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Presentation on theme: "1 CIRA/NOAA/ESRL, Boulder, CO"— Presentation transcript:

1 1 CIRA/NOAA/ESRL, Boulder, CO
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

2 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)

3 Prior Work Local effects on clouds Ackerman et al. (2000)
Johnson et al. (2004) Koren et al. (2004) Feingold et al. (2005) Menon et al. 2002 Regional Effects: Disruption in precipitation patterns in China: Drought in north; floods in south Cloud Fraction Smoke Optical Depth

4 Objectives: 1. Study the second aerosol indirect effect on warm cumulus clouds over land - Aerosol induced changes in LWP, cloud fraction, precipitation, etc…. 2. Examine the semi-direct effect - Evaluate the importance of coupling aerosol radiative properties to microphysics, dynamics, surface soil and vegetation model Consider counteracting effects of the 2nd aerosol indirect effect and the semi-direct effect

5 S1 Simulations: Aerosol-Cloud Interactions + Land Surface Model
Incoming solar radiation Surface sensible and latent heat fluxes balance

6 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

7 Table 1. Description of Experiments
Na , cm-3 ta Aerosol Heating S1-100 100 0.04 No S1-500 500 0.20 S1-1000 1000 0.40 S1-2000 2000 0.80 S2-100 Yes S2-500 S2-1000 S2-2000

8 Simulation of case from Amazon SMOCC experiment
Large Eddy Model (LES ~ Dx ~100m) Resolves aerosol and drop sizes + dissolved aerosol Resolves large eddy dynamics 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 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

9 S1: No Aerosol Heating CF Zdepth Unexpected:
LWP S1: No Aerosol Heating Na=100 100/cc 500/cc 2000/cc CF Zdepth Unexpected: No clear separation in LWP, cloud fraction, and cloud depth as Na increases. Zbase Expected: More aerosol  more drops  less rain Rain rate Nd Reduction in LWP and CF not evident here I would use this as a “wrap-up slide”

10 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

11 S2: With Aerosol-Radiative Coupling
LWP CF Zdepth Zbase Distinct decrease in LWP, cf, cloud depth, and cloud base especially for Na> 500/cc. Line types are the same as in previous figures. rain rate w’w’

12 τ S2: With Aerosol-Radiative Coupling: 5-h average vs Na LWP CF Tsfc
Non-monotonic behavior LWP τ CF Tsfc Rnet Nd,int Don’t know how to duplicate the labeling second time after picture frame 12. Fsen+lat Zdepth

13 τ S2: With Aerosol-Radiative Coupling LWP LWP 64% CF 58% Zdepth 62%
(S2(2000)-S2(100))/S2(100), % LWP 64% CF 58% Zdepth 62% Tsfc -1.31oC Rnet 31% Rsw 26% CF Tsfc CF Tsfc Rnet Nd,int Nd,int Rnet Zdepth Fsen+lat Zdepth Fsen+lat

14 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 and well 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

15 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

16 BOMEX SMOCC Cloud Fraction LWP (cloud ave.) LWP (domain ave.)
Note large std deviations! LWP (cloud ave.) 100 1000 10 500 1000 2000 Aerosol Conc., cm-3 Aerosol Conc., cm-3 Xue and Feingold 2006 Jiang and Feingold 2006 Excluding drizzle

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