bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of glaciation over High-Mountain Asia since the last glacial maximum
Authors: Yan Qing
Published: March 2020

Reasons for restricted and non-uniform glaciation over High-Mountain Asia (HMA) during last glacial maximum (LGM) have been intensively studied but remain elusive. Using a 1-km-resolution ice-sheet model, we show glaciers across HMA exhibit high region-variability in glaciation. Glaciers in western and southern HMA are the most sensitive to climate change and those in the interior are the least sensitive. Our model broadly reproduces the restricted glaciation across HMA during LGM, although it overestimates the extent of glaciation over western and southern HMA as compared with reconstructions. Modelled decreases in precipitation hampers glacier growth over northern HMA, while insufficient cooling hampers glacier advance over eastern HMA for LGM. Both reduced precipitation and insufficient cooling inhibit large-scale glaciation over inner HMA. Moreover, climatic conditions conducive to glaciation across the entire HMA include a reduction in temperature of ~10ºC and an increase in precipitation, unlikely to have occurred during any Quaternary glacial maximum.

Moreover, based on a transient climate-ice sheet simulation, we demonstrate that the glacier extent shrinks rapidly after the LGM and reaches the minimum around ~8‒7 ka, followed by a slight long-term advancing trend afterwards. Our results suggest a dominant role of summer temperature in controlling the overall trend of glacier response, with precipitation generally modulating the extent of glaciation. However, the timing and extent of glaciation varies across the Himalayan-Tibetan orogen on millennial timescale, especially between the monsoon-influenced southern and westerly-influenced western parts, further confirming previous speculations. 

 
Nailing the hyporheic zone: Rusting metal rods as a proxy for the depth of the oxic zone in hyporheic sediments
Authors: Kaule Robin , Gilfedder Benjamin , Frei Sven
Published: March 2020

Changing climatic drivers significantly endanger the function of the hyporheic zone (HZ). Increased temperature leads to an increase in respiration and expansion of anoxic areas in river sediments. Under conditions of low stream discharge (with high proportion of groundwater) reduced substances enter the upper parts of the HZ and surface water. Contact with dissolved oxygen (DO) leads to formation of areas of preferential oxidation of reduced substances (e.g. iron precipitation and clogging of pore spaces, nitrification).  Thus oxygen levels in the hyporhic zone are an important parameter for understanding biogeochemical cycles in the stream sediments. However, oxygen measurements are time consuming, prone to error and instruments are expensive.

In this work we hypothesize that iron nails can be used as a very simple and inexpensive tool for mapping the depth of oxygen penetration into hyporheic sediments. The experiments compared iron oxidation of nails inserted in a laboratory scale sand tank model for hyporheic flow as well as a riffle-pool sequence in northern Bavaria, Germany. We have combined this with a mathematical model that simulates flow and biogeochemical reactions in the subsurface and with direct oxygen measurements in the sediment.

Oxygen measurements showed that oxygen concentrations decrease from over 8 mg l-1 to less than 1 mg l-1 in the first 15 cm of the tank model. This agreed well with the mathematical model, which predicted the decrease of oxygen to approximately the same depth. The nails showed a clear rust (iron oxide) crust down to sub-oxic DO levels (at ~11 cm) while below this we observed a black precipitate indicating reducing conditions. In some cases, we found an area between the oxic and anoxic zones where there were no obvious signs of reaction on the nails surface. The mathematic model indicated that the water residence time in the oxic part of the tank was ~5 h while it took up to 19 h to pass through the anoxic zone and out of the tank.

The field results confirms that rust on the nails can be used to indicate oxic depths, but with a somewhat more complex pattern along the riffle-pool sequence.

Iron oxidation and associated rust on the metal nails gives us only qualitative data on the presence or absence of Oxygen. Quantitative data may be derived by determining the iron mineral phases on the nails (using e.g. Raman spectroscopy). Overall this appears to be a very inexpensive method for gaining high spatial resolution information of oxygen levels in the hyporheic zone, which is important for stream ecosystems as well as biogeochemistry.
Microplastic transport, deposition and burial in seafloor sediments by turbidity currents
Authors: Pohl Florian , Eggenhuisen Joris , Kane Ian , Clare Michael
Published: March 2020

Plastic pollution of the world’s oceans represents a threat to marine eco-systems and human health and has come under increasing scrutiny from the general public. Today the global input of plastic waste into the oceans is in the order of 10 million tons per year and predicted to rise by an order of magnitude by 2025; much of this plastic ends up on the seafloor. Plastics, and microplastics, are known to be concentrated in submarine canyons due to their proximity to terrestrial plastic sources, i.e. rivers. Plastics are transported in canyons by turbidity currents, mixtures of sediment and water which flow down-canyon due to their density; these flows can also ‘flush’ canyons, eroding and entraining the sediment lining the canyon walls and bottom. A single turbidity current can last for weeks and transport more sediment than the annual flux of all terrestrial rivers combined. Although it is known that these flows play a critical role in delivering terrestrial sediment and organic carbon to the seafloor, their ability to transport and bury plastics is poorly-understood. Using flume experiments we investigate turbidity currents as agents for the transport and burial of microplastic fragments and fibers. Microplastic fragments are focused at the flow base, whereas fibers are more homogeneously distributed throughout the flow. Surprisingly though, the resultant deposits show the opposite trend with fibers having a higher concentration that fragments. We explain this observation with a depositional mechanism whereby fibers are dragged out of suspension by settling sand grains, are trapped in the aggrading sediment bed and are buried in the deposits. Conversely, fragments may remain suspended in the flow and are less likely to be trapped on the bed. Our results suggest that turbidity currents can transport microplastics over long distances across the ocean floor, and that turbidity currents potentially distribute and bury large quantities of microplastics in seafloor sediments.
Towards the predictive simulation of complex high-mountain landslide cascades
Authors: Mergili Martin , Pudasaini Shiva P.
Published: March 2020

