bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gulf Stream Mean and Eddy Kinetic Energy: Three‐Dimensional Estimates From Underwater Glider Observations
Authors: Todd Robert E. 
Published: February 2021

AbstractThe strong, meandering, and eddy‐shedding Gulf Stream is a large oceanic reservoir of both mean and eddy kinetic energy in the northwestern Atlantic. Since 2015, underwater gliders equipped with Doppler current profilers have collected over 20,000 absolute velocity profiles in and near the Gulf Stream along the US East Coast. Those observations are used to make three‐dimensional estimates of mean and eddy kinetic energy, substantially expanding the geographic coverage of prior estimates of subsurface kinetic energy in the Gulf Stream. Glider observations are combined via weighted least squares fitting with anisotropic and inhomogeneous length scales to reflect both circulation and sampling density; this averaging technique can be applied to other quantities measured by the gliders. Mean and eddy kinetic energy decay approximately exponentially away from the surface. Vertical decay scales are longest within the high‐speed core of the Gulf Stream and somewhat shorter on the flanks of the Gulf Stream.
Evolution of Subtropical Pacific‐Onset El Niño: How Its Onset Location Controls Its Decay Evolution
Authors: Kim Ji‐Won , Yu Jin‐Yi 
Published: February 2021

AbstractIn the observations, El Niño events initiated by a subtropical Pacific mechanism (SP‐onset El Niños) show larger uncertainty in their decay evolution patterns than those initiated by a tropical Pacific mechanism. A 2,200‐year simulation of Community Earth System Model reproduces this observed feature and its SP‐onset El Niños are analyzed to understand the cause of the large uncertainty. Results show that the onset location of SP‐onset El Niño, which interacts with the eastern edge of the western Pacific warm pool, is a key factor controlling its decay evolution. When the onset is located east (west) of 155°E, the event has a strong tendency to reverse (maintain) its phase, leading to cyclic (multiyear) evolution. These two onset locations respectively activate Indo‐Pacific and tropical‐subtropical Pacific interactions to give rise to the different evolution patterns. The findings offer a potential way to predict the evolution of SP‐onset El Niños using their onset locations.
Ocean Acidification Reduces Skeletal Density of Hardground‐Forming High‐Latitude Crustose Coralline Algae
Authors: Williams B. , Chan P. T. W. , Westfield I. T. , Rasher D. B. , Ries J. 
Published: February 2021

AbstractCrustose coralline algae (CCA) function as foundation species by creating marine carbonate hardground habitats. High‐latitude species may be vulnerable to regional warming and acidification. Here, we report the results of an experiment investigating the impacts of CO2‐induced acidification (pCO2 ∼350, 490, 890, 3,200 µatm) and temperature (∼6.5°C, 8.5°C, 12.5°C) on the skeletal density of two species of high‐latitude CCA: Clathromorphum compactum and Clathromorphum nereostratum (CN). Skeletal density of both species significantly declined with pCO2. In CN, the density of previously deposited skeleton declined in the highest pCO2 treatment. This species was also unable to precipitate new skeleton at 12.5°C, suggesting that CN will be particularly sensitive to future warming and acidification. The decline in skeletal density exhibited by both species under future pCO2 conditions could reduce their skeletal strength, potentially rendering them more vulnerable to disturbance, and impairing their production of critical habitat in high‐latitude systems.
Auroral Energy Flux and Joule Heating Derived From Global Maps of Field‐Aligned Currents
Authors: Robinson R. M. , Zanetti L. J. 
Published: February 2021

AbstractWe calculate auroral energy flux and Joule heating in the high‐latitude ionosphere for 27 geomagnetically active days using two‐dimensional maps of field‐aligned currents determined by the Active Magnetosphere and Planetary Response Experiment. The energy input to the ionosphere due to Joule heating increases more rapidly with geomagnetic activity than that due to precipitating particles. The energy flux varies more smoothly with time than Joule heating, which is impulsive in nature on time scales from minutes to tens of minutes. These impulsive events correlate well with recoveries in the Sym‐H index, with the maximum correlation when compared to Sym‐H recoveries 70 min later. Because of prior studies that have associated transient recoveries of Sym‐H with substorm expansions, the delay found here suggests that dissipation of energy in the ionosphere occurs during the substorm growth phase prior to the release of magnetic energy caused by diversion of tail currents.
Lower Surface Temperature at Bright Ephemeral Feature Site on Titan's North Pole
Authors: Dhingra Rajani D. , Jennings Donald E. , Barnes Jason W. , Cottini Valeria 
Published: February 2021

