Pour voir les autres types de publications sur ce sujet consultez le lien suivant : Oceanic mixing.
Articles de revues sur le sujet « Oceanic mixing »
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les 50 meilleurs articles de revues pour votre recherche sur le sujet « Oceanic mixing ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Parcourez les articles de revues sur diverses disciplines et organisez correctement votre bibliographie.
1
Legg, Sonya. « Mixing by Oceanic Lee Waves ». Annual Review of Fluid Mechanics 53, no 1 (5 janvier 2021) : 173–201. http://dx.doi.org/10.1146/annurev-fluid-051220-043904.
Texte intégralRésumé :
Oceanic lee waves are generated in the deep stratified ocean by the flow of ocean currents over sea floor topography, and when they break, they can lead to mixing in the stably stratified ocean interior. While the theory of linear lee waves is well established, the nonlinear mechanisms leading to mixing are still under investigation. Tidally driven lee waves have long been observed in the ocean, along with associated mixing, but observations of lee waves forced by geostrophic eddies are relatively sparse and largely indirect. Parameterizations of the mixing due to ocean lee waves are now being developed and implemented in ocean climate models. This review summarizes current theory and observations of lee wave generation and mixing driven by lee wave breaking, distinguishing between steady and tidally oscillating forcing. The existing parameterizations of lee wave–driven mixing informed by theory and observations are outlined, and the impacts of the parameterized lee wave–driven mixing on simulations of large-scale ocean circulation are summarized.
2
McWilliams, James C. « Oceanic Frontogenesis ». Annual Review of Marine Science 13, no 1 (3 janvier 2021) : 227–53. http://dx.doi.org/10.1146/annurev-marine-032320-120725.
Texte intégralRésumé :
Frontogenesis is the fluid-dynamical processes that rapidly sharpen horizontal density gradients and their associated horizontal velocity shears. It is a positive feedback process where the ageostrophic, overturning secondary circulation in the cross-front plane accelerates the frontal sharpening until an arrest occurs through frontal instability and other forms of turbulent mixing. Several well-known types of oceanic frontal phenomena are surveyed, their impacts on oceanic system functioning are assessed, and future research is envisioned.
3
Zhu, Yuchao, Rong-Hua Zhang et Jichang Sun. « North Pacific Upper-Ocean Cold Temperature Biases in CMIP6 Simulations and the Role of Regional Vertical Mixing ». Journal of Climate 33, no 17 (1 septembre 2020) : 7523–38. http://dx.doi.org/10.1175/jcli-d-19-0654.1.
Texte intégralRésumé :
AbstractSubstantial model biases are still prominent even in the latest CMIP6 simulations; attributing their causes is defined as one of the three main scientific questions addressed in CMIP6. In this paper, cold temperature biases in the North Pacific subtropics are investigated using simulations from the newly released CMIP6 models, together with other related modeling products. In addition, ocean-only sensitivity experiments are performed to characterize the biases, with a focus on the role of oceanic vertical mixing schemes. Based on the Argo-derived diffusivity, idealized vertical diffusivity fields are designed to mimic the seasonality of vertical mixing in this region, and are employed in ocean-only simulations to test the sensitivity of this cold bias to oceanic vertical mixing. It is demonstrated that the cold temperature biases can be reduced when the mixing strength is enhanced within and beneath the surface boundary layer. Additionally, the temperature simulations are rather sensitive to the parameterization of static instability, and the cold biases can be reduced when the vertical diffusivity for convection is increased. These indicate that the cold temperature biases in the North Pacific can be largely attributed to biases in oceanic vertical mixing within ocean-only simulations, which likely contribute to the even larger biases seen in coupled simulations. This study therefore highlights the need for improved oceanic vertical mixing in order to reduce these persistent cold temperature biases seen across several CMIP models.
4
Whalen, Caitlin. « Measuring ocean mixing : From observing processes to quantifying impacts ». Journal of the Acoustical Society of America 152, no 4 (octobre 2022) : A151. http://dx.doi.org/10.1121/10.0015854.
Texte intégralRésumé :
The impacts of ocean mixing are varied, ranging from the local across-isopycnal transport of heat, salt, and nutrients, to the global overturning circulation with implications for climate. A full understanding of turbulent mixing, from driving processes to impacts, spans all oceanic time and length scales. Turbulent mixing in the ocean occur on scales less than centimeters and timescales less than hours, yet the processes that drive this turbulence occurs on meters to 100s of km length scales and the impact of the turbulent mixing spans the full range of oceanic spatiotemporal scales. Here, we will discuss current approaches to measuring ocean mixing and explore how to bridge this scale gap to link the turbulence measurements to the processes that drive ocean mixing and the subsequent impacts. Intriguing examples of ocean mixing processes and their influence on ocean dynamics will be discussed throughout.
5
Huang, Rui Xin. « Mixing and Energetics of the Oceanic Thermohaline Circulation* ». Journal of Physical Oceanography 29, no 4 (avril 1999) : 727–46. http://dx.doi.org/10.1175/1520-0485(1999)029<0727:maeoto>2.0.co;2.
Texte intégral
6
Grant, Alan L. M., et Stephen E. Belcher. « Wind-Driven Mixing below the Oceanic Mixed Layer ». Journal of Physical Oceanography 41, no 8 (1 août 2011) : 1556–75. http://dx.doi.org/10.1175/jpo-d-10-05020.1.
Texte intégralRésumé :
Abstract This study describes the turbulent processes in the upper ocean boundary layer forced by a constant surface stress in the absence of the Coriolis force using large-eddy simulation. The boundary layer that develops has a two-layer structure, a well-mixed layer above a stratified shear layer. The depth of the mixed layer is approximately constant, whereas the depth of the shear layer increases with time. The turbulent momentum flux varies approximately linearly from the surface to the base of the shear layer. There is a maximum in the production of turbulence through shear at the base of the mixed layer. The magnitude of the shear production increases with time. The increase is mainly a result of the increase in the turbulent momentum flux at the base of the mixed layer due to the increase in the depth of the boundary layer. The length scale for the shear turbulence is the boundary layer depth. A simple scaling is proposed for the magnitude of the shear production that depends on the surface forcing and the average mixed layer current. The scaling can be interpreted in terms of the divergence of a mean kinetic energy flux. A simple bulk model of the boundary layer is developed to obtain equations describing the variation of the mixed layer and boundary layer depths with time. The model shows that the rate at which the boundary layer deepens does not depend on the stratification of the thermocline. The bulk model shows that the variation in the mixed layer depth is small as long as the surface buoyancy flux is small.
7
MONAHAN, ADAM HUGH. « CORRELATION EFFECTS IN A SIMPLE STOCHASTIC MODEL OF THE THERMOHALINE CIRCULATION ». Stochastics and Dynamics 02, no 03 (septembre 2002) : 437–62. http://dx.doi.org/10.1142/s0219493702000510.
Texte intégralRésumé :
A simple model of the thermohaline circulation of the World Ocean is considered, in which fluctuations in internal oceanic mixing and in freshwater forcing are represented by stochastic processes. The effects on the stationary probability density function of correlations between fluctuations in mixing and freshwater forcing, and of finite autocorrelation time in oceanic mixing, are determined using a mixture of analytical and numerical techniques. The quantitative behaviour of the system is found to depend on the strength and correlation character of the noise processes, quite sensitively so in some regions of parameter space. The results of this analysis suggest the importance of accurately modelling high-frequency variability in nonlinear models of the climate system.
8
Heesterman, Aart. « Restoring or maintaining the vertical mixing of oceanic waters ». International Journal of Scientific and Research Publications (IJSRP) 11, no 6 (28 juin 2021) : 787–93. http://dx.doi.org/10.29322/ijsrp.11.06.2021.p114102.
Texte intégral
9
Hsu, S. A., Robert Fett et Paul E. La Violette. « Variations in atmospheric mixing height across oceanic thermal fronts ». Journal of Geophysical Research 90, no C2 (1985) : 3211. http://dx.doi.org/10.1029/jc090ic02p03211.
Texte intégral
10
Gibson, Carl H. « Fossil turbulence and intermittency in sampling oceanic mixing processes ». Journal of Geophysical Research 92, no C5 (1987) : 5383. http://dx.doi.org/10.1029/jc092ic05p05383.
Texte intégral
11
Chacón-Rebollo, T., M. Gómez-Mármol et S. Rubino. « Numerical investigation of algebraic oceanic turbulent mixing-layer models ». Nonlinear Processes in Geophysics 20, no 6 (6 novembre 2013) : 945–54. http://dx.doi.org/10.5194/npg-20-945-2013.
