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A Study of the Iceland–Faeroe Frontal Variability Using the Multiscale Energy and Vorticity Analysis

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  • 1 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts
  • | 2 Division of Engineering and Applied Sciences, and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts
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Abstract

The multiscale nonlinear interactive Iceland–Faeroe frontal (IFF) variability during 14–22 August 1993 is investigated for complex dynamics with the localized multiscale energy and vorticity analysis (MS-EVA). In terms of multiscale window transform, the cold meandering intrusion observed in the IFF experiment is represented on a mesoscale window. The resulting mesoscale energetics for the deep layer show an isolated center of transfer of potential energy from the large-scale window into the mesoscale window in the study domain. This large-to-mesoscale potential energy transfer, or BC for short, is a baroclinic instability indicator by the MS-EVA-based stability theory. Signatures on other energetics maps and the reconstructed mesoscale structures all support this baroclinic instability. On the BC map, the transfer hotspot originally resides near the western boundary. It travels along the front into the interior domain in a form of convective instability and then, on 19 August, changes into another instability that is absolute in character. Correspondingly, disturbances switch from a spatial growing pattern into a time growing mode, culminating on 21 August, the day just before the intrusion matures. The whole process lasts for about five days, limited within a small horizontal region and beneath a depth of approximately 150 m. By interaction analysis, the energy locally gained from this process goes to the submesoscale window as well, but most of it remains in the mesoscale window, serving to fuel the growth of the meandering intrusion.

Corresponding author address: X. San Liang, Harvard University, Pierce Hall G2H, 29 Oxford Street, Cambridge, MA 02138. Email: liang@deas.harvard.edu

Abstract

The multiscale nonlinear interactive Iceland–Faeroe frontal (IFF) variability during 14–22 August 1993 is investigated for complex dynamics with the localized multiscale energy and vorticity analysis (MS-EVA). In terms of multiscale window transform, the cold meandering intrusion observed in the IFF experiment is represented on a mesoscale window. The resulting mesoscale energetics for the deep layer show an isolated center of transfer of potential energy from the large-scale window into the mesoscale window in the study domain. This large-to-mesoscale potential energy transfer, or BC for short, is a baroclinic instability indicator by the MS-EVA-based stability theory. Signatures on other energetics maps and the reconstructed mesoscale structures all support this baroclinic instability. On the BC map, the transfer hotspot originally resides near the western boundary. It travels along the front into the interior domain in a form of convective instability and then, on 19 August, changes into another instability that is absolute in character. Correspondingly, disturbances switch from a spatial growing pattern into a time growing mode, culminating on 21 August, the day just before the intrusion matures. The whole process lasts for about five days, limited within a small horizontal region and beneath a depth of approximately 150 m. By interaction analysis, the energy locally gained from this process goes to the submesoscale window as well, but most of it remains in the mesoscale window, serving to fuel the growth of the meandering intrusion.

Corresponding author address: X. San Liang, Harvard University, Pierce Hall G2H, 29 Oxford Street, Cambridge, MA 02138. Email: liang@deas.harvard.edu

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