AbstractWe report a temperature difference in one of the regions on Titan that is, documented as a bright ephemeral feature (BEF). Spectra were recorded by Cassini's Composite Infrared Spectrometer. BEFs are 5 µm bright areas that appear, disappear, and shift from flyby to flyby at Titan's North Pole observed in Visual and Infrared Mapping Spectrometer (VIMS) data. They are inferred to be broad‐specular reflections caused by a smooth surface on Titan or a near surface fog—both of which indicate that the atmosphere interacted with the surface. We used 24 spectra for “on the BEF” and 51 spectra for “off the BEF” region to determine the temperature difference during the T121 flyby (July 25, 2016). At the 410–560 cm−1 window where surface emissions are perceptible we see a decrease in temperature by 1.2 ± 0.2 K. This decrease in temperature might indicate precipitative cooling after a fresh rainfall on Titan's land/sea surface.
Seismic and Aseismic Fault Slip During the Initiation Phase of the 2017 MW = 6.9 Valparaíso Earthquake
Authors: Caballero Emmanuel , Chounet Agnès , Duputel Zacharie , Jara Jorge , Twardzik Cedric , Jolivet Romain 
Published: February 2021

AbstractTransient deformation associated with foreshocks activity has been observed before large earthquakes, suggesting the occurrence of a detectable preseismic slow slip during the initiation phase. A critical issue consists in discriminating the relative contributions from seismic and aseismic fault slip during the preparation phase of large earthquakes. We focus on the April–May 2017 Valparaíso earthquake sequence, which involved a MW = 6.9 earthquake preceded by intense foreshock activity. To assess the relative contribution of seismic and aseismic slip, we compare surface displacement predicted from foreshocks source models with transient motion measured prior to the mainshock. The comparison between observed and predicted displacements shows that only half of the total displacement can be explained by the contribution of foreshocks. This result suggests the presence of aseismic pre‐slip during an initiation phase preceding the mainshock.
PrecipGAN: Merging Microwave and Infrared Data for Satellite Precipitation Estimation Using Generative Adversarial Network
Authors: Wang Cunguang , Tang Guoqiang , Gentine Pierre 
Published: February 2021

AbstractGlobal satellite precipitation estimation at high spatiotemporal resolutions is crucial for hydrological and meteorological applications but is still a challenging task. One major challenge is that the microwave data are discontinuous in space and time. We present a novel approach to merge incomplete passive microwave (PMW) precipitation estimates using the conditional information provided by complete infrared (IR) precipitation estimates based on the generative adversarial network (GAN), and name the algorithm PrecipGAN. PrecipGAN decomposes the precipitation system into content and evolution subspaces to propagate PMW estimates to regions outside the orbit coverage of PMW sensors. PrecipGAN can skillfully simulate the spatiotemporal changes of precipitation events, and produce precipitation estimates with overall better statistical performance than the baseline product Integrated MultisatellitE Retrievals for GPM (IMERG) Uncalibrated over the Continental US. PrecipGAN provides an alternative of accurate and computationally efficient algorithm that can be implemented globally to produce satellite‐based precipitation estimates.
Optimization of Radial Diffusion Coefficients for the Proton Radiation Belt During the CRRES Era
Authors: Lozinski Alexander R. , Horne Richard B. , Glauert Sarah A. , Del Zanna Giulio , Albert Jay M. 
Published: February 2021

