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Atmospheric and oceanic circulation from a thermodynamic perspective
Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

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.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Meteorology, Stockholm University , 2019. , s. 28
Nyckelord [en]
Atmospheric circulation, Ocean circulation, Stream functions
Nationell ämneskategori
Klimatforskning Meteorologi och atmosfärforskning Oceanografi, hydrologi och vattenresurser
Forskningsämne
atmosfärvetenskap och oceanografi
Identifikatorer
URN: urn:nbn:se:su:diva-172842ISBN: 978-91-7797-827-5 (tryckt)ISBN: 978-91-7797-828-2 (digital)OAI: oai:DiVA.org:su-172842DiVA, id: diva2:1350174
Disputation
2019-10-24, De Geersalen, Svante Arrhenius väg 14, Stockolm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Tillgänglig från: 2019-10-01 Skapad: 2019-09-10 Senast uppdaterad: 2019-09-23Bibliografiskt granskad
Delarbeten
1. The Coupled Ocean-Atmosphere Hydrothermohaline Circulation
Öppna denna publikation i ny flik eller fönster >>The Coupled Ocean-Atmosphere Hydrothermohaline Circulation
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2017 (Engelska)Ingår i: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 30, nr 2, s. 631-647Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The thermohaline circulation of the ocean is compared to the hydrothermal circulation of the atmosphere. The oceanic thermohaline circulation is expressed in potential temperature-absolute salinity space and comprises a tropical cell, a conveyor belt cell, and a polar cell, whereas the atmospheric hydrothermal circulation is expressed in potential temperature-specific humidity space and unifies the tropical Hadley and Walker cells as well as the midlatitude eddies into a single, global circulation. The oceanic thermohaline streamfunction makes it possible to analyze and quantify the entire World Ocean conversion rate between cold-warm and fresh-saline waters in one single representation. Its atmospheric analog, the hydrothermal streamfunction, instead captures the conversion rate between cold-warm and dry-humid air in one single representation. It is shown that the ocean thermohaline and the atmospheric hydrothermal cells are connected by the exchange of heat and freshwater through the sea surface. The two circulations are compared on the same diagramby scaling the axes such that the latent heat energy required to move an air parcel on the moisture axis is equivalent to that needed to move a water parcel on the salinity axis. Such a comparison leads the authors to propose that the Clausius-Clapeyron relationship guides both the moist branch of the atmospheric hydrothermal circulation and the warming branches of the tropical and conveyor belt cells of the oceanic thermohaline circulation.

Nationell ämneskategori
Geovetenskap och miljövetenskap
Forskningsämne
atmosfärvetenskap och oceanografi
Identifikatorer
urn:nbn:se:su:diva-140409 (URN)10.1175/JCLI-D-15-0759.1 (DOI)000391856300013 ()
Tillgänglig från: 2017-03-10 Skapad: 2017-03-10 Senast uppdaterad: 2019-09-11Bibliografiskt granskad
2. The effects of global warming on the coupled Ocean-Atmosphere Hydrothermohaline circulation
Öppna denna publikation i ny flik eller fönster >>The effects of global warming on the coupled Ocean-Atmosphere Hydrothermohaline circulation
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

Global warming will have an impact on the hydrological cycle affecting both the atmospheric and oceanic circulation. In this study we analyse these impacts from a thermodynamic perspective using streamfunctions defined in general thermodynamic coordinates. Both the atmospheric and oceanic circulation showed a weakening of the circulation in a future scenario but an expansion in both humidity and salinity directions. The Clausius-Clapeyron relationship is hence here extended to not only to give a relationship between air temperature and moisture but also with the sea-surface salinity. As a consequence, not only the atmospheric hydrothermal circulation, but also the oceanic thermohaline circulation, will follow the Clausius-Clapeyron relationship as climate warms up. This results in a direct relationship between the increase of atmospheric moisture and an increase of the ocean salinity as a consequence of the changes in the freshwater forcing at the sea surface.

