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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 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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  1. 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. 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)

  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…. • Consider counteracting effects of the 2nd aerosol • indirect effect andthesemi-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

  8. Large Eddy Model (LES ~ Dx ~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: 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

  9. 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

  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 rain rate w’w’ LWP CF Zdepth Zbase

  12. S2: With Aerosol-Radiative Coupling: 5-h average vs Na Non-monotonicbehavior LWP τ CF Tsfc Rnet Nd,int Fsen+lat Zdepth

  13. 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

  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 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

  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. 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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