# Publications

17. S. Elipot and L. M. Beal (2017), Observed Agulhas Current sensitivity to interannual and long-term trend atmospheric forcings, J. Clim., Online Early Release doi: 10.1175/JCLI-D-17-0597.1.

• This paper studies the atmosphere-driven interannual variability of the Agulhas jet transport based on the altimeter proxy derived in Beal and Elipot (2016). We find that 29% of the interannual variance of the Agulhas Current transport can be linearly related to six modes of Southern Hemisphere atmospheric variability, including ENSO and a SAM-related mode. The Agulhas transport proxy time series can be downloaded via the ACT website here.

16. Elipot, S., E. Frajka-Williams, C. W. Hughes, S. Olhede, and M. Lankhorst (2017), Observed basin-scale response of the North Atlantic Meridional Overturning Circulation to wind stress forcing, J. Clim., 30, 2029-2054, doi:10.1175/JCLI-D-16-0664.1. (Open access; if you download the PDF file, figures of this paper are best rendered in Adobe Acrobat or Adobe Reader).

• This paper explores the spatiotemporal covariance and forcing mechanisms of observed variability in the Atlantic meridional overturning circulation. We developed a novel statistical method (analytic SVD) to investigate the relation between overturning transports from four arrays in the North Atlantic (RAPID WAVE, LINE W, RAPID MOC/MOCHA and MOVE) and patterns of wind stress and its curl over the basin. We identify two significant modes of variability in the overturning circulation driven by surface winds. The first mode manifests on seasonal time scales and is interpreted in terms of Ekman transports and barotropic return flows. The second mode is evident on nonseasonal time scales and is interpreted in terms of horizontal gyre circulation anomalies, which couple to the variable bottom topography to yield overturning circulation changes.

15. Beal, L. M. and S. Elipot (2016), Broadening not strengthening of the Agulhas Current since the early 1990s, Nature, 540, 570573, doi:10.1038/nature19853.

• In this paper we show that, despite expectations, the Agulhas Current has not intensified since the early 1990s. Instead, we find that it has broadened as a result of more eddy activity.

14. Leber, G. M., L. M. Beal and S. Elipot (2016), Wind and current forcing combine to drive strong upwelling in the Agulhas Current, J. Phys. Oceanogr., 47, 123-134, doi:10.1175/JPO-D-16-0079.1.

• In this paper, we investigate upwelling events inshore of the Agulhas Current at 34S. These events exchange shelf and slope waters, potentially enhancing primary productivity along the shelf and advecting larvae offshore. Hydrographic observations of a wind-driven upwelling event nd a current-driven upwelling event show that they can advect central waters more than 130 m upward onto the continental shelf, resulting in a 9C cooling. We use satellite data to assess the frequency, strength and forcing mechanisms of cold events from January 2003 11 through December 2011.

13. Elipot S., R. Lumpkin, R. C. Perez, J. M. Lilly, J. J. Early, A. M. Sykulski (2016), A global surface drifter dataset at hourly resolution, J. Geophys. Res.-Oceans, 121, doi:10.1002/2016JC011716.

12. Elipot, S. and L.M. Beal (2015), Characteristics, Energetics, and Origins of Agulhas Current Meanders and their Limited Influence on Ring Shedding, J. Phys. Oceanogr., 45, 2294-2314, doi:10.1175/JPO-D-14-0254.1

• In this study we investigate in detail the variance of the Agulhas Current velocity field from the ACT array, especially focussing on what is happening during meanders, the so-called Natal Pulses. For this we lay out the details of a method of analysis of rotary variance, dubbed Rotary EOF (REOF). We also combined in-situ data from the ACT array with altimetry data to research the origins, and fate, of meanders.

11. Beal, L. M., S. Elipot, A. Houk, and G. Leber (2015), Capturing the Transport Variability of a Western Boundary Jet: Results from the Agulhas Current Time-series experiment (ACT), J. Phys. Oceanogr., 45, 1302-1324, doi:10.1175/JPO-D-14-0119.1 (Open Access)

• This paper presents the first results from the velocity moorings deployed as part of the Agulhas Current Time-Series Experiment, or ACT, that took place between 2010 and 2013 in the Indian Ocean. We provide the longest in-situ record to date of the Agulhas Current Jet transport.

