Decomposing Barotropic Transport Variability in a High-Resolution Model of the North Atlantic Ocean

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Wang, Yuan, Greatbatch, Richard J, Claus, Martin, Sheng, Jinyu
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 2020
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://livrepository.liverpool.ac.uk/3136473/; https://doi.org/10.1029/2019jc015516

A method using a linear shallow water model is presented for decomposing the temporal variability of the barotropic stream function in a high-resolution ocean model. The method is based on the vertically averaged momentum equations and is applied to the time series of annual mean stream function from the model configuration VIKING20 for the northern North Atlantic. An important result is the role played by the nonlinear advection terms in VIKING20 for driving transport. The method is illustrated by examining how the Gulf Stream transport in the recirculation region responds to the winter North Atlantic Oscillation (NAO). While no statistically significant response is found in the year overlapping with the winter NAO index, there is a tendency for the Gulf Stream transport to increase as the NAO becomes more positive. This becomes significant in lead years 1 and 2 when the mean flow advection and eddy momentum flux contributions, associated with nonlinear momentum advection, dominate. Only after 2 years, does the potential energy term, associated with the density field, start to play a role and it is only after 5 years that the transport dependence on the NAO ceases to be significant. It is also shown that the potential energy contribution to the transport stream function has significant memory of up to 5 years in the Labrador and Irminger Seas. However, it is only around the northern rim of these seas that VIKING20 and the transport reconstruction exhibit similar memory. This is due to masking by the mean flow advection and eddy momentum flux contributions.