bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of GIA models in north-east Greenland using densified GNSS measurements and refined estimates of present-day ice-mass changes
Authors: Kappelsberger Maria Theresia , Strößenreuther Undine , Scheinert Mirko , Horwath Martin , Groh Andreas , Knöfel Christoph , Lunz Susanne , Khan Shfaqat Abbas
Published: March 2021

Models of glacial-isostatic adjustment (GIA) exhibit large differences in north-east Greenland, reflecting uncertainties about glacial history and solid Earth rheology. The GIA uncertainties feed back to uncertainties in present-day mass-balance estimates from satellite gravimetry. We present results from repeated and continuous GNSS measurements which provide direct observables of the bedrock displacement. The repeated measurements were conducted within five measurement campaigns between 2008 and 2017. They reveal uplift rates in north-east Greenland in the range of 2.8 to 8.9 mm yr-1. We used the observed uplift rates to validate different GIA models in conjunction with estimates of the elastic load deformation induced by present-day ice-mass changes and ocean mass redistribution. To determine present-day ice-mass changes for both the Greenland Ice Sheet and the peripheral glaciers, we combined CryoSat-2 satellite altimetry data with GRACE satellite gravimetry data. The different GIA models were consistently used in all processing steps. Our comparison between observed and predicted uplift rates clearly favours GIA models that show low rates (0.7 to 4.4 mm yr-1 at the GNSS sites) over GIA models with higher rates of up to 8.3 mm yr-1. Applying the correction predicted by the GIA model favoured in north-east Greenland we estimate an ice-mass loss of 233 ± 43 Gt yr-1 for entire Greenland (including peripheral glaciers) over the period July 2010 to June 2017.
Sea ice protists in arctic marine sedaDNA records: origins, diversity, and vertical export of DNA from the sea surface to the seafloor 
Authors: Harðardóttir Sara , Lovejoy Connie , Seidenkrantz Marit-Solveig , Ribeiro Sofia
Published: March 2021

Arctic sea ice is declining at an unprecedented pace as the Arctic Ocean heads towards ice-free summers within the next few decades. Because of the role of sea ice in the Earth System such as ocean circulation and ecosystem functioning, reconstructing its past variability is of great importance providing insight into past climate patterns and future climate scenarios. Today, much of our knowledge of past sea-ice variability derives from a relatively few microfossil and biogeochemical tracers, which have limitations, such as preservation biases and low taxonomic resolution. Marine sedimentary ancient DNA (marine sedaDNA) has the potential to capture more of the arctic marine biodiversity compared to other approaches. However, little is known about how well past communities are represented in marine sedaDNA. The transport and fate of DNA derived from sea-ice associated organisms, from surface waters to the seafloor and its eventual incorporation into marine sediment records is poorly understood.  Here, we present results from a study applying a combination of methods to examine modern and ancient DNA to material collected along the Northeast Greenland Shelf. We characterized the vertical export of genetic material by amplicon sequencing the hyper-variable V4 region of the 18S rDNA at three water depths, in surface sediments, and in a dated sediment core.  The amplicon sequencing approach, as currently applied, includes some limitations for quantitative reconstructions of past changes such as primer competition, PCR errors, and variation of gene copy numbers across different taxa. For these reasons we quantified amplicons from a single species, the circum-polar sea ice dinoflagellate Polarella glacialis in the marine sedaDNA, using digital droplet PCR. The results will increase our understanding on the taphonomy of DNA in sea ice environments, how sedimentation differs among taxonomic groups, and provide indications to potentially useful marine sedaDNA-based proxies for climate and environmental reconstructions.
Small-scale Magnetic Flux Ropes with Field-aligned Flows via the PSP In-situ Observations
Authors: Chen Yu , Hu Qiang , Zhao Lingling
Published: March 2021

Magnetic flux rope, formed by the helical magnetic field lines, can sometimes remain its shape while carrying significant plasma flow that is aligned with the local magnetic field. We report the existence of such structures and static flux ropes by applying the Grad-Shafranov-based algorithm to the Parker Solar Probe (PSP) in-situ measurements in the first five encounters. These structures are detected at heliocentric distances, ranging from 0.13 to 0.66 au, in a total of 4-month time period. We find that flux ropes with field-aligned flows have certain properties similar to those of static flux ropes, such as the decaying relations of the magnetic fields within structures with respect to heliocentric distances. Moreover, these events are more likely with magnetic pressure dominating over the thermal pressure and occurring more frequently in the relatively fast-speed solar wind. Taking into account the high Alfvenicity, we also compare these events with switchbacks and present the cross-section maps via the new Grad-Shafranov type reconstruction. Finally, the possible evolution and relaxation of the magnetic flux rope structures are discussed.
New method to detect and quantify weather persistence associated with hydro-climatic extremes
Authors: Hoffmann Peter , Lehmann Jascha , Fallah Bijan , Hattermann Fred
Published: March 2021

Changes in weather persistence are of particular concern in the context of climate change as periods of longer persistence can reinforce weather extremes. In our study we apply structural image recognition methods to global ERA5 reanalysis data to identify when, where and how long isolines of atmospheric geopotential height fields run in similar tracks. We identify regions and episodes around the world in which, retrospectively, unusually long-lasting weather patterns repeatedly occurred. Concerning the temperature and precipitation meteorological fields, we derive a connection between the occurrence of weather persistence and hydro-climatic extreme events.

