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1

Currents and waves in the northern Gulf of Riga: measurement and long-term hindcast

Suursaar Ű., Kullas T., Aps R.

Oceanologia

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2012

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No. 54 (3)

421-447

EN

Based on measurements of waves and currents obtained for a period of 302 days with a bottom-mounted RDCP (Recording Doppler Current Profiler) at two differently exposed locations, a model for significant wave height was calibrated separately for those locations; in addition, the Gulf of Riga-Väinameri 2D model was validated, and the hydrodynamic conditions were studied. Using wind forcing data from the Kihnu meteorological station, a set of current, water exchange and wave hindcasts were obtained for the period 1966-2011. Current patterns in the Gulf and in the straits were wind-dependent with characteristic wind switch directions. The Matsi coast was prone to upwelling in persistent northerly wind conditions. During the hindcast period, currents increased along the Ko~iguste coast and in the Suur Strait, waves decreased noticeably off Ko~iguste but fluctuated without a clear linear trend near Matsi. The spatially contrasting results for differently exposed coasts were related to the corresponding variations in local wind conditions and to changes in atmospheric circulation patterns over northern Europe.

2

Waves, currents and sea level variations along the Letipea - Sillamäe coastal section of the southern Gulf of Finland

Suursaar Ű.

Oceanologia

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2010

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No. 52 (3)

391-416

EN

Variations in the hydrodynamic conditions were studied on the basis of 336 days of measurements with a Doppler current profiler. With wave data as a calibration reference, a semi-empirical hindcast of wave parameters is presented in the fetch-limited near-shore area for the period 1966-2008. A resultant 4-6 cm s-1 westward current dominated along the coast. Occasional fast sub-surface westward currents under modest wind forcing, as well as asymmetrical vertical profiles for westward and eastward currents indicated the influence of upwelling-related baroclinic coastal jets. The average frequency of upwelling was estimated at 17%; some of the events were identified in near-homothermic winter conditions on the basis of salinity and multi-layer flow records. While the mean sea level trend at Narva-Jo~esuu roughly approximated the global estimates for 1899-2009, the annual maximum sea level increase was 5-8 mm yr-1. Both mean and maximum wave heights declined as a result of decreasing winds from the north.

3

Decadal variations in wave heights off Cape Kelba, Saaremaa Island, and their relationships with changes in wind climate

Suursaar Ű., Kullas T.

Oceanologia

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2009

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No. 51 (1)

39-61

EN

Based on wind data from the Vilsandi meteorological station and a 5-month calibration measurement with a bottom-mounted Recording Doppler Current Profiler (RDCP), a semi-empirical hindcast of wave parameters near the quickly developing accumulative Kelba Spit is presented for the period 1966-2006. The significant wave heights with a gross mean value of 0.56 m exhibited some quasiperiodic cycles, with the last high stage in 1980-95 and a decreasing overall trend of -0.001 m per year. At the same time, both the frequency and intensity of high wave events showed rising trends, and the mean wave heights during winter (December to February) increased as well. As the study area has the longest fetches in westerly directions, the discussed tendencies in wave conditions are sensitive to regional changes in the wind climate and can be related to a decrease in the local average wind speed on the one hand, but an intensification of westerly winds, storm events and the wintertime NAO index on the other. The roughest wave storms on record were associated with prominent W-storms on 2 November 1969 and 9 January 2005; a few other extreme wind events (e.g. in 1967, 1999, 2001), however, did not yield equally prominent waves.

4

Spatio-temporal variations in hydro-physical and -chemical parameters during a major upwelling event off the southern coast of the Gulf of Finland in summer 2006

Suursaar Ű., Aps R.

Oceanologia

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2007

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No. 49 (2)

209-228

EN

The objective of the paper is to document and examine the major upwelling event that occurred along the northern coast of Estonia in August 2006. With a horizontal extension of 360 km, the event was caused by persistent easterlies and was noticed by a large number of holidaymakers, as it turned the temperature of the coastal sea to a chilly 5-10°C for about a month. In situ measurements from an RDCP current profiler revealed an along-wind coastal jet of up to 60 cm s-1 and a weak near-bottom countercurrent. The depths of the pycnocline and nutricline rose. The maximum drop in water temperature was 16°C, that of salinity was 3.6 PSU. Analysis of satellite images confirmed the large extension and the prominence of the event.