric Multiscale Mission, the Dual Electron Spectrometers (DES) were configured to generously utilize lossy compression. While this maximized the number of velocity distribution functions downlinked, it came at the expense of lost information content for a fraction of the frames. Following this period of lossy compression, the DES was reconfigured in a way that allowed for 95% of the frames to arrive to the ground without loss. Using this high‐quality set of frames from on‐orbit observations, we compressed and decompressed the frames on the ground to create a side‐by‐side record of the compression effect. This record was used to drive an optimization method that (a) derived basis functions capable of approximating the lossless sample space and with nonnegative coefficients and (b) fitted a function which maps the lossy frames to basis weights that recreate the frame without compression artifacts. This method is introduced and evaluated in this paper. Data users should expect a higher level of confidence in the absolute scale of density/temperature measurements and notice less sinusoidal bias in the velocity X and Y components (GSE)
Altitude of Two‐Stream Irregularities in Equatorial E Region Using Sounding Rocket Experiments From Thumba
Authors: Pandey Kuldeep , Gupta S. P. 
Published: April 2020

AbstractAmplitudes of two‐stream irregularities and equatorial electrojet (EEJ) current are known to peak around the same altitude. Sounding rocket‐borne magnetometer experiments have consistently shown that the EEJ current density maximizes around 105‐km altitude whereas the theoretical models predict the EEJ peak around 100 km. One of the propositions to bridge this difference in the altitude has been based on the inclusion of small‐scale turbulence (wavelength of <100 m) with the large‐scale dynamics (kilometer size). This proposition is examined based on in situ measurements of E region electron density and plasma irregularities (two‐stream and gradient‐drift irregularities) obtained at different times of the day and night. These measurements were obtained based on sounding rocket flight experiments conducted from Thumba Equatorial Rocket Launching Station (8.54° N, 76.86° E), a facility in the vicinity of the dip equator. Whenever two‐stream irregularities are present, the minimum electrojet current density is estimated based on the threshold velocity required for generation of these plasma irregularities. This method provides estimates of nighttime E region current also, which is difficult to measure. It is found that amplitudes of both two‐stream irregularities and the estimated EEJ current peak around 105‐km altitude irrespective of the presence or absence of the gradient‐drift irregularities at the base of electrojet (95‐ to 100‐km altitude).
Do Statistical Models Capture the Dynamics of the Magnetopause During Sudden Magnetospheric Compressions?
Authors: Staples F. A. , Rae I. J. , Forsyth C. , Smith A. R. A. , Murphy K. R. , Raymer K. M. , Plaschke F. , Case N. A. , Rodger C. J. , Wild J. A. , Milan S. E. , Imber S. M. 
Published: April 2020

AbstractUnder periods of strong solar wind driving, the magnetopause can become compressed, playing a significant role in draining electrons from the outer radiation belt. Also termed “magnetopause shadowing,” this loss process has traditionally been attributed to a combination of magnetospheric compression and outward radial diffusion of electrons. However, the drift paths of relativistic electrons and the location of the magnetopause are usually calculated from statistical models and, as such, may not represent the time‐varying nature of this highly dynamic process. In this study, we construct a database ∼20,000 spacecraft crossings of the dayside magnetopause to quantify the accuracy of the commonly used Shue et al. (1998, https://doi.org/10.1029/98JA01103) model. We find that, for the majority of events (74%), the magnetopause model can be used to estimate magnetopause location to within ±1 RE. However, if the magnetopause is compressed below 8 RE, the observed magnetopause is greater than 1 RE inside of the model location on average. The observed magnetopause is also significantly displaced from the model location during storm sudden commencements, when measurements are on average 6% closer to the radiation belts, with a maximum of 42%. We find that the magnetopause is rarely close enough to the outer radiation belt to cause direct magnetopause shadowing, and hence rapid outward radial transport of electrons is also required. We conclude that statistical magnetopause parameterizations may not be appropriate during dynamic compressions. We suggest that statistical models should only be used during quiescent solar wind conditions and supplemented by magnetopause observations wherever possible.
Implications for Magnetosphere‐Ionosphere Coupling From Jupiter's System IV Quasi‐Period
Authors: Coffin Drew , Delamere Peter , Damiano Peter 
Published: April 2020

