Benefits of radar-derived surface current assimilation for South of Africa ocean circulation
Tóm tắt
The oceanic circulation south of Africa is characterised by a complex dynamics with a strong variability due to the presence of the Agulhas current and numerous eddies. This area of interest is also the location of several natural gas fields under seafloor which are targeted for drilling and exploitation. The complex and powerful ocean currents induces significant issues for ship operations at the surface as well as under the surface for deep sea operations. Therefore, the knowledge of the state of the currents and the ability to forecast them in a realistic manners could greatly enforce the safety of various marine operation. Following this objective, an array of HF radar systems were deployed to allow a detailed knowledge of the Agulhas currents and its associated eddy activity. It is shown in this study that assimilation of HF radar allow to represent the surface circulation more realistically. Two kind of experiments have been performed, a one month analysis and nine consecutive forecast of two days each. The one month 4DVAR experiment have been compared to geostrophic currents issued from altimeters and highlight an important improvement of the geostrophic currents. Furthermore despite the restricted size of the area covered with HF radar, we show that the solution is improved almost in the whole domain, mainly upstream and downstream of the HF radar’s covered area. We also show that while benefits of the assimilation on the surface current intensity is significantly reduced during the second day of forecast, the correction in direction persists after 48 h.
Tài liệu tham khảo
Ardhuin F, Rascle N, Chapron B, Gula J, Molemaker J, Gille ST, Menemenlis D, Rocha C (2017) Small scale currents have large effects on wind wave heights. J Geophys Res 122(C6):4500–4517. https://doi.org/10.1002/2016JC012413
Arnone V, González-Dávila M, Santana-Casiano JM (2017) Co2 fluxes in the South African coastal region. Marine Chem 195:41–49. https://doi.org/10.1016/j.marchem.2017.07.008
Barth A, Alvera-Azcárate A, Gurgel KW, Staneva J, Port A, Beckers JM, Stanev EV (2010) Ensemble perturbation smoother for optimizing tidal boundary conditions by assimilation of high-frequency radar surface currents - application to the german bight. Ocean Sci 6(1):161–178. https://doi.org/10.5194/os-6-161-2010
Broquet G, Edwards C, Moore A, Powell B, Veneziani M, Doyle J (2009) Application of 4d-variational data assimilation to the california current system. Dyn Atmos Oceans 48(1):69–92. https://doi.org/10.1016/j.dynatmoce.2009.03.001
Broquet G, Moore A, Arango H, Edwards C (2011) Corrections to ocean surface forcing in the california current system using 4d variational data assimilation. Ocean Modelling 36(1):116–132. https://doi.org/10.1016/j.ocemod.2010.10.005
Copernicus Climate Change Service (C3S) (2017) ERA5: fifth generation of ECMWF atmospheric reanalyses of the global climate. Copernicus Climate Change Service Climate Data Store (CDS). https://cds.climate.copernicus.eu/cdsapp#!/home
Di Lorenzo E, Moore AM, Arango HG, Cornuelle BD, Miller AJ, Powell B, Chua BS, Bennett AF (2007) Weak and strong constraint data assimilation in the inverse regional ocean modeling system (roms): Development and application for a baroclinic coastal upwelling system. Ocean Modelling 16(3):160–187. https://doi.org/10.1016/j.ocemod.2006.08.002
Fairall CW, Bradley EF, Hare JE, Grachev AA, Edson JB (2003) Bulk parameterization of air–sea fluxes: Updates and verification for the coare algorithm. J Climate 16(4):571–591
Goschen W, Bornman T, Deyzel S, Schumann E (2015) Coastal upwelling on the far eastern agulhas bank associated with large meanders in the agulhas current. Continental Shelf Res 101:34–46. https://doi.org/10.1016/j.csr.2015.04.004
Guerra L, Paiva A, Chassignet E (2018) On the translation of agulhas rings to the western south atlantic ocean. Deep-Sea Res I 139:104–113. https://doi.org/10.1016/j.dsr.2018.08.005
Gürol S, Weaver AT, Moore AM, Piacentini A, Arango HG, Gratton S (2014) B-preconditioned minimization algorithms for variational data assimilation with the dual formulation. Quart J R Meteorol Soc 140(679):539–556. https://doi.org/10.1002/qj.2150
Halo I, Backeberg B, Penven P, Ansorge I, Reason C, Ullgren J (2014) Eddy properties in the mozambique channel:a comparison between observations and two numerical ocean circulation models. Deep-Sea Res II 100:38–53. https://doi.org/10.1016/j.dsr2.2013.10.015
Levin J, Arango HG, Laughlin B, Wilkin J, Moore AM (2019) The impact of remote sensing observations on cross-shelf transport estimates from 4d-var analyses of the mid-atlantic bight. Adv Space Res. https://doi.org/10.1016/j.asr.2019.09.012
