TY  - JOUR
A1  - Fürst, Johannes J.
A1  - Levermann, Anders
T1  - A minimal model for wind- and mixing-driven overturning  threshold behavior for both driving mechanisms
JF  - Climate dynamics : observational, theoretical and computational research on the climate system
N2  - We present a minimal conceptual model for the Atlantic meridional overturning circulation which incorporates the advection of salinity and the basic dynamics of the oceanic pycnocline. Four tracer transport processes following Gnanadesikan in Science 283(5410):2077-2079, (1999) allow for a dynamical adjustment of the oceanic pycnocline which defines the vertical extent of a mid-latitudinal box. At the same time the model captures the salt-advection feedback (Stommel in Tellus 13(2):224-230, (1961)). Due to its simplicity the model can be solved analytically in the purely wind- and purely mixing-driven cases. We find the possibility of abrupt transition in response to surface freshwater forcing in both cases even though the circulations are very different in physics and geometry. This analytical approach also provides expressions for the critical freshwater input marking the change in the dynamics of the system. Our analysis shows that including the pycnocline dynamics in a salt-advection model causes a decrease in the freshwater sensitivity of its northern sinking up to a threshold at which the circulation breaks down. Compared to previous studies the model is restricted to the essential ingredients. Still, it exhibits a rich behavior which reaches beyond the scope of this study and might be used as a paradigm for the qualitative behaviour of the Atlantic overturning in the discussion of driving mechanisms.
KW  - Meridional overturning circulation
KW  - Northern sinking
KW  - Critical freshwater threshold
KW  - Overturning sensitivity
KW  - Conceptual model
KW  - Stability
KW  - Atlantic meridional overturning circulation
KW  - Pycnocline depth
KW  - Driving mechanism
Y1  - 2012
U6  - https://doi.org/10.1007/s00382-011-1003-7
SN  - 0930-7575
VL  - 38
IS  - 1-2
SP  - 239
EP  - 260
PB  - Springer
CY  - New York
ER  -