Estimation of the Relation between the Dispersion Features of Free Internal Waves and the Density Field Vertical Structure in the Barents and Kara Seas

Abstract

Purpose. The aim of the paper is to investigate spatial-temporal dependences of the dispersion features of short-period free internal waves on the density field vertical structure in the Barents and Kara seas. Methods and Results. Based on the linearized equations of motion of the ideal incompressible and continuously stratified fluid, the dispersion features of free internal waves in the Barents and Kara seas were studied. Solution of the main boundary problem of the Sturm-Liouville type made it possible to obtain the own frequencies of five lowest modes and the own period of the internal waves’ first mode. To calculate the density field, the World Ocean Atlas 2013 reanalysis data on temperature and salinity for 1955–2012 with resolution 0.25° × 0.25° were applied. The relation between the dispersion features of free internal waves and the density field vertical structure was analyzed, and dispersion characteristics of theinternal waves in the Barents and Kara seas were compared. Conclusions. During the months when the density gradients are maximal, the internal waves of the highest frequency and the shortest period are observed. Among the intra-year maximums of the buoyancy depth-averaged frequency, the highest values (≈ 0.02 s) are observed in the Barents Sea in July and August, and those of the Kara Sea – in July–September (≈ 0.055 s) and in November (≈ 0.058 s). In the same months, noted are the maximum values of the averaged natural frequencies and the minimum values of the averaged own period of the internal waves. Thus, for the wavelength 1000 m, the highest averaged own frequency and the smallest averaged own period of the first mode in the Barents Sea constitute 0.0025 s and 45 min., and those in the Kara Sea – 0.0038 s and 30 min, respectively.