northern water problems institute (nwpi),
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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. Task 1. Data collection and analysis. Further development - PowerPoint PPT PresentationTRANSCRIPT
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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
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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)
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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)
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Performing field work.
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Win
d s
pe
ed
, m
·s-1
0
2
4
6
8
10
12
13.0
7.0
5
14.0
7.0
5
15.0
7.0
5
16.0
7.0
5
17.0
7.0
5
18.0
7.0
5
19.0
7.0
5
20.0
7.0
5
21.0
7.0
5
22.0
7.0
5
23.0
7.0
5
24.0
7.0
5
Win
d D
ire
ctio
n,
de
g
0
60
120
180
240
300
360
Wind speed and direction during the field campaign 2005
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a
13.0
7.05
14.0
7.05
15.0
7.05
16.0
7.05
17.0
7.05
18.0
7.05
19.0
7.05
20.0
7.05
21.0
7.05
22.0
7.05
23.0
7.05
24.0
7.05
Te
mp
era
ture
, 0 C
4
6
8
10
12
14
16
18
20
22
24
1.5 m 3.5 m 5.5 m 7.5 m 9.5 m 11.5 m 13.5 m 15.5 m 17.5 m 19.5 m
b
13.0
7.05
14.0
7.05
15.0
7.05
16.0
7.05
17.0
7.05
18.0
7.05
19.0
7.05
20.0
7.05
21.0
7.05
22.0
7.05
23.0
7.05
24.0
7.05
De
pth
, m
0
5
10
15
20
Development of the water temperature in time at st. 2: 13 July 2005, 19:50 - 23 July 2005, 09:50 (a); depth of 14C isotherm location calculated from thermistor chain data for the same period (b).
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a
13.0
7.05
14.0
7.05
15.0
7.05
16.0
7.05
17.0
7.05
18.0
7.05
19.0
7.05
20.0
7.05
21.0
7.05
22.0
7.05
23.0
7.05
24.0
7.05
Te
mp
era
ture
, 0 C
2
4
6
8
10
12
14
16
18
20
22
243.4 m 4.4 m 5.4 m 6.4 m 7.4 m 8.4 m 9.4 m 11.3 m 13.3 m 15.3 m 17.3 m 19.3 m 21.3 m 23.3 m 25.3 m 27.3 m 29.3 m 31.3 m
b
13.0
7.05
14.0
7.05
15.0
7.05
16.0
7.05
17.0
7.05
18.0
7.05
19.0
7.05
20.0
7.05
21.0
7.05
22.0
7.05
23.0
7.05
24.0
7.05
De
pth
, m
0
5
10
15
20
25
Development of the water temperature in time at st. 5: 13 July 2005, 22:20 - 23 July 2005, 09:20 (a); location of 12C isotherm calculated from thermistor chain data for the same period (b).
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13.0
7.05
14.0
7.05
15.0
7.05
16.0
7.05
17.0
7.05
18.0
7.05
19.0
7.05
20.0
7.05
21.0
7.05
22.0
7.05
23.0
7.05
24.0
7.05
Dep
th, m
0
5
10
15
20
25
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 12C isotherm calculated from vertical profiling data for the same period (b).
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The development of the Väisäla-Brent frequency in time at station 4, 14 July 2005, 09:00 - 23 July 2005, 09:00.
