Significant wave heights reconstructed from ship motion data were validated against freely available satellite observations (Ribal and Young,2019) for the entire ACE voyage (see scatter plot in Fig.B1). Mooring design using wave-state estimate from the Southern Ocean, J. But the uncertainties are too high for a reliable estimate of the time of AMOC tipping.. Lett., 39, L16606. Adv., 6, eaay8493, https://doi.org/10.1126/sciadv.aay8493, 2020.a, Thomas, S., Babanin, A.V., Walsh, K. J.E., Stoney, L., and Heil, P.: Effect This results in stripe-like patterns in the radar images that correspond to the waves (these patterns are known as sea clutters). The data set is the most extensive and comprehensive collection of observations of surface processes for the Southern Ocean and is intended to underpin improvements of wave prediction models around Antarctica and research of airsea interaction processes, including gas exchange and dynamics of sea spray aerosol particles. The presented database has further potentials to support research enhancing wave model performances in the Southern Ocean, wave dynamics, including occurrence of rogue waves, wave dissipation mechanisms as well as other coupled processes, including those interconnecting waves with the upper ocean and sea ice in the Antarctic marginal ice zone. 1985., Young, I.R., Fontaine, E., Liu, Q., and Babanin, A.V.: The Wave Climate of Significant wave height Hs follows the wind pattern, underpinning the dominance of wind seas on swell systems. Rodrguez-Ros, P., Corts, P., Robinson, C.M., Nunes, S., Hassler, tropical cyclones: Field observations on the Australian North-West Shelf, J. Geophys. Adv., 6, eaay8493, Thomas, S., Babanin, A.V., Walsh, K. J.E., Stoney, L., and Heil, P.: Effect The final leg was also characterised by intense storms with wind speeds notably above P50 for almost the entire leg. Expedition (ACE) 20th December 201619th March 2017, Zenodo, A summary of the range and accuracy of measured parameters is reported in AppendixA. Products. Metal Accumulations in Two Extreme-Environment Amphipods, Hadal Eurythenes gryllus and Antarctic Pseudorchomene plebs. where U is the wind speed, cp is the phase velocity, is the wave direction, and is the wind direction, is assumed to be associated with the wind sea. Surface heating occurs over the streamline of the Antarctic Circumpolar Current (ACC) and balances the heat transport associated with the global meridional overturning circulation. Annu. Tech., 30, 18421853, 2013.a, Lund, B., Graber, H.C., Hessner, K., and Williams, N.J.: On shipboard marine X-band radar near-surface current calibration, J. tropical cyclones: Field observations on the Australian North-West Shelf, J. Geophys. Climate change is making one of the world's strongest currents flow Change, 3, 509526. Latitudes are shown every 15 (from 15 to 90S) by thin lines; the route of the ACE voyage is reported as a black solid line; and the sea ice edge, defined by the 10% sea ice concentration, is shown as a grey solid line. Measurements were also compared against available observations from satellite-borne sensors to verify the robustness of the database. Other experts on the AMOC also cautioned that because the new study doesnt present new observations of the entire ocean system instead, it is extrapolating about the future based on past data from a limited region of the Atlantic its conclusions should be taken with a grain of salt. Atmos. Pt. The Atlantic Meridional Overturning Circulation (AMOC) - a large system of ocean currents that carry warm water from the tropics into the North Atlantic - could collapse by the middle of the . An approximation of R(f) for the Akademik Tryoshnikov was calculated solving the equation of motion with a model based on the boundary element method (NEMOH,Babarit and Delhommeau,2015) and taking into account the ship's heading, forward speed, and loading conditions. wind speed data based on altimeter observations, Sci. The root-mean squared error (RMSE) is 0.4m, the correlation coefficient (R) is 0.94, and the scatter index (SI) is 0.17. Considering the resolution of the image (12m) and the