global simulations of aerosol impaction scavenging with the echam5 ham gcm
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Betty Croft, and Randall V. Martin – Dalhousie University, Canada Ulrike Lohmann – ETH Zurich, Switzerland Philip Stier – Oxford University, U.K. Sabine Wurzler – Landesamt fur Umwelt, Natur, und Verbrauchershutz, Germany Johann Feichter – Max Planck Institute for Meteorology, Germany

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global simulations of aerosol impaction scavenging with the echam5 ham gcm

Betty Croft, and Randall V. Martin – Dalhousie University, Canada

Ulrike Lohmann – ETH Zurich, Switzerland

Philip Stier – Oxford University, U.K.

Sabine Wurzler – Landesamt fur Umwelt, Natur, und Verbrauchershutz, Germany

Johann Feichter – Max Planck Institute for Meteorology, Germany

Corinna Hoose – University of Oslo, Norway

Global Simulations of Aerosol Impaction Scavenging with the ECHAM5-HAM GCM

---------------- CMOS 2009 Congress ------------------- Radiation, Aerosols, and Cloud Session, June 3, 2009 ------------------------------------------------------------------

slide2

Outline:

  • Introduction to Aerosol Scavenging Processes
  • Impaction Scavenging by Rain and Snow
  • Impaction Scavenging by Cloud Droplets and Ice Crystals
  • Results of Global Simulations
  • Summary and Outlook
slide3

Aerosol Scavenging Processes:

Sedimentation and dry deposition

(Figure from Hoose et al. (2008))

Uncertainty in aerosol scavenging contributes to the uncertainties in the estimates of the direct and indirect radiative forcing of aerosols on climate.

slide4

Impaction Scavenging by Rain and Snow:

Stier et al. (2005) prescribed coefficients for rain of 4mm drops (red steps)

Stier et al. (2005) prescribed coefficient for snow (green)

(Figure from Croft et al. (2009))

slide5

Contribution of Impaction Scavenging By Rain and Snow to Global and Annual Mean Aerosol Deposition:

Size-dependent impaction

[%]

Prescribed coefficients

Sulfate

BC

POM

Dust

Sea Salt

Red: Snow; Blue: Rain; Left: Prescribed coefficients; Right: Size-dependent impaction

All results are for a 1-year T42 nudged simulationwith ECHAM5-HAM GCM

slide6

Global and Annual Mean Sea Salt and Dust Burdens:

Sea salt [mg m-2]

Change relative to prescribed coefficients [%]

Dust [mg m-2]

Change relative to prescribed coefficients [%]

slide7

Percent Change of Global and Annual Mean Sea Salt and Dust Mass Burdens Relative to Prescribed Coefficient Simulation:

Rain Drop spectra

Fixed 0.4 mm Drops

Fixed 4.0 mm Drops

DU

DU

SS

DU

SS

SS

Dust and sea salt burdens are sensitive to the impaction scavenging parameterization for rain and snow.

slide8

Impaction Scavenging by Cloud Droplets:

Example for CDNC 40cm-3, assuming a gamma distribution

Prescribed coefficients of Hoose et al. (2008) are shown with red steps

Number scavenging (solid lines); Mass scavenging (dashed lines) Data sources described in Croft et al. (2009)

slide9

Impaction Scavenging by Column and Plate Ice Crystals:

Prescribed coefficients of Hoose et al. (2008) (red steps)

Assume columns for T<238.15K

Assume plates for 238.15<T<273.15 K

(Data from Miller and Wang, (1991), and following Croft et al. (2009))

slide10

Mass mixing ratios:

Black carbon, particulate organic matter, and dust are sensitive to the in-cloud (IC) impaction parameterization in regions of mixed and ice clouds.

slide11

Percent Change in Aerosol Mass and Number Burdens Relative to A Simulation With No In-Cloud Impaction:

NS

SU

BC

POM

SS

DU

KS

AS

CS

KI

AI

CI

[%]

The dust mass, and the number of insoluble accumulation and coarse mode aerosols are most sensitive to impaction scavenging.

slide12

Dust: Fractional Contribution of Stratiform Cloud Processes to the Annual and Global Mean Mass Deposition:

[%]

Warm

Mixed

Ice

Warm

Mixed

Ice

T>273K

238<T<273K

T<238K

T>273K

238<T<273K

T<238K

Nucleation

Impaction

slide13

Comparison with observed zonal mean aerosol optical depth:

Observations are a MODIS, MISR, AERONET composite from Kinne, (2009)

AOD is more sensitive to impaction scavenging by rain and snow, as opposed to impaction with cloud droplets and ice crystals.

slide14

Summary and Outlook:

  • Size-dependent impaction scavenging by rain and snow reduced global sea salt burdens by 15%.
  • The assumption of a rain drop spectra as opposed to a fixed mean raindrop size changed the global sea salt burdens by near to 10%.
  • Size-dependent impaction scavenging by cloud droplets and ice crystals reduced concentrations by up to 25% and 100% for carbonaceous aerosols and dust, respectively, in the regions of mixed phase and ice clouds.  prediction of climate change due to absorbing aerosols, particularly in the polar regions, requires consideration of in-cloud impaction scavenging.
  • Impaction scavenging in convective clouds will be investigated in future work.
slide15

Acknowledgments:

Thanks!

Questions?

slide17

Percent Change in Aerosol Mass and Number Burdens Relative to A Simulation With No In-Cloud Impaction:

Aerosol Burden Sensitivity to In-Cloud Scavenging Parameterizations

[%]

SU

BC

POM

SS

DU

NS

KS

AS

CS

AI

CI

KI

Blue: Size-dependent impaction (diagnostic nucleation)

Red: Hoose et al. (2008) prescribed in-cloud impaction (diagnostic nucleation)

Yellow: Hoose et al. (2008) prescribed in-cloud impaction (prognostic aerosol cloud processing)

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