Based on our new method we find that weather persistence has been particularly increasing in Northern Hemisphere mid-latitudes in summer confirming earlier studies. Here, highly populated regions like Central Europe have experienced long-term increases in persistent weather conditions of up to 4-5% between 1981 and 2019 amplifying the risk of prolonged heat waves and droughts. Further, we show that climate models tend to have difficulties in capturing the dynamics of weather persistence and thus may severely underestimate the frequency and magnitude of future extremes events in their climate projections.
The influence of heterogeneity on the strength and stability of faults
Authors: Faulkner Daniel , Bedford John , Lapusta Nadia , Lambert Valère
Published: March 2021

Heterogeneity of fault zones is seen at all scales in nature. It may manifest itself in terms of the variability of material property distribution over the fault, of stress heterogeneity brought about by the history of previous earthquake ruptures, and of fault geometry. In this contribution, we consider the effect on fault strength and stability of small-scale heterogeneity in laboratory experiments and large-scale heterogeneity from numerical dynamic rupture modeling. In model laboratory faults at slow slip rates (0.3 and 3 microns/s), the area occupied by rate-weakening gouge (quartz) versus rate-strengthening gouge (clay) was systematically varied and the results compared with homogenized mixtures of the two gouges. We found that the heterogeneous experimental faults were weaker and less stable than their homogenized counterparts, implying that earthquake nucleation might be promoted by fault zone heterogeneity. In elasto-dynamic numerical simulations of sequences of earthquakes and aseismic slip based on rate and state friction but with enhanced dynamic weakening (EDW) through pore fluid pressurization, uniform material properties on the fault plane are assumed, and heterogeneity spontaneously develops by stress variations along the fault arising from differing histories of motion at points along the fault. In these models, ruptures spontaneously nucleate in favorably prestressed regions. Larger ruptures - that result in greater degrees of EDW - are capable of propagating through areas of lower shear stress that would arrest smaller events. This behavior leads to a relationship between rupture size and the average shear stress over the rupture plane before the earthquake occurs. Faults that host larger events may overall appear to be driven by lower average shear stress and hence appear ‘weaker’. It is clear that the apparent fault strength and stability is difficult to predict from either simple homogeneous gouge experiments, or from scaling up of these results. Heterogeneity at all scales will affect the slip behaviour of faults.
MEWS – a project for detecting and predicting avalanches
Authors: Suciu George , Iordache George , Trufin Dan , Segarceanu Svetlana , Petrescu Gabriel
Published: March 2021

The MEWS project describes all the stages of a system that monitors and predicts avalanches. In the project we use and present some of the latest technologies for avalanche detection and prediction. In this article we present a state of the art of the existing technologies when predicting avalanches and the technical and functional requirements of the MEWS project. The state of the art is presented because the MEWS project is based on existing technologies and we need to present what technologies are of interest for our project. The technical and functional requirements for the MEWS project describes what we want to do in the project. We can say that the MEWS project is one very important at european level, is build on modern technologies and is endorsed by the european community.
MAP-AQ: An international network for air quality forecasts
Authors: Brasseur Guy , Kumar Rajesh
Published: March 2021

MAP-AQ (Modeling, Analysis and Predictions of Air Quality) is an international network that contributes to the development and implementation of global and regional air pollution monitoring, analysis, prediction and attribution systems with downscaling capability in areas of the world particularly affected by high levels of atmospheric pollutants, in particular in low and middle-income countries. The project supports the development of the science and software engineering needed to improve air quality forecasts from the global to the regional and local scales, and to develop reliable attribution systems for air pollution sources. Capacity development is another focus of the project sponsored by WMO/GAW and by IGAC. The paper will present a number of activities currently supported by MAP-AQ and will outline a strategy for future initiatives and cooperations.
Bedrock outcrops: A window for enhanced midwinter recharge
Authors: Wright Stephanie , Novakowski Kent
Published: March 2021

