| 1. |
- Aldama Campino, Aitor, 1989-
(författare)
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Atmospheric and oceanic circulation from a thermodynamic perspective
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The climate system is continuously transporting and exchanging heat, freshwater, carbon and other tracers in different spatio-temporal scales. Therefore, analysing the system from a thermodynamic or biogeochemical framework is highly convenient. In this thesis the interaction between the ocean and the atmospheric circulation is analysed using thermodynamical and biogeochemical coordinates. Due to the dimensionality of the climate system stream functions are used to reduce this complexity and facilitate the understanding of the different processes that take place. The first half of this thesis, focuses on the interaction between the atmospheric and the ocean circulation from a thermodynamic perspective. We introduce the hydrothermohaline stream function which combines the atmospheric circulation in humidity-potential temperature (hydrothermal) space and the ocean circulation in salinity-temperature coordinates (thermohaline). A scale factor of 7.1 is proposed to link humidity and salinity coordinates. Future scenarios are showing an increase of humidity in the atmosphere due to the increase of temperatures which results in a widening of the hydrothermal stream function along the humidity coordinate. In a similar way, the ocean circulation in the thermohaline space expands along the salinity coordinate. The link between salinity and humidity changes is strongest at net evaporation regions where the gain of water vapour in the atmosphere results in a salinification in the ocean. In addition, the ocean circulation in latitude-carbon space is investigated. By doing so, we are able to distinguish the roles of different water masses and circulation pathways for ocean carbon. We find that the surface waters in the subtropical gyres are the main drivers of the meridional carbon transport in the ocean. By separating the carbon in its different constituents we show that the carbon transported by the majority of the water masses is a result of the solubility pump. The contribution of the biological pump is predominant in the deep Pacific Ocean. The effects of the Mediterranean Overflow Waters on the North Atlantic are discussed in the final part of the thesis.
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| 2. |
- Brannigan, Liam, et al.
(författare)
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Submesoscale Instabilities in Mesoscale Eddies
- 2017
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Ingår i: Journal of Physical Oceanography. - 0022-3670 .- 1520-0485. ; 47:12, s. 3061-3085
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Tidskriftsartikel (refereegranskat)abstract
- Submesoscale processes have been extensively studied in observations and simulations of fronts. Recent idealized simulations show that submesoscale instabilities also occur in baroclinic mesoscale cyclones and anticyclones. The instabilities in the anticyclone grow faster and at coarser grid resolution than in the cyclone. The instabilities lead to larger restratification in the anticyclone than in the cyclone. The instabilities also lead to changes in the mean azimuthal jet around the anticyclone from 2-km resolution, but a similar effect only occurs in the cyclone at 0.25-km resolution. A numerical passive tracer experiment shows that submesoscale instabilities lead to deeper subduction in the interior of anticyclonic than cyclonic eddies because of outcropping isopycnals extending deeper into the thermocline in anticyclones. An energetic analysis suggests that both vertical shear production and vertical buoyancy fluxes are important in anticyclones but primarily vertical buoyancy fluxes occur in cyclones at these resolutions. The energy sources and sinks vary azimuthally around the eddies caused by the asymmetric effects of the Ekman buoyancy flux. Glider transects of a mesoscale anticyclone in the Tasman Sea show that water with low stratification and high oxygen concentrations is found in an anticyclone, in a manner that may be consistent with the model predictions for submesoscale subduction in mesoscale eddies.
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| 3. |
- Gommenginger, Christine, et al.
(författare)
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SEASTAR: A mission to study ocean submesoscale dynamics and small-scale atmosphere-ocean processes in coastal, shelf and polar seas
- 2019
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 6:JUL
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- High-resolution satellite images of ocean color and sea surface temperature reveal an abundance of ocean fronts, vortices and filaments at scales below 10 km but measurements of ocean surface dynamics at these scales are rare. There is increasing recognition of the role played by small scale ocean processes in ocean-atmosphere coupling, upper-ocean mixing and ocean vertical transports, with advanced numerical models and in situ observations highlighting fundamental changes in dynamics when scales reach 1 km. Numerous scientific publications highlight the global impact of small oceanic scales on marine ecosystems, operational forecasts and long-term climate projections through strong ageostrophic circulations, large vertical ocean velocities and mixed layer re-stratification. Small-scale processes particularly dominate in coastal, shelf and polar seas where they mediate important exchanges between land, ocean, atmosphere and the cryosphere e.g. freshwater, pollutants. As numerical models continue to evolve towards finer spatial resolution and increasingly complex coupled atmosphere-wave-ice-ocean systems, modern observing capability lags behind, unable to deliver the high-resolution synoptic measurements of total currents, wind vectors and waves needed to advance understanding, develop better parameterizations and improve model validations, forecasts and projections. SEASTAR is a satellite mission concept that proposes to directly address this critical observational gap with synoptic two-dimensional imaging of total ocean surface current vectors and wind vectors at 1 km resolution and coincident directional wave spectra. Based on major recent advances in squinted along-track Synthetic Aperture Radar interferometry, SEASTAR is an innovative, mature concept with unique demonstrated capabilities, seeking to proceed towards spaceborne implementation within Europe and beyond.
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| 4. |
- Wu, Lichuan, et al.
(författare)
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Wave effects on coastal upwelling and water level
- 2019
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Ingår i: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 140
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Tidskriftsartikel (refereegranskat)abstract
- Traditional atmosphere, ocean and wave models are run independently of each other. This means that the energy and momentum fluxes do not fully account for the impact of the oceanic wave field at the air-sea interface. In this study, the Stokes drift impact on mass and tracer advection, the Stokes-Coriolis forcing, and the sea-state-dependent momentum and energy fluxes are introduced into an ocean circulation model and tested for a domain covering the Baltic Sea and the North Sea. Sensitivity experiments are designed to investigate the influence on the simulation of storms and Baltic Sea upwelling. Inclusion of wave effects improves the model performance compared with the stand-alone circulation model in terms of sea level height, temperature and circulation. The direct sea-state-dependent momentum and turbulent kinetic energy fluxes prove to be of higher importance than the Stokes drift related effects investigated in this study (i.e., Stokes-Coriolis forcing and Stokes drift advection on tracers and on mass). The latter affects the mass and tracer advection but largely balances the influence of the Stokes-Coriolis forcing. The upwelling frequency changes by > 10% along the Swedish coast when wave effects are included. In general, the strong (weak) upwelling probability is reduced (increased) when adding the wave effects. From the results, we conclude that inclusion of wave effects can be important for regional, high-resolution ocean models even on short time scales, suggesting that they should be introduced in operational ocean circulation models. However, care should be taken when introducing the Stokes-Coriolis forcing as it should be balanced by the Stokes drift in mass and tracer advection.
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