Tropical Pacific spatial trend patterns in observed sea level: internal variability and/or external forcing signature ?
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 past 2-D sea level reconstruction (over 1950-2009) -based on observations- and multi-century control runs from an ensemble of 8 CMIP3 coupled climate models, we investigate how these sea level trend patterns evolved during the last decades and centuries, and what are their characteristic time scales. Using 20th century model runs, we also examine whether we can already detect in the observed trend patterns some imprint of external forcing factors (solar or volcanic activity and anthropogenic forcing) or if they essentially result from natural climate variability. For this analysis, we computed sea level trend patterns over successive 17-year 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 in the past similar spatial trend patterns as those observed during the altimetry era. The patterns appear to have fluctuated with time following a low frequency (of period > 8 yr) modulation. The characteristic time scale of the patterns is on the order of 25-33 years. Similar behaviour is found in multi-centennial control runs of the coupled climate models. In these runs, that have no external forcing, sea level patterns resemble those seen in the observations. A similar analysis, performed with 20th century model runs (i.e., with anthropogenic and solar/volcanic forcing.) does not display significant differences with the previous analysis, suggesting that tropical pacific sea level trend patterns reported by altimeter satellites so far mostly reflect internal natural variability of the ocean-atmosphere coupled system.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.G21B0817M
- Keywords:
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- 1616 GLOBAL CHANGE / Climate variability;
- 1641 GLOBAL CHANGE / Sea level change;
- 4556 OCEANOGRAPHY: PHYSICAL / Sea level: variations and mean