bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pore Fluid Pressures and Strength Contrasts Maintain Frontal Fault Activity, Northern Hikurangi Margin, New Zealand
Authors: French Melodie E. , Morgan Julia K. 
Published: October 2020

AbstractDiverse modes of fault slip occur within shallow subduction zones, but their relationships to upper plate deformation are poorly understood. IODP Expedition 375 collected samples and data across the northern Hikurangi margin, where tsunamigenic earthquakes and slow slip events occur. Site U1518 intersected the Pāpaku fault, a splay fault within the frontal accretionary wedge. To constrain in situ physical conditions and strength of the system, we conducted isotropic loading and triaxial compression experiments on hanging wall and foot wall cores and interpreted the results using critical state soil mechanics theory. The hanging wall is relatively strong, reflecting its tectonic history, whereas the foot wall and fault are anomalously weak owing to elevated pore pressure (λ∗ ≥ 0.3). Critical state in both samples corresponds to a friction coefficient of 0.6, constraining the strength of the Pāpaku fault. Low fault strength, maintained by excess pore pressures, suggests that the Pāpaku fault may still be active.
Seasonal and Hemispheric Asymmetries of F Region Polar Cap Plasma Density: Swarm and CHAMP Observations
Authors: Hatch S. M. , Haaland S. , Laundal K. M. , Moretto T. , Yau A. W. , Bjoland L. , Reistad J. P. , Ohma A. , Oksavik K. 
Published: October 2020

AbstractOne of the primary mechanisms of loss of Earth's atmosphere is the persistent “cold” (
20 eV) ion outflow that has been observed in the magnetospheric lobes over large volumes with dimensions of order several Earth radii. As the main source of this cold ion outflow, the polar cap F region ionosphere and conditions within it have a disproportionate influence on these magnetospheric regions. Using 15 years of measurements of plasma density Ne made by the Swarm spacecraft constellation and the Challenging Mini Satellite Payload (CHAMP) spacecraft within the F region of the polar cap above 80° Apex magnetic latitude, we report evidence of several types of seasonal asymmetries in polar cap Ne. Among these, the transition between “winter‐like” and “summer‐like” median polar cap Ne occurs 1 week prior to local spring equinox in the Northern Hemisphere (NH) and 1 week after local spring equinox in the Southern Hemisphere (SH). Thus, the median SH polar cap Ne lags the median NH polar cap Ne by approximately 2 weeks with respect to hemispherically local spring and fall equinox. From interhemispheric comparison of statistical distributions of polar cap plasma density around each equinox and solstice, we find that distributions in the SH are often flatter (i.e., less skewed and kurtotic) than those in the NH. Perhaps of most significance to cold ion outflow, we find no evidence of an F region plasma density counterpart to a previously reported hemispheric asymmetry whereby cold plasma density is higher in the NH magnetospheric lobe than in the SH lobe.
Diverse Slip Behavior of the Banyak Islands Subsegment of the Sunda Megathrust in Sumatra, Indonesia
Authors: Morgan Paul M. , Feng Lujia , Meltzner Aron J. , Mallick Rishav , Hill Emma M. 
Published: October 2020

AbstractNearly every type of slip behavior of which megathrusts are known to be capable of has been observed within a narrow ~75‐km‐wide strip of the Sunda megathrust—the Banyak Islands subsegment. The diverse list of recorded slip events starts with the great 1861 MW ~ 8.5 earthquake and includes the 1907 MW ~ 8.2 shallow tsunami earthquake, the 1966–1981 slow slip event, the great 2005 MW 8.6 Nias‐Simeulue earthquake and associated afterslip, many small (M < 6) to moderate (6 ≤ M < 7) earthquakes, and the large 6 April 2010 MW 7.8 Banyak Islands earthquake. In this paper we map out the spatial and temporal relationships between these slip events to search for a pattern and possible controls on slip behavior. We use GPS and coral geodetic data to derive a coseismic slip distribution for the relatively understudied 2010 event and find that this event fits like a puzzle piece into a low slip patch left by the 2005 event. We compare the recent slip sequence with the historical sequence associated with the 1861 event and find that the modern slip pattern could be a repeat of the historical slip pattern, possibly suggesting the importance of stationary fault properties in controlling slip. The diverse set of slip events mostly fit our expectations within depth‐dependent rupture zones; however, the overlaps between events of different slip types may complicate this conceptual model. Along strike, we suggest that a subducting fracture zone could act to diversify the slip behavior, and we explore possible mechanisms for this slip control.
The Turbulent Structure of the Azores Current System: A Statistical Analysis
Authors: Silva‐Fernandes S. M. , Peliz A. J. 
Published: October 2020

