Resolution Dependence of Atmosphere–Ocean Interactions and Water Mass Transformation in the North Atlantic. Issue 4 (4th April 2022)

• Record Type: Journal Article
• Authors: Oldenburg, Dylan; Wills, Robert C. J.; Armour, Kyle C.; Thompson, LuAnne
• Is Part Of: Journal of geophysical research. Volume 127:Issue 4(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-04-04
• Subjects: Meridional Overturning Circulation -- North Atlantic climate variability -- water mass transformation -- coupled models; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC018102
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Water mass transformation (WMT) in the North Atlantic plays a key role in driving the Atlantic Meridional Overturning Circulation (AMOC) and its variability. Here, we analyze subpolar North Atlantic WMT in high‐ and low‐resolution versions of the Community Earth System Model version 1 (CESM1) and investigate whether differences in resolution and climatological WMT impact low‐frequency AMOC variability and the atmospheric response to this variability. We find that high‐resolution simulations reproduce the WMT found in a reanalysis‐forced high‐resolution ocean simulation more accurately than low‐resolution simulations. We also find that the low‐resolution simulations, including one forced with the same atmospheric reanalysis data, have larger biases in surface heat fluxes, sea‐surface temperatures, and salinities compared to the high‐resolution simulations. Despite these major climatological differences, the mechanisms of low‐frequency AMOC variability are similar in the high‐ and low‐resolution versions of CESM1. The Labrador Sea WMT plays a major role in driving AMOC variability, and a similar North Atlantic Oscillation‐like sea‐level pressure pattern leads AMOC changes. However, the high‐resolution simulation shows a pronounced atmospheric response to the AMOC variability not found in the low‐resolution version. The consistent role of Labrador Sea WMT in low‐frequency AMOC variability across high‐ and low‐resolution coupled simulations, including a simulation which accurately reproduces the WMT found in an atmospheric‐reanalysis‐forced high‐resolution ocean simulation, suggests that the mechanisms may be similar in nature. Plain Language Summary: Water mass transformation, which is a measure of density change in the surface ocean, plays an important role in variations in the Atlantic Meridional Overturning Circulation (AMOC). Here, we use high‐ and low‐resolution‐coupled model simulations to determine whether resolution and time‐mean water mass transformation patterns impact AMOC variations. We find that a high‐resolution coupled simulation reproduces the water mass transformation from our closest analog to observations and yields more realistic surface ocean features than its low‐resolution counterpart. Despite these differences, the mechanisms governing decadal and multidecadal AMOC variations are similar in the two simulations. In both simulations, the Labrador Sea plays a prominent role in driving decadal and multidecadal AMOC variations. Given that the high‐resolution simulation accurately reproduces the water mass transformation patterns found in our closest analog to observations, it is likely that the Labrador Sea plays a major role in driving AMOC variations in nature as well. Key Points: A high‐resolution coupled simulation skillfully reproduces climatological water mass transformation in the subpolar North Atlantic Despite climatological differences between low‐ and high‐resolution models, the Labrador Sea plays a major role in AMOC variability in both High‐resolution simulations show a larger atmospheric response to low‐frequency AMOC variability