As midwinter melt and rain-on-snow events become more common occurrences in the northern hemisphere under climate change, incorporating frozen processes when simulating winter-time recharge is increasingly necessary. The activation of infiltration pathways and recharge dynamics of shallow bedrock environments under frozen conditions has received relatively little attention. Over the 2019-2020 winter, hydrogeologic and cryospheric conditions of the surface, unsaturated, and saturated zones were monitored around a low-lying granitic outcrop in eastern Ontario, Canada. Interpretation of the data indicated that the soil-rock contact around outcrop margins was the key pathway enabling midwinter infiltration and recharge. To support this conceptual model and further explore the role of outcrops in enhancing midwinter bedrock recharge, a numerical investigation was undertaken. Measured climate data (hourly time step) was used to govern the surface energy and water balances of a 1D finite difference model that incorporates frozen processes. Measured snow depth, soil moisture content, and soil temperature profiles were simulated. Simulations with vertical infiltration alone could not account for observed increases in moisture content in the deepest soil horizons. This is attributed to additional lateral flow along the unfrozen soil-rock contact that bypasses the frozen soil layers. Preliminary results support the concept that bedrock outcrops provide a window for midwinter infiltration since repeated winter melts reduce frozen soil permeability and inhibits vertical infiltration until the ground thaws. Results from the surface/near-surface simulations are used to guide the development of a 2D finite element model that includes heat and flow transport and ground freeze-thaw. The impacts to bedrock recharge under different rainfall and snowmelt scenarios as well as various outcrop geometries are explored. Results from these numerical experiments help provide greater insight into the processes driving enhanced midwinter bedrock recharge under conditions of warmer winters.
Improved three-dimensional image of the tomographic inversion of the Arraiolos aftershock sequence.
Authors: Hamak Ines , Wachilala Piedade , Borges José , Dias Nuno , Rio Inês , Bezzeghoud Mourad
Published: March 2021

This work puts in light the several steps followed to obtain a 3D velocity model in Arraiolos, a region located in central Portugal. After the earthquake of January 2018 occurred, a set of stations were deployed around the main shock area and has recorded the aftershock sequence during a period of six months.

The first stage of this study used a set of data recorded along the 1st month by 21 temporary seismological stations. 317 aftershocks were used to invert a 3D P and S  velocity model, using LOTOS program, and showing an agglomeration of events in one local point leading to a poor resolution. Therefore, we added more stations and data to the second stage of study by integrating 437 aftershocks recorded during a period of 6 months by a set of 34 stations. The tomographic inversion of this extended aftershock sequence has shown a significant improvement of the 3D velocity model resolution and suggesting an alignment of the seismic events cluster. However, the imaged crustal volume was still too small and possessing low resolution on the edges of the area. To fix this issue, additional data and seismological stations were integrated to the study in order to increase the area of interest and cover it entirely in terms of ray density.

The step which we are currently conducting concerns the location of new events followed by their integration to the tomographic study using IPMA and DOCTAR station network records. Since the later phases PmP and SmS has the potential to increase the ray coverage as similarly as the resolution of an area, we will hopefully obtain, after their integration, significant improvements in terms of accuracy and reliability of the crustal image. The main purpose of this new stage of study is to finally provide significant interpretations and figure out precisely the tectonic processes having generated the Arraiolos seismicity.

Thanks are due to FCT for the financial support to the ICT project (UID/GEO/04683/2013) with the reference POCI-01- 0145-FEDER-007690, to the IDL project (UIDB/50019/2020 – IDL).
A climatology of the North Atlantic subpolar gyre boundary
Authors: Jones Sam , Cunningham Stuart , Fraser Neil , Inall Mark
Published: March 2021

Circulation at the boundary of the subpolar North Atlantic influences both the horizontal (gyre) and vertical (overturning) components of the flow structure. While boundary current transport projects directly onto subpolar gyre strength, recent modelling studies have highlighted that buoyancy fluxes between the basin interior and the boundary, followed by rapid buoyancy export by boundary currents, are crucial steps in projecting air-sea interaction onto the strength of the Atlantic Meridional Overturning Circulation (AMOC). This work seeks observational insights into these key boundary processes.
To achieve this, we have constructed a robust boundary climatology from quality controlled CTD and Argo hydrography since the turn of the millennium. Following the 1000 m isobath north of 47 °N and aggregating data into 100 km bins, we build a picture of the typical large-scale temperature and salinity structure for each month.
This product will allow us to identify where and when important interior-boundary buoyancy fluxes take place over a seasonal cycle. A first step is to evaluate geostrophic flow into the boundary, and hence describe the vertical structure of advective buoyancy exchange. By appealing to satellite altimetry and Argo trajectories, we can also estimate turbulent eddy fluxes both at the surface and 1000 m depth. Models indicate these parameters are key in dictating the pathways for the AMOC lower limb, and we will place our observational findings in the context of these results.
Boundary current strength is another key parameter dictating the export of dense water from the subpolar gyre. We will appeal to satellite altimetry to build corresponding climatologies for barotropic boundary flow. Furthermore, along-slope density gradients give rise to a baroclinic boundary current forcing term, which we aim to investigate here. Water density generally increases as we follow the gyre counter-clockwise, with the notable exception of the West Greenland Current section, and our product allows us to partition the spatially-varying contribution of temperature and salinity towards these density gradients. For example, we can evaluate the impact of cooling along the eastern boundary, or surface freshening around southern Greenland, on the dynamics of boundary flow. Ultimately, we would like to understand the evolution of the dynamical balance experienced by a hypothetical fluid parcel traversing the entire subpolar gyre.
Using OSL dating data for quartz provenance analysis in late Quaternary sediments of Amazonia 
Authors: Souza Priscila , Pupim Fabiano , del Río Ian , Rodrigues Fernanda , Mineli Thays , Porat Naomi , Hartmann Gelvam , Sawakuchi André
Published: March 2021

