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, Fanyi Zhang, Xiaofeng Zhang, , Zuosheng Yang, Bing Yuan,
Water Resources Research; https://doi.org/10.1029/2021wr030370

Abstract:
As a key component of global change, dam-induced sediment reduction occurs in large rivers worldwide, which has profound implications on the fluvial systems. However, the systematic change of suspended sediment concentration (SSC) and its dynamic processes are not well known. We summarize typical SSC changes and propose a new sediment modelling framework for heavily dammed fluvial systems with the Changjiang (Yangtze River) as a background. We find that the fluvial SSC has declined by an order of magnitude, i.e., from ∼1.0 to ∼0.1 kg/m3, and even to ∼0.01 kg/m3 locally. The SSC distribution pattern along the mainstream has changed remarkably, with the sediment source/sink being partially reversed. Downstream of the Three Gorges Dam, the SSC recovery capacity gradually decreases with the sediment erosion quantity accumulated over time, and the SSC contribution rate of a linked large lake (Dongting) will change from negative (ca. -39%) to positive (ca. 17%), in the coming decades.
Journal of Geophysical Research: Space Physics; https://doi.org/10.1029/2021ja029304

Abstract:
In steady state, magnetic flux conservation must be maintained in Saturn’s magnetosphere. The Enceladus plumes add mass to magnetic flux tubes in the inner magnetosphere, and centrifugal force pulls the mass-loaded flux tubes outward. Those flux tubes are carried outward to the magnetotail where they deposit their mass and return to the mass loading region. It may take days for the magnetic flux to be carried outward to the tail, but the return of the nearly empty flux tubes can last only several hours, with speeds of inward motion around 200km/s. Using time sequences of Cassini particle count rate, the difference in curvature drift and gradient drift is accounted for to determine the return speed, age and starting dipole L-shell of return flux tubes. Determination of this flux-return process improves our understanding of the magnetic flux circulation at Saturn, and provides insight into how other giant planets remove the mass added by their moons.
Juan Zhao, , Thomas A. Jones, Junjun Hu
Journal of Advances in Modeling Earth Systems, Volume 13; https://doi.org/10.1029/2021ms002486

Abstract:
Building on the results from the observing system simulation experiments (OSSEs) in Part I, this study investigates the impact of assimilating Geostationary Operational Environmental Satellites – 16 (GOES-16) derived Atmospheric Motion Vector (AMV) data on the convective scale numerical weather prediction (NWP) by using the National Severe Storms Laboratory (NSSL) three-dimensional variational (3DVAR) data assimilation (DA) system. The benefit of the AMV DA for short-term severe weather forecast is assessed with three high-impact weather events that occurred in spring 2018 and 2019 over the Great Plains of the United States. The results show that the wind and equivalent potential temperature fields associated with the storm environment and the nearby ongoing convection are improved by the AMV DA, which yields better simulation of the boundaries and the subsequent forecasts of storm evolution. For the quasi-linear or mesoscale convective system, the assimilation of AMVs has a positive impact on the 0–3 h forecasts of composite reflectivity and accumulated precipitation in terms of the shape, location, and magnitude. However, the AMV DA has difficulty in capturing the sharp moisture gradient associated with the dryline and mostly underpredicts the associated scattered storms.
, I.B. Fournier, , , , , J.B. Cotner, , S.E. Hampton, N.R. Lottig, et al.
Journal of Geophysical Research: Biogeosciences; https://doi.org/10.1029/2020jg006165

Abstract:
Millions of lakes worldwide are distributed at latitudes or elevations resulting in the formation of lake ice during winter. Lake ice affects the transfer of energy, heat, light, and material between lakes and their surroundings creating an environment dramatically different from open-water conditions. While this fundamental restructuring leads to distinct gradients in ions, dissolved gases, and nutrients throughout the water column, surprisingly little is known about the resulting effects on ecosystem processes and food webs, highlighting the lack of a general limnological framework that characterizes the structure and function of lakes under a gradient of ice cover. Drawing from the literature and three novel case studies, we present the Lake Ice Continuum Concept (LICC) as a model for understanding how key aspects of the physical, chemical, and ecological structure and function of lakes vary along a continuum of winter climate conditions mediated by ice and snow cover. We examine key differences in energy, redox, and ecological community structure and describe how they vary in response to shifts in physical mixing dynamics and light availability for lakes with ice and snow cover, lakes with clear ice alone, and lakes lacking winter ice altogether. Global change is driving ice covered lakes toward not only warmer annual average temperatures but also reduced, intermittent or no ice cover. The LICC highlights the wide range of responses of lakes to ongoing climate-driven changes in ice cover and serves as a reminder of the need to understand the role of winter in the annual aquatic cycle.
, , V. Bareš
Earth and Space Science; https://doi.org/10.1029/2021ea001911

Abstract:
An empirical model estimating water vapor density from the attenuation of electromagnetic waves at E-band frequencies is proposed and tested on seven months of 5-min attenuation observations from a 4.87-km-long full-duplex E-band commercial microwave link (CML) operating at 73.5 and 83.5 GHz. The model does not require in-situ calibration. Estimated water vapor density is compared to the observations from two meteorological stations located nearby the CML end nodes. Best performance is achieved for the 83.5 GHz sublink (RMSE = 1.46 g m-3, R2 = 0.85) when the actual temperature is used as a model input, in addition to the attenuation data. Use of temperature averaged over the whole evaluation period resulted in significantly worse performance. The study demonstrates the potential of E-band CMLs for measuring near-surface air humidity and the need for careful quality control when upscaling the water vapor monitoring to the entire network of E-band CMLs.
Man Yuan, , Zhuoran Li, , , Bingrong Sun, Hong Wang, Xin Liu, Shenghui Zhou, Lixin Wu
Journal of Advances in Modeling Earth Systems, Volume 13; https://doi.org/10.1029/2021ms002630

Abstract:
Turbulent vertical mixing in the stratified ocean interior has a huge impact on global ocean circulations and the climate system. Although parameterizations of vertical mixing furnished by internal tides have been built into state-of-the-art coupled global climate models (CGCMs), efforts in parameterizing wind-driven vertical mixing in CGCMs are still limited. In this paper, we apply a modified finescale parameterization (MFP) to an eddy-resolving Community Earth System Model (CESM) to represent the wind’s contribution to vertical mixing in the stratified ocean interior. The spatial pattern of the MFP-parameterized wind-driven vertical mixing in the thermocline agrees with the observation derived from the finestructure measurements of Argo floats, reproducing the enhanced values in the Kuroshio, Gulf Stream extensions, and the Southern Ocean where the winds inject great amount of energy into the internal wave field. The MFP also captures the observed seasonal variation of wind-driven vertical mixing in the thermocline of these regions that exhibits enhancement and weakening in winter and summer, respectively. Application of the MFP to a non-eddy-resolving CESM fails to reproduce the observed wind-driven vertical mixing. Specifically, the magnitude of parameterized wind-driven vertical mixing in the thermocline of Kuroshio, Gulf Stream extensions, and the Southern Ocean is systemically smaller than those in the observation and eddy-resolving CESM; so is the case for the amplitude of seasonal cycle. The results highlight the benefit of eddy-resolving CESM compared to its standard-resolution counterpart in parameterizing the wind-driven vertical mixing and provide insight into developing parameterizations for wind-driven vertical mixing in eddy-resolving CGCMs.
Geochemistry, Geophysics, Geosystems, Volume 22; https://doi.org/10.1029/2021gc009949

Abstract:
Focused fluid flow is common in sedimentary basins worldwide, where flow structures often penetrate through sandy reservoir rocks, tight shales, and clay-rich caprocks. To better understand the mechanisms forming such structures, the impacts of the viscoelastic deformation and strongly nonlinear porosity-dependent permeability of clay-rich materials are assessed from an experimental and numerical modeling perspective. The experimental methods to measure the poroviscoelastic and transport properties of intact and remolded shale have been developed, and the experimental data is used to constrain the numerical simulations. It is demonstrated that viscoelastic deformation combined with nonlinear porosity-dependent permeability triggers the development of localized flow channels, often imaged as seismic chimneys. The permeability inside a channel increases by several orders of magnitude compared to the background values. In addition, the propagation time scale and the channel size strongly depend on the material properties of the fluid and the rock. The time-dependent behavior of the clay-rich rock may play a key role in the long-term integrity of the subsurface formations.
Weibin Song, Xuping Feng, Gaoxiong Wu, Gongheng Zhang, Ying Liu,
Journal of Geophysical Research: Solid Earth; https://doi.org/10.1029/2021jb022027

