Eddies effect on low frequency variability of the Atlantic Meridional Overturning Circulation.
Eddies effect on low frequency variability of the Atlantic Meridional Overturning Circulation.
Abstract:
An increasing amount of evidence suggests that multidecadal and basin-scale variations of sea surface temperature in the North Atlantic are associated with AMOC variability. A proposed mechanism driving this variability is a large scale baroclinic instability of the North Atlantic Current giving rise to westward propagating planetary waves on interdecadal timescales. This mechanism has been studied extensively both in idealized and realistic setups.
However, due to the very long time scales involved (20 to 60 years) most of the numerical studies employ low spatial resolution and are thus unable to reproduce the high frequency part of the spectrum associated with mesoscale eddies. What is the profound nature of the interactions between the high-frequency motions and the low-frequency motions associated with these large-scale planetary waves remains to be determined.
To address this issue, we use an idealized setup of an Ocean General Circulation Model at eddy-permitting resolution (20km). Nonlinear scale interactions associated with eddy buoyancy transport are studied using cross-spectral analyses in the frequency domain.
A recent set of studies beginning with Arbic et al. 2014 shows that Kinetic Energy (KE) undergoes what has been called a temporal inverse cascade i.e. high frequencies are a source of low frequency KE. We show, however, that in our setup high frequency buoyancy variability is a sink for low frequency buoyancy variability, the latter being thus controlled by eddy-turbulence levels.
However, due to the very long time scales involved (20 to 60 years) most of the numerical studies employ low spatial resolution and are thus unable to reproduce the high frequency part of the spectrum associated with mesoscale eddies. What is the profound nature of the interactions between the high-frequency motions and the low-frequency motions associated with these large-scale planetary waves remains to be determined.
To address this issue, we use an idealized setup of an Ocean General Circulation Model at eddy-permitting resolution (20km). Nonlinear scale interactions associated with eddy buoyancy transport are studied using cross-spectral analyses in the frequency domain.
A recent set of studies beginning with Arbic et al. 2014 shows that Kinetic Energy (KE) undergoes what has been called a temporal inverse cascade i.e. high frequencies are a source of low frequency KE. We show, however, that in our setup high frequency buoyancy variability is a sink for low frequency buoyancy variability, the latter being thus controlled by eddy-turbulence levels.