| 1. |
- Aldama Campino, Aitor, 1989-
(author)
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Atmospheric and oceanic circulation from a thermodynamic perspective
- 2019
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Doctoral thesis (other academic/artistic)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. |
- Aldama-Campino, Aitor, et al.
(author)
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Mediterranean overflow water in the North Atlantic and its multidecadal variability
- 2020
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In: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 72:1, s. 1-10
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Journal article (peer-reviewed)abstract
- The Mediterranean overflow water is one of the most important intermediate-depth water masses in the North Atlantic. To investigate its properties a pre-industrial simulation with the earth system model EC- Earth is used. 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. The leading empirical orthogonal functions for the modelled salinity 900 m coincided with the modelled 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. This result indicates that the Mediterranean Sea acts as a storage of salt alternating between the two states. The negative phase of the North Atlantic oscillation appears to play a role driving the variability of the salt transport and its impact on the overturning circulation in the North Atlantic.
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| 3. |
- Aldama Campino, Aitor, et al.
(author)
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Meridional Ocean Carbon Transport
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Other publication (other academic/artistic)abstract
- 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.
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| 4. |
- Aldama-Campino, Aitor, et al.
(author)
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Meridional Ocean Carbon Transport
- 2020
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In: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 34:9
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Journal article (peer-reviewed)abstract
- The ocean's ability to take up and store CO2 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 CO2 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 streamfunctions 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 CO2, 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.
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| 5. |
- Aldama Campino, Aitor, et al.
(author)
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Multidecadal variability of the Mediterranean Overflow Water in the North Atlantic
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Other publication (other academic/artistic)abstract
- 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.
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| 6. |
- Aldama Campino, Aitor, et al.
(author)
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The effects of global warming on the coupled Ocean-Atmosphere Hydrothermohaline circulation
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Other publication (other academic/artistic)abstract
- 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.
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| 7. |
- Berglund, Sara, et al.
(author)
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The Water Mass Transformation in the Upper Limb of the Overturning Circulation in the Southern Hemisphere
- 2021
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In: Journal of Geophysical Research - Oceans. - 2169-9275 .- 2169-9291. ; 126:8
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Journal article (peer-reviewed)abstract
- The warming and salinification of the northwards flowing water masses from the Southern Ocean to the tropics are studied with Lagrangian trajectories simulated using fields from an Earth System Model. The trajectories are used to trace the geographical distribution of the water mass transformation and connect it with the pathways of the upper limb of the overturning circulation in the Southern Hemisphere. In the Antarctic Circumpolar Current water gains heat just below the mixed layer, mainly when the layer is thin during Austral spring and summer. This gain is therefore suggested to be a consequence of heat flux from the atmosphere and mixing processes at the base of the mixed layer. In the Southern Hemispheric subtropical gyres on the other hand, a large warming and salinification of the northwards flowing water results from internal mixing with other warmer and more saline water masses. Close to the Antarctic shelf waters are getting fresher as a result of ice melting, whereas further north, in the Antarctic Circumpolar current, waters are getting more saline as a result of evaporation. Our results show that it is not only the heat and freshwater fluxes through the sea surface that control the heat and salt changes of the upper limb of the overturning circulation in the Southern Hemisphere. In fact, internal mixing accounts for 25% of the heat change, and 22% of the salinity change.
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| 8. |
- Dey, Dipanjan, et al.
(author)
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A complete view of the atmospheric hydrologic cycle
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Other publication (other academic/artistic)abstract
- The global atmospheric water transport from the evaporation to the precipitation regions has beentraced using Lagrangian trajectories. A matrix has been constructed by selecting various groupof trajectories based on their starting (evaporation) and ending (precipitation) positions to show the connectivity of the atmospheric water transport within and between the three major ocean basins and the global landmass. The analysis reveals that a major portion of the evaporated water precipitates back into the same region, namely 67% for the Indian, 64% for the Atlantic, 85% for the Pacific Ocean and 72% for the global landmass. The evaporation from the subtropical regions of the Indian, Atlantic and Pacific Oceans is found to be the primary source of atmospheric water for precipitation over the Intertropical Convergence Zone (ITCZ) in the corresponding basins. The evaporated waters from the subtropical and western Indian Ocean were traced as the source for precipitation over the South Asian and Eastern African landmass, while Atlantic Ocean waters are responsible for rainfall over North Asia and Western Africa. Atlantic storm tracks were identified as the carrier of atmospheric water that precipitates over Europe, while the Pacific storm tracks were responsible for North American, eastern Asian and Australian precipitation. The bulk of South and Central American precipitation is found to have its source in the tropical Atlantic Ocean. The recycling of evapotranspirated water from land is pronounced over the western coast of South America, Northeastern Asia, Canada and Greenland. The ocean-to-land and land-to-ocean water transport through the atmosphere was computed to be 2×109 kg/s and 1×109 kg/s, respectively.The difference between them (net ocean-to-land transport), i.e. 1×109 kg/s, is transported to land. This net transport is approximately the same as found in previous Eulerian estimates
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| 9. |
- Dey, Dipanjan, 1991-, et al.
