Analyzing the Impact of ENSO on the Propagation of the Madden-Julian Oscillation

Since the convection related to MJO may interfere de(con)structively with the convection of ENSO over the tropics, it is necessary to understand how the SST anomalies of ENSO affect the development and propagation of MJO. We developed a statistical model, based on the constructed analog (CA) approach which can be used to diagnose MJO propagation as a function of the SST field at the initial time. The Wheeler and Hendon (2004) MJO index, used as the predictand, is determined from upper- and lower-level zonal winds and outgoing longwave radiation (OLR). The CA MJO forecast is an effective tool because it not only catches the intensity and propagation signals of the tropical convection but also accounts for the impacts of ENSO on MJO by incorporating the sea surface temperature (SST) information into the model. To estimate the impact of coupled air-sea feedbacks on the predictability of the MJO and the sensitivity to SST, a series of prediction experiments are conducted. The experimental results clearly show that the SST anomalies related to ENSO change the MJO amplitudes and propagation speed, but the impact is not simple since the result depends on the MJO phase itself. The result has clear practical implication because knowledge of global tropical SST should thus improve the MJO forecast.