Preprints
https://doi.org/10.5194/os-2020-110
https://doi.org/10.5194/os-2020-110

  03 Dec 2020

03 Dec 2020

Review status: this preprint is currently under review for the journal OS.

Spatio-temporal structure of Baltic free sea level oscillations in barotropic and baroclinic conditions from hydrodynamic modelling

Eugeny A. Zakharchuk1,2, Natalia Tikhonova1,2, and Elena Zakharova3,4 Eugeny A. Zakharchuk et al.
  • 1Saint-Petersburg University, Saint-Petersburg, 199004, Russia
  • 2State Oceanographic Institute. Saint-Petersburg Branch, Saint-Petersburg, 199397, Russia
  • 3Water Problem Institute, RAS, Moscow, 117971, Russia
  • 4EOLA, Toulouse, 31400, France

Abstract. Free sea level oscillations in barotropic and baroclinic conditions were examined using numerical experiments based on a 3D hydrodynamic model of the Baltic Sea. In a barotropic environment, the highest amplitudes of free sea level oscillations are observed in the northern Gulf of Bothnia, eastern Gulf of Finland, and south-western Baltic Sea. In these areas, the maximum variance appears within the frequency range corresponding to periods of 13–44 hr. In a stratified environment, after the cessation of meteorological forcing, water masses relax to the equilibrium state in the form of mesoscale oscillations at the same frequencies as well as in the form of rapidly decaying low-frequency (seasonal) oscillations. The total amplitudes of free baroclinic perturbations are significantly larger than those of barotropic perturbations, reaching 15–17 cm. Contrary to barotropic, oscillations in baroclinic conditions are strongly pronounced in the deep-water areas of the Baltic Sea Proper. Specific spatial patterns of amplitudes and phases of free barotropic and baroclinic sea level oscillations identified them as progressive-standing waves representing barotropic or baroclinic modes of gravity waves and topographic Rossby waves.

Eugeny A. Zakharchuk et al.

 
Status: open (until 28 Jan 2021)
Status: open (until 28 Jan 2021)
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Eugeny A. Zakharchuk et al.

Eugeny A. Zakharchuk et al.

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Short summary
Free sea level oscillations in stratified (baroclinic) and unstratified (barotropic) conditions were examined using numerical experiments based on a 3D hydrodynamic model of the Baltic Sea. We identified free barotropic oscillations of periods of 44, 41, 37, 29, 21, 16, and 15 h that have not been noted previously. In stratified basins both the high-frequency (daily/hourly scales) and the low-frequency free oscillations of seasonal scale have been recorded.