Texte intégralRésumé :
Abstract. In this paper we investigate the finite-time and asymptotic behaviour of algebraic turbulent mixing-layer models by numerical simulation. We compare the performances given by three different settings of the eddy viscosity. We consider Richardson number-based vertical eddy viscosity models. Two of these are classical algebraic turbulence models usually used in numerical simulations of global oceanic circulation, i.e. the Pacanowski–Philander and the Gent models, while the other one is a more recent model (Bennis et al., 2010) proposed to prevent numerical instabilities generated by physically unstable configurations. The numerical schemes are based on the standard finite element method. We perform some numerical tests for relatively large deviations of realistic initial conditions provided by the Tropical Atmosphere Ocean (TAO) array. These initial conditions correspond to states close to mixing-layer profiles, measured on the Equatorial Pacific region called the West-Pacific Warm Pool. We conclude that mixing-layer profiles could be considered as kinds of "absorbing configurations" in finite time that asymptotically evolve to steady states under the application of negative surface energy fluxes.
12
MacKinnon, Jennifer A., Zhongxiang Zhao, Caitlin B. Whalen, Amy F. Waterhouse, David S. Trossman, Oliver M. Sun, Louis C. St. Laurent et al. « Climate Process Team on Internal Wave–Driven Ocean Mixing ». Bulletin of the American Meteorological Society 98, no 11 (1 novembre 2017) : 2429–54. http://dx.doi.org/10.1175/bams-d-16-0030.1.
Texte intégralRésumé :
Abstract Diapycnal mixing plays a primary role in the thermodynamic balance of the ocean and, consequently, in oceanic heat and carbon uptake and storage. Though observed mixing rates are on average consistent with values required by inverse models, recent attention has focused on the dramatic spatial variability, spanning several orders of magnitude, of mixing rates in both the upper and deep ocean. Away from ocean boundaries, the spatiotemporal patterns of mixing are largely driven by the geography of generation, propagation, and dissipation of internal waves, which supply much of the power for turbulent mixing. Over the last 5 years and under the auspices of U.S. Climate Variability and Predictability Program (CLIVAR), a National Science Foundation (NSF)- and National Oceanic and Atmospheric Administration (NOAA)-supported Climate Process Team has been engaged in developing, implementing, and testing dynamics-based parameterizations for internal wave–driven turbulent mixing in global ocean models. The work has primarily focused on turbulence 1) near sites of internal tide generation, 2) in the upper ocean related to wind-generated near inertial motions, 3) due to internal lee waves generated by low-frequency mesoscale flows over topography, and 4) at ocean margins. Here, we review recent progress, describe the tools developed, and discuss future directions.
13
Fuhlbrügge, S., B. Quack, S. Tegtmeier, E. Atlas, H. Hepach, Q. Shi, S. Raimund et K. Krüger. « The contribution of oceanic halocarbons to marine and free troposphere air over the tropical West Pacific ». Atmospheric Chemistry and Physics Discussions 15, no 13 (2 juillet 2015) : 17887–943. http://dx.doi.org/10.5194/acpd-15-17887-2015.
Texte intégralRésumé :
Abstract. Emissions of halogenated very short lived substances (VSLS) from the tropical oceans contribute to the atmospheric halogen budget and affect tropospheric and stratospheric ozone. Here we investigate the contribution of natural oceanic VSLS emissions to the Marine Atmospheric Boundary Layer (MABL) and their transport into the Free Troposphere (FT) over the tropical West Pacific. The study concentrates in particular on ship and aircraft measurements of the VSLS bromoform, dibromomethane and methyl iodide and meteorological parameters during the SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) campaign in the South China and Sulu Seas in November 2011. Elevated oceanic concentrations of 19.9 (2.80–136.91) pmol L−1 for bromoform, 5.0 (2.43–21.82) pmol L−1 for dibromomethane and 3.8 (0.55–18.83) pmol L−1 for methyl iodide in particular close to Singapore and at the coast of Borneo with high corresponding oceanic emissions of 1486 ± 1718 pmol m−2 h−1 for bromoform, 405 ± 349 pmol m−2 h−1 for dibromomethane and 433 ± 482 pmol m−2 h−1 for methyl iodide characterize this tropical region as a strong source of these compounds. Unexpectedly atmospheric mixing ratios in the MABL were relatively low with 2.08 ± 2.08 ppt for bromoform, 1.17 ± 1.17 ppt for dibromomethane and 0.39 ± 0.09 ppt for methyl iodide. We use meteorological and chemical ship and aircraft observations, FLEXPART trajectory calculations and source-loss estimates to identify the oceanic VSLS contribution to the MABL and to the FT. Our results show that a convective, well-ventilated MABL and intense convection led to the low atmospheric mixing ratios in the MABL despite the high oceanic emissions in coastal areas of the South-China and Sulu Seas. While the accumulated bromoform in the FT above the region origins almost entirely from the local South China Sea area, dibromomethane is largely advected from distant source regions. The accumulated FT mixing ratio of methyl iodide is higher than can be explained with the local oceanic or MABL contributions. Possible reasons, uncertainties and consequences of our observations and model estimates are discussed.
14
Li, J., Z. Wang, G. Zhuang, G. Luo, Y. Sun et Q. Wang. « Mixing of Asian mineral dust with anthropogenic pollutants and its impact on regional atmospheric environmental and oceanic biogeochemical cycles over East Asia : a model case study of a super-duststorm in March 2010 ». Atmospheric Chemistry and Physics Discussions 12, no 1 (27 janvier 2012) : 2743–82. http://dx.doi.org/10.5194/acpd-12-2743-2012.
Texte intégralRésumé :
Abstract. Mixing of Asian mineral dust with anthropogenic pollutants allows pollutants (e.g. sulfate and nitrate) to be transported over longer distances (e.g. to the northern Pacific, even to North America) along with dust particles. This mixing therefore affects the atmospheric and oceanic environment at local, regional and even continental scales. In this study, we used a three-dimensional regional chemical transport model (NAQPMS) to examine the degree of mixing between Asian mineral dust and anthropogenic pollutants in a super-duststorm event during 19–22 March 2010. Influences of the mixing processes on regional atmospheric environmental and oceanic biogeochemical cycles were also investigated. A comparison with measurements showed that the model reproduced well the trajectory of long-range dust transport, the vertical dust profile, and the chemical evolution of dust particles. We found that along-path mixing processes during the long-range transport of Asian dust led to increasingly polluted particles. As a result, ~60% of the sulfate and 70–95% of the nitrate in the downwind regions was derived from active mixing processes of minerals with pollutants sourced from the North China Plain and enhanced by transport over South China. This mixing had a significant impact on the regional-scale atmospheric composition and oceanic biogeochemical cycle. Surface HNO3, SO2 and O3 were decreased by up to 90%, 40% and 30%, respectively, due to the heterogeneous reactions on dust particles. Fe solubility rose from ~0.5% in the Gobi region to ~3–5% in the northwestern Pacific, resulting from oxidization of SO2 on dust particles. Total Fe(II) deposition in the ocean region of East Asia reached 327 tons during the 4-day dust event, and created a calculated primary productivity of ~520 mgC m−2 d−1 in the Kuril Islands, which can support almost 100% of the observed mean marine primary productivity in spring in this region (526 mgC m−2 d−1).
15
Li, J., Z. Wang, G. Zhuang, G. Luo, Y. Sun et Q. Wang. « Mixing of Asian mineral dust with anthropogenic pollutants over East Asia : a model case study of a super-duststorm in March 2010 ». Atmospheric Chemistry and Physics 12, no 16 (21 août 2012) : 7591–607. http://dx.doi.org/10.5194/acp-12-7591-2012.
Texte intégralRésumé :
Abstract. Mixing of Asian mineral dust with anthropogenic pollutants allows pollutants (e.g. sulfate and nitrate) to be transported over longer distances (e.g. to the northern Pacific, even to North America) along with dust particles. This mixing therefore affects the atmospheric and oceanic environment at local, regional and even continental scales. In this study, we used a three-dimensional regional chemical transport model (Nested Air Quality Predicting Modeling System, NAQPMS) to examine the degree of mixing between Asian mineral dust and anthropogenic pollutants in a super-duststorm event during 19–22 March 2010. Influences of the mixing processes on regional atmospheric environmental and oceanic biogeochemical cycles were also investigated. A comparison with measurements showed that the model reproduced well the trajectory of long-range dust transport, the vertical dust profile, and the chemical evolution of dust particles. We found that along-path mixing processes during the long-range transport of Asian dust led to increasingly polluted particles. As a result, ~60% of the sulfate and 70–95% of the nitrate in the downwind regions was derived from active mixing processes of minerals with pollutants sourced from the North China Plain and enhanced by transport over South China. This mixing had a significant impact on the regional-scale atmospheric composition and oceanic biogeochemical cycle. Surface HNO3, SO2 and O3 were decreased by up to 90%, 40% and 30%, respectively, due to the heterogeneous reactions on dust particles. Fe solubility rose from ~0.5% in the Gobi region to ~3–5% in the northwestern Pacific, resulting from oxidization of SO2 on dust particles. Total Fe(II) deposition in the ocean region of East Asia reached 327 tons during the 4-day dust event, and created a calculated primary productivity of ~520 mgC m−2 d−1 in the Kuril Islands, which can support almost 100% of the observed mean marine primary productivity in spring in this region (526 mgC m−2 d−1).
