Evaluation of high-resolution forecasts with the non-hydrostaticnumerical weather prediction model Lokalmodell for urban air pollutionepisodes in Helsinki, Oslo and Valencia

The operational numerical weather prediction model Lokalmodell LM with 7,km horizontal resolution was evaluated for forecasting meteorological conditions during observed urban air pollution episodes. The resolution was increased to experimental 2.8 km and 1.1 km resolution by one-way interactive nesting without introducing urbanisation of physiographic parameters or parameterisations. The episodes examined are two severe winter inversion-induced episodes in Helsinki in December 1995 and Oslo in January 2003, three suspended dust episodes in spring and autumn in Helsinki and Oslo, and a late-summer photochemical episode in the Valencia area. The evaluation was basically performed against observations and radiosoundings and focused on the LM skill at forecasting the key meteorological parameters characteristic for the specific episodes. These included temperature inversions, atmospheric stability and low wind speeds for the Scandinavian episodes and the development of mesoscale recirculations in the Valencia area. LM forecasts often improved due to higher model resolution especially in mountainous areas like Oslo and Valencia where features depending on topography like temperature, wind fields and mesoscale valley circulations were better described. At coastal stations especially in Helsinki, forecast gains were due to the improved physiographic parameters (land fraction, soil type, or roughness length). The Helsinki and Oslo winter inversions with extreme nocturnal inversion strengths of 18°C were not sufficiently predicted with all LM resolutions. In Helsinki, overprediction of surface temperatures and low-level wind speeds basically led to underpredicted inversion strength. In the Oslo episode, the situation was more complex involving erroneous temperature advection and mountain-induced effects for the higher resolutions. Possible explanations include the influence of the LM treatment of snow cover, sea ice and stability-dependence of transfer and diffusion coefficients. The LM simulations distinctly improved for winter daytime and nocturnal spring and autumn inversions and showed good skill at forecasting further episode-relevant meteorological parameters. The evaluation of the photochemical Valencia episode concentrated on the dominating mesoscale circulation patterns and showed that the LM succeeds well in describing all the qualitative features observed in the region. LM performance in forecasting the examined episodes thus depends on the key episode characteristics and also the season of the year with a need to improve model performance in very stable inversion conditions not only for urban simulations

Evaluation of high-resolution forecasts with the non-hydrostaticnumerical weather prediction model Lokalmodell for urban air pollutionepisodes in Helsinki, Oslo and Valencia

International audienceThe operational numerical weather prediction model Lokalmodell LM with 7\,km horizontal resolution was evaluated for forecasting meteorological conditions during observed urban air pollution episodes. The resolution was increased to experimental 2.8 km and 1.1 km resolution by one-way interactive nesting without introducing urbanisation of physiographic parameters or parameterisations. The episodes examined are two severe winter inversion-induced episodes in Helsinki in December 1995 and Oslo in January 2003, three suspended dust episodes in spring and autumn in Helsinki and Oslo, and a late-summer photochemical episode in the Valencia area. The evaluation was basically performed against observations and radiosoundings and focused on the LM skill at forecasting the key meteorological parameters characteristic for the specific episodes. These included temperature inversions, atmospheric stability and low wind speeds for the Scandinavian episodes and the development of mesoscale recirculations in the Valencia area. LM forecasts often improved due to higher model resolution especially in mountainous areas like Oslo and Valencia where features depending on topography like temperature, wind fields and mesoscale valley circulations were better described. At coastal stations especially in Helsinki, forecast gains were due to the improved physiographic parameters (land fraction, soil type, or roughness length). The Helsinki and Oslo winter inversions with extreme nocturnal inversion strengths of 18°C were not sufficiently predicted with all LM resolutions. In Helsinki, overprediction of surface temperatures and low-level wind speeds basically led to underpredicted inversion strength. In the Oslo episode, the situation was more complex involving erroneous temperature advection and mountain-induced effects for the higher resolutions. Possible explanations include the influence of the LM treatment of snow cover, sea ice and stability-dependence of transfer and diffusion coefficients. The LM simulations distinctly improved for winter daytime and nocturnal spring and autumn inversions and showed good skill at forecasting further episode-relevant meteorological parameters. The evaluation of the photochemical Valencia episode concentrated on the dominating mesoscale circulation patterns and showed that the LM succeeds well in describing all the qualitative features observed in the region. LM performance in forecasting the examined episodes thus depends on the key episode characteristics and also the season of the year with a need to improve model performance in very stable inversion conditions not only for urban simulations

Equidimensional modelling of flow and transport processes in fractured porous systems I

