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Volcanic ash modeling systems are used to simulate the atmospheric dispersion of volcanic ash and to generate forecasts that quantify the impacts from volcanic eruptions on infrastructures, air quality, aviation, and climate. The efficiency of response and mitigation actions is directly associated to the accuracy of the volcanic ash cloud detection and modeling systems. Operational forecasts build on off-line coupled modeling systems where meteorological variables are updated at the specified coupling intervals. Despite the concerns from other communities regarding the accuracy of this strategy, the quantification of the systematic errors and shortcomings associated to the off-line modeling systems has received no attention. This paper employs the NMMB-MONARCH-ASH model to quantify these errors by employing different quantitative and categorical evaluation scores. The skills of the off-line coupling strategy are compared against those from an on-line forecast considered to be the best estimate of the true outcome. Case studies are considered for a synthetic eruption with constant eruption source parameters and for two historical events, which suitably illustrate the severe aviation disruptive effects of European (2010 Eyjafjallajökull) and South-American (2011 Cordón Caulle) volcanic eruptions. Evaluation scores indicate that systematic errors credited to off-line modeling are of the same order of magnitude that those associated to the source term uncertainties. In particular, traditional off-line forecasts employed in operational model setups can result in significant uncertainties, failing to reproduce, in the worst cases, up to 45-70% of the ash cloud of an on-line forecast. These inconsistencies are anticipated to be even more relevant in scenarios where the meteorological conditions change rapidly in time. The outcome of this paper encourages operational groups responsible for realtime advisories for aviation to consider employing computationally efficient on-line dispersal models. [ABSTRACT FROM AUTHOR]

On the 13 June 2015, the London Volcanic Ash Advisory Centre (VAAC) warned the Buenos Aires VAAC about a possible volcanic eruption from the Nevados Ojos del Salado volcano (6879 m), located in the Andes mountain range on the border between Chile and Argentina. A volcanic ash cloud was detected by the SEVIRI instrument on board the Meteosat Second Generation (MSG) satellites from 14:00 UTC on 13 June. Further studies concluded that the phenomenon was caused by remobilization of ancient pyroclastic deposits (circa 4.5 Ka Cerro Blanco eruption) from the Bolsón de Fiambalá (Fiambalá Basin) in northwestern Argentina. In this paper, we provide the first comprehensive description of the dust episode through observations and numerical simulations. We have investigated the spatio-temporal distribution of aerosols and the emission process over complex terrain to gain insight into the key role played by the orography and the condition that triggered the long-range transport episode. Numerical simulations of windblown dust were performed using the WRF-ARW/FALL3D modeling system with meteorological fields downscaled to a spatial resolution of 2 km in order to resolve the complex orography of the area. Results indicated that favourable conditions to generate dust uplifting occurred in northern Fiambalá Basin, where orographic effects caused strong surface winds. According to short-range numerical simulations, dust particles were confined to near-ground layers around the emission areas. On the other hand, dust aerosols were injected up to 5-6 km high in central and southern regions of the Fiambalá Basin, where intense ascending airflows are driven by horizontal convergence. Long-range transport numerical simulations were also performed to model dust cloud spreading over northern Argentina. Results of simulated vertical particle column mass were compared with the MSG-SEVIRI retrieval product. We tested two numerical schemes: with the default configuration of the FALL3D model, we found difficulties to simulate transport through orographic barriers, whereas an alternative configuration, using a numerical scheme to more accurately compute the horizontal advection in abrupt terrains, substantially improved the model performance. [ABSTRACT FROM AUTHOR]

