The Lofoten Vortex (LV) is an intense, permanent anticyclone in the Lofoten Basin of the Nordic Seas, characterised by a 1200 m thick core of Atlantic Water with a radius of about 20 km, in nearly solid-body rotation reaching speeds up to 0.8 m s-1. Potential vorticity in the core is nearly two orders of magnitude lower than the surroundings. It has been postulated that anticyclonic eddies shed from the Norwegian Atlantic Current along the Lofoten Escarpment merge into the LV, contributing to maintaining its large heat content and energetics, but such merging events have proven difficult to observe due to their transient nature.

In spring 2023, we coordinated a Seaglider mission with the fast-sampling calibration phase of SWOT (Surface Water Ocean Topography) altimetry, which had a cross-over at the LV’s mean location. The track of SWOT crosses the LV twice a day and offers 2-km horizontal resolution across its two 60km wide parallel swaths. The glider samples to 1000 m providing profiles typically every 2.7 h (2.5 km), and is controlled to repeatedly enter and exit the vortex. One quasi-synoptic eddy realization takes approximately 3 days. Referencing the profiles to the time-variable core location of the eddy, we construct a radial transect of the vortex out to 2-3 vortex radii.

An eddy merging event was observed between 10 and 17 April, confirmed by the daily absolute dynamic topography. The incoming eddy is characterised by higher temperatures, detectable to 600m. The merging eddy’s dynamical signature is observed in the velocity and the vorticity structure. The combination of high-resolution surface remote-sensing observations with subsurface glider observations offers a powerful means to improve our understanding of meso and submesoscale interactions in the ocean.