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The Lofoten Basin is a ‘hot spot’ of intense mesoscale eddy activity in the Nordic Seas. The mesoscale eddies of the Lofoten Basin can be coupled to the heat transport, local climate, and fisheries of the region. During the past two decades, the European satellite missions European Remote Sensing (ERS) satellite and Environmental Satellite (ENVISAT) have played a major part in delivering continuous altimeter measurements over the Lofoten Basin. In recent years, automated eddy detection and tracking methods have revolutionized the long-term monitoring of eddies in the Lofoten Basin from the gridded altimeter data. Another major recent development in this field is the possibility of monitoring eddies on a daily basis from the globally available daily gridded altimeter data. This study assesses the performance of the new daily data compared to the previous weekly data in terms of eddy detection and eddy statistics in the Lofoten Basin. Analysis found that the long-lived eddies detected using the weekly data are counted as separate short-lived eddies when using daily data. In addition, the daily data returns lower eddy intensities (22–40%) with higher eddy radius estimates, which is linked to the anisotropy in the grid spacing of the data. Interestingly, the mean eddy drift in the Lofoten Basin is better represented in the daily data. The daily data shows the westward movement of eddies from the slope current and their subsequent northwestward movement following the topography, before joining the cyclonic drift in the western Lofoten Basin. The study supports the need for a regional gridded data set with high temporal and spatial resolution (in both zonal and meridional scales), in order to optimize the use of satellite altimeter data in the Lofoten Basin. [ABSTRACT FROM PUBLISHER]

• Only one percent of the total mesoscale eddies detected by altimetry in the Lofoten Basin are long-lived (lifetime > 35 days). • The average drifting speed of long-lived eddies has a pronounced seasonal variation variability. • Cyclonic eddies surround the quasi-permanent anticyclonic Lofoten Vortex forming a shield around it. The paper presents a statistical analysis of long-lived detected mesoscale eddies in the Lofoten Basin (LB). An automated eddy identification and tracking method is applied to the altimeter data during the time-period 1993–2017 to detect and track anticyclonic (ACEs) and cyclonic eddies (CEs) in the LB. Our analysis found that only one percent of the eddies detected are long-lived (eddy-life > 35 days). Even though only 1%, the detected 330 long-lived mesoscale eddies (CEs, 120; ACEs, 210) account for >11,550 daily individual eddy-observations. The lifetime, occurrence, generation sites, size, intensity, and drift of these long-lived eddies are quantified. The average drift speed of long-lived eddies is found to show a pronounced seasonal variation with a maximum from October to March. Long-lived eddies in the LB are further divided into four groups based on their region of generation and dissipation. Long-lived eddies generated and dissipated outside the region of the Lofoten Vortex (group 2 eddies) are found to be the predominant type (CEs, 73.3%; ACEs, 69.5%). The eddies generated and dissipated in the region of the permanent Lofoten Vortex form the second dominant type (CEs, 14.3%; ACEs, 26.2%). Based on their lifetime, properties of the two predominant groups of eddies are examined in detail. The difference found in the temporal variability of the eddy characteristics of the two groups reflects their different genesis. The analysis revealed that the mesoscale eddies of group 2 have a longer life than eddies of group 1, and ACEs are more long-lived in comparison to CEs. The analysis also found three main areas of eddy generation in the frontal zone of the NwASC from where mesoscale eddies propagate to the north-west, forming three main corridors of trajectories. The study further provides evidence of long-lived cyclonic CEs surrounding the large quasi-permanent Lofoten Vortex (LV) and forming a shield around it. Small CEs located in two areas with centers at 69.5° N, 4° E, and 70° N, 2.5° E survive nearby the LV resisting the vortex-vortex interaction with the large and strong LV. [ABSTRACT FROM AUTHOR]