bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-term monitoring of the recruitment and dynamics of large wood in Kamienica Stream, Polish Carpathians
Authors: Mikuś Paweł , Wyżga Bartłomiej
Published: March 2020

Quantifying delivery and mobility of large woody debris in small mountain streams requires long-term and repeatable observations, so far very scarcely described. Such observations have been conducted in the upper course of Kamienica Stream, Polish Western Carpathians, where a sample of 429 trees growing along three separated sections of  the stream was tagged with metal plates and monitored during 10 years. The monitoring of standing and fallen trees has been conducted a few times per year, especially after heavy rainfall and windstorms. In this period, 96 trees (22.4% of the tagged sample) were recruited to the channel during high-intensity meteorological and hydrological events, mostly as a result of bank erosion during floods and windthrow, with recent bark beetle infestation of the riparian forest considerably accelerating the turnover of riparian trees. Large wood inventory performed in 2012 in the second- to fourth-order stream reaches and of the 10 years-long monitoring of tagged trees indicated variable mobility of large wood along the upper course of the stream. Wood mobility was negligible in the second-order reach, very small in the third-order reach, and higher, but still limited in the fourth-order reach. 46 trees were subjected to transport during five significant floods, and mean lengths of displacement of the tagged trees were small, not exceeding 32 m in sections A and B, whereas in section C they were a few times longer. However, an advanced state of decay of most pieces leads to their disintegration during floods, rather than to distant transport, and thus large wood retained in the upper stream course within a national park does not constitute an important flood hazard to downstream, inhabited valley reaches.
Remote sensing of air pollution from satellite and MAX-DOAS network in China
Authors: Liu Cheng , Hu Qihou , Liu Haoran , Zhang Chengxin , Tan Wei , Xing Chengzhi , Su Wenjing , Ji Xiangguang , Lin Hua
Published: March 2020

With the fast industrialization and urbanization in China, environmental pollution has become more serious and complex. Precise and real-time monitoring is the prerequisite for knowing the distribution characteristics and the evolution mechanism of the atmospheric pollutants. Over the last few years, we have successfully monitored atmospheric composition by using remote sensing from different platform, including satellite, ground and mobile vehicle, which have been validated to have good performance.

Remote sensing by satellite can describe the global distribution of various pollutants, which can also locate the emission point sources, such as factories etc. Ground-based MAX-DOAS monitor the vertical evolutions of these trace gases and aerosol at a fixed position, the column density of pollutants was divided into different layers, so we could detect transport plum in all altitude. Up to now, we have established a notional monitoring network with more than 30 MAX-DOAS, which could provide sufficient validation for satellite products and conduct scientific researches. Combining these two methods, which could provide precise horizontal and vertical distribution of pollutant, we could get a 3-D distribution of pollutants and the transport flux. Here, we analyzed the spatial distribution and temporal trends of satellite-observed air pollutants over eastern China during 2005–2017. We found significant decreasing trends in NO2 and SO2 since 2011 over most regions. Furthermore, we used the generalized additive models to clarify the relative contribution of local emissions and meteorological conditions. Our results show that meteorological determines daily changes in pollutants, while long-term, inter annual changes are determined by emissions. Emission reduction has played a decisive role in the recent reduction of the pollution!
Decadal variability of the Kuroshio Extension
Authors: Zhou Guidi , Cheng Xuhua
Published: March 2020

The decadal variability of the Kuroshio Extension (KE) is investigated using altimeter observations (AVISO) and the output of an ocean model (OFES). It is shown that the KE decadal variability is manifested in its strength, latitudinal position, and zonal extent, as well as the associated mesoscale eddy activity. Two differences between the two datasets are identified: (a) In OFES, the eddy activity positively correlates with the KE mode index when it leads by a few years, whereas in AVISO the two are negatively and concurrently correlated. (b) In OFES, the positive KE mode is associated with large meanders of the Kuroshio south of Japan, but in AVISO they are irrelevant. These differences indicate that the generation mechanism of KE's decadal variability is different in OFES and the real ocean. The sea surface height anomaly (SSHA) is then decomposed into major components including the wind-driven Rossby waves and residual (intrinsic) variability. The relationship between the two components are virtually the same in OFES and in AVISO, showing a negative correlation when the wind-driven part leads by a few years. Further diagnostics based on OFES reveals that the residual SSHA originates from the downstream region over the Shatsky Rise, slowly propagates westward, and is driven by eddy potential energy transfer. The OFES results partly conform to the intrinsic relaxation oscillation theory put forth by idealized model analyses, but in the latter the SSHA signal originates from the upstream Kuroshio. A new mechanism is then proposed for OFES: the decadal variability of the KE is first a result of the intrinsic relaxation oscillation probably excited by wind forcing, which regulates the strength of the KE’s inflow and thus modulates the downstream topography interaction, resulting in different downstream mesoscale eddy activity that further feeds back on the mean-flow. The mechanism for the real ocean is also reassessed.
Observation-based modelling of magnetised CMEs in the inner heliosphere with EUHFORIA
Authors: Scolini Camilla , Pomoell Jens , Chané Emmanuel , Poedts Stefaan , Rodriguez Luciano , Kilpua Emilia , Temmer Manuela , Verbeke Christine , Dissauer Karin , Veronig Astrid , Palmerio Erika , Dumbović Mateja
Published: March 2020

