The Canopy and Aerosol Particles Interactions in TOulouse Urban Layer (CAPITOUL) experiment

SummaryThe CAPITOUL experiment is a joint experimental effort in urban climate, including the energetic exchanges between the surface and the atmosphere, the dynamics of the boundary layer over the city and its interactions with aerosol chemistry. The campaign took place in the city of Toulouse in southwest France, for one year, from February 2004 to February 2005. This allowed the study of both the day-to-day and seasonal variability of urban climate processes. The observational network included surface stations (meteorology, energy balance, chemistry), profilers and, during intensive observing periods, aircraft and balloons.The urban Surface Energy Balance differs between summer and winter: in summer, the solar heat stored during the previous daytime period is enough to maintain the heat release at night, but in winter, almost all the energy comes from the anthropogenic heat released by space heating. Both processes produce the well known Urban Heat Island (UHI).The city is shown to impact the entire boundary layer on specific days, when an urban breeze is observed. In wintertime, fog is found to be modified due to the vertical structure of the nocturnal boundary layer above the city (which is slightly unstable and not stable).The measurements of aerosol properties in and downwind the city permitted documentation of the urban aerosol as well as the chemical transformation of these aerosols, in particular the ageing of carbonaceous aerosols during transport. The Toulouse aerosol is mainly composed of carbonaceous particles. There is important seasonal variation in the ratio of black carbon to organic carbon, in the concentration of sulfates and nitrates and in the related radiative aerosol impacts.SF6 was released as a tracer in a suburban area of Toulouse during anticyclonic conditions with weak winds. The tracer measurements show dispersion was mainly driven by the surface sensible heat flux, and was highly sensitive to the urban heat island and also to the transport of boundary layer clouds.Modeling was fully integrated into the campaign. Surface energy balance and urban boundary layer processes have already been used to complement the analyses of the physical processes observed during the campaign. Companion papers detail most of these observation or modeling studies.

[1]  T. Oke,et al.  The energy balance of central Mexico City during the dry season , 1999 .

[2]  J. A. Voogta,et al.  Thermal remote sensing of urban climates , 2003 .

[3]  Véronique Ducrocq,et al.  The Meso-NH Atmospheric Simulation System. Part I: adiabatic formulation and control simulations , 1997 .

[4]  Jean-Pierre Lagouarde,et al.  Monitoring the Sensible Heat Flux over Urban Areas using Large Aperture Scintillometry: Case Study of Marseille City During the Escompte Experiment , 2006 .

[5]  Joost C. B. Hoedjes,et al.  SMOSREX: A long term field campaign experiment for soil moisture and land surface processes remote sensing , 2006 .

[6]  E. Vermote,et al.  A synergetic approach for estimating the local direct aerosol forcing : Application to an urban zone during the Expérience sur site pour contraindre les Modèles de pollution et de transport d'Emission (ESCOMPTE) experiment , 2006 .

[7]  C. Lac,et al.  Evaluation of a mesoscale dispersion modelling tool during the CAPITOUL experiment , 2008 .

[8]  P. Drobinski,et al.  Temperature And Wind Velocity Oscillations Along a Gentle Slope During Sea-Breeze Events , 2005 .

[9]  Valéry Masson,et al.  Modeling the Surface Energy Balance of the Core of an Old Mediterranean City: Marseille , 2004 .

[10]  Valéry Masson,et al.  A Physically-Based Scheme For The Urban Energy Budget In Atmospheric Models , 2000 .

[11]  X. Briottet,et al.  ICARE: A physically-based model to correct atmospheric and geometric effects from high spatial and spectral remote sensing images over 3D urban areas , 2008 .

[12]  V. Masson,et al.  Simulation of fall and winter surface energy balance over a dense urban area using the TEB scheme , 2008 .

[13]  V. Masson,et al.  Anthropogenic heat release in an old European agglomeration (Toulouse, France) , 2007 .

[14]  J. Roger,et al.  Simulation of aerosol radiative properties with the ORISAM-RAD model during a pollution event (ESCOMPTE 2001) , 2006 .

[15]  X. Briottet,et al.  Acquisition and analysis of a spectral and bidirectional database of urban materials over Toulouse (France) , 2006, SPIE Defense + Commercial Sensing.

[16]  A. Dell'Acqua,et al.  Aerosol studies during the ESCOMPTE experiment: an overview , 2005 .

[17]  T. Oke.  The urban energy balance , 1988 .

[18]  C. Liousse,et al.  0-D-Modelling of Carbonaceous Aerosols over Greater Paris Focusing on the Organic Particle Formation , 2005 .

[19]  Jean-Pierre Lagouarde,et al.  Airborne experimental measurements of the angular variations in surface temperature over urban areas: case study of Marseille (France) , 2004 .

