Has it really stopped? Interplay between rheology, topography and mesh resolution in numerical modelling of snow avalanches
Saoirse Robin Goodwin, Thierry Faug, and Guillaume Chambon
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-123,2024
Preprint under review for NHESS (discussion: open, 0 comments)
This paper considers how we can objectivity define stoppage of numerically-modelled snow avalanches. When modelling real topographies, numerically-modelled avalanche snow velocities typically do not converge to 0, so stoppage is defined with arbitrary criteria, which must be tuned on a case-by-case basis. We propose a new objective arrest criterion based on local flow properties, in tandem with a newly-implemented physical yielding criterion.
Comparative Analysis of μ (I) and Voellmy-Type Grain Flow Rheologies in Geophysical Mass Flows: Insights from Theoretical and Real Case Studies
Yu Zhuang, Brian W. McArdell, and Perry Bartelt
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-87,2024
Preprint under review for NHESS (discussion: open, 0 comments)
This study reformulates the μ(I) rheology into a Voellmy-type relationship to elucidate its physical implications. The μ(I) rheology, incorporating a dimensionless inertial number, mimics granular temperature effects, reflecting shear thinning behavior of mass flows. However, its constant Coulomb friction coefficient limits accuracy in modeling deposition. Comparing μ(I) with Voellmy-type rheologies reveals strengths and limitations, enhancing mass flow modeling and engineering applications.
Abstract
(Ultra)high-pressure metamorphic rocks provide valuable insights into the properties of slab-derived fluids. Here, we report CH4-rich fluid inclusions in garnet of a metapelite from the Zermatt-Saas ophiolite, western Alps. Two types of metapelite, a CH4-bearing pelitic schist and a calcareous pelitic schist, were investigated to unravel favorable P-T-fO2 conditions for preservation of CH4 in high-pressure metapelite. In the CH4-bearing pelitic schist, CH4-rich fluid inclusions exclusively occur in the core of garnet (GrtI) rather than the rim (GrtII). GrtI records P-T conditions of ∼2.85 GPa and ∼555°C, whereas GrtII records a prograde P-T path from ∼1.75 GPa at 510°C to ∼2.0 GPa at 530°C. Compositional profile of garnet in the calcareous pelitic schist reflects a prograde metamorphic path from ∼1.9 GPa at 510°C to ∼2.12 GPa at 545°C. CH4-rich fluid formation may primarily rise from graphite reduction at high-pressure reduced conditions (ΔFMQ −3.5 to −4, 2.85 GPa, ∼550°C), while graphite and carbonates stabilize in a relatively oxidized environment (ΔFMQ ∼0, 2.12 GPa, 545°C). The initial redox budget of subducted sediments is primarily controlled by the amount of sedimentary carbonate and organic carbon, which plays the most important role in deciding the carbon speciation at different subduction depths. CH4 formation in COH fluids could primarily be attributed to the reduction of graphite. Subducted metasediments act as conduits for transporting non-oxidized fluids to arc magmas, which provides crucial evidence to support the heterogeneity for slab-derived COH fluids and offers new insights into the deep carbon cycle.
No abstract is available for this article.
Abstract
Coseismic rupture and aftershock development on a fault plane are complex and heterogeneous processes. The M
w 6.1 L’Aquila 2009 normal faulting earthquake is a perfect case to explore how fault geometry and rheology influence the rupture process and aftershocks distribution. In this study, we use for the first time a dense set of earthquake data to obtain enhanced images of the causative normal fault structure to the kilometer scale. The hypocenter of the emergent onset of the mainshock took place within a low V
p/V
s volume, while the large coseismic slip occurred a few kilometers above, as the rupture propagated through a high V
p and high V
p/V
s fluid-filled rock volume. The increase of V
p/V
s in the fault hanging wall during the sequence suggests a strong dehydration in the earthquake asperity, with an upward fluid pressure migration along the fault toward the host rock volume. We propose that the localization of deformation on the fault plane is favored by high fluid pressure, while the spreading of aftershocks on a wide volume around the fault is driven by the depletion of fluids from the slipped portion of the fault plane and migration to small segments within the fault host rocks.
