1. Modeling Mesoscale Cellular Structures and Drizzle in Marine Stratocumulus Wang and Feingold, JAS, 2009 Part I,II Wang et al, ACP, 2010 Feingold et al, Nature, 2010

2. Take home points The local circulation (precipitation gradient) transports moisture. -> propagate open cells A local circulation induced by ship plume: Open cells: rain rate ↓ ↑ albedo ↑, cloud fraction↑, LWP ↑ Closed cells: → CCN perturbation: cannot close open cells without dynamic support: cloud fraction↑, LWP ↓

3. Scientific Objectives The formation and evolution of open and closed cellular structures: separated ones, coexisted case, ship plume (in models) Aerosol–cloud–precipitation interactions and dynamical feedbacks (meso-scale circulations) How open cells interact with close cells How open cells response to a ship plume

4. Numerical model and experiments Advanced Research WRF model with a high-order monotonic advection scheme and a double-moment bulk microphysical scheme Initial conditions from DYCOMS II Domain: 180 km X 60km X 1.5km, Δx=300m; Δz=30m; 12 hours Radiation Schemes Ship plume heat and water vapor in ship exhausts are ignored

5. cloud albedo, cloud-base rain rate (Rzb), and column-average CCN Nc Rzb decreases smoothly Nc are diluted interactions Interactions Nc increases but albedo decreases Rain stops Nc and albedo increases,Rzb doesn’t decrease

6. Cloud, Drizzle, u’-w’ vectors Nc+Nd qv’ t=9h (i) clouds -> thicker(dynamical support and moisture convergence) (ii) high CCN are diluted by the lower ambient concentrations. Newly formed precipitation perturbs the old circulation (0<x<15km) Near-surface outflow (below-cloud drizzle in the downdrafts) and in- cloud inflow

7. y-direction average u’ winds and Rzb Outflow Inflow Correlate well with precipitating walls Inflow The contrast in precipitation is responsible for the circulation observed near the boundary The greater the precipitation contrast, the stronger the circulation. propagation of open-cell walls

9. Impact of ship emissions on cellular structures Cannot be simply explained by aerosol suppre. of precip. A local circulation formed Open cells It takes 5 h for the ship to traverse the 180 km

10. Closed cells Small change in cloud albedo Non-precipitating Open-cell regions are more favorable for the formation of ship tracks

11. Near-surface inbound & in-cloud outbound v relative to ship-track center. Nsc x-axis average LWP and Rzb ↑along the ship track but reduced near the lateral boundaries (the local circulation)

12. Decoupled more rapid dilution of ship plumes and cloud scavenging of CCN Well mixed and constrained

13. Discussion Impact of radiation: CONT, RRTM, FIXR(fixed), NOR(no radiation) Conclusion: - The formation of the observed circulations is not driven by the contrast in radiation between clear and cloudy regions, but indirectly closely related. - Rr ↔ LWP Rr, LWP, U’

14. Conceptual diagrams This local mesoscale circulation can either dissipate open cells or break up closed cells Sharon et al. (2006) The driving force is from both sides of the track and therefore the stronger moisture convergence and CCN divergence facilitate a faster formation of precipitation in the track.

15. Do clouds contaminated by ship plumes lose or gain liquid water?

16. Can an influx of CCN close open cells? Even a dramatic aerosol perturbation does not close open cells but instead dissipate those.

18. Solar heating, BL q and t perturbations, surface heat and moisture fluxes, and large-scale vertical motion What about diurnal cycle and meteorological perturbations?

19. Diurnal cycle and large scale subsidence are not sufficient for the formation and sustention of Cellular structures. Cloud responses to a CCN reducing (150 to 30 m g -1 ) faster but weaker than to q and t perturbations (+0.9 g kg −1 ; −1 K).