minimum dimension of the sub-area (600m), WaMoS-II can detect wavelengths between 15m and 600m, which correspond to wave periods from 3s to 16s. Tatzelt, C., Landwehr, S., Modini, R.L., Tummon, F., Johnson, J.S., Harris, Although there have been many expeditions crossing the Southern Ocean (see a general overview inSchmale etal.,2019), measurements have primarily been taken en route to Antarctic stations, leaving entire sectors undersampled. The inverse wave age is the ratio of wind speed to wave phase velocity (i.e.the ratio of wavelength to period). Abstract The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all three major basins of the global ocean. Two of these events were equal to or greater than the P90 for the season (15ms1). An ensemble average over all sub-areas is computed to derive the final wave spectrum E(kx,ky) from the input 64 images. Res., 113, C06013, https://doi.org/10.1029/2006JC004051, 2008.a, Eayrs, C., Holland, D., Francis, D., Wagner, T., Kumar, R., and Li, X.: layer, Geophys. These effects depend on the view geometry (height and range of the antenna). The vessel's forward speed and heading are used to derive the true current. . Figure1Map of the ACE voyage divided by legs. of Preindustrial-like Aerosols and Their Climate Effects (ACE-SPACE), B. Therefore, extreme sea states remain likely even during summer. (2019), Lund etal. The voyage was divided into three legs. The movement of the world's major ocean gyres helps drive the " ocean conveyor belt ." The ocean conveyor belt circulates ocean water around the entire planet. The marine radar forms images of the surrounding area based on the backscatter of radar beams. Chem. Waves Dataset from SAR, Australian Ocean Data Network. Onorato, M., Saunders, C., Skatulla, S., and Toffoli, A.: Effects of an C., Royer, S.-J., Estrada, M., Sala, M.M., and Sim, R.: Distribution How the Antarctic Circumpolar Current helps keep Antarctica frozen Leg1 was along the Indian Ocean from Cape Town, South Africa, to Hobart, Australia, with stops at Marion Island, Iles de Crozet et Kerguelen, and Heard Island. directional ocean waves: the role of the modulational instability in the Oceanic Waves: Field and Laboratory Experiments, Geophys. The Antarctic Circumpolar Current (ACC) is the world's strongest ocean current. https://doi.org/10.1007/978-1-4899-5352-0_15, 825991, 1986.a, Walton, D, W.H. and Thomas, J.: Cruise Report Antarctic Circumnavigation Res. Both current speed and direction can be quantified by minimising the distance between the position of the spectral energy in I(3)(kx,ky,) and the theoretical position given by Eq.(1) using least-squares techniques (Young etal.,1985). Altimeter sensors only measure specific variables, namely the significant wave height and the wind speed, whereas SAR imagery can be converted into a directional wave energy spectrum (e.g.Collard etal.,2009). Part 2. Oceanic Waves: Field and Laboratory Experiments, Geophys. Since there are no landmasses blocking its way, the West Wind Drift drives the water unhindered eastwards around. MDPI and/or Acting as an interface between the lower atmosphere and the upper ocean, waves entrap and release momentum, heat, moisture, and gases through breaking (Melville,1996; Csanady,2001; Veron,2015) and drive airsea fluxes (e.g.Humphries etal.,2016; Schmale etal.,2019; Thurnherr etal.,2020). measurements in Europe: applications of WaMoS II as a sensor for sea state, The objective of the expedition was to sample concomitant processes in the lower atmosphere, at the ocean surface, and in the upper-ocean layers all around the Antarctic continent in a single season (Rodrguez-Ros etal.,2020; Schmale etal.,2019; Smart etal.,2020; Thurnherr etal.,2020). directional wave spectra, J. Atmos. In the southern portion of the gyre, northwesterly (or southeastward-flowing) winds drive eastward-flowing currents that are difficult to distinguish from the northern boundary of the Antarctic Circumpolar Current. Chem. Res.