AbstractProton flux measurements from the Proton Telescope instrument aboard the CRRES satellite are revisited, and used to drive a radial diffusion model of the inner proton belt at 1.1 ≤ L ≤ 1.65. Our model utilizes a physics‐based evaluation of the cosmic ray albedo neutron decay (CRAND) source, and coulomb collisional loss is driven by a drift averaged density model combining results from the International Reference Ionosphere, NRLMSIS‐00 atmosphere and Radio Plasma Imager plasmasphere models, parameterized by solar activity and season. We drive our model using time‐averaged data at L = 1.65 to calculate steady state profiles of equatorial phase space density, and optimize our choice of radial diffusion coefficients based on four defining parameters to minimize the difference between model and data. This is first performed for a quiet period when the belt can be assumed to represent steady state. Additionally, we investigate fitting steady state solutions to time averages taken during active periods where the data exhibits limited deviation from steady state, demonstrated by CRRES measurements following the March 24, 1991 storm. We also discuss a way to make the optimization process more reliable by excluding periods of variability in plasmaspheric density from any time average. Lastly, we compare our resultant diffusion coefficients to those derived via a similar process in previous work, and diffusion coefficients derived for electrons from ground and in situ observations. We find that higher diffusion coefficients are derived compared with previous work, and suggest more work is required to derive proton diffusion coefficients for different geomagnetic activity levels.
A Case Study of Transversely Heated Low‐Energy Helium Ions by EMIC Waves in the Plasmasphere
Authors: Kim Khan‐Hyuk , Kwon Hyuck‐Jin , Lee Junhyun , Jin Ho , Seough Jungjoon 
Published: February 2021

AbstractThe Van Allen Probe A spacecraft observed strong ∼0.5‐Hz helium (He+) band and weak ∼0.8‐Hz hydrogen (H+) band EMIC waves on April 17, 2018, at L = ∼4.5–5.2, in the dawn sector, near the magnetic equator, and close to the plasmapause. We examined low‐energy ion fluxes observed by the Helium Oxygen Proton and Electron (HOPE) instrument onboard Van Allen Probe A during the wave interval and found that low‐energy He+ flux (<10 eV) enhancements occur nearly simultaneously with He‐band and H‐band EMIC wave power enhancements in a direction mostly perpendicular to the background magnetic field without significant low‐energy H+ and O+ flux variations. We suggest that cold He+ ions (<1 eV) are preferentially and transversely heated up 10 eV through the interaction with EMIC waves inside the plasmasphere. The low‐Earth orbit spacecraft observed localized precipitations of energetic protons in the upper ionosphere at subauroral latitudes near the magnetic field footprint of Van Allen Probe A. Our observations provide a clear evidence that EMIC waves play an important role in the overall dynamics in the inner magnetosphere, contributing to the high‐energy particle loss and low‐energy particle energization.
Determining the Temporal and Spatial Coherence of Plasmaspheric Hiss Waves in the Magnetosphere
Authors: Zhang Shuai , Rae I. Jonathan , Watt Clare E. J. , Degeling Alexander W. , Tian Anmin , Shi Quanqi , Shen Xiao‐Chen , Smith Andy W. , Wang Mengmeng 
Published: February 2021

AbstractPlasmaspheric hiss is one of the most important plasma waves in the Earth's magnetosphere to contribute to radiation belt dynamics by pitch‐angle scattering energetic electrons via wave‐particle interactions. There is growing evidence that the temporal and spatial variability of wave‐particle interactions are important factors in the construction of diffusion‐based models of the radiation belts. Hiss amplitudes are thought to be coherent across large distances and on long timescales inside the plasmapause, which means that hiss can act on radiation belt electrons throughout their drift trajectories for many hours. In this study, we investigate both the spatial and temporal coherence of plasmaspheric hiss between the two Van Allen Probes from November 2012 to July 2019. We find ∼3,264 events where we can determine the correlation of wave amplitudes as a function of both spatial distance and time lag in order to study the spatial and temporal coherence of plasmaspheric hiss. The statistical results show that both the spatial and temporal correlation of plasmaspheric hiss decrease with increasing L‐shell, and become incoherent at L > ∼4.5. Inside of L = ∼4.5, we find that hiss is coherent to within a spatial extent of up to ∼1,500 km and a time lag up to ∼10 min. We find that the spatial and temporal coherence of plasmaspheric hiss does not depend strongly on the geomagnetic index (AL*) or magnetic local time. We discuss the ramifications of our results with relevance to understanding the global characteristics of plasmaspheric hiss waves and their role in radiation belt dynamics.
A Bayesian Method for Real‐Time Earthquake Location Using Multiparameter Data
Authors: Zollo Aldo , Caruso Alessandro , De Landro Grazia , Colombelli Simona , Elia Luca 
Published: February 2021