Abstract:
Ambient seismic noise cross-correlation has been widely applied in surface wave tomography at regional to global scales, including for seismic exploration of near-surface structures. Reliable seismic imaging requires the accurate selection of dispersion curves. However, manual picking has become cumbersome work with the increase in available correlation traces; it is even more difficult when the number of dispersion curves increases by using frequency-Bessel (F-J) transform. Here, we show that the neural network Res-Unet++ can automatically and accurately extract both fundamental dispersion curves and overtones from the F-J dispersion spectra after training the network. Results show that selected dispersion curves had high accuracies in the synthetic data (greater than 95%). The network could effectively extract both the fundamental and higher modes in real data, and transfer learning improved the adaptability of neural networks for different geological areas. The obtained dispersion curves from the real data agreed well with those acquired manually and were advantageous for generating more effective dispersion points.
, D. A. Paton, E. J. Mortimer
Geochemistry, Geophysics, Geosystems; https://doi.org/10.1029/2021gc009897

Abstract:
The open availability of global scientific databases is key to advancing research of the Earth system and facilitating cross-disciplinary studies. There are numerous datasets available for investigating tectonics, but none that provide an internally consistent representation of the structural framework, crustal architecture, and geodynamics. We present Reclus, a suite of global, integrated databases that fill this gap, thereby providing the community with the key components for investigating the Earth system. Reclus includes databases of the following: (1) structural elements, which define the three-dimensional geometry of the rock volume, including folds and faults; (2) 'crustal' facies describing the geometry and composition/rheology of the lithosphere; (3) igneous features; and (4) geodynamics, representing the dominant thermo-mechanical processes acting on the lithosphere. These databases and workflows are applied to East Africa to investigate the geometry and heterogeneity of the margin and its hinterland. This margin is often summarized in the literature as a 'transform margin,' represented by a single structural feature, the ‘Davie Fracture Zone,’ but it is much more complicated. We show how the pre-existing structure, the superimposition of successive tectonic cycles, and crustal heterogeneity dictate the complexity observed.
, Mark J. Engebretson, , Erik S. Steinmetz, , Martin G. Connors, , , , , et al.
Journal of Geophysical Research: Space Physics; https://doi.org/10.1029/2021ja029839

Abstract:
Large changes of the magnetic field associated with magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5–10 min duration have been frequently observed within a few hours of midnight. This study compares the statistical location of nighttime MPEs with |dB/dt| ≥ 6 nT/s within the auroral current system observed during 2015 and 2017 at two stations, Cape Dorset and Kuujjuarapik, in Eastern Canada. Maps of the two dimensional nightside auroral current system were derived using the Spherical Elementary Current Systems (SECS) technique. Analyses were produced at each station for all events, and for premidnight and postmidnight subsets. We examine four MPE intervals in detail, two accompanied by auroral images, and show the varying associations between MPEs and overhead ionospheric current systems including electrojets and the field-aligned like currents. We find 225 of 279 MPEs occurred within the westward electrojet and only 3 within the eastward electrojet. For the premidnight MPEs 100 of 230 events occurred within the Harang current system while many of the remainder occurred within either the downward region 1 current system or the upward region 2 current system. Many of the 49 postmidnight MPEs occurred in either the downward region 1 (11 events) or upward region 2 current system (27 events). These result suggest that the source of MPEs in the premidnight sector is somewhere between the inner to mid plasma sheet and the source for the MPEs in the postmidnight sector is somewhere between the inner magnetosphere and the inner plasma sheet.
Andrés Barajas, , , Ludovic Margerin, Michel Campillo
Geochemistry, Geophysics, Geosystems; https://doi.org/10.1029/2021gc009742

Abstract:
Velocity variations obtained from ambient seismic noise are sensitive to many factors. We aimed to disentangle these processes in a 10-year-long recording of seismic noise from a single station in the Pollino region, in southern Italy. This region is characterized by aquifers and by a relatively short period of high seismic activity that included slow slip events and a earthquake that occurred on October 25, 2012. We apply two models that estimate the water level inside an aquifer, which show a good correlation with the measured , showing that the velocity variations are inversely proportional to the pore pressure inside the aquifer. Our interpretation is further confirmed by geodetic measurements that show that in a direction parallel to the strike angle of the fault rupture, the expansion-contraction displacement of the zone follows the same patterns observed in the models and in the velocity variations, as a result of the pressure generated by the water on its interior. Going one step further, we analyze the nature of the small discrepancies between the measured and modeled velocity variations. These correlate well with the rainfall and with the vertical geodetic measures, which indicates an elastic response of the zone to the loading generated by the rainwater. Comparisons between these variables allow us to clearly identify the period of the seismic activity in the zone, which is represented by the characteristic drop in the seismic velocity in the period from the beginning of 2012 to mid-2013.
Charles Owolabi, Haibing Ruan, , Jinfeng Li, , A. V. Eyelade, Shishir Priyadarshi, Akimasa Yoshikawa
Published: 23 October 2021
Abstract:
Given the potential importance of solar quiet (Sq) ionospheric current for geomagnetic field modeling, it is vital to obtain accurate parameters characterizing its variations, particularly the spatial and temporal variations. In this paper, we derived the Sq current function based on the spherical harmonic analysis (SHA) technique using a 14-year (2006-2019) quiet geomagnetic field record over the American sector. The empirical orthogonal function (EOF) analysis was then applied to deduce temporal and spatial variations of the Sq current. It is observed that the first EOF of the Sq current function is dominated by solar activity, while the second and third EOFs exhibit annual and semiannual variations, respectively. Also, the Artificial Neural Network (ANN) model of Sq current function was constructed to validate the EOF model predictions. While the Sq current intensity predicted by the ANN model is underestimated by 2.83%, the EOF model underpredicted the Sq current intensity by 1.92% relative to the observation. The root mean square error (RMSE) of the EOF model is 0.64 kA, this RMSE is about 79% smaller than the ANN model. In addition, both the EOF and ANN models capture the variation of the total Sq current () intensity with respect to solar activity. In principle, the EOF model had an optimal performance at nearly 98% accuracy, with the ANN model exhibiting almost the same degree of accuracy, which appears to be a reference point for ionospheric conditions when looking for space weather applications.
, Male Köster, , , Florence Schubotz, , Stephen A. Bowden, ,
Geochemistry, Geophysics, Geosystems, Volume 22; https://doi.org/10.1029/2021gc010133

Abstract:
Diagenesis can have a major impact on sedimentary mineralogy. Primary magnetic mineral assemblages can be modified significantly by dissolution or by formation of new magnetic minerals during early or late diagenesis. At International Ocean Discovery Program Site C0023, which was drilled in the protothrust zone of the Nankai Trough during Expedition 370, offshore of Shikoku Island, Japan, non-steady state conditions have produced a complex sequence of magnetic overprints. Detailed rock magnetic measurements, which characterize magnetic mineral assemblages in terms of abundance, grain size, and composition, were conducted to assess magnetic mineral alteration and diagenetic overprinting. Four magnetic zones (MZs) are identified down-core from ∼200 to 1100 meters below sea floor based on rock magnetic variations. MZ 1 is a high magnetic intensity zone that contains ferrimagnetic greigite, which formed at shallow depths and is preserved because of rapid sedimentation. MZs 2 and 4 are low magnetic intensity zones with fewer magnetic minerals, mainly coarse-grained (titano-)magnetite and hematite. This magnetic mineral assemblage is a remnant of a more complex assemblage that was altered diagenetically a few million years after deposition when the site entered the Nankai Trough. MZ 3 is a high magnetic intensity zone between MZs 2 and 4. It contains authigenic single-domain magnetic particles that probably formed from fluids that circulated through faults in the accretionary prism. Varying sediment supply and organic matter input through time, burial temperature, and tectonic fluid circulation are the primary drivers of magnetic mineral assemblage variations.
Paleoceanography and Paleoclimatology, Volume 36; https://doi.org/10.1029/2021pa004289

