A Two-Day Case Study: Comparison of Turbulence Data from an Unmanned Aircraft System with a Model Chain for Complex Terrain

The airborne measurement platform MASC-3 (Multi-Purpose Airborne Sensor Carrier) is used for measurements over a forested escarpment in the Swabian Alps to evaluate the wind field. Data from flight legs between 20 and 200 m above the ground on two consecutive days with uphill (westerly) flow in September 2018 are analyzed. In the lowest 140 m above the ground a speed-up is found with increased turbulence and changes in wind direction directly over the escarpment, whereas in the lowest 20 to 50 m above the ground a deceleration of the flow is measured. Additionally, simulation results from a numerical model chain based on the Weather Research and Forecasting (WRF) model and an OpenFOAM (Open Source Field Operation and Manipulation) model, developed for complex terrain, are compared to the data captured by MASC-3. The models and measurements compare well for the mean wind speed and inclination angle.

     

A machine learning approach for regional geochemical data:Platinum-group element geochemistry vs geodynamic settings of the North Atlantic Igneous Province

Whilst traditional approaches to geochemistry provide valuable insights into magmatic processes such as melting and element fractionation, by considering entire regional data sets on an objective basis using machine learning algorithms(MLAs), we can highlight new facets within the broader data structure and significantly enhance previous geochemical interpretations.The platinum-group element(PGE) budget of lavas in the North Atlantic Igneous Province(NAIP) has been shown to vary systematically according to age, geographic location and geodynamic environment.Given the large multi-element geochemical data set available for the region, MLAs were employed to explore the magmatic controls on these shifting concentrations.The key advantage of using machine learning in analysis is its ability to cluster samples across multi-dimensional(i.e., multi-element)space.The NAIP data set is manipulated using Principal Component Analysis(PCA) and t-Distributed Stochastic Neighbour Embedding(t-SNE) techniques to increase separability in the data alongside clustering using the k-means MLA.The new multi-element classification is compared to the original geographic classification to assess the performance of both approaches.The workflow provides a means for creating an objective high-dimensional investigation on a geochemical data set and particularly enhances the identification of metallogenic anomalies across the region.The techniques used highlight three distinct multi-element end-members which successfully capture the variability of the majority of elements included as input variables.These end-members are seen to fluctuate in prominence throughout the NAIP, which we propose reflects the changing geodynamic environment and melting source.Crucially, the variability of Pt and Pd are not reflected in MLA-based clustering trends, suggesting that they vary independently through controls not readily demonstrated by the NAIP major or trace element data structure(i.e., other proxies for magmatic differentiation).This data science approach thus highlights that PGE(here signalled by Pt/Pd ratio) may be used to identify otherwise localised or cryptic geochemical inputs from the subcontinental lithospheric mantle(SCLM) during the ascent of plume-derived magma, and thereby impact upon the resulting metallogenic basket.     

Long-term ocean simulations in FESOM: evaluation and application in studying the impact of Greenland Ice Sheet melting

The Finite Element Sea-ice Ocean Model (FESOM) is formulated on unstructured meshes and offers geometrical flexibility which is difficult to achieve on traditional structured grids. In this work, the performance of FESOM in the North Atlantic and Arctic Ocean on large time scales is evaluated in a hindcast experiment. A water-hosing experiment is also conducted to study the model sensitivity to increased freshwater input from Greenland Ice Sheet (GrIS) melting in a 0.1-Sv discharge rate scenario. The variability of the Atlantic Meridional Overturning Circulation (AMOC) in the hindcast experiment can be explained by the variability of the thermohaline forcing over deep convection sites. The model also reproduces realistic freshwater content variability and sea ice extent in the Arctic Ocean. The anomalous freshwater in the water-hosing experiment leads to significant changes in the ocean circulation and local dynamical sea level (DSL). The most pronounced DSL rise is in the northwest North Atlantic as shown in previous studies, and also in the Arctic Ocean. The released GrIS freshwater mainly remains in the North Atlantic, Arctic Ocean and the west South Atlantic after 120 model years. The pattern of ocean freshening is similar to that of the GrIS water distribution, but changes in ocean circulation also contribute to the ocean salinity change. The changes in Arctic and sub-Arctic sea level modify exchanges between the Arctic Ocean and subpolar seas, and hence the role of the Arctic Ocean in the global climate. Not only the strength of the AMOC, but also the strength of its decadal variability is notably reduced by the anomalous freshwater input. A comparison of FESOM with results from previous studies shows that FESOM can simulate past ocean state and the impact of increased GrIS melting well.

