Oceanography The Official Magazine of
The Oceanography Society
Volume 30 Issue 03

View Issue TOC
Volume 30, No. 3
Pages 110 - 119

OpenAccess

Internal Waves Along the Malvinas Current: Evidence of Transcritical Generation in Satellite Imagery

By Jorge M. Magalhães  and José C.B. da Silva 
Jump to
Article Abstract Citation Supplementary Materials References Copyright & Usage
Article Abstract

An extended satellite image data set is used to investigate the two-dimensional structure of internal waves (IWs) that propagate along the Patagonian shelf break and continental slope in the opposite direction of the Malvinas Current (MC). Intense surface manifestations of IWs are found throughout the semidiurnal and fortnightly tidal cycles, propagating more than 1,000 km in the along-slope direction between 38°S and 48°S. An instantaneous 800 km view provided by the Sentinel-2A satellite multispectral imager shows a nearly continuous IW field in which inter-packet distances do not fit the usual semidiurnal tidal scales observed in coastal waters. Instead, acoustic Doppler current profiler-measured currents and CTD station data are consistent with resonant generation mechanisms in which the MC flows over bottom topography and generates upstream-propagating waves in a transcritical regime. These conditions are known to cause extra dissipation and mixing, whose effects over time and along more than 1,000 km may be important to a wider scope of ocean applications.

Citation

Magalhães, J.M., and J.C.B. da Silva. 2017. Internal waves along the Malvinas Current: Evidence of transcritical generation in satellite imagery. Oceanography 30(3):110–119, https://doi.org/10.5670/oceanog.2017.319.

Supplementary Materials

Figure S1. An ensemble of climatological stratifications along the Patagonian shelf break and continental slope (highlighted in the left panel using selected isobaths). The blue envelope represents the maxima in the Brunt-Väisälä frequencies for all austral winter profiles between 200 m and 2,000 m as a function of latitude; average values for July along the 1,000 m isobath are shown as a black solid line. The orange envelope is the same for the austral summer, and in this case the solid black line is for January. > 96 KB pdf 

Figure S2. A mosaic from Sentinel-2A acquisitions dated February 19, 2016, between 22:57 and 23:02 UTC (corresponding to its spectral band 6 centered at 740 nm). Selected isobaths are also given for 200, 500, 1,000, and 2,000 m. > 562 KB pdf | 20.2 MB kmz

Figure S3. A synergy between two RGB composites dated January 31, 2016, acquired at 14:00 UTC (MODIS-Terra) and 17:20 UTC (Suomi-Viirs). > 498 KB pdf | 1.6 MB kmz

Figure S4. An RGB composite from a MODIS-Aqua acquisition dated January 6, 2014, at 17:45 UTC. > 582 KB pdf | 134 KB kmz

References

Alpers, W. 1985. Theory of radar imaging of internal waves. Nature 314:245–247, https://doi.org/​10.1038/314245a0.

Bell, T.H. Jr. 1975. Topographically generated internal waves in the open ocean. Journal of Geophysical Research 80:320–327, https://doi.org/10.1029/JC080i003p00320.

Bogucki, D., T. Dickey, and L.G. Redekopp. 1997. Sediment resuspension and mixing by resonantly generated internal solitary waves. Journal of Physical Oceanography 27:1,181–1,196, https://doi.org/10.1175/​1520-0485(1997)027​<1181:SRAMBR>2.0.CO;2.

Bogucki, D., and C. Garrett. 1993. A simple model for the shear induced decay of an internal solitary wave. Journal of Physical Oceanography 23:1–10, https://doi.org/10.1175/1520-0485(1993)023<1767:​ASMFTS>2.0.CO;2.

Buijsman, M.C., J.K. Ansong, B.K. Arbic, J.G. Richman, J.F. Shriver, P.G. Timko, A.J. Wallcraft, C.B. Whalen, and Z.X. Zhao. 2016. Impact of parameterized internal wave drag on the semidiurnal energy balance in a global ocean circulation model. Journal of Physical Oceanography 46(5):1,399–1,419, https://doi.org/10.1175/JPO-D-15-0074.1.

Chen, Z., Y. Nie, J. Xie, J. Xu, Y. He, and S. Cai. 2017. Generation of internal solitary waves over a large sill: From Knight Inlet to Luzon Strait. Journal of Geophysical Research 122:1,555–1,573, https://doi.org/10.1002/2016JC012206.

Combes, V., and R.P. Matano. 2014. Trends in the Brazil/Malvinas Confluence region. Geophysical Research Letters 41:8,971–8,977, https://doi.org/​10.1002/2014GL062523.

da Silva, J.C.B, M.C. Buijsman, and J.M. Magalhães. 2015. Internal waves on the upstream side of a large sill of the Mascarene Ridge: A comprehensive view of their generation mechanisms and evolution. Deep Sea Research Part I 99:87–104, https://doi.org/10.1016/j.dsr.2015.01.002.

da Silva, J.C.B., S.A. Ermakov, and I.S. Robinson. 2000. Role of surface films in ERS-SAR signatures of internal waves on the shelf: Part 3. Mode transitions. Journal of Geophysical Research 105:24,089–24,104, https://doi.org/10.1029/2000JC900053.

da Silva, J.C.B., and K.R. Helfrich. 2008. Synthetic Aperture Radar observations of resonantly generated internal solitary waves at Race Point Channel (Cape Cod). Journal of Geophysical Research 113, C11016, https://doi.org/10.1029/2008JC005004.

da Silva, J.C.B., A.L. New, and J.M. Magalhães. 2009. Internal solitary waves in the Mozambique Channel: Observations and interpretation. Journal of Geophysical Research 114, C05001, https://doi.org/10.1029/2008JC005125.

