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Ocean Surface Topography from Space
SCIENCE
The Role of Decadal Climate Variability in Global and Regional Sea Level Change


Author:

Benjamin Hamlington - (Old Dominion University Research Foundation)

Co-Investigator(s):
  Dr. John Reager
(Old Dominion University Research Foundation)


Abstract:
TIn the absence of sea level variability with timescales of a decade or longer, the now 23-year record of the satellite altimetry could potentially be used directly to estimate a trend and acceleration, with interannual and shorter term variability serving as noise about this trend. Several recent studies using both tide gauge and satellite altimetry data, however, have detailed the contribution of decadal variability to both regional and global sea level, serving to obscure the background secular trend. Without accounting for and subsequently removing this variability, the utility of the satellite altimeter record for understanding long-term sea level change will be limited. The overarching goal of this project is not to provide an improved estimate of the secular trend as measured by the satellite altimetry. Rather, the goal is to refine the understanding of the satellite altimeter record and the variability contained therein, as well as its major causes and mechanisms. Better representations of the secular trend will likely follow, but our primary focus here is on examining and explaining the influence of decadal variability in the satellite altimeter record. As specific objectives, we will
  1. provide improved representations and definitions of large-scale climate signals,
  2. use these improved representations to understand recent regional sea level variability,
  3. relate decadal trends in terrestrial water storage to decadal trends in the satellite altimetry data, and # improve the interpretation of the satellite altimeter record both globally and regional to provide an assessment of the next decade of sea level rise.

To meet these objectives, we will apply proven analysis techniques to a wide range of datasets. For sea level data, we will use NASA-hosted sea level reconstructions and gridded satellite altimetry data in tandem to understand the impact of the relatively short altimeter record on the ability to extract decadal variability. As complementary datasets, we will use GRACE and GLDAS-2 terrestrial water storage data along with GPCP precipitation data to understand the relationship between the movement of water between land and ocean on decadal timescales and decadal variability in sea level. We will use several analysis techniques, including empirical orthogonal function (EOF) analysis, cyclostationary empirical orthogonal function (CSEOF) analaysis, empirical mode decomposition (EMD) and windowed-trend analyses to extract the targeted decadal signals. By employing a range of proven and documented methods of analysis, we will understand the sensitivities associated with each technique while ideally obtaining results that are robust across each method.

A central element of NASA climate change research is to provide observations that pave the way for projections of climate change, and in particular for the focus of this proposal, sea level. However, as stated above, the current satellite records are still relatively short and separating natural variability from external climate change remains a challenge.

Without studies like this one that seek to separate signals that may be obscuring the secular trend, the ability to use satellite observations to project future sea level will remain limited. Improving our understanding of how decadal climate variability affects sea level will have a significant impact on how we interpret the satellite altimeter record, adding value to the past and future altimeter time series. This work will also underscore the importance of continued satellite measurements of the ocean.



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