Complex cascades of landslide processes in changing high-mountain areas have the potential to result in disasters with major loss of life and disruption of critical infrastructures. Simulation tools have been developed to anticipate and, consequently, more effectively manage, landslide hazards and risks. However, the detailed prediction of future events remains a major challenge particularly for complex cascading events. In the previous years, we have successfully back-calculated a set of well-documented historic landslide cascades with the mass flow simulation tool r.avaflow, deriving sets of optimized parameters. In the present contribution, we use the findings from these back-calculations to propose two approaches for predictive simulations with an updated version of r.avaflow, based on the multi-phase mass flow model by Pudasaini and Mergili (2019):

(i) Using the minima and maxima of the parameter sets summarized from the back-calculations to simulate areas of certain impact and areas of possible impact, and ranges of possible travel times and kinetic energies. The limitation of this method is that parameters often depend on the process magnitude and have to be spatially differentiated for zones of similar topography and process type, meaning that the process type has to be prescribed.

(ii) Deducing from the guiding parameter set a function that relates the key model parameters (particularly, friction parameters) to a suitable dynamic flow parameter (we suggest the kinetic energy). This approach has the advantage that the definition of zones becomes obsolete. However, much more research is necessary to constrain the proposed function.

We apply both approaches to the well-documented 2002 Kolka-Karmadon event in the Russian Caucasus, where an initial fall of ice and rock entrained almost an entire glacier, triggering a high-energy ice-rock avalanche followed by a distal mud flow. Both of the simulations (i) and (ii) yield empirically mostly adequate results in terms of impact areas, volumes, hydrographs, and flow velocities, leading to the preliminary conclusion that they represent a major step forward in our ability to predict high-mountain process chains. However, some aspects are not fully reproduced by (i), whereas others are not fully reproduced by (ii), calling for further research.

Pudasaini, S. P. and  Mergili, M. (2019): Journal of Geophysical Research – Earth Surface, doi:10.1029/2019JF005204

 
Telluric currents play a big role in interpreting geomagnetic variations
Authors: Viljanen Ari , Juusola Liisa
Published: March 2020

Fast geomagnetic variations of periods from seconds to hours and days are primarily produced by currents in the ionosphere and magnetosphere. There is always an associated secondary (internal, telluric) current system induced in the conducting ground and contributing to the total variation field measured by ground magnetometers. Mathematically, it is possible to fully explain the variation field by two equivalent current systems, one at the ionospheric altitude and another just below the ground. In practice, this separation is feasible using dense magnetometer networks.

A common way in space physics has been to implicitly neglect the internal part and interpret the ground field only in terms of ionospheric currents. As known from previous studies, this is often a reasonable assumption, since a typical internal contribution is about 30%. However, the situation is much different when the time derivative of the magnetic field (dB/dt) is considered. For the north European IMAGE magnetometer network, the internal part exceeds the external one nearly at all stations. The largest effects due to telluric currents occur at coastal sites close to highly-conducting ocean water and at inland locations close to highly-conducting near-surface anomalies.

This finding gives a new viewpoint for studies of geomagnetically induced currents (GIC), which are closely related to dB/dt. One key question is to understand which are the ionospheric drivers of big GIC events. We will demonstrate how the telluric currents can strongly modify field variations and especially dB/dt, and how this is correspondingly seen in equivalent current patterns. Consequently, it is recommended that the field separation is performed whenever it is feasible, i.e. a dense observation network is available.
Differential migration of interstitial immiscible liquids in the Skaergaard Layered Series
Authors: Holness Marian , Honour Victoria , Nicoli Gautier
Published: March 2020

The liquid line of descent of the Skaergaard magma intersects a binodal creating an immiscible conjugate pair comprising a dense Fe-rich liquid and a buoyant Si-rich liquid. These two liquids have different wetting properties: the Si-rich liquid wets plagioclase, whereas the Fe-rich liquid wets oxides, pyroxene and olivine. The two liquids may therefore undergo differential migration within a gabbroic crystal mush: the Fe-rich liquid sinks and accumulates in mafic layers, while the Si-rich liquid rises and accumulates in plagioclase-rich regions.

