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Tropical Atlantic Variability as Simulated by CAM3/CCSM3

Tropical Atlantic Variability as Simulated by CAM3/CCSM3. R. Saravanan National Center for Atmospheric Research. TAV. Intercomparison of Simulated Equatorial SST (STOIC: Davey et al., 2002). Topics. Effect of model improvements Role of atmospheric model resolution

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Tropical Atlantic Variability as Simulated by CAM3/CCSM3

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  1. Tropical Atlantic Variabilityas Simulated by CAM3/CCSM3 R. Saravanan National Center for Atmospheric Research

  2. TAV

  3. Intercomparison of Simulated Equatorial SST(STOIC: Davey et al., 2002)

  4. Topics • Effect of model improvements • Role of atmospheric model resolution • Potential predictability

  5. Model integrations • Coupled Experiments: • CCSM1 (T42), CCSM2 (T42), CCSM3 (T85) • Uncoupled experiments (1950-2000): • Vanilla AMIP: CCM3 (T42), CAM3 (T42/T85) • IPCC AMIP: CAM3 (T85)

  6. March-April-May mean SST OBS CCSM1 CCSM2 CCSM3

  7. March-April-May SST std. Dev. OBS CCSM1 CCSM2 CCSM3

  8. March-April-May mean PRECIP OBS CAM3/T42 CAM3/T85 CCSM3

  9. Potential Predictability P = E/T - I/N E = ensemble-mean variance I = internal variance T = total variance (= E + I) N = no. of ensemble members Effect of model version Effect of model resolution Effect of forcings

  10. Potential Predictability of PS MAM JJA CCM3 Vanilla AMIP CAM3 Vanilla AMIP CAM3 IPCC AMIP

  11. Conclusions • Some improvement in the coupled model simulations of Tropical Atlantic SST • Significant biases remain, both in the mean and in the variance • Coupled CCSM3 seems to have less of a double ITCZ structure than uncoupled AMIP runs! • Potential predictability in the Atlantic Sector • Not affected by model resolution • Not affected by presence of presence of Greenhouse Gas forcings etc. • But tropical SST signal is important

  12. Tropical Atmospheric Bridge(Klein et al, 1999)

  13. NAO

  14. CCSM2 SST Bias DJF JJA

  15. Questions • Evidence for remote influence of Tropical Atlantic SST anomalies on the Tropical Pacific • Seen in CAM2+slab, CAM2+POP, CCM3+slab, and CCM3+MOM. How about other models? • Observational data: dominated by ENSO signal

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