AbstractTwenty‐five years of satellite altimetry Sea Level Anomaly (SLA) and SLA‐derived eddy trajectories are used for a thorough characterization of the Azores Current (AzC) eddies' kinematic properties (i.e., amplitude, radius, and swirl velocity) and evolution above the Mid Atlantic Ridge (MAR) and the Seewarte seamount chain (around 28°W). Changes in the mean flow kinetic energy and eddy kinetic energy (EKE) along the AzC main axis (around 34.2°N) allow to divide its zonal structure into three sectors: The western one, between the MAR and 28°W, the central, until 24°W and the eastern, between 24°W and 20°W. A clear intensification of the western sector is visible in both distribution maps, as well in the median, Skewness, and Kurtosis of the SLA field. Two main patterns of the SLA turbulent field also emerge from the statistical analysis: a meridional asymmetry around the current mean axis and a zonal one. The kinematic properties of the detected eddies clearly demonstrate that cyclones are more intense and non‐linear than anticyclones, mainly in the western region, exhibiting higher values of EKE. High amplitude cyclones reported in several papers of the area (with a time‐mean amplitude above 16 cm) are rarities, with only six cyclones detected in the 25 years of data.
Bathymetric Influences on Antarctic Ice‐Shelf Melt Rates
Authors: Goldberg D. N. , Smith T. A. , Narayanan S. H. K. , Heimbach P. , Morlighem M. 
Published: October 2020

AbstractOcean bathymetry exerts a strong control on ice sheet‐ocean interactions within Antarctic ice‐shelf cavities, where it can limit the access of warm, dense water at depth to the underside of floating ice shelves. However, ocean bathymetry is challenging to measure within or close to ice‐shelf cavities. It remains unclear how uncertainty in existing bathymetry datasets affect simulated sub‐ice‐shelf melt rates. Here we infer linear sensitivities of ice‐shelf melt rates to bathymetric shape with grid‐scale detail by means of the adjoint of an ocean general circulation model. Both idealized and realistic‐geometry experiments of sub‐ice‐shelf cavities in West Antarctica reveal that bathymetry has a strong impact on melt in localized regions such as topographic obstacles to flow. Moreover, response of melt to bathymetric perturbation is found to be non‐monotonic, with deepening leading to either increased or decreased melt depending on location. Our computational approach provides a comprehensive way of identifying regions, where refined knowledge of bathymetry is most impactful, and also where bathymetric errors have relatively little effect on modeled ice sheet‐ocean interactions.
Sea‐Ice Melt Driven by Ice‐Ocean Stresses on the Mesoscale
Authors: Gupta Mukund , Marshall John , Song Hajoon , Campin Jean‐Michel , Meneghello Gianluca 
Published: October 2020

AbstractThe seasonal ice zone around both the Arctic and the Antarctic coasts is typically characterized by warm and salty waters underlying a cold and fresh layer that insulates sea‐ice floating at the surface from vertical heat fluxes. Here, we explore how a mesoscale eddy field rubbing against ice at the surface can, through Ekman‐induced vertical motion, bring warm waters up to the surface and partially melt the ice. We dub this the “Eddy‐Ice‐Pumping” (EIP) mechanism. When sea‐ice is relatively motionless, underlying mesoscale eddies experience a surface drag that generates Ekman upwelling in anticyclones and downwelling in cyclones. An eddy composite analysis of a Southern Ocean eddying channel model, capturing the interaction of the mesoscale with sea‐ice, shows that within the compact ice zone, the mixed layer depth (MLD) is shallow in anticyclones (∼20 m) due to sea‐ice melt and deep in cyclones (∼50–200m) due to brine rejection. “EIP” warms the core of anticyclones without significantly affecting the temperature of cyclones, producing a net upward vertical heat flux that reduces the mean sea‐ice thickness by 10% and shoals the MLD by 60% over the course of winter and spring. In the following months, the sea‐ice thickness recovers with an overshoot, due to strong negative feedbacks associated with atmospheric cooling and salt stratification. Consequently, the effect of “EIP” does not accumulate over the years, but modulates the seasonal cycle of ice within the compact ice zone.
Accurate Estimations of Sea‐Ice Thickness and Elastic Properties From Seismic Noise Recorded With a Minimal Number of Geophones: From Thin Landfast Ice to Thick Pack Ice
Authors: Moreau Ludovic , Weiss Jérôme , Marsan David 
Published: October 2020