Abstract:
The Mediterranean Sea is particularly sensitive to climate oscillations and represents a key location to study past climatic and oceanographic changes. One valuable source of paleoceanographic information is through molecular biomarkers in deep sea sediments. This approach has been applied in a number of studies in this basin, but only covering the most recent glacial/interglacial cycles. Here we present, for the first time in the Mediterranean Sea, a molecular biomarker record from the Strait of Sicily that covers the last million years until the present, almost continuously. We present data on alkenone derived index sea surface temperatures (SST) and provide insights on the evolution of the phytoplankton community composition and terrestrial inputs through the analysis of the concentrations of alkenones, brassicasterol and long-chain alcohols. The -SST record followed a climatic evolution modulated by glacial/interglacial cycles with a marked increase in the 100 kyr-amplitude of the glacial cycles at ∼430 ka, coincident with the Mid-Brunhes transition. In addition, SSTs were consistently higher compared with other records in the western Mediterranean, indicative of the progressive warming that surface waters experience along their transit from the Strait of Gibraltar to the Central Mediterranean. Regarding the concentrations of alkenones and brassicasterol, they displayed distinct alternate peaks, some of them coeval with the deposition of sapropels. This suggests that different environmental and oceanographic conditions characterized each sapropel which, together with changes in terrestrial inputs and the degree of oligotrophy, induced the alternate proliferation of coccolithophores and diatoms.
Ben Qin, Yan Wu, Linlin Cui, Naiqin Wu, Shuisheng Du, , Zhongli Ding
Paleoceanography and Paleoclimatology, Volume 36; https://doi.org/10.1029/2021pa004295

Abstract:
Modern investigations have shown that oxygen and carbon isotopes of land snail shells are useful indicators of climate and vegetation in monsoonal regions. However, stable isotope studies on snail fossil shells has seldom been done, and the reliability of those indicators needs further verification. Moreover, intrashell stable isotope analysis of individual snails is rather scarce, and seasonal variation in the glacial-interglacial monsoonal climate remains unclear. Therefore, we performed δ18O and δ13C analyses on fossil shells of cold-aridiphilous Cathaica pulveratrix and subhumidiphilous Metodontia yantaiensis from the loess section over the last two glacial cycles at the Beiyao site on the southern Chinese Loess Plateau. The δ18O values of fossil shells reflected monsoonal rainfall amounts and more rainfall during MIS3 and MIS7 than during MIS4 and MIS6. Meanwhile, the δ13C values of fossil shells indicated the relative abundance of C3/C4 plants and more C4 biomass during MIS3 and MIS7 than during MIS4 and MIS6. The δ18O and δ13C values of the two species from the same horizon are significantly different, reflecting differences in their growing season and/or physiological habits. Intrashell variations in stable isotopes showed that climatic seasonality was much stronger during the glacial periods than during the interglacials. Our findings provide an environmental background for explaining past human activities at the Beiyao site. The investigation of stone artifacts showed that ancient human activities were relatively strong during MIS3 and MIS7. During these stages, the warm and humid climate with smaller seasonal contrast was favorable for the regional expansion of human activities.
Journal of Geophysical Research: Planets, Volume 126; https://doi.org/10.1029/2020je006808

Abstract:
The brightness temperature of the Venus disk obtained by Longwave Infrared Camera (LIR) on board Akatsuki shows clear limb darkening at low and middle latitudes. The profile of limb brightness reflects the vertical distributions of atmospheric temperature and the optical thickness of cloud particles. Horizontal distributions of brightness temperature obtained by LIR during ∼5.8 Venusian years were analyzed to investigate the vertical structure of the brightness temperature distribution above the cloud tops based on the emission angle dependence of the sensing altitude. Emission angles were converted to sensing altitudes by a radiative transfer calculation with nominal temperature and cloud particle distributions based on past observations. We show a local time-altitude cross section of the brightness temperature deviation above the cloud tops for three latitudinal zones. The derived vertical amplitude distribution of the diurnal and semidiurnal tides above ∼68 km is mostly explained by the classical theory of thermal tides. A semidiurnal tide in which the phase shifts upstream with altitude is clearly seen in the equatorial region. By applying the dispersion relation of the internal gravity wave to the observed wave structure, it was found that the zonally averaged zonal wind velocity at altitudes of 66 to 71 km was approximately the same as the known superrotation velocity. By comparing the observed and simulated vertical phase structures, it is suggested that the tidal wave structure seen in the equatorial cloud tops is an aspect of upward propagation of a gravity wave generated in the upper cloud layer by solar heating.
Journal of Geophysical Research: Oceans, Volume 126; https://doi.org/10.1029/2020jc017043

Abstract:
Current down-scaling numerical modelling system around Hong Kong achieved a considerable prediction skill for the estuarine–shelf circulation off the Pearl River Estuary (PRE) without data assimilation (DA). In order to further improve the reliability of this modelling system, the cost-effective Ensemble optimal interpolation approach is implemented to test the potential benefits from assimilating the cruise temperature and salinity (T/S) profiles to reproduce the variable coast waters. Regarding assimilation parameters (e.g. assimilation window, observation spatiotemporal scales, and ensemble composition), four parallel experiments are conducted in summer 2015. Against the assimilated T/S profiles, the vertical structures of the analyzed T/S are improved by the DA, although the waters experience strong mixing on the shelf. Compared with the run without DA, the root mean square errors of the predicted T/S are generally reduced by 9.8%–23.5% and 4.2%–14.0% in the assimilation runs. The results also show the salinity stratification is improved in the shelf by the assimilation of T/S profiles, although the improvement is sensitive to the selected ensemble and the assimilation window. Further, we investigate the impact of the temporal scales of the river-estuary-shelf waters on the assimilation results by the sampling of the model-state ensemble. The water exchanges between the estuary and the shelf are also better captured through this assimilation. The assimilation impact analysis shows that DA has advantages in reproducing the distribution of water masses of the river-estuary-shelf waters, although the quality of the reproduced water mass distribution is related to the adopted sample ensemble in DA.
Journal of Geophysical Research: Solid Earth, Volume 126; https://doi.org/10.1029/2021jb022322

Abstract:
Seismic anisotropy in the Earth's mantle inferred from seismic observations is usually interpreted in terms of intrinsic anisotropy due to Crystallographic Preferred Orientation (CPO) of minerals, or extrinsic anisotropy due to Shape Preferred Orientation (SPO). The coexistence of both contributions confuses the origins of seismic anisotropy observed in tomographic models. It is thus essential to discriminate CPO from SPO. Homogenization/upscaling theory provides means to achieve this goal. It enables computing the effective elastic properties of a heterogeneous medium, as seen by long-period waves. In this work, we investigate the effects of upscaling an intrinsically-anisotropic and heterogeneous mantle. We show analytically in 1-D that the observed radial anisotropy parameter is approximately the product of the intrinsic and the extrinsic components: This law is verified numerically in the case of a homogenized 2-D marble cake model of the mantle in the presence of CPO obtained from a micro-mechanical model of olivine deformation. Our numerical findings predict that for wavelengths smaller than the scale of deformation patterns, tomography may overestimate intrinsic anisotropy due to significant extrinsic anisotropy. At longer wavelengths, intrinsic anisotropy is always underestimated due to spatial averaging. Therefore, we show that it is imperative to homogenize a CPO model first before drawing comparisons with tomographic models. As a demonstration, we use our composite law with a homogenized CPO model of a plate-driven flow underneath a mid-ocean ridge, to estimate the SPO contribution to an existing tomographic model of radial anisotropy.
, C. B. Connor, P. Wetmore, , L. J. Connor, M. Rodgers,
Journal of Geophysical Research: Solid Earth; https://doi.org/10.1029/2021jb022507

Abstract:
The Blackfoot Reservoir volcanic field (BRVF), Idaho, USA, is a bimodal volcanic field that has hosted silicic eruptions during at least two episodes, as recently as 58 ka. Using newly collected ground and boat-based gravity data, two large negative anomalies ( mGal) are modeled as shallow ( km) intrusions beneath a NE-trending alignment of BRVF rhyolite domes and tuff rings. Given the trade-off between density contrast and model volume, best-fit gravity inversion models yield a total intrusion volume of ; a density contrast of kg results in two intrusions, each km km and about 0.5 km thick, with cumulative volume of 100 . A network of trending faults lies directly above and on the margins of the mapped gravity anomalies. Most of these faults have m throw; one has throw up to m. We suggest that the emplacement of shallow sill-like intrusions produced this fault zone and also created a ENE-trending fault set, indicating widespread ground deformation during intrusion emplacement. The intrusions and silicic domes are located km E of a regional, 20 mGal step in gravity. We interpret this step in gravity as thickening of the Upper Precambrian to lowermost Cambrian quartzites in the Meade thrust sheet, part of the Idaho-Wyoming Thrust Belt. Silicic volcanism in the BRVF is a classic example of volcanotectonic interaction, influenced by regional structure and creating widespread deformation. We suggest volcanic hazard assessments should consider the possibility of large-volume silicic eruptions in the future.
Jiarong Wang, , ,
Journal of Geophysical Research: Atmospheres; https://doi.org/10.1029/2020jd034367

