Synchronized dipole-like oscillations in global Sea Surface Temperature Anomaly (SSTA)

This study investigates dipole-like oscillations in the sea surface temperature anomaly (SSTA), using reconstructed datasets from 1900 to 2011. Previous studies have explored the existence of dipole modes and their effects on local climate in their respective ocean basins. We have found seventeen, globally distributed, dipole-like, coupled oscillations (including four with Niño 3.4, and distinct from previously suggested dipoles), This founding is based on the direct comparison of global ocean SSTA, implemented by cross correlation coefficients in a 2 degree by 2 degree grid - 10988 points over global ocean - at annual, seasonal, and monthly scales. The dipole modes exist persistently at various time domains, though a few of them show a seasonally-dependent coupling strength. We discuss the specifics of these variations of modes, on both a seasonal and monthly scale. The dipole locations identified by this study are partially compatible with the results from Empirical orthogonal function (EOF) analysis. However, in most cases, EOF analysis fails to find the exact anomaly centers of the dipoles, which are synchronized by a Π/2 phase difference, and show maximum correlation coefficients there. It is necessary to look at the actual time series over the dipole regions to filter out any artifact generated by the EOF analysis. From the detected dipole modes, a dipole mode index (DMI) is defined as the difference between the first principal components of SSTA over 9 grid points around the detected anomaly centers. We investigate possible causes and effects of the dipoles, comparing the defined DMI with sea level pressure (SLP), wind, and other climate indices such as ENSO, PDO, AMO, NAO, and NPI. The DMI is also used to define the characteristics of each dipole, including whether they are synchronized to each other or oscillating independently. This study's goal is to create a better understanding and definition of the globally distributed teleconnections of the SSTA, their local effects, and their synchronization with various climate indices.