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Eric W. Leuliette
John M. Wahr


Though thermal effects dominate steric changes in sea level, the long-period contribution of thermal expansion to sea level is uncertain. Nerem et al. found that a global map of sea surface temperature (SST) trends and a corresponding map of TOPEX/Poseidon-derived sea surface height (SSH) trends were strongly correlated. This result is explored with a coupled pattern analysis (CPA) between five years of global SST and SSH, which allows for matching of modes of common temporal variability.

The dominant mode found is an annual cycle that accounts for nearly all (95.3%) of the covariance between the fields and has a strong SST/SSH spatial correlation (0.68). The spatial correlation is strong in both the Atlantic (0.80) and the Pacific (0.70). Good temporal and spatial agreement between the SSH and SST fields for the primary seasonal mode suggests that a robust regression between fields may have some physical significance with respect to thermal expansion and that the regression coefficient might be a proxy for the mixing depth of the mode. The value of the regression coefficient, H, scaled by a thermal expansion coefficient of 2 × 10−4 °C−1 is 40 m for this mode, and ranges from 33 to 47 m among the basins.

The primary mode of a nonseasonal CPA is an interannual mode that captures 38.0% of the covariance and has significant spatial correlations (0.54) between SSH and SST spatial patterns. The spatial pattern and temporal coefficients of this mode are correlated with ENSO events. A robust regression between fields finds that the nonseasonal modes have a regression coefficient 2–4 times that of the seasonal modes, indicative of deeper thermal mixing. The secondary nonseasonal mode captures most of the secular trend in both fields during the period examined. The temporal coefficients of this mode lag those of primary mode. Evidence is presented that this mode is consistent with the behavior expected from secular trends that are dominantly forced by thermal expansion.

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Cristina Martin-Puig
Eric Leuliette
John Lillibridge
, and
Mònica Roca


The Poseidon-3 altimeter on board Jason-2 includes a significant new capability with respect to its predecessors, an open-loop [Détermination Immédiate d’Orbite par Doris Embarqué (DIODE)/digital elevation model (DEM)] tracker mode. This innovative mode is capable of successfully tracking the backscatter signal over rapidly varying terrains, and thus it overcomes one of the limitations of the closed-loop Poseidon-2 tracker on board Jason-1. DIODE/DEM achieves this improvement thanks to a predetermined DEM on board that, when combined with DIODE orbit ephemeris, provides improved acquisition timing and reduced data loss in the coastal zone. As a further enhancement, Jason-3 and the Sentinel-3 programs will be capable of autonomously switching to this innovative mode in selected regions. To help recommend how these missions should utilize DIODE/DEM, the authors studied the impact of the tracker mode on the accuracy and precision of wave heights and wind speed, the continuity of the sea level climate data record, and the coverage in coastal regions. The results show close agreement between the open- and closed-loop tracker modes over the open ocean with the exception of some differences at high-tidal variability areas, the coastal zone, and sea ice regions. The DIODE/DEM tracker shows better performance than the closed-loop tracker mode at the coast and in the presence of sea ice. Jason-2, when operating in open-loop mode, allows for an approximately 5% increase of successful acquisitions at the ocean-to-land transition. However, open-loop tracking exhibits more variability in regions of high tides than closed-loop.

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