     

<Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr anomalies in Late Cretaceous-Early Tertiary strata of the Cauvery basin,south India: Constraints on nature and rate of environmental changes across K-T boundary

The Ariyalur-Pondicherry sub-basin of the Cauvery basin comprises a near complete stratigraphic record of Upper Cretaceous-Lower Tertiary periods. Earlier studies have documented variations of clay mineral assemblages, change in microtexture of siliciclasts and many geochemical and stable isotopic anomalies far below the Cretaceous-Tertiary boundary (KTB) in these strata. This paper documents the occurrences of two positive ⁸⁷Sr/⁸⁶Sr anomalies preceding K-T boundary in this basin and discusses plausible causes. Analysis of trace elemental and stable isotopic profiles, sedimentation history, petrography and mineralogy of the rocks reveal that while both the anomalies may be due to increased detrital influx caused by sea level and climatic changes, the second anomaly might have been influenced by Deccan volcanism which in turn predated KTB. Record of such anomalies preceding K-T boundary supports the view of multi-causal step-wise extinction of biota across KTB.     

Morphology and recent history of the Rhone River Delta in Lake Geneva (Switzerland)

The current topographic maps of the Rhone Delta—and of Lake Geneva in general—are mainly based on hydrographic data that were acquired during the time of F.-A. Forel at the end of the nineteenth century. In this paper we present results of a new bathymetric survey, based on single- and multi-beam echosounder data. The new data, presented as a digital terrain model, show a well-structured lake bottom morphology, reflecting depositional and erosional processes that shape the lake floor. As a major geomorphologic element, the sub-aquatic Rhone Delta extends from the coastal platform to the depositional fans of the central plain of the lake at 310 m depth. 9 canyons cut the platform edge of the delta. These are sinuous (“meandering”) channels formed by erosional and depositional processes, as indicated by the steep erosional canyon walls and the depositional levees on the canyon shoulders. Ripples or dune-like morphologies wrinkle the canyon bottoms and some slope areas. Subaquatic mass movements are apparently missing on the delta and are of minor importance on the lateral lake slopes. Morphologies of the underlying bedrock and small local river deltas are located along the lateral slopes of Lake Geneva. Based on historical maps, the recent history of the Rhone River connection to the sub-aquatic delta and the canyons is reconstructed. The transition from three to two river branches dates to 1830–1840, when the river branch to the Le Bouveret lake bay was cut. The transition from two to one river branch corresponds to the achievement of the correction and dam construction work on the modern Rhone River channel between 1870 and 1880.     

Pb isotopic constraints on the formation of the Dikulushi Cu–Pb–Zn–Ag mineralisation, Kundelungu Plateau (Democratic Republic of Congo)

Base metal–Ag mineralisation at Dikulushi and in other deposits on the Kundelungu Plateau (Democratic Republic of Congo) developed during two episodes. Subeconomic Cu–Pb–Zn–Fe polysulphide ores were generated during the Lufilian Orogeny (c. 520 Ma ago) in a set of E–W- and NE–SW-oriented faults. Their lead has a relatively unradiogenic and internally inhomogeneous isotopic composition (²⁰⁶Pb/²⁰⁴Pb = 18.07–18.49), most likely generated by mixing of Pb from isotopically heterogeneous clastic sources. These sulphides were remobilised and enriched after the Lufilian Orogeny, along reactivated and newly formed NE–SW-oriented faults into a chalcocite-dominated Cu–Ag mineralisation of high economic interest. The chalcocite samples contain only trace amounts of lead and show mostly radiogenic Pb isotope signatures that fall along a linear trend in the ²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb diagram (²⁰⁶Pb/²⁰⁴Pb = 18.66–23.65; ²⁰⁷Pb/²⁰⁴Pb = 15.72–16.02). These anomalous characteristics reflect a two-stage evolution involving admixture of both radiogenic lead and uranium during a young fluid event possibly c. 100 Ma ago. The Pb isotope systematics of local host rocks to mineralisation also indicate some comparable young disturbance of their U–Th–Pb systems, related to the same event. They could have provided Pb with sufficiently radiogenic compositions that was added to less radiogenic Pb remobilised from precursor Cu–Pb–Zn–Fe polysulphides, whereas the U most likely originated from external sources. Local metal sources are also suggested by the ²⁰⁸Pb/²⁰⁴Pb–²⁰⁶Pb/²⁰⁴Pb systematics of combined ore and rock lead, which indicate a pronounced and diversified lithological control of the immediate host rocks on the chalcocite-dominated Cu–Ag ores. The Pb isotope systematics of polysulphide mineralisation on the Kundelungu Plateau clearly record a diachronous evolution.     

