3D direct impacts of urgan aerosols on dynamics during the CAPITOUL field experiment

International audienceEvaluating the radiative impacts of aerosol particles is of great interest for understanding atmospheric physics and processes feedbacks. To respond to such objectives, the online fully coupled model Meso-NH is applied to a real case during a two-day Intensive Observation Period (IOP) of the CAPITOUL campaign. The aerosol optical properties are computed from the chemical composition and the size distribution of the particle population, and are compared to observations and analysed at local and regional scales. The differences between two simulations are then studied in order to isolate the direct radiative impacts of aerosols on dynamics. Results show that the aerosol particles generate a forcing on shortwave flux by a decrease of the amount reaching the surface up to 30 Wm−2. The resulting feedbacks lead to a cooling up to 0.6 K on the 2-meter temperature over the city of Toulouse and over the larger 125 km by 125 km area around Toulouse. This cooling is also modeled along the whole boundary layer, leading to a decrease of the boundary layer height up to −50 m during the afternoon and a decrease of the vertical velocities with an average of −3 %

High resolution modelling of aerosol dispersion regimes during the CAPITOUL field experiment: from regional to local scale interactions

High resolution simulation of complex aerosol particle evolution and gaseous chemistry over an atmospheric urban area is of great interest for understanding air quality and processes. In this context, the CAPITOUL (Canopy and Aerosol Particle Interactions in the Toulouse Urban Layer) field experiment aims at a better understanding of the interactions between the urban dynamics and the aerosol plumes. During a two-day Intensive Observational Period, a numerical model experiment was set up to reproduce the spatial distribution of specific particle pollutants, from the regional scales and the interactions between different cities, to the local scales with specific turbulent structures. Observations show that local dynamics depends on the day-regime, and may lead to different mesoscale dynamical structures. This study focuses on reproducing these fine scale dynamical structures, and investigate the impact on the aerosol plume dispersion. The 500-m resolution simulation manages to reproduce convective rolls at local scale, which concentrate most of the aerosol particles and can locally affect the pollutant dispersion and air quality

3D direct impacts of urban aerosols on dynamics during the CAPITOUL field experiment

. [1] Evaluating the radiative impacts of aerosol particles is of great interest for understanding atmospheric physics and processes feedbacks. To respond to such objectives, the online fully coupled model Meso-NH is applied to a real case during a two-day Intensive Observation Period (IOP) of the CAPITOUL campaign. The aerosol optical properties are computed from the chemical composition and the size distribution of the particle population, and are compared to observations and analysed at local and regional scales. The differences between two simulations are then studied in order to isolate the direct radiative impacts of aerosols on dynamics. Results show that the aerosol particles generate a forcing on shortwave flux by a decrease of the amount reaching the surface up to 30 Wm À2 . The resulting feedbacks lead to a cooling up to 0.6 K on the 2-meter temperature over the city of Toulouse and over the larger 125 km by 125 km area around Toulouse. This cooling is also modeled along the whole boundary layer, leading to a decrease of the boundary layer height up to À50 m during the afternoon and a decrease of the vertical velocities with an average of À3 %. Citation: Aouizerats, B., P. Tulet, and L. Gomes (2012), 3D direct impacts of urban aerosols on dynamics during the CAPITOUL field experiment, Geophys. Res. Lett., 39

Importance of transboundary transport of biomass burning emissions to regional air quality in Southeast Asia during a high fire event

10.5194/acp-15-363-2015Atmospheric Chemistry and Physics151363-37

Aerosol processing and CCN formation of an intense Saharan dust plume during the EUCAARI 2008 campaign

International audienceAtmospheric processing and CCN formation of Saharan dust is illustrated through the analysis of an intense Saharan dust event over northern Europe. The analysis of this dust event was realized through the use of different sets of observations and through the use of numerical models. The altitude of the dust plume was assessed using the CALIPSO observations and our model results. The major dust plume was transported over Europe between 2 and 5 km above sea level (a.s.l.). This altitude favored the interaction between the dust plume and the mountain ranges of Europe during its transport. This also led the dust becoming mixed with the European anthropogenic aerosol. The analyses of the simulation show that mineral dust particles accumulated soluble material through internal mixing over the Netherlands (51.97° N; 4.93° E). The value of the CCN0.2/CN ratio obtained over the Netherlands (~50%) is much greater than those observed over the Saharan region. In addition over the Netherlands, the CCN measurement reached 14 000 particles cm−3 at 0.63% supersaturation level on 30 May. Our model results reveal that more than 70% of the CCN concentration observed on 30 May can be explained by the presence of Saharan aged dust. The study reveals that heterogeneous reactions with inorganic salts converted this Saharan mineral dust into compounds that were sufficiently soluble to impact hygroscopic growth and cloud droplet activation over the Netherlands

Development of an online radiative module for the computation of aerosol optical properties in 3-D atmospheric models: validation during the EUCAARI campaign

International audienceObtaining a good description of aerosol optical properties for a physically and chemically complex evolving aerosol is computationally very expensive at present. The goal of this work is to propose a new numerical module computing the optical properties for complex aerosol particles at low numerical cost so that it can be implemented in atmospheric models. This method aims to compute the optical properties online as a function of a given complex refractive index deduced from the aerosol chemical composition and the size parameters corresponding to the particles.The construction of look-up tables from the imaginary and the real part of the complex refractive index and size parameters will also be explained. This approach is validated for observations acquired during the EUCAARI (European integrated project on aerosol cloud climate air quality interactions) campaign on the Cabauw tower during May 2008 and its computing cost is also estimated.These comparisons show that the module manages to reproduce the scattering and absorbing behaviour of the aerosol during most of the fifteen-day period of observation with a very cheap computationally cost

Overview of the Meso-NH model version 5.4 and its applications

This paper presents the Meso-NH model version 5.4. Meso-NH is an atmospheric non hydrostatic research model that is applied to a broad range of resolutions, from synoptic to turbulent scales, and is designed for studies of physics and chemistry. It is a limited-area model employing advanced numerical techniques, including monotonic advection schemes for scalar transport and fourth-order centered or odd-order WENO advection schemes for momentum. The model includes state-of-the-art physics parameterization schemes that are important to represent convective-scale phenomena and turbulent eddies, as well as flows at larger scales. In addition, Meso-NH has been expanded to provide capabilities for a range of Earth system prediction applications such as chemistry and aerosols, electricity and lightning, hydrology, wildland fires, volcanic eruptions, and cyclones with ocean coupling. Here, we present the main innovations to the dynamics and physics of the code since the pioneer paper of Lafore et al. (1998) and provide an overview of recent applications and couplings