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Attribution of observed climate trends over the United States during 1950-2000

Attribution of observed climate trends over the United States during 1950-2000. Hailan Wang 12 , Siegfried Schubert 1 , Max Suarez 1 , Junye Chen 13 , Martin Hoerling 4 , Arun Kumar 5, Philip Pegion 16 1 NASA/GMAO; 2 UMBC/GEST; 3 UMD/ESSIC; 4 NOAA/ESRL; 5 NOAA/NCEP/CPC; 6 SAIC.

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Attribution of observed climate trends over the United States during 1950-2000

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  1. Attribution of observed climate trends over the United States during 1950-2000 Hailan Wang12, Siegfried Schubert1, Max Suarez1, Junye Chen13, Martin Hoerling4, Arun Kumar5, Philip Pegion16 1NASA/GMAO; 2UMBC/GEST; 3UMD/ESSIC; 4NOAA/ESRL; 5NOAA/NCEP/CPC; 6SAIC NOAA 32nd Annual Climate Diagnostics and Prediction Workshop October 22-26, 2007

  2. Observed Seasonality and Regionality in Climate Trends over U.S. HadCRU; 1950-2000 Surface Air Temperature (T) Precip (P)

  3. Observed Seasonality and Regionality in Climate Trends over U.S. HadCRU; 1950-2000 3-mon RunMean 3-mon RunMean Black: US mean (235°E-285°E; 26°N-50°N) Gray: central US mean (250°E-275°E; 30°N-48°N) Distinct cooling and wetting trends during late summer and fall

  4. Motivation • Attribution of seasonality and regionality in observed climate trends over the U.S. during 1950-2000; specifically: • To what extent do the leading SST patterns explain the observed seasonality and regionality of the surface air temperature and precipitation trends over the U.S. during 1950-2000?

  5. Model (AMIP) vs Obs NASA NSIPP AMIP EnsMean(14) HadCRU

  6. NASA NSIPP AMIP EnsMean vs HadCRU: Seasonality NSIPP AMIP EnsMean HadCRU 3-mon RunMean Thin colored line: 14 indv members 3-mon RunMean The observed climate trends over the U.S. can be mostly explained by changes in SST

  7. Leading SST EOFs: Global Warming (GW) and Pacific Decadal Variability (PDV) Hadley SST; 1901-2000 32% 12% Chen et al. (2007a, b), J. Climate, Accepted

  8. Linear trend of SST: Total=GW+DV+Residual Hadley SST; 1950-2000 Global Warming (GW) Decadal Variability (DV) Total Residual EOF3+EOF4 Input for a set of idealized AGCM experiments

  9. Idealized AGCM Experiments NASA NSIPP-1 AGCM; 3deg • All runs are integrated for 100 years • Data averaged over the last 60 years taken as climatology • Climatological difference between control run and an anomaly run represents • effect of corresponding SST trend

  10. Surface Air Temperature (T) Response in Idealized AGCM Experiments Total GW DV Residual DJF MAM JJA SON

  11. Precip (P) Response in Idealized AGCM Experiments Total GW DV Residual DJF MAM JJA SON

  12. Seasonality (amplitude) in Idealized AGCM Experiments Total AMIP • GW: • lead to general warming • spatial pattern unimportant • DV • dominant for all seasons • mainly from Pacific • Residual • important in fall • mainly from NH tro Atlantic (not shown)

  13. Seasonality (spatial pattern) in Idealized AGCM Experiments Spatial Pattern Correlation btw AGCM(Total_SSTA) and: AMIP_EnsMean AGCM(GW_SSTA) AGCM(0.32K_SSTA) AGCM(DV_SSTA) AGCM(DV_SSTA_Pacific) AGCM(Residual_SSTA)

  14. Conclusions • The observed climate trends over the U.S. during 1950-2000 exhibit distinct seasonality and regionality. In particular, there are notable cooling and wetting trends in late summer and fall. • The observed climate trends can be mostly explained by changes in SST. • Among the leading SST patterns: • Global Warming (GW): • does not contribute; mainly leads to a general warming trend • spatial pattern unimportant • Pacific Decadal Variability (PDV): • plays a prominent role throughout all seasons • Residual: • mainly contribute in late summer and fall; contribution in fall comparable to that of PDV

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