Varied representation of the Atlantic Meridional Overturning across multidecadal ocean reanalyses

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is an integral part of the circulation in the Atlantic Ocean. The AMOC is typically characterized by the meridional streamfunction, which is also an indicator of the thermohaline circulation. This paper explores the mean state and long-term variability of the Atlantic meridional streamfunction and Atlantic meridional heat transport from six multidecadal ocean reanalysis. Statistics based on the meridional overturning streamfunction and the meridional heat transport are computed in the same manner across the products, and analyzed. The maximum streamfunction values in the Atlantic are located between 35°N and 50°N for the various ocean reanalyses. The Atlantic heat transport is greater between the Greater Antilles (at about 20°N) and 25°N, similar to the observations. The streamfunction and heat transport have stronger seasonality in the deep tropics. In the North Atlantic the annual harmonic of the streamfunction has greater amplitude in July between 40°N and 50°N. Even though there are differences in the mean strength of the streamfunction and the heat transport, there are robust similarities in their seasonal cycle across ocean reanalyses. Furthermore, although the year-to-year variability of the meridional heat transport is not consistent across products, there are other aspects that are consistent. The relationship between streamfunction and meridional heat transport at 30°N (i.e., in the northern hemisphere) shows greater consistency than that between streamfunction and meridional heat transport at 30°S (i.e., in the southern hemisphere). Also, even though the North Atlantic sea surface temperature (SST) anomalies are greatly consistent, their relationship with the meridional streamfunction is disparate. However, the relationship between North Atlantic SST anomalies and meridional heat transport shows some consistency with respect to the meridional profile. The greater numbers of temperature data assimilated may help in constraining the meridional heat transport more than the streamfunction, thereby indicating the meridional heat transport to be an important field to analyze with respect to observed changes in the AMOC.