Oceanography The Official Magazine of
The Oceanography Society
Volume 30 Issue 02

View Issue TOC
Volume 30, No. 2
Pages 116 - 125

OpenAccess

Measurements of Near-Surface Turbulence and Mixing from Autonomous Ocean Gliders

By Louis St. Laurent  and Sophia Merrifield 
Jump to
Article Abstract Citation References Copyright & Usage
Article Abstract

As autonomous sampling technologies have matured, ocean sensing concepts with long histories have migrated from their traditional ship-based roots to new platforms. Here, we discuss the case of ocean microstructure sensing, which provides the basis for direct measurement of small-scale turbulence processes that lead to mixing and buoyancy flux. Due to their hydrodynamic design, gliders are an optimal platform for microstructure sensing. A buoyancy-driven glider can profile through the ocean with minimal vibrational noise, a common limitation of turbulence measurements from other platforms. Moreover, gliders collect uncontaminated data during both descents and ascents, permitting collection of near-surface measurements unattainable from ship-based sensing. Persistence and the capability to sample in sea states not feasible for deck-based operations make glider-based microstructure sampling a profoundly valuable innovation. Data from two recent studies illustrate the novel aspects of glider-based turbulence sensing. Surface stable layers, characteristic of conditions with incoming solar radiation and weak winds, exemplify a phenomenon not easily sampled with ship-based methods. In the North Atlantic, dissipation rate measurements in these layers revealed unexpected turbulent mixing during times of peak warming, when enhanced stratification in a thin layer led to an internal wave mode that received energy from the deeper internal wave field of the thermocline. Hundreds of profiles were obtained in the Bay of Bengal through a barrier layer that separates a strongly turbulent surface layer from a surprisingly quiescent interior just 20 m below. These studies demonstrate the utility of buoyancy-driven gliders for collecting oceanic turbulence measurements.

Citation

St. Laurent, L., and S. Merrifield. 2017. Measurements of near-surface turbulence and mixing from autonomous ocean gliders. Oceanography 30(2):116–125, https://doi.org/10.5670/oceanog.2017.231.

References

Agarwal, N., R. Sharma, A. Parekh, S. Basu, A. Sarkar, and V.K. Agarwal. 2012. Argo observations of barrier layer in the tropical Indian Ocean. Advances in Space Research 50(5):642–654, https://doi.org/​10.1016/j.asr.2012.05.021.

Bogdanoff, A.S. 2017. Physics of Diurnal Warm Layers: Turbulence, Internal Waves, and Lateral Mixing. Doctoral dissertation, Massachusetts Institute of Technology.

Brainerd, K.E., and M.C. Gregg. 1993a. Diurnal restratification and turbulence in the oceanic surface mixed layer: 1. Observations. Journal of Geophysical Research 98(C12):22,645–22,656, https://doi.org/10.1029/93JC02297.

Brainerd, K.E., and M.C. Gregg. 1993b. Diurnal restratification and turbulence in the oceanic surface mixed layer: 2. Modeling. Journal of Geophysical Research 98(C12):22,657–22,664, https://doi.org/​10.1029/93JC02298.

D’Asaro, E.A. 1978. Mixed layer velocities induced by internal waves. Journal of Geophysical Research 83(C5):2,437–2,438, https://doi.org/​10.1029/JC083iC05p02437.

Dillon, T.M., J.A. Barth, A.Y. Erofeev, G.H. May, and H.W. Wijesekera. 2003. MicroSoar: A new instrument for measuring microscale turbulence from rapidly moving submerged platforms. Journal of Atmospheric and Oceanic Technology 20(11):1,671–1,684, https://doi.org/10.1175/​1520-0426(2003)020<1671:MANIFM>2.0.CO;2.

Goodman, L., E.R. Levine, and R.G. Lueck. 2006. On measuring the terms of the turbulent kinetic energy budget from an AUV. Journal of Atmospheric and Oceanic Technology 23(7):977–990, https://doi.org/​10.1175/JTECH1889.1.

