1. Aerosol Effects on Rainfall Patterns Yi Ming Geophysical Fluid Dynamics Laboratory Princeton, New Jersey

2. Most anthropogenic aerosols are in the NH mid-latitudes and tropics MODIS annual-mean aerosol optical depth (AOD)

3. Will the response be confined locally? EQ30N60N90N Forcing EQ30N60N90N Response Mid-latitudes Large f Large MTG balanced by thermal wind EQ30N60N90N Forcing EQ30N60N90N Response Tropics Small f Upper-level wind constrained by angular momentum conservation Cannot sustain large meridional temp. gradient (MTG) or

4. A rough sketch of a paradigm EQ30N60N90N Forcing EQ30N60N90N Response Stationary Rossby wave Eddies Local vs. non-local effects (validity? Ways to distinguish and quantify them?) Zonal-mean vs. zonal asymmetry Surface albedo feedback

5. Design of mixed-layer experiments Control AERO GAS BOTH +2.76 K -1.90 K +0.55 K -0.62 K (direct effect only) Sign of nonlinearity: BOTH (0.55 K) < AERO + GAS (0.86 K) Aerosol direct + indirect effects -2.1 W m -2 Ming and Ramaswamy (2009)

6. Zonal-mean changes

7. Zonal-mean responses to aerosols and greenhouse gases Surface temperature (K)Precipitation (mm day -1 ) AERO GAS BOTH SUM AERO GAS BOTH SUM Dipole pattern of tropical rainfall change; Role of the thermodynamic control (C-C).

8. Zonal-mean (Hadley) circulation change Meridional stream function (10 9 kg s -1 ) (clockwise circulation is positive) Weaker ascent Stronger ascent

9. How does the Tropical heat engine response to aerosol forcing, and why? From the viewpoint of atmospheric energy transport, the response gives rise to a cross-equatorial heat flux from SH to NH. GAS AERO BOTH Picking up energy Dumping energy Even the North Pole kicks in. Radiative cooling

10. Zonal-mean change in atmospheric energy transport (PW) Assumptions: No change in flow Small AEROGAS Total Dry Static Latent Dry Static LatentEst. latent Total

11. Zonally asymmetric changes (tropics)

12. Aerosol-induced changes in tropical circulation The thermodynamic argument (TA) (Held and Soden, 2006) For the entire globe (or the Tropics in isolation), Precip. Mixing ratio of water vapor in BL Convective mass flux Clausius-Clapeyron (CC) scaling

13. If one applies TA to greenhouse gases (GHG)- induced warming, 1 ~ 2 % K -1 -5 ~ -6 % K -1 Does this apply to aerosol cooling? 3.8 % K -1 -3.0 % K -1 The mixed-layer GCM simulations suggest Stronger Tropical mean circulation Allen & Ingram (2002) Held and Soden (2006) Stephens & Ellis (2008) ΔΔ ΔΔ

14. Number-crunching time! NH Zonal- mean NH Zonally- assy. SH Zonal- mean SH Zonally- assy. Aerosols -169.33016 Gases -6-18-7-30 Both -24-2238-9 Percentage differences in variance of M c (%) TA works well for GAS, but only partially for AERO. The zonal-mean response is dominated by AERO.

15. A drying trend over central-northern India during the second half of the 20 th century CRU IMR PREC/L UDEL JJAS rainfall (mm day -1 50 years -1 )

16. AR5 historical emissions (Tg/yr) of SO 2 Larmarque et al. (2010) South Asia – A region under global and regional changes

17. How aerosols and greenhouse gases may affect the South Asian summer monsoon? Aerosols Atmospheric heating enhances pre-monsoon rainfall (Lau and Kim, 2006); Surface cooling and reduced Indian Ocean SST gradient weaken monsoon (Ramanathan et al., 2005; Chung and Ramanathan, 2006). Greenhouse gases Slower tropical (especially Walker) circulation (Vecchi et al., 2006); Nonetheless, increased rainfall due to higher moisture content (Ueda et al., 2006).

18. Model physics and chemistry in the GFDL CM3 Model (used for AR5) Aerosol-Liquid Cloud Interactions A prognostic scheme of cloud droplet number concentration (Ming et al., 2007) with an explicit treatment of aerosol activation at cloud base (Ming et al., 2006). Convection Parameterization Move from the relaxed Arakawa-Schubert (RAS) in CM2 to the Donner deep convection scheme (Donner, 1993) and the University of Washington (UW) shallow convection scheme (Bretherton et al., 2003). By providing in-plume updraft velocity, the latter two are ideal for implementing aerosol/cloud microphysics. Online aerosol transport Tropospheric and stratospheric chemistry

19. Attribution of the recent trend of the South Asian summer monsoon using CM3 historical simulations Linear trends of average JJAS rainfall over central-northern Indian (mm day -1 ) GG All forcing CRU AERO

20. Student’s t-test Are the simulated trends statistically significant? Natural variation Ensemble-mean Ensemble member JJAS rainfall (mm day -1 50 years -1 )

21. Spatial pattern of linear trends of JJAS rainfall (mm day -1 50 years -1 ) CRU GG All forcing AERO

22. Spatial pattern of linear trends of vertical velocity (hPa day -1 50 years -1 ) All forcing AERO GG Ascent defined as negative

23. How Hadley and Walker circulations respond to green-house gases and aerosols? Climatology GG All forcing AERO

24. Zonally asymmetric changes (boreal winter mid-latitudes)

25. Change in surface temp. (K) RFP (W m -2 ) Different spatial structures over N. Pac. & N. Atl. Not obvious from “forcing”

26. Change in 300-hPa u (m s -1 ) Δ(T s ) (K) Consistent with T s

27. Change in circulation SLP (hPa) 500-hPa Z (10 m) 300-hPa eddy stream function (ESF) (10 6 m 2 s -1 )

28. Lau (1996) El Nino-like? 7 Warm Trop. Pac. minus 7 cold Trop. Pac. 500-hPa Z (10 m) ΔT s (K)

29. Change in precip. (mm day -1 ) EX TR-WTR-E

30. Setup of idealized model experiments Dry hydrostatic spectral dynamical core; T42 and 20 sigma-layers; No topography; Zonal-mean winds and temp. are nudged towards GCM simulations; Forced with GCM-simulated diabatic heating.

31. Change in 300-hPa ESF (10 6 m 2 s -1 ) Idealized model (TR-W) Idealized model (TR-E) Idealized model (TR) Trop. heating NW-SE tilt Extratropical heating NE-SW tilt

32. Conclusions Zonal-mean changes In the deep tropics, drier NH & wetter SH  In the subtropics & extratropics, the rich-get-poorer With the purpose of re-establishing interhemispheric energy balance; Zonally asymmetric changes In the tropics, Hadley circulation sensitive to aerosols, Walker circulation controlled by the tropical- mean ΔT s ; In the wintertime extratropics, the importance of the stationary Rossby wave excited by the tropical rainfall change.

33. Zonal-mean change in θ (K) AEROGASBOTHAERO+GA S -0.62.11.11.5 Δθ z (K) (10-35°N) Lower troposphere static stability

34. Zonal-mean change in u (m s -1 ) AEROGASBOTHAERO+GA S 1.2-0.31.50.9 Δu z (K) (10-35°N) Lower troposphere vertical wind shear

35. Zonal-mean change in tropopause height (hPa) 2 K km -1 Latitude Height Instability – source of nonlinearity? BOTH AER O+GA S Phillips criterion