Field-scale evidence of metre-scale differential migration of unmixed immiscible interstitial liquids is provided by paired felsic and mafic lenses spatially associated with gabbroic pegmatite bodies in the Skaergaard floor cumulates. These represent small batches of late-stage liquids rising from the pegmatite bodies into the overlying mush, and their subsequent separation into immiscible conjugates. The paired lenses form irregular, approximately layer-parallel clusters in thick mush, but thin concordant dendritic structures within strongly foliated thin mush. Invariably the melanocratic component lies stratigraphically below the felsic component.

Differential migration within the floor cumulates is also recorded by mm-scale mafic and felsic rims developed on the top and bottom margins of anorthositic blocks derived from the roof. Highly tabular blocks have an upper mafic rim and a lower leucocratic rim. As the block aspect ratio decreases, the rims disappear, with the mafic rim retained at lower aspect ratios than the leucocratic rim. We interpret rim formation as a consequence of trapping migrating unmixed interstitial liquid against the relatively impermeable blocks: tabular blocks are most effective at trapping these liquids.

On a smaller scale, the different wetting properties of the two immiscible conjugates result in post-accumulation pattern formation in rapidly deposited modally graded layers, imposing cm-scale internal layering on the overall modal grading. The tops of the modally-graded layers may also develop felsic flame-like structures interpreted as a consequence of upwards-migration of the immiscible Si-rich conjugate from high-porosity rapidly deposited layers into the overlying cumulates.

These observations demonstrate the complexity of behaviour in a crystal mush containing a two-phase interstitial liquid. Understanding cumulate evolution necessitates a consideration of the scale of migration of interstitial liquid and the possibility of the differential loss of one of the two conjugates.
The Effect of Cultivation on the Greenhouse Gases Emissions in wujiang river Basin, Yangtze River, China
Authors: wu xiaoling
Published: March 2020

Climate change has gained extensive international attention due to the impacts on the regional agriculture and water supply. According to IPCC, the global mean temperature will increase by 0.3-0.8 centigrade. Greenhouse gases such as CO2, CH4, and N2O will concentrate and global mean temperature are projected to be increasing. This study separately examines the Greenhouse gases effect arise from different tillage type (dry land and paddy crop) in Wujiang river basin using DeNitrification - DeComposition (DNDC) model. The simulations indicate that, the atmospheric CO2 and CH4 concentration increases with the paddy crop plants. Although between two irrigation periods, the field drying event can decrease the CH4 production effectively. In addition, the paddy soils in this region tend to increase the effect of carbon source resulted from the flooding irrigation. Especially in the first flood irrigation period, the N2O increases to the maximum value. By contrast, in crop land under rotation of rape and Maize, the effect of carbon sink induced from CO2 fertilization could generally offset the effect of carbon source. Meanwhile, the effect of carbon sink increased resulted by the plant grows. Thus, the production of CO2 is always negative. There is no CH4 production in crop land under rotation of rape and Maize. By contrast, with fertilization input, the N2O production increases from 0.05 kg C/kg to 0.5kg N/ha/day. The SOC from the top soils (0-10 cm) to bottom (40-50 cm) decreases from 0.021 kg C/kg to 0.014 kg C/kg in either dry land and paddy soils of the Wujiang River region from 1991 to 1994, respectively. These results suggest that SOC storage in paddy and dry land of this region is steady. For the dry land crop (rotation of rape and Maize), the N2O increased with the fertilization. But for the paddy soils, the irrigation time is the key point period for greenhouse gases production and the variation of carbon and nitrogen in soil. As a representative of paddy crop and dry land crop (rotation of rape and Maize) in western China, the insights gained from the Wujiang River basin may be potentially transferable to other similar agricultural practices in other part of China.
North Pacific Subtropical Mode Water Controlled by the Atlantic Multi-Decadal Variability
Authors: wu Baolan , lin Xiaopei , yu Lisan
Published: March 2020

The North Pacific Subtropical Mode Water (mode water hereafter) is a vertically homogeneous thermocline water mass, occupying the entire subtropical Western Pacific Ocean. By transporting mass, heat and nutrients from the surface into the subsurface ocean, it provides memory of climate variability and is a potential source of predictability. Previous studies attributed decadal variability of the mode water mean temperature to the Pacific Decadal Oscillation (PDO). Using available observations and reanalysis data, here we show that decadal to multi-decadal variability of the mode water mean temperature is controlled by the Atlantic Multi-Decadal Variability (AMV) instead. During an AMV positive phase, warm sea surface temperatures (SSTs) in the north Atlantic Ocean weaken the subtropical North Pacific westerlies, and the anomalous easterlies in the subtropical west Pacific drive an anomalous northward Ekman transport of warm water into the mode water formation area. This increases the mode water temperature through subduction, driving variability of the upper-layer ocean heat content and fish catches in the Northwestern Pacific. This mechanism is supported by a long pre-industrial model simulation with multiple AMV cycles and by a Pacemaker model experiment, in which the AMV forcing alone is shown to drive the variability of the mode water. Our finding suggests that the AMV is an important driver for decadal climate and ecosystem variability and provides memory for prediction in the Pacific Ocean.
Spatial distribution of soil organic carbon may be predominantly regulated by topography in a small revegetated watershed
Authors: Zha Tonggang , Yu Haiyan , Zhang Xiaoxia , yu Yang
Published: March 2020

