scholarly journals Brief communication: Characteristic properties of extreme wave events in the Baltic Sea

2017 ◽  
Author(s):  
Jan-Victor Björkqvist ◽  
Laura Tuomi ◽  
Niko Tollman ◽  
Antti Kangas ◽  
Heidi Pettersson ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Wave Height ◽  
Significant Wave Height ◽  
Wave Steepness ◽  
Extreme Wave ◽  
The Baltic Sea ◽  
Baltic Proper ◽  
Wave Conditions ◽  
The Baltic ◽  
Proper Wave

Abstract. A significant wave height of 7 m has been measured five times by the northern Baltic Proper wave buoy in the Baltic Sea, exceeding 8 m twice (2004 & 2017). We classified these storms into two groups by duration and wave steepness. Interestingly, the two highest events exhibited opposite properties, with the 2017 event being the longest storm on record. This storm is also the first where the harshest wave conditions were modelled to occur in the western part of the Baltic Proper. The metrics quantifying the storm's duration and steepness might aid in issuing warnings for extreme wave conditions.

scholarly journals Brief communication: Characteristic properties of extreme wave events observed in the northern Baltic Proper, Baltic Sea

2017 ◽  
Vol 17 (9) ◽  
pp. 1653-1658 ◽  
Author(s):  
Jan-Victor Björkqvist ◽  
Laura Tuomi ◽  
Niko Tollman ◽  
Antti Kangas ◽  
Heidi Pettersson ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Wave Height ◽  
Significant Wave Height ◽  
Wave Steepness ◽  
Extreme Wave ◽  
The Baltic Sea ◽  
Baltic Proper ◽  
Wave Conditions ◽  
The Baltic ◽  
Proper Wave

Abstract. A significant wave height of 7 m has been measured five times by the northern Baltic Proper wave buoy in the Baltic Sea, exceeding 8 m twice (2004 and 2017). We classified these storms into two groups by duration and wave steepness. Interestingly, the two highest events exhibited opposite properties, with the 2017 event being the longest storm on record. This storm is also the first where the harshest wave conditions were modelled to occur in the western part of the Baltic Proper. The metrics quantifying the storm's duration and steepness might aid in issuing warnings for extreme wave conditions.

scholarly journals Wave climatology in the Arkona Basin, the Baltic Sea

2011 ◽  
Vol 8 (6) ◽  
pp. 2237-2270 ◽  
Author(s):  
T. Soomere ◽  
R. Weisse ◽  
A. Behrens
Keyword(s):  
Baltic Sea ◽  
Wave Height ◽  
Significant Wave Height ◽  
Wave Climate ◽  
Extreme Wave ◽  
The Baltic Sea ◽  
Significant Wave ◽  
Wave Heights ◽  
The Baltic

Abstract. The basic features of the wave climate in the South-Eastern Baltic Sea are studied based on available long-term measurements and simulations. The analysis of average, typical and extreme wave conditions, frequency of occurrence of different wave parameters, variations in wave heights from weekly to decadal scales, etc., is performed based on waverider measurements at the Darss Sill since 1991. The measured climatology is compared against numerical simulations with the WAM wave model driven by downscaled reanalysis of wind fields for 1958–2002 and by adjusted geostrophic winds for 1970–2007. The wave climate in this region is typical for semi-enclosed basins of the Baltic Sea. The maximum wave heights are about half of those in the Baltic Proper. The overall reliably recorded maximum significant wave height HS =4.46 m occurred during a severe S-SW storm in 1993 when the 10-min average wind speed reached 28 m s−1. The long-term average significant wave height (0.75 m) shows modest interannual (about 12 % of the long-term mean) and substantial seasonal variation. The wave periods are mostly concentrated in a narrow range of 2.5–4 s and their distribution is almost constant over decades. The role of remote swell is very small. The annual wave properties show large interannual variability but no long-term trends in average and extreme wave heights can be observed.

scholarly journals Better Baltic Sea wave forecasts: improving resolution or introducing ensembles?