Quartz grains are resistant minerals and abundant on Earth´s surface. They have been extensively used for optically stimulated luminescence (OSL) dating of Quaternary sediments from a large range of depositional environments. Recently, it has been demonstrated that the luminescence properties of the quartz can also be a useful tool for provenance analysis, because of the signal properties inherited from its parent rock, weathering conditions, and depositional history (i.e. cycles of erosion, transport, and deposition). These provenance studies are based on the OSL sensitivity (i.e. the light emitted per unit mass per radiation dose) of the first second of the luminesce signal of the quartz, using relatively fast and low-cost measurements. Since laboratories worldwide already have an extensive database with results of quartz signals primarily measured for dating studies, these data could potentially be repurposed for sensitivity analysis.

Here, we investigate the use of OSL quartz signals, originally measured for dating, for now characterizing the quartz OSL sensitivity and their usefulness for provenance analysis. The samples we studied are from Amazon fluvial systems: two Holocene endmembers from the Xingu and Solimões rivers, representatives of cratonic and Andean sediment sources, respectively, and a Pleistocene sample from Içá Formation, a paleo-fluvial system whose provenance is not fully known. First, we evaluate our approach by calculating the OSL quartz sensitivity of all quartz signals (i.e. signals derived from the natural, regenerative, and test doses) measured in a dating sequence with the Single Aliquot Regenerative dose (SAR) protocol. Such analysis gives the basis for deciding which signal, if any, should be prioritized for sensitivity calculation. Then, we compare the OSL sensitivities derived from quartz signals measured using the conventional sensitivity protocol with those measured by the conventional dating protocol. Finally, we deduce the sediment source of the Pleistocene Içá Formation based on the modern analogues (the Holocene endmembers).

Our preliminary results show that: it is feasible to use data from dating sequences for sensitivity calculation; OSL quartz signal derived from the natural test doses (Ln) is the best candidate for sensitivity calculation; the sensitivities provided by our approach are slightly larger than those calculated using the conventional sensitivity protocol; and, the Pleistocene Içá Formation represents a mixed-source (Andean and Cratonic), which is different from the presumed modern analogue represented by the Solimões river, which is dominated by Andean sediments.
Plasma waves in the inner Jovian magnetosphere at low to mid-latitudes
Authors: Kurth William , Hospodarsky George , Sulaiman Ali , Elliott Sadie , Menietti John D. , Faden Jeremy , Piker Chris , Wilkinson Darrelle , Connerney John E. C. , Bolton Scott , Allegrini Frederic , Mauk Barry
Published: March 2021

Juno's highly eccentric polar orbit was designed to provide the first measurements at low altitudes over the poles to explore Jupiter’s polar magnetosphere and auroras.  Orbit precession moves the initially equatorial perijove to higher northern latitudes at a rate of about one degree per orbit.  One result of the precession is that Juno crosses the equator at decreasing radial distances during the inbound portion of the orbit. Recently, Juno has crossed the magnetic equator at distances of 10 Jovian radii (RJ) and less.  Voyager and Galileo observations have shown the magnetic equator inside of 10 RJ to be the site of numerous plasma wave phenomena including whistler-mode hiss, chorus, electron cyclotron harmonics and upper hybrid bands.  In addition, this is the location of the plasma sheet at the outer edge of the Io and Europa torii.  The Juno orbit, with its near-polar inclination carries the spacecraft through this intriguing region to higher latitudes.  This paper examines the evolution of whistler-mode chorus and hiss as well as electron cyclotron waves from the magnetic equator to higher latitudes.  While there are now statistical studies of electromagnetic waves at intermediate latitudes based on Galileo and Juno observations, this paper is designed to show details of these wave phenomena utilizing the Juno Waves instrument’s burst mode for high resolution.  Each of these wave phenomena has the potential to interact with the electrons in the inner magnetosphere and cause pitch-angle scattering and/or acceleration, so they are important in the flow of mass and energy through the Jovian system.
Cloud effects on surface radiation balance at Helheim and Jakobshavn Glaciers (Greenland) using ground-based observations 
Authors: Djoumna Georges , Mernild Sebastian H. , Holland David
Published: March 2021

The surface radiation budget is an essential component of the total energy exchange between the atmosphere and the Earth’s surface. Measurements of radiative fluxes near/on ice surfaces are sparse in the polar regions, including on the Greenland Ice Sheet (GrIS), and the effects of cloud on radiative fluxes are still poorly studied. In this work, we assess the impacts of cloud on radiative fluxes using two metrics: the longwave-equivalent cloudiness, derived from long-wave radiation measurements, and the cloud transmittance factor, obtained from short-wave radiation. The metrics are applied to radiation data from two automatic weather stations located over the bare ground near the ice front of Helheim (HG) and Jakobshavn Isbræ (JI) on the GrIS. Comparisons of meteorological parameters, surface radiation fluxes, and cloud metrics show significant differences between the two sites. The cloud transmittance factor is higher at HG than at JI, and the incoming short-wave radiation in the summer at HG is 50.0 W m−2 larger than at JI. Cloud metrics derived at the two sites reveal   a high dependency on the wind direction. The total cloud radiative effect (CREnet) generally increases during melt season at the two stations due to long-wave CRE enhancement by cloud fraction.  CREnet decreases from May to June and increases afterward, due to the strengthened short-wave CRE. The annually averaged CREnet were 3.0 ± 7.4 W m-2 and 1.9 ± 15.1 W m−2 at JI and HG.  CREnet estimated from AWS indicates that clouds cool the JI and HG during melt season at different rates.
Holocene sediment budget for wave-dominated Moruya coastline, southeastern Australia: sediment sources, transport and embayment interconnectivity
Authors: Oliver Thomas , Tamura Toru , Brooke Brendan , Short Andrew , Kinsela Michael , Woodroffe Colin , Thom Bruce
Published: March 2021

