Standing waves in the Gulf of Finland and their relationship to the basin-wide Baltic seiches (original) (raw)

Trends and extremes of wave fields in the north-eastern part of the Baltic Proper

Oceanologia, 2006

The paper analyses one of the longest contemporary wave measurements in the northern Baltic Sea, performed at Almagrundet 1978-2003. This record contains the roughest instrumentally measured wave conditions (significant wave height = c. 7.8 m) in the northern Baltic Proper until December 2004. The data for the years 1979-95, the period for which the data are the most reliable, show a linear rising trend of 1.8% per annum in the average wave height. The seasonal variation in wave activity follows the variation in wind speed. The monthly mean significant wave height varies from 0.5 m in May-July to 1.3-1.4 m in December-January. No corrections have been made in the analysis to compensate for missing values, for their uneven distribution, or for ice cover.

Wave climate in the Arkona Basin, the Baltic Sea

2012

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 H S = 4.46 m occurred on 3 November 1995. The wave height exhibits no long-term trend but reveals modest interannual (about 12 % of the longterm 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. Although the predominant SW winds usually excite the roughest wave conditions in the NE and Southeastern (SE) Baltic Proper (Schmager et al., 2008; Soomere et al., 2008), the wave climate in the SW Baltic is equally important. This Published by Copernicus Publications on behalf of the European Geosciences Union. Ocean Sci., 8, 287-300, 2012 www.ocean-sci.net/8/287/2012/

Wave regime differences along the eastern coast of the Baltic Proper

2008

An effort is made to identify the basic features of subdecadal and decadal changes in the wave climate at different locations in the eastern sector of the Baltic Proper based on the annual mean wave height. Comparison of Vilsandi and Almagrundet data from the northern Baltic Proper with visual observations from the Lithuanian coast during 1993-2005 shows that short-term variations (1-3 years) of the annual mean wave height have a similar nature at all sites but trends of decadal and subdecadal variability are very different in different parts of the Baltic Proper.

Spatial variations in the wave climate change in the eastern part of the Baltic Sea

Journal of Coastal Research

Zaitseva-Pärnaste, I., Soomere, T. and Tribštok, O., 2011. Spatial variations in the wave climate change in the eastern part of the Baltic Sea. The study presents new evidence of large spatial variations in wave properties along the eastern coast of the Baltic Sea. The short-term (1–3 years) interannual variability of the annual mean wave height is almost coherent along the entire eastern coast in 1958–1986. This coherence is completely lost from about 1987: since then the annual mean wave height at Narva-Jõesuu is in anti-phase with this height in the Baltic Proper. Also, in 1954– 1957 the mean wave height in the eastern part of the Baltic Proper gradually decreases but rapidly increases in the Gulf of Finland. The decadal course of wave activity match relatively well each other at Nida and Vilsandi until about 1992, after which the annual mean wave height behavior is completely different at these sites. The largest difference between the long-term course in the wave height is foun...

Wind-Driven, Coastal-Trapped Waves off the Island of Gotland, Baltic Sea

Journal of Physical Oceanography, 1998

An analysis is presented of repeated density and current profiles and recording current meter (RCM) data collected off the northwest coast of Gotland Island (Baltic Sea) during the late summer and fall of 1977. Large, low-frequency fluctuations were found in alongshore flow and isopycnal displacements and were significantly correlated with winds observed at Gotland's west coast. The best correlations were found with winds from the island's southern tip rather than with local winds. Coherence was high between RCM current fluctuations at 70 and at 90 m (100 m water depth, 4 km from the coast), whereby flow at 90 m led flow at 70 m. An EOF analysis of profile observations showed a 7-day, baroclinic wave with a two-and a three-layer current structure ''trapped'' in the coastal zone. The time series of the (weaker) three-layer mode was found to lag that of the (stronger) two-layer mode by about one day.

