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Ocean Surface Topography from Space
Estimating Mechanisms of the Trend and Decadal Variability of Sea Level Using an Ocean General Circulation Model Constrained by Satellite Altimetry Observations


Ichiro Fukumori - (Jet Propulsion Laboratory)

  Victor Zlotnicki
(California Institute of Technology - JPL)


Mechanisms underlying the trend and decadal changes of global large-scale sea level variability will be studied. While global mean sea level rise can be attributed to an overall increase in ocean heat content and mass of external origins, regional sea level variations are often dictated by water mass redistribution caused by transient variabilities in ocean circulation that obscure the changes associated with the global mean. Projections of future sea level rise require identifying where heat and mass anomalies are stored and understanding processes controlling their evolution.

This study aims to distinguish sea level variations due to pure diabatic changes of the ocean, such as those associated with global warming and related variabilities of the hydrologic cycle, from sea level changes due to kinematic water mass redistribution within the ocean, such as anomalous convergence and divergence of ocean circulation associated with El Niño and La Niña events. By doing so, the study seeks to identify where warming and freshening associated with global mean sea level rise is taking place and how it is evolving in time. Processes contributing to global mean and large-scale regional variations of sea level on decadal time-scales will be analyzed using an ocean general circulation model constrained by satellite sea level observations (TOPEX/Poseidon, Jason-1, Jason-2), in conjunction with satellite ocean mass observations (GRACE) and in situ temperature and salinity measurements of the ocean (e.g., Argo floats). The combined ocean state estimate provides a complete physical description of the ocean that allows quantitative accounting of the processes underlying the observations and their variability. Budgets of heat and mass will be analyzed and circulation pathways will be evaluated to identify diabatic changes of external origin on the one hand and redistribution of water masses on the other. Changes in water mass properties will be examined and their impact on sea level changes assessed. Forcings controlling the geographically varying anomalies of sea level, heat and freshwater content, and mass will be studied and the relationships among the changes will be investigated.

Distinguishing the processes contributing to the trend and decadal variability of sea level will help improve understanding of sea level rise and of the ocean s interactions with other components of the climate system, and will advance the scientific basis for estimating the ocean and climate s future evolution.

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