16
Abarzhi, S. I., et K. R. Sreenivasan. « Turbulent mixing and beyond ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 368, no 1916 (13 avril 2010) : 1539–46. http://dx.doi.org/10.1098/rsta.2010.0021.
Texte intégralRésumé :
Turbulence is a supermixer. Turbulent mixing has immense consequences for physical phenomena spanning astrophysical to atomistic scales under both high- and low-energy-density conditions. It influences thermonuclear fusion in inertial and magnetic confinement systems; governs dynamics of supernovae, accretion disks and explosions; dominates stellar convection, planetary interiors and mantle-lithosphere tectonics; affects premixed and non-premixed combustion; controls standard turbulent flows (wall-bounded and free—subsonic, supersonic as well as hypersonic); as well as atmospheric and oceanic phenomena (which themselves have important effects on climate). In most of these circumstances, the mixing phenomena are driven by non-equilibrium dynamics. While each article in this collection dwells on a specific problem, the purpose here is to seek a few unified themes amongst diverse phenomena.
17
Fu, Hongli, Jinkun Yang, Wei Li, Xinrong Wu, Guijun Han, Yuanfu Xie, Shaoqing Zhang, Xuefeng Zhang, Yingzhi Cao et Xiaoshuang Zhang. « A Potential Density Gradient Dependent Analysis Scheme for Ocean Multiscale Data Assimilation ». Advances in Meteorology 2017 (2017) : 1–13. http://dx.doi.org/10.1155/2017/9315601.
Texte intégralRésumé :
This study addresses how to maintain oceanic mixing along potential density surface in ocean data assimilation (ODA). It is well known that the oceanic mixing across the potential density surface is much weaker than that along the potential density surface. However, traditional ODA schemes allow the mixing across the potential density surface and thus may result in extra assimilation errors. Here, a new ODA scheme that uses potential density gradient information of the model background to rescale observational adjustment is designed to improve the quality of assimilation. The new scheme has been tested using a regional ocean model within a multiscale 3-dimensional variational framework. Results show that the new scheme effectively prevents the excessive unphysical projection of observational information in the direction across potential density surface and thus improves assimilation quality greatly. Forecast experiments also show that the new scheme significantly improves the model forecast skills through providing more dynamically consistent initial conditions
18
Gao, Yu, Igor Kamenkovich et Natalie Perlin. « Origins of mesoscale mixed-layer depth variability in the Southern Ocean ». Ocean Science 19, no 3 (11 mai 2023) : 615–27. http://dx.doi.org/10.5194/os-19-615-2023.
Texte intégralRésumé :
Abstract. Mixed-layer depth (MLD) exhibits significant variability, which is important for atmosphere–ocean exchanges of heat and atmospheric gases. The origins of the mesoscale MLD variability in the Southern Ocean are studied here in an idealised regional ocean–atmosphere model (ROAM). The main conclusion from the analysis of the upper-ocean buoyancy budget is that, while the atmospheric forcing and oceanic vertical mixing, on average, induce the mesoscale variability of MLD, the three-dimensional oceanic advection of buoyancy counteracts and partially balances these atmosphere-induced vertical processes. The relative importance of advection changes with both season and average MLD. From January to May, when the mixed layer is shallow, the atmospheric forcing and oceanic mixing are the most important processes, with the advection playing a secondary role. From June to December, when the mixed layer is deep, both atmospheric forcing and oceanic advection are equally important in driving the MLD variability. Importantly, buoyancy advection by mesoscale ocean current anomalies can lead to both local shoaling and deepening of the mixed layer. The role of the atmospheric forcing is then directly addressed by two sensitivity experiments in which the mesoscale variability is removed from the atmosphere–ocean heat and momentum fluxes. The findings confirm that mesoscale atmospheric forcing predominantly controls MLD variability in summer and that intrinsic oceanic variability and surface forcing are equally important in winter. As a result, MLD variance increases when mesoscale anomalies in atmospheric fluxes are removed in winter, and oceanic advection becomes a dominant player in the buoyancy budget. This study highlights the importance of oceanic advection and intrinsic ocean dynamics in driving mesoscale MLD variability and underscores the importance of MLD in modulating the effects of advection on upper-ocean dynamics.
19
HOLLAND, DAVID M., RODOLFO R. ROSALES, DAN STEFANICA et ESTEBAN G. TABAK. « Internal hydraulic jumps and mixing in two-layer flows ». Journal of Fluid Mechanics 470 (31 octobre 2002) : 63–83. http://dx.doi.org/10.1017/s002211200200188x.
Texte intégralRésumé :
Internal hydraulic jumps in two-layer flows are studied, with particular emphasis on their role in entrainment and mixing. For highly entraining internal jumps, a new closure is proposed for the jump conditions. The closure is based on two main assumptions: (i) most of the energy dissipated at the jump goes into turbulence, and (ii) the amount of turbulent energy that a stably stratified flow may contain without immediately mixing further is bounded by a measure of the stratification. As a consequence of this closure, surprising bounds emerge, for example on the amount of entrainment that may take place at the location of the jump. These bounds are probably almost achieved by highly entraining internal jumps, such as those likely to develop in dense oceanic over flows. The values obtained here are in good agreement with the existing observations of the spatial development of oceanic downslope currents, which play a crucial role in the formation of abyssal and intermediate waters in the global ocean.
20
Mcphee, Miles G. « On the Turbulent Mixing Length in the Oceanic Boundary Layer ». Journal of Physical Oceanography 24, no 9 (septembre 1994) : 2014–31. http://dx.doi.org/10.1175/1520-0485(1994)024<2014:ottmli>2.0.co;2.
Texte intégral
21
Odier, Philippe, Jun Chen et Robert E. Ecke. « Entrainment and mixing in a laboratory model of oceanic overflow ». Journal of Fluid Mechanics 746 (4 avril 2014) : 498–535. http://dx.doi.org/10.1017/jfm.2014.104.
Texte intégralRésumé :
AbstractWe present experimental measurements of a wall-bounded gravity current, motivated by characterizing natural gravity currents such as oceanic overflows. We use particle image velocimetry and planar laser-induced fluorescence to simultaneously measure the velocity and density fields as they evolve downstream of the initial injection from a turbulent channel flow onto a plane inclined at$10^\circ $with respect to horizontal. The turbulence level of the input flow is controlled by injecting velocity fluctuations upstream of the output nozzle. The initial Reynolds number based on the Taylor microscale of the flow,$R_{\lambda }$, is varied between 40 and 120, and the effects of the initial turbulence level are assessed. The bulk Richardson number$\mathit{Ri}$for the flow is${\sim }$0.3 whereas the gradient Richardson number$\mathit{Ri}_g$varies between 0.04 and 0.25, indicating that shear dominates the stabilizing effect of stratification. Kelvin–Helmholtz instability results in vigorous vertical transport of mass and momentum. We present baseline characterization of standard turbulence quantities and calculate, in several different ways, the fluid entrainment coefficient$E$, a quantity of considerable interest in mixing parameterization for ocean circulation models. We also determine the properties of mixing as represented by the flux Richardson number$\mathit{Ri}_f$as a function of$\mathit{Ri}_g$and diapycnal mixing parameter$K_{\rho }$versus the buoyancy Reynolds number$\mathit{Re}_b$. We find reasonable agreement with results from natural flows.
22
Nishioka, Jun, Takeshi Nakatsuka, Yutaka W. Watanabe, Ichiro Yasuda, Kenshi Kuma, Hiroshi Ogawa, Naoto Ebuchi et al. « Intensive mixing along an island chain controls oceanic biogeochemical cycles ». Global Biogeochemical Cycles 27, no 3 (septembre 2013) : 920–29. http://dx.doi.org/10.1002/gbc.20088.
Texte intégral
23
Mamberti, Marc, Henriette Lapierre, Delphine Bosch, Etienne Jaillard, Jean Hernandez et Mireille Polvé. « The Early Cretaceous San Juan Plutonic Suite, Ecuador : a magma chamber in an oceanic plateau ? » Canadian Journal of Earth Sciences 41, no 10 (1 octobre 2004) : 1237–58. http://dx.doi.org/10.1139/e04-060.
