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We present a robust and automatic method to generate an idealized surface geometry of a city landscape ready to be meshed for computer simulations. The city geometry is idealized for non viscous flow simulations and targets two main geometrical features: the topography and the city blocks. The procedure is fully automatic and demands no human interaction given the following source data: the city cadastre, a Digital Elevation Model (DEM) of all the target domain, and Light Detection And Ranging (LiDAR) data of the domain region covered by the cadastre. The geometry representation takes three main steps. First, a 2D mesh of the cadastre is generated, where the elements are marked according to street and block regions. Second, using a DEM of the city landscape the topography surface mesh is generated by finding the best surface mesh in the least-squares sense obtained by deforming the previous 2D mesh. Third, we extrude the block facades and we compute a planar ceiling taking into account all the buildings belonging to that city block. We describe the applicability of the geometry representation by presenting the work-flow required to generate an unstructured mesh valid for non-viscous flow or transport simulations. Finally, we illustrate the main application by obtaining a surface and tetrahedral mesh for the city of Barcelona in Spain. [ABSTRACT FROM AUTHOR]

The performance and scalability of atmospheric transport models on high performance computing environments is often far from optimal for multiple reasons including, for example, sequential input and output, synchronous communications, work unbalance, memory access latency or lack of task overlapping. We investigate how different software optimizations and porting to non general-purpose hardware architectures improve code scalability and execution times considering, as an example, the FALL3D volcanic ash transport model. To this purpose, we implement the FALL3D model equations in the WARIS framework, a software designed from scratch to solve in a parallel and efficient way different geoscience problems on a wide variety of architectures. In addition, we consider further improvements in WARIS such as hybrid MPI-OMP parallelization, spatial blocking, auto-tuning and thread affinity. Considering all these aspects together, the FALL3D execution times for a realistic test case running on general-purpose cluster architectures (Intel Sandy Bridge) decrease by a factor between 7 and 40 depending on the grid resolution. Finally, we port the application to Intel Xeon Phi (MIC) and NVIDIA GPUs (CUDA) accelerator-based architectures and compare performance, cost and power consumption on all the architectures. Implications on time-constrained operational model configurations are discussed. [ABSTRACT FROM AUTHOR]

The progress in data assimilation techniques that incorporate weather observations into high-resolution numerical weather prediction models is challenging because of handling surface data in terrain misrepresentation, balance approximations, instrument errors and sensor representativeness. In the framework of operational numerical weather prediction, two data assimilation systems are compared using conventional observations from surface Automatic Weather Stations (AWS), a three-dimensional variational analysis (3DVAR) and the Local Analysis and Prediction System (LAPS). The goal is to study the ability of these two systems to assimilate data from AWS and to assess which performs better for near-surface wind and temperature fields to initialize a short-range 1-km resolution forecast with the Weather Research and Forecasting (WRF) model. Results show that the 3DVAR assimilation patterns are unrealistic given the inhomogeneous nature of the near-surface fields in complex terrains. In contrast, LAPS analyses show a heterogeneous assimilation pattern, more consistent with the complexity of the terrain and the observations. During the model spin-up period, simulations initialized using both data assimilation methods approach rapidly the control simulation, initialized without assimilation. However, the 1 km resolution forecasts initialized with LAPS exhibit a significant improvement, particularly for the wind field module. [ABSTRACT FROM AUTHOR]

We present a methodology to estimate the impacts of volcanic ash dispersal on civil aviation and a software tool aimed at assisting air traffic management in the event of ash-contaminated airspace. The tool merges atmospheric dispersal model forecasts with air traffic data in a map-based platform to produce tables and maps showing potentially affected airports, flights and airspace sectors. Impacts can be estimated based on user-defined ash concentration thresholds, or on the amount of ash potentially ingested by airplanes flying through diluted ash clouds. The impact can be assessed on single Flight Level (FL) slabs, or across the whole vertical airspace. The procedure is automated within a Geographical Information System (GIS). For illustrative purposes, we estimate the potential impacts on the European air traffic of an eruption from Katla volcano in Iceland, assuming a “worst-case” meteorological scenario. We compare the capabilities of the tool with those of similar existing software and justify our design choices. Finally, we discuss the use of the tool in current and future air traffic management strategies during explosive volcanic eruptions. [ABSTRACT FROM AUTHOR]

Abstract: During the eruption of Eyjafjallajökull on Iceland in April/May 2010, air traffic over Europe was repeatedly interrupted because of volcanic ash in the atmosphere. This completely unusual situation in Europe leads to the demand of improved crisis management, e.g. European wide regulations of volcanic ash thresholds and improved ash dispersion forecasts. However, the quality of the forecast of fine volcanic ash concentrations in the atmosphere depends to a great extent on a realistic description of the erupted mass flux of fine ash particles, which is rather uncertain. Numerous aerosol measurements (ground based and satellite remote sensing, and in-situ measurements) all over Europe tracked the volcanic ash clouds during the eruption of Eyjafjallajökull offering the possibility for an interdisciplinary effort between volcanologists and aerosol researchers to analyse the release and dispersion of fine volcanic ash in order to better understand the needs for realistic volcanic ash forecasts. In this introductory paper, we provide a general introduction into magma fragmentation processes during explosive volcanic eruptions, describe the evolution of the eruption of Eyjafjallajökull, present the possibilities of ground based in-situ and remote measurements and numerical model studies of volcanic ash and summarise open questions and future directions. [Copyright &y& Elsevier]

Tacaná volcano is one of the dormant volcanoes in Mexico. Its activity is demonstrated by recent phreatic explosions occurred in 1949 and 1986. At least four Plinian to sub Plinian eruptions have been recorded in the eruptive history of this volcano, which produced pumice and ash deposits that blanketed a vast area straddling the Mexican and Guatemalan territory. Currently, there is no quantitative tephra hazard study of the volcano fallout deposits nor of the dispersion of ash in the atmosphere. In this work, we present the first probabilistic tephra hazard assessment for the Tacaná volcano. Probabilistic hazard maps were computed both, for the tephra deposit, and for critical thresholds of airborne ash concentration at different flight levels. The FALL3D numerical model was used to perform hazard maps for a Plinian scenario defined on the basis of the Sibinal Pumice eruption occurred ∼23.5 kyrs ago, which is the most studied deposit of this type in the volcano's surroundings, even when just few of their most distal outcrops are preserved. Results of this work show that at ground level, the disturbance for this type of hazard would affect mainly Guatemalan territory and the state of Chiapas in Mexico. It could cause serious repercussions on the economy of the region, which is characterized mainly by cocoa, coffee and banana plantations. The ash dispersion into the atmosphere could disturb the airspace and major airports in Mexican territory and neighboring countries. In fact, probability ash dispersal maps show that the level of affectation to the air traffic would involve the possible closure of at least 23 airports in Mexico, Guatemala, Belize, Honduras, El Salvador and Nicaragua. Another collateral damage would be the remobilization of ash by lahars considering the near 4000 mm of rain in average poured yearly in the Soconusco region that would increase the sediment load of the Coatán and Suchiate rivers, and then could produce a severe damage to the lowlands, which in the case of the Mexican territory, is the most populated one. • We present the first probabilistic tephra hazard assessment for Tacaná volcano. • The FALL3D code was used to compute hazard maps for a Plinian scenario at Tacaná. • We computed maps for tephra fallout deposits and ash dispersion in the atmosphere. • At ground level the fallout would be distributed over Guatemala and Mexico. • Airborne ash concentration would led to closure of 23 airports in 6 countries. [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]