Decadal Variability in the Pacific: observations, modelling and palaeoclimate

Our understanding of the Pacific Decadal Oscillation (PDO) and its related Pacific-wide manifestation, the Interdecadal Pacific Oscillation (IPO), is limited, due to short observational records, uncertainty in palaeoclimate reconstructions and imperfect model simulations. This presentation summarizes recent work on: (i) developing a new index for the IPO, (ii) reconstructing the IPO from a multi-proxy network of palaeoclimate data spanning the Pacific basin and (iii) assessing the performance of pre-industrial CMIP5 model experiments in characterizing the IPO. The newly-developed tripole index (TPI) tracks the distinct tripole pattern of Pacific sea surface temperature anomalies (SSTA) varying on decadal timescales. The index is computed as the difference between the SSTA averaged over the central equatorial Pacific and the average of the SSTA in the Northwest and Southwest Pacific. The TPI timeseries bears a close resemblance to previously published indices, is free from assumptions about the nature of global warming and has the advantage of being simpler to compute and more consistent with methods used to track other climate modes. A new multi-proxy palaeoclimate reconstruction of the IPO is also presented, incorporating palaeoclimate records from around the Pacific basin. The reconstruction provides the latest annually-resolved estimate of the temporal variability of the IPO in the past several centuries. The spatial and temporal representation of the IPO in CMIP5 models is also investigated and compared to observations. The implications for decadal-scale hydroclimatic variability and periods of surface warming acceleration and hiatus are discussed.