Modulation of equatorial turbulence by a tropical instability wave

Inoue, Ryuichiro; Lien, Ren‐Chieh; Moum, James N.

doi:10.1029/2011jc007767

Cited by 38 publications

(51 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Both du/dz and dv/dz contribute substantially to total vertical shear at all depths (Figures d and e), and often the contribution of dv/dz to the total shear squared exceeds that of du/dz (red and blue lines in Figure a, respectively). This differs from the equator where du/dz associated with the westward SECN, and the underlying eastward flowing Equatorial Undercurrent dominates the total shear as seen in the Pacific during a TIW season (e.g., Inoue et al, , ), and du/dz is often the only component documented in the equatorial Atlantic (e.g., Wenegrat & McPhaden, ).…”

Section: Resultsmentioning

confidence: 99%

Direct Measurements of Upper Ocean Horizontal Velocity and Vertical Shear in the Tropical North Atlantic at 4°Ν, 23°W

et al. 2019

View full text Add to dashboard Cite

The Tropical Atlantic Current Observations Study measured upper ocean horizontal velocity from a mooring at 4°N, 23°W, at discrete depths between 7 and 87 m, in order to observe the temporal and vertical structure of the currents. Between March 2017 and March 2018, mean zonal velocity and vertical shear were strongest between 32 and 37 m. Near‐surface mean eastward currents during this period were weaker than the long‐term mean but within the range of previously observed values given the high interannual variability. Interannual variability of the zonal velocity exceeded that of the meridional velocity, was primarily geostrophically driven, and was strongly influenced by the large‐scale currents. Energetic tropical instability waves (TIWs) were observed in early summer and late fall of 2017. Meridional velocity fluctuations associated with the TIWs were far larger than those of zonal velocity and extended down to 87 m. These fluctuations propagated upward to the surface with vertical phase speeds between 12 and 15 m/day. Coherent velocity and vertical shear variations emerged in a TIW composite. However, the vertical shears observed during the TIW season were modest compared to the large shear measured in spring 2017 and winter 2018. As a result, TIWs may be less crucial for vertical turbulent cooling at 4°N, 23°W than they are near the equator. To observe the intense winter/spring vertical shear events, fine vertical (less than 10 m) and diurnal temporal sampling is needed.

show abstract

Section: Resultsmentioning

confidence: 99%

Direct Measurements of Upper Ocean Horizontal Velocity and Vertical Shear in the Tropical North Atlantic at 4°Ν, 23°W

et al. 2019

View full text Add to dashboard Cite

show abstract

“…On 2 November, a front associated with a tropical instability wave passed the measurement point (sharp temperature jump in Fig. 1c), introducing a significantly different dynamical regime (Moum et al 2009;Inoue et al 2012). In particular, wave-generated currents reduced the regularity of the diurnal mixing cycle.…”

Section: A Measurementsmentioning

confidence: 99%

“…Our most recent equatorial measurements (Moum et al 2009;Inoue et al 2012) include velocity profiles with a vertical resolution considerably finer than was previously possible and that show new details of the near-surface currents. In particular, the measurements clearly reveal the evening descent of a shear layer that builds up at the surface during the day and then descends through the late afternoon and evening.…”

Section: Introductionmentioning

confidence: 99%

Diurnal Shear Instability, the Descent of the Surface Shear Layer, and the Deep Cycle of Equatorial Turbulence

Smyth

Thorpe

2013

Journal of Physical Oceanography

Self Cite

View full text Add to dashboard Cite

A new theory of shear instability in a turbulent environment is applied to eight days of velocity and density profiles from the upper-equatorial Pacific. This period featured a regular diurnal cycle of surface forcing, together with a clear response in upper-ocean mixing. During the day, a layer of stable stratification and shear forms at the surface. During late afternoon and evening, this stratified shear layer descends, leaving the nocturnal mixing layer above it. Using high-resolution current measurements, the detailed structure of the descending shear layer is seen for the first time. Linear stability analysis is conducted using a new method that accounts for the effects of preexisting turbulence on instability growth. Shear instability follows a diurnal cycle linked to the afternoon descent of the surface shear layer. This cycle is revealed only when the effect of turbulence is accounted for in the stability analysis. The cycle of instability leads the diurnal mixing cycle, typically by 2-3 h, consistent with the time needed for instabilities to grow and break. Late at night, the resulting turbulence suppresses further instabilities, lending an asymmetry to the mixing cycle that has not been noticed in previous measurements. Deep cycle mixing is triggered by instabilities formed as the descending shear layer merges with the marginally unstable shear of the Equatorial Undercurrent. In the morning, turbulence decays and the upper ocean restratifies. Wind accelerates the near-surface flow to form a new unstable shear layer, and the cycle begins again.

show abstract

“…Instead of sampling at a single location for a period of several days to several weeks (Peters et al 1988;Moum et al 1989Moum et al , 2009Lien et al 1995;Inoue et al 2012), profiling was done at several locations during a single cruise usually separated by 0.5° latitude on the meridional transects. This was accomplished by integrating microstructure profiling into the CTD station program during all cruises.…”

Section: Shipboard Observationsmentioning

confidence: 99%