Texte intégralRésumé :
Sections through an oceanic plateau are preserved in tectonic slices in the Western Cordillera of Ecuador (South America). The San Juan section is a sequence of maficultramafic cumulates. To establish that these plutonic rocks formed in an oceanic plateau setting, we have developed criteria that discriminate intrusions of oceanic plateaus from those of other tectonic settings. The mineralogy and crystallization sequence of the cumulates are similar to those of intra-plate magmas. Clinopyroxene predominates throughout, and orthopyroxene is only a minor component. Rocks of intermediate composition are absent, and hornblende is restricted to the uppermost massive gabbros within the sequence. The ultramafic cumulates are very depleted in light rare-earth elements (LREE), whereas the gabbros have flat or slightly enriched LREE patterns. The composition of the basaltic liquid in equilibrium with the peridotite, calculated using olivine compositions and REE contents of clinopyroxene, contains between 16% and 8% MgO and has a flat REE pattern. This melt is geochemically similar to other accreted oceanic plateau basalts, isotropic gabbros, and differentiated sills in western Ecuador. The Ecuadorian intrusive and extrusive rocks have a narrow range of εNdi (+8 to +5) and have a rather large range of Pb isotopic ratios. Pb isotope systematics of the San Juan plutonic rocks and mineral separates lie along a mixing line between the depleted mantle (DMM) and the enriched-plume end members. This suggests that the Ecuadorian plutonic rocks generated from the mixing of two mantle sources, a depleted mid-oceanic ridge basalt (MORB) source and an enriched one. The latter is characterized by high (207Pb/204Pb)i ratios and could reflect a contamination by recycled either lower continental crust or oceanic pelagic sediments and (or) altered oceanic crust (enriched mantle type I, EMI). These data suggest that the San Juan sequence represents the plutonic components of an Early Cretaceous oceanic plateau, which accreted in the Late Cretaceous to the Ecuadorian margin.
24
Booge, Dennis, Jerry F. Tjiputra, Dirk J. L. Olivié, Birgit Quack et Kirstin Krüger. « Natural marine bromoform emissions in the fully coupled ocean–atmosphere model NorESM2 ». Earth System Dynamics 15, no 3 (21 juin 2024) : 801–16. http://dx.doi.org/10.5194/esd-15-801-2024.
Texte intégralRésumé :
Abstract. Oceanic bromoform (CHBr3) is an important precursor of atmospheric bromine. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, global CHBr3 production in the ocean and its emissions are still poorly constrained in observations and are mostly neglected in climate models. Here, we newly implement marine CHBr3 in the second version of the state-of-the-art Norwegian Earth System Model (NorESM2) with fully coupled interactions of ocean, sea ice, and atmosphere. Our results are validated using oceanic and atmospheric observations from the HalOcAt (Halocarbons in the Ocean and Atmosphere) database. The simulated mean oceanic concentrations (6.61 ± 3.43 pmol L−1) are in good agreement with observations from open-ocean regions (5.02 ± 4.50 pmol L−1), while the mean atmospheric mixing ratios (0.76 ± 0.39 ppt) are lower than observed but within the range of uncertainty (1.45 ± 1.11 ppt). The NorESM2 ocean emissions of CHBr3 (214 Gg yr−1) are within the range of or higher than previously published estimates from bottom-up approaches but lower than estimates from top-down approaches. Annual mean fluxes are mostly positive (sea-to-air fluxes); driven by oceanic concentrations, sea surface temperature, and wind speed; and dependent on season and location. During winter, model results imply that some oceanic regions in high latitudes act as sinks of atmospheric CHBr3 due to their elevated atmospheric mixing ratios. We further demonstrate that key drivers for oceanic and atmospheric CHBr3 variability are spatially heterogeneous. In the tropical West Pacific, which is a hot spot for oceanic bromine delivery to the stratosphere, wind speed is the main driver for CHBr3 fluxes on an annual basis. In the North Atlantic, as well as in the Southern Ocean region, atmospheric and oceanic CHBr3 variabilities interact during most of the seasons except for the winter months, when sea surface temperature is the main driver. Our study provides an improved process-based understanding of the biogeochemical cycling of CHBr3 and more reliable natural emission estimates, especially on seasonal and spatial scales, compared to previously published model estimates.
25
Kantha, Lakshmi, et Hubert Luce. « Mixing Coefficient in Stably Stratified Flows ». Journal of Physical Oceanography 48, no 11 (novembre 2018) : 2649–65. http://dx.doi.org/10.1175/jpo-d-18-0139.1.
Texte intégralRésumé :
AbstractTurbulent mixing in the interior of the oceans is not as well understood as mixing in the oceanic boundary layers. Mixing in the generally stably stratified interior is primarily, although not exclusively, due to intermittent shear instabilities. Part of the energy extracted by the Reynolds stresses acting on the mean shear is expended in increasing the potential energy of the fluid column through a buoyancy flux, while most of it is dissipated. The mixing coefficient χm, the ratio of the buoyancy flux to the dissipation rate of turbulence kinetic energy ε, is an important parameter, since knowledge of χm enables turbulent diffusivities to be inferred. Theory indicates that χm must be a function of the gradient Richardson number. Yet, oceanic studies suggest that a value of around 0.2 for χm gives turbulent diffusivities that are in good agreement with those inferred from tracer studies. Studies by scientists working with atmospheric radars tend to reinforce these findings but are seldom referenced in oceanographic literature. The goal of this paper is to bring together oceanographic, atmospheric, and laboratory observations related to χm and to report on the values deduced from in situ data collected in the lower troposphere by unmanned aerial vehicles, equipped with turbulence sensors and flown in the vicinity of the Middle and Upper Atmosphere (MU) radar in Japan. These observations are consistent with past studies in the oceans, in that a value of around 0.16 for χm yields good agreement between ε derived from turbulent temperature fluctuations using this value and ε obtained directly from turbulence velocity fluctuations.
26
Williams, J. E., G. Le Bras, A. Kukui, H. Ziereis et C. A. M. Brenninkmeijer. « The impact of the chemical production of methyl nitrate from the NO + CH<sub>3</sub>O<sub>2</sub> ; reaction on the global distributions of alkyl nitrates, nitrogen oxides and tropospheric ozone : a global modeling study ». Atmospheric Chemistry and Physics Discussions 13, no 8 (2 août 2013) : 20111–63. http://dx.doi.org/10.5194/acpd-13-20111-2013.
Texte intégralRésumé :
Abstract. The formation, abundance and distribution of organic nitrates are relevant for determining the production efficiency and resident mixing ratios of tropospheric ozone (O3) at both regional and global scales. Here we investigate the effect of applying the recently measured direct chemical production of methyl nitrate (CH3ONO2) during NOx recycling involving the methyl-peroxy radical on the global tropospheric distribution of CH3ONO2 and the perturbations introduced towards tropospheric NOx and O3 using the TM5 global chemistry transport model. By comparing against numerous observations we show that the global surface distribution of CH3ONO2 can be largely explained by introducing the chemical production mechanism using a branching ratio of 0.3%, when assuming a direct oceanic emission source of ~0.29 Tg N yr−1. The resident mixing ratios are found to be highly sensitive towards the dry deposition velocity of CH3ONO2 that is prescribed, where more than 50% of the direct oceanic emission of CH3ONO2 is lost near the source regions thereby mitigating subsequent effects on tropospheric composition due to long range and convective transport. For the higher alkyl nitrates (C2 and above) we find improvements in their simulated distribution in the tropics in TM5 improves when introducing direct oceanic emissions of ~0.17 Tg N yr−1. For the tropical upper troposphere (UT) a significant low model bias for all alkly nitrates occurs due to either missing transport pathways or chemical precursors, although measurements show significant variability in resident mixing ratios at high altitudes with respect to both latitude and longitude. For total reactive nitrogen (NOy) ~20% originates from alkyl nitrates in the tropical and extra-tropical UT, where the introduction of both direct oceanic emission sources and the chemical production of CH3ONO2 only increases NOy by ~5% when compared with aircraft observations. We find that the increases in tropospheric O3 due to direct oceanic emissions are mitigated by introducing the direct chemical production of CH3ONO2 resulting in rather moderate effects on nitrogen oxides and tropospheric O3.
27
Sullivan, Peter P., et James C. McWilliams. « Oceanic Frontal Turbulence ». Journal of Physical Oceanography 54, no 2 (février 2024) : 333–58. http://dx.doi.org/10.1175/jpo-d-23-0033.1.
