Transcript Hodzic

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..
(*) [email protected]
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
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
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
CHIMERE Workshop, Paris 21-22 March 2005
http://smsc.cnes.fr/POLDER/
Aerosol retrieval from model simulations
(Hodzic et al., 2004, JGR)
Approach “Model to Observation”
CHIMERE
(Gas / Aerosols)
Chemical
speciation
MIE
code
Direct comparison of observed and
simulated backscattering lidar
profiles to avoid new hypothesis in
observations.
Mass
distribution
Aerosol Optical
Properties
m, SSA, AOT
Sun-photometer
AERONET
POLDER
Lidar Profiles
Lidar data
Pr2, PBL
SIRTA
Contribution of aerosol
mode to optical efficiency:
- Accumulation Mode: (0.16 – 2.5 µm): > 88%
- Nucleation Mode: (< 0.16 µm) : ~ 4%
- Coarse Mode: (>2.5 µm) : ~ 8%
CHIMERE Workshop, Paris 21-22 March 2005
Comparison with lidar data at Palaiseau
Pollution episode of 26 March 2003
Ground concentrations of PM10
LIDAR 532nm – 2003/03/26 – ln(Pr2)
11 GMT
 CHIMERE
LIDAR
Variability
Dust
RL
Integrated optical thickness at 532nm
PBL
CHIMERE 532nm – 2003/03/26 – ln(Pr2)
14 GMT
(Hodzic et al., 2004, JGR)
Example of comparison with satellite data
Monthly 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
Summer heat wave
4-13 August 2003
CHIMERE Workshop, Paris 21-22 March 2005
Evolution of AOT during the August 2003 heat wave episode
POLDER derived AOT at 865 nm due to Aerosols Accumulation Mode
Evolution of AOT from POLDER and CHIMERE
05 August 2003
11 August 2003
Systematic comparisons model/observations
Mean AOTs over Europe
Major discrepancies model/observations:
- General model overestimation
- Underestimation of peak values
on 5-6 August
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
The origin of discrepancies: model systematic bias
Comparison with AERONET-derived AOTs
2:1
1:1
Results:
1:2
- 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
AOT peaks : Advection of smoke particles from
Portugal forest fires
05 August 2003
Passive tracer run with CHIMERE
CHIMERE Workshop, Paris 21-22 March 2005
AOT peaks : Advection of smoke particles from
Portugal forest fires
Passive tracer runs with CHIMERE
CHIMERE Workshop, Paris 21-22 March 2005
Conclusion 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 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 properties
CHIMERE Workshop, Paris 21-22 March 2005