Abstract
In crustal faults dominated by granitoid gouges, the frictional-viscous transition marks a significant change in strength constraining the lower depth limit of the seismogenic zone. Dissolution-precipitation creep (DPC) may play an important role in initiating this transition, especially within polymineralic materials. Yet, it remains unclear to what extent DPC contributes to the weakening of granitoid gouge materials at the transition. Here we conducted sliding experiments on wet granitoid gouges to large displacement (15 mm), at an effective normal stress and pore fluid pressure of 100 MPa, at temperatures of 20–650°C, and at sliding velocities of 0.1–100 μm/s, which are relevant for earthquake nucleation. Gouge shear strengths were generally ∼75 MPa even at temperatures up to 650°C and at velocities >1 μm/s. At velocities ≤1 μm/s, strengths decreased at temperatures ≥450°C, reaching a minimum of 37 MPa at the highest temperature and lowest velocity condition. Microstructural observations showed that, as the gouges weakened, the strain localized into thin, dense, and ultrafine-grained (≤1 μm) principal slip zones, where nanopores were located along grain contacts and contained minute biotite-quartz-feldspar precipitates. The stress sensitivity exponent n decreased from a large number at 20°C to ∼2.2 at 650°C at the lowest velocities. These findings suggest that high temperature, slow velocity and small grain sizes promote DPC-accommodated granular flow over cataclastic frictional granular flow, leading to the observed weakening and strain localization. Field observations together with extrapolation suggest that DPC-induced weakening occurs at depths of 7–20 km depending on geothermal gradient.
Abstract
Convective dynamics in a supercell thunderstorm, a volcanic eruption, and two pyrocumulonimbus (pyroCb) events are compared by computing cloud-top divergence (CTD) with an optical flow technique called Deepflow. Visible 0.64-μm imagery sequences from Geostationary Operational Environmental Satellites (GOES)-R series Advanced Baseline Imager (ABI) are used as input into the optical flow algorithm. CTD is computed after post-processing of the retrieved motions. Analysis is performed on specific image times, as well as the full time series of each case. Multiple CTD-based parameters, such as the maximum and the two-dimensional area exceeding a specified CTD threshold, are examined along with the optical flow-retrieved wind speed. CTD is shown to accurately and quantitatively represent the behavior and magnitude of different deep convective phenomena, including distinguishing between convective pulses within each individual event. CTD captures updraft intensification as well as differences in convective activity between two pyroCb events and individual updraft pulses occurring within a single pyroCb event. Finally, the characteristics of high-altitude smoke plumes injected by two separate pyroCb pulses are linked to CTD using ultraviolet aerosol index and satellite imagery. Optical flow-derived parameters can therefore be applied to individual pyroCbs in real-time, with potential to characterize pyroCb smoke source inputs for downstream smoke modeling applications and to facilitate future tools supporting air quality modeling and firefighting efforts.
Abstract
Iron (Fe) has profound impacts on Earth's ecosystem and global biogeochemical cycles. Fe deposited onto glacier surfaces reduces snow and ice albedo, thereby accelerating glacier melting, and supplying downstream ecosystems with dissolved Fe. However, the origins of atmospheric Fe deposition in glacier regions of western China remain unclear. This study presents novel insights into Fe isotopic composition (refer to δ56Fe) and origins, gained from geochemical analysis of large-scale cryoconite samples collected from glaciers in western China, which encompass the Tibetan Plateau (TP) and the Tianshan Mountains. Results showed that cryoconite δ56Fe ranged from −1.06 ± 0.07‰ to 0.33 ± 0.04‰, regardless of their concentration. Moreover, anomalous δ56Fe values deviating significantly from the upper continental crust values (with an average of 0.09‰) were detected, indicating a significant impact of anthropogenic Fe materials on the investigated glaciers. This impact was particularly prominent in the margin regions of the TP and its surroundings, but was less apparent in the interior and southern of the plateau. Using MixSIAR isotope mixing model, we determined that coal combustion and other anthropogenic combustion sources (such as liquid fuel combustion and steel smelting) contributed to cryoconite Fe in the range of 6.9%–43.1% and 0.8%–23.4%, respectively. Among these, coal combustion was the predominant anthropogenic source of cryoconite Fe in western China's glaciers. Compared with other sink areas in the Northern Hemisphere, glaciers in western China are obviously affected by anthropogenically sourced Fe. This study has significant implications for understanding glacier-fed downstream ecosystems and the regional biogeochemical cycle.