Abstract:
Climate warming on the cryosphere could change catchment precipitation-runoff relation by additional water from glacier melting and more energy absorbed at the ground surface. These changes further alter the physical properties of the catchment. The combined effects of these changes on runoff are analyzed from upstream to downstream of the Yarlung-Zangpo River (YR) basin in southeastern Tibetan Plateau using statistical methods and a modified Budyko equation with consideration of glacier melting. Major results show that in the study period of 1980-2015 there was a jump in the mean annual temperature and precipitation around 1997. Since 1997, accelerated glacier melt and the thaw of permafrost have contributed to a nearly 80.9% increase in surface runoff in the upstream region of the YR basin. Meanwhile, the increase of runoff in the same period in downstream areas of the basin with warm and wet climate is smaller and has been mostly from an increase in annual precipitation. Part of that increase is offset by changes in catchment properties following the warming, such as the increase in vegetation coverage. Results of runoff responses to climate change and catchment properties across different sub-basins in the YR basin and between the two time periods separated in 1997 suggest that continued warming would reduce the buffering effect of glacial and permafrost on runoff in upstream areas of the basin, shortening the runoff response time to precipitation and increasing flood and drought vulnerability of the YR basin.
, , Xueyi Wang, , Xinliang Gao, Huigen Yang
Journal of Geophysical Research: Space Physics; https://doi.org/10.1029/2021ja029729

Abstract:
Recent satellite observations, combined with instability analyses, have shown that the background plasma density variation can modulate the magnetosonic (MS) waves by controlling the wave excitation. However, the detailed modulation process needs to be identified since the MS waves propagate nearly perpendicular to the background magnetic field. In this study, we investigate the MS wave modulation by background plasma density using a 2-D general curvilinear particle-in-cell (PIC) simulation in the meridian plane of a dipole magnetic field. The simulation model consists of three plasma components: the background cold electrons and protons and ring distribution protons. We find that MS waves can be locally generated by ring distribution protons in the low plasma density region, while no MS wave is generated in the high density region. These MS waves are confined near the local source region since they are damped by the background cold plasma. The background protons gain more energy than background electrons, implying the plasmaspheric protons may dominate the modulation of MS waves. Moreover, we have also investigated the generation and propagation of MS waves in the plasmapause density structure. Our simulation results demonstrate that the background plasma density variation can modulate the MS waves and may play an important role in the spatial distribution of MS waves.
Jady Carmichael
Published: 22 October 2021
Abstract:
By reviewing 44 studies, researchers make a scientific case for regulating agricultural pollution of streams and rivers by implementing conservation practices, including riparian buffer zones.
, Mahendra Bhandari, , , Matthew Perks, Deepak Raj Joshi, Sheng Wang, Toby Dogwiler, , , et al.
Water Resources Research; https://doi.org/10.1029/2021wr029925

Abstract:
The hydrologic sciences and water resources management have long depended on a combination of in-situ measurements and remotely-sensed data for research and regulatory purposes. In-situ measurements are constrained in their spatial distribution by both logistics and costs. Satellite- and manned aircraft-based remote sensing provide spatially broad data, but often of a coarse resolution. Furthermore, all these data collection methods are often limited in their ability to respond to specific short-term events when the data and imagery could inform real-time assessment and decision-making, especially during and immediately after natural disasters. Researchers and regulators are increasingly using Unmanned Aerial Vehicles (UAVs) to fill these gaps in both spatial and temporal data resolution. UAVs are often more cost-effective than traditional remote sensing or in-situ data collection methodologies and the availability of new advancements in UAV design, power supply, payload capacity, and sensors has been driving rapid innovations in their use in the hydrological sciences. This in-depth review explores these UAV technologies and how they are being employed for on-demand and cost-effective characterization, monitoring, assessment, and modeling of soil and water resources. Our discussion addresses both key opportunities and challenges in surface water and groundwater studies, land-atmosphere interaction studies, water management in agriculture and forestry, ecosystem monitoring, and hydrological modeling.
Journal of Geophysical Research: Oceans; https://doi.org/10.1029/2020jc017075

Abstract:
El Niño related sea surface temperature (SST) anomalies over the tropical Pacific Ocean impact global climates, but these impacts differ substantially for conventional cold tongue El Niño (CT El Niño) and the central Pacific El Niño (CP El Niño) events. This study is motivated by the need for a better understanding of the recharge/discharge processes associated with these two different flavors of El Niño. Composite analysis based on improved CT and CP El Niño identification methods applied to the Simple Ocean Data Assimilation demonstrates that the recharge/discharge processes are active during CT El Niño events. In contrast, for CP El Niño events, the recharge/discharge processes do not play a significant role. Prior to a CT El Niño, warm water accumulates over the western Pacific due to off-equatorial anticyclonic wind stress curl. The onset of a CT El Niño is closely associated with the formation of a cyclonic atmospheric circulation over the northwest Pacific in the winter and spring, which induces westerly wind anomalies in the equatorial western Pacific and initiates eastward warm water transport. This leads to peak warming in the eastern equatorial Pacific the following winter, followed by the poleward discharge of warm water. This quasi-cyclical behavior provides a measure of predictability. In contrast, the CP El Niño events do not show a precursor subsurface warming signal along the tropical Pacific thermocline. Instead, modest warm SST anomalies appear in boreal summer and peak in the fall, with weak subsurface warming mainly in the fall during CP El Niños. Hence, CP El Niños are less predictable in terms of an equatorial thermocline precursor than CT El Niño events.
, Ken O. Buesseler, , Margaret L. Estapa, Roger P. Kelly,
Global Biogeochemical Cycles, Volume 35; https://doi.org/10.1029/2021gb006985

Abstract:
To better quantify the ocean's biological carbon pump, we resolved the diversity of sinking particles that transport carbon into the ocean's interior, their contribution to carbon export, and their attenuation with depth. Sinking particles collected in sediment trap gel layers from four distinct ocean ecosystems were imaged, measured, and classified. The size and identity of particles was used to model their contribution to particulate organic carbon (POC) flux. Measured POC fluxes were reasonably predicted by particle images. Nine particle types were identified, and most of the compositional variability was driven by the relative contribution of aggregates, long cylindrical fecal pellets, and salp fecal pellets. While particle composition varied across locations and seasons, the entire range of compositions was measured at a single well-observed location in the subarctic North Pacific over one month, across 500 m of depth. The magnitude of POC flux was not consistently associated with a dominant particle class, but particle classes did influence flux attenuation. Long fecal pellets attenuated most rapidly with depth whereas certain other classes attenuated little or not at all with depth. Small particles (<100 μm) consistently contributed ∼5% to total POC flux in samples with higher magnitude fluxes. The relative importance of these small particle classes (spherical mini pellets, short oval fecal pellets, and dense detritus) increased in low flux environments (up to 46% of total POC flux). Imaging approaches that resolve large variations in particle composition across ocean basins, depth, and time will help to better parameterize biological carbon pump models.
Jianfeng Sun, , Jingbo Mao, Junri Zhao, , , Xinke Wang, Huiling Ouyang, Xu Tang, , et al.
Journal of Geophysical Research: Atmospheres, Volume 126; https://doi.org/10.1029/2021jd035139

Abstract:
Secondary inorganic ions are important constituents of PM2.5 that play an important role in global climate change through direct and indirect radiative forcing. To investigate the influence of ship emissions on coastal cities, we launched a cruise ship campaign offshore of the East China Sea (ECS) and two field observation sites in the megacity of Shanghai using one-hour time-resolved water-soluble ion chromatography from June 3rd to June 27th, 2017. Three main secondary inorganic soluble ions in the atmosphere of the ECS, i.e., non-sea-salt sulfate (nss-SO42-), NO3- and NH4+, were 8.87, 4.94 and 4.65 μg·m-3 , respectively. While their values at the Pudong (PD) station in urban Shanghai were 6.33, 9.47 and 4.74 μg·m-3 and at the Dianshanhu (DSH) station in suburban Shanghai were 7.33, 10.01 and 6.78 μg·m-3, respectively. Nss-SO42- was dominant in the PM2.5 in the atmosphere of the ECS (nss-SO42-/NO3- =1.8), and mainly distributed near the Zhoushan Islands of the ECS. This indicated significant contributions from ship emissions. Based on the Community Multiscale Air Quality (CMAQ) model, two main sources of nss-SO42- were identified: emissions and horizontal transport. These comprised over 90% of the nss-SO42-. The influence of ship emissions reached up to 31.6% of the total nss-SO42- alongside the cruise ship and near coastal parking ports in the Yangtze River Delta (YRD) area, suggesting that more attention should be paid to ship emissions.
, R. Leonhardt, R. Egli,
Journal of Geophysical Research: Solid Earth, Volume 126; https://doi.org/10.1029/2021jb022565

