Decadal-Multidecadal Variability of the Indian and Pacific Walker Cells: Do They Co-Vary with the Warm Pool Convection on these Timescales?

Previous studies investigated the centennial and multidecadal trends of the Pacific and Indian Ocean Walker Cells (WCs) during the past century, but obtained no consensus due to data uncertainties, different analysis methods and model limitations. Here, we combine satellite observations during recent decades with longer-term upgraded ocean-atmosphere datasets and model experiment results, to investigate the decadal-to-multidecadal variations of the Indian and Pacific WCs and associated sea level over the warm pool since the 1960s. To directly compare with existing studies, we focus on examining zonal surface winds - the surface branches of the Indian and Pacific WCs. Satellite, in situ and reanalysis winds reveal that the Indian and Pacific WCs exhibit apparent decadal (10-20yrs) and multidecadal (>20yrs) variations. These variations are supported by consistent changes in satellite observed sea surface height and in situ based upper 700m thermosteric sea level data. The Indian and Pacific WCs co-vary over the warm pool on both decadal and multidecadal timescales only during northern winter (Nov-Apr), when an intensified Pacific WC and easterlies correspond to an intensified Indian Ocean WC and westerlies, and they are significantly correlated with warm pool convection. During northern summer (May-Oct), the two WCs are essentially uncorrelated (r<0.1) and opposing changes occur on multidecadal timescales. While variability of the Pacific WC is dominated by ENSO (or IPO), variability of the Indian Ocean WC is affected by more complex factors (e.g., Decadal Indian Ocean SST basin mode, ENSO, Indian Ocean Dipole, Atlantic SST), and there is no single mode that dominates its variability.