may no longer be accessible. Adjoint Sensitivity of an Ocean General Circulation Model to Bottom Topography

• Main Authors: Martin Losch, Patrick Heimbach
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Deacon; Drake Passage; New Zealand; Iceland; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.461.9294; http://epic.awi.de/12986/1/Los2006a.pdf

Bottom topography, or more generally the geometry of the ocean basins, is an important ingredient in numer-ical ocean modeling. With the help of an adjoint model, it is shown that scalar diagnostics or objective functions in a coarse resolution model, such as the transport through Drake Passage, the strength of the Atlantic meridional overturning circulation, the Deacon cell, and the meridional heat transport across 32◦S, are sensitive to bottom topography as much as they are to surface boundary conditions. For example, adjoint topography sensitivities of the transport through Drake Passage are large in choke point areas such as the Crozet-Kerguélen Plateau and south of New Zealand; the Atlantic meridional overturning circulation is sensitive to topography in the western boundary region of the North Atlantic Ocean and along the Scotland-Iceland ridge. Many sensitivities are con-nected to steep topography and can be interpreted in terms of bottom form stress, that is, the product of bottom pressure and topography gradient. The adjoint sensitivities are found to agree to direct perturbation methods with deviations smaller than 30 % for significant perturbations on time scales of 100 years, so that the assump-tion of quasi-linearity that is implicit to the adjoint method holds. The horizontal resolution of the numerical model affects the sensitivities to bottom topography, but large scale patterns and the overall impact of changes in topography appear to be robust. The relative impact of changes in topography and surface boundary conditions