Mass-consistent Wind Model Research Articles

Downscaling surface wind predictions from numerical weather prediction models in complex terrain with WindNinja

Abstract. Wind predictions in complex terrain are important for a number of applications. Dynamic downscaling of numerical weather prediction (NWP) model winds with a high-resolution wind model is one way to obtain a wind forecast that accounts for local terrain effects, such as wind speed-up over ridges, flow channeling in valleys, flow separation around terrain obstacles, and flows induced by local surface heating and cooling. In this paper we investigate the ability of a mass-consistent wind model for downscaling near-surface wind predictions from four NWP models in complex terrain. Model predictions are compared with surface observations from a tall, isolated mountain. Downscaling improved near-surface wind forecasts under high-wind (near-neutral atmospheric stability) conditions. Results were mixed during upslope and downslope (non-neutral atmospheric stability) flow periods, although wind direction predictions generally improved with downscaling. This work constitutes evaluation of a diagnostic wind model at unprecedented high spatial resolution in terrain with topographical ruggedness approaching that of typical landscapes in the western US susceptible to wildland fire.

Wind Forecasting Based on the HARMONIE Model and Adaptive Finite Elements

In this paper, we introduce a new method for wind field forecasting over complex terrain. The main idea is to use the predictions of the HARMONIE meso-scale model as the input data for an adaptive finite element mass-consistent wind model. The HARMONIE results (obtained with a maximum resolution of about 1 km) are refined in a local scale (about a few metres). An interface between both models is implemented in such a way that the initial wind field is obtained by a suitable interpolation of the HARMONIE results. Genetic algorithms are used to calibrate some parameters of the local wind field model in accordance to the HARMONIE data. In addition, measured data are considered to improve the reliability of the simulations. An automatic tetrahedral mesh generator, based on the meccano method, is applied to adapt the discretization to complex terrains. The main characteristic of the framework is a minimal user intervention. The final goal is to validate our model in several realistic applications on Gran Canaria island, Spain, with some experimental data obtained by the AEMET in their meteorological stations. The source code of the mass-consistent wind model is available online at http://www.dca.iusiani.ulpgc.es/Wind3D/ .

Numerical model of gas dispersion emitted from volcanic sources

An Eulerian model for passive gas dispersion based on the K-theory for turbulent diffusion, coupled with a mass consistent wind model is presented. The procedure can be used to forecast gas concentration over large and com- plex terrains. The input to the model includes the topography, wind measurements from meteorological stations, atmospheric stability information and gas flow rate from the ground sources. Here, this model is applied to study the distribution of the CO2 discharged from the hot sources of the Solfatara Volcano, Naples, Italy, where the in- put data were measured during a 15 day campaign in June 2001 carried out to test an Eddy Covariance (EC) sta- tion by Osservatorio Vesuviano-INGV, Naples.

Experimental verification for real-time environmental emergency response system: WSPEEDI by European tracer experiment

Abstract Japan Atomic Energy Research Institute has developed an emergency response system WSPEEDI to forecast long-range atmospheric dispersions of radionuclides discharged into the atmosphere. The latest version of WSPEEDI consists of an atmospheric dynamic model MM5 for calculating meteorological fields and a particle random-walk model for atmospheric dispersion. The performance of WSPEEDI was evaluated by data obtained from a field tracer experiment over Europe (ETEX) in this paper. The model validation was done with respect to the following points: (1) the dependence of model accuracy on the temporal and spatial resolutions of the meteorological fields and (2) the superiority of an atmospheric dynamic model over a mass-consistent wind model. Regarding (1), it was shown that the calculation accuracy of the new version with high temporal resolution was improved, especially at the edge of the plume. Moreover, although the increase in horizontal spatial resolution of the old version had no substantial effect on the model performance, increase in horizontal resolution of the new version contributed to the significant improvement of the calculation accuracy. These results showed that the dynamically calculated meteorological field with the spatial resolution of the meso- β – γ scale greatly improved calculation accuracy.