AbstractA primary task of a network‐based, earthquake early warning system is the prompt event detection and location, needed to assess the magnitude of the event and its potential damage through the predicted peak ground shaking amplitude using empirical attenuation relationships. Most of real‐time, automatic earthquake location methods ground on the progressive measurement of the first P‐wave arrival time at stations located at increasing distances from the source but recent approaches showed the feasibility to improve the accuracy and rapidity of the earthquake location by using the additional information carried by the P‐wave polarization or amplitude, especially with unfavorable seismic network lay‐outs.Here, we propose an evolutionary, Bayesian method for the real‐time earthquake location which combines the information derived from the differential P‐wave arrival times, amplitude ratios and back‐azimuths measured at a minimum of two stations. As more distant stations record the P‐wave, the posterior pdf is updated and new earthquake location parameters are determined along with their uncertainty. To validate the location method, we performed a retrospective analysis of mainshocks (M > 4.5) occurred during the 2016–2017 Central Italy earthquake sequence by simulating the typical acquisition layouts of in‐land, coastal and linear array of stations.Results show that with the combined use of the three parameters, 2–4 s after the first P‐wave detection, the method converges to stable and accurate determinations of epicentral coordinates and depth even with a nonoptimal coverage of stations. The proposed methodology can be generalized and adapted to the off‐line analysis of seismic records collected by standard local networks.
On the Detection Capabilities of Underwater Distributed Acoustic Sensing
Authors: Lior Itzhak , Sladen Anthony , Rivet Diane , Ampuero Jean‐Paul , Hello Yann , Becerril Carlos , Martins Hugo F. , Lamare Patrick , Jestin Camille , Tsagkli Stavroula , Markou Christos 
Published: February 2021

AbstractThe novel technique of distributed acoustic sensing (DAS) holds great potential for underwater seismology by transforming standard telecommunication cables, such as those currently traversing various regions of the world’s oceans, into dense arrays of seismo‐acoustic sensors. To harness these measurements for seismic monitoring, the ability to record transient ground deformations is investigated by analyzing ambient noise, earthquakes, and their associated phase velocities, on DAS records from three dark fibers in the Mediterranean Sea. Recording quality varies dramatically along the fibers and is strongly correlated with the bathymetry and the apparent phase velocities of recorded waves. Apparent velocities are determined for several well‐recorded earthquakes and used to convert DAS S‐wave strain spectra to ground motion spectra. Excellent agreement is found between the spectra of nearby underwater and on‐land seismometers and DAS converted spectra, when the latter are corrected for site effects. Apparent velocities greatly affect the ability to detect seismic deformations: for the same ground motions, slower waves induce higher strains and thus are more favorably detected than fast waves. The effect of apparent velocity on the ability to detect seismic phases, quantified by expected signal‐to‐noise ratios, is investigated by comparing signal amplitudes predicted by an earthquake model to recorded noise levels. DAS detection capabilities on underwater fibers are found to be similar to those of nearby broadband sensors, and superior to those of on‐land fiber segments, owing to lower velocities at the ocean‐bottom. The results demonstrate the great potential of underwater DAS for seismic monitoring and earthquake early warning.
Dynamic Evolution of Induced Subduction Through the Inversion of Spreading Ridges
Authors: Qing Jiarong , Liao Jie , Li Lun , Gao Rui 
Published: February 2021

