A Comparison between WCS and OPeNDAP for Making Model Results and Data Products Available through the Internet

Numerical models produce output with a large number of variables, grid cells and time steps. The same applies to algorithms that produce gridded datasets from sparse or abundant raw data. Further use of the resulting data products has been challenging, especially for dissemination outside the institute of origin. Due to the gradually increasing size of data products, simply downloading copies of them is becoming impossible. A gradual transition from traditional download methods to web services is therefore observed. Web services allow for on‐the‐fly access to subsets of data that were hitherto considered as indivisible granules. Here we compare the most mature candidates to serve gridded data through the web: the Open‐source Project for a Network Data Access Protocol (OPeNDAP) and Web Coverage Service (WCS) protocols. In the framework of the new Dutch National Model and Data Centre (NMDC.eu) a distributed data storage has been created by coupling OPeNDAP servers. A WCS service layer is provided for the same data. This allows us to compare OPeNDAP and WCS. Using several use cases, we compare the usability, performance and features of the two protocols.     

Molecular modelling of rare earth element complexation in subduction zone fluids

Complexation of (trace) elements in fluids plays a critical role in determining element mobility in subduction zones, but to date, the atomic-scale processes controlling elemental solubilities are poorly understood. As a first step towards computer simulation of element complexation in subduction zone fluids, a thermodynamic cycle was developed to investigate the hydration environment and energetics of lanthanide complexes using density functional theory. The first solvation shell is explicitly defined and the remaining part of the aqueous fluid is modelled using a polarisable continuum model, which allows extrapolation to a broad pressure and temperature range.We illustrate our method by comparing solvation of lanthanide series elements in H₂O in the presence of fluoride or chloride for conditions relevant to subduction zones. The energetics of lanthanide- and lanthanide-fluoride/chloride hydration complexes were determined computationally. Calculated hydration free energies for trivalent lanthanides with explicit eight- and nine-fold coordinated first hydration shells show good agreement with literature data at room pressure and temperature. The hydration free energy is more negative for smaller complexes (heavy lanthanides) relative to larger complexes (light lanthanides), with the difference between La and Lu in water amounting to 361 kJ mol⁻¹. The hydration free energy of all lanthanide ions becomes less negative with increasing pressure (p) and temperature (T) up to 2.5 GPa and 1000 K (typical conditions in the upper part of subducting slabs). The free energy difference between light- and heavy-lanthanides remains essentially unchanged at elevated (p, T) conditions. There are minor geometrical differences in local hydration environment between light lanthanide-chloride (La-Nd) and heavy lanthanide-chloride (Pm-Lu) hydrated complexes, without a distinguishable energy difference. Complexation with fluoride is energetically more favourable than with chloride by 206 ± 4 kJ mol⁻¹ across the entire lanthanide series. The association of fluoride-water and chloride-water fragments with lanthanide-water complexes is energetically more favourable for aqueous lanthanide complexes surrounded by fewer first hydration shell water molecules.The methods developed in this study, in conjunction with simulation of the energetics of trace element incorporation into minerals, open the possibility to use molecular modelling to constrain elemental behaviour in subduction zones.     

Splash detachment of sand particles under varying contact stress field of wind-driven raindrop impact

The effects of wind-driven rain (WDR) on sand detachment were studied under various raindrop obliquities. Results suggested a significant reduction in compressive stress on sand surfaces for a two-dimensional experimental set-up in a wind tunnel. During experiments, sand particles in splash cups were exposed to both wind-free rain (WFR) and WDR driven by horizontal winds of 6.4, 8.9 and 12.8 m s⁻¹ and rainfall intensities of 50, 60, 75 and 90-mm h⁻¹ to assess the sand detachment rate (D, in g m⁻² s⁻¹). The effects of sand moisture state (dry and wet) on the detachment of different-sized particles (0.20–0.50 and 0.50–2.00 mm, respectively) were also tested. Factorial analysis of variance showed that shear and compressive stress components evaluated by horizontal and vertical kinetic energy flux terms (KE_x and KE_y, respectively, in J m⁻² s⁻¹) along with their vector sum (KE_r, in J m⁻² s⁻¹) explained the variation in D. Neither sand size nor sand moisture was statistically significant alone although binary interactions of KE_r, KE_x and KE_y with the sand size and three-way interaction of KE_x, sand size and moisture were statistically significant. These results can be explained by size-dependent variation in sand compressibility and surface friction related to the total stress field developed by a given partition of shear and compressive stresses of wind-driven oblique raindrops (KE_x/KE_y). Further analysis of the variation of the unit sand detachment rate (D_u = D/KE_r = g J⁻¹) with rain inclination (α, in degrees) better revealed the effect of WDR obliquity on D_u that further changed with sand size class and moisture state. Finally, the difference in the resulting stress field differentiable by the oblique raindrop trajectories of the experiment over sand surface significantly affected the non-cohesive particle detachment rates, to some extent interacted with size-dependent compressibility and interface shear strength of sand grains.     

