1. Application of Ice Microphysics to CAM Xiaohong Liu, S. J. Ghan (Pacific Northwest National Laboratory) M. Wang, J. E. Penner (University of Michigan) National Science Foundation

2. Motivation  Anthropogenic aerosol effects on cirrus cloud? Homogeneous ice nucleation of SO4 Heterogeneous ice nucleation of IN (soot & dust) Contact freezing of cloud droplets by IN  Processes in cirrus and mixed-phase clouds depend on ice number Vapor deposition, Bergeron-Findeison process Gravitational settling of crystals depends on sizes Radiation depends on effective radius

3. Prognostic ice crystal number in CAM R(Ni): advection, turbulence, and convective transport (detainment at the top of convective cloud) J nuc : nucleation of ice crystals J sec : secondary production of ice crystals Q agg : aggregation of ice crystals to form snow Q saci : accretion of ice crystals by snow Q mlt : melting of ice crystals

4. Detrainment from convective clouds (T<-35 C) Homogeneous nucleation of sulfate and heterogeneous immersion nucleation on soot in cirrus clouds with T<-35C (Liu & Penner, 2005): ice number depends on temperature, updraft velocity, sulfate and soot number, considering the competition between the two mechanisms.

5. Contact freezing of cloud droplets in mixed-phase clouds (-35 to 0 C) based on Young (1974), and assume contact IN to be mineral dust (Brownian coagulation) Deposition/condensation ice nucleation in mixed-phase clouds (-35 to 0 C) based on Meyers et al. (1992) Secondary ice production between -3 and -8 C (J secb ) based on Cotton et al. (1986) for Hallet-Mossop mutiplication Ice crystal sublimation based on homogeneous mixing: ice crystals sublimate completely only when the cloud dissipates

6. Ice supersaturation Hybrid RH in standard CAM: RHw (T > 0 C); RHi (T < -20 C); RHw & RHi (-20 < T < 0 C); Condensation and evaporation (C-E) scheme removes ice supersaturation (assume RHi=100% in ice cloud) Compare with MOZAIC data (year 1997): statistics at every three hours in cloud-free CAM grid cells (2.5x2) with flight tracks

7. CAM ModifiedCAM Standard C-E used only for liquid water, diagnosed from RHw and liquid cloud fraction (based on RHw); get rid of f ice (T) D v2i : vapor deposition on ice crystals in grid cells (Rotstayn et al., 2000), in proportion to (S i -1) Cloud fraction based on RHi is used in radiation r eff of ice crystals diagnosed from mass & number: number effects on radiation and ice gravitational settling

8. January Ice number Ice mass RHwT

9. Ice number balance (January) Nucleation (hf/immersion/deposition) Detrainment Contact freezing Secondary production

10. PrecipitationEvaporation

11. Effective radius of ice crystals (January) Modified CAM Standard CAM

12. Compare with MOZAIC data (year 1997): statistics at every three hours in cloud-free CAM grid cells (2.5x2) with flight tracks RHi from Modified CAM Compared with MOZAIC Data

13. Annual Mean Ice Water Content Modified CAM Standard CAM Aura MLS Pressure (hPa)

14. Ice Water Content at 316 hPa (January) Modified CAM Standard CAM Aura MLS

15. Zonal Mean Shortwave Cloud Forcing

16. Zonal Mean Longwave Cloud Forcing

17. ControlModifiedOBS LWP, g m -2 121.5144.1 IWP, g m -2 15.621.7 SWCF, W m -2 -54.6-59.2-54.2 (ERBE) LWCF, W m -2 30.632.230.4 (ERBE) FLNTC, W m -2 264.4262.9265.0 (ERBE) CLDTOT, %58.678.167.3 (ISCCP) CLDHGH, %32.257.121.8/33.6 (ISCCP/SAGE) Global Annual Means

18. Summary CAM modified to allow supersaturation; add water vapor deposition on ice to replace C-E for ice clouds; get rid of f(T); Water vapor increased significantly in the upper troposphere. However, still not too much at 200-500 hPa compared to MOZAIC data; Ice water content improved comparing with Aura MLS data; Ice number concentration is predicted with the dominant sources being detainment from convection and in situ ice nucleation balanced by precipitation and evaporation losses; Work needed: reduce LWP and IWP to improve SWCF.

19. Zonal Mean Water Vapor (January) Standard CAM Relative difference (%) between modified and standard CAM