Sediment budgets on wave-dominated coastlines are important in understanding shoreline behaviour. Coastal sediment compartments provide a means to investigate sediment budgets over a range of time and space scales. This study reconstructs the sediment budget over the mid- to late- Holocene for a secondary coastal compartment on the New South Wales (NSW) south coast ~26 km in length and containing five adjacent but discrete barriers: Barlings Beach, Broulee Beach, Bengello Beach, Moruya Heads Beach and Pedro Beach. Building upon existing morphostratigraphic studies in this region, a new set of Optically Stimulated Luminescence (OSL) ages are reported for foredune ridge successions at previously un-dated sites. Additional Ground Penetrating Radar (GPR) transects complement earlier stratigraphic data, and topographic and bathymetric LiDAR datasets capture the morphology of subaerial coastal deposits and the inner shelf. The results demonstrate two different sediment sources promoting shoreline progradation and coastal barrier construction. A quartz-rich sand, transported onshore from the shoreface as it evolved towards equilibrium, dominates the barrier sequences. Skeletal carbonate sand augmented the quartz sand supply for the northern Barlings and Broulee beaches after ~3000 years ago. Shoreline progradation at Bengello Beach was steady throughout the mid-to late- Holocene. Bengello Beach contains the largest volume of Holocene sand and accreted at an average rate of 3.1 m3/m/yr (for the current shoreline length). Changes in sediment accumulation rate has occurred for the other barrier systems as their shorelines prograded resulting in changes to their alongshore interconnectivity. Rapid infilling of the Pedro Beach embayment by ~4000 years ago initiated headland bypassing northwards to Moruya Heads Beach which only then commenced progradation. In contrast, as Broulee and Bengello Beaches prograded, a tombolo formed in the lee of Broulee Headland which restricted northward sand drift into the Broulee embayment. As these once continuous shorelines became two, a marked increase in skeletal carbonate content at Broulee occurred attesting to shoreline separation and independence of sediment budget. This study emphasises the importance of quantifying the long-term temporal variability in sediment budget and embayment interconnectivity in order to better understand shoreline response to contemporary anthropogenic influences and changing boundary conditions such as sea level and wave climate.
A Tarim-North India connection in northern Gondwana: Constraints from provenance of early Paleozoic sedimentary rocks in the Altyn Tagh orogen, southeastern Tarim
Authors: Liu Qian , Tsunogae Toshiaki , Zhao Guochun , Han Yigui , Yao Jinlong , Li Jianhua , Wang Peng
Published: March 2021

Amalgamation of northern Gondwana involves a wealth of present-day East Asian blocks (e.g., South China, North China, Alxa, Tarim, Indochina, Qiangtang, Sibumasu, Lhasa, etc.) due to consumption and closure of the Proto-Tethys Ocean. Locating the Tarim craton during assembly of northern Gondwana remains enigmatic, with different models separating Tarim from Gondwana by a paleoceanic domain throughout the Paleozoic, advocating a long-term Tarim-Australia linkage in the Neoproterozoic to the early Paleozoic, or suggesting a Tarim-Arabia connection in the early Paleozoic.

This study carried out field-based zircon U-Pb dating and Hf isotopic analyses for early Paleozoic sedimentary rocks in the Altyn Tagh orogen, southeastern Tarim. New dating results revealed that the early Paleozoic sedimentary rocks were deposited from ca. 494 to 449 Ma. Provenance tracing indicates the ca. 494-477 Ma sedimentary rocks were primarily sourced from the local Altyn Tagh orogen to the south of the North Altyn Ocean (one branch of the Proto-Tethys Ocean between southeastern Tarim and northern Gondwana). In contrast, the ca. 465-449 Ma sedimentary rocks have remarkably increasing ca. 840-780 Ma, 2.0-1.7 Ga, and 2.7-2.4 Ga detrital zircons, indicating an augmented supply of detritus from the Tarim craton to the north of the North Altyn Ocean. Such a significant provenance shift between ca. 477 and 465 Ma marks the timing of the final closure of the North Altyn Ocean. Combined with the timing of the final closure of other branches of the Proto-Tethys Ocean, the entire Proto-Tethys Ocean might have been progressively closed at ca. 500-420 Ma, resulting in the connection of most East Asian blocks with northern Gondwana. Based on detrital zircon U-Pb-Hf isotopic comparison, Tarim most likely shared a North Indian affinity with many East Asian blocks (such as North Qilian, North Qinling, South China, Indochina, South Qiangtang, etc.). This new finding argues against an Australian or Arabian affinity for the Tarim craton.

