Preprints
https://doi.org/10.5194/os-2021-62
https://doi.org/10.5194/os-2021-62

  06 Jul 2021

06 Jul 2021

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

Swell hindcast statistics for the Baltic Sea

Jan-Victor Björkqvist1,2, Siim Pärt1, Victor Alari1, Sander Rikka1, Elisa Lindgren2, and Laura Tuomi2 Jan-Victor Björkqvist et al.
  • 1Department of Marine Systems, Tallinn University of Technology, Akadeemia tee 15a, 12611, Tallinn, Estonia
  • 2Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland

Abstract. Swell dominates the global sea state and therefore significantly contributes to processes at the air and seabed interfaces. Nonetheless, smaller enclosed seas are detached from the global swell climate. We present swell statistics for the Baltic Sea using 20 years of swell partitioned model data. The swell significant wave height was mostly under 2 m, and in the winter (DJF) the mean significant swell height was typically less than 0.4 m; higher swell was found at limited nearshore areas. Swell waves were typically short (under 5 s), with mean periods over 8 s being rare. In open-sea areas the average ratio of swell energy (to total energy) was below 0.4 – significantly less than in World Ocean. Certain coastal areas were swell dominated over half the times, mostly because of weak winds (U < 5 ms−1) rather than high swell heights. Swell dominated events with a swell height over 1 m typically lasted under 10 h. A cross-correlation analysis indicates that swell in the open sea is mostly generated from local wind-sea when wind decays (dominant time lag roughly 15 h). Near the coast, however, the results suggests that the swell is partially detached from the local wind-waves, although not necessarily from the weather system that generates them.

Jan-Victor Björkqvist et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-62', Anonymous Referee #1, 25 Jul 2021
    • AC1: 'Reply on RC1', Jan-Victor Björkqvist, 24 Sep 2021
  • RC2: 'Comment on os-2021-62', Anonymous Referee #2, 29 Jul 2021
    • AC2: 'Reply on RC2', Jan-Victor Björkqvist, 24 Sep 2021

Jan-Victor Björkqvist et al.

Jan-Victor Björkqvist et al.

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Short summary
Waves that travel faster than the wind are called swell. Our study presents wave model statistics of swell waves in the Baltic Sea, since such statistics have not yet been reliably compiled. Our results confirms that long, high, and persistent swell is absent in the Baltic Sea. We found that the dependency between swell and wind waves differ in the open sea compared to nearshore areas. These distinctions are important for studies into how waves interact with the atmosphere and the sea bottom.