Global Modelling of Aerosol Microphysics

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Global Modelling of Aerosol Microphysics

• Ken Carslaw
• Dominick Spracklen, Graham Mann, Kirsty Pringle,
  Martyn Chipperfield

Funded through NERC, NCAS, UGAMP and DIAC
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Research Questions

• How well do we understand the global aerosol
  lifecycle?
• What controls the aerosol size distribution,
  composition and CCN spectrum in different
  regions?
• How important are uncertainties in microphysical
  processes?
• How is the size distribution affected by
  anthropogenic influence?
• How can we improve climate models?

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The Need for a Global Aerosol Microphysics Model

• Transport and transformation occur on
  inter-regional scales
• Were interested in more than locally highly
  polluted regions
• dust transport, marine DMS, biomass, etc.
• Reference model for simpler GCM schemes

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Description of Glomap

• The GLOMAP Model

• TOMCAT
• 3D Offline Global Eulerian CTM
• Forced by ECMWF Winds
• Convective transport
• Convective and resolved rain
• Typically run at 2.5ox2.5o

• GLOMAP
• Aerosol size spectrum ( 1 nm 24 mm)
• 2-moment (m and N) sectional scheme

Sources
Microphysics
Removal

• Dry Deposition
• Dry deposition of aerosol

• Emissions
• Anthrop volcanic SO2 emissions
• DMS emissions from wind stress and DMS sea
  surface concentration
• Sea salt aerosol generation function

• Nucleation and Condensation
• Binary H2SO4/H2O nucleation
• Condensational growth

• Clouds
• Prognostic convective and frontal rain
• In-cloud and below-cloud aerosol/gas scavenging
• Cloud-processing in diagnosed low-level cloud

• Coagulation
• Semi implicit fast numerical solution

• Sulfur Chemistry
• 8 sulfur species, 8 sulfur reactions
• Aqueous phase chemistry
• Oxidants from full chemistry run

• Hygroscopic Growth
• Equilibrium size given by Kohler equation

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Current GLOMAP Studies

• Maintenance of remote marine aerosol
• Mechanistic predictions of cloud drop number
• Regional aerosol nucleation bursts
• Hemispheric aerosol transport (DIAC)
• UK Chemistry and Aerosols Project (UKCA)

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Maintenance of Remote Marine Aerosol

• Baseline for understanding pollution
  perturbation
• Long-term remote marine observations
  (Heintzenberg et al., 2004) shown as pdf

GLOMAP
obs
dN/dlogdp (cm-3)
diameter (nm)
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Global Mechanistic Cloud Drop Prediction

• CDN based on fully resolved aerosol size
  distribution, cloud updraught and droplet
  activation process
• Comparison with simpler GCM empirical schemes

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Trans-continental Aerosol Transport
Iraq Sulphur Fire (June 24th 2003)
GLOMAP mean column number
MODIS aerosol optical depth at 0.55 µm

• Future work on ICCART and ITOP data

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Regional Aerosol Nucleation

• How do nucleation events affect the climate?

diameter / m
10-8
10-9
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UKCA

• NCAS-Met Office collaboration
• Development of a community aerosol and chemistry
  sub-program of the UM
• 2nd generation aerosol scheme
• Suitable for long integrations
• Should aim for consistent scheme across all
  scales

Information soon on ukca.ac.uk