Texte intégralRésumé :
Abstract Upper-ocean turbulence results from a complex set of interactions between submesoscale turbulence and local boundary layer processes. The interaction between larger-scale currents and turbulent fluctuations is two-way: large-scale shearing motions generate turbulence, and the resulting coherent turbulent fluxes of momentum and buoyancy feed back onto the larger flow. Here we examine the evolution and role of turbulence in the intensification, instability, arrest, and decay (i.e., the life cycle) of a dense filament undergoing frontogenesis in the upper-ocean boundary layer, i.e., cold filament frontogenesis (CFF). This phenomenon is examined in large-eddy simulations (LES) with resolved turbulent motions in large horizontal domains using 109 grid points. The boundary layer turbulence is generated by surface buoyancy loss (cooling flux) and is allowed to freely interact with an initially imposed cold filament, and the evolution is followed through the frontal life cycle. Two control parameters are explored: the initial frontal strength M2 = ∂xb and the surface flux . The former is more consequent: initially weaker fronts sharpen more slowly and become arrested at a later time with a larger width. This reflects a competition between the frontogenetic rate induced by the secondary circulation associated with vertical momentum mixing by the turbulence and the instability rate for the along-filament shear flow. The frontal turbulence is energized by the shear production of the latter, is nonlocally transported away from the primary production zone at the filament centerline, and cascades to dissipation in a broad region surrounding the filament. The turbulent momentum fluxes arresting the frontogenesis are supported across a wide range of horizontal scales.
28
Thomas, Jordan, Darryn Waugh et Anand Gnanadesikan. « Relationship between Ocean Carbon and Heat Multidecadal Variability ». Journal of Climate 31, no 4 (février 2018) : 1467–82. http://dx.doi.org/10.1175/jcli-d-17-0134.1.
Texte intégralRésumé :
The global ocean serves as a critical sink for anthropogenic carbon and heat. While significant effort has been dedicated to quantifying the oceanic uptake of these quantities, less research has been conducted on the mechanisms underlying decadal-to-centennial variability in oceanic heat and carbon. Therefore, little is understood about how much such variability may have obscured or reinforced anthropogenic change. Here the relationship between oceanic heat and carbon content is examined in a suite of coupled climate model simulations that use different parameterization settings for mesoscale mixing. The differences in mesoscale mixing result in very different multidecadal variability, especially in the Weddell Sea where the characteristics of deep convection are drastically changed. Although the magnitude and frequency of variability in global heat and carbon content is different across the model simulations, there is a robust anticorrelation between global heat and carbon content in all simulations. Global carbon content variability is primarily driven by Southern Ocean carbon variability. This contrasts with global heat content variability. Global heat content is primarily driven by variability in the southern midlatitudes and tropics, which opposes the Southern Ocean variability.
29
Brischoux, François, Cédric Cotté, Harvey B. Lillywhite, Frédéric Bailleul, Maxime Lalire et Philippe Gaspar. « Oceanic circulation models help to predict global biogeography of pelagic yellow-bellied sea snake ». Biology Letters 12, no 8 (août 2016) : 20160436. http://dx.doi.org/10.1098/rsbl.2016.0436.
Texte intégralRésumé :
It is well recognized that most marine vertebrates, and especially tetrapods, precisely orient and actively move in apparently homogeneous oceanic environments. Here, we investigate the presumptive role of oceanic currents in biogeographic patterns observed in a secondarily marine tetrapod, the yellow-bellied sea snake ( Hydrophis [ Pelamis ] platurus ). State-of-the-art world ocean circulation models show how H. platurus , the only pelagic species of sea snake, can potentially exploit oceanic currents to disperse and maintain population mixing between localities that spread over two-thirds of the Earth's circumference. The very close association of these snakes with surface currents seems to provide a highly efficient dispersal mechanism that allowed this species to range extensively and relatively quickly well beyond the central Indo-Pacific area, the centre of origin, abundance and diversity of sea snakes. Our results further suggest that the pan-oceanic population of this species must be extraordinarily large.
30
Bennis, Anne-Claire, Tomas Chacón Rebollo, Macarena Gómez Mármol et Roger Lewandowski. « Numerical modelling of algebraic closure models of oceanic turbulent mixing layers ». ESAIM : Mathematical Modelling and Numerical Analysis 44, no 6 (17 mars 2010) : 1255–77. http://dx.doi.org/10.1051/m2an/2010025.
Texte intégral
31
Chacón Rebollo, T., M. Gómez Mármol et S. Rubino. « Analysis of numerical stability of algebraic oceanic turbulent mixing layer models ». Applied Mathematical Modelling 38, no 24 (décembre 2014) : 5836–57. http://dx.doi.org/10.1016/j.apm.2014.04.050.
Texte intégral
32
Gnanadesikan, Anand, Marie‐Aude Pradal et Ryan Abernathey. « Isopycnal mixing by mesoscale eddies significantly impacts oceanic anthropogenic carbon uptake ». Geophysical Research Letters 42, no 11 (2 juin 2015) : 4249–55. http://dx.doi.org/10.1002/2015gl064100.
Texte intégral
33
Prakash, Kumar Ravi, Tanuja Nigam et Vimlesh Pant. « Estimation of oceanic subsurface mixing under a severe cyclonic storm using a coupled atmosphere–ocean–wave model ». Ocean Science 14, no 2 (3 avril 2018) : 259–72. http://dx.doi.org/10.5194/os-14-259-2018.
Texte intégralRésumé :
Abstract. A coupled atmosphere–ocean–wave model was used to examine mixing in the upper-oceanic layers under the influence of a very severe cyclonic storm Phailin over the Bay of Bengal (BoB) during 10–14 October 2013. The coupled model was found to improve the sea surface temperature over the uncoupled model. Model simulations highlight the prominent role of cyclone-induced near-inertial oscillations in subsurface mixing up to the thermocline depth. The inertial mixing introduced by the cyclone played a central role in the deepening of the thermocline and mixed layer depth by 40 and 15 m, respectively. For the first time over the BoB, a detailed analysis of inertial oscillation kinetic energy generation, propagation, and dissipation was carried out using an atmosphere–ocean–wave coupled model during a cyclone. A quantitative estimate of kinetic energy in the oceanic water column, its propagation, and its dissipation mechanisms were explained using the coupled atmosphere–ocean–wave model. The large shear generated by the inertial oscillations was found to overcome the stratification and initiate mixing at the base of the mixed layer. Greater mixing was found at the depths where the eddy kinetic diffusivity was large. The baroclinic current, holding a larger fraction of kinetic energy than the barotropic current, weakened rapidly after the passage of the cyclone. The shear induced by inertial oscillations was found to decrease rapidly with increasing depth below the thermocline. The dampening of the mixing process below the thermocline was explained through the enhanced dissipation rate of turbulent kinetic energy upon approaching the thermocline layer. The wave–current interaction and nonlinear wave–wave interaction were found to affect the process of downward mixing and cause the dissipation of inertial oscillations.
34
Löptien, Ulrike, et Heiner Dietze. « Reciprocal bias compensation and ensuing uncertainties in model-based climate projections : pelagic biogeochemistry versus ocean mixing ». Biogeosciences 16, no 9 (6 mai 2019) : 1865–81. http://dx.doi.org/10.5194/bg-16-1865-2019.
Texte intégralRésumé :
Abstract. Anthropogenic emissions of greenhouse gases such as CO2 and N2O impinge on the Earth system, which in turn modulates atmospheric greenhouse gas concentrations. The underlying feedback mechanisms are complex and, at times, counterintuitive. So-called Earth system models have recently matured to standard tools tailored to assess these feedback mechanisms in a warming world. Applications for these models range from being targeted at basic process understanding to the assessment of geo-engineering options. A problem endemic to all these applications is the need to estimate poorly known model parameters, specifically for the biogeochemical component, based on observational data (e.g., nutrient fields). In the present study, we illustrate with an Earth system model that through such an approach biases and other model deficiencies in the physical ocean circulation model component can reciprocally compensate for biases in the pelagic biogeochemical model component (and vice versa). We present two model configurations that share a remarkably similar steady state (based on ad hoc measures) when driven by historical boundary conditions, even though they feature substantially different configurations (parameter sets) of ocean mixing and biogeochemical cycling. When projected into the future the similarity between the model responses breaks. Metrics such as changes in total oceanic carbon content and suboxic volume diverge between the model configurations as the Earth warms. Our results reiterate that advancing the understanding of oceanic mixing processes will reduce the uncertainty of future projections of oceanic biogeochemical cycles. Related to the latter, we suggest that an advanced understanding of oceanic biogeochemical cycles can be used for advancements in ocean circulation modules.
35
Fuhlbrügge, Steffen, Birgit Quack, Susann Tegtmeier, Elliot Atlas, Helmke Hepach, Qiang Shi, Stefan Raimund et Kirstin Krüger. « The contribution of oceanic halocarbons to marine and free tropospheric air over the tropical West Pacific ». Atmospheric Chemistry and Physics 16, no 12 (21 juin 2016) : 7569–85. http://dx.doi.org/10.5194/acp-16-7569-2016.
