Using ECCO estimates for studies in geodesy
The ocean is a key factor in determining and understanding the geodetic properties of the Earth. For example, changes in the oceanic mass field can have important effects on crustal loading. Knowledge of the mean ocean surface circulation and dynamic topography can help determine the marine geoid and the gravity field. And variability in both ocean currents and bottom pressure can affect the Earth’s orientation in space.
The ECCO products make it possible to calculate geodetically relevant quantities such as the ocean angular momentum and center of mass, based on fields that are constrained to many data sets, most recently including GRACE-derived bottom pressure fields. Such time series, available at the Special Bureau for the Oceans/International Earth Rotation and Reference Systems Service (https://euler.jpl.nasa.gov/sbo/sbo_home.html), can be used to explore the role of the ocean in the excitation of Earth rotation changes.
The global coverage, continuity in time, and consistency with observations of the ECCO fields make them ideal for geodetic investigations of the role of the ocean on the Earth’s variable shape, rotation and gravity field.
Davis, J., and N. Vinogradova, 2017: Causes of accelerating sea level on the East Coast of North America. Geophys. Res. Lett., 44, doi:10.1002/2017GL072845.
Quinn, K. J., R. M. Ponte, P. Heimbach, I. Fukumori, and J.-M. Campin, 2019: Ocean angular momentum from a recent global state estimate, with assessment of uncertainties. Geophys. J. Int., 216(1), 584–597, doi:10.1093/gji/ggy452.
van Dam, T., X. Collilieux, J. Wuite, Z. Altamimi, and J. Ray, 2012: Nontidal ocean loading: amplitudes and potential effects in GPS height time series. J. Geod., 86, 1043–1057, doi:10.1007/s00190-012-0564-5.
Volkov, D. L., and V. Zlotnicki, 2012: Performance of GOCE and GRACE-derived mean dynamic topographies in resolving Antarctic Circumpolar Current fronts. Ocean Dyn., 62, 893–905, doi:10.1007/s10236-012-0541-9.
A New 20-year Ocean Climatology
A new 20-year ocean climatology is available for ocean circulation and climate studies based on the recent ECCO version 4 release 3 ocean state estimate. In comparison to conventional climatologies based on observations alone, the new ECCO climatology accounts for the very great inhomogeneity with which the ocean has been observed. The new climatology includes all conventional variables of a general circulation model over the entire water column and is consistent with the diversity of data available from the global observation system. All basic convservation rules for ocean circulation, including enthalpy and energy, are obeyed to machine precision in the model equations.
Fukumori, I., P. Heimbach, R. M. Ponte, and C. Wunsch, 2018: A Dynamically Consistent, Multivariable Ocean Climatology. Bull. Am. Meteorol. Soc., 99, 2107–2128, doi:10.1175/BAMS-D-17-0213.1.
Mechanisms of the recent decadal trend of the North Atlantic Ocean heat content
The subpolar North Atlantic (SPNA) reversed trends in ocean heat content from warming during 1994–2004 to cooling over 2005–2015. ECCO V4r3 reveals that this reversal is the result of anomalous horizontal midlatitude gyre circulation acting on the mean temperature gradient, rather than changes in overturning circulation. Results have implications for decadal predictability.
Piecuch, C. G., R. M. Ponte, C. M. Little, M. W. Buckley, and I. Fukumori (2017), Mechanisms underlying recent decadal changes in subpolar North Atlantic Ocean heat content, Journal of Geophysical Research: Oceans, 122(9), 7181-7197, doi:10.1002/2017JC012845.
Coherent Arctic Ocean Bottom Pressure Variations
Across the Arctic Ocean and the Nordic Seas, GRACE and in-situ observations identified a basin-wide mode of ocean bottom pressure and sea-level fluctuation with spatially near-uniform amplitude and phase. This basin-wide fluctuation is barotropic and dominates the region’s large-scale variability from sub-monthly to interannual timescales. Using ECCO v4 and its adjoint, the source of these coherent ocean bottom pressure variations were identified as being coastally-trapped waves generated by winds along the continental slopes of the Arctic Mediterranean and its neighboring seas including the North Atlantic Ocean. Winds drive Ekman transport across the large bathymetric gradients, forcing mass divergence between the shallow coastal area and the deep ocean basins and creating ocean bottom pressure anomalies of opposite signs in the two regions. The resulting propagation and mutual interaction of these waves gives rises to the observed pressure anomalies. This study illustrates the utility of using the model’s adjoint for identifying causal mechanisms underlying a complex system
I. Fukumori, O. Wang, W. Llovel, I. Fenty and G. Forget, 2015: A near-uniform fluctuation of ocean bottom pressure and sea level across the deep ocean basins of the Arctic Ocean and the Nordic Seas. Prog. Oceanogr., 134, 152-172.