Hindcast of the mesoscale eddy field in the Southeastern Baltic Sea: Model output vs satellite imagery

Zhurbas, Victor; ̈Ali, Germo V; Kostianoy, Andrey G.; Lavrova, Olga

doi:10.2205/2019es000672

Cited by 11 publications

(6 citation statements)

References 29 publications

(29 reference statements)

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“…Halocline is persistent at 50-70 m in most of the deeper areas (e.g., Alenius et al, 2003;Liblik and Lips, 2017), and the seasonal thermocline usually develops above 20 m during spring (e.g., Alenius et al, 1998;Liblik and Lips, 2017). The presence of submesoscale flows and features has been often indicated together with rich mesoscale variability (Kikas and Lips, 2016;Zhurbas et al, 2019). Numerous upwelling and downwelling events, fronts, and eddies are characteristic features of the Baltic Sea (Pavelson et al, 1997;Myrberg and Andrejev, 2003;Lehmann et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Submesoscale variability in a mesoscale front captured by a glider mission in the Gulf of Finland, Baltic Sea

2023

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Modern research methods enable unfolding the structure of the water column with higher resolution than ever, revealing the importance of submesoscale. Submesoscale processes have intermediate space and time scales of <5 km and a few days in the Baltic Sea. A glider mission was conducted in the Gulf of Finland in May 2018. The appearance of a mesoscale front as a response to the persisting NE–E winds was observed. Within the front, smaller scale features at a lateral scale of a km were apparent. The tracer patterns indicated the presence of two adjacent motions – cold (warm) water penetrating upward (downward) on the lighter (denser) side of the front. We suggest they were traces of ageostrophic secondary circulation emerging while the loss of the upwelling-favorable forcing arrested the strengthening of the front. The analysis showed favorable conditions for the baroclinic and wind-driven instability. Such circulations could work to equalize the differences in cross-front direction, affecting the stratification and acting against the persistence of the mesoscale front. The spatial spectra of isopycnal tracer variance revealed the depth-dependence of the spectral slopes at the lateral scales of 1–10 km in the upper part of the water column. The differing of the slopes in the density layers associated with the mesoscale front indicates that frontal dynamics contribute to the energy cascade.

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Section: Introductionmentioning

confidence: 99%

Submesoscale variability in a mesoscale front captured by a glider mission in the Gulf of Finland, Baltic Sea

2023

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“…Consequently, these models have rarely been validated with respect to their long-term performance, such as in multidecadal transient simulations. Finally, the BMIP also includes model setups with horizontal resolutions in the range of a few tens of meters to ∼ 200 m, as they allow the resolution of submesoscale dynamics and mesoscale eddy fields (Väli et al, 2017(Väli et al, , 2018Zhurbas et al, 2019b;Onken et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

The Baltic Sea Model Intercomparison Project (BMIP) – a platform for model development, evaluation, and uncertainty assessment

Gröger

Placke²,

Meier³

et al. 2022

Geosci. Model Dev.

