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Introduction 1. Advantages and difficulties related to the use of optical data

Laboratoire de Météorologie Dynamique - École Polytechnique - Paris. Aerosol model validation using optical measurements Evolution of AOT over Europe during the 2003 summer heat wave as seen from CHIMERE simulations and POLDER-2 data.

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Introduction 1. Advantages and difficulties related to the use of optical data

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  1. Laboratoire de Météorologie Dynamique - École Polytechnique - Paris Aerosol model validation using optical measurements Evolution of AOT over Europe during the 2003 summer heat wave as seen from CHIMERE simulations and POLDER-2 data Hodzic Alma*, Vautard R., Chepfer H., Goloub P., Menut L., Chazette P., Deuzé J.L., Apituley A., Couvert P.. (*) hodzic@lmd.polytechnique.fr Introduction 1. Advantages and difficulties related to the use of optical data 2. Aerosol retrieval and comparison methodology 3. Results of the comparison model/observations during: - The pollution episode of 26 March 2003 - The August 2003 heat wave episode Conclusion and Perspectives CHIMERE Workshop, Paris 21-22 March 2005

  2. Why using optical data for model evaluation ?Advantages/Difficulties Evaluation of aerosol models : • Surface measurements (AIRPARIF network) • Continuous measurements of PM10 and PM2.5 => spatial distribution • Lack of information on the vertical mixing. • Airborne measurements (ESQUIF, ESCOMPTE) • Aerosol chemical composition and size distribution • Short data series. • Remote sensing • Quasi-continuous measurements of the aerosol vertical distribution at great number of sites (Lidar and Sun-photometer data) • Wide spatial coverage of satellite data • No one-to-one correspondence between the measured signal and model outputs (aerosol concentrations): • AOT / backscattering signal is proportional to the aerosol load • Rarely used for the validation of aerosol models at urban scale. CHIMERE Workshop, Paris 21-22 March 2005

  3. Available optical measurements Ground-based measurements SIRTA Data Base : Backscattering lidar LNA (532nm) http://sirta.lmd.polytechnique.fr EARLINET Data Base : European aerosol lidar network http://lidarb.dkrz.de/earlinet/ AERONET Data Base : Global Sun-photometer network Aerosol optical properties (AOT, Albedo, refractive index) http://aeronet.gsfc.nasa.gov/ Satellite measurements (King et al., 1999) • POLDER remote sensing on board the ADEOS satellite • Radiometer that measures spectral, directional • and polarized radiance over land and oceans. • Retrieval of AOT at 865nm for accumulation mode • (large or non spherical particules not detected bc of • their low polarization). (Deuzé et al., 2001) • 7 months of data : April – October 2003 • satellite overpass time around 11:00 UTC http://smsc.cnes.fr/POLDER/ CHIMERE Workshop, Paris 21-22 March 2005

  4. Aerosol retrieval from model simulations (Hodzic et al., 2004, JGR) Approach “Model to Observation” Direct comparison of observed and simulated backscattering lidar profiles to avoid new hypothesis in observations. CHIMERE (Gas / Aerosols) Chemical speciation Mass distribution Aerosol Optical Properties m, SSA, AOT Sun-photometer AERONET POLDER MIE code Lidar Profiles Pr2, PBL Lidar data SIRTA • Accumulation Mode: (0.16 – 2.5 µm): > 88% • Nucleation Mode: (< 0.16 µm) : ~ 4% • Coarse Mode: (>2.5 µm) : ~ 8% Contribution of aerosol mode to optical efficiency: CHIMERE Workshop, Paris 21-22 March 2005

  5. Comparison with lidar data at Palaiseau Pollution episode of 26 March 2003 LIDAR 532nm – 2003/03/26 – ln(Pr2) Ground concentrations of PM10 11 GMT • CHIMERE LIDAR Variability Dust RL PBL Integrated optical thickness at 532nm CHIMERE 532nm – 2003/03/26 – ln(Pr2) 14 GMT (Hodzic et al., 2004, JGR)

  6. Summer heat wave 4-13 August 2003 Example of comparison with satellite dataMonthly mean AOT over Europe from POLDER data (Hodzic et al., 2005, submitted to ACP) POLDER derived AOT at 865 nm due to Aerosols Accumulation Mode CHIMERE Workshop, Paris 21-22 March 2005

  7. Evolution of AOT during the August 2003 heat wave episode POLDER derived AOT at 865 nm due to Aerosols Accumulation Mode

  8. Evolution of AOT from POLDER and CHIMERE 05 August 2003 11 August 2003

  9. Major discrepancies model/observations: • General model overestimation • Underestimation of peak values • on 5-6 August Systematic comparisons model/observations Mean AOTs over Europe Correlaton model/obs. over Europe Uncertainties in aerosol retrievals from both satellite and model data - Off-set in POLDER data? - Aerosol parameterization used in the model? CHIMERE Workshop, Paris 21-22 March 2005

  10. 2:1 1:1 1:2 The origin of discrepancies: model systematic bias Comparison with AERONET-derived AOTs • Results: • POLDER underestimates • AERONET data • Good agreement • CHIMERE/AERONET • except on 05-06 August Model overestimation due to negative off-set in POLDER data CHIMERE Workshop, Paris 21-22 March 2005

  11. Passive tracer run with CHIMERE AOT peaks : Advection of smoke particles from Portugal forest fires 05 August 2003 CHIMERE Workshop, Paris 21-22 March 2005

  12. AOT peaks : Advection of smoke particles from Portugal forest fires Passive tracer runs with CHIMERE CHIMERE Workshop, Paris 21-22 March 2005

  13. Conclusion and Perspectives • General model/observation comparison results : • Remote sensing (lidar and sun-photometer) provide useful routinemeasurements of the vertical aerosol distribution that can be easily used for the evaluation of mesoscale aerosol models. • Ability of the model to reproduce with reasonable skill both the observed optical thickness and the vertical backscatter lidar profiles. • Comparison allows identifyingmissing processes and emission sources in model simulations. • Reveals difficulties of comparing simulated and POLDER-derived AOTs due to uncertainties in satellite and model retrievals of aerosol optical properties. CHIMERE Workshop, Paris 21-22 March 2005

  14. Conclusion and Perspectives • Comparison results during the heat wave episode : • Model reproduces main spatial structures during the heat wave episode. • Model simulates generally higher AOTs than POLDER due to negative bias in POLDER retrievals identified by comparison with AERONET ground-based measurements. • AOTs peaks due to smoke particles advected from Portugueseforest fires are missed in model simulations. • Necessity to include emissions and high-altitude transport of smoke from Portuguese wildfires to explain the observed AOT peaks over Europe. • Future work: • Introduction of forest fire real emissions and evaluation of their impact on AOT • Take into account the transport of thin layers • Comparison with MODIS- and GLAS-derived aerosol optical properties CHIMERE Workshop, Paris 21-22 March 2005

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