AbstractThe Io plasma torus exhibits a fundamental rotational periodicity distinct from the rotation of the magnetic field that is easily observed in physical components such as ultraviolet emission or ionic mixing ratios, yet this distinct periodicity has no widely accepted explanation. To seek the origins of this additional periodicity, called System IV, a two‐dimensional (radial and azimuthal) physical chemistry model (Copper et al., 2016), is used to investigate the torus response to a prescribed System III hot electron modulation following Steffl et al. (2008) and an additional hot electron modulation that we relate to various transport and mass loading parameters. The model thus self‐consistently generates a radially independent periodicity consistent with that of System IV. We argue that the origin of this periodicity is the interplay between chemical and transport time scales working to prevent an azimuthal shearing of the hot electron modulation due to the physical subcorotation profile. We also examine recent observations (Tsuchiya et al., 2019,) that volcanic eruptions return the System IV periodicity toward rigid corotation with System III, counter to previous magnetosphere‐ionosphere(MI) coupling models that examined mass loading (Pontius & Hill, 1982, ). Instead, the return to corotation implies improved MI coupling, possibly due to a transport‐related increase in hot electrons following the eruption. Thus, we argue that the System IV periodicity is a diagnostic of MI coupling efficiency at Jupiter and the ultimate result of energy dissipation associated with Alfvénic coupling to the planet.
Electron Acceleration and Thermalization at Magnetotail Separatrices
Authors: Norgren C. , Hesse M. , Graham D. B. , Khotyaintsev Yu. V. , Tenfjord P. , Vaivads A. , Steinvall K. , Xu Y. , Gershman D. J. , Lindqvist P.‐A. , Plaschke F. , Burch J. L. 
Published: April 2020

AbstractIn this study we use the Magnetospheric Multiscale mission to investigate the electron acceleration and thermalization occurring along the magnetic reconnection separatrices in the magnetotail. We find that initially cold electron lobe populations are accelerated toward the X line forming beams with energies up to a few kiloelectron volts, corresponding to a substantial fraction of the electron thermal energy inside the exhaust. The accelerated electron populations are unstable to the formation of electrostatic waves which develop into nonlinear electrostatic solitary waves. The waves' amplitudes are large enough to interact efficiently with a large part of the electron population, including the electron beam. The wave‐particle interaction gradually thermalizes the beam, transforming directed drift energy to thermal energy.
Extreme Magnetosphere‐Ionosphere‐Thermosphere Responses to the 5 April 2010 Supersubstorm
Authors: Nishimura Y. , Lyons L. R. , Gabrielse C. , Sivadas N. , Donovan E. F. , Varney R. H. , Angelopoulos V. , Weygand J. M. , Conde M. G. , Zhang S. R. 
Published: April 2020

AbstractThe extreme substorm event on 5 April 2010 (THEMIS AL = −2,700 nT, called supersubstorm) was investigated to examine its driving processes, the aurora current system responsible for the supersubstorm, and the magnetosphere‐ionosphere‐thermosphere (M‐I‐T) responses. An interplanetary shock created shock aurora, but the shock was not a direct driver of the supersubstorm onset. Instead, the shock with a large southward IMF strengthened the growth phase with substantially larger ionosphere currents, more rapid equatorward motion of the auroral oval, larger ionosphere conductance, and more elevated magnetotail pressure than those for the growth phase of classical substorms. The auroral brightening at the supersubstorm onset was small, but the expansion phase had multistep enhancements of unusually large auroral brightenings and electrojets. The largest activity was an extremely large poleward boundary intensification (PBI) and subsequent auroral streamer, which started ~20 min after the substorm auroral onset during a steady southward IMF Bz and elevated dynamic pressure. Those were associated with a substorm current wedge (SCW), plasma sheet flow, relativistic particle injection and precipitation down to the D‐region, total electron content (TEC), conductance, and neutral wind in the thermosphere, all of which were unusually large compared to classical substorms. The SCW did not extend over the entire nightside auroral activity but was localized azimuthally to a few 100 km in the ionosphere around the PBI and streamer. These results reveal the importance of localized magnetotail reconnection for releasing large energy accumulation that can affect geosynchronous satellites and produce the extreme M‐I‐T responses.
Bidirectional Volume Exchange Between Kuroshio and East China Sea Shelf Water Based on a Whole‐Region Passive‐Tracing Method
Authors: Hu Fang , Liu Yahao , Xu Zhenhua , Yin Yuqi , Hou Yijun 
Published: April 2020