Texte intégralRésumé :
Abstract. Emissions of halogenated very-short-lived substances (VSLSs) from the oceans contribute to the atmospheric halogen budget and affect tropospheric and stratospheric ozone. Here, we investigate the contribution of natural oceanic VSLS emissions to the marine atmospheric boundary layer (MABL) and their transport into the free troposphere (FT) over the tropical West Pacific. The study concentrates on bromoform, dibromomethane and methyl iodide measured on ship and aircraft during the SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) campaign in the South China and Sulu seas in November 2011. Elevated oceanic concentrations for bromoform, dibromomethane and methyl iodide of on average 19.9, 5.0 and 3.8 pmol L−1, in particular close to Singapore and to the coast of Borneo, with high corresponding oceanic emissions of 1486, 405 and 433 pmol m−2 h−1 respectively, characterise this tropical region as a strong source of these compounds. Atmospheric mixing ratios in the MABL were unexpectedly relatively low with 2.08, 1.17 and 0.39 ppt for bromoform, dibromomethane and methyl iodide. We use meteorological and chemical ship and aircraft observations, FLEXPART trajectory calculations and source-loss estimates to identify the oceanic VSLS contribution to the MABL and to the FT. Our results show that the well-ventilated MABL and intense convection led to the low atmospheric mixing ratios in the MABL despite the high oceanic emissions. Up to 45 % of the accumulated bromoform in the FT above the region originates from the local South China Sea area, while dibromomethane is largely advected from distant source regions and the local ocean only contributes 20 %. The accumulated methyl iodide in the FT is higher than can be explained with local contributions. Possible reasons, uncertainties and consequences of our observations and model estimates are discussed.
36
Károly, György, Rudolf Dániel Prokaj, István Scheuring et Tamás Tél. « Climate change in a conceptual atmosphere–phytoplankton model ». Earth System Dynamics 11, no 3 (16 juillet 2020) : 603–15. http://dx.doi.org/10.5194/esd-11-603-2020.
Texte intégralRésumé :
Abstract. We develop a conceptual coupled atmosphere–phytoplankton model by combining the Lorenz'84 general circulation model and the logistic population growth model under the condition of a climate change due to a linear time dependence of the strength of anthropogenic atmospheric forcing. The following types of couplings are taken into account: (a) the temperature modifies the total biomass of phytoplankton via the carrying capacity; (b) the extraction of carbon dioxide by phytoplankton slows down the speed of climate change; (c) the strength of mixing/turbulence in the oceanic mixing layer is in correlation with phytoplankton productivity. We carry out an ensemble approach (in the spirit of the theory of snapshot attractors) and concentrate on the trends of the average phytoplankton concentration and average temperature contrast between the pole and Equator, forcing the atmospheric dynamics. The effect of turbulence is found to have the strongest influence on these trends. Our results show that when mixing has sufficiently strong coupling to production, mixing is able to force the typical phytoplankton concentration to always decay globally in time and the temperature contrast to decrease faster than what follows from direct anthropogenic influences. Simple relations found for the trends without this coupling do, however, remain valid; just the coefficients become dependent on the strength of coupling with oceanic mixing. In particular, the phytoplankton concentration and its coupling to climate are found to modify the trend of global warming and are able to make it stronger than what it would be without biomass.
37
Byrne, David, Lukas Papritz, Ivy Frenger, Matthias Münnich et Nicolas Gruber. « Atmospheric Response to Mesoscale Sea Surface Temperature Anomalies : Assessment of Mechanisms and Coupling Strength in a High-Resolution Coupled Model over the South Atlantic* ». Journal of the Atmospheric Sciences 72, no 5 (1 mai 2015) : 1872–90. http://dx.doi.org/10.1175/jas-d-14-0195.1.
Texte intégralRésumé :
Abstract Many aspects of the coupling between the ocean and atmosphere at the mesoscale (on the order of 20–100 km) remain unknown. While recent observations from the Southern Ocean revealed that circular fronts associated with oceanic mesoscale eddies leave a distinct imprint on the overlying wind, cloud coverage, and rain, the mechanisms responsible for explaining these atmospheric changes are not well established. Here the atmospheric response above mesoscale ocean eddies is investigated utilizing a newly developed coupled atmosphere–ocean regional model [Consortium for Small-Scale Modeling–Regional Ocean Modelling System (COSMO-ROMS)] configured at a horizontal resolution of ~10 km for the South Atlantic and run for a 3-month period during austral winter of 2004. The model-simulated changes in surface wind, cloud fraction, and rain above the oceanic eddies are very consistent with the relationships inferred from satellite observations for the same region and time. From diagnosing the model’s momentum balance, it is shown that the atmospheric imprint of the oceanic eddies are driven by the modification of vertical mixing in the atmospheric boundary layer, rather than secondary flows driven by horizontal pressure gradients. This is largely due to the very limited ability of the atmosphere to adjust its temperature over the time scale it takes for an air parcel to pass over these mesoscale oceanic features. This results in locally enhanced vertical gradients between the ocean surface and the overlying air and thus a rapid change in turbulent mixing in the atmospheric boundary layer and an associated change in the vertical momentum flux.
38
Pasquero, Claudia, et Eli Tziperman. « Statistical Parameterization of Heterogeneous Oceanic Convection ». Journal of Physical Oceanography 37, no 2 (1 février 2007) : 214–29. http://dx.doi.org/10.1175/jpo3008.1.
Texte intégralRésumé :
Abstract A statistical convective adjustment scheme is proposed that attempts to account for the effects of mesoscale and submesoscale variability of temperature and salinity typically observed in the oceanic convective regions. Temperature and salinity in each model grid box are defined in terms of their mean, variance, and mutual correlations. Subgrid-scale instabilities lead to partial mixing between different layers in the water column. This allows for a smooth transition between the only two states (convection on and convection off) allowed in standard convective adjustment schemes. The advantage of the statistical parameterization is that possible instabilities associated with the sharp transition between the two states, which are known to occasionally affect the large-scale model solution, are eliminated. The procedure also predicts the generation of correlations between temperature and salinity and the presence of convectively induced upgradient fluxes that have been obtained in numerical simulations of heterogeneous convection and that cannot be represented by standard convective adjustment schemes.
39
Xu, Suqing, Keyhong Park, Yanmin Wang, Liqi Chen, Di Qi et Bingrui Li. « Variations in the summer oceanic <i>p</i>CO<sub>2</sub> ; and carbon sink in Prydz Bay using the self-organizing map analysis approach ». Biogeosciences 16, no 3 (13 février 2019) : 797–810. http://dx.doi.org/10.5194/bg-16-797-2019.
Texte intégralRésumé :
Abstract. This study applies a neural network technique to produce maps of oceanic surface pCO2 in Prydz Bay in the Southern Ocean on a weekly 0.1∘ longitude × 0.1∘ latitude grid based on in situ measurements obtained during the 31st CHINARE cruise from February to early March 2015. This study area was divided into three regions, namely, the “open-ocean” region, “sea-ice” region and “shelf” region. The distribution of oceanic pCO2 was mainly affected by physical processes in the open-ocean region, where mixing and upwelling were the main controls. In the sea-ice region, oceanic pCO2 changed sharply due to the strong change in seasonal ice. In the shelf region, biological factors were the main control. The weekly oceanic pCO2 was estimated using a self-organizing map (SOM) with four proxy parameters (sea surface temperature, chlorophyll a concentration, mixed Layer Depth and sea surface salinity) to overcome the complex relationship between the biogeochemical and physical conditions in the Prydz Bay region. The reconstructed oceanic pCO2 data coincide well with the in situ pCO2 data from SOCAT, with a root mean square error of 22.14 µatm. Prydz Bay was mainly a strong CO2 sink in February 2015, with a monthly averaged uptake of 23.57±6.36 TgC. The oceanic CO2 sink is pronounced in the shelf region due to its low oceanic pCO2 values and peak biological production.
40
Luo, G., et F. Yu. « A numerical evaluation of global oceanic emissions of α-pinene and isoprene ». Atmospheric Chemistry and Physics 10, no 4 (19 février 2010) : 2007–15. http://dx.doi.org/10.5194/acp-10-2007-2010.