-Oceans, 113, C02S03. Time series of Hs derived from the IMU sensor and calibrated Hs from WaMoS-II are shown in Fig.4. https://doi.org/10.1029/2018RG000631, 2019.a, b, Fadaeiazar, E., Leontini, J., Onorato, M., Waseda, T., Alberello, A., and 2020a.a, b, Alberello, A., Bennetts, L., and Toffoli, A.: Antarctic Circumnavigation The reference values were reconstructed from records of ship motion, which were measured throughout the expedition with an inertial measurement unit (IMU) at a sampling rate of 1Hz (Alberello etal.,2020b; Landwehr etal.,2021). Aouf, L., Hauser, D., Chapron, B., Toffoli, A., Tourrain, C., and Peureux, C.: New directional wave satellite observations: Towards improved wave forecasts and climate description in Southern Ocean, Geophys. Within this band, the strong eastward flow of the Antarctic Circumpolar Current (ACC) connects each of the ocean basins. the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, Carslaw, K.S.: Overview of the Antarctic Circumnavigation Expedition: Study The ACC. 1, Australian Antarctic Data Centre, https://doi.org/10.26179/5e9d038c396f2, 2020.a, b, Donelan, M.A., Hamilton, J., and Hui, W.H.: Directional spectra of Huang, S.; Zhu, L.; Jiang, S.; Zhai, W.; Pan, B.; Wu, Z.; Xu, Q. Nevertheless, there is a notable RMSE3.2ms1, with R0.70 and SI0.360. Photo: Isa Rosso/SOCCOM Independent analysis of both data sets showed that the Antarctic Circumpolar Current accelerated significantly between 48 and 58S, with its velocity increasing most in the Pacific sector and the eastern Indian Ocean. of Preindustrial-like Aerosols and Their Climate Effects (ACE-SPACE), B. These include, but are not limited to, airsea fluxes (mass, gas, heat, and momentum), aerosol concentrations, stable water isotopologues, and micro-fibres. The basic configuration for the X-band radar requires an antenna with rotation speed of 24rpm, horizontal opening angle of 0.9, and radar pulse width of 80ns. Young waves were recorded during all storm events with steepness generally in excess of 0.1. Observations at both locations exceeded P90 notably. Ocean. and Drivers of Marine Isoprene Concentration across the Southern Ocean, The South Atlantic Gyre is the subtropical gyre in the south Atlantic Ocean. Data, 13, 11891209, https://doi.org/10.5194/essd-13-1189-2021, 2021. Lett., 37, L05603, https://doi.org/10.1029/2009GL041771, 2010.a, b, Toffoli, A., McConochie, J., Ghantous, M., Loffredo, L., and Babanin, A.V.: Oceanogr., 5, 750760, 1975.a, Montiel, F., Squire, V.A., and Bennetts, L.G.: Attenuation and directional Feature papers are submitted upon individual invitation or recommendation by the scientific editors and must receive The remaining (filtered) three-dimensional image spectrum is integrated over the positive frequency domain to obtain a wave number image spectrum I(kx,ky). For more information, please refer to Sens., 11, 1030, https://doi.org/10.3390/rs11091030, 2019.a, b, Holthuijsen, L.H.: Waves in oceanic and coastal waters, Cambridge University Close to the Antarctic continent and outside the belt of the strong westerly winds (south of the 70th parallel), wind speed weakens with P50 reducing to 3ms1 and P90 to 10ms1. The shift would be as abrupt and irreversible as turning off a light switch, and it could lead to dramatic changes in weather on either side of the Atlantic. V W X Y Z ALL This field describes the major ocean currents found in the ocean basins. Mech., 790, 492522, Newman, J.N.: Marine hydrodynamics, MIT press, Cambridge, USA, 2018., Nielsen, U.D.: A concise account of techniques available for shipboard sea Collocated SAR spectra from Sentinel-1A/1B missions within area of 0.50.5 and maximum temporal difference of 6h were retrieved from the Australian Ocean Data Network (AODN) portal (Khan etal.,2020b). Figure10Comparison of integrated parameters (WaMoS-II versus SAR): significant wave height (Hs, panel a), energy wave period (Tm10, panel b), and wave directional spreading (, panel c). This is achieved with the linear regression equation (seeNietoBorge etal.,1999, 2004). Onorato, M., and Toffoli, A.: Drift of Pancake Ice Floes in the Winter 6, 74, https://doi.org/10.3389/fmars.2019.00074, 2019.a, Veron, F.: Ocean spray, Annu. The Antarctic Circumpolar Current (ACC) is the dominant feature of ocean circulation in the