Oceanologia No. 65 (3) / 23

Contents

Original research article

Original research article


Effects of Eulerian current, Stokes drift and wind while simulating surface drifter trajectories in the Baltic Sea
Oceanologia 2023, 65(3), 453-465
https://doi.org/10.1016/j.oceano.2023.02.001

Ove Pärn1,*, Lina Davulienė2, Diego Macias Moy1, Kaimo Vahter3, Adolf Stips3, Tomas Torsvik4
1European Commission, Joint Research Centre, Ispra, Varese, Italy;
e-mail: Ove.PARN@ext.ec.europa.eu
2SRI Center for Physical Sciences and Technology (FTMC), Vilnius, Lithuania
3Department of Marine Systems, School of Science, Tallinn University of Technology, Tallinn, Estonia
4Geophysical Institute, University of Bergen, Bergen, Norway
*corresponding author

keywords: Litter modelling, OceanParcels framework, Surface drifter trajectories, Stokes drift, Wind effect

Received 8 April 2022, Revised 29 January 2023, Accepted 3 February 2023, Available online 16 February 2023, Version of Record 19 June 2023.

Abstract

The simulation of Lagrangian drift is an important task in applications such as dispersion of pollutants, larvae and search and rescue activities. In this study, the Eulerian current, Stokes drift and wind effect on the simulation of observed drifters were analysed. The Lagrangian OceanParcels model was used, and the surface trajectories were assessed by comparison with 9 GPS drifter trajectories in the Gulf of Finland, Gulf of Riga and Lithuanian coast. The Normalised Cumulative Lagrangian Separation (NCLS) distance between the simulated and the satellite-tracked drifter trajectories, and the mean absolute error (MAE) were used as comparison metrics. The present study suggests the need to consider the Stokes drift and the wind factor in addition to the modelled Eulerian currents to obtain a better description of the trajectories of particles. By making these considerations, the OceanParcels model could adequately simulate particle trajectories in the sub-basins within the Baltic Sea. The realized model tests showed that motion of surface drifters are strongly controlled by the Stokes drift when the significant wave height is >1 m, whereas the wind component and the Eulerian currents are crucial when the significant wave height is <0.6 m or the wave (Stokes drift) directions do not match the wind direction.
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Variations of temperature, salinity and oxygen of the Baltic Sea for the period 1950 to 2020
Oceanologia 2023, 65(3), 466-483
https://doi.org/10.1016/j.oceano.2023.02.002

Vera Stockmayer, Andreas Lehmann*
GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany;
e-mail: alehmann@geomar.de
*corresponding author

keywords: Climate variability, Temperature, salinity and oxygen evolution, Baltic Sea, Time series analysis

Received 31 August 2021, Revised 6 July 2022, Accepted 25 July 2022, Available online 8 August 2022, Version of Record 17 April 2023.

Abstract

Variations of temperature, salinity and oxygen of the Baltic Sea on interannual to decadal timescales were studied for the period from 1950 to 2020. Both observational data and the output of a numerical circulation model of the Baltic Sea were analyzed. In addition, we investigated the influence of atmospheric parameters and river runoff on the observed hydrographic variations. Variability of sea surface temperature (SST) closely follows that of air temperature in the Baltic on all timescales examined. Interannual variations of SST are significantly correlated with the North Atlantic Oscillation in most parts of the sea in winter. The entire water column of the Baltic Sea has warmed over the period 1950 to 2020. The trend is strongest in the surface layer, which has warmed by 0.3–0.4°C decade−1, noticeably stronger since the mid-1980s. In the remaining water column, characterized by permanent salinity stratification in the Baltic Sea, warming trends are slightly weaker. A decadal variability is striking in surface salinity, which is highly correlated with river runoff into the Baltic Sea. Long-term trends over the period 1950–2020 show a noticeable freshening of the upper layer in the whole Baltic Sea and a significant salinity increase below the halocline in some regions. A decadal variability was also identified in the deep layer of the Baltic Sea. This can be associated with variations in saltwater import from the North Sea, which in turn are influenced by river runoff: fewer strong saltwater inflows were observed in periods of enhanced river runoff. Furthermore, our results suggest that changes in wind speed have an impact on water exchange with the North Sea. Interannual variations of surface oxygen are strongly anti-correlated with those of SST. Likewise, the positive SST trends are accompanied by a decrease in surface oxygen. In greater depths of the Baltic Sea, oxygen decrease is stronger, which is partly related to the observed increase of the vertical salinity gradient.
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Bed forms under the combined action of waves and wind-driven currents in the remote foreshore of the non-tidal sea
Oceanologia 2023, 65(3), 484-493
https://doi.org/10.1016/j.oceano.2023.03.001

Magdalena Stella-Bogusz*
Institute of Hydro-Engineering, Polish Academy of Sciences, Gdańsk, Poland;
e-mail: m.stella@ibwpan.gda.pl
*corresponding author

keywords: Wave-current interaction, Sand wave height, Sand wave length, Bed forms characteristics

Received 30 June 2022, Revised 15 February 2023, Accepted 27 March 2023, Available online 18 April 2023, Version of Record 19 June 2023.

