Periodic Reporting for period 1 - WaTurSheD (Small Flows with Big Consequences: Wave-, Turbulence- and Shear current-Driven mixing under a water surface)
Período documentado: 2023-01-01 hasta 2025-06-30
Project WaTurSheD focusses on how the waters in the upper layer of the ocean are mixed into the deep, by “bringing the ocean into the lab”. The interchange of heat and gas between the ocean and atmosphere is at the centre of the Earth’s climate system. When the water in the topmost layer is saturated with gas, it needs to be mixed into the deep before more gas and heat can enter or exit, like chocolate powder must be mixed into a glass of milk with a spoon. There are many “spoons” that stir the oceans, and WaTurSheD studies perhaps the least understood of them: the combined effect of waves, turbulence and currents (WTC). With a one-of-a-kind laboratory in Trondheim, Norway, we are able to make a scale model of the uppermost layer of the ocean, where all these three components can be tailored and controlled individually, so that the mixing of water due to WTC can be studied systematically. The goal is to discover how the local conditions in the sea determine how efficient the “spoon” is, so that predictions of weather and climate can be better and less uncertain. Today, WTC mixing is represented in climate models in a crude way because the knowledge necessary to do it better is lacking. With a major laboratory study well under way combined with theory and new data analysis methods we hope to contribute the key knowledge needed to improve our ability to predict the future of the oceans and climate and respond appropriately.
WaTurSheD involves experimental campaigns which combine a suit of techniques in ways not done before, so a large amount of experimental methods development and preliminary tests have been necessary. We have successfully developed a method whereby the detailed time-resolved motion of an area of a water surface can be measured with high accuracy, while the flow velocity field directly underneath the surface is acquired simultaneously. This has given us unprecedented experimental access to the coupling between the water surface and the turbulent mixing below. The first major experiment of WaTurSheD was recently performed with this technique, a large step towards one main objective.
Very recently, the acquisition stage of the second and so far greatest experimental campaign was concluded, where three state-of-the-art measurement techniques were used simultaneously to study the full wave-turbulence-current system: the velocity field in a vertical plane beneath the wavy surface, the mixing in of a fluorescent agent which represents transported gas-saturated water, and infrared imaging of the surface to visualise the turbulence at the surface itself. We can now directly observe how the background turbulence is drastically changed by incoming waves, creating long cylinder-like eddies. We can literally watch how these eddies grab hold of the water at the surface and pulls it into the deep, replacing it with new water, precisely the process whereby gas and heat enter the real-world ocean. Extracting the results from the raw data will take some time, but will provide an unprecedented look into the processes that mix the upper ocean, at a level of detail, control and completeness not achieved before. The result of more than a year of planning and testing, this experiment is a major milestone and will give insights– and almost certainly new questions – which will guide the final stages of the project.
When flowing water, such as a river, is viewed from above, the surface is not quite flat but full of a multitude of patterns, imprints of the turbulent flow below. A goal is to understand what these imprints tell us about the mixing underneath. Using numerical simulation data from a collaborator we have discovered how long, thin "scars" on the water surface signify a particular kind of vortex underneath, giving us a far more complete intuitive picture. We eagerly await the data from the newest experiments, where we can study the phenomenon experimentally.
Very recently, the acquisition stage of the second and so far greatest experimental campaign was concluded, where three state-of-the-art measurement techniques were used simultaneously to study the full wave-turbulence-current system: the velocity field in a vertical plane beneath the wavy surface, the mixing in of a fluorescent agent which represents transported gas-saturated water, and infrared imaging of the surface to visualise the turbulence at the surface itself. We can now directly observe how the background turbulence is drastically changed by incoming waves, creating long cylinder-like eddies. We can literally watch how these eddies grab hold of the water at the surface and pulls it into the deep, replacing it with new water, precisely the process whereby gas and heat enter the real-world ocean. Extracting the results from the raw data will take some time, but will provide an unprecedented look into the processes that mix the upper ocean, at a level of detail, control and completeness not achieved before. The result of more than a year of planning and testing, this experiment is a major milestone and will give insights– and almost certainly new questions – which will guide the final stages of the project.
When flowing water, such as a river, is viewed from above, the surface is not quite flat but full of a multitude of patterns, imprints of the turbulent flow below. A goal is to understand what these imprints tell us about the mixing underneath. Using numerical simulation data from a collaborator we have discovered how long, thin "scars" on the water surface signify a particular kind of vortex underneath, giving us a far more complete intuitive picture. We eagerly await the data from the newest experiments, where we can study the phenomenon experimentally.
So far, two types of experiments have been conducted in the WaTurSheD project, both of them well beyond the state of the art both in design, method and the key questions that can be answered about how waves, currents and turbulence mix waters from the sea surface into the deep. The experiments themselves constitute major achievements which will set new standards in the field. The data acquired from these pinnacle experiments is currently being processed by computers, and we await the results with great eagerness.
Two experiments early in the project have already provided potentially impactful insights. While the most recent experiment mentioned above is far more ambitious, the early campaigns were already well beyond the state of the art. Serendipitously we discovered a change in the current itself due to wave-turbulence interactions which could have very important consequences indeed for how floating matter like microplastics, algae, nutrients, phytoplankton and oil spills are transported around the oceans.
Our second major result was to quantify how the waves transform the turbulence underneath under different conditions, and how turbulence scatters waves, both of direct importance to the wave and turbulence climate. We were the first to show how these key process depends on turbulence properties, knowledge needed in order to implement them in ocean and climate models.
On the topic of understanding turbulence close beneath a water surface, we recently reported a new discovery, namely how long, thin "scars" on the water surface of flowing water (like a river) signify a particular kind of vortex underneath, adding a key missing component to our intuitive (and quantitative) understanding.
Two experiments early in the project have already provided potentially impactful insights. While the most recent experiment mentioned above is far more ambitious, the early campaigns were already well beyond the state of the art. Serendipitously we discovered a change in the current itself due to wave-turbulence interactions which could have very important consequences indeed for how floating matter like microplastics, algae, nutrients, phytoplankton and oil spills are transported around the oceans.
Our second major result was to quantify how the waves transform the turbulence underneath under different conditions, and how turbulence scatters waves, both of direct importance to the wave and turbulence climate. We were the first to show how these key process depends on turbulence properties, knowledge needed in order to implement them in ocean and climate models.
On the topic of understanding turbulence close beneath a water surface, we recently reported a new discovery, namely how long, thin "scars" on the water surface of flowing water (like a river) signify a particular kind of vortex underneath, adding a key missing component to our intuitive (and quantitative) understanding.