%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Chen, R.
%A McWilliams, J. C.
%A Renault, Lionel
%T Momentum governors of California undercurrent transport
%D 2021
%L fdi:010084285
%G ENG
%J Journal of Physical Oceanography
%@ 0022-3670
%K Ocean ; Coastal flows ; Eddies ; Momentum ; Topographic effects ; Regional models
%K PACIFIQUE
%K CALIFORNIE
%M ISI:000752706700013
%N 9
%P 2915-2932
%R 10.1175/jpo-d-20-0234.1
%U https://www.documentation.ird.fr/hor/fdi:010084285
%> https://www.documentation.ird.fr/intranet/publi/2022-03/010084285.pdf
%V 51
%W Horizon (IRD)
%X The California Undercurrent (CUC) transport, with significant variability ranging from weeks to decades, has consequences for both the climate and biogeochemistry of the California Current system. This study evaluates the governors of the CUC transport and its temporal variability from a momentum perspective, using a mesoscale-resolving regional model. From a 16-yr mean perspective, the along-isobath pressure gradient acts to accelerate the CUC, whereas eddy advection retards it. The topographic form stress, which is part of the volume integrated along-isobath pressure gradient, not only acts in the direction of the time-mean CUC, but also greatly modulates the temporal variability of the CUC transport. This temporal variability is also correlated with the eddy momentum advection. The eddy stress plays a role in transferring both the equatorward wind stress and poleward CUC momentum downward. A theory is formulated to show that, in addition to the conventional vertical redistribution of momentum, the eddy stress can also redistribute momentum horizontally in the area where the correlation between the pressure anomaly and isopycnal fluctuations has large spatial variability.
%$ 032 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Kessouri, F.
%A McLaughlin, K.
%A Sutula, M.
%A Bianchi, D.
%A Ho, M. N.
%A McWilliams, J. C.
%A Renault, Lionel
%A Molemaker, J.
%A Deutsch, C.
%A Leinweber, A.
%T Configuration and validation of an oceanic physical and biogeochemical model to investigate coastal eutrophication in the Southern California bight
%D 2021
%L fdi:010083918
%G ENG
%J Journal of Advances in Modeling Earth Systems
%K biogeochemical modeling ; eastern boundary upwelling system ; model ; validation ; oxygen and carbonate system ; anthropogenic nutrients ; coastal processes
%K PACIFIQUE ; CALIFORNIE
%M ISI:000739722900015
%N 12
%P e2020MS002296 [34 ]
%R 10.1029/2020ms002296
%U https://www.documentation.ird.fr/hor/fdi:010083918
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2022-02/010083918.pdf
%V 13
%W Horizon (IRD)
%X The Southern California Bight (SCB), an eastern boundary upwelling system, is impacted by global warming, acidification, and oxygen loss and receives anthropogenic nutrients from a coastal population of 20 million people. We describe the configuration, forcing, and validation of a realistic, submesoscale-resolving ocean model as a tool to investigate coastal eutrophication. This modeling system represents an important achievement because it strikes a balance of capturing the forcing by U.S. Pacific Coast-wide phenomena, while representing the bathymetric features and submesoscale circulation that affect the transport of nutrients from natural and human sources. Moreover, the model allows simulations at time scales that approach the interannual frequencies of ocean variability. The model simulation is evaluated against a broad suite of observational data throughout the SCB, showing realistic depiction of the mean state and its variability with satellite and in situ measurements of state variables and biogeochemical rates. The simulation reproduces the main structure of the seasonal upwelling front, the mean current patterns, the dispersion of wastewater plumes, as well as their seasonal variability. Furthermore, it reproduces the mean distributions of key biogeochemical and ecosystem properties and their variability. Biogeochemical rates reproduced by the model, such as primary production and nitrification, are also consistent with measured rates. This validation exercise demonstrates the utility of using fine-scale resolution modeling and local observations to identify, investigate, and communicate uncertainty to stakeholders to support management decisions on local anthropogenic nutrient discharges to coastal zones.
%$ 032 ; 038 ; 036 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Ramanantsoa, J. D.
%A Penven, Pierrick
%A Raj, R. P.
%A Renault, Lionel
%A Ponsoni, L.
%A Ostrowski, M.
%A Dilmahamod, A. F.
%A Rouault, M.
%T Where and how the East Madagascar current retroflection originates ?
%D 2021
%L fdi:010083810
%G ENG
%J Journal of Geophysical Research : Oceans
%@ 2169-9275
%K EMC ; retroflection ; eddies ; SICC ; bloom phytoplankton ; Indian Ocean
%K OCEAN INDIEN ; MADAGASCAR
%M ISI:000723095600033
%N 11
%P e2020JC016203 [22 ]
%R 10.1029/2020jc016203
%U https://www.documentation.ird.fr/hor/fdi:010083810
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2022-01/010083810.pdf
%V 126
%W Horizon (IRD)
%X The East Madagascar Current (EMC) is one of the western boundary currents of the South Indian Ocean. As such, it plays an important role in the climate system by transporting water and heat toward the pole and recirculating to the large-scale Indian Ocean through retroflection modes of its southern extension. Five cruise data sets and remote sensing data from different sensors are used to identify three states of the southern extension of the EMC: early retroflection, canonical retroflection, and no retroflection. Retroflections occur 47% of the time. EMC strength regulates the retroflection state, although impinged mesoscale eddies also contribute to retroflection formation. Early retroflection is linked with EMC volume transport. Anticyclonic eddies drifting from the central Indian Ocean to the coast favor early retroflection formation, anticyclonic eddies near the southern tip of Madagascar promote the generation of canonical retroflection, and no retroflection appears to be associated with a lower eddy kinetic energy (EKE). Knowledge of the EMC retroflection state could help predict (a) coastal upwelling south of Madagascar, (b) the southeastern Madagascar phytoplankton bloom, and (c) the formation of the South Indian Ocean Counter Current (SICC).