Ocean Science ◽  
2018 ◽  
Vol 14 (6) ◽  
pp. 1435-1447
Author(s):  
Torben Schmith ◽  
Jacob Woge Nielsen ◽  
Till Andreas Soya Rasmussen ◽  
Henrik Feddersen
Keyword(s):  
Baltic Sea ◽  
Wave Height ◽  
Spectral Resolution ◽  
Significant Wave Height ◽  
Initial Conditions ◽  
A Priori ◽  
The Baltic Sea ◽  
Significant Wave ◽  
Operational Forecasts ◽  
The Baltic

Abstract. The performance of short-range operational forecasts of significant wave height (SWH) in the Baltic Sea is evaluated. Forecasts produced by a base configuration are intercompared with forecasts from two improved configurations: one with improved horizontal and spectral resolution and one with ensembles representing uncertainties in the physics of the forcing wind field and the initial conditions of this field. Both of the improved forecast classes represent an almost equal increase in computational costs. Therefore, the intercomparison addresses the question of whether more computer resources would be more favorably spent on enhancing the spatial and spectral resolution or, alternatively, on introducing ensembles. The intercomparison is based on comparisons with hourly observations of significant wave height from seven observation sites in the Baltic Sea during the 3-year period from 2015 to 2017. We conclude that for most wave measurement sites, the introduction of ensembles enhances the overall performance of the forecasts, whereas increasing the horizontal and spectral resolution does not. These sites represent offshore conditions, in that they are well exposed from all directions, are a large distance from the nearest coast and in deep water. Therefore, there is the a priori expectation that a detailed shoreline and bathymetry will not have any impact. Only at one site do we find that increasing the horizontal and spectral resolution significantly improves the forecasts. This site is situated in nearshore conditions, close to land and a nearby island, and is therefore shielded from many directions. Consequently, this study concludes that to improve wave forecasts in offshore areas, ensembles should be introduced. For near shore areas, in comparison, the study suggests that additional computational resources should be used to increase the resolution.

scholarly journals Better Baltic Sea wave forecasts: Improving resolution or introducing ensembles?

2018 ◽  
Author(s):  
Torben Schmith ◽  
Jacob Woge Nielsen ◽  
Till Andreas Soya Rasmussen
Keyword(s):  
Baltic Sea ◽  
Wave Height ◽  
Spectral Resolution ◽  
Significant Wave Height ◽  
Initial Conditions ◽  
A Priori ◽  
The Baltic Sea ◽  
Significant Wave ◽  
Operational Forecasts ◽  
The Baltic

Abstract. The performance of short-range operational forecasts of significant wave height in the Baltic Sea in three different configurations is evaluated. Forecasts produced by a base configuration are inter-compared with forecasts from two improved configurations: one with improved horizontal and spectral resolution and one with ensembles representing uncertainties in the physics of the forcing wind field and the initial conditions of this field. Both the improved forecast classes represent an almost equal increase in computational costs. The inter-comparison therefore addresses the question: would more computer resources most favorably be spent on enhancing the spatial and spectral resolution or, alternatively, on introducing ensembles? The inter-comparison is based on comparisons with hourly observations of significant wave height from seven observation sites in the Baltic Sea during the three-year period 2015–2017. We conclude that for most stations, the introduction of ensembles enhances the overall performance of the forecasts, whereas increasing the horizontal and spectral resolution does not. These stations represent offshore conditions, well exposed from all directions with a large distance to the nearest coast and with a large water depth. Therefore, the detailed shoreline and bathymetry is also a priori not expected to have any impact. Only for one station, we find that increasing the horizontal and spectral resolution significantly improved the forecasts. This station is situated in nearshore conditions, close to land, with a nearby island and therefore shielded from many directions. This study therefore concludes that to improve wave forecasts in offshore areas, ensembles should be introduced, while for nearshore areas better resolution may improve results.

scholarly journals Freak waves of different types in the coastal zone of the Baltic Sea

2010 ◽  
Vol 10 (9) ◽  
pp. 2021-2029 ◽  
Author(s):  
I. Didenkulova ◽  
C. Anderson
Keyword(s):  
Baltic Sea ◽  
Coastal Zone ◽  
Wave Height ◽  
Significant Wave Height ◽  
The Baltic Sea ◽  
Frequency Spectra ◽  
Freak Waves ◽  
Time Frequency ◽  
Significant Wave ◽  
The Baltic

