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  • 1.
    Hieronymus, Magnus
    Stockholm University, Faculty of Science, Department of Meteorology .
    A note on the influence of spatially varying diffusivities on the evolution of buoyancy with a nonlinear equation of state2014In: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 44, no 12, p. 3255-3261Article in journal (Refereed)
    Abstract [en]

    The oceanic buoyancy sinks from thermobaricity and cabbeling are quantified using hydrography and parameterized diffusive fluxes of heat and salt. A novelty in this study is that the effect of spatially varying diffusivities is considered and quantified. The spatial distribution as well as averages from different ocean basins of the cabbeling and thermobaricity sinks are shown and discussed. The contributions from isoneutral and dianeutral diffusion to the cabbeling and thermobaricity sinks are calculated separately, and their relative importance is seen to vary in the different ocean basins.

  • 2.
    Hieronymus, Magnus
    Stockholm University, Faculty of Science, Department of Meteorology .
    An investigation into ocean thermodynamics and water-mass transformation2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents oceanic budgets of potential temperature, salinity and buoyancy as well as a novel way of diagnosing water-mass transformation in salinity-temperature space. The buoyancy of seawater is given by a nonlinear function of temperature, salinity and pressure and much of the work in this thesis revolves around how fluxes of heat and salinity influence the buoyancy of seawater through these nonlinearities.

    Another large part of the material in this thesis is aimed at quantifying the relative importance of different processes for the vertical transport of heat and salinity in the ocean. Careful analysis of those fluxes in an ocean model reveal the different effects of e.g. advection, diffusion and penetrative shortwave radiation. An interesting finding is that the diffusive fluxes due to isoneutral diffusion (diffusion along density surfaces) and dianeutral diffusion (diffusion across density surfaces) have opposing effects on the oceanic heat and salinity budgets.

    The final major topic of this thesis is water-mass transformation. A quantitative framework for the study of water-mass transformation in salinity-temperature space is introduced. A continuity equation is also derived for salinity-temperature space, which can be used to calculate the time rate of change of volume in a small salinity-temperature interval. The water-mass transformation framework is applied in an ocean general circulation model, and it is shown how the volume distribution in salinity-temperature space is affected by the different tracer fluxes in the model. It is also shown how the transformation framework is related to earlier work on thermohaline streamfunctions.

  • 3.
    Hieronymus, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Water Mass Transformation in Salinity–Temperature Space2014In: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 44, no 9, p. 2547-2568Article in journal (Refereed)
    Abstract [en]

    This article presents a new framework for studying water mass transformations in salinity–temperature space that can, with equal ease, be applied to study water mass transformation in spaces defined by any two conservative tracers. It is shown how the flow across isothermal and isohaline surfaces in the ocean can be quantified from knowledge of the nonadvective fluxes of heat and salt. It is also shown how these cross-isothermal and cross-isohaline flows can be used to form a continuity equation in salinity–temperature space. These flows are then quantified in a state-of-the-art ocean model. Two major transformation cells are found: a tropical cell driven primarily by surface fluxes and dianeutral diffusion and a conveyor belt cell where isoneutral diffusion is also important. Both cells are similar to cells found in earlier work on the thermohaline streamfunction. A key benefit with this framework over a streamfunction approach is that transformation due to different diabatic processes can be studied individually. The distributions of volume and surface area in ST space are found to be useful for determining how transformations due to these different processes affect the water masses in the model. The surface area distribution shows that the water mass transformations due to surface fluxes tend to be directed away from ST regions that occupy large areas at the sea surface.