(author)
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Atmospheric water transport connectivity within and between ocean basins and land
- 2023
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In: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 27:2, s. 481-493
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Journal article (peer-reviewed)abstract
- The global atmospheric water transport from the net evaporation to the net precipitation regions has been traced using Lagrangian trajectories. A matrix has been constructed by selecting various group of trajectories based on their surface starting (net evaporation) and ending (net precipitation) positions to show the connectivity of the 3-D atmospheric water transport within and between the three major ocean basins and the global landmass. The analysis reveals that a major portion of the net evaporated water precipitates back into the same region, namely 67 % for the Indian Ocean, 64 % for the Atlantic Ocean, 85 % for the Pacific Ocean and 72 % for the global landmass. It has also been calculated that 58 % of the net terrestrial precipitation was sourced from land evaporation. The net evaporation from the subtropical regions of the Indian, Atlantic and Pacific oceans is found to be the primary source of atmospheric water for precipitation over the Intertropical Convergence Zone (ITCZ) in the corresponding basins. The net evaporated waters from the subtropical and western Indian Ocean were traced as the source for precipitation over the South Asian and eastern African landmass, while Atlantic Ocean waters are responsible for rainfall over North Asia and western Africa. Atlantic storm tracks were identified as the carrier of atmospheric water that precipitates over Europe, while the Pacific storm tracks were responsible for North American, eastern Asian and Australian precipitation. The bulk of South and Central American precipitation is found to have its source in the tropical Atlantic Ocean. The land-to-land atmospheric water transport is pronounced over the Amazon basin, western coast of South America, Congo basin, northeastern Asia, Canada and Greenland. The ocean-to-land and land-to-ocean water transport through the atmosphere was computed to be 2x10(9) and 1x10(9) kg s(-1), respectively. The difference between them (net ocean-to-land transport), i.e. 1x10(9) kg s(-1), is transported to land. This net transport is approximately the same as found in previous estimates which were calculated from the global surface water budget.
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| 10. |
- Dey, Dipanjan, 1991-
(author)
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Tracing water transport pathways in the coupled ocean-atmosphere system
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Water is the most precious substance on the Earth and thus it is important to know how it moves around and is recycled.This knowledge will be useful to formulate educated future strategies about water usage in society and also to understand the near-surface salinity contrasts in the world ocean.In this thesis, water movement around the globe, known also as the hydrological or water cycle, have been traced regardless of in which phase the water is.Water is always on the move through space and in time and thus to reduce the dimensionality and complexity of the system, a stream-function approach was applied to gain a better understanding of the processes that govern the water cycle.The present work provides a unique picture of the complete hydrological cycle and how the water circulation in the atmosphere and ocean is connected at the surface by evaporation and precipitation.In addition, emphasize was given to track and understand the atmospheric part of the water circulation, which was accomplished using an Eulerian and a novel Lagrangian framework. The first half of the thesis was focused on making use of a water-mass conservation equation for the atmosphere derived by computing the rate of change of the water-mass content inside a grid box and water transport through its faces. The vertical water transport calculated from this conservation equation thus not only consist of vertical advection of the water vapor, but also includes the evaporation and precipitation.This Eulerian methodology and the overturning stream function diagnostic was then used to present average atmospheric water circulation pathways along with their oceanic counterparts in a meridional-vertical coordinate system. Six coupled atmosphere-ocean water cells were discovered, which show the redistribution of the freshwater in the climate system.A warmer-climate scenario indicates a strengthening of these cells, which implies that the wet regions will be wetter and dry regions will get drier.In addition, atmospheric water transport from the Atlantic to the Pacific Ocean was computed from a Lagrangian perspective.The results shows that westerly winds, which prevail in the mid-latitudes and flow across Afro-Eurasia, actually contribute about 60% of the total Atlantic-to-Pacific atmospheric water transport, significantly more than previously thought.In the latter half of the thesis, the origin and its variability responsible for the South Asian Summer monsoon precipitation was traced using Lagrangian atmospheric water trajectories.The Central and South Indian Ocean was found to be the main contributor to the precipitation and its variability over South Asia during the monsoon months.A complete view of the atmospheric hydrological cycle was finally achieved by tracing the global atmospheric water transport from the evaporation to the precipitation regions using Lagrangian trajectories. A matrix was constructed by sorting trajectories based on their starting (evaporation) and ending (precipitation) positions to show the atmospheric water transport connectivity within and between the three major ocean basins and the global landmass. In addition, a simplified schematic of the annual mean atmospheric water transports between global ocean and land was provided based on Eulerian and Lagrangian perspectives.This schematic reflects the advantage of using a Lagrangian framework, from which ocean-to-ocean, ocean-to-land, land-to-land and land-to-ocean atmospheric water transport could be and was calculated. The ocean-to-land and land-to-ocean water transport through the atmosphere was computed to be 2×109 kg/s and 1×109 kg/s respectively, a result which is not possible to achieve by using an Eulerian perspective.
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