Texte intégralRésumé :
Abstract. A numerical evaluation of global oceanic emissions of α-pinene and isoprene based on both "bottom-up" and "top-down" methods is presented. We infer that the global "bottom-up" oceanic emissions of α-pinene and isoprene are 0.013 TgC yr−1 and 0.32 TgC yr−1, respectively. By constraining global chemistry model simulations with the shipborne measurement of Organics over the Ocean Modifying Particles in both Hemispheres summer cruise, we derived the global "top-down" oceanic α-pinene source of 29.5 TgC yr−1 and isoprene source of 11.6 TgC yr−1. Both the "bottom-up" and "top-down" values are subject to large uncertainties. The incomplete understanding of the in-situ phytoplankton communities and their range of emission potentials significantly impact the estimated global "bottom-up" oceanic emissions, while the estimated total amounts of the global "top-down" oceanic sources can be influenced by emission parameterizations, model and input data spatial resolutions, boundary layer mixing processes, and the treatments of chemical reactions. The global oceanic α-pinene source and its impact on organic aerosol formation is significant based on "top-down" method, but is negligible based on "bottom-up" approach. Our research highlights the importance of carrying out further research (especially measurements) to resolve the large offset in the derived oceanic organic emission based on two different approaches.
41
St. Laurent, Louis, et Harper Simmons. « Estimates of Power Consumed by Mixing in the Ocean Interior ». Journal of Climate 19, no 19 (1 octobre 2006) : 4877–90. http://dx.doi.org/10.1175/jcli3887.1.
Texte intégralRésumé :
Abstract Much attention has focused on the power required for driving mixing processes in the ocean interior, the thermohaline circulation, and the related meridional overturning circulation (MOC). Recent estimates range from roughly 0.5 to 2 TW (1 TW = 1 × 1012 W), based on differing arguments for the closure of the MOC mass budget. While these values are both O(1) TW, the thermodynamic implications of the estimates are significantly different. In addition, these numbers represent an integral constraint on the global circulation, and the apparent discrepancy merits careful examination. Through basic thermodynamic considerations on water mass mixing, a mechanical power consumption of 3 ± 1 TW is found to be consistent with a basic knowledge of the distribution and magnitude of oceanic turbulence diffusivities. This estimate is somewhat independent of any specific model for mass closure of the MOC. In addition, this estimate is based on a thermocline diffusivity of only 0.1 cm2 s−1, with enhanced diffusivities acting only in the deep and bottom waters. Adding enhanced diffusivities in the upper ocean, or lowering the mixing efficiency below 20%, will increase the power estimate. Moreover, 3 TW is a reasonable estimate for the power availability to processes acting beneath the oceanic mixed layer.
42
ALDANMAZ, E., M. K. YALINIZ, A. GÜCTEKIN et M. C. GÖNCÜOĞLU. « Geochemical characteristics of mafic lavas from the Neotethyan ophiolites in western Turkey : implications for heterogeneous source contribution during variable stages of ocean crust generation ». Geological Magazine 145, no 1 (30 novembre 2007) : 37–54. http://dx.doi.org/10.1017/s0016756807003986.
Texte intégralRésumé :
AbstractThe Late Triassic to Late Cretaceous age mafic lavas from the Neotethyan suture zone ophiolites in western Turkey exhibit a wide diversity of geochemical signatures, indicating derivation from extremely heterogeneous mantle sources. The rocks as a whole can be divided into three broad subdivisions based on their bulk-rock geochemical characteristics: (1) mid-ocean ridge basalts (MORB) that range in composition from light rare earth element (LREE)-depleted varieties (N-MORB; (La/Sm)N<1) through transitional MORB to LREE enriched types (E-MORB; (La/Sm)N>1); (2) the ocean island basalt (OIB)-type alkaline volcanic rocks with significant enrichment in LILE, HFSE and L-MREE, and a slight depletion in HREE, relative to normal mid-ocean ridge basalts (N-MORB); and (3) the supra-subduction zone (SSZ)-type tholeiites originated from arc mantle sources that are characterized by selective enrichments in fluid-soluble large ion lithophile elements (LILE) and LREE relative to the high field strength elements (HFSE). The formation of MORB tholeiites with variable enrichments and depletions in incompatible trace elements is probably related to the processes of crust generation along an oceanic spreading system, and the observed MORB–OIB associations can be modelled by heterogeneous source contribution and mixing of melts from chemically discrete sources from sub-lithospheric reservoirs. Evaluation of trace element systematics shows that the inferred heterogeneities within the mantle source regions are likely to have originated from continuous processes of formation and destruction of enriched mantle domains by long-term plate recycling, convective mixing and melt extraction. The origin of SSZ-type tholeiites with back-arc basin affinities, on the other hand, can be attributed to the later intra-oceanic subduction and plate convergence which led to the generation of supra-subduction-type oceanic crust as a consequence of imparting a certain extent of subduction component into the mantle melting region. Mixing of melts from a multiply depleted mantle source, which subsequently received variable re-enrichment with a subduction component, is suggested to explain the generation of supra-subduction-type oceanic crust. The geodynamic setting in which much of the SSZ-type ophiolitic extrusive rocks from western Turkey were generated can be described as an arc-basin system that is characterized by an oceanic lithosphere generation most probably associated with melting of mantle material along a supra-subduction-type spreading centre.
43
Gačić, Miroslav, et Manuel Bensi. « Ocean Exchange and Circulation ». Water 12, no 3 (20 mars 2020) : 882. http://dx.doi.org/10.3390/w12030882.
Texte intégralRésumé :
The great spatial and temporal variability, which characterizes the marine environment, requires a huge effort to be observed and studied properly since changes in circulation and mixing processes directly influence the variability of the physical and biogeochemical properties. A multi-platform approach and a collaborative effort, in addition to optimizing both data collection and quality, is needed to bring the scientific community to more efficient monitoring and predicting of the world ocean processes. This Special Issue consists of nine original scientific articles that address oceanic circulation and water mass exchange. Most of them deal with mean circulation, basin and sub-basin-scale flows, mesoscale eddies, and internal processes (e.g., mixing and internal waves) that contribute to the redistribution of oceanic properties and energy within the ocean. One paper deals with numerical modelling application finalized to evaluate the capacity of coastal vegetated areas to mitigate the impact of a tsunami. The study areas in which these topics are developed include both oceanic areas and semi-enclosed seas such as the Mediterranean Sea, the Norwegian Sea and the Fram Strait, the South China Sea, and the Northwest Pacific. Scientific findings presented in this Special Issue highlight how a combination of various modern observation techniques can improve our understanding of the complex physical and biogeochemical processes in the ocean.
44
Sokolov, Andrei P., Chris E. Forest et Peter H. Stone. « Comparing Oceanic Heat Uptake in AOGCM Transient Climate Change Experiments ». Journal of Climate 16, no 10 (15 mai 2003) : 1573–82. http://dx.doi.org/10.1175/1520-0442-16.10.1573.
Texte intégralRésumé :
Abstract The transient response of both surface air temperature and deep ocean temperature to an increasing external forcing strongly depends on climate sensitivity and the rate of the heat mixing into the deep ocean, estimates for both of which have large uncertainty. In this paper a method for estimating rates of oceanic heat uptake for coupled atmosphere–ocean general circulation models from results of transient climate change simulations is described. For models considered in this study, the estimates vary by a factor of 2½. Nevertheless, values of oceanic heat uptake for all models fall in the range implied by the climate record for the last century. It is worth noting that the range of the model values is narrower than that consistent with observations and thus does not provide a full measure of the uncertainty in the rate of oceanic heat uptake.
45
Fuhlbrügge, Steffen, Birgit Quack, Elliot Atlas, Alina Fiehn, Helmke Hepach et Kirstin Krüger. « Meteorological constraints on oceanic halocarbons above the Peruvian upwelling ». Atmospheric Chemistry and Physics 16, no 18 (29 septembre 2016) : 12205–17. http://dx.doi.org/10.5194/acp-16-12205-2016.
Texte intégralRésumé :
Abstract. During a cruise of R/V METEOR in December 2012 the oceanic sources and emissions of various halogenated trace gases and their mixing ratios in the marine atmospheric boundary layer (MABL) were investigated above the Peruvian upwelling. This study presents novel observations of the three very short lived substances (VSLSs) – bromoform, dibromomethane and methyl iodide – together with high-resolution meteorological measurements, Lagrangian transport and source–loss calculations. Oceanic emissions of bromoform and dibromomethane were relatively low compared to other upwelling regions, while those for methyl iodide were very high. Radiosonde launches during the cruise revealed a low, stable MABL and a distinct trade inversion above acting as strong barriers for convection and vertical transport of trace gases in this region. Observed atmospheric VSLS abundances, sea surface temperature, relative humidity and MABL height correlated well during the cruise. We used a simple source–loss estimate to quantify the contribution of oceanic emissions along the cruise track to the observed atmospheric concentrations. This analysis showed that averaged, instantaneous emissions could not support the observed atmospheric mixing ratios of VSLSs and that the marine background abundances below the trade inversion were significantly influenced by advection of regional sources. Adding to this background, the observed maximum emissions of halocarbons in the coastal upwelling could explain the high atmospheric VSLS concentrations in combination with their accumulation under the distinct MABL and trade inversions. Stronger emissions along the nearshore coastline likely added to the elevated abundances under the steady atmospheric conditions. This study underscores the importance of oceanic upwelling and trade wind systems on the atmospheric distribution of marine VSLS emissions.