Coronal Mass Ejections (CMEs) are the primary source of strong space weather disturbances at Earth and other locations in the heliosphere. Understanding the physical processes involved in their formation at the Sun, propagation in the heliosphere, and impact on planetary bodies is therefore critical to improve current space weather predictions throughout the heliosphere. The capability of CMEs to drive strong space weather disturbances at Earth and other planetary and spacecraft locations primarily depends on their dynamic pressure, internal magnetic field strength, and magnetic field orientation at the impact location. In addition, phenomena such as the interaction with the solar wind and other solar transients along the way, or the pre-conditioning of interplanetary space due to the passage of previous CMEs, can significantly modify the properties of individual CMEs and alter their ultimate space weather impact. Investigating and modeling such phenomena via advanced physics-based heliospheric models is therefore crucial to improve the space weather prediction capabilities in relation to both single and complex CME events. 

In this talk, we present our progress in developing novel methods to model CMEs in the inner heliosphere using the EUHFORIA MHD model in combination with remote-sensing solar observations. We discuss the various observational techniques that can be used to constrain the initial CME parameters for EUHFORIA simulations. We present current efforts in developing more realistic magnetised CME models aimed at describing their internal magnetic structure in a more realistic fashion. We show how the combination of these two approaches allows the investigation of CME propagation and evolution throughout the heliosphere to a higher level of detail, and results in significantly improved predictions of CME impact at Earth and other locations in the heliosphere. Finally, we discuss current limitations and future improvements in the context of studying space weather events throughout the heliosphere.
How likely are widespread floods in US river basins? Seeking answers using a stochastic, wavelet-based approach
Authors: Brunner Manuela Irene , Papalexiou Simon , Gilleland Eric
Published: March 2020

Flooding can affect large regions leading to high economic and societal costs. Estimating regional flood risk is crucial for developing adaptation strategies, public awareness policies, and protection structures. Yet, estimating regional flood hazard is not trivial because of the few large flood events observed. Here, we derive regional flood hazard estimates for large river basins in the United States by using a stochastic streamflow generator. This allows us to increase the number of flood events available for the analysis and to investigate the simultaneous occurrence of flooding in different parts of a river basin.
We propose the continuous, stochastic simulation approach (PRSim.wave), which combines a non-parametric spatio-temporal model based on the wavelet transform with the parametric kappa distribution. The model reproduces the temporal and distributional characteristics of streamflow at individual sites and retains the spatial dependencies between sites even for spatial extremes. We use PRSim.wave to generate long and spatially consistent time series of daily discharge for a large set of catchments in the conterminous United States. For each catchment, we extract flood events from the simulated series using a peak-over-threshold approach to derive a spatial dataset of flood occurrences. Using this dataset, we estimate how probable it is that a certain percentage of stations within a specific river basin is jointly flooded. We show that: (1) there are strong regional differences in the likelihood of joint and potentially widespread flooding and (2) there are spatial differences in regional flood hazard estimates which could not be derived from observed data only. We deem our approach a valuable tool for water managers and policy makers to make informed decisions on the risk of widespread flooding.
Subduction processes on the Mariana trench and northern Manila trench: implications for the intra-oceanic and ocean-continent convergent margins
Authors: Liu Yang , Wu Ziyin , Shang Jihong , Zhao Dineng , Zhou Jieqiong
Published: March 2020

Different tectonic backgrounds often produce different subduction mechanisms. The Mariana subduction zone is a typical erosive margin, and the mode of material transportation is mainly controlled by subduction erosion, while the subduction process in the northern Manila subduction zone is dominated by subduction accretion. However, there are little comparative investigation about the subduction mechanisms between the Mariana subduction zone and northern Manila subduction zone. In this study, the high-resolution bathymetric data obtained by using the multi-source data fusion method and collected multichannel seismic profiles are used to research the subduction mechanisms and to develop the subduction modes for the Mariana subduction zone and northern Manila subduction zone. We propose that the Mariana subduction zone formed at the intra-oceanic convergent margins with rare continental sediments tends to occur subduction erosion. A rough seafloor morphology (e.g. seamounts, horst and graben topography) of the subducting Pacific Plate, with a convergence rate of 8.4 cm/yr, and the steep slope of the inner trench, promote subduction erosion at the Mariana margin. The northern Manila subduction zone is the result of the convergence of ocean-continent plates. The continental sediments of the overlying plate usually undergo subduction accretion during the subducting process, forming an accretionary wedge along the northern Manila margin. With the continuously subducting of the continental crust, a series of folds and thrust faults are formed inside the accretionary wedge. Both the Mariana subduction zone and northern Manila subduction zone are distinctive types of the convergent margins in the world. The comparison of subduction mechanisms has important reference significance for the study of the subduction process, evolution and inter-plate interaction of global intra-oceanic and ocean-continent convergent margins.
Mode-Decomposed Equation Diagnosis for Atmospheric Blocking Development
Authors: Inatsu Masaru , Aikawa Takuya , Nakano Naoto
Published: March 2020