Atmospheric dispersal of a gas denser than air can threat the environment and surrounding communities if the terrain and meteorological conditions favor its accumulation in topographic depressions, thereby reaching toxic concentration levels. Numerical modeling of atmospheric gas dispersion constitutes a useful tool for gas hazard assessment studies, essential for planning risk mitigation actions. In complex terrains, microscale winds and local orographic features can have a strong influence on the gas cloud behavior, potentially leading to inaccurate results if not captured by coarser-scale modeling. We introduce a methodology for microscale wind field characterization based on transfer functions that couple a mesoscale Numerical Weather Prediction Model with a microscale Computational Fluid Dynamics (CFD) model for the atmospheric boundary layer. The resulting time-dependent high-resolution microscale wind field is used as input for a shallow-layer gas dispersal model (TWODEE-2.1) to simulate the time evolution of CO2 gas concentration at different heights above the terrain. The strategy is applied to review simulations of the 1986 Lake Nyos event in Cameroon, where a huge CO2 cloud released by a limnic eruption spread downslopes from the lake suffocating thousands of people and animals across the Nyos and adjacent secondary valleys. Besides several new features introduced in the new version of the gas dispersal code (TWODEE-2.1), we have also implemented a novel impact criterion based on the percentage of human fatalities depending on CO2 concentration and exposure time. New model results are quantitatively validated using the reported percentage of fatalities at several locations. The comparison with previous simulations that assumed coarser-scale steady winds and topography illustrates the importance of high-resolution modeling in complex terrains. [ABSTRACT FROM AUTHOR]

Traditionally, tephra transport and dispersal models have evolved decoupled (off-line) from numerical weather prediction models. There is a concern that inconsistencies and shortcomings associated to this coupling strategy might lead to errors in the ash cloud forecast. Despite this concern, and the significant progress to improve the accuracy of tephra dispersal models in the aftermath of the 2010 Eyjafjallajökull and 2011 Cordón Caulle eruptions, to date, no operational on-line dispersal model is available to forecast volcanic ash. Here, we describe and evaluate NMMB/BSC-ASH, a new on-line multiscale meteorological and transport model that attempts to pioneer the forecast of volcanic aerosols at operational level. The model predicts volcanic ash cloud trajectories, concentration of ash at relevant flight levels, and the expected deposit thickness for both regional and global configurations. Its on-line coupling approach improves the current state-of-the-art of tephra dispersal models, especially in situations where meteorological conditions are changing rapidly in time, two-way feedbacks are significant, or distal ash cloud dispersal simulations are required. This work presents the model application for the first phases of the 2011 Cordón Caulle and 2001 Mt. Etna eruptions. The computational efficiency of NMMB/BSC-ASH and its application results compare favorably with other long-range tephra dispersal models, supporting its operational implementation. [ABSTRACT FROM AUTHOR]

FALL3D-8.0 is the new release of the FALL3D model (Folch et al., 2009;doi:10.1016/j.cageo.2008.08.008), a three-dimensional time-dependent Eulerian model foratmospheric transport and deposition based on the advection–diffusion–sedimentationequation (Folch et al., 2009; doi:10.1016/j.cageo.2008.08.008). The model upgradeincorporates dramatic improvements both in terms of physics and numerical algorithms andperformance. In terms of model physics, the original tephra transport model has beenextended to include mineral dust, radionuclides, and chemistry of SO2. Besides theexisting models describing phenomena such as particle resuspension, volcanic plumes,gravity spreading in the umbrella region, particle size distribution, and particleaggregation, different new parameterizations have also been introduced in order todescribe eddy diffusivity, dry and wet deposition, and transport of radionuclides.In terms of numerical algorithms and performance, FALL3D-8.0 uses a verticalσ-coordinate to better capture local terrain effects, a Runge-Kutta forth-order intime explicit scheme, and a much more efficient high-resolution central-upwindscheme (Kurganov and Tadmor, 2000; doi:10.1006/jcph.2000.6459). The MPI-basedparallelization of the code, written in FORTRAN 90, has also been reformulated in order todramatically increase its performance on Petascale machines, including a better domaindecomposition, parallel I/O, a parallel preprocess in which coupling with multiple drivingmeteorological models has been made more efficient, and a better memory management toreduce communications and improve code scalability. A few examples for differentkind of applications are presented and the improve in code performance discussed. [ABSTRACT FROM AUTHOR]