Farrar, J.T., L. Rainville, A.J. Plueddemann, W.S. Kessler, C. Lee, B.A. Hodges, and D.M. Fratantoni. 2015. Salinity and temperature balances at the SPURS central mooring during fall and winter. Oceanography 28(1):56–65, https://doi.org/​10.5670/oceanog.2015.06.

Fer, I., A.K. Peterson, and J.E. Ullgren. 2014. Microstructure measurements from an underwater glider in the turbulent Faroe Bank Channel overflow. Journal of Atmospheric and Oceanic Technology 31(5):1,128–1,150, https://doi.org/10.1175/JTECH-D-13-00221.1.

Grant, H.L., R.W. Stewart, and A. Moilliet. 1962. Turbulence spectra from a tidal channel. Journal of Fluid Mechanics 12(2):241–268, https://doi.org/​10.1017/S002211206200018X.

Gregg, M.C. 1999. Uncertainties and limitations in measuring ε and χ T. Journal of Atmospheric and Oceanic Technology 16(11):1,483–1,490, https://doi.org/10.1175/1520-0426(1999)016​<1483:UALIMA>2.0.CO;2.

Hinze, J.O. 1975. Turbulence, 2nd ed. McGraw-Hill, 790 pp.

Hodges, B.A., and D.M. Fratantoni. 2014. AUV observations of the diurnal surface layer in the North Atlantic salinity maximum. Journal of Physical Oceanography 44:1,595–1,604, https://doi.org/​10.1175/JPO-D-13-0140.1.

Jinadasa, S.U.P., I. Lozovatsky, J. Planella-Morató, J.D. Nash, J.A. MacKinnon, A.J. Lucas, and H.J. Fernando. 2016. Ocean turbulence and mixing around Sri Lanka and in adjacent waters of the northern Bay of Bengal. Oceanography 29(2):170–179, https://doi.org/​10.5670/oceanog.2016.49.

Kunze, E., M.G. Briscoe, and A. Williams. 1990. Interpreting shear and strain fine structure from a neutrally buoyant float. Journal of Geophysical Research 95:18,111–18,125, https://doi.org/10.1029/JC095iC10p18111.

Lindstrom, E., F. Bryan, and R. Schmitt. 2015. SPURS: Salinity Processes in the Upper-Ocean Regional Study—The North Atlantic Experiment. Oceanography 28(1):14–19, https://doi.org/10.5670/oceanog.2015.01.

Lueck, R. 2003. Rockland Scientific Technical Note 28. http://www.rocklandscientific.com.

Lueck, R.G., F. Wolk, and H. Yamazaki. 2002. Oceanic velocity microstructure measurements in the 20th century. Journal of Oceanography 58(1):153–174, https://doi.org/10.1023/A:1015837020019.

Mahadevan, A., G.S. Jaeger, M. Freilich, M.M. Omand, E.L. Shroyer, and D. Sengupta. 2016. Freshwater in the Bay of Bengal: Its fate and role in air-sea heat exchange. Oceanography 29(2):72–81, https://doi.org/​10.5670/oceanog.2016.40.

Mater, B.D., S.K. Venayagamoorthy, L. St. Laurent, and J.N. Moum. 2015. Biases in Thorpe-scale estimates of turbulence dissipation: Part I. Assessments from large-scale overturns in oceanographic data. Journal of Physical Oceanography 45(10):2,497–2,521, https://doi.org/​10.1175/JPO-D-14-0128.1.

Merckelbach, L., D. Smeed, and G. Griffiths. 2010. Vertical water velocities from underwater gliders. Journal of Atmospheric and Oceanic Technology 27:547–563, https://doi.org/​10.1175/2009JTECHO710.1.

Moum, J.N., D.R. Caldwell, and C.A. Paulson. 1989. Mixing in the equatorial surface layer and thermocline. Journal of Geophysical Research 94(C2):2,005–2,022, https://doi.org/​10.1029/JC094iC02p02005.

