Direct Temporal Cascade of Temperature Variance in Eddy-Permitting Simulations of Multidecadal Variability

• Published in: Journal of climate Vol. 33; no. 21; pp. 9409 - 9425
• Main Authors: Hochet, Antoine, Huck, Thierry, Arzel, Olivier, Sévellec, Florian, de Verdière, Alain Colin, Mazloff, Matthew, Cornuelle, Bruce
• Format: Journal Article
• Language: English
• Published: Boston American Meteorological Society 01.11.2020
• Subjects: 20th century; Baroclinic instability; Diagnostic systems; Eddies; Fluxes; General circulation models; Mathematical models; Mesoscale eddies; Mesoscale phenomena; North Atlantic Current; Numerical models; Ocean circulation; Ocean, Atmosphere; Oceanic general circulation model; Resolution; Sciences of the Universe; Sea surface; Sea surface temperature; Surface temperature; Temperature gradients; Variability; Vortices
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/JCLI-D-19-0921.1

The North Atlantic is characterized by basin-scale multidecadal fluctuations of the sea surface temperature with periods ranging from 20 to 70 years. One candidate for such a variability is a large-scale baroclinic instability of the temperature gradients across the Atlantic associated with the North Atlantic Current. Because of the long time scales involved, most of the studies devoted to this problem are based on low-resolution numerical models leaving aside the effect of explicit mesoscale eddies. How high-frequency motions associated with the mesoscale eddy field affect the basin-scale low-frequency variability is the central question of this study. This issue is addressed using an idealized configuration of an ocean general circulation model at eddy-permitting resolution (20 km). A new diagnostic allowing the calculation of nonlinear fluxes of temperature variance in frequency space is presented. Using this diagnostic, we show that the primary effect of mesoscale eddies is to damp low-frequency temperature variance and to transfer it to high frequencies.