11:00 AM - 1:00 PM
[ACG35-P05] Reexamining the tropical Atlantic influence on ENSO in perfect model prediction experiments
Keywords:tropical Atlantic, ENSO, basin interaction
Here we use a set of GCM sensitivity experiments to quantify the strength of the Atlantic-Pacific link. The starting point is a 1000-year free-running control simulation with the GFDL CM 2.1 model. From this control simulation, we pick years in which a cold AZM event in JJA is followed by an El Niño in DJF. These years serve as initial conditions for “perfect model” 10-member prediction experiments. In control, the predictions evolve freely for 12 months from January 1 of each selected year. In the second set of predictions, SSTs in the tropical Atlantic are gradually relaxed to climatology, so that the cold AZM event is suppressed. In the third set of predictions, we restore the tropical Pacific SSTs to climatology, so that the El Niño event is suppressed.
The results suggest that, on average, the tropical Atlantic SST anomalies increase the strength of El Niño in the following winter by about 10-20%. If, on the other hand, El Niño development is suppressed, the amplitude of the cold AZM event also reduces at least by a similar amount and sometimes fails to develop at all. The results suggest that, in the context of this GCM, the influence of AZM events on ENSO development is relatively weak but not negligible. The fact that ENSO also influences the AZM in boreal spring highlights the complex two-way interaction between these two modes of variability.