Reports

Research Stay in Hokkaido by Nicolas Dettling (Nov 23)

My name is Nicolas Dettling, I am a PhD student in subproject T3 „Energy Transfers in Gravity Currents“. So far I have worked on applying and improving eddy parameterizations in the presence of gravity currents, such as the ones exporting dense water from the Antarctic continental shelves. Now, it is time to apply what we have found in idealised models to regional models of the Antarctic marginal seas.

For this purpose, I visited Prof. Yoshihiro Nakayama and his research group at the Institute for Low Temperature Science at Hokkaido University, Japan in November. Over the last years, Prof. Nakayama and his group have set up a number of regional ocean model simulations targeting key questions concerning the dynamics of the ocean around the Antarctic continental shelf and slope. Over the course of three weeks, I was introduced to a model of the Cape Darnley region, where dense water flows down the continental slope into the abyssal ocean, providing a nice test case for my previous parameterization work. I learned how to set up, run and interpret the model at different resolutions and we discussed the steps towards applying an eddy parameterization in the model. I am very grateful for the support and the fruitful discussions during my time at the institute.

The Hokkaido University campus is centred around a park and every morning I would walk along the Ginkgo Avenue enjoying the autumn colours on my way to work. Fortunately, there was also time to explore the City of Sapporo and the beautiful nature of Hokkaido, where the first snow of the season had already arrived. Luckily, the next Hokkaido Soup Curry or a bunch of Gyozas (fried dumplings) were never far away to recover after working or travelling.

I genuinely enjoyed to work in Japan and to engage in this cultural exchange. I would like to thank Prof. Nakayama and his group for their hospitality and I am very much looking forward to working together again in the future. Finally I want to thank the TRR 181 for funding the research visit.

To resolve or not to resolve?

I’m investigating effects of grid resolution on the modification of overflow and ocean energetics.
Deniz Aydin, PhD T3

Bathymetry of the study region with different resolutions.

I am Deniz and I work on the T3 ‘Energy transfers in gravity plumes’ project as a PhD candidate at AWI. In particularly we are interested in the Denmark Strait Overflow (DSO) which is between Greenland and Iceland. This location is special because the DSO carries most of the dense and cold Arctic water entering the North Atlantic. Thus contributing to the deep southward flowing part of the Atlantic meridional overturning circulation.

As soon as the dense water on the sill starts descending, it undergoes a significant amount of mixing and entrainment of ambient water. By 200km downstream of the sill, volume and tracer properties of the overflow water are substantially modified due to combination of different processes. In our subproject we try to understand the interactions of all these different processes at different scales using observational and numerical modeling analysis.

It’s difficult to properly represent overflows in a global ocean model with the coarse resolution climate models generally have. For my part in this subproject, I use a general circulation model (MITgcm) in a regional setup with a 1year of simulation period. I’m investigating effects of grid resolution on the modification of overflow and ocean energetics. For this purpose I use 6 different horizontal resolutions ranging from eddy resolving (1km) to coarse resolution (36km). At the moment, I am analyzing the results from higher resolution simulations. Soon coarser resolutions will come into the picture and analysis of eddy parameterization schemes along with them. My research will contribute to a better understanding of consequences of lacking smaller scale processes and better representation of them in coarser models.

Energy transfers in gravity plumes

The next step will be connecting this mesoscale activity with high frequency variability and mixing parameters in the plume.
Stylianos Kritsotalakis, PhD T3

Schematic illustrating the observed mesoscale activity ~120km downstream of the Denmark Strait Sill. The position of the moorings on the Greenland slope is marked with black dots. The direction of the mean flow is indicated with a solid black arrow.

Hello everyone, my name is Stylianos Kritsotalakis and I am a PhD student in the subproject “Energy transfers in gravity plumes” at AWI/MARUM. The aim of the project is to understand the pathways and processes by which kinetic energy is transferred from the mesoscale eddy field to submesoscales and dissipative turbulent scales. Using observational and numerical modeling efforts the project focuses in tackling the above problem within the Denmark Strait Overflow plume.

I am working , primarily, with mooring data aquired ~120km downstream of the Denmark Strait in late summer 2018. I have identified the mesoscale field associated with the plume which consists of eddy pairs with opposing sense of rotation (Fig.1) and at the moment I am comparing these findings with the existing literature. The next step will be connecting this mesoscale activity with high frequency variability and mixing parameters in the plume.

Investigating the Denmark Strait Overflow plume

Using the results of the observational and modeling components, we will investigate the role entrainment plays in the evolution of the plume.
Ryan North, Postdoc in T3

In October 2016 I joined the TRR 181 as a postdoc at the Universität Hamburg in the T3 subproject: Energy transfers in gravity plumes. Our subproject aims to improve our ability to parameterize the energetics and mixing within gravity plumes by investigating the Denmark Strait Overflow plume. This plume was chosen as an ideal study case because of its relevance to the global ocean circulation, and the long history of observational data in the Strait. My role within the subproject mainly involves working with this historical data and the collection of new data. The data will be used both on its own and for collaborative modelling work. Using the results of the observational and modeling components, we will investigate the role entrainment plays in the evolution of the plume. In particular, we are interested in investigating the hypothesis that enhanced entrainment occurs where the plume interacts with mesoscale eddies or topography. The modeling component will help to put the results in perspective across a range of scales, from the turbulent scale up to the mesoscale.

Prior to joining the Institute of Oceanography I followed a winding career path. Beginning at Canada’s Queen’s University, my career has taken me through structural and coastal engineering, lake, river and coastal hydrodynamic modeling, climate related hypoxia in lakes, and submesoscale eddies in the coastal ocean (at HZG in nearby Geesthacht). With this new position I have finally managed to move beyond inland waters and the coastal shelf break to reach properly deep water!

I am looking forwarding to meeting more members of TRR 181, and to opportunities to work together in the near future. Currently, I am onboard the FS Meteor helping out fellow TRR project members investigate filaments forming within the Benguela upwelling system off the coast of Namibia.