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Stronger constraints on the anthropogenic indirect Aerosol Effect

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8 months of space-born measurements are done by the Polder satellite. ... The outcomes of simulations are compared with the data from the POLDER satellite ... – PowerPoint PPT presentation

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Title: Stronger constraints on the anthropogenic indirect Aerosol Effect


1
Stronger constraints on the anthropogenic
indirect Aerosol Effect
  • A paper from Ulrike Lohmann and Glen Lesins
  • Presentation by Abdel Nnafie and Jasper Donker

2
Contents
  • Introduction
  • Observations by Polder satellite
  • Model
  • Results
  • Conclusion
  • About the paper

3
Introduction
  • The amount of aerosol in the atmosphere has
    increased due to human activities
  • Direct effect this concerns scattering,
    absorption and reflection of solar radiation by
    cloud
  • Indirect effect aerosol act as cloud
    condensation nuclei, thereby affecting the
    initial cloud droplet number concentration (CDNC)
  • ?increase in cloud albedo (cloud albedo effect)
  • ?reductions in precipitation efficiency and
    increase of cloud lifetime (cloud lifetime
    effect)
  • Cooling from these two effects causes a radiative
    forcing between -1 and -4.4 W/m2 (this great
    range causes large uncertainties in projections
    of future climate change) (IPCC)
  • The anthropogenic indirect aerosol effect (aie)
    cannot be deduced from observations along but
    require a modeling component.
  • Historical climate data together with simulations
    constrain this effect to a range of 0 to -1.2
    W/m2.
  • In this paper a model is used for a more accurate
    study of the anthropogenic indirect aerosol
    effect, by using satellite observations

4
IPCC
5
Observations by Polder satellite
  • 8 months of space-born measurements are done by
    the Polder satellite.
  • These data were used to derive aerosol
    concentrations and cloud droplet effective radii
    (CDR).
  • Results the cloud droplet size decreases with
    increasing aerosol index (AIthis represent the
    aerosol column number concentration)
  • These data are not sufficient to quantify the
    magnitude of the global indirect aerosol effect.

6
Model
  • The ECHAM4 general circulation model is used in
    this research.
  • 4 different simulation have been made
  • Reference simulation ECHAM-CTL (includes both
    indirect effects)
  • Simulation ECHAM-2ND-AIE (without the albedo
    effect)
  • Simulation ECHAM-NO-AIE (without the aerosol
    indirect effect)
  • Simulation ECHAM-PI (Pre Industrial simulation
    without anthropogenic aerosol)
  • The outcomes of simulations are compared with
    the data from the POLDER satellite

7
ResultsAI
8
ResultsCDR
9
Question?
  • Do we need the anthropogenic aerosol indirect
    effects to explain the observed anticorrelation
    between AI and CDR?
  • Or is this anticorrelation only determined purely
    by geographic variations in the liquid water
    path?

10
  • Oceanic slope is larger
  • Polder oceanic and continental CDR converge
    approximately toward
  • same limit (8 µm)
  • Both aerosol indirect effects are needed to
    reproduce the outcomes
  • of POLDER
  • ECHAMs clouds are more susceptible to aerosols
    than the observed clouds
  • ?ECHAM very likely overestimates the IAE.
  • Oceanic slope overestimation 25.9/19.9 1.30
  • Continental slope overestimation 21.6/7.00 3.09

11
  • With increasing AI CDR decreases and the liquid
    water path increases
  • ?detection of anthropogenic AIE from observation
    only is complex
  • ?using models together with observations is
    important.

12
conclusions
  • The climate model simulations including -1.8
    W/m2.
  • ?longwave radiation 1.4 W/m2.
  • ? net decrease 1.4 W/m2.
  • ECHAM simulates an aerosol effect of -1.28 W/m2
    over oceans
  • After correction -0.98 W/m2.
  • Over land this is -1.62 W/m2 ? after
    correction -0.53 W/m2.
  • NET GLOBLA MEAN -0.85 W/m2.
  • This value is consistent with of 0 to -1.2 W/m2.

13
About the paper
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