The figure shows the six-year time mean wind stress field and topographic form stress field from SOSE, looking north from Antarctica. South America appears on the right, Australia in the middle, and the southern tip of Africa on the very top left; black lines show the mean Antarctic Circumpolar Current streamfunction. Red indicates eastward stress, wherein the wind or the solid earth pushes the fluid eastward. All of the wind stress at the surface pushes eastward, and some regions of topography push eastward as well. Most of the larger-scale topography is blue, though, indicating that these ridges and continents are pushing the fluid to the west, balancing the eastward wind stress. Click to expand. – Image courtesy: J. Masich
story by Helen Hill
The Southern Ocean State Estimate (SOSE) is a 1/6 degree , eddy-permitting model of the Southern Ocean based on the MITgcm. In their new study Topographic Form Stress in the Southern Ocean State Estimate, researchers from Scripps Institution of Oceanography, graduate student Jessica Masich, PhD advisor Teresa Chereskin and long time MITgcm user Matthew Mazloff diagnose the momentum balance in a six year run of the state estimate to evaluate the role form stress across bottom topography might play in balancing the input of stress by wind at the surface.
The team find that 95% of the zonal momentum input via wind stress at the surface is balanced by topographic form stress across ocean ridges, while the remaining 5% is balanced via bottom friction and momentum flux divergences at the northern and southern boundaries of the analysis domain.
Although Masich et al find the time-mean zonal wind stress field exhibits a relatively uniform spatial distribution, they note the time-mean topographic form stress is concentrated at shallow ridges and across the continents that lie within the Antarctic Circumpolar Current (ACC) latitudes; nearly 40% of topographic form stress occurs across South America, while the remaining 60% occurs across the major submerged ridges that underlie the ACC.
In addition they find that the topographic form stress divides into shallow and deep regimes: the shallow regime contributes most of the westward form stress that serves as a momentum sink for the ACC system, while the deep regime consists of strong eastward and westward form stresses that largely cancel in the zonal integral.
Finally they report that the time-varying form stress signal, integrated longitudinally and over the ACC latitudes, tracks closely with the wind stress signal integrated over the same domain; at zero lag, 88% of the variance in the 6 year form stress time series can be explained by the wind stress signal, suggesting that changes in the integrated wind stress signal are communicated via rapid barotropic response down to the level of bottom topography.
To find out more about this work contact Jessica.
About the Researcher
Jessica Masich
Jessica Masich has been using MITgcm via SOSE throughout her PhD research, comparing SOSE results to observations from the cDrake Experiment in the Drake Passage. When she is not hard at work MITgcming she spends much of her free time swimming in the pool and — when it’s warm enough — with the seals and (friendly!) Leopard sharks in La Jolla Cove.
Look out for her at Ocean Sciences where she will give a poster (PC14D-2091, “Momentum balance in the Southern Ocean”) on Monday, Feb 22, from 4pm to 6pm. The poster will push the work described in Masich et al. forward by including the teams initial exploration of mechanisms of vertical momentum transfer in SOSE and in the cDrake Experiment observations, from surface source to seafloor sink!