Comparison of Meteoroid Flux Models for Near Earth Space

Over the last decade several new models for the sporadic interplanetary meteoroid flux have been developed. These include the Divine-Staubach and the Dikarev model. They typically cover mass ranges from 10⁻¹⁸ g to 1 g and are applicable for model specific Sun distance ranges between 0.1 AU and 20 AU Near 1 AU averaged fluxes (over direction and velocities) for all these models are tuned to the well established interplanetary model by Grün et al. However, in many respects these models differ considerably. Examples are the velocity and directional distributions and the assumed meteoroid sources. In this paper flux predictions by the various models to Earth orbiting spacecraft are compared. Main differences are presented and analysed. The persisting differences even for near Earth space can be seen as surprising in view of the numerous ground based (optical and radar) and in situ (captured Inter Stellar Dust Particles, in situ detectors and analysis of retrieved hardware) measurements and simulations.     

Impact of reservoir operation and climate change on the hydrological regime of the Sesan and Srepok Rivers in the Lower Mekong Basin

The transboundary Sesan and Srepok sub-basins (2S) are the “hot-spot” areas for reservoir development in the Lower Mekong region, with 12 reservoirs built in the Vietnam territory. This study examines the impacts of reservoir operations in Vietnam and projected climate change on the downstream hydrologic regime of the 2S Rivers by jointly applying the Soil Water Assessment Tool (SWAT) and Water Evaluation and Planning (WEAP) models. Different scenarios of reservoir operation are considered and simulated to assess their impact on annual, seasonal, and monthly flow regimes under maximum hydropower capacity generation with and without taking into account the minimum flow requirement downstream near the Vietnam border with Cambodia. The precipitation and temperature projections from the high-resolution regional climate model HadGEM3-RA under two Representative Concentration Pathways, 4.5 and 8.5, of HadGEM2-AO are used as future climate change scenarios for the impact assessment. The study results show that reservoir operation leads to an increase in the dry season stream flows and a decrease in the wet season stream flows. The monthly flow regime exhibits considerable changes for both the Sesan and Srepok Rivers but with different magnitudes and patterns of increase and decrease. Climate change is likely to induce considerable changes in stream flows, though these changes are comparatively lower than those caused by reservoir operation. Climate change is likely to have both counterbalancing and reinforcing effects over the impact of reservoir operation, reducing changes during dry season but increasing changes in most of the other months.     

卫星遥感结合地面观测估算非均匀地表区域能量通量

卫星遥感在研究非均匀陆面上地－气间能量和水循环过程时有其独到的作用。文中介绍了一种利用ＬＡＮＤＳＡＴＴＭ资料进行非均匀陆面上区域能量平衡研究的参数化方案。并以夏季和深秋两个景的ＴＭ资料为个例,结合“黑河实验”（ＨＥＩＦＥ）期间的地面观测资料分析了实验区非均匀陆面上地表特征参数及能量平衡各分量的区域分布及季节差异,同时将所得的结果与地面观测的“真值”作了比较,所得的这些结果是基本可信的。这种方法仍然处于发展的初始阶段,对此也进行了讨论。     

Impact of grazing by benthic eukaryotic organisms on the nitrogen sediment–water exchange in the North Sea

The metabolic inhibitor cycloheximide was used to estimate the influence of primarily unicellular eukaryotes (heterotrophic protozoa) on nutrient recycling in different types of sediments in the North Sea. Fluxes of dissolved inorganic nitrogen across the sediment–water interface were measured in undisturbed sediment cores (controls) and compared to fluxes in sediment cores with cycloheximide added. If eukaryotes play an important role in nutrient recycling, one would expect to find lower nitrogen sediment–water effluxes in cores with cycloheximide due to the inactivation of eukaryotes. This important role hypothesised for eukaryotes was not generally observed: Only at four of the nineteen stations were ammonium effluxes significantly higher in controls than in cores with cycloheximide, and at five stations nitrate effluxes were significantly higher in the controls than in the cores with cycloheximide. Eukaryotic activity apparently contributed to the sediment–water exchange of ammonium through mineralisation of organic matter, nitrification and the subsequent release of ammonium and nitrate at these stations. At most other stations no differences were obtained between controls and cores with cycloheximide. This suggests that bacteria were the most important nutrient mineralisers at these stations at the time of the cruises.     

