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

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

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 physics1

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 physics2

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 and MIRAGE


Cam aerosol properties

CAM Aerosol Properties


Estimating direct and indirect effects

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 effects1

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 effects2

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 effects3

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

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


No 2nd indirect effect

No 2nd indirect effect


No nudging

No nudging


Change lwp w w o nudging

Change LWP w/, w/o nudging

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


Zonal mean ie

Zonal mean IE


Ndrop cam mirage

Ndrop cam, mirage

Ndrop cam progaer no2ndindir tau=0

Mirage prognaer no2ndindir nudge

Anthro, noanthro


Ccn3 cam mirage 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

Ndrop cam updraft spectrum mirage updraft spectrum


De ie cam updraft spectrum

DE, IE cam updraft spectrum


Background aerosol

Background aerosol


Noanthro ccn3 cam tau 0 0 01 0 02

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

Sensitivity to size

r=0.05 for oc, bc, volcanic


Conclusions

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

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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