This work was financially supported by National Natural Science Foundation of China Projects (grants 41730213, 42072264, 41902229, 41972237, and 41888101), Hong Kong Research Grants Council General Research Fund (grant 17307918), and Grant-in-Aids for Scientific Research from Japan Society for the Promotion of Science (JSPS) to Prof. Toshiaki Tsunogae (No. 18H01300) and to Dr. Qian Liu (No. 19F19020). JSPS fellowship is also much appreciated.
The Atlantic jet response to forcing: a regime perspective
Authors: Goss Michael , Sheshadri Aditi , Lindgren Erik , Diffenbaugh Noah
Published: March 2021

The winter jet stream in the North Atlantic has been shown to preferentially occur at three distinct latitudes [Woolings et al., 2010; Woolings et al., 2018], which we will call the three Atlantic “jet regimes.” Distinct physical mechanisms may be responsible for each of the three jet regimes—for example, the northernmost jet regime is strongly linked to the Greenland tip jet [White et al., 2019]. We seek to investigate the role of stratospheric and CO2 forcing, such as from sudden stratospheric warmings (SSWs), strong polar vortex events (SPVs), and anthropogenic global warming, on the Atlantic jet in the context of these jet regimes.

To do so, we use a “jet latitude index” (JLI), which is determined by finding the latitude of the peak zonal winds over some latitude range, averaged over some longitude range, to show that sudden stratospheric warmings (SSWs) impact the likelihood that the Atlantic jet will be in any particular jet regime. These calculations are performed in the ECMWF Interim Reanalysis (ERAI) data set, an in-house 200-year Whole Atmosphere Community Climate Model (WACCM) run, and in a subset of CMIP6 models. We seek to investigate how changes in the composite response of the jet over the Atlantic associated with SSWs, SPVs, and greenhouse gas forcing, are borne out in the context of the three Atlantic jet regimes. We find that, following SSWs, the northern regime becomes less frequent, and the southern regime becomes more frequent, while the jet latitude peaks of the regimes do not notably shift. Following SPVs, the northern regime becomes more frequent, the southern regime becomes less frequent, and again, the peak latitudes do not shift. Under CO2 forcing, we do not find a consistent signal from model to model, and we test whether these differences may be related to model differences in local meridional temperature gradients over the Atlantic.
Topography-correlated atmospheric signal mitigation for InSAR applications in the Tibetan plateau based on global atmospheric models
Authors: Wang Yuqing , Chang Ling , Feng Wanpeng , Samsonov Sergey , Zheng Wenjun
Published: March 2021

Atmospheric heterogeneity mainly exposes itself as tropospheric phase delay in satellite interferometric synthetic aperture radar (InSAR) observations, which smears or even overshadows the deformation component of InSAR measurements. In this study, we estimated the performance of four global atmospheric models (GAMs), i.e. ERA5, ERA-Interim (ERA-I), MERRA2 and GACOS, for tropospheric phase delay reduction in InSAR applications in the Tibetan plateau, of which ERA5 is the latest global atmospheric model released by ECMWF. We demonstrated the effectiveness of atmospheric phase screen (APS) correction using the four GAMs for more than 700 Sentinel-1 TOPS interferograms covering two study areas in the southern (R1) and northwest margins (R2) of the Tibetan plateau. Topography-correlated signals have been widely observed in these interferograms, which are most likely due to the APS effects. We calculated the standard deviations (STD) and correlation coefficients between InSAR Line of Sight (LOS) measurements and topography before and after applying APS correction. The results show that the STDs of non-deformation areas from the GAMs decrease to ~4 mm from ~10 mm and ~12 mm originally on average for R1 and R2, respectively, and the correlation coefficients after the APS correction are reduced below 0.4 from ~0.8 for the selected interferometric pairs. In addition, as the newly released GAM, ERA5 has similar performance with GACOS products and outperforms other models generally. This suggests that GAMs, particularly ERA5, have great potentials in the APS correction for InSAR applications in the Tibetan plateau.
Root bio-hydro-mechanical reinforcement of unsaturated vegetated soil: experiments and modelling
Authors: Leung Anthony , Boldrin Davide , Karimzadeh Ali Akbar , Wu Zhaoyi , Ganesan Suriya
Published: March 2021