A new Center of Excellence on HPC has been funded (2019-2021) under Horizon 2020 Research and Innovation Programme to promote the use of upcoming Exascale and extreme performance computing capabilities in the area of Solid Earth. The Center of Excellence for Exascale in Solid Earth (ChEESE; https://cheese-coe.eu) will address extreme computing scientific and societal challenges by harnessing European institutions in charge of operational monitoring networks, tier-0 supercomputing centers, academia, hardware developers and third-parties from SMEs, Industry and public-governance. The scientific challenging ambition is to prepare 10 open-source flagship codes to solve Exascale problems on computational seismology, magnetohydrodynamics, physical volcanology, tsunamis, and data analysis and predictive techniques, including machine learning and predictive techniques from monitoring earthquake and volcanic activity. The codes will be optimized at both intranode level (including heterogeneous computing nodes) and internode level on heterogeneous hardware prototypes for the upcoming Exascale architectures, thereby ensuring commitment with a co-design approach. Preparation to Exascale will consider also code inter-kernel aspects of simulation workflows like data management and sharing, I/O, post-process and visualization. The ChEESE Center of Excellence builds on three pillars: pilot demonstrators, services and training. First, the project will develop pilot demonstrators for scientific challenging problems requiring of Exascale computing in alignment with the vision of European Exascale roadmaps. This includes near real-time seismic simulations and full-wave inversion, ensemble-based volcanic ash dispersal forecasts, faster than real-time tsunami simulations and physics-based hazard assessments for seismics, volcanoes and tsunamis. Second, pilots are also intended for enabling of operational services requiring of extreme HPC on urgent computing, early warning forecast of geohazards, hazard assessment and data analytics. Selected pilots will be tested in an operational environment to make them available to a broader user community. Additionally, and in collaboration with the European Plate Observing System (EPOS), ChEESE will promote and facilitate the integration of HPC services to widen the access to codes and fostering transfer of know-how to Solid Earth user communities. Finally, the third pillar of ChEESE aims at acting as a hub to foster HPC across the Solid Earth Community and related stakeholders and to provide specialised training on services and capacity building measures. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing interest in ensemble approaches for modelling the atmospheric transport of volcanic aerosol, ash, and lapilli (tephra). The development of such techniques enables the exploration of novel methods for incorporating real observations into tephra dispersal models. However, traditional data assimilation algorithms, including ensemble Kalman filter (EnKF) methods, can yield suboptimal state estimates for positive-definite variables such as those related to volcanic aerosols and tephra deposits. This study proposes two new ensemble-based data assimilation techniques for semi-positive-definite variables with highly skewed uncertainty distributions, including aerosol concentrations and tephra deposit mass loading: the Gaussian with non-negative constraints (GNC) and gamma inverse-gamma (GIG) methods. The proposed methods are applied to reconstruct the tephra fallout deposit resulting from the 2015 Calbuco eruption using an ensemble of 256 runs performed with the FALL3D dispersal model. An assessment of the methodologies is conducted considering two independent datasets of deposit thickness measurements: an assimilation dataset and a validation dataset. Different evaluation metrics (e.g. RMSE, MBE, and SMAPE) are computed for the validation dataset, and the results are compared to two references: the ensemble prior mean and the EnKF analysis. Results show that the assimilation leads to a significant improvement over the first-guess results obtained from the simple ensemble forecast. The evidence from this study suggests that the GNC method was the most skilful approach and represents a promising alternative for assimilation of volcanic fallout data. The spatial distributions of the tephra fallout deposit thickness and volume according to the GNC analysis are in good agreement with estimations based on field measurements and isopach maps reported in previous studies. On the other hand, although it is an interesting approach, the GIG method failed to improve the EnKF analysis. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing interest in ensemble approaches for modelling volcanic plumes. The development of such techniques enables the exploration of novel methods for incorporating real observations into tephra dispersal models. However, traditional data assimilation algorithms, including ensemble Kalman filter methods, can yield suboptimal state estimates for positive-definite variables such as volcanic aerosols and tephra deposits. This study proposes two new ensemble-based data assimilation techniques for semi-positive-definite variables with highly skewed uncertainty distributions, including aerosol concentrations and tephra deposit mass loading. The proposed methods are applied to reconstruct the tephra fallout deposit resulting from the 2015 Calbuco eruption using an ensemble of 256 runs performed with the FALL3D dispersal model. Two datasets of deposit thickness measurements are considered: an assimilation dataset including 161 observations, and a validation dataset for an independent assessment of the methods. Results show that the assimilation leads to a significant improvement over the first-guess results, obtained from the simple ensemble forecast. The spatial distribution of the tephra fallout deposit thickness and the ashfall volume according to the analyses are in good agreement with estimations based on field measurements and isopach maps reported in previous studies. Both assimilation methods show a similar performance in terms of evaluation metrics and spatial distribution of the deposit. Finally, the potential application of the methodologies for the improvement of ash-cloud forecasts produced for operational models is also discussed. [ABSTRACT FROM AUTHOR]

