1 / 16

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

Investigating the impact of aerosols on warm cumulus clouds over land, examining the second aerosol indirect effect and semi-direct effect, through simulations integrating aerosol interactions, radiation, and land surface models.

levib
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related