Cassiani et al. 2010 ACP published

The paper “Stochastic fields method for sub-grid scale emission heterogeneity in mesoscale atmospheric dispersion models” by M. Cassiani, J. F. Vinuesa, S. Galmarini, and B. Denby has been published in Atmospheric Chemistry and Physics.

Abstract. The stochastic fields method for turbulent reacting flows has been applied to the issue of sub-grid scale emission heterogeneity in a mesoscale model. This method is a solution technique for the probability density function (PDF) transport equation and can be seen as a straightforward extension of currently used mesoscale dispersion models. It has been implemented in an existing mesoscale model and the results are compared with Large-Eddy Simulation (LES) data devised to test specifically the effect of sub-grid scale emission heterogeneity on boundary layer concentration fluctuations. The sub-grid scale emission variability is assimilated in the model as a PDF of the emissions. The stochastic fields method shows excellent agreement with the LES data without adjustment of the constants used in the mesoscale model. The stochastic fields method is a stochastic solution of the transport equations for the concentration PDF of dispersing scalars, therefore it possesses the ability to handle chemistry of any complexity without the need to introduce additional closures for the high order statistics of chemical species. This study shows for the first time the feasibility of applying this method to mesoscale chemical transport models.

Vinuesa and Galmarini BLM 09 published

The paper “Turbulent Dispersion of Non-uniformly Emitted Passive Tracers in the Convective Boundary Layer” by J.-F. Vinuesa and S. Galmarini has been published in Boundary-Layer Meteorology.

Abstract The impact of spatially non-uniform emissions on the turbulence dispersion of passive tracers in the convective boundary layer is studied by means of large-eddy simulation. We explicitly calculated the different terms of the budget equations for the concentrations, fluxes and variances, and used sub-domain averaging where each sub-domain is the typical size of a large-scale model grid cell. We found that the concentration profiles in the sub-domain where the emission takes place are lightly affected by the size of the emission release. This effect becomes more relevant in the downwind sub-domain. Although sub-domain averaged fluxes are not affected by the emission source size, concentration variances are dramatically increased when the emission shrinks. This increase originates from the mixing of highly concentrated air parcels with those of low concentrations. We also found that the concentration variance at the surface is driven neither by the position of the emission source nor the strength of the shear forcing but solely by the emission variance.

Keywords Convective boundary layer – Large-eddy simulation – Non-uniform emission – Scalar flux – Scalar variance – Turbulent dispersion

De Meij et al ACP 2009 published

The paper “The impact of MM5 and WRF meteorology over complex terrain on CHIMERE model calculations” by A. de Meij, A. Gzella, P. Thunis, C. Cuvelier, B. Bessagnet, J. F. Vinuesa, and L. Menut has been published in Atmospheric Chemistry and Physics.

Abstract. The objective of this study is to evaluate the impact of meteorological input data on calculated gas and aerosol concentrations. We use two different meteorological models (MM5 and WRF) together with the chemistry transport model CHIMERE. We focus on the Po valley area (Italy) for January and June 2005.

Firstly we evaluate the meteorological parameters with observations. The analysis shows that the performance of both models in calculating surface parameters is similar, however differences are still observed.

Secondly, we analyze the impact of using MM5 and WRF on calculated PM10 and O3 concentrations. In general CHIMERE/MM5 and CHIMERE/WRF underestimate the PMv concentrations for January. The difference in PM10 concentrations for January between CHIMERE/MM5 and CHIMERE/WRF is around a factor 1.6 (PM10 higher for CHIMERE/MM5). This difference and the larger underestimation in PM10 concentrations by CHIMERE/WRF are related to the differences in heat fluxes and the resulting PBL heights calculated by WRF. In general the PBL height by WRF meteorology is a factor 2.8 higher at noon in January than calculated by MM5. This study showed that the difference in microphysics scheme has an impact on the profile of cloud liquid water (CLW) calculated by the meteorological driver and therefore on the production of SO4 aerosol.

A sensitivity analysis shows that changing the Noah Land Surface Model (LSM) in our WRF pre-processing for the 5-layer soil temperature model, calculated monthly mean PMv concentrations increase by 30%, due to the change in the heat fluxes and the resulting PBL heights.

For June, PM10 calculated concentrations by CHIMERE/MM5 and CHIMERE/WRF are similar and agree with the observations. Calculated O3 values for June are in general overestimated by a factor 1.3 by CHIMERE/MM5 and CHIMERE/WRF. High temporal correlations are found between modeled and observed O3 concentrations.

Cassiani et al. ACPD 2009 published

The paper “Stochastic fields method for sub-grid scale emission heterogeneity in mesoscale atmospheric dispersion models” by M. Cassiani, J. F. Vinuesa, S. Galmarini, and B. Denby has been published in Atmospheric Chemistry and Physics Discussions.

Abstract. The stochastic fields method for turbulent reacting flows has been applied to the issue of sub-grid scale emission heterogeneity in a mesoscale model. This method is a solution technique for the probability density function (PDF) transport equation and can be seen as a straightforward extension of currently used mesoscale dispersion models. It has been implemented in an existing mesoscale model and the results compared with Large-Eddy Simulation (LES) data devised to test specifically the effect of sub-grid scale emission heterogeneity on boundary layer concentration fluctuations. The sub-grid scale emission variability is assimilated in the model as a PDF of the emissions. The stochastic fields method shows excellent agreement with the LES data without the need of any additional model constants, nor the adjustment of the constants already used in the mesoscale model. The stochastic fields method solves transport equations of the concentration PDF for dispersing scalars and therefore it possesses the ability to handle chemistry of any complexity without closure assumptions. This study shows for the first time the feasibility of applying this method to mesoscale chemical transport models.

Vinuesa and Galmarini BLM 09 accepted

The paper “Turbulent dispersion of non-uniformly emitted passive tracers in convective boundary layers” by J.-F. Vinuesa and S. Galmarini has been accepted for publication in BLM.