Long‐lasting, hybrid eruptions can be of complex description and classification, especially when associated with multiple eruptive styles and multiple products. The 2021 Tajogaite eruption of La Palma, Canary Islands, was associated with a magma‐gas decoupled system that resulted in the simultaneous emission of lava flows and tephra plumes from various vents. Even though the tephra blanket (∼2 × 107 m3) represents only 7%–16% of the total erupted volume, it provides fundamental insights into the overall eruptive dynamics. Tephra was mostly dispersed NE‐SW due to a complex regional and local wind patterns and was subdivided into 3 units and 11 layers that well correlate at different distances from the vent and with both tremor data and lava emission rate. While plume height varied at the temporal scale of a few hours, the average mass eruption rate associated with the tephra blanket of the different units remained relatively constant (∼3–4 × 103 kg s−1). In contrast, the emission rate of lava largely increased after the first week and remained higher than the overall emission of tephra throughout the whole eruption (average value of ∼6 × 104 kg s−1). Based on a detailed characterization of the tephra blanket in combination with atmospheric wind, tremor, and lava emission trend, we demonstrate the need of (a) multidisciplinary strategies for the description of hybrid eruptions that account for both the duration of individual phases and the quantification of the mass of multiple products, and of (b) dedicated ash dispersal forecasting strategies that account for the frequent variations of eruptive and atmospheric conditions. Plain Language Summary: Volcanic eruptions are mostly subdivided into effusive and explosive when they are associated with the emission of lava flows or with the fragmentation of magma that results in the generation of widespread deposits (i.e., tephra). The September–December 2021 Tajogaite eruption of La Palma Island (Spain) represents a typical example of long‐lasting, hybrid eruption with alternation, or, more often, contemporaneous emission of lava flows and tephra. The lava field extended toward the western sector of the island, while the tephra blanket was mostly dispersed NE‐SW due to a complex regional and local wind pattern. Even though the tephra blanket represents only 7%–16% of the total erupted volume, it provides fundamental insights into the overall eruptive dynamics. Based on a detailed characterization of the tephra blanket, in combination with wind, seismic tremor, and lava emission trend, we demonstrate the need of dedicated strategies for the description of hybrid, long‐lasting eruptions that account for both eruption duration and for the quantification of multiple products (tephra blanket, tephra cone, lava flows). We also show the need of dedicated strategies of short‐range ash dispersal forecasting that account for the frequent variations of eruptive and atmospheric conditions. Key Points: Tephra blanket of the 2021 Tajogaite eruption is only 7%–16% of the total volume but is key to decipher the variable eruptive dynamicsTephra blanket shows distinct layers and units at different distances from vents that well correlate with tremor and lava emission rateHybrid eruptions are best described based on both event duration and mass associated with multiple products (tephra blanket, cone, lava) [ABSTRACT FROM AUTHOR]

To increase the probability of detecting odour plumes, and so increase prey capture success, when winds are stable central place foraging seabirds should fly crosswind to maximize the round-trip distance covered. At present, however, there is no empirical evidence of this theoretical prediction. Here, using an extensive GPS tracking dataset, we investigate, for the first time, the foraging movements of Bulwer's petrels (Bulweria bulwerii) in the persistent North Atlantic trade winds. To test the hypotheses that, in stable winds, petrels use crosswind to maximize both the distance covered and the probability of detecting olfactory cues, we combine state-space models, generalized additive models and Gaussian plume models. Bulwer's petrels had the highest degree of selectivity for crosswinds documented to date, often leading to systematic zig-zag flights. Crosswinds maximized both the distance travelled and the probability of detecting odour plumes integrated across the round-trip (rather than at any given point along the route, which would result in energetically costly return flight). This evidence suggests that petrels plan round-trip flights at departure, integrating expected costs of homeward journeys. Our findings, which are probably true for other seabirds in similar settings, further highlight the critical role of wind in seabird foraging ecology. [ABSTRACT FROM AUTHOR]

