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Aerosol Indirect Effects in CAM and MIRAGE

Aerosol Indirect Effects in CAM and MIRAGE. Steve Ghan Pacific Northwest National Laboratory Jean-Francois Lamarque, Peter Hess, and Francis Vitt, NCAR. Indirect Effects Physics. N k = droplet number mixing ratio in layer k A k = droplet loss by autoconversion of droplets

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Aerosol Indirect Effects in CAM and MIRAGE

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  1. Aerosol Indirect Effects in CAM and MIRAGE Steve Ghan Pacific Northwest National Laboratory Jean-Francois Lamarque, Peter Hess, and Francis Vitt, NCAR

  2. Indirect Effects Physics Nk = droplet number mixing ratio in layerk Ak = droplet loss by autoconversion of droplets Ck = droplet loss by collection by precipitation Ek = droplet loss by evaporation Sk = droplet nucleation source in layer k

  3. Indirect Effects Physics Nk = droplet number mixing ratio in layerk Ak = droplet loss by autoconversion of droplets Ck = droplet loss by collection by precipitation Ek = droplet loss by evaporation Sk = droplet nucleation source in layer k f = cloud fraction w = updraft velocity Nn = number nucleated (parameterized in terms of w and aerosol) p(w) = probability density function ofw w* = σw= characteristic updraft velocity in growing part of cloud

  4. Indirect Effects Physics Nk = droplet number mixing ratio in layerk Ak = droplet loss by autoconversion of droplets Ck = droplet loss by collection by precipitation Ek = droplet loss by evaporation Sk = droplet nucleation source in layer k f = cloud fraction w = updraft velocity Nn = number nucleated (parameterized in terms of w and aerosol) p(w) = probability density function ofw w* = σw= characteristic updraft velocity in growing part of cloud 1st IE: 2nd IE: Autoconversion connected to droplet number.

  5. CAM and MIRAGE

  6. CAM Aerosol Properties

  7. Estimating Direct and Indirect Effects Two simulations: All aerosol sources All sources except anthropogenic sulfate Each simulation calculates radiative fluxes with (Faer) and without aerosol (Fnoaer).

  8. Estimating Direct and Indirect Effects Two simulations: All aerosol sources All sources except anthropogenic sulfate Each simulation calculates radiative fluxes with (Faer) and without aerosol (Fnoaer). Direct effect of all aerosol in a simulation is Fdirect = Faer -Fnoaer.

  9. Estimating Direct and Indirect Effects Two simulations: All aerosol sources All sources except anthropogenic sulfate Each simulation calculates radiative fluxes with (Faer) and without aerosol (Fnoaer). Direct effect of all aerosol in a simulation is Fdirect = Faer -Fnoaer. Difference between simulations is . Then Fdirect = Faer -Fnoaer

  10. Estimating Direct and Indirect Effects Two simulations: All aerosol sources All sources except anthropogenic sulfate Each simulation calculates radiative fluxes with (Faer) and without aerosol (Fnoaer). Direct effect of all aerosol in a simulation is Fdirect = Faer -Fnoaer. Difference between simulations is . Then Fdirect = Faer -Fnoaer Findirect = Faer -Fdirect = Fnoaer

  11. IE, DE with 2nd IE CAM tau=0, MIRAGE nudge

  12. No 2nd indirect effect

  13. No nudging

  14. Change LWP w/, w/o nudging lwp cam no2ndindir, mirage no2ndindir nudge, mirage no2ndindir nonudge

  15. Zonal mean IE

  16. Ndrop cam, mirage Ndrop cam progaer no2ndindir tau=0 Mirage prognaer no2ndindir nudge Anthro, noanthro

  17. Ccn3 cam, mirage, anthro, noanthro CCN3 cam progaer no2ndindir tau=0 Mirage prognaer no2ndindir nudge Anthro, noanthro

  18. Ndrop cam updraft spectrum mirage updraft spectrum

  19. DE, IE cam updraft spectrum

  20. Background aerosol

  21. Noanthro ccn3 cam tau=0,0.01, 0.02 Noanthro [CCN3] cam progaer no2ndindir tau=0, 0.01, 0.02 Mirage prognaer no2ndindir nonudge

  22. Sensitivity to size r=0.05 for oc, bc, volcanic

  23. Conclusions • The much larger indirect effect produced by CAM has not been completely explained. • The much larger feedback of liquid water path explains at least part of larger indirect effect. • The larger relative sensitivity of CCN to emissions in CAM may also contribute. • The CAM CCN and IE are insensitive to the size distribution of OC and volcanic. • A background aerosol reduces the IE from CAM, but cannot be justified.

  24. Future Work • Resolve differences between CAM and MIRAGE: insert monthly mean aerosol from each model into simulations by the other. • Add detrainment of droplet number from cumulus. • Integrate with UW turbulence and shallow cumulus schemes. • Couple with MIRAGE treatment of aerosol dynamics and mixing state. • Add nucleation scavenging and size-dependent impaction scavenging. • Size and composition dependent optical properties. • Add primary and secondary marine organic emissions.

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