Abstract. We present a statistical analysis of freak waves1 measured during the 203 h of observation on sea surface elevation at a location in the coastal zone of the Baltic Sea (2.7 m depth) during June–July 2008. The dataset contains 97 freak waves occurring in both calm and stormy weather conditions. All of the freak waves are solitary waves, 63% of them having positive shape, 17.5% negative shape and 19.5% sign-variable shape. It is suggested that the freak waves can be divided into two groups. Those of the first group, which includes 92% of the freak waves, have an amplification factor (ratio of freak wave height to significant wave height) which does not vary from significant wave height and has values largely within the range of 2.0 to 2.4; while for the second group, which contain the most extreme freak waves, amplification factors depend strongly on significant wave height and can reach 3.1. Analysis based on the Generalised Pareto distribution is used to describe the waves of the first group and lends weight to the identification of the two groups. It is suggested that the probable mechanism of the generation of freak waves in the second group is dispersive focussing. The time-frequency spectra of the freak waves are studied and dispersive tracks, which can be interpreted as dispersive focussing, are demonstrated. 1 taken to be waves whose height is 2 or more times greater than the significant wave height

scholarly journals Wave conditions in the Baltic Proper and in the Gulf of Finland during windstorm Gudrun

2008 ◽  
Vol 8 (1) ◽  
pp. 37-46 ◽  
Author(s):  
T. Soomere ◽  
A. Behrens ◽  
L. Tuomi ◽  
J. W. Nielsen
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Weather Forecast ◽  
Gulf Of Finland ◽  
Marine Research ◽  
Significant Wave ◽  
Baltic Proper ◽  
Wave Conditions ◽  
The Baltic ◽  
The Gulf Of Finland

Abstract. Wave conditions in the northern Baltic Proper during windstorm Erwin/Gudrun (January 2005) are analysed based on in situ measurements in three locations and output of operational wave models from the German Weather Forecast Service, the Danish Meteorological Institute and the Finnish Institute of Marine Research. The measured significant wave height reached 7.2 m in the northern Baltic Proper and 4.5 m in the Gulf of Finland. The roughest wave conditions, estimated from the comparison of the forecast and measured data, occurred remote from the sensors, off the coasts of Saaremaa and Latvia where the significant wave height was about 9.5 m. Peak periods exceeded 12 s in a large part of the northern Baltic Proper and in the central part of the Gulf of Finland.

scholarly journals Long-term spatial variations in the Baltic Sea wave fields

Ocean Science ◽  
2011 ◽  
Vol 7 (1) ◽  
pp. 141-150 ◽  
Author(s):  
T. Soomere ◽  
A. Räämet
Keyword(s):  
Baltic Sea ◽  
Spatial Variations ◽  
Extreme Wave ◽  
The Baltic Sea ◽  
Wave Fields ◽  
Wave Heights ◽  
The Baltic ◽  
Wave Properties ◽  
Sea Wave

Abstract. This study focuses on spatial patterns in linear trends of numerically reconstructed basic wave properties (average and extreme wave heights, wave periods) in the Baltic Sea under the assumption of no ice cover. Numerical simulations of wave conditions for 1970–2007, using the WAM wave model and adjusted geostrophic winds, revealed extensive spatial variations in long-term changes in both average and extreme wave heights in the Baltic Sea but almost no changes in the basinwide wave activity and wave periods. There has been a statistically significant decrease in the annual mean significant wave height by more than 10% between the islands of Öland and Gotland and in the southward sea area, and a substantial increase to the south-west of Bornholm, near the coast of Latvia, between the Åland Archipelago and the Swedish mainland, and between the Bothnian Sea and the Bothnian Bay. Variations in extreme wave heights (defined as the threshold for 1% of the highest waves each year) show similar patterns of changes. In several areas the trends in average and extreme wave heights are different. Such a complicated pattern of changes indicates that (i) different regions of the Baltic Sea basin have experienced widespread but essentially different changes in wind properties and (ii) many seemingly controversial trends and variations established in wave properties at different sites in the recent past may reflect the natural spatial variability in the Baltic Sea wave fields.

