# Presentation: 855353

## Toward AM3: GFDL’s Next-Generation Atmospheric General Circulation Model

- Leo Donner, Chris Golaz, Yi Ming, Andrew Wittenberg, Bill Stern, Ming Zhao, Paul Ginoux, Jeff Ploshay,
- S.J. Lin, Charles Seman

- NCEP, 20 May 2008

## New Science Questions for Next-Generation Model

- What are the roles of aerosol-cloud interactions in climate and climate change?
- How will land and ocean carbon cycles interact with climate change?
- To what extent is decadal prediction possible?
- What are the dominant chemistry-climate feedbacks?

## Model Development to Address New Scientific Questions

- Interactive chemistry to link emissions to aerosol composition
- Sub-grid vertical velocity PDFs for convective and stratiform clouds => Supersaturation at ***cloud ***scale for aerosol activation
- Sufficiently realistic tropical land precipitation for land carbon model
- Stratospheric model for chemistry and possible links to troposphere on multi-year time scales

##  Cumulus Convection

- AM2 (IPCC AR4): Relaxed Arakawa-Schubert (Moorthi and Suarez, 1992, *Mon. Wea. Rev.*) with ensemble of deep and shallow plumes characterized by mass fluxes. Precipitation proportional to condensate.
- AM3 Deep: Donner (2001, *J. Clim.*), Wilcox and Donner (2007, *J. Clim.*) with ensemble of deep plumes with mass fluxes and vertical velocities. Simple bulk microphysics. Mesoscale updrafts and downdrafts.
- AM3 Shallow: Bretherton *et al. *(2004, *Mon. Wea. Rev.*) with buoyancy-sorting, entraining-detraining plume and vertical velocity.

## Slide 6

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- ARM

- CRM results from Cris Batstone, CDC; *,*,* from Donner (1993) entrainment PDF

- *Low PW and Rain Rate
- *High PW and Rain Rate
- *High PW and Low Rain Rate

- CRM results provide independent evaluation of entrainment PDF

## Slide 8

## Vertical Velocity Variability in Stratiform Clouds 

- As in AM2, basic stratiform parameterization is Tiedtke (1993, *Mon. Wea. Rev.*)
- Prognostic cloud fraction; linked to bulk microphysics (Rotstayn, 1997, *QJRMS*)
- Uniform vertical velocity (non-convective grid mean) replaced for purposes of droplet activation

## Activation (Ming et al., 2006,JAS)

- Activation (Ming *et al., *2006*,JAS*)

## updraft: activation

- downdraft: evaporation

- ~ 12.9 km

## Large-scale CCN activation

## Large-scale CCN activation

- In AM2, we don’t have             *. *For now, assume a Gaussian distribution.
- Distribution width is related **empirically** to mixing coefficients Kh.
- CCN activation is computed by integration over the distribution using a Gauss-Hermite quadrature.

## ocean

- land

- Deep & Shallow Cu Work Fcn
*w *Estimate

- Shallow Cu Work Fcn
- Sub-grid Statiform Variability
*w *Estimate

- GFDL AM

## Slide 15

## Slide 16

## Slide 17

## Dynamical Core and Boundary Layer

- Finite-volume dy-core (Lin, 2004, *Mon. Wea. Rev.*)
- Cubed-sphere implementation, composed of 6 rectangular domains
- No singularity associated with spherical pole
- PBL, as in AM2, follows Lock *et al. *(2001, *J. Atmos. Sci.*)

## 3 ways to visualize the Cubed Sphere

***3 ways to visualize the Cubed Sphere***

**Precipitation: C360 HiRam-2**

## Mean climate in AM3 generally similar to AM2

## Slide 21

## Slide 22

## Ocean

- Coupling

## Transients are exhibiting strong dependence on details of closure for cumulus parameterization

## Zhang (2002, JGR) closure without low-level lift req’d

- Zhang (2002, *JGR*) closure without low-level lift req’d

## CAPE relaxation closure

## Zhang (2002, JGR) closure with low-level lift req’d

- Zhang (2002, *JGR*) closure with low-level lift req’d

## CAPE 

- CAPE
- relax
- closure

- Ocean
- Coupling

## Zhang

- (2002,
*JGR*)
- closure

- Ocean
- Coupling

## Zhang (2002, JGR)

- Zhang (2002, *JGR*)
- closure w/
- low-level lift req’d

## Zhang

- (2006, *JGR*)
- without
- low-level
- lift req’d

## CAPE

- relaxation
- closure

## CAPE relaxation

- closure

## Zhang (2002, JGR)

- Zhang (2002, *JGR*)
- closure with low-level
- lift req’d

## Zhang (2002, JGR)

- Zhang (2002, *JGR*)
- closure without
- low-level lift req’d

## Development Issues-Injection of Water Vapor into Stratosphere

- Donner (2003, *J. Clim.*) cumulus parameterization allows overshooting towers and stratospheric water vapor injection
- Stratospheric water vapor sensitive to details of cumulus closure

## No Chemistry

- No Link between
- PBL TKE
- and cumulus
- entrainment

## No 

- No
- Chemistry
- Link between
- Cumulus
- Entrainment
- and PBL TKE

## “Indirect Effect” and 20th Century Climate

- AM2 (IPCC AR4) Sulfate+OC+BC forcing ~   -0.4 W m-2      (external mix)
- AM2 Sulfate+OC+BC PD-PI “pseudo-forcing” ~ -0.8 W m-2   (external mix)
- Aerosol-cloud interaction AM with external mix “pseudo-forcing” ~ -3.0 W m-2
- Aerosol-cloud interaction AM with sulfate-hydrophilic carbon internal mix “pseudo-forcing” ~ -2.6 W m-2

## External Mixture

- Internal Mixture-Sulfate and Hydrophilic Carbon

## Excessive Cooling by Indirect Effect (Lohmann et al., 2007, BAMS) ?

- Less direct effect (internal mixing)
- Extent of warm-cloud nucleation by organics
- PI – PD aerosol concentrations
- Warming by ice cloud-aerosol interactions
- Dispersion and other microphysics
- Cloud-scale instabilities limiting increased liquid at high aerosol (Ackerman *et al., *2004, *Nature)*
- Fundamental issues with cloud macrophysics, N.B., ERBE net cloud forcing ~ -20 W m-2

## Summary

- Sub-grid vertical velocity PDFs have been added to GFDL AM for convective and stratiform clouds
- Vertical velocity PDFs used to activate aerosols for liquid clouds to study cloud-aerosol interactions
- Limited changes in mean climate
- Large changes in transients, depending on cumulus closure