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Simulation of 20 th Century North American Hydroclimate Variability by the Drought Working Group Models: A Quick First Look. Alfredo Ruiz-Barradas Sumant Nigam. University of Maryland. March 8, 2008. Objective.

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Alfredo ruiz barradas sumant nigam

Simulation of 20th Century North American Hydroclimate Variability by the Drought Working Group Models:A Quick First Look

Alfredo Ruiz-Barradas

Sumant Nigam

University of Maryland

March 8, 2008


Objective

Objective

Assess capabilities of the DWG atmospheric models in simulating seasonal and low-frequency summer hydroclimate variability over North America

Models examined:

  • NSIPP (NASA/GSFC; 2.5lon x 2.0lat, 5th AMIP ens mem, 1930-2004)

  • CCM3 (LDEO; T-42 goga_new runs atm, 1st ens mem, 1856-2007)

  • CAM3.5 (NCAR; T-85, one run completed recently, 1871-2006)

  • GFS (NOAA/NCEP; T62L64 version of current CFS, 1950-2001)

  • AM2.1 (NOAA/GFDL; AMIP run data requested/awaited xxxx-yyyy)


Summer precipitation 1950 2000 ci 1 0 mm day clim 2 0 shaded ci 0 3 mm day std 1 5 shaded

JJA CLIM

Monthly STD

Summer Precipitation(1950-2000)CI: 1.0 mm/day (CLIM); >2.0 shadedCI: 0.3 mm/day (STD); >1.5 shaded

US-MEX

CAM3.5

  • Climatology

  • GFS has a dry bias while CCM3 is too wet over central United States

  • CAM3.5 is fairly realistic except for large values on the eastern seaboard

  • All models are dry over the Gulf Coast states, particularly, eastern TX & Louisiana

  • GFS, CCM3, and NSIPP have a wet bias over the Northern Great Plains (western & central Canadian provinces)

  • Standard Deviation

  • CAM3.5, NSIPP, and CCM3 have something resembling the observed STD maximum over central US

GFS

CCM3

NSIPP


Alfredo ruiz barradas sumant nigam

Great Plains Precipitation AnomalySeasonal precipitation anomalies smoothed by 12 applications of 1-2-1 averagingThe smoothed PRECIP index mimics PDSI (correlation of detrended series ~0.85)

Full Century (1901-2002)

Half Century (1950-2000)

Full Century (1901-2002) Correlations

[CRU_P, CCM3_P] =0.36 (0.37 detrend)

[CRU_P, CAM3.5_P]=0.32 (0.33 detrend)

[CRU_P, PDSI] =0.82 (0.84 detrend)

Half Century (1950-2000) Correlations

[CRU_P, CCM3_P] =0.58 (0.50 detrend)

[CRU_P, CAM3.5_P]=0.38 (0.19 detrend)

[CRU_P, GFS_P] =0.28 (0.19 detrend)

[CRU_P, NSIPP_P] =0.27 (0.04 detrend)


Alfredo ruiz barradas sumant nigam

SST Correlations of the Great Plains SummerPRECIP Indices (1950-2000)All-season precipitation indices are first detrended and then smoothed(as before) to generate PDSI proxies. The summertime proxy indices are then correlated with detrended SSTs.

CRUTS2.1

CAM3.5

  • GFS has fairly realistic correlations over the Pacific but not the Atlantic

  • CCM3’s Pacific correlations are too strong, NSIPP’s too weak, and CAM3.5’s somewhere in between

  • Atlantic links are comparable to the Pacific ones in observations but weaker in model simulations (with less accord among them as well)

  • CCM3 and CAM3.5 exhibit Indian Ocean connectivity, with little support from observations

CCM3

GFS

NSIPP


Concluding remarks

Concluding Remarks

This first look, based on evaluation of a SINGLE ensemble member from each center’s AMIP simulations, indicates

  • Significant differences in the summer precipitation climatology and monthly SD distribution

  • Modest skill in simulating low-frequency variability of precipitation (or proxy PDSI): Correlations for the Great Plains region are in the 0.0-0.5 range in the 1950-2000 record

  • SST links of the Great Plains proxy drought index are more focused in the Pacific in model simulations, but not in 1950-2000 observations which show significant connectivity to the Atlantic basin as well

  • The spread in models’ performance makes the CLIVAR Drought Modeling exercise worthwhile


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