The wave climate and its seasonal variability in the northeastern Baltic Sea

Estonian Journal of Earth Sciences, 2010

The basic features of wave properties in the Baltic Sea and their seasonal variations are estimated by the use of a highresolution version (3 miles) of the wave model, WAM, driven by adjusted geostrophic winds for 1970-2007 under ice-free conditions. The model qualitatively reproduces the time series of the sea state and adequately replicates the seasonal patterns of wave intensity and the probability distribution functions for different wave heights in both offshore and coastal regions of the northern Baltic Proper and the Gulf of Finland. The areas of the largest overall wave activity are located in the eastern parts of the Bothnian Sea and northern Baltic Proper, south of Gotland, and in the Arkona Basin. The windiest season (September-February) and the time with the largest measured or modelled wave activity (October-March) occur with a time lag of 0.5-2 months.

Changes in wave dynamics at the south-eastern coast of the Baltic Proper during 1993―2008

Using data gathered by visual wave observations at three Lithuanian coastal observation sites during 1993-2008, we make an attempt to relate the recent changes in the intensity of coastal processes on the Lithuanian coast to changes in the local wave regime. There exist considerable interannual variations in the overall wave activity but no statistically significant trends in wave heights for the study period. The directional distribution of wave approach directions has become considerably narrower since about 2002. This feature is most prominent at Palanga where since 2002 almost all waves have approached from SW. This change apparently leads to a decrease in the sediment supply to the Curonian Spit and to a certain starvation of the Lithuanian coast.

Extreme waves and wave events in the Baltic Sea

Records of free-surface elevations from the Polish territorial waters are analyzed with emphases on the presence of extreme waves, wave groups and extreme wave events occurring in the Baltic Sea. The results are applied to derive extreme wave statistics and to eventually indicate periods and areas where extreme waves occur more frequently.

Natural and anthropogenic wave forcing in the Tallinn Bay, Baltic Sea

2003

The Tallinn Bay is a 10x20-km semi-enclosed area of the Gulf of Finland. Since tidal currents are negligible in this area, wind waves and local currents that both cause moderate near-bottom velocities off shoreline govern the beach processes. In recent years, high-speed ship traffic has increased considerably and amounts to 70 traverse per day. The ships frequently sail with speeds close to the critical velocity. Comparison of a long-term reconstruction of wind wave climate with the direct ship wave measurement shows that, in the coastal zone of the bay the mean energy of ship waves is 7-10% from the bulk wave energy and waveinduced power as high as 40% from the bulk wave power. The annual maximum of significant wind wave heights is frequently 4. 5 m (periods 5-6 S) whereas fast ferries generate waves with the heights about 1 m. The highest component of ship wake has frequently periods 10-15 S and causes unusually high nearbottom velocities at the depths of 5-20 m. Thus, the wake of fast ferries is a new forcing component of vital impact on the local ecosystem that may cause considerable intensification of beach processes as well as enhanced vertical mixing in the water body and have significant influence on the aquatic wildlife.

Numerical modeling of the wave climate in the southern Baltic Sea

Journal of coastal research, 2001

The numerical spectral wave generation and propagation model WAVAD was used to derive the wave climate over 19 years at four locations in the southern Baltic Sea, namely in the Pomeranian Bay, and outside the Polish, Lithuanian, and Latvian coasts. One-, 10-, and 50-year wave heights were estimated based on the obtained wave climates. Quantitative knowledge about wave climate is important when modeling regional fluxes of sediment and matter, which is the main objective of the BASYS-project, under which this study was carried out. A validation of the model against wave measurements obtained at three locations in the Baltic Sea showed satisfactory model predictions of significant wave height and moderately accurate predictions of peak spectral wave period and direction. Also, the frequency spectrum could be calculated with fair accuracy, whereas the agreement between predicted and measured directional-frequency spectra was less good. The latter most likely depends on the "pre-determined" modeled spectral shape (WAVAD being a 2 nd-generation model), a somewhat crude description of spatial and temporal variation of the wind field, and the method used to derive the spectrum from measurements.