AbstractDespite their high potential for accurate sea ice properties estimation, seismic methods are still limited by the difficulty of access and the challenging logistics of polar environments. Conventional seismic methods generally require tens of geophones together with active seismic sources for monitoring applications. While this is not an issue for mainland environment, it is restrictive for sea ice and prevents long‐term monitoring. We introduce a method to estimate sea ice thickness and elastic properties from passive recordings of the ambient seismic field with a minimal number of geophones. In comparison with our previous work (Moreau et al., 2020; https://doi.org/10.1029/2019JC015709) where about 50 sensors were used, the number of geophones is reduced by 1 order of magnitude, thanks to a new strategy of inversion of the passive seismic data. The method combines noise interferometry for estimating the elastic properties, with a Bayesian inversion of the dispersion in the waveforms of icequakes for inferring ice thickness, based on passive recordings from only 3–5 geophones, depending on the signal to noise ratio. We demonstrate its potential both on data recorded on thin landfast ice in Svalbard, and on data recorded on thick pack ice in the Arctic ocean.
Temperature Gradients and Inversions in a Forested Cascade Range Basin: Synoptic‐ to Local‐Scale Controls
Authors: Rupp David E. , Shafer Sarah L. , Daly Christopher , Jones Julia A. , Frey Sarah J. K. 
Published: October 2020

AbstractCold‐air pooling and associated air temperature inversions are important features of mountain landscapes, but incomplete understanding of their controlling factors hinders prediction of how they may mediate potential future climate changes at local scales. We evaluated how topographic and forest canopy effects on insolation and local winds altered the expression of synoptic‐scale meteorological forcing on near‐surface air temperature inversions and how these effects varied by time of day, season, and spatial scale. Using ~13 years of hourly temperature measurements in forest canopy openings and under the forest canopy at the H.J. Andrews Experimental Forest in the western Cascade Range of Oregon (USA), we calculated air temperature gradients at the basin scale (high vs. low elevation) and at the cross‐valley scale for two transects that differed in topography and forest canopy cover. ERA5 and NCEP NCAR R1 reanalysis data were used to evaluate regional‐scale conditions. Basin and cross‐valley temperature inversions were frequent, particularly in winter and often persisted for several days. Nighttime inversions were more frequent at the cross‐valley scale but displayed the same intra‐annual pattern at the basin and regional scales, becoming most frequent in summer. Nighttime temperature gradients at basin and cross‐valley scales responded similarly to regional‐scale controls, particularly free‐air temperature gradients, despite differences in topography and forest cover. In contrast, the intra‐annual pattern of daytime inversions differed between the basin and cross‐valley scales and between the two cross‐valley transects, implying that topographic and canopy effects on insolation and local winds were key controls at these scales.
Near‐Global CFC‐11 Trends as Observed by Atmospheric Infrared Sounder From 2003 to 2018
Authors: Chen Xiuhong , Huang Xianglei , Strow L. Larrabee 
Published: October 2020

AbstractRecent studies have indicated a slowdown of the decline of CFC‐11 concentration since 2012. Ground‐based observations used in such studies have their limitations in terms of global coverage. Here we show that the CFC‐11 time‐varying behaviors can be seen by double differencing nadir‐view, clear‐sky brightness temperatures of four AIRS (Atmospheric Infrared Sounder) channels in an infrared CFC‐11 absorption band. Assuming that CFC‐11 is vertically well mixed through the troposphere, we retrieve CFC‐11 surface concentration and its secular trend using such AIRS observations over the near globe (55°S to 55°N) from January 2003 to December 2018. The retrieved trends of CFC‐11 at the 11 ground sites agree well with the trends derived from in situ measurements at those sites. Our results show that, from 55°S to 55°N, the CFC‐11 trends from January 2003 to December 2012 are all negative, ranging from −2.5 to −1 ppt/year. The trends from January 2003 to December 2018 are less negative by as much as ~0.5–1 ppt/year over the Shandong peninsula, the Arabian Peninsula, and north India and Nepal area, and such differences in the trends are statistically significant. Factors other than the CFC‐11 that can affect the retrievals and trends are also discussed. These findings can help us depict the near‐global spatial distribution of the CFC‐11 trends from 2003 to 2018. The analysis described here has the potential to be used with current and future hyperspectral sounders to help monitor the CFC‐11 from space.
Increased Role of Late Winter Sea Surface Temperature Variability Over Northern Tropical Atlantic in Spring Precipitation Prediction Over Northeast China
Authors: Zhang Mengqi , Sun Jianqi 
Published: October 2020