%$ 032

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Stevens, B.
%A Bony, S.
%A Farrell, D.
%A Ament, F.
%A Blyth, A.
%A Fairall, C.
%A Karstensen, J.
%A Quinn, P. K.
%A Speich, S.
%A Lefèvre, Nathalie
%A Person, Renaud
%A Renault, Lionel
%A et al.
%T EUREC(4)A
%D 2021
%L fdi:010082778
%G ENG
%J Earth System Science Data
%@ 1866-3508
%M ISI:000691291500001
%N 8
%P 4067-4119
%R 10.5194/essd-13-4067-2021
%U https://www.documentation.ird.fr/hor/fdi:010082778
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2021-10/010082778.pdf
%V 13
%W Horizon (IRD)
%X The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic - eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced groundbased cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air-sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored - from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation - are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement.
%$ 021 ; 032 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Renault, Lionel
%A Mc Williams, J. C.
%A Kessouri, F.
%A Jousse, A.
%A Frenzel, H.
%A Chen, R.
%A Deutsch, C.
%T Evaluation of high-resolution atmospheric and oceanic simulations of the California Current System
%D 2021
%L fdi:010082152
%G ENG
%J Progress in Oceanography
%@ 0079-6611
%K California current ; Upwelling system ; Mesoscale activity ; Oceanic ; Atmospheric modeling
%K PACIFIQUE NORD EST ; CALIFORNIE COURANT
%M ISI:000660310500003
%P 102564 [26 ]
%R 10.1016/j.pocean.2021.102564
%U https://www.documentation.ird.fr/hor/fdi:010082152
%> https://www.documentation.ird.fr/intranet/publi/2021-08/010082152.pdf
%V 195
%W Horizon (IRD)
%X This paper is the first of two that present a 16-year hindcast solution from a coupled physical and biogeochemical model of the California Current System (CCS) along the U. S. West Coast and validate the physical solution with respect to mean, seasonal, interannual, and subseasonal fields and, to a lesser degree, eddy variability. Its companion paper is Deutsch et al. (2021). The intent is to construct and demonstrate a modeling tool that will be used for mechanistic explanations, attributive causal assessments, and forecasts of future evolution for circulation and biogeochemistry, with particular attention to the increasing oceanic stratification, deoxygenation, and acidification. A well-resolved mesoscale (dx = 4 km) simulation of the CCS circulation is made with the Regional Oceanic Modeling System over a hindcast period of 16 years from 1995 to 2010. The oceanic solution is forced by a high-resolution (dx = 6 km) regional configuration of the Weather and Research Forecast (WRF) atmospheric model. Both of these high-resolution regional oceanic and atmospheric simulations are forced by lateral open boundary conditions taken from larger-domain, coarser-resolution parent simulations that themselves have boundary conditions from the Mercator and Climate Forecast System reanalyses, respectively. We show good agreement between the simulated atmospheric forcing of the oceanic and satellite measurements for the spatial patterns and temporal variability for the surface fluxes of momentum, heat, and freshwater. The simulated oceanic physical fields are then evaluated with satellite and in situ measurements. The simulation reproduces the main structure of the climatological upwelling front and cross-shore isopycnal slopes, the mean current patterns (including the California Undercurrent), and the seasonal, interannual, and subseasonal variability. It also shows agreement between the mesoscale eddy activity and the windwork energy exchange between the ocean and atmosphere modulated by influences of surface current on surface stress. Finally, the impact of using a high frequency wind forcing is assessed for the importance of synoptic wind variability to realistically represent oceanic mesoscale activity and ageostrophic inertial currents.
%$ 032 ; 020 ; 021

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Kessouri, F.
%A McWilliams, J. C.
%A Bianchi, D.
%A Sutula, M.
%A Renault, Lionel
%A Deutsch, C.
%A Feely, R. A.
%A McLaughlin, K.
%A Ho, M. N.
%A Howard, E. M.
%A Bednarsek, N.
%A Damien, P.
%A Molemaker, J.
%A Weisberg, S. B.
%T Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system
%D 2021
%L fdi:010082114
%G ENG
%J Proceedings of the National Academy of Sciences of the United States of America
%@ 0027-8424
%K coastal eutrophication ; human impacts ; acidification and oxygen loss ; marine habitats ; Southern California upwelling ecosystem
%K MEXIQUE ; ETATS UNIS ; PACIFIQUE
%K CALIFORNIE COURANT
%M ISI:000659439900014
%N 21
%P e2018856118 [8 ]
%R 10.1073/pnas.2018856118
%U https://www.documentation.ird.fr/hor/fdi:010082114
%> https://www.documentation.ird.fr/intranet/publi/2021-07/010082114.pdf
%V 118
%W Horizon (IRD)
%X Global change is leading to warming, acidification, and oxygen loss in the ocean. In the Southern California Bight, an eastern boundary upwelling system, these stressors are exacerbated by the localized discharge of anthropogenically enhanced nutrients from a coastal population of 23 million people. Here, we use simulations with a high-resolution, physical-biogeochemical model to quantify the link between terrestrial and atmospheric nutrients, organic matter, and carbon inputs and biogeochemical change in the coastal waters of the Southern California Bight. The model is forced by large-scale climatic drivers and a reconstruction of local inputs via rivers, wastewater outfalls, and atmospheric deposition; it captures the fine scales of ocean circulation along the shelf; and it is validated against a large collection of physical and biogeochemical observations. Local land-based and atmospheric inputs, enhanced by anthropogenic sources, drive a 79% increase in phytoplankton biomass, a 23% increase in primary production, and a nearly 44% increase in subsurface respiration rates along the coast in summer, reshaping the biogeochemistry of the Southern California Bight. Seasonal reductions in subsurface oxygen, pH, and aragonite saturation state, by up to 50 mmol m(-3), 0.09, and 0.47, respectively, rival or exceed the global open-ocean oxygen loss and acidification since the preindustrial period. The biological effects of these changes on local fisheries, proliferation of harmful algal blooms, water clarity, and submerged aquatic vegetation have yet to be fully explored.
