V. Berzins (1), U. Bethers (2), J.Sennikovs (2)
(1) Latvian Fisheries Research Institute, (2) Laboratory for Mathematical Modelling of Environmental and Technological Processes, University of Latvia.
jsenniko@com.latnet.lv/Fax: +371-7615711
 

Definitive two-layer stratification exists in the Gulf of Riga during April-November allowing formation and propagation of internal waves on the interface.
Several series of continuous (up to 2-days long) temperature and salinity measurements at the depth of pycnocline were performed in the Gulf by a CTD sound with time resolution 15 seconds. Simultaneous vertical TS profiling have been carried out.
Amplitude and main frequencies of oscillations on the interface have been determined. The trains of short-period (2-4 min.) internal waves as well as internal seiches with period of approximately 12 hours have been resolved. Determined period of internal seiches is in agreement with that calculated from basin geometry while period of short waves corresponds to that obtained from local Brunt-Väisälä frequency.
Model of vertical TS structure has been applied for the measurement periods. Meteorological data of high time resolution including in-situ measurements has been used for model forcing. Model results give the overall trend of the depth of pycnocline simplifying removal of this trend from the measurement data and resolving of the periodic internal oscillations.