Award: OCE-2038449

Large-scale ocean currents carry and redistribute heat and freshwater throughout different part of ocean basins, hence play an important role in the earth climate system. Numerical models that can truthfully represent these currents are a useful tool for our understanding of the mechanisms behind the change in these currents. The overall goal of the UK-US collaborative project “Subpolar North Atlantic Processes” is to use observations and numerical models to improve our understanding of the currents in the subpolar North Atlantic. Our research focused on numerical models of the North Atlantic Ocean, and we tackled basic questions like how important is vertical resolution (that is to resolve different water masses in the ocean) in representing these currents? Do small scale bathymetry details matter in the pathway and variability of the major current like the Gulf Stream? And what is nature of the variability that is in the subpolar North Atlantic? The main outcomes of the project include 3 scientific papers (2 led by the PIs) published in Journal of Physical Oceanography and Ocean modelling, and 1 manuscript to be submitted to Journal of Geophysical Research-Oceans. These studies help us understand the detail spatial structure of these currents as part of the basin scale ocean circulation that is fundamental to the earth climate system.

The selected five figures in this outcome report highlight

a)     the impact of relatively small details in the bathymetry of the New England Seamount Chain on the path and variability of the Gulf Stream. The results are based on 1/50° simulations and they show that including the fine-scale details of the New England Seamount Chain led to a more realistic path and variability pattern as observed (Figure 1).

b)    the impact of vertical resolution on the spatial structure of the Atlantic circulation. The results are based on 1/12° simulations and they show that, as the vertical resolution increases, the vertical structure of the modeled AMOC streamfunction is improved toward a closer agreement with the observations (Figure 2). The difference from 24 to 96 layer, however, is relatively small, indicating that the modeled AMOC structure is robust when the vertical resolution is adequate for a reasonable representation of the key water masses in the North Atlantic. Similarly, these four models with vertical resolution ranging from 24 to 96 layers represent a similar the horizontal circulation pattern that agree with the observations (Figure 3).

c)     the AMOC variability in the subpolar North Atlantic. The results based on interannually forced nature run show that the model represent a significant part of the observed AMOC variability (Figure 4). The seasonal variability of the AMOC is contributed from the variability in the East Greenland Current, which is modulated by the up and down movements in density surfaces due to seasonal warming/cooling in the western Irminger Sea (Figure 5); the shorter, intraseasonal variability is primarily contributed directly from the wind variability over the full trans-Atlantic section through Ekman transport.

Xu, X., Chassignet, E. P., and A. J. Wallcraft, 2023, Impact of vertical resolution on representing baroclinic modes and water mass distribution in the North Atlantic, Ocean Modelling, doi: 10.1016/j.ocemod.2023.102261.

Chassignet, E. P., X. Xu, A. Bozec, and T. Uchida, 2023, Impact of the New England seamount chain on Gulf Stream pathway and variability, Journal of Physical Oceanography, doi:10.1175/JPO-D-23-0008.1

Lozier, M. S., A. S. Bower, H. H. Furey, K. L. Drouin, X. Xu, and S. Zou, 2022, Overflow water pathways in the North Atlantic, Progress in Oceanography, doi:10.1016/j.pocean.2022.102874

Xu, X. and E. P. Chassignet, 2024, Subpolar North Atlantic in 2014-2020, what do we learn from comparing high-resolution numerical simulation and observations? manuscript to be submitted to Journal of Geophysical Research: Oceans

Last Modified: 10/31/2024
Modified by: Xiaobiao Xu