Impacts of explosive volcanic eruptions on civil aviation were reconsidered after the 2010 Eyjafjallajökull eruption in Iceland, which caused unprecedented disruptions of air traffic operations in Europe. During and after the aviation breakdown of April–May 2010, communication between the involved stakeholders was recognized as a major concern. Due to the complexity and multidisciplinary nature of the topic, a great number of actors are involved, which often have little interaction outside these exceptional events. In this work, we aim at identifying the relationships between the stakeholders involved in aviation management during eruptions, as well as their needs and priorities. We perform an anonymous on-line survey, focused mainly on the use of tephra dispersal models for civil aviation purposes. We collect feedback on recent developments including our current impact assessment research, which produced a GIS-based software tool to estimate impacts on aviation based on tephra dispersal forecasts. Answers allow identifying stakeholders' requirements on ash dispersal forecasts and their use for aviation management purposes. We underline the main differences between three homogeneous groups (aviation managers and employees, modellers and field scientists, other stakeholders) and identify main end-user requirements for developing tools similar to ours. This work provides useful insights for the development of tools to support aviation stakeholders during volcanic eruptions. [ABSTRACT FROM AUTHOR]

A new topography adapted mesh generation framework tailored to simulate Atmospheric Boundary Layer (ABL) flows on complex terrains is presented. The mesher is fully automatic given: the maximum and minimum surface mesh size, and the mesh size at the top of the ABL. The following contributions to the meshing workflow for ABL flow simulation are performed. First, we present a smooth topography modeling to query first and second-order geometry derivatives. Second, we propose a new adaptive meshing procedure to discretize the topography based on two different metrics. Third, we present the ABL mesher, featuring both prisms and tetrahedra. We extrude the triangles of the adapted surface mesh, generating prisms that reproduce the Surface Boundary Layer. Then, the rest of the domain is meshed with an unstructured tetrahedral mesh. In addition, we detail a hybrid quality optimization approach for both the surface and volume meshers, analyzing its impact on the solver for high-complexity terrains. We analyze the convergence of the triangle adaptive approach, obtaining quadratic convergence to the geometry and reducing to one-half the error for the same amount of degrees of freedom than without adaptivity and optimization. We also study the mesh convergence of our Reynolds-averaged Navier–Stokes (RANS) solver, obtaining quadratic mesh convergence to the solution, and using a 30% of the degrees of freedom while reducing a 20% of the error of standard semi-structured approaches. Finally, we present the generated meshes and the simulation results for a complete complex topographic scenario. • Topography modeling to query first and second-order derivatives of the geometry. • Metric-driven mesh adaptation procedure for topographic scenarios. • Hybrid meshing framework for ABL flow simulation on complex topographies. • Hybrid optimization framework, detailing the impact on the RANS solver. • Analysis of the convergence to the topography geometry and to the solution. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: El Chichón volcano, Chiapas, Mexico, erupted explosively on March 29th, 1982, after a repose period of about 550years. Amongst ten eruptive episodes documented between March 29th and April 4th, only the three that occurred on March 29th and April 4th produced significant pyroclastic tephra deposits. Here we use analytical (HAZMAP) and numerical (FALL3D) tephra transport models to reconstruct the deposits and the atmospheric plume dispersal associated with the three main fallout units of the 1982 eruption. On the basis of such a reconstruction, we produce hazard maps of tephra fallout associated to a Plinian eruption and discuss the implications of such a severe eruption scenario. [Copyright &y& Elsevier]