Understanding the spatial distribution and controlling factors of soil organic carbon (SOC) at different scales is essential for an accurate estimation of soil organic carbon stocks. Furthermore, this understanding is vital for evaluating the impact of soil management on both soil quality and climate change. This study was conducted in a Loess revegetated small watershed and the effects of the topography and vegetation factors on the content and distribution of SOC at different soil depths were evaluated. Soil profiles (0-200 cm; n = 122) were sampled that represent six vegetation types (i.e., natural mixed forests, artificial mixed forests, artificial forests with a single tree species, shrubbery, and grassland) and four topographic factors (i.e., elevation, slope gradient, slope position, and slope aspect). The following results were obtained: (1) The mean SOC of the 200 cm soil profile ranged from 2.34 g kg-1 to 5.70 g kg-1, decreasing with increasing soil depth. (2) The interactions between vegetation type and topography and soil depth significantly impacted SOC (P < 0.05). Significant differences in the SOC content (P < 0.05) were also found for slope gradient, slope position, slope aspect, and elevation for 0-200cm, 0-160cm, 0-120 cm and 0-200 cm, respectively. (3) The relative contribution of topographic factors to the SOC content exceeded that of vegetation type in entire soil profile. Topography was the dominant factor controlling the spatial distribution of SOC in the studied small watershed. Therefore, topographic factors should be considered more than vegetation types for an accurate estimation of SOC storage in a revegetated small watershed. This is particularly important for the complicated topography of the loess-gully region.
Interplanetary shocks at 5 AU and their effects on Jupiter's decametric radio emissions
Authors: Echer Ezequiel
Published: March 2020

Interplanetary shocks cause large and abrupt changes in solar wind plasma and magnetic field parameters. Shock occurrence and strength are dependent on the heliocentric distance. Further, shocks have important effects on planetary magnetospheres, such as causing large magnetospheric compressions or expansions, and triggering auroral activity emissions. In this work recent results regarding interplanetary shock parameters determined from analysis of in-situ spacecraft plasma and magnetic field data measured near Jupiter’s orbit are presented. The distribution of parameters for both fast forward and fast reverse shocks is analysed and compared with interplanetary shocks detected at other heliocentric distances, Further, an analysis of  interplanetary shock effects on Jupiter decametric auroral radio emissions independent of Io (non-Io DAM) is presented. 
A novel global AR identification algorithm
Authors: Lu Mengqian , Pan Mengxin
Published: March 2020

Atmospheric river (AR), which is defined as long, narrow and transient corridor with enhanced moisture transport, received more and more scientific attention because of its crucial roles in the global water cycle, water resource management and hydrometeorological extremes. In recent years, dozens of AR identification algorithms are proposed to detect and quantify ARs. However, limitations still exist. In this study, a novel global AR identification algorithm is developed to address some limitations among all the state-of-the-art AR algorithms. First, in the AR pathway detection, a coupled quantile and Gaussian kernel smoothing technique is implemented to define the IVT threshold to make a balance in capturing the spatiotemporal variation of IVT climatology and avoiding largely biased estimation. Second, in spite of the variety of AR shape, orientation and curvature, more reliable AR metrics (e.g., length and width) can be determined based on the smooth AR trajectory, which is generated by modifying and integrating the concept of local regression and K-nearest-neighbors. Third, a robust and resilient criterion is developed to filter the tropical moisture swell. Four, an exquisite metric (turning angle series) is proposed, which is helpful to distinguish the tropical cyclone-like (TC-like) features and quantify the AR curvature which may bridge the ARs to the atmospheric circulation system. Last but not least, another novel metric () is developed to measure the localized IVT coherence on the AR pathway. For each grid, the  is defined as the inter-decile range of the IVT direction of its neighbor grids. The IVT coherent/discordant segments on the AR pathway are extracted by an image segmentation algorithm according to their spatial pattern and  values. The coherent segments are more likely to carry on long-distance moisture transport,  governed by the persistent and large-scale circulation system and related to hydrometeorological extreme, while discordant segments are more likely to be corresponding to the localized turbulence, low pressure system or TC-like features. So, flagging the segments into different categories will be significant in the study of the climatic modulation of AR occurrence, intensity, spatial pattern and the associated rainfall predictability. We believe that this algorithm with various metric will facilitate further quantitative investigations by the AR research community in terms of water resource management, hydrometeorological extreme predictability and climate change projections.
Response of South and East Asian summer climate to North Atlantic SST anomalies: sensitivity to SST patterns
Authors: Bishoyi Ratna Satyaban , Osborn Timothy , Joshi Manoj , Luterbacher Juerg
Published: March 2020