46
Stevens, C. L., C. L. Stewart, N. J. Robinson, M. J. M. Williams et T. G. Haskell. « Flow and mixing around a glacier tongue ». Ocean Science Discussions 7, no 4 (11 août 2010) : 1439–67. http://dx.doi.org/10.5194/osd-7-1439-2010.
Texte intégralRésumé :
Abstract. A glacier tongue floating in the coastal ocean presents a significant obstacle to the local flow and influences oceanic mixing and transport processes. Here ocean shear microstructure observations at a glacier tongue side-wall show tidally-induced flow pulses and vortices as well as concomitant mixing. Flow speeds within the pulses reached around three times that of the ambient tidal flow amplitude and generated vertical velocity shear as large as 3×10−3 s−1. During the maximum flow period turbulent energy dissipation rates reached a maximum of 10−5 m2 s−3, around three decades greater than local background levels. This is in keeping with estimates of the gradient Richardson Number which dropped to around unity. Associated vertical diffusivities are higher that expected from parameterization, possibly reflecting the proximity of the cryotopography.
47
Williams, J. E., G. Le Bras, A. Kukui, H. Ziereis et C. A. M. Brenninkmeijer. « The impact of the chemical production of methyl nitrate from the NO + CH<sub>3</sub>O<sub>2</sub> ; reaction on the global distributions of alkyl nitrates, nitrogen oxides and tropospheric ozone : a global modelling study ». Atmospheric Chemistry and Physics 14, no 5 (7 mars 2014) : 2363–82. http://dx.doi.org/10.5194/acp-14-2363-2014.
Texte intégralRésumé :
Abstract. The formation, abundance and distribution of organic nitrates are relevant for determining the production efficiency and resident mixing ratios of tropospheric ozone (O3) on both regional and global scales. Here we investigate the effect of applying the recently measured direct chemical production of methyl nitrate (CH3ONO2) during NOx recycling involving the methyl-peroxy radical on the global tropospheric distribution of CH3ONO2 and the perturbations introduced towards tropospheric NOx and O3 using the TM5 global chemistry transport model. By comparisons against numerous observations, we show that the global surface distribution of CH3ONO2 can be largely explained by introducing the chemical production mechanism using a branching ratio of 0.3%, when assuming a direct oceanic emission source of ~0.15 Tg N yr−1. On a global scale, the chemical production of CH3ONO2 converts 1 Tg N yr−1 from nitrogen oxide for this branching ratio. The resident mixing ratios of CH3ONO2 are found to be highly sensitive to the dry deposition velocity that is prescribed, where more than 50% of the direct oceanic emission is lost near the source regions, thereby mitigating the subsequent effects due to long-range and convective transport out of the source region. For the higher alkyl nitrates (RONO2) we find improvements in the simulated distribution near the surface in the tropics (10° S–10° N) when introducing direct oceanic emissions equal to ~0.17 Tg N yr−1 . In terms of the vertical profile of CH3ONO2, there are persistent overestimations in the free troposphere and underestimations in the upper troposphere across a wide range of latitudes and longitudes when compared against data from measurement campaigns. This suggests either a missing transport pathway or source/sink term, although measurements show significant variability in resident mixing ratios at high altitudes at global scale. For the vertical profile of RONO2, TM5 performs better at tropical latitudes than at mid-latitudes, with similar features in the comparisons to those for CH3ONO2. Comparisons of CH3ONO2 with a wide range of surface measurements shows that further constraints are necessary regarding the variability in the deposition terms for different land surfaces in order to improve on the comparisons presented here. For total reactive nitrogen (NOy) ~20% originates from alkyl nitrates in the tropics and subtropics, where the introduction of both direct oceanic emissions and the chemical formation mechanism of CH3ONO2 only makes a ~5% contribution to the total alkyl nitrate content in the upper troposphere when compared with aircraft observations. We find that the increases in tropospheric O3 that occur due oxidation of CH3ONO2 originating from direct oceanic emission is negated when accounting for the chemical formation of CH3ONO2, meaning that the impact of such oceanic emissions on atmospheric lifetimes becomes marginal when a branching ratio of 0.3% is adopted.
48
Fiehn, Alina, Birgit Quack, Irene Stemmler, Franziska Ziska et Kirstin Krüger. « Importance of seasonally resolved oceanic emissions for bromoform delivery from the tropical Indian Ocean and west Pacific to the stratosphere ». Atmospheric Chemistry and Physics 18, no 16 (21 août 2018) : 11973–90. http://dx.doi.org/10.5194/acp-18-11973-2018.
Texte intégralRésumé :
Abstract. Oceanic very short-lived substances (VSLSs), such as bromoform (CHBr3), contribute to stratospheric halogen loading and, thus, to ozone depletion. However, the amount, timing, and region of bromine delivery to the stratosphere through one of the main entrance gates, the Indian summer monsoon circulation, are still uncertain. In this study, we created two bromoform emission inventories with monthly resolution for the tropical Indian Ocean and west Pacific based on new in situ bromoform measurements and novel ocean biogeochemistry modeling. The mass transport and atmospheric mixing ratios of bromoform were modeled for the year 2014 with the particle dispersion model FLEXPART driven by ERA-Interim reanalysis. We compare results between two emission scenarios: (1) monthly averaged and (2) annually averaged emissions. Both simulations reproduce the atmospheric distribution of bromoform from ship- and aircraft-based observations in the boundary layer and upper troposphere above the Indian Ocean reasonably well. Using monthly resolved emissions, the main oceanic source regions for the stratosphere include the Arabian Sea and Bay of Bengal in boreal summer and the tropical west Pacific Ocean in boreal winter. The main stratospheric injection in boreal summer occurs over the southern tip of India associated with the high local oceanic sources and strong convection of the summer monsoon. In boreal winter more bromoform is entrained over the west Pacific than over the Indian Ocean. The annually averaged stratospheric injection of bromoform is in the same range whether using monthly averaged or annually averaged emissions in our Lagrangian calculations. However, monthly averaged emissions result in the highest mixing ratios within the Asian monsoon anticyclone in boreal summer and above the central Indian Ocean in boreal winter, while annually averaged emissions display a maximum above the west Indian Ocean in boreal spring. In the Asian summer monsoon anticyclone bromoform atmospheric mixing ratios vary by up to 50 % between using monthly averaged and annually averaged oceanic emissions. Our results underline that the seasonal and regional stratospheric bromine injection from the tropical Indian Ocean and west Pacific critically depend on the seasonality and spatial distribution of the VSLS emissions.
49
Zhang, Xiaoqian, David C. Smith, Steven F. DiMarco et Robert D. Hetland. « A Numerical Study of Sea-Breeze-Driven Ocean Poincare Wave Propagation and Mixing near the Critical Latitude ». Journal of Physical Oceanography 40, no 1 (1 janvier 2010) : 48–66. http://dx.doi.org/10.1175/2009jpo4216.1.
Texte intégralRésumé :
Abstract Near the vicinity of 30° latitude, the coincidence of the period of sea breeze and the inertial period of the ocean leads to a maximum near-inertial ocean response to sea breeze. This produces a propagating inertial internal (Poincare) wave response that transfers energy laterally away from the coast and provides significant vertical mixing. In this paper, the latitudinal dependence of this wave propagation and its associated vertical mixing are investigated primarily using a nonlinear numerical ocean model. Three-dimensional idealized simulations show that the coastal oceanic response to sea breeze is trapped poleward of 30° latitude; however, it can propagate offshore as Poincare waves equatorward of 30° latitude. Near 30° latitude, the maximum oceanic response to sea breeze moves offshore slowly because of the near-zero group speed of Poincare waves at this latitude. The lateral energy flux convergence plus the energy input from the wind is maximum near the critical latitude, leading to increased local dissipation by vertical mixing. This local dissipation is greatly reduced at other latitudes. The implications of these results for the Gulf of Mexico (GOM) at ∼30°N is considered. Simulations with realistic bathymetry of the GOM confirm that a basinwide ocean response to coastal sea-breeze forcing is established in form of Poincare waves. Enhanced vertical mixing by the sea breeze is shown on the model northern shelf, consistent with observations on the Texas–Louisiana shelf. Comparison of the three-dimensional and one-dimensional models shows some significant limitations of one-dimensional simplified models for sea-breeze simulations near the critical latitude.
50
Ku, Teh-Lung, et Shangde Luo. « New appraisal of radium 226 as a large-scale oceanic mixing tracer ». Journal of Geophysical Research 99, no C5 (1994) : 10255. http://dx.doi.org/10.1029/94jc00089.
Texte intégral