Munk, W. 1981. Internal waves and small-scale mixing processes. Pp. 264–290 in Evolution of Physical Oceanography. B.A. Warren and C. Wunsch, eds, MIT Press.

Nasmyth, P.W. 1970. Oceanic Turbulence. Doctoral dissertation, University of British Columbia.

Osborn, T.R. 1980. Estimates of the local rate of vertical diffusion from dissipation measurements. Journal of Physical Oceanography 10(1):83–89, https://doi.org/10.1175/1520-0485(1980)010​<0083:EOTLRO>2.0.CO;2.

Paka, V.T., V.N. Nabatov, I.D. Lozovatsky, and T.M. Dillon. 1999. Oceanic microstructure measurements by BAKLAN and GRIF. Journal of Atmospheric and Oceanic Technology 16(11):1,519–1,532, https://doi.org/​10.1175/1520-0426(1999)016<1519:OMMBBA>​2.0.CO;2.

Rainville, L., J.I. Gobat, C.M. Lee, and G.B. Shilling. 2017. Multi-month dissipation estimates using microstructure from autonomous underwater gliders. Oceanography 30(2):49–50, https://doi.org/​10.5670/oceanog.2017.219.

Schmitt, R.W., J.M. Toole, R.L. Koehler, E.C. Mellinger, and K.W. Doherty. 1988. The development of a fine- and microstructure profiler. Journal of Atmospheric and Oceanic Technology 5(4):484–500, https://doi.org/10.1175/1520-0426(1988)005​<0484:TDOAFA>2.0.CO;2.

Schofield, O., J. Kohut, D. Aragon, L. Creed, J. Graver, C. Haldeman, J. Kerfoot, H. Roarty, C. Jones, D. Webb, and S. Glenn. 2007. Slocum gliders: Robust and ready. Journal of Field Robotics 24(6):473–485, https://doi.org/10.1002/rob.20200.

Shroyer, E.L., D.L. Rudnick, J.T. Farrar, B. Lim, S.K. Venayagamoorthy, L. St. Laurent, and J.N. Moum. 2016. Modification of upper-ocean temperature structure by subsurface mixing in the presence of strong salinity stratification. Oceanography 29(2):62–71, https://doi.org/​10.5670/oceanog.2016.39.

St. Laurent, L., A.C. Naveira Garabato, J.R. Ledwell, A.M. Thurnherr, J.M. Toole, and A.J. Watson. 2012. Turbulence and diapycnal mixing in Drake Passage. Journal of Physical Oceanography 42:2,143–2,152, https://doi.org/10.1175/JPO-D-12-027.1.

Thorpe, S.A. 1977. Turbulence and mixing in a Scottish loch. Philosophical Transactions of the Royal Society of London A 286(1334):125–181, https://doi.org/10.1098/rsta.1977.0112.

Thorpe, S. 2007. An Introduction to Ocean Turbulence. Cambridge University Press, 267 pp.

Webb, D.C., P.J. Simonetti, and C.P. Jones. 2001. SLOCUM: An underwater glider propelled by environmental energy. IEEE Journal of Oceanic Engineering 26(4):447–452, https://doi.org/​10.1109/48.972077.

Weller, R.A., J.T. Farrar, J. Buckley, S. Mathew, R. Venkatesan, J.S. Lekha, and B.P. Kumar. 2016. Air-sea interaction in the Bay of Bengal. Oceanography 29(2):28–37, https://doi.org/​10.5670/oceanog.2016.36.

Winkel, D.P., M.C. Gregg, and T.B. Sanford. 1996. Resolving oceanic shear and velocity with the Multi-Scale Profiler. Journal of Atmospheric and Oceanic Technology 13:1,046–1,073, https://doi.org/10.1175/1520-0426(1996)013​<1046:ROSAVW>2.0.CO;2.

Wolk, F., R.G. Lueck, and L. St. Laurent. 2009. Turbulence measurements from a glider. Pp. 1–6 in OCEANS 2009, MTS/IEEE Biloxi - Marine Technology for Our Future: Global and Local Challenges. October 26–29, 2009.

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.