AbstractThe Kuroshio intrusion has a profound influence on the marine dynamic and ecological environment in the East China Sea (ECS) shelf. In most previous studies, the intrusion has been evaluated by the volume transport across the 200 m isobath. However, this approximate substitution leads to an underestimation of the Kuroshio intruding flux as it fails to separate the onshore and offshore transport of Kuroshio and shelf water. In this paper, a whole‐region passive‐tracing modeling method is proposed to quantitatively explore the bidirectional exchange of Kuroshio and shelf water, by introducing the Kuroshio water concentration as a passive tracer into the flux calculations. In terms of the climatological annual mean, the Kuroshio intrusion onto the ECS shelf is as high as 1.85 Sv (1 Sv = 106 m3 s−1), with a shelf water outflow rate of 0.42 Sv. The real Kuroshio intruding flux is about 30% higher than the net volume transport across the 200 m isobath (1.43 Sv), which indicates that the influence of the Kuroshio intrusion on the ECS may be far greater than believed before. The volume exchange on the inner shelf of the ECS is also discussed. Analyses of the momentum balances indicate that the exchanges on both the shelf break and the inner shelf are generally dominated by the geostrophic balance, but the exchange on the shelf break is more susceptible to nonlinear effects. The results of a set of sensitivity experiments show that variation of the Kuroshio intrusion is mainly regulated by the combined effect of the Kuroshio transport, the Taiwan Strait current, and the local wind stress. In contrast, the local wind stress has a predominant effect on the outflow of shelf water.
Evidence of Eddy‐Enhanced Winter Chlorophyll‐a Blooms in Northern Arabian Sea: 2017 Cruise Expedition
Authors: Wang Tianyu , Du Yan , Liao Xiaomei , Xiang Chenhui 
Published: April 2020

AbstractThe temperature, salinity, and chlorophyll‐a (Chl‐a) profiles of the upper ocean (0–200 m) were measured during the China‐Pakistan Joint Expedition, 2017. The cruise track passed through an identified cyclonic eddy, and the multi‐disciplinary records thus verify the eddy contributions to winter blooms in the northern Arabian Sea (AS). The records show that the strength of upper blooms within the mixed layer is mainly dominated by surface phytoplankton biomass (the Chl‐a concentration), which increases simultaneously with the shallow mixed layer and uplifted thermocline. A composite analysis of eddy‐tracked sea level anomalies (SLA) and Chl‐a reveals the pumping and stirring effects that cyclonic eddies make to the ocean surface nutrient supply. Based on the high‐resolution Ocean General Circulation Model for the Earth Simulator (OFES) outputs, a mixed layer nitrogen budget calculation was subsequently conducted to quantify the contributions of mesoscale eddies to 10‐year climatological winter blooms. The results indicate that eddy flows are primary contributors to the increased nutrients in the coastal north AS during the mature period (usually in January and February) of the winter blooms, with a concentration histogram double that of convective mixing. The concentration decreases from the north to south, agreeing well with the seasonal northward nutrition gradient. This confirms that (i) the growth of nutrients over the northern AS, which is known to be triggered by convective mixing, would be further maintained by eddy‐induced advection; and (ii) higher concentration of nutrients would facilitate an easier response of Chl‐a to eddy dynamics.
Capturing a Mode of Intermediate Water Formation in the Red Sea
Authors: Asfahani Khaled , Krokos George , Papadopoulos Vassilis P. , Jones Burton H. , Sofianos Sarantis , Kheireddine Malika , Hoteit Ibrahim 
Published: April 2020

AbstractFormation of intermediate waters in the northern Red Sea was captured by Seagliders during the winter of 2016. The analysis is based on measurements collected by consequent deployments of Seaglider autonomous underwater vehicles along a 70 km transect, which was run repeatedly from the coast to midbasin during the period from October 2015 to May 2016. The observations revealed typical open ocean convection processes including a preconditioning phase followed by deep convection and spreading of the newly formed waters through lateral exchange. Winter conditions were characterized by surface cooling and enhanced evaporation, which were observed from late October until late February. During this period, the gradual surface cooling and salinity increase resulted in the weakening of the surface stratification. Recurrent cyclonic gyres forced by strong atmospheric events led to episodic convection and the formation of intermediate seawater typical of the upper overturning circulation cell of the Red Sea. Following deep mixing, a remarkable bloom of chlorophyll was detected at the top layer of the water column in response to the nutrients delivery from the deeper layers. The end of winter was marked by the intrusion of lower salinity water presumably advected from the south and the reestablishment of the general cyclonic circulation, typical for the northernmost part of the Red Sea. To the best of our knowledge, this is the first observation study of such convection events in the northern Red Sea.
Tidal Effect on Water Export Rate in the Eastern Shelf Seas of China
Authors: Lin Lei , Liu Dongyan , Guo Xinyu , Luo Chongxin , Cheng Yao 
Published: April 2020

