التفاصيل البيبلوغرافية
| العنوان: |
Vertical Momentum Transport by Internal Gravity Waves Above the Equatorial Undercurrent at 140°W. |
| المؤلفون: |
Pinkel, R.1 (AUTHOR) rpinkel@ucsd.edu, Nguyen, S.1 (AUTHOR), Smith, J. A.1 (AUTHOR), Lucas, A. J.1,2 (AUTHOR), Reineman, B. D.1 (AUTHOR), Waterhouse, A. F.1 (AUTHOR) |
| المصدر: |
Geophysical Research Letters. 7/28/2023, Vol. 50 Issue 14, p1-10. 10p. |
| مصطلحات موضوعية: |
*GRAVITY waves, *INTERNAL waves, *TRADE winds, *DOPPLER radar, *WIND shear, *SURFACE scattering, *ROSSBY waves, *RAYLEIGH number |
| مستخلص: |
Strong vertical shears occur in the upper Equatorial Ocean as the trade winds drive the South Equatorial Current westward above the eastward flowing Equatorial Undercurrent. An extremely large "effective viscosity" or vertical momentum transport is required to maintain the speed‐differential between the currents as observed. In the 2012 EquatorMix Experiment data from a 1.8 km optical fiber temperature array and a surface scattering radar were combined with high‐resolution shipboard profiling CTD and Doppler sonar measurements to determine the directionality of energetic ∼600 m wavelength internal waves existing above the Undercurrent. A large vertical momentum flux is found (∼10−4 m2 s−2), with waves excited by nocturnal sea surface convection and maintained by near‐surface critical layer over‐reflection. The net downward‐westward momentum flux is an index of the energy lost during reflection below the Undercurrent. Together with near‐surface‐turbulence, these waves provide the momentum transport needed to balance the large‐scale forcing of the equatorial current system. Plain Language Summary: The trade winds push equatorial surface waters westward over the eastward flowing Equatorial Undercurrent ∼100 m below. Given the known basin‐scale forcing, the observed velocity difference between these opposing flows, ∼1.5 m s−1, is understandable provided the upper ocean has an "effective viscosity" roughly equivalent to that of honey. Observed turbulence levels are insufficient to support this level of viscosity at depth. In the 2012 EquatorMix Experiment, sea surface spatial observations from a 1.8 km optical fiber temperature‐sensing array and a Doppler radar were combined with rapidly‐sampled vertical profiles of ocean density and velocity to identify a class of ∼600 m wavelength internal gravity waves that exist above the Undercurrent. These exchange the westward momentum of the sea surface with the Undercurrent's eastward momentum. The waves are triggered by convection resulting from the nocturnal cooling of the sea surface. They propagate downward and westward, reflecting below the Undercurrent Core. The net momentum deposition is associated with the degree of dissipation in the deep reflection process. The upward‐reflected waves arrive at the surface and subsequently reflect back downward, receiving additional energy and momentum from the wind‐driven shear in a process known as critical layer over‐reflection. Key Points: Energetic internal waves are found in the highly sheared region above the Equatorial Undercurrent in the Eastern Equatorial PacificThe waves support a large momentum exchange between the westward flowing S. Equatorial Current and the eastward moving Undercurrent belowThe waves are triggered by nocturnal convection, fueled by wind driven shear, and maintained by over‐reflection at a near‐surface critical layer [ABSTRACT FROM AUTHOR] |
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