Abstract:
Although a large number of magnetic declination and inclination measurements are available for the historical period from 1400 to 1900 CE, even the evolution of the axial dipole moment, the most prominent quantity of the geomagnetic field, is highly disputed for this time interval. Here, a new iterative Bayesian spherical harmonic model is constructed that combines historical (direct) and archeomagnetic or volcanic (indirect) records to better constrain the geomagnetic field evolution over this historical epoch. The resulting geomagnetic field reconstruction (BIGMUDIh.1) benefits from recently published and revised data for critical periods and regions. The highly variable data uncertainties and qualities are tackled with a weighting and selection scheme. Model uncertainties are mainly controlled by selection criteria applied to indirect intensity records, and are estimated using a bootstrapping approach. A major improvement with respect to the established historical model gufm1 consists in the incorporation of archeointensities, which enables a direct estimation of the axial dipole evolution prior to 1840 CE. BIGMUDIh.1 yields a 2 µT (6%) decrease of the axial dipole component between 1500 and 1600 CE, followed by a relatively stable period until 1900 CE. Modeled declinations agree well with historical records and the gufm1 model derived from such records. Furthermore, the evolution of the South Atlantic Anomaly, driven by reverse flux patches (RFPs) at the core-mantle boundary, is outlined. Periods of accelerated movement of the northern magnetic dip pole appear to be connected to the formation and changes of RFPs in the Northern hemisphere.
Journal of Geophysical Research: Solid Earth, Volume 126; https://doi.org/10.1029/2020jb020799

Abstract:
New and published (U-Th)/He data on zircon, apatite and zircon fission track ages constrain the thermal overprint and cooling history of the eastern Aar Massif, Switzerland. The timing and pattern of cooling is in agreement with independent kinematic and age constraints from exposed shear zones. This suggests that the cooling ages mainly reflect exhumation and that long-term exhumation-dynamics were mainly controlled by crustal-scale tectonic processes. Results of a statistical inverse model reveal significant diachrony in the timing of exhumation in the along-strike direction. Maximum exhumation rates (1 mm/yr) were initially located in the central Aar Massif (from 22–10 Ma), then gradually migrated to the east between 10 Ma and present, while the central Aar Massif continued to exhume at slower rates (0.5 mm/yr). The diachrony in the timing of exhumation may be explained by lateral variations in the inherited thickness or the density of the accreted European crust. We attribute the increase in exhumation rates between 2 Ma and present to enhanced glacial erosion. Nevertheless, the post 2 Ma exhumation pattern reflects a continuation of non-cylindrical massif ”growth” in the eastward orogen-parallel direction. This indicates that – although at slow rates – thick-skinned and buoyancy-driven compressional deformation, likely enhanced by the presence of easily erodible flysch units at the surface, might still be ongoing especially in the eastern Aar Massif. Non-cylindrical massif-growth is likely to also affect other External Crystalline Massifs or orogens, but may be overlooked because studies often focus on single orogen-perpendicular transects.
, Rezaul Mahmood, , Clinton Rowe, , Martha Shulski, Sharon Medcalf, Rachel Lookadoo,
Published: 22 October 2021
Abstract:
Heatwaves cause excess mortality and physiological impacts on humans throughout the world, and climate change will intensify and increase the frequency of heat events. Many adaptation and mitigation studies use spatial distribution of highly vulnerable local populations to inform heat reduction and response plans. However, most available heat vulnerability studies focus on urban areas with high heat intensification by Urban Heat Islands (UHIs). Rural areas encompass different environmental and socioeconomic issues that require alternate analyses of vulnerability. We categorized Nebraska census tracts into four urbanization levels, then conducted factor analyses on each group and captured different patterns of socioeconomic vulnerabilities among resultant Heat Vulnerability Indices (HVIs). While disability is the major component of HVI in two urbanized classes, lower education, and races other than white have higher contributions in HVI for the two rural classes. To account for environmental vulnerability of HVI, we considered different land type combinations for each urban class based on their percentage areas and their differences in heat intensifications. Our results demonstrate different combinations of initial variables in heat vulnerability among urban classes of Nebraska and clustering of high and low heat vulnerable areas within the highest urbanized sections. Less urbanized areas show no spatial clustering of HVI. More studies with separation on urbanization level of residence can give insights into different socioeconomic vulnerability patterns in rural and urban areas, while also identifying changes in environmental variables that better capture heat intensification in rural settings.
Jun Liu, , Yanling Wu, Tang Li, ,
Geophysical Research Letters, Volume 48; https://doi.org/10.1029/2021gl094407

Abstract:
In the present research, IOD prediction was explored using statistical methods based on deep learning techniques. First, convolutional neural network (CNN) models were trained using sea-surface-temperature anomaly (SSTA) maps of the Indian Ocean from 1854 to 1989, and the properly trained CNN models were then validated with the period from 1991 to 2019. The results indicate that the deep learning approach is capable of forecasting the IOD at lead times up to seven months. The forecast skills of CNN are superior to those of the dynamic models in the North American Multi-Model Ensemble (NMME). The CNN outperforms the NMME with lower sensitivity to predictability barriers and fewer systematic errors. Moreover, the gradient heat map analysis demonstrates that the triggering precursors selected by CNN models for IOD events are novel and physically sensible. These results suggest the CNN to be a new and effective tool for both IOD prediction and comprehension.
Helge Winkelbauer, Kathy Cordova‐Rodriguez, Dharma Reyes‐Macaya, Jennifer Scott, Nicolaas Glock, , , , Phil Holdship, Charlotte Dormon, et al.
Geochemistry, Geophysics, Geosystems; https://doi.org/10.1029/2021gc009811

Abstract:
Planktic and benthic foraminiferal iodine (I) to calcium (Ca) molar ratios have been proposed as an exciting new proxy to assess subsurface and bottom water oxygenation in the past. Compared to trace metals, the analysis of iodine in foraminiferal calcite is more challenging, as iodine is volatile in acid solution. Here we compare previous analyses that use tertiary amine with alternative analyses using tetramethylammonium hydroxide (TMAH) and ammonium hydroxide (NH4OH) to stabilize iodine in solution. In addition, we assess the effect of sample size and cleaning on planktic and benthic foraminiferal I/Ca. Our stabilization experiments with TMAH and NH4OH show similar trends as those using tertiary amine, giving relatively low I/Ca ratios for planktic and benthic foraminifera samples from poorly oxygenated waters, and high ratios for well oxygenated waters. This suggests that both alternative methods are suitable to stabilize iodine initially dissolved in acid. Samples that contain 5 to 10 specimens show a wide spread in I/Ca. Samples containing 20 specimens or more show more centered I/Ca values, indicating that a larger sample size is more representative of the average planktic foraminifera community. The impact of cleaning on planktic and benthic foraminifera I/Ca ratios is very similar to Mg/Ca, with the largest effect occurring during the clay removal step. The largest iodine contaminations were recorded at locations characterized by moderate to high organic carbon contents. In those circumstances, we recommend doubling the oxidative cleaning steps (4 instead of 2 repetitions) to ensure that all organic material is removed.
Journal of Geophysical Research: Space Physics; https://doi.org/10.1029/2021ja029841

Abstract:
A method based on electron magnetohydrodynamics (EMHD) for the reconstruction of steady, two-dimensional plasma and magnetic field structures from data taken by a single spacecraft, first developed by Sonnerup et al. (2016), is extended to accommodate inhomogeneity of the electron density and temperature, electron inertia effects, and guide magnetic field in and around the electron diffusion region (EDR), the central part of the magnetic reconnection region. The new method assumes that the electron density and temperature are constant along, but may vary across, the magnetic field lines. We present two models for the reconstruction of electron streamlines, one of which is not constrained by any specific formula for the electron pressure tensor term in the generalized Ohm’s law that is responsible for electron unmagnetization in the EDR, and the other is a modification of the original model to include the inertia and compressibility effects. Benchmark tests using data from fully kinetic simulations show that our new method is applicable to both antiparallel and guide-field (component) reconnection, and the electron velocity field can be better reconstructed by including the inertia effects. The new EMHD reconstruction technique has been applied to an EDR of magnetotail reconnection encountered by the Magnetospheric Multiscale spacecraft on 11 July 2017, reported by Torbert et al. (2018) and reconstructed with the original inertia-less version by Hasegawa et al. (2019), which demonstrates that the new method better performs in recovering the electric field and electron streamlines than the original version.
Water Resources Research; https://doi.org/10.1029/2021wr030391