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Rank 2 Eqn 6870 Chebyshev=>Std Polynomial Order 20r^2=0.94915981 DF Adj r^2=0.94877002 FitStdErr=0.8750996 Fstat=2557.7185
0 2e+05 4e+05 6e+05 8e+05Time index
0
2.5
5
7.5
10
12.5
15
17.5
20
De
pth
, m
0
2.5
5
7.5
10
12.5
15
17.5
20
De
pth
, m
Rank 2 Eqn 6870 Chebyshev=>Std Polynomial Order 20r^2=0.94915981 DF Adj r^2=0.94877002 FitStdErr=0.8750996 Fstat=2557.7185
0 2e+05 4e+05 6e+05 8e+05Time index
-3
-2
-1
0
1
2
3
Resid
uals
-3
-2
-1
0
1
2
3
Resid
uals
5090959999.9
9.425e-06
1.239e-05
1.5496e-05
1.8891e-05
2.2085e-05
2.3882e-05
2.6716e-05
3.0105e-05
3.2529e-05
3.5997e-05
4.2355e-05
0 1e-05 2e-05 3e-05 4e-05 5e-05Frequency, Hz
0
50
100
150
200
250
300
350
PS
D S
SA
, m
2 /H
z
0
50
100
150
200
250
300
350
Frequency, Hz Period, h PSD SSA
9,43E-06 29,5 187,14
1,24E-05 22,4 319,44
1,55E-05 17,9 346,95
1,89E-05 14,7 38,71
2,21E-05 12,6 92,99
2,39E-05 11,6 121,08
2,67E-05 10,4 25,23
3,01E-05 9,2 39,89
3,25E-05 8,5 20,99
3,60E-05 7,7 36,67
4,24E-05 6,6 19,30
PSD calculated for 14C 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.
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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.
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0
2
4
6
8
10
12
14
16
18
20
22
24
26
09
.07
.19
77
00
:00
10
.07
.19
77
00
:00
11
.07
.19
77
00
:00
12
.07
.19
77
00
:00
13
.07
.19
77
00
:00
14
.07
.19
77
00
:00
15
.07
.19
77
00
:00
16
.07
.19
77
00
:00
17
.07
.19
77
00
:00
18
.07
.19
77
00
:00
19
.07
.19
77
00
:00
20
.07
.19
77
00
:00
21
.07
.19
77
00
:00
22
.07
.19
77
00
:00
23
.07
.19
77
00
:00
24
.07
.19
77
00
:00
25
.07
.19
77
00
:00
26
.07
.19
77
00
:00
27
.07
.19
77
00
:00
28
.07
.19
77
00
:00
29
.07
.19
77
00
:00
30
.07
.19
77
00
:00
Dep
th, m
15
16
17
18
19
20
21
22
23
19
.07
.19
77
00
:00
19
.07
.19
77
06
:00
19
.07
.19
77
12
:00
19
.07
.19
77
18
:00
20
.07
.19
77
00
:00
20
.07
.19
77
06
:00
Dep
th, m
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Izo_11,5Detrend Data
0 20000 40000 60000 80000Time index
17
18
19
20
21
22
23
17
18
19
20
21
22
23
Izo_11,5Fourier Frequency Spectrum
50
90
95
99
99.9
3.5484e-05
9.7472e-05 0.00018197 0.00020506
0 0.0002 0.0004 0.0006 0.0008Frequency
0
5
10
15
20
25
PS
D S
SA
0
5
10
15
20
25
Frequency, Hz
PSD SSA Period, h
3,55E-05 24,4 7,8
9,75E-05 1,5 2,8
0,000182 1,4 1,5
0,000205 1,0 1,4
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Izo_11,5Rank 3 Eqn 6820 Chebyshev Polynomial Order 20
r^2=0.93126573 DF Adj r^2=0.91882246 FitStdErr=0.28249478 Fstat=79.260384
0 20000 40000 60000 80000X
17
18
19
20
21
22
17
18
19
20
21
22
-0.5
0
0.5
Res
idua
ls [5
2]
-0.5
0
0.5
Res
idua
ls [5
2]Residuals
Fourier Frequency Spectrum
50
90
95
99
9.432e-05
0.00012523
0.0001816
0.00020517
0.00026528
0.0005811
0 0.0002 0.0004 0.0006 0.0008Frequency
0
0.25
0.5
0.75
1
1.25
1.5
PS
D S
SA
0
0.25
0.5
0.75
1
1.25
1.5
Frequency, Hz PSD SSA Period, h
