Meridional overturning transports at 7.5N and 24.5N in the Atlantic Ocean during 1992–93 and 2010–11

Atlantic Meridional Overturning Circulation at 14.5° N in 1989 and 2013 and 24.5° N in 1992 and 2015: volume, heat, and freshwater transports

“…The 1992 realization at 24.5 • N has been used in several previous studies (e.g., Ganachaud, 2003;Lumpkin and Speer, 2003;Hernández-Guerra et al, 2014); we found that the circulation structure and strength is very stable among these studies, even though different hydrographic sections were combined with this realization to build the box inverse models. This can be attributed to the similar steady-state initial condition and constraints applied to the box inverse models.…”

“…At 24.5 • N, the water mass properties have been described extensively (e.g., Roemmich and Wunsch, 1985;Hernández-Guerra et al, 2014). Here we briefly describe the water mass properties and emphasize property differences between 1989/1992 and 2013/2015 along the two sections.…”

“…For the 14.5 • N section, the reference level for both realizations was chosen following Klein et al (1995) as the surface of γ n = 27.82 kg m −3 , which separates the AAIW and the UN-ADW. For the two realizations along the 24.5 • N section, the reference level was defined by γ n = 28.141 kg m −3 , which separates the LNADW and AABW Hernández-Guerra et al, 2014). The neutral surfaces with γ n ≥ 28.141 kg m −3 tilt upward toward the east on the western side of the MAR.…”

“…Except for the 2013 realizations at 14.5 • N, we set the a priori uncertainties for the reference velocity of the other three realizations to be 0.04 m s −1 at the western boundary region and 0.02 m s −1 for the rest of the station pairs following Hernández-Guerra et al (2014). Since no direct velocity observations are available for these three realizations, the choice of the a priori uncertainty is relatively arbitrary.…”

“…The 24.5 • N section, aligned with the RAPID array, is one of the most frequently surveyed basin-wide zonal sections in the North Atlantic. Many aspects of the AMOC along 24.5 • N, in terms of transport components, circulation patterns, and heat and freshwater transports, are well described and provide reliable information on constraining a box inverse model (Roemmich and Wunsch, 1985;Ganachaud, 2003;Lumpkin and Speer, 2003;Atkinson et al, 2012;Hernández-Guerra et al, 2014). Therefore, we chose this section in combination with the 14.5 • N section for the box inverse model, which allow us to pay more attention to the less well-studied features associated with the 14.5 • N section.…”