Northern Water Problems Institute (NWPI),

1. Strongly non-linear waves in lakes:generation, transformation and meromixis(project INTAS–03-51-3728) Northern Water Problems Institute (NWPI), Karelian Scientific Centre, Russian Academy of Sciences, Petrozavodsk, Russia

2. Task 1. Data collection and analysis. Further development Source of data: • field measurements in Bol’shoe Onego Bay, Lake Onega (July 2005) • field measurements in the Bol’shoe Onego Bay (Osetrovskaya Bank), Lake Onega (May-September 1977) • field measurements in Lizhemskaya Guba, Bol’shoe Onego Bay, Lake Onega (August-September 1987)

4. Red box: 1-5 – stations of field measurements in 2004-2005; 6 – RCM (1977), 7 – TR (1977) Blue box: 1, 2, 4, 5 – TRs; 3 – RCM; 6 – АЦИТТ [ADCTM]; 7 – БПВ [LPCM] (АЦИТТ – Autonomic Digital Current & Temperature Meter; БПВ – Letter-Printing Current Meter)

5. Performing field work.

6. Wind speed and directionduring the field campaign 2005

7. Development of the water temperature in time at st. 2: 13 July 2005, 19:50 - 23 July 2005, 09:50 (a); depth of 14C isotherm location calculated from thermistor chain data for the same period (b).

8. Development of the water temperature in time at st. 5: 13 July 2005, 22:20 - 23 July 2005, 09:20 (a); location of 12C isotherm calculated from thermistor chain data for the same period (b).

9. Development of the water temperature in time at st. 4: 14 July 2005, 09:00 - 23 July 2005, 09:00 (absciss axis shows a number of profiles, 96 of which correspond to one day) (a); location of 12C isotherm calculated from vertical profiling data for the same period (b).

10. The development of the Väisäla-Brent frequency in time at station 4, 14 July 2005, 09:00 - 23 July 2005, 09:00.

11. PSD calculated for 14C DIL, st. 2: the Curve-Fit Graph (a), the residuals (b), and the Fourier spectrum (c). Horizontal lines mark five significance levels (50%, 90%, 95%, 99%, and 99.9%). The table presents corresponding periods.

12. Temporal evolution of the vertical thermal structure and currents at the Osetrovskaya Banka [shoal] during the period 27 May – 11 October 1977 (data from thermistor chain registrations). Depth of location 30 m.

19. August-September 1987: Development of water temperature inLizhemskaya Guba, Bol’shoe Onego Bay, Lake Onega

21. The water temperature development at Station 2, depth 58 m.

23. St. 1

24. St. 2

25. Depth of 11.85°C location at stations 1 and 2.

26. St. 1,depth of 11.85°Cisotherm location,28.08.1987, 20:55 – 31.08.1987, 16:35

27. St. 2,depth of 11.85°Cisotherm location,28.08.1987, 20:55 – 31.08.1987, 16:35

28. St. 1,depth of 11.85°Cisotherm location,01.09.1987, 3:25 – 05.09.1987, 8:05

29. St. 2,depth of 11.85°C isotherm location,01.09.1987, 3:25 – 05.09.1987, 8:05

30. Evolution of the vertical temperature profile at St. 2during the 29 – 30.08.1987 period.

32. The development of the Väisäla-Brent frequency in time at stations 1, 2, and 4 during the 28.08 – 05.09.1987 period.

33. Preliminary conclusions • The development of non-linear internal waves may eventually invoke vertical mixing within the lake thermocline (data 2004); • This is not a synoptical event (data 1997); • The wave activity may lead to the complete mixing of a water column mostly in late summer when the stratification becomes weaker (data 1977 – indirectly & 1987); • [not for eyes of Brussels] The selection of the measurement sites/s is very important issue (data 1977)

34. Thanks for your attention!