Modeling of Diffusion in a Wide Alpine Valley

A K-type diffusion model coupled with a massconsistent wind model is applied for one of the rural biological waste disposal sites in Austrian Alps. The site is situated in the Pols valley in the eastern Alps, 250 km south-west of Vienna in Austria Aim of the study is to demonstrate dispersion of H2S from the site to near by village. Model simulations are carried out each for an evening and a morning transition case characterized by flow reversals. The role of locally generated wind in changing the pollutant distribution over nearby residential area is investigated. Surface observations at two stations toward the open boundaries of the main valley are used to derive the turbulence parameters and then to obtain initial inputs of wind profiles. The turbulence parameters behave analogous to that over a plane terrain after the establishment of the valley wind. The model simulations are done for eight hours during the evening transition and eighteen hours for the morning transition by incorporating the wind field from a mass consistent wind model. The results are compared with SF6 tracer experiments conducted during those periods. The model outputs and the observations at various points inside the valley are in good correlation except for NW part of the valley after the reversal of valley wind. The results also reveal the potential of a simple approach with minimized inputs.

Transport of a Power Plant Tracer Plume over Grand Canyon National Park

Meteorological and air-quality data, as well as surface tracer concentration values, were collected during 1990 to assess the impacts of Navajo Generating Station (NGS) emissions on Grand Canyon National Park (GCNP) air quality. These data have been used in the present investigation to determine between direct and indirect transport routes taken by the NGS plume to produce measured high-tracer concentration events at GCNP. The meteorological data were used as input into a three-dimensional mass-consistent wind model, whose output was used as input into a horizontal forward-trajectory model. Calculated polluted air locations were compared with observed surface-tracer concentration values. Results show that complex-terrain features affect local wind-flow patterns during winter in the Grand Canyon area. Local channeling, decoupled canyon winds, and slope and valley flows dominate in the region when synoptic systems are weak. Direct NGS plume transport to GCNP occurs with northeasterly plume-height winds, while indirect transport to the park is caused by wind direction shifts associated with passing synoptic systems. Calculated polluted airmass positions along the modeled streak lines match measured surface-tracer observations in both space and time.

Investigation of air pollution distribution in Linz: case studies to evaluate a K-type diffusion model coupled with a mass-consistent wind model

An Eulerian diffusion model coupled with a refined mass consistent wind model is developed for the operational forecasting of pollution distribution in complex terrain. The model is evaluated for a city situated in complex terrain. The study is carried out for a 20×20 km 2 area surrounding Linz, one of the industrial cities of Austria. The models are initialized with routinely measured meteorological parameters and topology information derived from the Geographical Information Systems (GIS). Four case studies, representative for major pollution episodes, are presented for model evaluation. The case studies include presence of a thermally induced wind system, presence of cold front an easterly southeasterly flow and a westerly–northwesterly flow. In presence of thermally induced wind systems, the flow field is most complex and existence of a shallow mixed layer with residual layer aloft enhances the pollution levels inside the city. Second case is used to study the development of pollution distribution inside the city in presence of low-level inversions and associated with low surface wind speeds. The low wind speeds in the surface layer lead to less mechanical generation of turbulence and lateral transport. The case studies of easterly and westerly flow fields are carried out to assess the capability of model under most frequently observed meteorological situations. The model is able to reproduce the pollution distribution near the slopes. There were over prediction inside the city in presence of thermally induced wind systems and is attributed to inadequate model physics during convective case. The present model setup is found to be a useful tool for the routine forecasting of pollution and could also be tested for other complex terrains.

A simple procedure to account for non-kinematic effects in a mass-consistent wind model

Abstract In recent years, attention has been paid to the role of surface features in extracting momentum from the atmosphere. In the present study, the simulations performed with a “standard” mass-consistent model over the hills already simulated by Wood and Mason, are shown. Furthermore, an empirical method (named “Rising Orography” (RO) method), which improves the final mass-consistent wind field near the surface, is proposed. The results obtained with the RO method were then compared with those obtained by Wood and Mason, showing the superiority of the RO method over the “standard procedure”, mainly for better reliability of the wind field near the surface.