10. Elipot, S., E. Frajka-Williams, C. Hughes and J. Willis (2014), The Observed North Atlantic Meridional Overturning Circulation, its Meridional Coherence and Ocean Bottom Pressure, J. Phys. Oceanogr., 44, 517-537, doi:10.1175/JPO-D-13-026.1 (Open Access)

9. Polton, J., Y.-D. Lenn, S. Elipot, T. K. Chereskin and J. Sprintall (2013), Can Drake Passage observations match Ekman’s classic theory? J. Phys. Oceanogr., 43, 1733-1740, doi:10.1175/JPO-D-13-034.1 (Open Access)

• Ekman’s theory of the wind-driven ocean surface boundary layer assumes a constant eddy viscosity and predicts that the current rotates with depth at the same rate as it decays in amplitude. This study presents a method for estimating ageostrophic currents from shipboard acoustic Doppler current profiler data in Drake Passage and finds that observations are consistent with Ekman’s theory.

8. Elipot, S., C. Hughes, S. Olhede and J. Toole (2013), Coherence of western boundary pressure at the RAPID WAVE array: boundary wave adjustements or deep western boundary current advection?, J. Phys. Oceanogr., 43, 744-765, doi:10.1175/JPO-D-12-067.1 (Open Access)

• This study investigates the coherence between ocean bottom pressure signals at the Rapid Climate Change programme (RAPID) West Atlantic Variability Experiment (WAVE) array on the western North Atlantic continental slope, including the Woods Hole Oceanographic Institution Line W. We find several types of coherent signals: barotropic kelvin-like waves that propagates at speeds in excess of $$128\, m s^{-1}$$, and pressure-difference signals propagating at about $$1\, m s^{-1}$$, roughly consistent iwth coastally-trapped waves. These last signals are expected to be associated with depth-dependent basinwide meridional transport variations or an overturning circulation.

7. Hughes, C., S. Elipot, M.A. Morales Maqueda, and J. Loder (2013) Test of a Method for Monitoring the Geostrophic Meridional Overturning Circulation Using Only Boundary Measurements, J. Atmosph. Ocean. Techn., 30,789–809, doi:10.1175/JTECH-D-12-00149.1 (Open Access)

6. Lumpkin, R. and S. Elipot, (2010), Surface Drifter Pair Spreading in the North Atlantic, J. Geophys. Res.-Oceans, 115, C12017, doi:10.1029/2010JC006338.

5. Elipot, S., R. Lumpkin and G. A. Prieto (2010), Modification of inertial oscillations by the mesoscale eddy field, J. Geophys. Res.-Oceans, 115, C09010, doi:10.1029/2009JC005679.

4. Elipot, S. and S. T. Gille (2009), Estimates of wind energy input to the Ekman layer in the Southern Ocean from surface drifter data, J. Geophys. Res., 114, C06003, doi:10.1029/2008JC-005170.

3. Elipot, S. and S. T. Gille (2009), Ekman layers in the *Southern Ocean: spectral models and observations, vertical viscosity and boundary layer depth*, Ocean Sci., 5, 115-139, doi:10.5194/os-5-115-2009.

2. Elipot, S. and R. Lumpkin (2008), Spectral description of oceanic near-surface variability, Geophys. Res. Lett., 35, L05606, doi:10.1029/2007GL032589.

1. Beal, L. M. , T. K. Chereskin, Y.-D. Lenn , and S. Elipot (2006), The sources and mixing characteristics of the Agulhas Current, J. Phys. Oceanogr., 36, 2060-2074, doi:10.1175/JPO2964.1.

### Others

a. MacKinnon, J.A., Alford, M., Bouruet-Aubertot, P., Bindoff, N., Elipot, S., Gille, S., Girton, J., Gregg, M.C., Hallberg, R., Kunze, E., Naveira Garabato, A., Phillips, H., Pinkel, R., Polzin, K., Sanford, T., Simmons, H., and Speer, K., (2010), Using global arrays to investigate internal-waves and mixing, in Proceedings of the OceanObs09: Sustained Ocean Observations and Information for Society Conference (Vol. 1), Venice, Italy, 21-25 September 2009, Hall, J., Harrison D.E. and Stammer, D., Eds., ESA Publication WPP-306.

b. Elipot, S. (2006), Spectral characterization of Ekman velocities in the Southern Ocean based on surface drifter trajectories, Ph.D. dissertation, University of California, San Diego.