Equation (5) is the delayed oscillator of Eq. (1).
The recharge oscillator considers variations of eastern Pacific SST and western Pacific thermocline anomalies. As argued by Jin [1997], equatorial wave dynamics are important in adjustment of the equatorial ocean, but wave propagations are not explicitly in the recharge model. If the time derivatives in Eqs. (4c) and (4d) are dropped and all delay parameters are set to zero, i.e., , , and , the unified oscillator reduces to:
. (5)
, 
, and 
, the unified oscillator reduces to: