Thermosteric Effects on Interannual and Long-term Global Mean Sea Level Changes

We investigate global mean sea level (MSL) changes and different geophysical contributions at interannual and long-term (decadal) time-scales. Thermosteric effects of global MSL changes are estimated from ocean temperature anomaly data for the period 1955 2003 from the World Ocean Database 2001 (WOD01), plus additional data processed through June 2004. Estimates based on WOD01 show significant differences to previously published results based on similar temperature anomaly data from the World Ocean Database 1998 (WOD98), especially during the period overlapping with the TOPEX/Poseidon satellite altimeter mission. During this period (1993 2004), the WOD01-estimated thermosteric contribution of global MSL change is less than half of the estimate from WOD98 (1.3 \textpm 0.1 vs. 3.0 \textpm 0.6 mm/year), as compared to the rate of 2.6 \textpm 0.06 mm/year observed by satellite altimeters. The larger uncertainty in ocean temperature profiles and incomplete data collection in WOD98, especially in the later years (1997 and 1998) appear to be the major error sources to the overestimated steric effects by WOD98. During the entire 50-year period, the steric effect on global MSL change amounts to about 0.34 0.39 (\textpm0.05) mm/year. Strong interannual and decadal variability exists in estimated thermosteric contributions to the global MSL change, and (surprisingly) the thermosteric effect does not show any pronounced contribution to the strong interannual variability during the 1997/1998 El Ni\~no/La Ni\~na event. Our analysis based on the National Centers for Environmental Prediction reanalysis atmospheric model and the National Oceanic and Atmospheric Administration Climate Prediction Center global land data assimilation system indicates that atmospheric water vapor and terrestrial water storage changes show strong interannual variability that is well correlated with observed global MSL change, and could have significant effects on interannual global MSL changes.