Journal: EGUsphere

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Copernicus

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2020 - 2026437
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Publications 1 - 10 of 437
  • Application of pulse-Doppler radar and 3D LiDAR for high-resolution velocity measurements of three debris flows at Illgraben (Switzerland)
    Item type: Other Conference Item
    Schöffl, Tobias; Aaron, Jordan; Kaitna, Roland; et al. (2023)
    EGUsphere
    The surface velocity of debris flows is constantly subject to strong temporal and spatial fluctuations. These are amplified by the pulse-like occurrence of surges throughout the event and by the high variance of the solids fraction. However, continuous information on velocities of multiple consecutive surges within a single debris-flow event with high temporal resolution is rare. In this study, we test a pulse-Doppler (PD) radar over a total torrent length of 180 m. The PD radar utilizes pulsed transmission and provides spatially resolved cells, called range gates, that extend over a width of 20 meters. Doppler velocity spectra composed of velocity classes and echo intensities are obtained at 4 Hz for each range gate. From these, we derived continuous velocity-time data sets. We present PD radar data for three debris flows that occurred on 05.06, 30.06, and 08.09.2022 at the Illgraben creek, Switzerland. The radar data were validated at the first event with a velocity data set obtained from a LiDAR scanner installed at the same location. This novel method collects high-resolution 3D point clouds at 10 Hz. This data was used to derive a high-resolution velocity vector field for one of the events. We isolate a ~ 2x2 m box in the middle of the channel and compare the LiDAR derived velocities at this location to those measured by the PD radar. Our comparison shows a strong correlation between the two data sets, with a coefficient of determination of 0.85. In addition, we note a minor consistent offset in the two velocity data sets of 0.5 m/s. We attribute this to the nature of the different measurement methods and conclude that the two methods may be sensitive to different features of the surface of the flow. However, our results show the high effectiveness and reliability of both methods in debris-flow monitoring. We anticipate that further analysis of the data sets will provide new insights into the geophysical principles of debris flows.
  • Investigating the influence of changing ice surfaces on gravity wave formation and glacier boundary-layer flow with large-eddy simulations
    Item type: Working Paper
    Goger, Brigitta; Nicholson, Lindsey; Ouy, Matthis; et al. (2024)
    EGUsphere
    Mountain glaciers are located in highly complex terrain and their local micro-climate is influenced by mountain boundary layer processes and dynamically-induced gravity waves. Observations (turbulence flux towers) and simulations (large-eddy simulation) over the Hintereisferner (HEF) glacier in the Austrian Alps have shown that down-glacier winds are often disturbed by cross-glacier flow from the North-West associated with gravity waves. In this work, we explore how the glaciers located upstream of HEF influence the gravity wave formation and intensity and and the feedback this has on boundary layer flow over HEF. In semi-idealized large-eddy simulations, we explore the impact of changing surface properties on HEF's microclimate by removing the upstream glaciers only (NO_UP) and removing all ice surfaces (NO_GL). Simulations suggest that removing the upstream glaciers (which causes a change of boundary layer stratification from stable to unstable) leads to a weaker gravity wave breaking earlier than in the reference simulation and leading to enhanced turbulent mixing over HEF. As a consequence, this results in higher temperatures, sensible heat fluxes, and stronger warm-air advection over HEF tongue. Removing all glaciers results – as expected – in higher temperatures of up to 5 K over the missing ice surfaces, while the gravity wave pattern is similar as in the NO_UP simulation, indicating that the upstream boundary layer exerts dominant control over downstream response in such highly dynamic conditions. This study shows that a single glacier tongue is never isolated from its environment and that surrounding glaciers and local topography have to be taken into account when studying glacier boundary-layer processes. Furthermore, glaciers have a stabilizing effect on the boundary layer, impacting gravity wave formation and downslope windstorm intensity and their impact on the flow structure in valleys downstream.