%$ 038 ; 032 ; 036

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Gévaudan, M.
%A Jouanno, Julien
%A Durand, Fabien
%A Morvan, Guillaume
%A Renault, Lionel
%A Samson, G.
%T Influence of ocean salinity stratification on the tropical Atlantic Ocean surface
%D 2021
%L fdi:010081085
%G ENG
%J Climate Dynamics
%@ 0930-7575
%K Ocean vertical mixing ; Air-sea coupling ; Regional modeling ; Mixed layer ; heat budget ; Atlantic cold tongue ; Barrier layer
%K ATLANTIQUE ; ZONE TROPICALE
%M ISI:000629110200001
%N 1-2
%P 321-340
%R 10.1007/s00382-021-05713-z
%U https://www.documentation.ird.fr/hor/fdi:010081085
%> https://www.documentation.ird.fr/intranet/publi/2021/03/010081085.pdf
%V 57
%W Horizon (IRD)
%X The tropical Atlantic Ocean receives an important freshwater supply from river runoff and from precipitation in the intertropical convergence zone. It results in a strong salinity stratification that may influence vertical mixing, and thus sea surface temperature (SST) and air-sea fluxes. The aim of this study is to assess the impact of salinity stratification on the tropical Atlantic surface variables. This is achieved through comparison among regional 1/4 degrees coupled ocean-atmosphere simulations for which the contribution of salinity stratification in the vertical mixing scheme is included or discarded. The analysis reveals that the strong salinity stratification in the northwestern tropical Atlantic induces a significant increase of SST (0.2 degrees C-0.5 degrees C) and rainfall (+ 19%) in summer, hereby intensifying the ocean-atmosphere water cycle, despite a negative atmospheric feedback. Indeed, the atmosphere dampens the oceanic response through an increase in latent heat loss and a reduction of shortwave radiation reaching the ocean surface. In winter, the impacts of salinity stratification are much weaker, most probably because of a deeper mixed layer at this time. In the equatorial region, we found that salinity stratification induces a year-round shoaling of the thermocline, reinforcing the cold tongue cool anomaly in summer. The concept of barrier layer has not been identified as relevant to explain the SST response to salinity stratification in our region of interest.
%$ 032 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Renault, Lionel
%A Arsouze, T.
%A Ballabrera-Poy, J.
%T On the influence of the current feedback to the atmosphere on the Western Mediterranean sea dynamics
%D 2021
%L fdi:010081063
%G ENG
%J Journal of Geophysical Research - Oceans
%@ 2169-9275
%K MEDITERRANEE
%M ISI:000623522000015
%N 1
%P e2020JC016664 [23 ]
%R 10.1029/2020jc016664
%U https://www.documentation.ird.fr/hor/fdi:010081063
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers21-03/010081063.pdf
%V 126
%W Horizon (IRD)
%X The ocean Current FeedBack to the atmosphere (CFB) has been shown to be an unambiguous physical process to achieve proper equilibrium in the Ocean. However, its effects on the Western Mediterranean Sea (WMS) are not known. In this study, eddy-rich coupled ocean-atmosphere simulations are carried out for the WMS to assess the extent to which CFB alters the WMS circulation and to characterize the low-level wind and surface stress responses to CFB. By generating conduits of energy from oceanic currents to the atmosphere, CFB slows the mean circulation by about 10% and acts as an oceanic eddy killer, reducing the mesoscale activity by 25% and attenuating the intensity of their intermittency. It also alters the mean barotropic vorticity balance of the WMS Gyre, reducing the role of wind stress curl, nonlinear torque, and bottom pressure torque. By reducing the eddy-mean flow interaction, CFB has a large influence on the properties of the Algerian Current, reducing the presence of standing eddies near Sardinia and improving the realism of the circulation. It also modifies the Alboran Gyres formation and the Northern Current retroflection. Finally, coupling coefficients from the coupled simulations are estimated and are consistent with those for other regions. The CFB coupling coefficients can be used to parameterize the CFB in a forced ocean model. Overall, our results show that, as for other regions, the CFB is another physical mechanism to be considered for the representation of the WMS circulation.
%$ 032 ; 021 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Solodoch, A.
%A McWilliams, J. C.
%A Stewart, A. L.
%A Gula, J.
%A Renault, Lionel
%T Why does the deep western boundary current "Leak" around Flemish Cap ?
%D 2020
%L fdi:010080924
%G ENG
%J Journal of Physical Oceanography
%@ 0022-3670
%K ATLANTIQUE NORD ; TERRE NEUVE ET LABRADOR
%M ISI:000617314700010
%N 7
%P 1989-2016
%R 10.1175/jpo-d-19-0247.1
%U https://www.documentation.ird.fr/hor/fdi:010080924
%> https://www.documentation.ird.fr/intranet/publi/2021/03/010080924.pdf
%V 50
%W Horizon (IRD)
%X The southward-flowing deep limb of the Atlantic meridional overturning circulation is composed of both the deep western boundary current (DWBC) and interior pathways. The latter are fed by "leakiness' from the DWBC in the Newfoundland Basin. However, the cause of this leakiness has not yet been explored mechanistically. Here the statistics and dynamics of the DWBC leakiness in the Newfoundland Basin are explored using two float datasets and a high-resolution numerical model. The float leakiness around Flemish Cap is found to be concentrated in several areas (hot spots) that are collocated with bathymetric curvature and steepening. Numerical particle advection experiments reveal that the Lagrangian mean velocity is offshore at these hot spots, while Lagrangian variability is minimal locally. Furthermore, model Eulerian mean streamlines separate from the DWBC to the interior at the leakiness hot spots. This suggests that the leakiness of Lagrangian particles is primarily accomplished by an Eulerian mean flow across isobaths, though eddies serve to transfer around 50% of the Lagrangian particles to the leakiness hot spots via chaotic advection, and rectified eddy transport accounts for around 50% of the offshore flow along the southern face of Flemish Cap. Analysis of the model's energy and potential vorticity budgets suggests that the flow is baroclinically unstable after separation, but that the resulting eddies induce modest modifications of the mean potential vorticity along streamlines. These results suggest that mean uncompensated leakiness occurs mostly through inertial separation, for which a scaling analysis is presented. Implications for leakiness of other major boundary current systems are discussed.