Artificial recharge efficiency assessment by soil water balance and modelling approaches in a multi-layered vadose zone in a dry region

To assess recharge through floodwater spreading, three wells, approx. 30 m deep, were dug in a 35-year-old basin in southern Iran. Hydraulic parameters of the layers were measured. One well was equipped with pre-calibrated time domain reflectometry (TDR) sensors. The soil moisture was measured continuously before and after events. Rainfall, ponding depth and the duration of the flooding events were also measured. Recharge was assessed by the soil water balance method, and by calibrated (inverse solution) HYDRUS-1D. The results show that the 15 wetting front was interrupted at a layer with fine soil accumulation over a coarse layer at the depth of approx. 4 m. This seemed to occur due to fingering flow. Estimation of recharge by the soil water balance and modelling approaches showed a downward water flux of 55 and 57% of impounded floodwater, respectively.     

Talus slope geomorphology investigated at multiple time scales from high-resolution topographic surveys and historical aerial photographs (Sanetsch Pass,Switzerland)

Talus slopes are common places for debris storage in high-mountain environments and form an important step in the alpine sediment cascade. To understand slope instabilities and sediment transfers, detailed investigations of talus slope geomorphology are needed. Therefore, this study presents a detailed analysis of a talus slope on Col du Sanetsch (Swiss Alps), which is investigated at multiple time scales using high-resolution topographic (HRT) surveys and historical aerial photographs. HRT surveys were collected during three consecutive summers (2017–2019), using uncrewed aerial vehicle (UAV) and terrestrial laser scanning (TLS) measurements. To date, very few studies exist that use HRT methods on talus slopes, especially to the extent of our study area (2 km²). Data acquisition from ground control and in situ field observations is challenging on a talus slope due to the steep terrain (30–37°) and high surface roughness. This results in a poor spatial distribution of ground control points (GCPs), causing unwanted deformation of up to 2 m in the gathered UAV-derived HRT data. The co-alignment of UAV imagery from different survey dates improved this deformation significantly, as validated by the TLS data. Sediment transfer is dominated by small-scale but widespread snow push processes. Pre-existing debris flow channels are prone to erosion and redeposition of material within the channel. A debris flow event of high magnitude occurred in the summer of 2019, as a result of several convective thunderstorms. While low-magnitude (<5,000 m³) debris flow events are frequent throughout the historical record with a return period of 10–20 years, this 2019 event exceeded all historical debris flow events since 1946 in both extent and volume. Future climate predictions show an increase of such intense precipitation events in the region, potentially altering the frequency of debris flows in the study area and changing the dominant geomorphic process which are active on such talus slopes. © 2020 John Wiley & Sons, Ltd.     

Lithostratigraphy, Sedimentology, and Provenance of the Balfour Formation (Beaufort Group) in the Fort Beaufort–Alice Area, Eastern Cape Province, South Africa

Abstract: The Balfour Formation has a pronounced lithological variation that is characterized by alternating sandstone- and mudstone-dominated members. The sandstone-dominated Oudeberg and Barberskrans Members are composed of lithofacies that range from intraformational conglomerates to fine-grained sediments, whereas the mudstone-dominated members (Daggaboersnek, Elandsberg, and Palingkloof) are dominated by the facies Fm and Fl. Petrography, geochemistry, and a paleocurrent analysis indicated that the source rock of the Balfour Formation was to south east and the rocks had a transitional/dissected magmatic arc signature. The sandstones-rich members were deposited by seasonal and ephemeral high-energy, low-sinuous streams, and the fine-grained-rich members were formed by ephemeral meandering streams. The paleoclimates have been equated to present temperate climates; they were semiarid becoming arid towards the top of the Balfour Formation. This has been determined by reconstructing the paleolatitude of the Karoo Basin, geochemistry, paleontology, sedimentary structures, and other rock properties, like color.