Abstract

The paper presents a prediction of bed form parameters (length and height) in the remote foreshore of the non-tidal sea. The study site is located in the south Baltic region, near the Coastal Research Station (CRS) in Lubiatowo, Poland (ca. 1–2 Nm off the shoreline at depths of around 16–20 m). The study site is an area with hydrodynamics and lithodynamics typical of the south Baltic coast, built of fine sands. Predictions are based on numerical modelling with an input of measured data. Numerical modelling uses assumptions of specific relations of sand wave height and length with shear stress, grain size, kinematic viscosity, or storm event frequency. To establish these relations for the study area, wave, sea temperature and wind data were collected near CRS Lubiatowo. To verify the predictions made in this research, bathymetric data from a field survey in the study area was used. The results show that the flow is mostly current-dominated. Sand waves formed by hydrodynamic conditions in this area have a steepness of 0.01 to 0.02, a length of 40 to 70 m and a height of 0.6 to 2.3 m.
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General characteristics of tidal currents in the entrance of Khor Abdullah, northwest of Arabian Gulf
Oceanologia 2023, 65(3), 494-502
https://doi.org/10.1016/j.oceano.2023.03.002

Ali Abdulridha Lafta*
Marine Science Center, University of Basrah, Iraq;
e-mail: ali.lafta@uobasrah.edu.iq
*corresponding author

keywords: Tidal currents, Arabian Gulf, Harmonic analysis, Residual currents, Khor Abdullah

Received 19 November 2022, Revised 5 March 2023, Accepted 27 March 2023, Available online 18 April 2023, Version of Record 19 June 2023.

Abstract

The general characteristics of tidal currents in the entrance of the Khor Abdullah at Iraq marine water, located at the northwest tip of the Arabian Gulf, were studied based on realistic current measurements. The velocity measurements used in this study extended to about one year, which was never previously available in this vital region of the Arabian Gulf. The results illustrated that this area is characterized by strong currents exceeding 1 m/s during both ebb and flood tides, driven by local water level variations. The maximum currents recorded during the study period were 1.65 and 1.36 m/s at the ebb and flood tides, respectively. Additionally, the monthly averages of ebb currents are higher than those of flood currents. The harmonic analysis results revealed that the tidal effect explained approximately 98% of the variation in water currents, with the remaining percentage due to residual currents. Among the 35 tidal components used in harmonic analysis, the M2 component was the main contributor to tidal currents variation in the area, followed by S2, K1, N2, and O1. The residual current seems to have a low effect on the currents variations in the area, with maximum values not exceeding 0.0677 and 0.058 m/s during the ebb and flood tides, respectively. The results obtained give a general view of the tidal current behavior and could be beneficial for several aspects of marine and coastal engineering as well as shipping and navigation activities in this region.
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Remotely induced storm effects on the coastal flooding along the southwest coast of India
Oceanologia 2023, 65(3), 503-516
https://doi.org/10.1016/j.oceano.2023.03.003

P.S. Swathy Krishna1,2, Valliyil Mohammed Aboobacker3, Madipally Ramesh1,2,*, L. Sheela Nair1
1National Centre for Earth Science Studies, Thiruvananthapuram, Kerala, India;
e-mail: ramesh.madipally@ncess.gov.in
2Cochin University of Science and Technology, Cochin, Kerala, India
3UNESCO Chair in Marine Sciences, Environmental Science Center, Qatar University, Doha, Qatar

keywords: IASO swells, ERA5 winds, Indian Ocean, Kerala coast, Coastal inundation, Wave runup

Received 9 January 2023, Revised 29 March 2023, Accepted 29 March 2023, Available online 18 April 2023, Version of Record 19 June 2023.

Abstract

The southwest coast of India is exposed to long-period swells propagated from the South Indian Ocean during pre- and post-monsoon seasons. Although swells from the Southern Ocean and Atlantic Ocean were identified in the North Indian Ocean, their existence and impact along the southwest coast of India were not well investigated. On 19 March 2019, the Valiyathura-Shangumukham coastal stretch along the southwest coast of India experienced an unexpected coastal inundation without having a prompt forecast/warning, and not induced by a storm/cyclone in its vicinity. The present study investigates the causative forces of this inundation and estimates the wave runup and inundation. The study reveals that an unusual swell system was developed in the Indian-Atlantic-Southern Oceans (IASO) interface during 10–12 March and propagated towards the southwest coast of India. The measured wave spectra off Varkala clearly depicts the presence of long-period swells (Tp>18 s), which dominantly occurred as single-peaked. Wave modelling has been carried out to characterize the wave transformation associated with the “IASO interface swells” along the southern Kerala coast. A wave runup of up to 0.93 m height and a coastal inundation of up to 83 m onshore have been estimated during this event.
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