St Petersburg University oceanographers reveal the peculiarities of energy transformation in ocean vortices
St Petersburg University scientists have found out that mesoscale ocean vortices can transfer their potential and kinetic energy to thin vortex filaments. The Norwegian Sea was chosen as the object of the study.
Ocean or mesoscale vortices are circular or spiral motions of water in the oceans that are formed by currents, wind, gravity and other forces. Vortices are one of the main mechanisms of lateral mixing and are capable of transferring heat, salt, mass, kinetic energy, and biogeochemical characteristics to thousands of kilometres from the region of their formation. The presence of warm or cold ocean vortices determines local coastal weather and influences climate. Additionally, mesoscale vortices play an important role in global ocean circulation.
The findings of the research supported by a grant from the Russian Science Foundation are published in the Journal of Marine Science and Engineering.
Despite their ubiquity, areas of vortex activity are usually confined to regions of instability of large circulation structures. It is the instability of intense jet currents in the ocean, such as the Gulf Stream or the Kuroshio Current, that gives rise to vortices. Another important reason for their generation is their coalescence and the interaction of vortices with the bottom topography.
Despite significant progress in the study of the kinematic and dynamic properties of vortices, many phenomena remain unexplained. For example, the scientific community does not yet understand how vortices manage to persist in inhomogeneous external currents.
The Lofoten Basin of the Norwegian Sea is the most dynamically active transit region, characterised by local maxima of ocean level dispersion and the kinetic energy of vortices. The dynamic activity in this region is mainly due to mesoscale vortices formed in the Norwegian Current, which transports Atlantic water to the Arctic. At the same time, the Lofoten Basin has a unique natural feature: it is a quasi-permanent anticyclone located in the centre, and the basin itself is literally "swarming" with mesoscale vortices due to its hydrodynamic conditions and topographic features.
The project "Investigation of the dynamics of isolated vortices in the ocean using remote sensing, in situ and simulated data" was supported by a grant from the Russian Science Foundation. For reference: last year, St Petersburg University ranked first in Russia in terms of the number of grants from the Russian Science Foundation. The University researchers received 112 grants, which is 5.5% of the total number of winning projects and the largest number of grants from a single organisation.
St Petersburg University, the oldest university in Russia was founded on 28 January (8 February) 1724. This is the day when Peter the Great issued a decree establishing the University and the Russian Academy of Sciences. Today, St Petersburg University is an internationally recognised centre for education, research and culture. In 2024, St Petersburg University will celebrate its 300th anniversary.
The plan of events during the celebration of the anniversary of the University was approved at the meeting of the Organising Committee for the celebration of St Petersburg University’s 300th anniversary. The meeting was chaired by Dmitry Chernyshenko, Deputy Prime Minister of the Russian Federation. Among the events are: the naming of a minor planet in honour of St Petersburg University; the issuance of bank cards with a special design; the creation of postage stamps dedicated to the history of the oldest university in Russia; and the branding of the aircraft of the Rossiya Airlines to name just a few. Additionally, the University has launched a website dedicated to the upcoming holiday. The website contains information about outstanding University staff, students, and alumni; scientific achievements; and details of preparations for the anniversary.
St Petersburg University scientists have found that during the evolution of mesoscale vortices against the background of the flow deforming them, energy transfer from vortices to filaments − vortex filaments − should be expected to manifest.
‘The main conclusion of the research is that during the evolution of mesoscale vortices we should expect energy transfer from vortices to filaments, i.e. from mesoscale motions to submesoscale motions. This is a direct energy cascade and is related to the unbounded stretching of vortices into vortex filaments. However, the process of stretching vortices is accompanied by a loss of energy, which returns to the current (inverse energy cascade),’ said Tatyana Belonenko, Professor in the Department of Oceanology at St Petersburg University.
For the study, the scientists have attracted satellite and simulated data, including reanalyses in which the global hydrodynamic model assimilates satellite and in situ measurements. As Tatyana Belonenko noted, in future the scientists plan to study the interactions between mesoscale vortices, fronts, marine topography and biological productivity of the ocean, as well as the impact of these factors on ocean ecosystems.