%$ 032 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Howard, E. M.
%A Frenzel, H.
%A Kessouri, F.
%A Renault, Lionel
%A Bianchi, D.
%A McWilliams, J. C.
%A Deutsch, C.
%T Attributing causes of future climate change in the California Current System with multimodel downscaling
%D 2020
%L fdi:010080436
%G ENG
%J Global Biogeochemical Cycles
%@ 0886-6236
%K climate forcings ; California Current ; biogeochemistry ; winds ; stratification ; downscaling
%K PACIFIQUE NORD ; AMERIQUE DU NORD
%M ISI:000595748400007
%N 11
%P e2020GB006646 [16 ]
%U https://www.documentation.ird.fr/hor/fdi:010080436
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers20-12/010080436.pdf
%V 34
%W Horizon (IRD)
%X Coastal winds in the California Current System (CCS) are credited with the high productivity of its planktonic ecosystem and the shallow hypoxic and corrosive waters that structure diverse macrofaunal habitats. These winds thus are considered a leading mediator of climate change impacts in the CCS and other Eastern Boundary Upwelling systems. We use an eddy-permitting regional model to downscale the response of the CCS to three of the major distinct climate changes commonly projected by global Earth System Models: regional winds, ocean warming and stratification, and remote water chemical properties. An increase in alongshore winds intensifies spring upwelling across the CCS, but this response is muted by increased stratification, especially during summer. Despite the seasonal shift in regional wind-driven upwelling, basin-scale changes are the decisive factor in the response of marine ecosystem properties including temperature, nutrients, productivity, and oxygen. Downscaled temperature increases and dissolved oxygen decreases are broadly consistent with coarse resolution Earth System Models, and these projected changes are large and well constrained across the models, whereas nutrient and productivity changes are small compared to the intermodel spread. These results imply that global models with poor resolution of coastal processes nevertheless yield important information about the dominant climate impacts on coastal ecosystems.
%$ 032 ; 021

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Kessouri, F.
%A Bianchi, D.
%A Renault, Lionel
%A McWilliams, J. C.
%A Frenzel, H.
%A Deutsch, C. A.
%T Submesoscale currents modulate the seasonal cycle of nutrients and productivity in the California Current System
%D 2020
%L fdi:010079941
%G ENG
%J Global Biogeochemical Cycles
%@ 0886-6236
%K California Current System ; Submesoscale eddies ; primary production ; nitrogen cycle
%K PACIFIQUE NORD ; ETATS UNIS ; CALIFORNIE
%M ISI:000586572100009
%N 10
%P e2020GB006578 [15 ]
%R 10.1029/2020gb006578
%U https://www.documentation.ird.fr/hor/fdi:010079941
%> https://www.documentation.ird.fr/intranet/publi/2020/11/010079941.pdf
%V 34
%W Horizon (IRD)
%X In the California Current, subduction by mesoscale eddies removes nutrients from the coastal surface layer, counteracting upwelling and quenching productivity. Submesoscale eddies are also ubiquitous in the California Current, but their biogeochemical role has not been quantified yet in the region. Here, we present results from a physical-biogeochemical model of the California Current run at a resolution of 1 km, sufficient to represent submesoscale dynamics. By comparing it with a coarser simulation run at 4 km resolution, we demonstrate the importance of submesoscale currents for the seasonal cycles of nutrients and organic matter and highlight the existence of different regimes along a cross-shore gradient. In the productive coastal region, submesoscale currents intensify quenching and reduce productivity, further counteracting wind-driven upwelling. In the offshore oligotrophic region, submesoscale currents enhance the upward transport of nutrients, fueling a dramatic increase in new production. These effects are modulated by seasonality, strengthening near the coast during upwelling and offshore in wintertime. The intensification of the transport by submesoscale eddies drives an adjustment of the planktonic ecosystem, with a reduction of plankton biomass, productivity, and size near the coast and an increase offshore. In contrast, organic matter export by sinking particles and subduction of detritus and living cells are enhanced nearly everywhere. Similar processes are likely important in other regions characterized by seasonal upwelling, for example, other eastern boundary upwelling systems.
%$ 032 ; 036

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Howard, E. M.
%A Penn, J. L.
%A Frenzel, H.
%A Seibel, B. A.
%A Bianchi, D.
%A Renault, Lionel
%A Kessouri, F.
%A Sutula, M. A.
%A McWilliams, J. C.
%A Deutsch, C.
%T Climate-driven aerobic habitat loss in the California Current System
%D 2020
%L fdi:010078063
%G ENG
%J Science Advances
%@ 2375-2548
%K PACIFIQUE NORD ; CALIFORNIE COURANT
%M ISI:000533573300007
%N 20
%P art. eaay3188 [11 ]
%R 10.1126/sciadv.aay3188
%U https://www.documentation.ird.fr/hor/fdi:010078063
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers20-06/010078063.pdf
%V 6
%W Horizon (IRD)
%X Climate warming is expected to intensify hypoxia in the California Current System (CCS), threatening its diverse and productive marine ecosystem. We analyzed past regional variability and future changes in the Metabolic Index (Phi), a species-specific measure of the environment's capacity to meet temperature-dependent organismal oxygen demand. Across the traits of diverse animals, Phi exhibits strong seasonal to interdecadal variations throughout the CCS, implying that resident species already experience large fluctuations in available aerobic habitat. For a key CCS species, northern anchovy, the long-term biogeographic distribution and decadal fluctuations in abundance are both highly coherent with aerobic habitat volume. Ocean warming and oxygen loss by 2100 are projected to decrease Phi below critical levels in 30 to 50% of anchovies' present range, including complete loss of aerobic habitat-and thus likely extirpation-from the southern CCS. Aerobic habitat loss will vary widely across the traits of CCS taxa, disrupting ecological interactions throughout the region.