Lutjeharms J, Cooper J, Roberts M (2000) Upwelling at the inshore edge of the agulhas current. Continental Shelf Res 20(7):737–761. https://doi.org/10.1016/S0278-4343(99)00092-8
Lutjeharms J, Penven P, Roy C (2003) Modelling the shear edge eddies of the southern agulhas current. Continental Shelf Res 23(11):1099–1115. https://doi.org/10.1016/S0278-4343(03)00106-7
Lutjeharms JRE (1981) Spatial scales and intensities of circulation in the ocean areas adjacent to south africa. Deep-Sea Res 28A:1289–1302
Messager C, Stuart S (2016) Significant atmospheric boundary layer change observed above an agulhas current warm cored eddy. Adv Meteorol. https://doi.org/10.1155/2016/3659657
Meyer I, Niekerk JLV (2016) Towards a practical resource assessment of the extractable energy in the agulhas ocean current. Int J Mar Energy 16:116–132. https://doi.org/10.1016/j.ijome.2016.05.010
Moore AM, Arango HG, Broquet G, Edwards C, Veneziani M, Powell B, Foley D, Doyle JD, Costa D, Robinson P (2011a) The regional ocean modeling system (roms) 4-dimensional variational data assimilation systems: Part ii - performance and application to the california current system. Progr Oceanogr 91(1):50–73. https://doi.org/10.1016/j.pocean.2011.05.003
Moore AM, Arango HG, Broquet G, Edwards C, Veneziani M, Powell B, Foley D, Doyle JD, Costa D, Robinson P (2011b) The regional ocean modeling system (roms) 4-dimensional variational data assimilation systems: Part iii - observation impact and observation sensitivity in the california current system. Progr Oceanogr 91(1):74–94. https://doi.org/10.1016/j.pocean.2011.05.005
Moore AM, Arango HG, Broquet G, Powell BS, Weaver AT, Zavala-Garay J (2011) The regional ocean modeling system (roms) 4-dimensional variational data assimilation systems: Part i - system overview and formulation. Progr Oceanogr 91(1):34–49. https://doi.org/10.1016/j.pocean.2011.05.004
Penven P, Lutjeharms JRE, Florenchie P (2006) Madagascar: A pacemaker for the agulhas current system? Geophys Res Lett. https://doi.org/10.1029/2006GL026854
Powell B, Arango H, Moore A, Di Lorenzo E, Milliff R, Foley D (2008) 4dvar data assimilation in the intra-americas sea with the regional ocean modeling system (roms). Ocean Modelling 23(3):130–145. https://doi.org/10.1016/j.ocemod.2008.04.008
Powell BS, Moore AM (2009) Estimating the 4dvar analysis error of godae products. Ocean Dynamics 59(1):121–138
Quilfen Y, Yurovskaya M, Chapron B, Ardhuin F (2018) Storm waves focusing and steepening in the agulhas current: satellite observations and modeling. Rem Sens Environ 216:561–571. https://doi.org/10.1016/j.marchem.2017.07.0081
Reason C, Luthjeharms HJJRE, Biastoch A, Roman R (2003) Inter-ocean fluxes south of africa in an eddy-permitting model. Deep-Sea Res II 50:281–298
Rouault MJ, Mouche A, Collard F, Johannessen JA, Chapron B (2010) Mapping the Agulhas Current from space: An assessment of ASAR surface current velocities. J Geophys Res. https://doi.org/10.1016/j.marchem.2017.07.0082
Shchepetkin AF, McWilliams JC (2003) A method for computing horizontal pressure-gradient force in an oceanic model with a nonaligned vertical coordinate. J Geophys Res Oceans. https://doi.org/10.1029/2001JC001047
Shchepetkin AF, McWilliams JC (2005) The regional oceanic modeling system (roms): a split-explicit, free-surface, topography-following-coordinate oceanic model. Ocean Modelling 9(4):347–404. https://doi.org/10.1016/j.marchem.2017.07.0083
Shchepetkin AF, McWilliams JC (2009) Correction and commentary for “ocean forecasting in terrain-following coordinates: Formulation and skill assessment of the regional ocean modeling system” by haidvogel et al., j. comp. phys. 227, pp. 3595–3624. J Comput Phys 228(24):8985–9000. https://doi.org/10.1016/j.jcp.2009.09.002
Song H, Edwards CA, Moore AM, Fiechter J (2016) Data assimilation in a coupled physical-biogeochemical model of the california current system using an incremental lognormal 4-dimensional variational approach: Part 1–model formulation and biological data assimilation twin experiments. Ocean Modelling 106:131–145. https://doi.org/10.1016/j.marchem.2017.07.0085
Tedesco P, Gula J, Ménesguen C, Penven P, Krug M (2019) Generation of submesoscale frontal eddies in the agulhas current. J Geophys Res Oceans 124(11):7606–7625. https://doi.org/10.1016/j.marchem.2017.07.0086
Van-Aken H, Lutjeharms J, Rouault M, Whittle C, de Ruijter W (2013) Observations of an early agulhas current retroflection event in 2001: a temporary cessation of inter-ocean exchange south of africa? Deep Sea Research Part I: Oceanogr Res Papers 72:1–8. https://doi.org/10.1016/j.marchem.2017.07.0087
Warner JC, Sherwood CR, Arango HG, Signell RP (2005) Performance of four turbulence closure models implemented using a generic length scale method. Ocean Modelling 8(1):81–113. https://doi.org/10.1016/j.marchem.2017.07.0088