Who leads when El Niņo Dances with the Indian Monsoon?

The sudden demise and failed forecasts of the 2012 El Niņo-Southern Oscillation (ENSO) were accompanied by an erratic evolution of the Indian summer monsoon (ISM). AN eerily similar scenario is being played out in the summer of 2014 with a delayed ISM onset and deficient rainfall over June and early July. An additional factor has been the basin-wide warming of the tropical Pacific which is a distinct pattern of SST anomalies compared to the canonical ENSO summers. A similar basin-wide warming was observed in 2009 and was argued to be associated with the emergence of the global warming signal in the tropical Pacific Ocean. The consensus forecasts of 2014 were pointing to a systematic evolution of ENSO for the fall and winter of 2014 but the subsurface warm waters in the deep tropical Pacific had dissipated by June 2014 and the conjectures of a strong ENSO also appear to be dissipating. While it has been known for several decades that the ISM and ENSO are an interacting coupled system, the exact nature of the feedbacks have never been consistently observed or modeled. The impact of ENSO on the monsoon is much better known in terms of a deficient ISM during ENSO years. But many ISM drought years are not associated with ENSO and the emergence of the basin-wide warming pattern in the tropical Pacific is confounding the ENSO-monsoon dance. The ISM itself is observed to be experiencing a downward decadal trend contrary to the expected strengthening due to the rapid warming of the land compared to the oceans. This exacerbates the challenges to seasonal ISM prediction and process understanding is urgently needed to fully understand the ISM-ENSO interactions in a warming world. The evolution of ENSO that maybe independent of its flavor (Eastern vs Central Pacific ENSO) and the seasonality of the ISM evolution and their likely relation to the Indo-Pacific warming are discussed in the context of seasonal-to-interannual climate prediction efforts.

Can we still rely on ENSO predictability for skill in ISM predictions? Can we exploit the multi-seasonal timescale of ENSO evolution to devise strategies to enhance ISM forecast skills? Such questions can only be answered by understanding the secular trends in the ISM and the seasonality of the Indo-Pacific warming in addition to the surface expression of the ENSO itself. Diagnoses of the CFSv2 hindcasts are combined with some model sensitivity experiments to deconvolve some of the potential causal linkages between the ISM and ENSO and their response to the ocean warming patterns. Remote impacts of model biases from the Pacific and the Atlantic are also analyzed to understand the impact of regional biases on the ISM evolution and forecasts. Some preliminary suggestions are offered on ways forward to exploiting single and multi-model ensembling to explore additional skill for ISM predictions at seasonal timescales. ISM-ENSO interactions and the Indo-Pacific warming are also considered in the context of the intraseasonal variability of ISM.