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A. Gettelman, X. Liu, H. Morrison, S. Ghan

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Presentation on theme: "A. Gettelman, X. Liu, H. Morrison, S. Ghan"— Presentation transcript:

1 A. Gettelman, X. Liu, H. Morrison, S. Ghan
Latest Microphysics Developments & Ice Microphysics and Indirect effects for CAM4 A. Gettelman, X. Liu, H. Morrison, S. Ghan Gettelman - Ice AMWG 2008

2 Outline Motivation CAM Microphysics Status
New Ice Nucleation Description Basic Results Status and future plans Gettelman - Ice

3 MG Microphysics Status
Code Running in Coupled Model Produces ‘reasonable’ climate Microphysics look good ENSO good in coupled system Too much sea ice in coupled run See R. Neale talk Indirect effects diagnosed New Optics being built for RRTM (Conley talk) Gettelman - Ice

4 MG Coupled Run: ENSO ENSO Gettelman - Ice

5 MG Coupled Run: Cloud Forcing
Cloud Forcing v. CERES Obs Longwave Shortwave Gettelman - Ice

6 MG Coupled Run: NH Sea Ice
Sea Ice too thick/extensive Cloud Forcing v. Obs ENSO Sea Ice concentration Gettelman - Ice

7 Aerosol Indirect Effects (AIE)
1750 Aerosols – 2000 Aerosols Gettelman - Ice

8 AIE Key Findings Model produces reasonable effects compared to observations Not a strong global constraint Aerosol Indirect Effects are ~1-2 W/m2 with direct effects of W/m2 Depends on Pre-industrial emissions AIE numbers are only weakly dependent (10%) on whether aerosol mass is prescribed or prognostic Oxidant levels also seem to matter for AIE Changes AIE by 20-30% Gettelman - Ice

9 AIE Next Steps Waiting on: Near final Configuration Options (BAM):
RRTM radiation interface: more flexible New Radiation and New Cloud Optics Final Aerosol Code (BAM/Modal, scavenging) Near final Configuration PBL, Macrophysics Options (BAM): Add aerosol species (Biogenic), Change size distributions Minimum Droplet Number Modify Microphysics (Park) Gettelman - Ice 9

10 Ice Processes: Motivation
Cirrus and ice nucleation uncertain Supersaturation over ice common CAM does not permit it Cirrus radiative forcing important Cirrus affects stratospheric H2O Better description allows process level testing with observations Gettelman - Ice

11 Ice Microphysics in MG Micro
New microphysics has limited ice nucelation Ni=f(T) following Cooper (1986) Ni=const below -35C Goal Explore ice processes & sensitivity Bergeron Hallet Mossop ice multiplication Parameterize ice nucleation Allow supersaturation Gettelman - Ice

12 Ice Nucleation Add ice nucleation treatment of Liu & Penner 2005, following Liu et al 2007 Homogenous and Heterogenous immersion nucleation Relax Zhang et al closure for ice to allow supersaturation (C-E w.r.t. liquid) Based on parameterizing nucleation results from a detailed parcel model Pro: detailed model Con: lots of fixed numbers Gettelman - Ice

13 Liu et al 2007: in CAM3.0 LIU CAM MLS RHi Gettelman - Ice AMWG 2008

14 Allowing Supersaturation
Goal: adjust closure for supersaturation Principle: Separate ice and liquid cloud fractions Bulk condensation only w.r.t water (liquid). Ice formation requires Existing ice (vapor deposition onto ice) Liu et al 2007 parameterized ice nucleation Process rates & sedimentation govern ice Ice cloud fraction closed using IWC Empirical fit to mid-lat cirrus observations (Wang & Sassen 2002, JAS) Gettelman - Ice

15 Key Results: Current Version
Reasonable TOA distributions Reduction of High Latitude Cloud Especially mid-high clouds Increased UT humidity SW & LW Cloud Forcing 3W/m2 less 30% lower IWP Gettelman - Ice

16 Cloud Fraction New Ice Base Case Gettelman - Ice

17 Downward JJA SW New Ice - Base Case (avg +8W/m2) Gettelman - Ice 17

18 Ice Cloud Indirect Effects
Sensitivity Experiments Increase ice nuclei by factor of 10, 100 (global) Results: x10: IWP + 25%, tropical CF ±8-10W/m2 x100: IWP +100%, tropical CF ±16-20W/m2 X100: regional decreases in precipitation rate Need to explore sensitivity to aerosols Vertical distribution of aerosols Gettelman - Ice AMWG 2008

19 Change in Ice Number High IN (x10) Std IN Gettelman - Ice

20 Change in Precip Base High IN-Base (x100) Gettelman - Ice

21 Status and Plans Finalize and Harmonize code Write up description
Rewriting mixed phase code now Perhaps separate process rates by individual cloud fractions Write up description Target for end of summer Port to latest version of trunk Harmonize macrophysics and closure with Park/Rasch work Propose for CAM4 Gettelman - Ice

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