[20]  Henri Wortham,et al.  The ESCOMPTE program: an overview , 2004 .

[21]  V. Masson,et al.  Sea-town interactions over Marseille: 3D urban boundary layer and thermodynamic fields near the surface , 2006 .

[22]  J. Gastellu-Etchegorry.  3D modeling of satellite spectral images, radiation budget and energy budget of urban landscapes , 2008 .

[23]  C. Liousse,et al.  Chemical composition of urban aerosols in Toulouse, France during CAPITOUL experiment , 2008 .

[24]  J. Noilhan,et al.  The urban boundary-layer field campaign in marseille (ubl/clu-escompte): set-up and first results , 2005 .

[25]  J. Deardorff,et al.  A laboratory model of diffusion into the convective planetary boundary layer , 1976 .

[26]  V. Masson,et al.  Vertical Structure of the Urban Boundary Layer over Marseille Under Sea-Breeze Conditions , 2006 .

[27]  C. S. B. Grimmond,et al.  Temporal variations in heat fluxes over a central European city centre , 2006 .

[28]  Timothy R. Oke,et al.  Flux and turbulence measurements at a densely built‐up site in Marseille: Heat, mass (water and carbon dioxide), and momentum , 2004 .

[29]  T. Oke,et al.  Area-Averaged Sensible Heat Flux and a New Method to Determine Zero-Plane Displacement Length over an Urban Surface using Scintillometry , 2002 .

[30]  Jean-Pierre Lagouarde,et al.  Directional anisotropy in thermal infrared measurements over Toulouse city centre during the CAPITOUL measurement campaigns: first results , 2008 .

[31]  T. Oke,et al.  Complete urban surface temperatures , 1997 .

[32]  V. Masson,et al.  Urban-breeze circulation during the CAPITOUL experiment: numerical simulations , 2008 .

[33]  R. Vautard,et al.  Measurements and modelling of atmospheric pollution over the Paris area: an overview of the ESQUIF Project , 2000 .

[34]  V. Masson.  Urban surface modeling and the meso-scale impact of cities , 2006 .

[35]  D. Steyn.  Scaling the Vertical Structure of Sea Breezes Revisited , 2003 .

[36]  V. Masson,et al.  Divergence of turbulent fluxes in the surface layer: case of a coastal city , 2007 .

[37]  Timothy R. Oke,et al.  Evaluation of the Town Energy Balance (TEB) Scheme with Direct Measurements from Dry Districts in Two Cities , 2002 .

[38]  A. Christen,et al.  Energy and radiation balance of a central European city , 2004 .

[39]  Michael Schatzmann,et al.  BUBBLE – an Urban Boundary Layer Meteorology Project , 2005 .

[40]  C. Liousse,et al.  Modelling of strong heterogeneities in aerosol single scattering albedos over a polluted region , 2005 .

[41]  C. Liousse,et al.  Aerosol modelling and validation during ESCOMPTE 2001 , 2005 .

[42]  K. J. Allwine,et al.  OVERVIEW OF URBAN 2000 A Multiscale Field Study of Dispersion through an Urban Environment , 2002 .

[43]  Timothy R. Oke,et al.  Effects of urban surface geometry on remotely-sensed surface temperature , 1998 .

[44]  V. Masson,et al.  Urban-breeze circulation during the CAPITOUL experiment: observational data analysis approach , 2008 .

[45]  C. Sarrata,et al.  Impact of urban heat island on regional atmospheric pollution , 2006 .

[46]  J. Monteith,et al.  Boundary Layer Climates. , 1979 .

[47]  X. Briottet,et al.  Spectral variability and bidirectional reflectance behaviour of urban materials at a 20 cm spatial resolution in the visible and near‐infrared wavelengths. A case study over Toulouse (France) , 2005 .

[48]  Akira Ishimaru,et al.  Wave Propagation in Random Media (Scintillation) , 1993 .

[49]  Matthias Roth,et al.  Methodological Considerations Regarding the Measurement of Turbulent Fluxes in the Urban Roughness Sublayer: The Role of Scintillometery , 2006 .

[50]  H. Power.  Air pollution III , 1995 .

[51]  Valéry Masson,et al.  Simulation of a Summer Urban Breeze Over Paris , 2002 .

[52]  James A. Voogt,et al.  Modeling Surface Sensible Heat Flux Using Surface Radiative Temperatures in a Simple Urban Area , 2000 .

[53]  J. Roger,et al.  Effects of the physical and optical properties of urban aerosols measured during the CAPITOUL summer campaign on the local direct radiative forcing , 2008 .

[54]  V. Masson,et al.  Urban Thermodynamic Island in a Coastal City Analysed from an Optimized Surface Network , 2006 .