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

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” clouds over land

  • 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 clouds over land

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)


  • 2. clouds over landExamine 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


S1 Simulations: Aerosol-Cloud Interactions + clouds over land

Land Surface Model

Incoming

solar radiation

Surface sensible and

latent heat fluxes

balance


S2 Simulations: Aerosol-Cloud Interactions + clouds over land

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



Simulation of case from amazon smocc experiment

Large Eddy clouds over landModel (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


LWP clouds over land

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


S1: No Aerosol Heating: 5-h averages vs N clouds over landa

  • 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


S2: With Aerosol-Radiative Coupling clouds over land

rain rate

w’w’

LWP

CF

Zdepth

Zbase


S2: With Aerosol-Radiative Coupling: 5-h average vs N clouds over landa

Non-monotonicbehavior

LWP

τ

CF

Tsfc

Rnet

Nd,int

Fsen+lat

Zdepth


S2: With Aerosol-Radiative Coupling clouds over land

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 clouds over land

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 clouds over land

  • 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


Cloud Fraction clouds over land

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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