This paper proposes a new method to identify atmospheric blocking development without the time filtering used in previous studies. A mode-decomposed vorticity equation is formulated from the principal components (PCs) of 500-hPa geopotential height by applying a new idea; the orthonormality of PCs allows any variable to be decomposed into a projection corresponding to the PCs. To test this, sectorial blocking episodes in Northern Hemisphere winter were identified by Barriopedro’s method. A blocking index was defined for each longitudinal range as the linear combination of the 10 largest PCs by means of the composite for the blocking episodes. Blocking development was diagnosed, in terms of the low modes of PC1–PC10 and the high modes of PC11–PC50. The results suggest that the intensification of blocking over the North Pacific and Eurasia is associated with nonlinear interaction among high modes, whereas the intensification (decay) of North Atlantic blocks is related mainly to enhanced nonlinear interaction among low-frequency (high-frequency) eddies. This main result is insensitive to the choice of definition for blocks and the choice of the mode separation boundary.
Minimizing biodiversity trade-offs of future global hydropower reservoirs by strategic site selection
Authors: Dorber Martin , Arvesen Anders , Gernaat David , Verones Francesca
Published: March 2020

The Sustainable Development Goals (SDG) require increased hydropower electricity production to reach SDG 7. However, a balance between related positive synergies and negative trade-offs needs to be found. So far there has been a strong focus on the technical development potential (SDG 7), and the positive synergies of hydropower, for example in relation to SDG 13 (Climate change). However, hydropower can also cause, for instance, biodiversity impacts, leading to a negative biodiversity trade-off with SDG 6 (Clean water and sanitation) and SDG 15 (Life on land). Although conservation of biodiversity has been identified as a key parameter for sustainable development, global assessments accounting for site specific biodiversity trade-offs of hydropower sites are still lacking.

To fill this research gap, we performed the first global and reservoir explicit assessment of terrestrial and aquatic biodiversity impacts of 2000 possible future hydropower reservoirs. We adapted the latest spatially explicit impact assessment methods available from the field of life cycle assessment, with a high-resolution and location-specific technical assessment of future economic hydropower potentials (Gernaat et al., Nature Energy 2017). More specially we collected site-specific environmental information from geographic information system databases to quantify potential reservoir-specific, net land occupation, net water consumption and methane emissions. Subsequently, we quantified the related terrestrial and aquatic biodiversity impact in units of potentially disappeared fraction of species (PDF).

Our results show that future hydropower electricity production can have a spatially highly variable biodiversity impact (varying by orders of magnitude) which can interfere with SDG 6 and SDG 15. Furthermore, we show that careful selection of reservoirs on a macro level has a large potential to limit biodiversity impacts. Thus, sustainable hydropower development requires an assessment of potential biodiversity impacts.  This in turn means, that if mitigating climate change for SDG 13 is the main motivation for increased hydropower production, as it can score favorable in studies comparing GHG emissions, it is likely that potential biodiversity impacts are overlooked. However, in order to move towards overall sustainability, taking biodiversity impacts into account next to climate change and other impacts, is of utmost importance.
How climate change affected the evolution of ancient civilizations in eastern Ancient Silk Road?
Authors: Dong Guanghui , Li Ruo , Zhang Shanjia , Liu Fengwen
Published: March 2020

The study of the coupling relationship between climate change and civilization evolution along the Ancient Silk, can provide valuable insights for understanding the history, pattern and mechanism of man-land relation evolution from a long-run perspective. Here we provide two case studies from the Hexi Corridor and Qaidam basin in northwest China, where locates at eastern Ancient Silk Road, and became a center for trans-continental exchange since the second Millennium BC, hydrological change in these areas is very drastic. The results reveal three significant desertification events occurred in these two areas during late Holocene, which was likely related to precipitation variation in surrounding mountains instead of basins, and triggered the shrinkage of ancient oases and then the decline of ancient civilizations. We also try to explain the linkage between climate change and the evolution of ancient civilizations in the two areas.
Detect groundwater storage in an island watershed by GRACE gravimetry
Authors: Huang Chung-Chieh , Lin Hong-Ru , Chen Jyun-Lin , Huang Shao-Yang , Wen Jet-Chau , Yeh Jen-Feng P , Jarihani Ben
Published: March 2020

         Since the successful launch of the Gravity Recovery and Climate Experiment (GRACE) on March 17th, 2002, a number of scientists have adopted satellite gravimetry for the detection of variations on terrestrial water storage (TWS). Use of high-precision GRACE gravimetry presents advantages in hydrogeologic studies, such as providing accurate estimates of currents and gravity fields. Many studies have proven that the high-precision GRACE gravimetry can observe large-scale (over 50,000 km2) variations in groundwater storage (GWS). However, relatively few studies conducted using satellite gravimetry have focused on scales smaller than 5,000 km2.

