Aerosol indirect effects in cam and mirage
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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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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

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


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


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.


CAM and MIRAGE


CAM Aerosol Properties


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).


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.


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


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


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


No 2nd indirect effect


No nudging


Change LWP w/, w/o nudging

lwp cam no2ndindir, mirage no2ndindir nudge, mirage no2ndindir nonudge


Zonal mean IE


Ndrop cam, mirage

Ndrop cam progaer no2ndindir tau=0

Mirage prognaer no2ndindir nudge

Anthro, noanthro


Ccn3 cam, mirage, anthro, noanthro

CCN3 cam progaer no2ndindir tau=0

Mirage prognaer no2ndindir nudge

Anthro, noanthro


Ndrop cam updraft spectrum mirage updraft spectrum


DE, IE cam updraft spectrum


Background aerosol


Noanthro ccn3 cam tau=0,0.01, 0.02

Noanthro [CCN3] cam progaer no2ndindir tau=0, 0.01, 0.02

Mirage prognaer no2ndindir nonudge


Sensitivity to size

r=0.05 for oc, bc, volcanic


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.


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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