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

Hodzic Alma**, Vautard R., Chepfer H., Goloub P., Menut L., Chazette P., Deuzé J.L., Apituley A., Couvert P..

CHIMERE Workshop, Paris 21-22 March 2005

Aerosol model validation using optical measurementsAerosol model validation using optical measurements

Evolution of AOT over Europe during Evolution of AOT over Europe during the 2003 summer heat wave as seen from CHIMERE the 2003 summer heat wave as seen from CHIMERE

simulations and POLDER-2 datasimulations and POLDER-2 data

Laboratoire de Météorologie Dynamique - École Polytechnique - Paris

(*) hodzic@lmd.polytechnique.fr

Why using optical data for model evaluation ?Why using optical data for model evaluation ?Advantages/DifficultiesAdvantages/Difficulties

• Surface measurements (AIRPARIF network)+ Continuous measurements of PM10 and PM2.5 => spatial distribution

- Lack of information on the vertical mixing.

• 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.

• Airborne measurements (ESQUIF, ESCOMPTE)+ Aerosol chemical composition and size distribution

- Short data series.

Evaluation of aerosol models :

CHIMERE Workshop, Paris 21-22 March 2005

Available optical measurementsAvailable optical measurements

CHIMERE Workshop, Paris 21-22 March 2005

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 networkAerosol 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/

Aerosol retrieval from model simulationsAerosol retrieval from model simulations

Approach “Model to Observation”

CHIMERE Workshop, Paris 21-22 March 2005

- 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:

((Hodzic et al., 2004, JGR)

CHIMERE(Gas / Aerosols)

Chemicalspeciation

Massdistribution

Aerosol Optical Properties

m, SSA, AOT

Lidar ProfilesPr2, PBL

MIE code

Sun-photometerAERONETPOLDER

Lidar dataSIRTA

Direct comparison of observed and simulated backscattering lidar profiles to avoid new hypothesis in observations.

Comparison with lidar data at Palaiseau Comparison with lidar data at Palaiseau Pollution episode of 26 March 2003Pollution episode of 26 March 2003

LIDAR 532nm – 2003/03/26 – ln(Pr2)LIDAR 532nm – 2003/03/26 – ln(Pr2)

CHIMERE 532nm – 2003/03/26 – ln(Pr2)CHIMERE 532nm – 2003/03/26 – ln(Pr2)

DustDust

PBLPBLRLRL

11 GMT

14 GMT

CHIMERE LIDAR Variability

(Hodzic et al., 2004, JGR)

Integrated optical thickness at 532nm

Ground concentrations of PM10

POLDER derived AOT at 865 nm due to Aerosols Accumulation Mode

Example of comparison with satellite dataExample of comparison with satellite dataMonthly mean Monthly mean AOT over Europe from POLDER dataAOT over Europe from POLDER data

(Hodzic et al., 2005, submitted to ACP)

CHIMERE Workshop, Paris 21-22 March 2005

Summer heat waveSummer heat wave4-13 August 20034-13 August 2003

POLDER derived AOT at 865 nm due to Aerosols Accumulation Mode

Evolution of AOT during the August 2003 heat wave episodeEvolution of AOT during the August 2003 heat wave episode

Evolution of AOT from POLDER and CHIMEREEvolution of AOT from POLDER and CHIMERE

05 August 200305 August 2003

11 August 200311 August 2003

Systematic comparisons model/observationsSystematic comparisons model/observations

CHIMERE Workshop, Paris 21-22 March 2005

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?

Major discrepancies model/observations:

- General model overestimation

- Underestimation of peak values on 5-6 August

The origin of discrepancies: model systematic biasThe origin of discrepancies: model systematic bias

CHIMERE Workshop, Paris 21-22 March 2005

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

1:12:1

1:2

AOT peaks : Advection of smoke particles from AOT peaks : Advection of smoke particles from Portugal forest firesPortugal forest fires

CHIMERE Workshop, Paris 21-22 March 2005

05 August 200305 August 2003

Passive tracer run with CHIMERE Passive tracer run with CHIMERE

AOT peaks : Advection of smoke particles from AOT peaks : Advection of smoke particles from Portugal forest firesPortugal forest fires

Passive tracer runs with CHIMERE Passive tracer runs with CHIMERE

CHIMERE Workshop, Paris 21-22 March 2005

Conclusion and PerspectivesConclusion and Perspectives

General model/observation comparison results :

• Remote sensing (lidar and sun-photometer) provide useful routine measurements 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 identifying missing 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

Conclusion and PerspectivesConclusion 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 Portuguese forest 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 propertiesCHIMERE Workshop, Paris 21-22 March 2005