Southern Hemisphere 1. Antarctic Marginal Ice Zone During Polar Cyclones, J. Geophys. Ocean. MHD was partially supported by a PhD top-up scholarship from the Australian Bureau of Meteorology. Our knowledge of glacial-interglacial changes in ACC dy. (2019), Rodrguez-Ros etal. Definitions of the variables are reported in AppendixA. Figure6Time series of sea state variables in Leg1 (blue), Leg2 (green), and Leg3 (red): (a) wind speed from the automated weather station, (b) significant wave height, and (c) current speed. Understanding the Seasonal Cycle of Antarctic Sea Ice Extent in the Context ocean waves, Geophys. The ocean's dominant feature, extending up to two miles deep and as much as 1,200 miles wide, is the Antarctic Circumpolar Current, by far the largest current in the world. We remark that P50 and P90 include the contribution of geostrophic surface currents and wind stresses. During Leg1, the expedition went through six storm events with wind speeds reported in excess of 12ms1 (P50 10ms1). Rev. Chem. Res. a measure of average wave height that is defined as Hs=4m0. Current direction is generally in better agreement with satellite observations than speed (see Fig.12a and b). Overall, the observed median wind speed was 7.25ms1, with an interquartile (IQ) of 5.1ms1. The current moves more water than any other current. Antarctic Circumpolar Current | Direction, Location, Map, & Facts J. Mar. Antarctic circumpolar current revealed by mixing zone depths. Soc., 100, 22602283, Schulz, E., Grosenbaugh, M.A., Pender, L., Greenslade, D., and Trull, T.W.: T. R. Soc. The scientific evidence now is that we cant even rule out crossing a tipping point already in the next decade or two., Longer stories and investigations that go deep, Scientists detect sign that a crucial ocean current is near collapse. The tilt of the isopycnals of the ACC, in response to strong westerlies, serves to thermally isolate the Antarctic continent from directly receiving the overwhelming subtropical ocean surface heat. These authors contributed equally to this work. Landwehr, S., Thurnherr, I., Cassar, N., Gysel-Beer, M., and Schmale, J.: Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements, Atmos. Besides the Antarctic Circumpolar Current, ACE crossed two regions with strong currents: the Agulhas region, where P90 excess 1.5ms1; and the Argentine basin (beginning of Leg3), where a northward extension of the Antarctic Circumpolar Current forces water flow to speeds of approximately 1ms1. The significant wave height was validated against freely available satellite altimeter data (Ribal and Young,2019); the scatter plot of satellite observations versus reconstructed Hs is presented in Fig.B1 of AppendixB. Coefficients A and B in Eq.(2) were estimated using a maximum likelihood method for the period 911December2016 (Leg0). The crossing of the Drake Passage at the end of Leg2 did not record significantly large waves, with Hs4m at most. The authors declare that they have no conflict of interest. Please let us know what you think of our products and services. See further details. The consequences would not be nearly as dire as they appear in the 2004 sci-fi film The Day After Tomorrow, in which a sudden shutdown of the current causes a flash freeze across the Northern Hemisphere. They fuel the Antarctic Circumpolar Current (the worlds largest ocean current, e.g.Park etal.,2019), which mixes warm waters descending from the Atlantic, Indian, and Pacific oceans with northward cold streams from the Antarctic. Figure2Examples of sea state conditions: ocean surface during storm conditions (a), sailing through a storm (b), and the marginal ice zone (c). Res., 117, C00J24, https://doi.org/10.1029/2011JC007780, 2012.a, Toffoli, A., Bennetts, L.G., Meylan, M.H., Cavaliere, C., Alberello, A., Press, Cambridge, 2007.a, b, c, Humphries, R. S., Klekociuk, A. R., Schofield, R., Keywood, M., Ward, J., and Wilson, S. R.: Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea ice, Atmos. Rikiishi, K.: Observations of the directional spectrum of ocean WavesUsing a cloverleaf buoy, J. Phys. Wind measurements were acquired at a rate of 