9,43E-05 0,5 2,9
0,000125 0,8 2,2
0,000182 1,3 1,5
0,000205 1,0 1,4
0,000265 0,5 1,0
0,000581 0,5 0,5
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0
2
4
6
8
10
12
14
16
18
20
22
24
26
09
.07
.19
77
00
:00
10
.07
.19
77
00
:00
11
.07
.19
77
00
:00
12
.07
.19
77
00
:00
13
.07
.19
77
00
:00
14
.07
.19
77
00
:00
15
.07
.19
77
00
:00
16
.07
.19
77
00
:00
17
.07
.19
77
00
:00
18
.07
.19
77
00
:00
19
.07
.19
77
00
:00
20
.07
.19
77
00
:00
21
.07
.19
77
00
:00
22
.07
.19
77
00
:00
23
.07
.19
77
00
:00
24
.07
.19
77
00
:00
25
.07
.19
77
00
:00
26
.07
.19
77
00
:00
27
.07
.19
77
00
:00
28
.07
.19
77
00
:00
29
.07
.19
77
00
:00
30
.07
.19
77
00
:00
Dep
th, m
18,5
19,0
19,5
20,0
20,5
21,0
21,5
22,0
20
.07
.19
77
00
:00
20
.07
.19
77
06
:00
20
.07
.19
77
12
:00
20
.07
.19
77
18
:00
21
.07
.19
77
00
:00
21
.07
.19
77
06
:00
Dep
th, m
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Izo_11,5Detrend Data
0 20000 40000 60000 80000 1e+05Time index
18.5
19
19.5
20
20.5
21
21.5
22
18.5
19
19.5
20
20.5
21
21.5
22
Izo_11,5Fourier Frequency Spectrum
50
90
95
99
99.9
2.1633e-05
6.2746e-05
9.2459e-05
0.00014277
0 0.0002 0.0004 0.0006 0.0008Frequency
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
PS
D S
SA
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Frequency, Hz
PSD SSA
Period, h
2,16E-05 4,7 12,8
6,27E-05 2,0 4,4
9,25E-05 0,5 3,0
0,000143 1,1 1,9
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Izo_11,5Rank 3 Eqn 6820 Chebyshev Polynomial Order 20
r^2=0.87470349 DF Adj r^2=0.85604231 FitStdErr=0.21409614 Fstat=49.565585
0 20000 40000 60000 80000 1e+05X
18.5
19
19.5
20
20.5
21
21.5
18.5
19
19.5
20
20.5
21
21.5
-0.5
0
0.5
Res
idua
ls [5
3]
-0.5
0
0.5
Res
idua
ls [5
3]Residuals
Fourier Frequency Spectrum with tapering window
50
90
95
99
99.9
8.875e-05
0.00014256
0.00019435
0.000243 0.00034703
0 0.0002 0.0004 0.0006 0.0008Frequency
0
0.25
0.5
0.75
1
1.25
1.5
PS
D S
SA
0
0.25
0.5
0.75
1
1.25
1.5
PS
D S
SA
Frequency, Hz PSD SSA Period, h
8,88E-05 0,2 3,1
0,000143 1,3 1,9
0,000194 0,3 1,4
0,000243 0,2 1,1
0,000347 0,3 0,8
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August-September 1987: Development of water temperature in Lizhemskaya Guba, Bol’shoe Onego Bay, Lake Onega
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7 m
Cur
rent
vel
ocity
, cm
·s-1
-500
-400
-300
-200
-100
0
100
200
300
400
500
17 m
Cur
rent
vel
ocity
, cm
·s-1
-500
-400
-300
-200
-100
0
100
200
300
400
500
22 m
Cur
rent
vel
ocity
, cm
·s-1
-500
-400
-300
-200
-100
0
100
200
300
400
500
20.0
8.8
7
21.0
8.8
7
22.0
8.8
7
23.0
8.8
7
24.0
8.8
7
25.0
8.8
7
26.0
8.8
7
27.0
8.8
7
28.0
8.8
7
29.0
8.8
7
30.0
8.8
7
31.0
8.8
7
01.0
9.8
7
02.0
9.8
7
03.0
9.8
7
04.0
9.8
7
05.0
9.8
7
06.0
9.8
7
07.0
9.8
7
08.0
9.8
7
09.0
9.8
7
10.0
9.8
7
11.0
9.8
7
12.0
9.8
7
13.0
9.8
7
![Page 21: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/21.jpg)
The water temperature development at Station 2, depth 58 m.
