Rigorous fusion of gravity field, altimetry and stationary ocean models

Abstract

Many characteristics of the ocean circulation are reflected in the mean dynamic topography (MDT). Therefore observing the MDT provides valuable information for evaluating or improving ocean models. Using this information is complicated by the inconsistent representation of MDT in observations and ocean models. This problem is addressed by a consistent treatment of satellite altimetry and geoid height information on an ocean model grid. The altimetric sea surface is expressed as a sum of geoid heights represented by spherical harmonic functions and the mean dynamic topography parameterized by a finite element method. Within this framework the inversion and smoothing processes are avoided that are necessary in step-by-step approaches, such that the normal equations of the MDT can be accumulated in a straightforward way. Conveniently, these normal equations are the appropriate weight matrices for model-data misfits in least-squares ocean model inversions.Two prototypes of these rigorously combined MDT models, with an associated complete error description including the omission error, are developed for the North Atlantic Ocean and assimilated into a 3D-inverse ocean model. Preprint submitted to ElsevierJuly 26, 2011The ocean model solutions provide evidence that satellite observations and oceanographic data are consistent within prior errors.

A Tailored Computation of the Mean Dynamic Topography for a Consistent Integration into Ocean Circulation Models

“…Koch and Kusche, 2002;Brockmann and Schuh, 2010) in contrast to the previous studies presented in Becker et al (2012) and Becker (2012).…”

“…Even these low numbers represent an important contribution to the net heat budget. Figure 8 shows the oceanic heat transport estimated by IFEOM with and without the new geodetic ITG MDT; also shown are independent estimates obtained from individual hydrographic cruises across the Atlantic Ocean and a previous estimate by Becker et al (2012). After adjusting to the geodetic ITG MDT, the heat transport in IFEOM has changed towards a better agreement with all cited previous estimates except for the estimates of Macdonald and Wunsch (1996) who estimate lower heat transports at 24…”

“…figure 5(b)) with a stronger circulation. Further, the reduced buoyancy (increased salinity) favors vertical convection and leads to more meridional overturning circulation in the model as discussed in Becker et al (2012). The modified hydrography has a profound effect on other properties of the solution, for example the oceanic heat transport.…”

“…(8) reduce to diagonal matrices. As in Becker et al (2012), IFEOM is extended by taking into account the full inverse mean dynamic topography error covariances Σ{η} −1 (or weight matrix W {η}) (Freiwald, 2012). The particular cost function contribution can be written as…”

“…Note, that the previously presented results in Becker et al (2012) were based on an absolutely different model configuration regarding the data sets (gravity field model ITG-Grace2010s (Mayer-Gürr et al, 2010), mean sea surface model MSS CNES CLS10 (MSS CNES CLS10, 2010) extracted on a 0.5…”