Plant roots affect soil water regime through root-water uptake upon transpiration. This process induces soil matric suction, which affects soil hydraulic conductivity, soil shear strength and hence shallow soil stability. This is referred to as plant hydrological reinforcement in the soil bioengineering application. Recent experimental evidence put forward by the authors has demonstrated that plant hydrological reinforcement should not be exclusively limited to the effects of root-water uptake and plant transpiration. The presentation will provide some new evidence of other potential aspects of plant hydrological reinforcement, namely (1) root-induced changes in soil hydraulic properties, (2) root water-dependent bio-hydro-mechanical properties. In aspect (1), laboratory test results on how root growth dynamic alter the soil pore size distribution and hence affect both the soil water retention curve and hydraulic conductivity will be presented. To highlight the effects of these root-induced changes in soil properties on slope water regime and slope stability, numerical simulation employing a dual-permeability water transport model in unsaturated rooted soil will be discussed. In aspect (2), a new concept, hysteretic root water retention curve (relationship between root water content and root water potential), will be introduced with support of some preliminary data. How root water retention affects the root biomechanical properties including not only tensile strength and Young’s modulus that have received wide attention in the soil bioengineering literature but also breakage strain will be presented. New data will be provided in order to attempt to use root water content to explain the large variability of biomechanical properties observed in the literature.
Time-scale dependent mechanism of atmospheric CO2 concentration drivers of watershed water-energy balance
Authors: Zhao Jing
Published: March 2021

The elevated atmospheric carbon dioxide concentration (CO2), as a key variable linking human activities and climate change, seriously affects the watershed hydrological processes. However, whether and how atmospheric CO2 influences the watershed water-energy balance dynamics at multiple time scales have not been revealed. Based on long-term hydrometeorological data, the variation of non-stationary parameter n series in the Choudhury's equation in the mainstream of the Wei River Basin (WRB), the Jing River Basin (JRB) and Beiluo River Basin (BLRB), three typical Loess Plateau regions in China, was examined. Subsequently, the Empirical Mode Decomposition method was applied to explore the impact of CO2 on watershed water-energy balance dynamics at multiple time scales. Results indicate that (1) in the context of warming and drying condition, annual n series in the WRB displays a significantly increasing trend, while that in the JRB and BLRB presents non-significantly decreasing trends; (2) the non-stationary n series was divided into 3-, 7-, 18-, exceeding 18-year time scale oscillations and a trend residual. In the WRB and BLRB, the overall variation of n was dominated by the residual, whereas in the JRB it was dominated by the 7-year time scale oscillation; (3) the relationship between CO2 concentration and n series was significant in the WRB except for 3-year time scale. In the JRB, CO2 concentration and n series were significantly correlated on the 7- and exceeding 7-year time scales, while in the BLRB, such a significant relationship existed only on the 18- and exceeding 18-year time scales. (4) CO2-driven temperature rise and vegetation greening elevated the aridity index and evaporation ratio, thus impacting watershed water-energy balance dynamics. This study provided a deeper explanation for the possible impact of CO2 concentration on the watershed hydrological processes.
Nitrous oxide emission from agricultural soils in response to nitrification inhibitor and N-fertilizer amount
Authors: Tariq Azeem , Larsen Klaus Steenberg , Hansen Line Vinther , Jensen Lars Stoumann , Bruun Sander
Published: March 2021

Nitrogen (N) fertilization in agricultural soils significantly contributes to the atmospheric increase of nitrous oxide (N2O). Application of nitrification inhibitors (NIs) is a promising strategy to mitigate N2O emissions and improve N use efficiency in agricultural systems. We studied the effect of 3,4-dimethylpyrazol phosphate (DMPP) as an NI on N2O mitigation from soils with spring barley and spring rape. We used both manual and automatic chamber technologies to capture the spatial and temporal dynamics of N2O emissions. Intensive manual chamber measurements were conducted two months after fertilization and fortnightly afterwards. A mini-plot experiment with different levels (0 %, 50 %, 100 %, 150 %, and 200 %) of standard N fertilizer application and 100% N with NI was also conducted for two months in soil planted with spring barley. N2O emissions were affected by the N amount and by the use of NI. Higher emissions were observed in treatments with high N levels and without NI. The effect of NI in reducing N2O emissions from spring barley plots was significant in the small chamber experiments, where NI reduced N2O emissions by 47 % in the first two months after fertilization. However, the effect of NI on N2O reduction was non-significant in the full-plot chamber experiment for the whole season. In contrast, NI significantly reduced (56 %) the seasonal N2O emissions from the soils planted with spring rape. After the initial peaks following the fertilizer application, high N2O fluxes were observed following substantial rain events. The continuous flux measurements in automated chambers showed the dynamic of N2O changes during the whole season, including some peaks that were unobservable with manual chambers because of the low temporal resolution. The concentration of nitrate was higher in the soils treated with mineral N without NI compared to soils treated with NI, which clearly showed the inhibition of the nitrification process with the application of NI. The grain and biomass yield were not affected by the use of NI. In conclusion, application of NI is an efficient mitigation technology for N2O emissions in the period following the fertilizer application, but had little effect on subsequent emissions following rain events.