New explicit formulae for the settling speed of prolate spheroids in the atmosphere: theoretical background and implementation in AerSett v2.0.2
Sylvain Mailler, Sotirios Mallios, Arineh Cholakian, Vassilis Amiridis, Laurent Menut, and Romain Pennel
Geosci. Model Dev., 17, 5641–5655, https://doi.org/10.5194/gmd-17-5641-2024, 2024
We propose two explicit expressions to calculate the settling speed of solid atmospheric particles with prolate spheroidal shapes. The first formulation is based on theoretical arguments only, while the second one is based on computational fluid dynamics calculations. We show that the first method is suitable for virtually all atmospheric aerosols, provided their shape can be adequately described as a prolate spheroid, and we provide an implementation of the first method in AerSett v2.0.2.
A measurement system for CO2 and CH4 emissions quantification of industrial sites using a new in situ concentration sensor operated on board uncrewed aircraft vehicles
Jean-Louis Bonne, Ludovic Donnat, Grégory Albora, Jérémie Burgalat, Nicolas Chauvin, Delphine Combaz, Julien Cousin, Thomas Decarpenterie, Olivier Duclaux, Nicolas Dumelié, Nicolas Galas, Catherine Juery, Florian Parent, Florent Pineau, Abel Maunoury, Olivier Ventre, Marie-France Bénassy, and Lilian Joly
Atmos. Meas. Tech., 17, 4471–4491, https://doi.org/10.5194/amt-17-4471-2024, 2024
We present a top-down approach to quantify CO2 and CH4 emissions at the scale of an industrial site, based on a mass balance model relying on atmospheric concentrations measurements from a new sensor embarked on board uncrewed aircraft vehicles (UAVs). We present a laboratory characterization of our sensor and a field validation of our quantification method, together with field application to the monitoring of two real-world offshore oil and gas platforms.
A Bias Correction Scheme for FY-3E/ HIRAS-II Observation Data Assimilation
Hongtao Chen and Li Guan
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-65,2024
Preprint under review for AMT (discussion: open, 0 comments)
In order to correctly assimilate satellite radiance observations in data assimilation systems, the systematic observation biases must be corrected to conform to a Gaussian normal distribution with a mean of 0.In this paper, a two-step bias correction scheme is established based on radiation observations of HIRAS-II (Hyperspectral Infrared Atmospheric Sounder-II) carried on FY-3E.
Harmonizing seismicity information in Central Asian countries: earthquake catalogue and active faults
Valerio Poggi, Stefano Parolai, Natalya Silacheva, Anatoly Ischuk, Kanatbek Abdrakhmatov, Zainalobudin Kobuliev, Vakhitkhan Ismailov, Roman Ibragimov, Japar Karaev, Paola Ceresa, and Paolo Bazzurro
Nat. Hazards Earth Syst. Sci., 24, 2597–2613, https://doi.org/10.5194/nhess-24-2597-2024, 2024
As part of the Strengthening Financial Resilience and Accelerating Risk Reduction in Central Asia (SFRARR) programme, funded by the European Union in collaboration with the World Bank and GFDRR, a regionally consistent probabilistic multi-hazard and multi-asset risk assessment has been developed. This paper describes the preparation of the input datasets (earthquake catalogue and active-fault database) required for the implementation of the probabilistic seismic hazard model.
ZJU-AERO V0.5: an Accurate and Efficient Radar Operator designed for CMA-GFS/MESO with the capability to simulate non-spherical hydrometeors
Hejun Xie, Lei Bi, and Wei Han
Geosci. Model Dev., 17, 5657–5688, https://doi.org/10.5194/gmd-17-5657-2024, 2024
A radar operator plays a crucial role in utilizing radar observations to enhance numerical weather forecasts. However, developing an advanced radar operator is challenging due to various complexities associated with the wave scattering by non-spherical hydrometeors, radar beam propagation, and multiple platforms. In this study, we introduce a novel radar operator named the Accurate and Efficient Radar Operator developed by ZheJiang University (ZJU-AERO) which boasts several unique features.