        The purpose of this study is to investigate the potential for using GRACE gravimetry to observe small-scale variations in GWS specifically, this paper presents a case study of the Zhoushui River alluvial fan (~2,560 km2) in central Taiwan as an example of how well GRACE data compare to field-based data for ascertaining small-scale variations in GWS. Field measurements of groundwater level in 52 observation wells (2002-2017) were used to analyze variations in GWS. Results of this field-based analysis were compared to results obtained using the GWS data (2002-2017) obtained by GRACE gravimetry. This comparison allowed us to evaluate the similarities and differences in both methods as well as to prove the feasibility of using GRACE gravimetry in small-scale regions. Results of our comparative analysis indicate that water resources in small watershed can be successfully managed using gravimetric data collected by GRACE satellite.

 

Keywords: Groundwater storage, GRACE, Watershed
Streaming flow on polythermal mountain glaciers: In-situ observations on Jarvis Glacier, Alaska
Authors: Lee Ian , Hawley Robert , Gerbi Christopher
Published: March 2020

Accelerated melting of glaciers and ice caps has raised serious concerns about sea level rise. As we work towards a solution to address these concerns, it has become a chief priority to rapidly improve predictions of future changes in global ice mass balance. Numerical simulations projecting ice loss have uncovered a strong sensitivity to mechanical and/or rheological weakening of the shear margins of streaming ice. To accurately project sea level rise, future models will require careful treatment of shear margins. This necessitates a deeper understanding of the flow dynamics at shear margins and how streaming flow relates to the constitutive flow law for ice.

 

We developed an open source inexpensive tilt sensor (∼20% the cost of commercial sensors) for studying ice deformation and installed our tilt sensor systems in two boreholes drilled close to the shear margin of Jarvis Glacier, Alaska to obtain kinematic measurements of streaming ice. We used the collected tilt data to calculate borehole deformation by tracking the orientation of the sensors over time. The sensors' tilts generally trended down-glacier, with an element of cross-glacier flow in the borehole closer to the shear margin. We also evaluated our results against flow dynamic parameters derived from Glen's exponential flow law and explored the parameter space of the stress exponent n and enhancement factor E. Comparison with values from ice deformation experiments shows that the ice on Jarvis is characterized by higher n values than that is expected in regions of low stress, particularly at the shear margin (~3.4). The higher n values could be attributed to the observed high total strains coupled with potential dynamic recrystallization, causing anisotropic development and consequently sped up ice flow. Jarvis' n values place the creep regime of the ice between basal slip and dislocation creep. Tuning E towards a theoretical upper limit of 10 for anisotropic ice with single-maximum fabric reduces the n values by 0.2.
Relationship between water level temporal changes and seismicity in the Mingechevir reservoir (Azerbaijan)
Authors: Gadirov (Kadirov) Fakhraddin , Telesca Luciano , Babayev Gulam , Yetirmishli Gurban , Safarov Rafig
Published: March 2020

Reservoir-induced seismicity has been studied worldwide due to its potential to provoke damage to buildings and constructions, and, more important, human loss. Reservoir-induced seismicity (RIS) is normally related with additional static loading (the weight of the water reservoir and its seasonal variations), tectonic faults, liquefaction and pore pressure variations.The Mingechevir reservoir is located in the north-west of Azerbaijan on the Kurriver. This water reservoir is extended from north-west towards south-east through Kur river valley by 75 km. The area of the dam is 625 km2 with the average width accounting for 6-8 km. The volume of the dam is 16 km3. The dam filling started in 1953. This reservoir is the largest one in the Caucasus and carries a number of geo-hazards interrelated with geodynamics and technogenic factors. The aim of the present study in the Mingechevir reservoir is to investigate relationship between the fluctuations of the water level and the onset of seismicity in the area around the dam more in detail, by using several and independent statistical methods.The temporal variations of the instrumental seismicity (0.5≤ML≤3.5) recorded in the Mingechevir area (Azerbaijan) between January 2010 to April 2018 and its relationship with the level variation of the water reservoir was analysed in this study. Due to the relative high completeness magnitude (MC = 1.6) of the seismic catalogue of the area, only 136 events were selected over a period of more than 8 years. Thus, the monthly number of events was analysed by using the correlogram-based periodogram, the singular spectrum analysis (SSA) and the empirical mode decomposition (EMD), which are robust against the short size of the time series. Our results point out to the following findings: 1) annual periodicity was found in one SSA reconstructed component of the monthly number of events; 2)quasi-annual periodicity was found in one EMD intrinsic mode function of the monthly number of earthquakes. These obtained results could support in a rigorously statistical manner that the seismicity occurring in Minghechevir area could be triggered by the yearly cycle of the water level of the reservoir.