AbstractWater export rate of shelf seas is a pivotal factor impacting the global carbon cycle. Tides have important impacts on shelf hydrodynamics but are excluded in many climate models. To assess the effect of tides on export rates of shelf water, this study used a regional hydrodynamic model and a water residence time (WRT) adjoint model and examined model runs with and without tides for the eastern shelf seas of China. The results show that the average WRTs in the Bohai, Yellow, and East China seas were 11.60, 4.95, and 0.39 years, respectively. When tides were excluded, the WRTs decreased by >70% in the Bohai and Yellow seas and by ~10% in the East China Sea, indicating a significant acceleration in the shelf water export due to the absence of tides. The tidal effect has spatial variability associated with the water depth. Sensitivity experiments suggest that the tidal effect on the mean WRT was stronger than the effect of other dynamical factors (winds, rivers, and boundary currents). In the model with tides, tides weakened the wind‐driven coastal current by intensifying the bottom resistance and thus slowed water export in the inner and middle portions of the shelf, compared to the model without tides. Parameterization of the tidal bottom friction in the model without tides could significantly improve the WRT result. This study highlights the crucial role of tides on the long‐term transport of shelf seas and the significance of parameterizing the effect of tidal friction in climate models.
Enhanced Dust Influx to South Atlantic Sector of Antarctica During the Late‐20th Century: Causes and Contribution to Radiative Forcing
Authors: Laluraj C. M. , Rahaman Waliur , Thamban Meloth , Srivastava Rohit 
Published: April 2020

AbstractAtmospheric dust influences global climate and ocean biogeochemistry. Here we present a high‐resolution ice core dust record (1905–2005 CE) from coastal Dronning Maud Land (71°20′S, 11°35′E), East Antarctica, to understand dust flux variability, its causes, and potential contribution to radiative forcing during the 20th century in the South Atlantic sector of East Antarctica (SASA). The dust flux profile (sum of 1–25 μm size fractions) reveals three stepwise increase during 1905–1929, 1930–1979, and 1980–2005 CE time with an average of 0.83, 4.7, and 12.88 mg·m−2·year−1, respectively. Our investigation for such dramatic dust flux increase reveals that the increased aridity and favorable wind conditions over Southern South America (SSA), a potential dust source to Antarctica, caused increase in dust production and transport during the late 20th century. The dust flux variability in Southern Hemisphere is concomitant with in‐phase relationship between El‐Niño Southern Oscillation and Pacific Decadal Oscillations, which influenced the spatial distribution of global wet‐dry phase (precipitation pattern). Further, shifting of Southern Annular Mode to positive phase made wind conditions more conducive for long‐range dust transport from SSA to coastal Dronning Maud Land region. To the best of our knowledge, this is the first report of past radiative forcing estimates for Antarctica using ice core dust record into a radiative transfer model. Our estimates of radiative forcing corresponding to the enhanced dust flux yield nearly 30% increase in aerosol forcing during the late 20th century. This has resulted 40% decrease in atmospheric cooling rate, which contributed to net atmospheric warming over SASA.
Determining Electric Fields in Thunderclouds With the Radiotelescope LOFAR
Authors: Trinh T. N. G. , Scholten O. , Buitink S. , Ebert U. , Hare B. M. , Krehbiel P. R. , Leijnse H. , Bonardi A. , Corstanje A. , Falcke H. , Huege T. , Hörandel J. R. , Krampah G. K. , Mitra P. , Mulrey K. , Nelles A. , Pandya H. , Rachen J. P. , Rossetto L. , Rutjes C. , ter Veen S. , Winchen T. 
Published: April 2020

AbstractAn analysis is presented of electric fields in thunderclouds using a recently proposed method based on measuring radio emission from extensive air shower events during thunderstorm conditions. This method can be regarded as a tomography of thunderclouds using cosmic rays as probes. The data cover the period from December 2011 till August 2014. We have developed an improved fitting procedure to be able to analyze the data. Our measurements show evidence for the main negative‐charge layer near the −10° isotherm. This we have seen for a winter as well as for a summer cloud where multiple events pass through the same cloud and also the vertical component of the electric field could be reconstructed. On the day of measurement of some cosmic‐ray events showing evidence for strong fields, no lightning activity was detected within 100 km distance. For the winter events, the top heights were between 5 and 6 km, while in the summer, typical top heights of 9 km were seen. Large horizontal components in excess of 70 kV/m of the electric fields are observed in the middle and top layers.