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Abstract:
The El Niño Southern Oscillation (ENSO) is a multi-year climate pattern with important teleconnections to global temperature and rainfall. The relative frequency of eastern and central Pacific ENSO events has been changing. Our short instrumental record severely limits our ability to formally characterise the nature of ENSO and to therefore draw firm conclusions regarding its variability, predictability, and long-term future. In this work, we aim to extend the climate record of the Pacific Ocean using paleoclimate data assimilation (PDA). Data assimilation (DA) combines modelled climate fields and observations and has been implemented successfully in meteorology and numerical weather forecasting. DA methods have been used to assimilate paleoclimate proxy data, such as tree rings, ice cores and coral carbonate, to produce ‘paleoclimate reanalysis’ products. Due to the nature of proxy data sources, most existing PDA reconstructions are annually resolved and have used an offline-DA approach, which does not propagate knowledge of a climate state forward in time. However, some coral records are available at seasonal to near-monthly resolution for several hundred years, potentially allowing PDA reconstructions at monthly timescales. At this temporal resolution, we expect to be able to increase the accuracy of these fields by assimilating coral carbonate proxy records into an isotopically enabled online-DA approach, where knowledge of the climate field is propagated forward. By extending the monthly climate record over the Pacific, we can examine ENSO intra-annual to decadal variability to deepen our understanding and predictive capabilities of this climate system.