%$ 036 ; 032 ; 021

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Bettencourt, J.
%A Rossi, V.
%A Renault, Lionel
%A Haynes, P.
%A Morel, Y.
%A Garcon, V.
%T Effects of upwelling duration and phytoplankton growth regime on dissolved-oxygen levels in an idealized Iberian Peninsula upwelling system
%D 2020
%L fdi:010078124
%G ENG
%J Nonlinear Processes in Geophysics
%@ 1023-5809
%K ATLANTIQUE NORD EST ; IBERIQUE PENINSULE
%M ISI:000537115200001
%N 2
%P 277-294
%R 10.5194/npg-27-277-2020
%U https://www.documentation.ird.fr/hor/fdi:010078124
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers20-06/010078124.pdf
%V 27
%W Horizon (IRD)
%X We apply a coupled modelling system composed of a state-of-the-art hydrodynamical model and a low-complexity biogeochemical model to an idealized Iberian Peninsula upwelling system to identify the main drivers of dissolved-oxygen variability and to study its response to changes in the duration of the upwelling season and in the phytoplankton growth regime. We find that the export of oxygenated waters by upwelling front turbulence is a major sink for nearshore dissolved oxygen. In our simulations of summer upwelling, when the phytoplankton population is generally dominated by diatoms whose growth is boosted by nutrient input, net primary production and air-sea exchange compensate dissolved-oxygen depletion by offshore export over the shelf. A shorter upwelling duration causes a relaxation of upwelling winds and a decrease in offshore export, resulting in a slight increase of net dissolved-oxygen enrichment in the coastal region as compared to longer upwelling durations. When phytoplankton is dominated by groups less sensitive to nutrient inputs, growth rates decrease, and the coastal region becomes net heterotrophic. Together with the physical sink, this lowers the net oxygenation rate of coastal waters, which remains positive only because of air-sea exchange. These findings help in disentangling the physical and biogeochemical controls of dissolved oxygen in upwelling systems and, together with projections of increased duration of upwelling seasons and phytoplankton community changes, suggest that the Iberian coastal upwelling region may become more vulnerable to hypoxia and deoxygenation.
%$ 036 ; 032

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Renault, Lionel
%A Masson, S.
%A Arsouze, T.
%A Madec, G.
%A McWilliams, J. C.
%T Recipes for how to force oceanic model dynamics
%D 2020
%L fdi:010078881
%G ENG
%J Journal of Advances in Modeling Earth Systems
%K Air-Sea interaction ; Current Feedback ; Parameterization ; Forced Ocean ; Model ; Reanalysis ; Scatterometers
%M ISI:000519728500006
%N 2
%P e2019MS001715 [27]
%R 10.1029/2019ms001715
%U https://www.documentation.ird.fr/hor/fdi:010078881
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers20-04/010078881.pdf
%V 12
%W Horizon (IRD)
%X The current feedback to the atmosphere (CFB) contributes to the oceanic circulation by damping eddies. In an ocean-atmosphere coupled model, CFB can be correctly accounted for by using the wind relative to the oceanic current. However, its implementation in a forced oceanic model is less straightforward as CFB also enhances the 10-m wind. Wind products based on observations have seen real currents that will not necessarily correspond to model currents, whereas meteorological reanalyses often neglect surface currents or use surface currents that, again, will differ from the surface currents of the forced oceanic simulation. In this study, we use a set of quasi-global oceanic simulations, coupled or not with the atmosphere, to (i) quantify the error associated with the different existing strategies of forcing an oceanic model, (ii) test different parameterizations of the CFB, and (iii) propose the best strategy to account for CFB in forced oceanic simulation. We show that scatterometer wind or stress are not suitable to properly represent the CFB in forced oceanic simulation. We furthermore demonstrate that a parameterization of CFB based on a wind-predicted coupling coefficient between the surface current and the stress allows us to reproduce the main characteristics of a coupled simulation. Such a parameterization can be used with any forcing set, including future coupled reanalyses, assuming that the associated oceanic surface currents are known. A further assessment of the thermal feedback of the surface wind in response to oceanic surface temperature gradients shows a weak forcing effect on oceanic currents.
%$ 032 ; 021 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Jullien, S.
%A Masson, S.
%A Oerder, V.
%A Samson, G.
%A Colas, François
%A Renault, Lionel
%T Impact of ocean-atmosphere current feedback on ocean mesoscale activity : regional variations and sensitivity to model resolution
%D 2020
%L fdi:010078009
%G ENG
%J Journal of Climate
%@ 0894-8755
%K Currents ; Feedback ; Mesoscale processes ; Air-sea interaction ; Coupled models ; Mesoscale models
%M ISI:000517554400001
%N 7
%P 2585-2602
%R 10.1175/jcli-d-19-0484.1
%U https://www.documentation.ird.fr/hor/fdi:010078009
%> https://www.documentation.ird.fr/intranet/publi/2020/03/010078009.pdf
%V 33
%W Horizon (IRD)
%X Ocean mesoscale eddies are characterized by rotating-like and meandering currents that imprint the low-level atmosphere. Such a current feedback (CFB) has been shown to induce a sink of energy from the ocean to the atmosphere, and consequently to damp the eddy kinetic energy (EKE), with an apparent regional disparity. In a context of increasing model resolution, the importance of this feedback and its dependence on oceanic and atmospheric model resolution arise. Using a hierarchy of quasi-global coupled models with spatial resolutions varying from 1/4 degrees to 1/12 degrees, the present study shows that the CFB induces a negative wind work at scales ranging from 100 to 1000 km, and a subsequent damping of the mesoscale activity by 30% on average, independently of the model resolution. Regional variations of this damping range from 20% in very rich eddying regions to 40% in poor eddying regions. This regional modulation is associated with a different balance between the sink of energy by eddy wind work and the source of EKE by ocean intrinsic instabilities. The efficiency of the CFB is also shown to be a function of the surface wind magnitude: the larger the wind, the larger the sink of energy. The CFB impact is thus related to both wind and EKE. Its correct representation requires both an ocean model that resolves the mesoscale field adequately and an atmospheric model resolution that matches the ocean effective resolution and allows a realistic representation of wind patterns. These results are crucial for including adequately mesoscale ocean-atmosphere interactions in coupled general circulation models and have strong implications in climate research.