  • Implications of zircon Th/U for global continental crustal evolution and geodynamics
    Item type: Other Conference Item
    Wu, Yujing; Fang, Xianjun; Ji, Jianqing (2023)
    EGUsphere
    The continental crust is formed by the mantle’s successive crystallization differentiation and then aggregation, which is the result of the continuous energy acquisition and evolution of the mantle. This process has been objectively recorded in the growth of zircons which are widely present in the continental crust, owing to the close relationship between the zircon Th/U ratio and the crystallization temperature of zircons. As shown by theoretical calculations, phenomenon statistics, and/or crystallization simulations, higher zircon Th/U generally indicates higher zircon (re)crystallization temperature in metamorphic and magmatic systems. Here, we compiled ~600,000 zircon Th/U data from the global continental crust and obtained the time series of zircon Th/U ratios. The average level of the Th/U ratio in global zircons has a slow growth trend from old to new and fluctuates quasi-periodically around 0.5. There are two significant cycles of zircon Th/U ratios, ca. 600 and 120 Myr, which are associated with the supercontinent cycle and whole-mantle convection, respectively. It is inferred that the zircon Th/U periodicity is related to the periodic thermal state changes in the mantle, which might be regulated by tidal energy dissipation.
  • Source-to-Sink Sediment Tracing in the Glogn River Catchment
    Item type: Other Conference Item
    Garipova, Sofia; Mair, David; Demmel, Sophia; et al. (2024)
    EGUsphere
  • Imaging noise sources: comparing and combining a matched-field processing technique with finite-frequency noise source inversions
    Item type: Other Conference Item
    Igel, Jonas K.H.; Bowden, Daniel; Sager, Korbinian; et al. (2021)
    EGUsphere
    Imaging the spatio-temporal variations of ambient seismic noise sources can provide important information to improve near real-time monitoring and noise tomography. Various methods have been developed to tackle this problem. For example, Matched-Field Processing (MFP) offers an efficient data-driven approach by testing different noise source locations and subsequently correlating and stacking. A more rigorous approach is treating it as a finite-frequency full-waveform inversion problem. In contrast to the MFP technique, an inversion framework allows for the incorporation of prior information and subsequent iterative updates of the noise source distribution by numerically modelling correlations and source sensitivity kernels. Bowden et al. (2020) discuss the similarities between these two methods and how one can be derived from the other. We aim to compare and contrast the two methods using real data from a regional to a global scale to locate the secondary microseismic sources in the ocean. Igel et al. (2021, in prep) use a logarithmic energy ratio as measurement for the sensitivity kernels, which is chosen due to its robustness with respect to unknown 3D Earth structures. However, some disadvantages of this type of measurement are not considering absolute amplitudes and discarding information outside of the expected surface wave arrival time window. By combining the two methods and first using MFP to create an initial model for the inversion, we are able to steer the inversion in the right direction, allowing us to use a more elaborate full-waveform measurement in the inversion and hence increasing the resolution and quality of the final model. Results for noise source inversions in the ocean on a daily basis using the combination of the two methods will be presented. This work paves the way for publicly available, daily, multi-scale ambient noise source maps.
  • Estimating mixing processes of sources contributing to baseflow in Alpine headwater catchments
    Item type: Other Conference Item
    Floriancic, Marius; Roques, Clément; Jimenez-Martinez, Joaquin (2020)
    EGUsphere
  • Convective-Permitting Modeling for Retrospective Subseasonal-to-Seasonal (S2S) Forecasting Using the Framework of the Coordinated Regional Ensemble Downscaling Experiment (CORDEX)
    Item type: Other Conference Item
    Castro, Christopher L.; Chang, Hsin-I; Prein, Andreas F.; et al. (2020)
    EGUsphere
    Convective-permitting modeling (CPM) yields step improvements in the representation of precipitation, as has been demonstrated in applications of numerical weather prediction and climate modeling. While CPM has been used in the context of historical climate simulations and climate change projections, its application to the sub-seasonal to seasonal (S2S) forecast timescale (weeks to months) is comparatively underexplored. New, long-term S2S reforecast products have recently been generated from operational global forecast models, for example as part of the S2S Project and North American Multimodel Ensemble (NMME). These are analogous to CMIP models used for climate change projection. It is now technically possible to dynamically downscale these reforecast data to CPM scale, to asess potential improvement in S2S forecast skill and create new S2S forecast metrics for extreme events. The Coordinated Regional Ensemble Downscaling Experiment (CORDEX) provides an existing robust community framework that can be leveraged to dynamically downscale S2S reforecast data, in a globally unified way. This overview presentation will highlight outcomes from a community discussion on this topic that took place at the 2019 Latsis Symposium "High-Resolution Climate Modeling: Perspectives and Challenges" at ETH Zurich, including a summary of the current state of the science, collective identification of research priorities, and proposed action items proceeding forward.
