A Note on the Stability Indicator of the Atlantic Meridional Overturning Circulation

Abstract

his study examines the validity of the net freshwater transport ?Mov as a stability indicator of the Atlantic meridional overturning circulation (AMOC) in a low-resolution version of the NCAR Community Climate System Model, version 3 (CCSM3). It is shown that the sign of ?Mov indicates the monostability or bistability of the AMOC, which is based on a hypothesis that a collapsed AMOC induces a zero net freshwater transport. In CCSM3, this hypothesis is satisfied in that the collapsed AMOC, with a nonzero strength, induces a zero net freshwater transport ?Mov across the Atlantic basin by generating equivalent freshwater export MovS and freshwater import MovN at the southern and northern boundaries, respectively. Because of the satisfaction of the hypothesis, ?Mov is consistent with a generalized indicator L for a slowly evolving AMOC, both of which correctly monitor the AMOC stability.