%$ 021 ; 032 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Contreras, M.
%A Pizarro, O.
%A Dewitte, Boris
%A Sepulveda, H. H.
%A Renault, Lionel
%T Subsurface mesoscale eddy generation in the ocean off Central Chile
%D 2019
%L fdi:010077124
%G ENG
%J Journal of Geophysical Research : Oceans
%@ 2169-9275
%K CHILI ; PACIFIQUE SUD
%M ISI:000490464200021
%N 8
%P 5700-5722
%R 10.1029/2018jc014723
%U https://www.documentation.ird.fr/hor/fdi:010077124
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers19-11/010077124.pdf
%V 124
%W Horizon (IRD)
%X Off the coast of central Chile, subsurface anticyclonic eddies are a salient feature of the oceanic circulation, transporting a significant fraction of coastal water that is rich in nutrients and poor in dissolved oxygen offshore. In this study, the formation mechanism of these eddies is analyzed through a high-resolution (similar to 0.3 km) and low-resolution (similar to 3 km) oceanic model that realistically simulate the regional mean circulation, including the Peru-Chile Undercurrent (PCUC). An analysis of the vorticity and eddy kinetic energy in both simulations indicated that the subsurface eddies can be triggered through a combination of processes that are associated with instabilities of the PCUC. In the high-resolution simulation, we observed that the interaction between the PCUC and topographic slope generates anticyclonic vorticity and potential vorticity close to zero in the bottom boundary layer. The separation of the undercurrent from the slope favors the intensification of anticyclonic vorticity. It reaches magnitudes that are larger than the planetary vorticity while kinetic energy is converted from the PCUC to the eddy flow. These processes set the necessary conditions for the development of centrifugal instabilities, which can form submesoscale structures. The coalescence of submesoscale structures generates a subsurface anticyclonic mesoscale eddy. In the low-resolution simulations (>3 km) centrifugal instabilities are not simulated, and the barotropic conversion of the mean kinetic energy into eddy kinetic energy appears as the main process of eddy formation. We showed that the vertical structure of these eddies is sensitive to the spatial resolution of the model. Plain Language Summary Subsurface mesoscale eddies are swirling masses of water observed below the surface layer of the ocean (around 100- to 400-m depth). Off central Chile, these eddies have typical diameters of few tens of kilometers. They are formed near the coast, where an intense subsurface poleward flow, namely, the Peru-Chile Undercurrent (PCUC), interacts with the continental slope and the seaward border of the continental shelf. These eddies can travel long distances, toward the open ocean, transporting coastal waters with low dissolved oxygen and high nutrient concentrations and impacting the regional marine ecosystems. We use a high-resolution numerical oceanic model (similar to 0.3 km) to analyze the formation of an eddy near 33.5 degrees S off Chile. We showed that the eddy formation process requires the undercurrent to destabilize and detach from the coast, promoting the generation of submesoscale eddies (diameters -10 km). This means that in regions of eddy formation, initially, the PCUC drifts offshore transferring momentum to submesoscale eddies. Later on, these eddies begin to coalesce to form an eddy with larger dimensions. We also showed that the spatial resolution of the numerical model can impact the mechanism of transfer of momentum and the vertical structure of eddies.
%$ 032

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Renault, Lionel
%A Lemarie, F.
%A Arsouze, T.
%T On the implementation and consequences of the oceanic currents feedback in ocean-atmosphere coupled models
%D 2019
%L fdi:010076663
%G ENG
%J Ocean Modelling
%@ 1463-5003
%K Coupled ocean-atmosphere models ; Current feedback to the atmosphere ; Implementation of the current Feedback in Coupled Models ; Consequences of a poor implementation ; Oceanic mesoscale activity
%M ISI:000483922300001
%P art. 101423 [6 ]
%R 10.1016/j.ocemod.2019.101423
%U https://www.documentation.ird.fr/hor/fdi:010076663
%> https://www.documentation.ird.fr/intranet/publi/2019/09/010076663.pdf
%V 141
%W Horizon (IRD)
%X The Current FeedBack (CFB) to the atmosphere simply represents the influence of the surface oceanic currents on near-surface wind and surface stress. As the CFB has a significant influence on the oceanic circulation, it is crucial to implement it properly in a coupled ocean-atmosphere model. In this study, we first detail the modifications to be implemented into atmospheric models to account for the CFB. In the computation of air-sea fluxes, the relative winds, i.e., the difference between the near-surface winds and the surface oceanic currents, instead of absolute winds have to be used (Modification M1). However, because of the implicit treatment of the bottom boundary condition in most atmospheric models, the use of relative winds also involves a modification of the tridiagonal problem associated with the discretization of the vertical turbulent viscosity (Modification M2). Secondly, we show both analytically and using global coupled simulations that omitting M2 leads to a large underestimation of the surface stress curl response to the CFB and, subsequently, of the coupling coefficient between mesoscale surface stress curl and surface current vorticity. As a consequence, the dampening of the mesoscale activity induced by the CFB is strongly reduced (by a minimum a factor of 2 or more). The practical implementation of the CFB must be done carefully in the atmospheric component of a coupled model in order to avoid a large underestimation of the CFB effect on the oceanic circulation.