This Month’s Featured Publication
- Jessica Masich, Teresa K. Chereskin, Matthew Mazloff (2015), Topographic form stress in the Southern Ocean State Estimate, accepted in Journal of Geophysical Research, Oceans, doi: 10.1002/2015JC011143
Other New Publications this Month
Ryan Abernathey and David Ferreira (2015), Southern Ocean isopycnal mixing and ventilation changes driven by winds, Geophysical Research Letters, doi: 10.1002/2015GL066238
Yosef Ashkenazy and Eli Tziperman (2015), Variability, instabilities and eddies in a Snowball ocean, Journal of Climate 2015 ; e-View, doi: 10.1175/JCLI-D-15-0308.1
Annalisa Falace, Sara Kaleb, Daniele Curiel, Chiara Miotti, Giovanni Galli, Stefano Querin, Enric Ballesteros, Cosimo Solidoro, Vinko Bandelj (2015), Calcareous Bio-Concretions in the Northern Adriatic Sea: Habitat Types, Environmental Factors that Influence Habitat Distributions, and Predictive Modeling, PLOS one, November 11, 2015, doi: 10.1371/journal.pone.0140931
Ute Hausmann, Arnaud Czaja, John Marshall (2015), Estimates of air-sea feedbacks on sea surface temperature anomalies in the Southern Ocean, Journal of Climate 2015 ; e-View, doi: 10.1175/JCLI-D-15-0015.1
Alok Kumar Mishra, Suneet Dwivedi, Atul Shrivastava. High resolution simulation of the salinity variability in the Bay of Bengal and Arabian Sea during the years 1998-2014 using an ocean circulation model. Discovery, 2015, 39(180), 173-179, PDF
Christopher G. Piecuch, Patrick Heimbach, Rui M. Ponte, Gaël Forget (2015), Sensitivity of contemporary sea level trends in a global ocean state estimate to effects of geothermal fluxes, Ocean Modelling, Volume 96, Part 2, December 2015, Pages 214–220, doi: doi:10.1016/j.ocemod.2015.10.008
Himansu K. Pradhan, A. D. Rao & Madhu Joshi (2015), Neap—spring variability of internal waves over the shelf-slope along western Bay of Bengal associated with local stratification, Natural Hazards, Journal of the International Society for the Prevention and Mitigation of Natural Hazards, doi: 10.1007/s11069-015-2027-9
Joseph Schoonover, William Dewar, Nicolas Wienders, Jonathan Gula, James C. McWilliams, M. Jeroen Molemaker, Susan C. Bates, Gokhan Danabasoglu, and Stephen Yeager (2015), Journal of Physical Oceanography 2015 ; e-View, doi: 10.1175/JPO-D-15-0133.1
Emily L. Shroyer, Roger M. Samelson, Laurie Padman, Andreas Münchow (2015), Modeled ocean circulation in Nares Strait and its dependence on landfast-ice cover, accepted for Journal of Geophysical Research, Oceans, doi: 10.1002/2015JC011091
Atul Srivastava, Suneet Dwivedi, Alokkumar Mishra (2015), High resolution numerical modeling of the Indian Ocean surface Hydrography and circulation. Discovery, 2015, 40(181), 34-40, PDF
Christoph Vo ̈lker (2015), Nonlinearities in seawater carbonate chemistry and the distribution of anthropogenic carbon uptake, Ocean ice and atmosphere seminar, Bremen, 10.11.2015, PDF
Max Yaremchuk, Paul Martin, Andrey Koch, Christopher Beattie (2015), Comparison of the adjoint and adjoint-free 4dVar assimilation of the hydrographic and velocity observations in the Adriatic Sea, Ocean Modelling (in press), doi: 10.1016/j.ocemod.2015.10.010
Xiaowei Wang, Shiqiu Peng, Zhiyu Liu, Rui Xin Huang, Yu-Kun Qian, and Yineng Li (2015), Tidal Mixing in the South China Sea: An Internal-Tide-Energetics-Based Estimate, Journal of Physical Oceanography 2015; e-View, doi: 10.1175/JPO-D-15-0082.1
Yaochu Yuan, Xiaohua Zhu, Feng Zhou (2015), Progress of studies in China from July 2010 to May 2015 on the influence of the Kuroshio on neighboring Chinese seas and the Ryukyu Current, Acta Oceanologica Sinica, pp 1-10, First online: 10 November 2015, doi: 10.1007/s13131-015-0771-z
Zalucha, Angela M. (2015), Long-term Simulations of Pluto’s Atmosphere and Surface as a Coupled System, American Astronomical Society, DPS meeting #47, #210.24
Xiaoming Zhai (2015), Latitudinal Dependence of Wind-Induced Near-Inertial Energy, J. Phys. Oceanogr., 45, 3025–3032., doi: 10.1175/JPO-D-15-0166.1
Zhang, Xi; Showman, Adam P. (2015), On the parameterization of 1D vertical mixing in planetary atmospheres: insights from 2D and 3D simulations, American Astronomical Society, DPS meeting #47, #416.08
Do you have news about research using MITgcm? We are looking for contributions to these pages. If you have an interesting MITgcm project (ocean, atmosphere, sea-ice, physics, biology or otherwise) that you want to tell people about, get in touch. To make a post, contact Helen