Abstract:
Bayesian model selection (BMS) is a statistically rigorous approach to assess the plausibility of competing models. It naturally accounts for uncertainties in models and data. In this study, we discuss the role of measurement noise in BMS deeper than in past literature. We distinguish between four cases, accounting for noise in models and/or data: (1) no-no, (2) no-yes, (3) yes-no, (4) yes-yes. These cases differ mathematically and philosophically. Only two out of , these four cases are logically consistent, and they represent two potentially conflicting research questions: “Which model is best in modeling the pure physics?” (Case 1) and “which model is best in predicting the data-generating process (i.e., physics plus noise)?” (Case 4). If we are interested in the “pure physics question”, we face two practical challenges: First, we would need noise-free data, which is impossible to obtain; and second, the numerical approximation of Bayesian model evidence can be hard when neglecting noise. We discuss how to address both challenges and reveal that a fallback to the easier “data-generation question” as a proxy for the “physics question” is not appropriate. We demonstrate on synthetic scenarios and a real-world hydrogeological case study that the choice of case has a significant impact on the outcome of posterior model weights, and hence on results of model ranking, model selection, model averaging, model confusion analysis, and uncertainty quantification. Reality might force us to use a different case than philosophy would suggest, and we provide guidance on how to interpret model probabilities under such conditions.
, , B. Cao, F.M. Ralph, M. Zheng, L. Delle Monache
Journal of Geophysical Research: Atmospheres; https://doi.org/10.1029/2021jd034865

Abstract:
Variations in the water vapor that atmospheric rivers (ARs) carry towards North America within Pacific storms strongly modulates the spatio-temporal distribution of west-coast precipitation. The “AR Recon” program was established to improve forecasts of landfalling Pacific-coast ARs and their associated precipitation. Dropsondes are deployed from weather reconnaissance aircraft and pressure sensors have been added to drifting ocean buoys to fill a major gap in standard weather observations, while research is being conducted on the potential for airborne Global Navigation Satellite System (GNSS) radio occultation (ARO) to also contribute to forecast improvement. ARO further expands the spatial coverage of the data collected during AR Recon flights. This study provides the first description of these data, which provide water vapor and temperature information typically as far as 300 km to the side of the aircraft. The first refractivity profiles from European Galileo satellites are provided and their accuracy is evaluated using the dropsondes. It is shown that spatial variations in the refractivity anomaly (difference from the climatological background) are modulated by AR features, including the low-level jet and tropopause fold, illustrating the potential for RO measurements to represent key AR characteristics. It is demonstrated that assimilation of ARO refractivity profiles can influence the moisture used as initial conditions in a high-resolution model. While the dropsonde measurements provide precise, in-situ wind, temperature and water vapor vertical profiles beneath the aircraft, and the buoys provide surface pressure, ARO provides complementary thermodynamic information aloft in broad areas not otherwise sampled at no additional expendable cost.
, Yixin Yang,
Water Resources Research; https://doi.org/10.1029/2021wr030883

Abstract:
Characterizing the upper tail of flood peak distributions remains a challenge due to the elusive nature of extreme floods. China has experienced some of the most extreme floods on Earth and is therefore an important setting for extreme flood research. Here we examine the upper tail of flood peaks over China based on a comprehensive flood dataset that integrates systematic observations from 1759 stream gaging stations and 14,779 historical flood surveys. Floods with large upper tail ratios (i.e., flood peak discharge normalized by sample 10-year flood) cluster spatially in the windward regions of mountainous terrain with basin mean annual rainfall of around 550 mm. Large upper tail ratio floods are associated with a mixture of rainfall generation processes. These processes are characterized by anomalous moisture transport (e.g., zonal water vapor pathways) and/or synoptic configurations (e.g., blocking), with respect to flood-producing storms for annual flood peaks. Downscaling simulations with the Weather Research and Forecasting model for the 1939, 1963, and 2016 floods over the North China Plain region highlight the role of interactions between complex terrain and large-scale environment in defining the world envelope curve of flood peaks. The upper-tail floods demonstrate a combination of ingredients producing extreme rainfall. Our results provide important insights to extreme floods in China and a frame of reference for assessing the largest floods on Earth.
, , , Naotaka Y. Chikasada, , Takeshi Nakamura, Hiroaki Tsushima
Journal of Geophysical Research: Solid Earth, Volume 126; https://doi.org/10.1029/2021jb022223

Abstract:
Tsunamis with amplitudes of up to 40 cm, related to the Mw 7.1 normal-faulting earthquake off Fukushima, Japan, on November 21, 2016, were clearly recorded by a new offshore wide and dense ocean-bottom pressure gauge network, S-net, with high azimuthal coverage located closer to the focal area. We processed the S-net data and found some stations included the tsunami-irrelevant drift and step signals. We analyzed the S-net data to infer the tsunami source distribution. A subsidence region with a narrow spatial extent (∼40 km) and a large peak (∼200 cm) was obtained. The other near-coastal waveforms not used for the inversion analysis were also reproduced very well. Our fault model suggests the maximum stress drop across the fault plane of > ∼10 MPa and the average of 4.2 MPa, whereas the shear stress increase along the fault caused by the 2011 Tohoku earthquake was only ∼2 MPa. Past studies have suggested that horizontal compressional stress around this region switched to horizontal extensional stress after the Tohoku earthquake due to its stress perturbation. The present result, however, suggests that the horizontal extensional stress was locally predominant at the shallowest surface around the focal area even before 2011. The present study demonstrates that the S-net high-azimuthal-coverage pressure data provides a significant constraint on the fault modeling, which enables us to discuss the stress regime within the overriding plate at the offshore. Our analysis provides an implication for crustal stress states, which is important for understanding generation mechanisms of intraplate earthquakes.
, , A. Sánchez‐Lavega
Journal of Geophysical Research: Planets, Volume 126; https://doi.org/10.1029/2021je006889

Abstract:
The atmosphere of Mars presents a strong response to aerosol radiative forcing compared to that of the Earth, thus atmospheric models should have accurate radiative transfer algorithms for the simulation of temperatures and circulation. In this work, we evaluate the radiative effects of dust aerosol calculated by different radiative transfer schemes and the influence of dust properties in these calculations. Two-stream solutions were compared with multi-stream discrete ordinate methods. Fluxes and heating rates were evaluated for a variety of atmospheric conditions, including dust storms. The results show that in low-to-medium dust opacity scenarios, the highly efficient two-stream methods provide accurate estimations, with heating rate errors of less than 2 K/sol. These errors increase with opacity, when differences of 20 K/sol are reached, which may be relevant in the simulations of temperature fields and atmospheric circulation under regional and global dust storm conditions. In such cases, the use of 4-stream or higher order methods may be required, although accuracy improvements for 8- or higher-stream schemes were negligible. The influence of dust particle properties in aerosol radiative forcing estimations is mainly due to the particle size, where variations of 20% of the effective radius resulted in differences of 5 K/sol; the shape of the particles showed a minor impact, with differences of < 2 K/sol. The results of this study contribute to quantification of the uncertainties in current Mars climate models and may help modellers to select the appropriate approach depending on the scenario.
, Max M. Garvue
Published: 22 October 2021
Abstract:
The Eastern California Shear Zone is a complex set of dextral faults that accommodates significant plate motion and has produced large earthquakes. The evolution of this system and why it consists of closely spaced, irregular faults that fail in multi-fault ruptures are not well understood. Here we analyze the geometry, spatial distribution, and Quaternary slip activity of right-lateral faults in the southern Mojave block. We find these faults are oriented favorably for accommodating regional dextral plate motion and do not show evidence of replacement following counterclockwise rotation to unfavorable positions, although activity may be migrating westward as previously proposed. We also confirm that the shear zone is transpressive, with widespread restraining bends, distributed convergent deformation, and significant impact on near-fault topography. Observations also show that faults are geometrically complex, as represented by along-strike variability in fault strike. We document a correlation between strike variability and fault activity (slip rate or net slip), which is evident within the shear zone as well as for a control group of other faults. We suggest that strike variability represents a form of geometric roughness, which may inhibit fault slip and result in complex ruptures, slip-strengthening behavior, and a prevalence of off-fault deformation. Other factors, including preexisting crustal fabric, edge effects, and changes in the stress field, may further complicate kinematics. These results suggest that faults of the shear zone are still juvenile and somewhat unique, yet offer an important window into how broadly distributed shear may evolve into a through-going continental transform system.
, Andrew M. Hilger, , , Thomas M. Jordan, , , Donald D. Blankenship,
Journal of Geophysical Research: Earth Surface, Volume 126; https://doi.org/10.1029/2021jf006296