AbstractLithospheric weakness is essential in subduction initiation. Spreading ridges are divergent plate boundaries which may represent lithospheric weakness and promote subduction initiation. Natural examples of ridge‐inversed subduction along spreading ridges have been proposed (e.g., the Proto‐South China Sea subduction). Although, the dynamic evolution of ridge‐inversed subduction has been investigated by geodynamical numerical modeling previously, it remains obscure, especially the influence of the thermal state and geometries of spreading ridges on subduction initiation and dynamic evolution. We establish two‐dimensional thermomechanical coupled numerical models to simulate the dynamic evolution of forced subduction along spreading ridges, and quantify the influence of four major parameters on subduction development (i.e., the spreading rate and cooling age of spreading ridges, forced convergence rate and asymmetric ridge geometry). Our model results suggest the following findings. (1) The cooling age of spreading ridges and the forced convergence rate are the most important parameters controlling ridge‐inversed subduction initiation, and the thresholds of the two parameters are revealed, that is, subduction may easily initiate with a cooling age less than ∼20 Myr and a forced convergence rate lager than ∼4 cm/yr. (2) The spreading rate of ridges prior to forced convergence and asymmetric ridge geometries play a secondary role in subduction development. (3) Ridge‐inversed subduction of the Proto‐South China Sea along the Palawan spreading ridge was proposed geologically, and our numerical modeling results support this scenario.
Seismic Source Tracking With Six Degree‐of‐Freedom Ground Motion Observations
Authors: Yuan Shihao , Gessele Kilian , Gabriel Alice‐Agnes , May Dave A. , Wassermann Joachim , Igel Heiner 
Published: February 2021

AbstractBack azimuth (BAz) information can be determined from combined measurements of rotations and translations at a single site. Such six degree‐of‐freedom (6‐DoF) measurements are reasonably stable in delivering similar information compared to a small‐scale array of three‐component seismometers. Here we investigate whether a 6‐DoF approach is applicable to tracking seismic sources. While common approaches determining the timing and location of energy sources generating seismic waves rely on the information of P‐waves, here we use S‐waves. We track back azimuths of directly arriving SH‐waves in the two‐dimensional case, P‐converted SV‐waves, direct SV‐ and direct SH‐waves in the three‐dimensional case. For data analysis, we compare a cross‐correlation approach using a grid‐search optimization algorithm with a polarization analysis method. We successfully recover the rupture path and rupture velocity with only one station, under the assumption of an approximately known fault location. Using more than one station, rupture imaging in space and time is possible without a priori assumptions. We discuss the effects of rupture directivity, supershear rupture velocity, source‐receiver geometry, wavefield interference, and noise. We verify our approach with the analysis of moving traffic noise sources using 6‐DoF observations. The collocated classic seismometer and newly built ring laser gyroscope ROMY near Munich, Germany, allow us to record high‐fidelity, broadband 6‐DoF (particle velocity and rotational rate) ground motions. We successfully track vehicles and estimate their speed while traveling along a nearby highway using the estimated BAz as a function of time of a single station observation.
Effective Radiative Forcing in a GCM With Fixed Surface Temperatures
Authors: Andrews Timothy , Smith Christopher J. , Myhre Gunnar , Forster Piers M. , Chadwick Robin , Ackerley Duncan 
Published: February 2021

AbstractEffective radiative forcing (ERF) is evaluated in the ACCESS1.0 General Circulation Model (GCM) with fixed land and sea‐surface‐temperatures (SST) as well as sea‐ice. The 4xCO2 ERF is 8.0 W m−2. In contrast, a typical ERF experiment with only fixed SST and sea‐ice gives rise to an ERF of only 7.0 W m−2. This difference arises due to the influence of land warming in the commonly used fixed‐SST ERF experimental design, which results in: (i) increased emission of longwave radiation to space from the land surface (−0.45 W m−2) and troposphere (−0.90 W m−2), (ii) reduced land snow‐cover and albedo (+0.17 W m−2), (iii) increased water‐vapor (+0.49 W m−2), and (iv) a cloud adjustment (−0.26 W m−2) due to reduced stability and cloudiness over land (positive ERF) counteracted by increased lower tropospheric stability and marine cloudiness over oceans (negative ERF). The sum of these radiative adjustments to land warming is to reduce the 4xCO2 ERF in fixed‐SST experiments by ∼1.0 W m−2. CO2 stomatal effects are quantified and found to contribute just over half of the land warming effect and adjustments in the fixed‐SST ERF experimental design in this model. The basic physical mechanisms in response to land warming are confirmed in a solar ERF experiment. We test various methods that have been proposed to account for land warming in fixed‐SST ERFs against our GCM results and discuss their strengths and weaknesses.