Keywords: nitrification inhibitors, DMPP, nitrous oxide, mitigation, agricultural soils
Structure and connectivity of CME-driven shocks and sheaths through the inner heliosphere
Authors: Palmerio Erika , Lee Christina , Odstrcil Dusan , Mays Leila
Published: March 2021

The evolution of coronal mass ejections (CMEs) as they travel away from the Sun is one of the major issues in heliophysics and space weather. During propagation, CMEs and the structures ahead of them (i.e., interplanetary shocks and sheath regions, if present) are significantly affected by the ambient solar wind, which is able to alter their speed, trajectory, and orientation. The scarcity of multi-spacecraft measurements of the same CME, however, implies that little is known about how and where (in terms of distance from the Sun) these various processes exactly come into play.

To address this issue, we run a series of 3D magnetohydrodynamic simulations using the coupled solar–heliospheric WSA–Enlil model, in which we launch idealised CMEs as hydrodynamic (non-magnetised) structures. This allows us to focus on the evolution of CME-driven shocks and sheath regions through a multi-point study. We launch CMEs of various speeds through different solar wind backgrounds and at different heliolongitudes with respect to the streamer belt position. Then, we investigate the resulting magnetic field and plasma parameters at a series of synthetic spacecraft placed at various longitudes around the CME apex and at various heliocentric distances between 0.5 AU and 2 AU. We also analyse how the magnetic connectivity at these spacecraft evolves as the CME propagates. This work represents a comprehensive study of the interaction of CME-driven shocks and sheath regions with the large-scale solar wind structure throughout the inner heliosphere, with the aim to establish a range of expected behaviours and outcomes useful to interpret real events.
Recurring magnetic field anomalies in the South Atlantic and the first palaeointensities from Saint Helena
Authors: Engbers Yael , Biggin Andy , Grappone J. Michael
Published: March 2021

A long-lived hypothesis is that, if averaged over sufficient time (ca 10 million years), the Earth’s magnetic field approximates a geocentric axial dipole (GAD). Despite this common assumption, the question of how significant the non-GAD features are in the time-averaged field is an important and unresolved one. In the present-day field, the South Atlantic Anomaly (SAA) is the biggest irregularity in the field. We know that this anomaly has not always been a part of the field, but in Engbers et al., 2020, it was shown that the magnetic field shows irregular behaviour in this region on a million-year timescale. The irregular behaviour was demonstrated through a substantially high VGP dispersion (21.9º) for lava flows from Saint Helena that are between 8 and 11 million years old. The island of Saint Helena is located at the margin of the present-day SAA and has declination -16.6º, inclination -57.5º relative to expected GAD values of 0.0º/-7.8º (Dec/Inc). We have now commenced the measurements of absolute palaeointensity data from this location. So far, we have performed thermal and microwave IZZI-Thellier experiments on 2 localities from Saint Helena. The site mean results show variable but generally very low field intensities, although further work is required to make these sufficiently robust. Our low field estimates suggest a field in the South Atlantic that is not only unstable, but mainly weaker than expected. This could mean that recurring reversed flux patches (RFP) are responsible for the irregularities and weaknesses in the field in this region, stretching back up to 11 million years ago.
Climatic Effects on GPS PPP Accuracy
Authors: Saraçoğlu Aziz , Şanlı Doğan Uğur
Published: March 2021

Recently researchers revealed that meteorological seasons have an effect on the accuracy of GPS. This modified the conventional prediction formulation in which the accuracy was dependent on observing session duration. However, the available accuracy model is from a major climate zone classification. In this study, we evaluate climatic effects on PPP accuracy from a different climate classification: the widely used Köppen Geiger climate zones. GPS data are obtained from SOPAC (Scripps Orbit and Permanent Array Centre) archives. Synthetic GPS campaigns are generated from the permanent stations of the IGS (International GNSS Service). The data are processed using the PPP module of the NASA/JPL's GipsyX software. The RMS values obtained from the processing solutions are used to determine the effect of climate on PPP accuracy. Eventually, we compare the two climate classifications and present our initial impressions from a core network across the new climate zones.

Keywords: GPS, GNSS, accuracy, PPP, climatic effects
A self-consistent simulation of proton acceleration and transport near a high-speed solar wind stream
Authors: Wijsen Nicolas , Samara Evangelia , Aran Àngels , Lario David , Pomoell Jens , Poedts Stefaan
Published: March 2021

Solar wind stream interaction regions (SIRs)  are often characterised by energetic ion enhancements. The mechanisms accelerating these particles as well as the locations where the acceleration occurs, remains debated. Here, we report the findings of a simulation of a SIR-event observed by Parker Solar Probe at 0.56 au and the Solar Terrestrial Relations Observatory-Ahead at 0.96 au in September 2019 when both spacecraft were approximately radially aligned with the Sun. The simulation reproduces the solar wind configuration and the energetic particle enhancements observed by both spacecraft. Our results show that the energetic particles are produced at the compression waves associated with the SIR and that the suprathermal tail of the solar wind is a good candidate to provide the seed population for particle acceleration. The simulation confirms that the acceleration process does not require shock waves and can already commence within Earth's orbit, with an energy dependence on the precise location where particles are accelerated. The three-dimensional configuration  of the solar wind streams strongly modulates the energetic particle distributions, illustrating the necessity of advanced models to understand  these particle events.

This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870405 (EUHFORIA 2.0).

 