Tropical Pacific spatial trend patterns in observed sea level: internal variability and/or anthropogenic signature?
1LEGOS/CNES, UMR5566, 14, avenue E. Belin, 31400 Toulouse, France
2Météo-France CNRM/GMGEC CNRS/GAME, 31000 Toulouse, France
3JPL, California Institute of Technology, Pasadena, California, USA
*now at: University of Cayenne, Guyane, France
Abstract. We investigate the spatio-temporal variability of sea level trend patterns observed by satellite altimetry since 1993, focusing on the Tropical Pacific. The objective of this study is two fold. On the basis of a 2-D past sea level reconstruction (over 1950–2009) – based on a combination of observations and ocean modelling – and multi-century control runs (i.e. with constant, preindustrial external forcing) from eight coupled climate models, we investigate how these sea level trend patterns evolved during the last decades and centuries, and what their characteristic time scales are. Using 20th century coupled climate model runs, we also examine whether observed trend patterns are driven by external forcing factors (i.e. solar plus volcanic variability and changes in anthropogenic forcing) or if they essentially result from natural climate variability. For this analysis, we computed sea level trend patterns over successive 17 yr windows (i.e. the length of the altimetry record) both for the reconstructed sea level and model runs. We compared them to altimetry-based observed trends. The 2-D sea level reconstruction shows similar spatial trend patterns to those observed during the altimetry era. The patterns appear to have fluctuated with time with a characteristic time scale of the order of 25–30 yr. Similar behaviour is found in multi-centennial control runs of the coupled climate models. The same analysis, performed on 20th century model runs does not display significant differences. This suggests that Tropical Pacific sea level trend fluctuations are still dominated by the internal natural variability of the ocean-atmosphere coupled system. While our analysis cannot rule out any influence of anthropogenic forcing, it concludes that the latter effects on the regional sea level patterns are still hardly detectable.