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Dynamical Contribution to the Extratropical Precipitation Extremes

Dynamical Contribution to the Extratropical Precipitation Extremes. JIAN LU, L. RUBY LEUNG, QING YANG G. Chen, W. COLLINS, FUYU LI, J. HOU AND X. FENG. Atmospheric Science and Global Change Division. Pacific Northwest National Laboratory, US Department of Energy. Background and Motivation.

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Dynamical Contribution to the Extratropical Precipitation Extremes

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  1. Dynamical Contribution to the Extratropical Precipitation Extremes JIAN LU, L. RUBY LEUNG, QING YANG G. Chen, W. COLLINS, FUYU LI, J. HOU AND X. FENG Atmospheric Science and Global Change Division Pacific Northwest National Laboratory, US Department of Energy

  2. Background and Motivation • Circulation shifts/expands under global warming • Dynamical impacts on extratropical hydrological cycle • Possible convergence on the extratropical climate and extremes Increase of of 50-yr return level under scenario RCP8.5 JJA DJF 2060-2099 2020-2059 Toreti et al. (2013)

  3. Model and data Model: NCAR CAM3, Spectral dycore, Aquaplanet configuration. Simulations: T42, T85, T170, T340; 5 min time step, 26 levels for each resolution: control, 3K, sstgra (only daily data at selected levels are available) Li et al. (2011)

  4. Convergence of Precip PDF log10(PDF3K/PDFcntr), T85 log10(PDF3K/PDFcntr), T42 1/1000 events log10(PDF3K/PDFcntr), T340 log10(PDF3K/PDFcntr), T170

  5. Interpretation of PDF change + = Shift in y direction Shift in p direction 7

  6. CC rate Minimization of frac variance (α) (in units of jet shift)

  7. (PDF3K-PDFcntr)/PDFcntr (PDFshift-PDFcntr)/PDFcntr [C] [A] pdf diff due to 3K, normalized by climpdf pdf diff due to the plwrd shift (45%) Decomposition of precippdf into dyn and thermodyn shifts C+D (PDFth-PDFcntr)/PDFcntr (90%) [B] [D] Pdf diff due to thermodyn (80%)

  8. Alternative: scaling of the percentiles “precip efficiency” dynamical column moisture 10

  9. Convergence of effective diffusivity Sign of dynamical convergence Keff/k k−1 At large Pe (>200), Keff/k  k-1 Keff  const. (Marshall et al. 2006)

  10. Conclusions • Sign of convergence emerges for certain range of extremes, at least within the modeling framework. • Circulation change exerts profound influence on the change of precip extremes by shifting the pdfpoleward. • The poleward shift of the precippdf can be accounted for by the poleward shift of the zonal mean zonal wind and the associated transients. • The sub-CC contribution from the thermodynamics hints at a reduction of “precipitation efficiency”. • Sign of dynamical convergence at resolutions > T170: effective diffusivity becomes independent of numerical diffusion coefficient.

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