![Page 22: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/22.jpg)
7 m (19.08.1987 18:50 - 13.09.1987 09:20)
Distance E, m
-40000 -20000 0 20000 40000 60000
Dis
tanc
e N
, m
-40000
-20000
0
20000
40000
60000
17 m (19.08.1987 18:40 - 13.09.1987 08:30)
Distance E, m
-60000 -40000 -20000 0 20000 40000
Dis
tanc
e N
, m
-40000
-20000
0
20000
40000
60000
22 m (19.08.1987 18:50 - 13.09.1987 08:40)
Distance E, m
-40000 -20000 0 20000 40000 60000
Dis
tanc
e N
, m
-40000
-20000
0
20000
40000
60000
![Page 23: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/23.jpg)
St. 1
![Page 24: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/24.jpg)
St. 2
![Page 25: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/25.jpg)
28.0
8.87
29.0
8.87
30.0
8.87
31.0
8.87
01.0
9.87
02.0
9.87
03.0
9.87
04.0
9.87
05.0
9.87
06.0
9.87
Dep
th, m
0
5
10
15
20
25
30
35
40
station 1 station 2
Depth of 11.85°C location at stations 1 and 2.
![Page 26: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/26.jpg)
st1_11,85Rank 3 Eqn 6820 Chebyshev Polynomial Order 20
r^2=0.98069403 DF Adj r^2=0.98018148 FitStdErr=0.59347182 Fstat=2011.5791
0 50000 1e+05 1.5e+05 2e+05 2.5e+05X
5
10
15
20
5
10
15
20
-2
-1
0
1
2
Resid
uals
[128
]
-2
-1
0
1
2
Resid
uals
[128
]Residuals
Fourier Frequency Spectrum (Chebyshev data tapeirng window)
50
909599
99.9
3.3632e-05
9.4737e-05
0.00012424
0 0.0001 0.0002 0.0003 0.0004 0.0005Frequency
0
10
20
30
40
50
60
PS
D S
SA
0
10
20
30
40
50
60
PS
D S
SA
Frequency, Hz
PSD SSA
Period, h
3,36E-05 54,5 8,3
9,47E-05 4,9 2,9
0,000124 6,9 2,2
St. 1, depth of 11.85°C isotherm location, 28.08.1987, 20:55 – 31.08.1987, 16:35
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st2_11,85Rank 3 Eqn 6820 Chebyshev Polynomial Order 20
r^2=0.98922225 DF Adj r^2=0.98893612 FitStdErr=0.66393226 Fstat=3634.6379
0 50000 1e+05 1.5e+05 2e+05 2.5e+05X
10
15
20
25
30
35
10
15
20
25
30
35
-1.5
-0.5
0.5
1.5
2.5
Res
idua
ls [1
77]
-1.5
-0.5
0.5
1.5
2.5
Res
idua
ls [1
77]
ResidualsFourier Frequency Spectrum (Chebyshev data tapeirng window)
50
9095
99
99.9
3.8741e-05
6.4692e-05
9.1599e-05
0.00017587
0 0.0001 0.0002 0.0003 0.0004 0.0005Frequency
0
5
10
15
20
25
30
35
40
45
PS
D S
SA
0
5
10
15
20
25
30
35
40
45
PS
D S
SA
Frequency, Hz
PSD SSA
Period, h
3,87E-05 43,2 7,2
6,47E-05 13,9 4,3
9,16E-05 8,3 3,0
0,000176 3,2 1,6
St. 2, depth of 11.85°C isotherm location, 28.08.1987, 20:55 – 31.08.1987, 16:35
![Page 28: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/28.jpg)
st1_11,85Rank 3 Eqn 6820 Chebyshev Polynomial Order 20
r^2=0.93803767 DF Adj r^2=0.93694146 FitStdErr=0.85027248 Fstat=899.247
0 1e+05 2e+05 3e+05 4e+05X
10
12.5
15
17.5
20
22.5
10
12.5
15
17.5
20
22.5
-2
0
2
Resid
uals
[142
]
-2
0
2
Resid
uals
[142
]Residuals
Fourier Frequency Spectrum (Chebyshev data tapeirng window)
50909599
99.9
2.146e-05
3.1365e-05
4.2728e-05
5.4242e-05
0 0.0001 0.0002 0.0003 0.0004 0.0005Frequency
0
25
50
75
100
125
150
PS
D S
SA
0
25
50
75
100
125
150
PS
D S
SA
Frequency, Hz
PSD SSA
Period, h
2,15E-05 130,5 12,9
3,14E-05 48,6 8,9
4,27E-05 74,8 6,5
5,42E-05 18,3 5,1
0,000117 8,5 2,4
St. 1, depth of 11.85°C isotherm location, 01.09.1987, 3:25 – 05.09.1987, 8:05
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11,85 gradRank 3 Eqn 6820 Chebyshev Polynomial Order 20
r^2=0.97142287 DF Adj r^2=0.9709173 FitStdErr=1.2092816 Fstat=2019.1855
