Sea level trends, interannual and decadal variability in the Pacific Ocean

Abstract

[1] Linear trend analysis is commonly applied to quantify sea level change, often over short periods because of limited data availability. However, the linear trend computed over short periods is complicated by large-scale climate variability which can affect regional sea level on interannual to inter-decadal time scales. As a result, the meaning of a local linear sea level trend over the short altimeter era (since 1993; less than 20 years) is unclear, and it is not straightforward to distinguish the regional sea level changes associated with climate change from those associated with natural climate variability. In this study, we use continuous near-global altimeter measurements since 1993 to attempt to separate interannual and decadal sea level variability in the Pacific from the sea level trend. We conclude that the rapid rates of sea level rise in the western tropical Pacific found from a single variable linear regression analysis are partially due to basin-scale decadal climate variability. The negligible sea level rise, or even falling sea level, in the eastern tropical Pacific and US west coast is a result of the combination of decreasing of sea level associated with decadal climate variability and a positive sea level trend. The single variable linear regression analysis only accounts for slightly more than 20% of the observed variance, whereas a multiple variable linear regression including filtered indices of the El Nino-Southern Oscillation and the Pacific Decadal Oscillation accounts for almost 60% of the observed variance.

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

“…It is significantly correlated with ENSO (e.g., Alexander et al 2002;Newman et al 2003;Deser et al 2004;Schneider and Cornuelle 2005;Vimont 2005). On decadal timescales, the PDO is highly correlated with ENSO (Zhang and Church 2012) and the Interdecadal Pacific Oscillation (IPO), a basin-wide decadal climate mode associated with decadal SST variability in the Pacific (e.g., Power et al 1999;Folland et al 2002;Meehl and Hu 2006). The correlation coefficients for PDO-IPO and IPO-NINO3.4 indices (8-year low-passed) are both 0.88 over the period of 1900(Han et al 2014aZhang and Church 2012).…”

“…On decadal timescales, the PDO is highly correlated with ENSO (Zhang and Church 2012) and the Interdecadal Pacific Oscillation (IPO), a basin-wide decadal climate mode associated with decadal SST variability in the Pacific (e.g., Power et al 1999;Folland et al 2002;Meehl and Hu 2006). The correlation coefficients for PDO-IPO and IPO-NINO3.4 indices (8-year low-passed) are both 0.88 over the period of 1900(Han et al 2014aZhang and Church 2012). Given their high correlations on decadal timescales, it has been suggested that the IPO may not be confidently treated as an independent climate mode to ENSO decadal variability (e.g., Trenberth et al 2007) or that the PDO is a statistic mode rather than a physical mode with a single mechanism (see review by Newman et al 2016).…”

“…Modeling studies suggest that warming of the tropical Indian and Atlantic Oceans enhances surface easterly trade winds and thus contributes to the intensified SLR (e.g., Luo et al 2012;Han et al 2014a;Hamlington et al 2014;England et al 2014;McGregor et al 2014); however, a large portion of this rapid SLR-together with weak falls in the eastern basin-is part of the basin-scale sea level pattern associated with the Pacific Decadal Oscillation (PDO) or decadal variability of ENSO (Bromirski et al 2011;Merrifield et al 2012;Meyssignac et al 2012;Zhang and Church 2012;Hamlington et al 2013Hamlington et al , 2014Moon et al 2013;Han et al 2014a; Palanisamy et al 2015). The PDO is defined as the leading empirical orthogonal function (EOF) of sea surface temperature (SST) anomaly over the North Pacific ([20°N), and the leading principal component (PC1) is referred to as the PDO index (e.g., Mantua et al 1997;Minobe 1997;Zhang et al 1997;Garreaud and Battisti 1999; see review papers by Alexander 2010;Liu 2012).…”

“…The EOF1 patterns shown in Fig. 1a resemble the multiple linear regression patterns over the Pacific Ocean (e.g., Zhang and Church 2012;Si and Xu 2014;Frankcombe et al 2015) (second row of Fig. 3) by regressing the observed, ocean model-simulated and reanalysis sea level data onto the PDO index.…”

Seasonal prediction of global sea level anomalies using an ocean–atmosphere dynamical model

“…5, 6) and observations (not shown) are dominated by ENSO and the IOD. It should be noted that this study does not seek to resolve lower frequency components of signals such as the PDO or NAO which also influence global and local sea levels (Zhang and Church 2012).…”