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By Alfredo Ruiz-Barradas and Sumant Nigam Department of Meteorology

Interannual Variability of North American Summer Precipitation in NASA/NSIPP and NCAR/CAM2.0 AMIP Simulations. By Alfredo Ruiz-Barradas and Sumant Nigam Department of Meteorology University of Maryland September 3, 2003. Goal.

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By Alfredo Ruiz-Barradas and Sumant Nigam Department of Meteorology

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  1. Interannual Variability of North American Summer Precipitation in NASA/NSIPP and NCAR/CAM2.0 AMIP Simulations By Alfredo Ruiz-Barradas and Sumant Nigam Department of Meteorology University of Maryland September 3, 2003

  2. Goal • To assess interannual variability of precipitation over North America in AMIP-like runs of CAM2.0 and NSIPP models during summer months (June, July, August).

  3. Data • Precipitation: • Retrospective US and Mexico analysis. • Hulme (University of East Anglia) data set. • Xie/Arkin precipitation data set. • SST from Hadley Center. • NCAR/NCEP Reanalysis. • AMIP simulation (ensemble no. 5) from the NSIPP model. • AMIP simulation (case newsstamip06) from the CAM model.

  4. Method • Reanalysis and simulations extrapolated to a 5°2.5 grid on 17 pressure levels. • Monthly climatology for the 1950-1998 period. • Monthly anomalies wrt 1950-1998 climatology. • JJA is the mean of June, July, August. • Assessment through: • Standard Deviation • Precipitation Index • Multivariate analysis

  5. ~12 years peak ~5 years peak ~5 years peak

  6. Remarks • Large precipitation variability in observations and simulations over central US. Although it is shifted in simulations. • Great Plains precipitation indices from simulations do not correlate with the observed index. • SST regressions on the Great Plains index suggest linkage with Pacific midlatitude variability. CAM however emphasizes the tropical influence.

  7. Remarks • Multivariate analysis indicates: • Great Plains precipitation variability is the main mode of summer variability in observations; • This is however not the case in both model simulations; • Wet/dry events are cold/warm events in both observed and simulated summers.

  8. Remarks • PC regressions on moisture fluxes and geopotential heights indicate: • Observed precipitation variability is linked to a coherent, barotropic circulation that enhances/diminishes southerly stationary moisture flux from the Gulf of Mexico; • Model simulated variability does not have such circulation linkages.

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