Cooperative Institute for Research in Environmental Sciences

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Decadal Changes in CCSM3.5 ENSO Dynamics

Samantha Stevenson (1), Baylor Fox-Kemper (1), Markus Jochum (2)

(1) CIRES, (2) NCAR

The new convection scheme recently introduced to the Community Climate System Model (CCSM) yields substantial improvement in the simulation of the modern El Nino/Southern Oscillation (ENSO). Still, ENSO dynamics shift on decadal timescales in the model, meaning that long-baseline studies are required to fully quantify ENSO variability. This study uses an orthogonal mode decomposition to show that both wave reflection and heat discharge play a role in driving ENSO events, but that the relative importance of these distinct dynamical processes changes dramatically, even in the absence of changes in oceanic mean state. We also find that ENSO dynamics may be sensitive to distinct regions of the tropical Pacific at different times, possibly indicating that current oscillator models are not sufficient to describe decadal changes in the system.