Aerosol-cloud-surface flux Interactions in warm cumulus clouds over land
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Aerosol-cloud-surface flux Interactions in warm cumulus clouds over land. Hongli Jiang 1 Graham Feingold 2 1 CIRA/NOAA/ESRL, Boulder, CO 2 NOAA/E SR L, Boulder, CO RICO workshop, Sept. 21, 2006. The “First Aerosol Indirect Effect”.

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Aerosol-cloud-surface flux Interactions in warm cumulus clouds over land

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Aerosol cloud surface flux interactions in warm cumulus clouds over land

Aerosol-cloud-surface flux Interactions in warm cumulus clouds over land

Hongli Jiang1

Graham Feingold2

1 CIRA/NOAA/ESRL, Boulder, CO

2 NOAA/ESRL, Boulder, CO

RICO workshop, Sept. 21, 2006


The first aerosol indirect effect

The “First Aerosol Indirect Effect”

  • More aerosol  more drops while LWC remains constant (Twomey 1974)

The “Second Aerosol Indirect Effect”

  • More aerosol  more drops  suppressed coalescence  less rain  larger LWP  longer lifetime (Warner ’68, Albrecht 1989)


Prior work

Cloud Fraction

Smoke Optical Depth

Regional Effects:

Disruption in precipitation

patterns in China:

Drought in north; floods in south

Menon et al. 2002

Prior Work

  • Local effects on clouds

    • Ackerman et al. (2000)

    • Johnson et al. (2004)

    • Koren et al. (2004)

    • Feingold et al. (2005)


Aerosol cloud surface flux interactions in warm cumulus clouds over land

  • 2. Examine the semi-direct effect

    - Evaluate the importance of coupling aerosol radiative properties to microphysics, dynamics, surface soil and vegetation model

Objectives:

  • 1. Study the second aerosol indirect effect on warm cumulus clouds over land

    • - Aerosol induced changes in LWP, cloud fraction, precipitation, etc….

  • Consider counteracting effects of the 2nd aerosol

  • indirect effect andthesemi-direct effect


Aerosol cloud surface flux interactions in warm cumulus clouds over land

S1 Simulations: Aerosol-Cloud Interactions +

Land Surface Model

Incoming

solar radiation

Surface sensible and

latent heat fluxes

balance


Aerosol cloud surface flux interactions in warm cumulus clouds over land

S2 Simulations: Aerosol-Cloud Interactions +

Aerosol Radiation +

Land Surface Model

Incoming

solar radiation

Aerosol

scattering &

absorption

Incoming

solar radiation

diminished by

aerosol

Surface sensible and latent

heat fluxes reduced

balance


Table 1 description of experiments

Table 1. Description of Experiments


Simulation of case from amazon smocc experiment

Large Eddy Model (LES ~ Dx ~100m)

Resolves aerosol and drop sizes + dissolved aerosol

Resolves large eddy dynamics ([email protected])

Radiation model (Harrington et al., 2000)

Radiatively-active aerosol – absorbing aerosol heats atmosphere locally

Soil and vegetation model (Walko et al., 2000)

Domain size: x=y=6.4 km; z= 5.0 km

Grid size: Dx=Dy=100 m; Dz=50 m

Dt = 2 sec

Simulation of case from Amazon SMOCC experiment

  • Smoke:

  • ωo ~ 0.9 (dry)

  • Optical properties calculated in 8 λ bands (SW and LW)

  • Effects of uptake of water vapor on size and composition

  • Various values of concentration Na, but constant with height


Aerosol cloud surface flux interactions in warm cumulus clouds over land

LWP

100/cc

500/cc

2000/cc

Rain rate

Expected:

More aerosol  more drops

 less rain

Nd

S1: No Aerosol Heating

Na=100

CF

Zdepth

Unexpected:

No clear separation in LWP, cloud fraction, and cloud depth as Na increases.

Zbase


Aerosol cloud surface flux interactions in warm cumulus clouds over land

S1: No Aerosol Heating: 5-h averages vs Na

  • When raindrops are excluded in the LWP calculation, second aerosol indirect effect is simulated

  • Dynamic variability is much larger than aerosol effects on LWP, CF, cloud depth

Standard deviation


Aerosol cloud surface flux interactions in warm cumulus clouds over land

S2: With Aerosol-Radiative Coupling

rain rate

w’w’

LWP

CF

Zdepth

Zbase


Aerosol cloud surface flux interactions in warm cumulus clouds over land

S2: With Aerosol-Radiative Coupling: 5-h average vs Na

Non-monotonicbehavior

LWP

τ

CF

Tsfc

Rnet

Nd,int

Fsen+lat

Zdepth


Aerosol cloud surface flux interactions in warm cumulus clouds over land

S2: With Aerosol-Radiative Coupling

LWP

τ

LWP

(S2(2000)-S2(100))/S2(100), %

CF

Tsfc

CF

Tsfc

Rnet

Nd,int

Nd,int

Rnet

Zdepth

Fsen+lat

Zdepth

Fsen+lat


Summary

Summary

S1 simulations (2nd indirect effect only):

  • Increase in Na leads to

    • increase in Nd, cloud optical depth t,

    • decrease in reff,

    • reduction in surface precip

  • Aerosol effects on LWP, cloud fraction are small andwell within the dynamical variability at a given Na

    S2 simulations (2nd indirect + semi-direct effects):

  • The aerosol blocks up to 26 % of incoming solar radiation from reaching the surface;

  • Reduced surface radiative fluxes  reduction in surface heat fluxes  strong decrease in LWP, cloud fraction, cloud depth, and weaker convection;

  • Possible non-monotonic response of cloud properties to increases in aerosol


Final comments

Final Comments

  • Current work focused on determining the effects of poor representation of mixing in LES

    • Damkohler No. = teddy/tevap (homogeneous/inhomogeneous)

    • Evaporation limiters: (C. Jeffery, J. Reisner, JAS 2006)

    • W. Grabowski (J. Climate 2006)

    • S. Krueger: EMPM


Aerosol cloud surface flux interactions in warm cumulus clouds over land

Cloud Fraction

BOMEX

SMOCC

LWP (cloud ave.)

LWP (domain ave.)

Note large std deviations!

LWP (cloud ave.)

100

1000

10

2000

500

1000

Aerosol Conc., cm-3

Aerosol Conc., cm-3

Xue and Feingold 2006

Jiang and Feingold 2006

Excluding drizzle


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