Highlights • New automatic meshing framework for Atmospheric Boundary Layer (ABL) simulation on wind farms. • Conformal hybrid meshes of the ABL, topography and actuator discs, and with smooth size transitions. • New quality-based sweeping technique to generate hexahedral ABL conformal with the topography. • Mesh sizing characterization for different turbines in offshore and onshore cases. • Quadratic mesh convergence of the solver to the quantity of interest (flow across the turbine hub). Abstract A new mesh generation process for wind farm modeling is presented together with a mesh convergence and sizing analysis for wind farm flow simulations. The generated meshes are tailored to simulate Atmospheric Boundary Layer (ABL) flows on complex terrains modeling the wind turbines as actuator discs. The wind farm mesher is fully automatic and, given the topography and the turbine characteristics (location, diameter and hub height), it generates a hybrid mesh conformal with the actuator discs and refined upwind and downstream. Moreover, it presents smooth element size transitions across scales and avoids extending high-resolution areas to all the domain. We take advantage of our automatic and robust mesher to study the mesh convergence of our RANS solver with linear elements, obtaining quadratic mesh convergence for a quantity of interest in all the tested cases. In addition, we quantify the mesh resolution at the terrain surface and at the actuator discs required to achieve a given numerical error in simulations in onshore and offshore frameworks. Finally, we present the generated meshes and the simulation results for an offshore and an onshore wind farm. We analyze in detail one particular wind direction for both cases, and for the onshore wind farm we use our automatic framework to estimate the yearly production of energy and measuring the error against the actual produced one. [ABSTRACT FROM AUTHOR]

Tungurahua volcano, located in the central area of the Ecuadorian Sierra, is erupting intermittently since 1999 alternating between periods of quiescence and explosive activity. Volcanic ash has been the most frequent and widespread hazard provoking air contamination episodes and impacts on human health, animals and crops in the surrounding area. After two months of quiescence, Tungurahua erupted violently on 14th July 2013 generating short-lived eruptive columns rising up to 9 km above the vent characterized as a vulcanian eruption. The resulting fallout deposits were sampled daily during and after the eruptions to determine grain size distributions and perform morphological and componentry analyses. Dispersion and sedimentation of ash were simulated numerically coupling the meteorological Weather Research Forecasting (WRF) with the volcanic ash dispersion FALL3D models. The combination of field and numerical studies allowed constraining the Eruption Source Parameters (ESP) for this event, which could be used to forecast ash dispersion and deposition from future vulcanian eruptions at Tungurahua. This set of pre-defined ESP was further validated using two different eruptions, as blind test, occurring on 16th December 2012 and 1st February 2014. [ABSTRACT FROM AUTHOR]

Popocatépetl is one of Mexico's most active volcanoes threatening a densely populated area that includes Mexico City with more than 20 million inhabitants. The destructive potential of this volcano is demonstrated by its Late Pleistocene-Holocene eruptive activity, which has been characterized by recurrent Plinian eruptions of large magnitude, the last two of which destroyed human settlements in pre-Hispanic times. Popocatépetl's reawakening in 1994 produced a crisis that culminated with the evacuation of two villages on the northeastern flank of the volcano. Shortly after, a monitoring system and a civil protection contingency plan based on a hazard zone map were implemented. The current volcanic hazards map considers the potential occurrence of different volcanic phenomena, including pyroclastic density currents and lahars. However, no quantitative assessment of the tephra hazard, especially related to atmospheric dispersal, has been performed. The presence of airborne volcanic ash at low and jet-cruise atmospheric levels compromises the safety of aircraft operations and forces re-routing of aircraft to prevent encounters with volcanic ash clouds. Given the high number of important airports in the surroundings of Popocatépetl volcano and considering the potential threat posed to civil aviation in Mexico and adjacent regions in case of a Plinian eruption, a hazard assessment for tephra dispersal is required. In this work, we present the first probabilistic tephra dispersal hazard assessment for Popocatépetl volcano. We compute probabilistic hazard maps for critical thresholds of airborne ash concentrations at different flight levels, corresponding to the situation defined in Europe during 2010, and still under discussion. Tephra dispersal mode is performed using the FALL3D numerical model. Probabilistic hazard maps are built for a Plinian eruptive scenario defined on the basis of geological field data for the 'Ochre Pumice' Plinian eruption (4965 C yr BP). FALL3D model input eruptive parameters are constrained through an inversion method carried out with the semi-analytical HAZMAP model and are varied by sampling them using probability density functions. We analyze the influence of seasonal variations on ash dispersal and estimate the average persistence of critical ash concentrations at relevant locations and airports. This study assesses the impact that a Plinian eruption similar to the Ochre Pumice eruption would have on the main airports of Mexico and adjacent areas. The hazard maps presented here can support long-term planning that would help minimize the impacts of such an eruption on civil aviation. [ABSTRACT FROM AUTHOR]