Abstract
Sea-air methane flux was measured directly by the eddy-covariance method across approximately 60,000 km of Arctic and Antarctic cruises during a number of summers. The Arctic Ocean (north of 60°N, between 20°W and 50°E) and Southern Ocean (south of 50°S, between 70°W and 30°E) are found to be on-shelf sources of atmospheric methane with mean sea-air fluxes of 9.17 ± 2.91 (SEM (standard error of the mean)) μmol m−2 d−1 and 8.98 ± 0.91 μmol m−2 d−1, respectively. Off-shelf, this region of the Arctic Ocean is found to be a source of methane (mean flux of 2.39 ± 0.68 μmol m−2 d−1), while this region of the Southern Ocean is found to be a methane sink (mean flux of −0.77 ± 0.37 μmol m−2 d−1). The highest fluxes observed are found around west Svalbard, South Georgia, and South Shetland Islands and Bransfield Strait; areas with evidence of the presence of methane flares emanating from the seabed. Hence, this study may provide evidence of direct emission of seabed methane to the atmosphere in both the Arctic and Antarctic. Comparing with previous studies, the results of this study may indicate an increase in sea-air flux of methane in areas with seafloor seepage over timescales of several decades. As climate change exacerbates rising water temperatures, continued monitoring of methane release from polar oceans into the future is crucial.
Abstract
The Carpathian belt is one of Europe's major metallogenic provinces, where magmatic ore mineralization is associated with the past subduction environment. The upper crust is mapped for the first time in the Northeast Carpathian Volcanic Arc using magnetotelluric data inversion. The obtained 3-D electrical resistivity model is interpreted in conjunction with geological information and magnetic anomaly data. The model illustrates the deep magmatic plumbing system including kilometer-scale plutonic bodies at a depth of 2–7 km. The model implies that the transport of magma and fluids in the uppermost crust was controlled by pre-existing faults and décollement horizons. Present ore mineralization, mined since historical times, can be attributed to an electrically conductive conduit that is mapped from the surface to a depth of about 30 km. It is suggested that this conduit connected a shallow magmatic chamber to a deep source region in the southeast during late Miocene time. An observed northwest deflection of the deep magmatic conduit at a depth of more than 10 km may explain the spatial gap in the distribution of the Miocene volcanic activity along the Eastern Carpathians.
Abstract
Two solar eclipse events in 2023 appeared to produce considerable enhancements in the thermospheric column density ratio of monatomic oxygen to molecular nitrogen (ΣO/N2) as measured by TIMED GUVI. We quantify potential sources for eclipse-induced ΣO/N2 changes and find that the observed enhancements arise from the ionospheric O+ radiative recombination contribution to the OI 135.6 nm emission from which ΣO/N2 is derived. Variations in the solar Extreme Ultra Violet (EUV) and X-ray spectrum, due to the difference between the disk spectrum and the coronal spectrum, are also considered but shown to have negligible contributions to the ΣO/N2 enhancements. After accounting for the radiative recombination contribution, we constrain the real thermospheric compositional change to the uncertainty level of the measurements of 5%–10%. These results are valuable for the interpretation of eclipse-induced ΣO/N2 changes that will further first-principle model comparisons and lead to a better understanding of the response of the thermosphere to localized variations in solar EUV and X-ray forcing.
Abstract
There are growing concerns about the effect of solar flares on the ionosphere, mainly due to possible deterioration or damage to our communication and navigation satellite systems. On 3 July 2021, and 28 October 2021, there were solar flares (SFs) classified as X1.59 and X1.0, respectively. These two SFs were the only ones of X-class that occurred during the last low solar activity (LSA:2018–2021). Data from magnetometers and Global Positioning System (GPS)—Total Electron Content (TEC) are used to investigate the spatial-temporal electrodynamics of the ionosphere from pole-to-pole in the American sector. Employing ∆H and vertical TEC, along with the ROT (rate of change of VTEC) parameter. Rapidly ∆H disturbances closely follow the X-ray variation and the ∆H valleys and peaks are well-synchronized during the SFs, indicating that they are linked. Major disturbances in the ∆H are noticed in the mid-low-equatorial latitudes. However, minor disturbances were seen at high latitudes. Also, |ROT| is a good indicator of the electron density changes during the SFs, especially when the X-ray intensity rises to the peak.
