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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/ESRL, Boulder,

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Presentation on theme: "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/ESRL, Boulder,"— Presentation transcript:

1 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/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) Cloud Fraction Smoke Optical Depth Menon et al. 2002 Regional Effects: Disruption in precipitation patterns in China: Drought in north; floods in south

4 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…. 3.Consider counteracting effects of the 2 nd aerosol indirect effect and the semi-direct effect

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

6 Incoming solar radiation Incoming solar radiation diminished by aerosol Surface sensible and latent heat fluxes reduced Aerosol scattering & absorption balance S2 Simulations: Aerosol-Cloud Interactions + Aerosol Radiation + Land Surface Model

7 Table 1. Description of Experiments EXPN a, cm -3 aa Aerosol Heating S1-1001000.04No S1-5005000.20No S1-100010000.40No S1-200020000.80No S2-100100Yes S2-500500Yes S2-10001000Yes S2-20002000Yes

8 Simulation of case from Amazon SMOCC experiment Smoke: ω o ~ 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 N a, but constant with height Large Eddy Model (LES ~  x ~100m) –Resolves aerosol and drop sizes + dissolved aerosol –Resolves large eddy dynamics (rams@noaa) –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:  x=  y=100 m;  z=50 m  t = 2 sec

9 Expected: More aerosol  more drops  less rain Rain rate NdNd Unexpected: No clear separation in LWP, cloud fraction, and cloud depth as N a increases. Na=100 LWP CF Z depth Z base S1: No Aerosol Heating 100/cc 500/cc 2000/cc

10 Dynamic variability is much larger than aerosol effects on LWP, CF, cloud depth When raindrops are excluded in the LWP calculation, second aerosol indirect effect is simulated S1: No Aerosol Heating: 5-h averages vs N a Standard deviation

11 rain rate w’w’ S2: With Aerosol-Radiative Coupling LWP CF Z depth Z base

12 S2: With Aerosol-Radiative Coupling: 5-h average vs N a LWP CF N d,int Z depth τ T sfc Rnet Fsen+lat Non-monotonic behavior

13 (S2(2000)-S2(100))/S2(100), % S2: With Aerosol-Radiative Coupling CF N d,int Z depth T sfc Rnet Fsen+lat LWP τ CF T sfc N d,int Rnet Z depth Fsen+lat LWP64% CF58% Z depth 62% T sfc -1.31 o C R net 31% R sw 26% LWP

14 Summary S1 simulations (2nd indirect effect only): Increase in N a leads to  increase in N d, cloud optical depth   decrease in r eff,  reduction in surface precip Aerosol effects on LWP, cloud fraction are small and well within the dynamical variability at a given N a 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. =  eddy /  evap (homogeneous/inhomogeneous) –Evaporation limiters: (C. Jeffery, J. Reisner, JAS 2006) –W. Grabowski (J. Climate 2006) –S. Krueger: EMPM

16 Aerosol Conc., cm -3 Cloud Fraction LWP (domain ave.) LWP (cloud ave.) BOMEX 10 1001000 LWP (cloud ave.) Aerosol Conc., cm -3 5001000 2000 SMOCC Excluding drizzle Note large std deviations! Xue and Feingold 2006Jiang and Feingold 2006


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