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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 Variabilityas Simulated by CAM3/CCSM3 R. Saravanan National Center for Atmospheric Research
Intercomparison of Simulated Equatorial SST(STOIC: Davey et al., 2002)
Topics • Effect of model improvements • Role of atmospheric model resolution • Potential predictability
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)
March-April-May mean SST OBS CCSM1 CCSM2 CCSM3
March-April-May SST std. Dev. OBS CCSM1 CCSM2 CCSM3
March-April-May mean PRECIP OBS CAM3/T42 CAM3/T85 CCSM3
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
Potential Predictability of PS MAM JJA CCM3 Vanilla AMIP CAM3 Vanilla AMIP CAM3 IPCC AMIP
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
CCSM2 SST Bias DJF JJA
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