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Low-Latitude Cloud Feedbacks CPT

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.

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Low-Latitude Cloud Feedbacks CPT

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  1. 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. • 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. Chris Bretherton University of Washington

  2. 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.

  3. 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 K Both 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.

  4. 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.

  5. 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.

  6. 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)

  7. 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.

  8. 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

  9. Some sample diagnostics so far… • Climatologies • Bony-grams (binning vs. 500 mb w)

  10. Control runsAnnual mean W(500 hPa) ERA15 w(500 mb) (mb d-1) NCAR Annual mean Control run GFDL GMAO

  11. ERBE Annual meanControl run -SWCF (W m-2) NCAR GFDL GMAO

  12. NCARSST + 2Bonygram

  13. SST+2Bonygramcomparison NCAR GFDL GMAO

  14. NCARSST+2 vs. 2xCO2 SOM NCAR SST+2 vs. SOM 2xCO2

  15. Summary • CPT is spinning up. • Regular reports at AMWG meetings • Many opportunities for collaboration with other AMWG members.

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