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Abstract. While advanced computational capabilities have enabled the development of complex ocean general circulation models (OGCMs) for marginal seas, systematic comparisons of regional ocean models and their setups are still rare. The Baltic Sea Model Intercomparison Project (BMIP), introduced herein, was therefore established as a platform for the scientific analysis and systematic comparison of Baltic Sea models. The inclusion of a physically consistent regional reanalysis data set for the period 1961–2018 allows for standardized meteorological forcing and river runoff. Protocols to harmonize model outputs and analyses are provided as well. An analysis of six simulations performed with four regional OGCMs differing in their resolution, grid coordinates, and numerical methods was carried out to explore intermodel differences despite harmonized forcing. Uncertainties in the modeled surface temperatures were shown to be larger at extreme than at moderate temperatures. In addition, a roughly linear increase in the temperature spread with increasing water depth was determined and indicated larger uncertainties in the near-bottom layer. On the seasonal scale, the model spread was larger in summer than in winter, likely due to differences in the models' thermocline dynamics. In winter, stronger air–sea heat fluxes and vigorous convective and wind mixing reduced the intermodel spread. Uncertainties were likewise reduced near the coasts, where the impact of meteorological forcing was stronger. The uncertainties were highest in the Bothnian Sea and Bothnian Bay, attributable to the differences between the models in the seasonal cycles of sea ice triggered by the ice–albedo feedback. However, despite the large spreads in the mean climatologies, high interannual correlations between the sea surface temperatures (SSTs) of all models and data derived from a satellite product were determined. The exceptions were the Bothnian Sea and Bothnian Bay, where the correlation dropped significantly, likely related to the effect of sea ice on air–sea heat exchange. The spread of water salinity across the models is generally larger compared to water temperature, which is most obvious in the long-term time series of deepwater salinity. The inflow dynamics of saline water from the North Sea is covered well by most models, but the magnitude, as inferred from salinity, differs as much as the simulated mean salinity of deepwater. Marine heat waves (MHWs), coastal upwelling, and stratification were also assessed. In all models, MHWs were more frequent in shallow areas and in regions with seasonal ice cover. An increase in the frequency (regionally varying between ∼50 % and 250 %) and duration (50 %–150 %) of MHWs during the last 3 decades in all models was found as well. The uncertainties were highest in the Bothnian Bay, likely due to the different trends in sea ice presence. All but one of the analyzed models overestimated upwelling frequencies along the Swedish coast, the Gulf of Finland, and around Gotland, while they underestimated upwelling in the Gulf of Riga. The onset and seasonal cycle of thermal stratification likewise differed among the models. Compared to observation-based estimates, in all models the thermocline in early spring was too deep, whereas a good match was obtained in June when the thermocline intensifies.

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“…Submesoscale structures and the associated instabilities were simulated using high-resolution circulation models in various areas of the World Ocean such as the California Current System (Capet et al, 2008;Dewar et al, 2015;, the Gulf Stream (Gula et al, 2016) and the Gulf of Mexico (Barkan et al, 2017). Similarly, highresolution circulation models with a horizontal grid of less than 0.6 km were implemented to also study submesoscale dynamics in the Baltic Sea (Vankevich et al, 2016;Väli et al, 2017Väli et al, , 2018Vortmeyer-Kley et al, 2019;Zhurbas et al, 2019;Onken et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Rotation of floating particles in submesoscale cyclonic and anticyclonic eddies: a model study for the southeastern Baltic Sea

2019

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Abstract. We hypothesized that the overwhelming dominance of cyclonic spirals on satellite images of the sea surface could be caused by some differences between the rotary characteristics of submesoscale cyclonic and anticyclonic eddies. This hypothesis was tested by means of numerical experiments with synthetic floating Lagrangian particles embedded offline in a regional circulation model of the southeastern Baltic Sea with very high horizontal resolution (0.125 nautical mile grid). The numerical experiments showed that the cyclonic spirals can be formed from both a horizontally uniform initial distribution of floating particles and from the initially lined-up particles during an advection time of the order of 1 d. Statistical processing of the trajectories of the synthetic floating particles allowed us to conclude that the submesoscale cyclonic eddies differ from the anticyclonic eddies in three ways favoring the formation of spirals in the tracer field: they can be characterized by (a) a considerably higher angular velocity, (b) a more pronounced differential rotation and (c) a negative helicity.

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Hindcast of the mesoscale eddy field in the Southeastern Baltic Sea: Model output vs satellite imagery

Cited by 11 publications

References 29 publications

Submesoscale variability in a mesoscale front captured by a glider mission in the Gulf of Finland, Baltic Sea

Submesoscale variability in a mesoscale front captured by a glider mission in the Gulf of Finland, Baltic Sea

The Baltic Sea Model Intercomparison Project (BMIP) – a platform for model development, evaluation, and uncertainty assessment

Rotation of floating particles in submesoscale cyclonic and anticyclonic eddies: a model study for the southeastern Baltic Sea

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