Projected Changes in Wave Conditions in the Baltic Sea by the end of 21st Century and the Corresponding Shoreline Changes

2016 ◽  
Vol 75 (sp1) ◽  
pp. 1012-1016 ◽  
Author(s):  
Ülo Suursaar ◽  
Hannes Tõnisson ◽  
Victor Alari ◽  
Urmas Raudsepp ◽  
Henri Rästas ◽  
...  
Keyword(s):  
Baltic Sea ◽  
21St Century ◽  
The Baltic Sea ◽  
Shoreline Changes ◽  
Wave Conditions ◽  
The Baltic ◽  
Projected Changes

scholarly journals Nutrient transports in the Baltic Sea – results from a 30-year physical–biogeochemical reanalysis

2017 ◽  
Vol 14 (8) ◽  
pp. 2113-2131 ◽  
Author(s):  
Ye Liu ◽  
H. E. Markus Meier ◽  
Kari Eilola
Keyword(s):  
Baltic Sea ◽  
Cross Sections ◽  
Ocean Model ◽  
Optimal Interpolation ◽  
Nutrient Concentrations ◽  
Biogeochemical Model ◽  
The Baltic Sea ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. Long-term oxygen and nutrient transports in the Baltic Sea are reconstructed using the Swedish Coastal and Ocean Biogeochemical model (SCOBI) coupled to the Rossby Centre Ocean model (RCO). Two simulations with and without data assimilation covering the period 1970–1999 are carried out. Here, the weakly coupled scheme with the Ensemble Optimal Interpolation (EnOI) method is adopted to assimilate observed profiles in the reanalysis system. The reanalysis shows considerable improvement in the simulation of both oxygen and nutrient concentrations relative to the free run. Further, the results suggest that the assimilation of biogeochemical observations has a significant effect on the simulation of the oxygen-dependent dynamics of biogeochemical cycles. From the reanalysis, nutrient transports between sub-basins, between the coastal zone and the open sea, and across latitudinal and longitudinal cross sections are calculated. Further, the spatial distributions of regions with nutrient import or export are examined. Our results emphasize the important role of the Baltic proper for the entire Baltic Sea, with large net transport (export minus import) of nutrients from the Baltic proper into the surrounding sub-basins (except the net phosphorus import from the Gulf of Riga and the net nitrogen import from the Gulf of Riga and Danish Straits). In agreement with previous studies, we found that the Bothnian Sea imports large amounts of phosphorus from the Baltic proper that are retained in this sub-basin. For the calculation of sub-basin budgets, the location of the lateral borders of the sub-basins is crucial, because net transports may change sign with the location of the border. Although the overall transport patterns resemble the results of previous studies, our calculated estimates differ in detail considerably.

scholarly journals Wave climate in the Arkona Basin, the Baltic Sea

Ocean Science ◽  
2012 ◽  
Vol 8 (2) ◽  
pp. 287-300 ◽  
Author(s):  
T. Soomere ◽  
R. Weisse ◽  
A. Behrens
Keyword(s):  
Baltic Sea ◽  
Wave Height ◽  
Wave Model ◽  
Wave Climate ◽  
Wind Fields ◽  
The Baltic Sea ◽  
Wave Heights ◽  
The Baltic ◽  
Basic Features

Abstract. The basic features of the wave climate in the Southwestern Baltic Sea (such as the average and typical wave conditions, frequency of occurrence of different wave parameters, variations in wave heights from weekly to decadal scales) are established based on waverider measurements at the Darss Sill in 1991–2010. The measured climate is compared with two numerical simulations with the WAM wave model driven by downscaled reanalysis of wind fields for 1958–2002 and by adjusted geostrophic winds for 1970–2007. The wave climate in this region is typical for semi-enclosed basins of the Baltic Sea. The maximum wave heights are about half of those in the Baltic Proper. The maximum recorded significant wave height HS =4.46 m occurred on 3 November 1995. The wave height exhibits no long-term trend but reveals modest interannual (about 12 % of the long-term mean of 0.76 m) and substantial seasonal variation. The wave periods are mostly concentrated in a narrow range of 2.6–4 s. Their distribution is almost constant over decades. The role of remote swell is very small.

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