Egbert, G.D., and S.Y. Erofeeva. 2002. Efficient inverse modeling of barotropic ocean tides. Journal of Oceanic and Atmospheric Technology 19:183–204, https://doi.org/10.1175/1520-0426(2002)019<0183:EIMOBO>2.0.CO;2.

Etcheverry, L.A.R., M. Saraceno, A.R. Piola, and P.T. Strub. 2016. Sea level anomaly on the Patagonian continental shelf: Trends, annual patterns and geostrophic flows. Journal of Geophysical Research 121:2,733–2,754, https://doi.org/​10.1002/2015jc011265.

Farmer, D.M., and L. Armi. 1999. The generation and trapping of internal solitary waves over topography. Science 283:188–190, https://doi.org/10.1126/science.283.5399.188.

Jackson, C.R. 2004. An Atlas of Internal Solitary-like Waves and their Properties, 2nd ed. Global Ocean Associates, Alexandria, VA, 560 pp., http://www.internalwaveatlas.com.

Jackson, C.R. 2007. Internal wave detection using the Moderate Resolution Imaging Spectroradiometer (MODIS). Journal of Geophysical Research 112, C11012, https://doi.org/10.1029/2007JC004220.

Jackson, C.R., and W. Alpers. 2010. The role of the critical angle in brightness reversals on sunglint images of the sea surface. Journal of Geophysical Research 115, C09019, https://doi.org/10.1029/2009JC006037.

Jackson, C.R., J.C.B. da Silva, and G. Jeans. 2012. The generation of nonlinear internal waves. Oceanography 25(2):108–123, https://doi.org/​10.5670/oceanog.2012.46.

Kodaira, T., T. Waseda, and Y. Miyazawa. 2014. Nonlinear internal waves generated and trapped upstream of islands in the Kuroshio. Geophysical Research Letters 41:5,091–5,098, https://doi.org/​10.1002/2014GL060113.

Lentini, C.A.D., J.M. Magalhães, J.C.B. da Silva, and J.A. Lorenzzetti. 2016. Transcritical flow and generation of internal solitary waves off the Amazon River: Synthetic aperture radar observations and interpretation. Oceanography 29(4):187–195, https://doi.org/10.5670/oceanog.2016.88.

Magalhães, J.M., and J.C.B. da Silva. 2012. SAR observations of internal solitary waves generated at the Estremadura Promontory off the west Iberian coast. Deep-Sea Research Part I 69:12–24, https://doi.org/​10.1016/j.dsr.2012.06.002.

Melville, W.K., and K.R. Helfrich. 1987. Transcritical two-layer flow over topography. Journal of Fluid Mechanics 178:31–52, https://doi.org/10.1017/S0022112087001101.

Mugetti, A., C. Brieva, S. Giangiobbe, E. Gallicchio, F. Pacheco, A. Pagani, A. Calcagno, S. González, O. Natale, M. Faure, and others. 2004. Patagonian Shelf, GIWA Regional Assessment 38. UNEP, University of Kalmar, Kalmar, Sweden, 164 pp. plus appendixes, http://wedocs.unep.org/handle/20.500.11822/8792.

Nikurashin, M., and R. Ferrari. 2010. Radiation and dissipation of internal waves generated by geostrophic flows impinging on small-scale topography: Theory. Journal of Physical Oceanography 40:1,055–1,074, https://doi.org/​10.1175/2009JPO4199.1.

Nikurashin, M., and R. Ferrari. 2011. Global energy conversion rate from geostrophic flows into internal lee waves in the deep ocean. Geophysical Research Letters 38, L08610, https://doi.org/​10.1029/2011GL046576.

Piola, A.R., B.C. Franco, E.D. Palma, and M. Saraceno. 2013. Multiple jets in the Malvinas Current. Journal of Geophysical Research 118:2,107–2,117, https://doi.org/​10.1002/jgrc.20170.

Redekopp, L.G., and Z. You. 1995. Passage through resonance for the forced Korteweg de Vries equation. Physical Review Letters 74(26):5,158–5,161, https://doi.org/10.1103/physrevlett.74.5158.

Smith, W.H.F., and D.T. Sandwell. 1997. Global seafloor topography from satellite altimetry and ship depth soundings. Science 277:1,957–1,962, https://doi.org/10.1126/science.277.5334.1956.

Smyth, W.D., J.N. Moum, and J.D. Nash. 2011. Narrowband oscillations in the upper equatorial ocean: Part II. Properties of shear instabilities. Journal of Physical Oceanography 41(3):412–428, https://doi.org/10.1175/2010JPO4451.1.

Thompson, D.R., and R.F. Gasparovic. 1986. Intensity modulation in SAR images of internal waves. Nature 320:345–348, https://doi.org/​10.1038/320345a0.

Trossman, D.S., B.K. Arbic, J.G. Richman, S.T. Garner, S.R. Jayne, and A.J. Wallcraft. 2016. Impact of topographic internal lee wave drag on an eddying global ocean model. Ocean Modelling 97:109–128, https://doi.org/10.1016/j.ocemod.2015.10.013.

Copyright & Usage

This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.