We simulate the response of Asian summer climate to AMO-like (Atlantic Multidecadal Oscillation) sea surface temperature (SST) anomalies using the Intermediate General Circulation Model version 4 (IGCM4). Separate AMO SST patterns are obtained from seven Coupled Model Intercomparison Project phase 5 (CMIP5)/Paleoclimate Model Intercomparison Project phase 3 (PMIP3) global climate models, to explore the sensitivity of the atmospheric response to the SST pattern. Experiments are performed with seven individual and composited AMO SST anomalies globally, and over the North Atlantic Ocean only, for both the positive and negative phases of the AMO. During the positive AMO phase, a Rossby wave train propagates eastward, causing a high pressure anomaly over eastern China/Japan region, associated with a low level anomalous anticyclonic circulation along with warm and dry anomalies. In contrast, the mid-latitude Rossby wave train is less robust in response to the cold phase of the AMO. The circulation response and the associated temperature and precipitation anomalies are sensitive to the AMO SST anomaly patterns. The comparison between global SST and N Atlantic SST experiments indicates that midlatitude East Asian climate anomalies are forced from the North Atlantic region. However, global SST anomaly experiments show that the SST anomalies outside the North Atlantic region, but still associated with AMO, strongly influence South Asian climate as they either strengthen or reduce the precipitation. Experiments with different amplitudes of negative and positive AMO anomalies test the linearity of the response. Over a large region of South and East Asia, temperature has a linear response to the amplitude of North Atlantic SST anomaly associated with both positive and negative AMO conditions, but the precipitation response is nonlinear.
Modelling of the earthquake socio-economic and legal consequences at the urban scale
Authors: Dollet Cyrielle , Guéguen Philippe
Published: March 2020

In moderate-to-low seismic hazard regions, estimating the socio-economic consequences of an earthquake on the urban scale is a costly and difficult task. This study analyses existing global earthquake databases to build a loss flat file of 445 earthquakes since 1967 with a magnitude greater than 4.5. The flat file includes information on the social consequences (fatalities, etc.) and economic losses (direct and indirect costs, number of buildings destroyed or damaged, etc.) of each earthquake. In this study, exposed population and GDP at the date of the earthquake complete the flat file information, estimated in relation to the ground motion footprint provided by USGS ShakeMap. TThe completeness of our catalog of social and economic losses is tested thanks to the creation of a synthetic database of losses of the 22 856 earthquakes between 1967 and 2015 affecting at least one country from the ISC-gem database. From these data, we propose a more realistic loss models. Then, occurrence models of human and direct economic losses relative to the exposed population and GDP per capita are derived showing that, although the number of casualties and the absolute magnitude of losses increase as a consequence of urban concentration, global losses relative to exposure decrease. Finally, the projection of future losses is discussed.
Circular economy in cities: Reviewing how environmental research aligns with local practices
Authors: Petit-Boix Anna , Leipold Sina
Published: March 2020

Circular economy (CE) is gaining popularity at different levels with the promise of creating more sustainable processes. In this context, cities are implementing a number of initiatives that aim to turn them into sustainable circular systems. Whether these initiatives achieve their sustainability goals, however, is largely unknown. Nevertheless, as the application of CE strategies is actively encouraged by many policies across the globe, there is a need to quantify the environmental impacts and to identify the strategies that support urban sustainability. This paper analyses the extent to which research focuses on quantifying the environmental balance of CE initiatives promoted at the municipal level. To this end, the analysis scanned CE initiatives reported in cities around the globe and classiﬁed them into urban targets and CE strategies. In parallel, the paper conducted a review of the literature that uses industrial ecology tools to account for the environmental impacts of CE strategies. Results show a diverse geographical representation, as reported cities concentrated in Europe, whereas for environmental research, the main results came from China. In general, cities encourage strategies relating to urban infrastructure (47%), with and additional focus on social consumption aspects, such as repair and reuse actions. In comparison, research mainly addressed industrial and business practices (58%), but the approach to infrastructure was similar to that of cities, both with a special interest in waste management. Research has yet to assess social consumption and urban planning strategies, the latter essential for deﬁning the impacts of other urban elements. Hence, there is a need to deﬁne the environmental impacts of the strategies that cities select in their quest for circularity. Research and practice can also beneﬁt from working collaboratively so as to prioritize the CE strategies that best ﬁt into the features of each urban area.
An analysis of terrestrial water and groundwater storage changes in North America using recent GRACE products
Authors: Sideris Michael , Piretzidis Dimitrios
Published: March 2020

In this study, we use temporal solutions of the Gravity Recovery and Climate Experiment (GRACE) satellite mission to study the surface mass variations of hydrological origin in North America. The most recent release (RL06) of GRACE Level 2 data from three processing centers (CSR, JPL, GFZ) and mascon products are used in a combination scheme to produce estimates of terrestrial water storage (TWS) changes for the period 2002–2016. The land hydrology signal is isolated from GRACE data by removing the contribution of two major non-hydrologic processes, i.e., the glacial isostatic adjustment (GIA) and the ice mass melting from the glaciated areas of Alaska, Greenland and the Canadian Arctic.

The examination of long-term TWS trends revealed strong signatures of the 2011–2015 droughts in California and Texas, as well as accumulation of TWS in the central part of North America. Negative long-term TWS trends associated with ice melting were found around the Hudson Bay region. The TWS changes are dominated by a strong annual and semi-annual signal with higher magnitude in Alaska and along the west coast of North America.