AbstractThe present study investigates the relationship between the winter North Atlantic sea surface temperature (SST) and spring Northeast China (NEC) precipitation during 1961–2016 from a seasonal prediction aspect. The results show that the February SST variability over the northern tropical Atlantic (NTA) has an enhanced relationship with the spring NEC precipitation after the late 1970s, consequently providing a prediction source for the spring NEC precipitation during the period. Such an interdecadal change in the relationship between February NTA SST and spring NEC precipitation is associated with the interdecadal change in the tropical SST around the late 1970s. The NTA SST exhibits good persistence from late winter to spring. Under the warmer SST background after the late 1970s, the NTA SST is related to more active tropical convection and diabatic heating anomalies in spring, consequently leading to an enhanced connection between the NTA SST and atmospheric circulations over the middle‐to‐high latitude North Atlantic during the period. Anomalous atmospheric circulations over the North Atlantic can further excite Rossby wave train that propagates eastward to East Asia, consequently influencing the moisture and dynamic conditions over NEC. Through the aforementioned physical processes, the NTA SST variability can lead to anomalous precipitation over NEC. The physical processes linking the NTA SST anomalies and spring NEC precipitation are further confirmed by an atmospheric general circulation model experiment forced with idealized NTA warming. The 1‐month lead information of the NTA SST provides a prediction source for spring precipitation over NEC, which has potential usage in operational forecasting.
Effects of the Largest Lake of the Tibetan Plateau on the Regional Climate
Authors: Su Dongsheng , Wen Lijuan , Gao Xiaoqing , Leppäranta Matti , Song Xingyu , Shi Qianqian , Kirillin Georgiy 
Published: October 2020

AbstractQinghai Lake is the largest lake in China. However, its influence on the local climate remains poorly understood. By using an atmosphere‐lake coupled model, we investigated the impact of the lake on the local climate. After the adjustment of four key parameters, the model reasonably reproduced the lake‐air interaction. Superimposed by the orographic effects on lake‐land breeze circulation, the presence of the lake enhanced precipitation over the southern part of the lake and its adjacent land, while slightly reduced precipitation along the northern shore of the lake. The lake effect on local precipitation revealed a distinct seasonal and diurnal variability, reducing precipitation in May (−6.6%) and June (−4.5%) and increasing it from July (5.7%) to November (125.6%). During the open water season, the lake's daytime cooling effect weakened and the nighttime warming effect strengthened, affecting spatial distribution and intensity of lake‐induced precipitation. In early summer, precipitation slightly decreased over the north part of the lake due to the lake's daytime cooling. In turn, lake‐induced nighttime warming increased precipitation over the southern section of the lake and its adjacent land. With the start of the autumn cooling in September, heat and moisture fluxes from the lake resulted in precipitation increase in both daytime and nighttime over the entire lake. In October, the background atmospheric circulation coupled with the strong lake effects lead to a small amount but high proportion of lake‐induced precipitation spreading evenly over the lake.
Dingo Gap: Curiosity Went Up a Small Transverse Aeolian Ridge and Came Down a Megaripple
Authors: Zimbelman James R. , Foroutan Marzieh 
Published: October 2020

