How well is Argo measuring the steric component of global sea level?

John Gilson, Dean Roemmich

SIO
UCSD
9500 Gilman Drive
La Jolla,
CA 92093
USA


A major challenge for global change research is to separate the steric and eustatic components of sea level variability. This decomposition is important both for understanding the present state of the climate system as well as for improving forecasts of future sea level rise. The aim of the present work is to evaluate Argo&Mac226;s ability to estimate both the thermosteric and halosteric sea level change on a month-to-month basis. The Argo array achieved sparse global coverage in early 2005, and is presently delivering about 6000 profiles per month from all of the oceans. We estimate the 2005 annual cycle and errors, for both the regional and global mean steric height of the sea surface relative to 2000 dbar. Errors are estimated in several different ways: based on subsampled datasets, on intrinsic noise levels due to mesoscale variability, and by using altimetric height to assess sampling errors. The adequacy of Argo&Mac226;s present sampling and of its real-time data stream are addressed with respect to the present application and its extension to interannual variability. Finally, steric height and altimetric height annual variability are examined for consistency with published estimates of annual variability in eustatic sea level from the GRACE mission.