Robustness of the modes of Indo-Pacific sea level variability

This study evaluates the influence of various climate modes on sea level. The altimetry record has excellent spatial coverage but the limited length becomes an issue when evaluating low frequency variability in the presence of a trend. We use altimetry along with two ocean models to study how the relationship between sea surface height (SSH) in the Indian and Pacific Oceans and four climate modes [the Pacific Decadal Oscillation (PDO), the El Nio-Southern Oscillation, the Indian Ocean Dipole and the Southern Annular Mode] depends on the length of the time series. For low frequency variability such as the PDO, a time series on the order of 50 years in length is required to separate variability from the trend. Using shorter time series results in aliasing of the SSH trend and low frequency variability, which has implications for ascertaining the role of the PDO in the SSH trends. We find that the regression of SSH on to the PDO during the altimetry period, which is thought to have been responsible for a large fraction of the recent western Pacific SSH trend, is not representative of the SSH-PDO relationship in the longer-term record.