AbstractRover data can provide important constraints on the possible origin of wind‐related martian features that have been termed “Transverse Aeolian Ridges” (TARs). The large aeolian bedform traversed by Curiosity at Dingo Gap has a planform and albedo similar to members of nearby TAR fields, so that the crossing at Dingo Gap revealed the surface characteristics of a small TAR. Mars Hand Lens Imager images documented 1–2 mm diameter, well‐rounded particles on the Dingo Gap bedform, along with numerous images obtained from the Mastcam, Hazcam, and Navcam science and engineering cameras on the rover. These images confirm that this feature (and, by extension, all small TARs) can be considered a megaripple whose surface is coated by rounded particles that are too large to be set into motion through saltation, but they may be induced to roll (creep) along the surface by the impact of saltating sand grains (a characteristic of megaripples on Earth). The images also confirm that a bimodal wind was present here, a condition that could have contributed to the symmetrical profile of the bedform. The bearing strength at Dingo Gap was better than that of the Purgatory megaripple that trapped Opportunity for several weeks, so that all megaripples should not be automatically presumed to represent a trafficability hazard for a rover.
Inclusion of Building‐Resolving Capabilities Into the FastEddy® GPU‐LES Model Using an Immersed Body Force Method
Authors: Muñoz‐Esparza Domingo , Sauer Jeremy A. , Shin Hyeyum Hailey , Sharman Robert , Kosović Branko , Meech Scott , García‐Sánchez Clara , Steiner Matthias , Knievel Jason , Pinto James , Swerdlin Scott 
Published: October 2020

AbstractAs a first step toward achieving full physics urban weather simulation capabilities within the resident‐GPU large‐eddy simulation (LES) FastEddy® model, we have implemented and verified/validated a method for explicit representation of building effects. Herein, we extend the immersed body force method (IBFM) from Chan and Leach (2007, https://doi.org/10.1175/2006JAMC1321.1) to (i) be scale independent and (ii) control building surface temperatures. Through a specific drag‐like term in the momentum equations, the IBFM is able to enforce essentially zero velocities within the buildings, in turn resulting in a no‐slip boundary condition at the building walls. In addition, we propose similar forcing terms in the energy and mass conservation equations that allow an accurate prescription of the building temperature. The extended IBFM is computationally efficient and has the potential to be coupled to building energy models. The IBFM exhibits excellent agreement with laboratory experiments of an array of staggered cubes at a grid spacing of
mm, demonstrating the applicability of the method beyond the atmospheric scale. In addition, the IBFM is validated at atmospheric scale through simulations of downtown Oklahoma City (
m) using data collected during the Joint Urban 2003 (JU03) field campaign. Our LES IBFM results for mean wind speed, turbulence kinetic energy, and SF6 transport and dispersion compare well to observations and produce turbulence spectra that are in good agreement with sonic anemometer data. Statistical performance metrics for the JU03 simulations are within the range of other LES models in the literature.
Tectonic Switching of the Trans‐North China Orogen in the Middle Paleoproterozoic: Insights From Mafic Magmatism in the Lüliang Complex
Authors: Liu Chaohui , Zhao Guochun , Liu Fulai , Xu Wang 
Published: October 2020

AbstractRecognition of tectonic switching is of great significance for understanding the formation and evolution of ancient accretionary orogens. In this study, whole‐rock geochemical and Sm‐Nd isotopic and zircon U‐Pb, Lu‐Hf isotopic, and trace element data are reported for two generations of metamorphosed mafic rocks from the Lüliang Complex, middle Trans‐North China Orogen. Although both episodes of mafic magmatism were derived from variable degrees of interaction between a subcontinental lithospheric mantle and slab‐derived hydrous fluids and melts, the younger ones (2.09–2.06 Ga) had higher whole‐rock εNd(t) and zircon εHf(t) values, higher (Ta/La)N ratios, and weaker Nb, Ta, and Ti anomalies in the primitive mantle‐normalized trace element diagram compared with the older ones (2.18–2.15 Ga), implying a less‐enriched mantle source and subdued subduction features. More importantly, a decrease of U/Yb and Ce/Ce* ratios of magmatic zircons and whole‐rocks V/Ti ratios from the older to younger ones implied less slab‐derived fluid addition, and a decrease of whole‐rock (Sm/Yb)N and Hf/Lu ratios suggests decreasing pressure of melt extraction and so lithosphere thickness. In consideration of other tectonothermal activity and paleogeography observed from the middle Trans‐North China Orogen, we propose a tectonic switching model to explain the middle to late Paleoproterozoic tectonic evolution caused by early subduction hinge retreat to later advance and ultimately continental collision.