Potential Vorticity Dynamics of Tropical Instability Vortices

Holmes, R. M.; Thomas, Leif N.; Thompson, LuAnne; Darr, David

doi:10.1175/jpo-d-13-0157.1

Cited by 39 publications

(56 citation statements)

References 45 publications

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“…Thus, the dynamic features of fronts over the shelf are different under the typical downwelling and upwelling seasons. The differences in dynamics can significantly influence the stability of fronts in the upper ocean by driving lateral mixing and vertical exchange between the ocean surface and interior [ Haine and Marshall , ; Fox‐Kemper et al ., ; D'Asaro et al ., ; Thomas et al ., ; Holmes et al ., ; Zhang and Gawarkiewicz , ; R. D. Hetland, Suppression of baroclinic instabilities in buoyancy driven flow over sloping bathymetry, manuscript in preparation, 2015].…”

Section: Results and Analysismentioning

confidence: 99%

“…The potential vorticity (PV) is a dynamical tracer of critical importance for the stability of ocean circulation and multiscale processes, as its distribution strongly affects the hydrostatic and geostrophic balances [ Hoskins , ; Thomas , ; Molemaker et al ., ; Capet et al ., ; Thomas et al ., ; Holmes et al ., ; Haney et al ., ]. A variety of instabilities can develop when the Ertel potential vorticity (PV),

q

, takes the opposite sign of the Coriolis parameter [ Hoskins , ].…”

Section: Methodsmentioning

confidence: 99%

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Seasonal thermal fronts on the northern South China Sea shelf: Satellite measurements and three repeated field surveys

Jing

Fox‐Kemper

et al. 2016

JGR Oceans

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Seasonal thermal fronts associated with wind‐driven coastal downwelling/upwelling in the northern South China Sea are investigated using satellite measurements and three repeated fine‐resolution mapping surveys in winter, spring, and summer. The results show that vigorous thermal fronts develop over the broad shelf with variable widths and intensities in different seasons, which tend to be approximately aligned with the 20–100 m isobaths. Driven by the prevailing winter/summer monsoon, the band‐shaped fronts were observed with a magnitude exceeding 0.1°C/km in the subsurface, and accompanied by energetic coastal downwelling/upwelling due to shoreward/offshore Ekman transport. The downward/upward tilting of seasonal thermoclines across the shelf exceeds 20 m, significantly contributing to the development of thermal fronts over the shelf. In addition, the diagnostic analysis of Potential Vorticity (PV) suggests that the summer frontal activities induced by the coastal upwelling are more stable to convection and symmetric instabilities in comparison to the winter fronts associated with downwelling‐favorable monsoon forcing. This is primarily due to their essential differences in the upper ocean stratification and horizontal buoyancy gradients arising from wind forcing. At the same time, the coastal currents are substantially regulated by the seasonal winds. An expected lag correlation between the velocity from mooring measurements and alongshore wind stress is detected near the frontal region. These results indicate that seasonal wind forcing plays an important role in the frontal activities and coastal water transport over the shelf.

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Section: Results and Analysismentioning

confidence: 99%

q

, takes the opposite sign of the Coriolis parameter [ Hoskins , ].…”

Section: Methodsmentioning

confidence: 99%

Seasonal thermal fronts on the northern South China Sea shelf: Satellite measurements and three repeated field surveys

Jing

Fox‐Kemper

et al. 2016

JGR Oceans

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{bold-italicω}_{h} \cdot {bold∇}_{h} (- ρ / ρ_{0})

, where

{bold-italicω}_{h}

is the horizontal component of the absolute vorticity

ω = f \overset{truê}{bold-italick} + \nabla \times u

) might not be negligible in this region [ Holmes et al ., ]. Indeed, Godfrey et al .…”

Section: Discussionmentioning

confidence: 99%

“…In this study, only the vertical component of the Ertel potential vorticity equation is considered. However, since we have seen that a steep slope in the pycnocline is observed at the separation latitude, the horizontal component (the baroclinic term) of the Ertel potential vorticity equation (given by x h Á $ h ð2q=q 0 Þ, where x h is the horizontal component of the absolute vorticity x5fk1 $3u) might not be negligible in Journal of Geophysical Research: Oceans 10.1002/2015JC011133 this region [Holmes et al, 2014]. Indeed, Godfrey et al [1980b] find low Richardson numbers at the separation latitude indicating that horizontal density gradients and shear might be of importance.…”