An additional study on the estimation of groundwater storage (GWS) changes is performed using the Global Land Data Assimilation System (GLDAS) model. The GLDAS data are pre-filtered using the same strategy as GRACE data to ensure spectral consistency between them. The general behavior of GWS agrees well with the TWS, especially in terms of positive long-term GWS trends in central North America and strong annual signal in Alaska. Positive GWS trends are also identified in the east US coast.
New estimates of minimum geological convergence for the eastern Himalaya, India
Authors: Mishra Rajeeb Lochan , Jayangondaperumal Ramakrishnan , Pandey Arjun , Singh Vimal , Srivastava Pradeep
Published: March 2020

We re-investigate the geological slip along the frontal Nameri Thrust, a local name for the Himalayan Frontal Thrust in the eastern Himalaya, India. Four levels of tectonically displaced and uplifted fluvial terraces preserved along the Kameng River were dated using the Optically Stimulated Luminescence (OSL) method. The OSL ages of the terraces bracket the timing of their abandonment post ~14, 11, 7.2 and 3 ka respectively. Considering the minimum timing of vertical uplift and height of the uplifted and incised bedrock strath beneath the lowermost river terrace T1, we use trigonometric method to infer a vertical uplift rate of ~0.44 mm/a on the Nameri Thrust during the Holocene Period. The mismatch in the geodetic convergence and the geological slip rates proposed for the Himalayan Frontal Thrust in the eastern Himalaya in earlier studies provoked us to re-evaluate the scenario of geological slip in the area. Our results suggest a contrasting estimate of geological slip rate as compared to the earlier studies. Though the results are indicative of a decrease in the Indo-Eurasian convergence in the eastern Himalaya in accordance with the recent GPS observations and models proposed for the region, we, however, suggest that the lower estimation in our study compared to that reported previously could be due to the use of different dating methods for the materials obtained for assigning chronology to the landforms and events. Since the 14C AMS radiocarbon dating method requires a contemporary organic component in the sediments to be dated, an overestimation of the dates is also possible if the sediment has mixed with old carbon, which makes it inferior to the OSL method in which the mineral grains are assumed to have been fully bleached before their burial. This makes the OSL method more reliable to date sediments since it does not encounter the ‘old-carbon’ error problem of overestimation of the ages. Two additional samples obtained to the south of the active mountain front yield southwardly-increasing luminescence ages of ~19 and 26 ka suggesting deposition of older sediments toward downstream by the Kameng River as a result of rampant incision in the upstream triggered by episodes of tectonic uplift prior to ~26 ka.
Particle acceleration by transient structures around Earth’s bow shock
Authors: Liu Terry Zixu , Angelopoulos Vassilis , Hietala Heli , Lu San , Turner Drew
Published: March 2020

Upstream of Earth’s bow shock, the foreshock is filled with particles that have been reflected at the bow shock and are streaming away from it. Interaction of these particles with solar wind particles and discontinuities within this region can cause foreshock transients to form. Downstream of Earth’s bow shock, localized magnetosheath jets with high dynamic pressure are frequently observed. When such a fast magnetosheath jet compresses the ambient magnetosheath plasma, an earthward compressional bow wave/shock can form. Here we present that foreshock transients and magnetosheath jets can accelerate particles through shock drift acceleration, Fermi acceleration, and the betatron acceleration. Foreshock transients and magnetosheath jets therefore can increase the particle acceleration efficiency of the parent shock by providing additional acceleration. The shock environment relevant for particle acceleration is not just the shock itself, but also the nonlinear transient structures both upstream and downstream of it.
Basin scale hypsometry of the Himalayan fold-and-thrust belt and its tectonic implications
Authors: Obaid Ahmed
Published: March 2020

The style of deformation of the Himalaya has been proposed to be localized along the Main Himalayan Thrust (MHT), underlying the entire range and becoming emergent at the Main Frontal Thrust (MFT). An alternative model focuses on the significance of a physiographic boundary known as PT2, south of the Main Central Thrust (MCT), and proposes out-of-sequence deformation. It is interesting to test these models using variations in drainage basin scale hypsometry of the Himalayan range, and to understand the relation between these variations and the main tectonic structures of the Himalaya. This study utilises SRTM 30 m datasets to extract Hypsometric Index (HI) values for the 3rd order river basins of the Himalayan range and southern Tibetan Plateau.