A new method to determine the direction of impact: Asymmetry of concentric impact craters as observed in the field (Lockne), on Mars,in experiments,and simulations

Most impacts occur at an angle with respect to the horizontal plane. This is primarily reflected in the ejecta distribution, but at very low angle structural asymmetries such as elongation of the crater and nonradial development of the central peak become apparent. Unfortunately, impact craters with pristine ejecta layers are rare on Earth and also in areas with strong past or ongoing surface erosion on other planetary bodies, and the structural analysis of central peaks requires good exposures or even on‐site access to outcrop. However, target properties are known to greatly influence the shape of the crater, especially the relatively common target configuration of a weaker layer covering a more rigid basement. One such effect is the formation of concentric craters, i.e., a nested, deeper, inner crater surrounded by a shallow, outer crater. Here, we show that with decreasing impact angle there is a downrange shift of the outer crater with respect to the nested crater. We use a combination of (1) field observation and published 3‐D numerical simulation of one of the best examples of a terrestrial, concentric impact crater formed in a layered target with preserved ejecta layer: the Lockne crater, Sweden; (2) remote sensing data for three pristine, concentric impact craters on Mars with preserved ejecta layers further constraining the direction of impact; as well as (3) laboratory impact experiments, to develop the offset in crater concentricity into a complementary method to determine the direction of impact for layered‐target craters with poorly preserved ejecta layers.     

Post-drought increase in regional-scale groundwater nitrate in southwest Germany

Elevated nitrate concentrations in groundwater are a common challenge for water management. One important factor in this context is higher frequencies and intensities of wet-dry cycles that may cause increased nitrate concentrations in groundwater due to nitrate flushes after drought termination. Yet systematic studies on regional-scale impacts of droughts on groundwater nitrate concentrations are missing so far. Here we analyzed time series of 44 shallow groundwater wells and 41 springs all across the German Federal State Baden-Wuerttemberg from 2000 to 2018 to characterize patterns of post-drought nitrate increase in groundwater. In general, half of the exceptional nitrate concentrations, which exceeded the 80th percentile of long-term nitrate measurements, could be related to droughts in the research timeframe. The 2003 drought event stood out in terms of drought severity and post-drought nitrate concentration increases in our data. The great majority (91%) of all monitoring sites showed at least one exceptionally high nitrate concentration in the 4 years following the 2003 drought event. Springs were mainly located in forests of steep low mountain ranges and wells in cropland of flat river valleys. Therefore, delay times between drought intensity and nitrate concentration increases as well as magnitudes of nitrate concentration increase were diverse among wells and springs. We derived two distinct nitrate response patterns: (i) nitrate increases immediately following drought events (more common for springs and fractured rock aquifers) and (ii) delayed nitrate increases (more common for wells and porous aquifers). Springs generally showed quicker (median of 101 days) but weaker (median of +1.3 mg/L) post-drought nitrate increases than wells (185 days, +3.4 mg/L). Only few sites exhibited no post-drought nitrate increase and post-drought mean-nitrate concentrations of groundwater reservoirs were extraordinarily high in 2006. Overall, we demonstrate that post-drought nitrate increase in groundwater is omnipresent, while different landscapes and hydrogeological characteristics create a diverse regional pattern. As severe droughts become more frequent in a changing climate, post-drought nitrate increase may intensify problems regarding water quality and supply.     

Towards a Validation of Scintillometer Measurements: The LITFASS-2009 Experiment

Scintillometry has been increasingly used over the last decade for the experimental determination of area-averaged turbulent fluxes at a horizontal scale of a few kilometres. Nevertheless, a number of assumptions in the scintillometer data processing and interpretation still call for a thorough evaluation, in particular over heterogeneous terrain. Moreover, a validation of the path-averaged structure parameters derived from scintillometer data (and forming the basis for the flux calculations) by independent measurements is still missing. To achieve this, the LITFASS-2009 field campaign has been performed around the Meteorological Observatory Lindenberg ?C Richard-A?mann-Observatory of the German Meteorological Service (DWD) in July 2009. The experiment combined tower-based in-situ turbulence measurements, field-scale laser scintillometers, long-range optical (large-aperture) and microwave scintillometers, and airborne turbulence measurements using an automatically operating unmanned aircraft. The paper describes the project design and strategy, and discusses first results. Daytime near-surface values of the temperature structure parameter, ${C_{T}^{2}}$ , over different types of farmland differ by more than one order of magnitude in their dependence on the type and status of the vegetation. Considerable spatial variability in ${C_{T}^{2}}$ was also found along the flight legs at heights between 50 and 100?m. However, it appeared difficult to separate the effects of heterogeneity from the temporal variability of the turbulence fields. Aircraft measurements and scintillometer data agreed in magnitude with respect to the temporal variation of the path-averaged ${C_{T}^{2}}$ values during the diurnal cycle. The decrease of ${C_{T}^{2}}$ with height found from the scintillometer measurements close to the surface and at 43?m under daytime convective conditions corresponds to free-convection scaling, whereas the aircraft measurements at 54 and 83?m suggest a different behaviour.