%$ 032 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Renault, Lionel
%A Masson, S.
%A Oerder, V.
%A Jullien, S.
%A Colas, François
%T Disentangling the mesoscale ocean-atmosphere interactions
%D 2019
%L fdi:010075623
%G ENG
%J Journal of Geophysical Research : Oceans
%@ 2169-9275
%K mesoscale-air-sea-interactions ; current feedback ; thermal feedback ; scatterometters ; coupling coefficients ; coupled models
%M ISI:000464656900044
%N 3
%P 2164-2178
%R 10.1029/2018jc014628
%U https://www.documentation.ird.fr/hor/fdi:010075623
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers19-05/010075623.pdf
%V 124
%W Horizon (IRD)
%X In the decades, the use of scatterometer data allowed to demonstrate the global ubiquity of the ocean mesoscale thermal feedback (TFB) and current feedback (CFB) effects on surface winds and stress. Understanding these air-sea interactions is of uttermost importance as the induced atmospheric anomalies partly control the ocean circulation and thus can influence the Earth climate. Whether the TFB and CFB effects can be disentangled, and whether satellite scatterometers can properly reveal them, remain rather unclear. Here, using satellite observations and ocean-atmosphere coupled mesoscale simulations over 45 degrees S to 45 degrees N, we show that the CFB effect can be properly characterized and unraveled from that due to the TFB. We demonstrate that the TFB can be unambiguously characterized by its effect on the stress (and wind) divergence and magnitude. However, its effect on the wind and stress curl is contaminated by the CFB and thus cannot be estimated from scatterometer data. Finally, because scatterometers provide equivalent neutral stability winds relative to the oceanic currents, they cannot characterize adequately the CFB wind response and overestimate the TFB wind response by approximate to 25%. Surface stress appears to be the more appropriate variable to consider from scatterometer data.
%$ 032 ; 021 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Renault, Lionel
%A Marchesiello, Patrick
%A Masson, S.
%A McWilliams, J. C.
%T Remarkable control of western boundary currents by Eddy Killing, a mechanical air-sea coupling process
%D 2019
%L fdi:010075542
%G ENG
%J Geophysical Research Letters
%@ 0094-8276
%K eddy-mean flow interactions is reduced by current feedback ; stabilization of the western boundary currents ; validation with satellite data ; satellite data underestimates the eddy-mean flow ; interactions ; eddy killing induced by current feedback
%K ATLANTIQUE
%K GULF STREAM ; AGULHAS COURANT
%M ISI:000462612900046
%N 5
%P 2743-2751
%R 10.1029/2018gl081211
%U https://www.documentation.ird.fr/hor/fdi:010075542
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers19-04/010075542.pdf
%V 46
%W Horizon (IRD)
%X Western boundary currents (WBCs) are critical to Earth's climate. In the last decade, mesoscale air-sea interactions emerged as an important factor of WBC dynamics. Recently, coupled models including the feedback of surface oceanic currents to the atmosphere confirmed the existence of a physical process called eddy killing, which may correct long-lasting biases in the representation of WBCs by providing an unambiguous energy sink mechanism. Using ocean-atmosphere coupled simulations of the Gulf Stream and the Agulhas Current, we show that eddy killing reduces the eddy-mean flow interaction (both forward and inverse cascades) and leads to more realistic solutions. Model and data fluxes are in good agreement when the same coarse grid is used for their computation, although in this case they are underestimated. We conclude that the uncoupled approach is no longer suitable for continued ocean model improvement and discuss new formulations that should better account for air-sea interactions. Plain Language Summary Western boundary currents (WBCs), such as the Gulf Stream and the Agulhas Current play a crucial role in global ocean circulation and in determining and stabilizing the Earth's climate. In the last decade, mesoscale air-sea interactions emerged as important in WBC dynamics. Recently, coupled models including the feedback of surface oceanic currents to the atmosphere revealed a process called eddy killing, which potentially corrects long-lasting biases in the representation of WBCs. In this study, using ocean-atmosphere coupled simulations of the Gulf Stream and Agulhas Current, we show that eddy killing reduces the interactions between eddies and mean flow. The influence of the eddies on the mean flow can be measured by the cascade of energy, and, in particular, the inverse cascade of energy. The reduction of inverse energy flux by eddy killing leads to realistic solutions and, in particular, to the observed stabilization of WBCs. Model and data fluxes are in good agreement when the same coarse grid is used for their computation, although in this case they are underestimated. We conclude that uncoupled models are no longer suitable for continuing our model improvement of ocean dynamics and discuss new formulations that should better account for air-sea interactions.
%$ 032 ; 020 ; 126

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Meroni, A. N.
%A Renault, Lionel
%A Parodi, A.
%A Pasquero, C.
%T Role of the oceanic vertical thermal structure in the modulation of heavy precipitations over the Ligurian Sea
%D 2018
%L fdi:010074404
%G ENG
%J Pure and Applied Geophysics
%@ 0033-4553
%K Heavy precipitation events ; mesoscale convective systems ; air-sea interactions ; coupled numerical simulations
%K MEDITERANNEE ; LIGURIE MER
%M ISI:000449299300023
%N 11
%P 4111-4130
%R 10.1007/s00024-018-2002-y
%U https://www.documentation.ird.fr/hor/fdi:010074404
%> https://www.documentation.ird.fr/intranet/publi/2018/11/010074404.pdf
%V 175
%W Horizon (IRD)
%X The importance of the upper ocean thermal vertical structure (mixed-layer depth and stratification) in the control of the precipitation during a heavy-rain-producing mesoscale convective system is investigated by means of numerical simulations. In particular, the fully compressible, nonhydrostatic Euler equations for the atmosphere and the hydrostatic Boussinesq equations for the ocean are numerically integrated to study the effect of the ocean-atmosphere coupling both with realistic initial and boundary conditions and with simpler, analytical vertical temperature profile forcing. It is found that the action of the winds associated with the synoptic system, in which the heavy precipitation event is embedded, can entrain deep and cold water in the oceanic mixed layer, generating surface cooling. In the case of a shallow mixed layer and strongly stratified water column, this decrease in sea surface temperature can significantly reduce the air column instability and, thus, the total amount of precipitation produced.
