ENSO mechanisms in the new CCSM

The new version of CCSM, CCSM3.5, will be introduced and its ENSO characteristics and mechanisms will be discussed. It is shown that the new CCSM now features spectral peaks in the NINO3 spectrum which are, like in the observations, at 3 and 5 years. This improvement over the old CCSM3 has been brought about by changes to the convection scheme. It is further shown that ENSO in CCSM3 is dominated by the delayed oscillator mechanism, whereas in CCSM3.5 it is controlled by westerly wind bursts. The key to weaken the spurious delayed oscillator dynamics has been to weaken the ocean-atmosphere coupling in the off-equatorial trades.