A major change in HI values is coincident with the trace of the Main Frontal Thrust (MFT), with higher values north of this structure than in the foreland to the south. There is smaller magnitude increase in HI across PT2. Results also show a pronounced drop in HI on the northern side of the Himalaya, which is roughly coincident with the location of the South Tibetan Detachment Fault (STDF). The sharp rise in HI values across the MFT is consistent with slip along the MHT raising the entire crustal wedge above it, but the limited rise across PT2 offers no strong support for the out-of-sequence model. The drop in HI across the STDF could represent geomorphic control by the STDF, but this fault has been inactive for millions of years. An alternative explanation is that the decrease in HI values is controlled by underlying changes on the MHT, and the transition from locked to creeping behaviour on this structure.
Retrieval of FY-4A Land Surface Temperature for Operational Application
Authors: Dong Lixin , Xu Na , Chen Lin
Published: March 2020

The FY-4A satellite is the first quantitative remote sensing satellite of a three-axis stabilization structure on geostationary orbit launched by China in 2016. The capability and efficiency are improved with the new variety of instruments in earth observation. The thermal infrared (TIR) channels of Advanced Geosynchronous Radiation Imager (AGRI) which one of the new instruments onboard FY-4A provides high-frequency, high-precision, and quantitative observation data to obtain diurnal variation of land surface temperature (LST). In this paper, nine candidate split window LST algorithms were applied to evaluate the applicability of the different algorithm for FY-4A, and the Ulivieri & Cannizzaro (1985) algorithm was selected. Then different algorithms in day and night for dry and wet atmosphere conditions are developed and optimized to improve the accuracy of retrieved FY-4A LST. Then, the operational products of FY-4A LST are produced in clear sky. Results show that the diurnal variation characteristics of LST can be efficiently obtained. And the validation shows the following: 1) the root mean square errors (RMSE) is 3.5 K in day and 4.24 K in night when compared with the Himawari8 LST product; 2) compared with ground-measured data, the average accuracy of our algorithm is 2.5 K in day and 3.56 K in night. Sensitivity analysis shows that emissivity is lower sensitive to the algorithm accuracy, and the atmospheric water vapor content is higher sensitive to the algorithm accuracy with the view angle increased. In general, our algorithm exhibits good accuracy and is an easy retrieval approach to produce LST operational products on a regional scale. And the FY-4A LST operational products will help to the weather services, climate change, land–atmosphere interaction research, and ecological civilization construction, and so on.
Distribution, morphology and magnetic characteristics of near-axis seamounts along the KR1, the easternmost segment of the Australian-Antarctic Ridge
Authors: Choi Hakkyum , Kim Seung-Sep , Park Sung-Hyun
Published: March 2020

The Australian-Antarctic Ridge (AAR) is the spreading boundary between the Australian and the Antarctic plates, and extended from the Southeast Indian Ridge (SEIR) to the Macquarie Triple Junction (MTJ) of Australian-Antarctic-Pacific plates. The KR1 is the easternmost segment of AAR, with a quite large variation in axial morphology. In this study, we identified 3-volcanic seamount chains aligned linearly parallel to the spreading direction of the KR1. The spatial distribution, morphology and summit types for the isolated volcanic structures composing the seamount chains were determined. Eastern seamount chain has the 3-isolated volcanoes which are significantly steep and located at a considerable distance away from the ridge-axis. The central seamount chain is morphologically connected to the ridge-axis, and relatively small and less isolated compared to the other seamount chains. Western seamount chain shows a massive volcanic eruption with significantly large volcanic structures. In usual, a seamount is formed on pre-existing seafloor, and the observed magnetic signal of the seamount is correspond to that of the underlying seafloor when the seamount formation occurs nearly simultaneously with the formation of the underlying seafloor. However, if the observed magnetic anomalies of the seamount have a large misfit or/and reversed geomagnetic polarities with respect to the modeled magnetic anomalies of the underlying seafloor, it implies that there is a sufficiently large temporal gap between the formations of the seamount and the underlying seafloor. Applying this assumption, we forced the relatively younger geomagnetic history to move into the seamount having such misfits, and finally reduced the misfits. As a result, our magnetic model for the seamount chains shows that the isolated volcanoes were mostly originated from off-axis volcanisms of 7~20 km, and have a time span of less than ~600 kyrs to build. In particular, it is assumed that the seamount formations were intensively active during four-periods of 0.3~0.8 Ma, 0.9~1.1 Ma, 1.6~2.1 Ma and 2.2~2.7 Ma.
Lignin's ability to nucleate ice via immersion freezing
Authors: Bogler Sophie , Borduas-Dedekind Nadine
Published: March 2020

Uncertainties in current predictions for the atmosphere’s radiative balance are dominated by the impact of clouds. Ice nucleating particles (INPs) play a dominant role in the formation of mixed-phase clouds, however there is still a lack of understanding of how INPs interact with water in the freezing process. Detailed elucidations of the organic aerosol chemical composition from IN active atmospheric samples are scarce which is due to the analytical challenge of resolving their high complexity. We chose to reduce sample complexity by investigating the IN activity of a specific sub-component of organic aerosols, the biopolymer lignin. This approach facilitates connecting ice nucleating abilities to molecular properties. Ice nucleation experiments were conducted in our home-built Freezing Ice Nuclei Counter (FINC) to measure freezing temperatures in the immersion freezing mode which is the dominant IN mechanism in mixed-phase clouds. We find that lignin acts as an INP at temperatures relevant for mixed-phase cloud processes (e.g. 50% activated fraction at – 20 °C concentrated 20 mg C/L). Photochemistry and ozonation experiments were subsequently conducted to test the effect of atmospheric processing on lignin’s IN activity. We discovered that this activity was not susceptible to change under environmentally relevant conditions even though structural changes were introduced by monitoring UV/Vis absorbance. Additionally to atmospheric processing, laboratory treatments including heating, sonication and oxidation with hydrogen peroxide were done, where only the heating experiments had a decreasing effect on lignin’s IN activity.  Based on these results, we present a thorough INP characterization of lignin, a specific organic matter subcomponent, and contribute to the understanding of how organic material present in the atmosphere can nucleate ice.
The behavior of Graviy wave during the unusual QBO structure in 2015/2016
Authors: Li Haiyan , Li Qingxiang
Published: March 2020

