Propagation of signals in basin‐scale ocean bottom pressure from a barotropic model

Abstract

[1] The exchange of atmospheric plus oceanic mass between ocean basins is investigated using a global barotropic ocean model. We find two particular cases of exchange between two basins. At periods of 4-6 days, the exchange is between the Atlantic and Pacific basins, and represents a known oscillation forced by atmospheric pressure. This mode represents a failure of the inverse-barometer relationship due to the large scale and high frequency of atmospheric forcing, and the presence of continents. Significant exchange between Atlantic and Pacific also occurs at longer periods. The second case is most prominent at periods longer than 30 days (strongest at periods longer than 100 days), and represents a mass exchange between the Southern Ocean and the Pacific. The Southern Ocean part of this exchange is clearly related to the Southern Mode of fluctuations in Antarctic circumpolar transport, forced by Southern Ocean wind stress. The reason for the exchange being with the Pacific rather than other basins is explored, and is found to be related to the balance of wind stress by form stress in Drake Passage: exchange with the Atlantic and Indian oceans becomes dominant if Drake Passage topography is removed. While recognizing the limitations of a barotropic model, we contend that it is necessary to understand the barotropic adjustment process in order to make sense of longer timescale processes. Accordingly, we end with speculation on the possible importance of the barotropic results for global sea level and tropical dynamics.

Coherence of Western Boundary Pressure at the RAPID WAVE Array: Boundary Wave Adjustments or Deep Western Boundary Current Advection?

“…If this also occurs at our latitudes, any net northward transports associated with these barotropic pressure perturbations are likely to be smaller than the 12.5 Sv number estimated above when the eastern boundary is constant. Nevertheless, these perturbations still produce net meridional transports across latitudes, on synoptic atmospheric time scales associated with global oscillations of masses between ocean basins (Stepanov and Hughes 2006). Detection of these signals, and their spatial coherence over large distances, demonstrates that the instruments are producing good quality data and are capable of detecting propagating signals.…”

Arctic Ocean Circulation Patterns Revealed by GRACE

“…With simultaneous observations of OBP in different locations, the barotropic mass transport between the locations may be determined (Wearn and Baker 1980;Morison 1991). Ocean mass transport may be used to study overturning flow variations (Roussenov et al 2008), mass exchange between ocean basins (Hughes and Stepanov 2004;Stepanov and Hughes 2006;Chambers and Willis 2009), and freshwater changes in the ocean (Morison et al 2007(Morison et al , 2012. On a broader scale, changes in mass, and therefore changes in OBP, are directly related to water mass exchanges among the ocean, cryosphere, and hydrosphere (Wahr et al 1998).…”

GRACE, time-varying gravity, Earth system dynamics and climate change

“…Although previous studies based on models demonstrated there are large-scale redistributions of mass within the ocean at periods of a year or shorter [282,277,283], interannual variations were considered suspect due to potential drift in the models. Chambers and Willis [284], however, demonstrated large, coherent mass exchanges between the Indo-Atlantic and Pacific oceans, on time-scales longer than 1-year ( Figure 27).…”