Application of the theory of columnar Q-vortices with helical structure for the Lofoten vortex in the Norwegian Sea

Abstract

In this paper, dynamic characteristics of mesoscale vortices in the ocean are considered using the theory of columnar vortices with a helical structure. The radial profile of the relative vorticity is approximated with the Q-distribution. Expressions connecting the distributions of the horizontal and vertical velocity components in this type of vortices are obtained. The limitations for the applicability of the analytical solution are derived. The advantages and disadvantages of this model are shown in comparison with the radial distributions of the corresponding parameters in Scully and in Rayleigh vortices. In particular, it is shown that the Q-distribution can, in some sense, be considered as a compromise solution between the two distributions above. The theory of columnar Q-vortices with helical structure is applied to the permanently existing anticyclonic Lofoten vortex of the Norwegian Sea. The mean radial distributions of various dynamics characteristics of the Lofoten vortex are obtained using simulations with the regional hydrodynamic model MIT. The reasons for formation of the observed vertical velocity structure are analyzed. It is shown that, in contrast to atmospheric synoptic structures, divergence of Ekman fluxes in the bottom layer affects only the lower part of the vortex. In the upper ocean, ascending vertical motion is observed in the Lofoten vortex. It is assumed that horizontal dispersion of vortex energy, the most intense in the surface layer, plays an essential role in the formation of the field of vertical velocities in the upper part of its core. Refs 36. Figs 3.