low-latitude cloud feedbacks cpt
DESCRIPTION
Low-Latitude Cloud Feedbacks CPT. US CLIVAR activity sponsored by NSF and NOAA at ~$1M/yr, along with 2 ocean ‘climate process teams.’ 1 Oct. 2003-30 Sept. 2006. - PowerPoint PPT PresentationTRANSCRIPT
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Low-Latitude Cloud Feedbacks CPT
Chris Bretherton
University of Washington
• US CLIVAR activity sponsored by NSF and NOAAat ~$1M/yr, along with 2 ocean ‘climate process teams.’
• 1 Oct. 2003-30 Sept. 2006.• A pilot project – can a multi-institution, multi-model
effort integrating observationalists, diagnosticians, process-scale and large-scale modelers improve climate models faster?
• NCAR, GFDL, GMAO(NASA) models.
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Low-latitude cloud feedback CPT
Goal: Reduce uncertainty in low-latitude cloud feedbacks on climate sensitivity.
• In-depth diagnosis of cloud feedbacks in models.
• Implement ‘best-practices’ parameterizations honed via single-column methods.
• Start with boundary-layer clouds, move to deep convective systems.
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The time is ripe…
• Cloud feedbacks on climate sensitivity are a long-standing problem.
• ~1 yr ago, CAM2 climate sensitivity was 1.5 K, AM2.10 was ~5 K for
2xCO2
Subtropical PBL cloud feedbacks responsible for much of this difference.Now, CAM3 climate sensitivity is ~2.9 K
AM2.12 is ~2.6 KBoth models have evolved, but this demands clear explanation...can we prove newer is better?
• Over short run, diagnostic findings may help IPCC AR4.Over longer run, IPCC model finalization allows more thoughtful parameterization development.
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CPT organization
• Core group (C. Bretherton, M. Khairoutdinov, C. Lappen, B. Mapes, J. Norris, R. Pincus, B. Stevens, K. Xu, M. Zhang): Parameterization, diagnosis, observational hooks.
• Advisory group (B. Albrecht, A. Betts, C. Fairall, T. del Genio, S. Ghan, G. McFarquhar, R. Mechoso, H. Pan, D. Randall, D. Raymond, J. Teixeira, R. Weller)
• NCAR–Kiehl, Rasch, Collins; Liaison: hiring underway GFDL-Klein (thru 3/04), Held, Donner; Liaison: Zhao GMAO-Bacmeister, Suarez.• Not an exclusive effort - active coordination with CCSM
AMWG (one reason for this talk!), GCSS, European, Canadian efforts, CFMIP.
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Strategy• Hypothesis-driven diagnoses of biases, cloud
feedbacks• Single-column methods and intercomparison .• PI-specific efforts
- New PBL, ShCu, microphysical parameterizations- Superparameterization cloud response to climate
change (e.g. specified dSST)- Use of long-term cloud datasets and new satellite
obs.- CRM/LES simulations of cloud feedbacks to specified
greenhouse-type large-scale forcing changes.- Novel model diagnostics.
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CPT Meeting 20-21 Nov, 2003 at NCAR
1. Focus teams for process diagnosis and new physics:- Cloud topped boundary layers (Bretherton)- Deep tropical convective systems (Mapes)- Representing subgrid heterogeneity in microphysics
and radiation (Pincus)
2. Multimodel simulation archive
3. Column output locations
4. Group projects- Rad.-conv. equilibrium intercomparison- Intercomp. of CTBL response to different climate
forcing components (e.g. changed free-tropospheric subsidence and humidity, LTS)
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Cloud response mechanisms to climate change
• Deep convective clouds
- Freezing level increase
- Anvil top temperature feedbacks (Hartmann)
- LWCF vs. SWCF – is cancellation universal?• PBL clouds:
- Stronger trade inversion due to stabler moist adiabat
- More emissive free troposphere.
- Subsidence changes.
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Simulation archive
Monthly climatology history files from recent versions of models suitable for climate sensitivity analysis.
GFDL NCAR GMAO AM2.12 (59e) CAM3(rio33) NSIPP
ctrl y y y
dSST +2/[-2] y y y
dSST_CMIP y y y
SOM (1x,2x CO2) y y
Single column model y y
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Some sample diagnostics so far…
• Climatologies• Bony-grams (binning vs. 500 mb
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Control runsAnnual mean(500 hPa)
ERA15
NCAR
GFDL
Annual meanControl run
500 mb)(mb d-1)
GMAO
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Annual meanControl run
-SWCF(W m-2)
ERBE
NCAR
GFDL
GMAO
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NCARSST + 2
Bonygram
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SST+2Bonygram
comparison
NCAR
GFDL
GMAO
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NCARSST+2
vs. 2xCO2 SOM NCAR
SST+2vs.
SOM 2xCO2
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Summary
• CPT is spinning up.• Regular reports at AMWG meetings • Many opportunities for collaboration with other
AMWG members.