The annual cycle in ENSO growth rate as a cause of the spring predictability barrier

The spring predictability barrier increases the uncertainty in ENSO forecasts starting before and during the boreal spring. Recent work has shown that the annual cycle of ENSO growth rate is responsible for phase locking of peak ENSO development to the boreal winter, suggesting that this annual cycle may play a role in the spring predictability barrier. To test this hypothesis, the annual cycle of ENSO growth rate is added to a damped, noise‐driven conceptual recharge oscillator model. When the annual cycle of ENSO growth rate is included, a spring predictability barrier develops, whereas without it ENSO predictability is independent of the forecast start date. When state‐dependent noise is included in the simulations in addition to the annual cycle of the growth rate, the spring predictability barrier is enhanced and more realistic.