Abstract:
The Amundsen Sea Embayment of the West Antarctic Ice Sheet contains Thwaites and Pine Island Glaciers, two of the most rapidly changing glaciers in Antarctica. To date, Pine Island and Thwaites Glaciers have only been observed by independent airborne radar sounding surveys, but a combined cross-basin analysis that investigates the basal conditions across the Pine Island-Thwaites Glaciers boundary has not been performed. Here, we combine two radar surveys and correct for their differences in system parameters to produce unified englacial attenuation and basal relative reflectivity maps spanning both Pine Island and Thwaites Glaciers. Relative reflectivities range from -24.8 to +37.4 dB with the highest values beneath fast-flowing ice at the ice sheet margin. By comparing our reflectivity results with previously derived radar specularity and trailing bed echoes at Thwaites Glacier, we find a highly diverse subglacial landscape and hydrologic condition that evolve along flow. Together, these findings highlight the potential for joint airborne radar analysis with ground-based seismic and geomorphological observations to understand variations in the bed properties and cross-catchment interactions of ice streams and outlet glaciers.
, , , , , Helen Burns, Richard Rigby, Nicolás Borchers‐Arriagada, , Laura Kiely, et al.
Published: 22 October 2021
Abstract:
The Australian 2019/2020 bushfires were unprecedented in their extent and intensity, causing a catastrophic loss of habitat, human and animal life across eastern-Australia. We use a regional air quality model to assess the impact of the bushfires on particulate matter with a diameter less than 2.5 µm (PM2.5) concentrations and the associated health impact from short-term population exposure to bushfire PM2.5. The mean population AQI exposure between September and February in the fires and no fires simulations indicates an additional ∼437,000 people were exposed to ‘Poor’ or worse AQI levels due to the fires. The AQ impact was concentrated in the cities of Sydney, Newcastle-Maitland, Canberra-Queanbeyan and Melbourne. Between October and February 171 (95% CI: 66 – 291) deaths were brought forward due to short-term exposure to bushfire PM2.5. The health burden was largest in New South Wales (NSW) (109 (95% CI: 41 – 176) deaths brought forward), Queensland (15 (95% CI: 5 – 24)) and Victoria (35 (95% CI: 13 – 56)). This represents 38%, 13% and 30% of the total deaths brought forward by short-term exposure to all PM2.5. At a city-level 65 (95% CI: 24 – 105)), 23 (95% CI: 9 –38)) and 9 (95% CI: 4 – 14)) deaths were brought forward from short-term exposure to bushfire PM2.5, accounting for 36%, 20% and 64% of the total deaths brought forward from all PM2.5. Thus, the bushfires caused substantial AQ and health impacts across eastern-Australia. Climate change is projected to increase bushfire risk, therefore future fire management policies should consider this.
Ye Yang, Li‐Feng Cui, , ,
Journal of Geophysical Research: Earth Surface, Volume 126; https://doi.org/10.1029/2021jf006111

Abstract:
Fluvial incision, regarded as one of the fundamental geomorphic processes, drives the evolution of mountainous landscapes. The transitional landscape from low-relief to high-relief in the central Tibetan Plateau is rapidly evolving as it is influenced by river dynamics, climate change and tectonic uplift. Combining cosmogenic 10Be depth profile dating and topographic analysis, this study provides new constraints on the formation and destruction of low-relief surfaces in the central Tibetan Plateau. We find that the high-relief landscape in the Suoqu area (a major tributary of the upper Nu River) shows a rapid fluvial incision rate of 710 ± 70 mm kyr-1 since the late Pleistocene, while the low-relief topography in the adjacent Xiaqiuqu area presents an order of magnitude lower incision rate of 70 ± 10 mm kyr-1. These results are consistent with the long-term (multi-million-year) exhumation rates derived from low-temperature thermochronology, suggesting that this region has experienced an evolving incision history. We interpret that the higher relief was caused by enhanced fluvial incision, and the lower relief was slowly developed by sedimentation and relatively steady low exhumation rate. The presence of a knickzone appears to mark the boundary between these differentially incising landscapes, which may be caused by rapid headward retreat and higher river discharge in the Suoqu River. The coincidence of fluvial terraces ages with climate-driven events, in addition to paleodenudation rates, indicates that the formation of fluvial terraces in the Xiaqiuqu and Suoqu areas might be associated with the quick sedimentation of weathered materials in early warming periods.
Joshua S. Evans, Ann‐Lise Norman,
Water Resources Research, Volume 57; https://doi.org/10.1029/2021wr030069

Abstract:
Large wildland fires generate smoke that can compromise air quality over a wide area. Limited studies have suggested that smoke constituents may enter natural water bodies. In an 18-year water monitoring study, we examined whether smoke from distant wildland fires had a detectable effect on ion content in a mountain river in an unburned watershed. Significant local smoke occurred in six years as traced by MODIS satellite data of fires, regional and local atmospheric fine particulate matter (PM2.5), and the amount of potassium (K+) in PM2.5 as a marker of vegetation combustion. Rainwater had elevated K+ and calcium (Ca2+, also associated with wildland fire smoke) in high-smoke years compared to low-smoke years, and was the primary route of atmospheric deposition. Similarly, river water in high-smoke years had elevated concentrations of K+ and Ca2+, with a higher ratio of K+ to Ca2+ compared to low-smoke years. River concentrations were generally unrelated to river discharge and observed K+ concentrations in high-smoke and low-smoke years could be accounted for by atmospheric deposition. Our study provides early evidence that wildland fires affect water quality far beyond the watersheds where they occur. Wildland fires distribute vast quantities of smoke containing nutrients, toxins and microbes and are increasing in North America. Potassium is a routinely-measured water quality parameter that can act as an indicator of biomass smoke inputs. Further work is needed on the patterns and processes by which wildfire smoke enters water as well as on the consequences for ecosystems and human health.
, S. Tulasi Ram, V. Manu, Lingxin Zhao, Zan‐Yang Xing, Qing‐He Zhang
Journal of Geophysical Research: Space Physics, Volume 126; https://doi.org/10.1029/2020ja028854

Abstract:
A quasi-semidiurnal type pattern was observed earlier in the diurnal UT variation of the geomagnetic storms studied using mainly Kyoto Dst (disturbance storm-time) index. However, the pattern has been argued as apparent due to uneven longitude distribution of the four Dst observatories. Unlike earlier studies, this paper investigates the diurnal UT variation of the storms automatically identified in six available indices including Kyoto Dst, USGS (United States Geological Survey) Dst, SymH (symmetric-H), RC (ring current), Dcx (corrected extended Dst) and AER (Atmospheric and Environmental Research) in 50, 50, 36, 21, 5 and 7 years, respectively. The indices are derived using 4, 4, 12, 14 and 15 ground observatories (with maximum longitude separations of ∼120º, 120º, 70º, 110º and 50º) and 4 DMSP (Defense Meteorology Satellite Program) satellites, respectively. The UT distribution of the storm intensity (minimum value of an index during the storm main phase) in all indices shows a striking quasi-semidiurnal type variation with maxima around 06-08 UT and 21-23 UT and minima around 03-05 UT and 13-15 UT. Similar quasi-semidiurnal variation is also observed in the computed values of the main energy input in the ring current. The variation correlates well with the variations of the dipole tilt angles μ and θ involved in the equinoctial hypothesis and Russell–McPherron (RM) effect, respectively. These observations indicate that the quasi-semidiurnal variation is real.
Journal of Geophysical Research: Space Physics, Volume 126; https://doi.org/10.1029/2021ja029944