1Hz, averaged over 175s and converted from the measurement height to a neutral 10m wind speed (U10) by assuming a logarithmic profile (seeHolthuijsen,2007) before being passed on to the WaMoS-II. articles published under an open access Creative Common CC BY license, any part of the article may be reused without For consistency, wave spectra from WaMoS-II have been filtered to eliminate high-frequency modes that are not detected by SAR (f>0.117Hz or wavelength L<115m). https://doi.org/10.1002/2015GL065937, 2015.a, Toffoli, A., Proment, D., Salman, H., Monbaliu, J., Frascoli, F., Dafilis, M., Stramignoni, E., Forza, R., Manfrin, M., and Onorato, M.: Wind Generated In addition, time series of wind, current, and wave variables from mean directional wave spectra are archived in monthly summary files. Both variables are associated with nonlinear mechanisms that lead to large (extreme) waves (Onorato etal.,2009; Toffoli etal.,2017), wave breaking (Toffoli etal.,2010), and, thus, oceanatmosphere fluxes (Schmale etal.,2019; Thurnherr etal.,2020). (2020). You seem to have javascript disabled. Sentinel-1 and WAVEWATCH III around Australia, J. Geophys. Figure8Wind from the automated weather station and significant wave height from WaMoS-II versus satellite observations: scatter diagrams (a, b) and geographical distribution of biases (c, d). The study published Tuesday in the journal Nature Communications. The effect of wave-induced turbulence on the ocean mixed layer during A, 374, 20150201, 2016., Reichert, K., Hessner, K., NietoBorge, J.C., and Dittmer, J.: WaMoS-II: A This system of currents, known as the Atlantic Meridional Overturning Circulation, or AMOC, moves 15 million cubic meters of water per second. The wave spectrum E(f,) was sampled at 175s, assuming no gaps or corrupted images occur during the sampling of 64 consecutive radar images. Tech., 18, 277293, 2001., Hasselmann, S., Brning, C., Hasselmann, K., and Heimbach, P.: An improved algorithm for the retrieval of ocean wave spectra from synthetic aperture radar image spectra, J. Geophys. Res., 124, 45114528, 2019.a, Perovich, D.K., Richter-Menge, J.A., Jones, K.F., and Light, B.: Sunlight, Antarctic sea ice has usually been able to recover in winter. Sea state observations were recorded with the wave and surface current monitoring system WaMoS-II (details on software, hardware, and measurement principles can be found inReichert etal.,1999). Moving northward, away from Antarctica, the water temperatures. Phys., 20, 58115835, https://doi.org/10.5194/acp-20-5811-2020, 2020.a, b, c, d, e, f, Toffoli, A., Babanin, A., Onorato, M., and Waseda, T.: Maximum Steepness of The calibration of coefficients A and B in Eq.(2) was performed by forcing the SNR to match independent benchmark observations of Hs. Leg3 crossed the Atlantic Ocean back to Cape Town via South Georgia, South Sandwich Islands, and Bouvetya. Thereafter, Hs was less than 2m as a result of the interaction with sea ice (see Fig.2c). It extends from the sea surface to the bottom of the ocean, and encircles Antarctica. Interestingly, observations were notably higher than P90 for the majority of the expedition. Surface current biases between WaMoS-II and satellite observations for current speed (c) and direction (d). analysis of ocean waves in the Antarctic marginal ice zone, Geophys. Res., 114, C07023, Csanady, G.T.: Air-sea interaction: laws and mechanisms, Cambridge University Press, Cambridge, 2001.. In situ observations of atmospheric and oceanographic properties are scarce due to the remoteness of the region. Susanne Ditlevsen, a statistician at the University of Copenhagen, then developed an advanced mathematical model to predict how much more wobbling the AMOC system can handle. Tech., 30, 18421853, 2013., Lund, B., Graber, H.C., Hessner, K., and Williams, N.J.: On shipboard marine X-band radar near-surface current calibration, J. More broadly, it refers to the body of water south of the main landmasses of Africa, Australia, and South America, with a northern limit at approximately 40S (see, for example,Young etal.,2020).
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