•

__ 46·

ichtptcoten

22 m G) ..

I E3 F3 I

15m .......------

80m •••-----

5 0

92'" 91'" 90· 8'· 88'" 87· 66'" 8!:J·

-1----·-......----~----..:..;----"1---=-r---=r---------

1-15 SEPTEMBER 67 ---1----+------.::-A----~T ---+-----\----,,,'

'8"

.g'

·,,.

Muftraing

L-----l---------t-----+-----1r---~i'G. KILOMETERS 'G' .... .... .... .. 0 .. STATUTE WILES , ...... ...... .. .. 92' 9" 90' 89' 88' 8" B6" B;'

Figure lOb. (FWPCA) half~month a:verage current vectors, 1-15 September 1967,

15, 22, and 60 m.

22
The second half of September (fig. 11a, b) seemed to contain a change

in the flow pattern as a current flowed from the Keweenaw Peninsula toward

Isle Royale at 15 m at station 9, and at 10 and 15 m at station 11. Winds

were predominantly from the north. There was still evidence of a strong

counterclockwise circulation west of 88°W to the tip of the lake and of

another cell occupying the eastern half. The cross-lake current from

station 9 may have been an artifact of the hardware used in data collection

or reduction. Thu~, the suggestion of two counterclockwise cells in the

lake can be inferred from the data, but certainly not proved conclusively.

October (fig. 12a, band 13a, b) was the last month in which a significant number of moorings were left; only five still reported at 10 m for

1-15 October. The late September pattern was continued. A strong northeastward coastal current was found at stations 2 and 3 at 10 and 30 m and

at station 15 at 60 m. For 16-31 October four stations still reported

flows at 10 m, including the suspiciously steady north-northwest flow at

station 9. Deeper flows for this period were still parallel to bathymetry

at stations 2, 3, and 15, but strong and divergent in direction at station

5, which showed such behavior all season. The scatter of directions at

mooring 5 is probably due to its location in a confined bay and out of the

mainstream of the basic counterclockwise lake circulation.

3.2 FWPCA Observations - Summer 1967, Summary

Five and one-half months of current data from a network of moorings in

Lake Superior revealed a persistent counterclockwise circulation covering

the whole lake once stratification had set in. Serious deficiencies in

data reduction techniques and equipment during the original processing by

the FWPCA and contracted data processors rendered a significant fraction

of the data sample useless, so that only general features of long-term circulation patterns could be inferred. Monthly summaries of summer current

components are given in table 1.

3.3 CCIW Observations - Summer 1973

Figures 14-21 display half-monthly averages of CCIW data for the period

1 June-30 September 1973. A detailed, month-by-month discussion will not

be made here, since the patterns already determined from the FWPCA data are

again present. There are, however, some significant differences. CCIW

mooring 4 reported a con~istent, strong east-northeast Keweenaw Current at

speeds exceeding 30 em s from a location near FWPCA site 9, which showed

north-northwest currents at 10 m with lower speeds for a similar season.

Currents at CCIW site 3 showed an extension of the Keweenaw Current as it

swept around with the bathymetry although some of the data from FWPCA site

13 showed this flow continuing to the south-southwest.

23
i; .:'

"

i'

9'- 90' 8" 88' 8" 88' R!,·

----- 4"· 49<- 16 - 30 SEPTEMBER 67

10m •

30m @ .......................

cm·s-1

I R R I 1 I 5 0 10

ich~-- 48' 48'

,

.."... , :l

Si'l..,.,. a8Y • .ll'

.-.....

... ... ,.".. ....... Wunisin9

KILOMETERS '8'

'8' .... .... .... 50 0 ... STATUTE WILES I ........ ..... .. .. 92' 9" '0' 8" 88' 8" 88' 8"

11

I,!

,

j

hr

Figure 11a, (FWPCA) half-month average au1'1'ent vectors, 16-30 September 1967,

10 and 30 m.

24

j
..

r to' .., 00' 0" 06' 05'

'9' -16 - 30 SEPTEMBER 67 4"

15m •

22m @ .......................

80m • cm·.-1 48'

48' - I H 8 I

1 I5 0 10 -

• • -- •

..-

r/ 'ond

....,..ie

hluniaing

46' KILOMETERS -- ---- 46'

.... .... .... so 0 so

STATUTE IIILES

so

i ...... ....... =so

92' ,,' 90' 09' 88' 8" 8E''' R<;-

! Figure 11b. (FWPCA) half-month average current vector8~ 16-30 September 1967~

15~ 22~ and 60 m.