 

Keywords:water reservoir, induced seismicity, water level change, Mingechevir reservoir, Azerbaijan
Retrieval of Water Quality Parameters in Lake Ontario Based on Hyperspectral Remote Sensing Data and Intelligent Algorithms
Authors: Li Yu , Sun Youyue , Huang Jinhui Jeanne , McBean Edward
Published: March 2020

With the increasingly prominent ecological and environmental problems in lakes, the monitoring water quality in lakes by satellite remote sensing is becoming more and more high demanding. Traditional water quality sampling is normally conducted manually and are time-consuming and labor-costly. It could not provide a full picture of the waterbodies over time due to limited sampling points and low sampling frequency. A novel attempt is proposed to use hyperspectral remote sensing in conjunction with machine learning technologies to retrieve water quality parameters and provide mapping for these parameters in a lake. The retrieval of both optically active parameters: Chlorophyll-a (CHLA) and dissolved oxygen concentration (DO), as well as non-optically active parameters: total phosphorous (TP), total nitrogen (TN), turbidity (TB), pH were studied in this research. A comparison of three machine learning algorithms including Random Forests (RF), Support Vector Regression (SVR) and Artificial Neural Networks were conducted. These water parameters collected by the Environment and Climate Change Canada agency for 20 years were used as the ground truth for model training and validation. Two set of remote sensing data from MODIS and Sentinel-2 were utilized and evaluated. This research proposed a new approach to retrieve both optically active parameters and non-optically active parameters for water body and provide new strategy for water quality monitoring.
Measurement capabilities of strato-mesospheric winds in the Arctic region
Authors: Kajtár Rita Edit , Milz Mathias , Raffalski Uwe , Mendrok Jana
Published: March 2020

There is a need for inferring mid-stratosphere to mid-mesosphere wind profiles between approximately 25 and 75 km altitude as a consequence of the relatively poor characterization of the complex atmospheric dynamics at these altitudes by the existing monitoring techniques. A better knowledge of the wind field could help improve the quality of global circulation models for this region of the atmosphere. Our goal is to measure strato-mesospheric horizontal wind profiles over the Arctic region. To this objective, we are using data from continuous measurements recorded for ozone chemistry monitoring purposes that have been ongoing since 2002 and from dedicated wind measurements recorded since 2014. An accurate interpretation of the wind patterns could give us an insight into past and present wind dynamics in the Arctic. For the measurements, we are using the ground-based millimeter-wave radiometer KIMRA [Raffalski et al., 2002] with a spectral range between 195-233GHz, situated at the Swedish Institute of Space Physics, in Kiruna, Sweden. Within KIMRA’s spectral range, the thermal emission spectrum of a strong ozone line at 231.3GHz has been used for ozone monitoring, and it might also be the most suitable to use for inferring wind speeds. It has both a strong contribution compared to other, secondary gases identified in this frequency region, and it has an enhanced spectral signature compared to the baseline effects induced by the radiometer itself. By determining the difference between the observed (wind-affected) and the simulated reference spectra (without wind), we can characterize the Doppler shift of the line with the help of our retrieval system and subsequently infer the speeds of the winds that induced the shift. The wind profile retrievals are performed with the Qpack2 package [Eriksson et al., 2005] for inverting the set of observations using an optimal estimation retrieval approach (OEM). The OEM provides the best solution given the measurements and their errors and the a priori knowledge and its errors. The a priori knowledge that we consider has been estimated from ERA5 re-analysis data downloaded from the Copernicus Climate Data Store. In connection with Qpack2, we use the Atmospheric Radiative Transfer Simulator (ARTS-2) [Bühler et al., 2018] as a forward model. We test the retrieval capabilities of strato-mesospheric horizontal wind profiles and assess if the retrieval can be performed with sufficient accuracy. In addition, we intend to evaluate the technical capabilities of KIMRA regarding possible improvements to the instrument’s performance. Besides the implementation of new hardware, we will analyze how adjusting certain parameters that currently limit its spectral resolution affects the sensitivity of the measurements. Furthermore, we will aim to decrease the intrinsic noise of the radiometer and increase its stability over time.
The Role of Soil Pipes and Pipeflow in Headcut Migration Processes
Authors: Xu Ximeng , Wilson Glenn V. , Zheng Fenli , Tang Qiuhong
Published: March 2020

Headcut formation and migration is sometimes mistaken as the result of overland flow without realizing that the headcut was formed by or significantly influenced by flow through soil pipes into the headcut. To determine the effects of a soil pipe and flow through a soil pipe on headcut migration, laboratory experiments were conducted under free-drainage conditions and conditions of a shallow water table. Soil beds with a 3-cm deep initial headcut were formed in a flume with a 1.5-cm diameter soil pipe 15 cm below the bed surface. Overland flow and flow into the soil pipe was applied at a constant rate of 68 L/min and 1 L/min, respectively, at the upper end of the flume. The headcut migration rate and sediment concentrations in both surface (channel) and subsurface (soil pipe) flows were measured with time. The typical response without a soil pipe was the formation of a headcut that extended in depth until an equilibrium scour hole was established at which time the headcut migrated upslope. The presence of a soil pipe below the channel, and particularly the phenomena of flow through a soil pipe and into the headcut, whether by seepage from a shallow water table or upslope inflow, significantly impacted the headcut migration. Pipeflow caused erosion inside of the soil pipe at the same time that runoff was causing a scour hole to deepen and migrate. When the headcut extended to the depth of the soil pipe, surface runoff entering the scour hole interacted with flow from the soil pipe also entering the scour hole. This interaction dramatically altered the headcut processes, greatly accelerated the headcut migration rates and sediment concentrations. Conditions in which a perched water table provided seepage into the soil pipe in addition to pipeflow increased the sediment concentration by 42% and the headcut migration rate by 47% compared with pipeflow under free-drainage conditions. The time that overland flow converged with subsurface flow was advanced under seepage conditions by 2.3 and 5.0 minutes compared with free-drainage condition. This study confirmed that pipeflow dramatically accelerates headcut migration especially under conditions of shallow perched water tables and highlights the importance of understanding these processes in headcut migration processes.
Sensitivity of high resolution WRF model to land surface schemes in simulating boreal summer climate over Central Asia
Authors: Lu Sha , Guo Weidong , Xue Yongkang , Huang Fang
Published: March 2020