Nationell ämneskategori
Geovetenskap och miljövetenskap
Forskningsämne
atmosfärvetenskap och oceanografi
Identifikatorer
urn:nbn:se:su:diva-172839 (URN)
Tillgänglig från: 2019-09-10 Skapad: 2019-09-10 Senast uppdaterad: 2019-09-11Bibliografiskt granskad
3. Meridional Ocean Carbon Transport
Öppna denna publikation i ny flik eller fönster >>Meridional Ocean Carbon Transport
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

The ocean's ability to take up and store CO$_{2}$ is a key factor for understanding past and future climate variability. However, qualitative and quantitative understanding of surface-to-interior pathways, and how the ocean circulation affects the CO$_2$ uptake, is limited. Consequently, how changes in ocean circulation may influence carbon uptake and storage and therefore the future climate remains ambiguous.Here we quantify the roles played by ocean circulation and various water masses in the meridional redistribution of carbon.We do so by calculating stream functions defined in Dissolved Inorganic Carbon (DIC) and latitude coordinates, using output from a coupled biogeochemical-physical model. By further separating DIC into components originating from the solubility pump and a residual including the biological pump, air-sea disequilibrium and anthropogenic CO$_2$, we are able to distinguish the dominant pathways of how carbon enters particular water masses.With this new tool, we show that the largest meridional carbon transport occurs in a pole-to-equator transport in the subtropical gyres in the upper ocean. We are able to show that this pole-to-equator DIC transport, and the Atlantic Meridional Overturning Circulation (AMOC) related DIC transport, are mainly driven by the solubility pump. By contrast, the DIC transport associated with deep circulation, including that in Antarctic Bottom Water and Pacific Deep Water, is mostly driven by the biological pump. As these two pumps, as well as ocean circulation, are widely expected to be impacted by anthropogenic changes, these findings have implications for the future role of the ocean as a climate-buffering carbon reservoir.

Nationell ämneskategori
Geovetenskap och miljövetenskap
Forskningsämne
atmosfärvetenskap och oceanografi
Identifikatorer
urn:nbn:se:su:diva-172840 (URN)
Tillgänglig från: 2019-09-10 Skapad: 2019-09-10 Senast uppdaterad: 2020-02-06Bibliografiskt granskad
4. Multidecadal variability of the Mediterranean Overflow Water in the North Atlantic
Öppna denna publikation i ny flik eller fönster >>Multidecadal variability of the Mediterranean Overflow Water in the North Atlantic
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

The Mediterranean overflow water is one of the most important intermediate--depth water masses in the North Atlantic. This water mass, formed in the Mediterranean Sea, produces a saline and warm water tongue at a depth of 1000 m that spreads out from the Strait of Gibraltar and fills a large area of the North Atlantic basin. The production of  this dense water is a result of the excess of evaporation over precipitation and river runoff. A pre-industrial simulation with the earth system model EC-Earth is used to investigate the overflow water. The multidecadal variability of the outflow is analysed by examining the modelled volume and salt transports through the Strait of Gibraltar as well as different atmospheric patterns (such as the wind pattern and the net freshwater fluxes). The salinity evolution in the main core of the outflow in the mid Atlantic is also taken into account.  \ald{The leading empirical orthogonal functions for the modeled salinity 1000 m coincided with the modeled distribution of outflow water}. The associated principal component showed a multidecadal variability of the salinity field. The variability of the net salt transport through the Strait of Gibraltar showed a similar behaviour where the Atlantic--Mediterranean system manifested two clear states. One of these is when the Mediterranean imports salt from the Atlantic and the other is where salt export to the Atlantic predominates. \ald{This result indicates that the Mediterranean Sea acts as a storage of salt alternating between the two states.

Nyckelord
Salt transport, Strait of Gibraltar, Earth system model, AMOC, NAO
Nationell ämneskategori
Geovetenskap och miljövetenskap
Forskningsämne
atmosfärvetenskap och oceanografi
Identifikatorer
urn:nbn:se:su:diva-172841 (URN)
Tillgänglig från: 2019-09-10 Skapad: 2019-09-10 Senast uppdaterad: 2019-09-11Bibliografiskt granskad

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