  • 4.
    Hieronymus, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    The budgets of heat and salinity in NEMO2013In: Ocean Modelling, ISSN 1463-5003, E-ISSN 1463-5011, Vol. 67, p. 28-38Article in journal (Refereed)
    Abstract [en]

    The near steady state heat and salinity budgets under surfaces of constant depth are examined in the Nucleus for European Modelling of the Ocean (NEMO) model. It is seen that the heat fluxes in NEMO are difficult to reconcile with the idea of a deep ocean in advection-diffusion balance. Some reasons for this are that the resolved heat advection is downward above 2000 m, and that geothermal heating is, in fact, a major heat source in the deeper parts of the domain. It is also seen that isoneutral diffusion gives a very large contribution to the budgets and that the fluxes from isoneutral diffusion is in general upward. It is explained how the sign of these fluxes depends on the stratification. The heat budget for the upper 100 m of the ocean is seen to be dominated by penetrative shortwave radiation, which is so influential that we would have a mixed layer of considerable thickness even in the absence of other sources of turbulent mixing. Penetrative shortwave radiation is therefore a considerable source of potential energy.

  • 5.
    Hieronymus, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    The buoyancy budget with a nonlinear equation of state2013In: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 43, no 1, p. 176-186Article in journal (Refereed)
    Abstract [en]

    The nonlinear equation of state of seawater introduces a sink or source of buoyancy when water parcels of unequal salinities and temperatures are mixed. This article contains quantitative estimates of these nonlinear effects on the buoyancy budget of the global ocean. It is shown that the interior buoyancy sink can be determined from surface buoyancy fluxes. These surface buoyancy fluxes are calculated using two surface heat flux climatologies, one based on in situ measurements and the other on a reanalysis, in both cases using a nonlinear equation of state. It is also found that the buoyancy budget in the ocean general circulation model Nucleus for European Modeling of the Ocean (NEMO) is in good agreement with the buoyancy budgets based on the heat flux climatologies. Moreover, an examination of the vertically resolved buoyancy budget in NEMO shows that in large parts of the ocean the nonlinear buoyancy sink gives the largest contribution to this budget.

  • 6.
    Hieronymus, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish Meteorological and Hydrological Institute, Sweden.
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Döös, Kristofer
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hallberg, Robert
    Oceanic Overturning and Heat Transport: The Role of Background Diffusivity2019In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 32, no 3, p. 701-716Article in journal (Refereed)
    Abstract [en]

    The role of oceanic background diapycnal diffusion for the equilibrium climate state is investigated in the global coupled climate model CM2G. Special emphasis is put on the oceanic meridional overturning and heat transport. Six runs with the model, differing only by their value of the background diffusivity, are run to steady state and the statistically steady integrations are compared. The diffusivity changes have large-scale impacts on many aspects of the climate system. Two examples are the volume-mean potential temperature, which increases by 3.6 degrees C between the least and most diffusive runs, and the Antarctic sea ice extent, which decreases rapidly as the diffusivity increases. The overturning scaling with diffusivity is found to agree rather well with classical theoretical results for the upper but not for the lower cell. An alternative empirical scaling with the mixing energy is found to give good results for both cells. The oceanic meridional heat transport increases strongly with the diffusivity, an increase that can only partly be explained by increases in the meridional overturning. The increasing poleward oceanic heat transport is accompanied by a decrease in its atmospheric counterpart, which keeps the increase in the planetary energy transport small compared to that in the ocean.

  • 7. Hordoir, Robinson
    et al.
    Axell, Lars
    Höglund, Anders
    Dieterich, Christian
    Fransner, Filippa
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gröger, Matthias
    Liu, Ye
    Pemberton, Per
    Schimanke, Semjon
    Andersson, Helen
    Ljungemyr, Patrik
    Nygren, Petter
    Falahat, Saeed
    Nord, Adam
    Jönsson, Anette
    Lake, Iréne
    Döös, Kristofer
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hieronymus, Magnus
    Stockholm University, Faculty of Science, Department of Meteorology .
    Dietze, Heiner
    Löptien, Ulrike
    Kuznetsov, Ivan
    Westerlund, Antti
    Tuomi, Laura
    Haapala, Jari
    Nemo-Nordic: A NEMO based ocean model for Baltic & North Seas, research and operational applicationsIn: Geoscientific Model Development Discussions, ISSN 1991-9611, E-ISSN 1991-962XArticle in journal (Refereed)
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