The Land surface scheme is crucial for the performance of regional climate models in dynamic downscaling application. In this study, we investigate the sensitivity of the simulation  with high resolution (10km) WRF model to the land surface schemes over Central Asia. The high resolution WRF simulations for 19 summers from 2000 to 2018 are conducted with four different land surface schemes (hereafter referred to as Exp-CLM, Exp-Noah-MP, Exp-PX and Exp-SSiB, respectively). The initial and boundary conditions for the WRF model simulations are provided from the NCEP-FNL analysis product. The ERA-Interim reanalysis (ERA), the GHCN-CAMS (CAMS) and the CRU gridded data are used to comprehensively evaluate the WRF simulations. Compared with verification data, the WRF model with high resolution can reasonably reproduce the spatial patterns of summer mean large scale atmospheric circulation, 2-m temperature and precipitation. The simulation results, however, are sensitive to the option of land surface scheme. The performance of Exp-CLM4 and Exp-SSiB are better than that of Exp-Noah-MP and Exp-PX assessed by the multivariable integrated evaluation method. To comprehensively understand the dynamic and physical mechanisms behind the WRF model sensitivity to land surface schemes, the differences in the surface energy balance between the ensemble means Ens-CLM4-SSiB and Ens-NoanMP-PX are analyzed in detail. The results demonstrate that the intensity of the simulated sensible heat flux over Central Asia is weaker in Ens-CLM4-SSiB than that in Ens-NoahMP-PX. As a result, large differences in geopotential height occur over the model simulation domain. The simulated wind fields are subsequently affected due to the geostrophic adjustment process, thus the simulation of 2-m temperature, precipitation, surface soil moisture and surface skin temperature are all affected.
Impact of wind speeds on turbulent transport of carbon dioxide (CO2) fluxes at a tropical location in Ile - Ife, southwest Nigeria
Authors: Bello Theodora , Ajao Adewale , Jegede Oluwagbemiga
Published: March 2020

The study investigates impact of wind speeds on the turbulent transport of CO2 fluxes for a land-surface atmosphere interface in a low-wind tropical area between May 28th and June 14th, 2010; and May 24th and June 15th, 2015. Eddy covariance technique was used to acquire turbulent mass fluxes of CO2 and wind speed at the study site located inside the main campus of Obafemi Awolowo University, Ile – Ife, Nigeria. The results showed high levels of CO2 fluxes at nighttime attributed to stable boundary layer conditions and low wind speed. Large transport and distribution of CO2 fluxes were observed in the early mornings due to strong wind speeds recorded at the study location. In addition, negative CO2 fluxes were observed during the daytime attributed to prominent convective and photosynthetic activities. The study concludes there was an inverse relationship between turbulent transport of CO2 fluxes and wind speed for daytime period while nighttime CO2 fluxes showed no significant correlation.

Keywords: CO2 fluxes, Wind speed, Turbulent transport, Low-wind tropical area, Stable boundary layer
Modelling the global biological microplastic particle sink
Authors: Kvale Karin , Prowe AE Friederike , Chien Chia-Te , Landolfi Angela , Oschlies Andreas
Published: March 2020

Forty percent of the plastic produced annually ends up in the ocean. What happens to the plastic after that is poorly understood, though a growing body of data suggests it is rapidly spreading throughout the ocean. The mechanisms of this spread are not straightforward for small, weakly or neutrally buoyant plastic size fractions (the microplastics), in part because they aggregate in marine snow and are consumed by zooplankton. This biological transport pathway is suspected to be a primary surface microplastic removal mechanism, but exactly how it might work in the real ocean is unknown. We search the parameter space of a new microplastic model embedded in an earth system model to show biological uptake significantly shapes global microplastic inventory and distributions, despite its being an apparently inefficient removal pathway.
Experimental Investigation on the cavitation erosion properties of concrete with different damage degrees under ultrasonic cavitation
Authors: Lu Xiang , Chen Jiankang , Pei Liang , Wu Zhenyu
Published: March 2020

