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The scheme: A short intro Some relevant case results Why a negative feedback?

The scheme: A short intro Some relevant case results Why a negative feedback?. EDMF-DualM results for the CFMIP-GCSS intercomparison case: Impacts of a SST perturbation on updraft transport. Roel Neggers, Pier Siebesma CFMIP-GCSS meeting, UBC Vancouver, 8-12 June 2009.

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The scheme: A short intro Some relevant case results Why a negative feedback?

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  1. The scheme: A short intro Some relevant case results Why a negative feedback? EDMF-DualM results for the CFMIP-GCSS intercomparison case:Impacts of a SST perturbation on updraft transport Roel Neggers, Pier Siebesma CFMIP-GCSS meeting, UBC Vancouver, 8-12 June 2009

  2. The Eddy Diffusivity Mass Flux (EDMF) approach Combining the diffusive and advective models in the parameterization of the turbulent-convective flux: The single updraft limit of EDMF Applicable to well-mixed layers: Implemented in: ECMWF IFS KNMI RACMO etc. Transporting updraft K diffusion AK Aup

  3. Test parcel Flexible area partitioning * Continuous (flexible) updraft area partitioning is applied, as a function of moist convective inhibition at cloud base * A non-transporting extreme test parcel is included to provide information about the variance amongst updrafts The dual updraft limit of EDMF: shallow cumulus Moist updraft Dry updraft K diffusion au1 au2 AK Aup * The single transporting updraft of EDMF is further partitioned into a dry updraft and a moist (condensed) updraft

  4. * Reconstructing a double PDF in conserved variable space Extending EDMF into the statistical modelling of clouds Test parcel Moist updraft PDF: tied to the test parcel and moist parcel x Moist parcel x Diffusive PDF: residual of diagnostic variance budget and moist updraft PDF The Dual Mass flux scheme, Part I: Transport. Neggers et al. (JAS, 2009, vol. 66, 1465-1489) Part II: Clouds. Neggers (JAS, 2009, vol. 66, 1490-1506)

  5. Why two updrafts?  One scheme fits all: 1 updraft 2 updrafts 1 updraft

  6. Submitted version of EDMF-DualM for CFMIP-GCSS Developed for the ECMWF Integrated Forecasting System (IFS) Status: Implementation completed, now in test phase (scores optimalization) K diffusion model: * K-profile method for the well-mixed layer * Explicit flux at mixed-layer top * Ri-diffusion in the cloud layer and at cloud top StCu triggering criterion (single moist updraft mode): * LTS (as in operational IFS) SCM code details: * IFS/RACMO version CY31R1 * Native deep convection scheme switched off: EDMF-DualM scheme does all convective transport

  7. Case results - Cloud fraction S6 S11 S12 S12: Stable equilibrium, single well-mixed layer S11: Stable equilibrium, decoupled S6: After an initial shallow cu period, the scheme tries to ‘go deep’ (updraft rain disturbes mixed layer, causing oscillation)

  8. Where do our simulations sit in the transition? S11 S6 S12 (Albrecht 1996)

  9. Humidity structure S6: fair weather cu (very weak inversion) S11: decoupled S12: well mixed +2K SST: PBL depth increases

  10. Cloud fraction – EDMF contributions S6 S11 S12 +2K SST: Total cloud fraction doesn’t change much (no discrete regime change) LCL unchanged for the cumulus regimes S6 and S11

  11. Cloud condensate – EDMF contributions S6 S11 S12 +2K SST: Condensate on the diffusive PDF increases for S11 and S12 Deeper condensate layer in S6 (carried by upraft PDF)

  12. Cloud-radiative impacts Why?

  13. Surface heat fluxes The surface buoyancy forcing remains more or less unchanged

  14. A bulk mixed-layer interpretation: qsat(SST) and q+ z Boundary fluxes act on the jumps qt+ Top entrainment flux Inversion jump qtPBL Surface evaporation qsat(SST) Surface jump q

  15. +2K SST: qsat(SST) changes much more than qt+

  16. Control +2K SST qt+ Top entrainment flux qtPBL Evaporation qsat(SST) Both jumps increase: The new equilibrium is associated with stronger fluxes at the boundaries

  17. Impacts of increased surface evaporation on the EDMF transporting updrafts Through the updraft initialization scheme, a stronger E leads to larger updraft initial qt excesses updraft fraction variance As a result, the total updraft qt flux increases

  18. The updrafts are efficient in transporting moisture upwards to the top of the PBL This favors capping cloud formation if the inversion remains strong enough

  19. Summary The negative cloud-climate feedback in EDMF-DualM seems related to the increase in surface evaporation Through the updraft initialization scheme, the enhanced evaporation leads to increased updraft initial humidity excesses. This extra humidity is efficiently transported by the updrafts to the PBL top, which favors the buildup of condensate in the capping cloud layer The PBL updrafts do not get more energetic; they just carry more humidity around Remaining question: how and why does the top entrainment flux in the model change? General remark: In studying feedbacks of PBL clouds on climate, the change in free tropospheric humidity is as important as the change in SST Should we try some experiments with a different change in qt+?

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