Chien Wang Massachusetts Institute of Technology

1. A Close Look at the Aerosol-Cloud Interaction in Tropical Deep Convection Chien Wang Massachusetts Institute of Technology

2. Why Does Aerosol Matter to Clouds Saturation requirement to form new particles through homogeneous homo-molecular nucleation in the atmosphere: S > 3.5 Note: Typically, in-cloud S < 1.01 • Lowering the required S • Mixed vapor of 2 (binary) or 3 (ternary) species – hetero-molecular homogeneous nucleation: mainly aerosol nucleation • Existing surface – heterogeneous nucleation on insoluble (with small contact angle) or soluble aerosols (ion factor as well)

3. H2O(g) IN Ice crystal Heterogeneous deposition cloud droplet Condensation-freezing Immerse Contact Heterogeneous nucleation of droplets and ice crystals Water droplet nucleation: Hygroscopic aerosols acting as nuclei. Note that it is existing aerosol NOT molecular collision efficiency that determines the nucleation rate Four ice nucleation modes:

4. water vapor CCN IN cloud droplet ice crystal snowflake rain drop graupel hailstone Aerosol and Cloud microphysical processes nucleation condensation/ evaporation riming/ freezing melting collection/ coagulation/ conversion precipitation

5. Scavenging: nucleation & impaction Production: evaporation (recycling)

6. Aerosol-Cloud Interaction and Its Impact on Radiation Radiation Clouds Aerosol Indirect Effect Aerosols Cloud Indirect Effect(?!)

7. 1b Aerosols: N of CCN, IN or Multiple mode multi-moment model Radiation: -four-stream including ice cloud 1a 2 Cloud Properties: winds, T, P, Qv, lightning 7 Hydrometeors (Q & N) 40+ microphysical conversions 3b 3a 2 6b 6a 1 Chemistry: Species: 25g+16c,r+7i Reactions: 35g + 21eq + 32aq + 7h Environment: large-scale forcings and input fluxes 5 4a 4b A Three-Dimensional Cloud-Resolving Model References: Wang and Chang, 1993; Wang et al., 1995; Wang and Prinn, 2000; Wang 2005; Ekman et al., 2004; 2006

8. Research Issues • How does tropical deep convection respond to the 1) increase of CCN concentration; 2) change of aerosol chemical composition; and 3) modified aerosol properties at different altitudes? • What are the chemical and physical consequences of aerosol effect on convection? Model and Simulations • CEPEX March 8 soundings; 200  100  50 grids with 2  2  0.5 km resolution; 4 hours simulation; supporting runs with 1.0 – 0.25 km horizontal and 250 – 50 m vertical resolutions. • Prognostic CCN (hygroscopic, Aitken or accumulation mode) and IN (water-insoluble); activation of CCN: N = CSk • No “external sources” • 90 runs with 30 initial concentrations of CCN, CCN0 from 100 to 5500/cc with a increment of 200/cc; also 50 and 6000/cc; different autoconversion. A 3-D CRM Study (Wang 2005a&b; JGR)

9. The Response of Cloud Particle Number Concentrations to the Increase of Initial CCN Concentration Note: All runs use the same initial IN profile.

10. Effective Radius of Hydrometeors vs. Initial CCN Concentration

11. Total Precipitation vs. Initial CCN Concentration Maximum Coverage of Cloud vs. Initial CCN Concentration

12. Budget of Water: • Supply and consumption of water vapor increases with CCN0; • precipitation efficiency varies little with CCN0

13. 60 min. 90 min. 100/cc 100/cc 60 min. 90 min. 700/cc 700/cc 60 min. 90 min. 3100/cc 3100/cc Surfaces of Updraft  5m/s (Brown) or Downdraft  2 m/s (Blue)

14. Budget of rain: The dominant role of Ice-phase microphysics Correlations of microphysical conversions and precipitation: The importance of riming

15. Radiative Effects Domain-Mean Cloud Shortwave Forcing vs. Initial CCN Concentration Cloud-Area-Mean Cloud Shortwave Forcing vs. Initial CCN Concentration

16. Water vapor redistribution by the modeled convection

17. Efficiency of vertical transport of gaseous species from the lower to upper troposphere

18. Scavenging efficiency of a fast soluble gas Y(Cohan et al., 1999): Here, the dilution factor of a species X: CO is used as the reference species in the modeled case with β = 82-88%.

19. Influence of the Modeled Cloud on Gaseous Chemistry: Total condensed water (0.1 g/kg surfaces in yellow color) and NO2(g)/NO(g) ratio (2.0 surfaces in blue color), all from CCN0 = 100/cm3 run

20. Redistribution of OH Radicals

21. Influence of the Modeled Cloud on Heterogeneous ChemistryO3(s)  2 pptm (blue), CH3OOH(s)  2 pptm (green), and HNO3(s)  1 pptm (brown); all from CCN0=100/cm3 run.

22. Likely changing color for continental cases Summary Radiative forcing UT reactions LT photolysis Freezing Level & Q Qi Cld area Subl. Tracers  Precip QI W Warm QR Total QR Soluble  LWC CCN CDNC CD re

23. Important Points: • Many properties of modeled tropical deep convection DOES NOT respond MONOTONICALLY to the change in CCN0. • Aerosol effect could be more substantial in clean environment (low CCN0 cases). • Dynamics AND microphysics are equally important in determining the response of convective cloud to CCN0. • Ice-phase microphysics plays an important role in precipitation formation and development of modeled cloud. • Some conclusions drawn from this study perhaps can be only applied to the specific cloud type.

24. Aitken mode (6nm<d<30nm) 20 Altitude (km) 10 0 50 250 Horizontal distance (km) 100.0 177.5 316.2 562.5 1000.0 Concentration (100 cm-3) Acc. mode aerosol (d>30nm) 20 Altitude (km) 10 0 50 250 Horizontal distance (km) 0.1 1.0 10.0 100.0 1000.0 Concentration (cm-3) Importance of Including Prognostic Aerosol Properties in the Model: Results of a Size-Resolving Aerosol Model (Ekman et al., 2004) Note: Observed. max. value (>7nm) in anvil: 2.5·104 Modeled max. value (>6nm) in anvil: 5.5 ·104