Cavitation erosion, widely existing in many flood discharge structures of concrete dams, has a direct impact on the performance of concrete. Understanding the cavitation erosion properties of concrete with different damage degrees is vital to the long-term operation safety of concrete dams. In this study, the cavitation erosion properties of concrete with different damage degrees under ultrasonic cavitation are systematically investigated in the laboratory, including three damage degrees and three ultrasonic cavitation intensities. Based on the stress-strain curve of concrete under uniaxial compression, the damage variable is defined and the corresponding concrete specimens are pre-treated. The experimental results reveal the influence of the damage degrees on the cavitation erosion properties of concrete, regarding the mass erosion characteristics, the predominant failure behaviour, and the coupling effect mechanism. Image analysis of the specimens shows some level of deterioration at the surface and inside the specimens. Under higher damage degree or cavitation intensity, the concrete is characterized by higher mass erosion rate, higher cumulative cavitation damage and worse surface smoothness. Furthermore, the micro-cracks caused by concrete damage aggravate the aggregate liberation of concrete under ultrasonic cavitation, and the crack propagation under coupling effect of damage and cavitation is most likely driven by the combination of fatigue-like crack growth and deformation, thereby reducing the service life of concrete.
Radiocarbon in modern Carbon Cycle research
Authors: Levin Ingeborg
Published: March 2020

Atmospheric nuclear weapon testing in the 1950s and 1960s has been worrying, however, in many aspects it was extremely beneficial for environmental sciences. The artificial production of more than 6 x 1028 atoms or about 0.6 tons of 14C, leading to a doubling of the 14C/C ratio in tropospheric CO2 of the Northern Hemisphere has generated a prominent 14C spike in 1963. This “bomb-spike” has been used as transient tracer in all compartments of the carbon cycle, but also to study atmospheric dynamics, such as inter-hemispheric and stratosphere-troposphere air mass exchange. Moreover, our attempt to accurately determine total bomb produced 14C led to improved estimates of the atmosphere-ocean gas exchange rate and to a new constraint of the residence time of carbon in the terrestrial biosphere. Today, the transient bomb-radiocarbon signal has levelled off, and the anthropogenic input of radiocarbon-free fossil fuel CO2 into the atmosphere has become the dominant driver of the decreasing 14C/C ratio in atmospheric CO2; the observed trend may thus help scrutinising the total global release of fossil fuel CO2 into the atmosphere. Prominent examples where the bomb 14C disturbance has been successfully used to study dynamic processes in the carbon cycle are discussed as well as our current activities applying this unique isotope tracer for continental scale carbon cycle budgeting.
High-resolution hydrologic dynamics of the Nadadish experimental catchment in Chuzhou Hydrology Laboratory, China
Authors: Liao Aimin , Liu Jiufu , Liu Hongwei , Zhang Haixia , Wang Niu , Gu Weizu
Published: March 2020

To obtain new hydrologic data and reveal new hydrologic mechanisms, it is key to perform high-resolution observation of hydrologic dynamics in experimental catchments. Supported by Chuzhou Hydrology Laboratory, this study conducted experimental investigation of hydrologic dynamics in Nandadish experimental catchment during 2015-2019. Nandadish with an area of 7897 m2 is a natural experimental catchment covered by forest whose dominant tree species are B. papyrifera and Q. acutissima. The surface surrounding boundary was sealed by concrete so that Nadadish forms an excellent critical zone experimental block (CZEB). Four rain gauges were installed over the towers to measure the rain over the trees (inferred as P); 144 rain gauges were used to measure the rain under the trees (i.e. throughfall); and 31 trees were equipped to collect stem flow. A separate runoff observation system was constructed to measure the runoffs in different layers: the uppermost trough collects throughfall; the next lower trough collects surface runoff (RS); the two lower troughs collect subsurface flow from soil layers with the depths of 0–50, and 50–100 cm (inferred as R50 and R100). Soil moisture was observed by 31 profile-type sensors with 9, 12 or 15 sensor points with a depth spacing of 10 cm. An array of 30 galvanized tube wells intersected through the soil till the bed rock. Water table measurement was performed with pressure-type sensors at the bottom of each well. According experimental results, conclusions are determined as following: (1) Throughfall variability during the leafed period was slightly higher than that during the leafless period inferred from the coefficient of variation of throughfall amounts, with 13.2-40.9% and 18.7-31.9%, respectively. The multiple regression model analysis suggested that the controlling factors of throughfall variability were significant differently in different periods. (2) B. papyrifera required less precipitation amount (4.3 to 5.8 mm) to initially trigger stemflow than Q. acutissima (5.4 to 6.0 mm). (3) Under the condition of P≥25 mm, the proportion of RS, R50 and R100 was 46.3%, 15.2% and 38.5%, and thus the subsurface runoff dominated the runoff. The synthetic runoff coefficient of total runoff was 0.33; the synthetic runoff coefficients of Rs, R50 and R100 were 0.15, 0.05 and 0.13, respectively. (4) The depths of soil distinction layers were located at the range of 80-90 cm based on the data of profile soil moisture. (5) Saturated overland flow occurred in the area where the gentle slope with soil depth of less than 1 m was located at the mid-downstream through analyzing the water table dynamics. This investigation can enhance the in-depth understanding of hydrologic dynamics in the small forest headwater catchments.
Using a first-order autonomous dynamical system to evaluate residence time of the Greenland freshwater anomaly in the Subpolar Gyre
Authors: Dukhovskoy Dmitry
Published: March 2020