Flow and transport in fractured porous media play an important role for many environmental applications, e.g. the design of disposal systems for hazardous waste. The different hydraulic properties of the fractures and the surrounding rock matrix have a strong influence on the behaviour of the physical processes existing on site. In the two papers of this conference, we will present a new numerical concept to describe saturated flow and transport processes in arbitrarily fractured porous media. We will use an equidimensional approach where fracture and matrix are discretized with elements of the same dimension. To solve the problem, we developed a two-level multigrid method based on a hierarchical decomposition into a fracture problem and a matrix problem. This decoupled treatment of fracture and matrix allows us to handle the locally governing physical processes appropriately. In this paper we will also present convergence comparisons with classical multigrid and algebraic multigrid methods (AMG). In Neunhäuserer et al. (this issue, part II) we will discuss the effect of equidimensionality on the modelling results and the influence of the chosen transport discretisation technique

Equidimensional modelling of flow and transport processes in fractured porous systems II

In fractured formations, the vastly different hydraulic properties of fractures and porous matrix lead to a considerable mass exchange between fracture and matrix, strongly affecting the flow and transport conditions in the domain of interest. This plays an important role for many environmental applications, e.g. the design of disposal systems for hazardous waste. In two papers, we display a new numerical concept describing saturated flow and transport processes in arbitrarily fractured porous media. An equidimensional approach is developed using elements of the same dimension for fracture and matrix discretisation. In Gebauer et al. (this issue, part I) we introduced a two-level multigrid method based on a hierarchical decomposition designed to solve equidimensional fracture-matrix-problems. In this paper we will discuss the effect of equidimensionality on the modelling results. Furthermore, the influence of the chosen transport discretisation technique will be shown

Mehrgittermethoden und adaptive Diskretisierungsverfahren zur Simulation von Strömungs- und Transportprozessen in Kluftaquiferen

Im Zusammenhang mit der Deponierung von Schadstoffen und der Trinkwassergewinnung kommt der Simulation von Strömungs- und Transportprozessen in geklüfteten Bodenzonen eine große Bedeutung zu. Die oft sehr unterschiedlichen hydraulischen Eigenschaften von Kluftsystem und umgebender Gesteinsmatrix prägen das Strömungs- und Transportverhalten stark. Die daraus resultierende Heterogenität der physikalischen Prozesse ebenso wie die Komplexität der zugrundeliegenden Geometrie stellt hohe Anforderungen an die numerische Modellierung. In der vorliegenden Arbeit werden Modellansätze verwendet, die Klüfte und Matrix diskret beschreiben. Um die Nachteile der bisher verwendeten Kopplung von Elementen unterschiedlicher Dimension (keine Flußerhaltung am Kluft-Matrix-Übergang) zu vermeiden, werden Kluft und Matrix mit Elementen gleicher Dimension vernetzt, wobei in den Klüften degenerierte Elemente zugelassen werden. Alle weiteren Bausteine des Lösungsprozesses müssen daher robust gegenüber verschwindender Kluftweite (reduziertes Problem) sein. Die Diskretisierung der Strömungsgleichung wird mit einem Standard-Galerkin-Finite-Elemente-Verfahren durchgeführt, für die Transportgleichung wird ein modifiziertes Boxverfahren eingesetzt. Zur Lösung der Strömungsgleichung wird ein neuartiges Mehrgitterverfahren verwendet, das eine hierarchische Zerlegung des Lösungsraums in einen Kluft- und einen Matrixraum beinhaltet. Dies ermöglicht zu einem späteren Zeitpunkt die Anwendung unterschiedlicher, an den jeweils dominanten physikalischen Prozeß angepaßter Diskretisierungsverfahren in Kluft und Matrix

Evaluación y comparación de dos sistemas de predicción meteorológica en las costas mediterráneas de la Península Ibérica

Ponencia presentada en: XXIX Jornadas Científicas de la AME y el VII Encuentro Hispano Luso de Meteorología celebrado en Pamplona, del 24 al 26 de abril de 2006.Este proyecto ha sido financiado por la Comisión Europea, proyecto FUMAPEX – EVK4-CT-2002-00097; y por el Ministerio de Educación y Ciencia, REN2002-10681-E/CLI

The Hausdorff and dynamical dimensions of self-affine sponges : a dimension gap result

We construct a self-affine sponge in R 3 whose dynamical dimension, i.e. the supremum of the Hausdorff dimensions of its invariant measures, is strictly less than its Hausdorff dimension. This resolves a long-standing open problem in the dimension theory of dynamical systems, namely whether every expanding repeller has an ergodic invariant measure of full Hausdorff dimension. More generally we compute the Hausdorff and dynamical dimensions of a large class of self-affine sponges, a problem that previous techniques could only solve in two dimensions. The Hausdorff and dynamical dimensions depend continuously on the iterated function system defining the sponge, implying that sponges with a dimension gap represent a nonempty open subset of the parameter space