0 1e+05 2e+05 3e+05 4e+05X
5
10
15
20
25
30
35
5
10
15
20
25
30
35
-2
0
2
4
Res
idua
ls [1
04]
-2
0
2
4
Res
idua
ls [1
04]
ResidialFourier Frequency Spectrum (Chebyshev data tapering window)
50
9095
99
99.9
3.3295e-05
3.9081e-05
4.9086e-05
7.9725e-05
0 0.0001 0.0002 0.0003 0.0004 0.0005Frequency
0
50
100
150
200
250
PS
D S
SA
0
50
100
150
200
250
PS
D S
SA
Frequency, Hz
PSD SSA
Period, h
3,34E-05 240,7 8,3
4,92E-05 57,5 5,6
7,95E-05 16,1 3,5
0,000181 10,2 1,5
St. 2, depth of 11.85°C isotherm location, 01.09.1987, 3:25 – 05.09.1987, 8:05
![Page 30: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/30.jpg)
29/08/1987 08:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4029/08/1987 09:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
29/08/1987 10:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4029/08/1987 11:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
29/08/1987 12:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4029/08/1987 13:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
29/08/1987 14:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4029/08/1987 15:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
Evolution of the vertical temperature profile at St. 2 during the 29 –
30.08.1987 period.
30/08/1987 16:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4030/08/1987 17:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
30/08/1987 18:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4030/08/1987 19:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
30/08/1987 20:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
3008/1987 22:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4030/08/1987 23:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
30/08/1987 21:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
![Page 31: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/31.jpg)
01/09/1987 00:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4001/09/1987 01:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
01/09/1987 02:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4001/09/1987 03:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
01/09/1987 04:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4001/09/1987 05:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
01/09/1987 06:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
4001/09/1987 07:00
Temperature, 0C
5 6 7 8 9 10 11 12 13 14
Dep
th, m
0
5
10
15
20
25
30
35
40
![Page 32: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/32.jpg)
The development of the Väisäla-Brent frequency in time at stations 1, 2, and 4 during the 28.08 – 05.09.1987 period.
![Page 33: Northern Water Problems Institute (NWPI),](https://reader034.vdocument.in/reader034/viewer/2022051316/568145ad550346895db2a629/html5/thumbnails/33.jpg)
Preliminary conclusionsPreliminary conclusions
• The development of non-linear internal waves may eventually invoke vertical mixing within the lake thermocline (data 2004data 2004);
• This is not a synoptical event (data 1997data 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 & data 1977 – indirectly & 19871987);
• [not for eyes of Brussels] The selection of the measurement sites/s is very important issue (data 1977data 1977)
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Thanks for your attention!