  • Tropospheric delay parameters derived from GNSS-tracking data of a fast-moving fleet of trains
    Item type: Other Conference Item
    Aichinger-Rosenberger, Matthias; Hanna, Natalia; Weber, Robert (2021)
    EGUsphere
    Electromagnetic signals, as broadcasted by Global Navigation Satellite Systems (GNSS), are delayed when travelling through the Earth’s atmosphere due to the presence of water vapour. Parametrisations of this delay, most prominently the Zenith Total Delay (ZTD) parameter, have been studied extensively and proven to provide substantial benefits for atmospheric research and especially the Numerical Weather Prediction (NWP) model performance. Typically, regional/global networks of static reference stations are utilized to derive ZTD along with other parameters of interest in GNSS analysis (e.g. station coordinates). Results are typically used as a contributing data source for determining the initial conditions of NWP models, a process referred to as Data Assimilation (DA). This contribution goes beyond the approach outlined above as it shows how reasonable tropospheric parameters can be derived from highly kinematic, single-frequency (SF) GNSS data. The utilized data was gathered at trains by the Austrian Federal Railways (ÖBB) and processed using the Precise Point Positioning (PPP) technique. Although the special nature of the observations yields several challenges concerning data processing, we show that reasonable results for ZTD estimates can be obtained for all four analysed test cases by using different PPP processing strategies. Comparison with ZTD calculated from ERA5 reanalysis data yields a very high correlation and an overall agreement from the low millimetre-range up to 5 cm, depending on solution and analysed travelling track. We also present the first tests of assimilation into a numerical weather prediction (NWP) model which show the reasonable quality of the results as between 30-100 % of the observations are accepted by the model. Furthermore, we investigate means to transfer the developed ideas to an operational stage in order to exploit the huge benefits (horizontal/temporal resolution) of this special dataset for operational weather forecasting.
  • Can we get more out of rainfall thresholds? The temporal resolution tradeoff and the role of antecedent wetness and rainfall spatial variability
    Item type: Other Conference Item
    Leonarduzzi, Elena; Molnar, Peter (2020)
    EGUsphere
    Rainfall event properties like maximum intensity, total rainfall depth, or their representation in the form of intensity-duration (ID) or total rainfall-duration (ED) curves, are commonly used to determine the triggering rainfall (event) conditions required for landslide initiation. This rainfall data-driven prediction of landsliding can be extended by the inclusion of antecedent wetness conditions. Although useful for first order assessment of landslide triggering conditions in warning systems, this approach relies heavily on data quality and temporal resolution, which may affect the overall predictive model performance as well as its reliability. In this work, we address three key aspects of rainfall thresholds when applied at large spatial scales: (a) the tradeoffs between higher and lower temporal resolution (hourly or daily) (b) the spatial variability associated with long term rainfall, and (c) the added value of antecedent rainfall as predictor. We explore all of these by utilizing a long-term landslide inventory, containing more than 2500 records in Switzerland and 3 gridded rainfall records: a long daily rainfall dataset and two derived hourly products, disaggregated using stations or radar hourly measurements. We observe that while predictive performances improve slightly when utilizing high quality hourly record (using radar information), the length of the record decreases, as well as the number of landslides in the inventory, which affects the reliability of the thresholds. A tradeoff has to be found between using long records of less accurate daily rainfall data and landslide timing, and shorter records with highly accurate hourly rainfall data and landslide timing. Even daily rainfall data may give reasonable predictive performance if thresholds are estimated with a long landslide inventory. Good quality hourly rainfall data significantly improve performance, but historical records tend to be shorter or less accurate (e.g. fewer stations available) and landslides with known timing are fewer. Considering antecedent rainfall, we observe that it is generally higher prior to landslide-triggering events and this can partially explain the false alarms and misses of an intensity-duration threshold. Nevertheless, in our study antecedent rainfall shows less predictive power by itself than the rainfall event characteristics. Finally, we show that we can improve the performances of the rainfall thresholds by accounting for local climatology in which we define new thresholds by normalizing the event characteristics with a chosen quantile of the local rainfall distribution or using the mean annual precipitation.