We explored the gravity wave behavior and its role for the unusual QBO structure in 2015/2016 by analyzing the data of U.S. radiosonde with high vertical resolution over four equatorial stations from 1998 to 2017. The result implies that the gravity wave behavior should play an important role during the QBOW phase interrupted around 22 km in 2015/2016 winter. While the role of gravity wave was not as important as Kelvin waves during the prolonged and upward propagating westerly zonal wind around 27 km. The enhanced gravity wave may be generated by the instability of the stratospheric atmosphere rather than the tropospheric convection because the convection is weak during the unusual QBO structure over the four equatorial stations.
Forward and Backward Lagrangian Particle Tracking in Ensemble Flow Fields
Authors: El Mohtar Samah , Hoteit Ibrahim , Knio Omar , Issa Leila , Lakkis Issam
Published: March 2020

Ocean ensemble data assimilation systems generate ensembles of independent velocity field realizations after every assimilation cycle. Lagrangian tracking of passive tracers within such a framework is challenging due to the exponential growth in the number of particles that arises from describing the behavior of velocity over time as a set of possible combinations of the different realizations. This contribution addresses the problem of efficiently advecting particles, forward and backward in time, in ensemble flow fields, whose statistics are prescribed by an underlying assimilated ensemble. To this end, a parallel adaptive binning procedure that conserves the zeroth, first and second moments of probability is introduced to control the growth in the number of particles. The adaptive binning process offers a tradeoff between speed and accuracy by limiting the number of particles to a desired maximum. To validate the proposed method, we conducted various forward and backward particle tracking experiments within a realistic high-resolution ensemble assimilation setting of the Red Sea, focusing on the effect of the maximum number of particles, the time step, the variance of the ensemble, the travel time, the source location, and history of transport.
Estimates of anthropogenic CO2 emissions from satellite and ground based measurements
Authors: Timofeyev Yury , Nerobelov George , Smyshlyaev Sergey , Berezin Ivan , Virolainen Yana , Makarova Maria , Poberovsky Anatoly , Polyakov Alexander , Foka Stefania
Published: March 2020

In recent years, satellite methods have played an important role in CO2 monitoring. Various satellite instruments (SCIAMACHY, AIRS, GOSAT, OCO-2, etc.) validated by ground-based and aircraft measurements allow to retrieving the column averaged CO2 mixing ratio (XCO2) with high accuracy (0.25–1.0%). The relatively high spatial resolution of a number of instruments (for example, OCO-2) allows studies of spatial and temporal CO2 variations, that, under appropriate conditions, makes it possible to estimate anthropogenic emissions from different cities.

Various techniques (source pixel mass balance method, plume dispersion model and atmospheric inversion system) for determining anthropogenic greenhouse gas emissions from data of satellite measurements are considered.

On the basis of three-dimensional modeling and comparison with the results of various local and remote measurements, numerical models of the atmosphere were adapted to different megacities of Russia. Based on numerical experiments, the errors of various satellite techniques for determining emissions caused by various factors (measurement errors, quality of used a priori and additional experimental information, adequacy of used numerical atmospheric model, etc.) were evaluated. Anthropogenic CO2 emissions in St. Petersburg, Moscow and other cities of Russia are estimated using various satellite measurements. These estimates of anthropogenic emissions are compared with data obtained by different methods and for different cities.
Estimation of Earth- and satellite-related parameters in radiation pressure modeling from space-borne accelerometry
Authors: Vielberg Kristin , Kusche Jürgen
Published: March 2020

Space-borne accelerometers measure the sum of all non-gravitational forces, which interact with the surface of a spacecraft. For low Earth orbit satellites, the atmospheric drag is the largest non-gravitational force. With increasing satellite altitude, the acceleration due to the Earth radiation pressure becomes less relevant, whereas the effect of the Solar radiation pressure becomes prevalent. Accurately modeled non-gravitational forces are necessary for precise orbit determination, satellite gravimetry, or thermospheric density estimation.

In this study, we apply an inverse procedure with the aim to overcome remaining limitations in state-of-the-art radiation pressure force models. We estimate corrections of limiting parameters such as the satellite’s thermo-optical material properties or systematic errors in Earth radiation data sets. We define different parameterizations and analyse their estimability in terms of rank deficiency and condition numbers. Correlation analyses between estimated parameters will help to detect and overcome multicollinearity. The results are expected to improve the estimation of certain physical radiation pressure model parameters from satellite accelerometer data. Here, the inverse modeling is based on calibrated accelerometer measurements from the satellite mission Gravity Recovery and Climate Experiment (GRACE).