Interactive chemistry in CAM

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Interactive chemistry in CAM

• Jean-François Lamarque, D. Kinnison and S.
  Walters
• Atmospheric Chemistry Division
• NCAR

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Goal

• Provide a flexible framework for the study of
  chemistry-climate interactions in CCSM, including
  land/ocean interactions
• Include gas-phase and aerosols
• Focus on the troposphere and stratosphere

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Computational approach

• Chemical scheme is input in a preprocessor that
  creates a set of subroutines added to the
  standard CAM
• Reads a set of external files (for emissions,
  deposition velocities and photolysis rates)
• Uses the finite volume dynamical core for the
  advection of tracers
• Convective and diffusive transport of tracers is
  considered

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Main features

• Photolysis and chemical reactions solved with an
  implicit/explicit set of solvers
• Lookup table photolysis rates, including cloud
  correction (but not aerosols)
• Wet (first-order loss linked to precipitation in
  CAM) and dry removal
• Surface emissions (fixed, monthly averages)
• Lightning NO production linked to convection in
  CAM

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Current status

• Implementation in WACCM of combined tropospheric
  (regional and global scale) and stratospheric
  chemistry (including PSCs) 105 species, over
  300 chemical reactions
• Simulations performed with 52 levels, extending
  up to 85 km.
• Stratosphere-troposphere flux is explicitly
  calculated
• Horizontal resolution of 2x2.5
• 25 years of present-day simulations, using fixed
  SST

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Performance

• In the present configuration, inclusion of
  chemistry (including transport of tracers)
  approximately doubles the cost of the equivalent
  WACCM simulation this ratio will be a little
  worse for CAM
• On bluesky, 96 CPUs, 1 year in 2 days

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Mid-tropospheric ozone
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Model evaluation

• Comparison with tropospheric and stratospheric
  observations
• Comparison with TOMS total ozone column

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Comparison with observations (1)
Red model results Blue observations
Barrow, Alaska
Black sea, Romania
Mauna Loa, Hawaii
Halley station, Antarctica
Month
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Comparison with observations (2)
Ozone mixing ration (ppbv)
Month
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Comparison with observations (3)
NOx NO NO2
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Comparison with observations (4)
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Summary

• Working version of interactive tropospheric/strato
  spheric chemistry
• Analysis of results indicate a good overall
  representation of the chemistry in the atmosphere
• Biases are similar to the ones found in MOZART
  results, on which the chemistry is based

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Next steps (1)

• Develop a CAM version (requires the addition of
  upper-boundary conditions) expected to happen
  within a month
• Inclusion of aerosols (ammonium, sulfate,
  sea-salt, dust,organic and black carbon X.X.
  Tie, P. Hess N. Mahowald and P. Rasch)
• Better representation of wet removal (P. Hess and
  P. Rasch)
• Interactions with CLM (deposition emissions of
  BVOCs (C. Wiedinmyer and S. Levis) soil NO)

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Next steps (2)

• Interactive calculation of photolysis rates
• Development of a variety of chemical packages for
  ease of use
• Coupling with ocean biogeochemistry
• Coupling between the nitrogen and the carbon
  cycle through CLM (P. Thornton)
• Interactive emissions from wetlands