WHOI PO

"Can stratospheric temperature control the linkagebetween the AMOC and Atlantic multidecadal variability"

The ocean’s role in AtlanticMultidecadal Variability (AMV) remains intensely debated. The core issue iswhether AMV is driven by variations in Atlantic Meridional OverturningCirculation (AMOC) or atmospheric processes. Climate models exhibit wide diversityin AMOC-AMV linkages, but no robust explanation for these differences exists.Here, using a multi-model intercomparison and perturbation experiments, wepropose a dynamical mechanism relating the strength of AMOC-AMV linkage inclimate models to stratospheric temperature. This mechanism includes (1)tropospheric midlatitude jet response to stratospheric mean-state temperatureanomalies in mid-latitudes and (2) resulting ocean surface density changes thatalter the spatial structure of deep-water formation in the subpolar NorthAtlantic and hence AMOC-AMV connection. Specifically, colder stratospherictemperatures produce tighter linkage through the northward shift of the jet anda stronger AMOC, with enhanced deep-water formation in the Labrador and IrmingerSeas relative to the Nordic Seas. Models with a warm stratospheric bias tend toproduce weaker linkage. Perturbations experiments imposing stratosphericcooling at mid to high latitudes within two different climate models supportthese conclusions. Furthermore, we find that models with stronger AMOC-AMVlinkage predict a stronger North Atlantic “warming hole” and weaker21st-century Arctic amplification, critical for climate projections.