VOCALSUK Regional Modelling Using WRFCHEM

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VOCALS-UKRegional ModellingUsing WRF-CHEM

• Michael Bane, Douglas Lowe,Gordon McFiggans
• Centre for Atmospheric Science
• University of Manchester

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Regional Modelling

• Use of WRF-CHEM for VOCALS-UK
• WP 2.4 prediction of aerosol composition
  properties over the SEP region
• WP 5.2 evaluation/comparison of aerosol
  thermodynamic schemes in WRF-CHEM in predicting
  activation
• WP 5.3 case studies of aerosol transformation
  cloud interaction
• WRF-CHEM
• Fast, Gustafson et al _at_ PNNL Grell, Peckham _at_
  NOAA NCAR many others

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Why WRF-CHEM

• WRF doesn't capture explicit cloud-aerosol-chemis
  try interactions
• WRF-CHEM does
• cloud droplet number source as function of
  aerosol activation (moving into cloud)
• prognostic droplet nucleationscheme gives max
  supersaturation,S_max, in updrafts
• aerosol particles with critical S lt S_max are
  activated
• phase transitions activation/evaporation

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WRF-CHEM aerosol

• Physics nucleation, coagulation, dry dep
• Thermodynamics
• MTEM (mixing rules,activity coeffs), MESA (TD
  equilibriumsolver for diff/mixed phases), ASTEM
  (dynamic integration of coupled gas-aerosol
  partitioning ODEs) Zaveri et al (2005ab, 2007)
• PD-FiTE (Topping, UoM) to be included later
• Species modelled
• SO42-, NO3-, NH4, Cl-, Na, other inorgs,
  organic matter, black carbon, liquid water, num
  (optional calcium, carbonate, methanesulfonate)

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WRF-CHEM aerosol representation

• MADE/SORGAM
• modal Modal AerosolDynamics model forEurope
  (Ackermann 1998)
• includes SOA by SORGAM Secondary Organic Aerosol
  Model (Schell at al, 2001)
• MOSAIC
• Model for Simulating Aerosol Interactions and
  Chemistry
• sectional (currently 4 or 8) mass-size rep,
  inter-bin mass transfer 2-moment or moving
  centre
• no SOA
• UoM will be providing SOA module

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WRF-CHEM aerosol-cloud interactions

• direct aerosol feedbacks
• absorption/scattering by aerosol fed back into
  met
• FAST-J (spherical Mie code)
• for given num, RI wet radius
• provides AOD, SSA, asymmetry factor extinction
• coupled to Goddard shortwave radiation code
• indirect cloud-aerosol feedbacks (work in
  progress)
• using Lin et al microphysics schemes
• aqueous phase chemistry
• increased cloud-borne sulphate, nitrate, ammonium
• wet deposition (in-cloud below-cloud)

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WRF-CHEM computational burden

• much more expensive than just WRF
• additional computations
• chemistry/aerosol
• yet to implementdynamic aerosolschemes
• higher computationalcosts

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Thanks...

• Fast, Grell Gustafson
• slides from various presentations

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Optional extras...
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• WRF-CHEM built upon WRF ARW dynamic core
• Aerosol species transported using same as WRF for
  hori/vert coords (no interpolation in x,y,z) and
  same physics parameterisation (no interpolation
  in time)

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WRF-CHEM chemistry

• radm2
• CBM-Z
• (Zaveri Peters, 1999)
• extended CBM-IV to include long-lived species,
  their intermediates, isoprene chem, DMS chem
  lumped structure for organics (similar C bonds)
• Use of KPP to generate (new?) chemical mechanisms
  adjoints
• FAST-J photolysis (based on Wild et al, 2000)
  alternatively, TUV scheme

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RATIONALE why WRF-CHEM Aerosol-Cloud
Interactions may have a significant impact on
climate on global and regional scales. HOWEVER
The detailed processes are poorly known and the
bases for their representation in global models
is at present limited ie need coupled model (not
just WRF) to capture all cloud-aerosol-chemistry
interactions
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Emissions (to be written)

• MEGAN (global biogenic emis model)

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the end

• http//www.cas.manchester.ac.uk