Evaluation of diagnostic and prognostic flow fields over prealpine complex terrain by comparison of the Lagrangian prediction of concentrations with tracer measurements

A short range tracer experiment was carried out under fair-weather conditions over prealpine complex terrain in Switzerland. The prevailing wind direction in the troposphere over the Swiss Plateau was characterized by a northeasterly flow condition that is called bise in Switzerland. This wind system is oriented along the Swiss Plateau due to channelling effects between the Alps in the south and the Jura mountains in the north. Over the prealpine experiment area, however, the SODAR measurements gave evidence of the presence of a thermally driven wind system with a diurnal cycle. The air pollution dispersion scenario of the tracer experiment was simulated by a Lagrangian air quality model for passive air constituents called PARTRAC. The calculated data were compared to the measured tracer concentrations. PARTRAC requires 3D-flow fields which were either generated diagnostically by the mass consistent wind model CONDOR, or prognostically by the non-hydrostatic mesoscale meteorological model MEMO. The sensitivity of the CONDOR wind fields to varying input of measured wind data was investigated by comparing the calculated concentration fields to observational data. The reliability of the concentration predictions was assessed on the basis of statistical performance measures by comparing the predicted half-hourly concentrations to the corresponding measured data paired at equal locations and times. This sensitivity study was aimed at providing PARTRAC with the most representative diagnostic flow fields in order to numerically reproduce the observations as reliably as possible and to establish a benchmark to which the prognostic modelling results were compared in a second step. The prognostic flow fields were generated by a passive model nesting technique in order to reproduce the thermally driven diurnal flow circulation between the prealpine part of the Swiss Plateau and the Alps. The occurrence of this wind regime was suggested by the SODAR measurements and by the dispersion model results relying on the diagnostic wind fields. The initial conditions for the prognostic model MEMO were delivered by a regional weather forecast model that is in operation both at the weather services in Germany (DWD) and Switzerland (SMA). As will be demonstrated in the first part of this paper, the diagnostic transport and dispersion modelling does not necessarily produce a reliable description of an air pollution episode over complex terrain, such as the Swiss Plateau. Therefore, the density of the permanently operating network of weather stations in Switzerland—ANETZ and ENET—definitely appears to be too small to be considered as a sufficient data base for reliable diagnostic concentration predictions in the case of an emergency situation. On the other hand, the prognostic mesoscale modelling of flow fields in complex terrain suffers from the same deficiency as the diagnostic approach inasmuch as reliable results often require a sensitivity study with the nesting of flow fields originating from different meteorological processes at different scales. Therefore, the data selection for such a grid nesting procedure requires a phenomenological knowledge of the different meteorological processes involved. In the case of MEMO at the time of this study, this data selection could be accomplished in different ways, which did not necessarily produce always identical results.

On the applicability of numerical mass-consistent wind field models

A three-dimensional nonhydrostatic model is used to calculate the complex wind field in a coastal and a hilly region. These results are used to test the applicability of a mass-consistent wind model for different numbers of input wind data. While for the coastal area the mass consistent model calculates reasonable results even for a small number of input wind data, this number increases significantly in complex terrain.

Mass-Consistent Wind Model as a Meteorological Preprocessor for Tracer Transport Models

Abstract Atmospheric transport models usually require the mass conservation of the advective meteorological field. Even if the advection field is provided by sophisticated initialization or prediction models of meteorological centers, some mass imbalance may be introduced when the data are converted to the grid system specific to each tracer transport model. The mass-consistent wind model described here is used to impose mass continuity on the meteorological field, which is converted to a new grid system. The model is formulated in map coordinates. In the vertical, a terrain-following height coordinate is used. The model is unique in that a compressible continuity equation is used as a strong constraint, and in that the map scale factor, which is associated with conformal mapping, is incorporated. The weight on the adjustment of each wind component can be a spatial function. Some testing results of the model and an application are presented.