Increasing Greenland discharge has contributed more than 5000 km3 of surplus fresh water to the Subpolar North Atlantic since the early 1990s. The volume of this freshwater anomaly is projected to cause freshening in the North Atlantic leading to changes in the intensity of deep convection and thermohaline circulation in the subpolar North Atlantic. This is roughly half of the freshwater volume of the Great Salinity Anomaly of the 1970s that caused notable freshening in the Subpolar North Atlantic. In analogy with the Great Salinity Anomaly, it has been proposed that, over the years, this additional Greenland freshwater discharge might have a great impact on convection driving thermohaline circulation in the North Atlantic with consequent impact on climate. Previous numerical studies demonstrate that roughly half of this Greenland freshwater anomaly accumulates in the Subpolar Gyre. However, time scales over which the Greenland freshwater anomaly can accumulate in the subpolar basins is not known. This study estimates the residence time of the Greenland freshwater anomaly in the Subpolar Gyre by approximating the process of the anomaly accumulation in the study domain with a first order autonomous dynamical system forced by the Greenland freshwater anomaly discharge. General solutions are obtained for two types of the forcing function. First, the Greenland freshwater anomaly discharge is a constant function imposed as a step function. Second, the surplus discharge is a linearly increasing function. The solutions are deduced by utilizing results from the numerical experiments that tracked spreading of the Greenland fresh water with a passive tracer. The residence time of the freshwater anomaly is estimated to be about 10–15 years. The main differences in the solutions is that under the linearly increasing discharge rate, the volume of the accumulated Greenland freshwater anomaly in the Subpolar Gyre does not reach a steady state. By contrast, solution for the constant discharge rate reaches a steady state quickly asymptoting the new steady state value for time exceeding the residence time. Estimated residence time is compared with the numerical experiments and observations.
Tree species classification by using computer vision and deep learning techniques for the analysis of drone images of mixed forests in Japan
Authors: Kentsch Sarah , Lopez Caceres Maximo Larry , Diez Donoso Yago
Published: March 2020

Forests become more important in times of changing climate, increasing demand of renewable energies and natural resources, as well as the high demand of information for economical and management issues. Several previous studies were carried out in the field of forest plantations but there is still a gap in knowledge when it comes to natural mixed forests, which are ecological complex due to varying distributions and interaction of different species. The applicability of Unmanned Aerial Vehicles (UAVs) for forest applications by using image analysis became a common tool because it is cost-efficient, time-saving and usable on a large-scale. Additionally, technologies like Deep Learning (DL) fasten the proceeding of a high number of images. Deep learning is a relatively new tool in forest applications and especially in the case of natural dense mixed forests in Japan. Our approach is to introduce the DL-based ResNet50 network for automatic tree species classification and segmentation, which uses transfer learning to reduce the amount of required data. A comparison between the ResNet50 algorithm and the common UNet algorithm, as well as a quantitative analysis of model setups are presented in this study. Furthermore, the data were analysed regarding difficulties and opportunities. We showed the outperformance of UNet with a DICE coefficient of 0.6667 for deciduous trees and 0.892 for evergreen trees, while ResNet 50 was reaching 0.733 and 0.855. A refinement of the segmentation was performed by the watershed algorithm increasing the DICE coefficient to values of up to 0.777 and 0.873. The results of the transfer learning analysis confirmed the increasing accuracy by adding image classification data basis for the model training. We were able to reduce the number of images required for the application. Therefore, the study showed the applicability and effectiveness of those techniques for classification approaches. Furthermore, we were able to reduce the training time by 16 times for the ResNet 50 performance and by 3.6 times with the watershed approach in comparison to the UNet algorithm. To the best of our knowledge this is the first study using deep learning applications for forestry research in Japan and the first study dealing with images of natural dense mixed forests.
GPR coherence attribute applied to the structure interpretation of limestone epikarst in Guizhou karst plateau
Authors: Gao Qiangshan , Peng Tao , Wang Shijie , Yang Tianchun
Published: March 2020

    The epikarst ecosystem of karst environments plays a key role in biogeochemical cycling and material storage and transport. Many geochemistry and geophysical methods have been used to research the epikarst. Coherence attributes have already showed advantages in many aspects. Although ground penetrating radar (GPR) has been introduced to characterize karst structure long before, GPR coherence attributes are paid less attention in the interpretation of epikarst structure. Coherence attribute can describe the waveform similarity of traces by the classical mutual correlation algorithm and reflect the discontinuities of media. Two typical limestone epikarst profiles which develop shallow and deep fissure soil in Guizhou karst plateau were chosen. We used MALA GPR equipment to acquire data. After the data processed by conventional methods, we then extracted the coherence attribute data from the GPR data by the procedure coded in C Programing Language. The results show that: (i) coherence attribute displays the valid and invalid signals area of the GPR profiles; (ii) the epikarst is corresponding to the valid area and the bedrock below epikarst is corresponding to the invalid area; (iii) the boundary of valid and invalid areas reflects generally the lower boundary of epikarst. Coherence attribute provides additional evidence that the epikarst developed lots of fractures but the bedrock below is complete. The validity of GPR signals is useful to analyze the structure research of epikarst.