Abstract:
The effective polytropic index, , of small-scale magnetic flux ropes in the solar wind is investigated using the Wind observations near 1 AU. A total of 59 flux ropes were selected with a good estimation on and divided into two categories, namely, CAT1 for flux ropes accompanied with torsional Alfvén waves and CAT2 for those without. These 59 flux ropes were satisfied the constant-alpha, force-free flux rope model. It is found that the index ranges between 1.05 and 2.34, with a mean of 1.68 0.43, for CAT1, while it ranges between 0.71 and 2.42, with a mean of 1.52 0.44, for CAT2. Apparently, the mean of CAT1 flux ropes is closer to the adiabatic condition ( = 5/3), as compared to CAT2 ones. No clear correlation of the index with the solar wind speed and flux rope size is found for these 59 flux ropes. For each flux rope category, the flux ropes are further distinguished by the presence of counterstreaming suprathermal electrons (CSEs) inside it. For both CAT1 and CAT2 flux ropes, it seems that the median and mean of are less than 5/3 for flux ropes associated with CSEs but greater than 5/3 for those without. Since the index spreads over a wide range of values, it is suggested that various polytropic processes may happen within the flux ropes during their propagation in the solar wind.
Zhicheng Zhang, , Wanjing Li
Journal of Advances in Modeling Earth Systems, Volume 13; https://doi.org/10.1029/2021ms002802

Abstract:
Vegetation plays a key role in regulating the material and energy exchanges among the biosphere, the atmosphere, and the pedosphere. Modeling and predicting vegetation key variables such as leaf area index (LAI) and gross primary productivity (GPP) is crucial to understand and project the processes of vegetation growth in response to climate change. While a number of studies developed models to simulate vegetation GPP using satellite-derived LAI, the requirement of satellite-based model inputs largely limits the predicting power of these developed models. This study developed a machine learning scheme, utilizing both support vector regression (SVR) and random forests (RF), which are capable of modeling LAI and GPP time series using only meteorological variables. We first simulated the LAI time series directly using meteorological variables as inputs and then buffered its unrealistic day-to-day fluctuation, and further modeled the GPP time series using meteorological variables and modeled LAI time series. This scheme enhanced the interpretability of machine learning models by considering the non-negligible coupling between LAI and GPP. We tested our methods for four main plant functional types across North America and evaluated the models using both satellite-based and flux tower data. The results demonstrated that the machine learning models perform well on simulating the time series of both LAI and GPP. We identified that there is a need to improve the phenology representation in the Biome-BGCMuSo model. The machine learning models provide an alternative way to predict time series of LAI and GPP using only meteorological variables across large geographic regions, and also provide benchmarking accuracies for future developments of the process-based models.
, K. G. Hanley, J. P. McFadden, , J. W. Bonnell, , J. R. Espley, , , , et al.
Journal of Geophysical Research: Space Physics, Volume 126; https://doi.org/10.1029/2021ja029615

Abstract:
We present MAVEN observations of low frequency steepened fast magnetosonic waves in the Martian magnetosphere and ionosphere. Solar wind pressure pulses generated in the upstream foreshock region impact the magnetopause and generate the magnetosonic waves within the magnetosphere, in a process analogous to the production of magnetic Pc pulsations in the terrestrial magnetosphere. The draped nature of the IMF about Mars, combined with the near-perpendicular propagation of these waves across the magnetic field, act to channel these waves into the nightside ionosphere, where they are observed in their non-linear steepened form. Coincident-in-time ion observations show that the light (H+) and heavy (O+, O2+, CO2+) planetary ion distribution functions possess significant suprathermal energetic tails, arising from wave-particle interactions with the steepened waves. The short gyro period and small gyro radius of the protons, relative to the steepened waves, results in proton heating via adiabatic compression. In contrast, the long gyro period of the heavy ions relative to the wave frequency leads to non-adiabatic heating via wave-trapping processes. The light and heavy ion species are heated above escape energy by these waves, even down close to the exobase. A limited statistical study of 101 neighboring orbits found that similar wave events occurred on 28% of orbits analyzed, suggesting that such wave-heating events may be important drivers of the Mars nightside ionospheric dynamics and energy budget. Our discussion includes placing our results in the context of solar wind energy transfer to the ionospheres of unmagnetized and magnetized bodies in general. This article is protected by copyright. All rights reserved.
, C. Troy, H. Bootsma, , R. Maclellan‐Hurd
Journal of Geophysical Research: Oceans; https://doi.org/10.1029/2021jc017533

Abstract:
In this study, we report on turbulent mixing observed during the annual stratification cycle in the hypolimnetic waters of Lake Michigan (USA), highlighting stratified, convective, and transitional mixing periods. Measurements were collected using a combination of moored instruments and microstructure profiles. Observations during the stratified summer showed a shallow, wind-driven surface mixed layer with locally elevated dissipation rates in the thermocline () potentially associated with internal wave shear. Below the thermocline, turbulence was weak () and buoyancy-suppressed ( < 8.5), with low hypolimnetic mixing rates () limiting benthic particle delivery. During the convective winter period, a diurnal cycle of radiative convection was observed over each day of measurement, where temperature overturns were directly correlated with elevated turbulence levels throughout the water column (; ). A transitional mixing period was observed for spring conditions when surface temperatures were near the temperature of maximum density (TMD3.98) and the water column began to stably stratify. While small temperature gradients allowed strong mixing over the transitional period (), hypolimnetic velocity shear was overwhelmed by weakly stable stratification (; ), limiting the development of the surface mixed layer. These results highlight the importance of radiative convection for breaking down weak hypolimnetic stratification and driving energetic, full water column mixing during a substantial portion of the year (>100 days at our sample site). Ongoing surface water warming in the Laurentian Great Lakes is significantly reducing the annual impact of convective mixing, with important consequences for nutrient cycling, primary production, and benthic-pelagic coupling.
Published: 22 October 2021
Abstract:
Well-switching programs in Bangladesh have successfully lowered arsenic exposure. In these programs, households switch from wells that are labeled “unsafe” to nearby wells labeled “safe,” but these designations are usually based on inherently inaccurate field kit measurements. Here, we (1) compare the efficacy of field-kit measurements to accurate laboratory measurements for well switching, (2) investigate the potential impact on well switching of the chosen “safe” threshold, and (3) consider the possible benefits of providing more detailed concentration information than just “safe” and “unsafe”. We explore different hypothetical mitigation scenarios by combining two extensive data sets from Araihazar Bangladesh, a blanket survey of 6595 wells over 25 km2 based on laboratory measurements and 943 paired kit and laboratory measurements from the same area. The results indicate that the decline in average arsenic exposure from relying on kit rather than laboratory data is modest in relation to the logistical and financial challenge of delivering exclusively laboratory data. The analysis further indicates that the 50 μg/L threshold used in Bangladesh to distinguish safe and unsafe wells, rather than the WHO guideline of 10 μg/L, is close to optimal in terms of average exposure reduction. We also show, however, that providing kit data at the maximum possible resolution rather than merely classifying wells as unsafe or safe would be even better. These findings are relevant as the government of Bangladesh is about to launch a new blanket testing campaign of millions of wells using field kits.
Richard Sima
Published: 22 October 2021
Abstract:
Poor infrastructure is responsible for tens of thousands of pharmaceutical doses that flow through Baltimore’s streams each year.
Longfei Han, Xiaoqin Yu, Youpeng Xu, Xiaojun Deng, Liu Yang, Zhongwu Li, Dianqing Lv,
Journal of Geophysical Research: Atmospheres; https://doi.org/10.1029/2021jd035009

Abstract:
In this study, we examined the summertime climatic effects of urban expansion during 1990-2010 in the Yangtze River Delta (YRD) region by analyzing station observations and performing numerical simulations with the Weather Research and Forecast (WRF) model. Long-term observations showed that urban area experienced a larger increase in summertime 2-m air temperature than rural part during 1980-2018, and the influence of urbanization on the urban-rural contrast was greater in the late stage (after 2000) than the early stage (before 2000). We applied the WRF model incorporated with historical land surface cover data (year 1990, 2000 and 2010) to further evaluate the climatic effects of long-term urbanization. On average, urban expansion over 1990-2010 led to 0.75˚C increase in daily average temperature (1.06˚C in daily minimum and 0.45 ˚C in daily maximum) during the summer. The summertime daily temperature range decreased by 0.61 ˚C in urban environment during the same period. Compared to the warming effect of urbanization in the 1990s, both the magnitude and affected area have increased after the millennium. Also, urban expansion reduced moisture in low-level atmosphere, and this urban dry island (UDI) effect was enhanced in the late-stage. Less moisture in the atmosphere offset heat stress index induced by the warming temperature. We also found that the partitioning of net radiation between sensible and latent heat was the key factor that controlled urban warming effect.
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