  • MoMuCAMS: A new modular platform for boundary layer aerosol and trace gas vertical measurements in extreme environments
    Item type: Working Paper
    Pohorsky, Roman; Baccarini, Andrea; Tolu, Julie; et al. (2024)
    EGUsphere
    The Modular Multiplatform Compatible Air Measurement System (MoMuCAMS) is a newly developed in situ aerosol and trace gas measurement payload for lower atmospheric vertical profiling in extreme environments. MoMuCAMS is a multiplatform compatible system, primarily designed to be attached to a helikite, a rugged tethered balloon type that is suitable for operations in cold and windy conditions. The system addresses the need for detailed vertical observations of atmospheric composition in the boundary layer and lower free-troposphere, especially in polar and alpine regions. These regions are known to frequently experience strong temperature inversions, preventing vertical mixing of aerosols and trace gases, and therefore reducing the representativeness of ground-based measurements for the vertical column, causing a large informational gap. The MoMuCAMS encompasses a box that houses instrumentation, a board computer to stream data to the ground for inflight decisions, and a power distribution system. The enclosure has an internal volume of roughly 100 L and can accommodate various combinations of instruments within its 20 kg weight limit. This flexibility represents a unique feature, allowing the simultaneous study of multiple aerosol properties (number concentration, size distribution, cluster ions, optical properties, chemical composition and morphology), as well as trace gases (e.g. CO, CO2, O3, N2O) and meteorological variables (e.g., wind speed and direction, temperature, relative humidity, pressure) . To the authors’ knowledge, it is the first tethered balloon based system equipped with instrumentation providing a full size distribution for aerosol particles starting from 8 nm, which is vital to understanding atmospheric processes of aerosols and their climate impacts through interaction with direct radiation and clouds. MoMuCAMS has been deployed during two field campaigns in Swiss Alpine valleys in winter and fall 2021. It has been further deployed in Fairbanks, Alaska (USA) in January–February 2022, as part of the ALPACA (Alaskan Layered Pollution and Chemical Analysis) campaign and in Pallas, Finland, in September–October 2022, as part of the PaCE2022 (Pallas Cloud Experiment) study. The system flew successfully at temperatures of −36° C, in wind speeds above 15 m s−1 and in clouds. Here we present a full characterization of the specifically developed inlet system and novel, hitherto not yet characterized, instruments, most notably a miniaturized scanning electrical mobility spectrometer and a near-infrared carbon monoxide monitor. Three cases from one of the Swiss Alpine studies are presented to illustrate the capability of MoMuCAMS to perform high-resolution measurements with different instrumental setups. We show two case studies with surface-based inversions in the morning that allowed for observation of aerosol and trace gas dynamics in evolving boundary layer conditions. The vertical structure of the boundary layer featured in both cases a surface layer (SL) with a top between 50 and 70 m above ground level, dominated by traffic emissions leading to particle number concentrations up to seven times higher than in the residual layer above. Following sunrise, turbulent mixing led to rapid development of a mixed boundary layer and dilution of the SL within one to two hours. The third case study illustrates the capability of the system to perform aerosol sampling at a chosen altitude over several hours, long enough in low aerosol concentrations environments to perform chemical analyses. Trace elements were analyzed using inductively coupled plasma tandem mass spectrometry. The samples were also analyzed under a scanning electron microscope with energy dispersive x-ray and a transmission electron microscope to gain additional insights into their morphology and chemical composition. Such analyses are suitable to gain deeper insights into particles’ origins, and their physical and chemical transformation in the atmosphere. Overall, MoMuCAMS is an easily deployable tethered balloon payload with high flexibility, able to cope with the rough conditions of extreme environments. Compared to uncrewed aerial vehicles (drones) it allows to observe aerosol processes in detail over multiple hours providing insights on their vertical distribution and processes, e.g. in clouds, that were difficult to obtain beforehand.
Publications 1 - 10 of 437