%$ 032 ; 021 ; 020

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Desbiolles, F.
%A Blamey, R.
%A Illig, Serena
%A James, R.
%A Barimalala, R.
%A Renault, Lionel
%A Reason, C.
%T Upscaling impact of wind/sea surface temperature mesoscale interactions on southern Africa austral summer climate
%D 2018
%L fdi:010074088
%G ENG
%J International Journal of Climatology
%@ 0899-8418
%K atmospheric circulation ; mesoscale SST forcing ; rainfall variability ; southern Africa summer climate ; upscaling effects of mesoscale air-sea interactions
%K BOTSWANA ; ZIMBABWE ; AFRIQUE DU SUD ; MOZAMBIQUE ; NAMIBIE ; ANGOLA ; MADAGASCAR ; AGULHAS COURANT ; BENGUELA ; MOZAMBIQUE CANAL ; OCEAN INDIEN ; ATLANTIQUE SUD ; ZONE TROPICALE
%M ISI:000446279100022
%N 12
%P 4651-4660
%R 10.1002/joc.5726
%U https://www.documentation.ird.fr/hor/fdi:010074088
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers18-10/010074088.pdf
%V 38
%W Horizon (IRD)
%X Mesoscale sea surface temperature (SST) variability plays an important role in shaping local atmospheric boundary layers through thermodynamic processes. This study focuses on the upscaling effects of mesoscale SST gradients in sensitive areas on the southern Africa regional atmospheric circulation. Using regional atmospheric model sensitivity experiments which differ only in the mesoscale SST forcing characteristics (either the full spectrum of SST variability or only its large-scale components are included), we first quantify the importance of SST gradients on regional atmospheric conditions. Agulhas eddies and meanders influence the vertical air column up to the troposphere, and mesoscale ocean patterns significantly modify incoming landwards moisture fluxes. The austral summer mean state is then modified in terms of air temperature, cloud cover and mean rainfall, with notable differences in tropical rainbands over southwestern Africa. Mesoscale SST variability favours tropical-extra-tropical interactions and cloudband development over the continent. These results stress the importance of high-resolution ocean forcing for accurate atmospheric simulations.
%$ 032 ; 020 ; 021

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Renault, Lionel
%A McWilliams, J. C.
%A Gula, J.
%T Dampening of submesoscale currents by air-sea stress coupling in the Californian upwelling system
%D 2018
%L fdi:010073991
%G ENG
%J Scientific Reports - Nature
%@ 2045-2322
%K PACIFIQUE ; CALIFORNIE
%M ISI:000443803300004
%P art. 13388 [8 ]
%R 10.1038/s41598-018-31602-3
%U https://www.documentation.ird.fr/hor/fdi:010073991
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers18-09/010073991.pdf
%V 8
%W Horizon (IRD)
%X Oceanic submesoscale currents (SMCs) occur on an scale of 0.1-10 km horizontally and have a large influence on the oceanic variability and on ecosystems. At the mesoscale (10-250 km), oceanic thermal and current feedbacks are known to have a significant influence on the atmosphere and on oceanic dynamics. However, air-sea interactions at the submesoscale are not well known because the small size of SMCs presents observational and simulation barriers. Using high-resolution coupled oceanic and atmospheric models for the Central California region during the upwelling season, we show that the current feedback acting through the surface stress dominates the thermal feedback effect on the ocean and dampens the SMC variability by approximate to 17% +/- 4%. As for the mesoscale, the current feedback induces an ocean sink of energy at the SMCs and a source of atmospheric energy that is related to induced Ekman pumping velocities. However, those additional vertical velocities also cause an increase of the injection of energy by baroclinic conversion into the SMCs, partially counteracting the sink of energy by the stress coupling. These stress coupling effects have important implications in understanding SMC variability and its links with the atmosphere and should be tested in other regions.
%$ 032 ; 021

%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Dewitte, Boris
%A Purca, S.
%A Illig, Serena
%A Renault, Lionel
%A Giese, B. S.
%T Low-frequency modulation of intraseasonal equatorial Kelvin wave activity in the Pacific from SODA : 1958-2001
%D 2008
%L fdi:010044143
%G ENG
%J Journal of Climate
%@ 0894-8755
%M ISI:000261107800021
%N 22
%P 6060-6069
%R 10.1175/2008jcli2277.1
%U https://www.documentation.ird.fr/hor/fdi:010044143
%> https://www.documentation.ird.fr/intranet/publi/2008/12/010044143.pdf
%V 21
%W Horizon (IRD)
%X Intraseasonal equatorial Kelvin wave activity (IEKW) at a low frequency in the Pacific is investigated using the Simple Ocean Data Assimilation (SODA) oceanic reanalyses. A vertical and horizontal mode decomposition of SODA variability allows estimation of the Kelvin wave amplitude according to the most energetic baroclinic modes. A wavenumber-frequency analysis is then performed on the time series to derive indices of modulation of the IEKW at various frequency bands. The results indicate that the IEKW activity undergoes a significant modulation that projects onto baroclinic modes and is not related in a straightforward manner to the low-frequency climate variability in the Pacific. Linear model experiments corroborate that part of the modulation of the IEKW is tightly linked to change in oceanic mean state rather than to the low-frequency change of atmospheric equatorial variability.
%$ 021