Section: 1002/2015jc011133mentioning

confidence: 92%

“…The planetary vorticity is negative in the southern hemisphere and the Rossby number (

R o = | ζ / f |

) calculated from the MOM025 fields in this region reaches values of 0.2, indicating that planetary vorticity is larger in magnitude than the relative vorticity. The minus sign in equation is chosen such that the potential vorticity will be negative in most locations in order to match other definitions of potential vorticity [ Holmes et al ., ].…”

Section: Methodsmentioning

confidence: 99%

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The separation of the East Australian Current: A Lagrangian approach to potential vorticity and upstream control

et al. 2016

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The East Australian Current (EAC) is the western boundary current flowing along the east coast of Australia separating from the coast at approximately 34°S. After the separation two main pathways can be distinguished, the eastward flowing Tasman Front and the extension of the EAC flowing southward. The area south of the separation latitude is eddy‐rich and the separation latitude of the EAC is variable. Little is known of the properties of the water masses that separate at the bifurcation of the EAC. This paper presents new insights from the Lagrangian perspective, where the water masses that veer east and those that continue south are tracked in an eddy‐permitting numerical model. The transport along the two pathways is computed, and a 1:3 ratio between transport in the EAC extension and transport in the Tasman Front is found. The results show that the “fate” of the particles is to first order already determined by the particle distribution within the EAC current upstream of the separation latitude, where 85% of the particles following the EAC extension originate from below 460 m and 90% of the particles following the Tasman Front originate from the top 460 m depth at 28°S. The separation and pathways are controlled by the structure of the isopycnals in this region. Analysis of anomalies in potential vorticity show that in the region where the two water masses overlap, the fate of the water depends on the presence of anticyclonic eddies that push isopycnals down and therefore enable particles to travel further south.

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Downward lee wave radiation from tropical instability waves in the central equatorial Pacific Ocean: A possible energy pathway to turbulent mixing

Tanaka

Hibiya

Sasaki³

2015

JGR Oceans

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Turbulent mixing in the equatorial Pacific Ocean is an important process that controls diapycnal heat transport and hence affects the air‐sea interactions and global climate. It is recently shown that, in the eastern equatorial Pacific, strong mixing is induced in the thermocline by enhanced vertical shear associated with tropical instability waves (TIWs), which propagate westward along the equator at a speed of ∼0.5 m normals−1 with a wavelength of ∼1000 km. In this study, using a high‐resolution ocean general circulation model, we show that the TIWs can play an important role in inducing turbulent mixing in the thermocline also in the central equatorial Pacific, although the thermocline is too deep to be directly affected by the vertical shear of the TIWs. The front of the TIW is clearly manifested as a narrow strip of strong convergence of horizontal surface flow, from which area downward and westward propagating internal waves are intermittently emanated. These internal waves can be interpreted as lee waves generated by the surface‐flow convergence zone, which acts like an inverted obstacle moving along the stratified ocean surface by inducing downward flow. The associated downward energy flux below the surface mixed layer increases as the TIW structure becomes deeper toward the central equatorial Pacific, so that the energy pathway to turbulent mixing in the thermocline can be created. The downward energy flux integrated over the entire equatorial Pacific and averaged during January 2011 amounts to ∼8.1 GW, occupying a significant fraction of the energy input to the TIWs.

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Potential Vorticity Dynamics of Tropical Instability Vortices

Cited by 39 publications

References 45 publications

Seasonal thermal fronts on the northern South China Sea shelf: Satellite measurements and three repeated field surveys

Seasonal thermal fronts on the northern South China Sea shelf: Satellite measurements and three repeated field surveys

The separation of the East Australian Current: A Lagrangian approach to potential vorticity and upstream control

Downward lee wave radiation from tropical instability waves in the central equatorial Pacific Ocean: A possible energy pathway to turbulent mixing

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