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Marginal instability and deep cycle turbulence in the eastern equatorial Pacific Ocean
Author(s) -
Smyth W. D.,
Moum J. N.
Publication year - 2013
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2013gl058403
Subject(s) - turbulence , instability , stratification (seeds) , zonal flow (plasma) , geology , climatology , forcing (mathematics) , physics , atmospheric sciences , meteorology , environmental science , mechanics , plasma , biology , seed dormancy , germination , botany , quantum mechanics , dormancy , tokamak
Deep cycle mixing in the cold tongue of the equatorial Pacific Ocean is associated with a mean flow regime in which the gradient Richardson number R i (a ratio of stratification to shear that affects the evolution of turbulence) fluctuates about a critical value near1 4 . This is the state of marginal instability (MI), a stable equilibrium between forcing by the trade winds (which works to reduce R i ) and turbulence (which works to increase R i ). Besides providing insight into the physics of deep cycle turbulence, MI is easily recognized in moored records of currents and density, and may therefore provide a valuable indicator of turbulence in historical data where direct turbulence measurements were not made. In this initial study, the seasonal cycle of MI is described. MI is present for 9 months of the year but disappears in March, April, and May, consistent with the recently discovered springtime minimum of equatorial turbulence.