25

-
8,'

8,'

86'

•

Muniaing

88' 81'

,_/_.\------+-1,~:;;,::::.-1 "'"""~~----+--

90' 89'

50

5 10

26

(FWPCA) haZf-month avel'age a'Ul'l'ent veat01'8~ 1-15 Oatobel' 1967~

10 and 30 m.

9"

30m @ .

__ STATUTE .....-oc MILES

92'

10 m ee-------

I H R I 5 0

KILOMETERS

sr--~ 50

Figul'e 12a.

46'

9?- 91- 90· ar 8e- ·l--·-··-·-j----T--'T-----'T--

49" - 1 -15 OCTOBER 67 ~----J--___._A.---_+---+--.--T--149'
•

at' 88' 8" 86' 85'

---L +------f~=:::;:::::=RfoOhii;;;;~48

'0'

-l- .....,.4 +-------t------I----l49'

47·I-T--::;if-----::;-~~~·U----+----_r..j.ti'4ou!,....o\"y!I_:_t_----__+---

49'

1 -15 OCTOBER 67

15m •

22m $ .......................

80m •

48' cm·.-1

i F3 R I 5 0

KILOMETERS 46' .... .... ....

'0 . 0 so '00

STATUTE MILES I ........ ........ so so I

92' 9" 90' 89' 88' 8"

46'

Figuxae 12b. (FWPCA) half-month avexaage cnaTent veot01'8~ 1-15 Ootobexa 196?~

15~22~ and 60 m.

27
IIii

T.

•

9Z" 90' 19' 88' 8'" 86' 8~'

49' - 49"

16 - 31 OCTOBER 67

:ii, 10 m • ;

i!

" 30 m @ ....................... 'i

:l! cm·.-1

I E3 E3 I

h I 5 0 10

48'

! i

\ 'll

iii,

Ill! • 1" j'lli' I " Ii' , Jii'

1,1"

Iii,' ; Pi'

!];! 81Nk Rivw

11,i

I':! "uniai",

II! !,:i

)1'1 KILOMETERS 46'

1[1 46' - .... .... .... ----~-

Ii} " , .. STATUTE MILES '" :il' i ...... " -- " [I:: ..L__ u __________ •

iii: oz' 9'" 90' 89" 88' 8" 86" ,,' , ,

!:I,

,! !

Figure 13a. (FWPCA) haZf-month average CUl'!'ent veators, 16-31 Oatober 1967,

10 and 30 m.

28
48"

- -l.r-'Wh::;C-jtefiah Pt.

88" .," 8."

•

90" .,"

-L---I--------.---,.ql------+---t--j-- 4.- 16 - 31 OCTOBER 67

22m 8 · ..

80m •••-----

15 m ••~------

4'"

KILOMETERS .." .... -- -- so . so ... STATUTE MILES I

-- ...... so so

9Z" .." '0" '.89· ... 8'"

.."

86"

Figure 13b. (PWPCA) half-month average aurrent vectors, 16-31 October 1967,

15, 22, and 60 m.

29

I _J
! '

'I

TabZe 1. (PWPCA) Current Components (East cOTJionent PoUowed by North

Component; Both in C!/Tl/s-)
Table 1. (PWPCA) Curzaent Components (East Component Pollowed by Nopth

Component; Both in am/s-1) (continued)

Depth

Date Station 60 m 90 m 120 m 150 m

• June 1967 1

2

3 -0.25, -0.12

4

5 -0.20, 0.28

6

7 -0.22, -0.24 0.96, 0.24

8

9 4.56, 0.92 6.95, 2.08 7.16, 1.46 -0.38, 3.21

11

12 -0.76, -1.07 -0.89, 0.16

13

14

15

16

17

July 1967 1

2

3 -0.79, -2.65

4

5 0.02, 0.00

6

7 0.92, 0.16 0.74, 0.07

8

9 4.50, 0.39 6.28, 1. 74 3.93, 2.36 4.80, 1. 25

11 -0.37, -0.08

12 -0.54, -0.76

13

14 -0.30, 1.62

15 5.00, 1. 74

16

17

August 1967 1

2

3 -1.61, -0.92

4

5 0.38, -0.54

6

7 0.23, 0.09 0.02, 0.19

8

9 3.10, 1.08 4.08, 2.26 2.65, 0.80 -1.08, 0.90

11 -0.41, -0.07

12

13

14 -0.16, 1.54

15 3.98, 7.34

16

17

31
TabZe 1. (FWPCA) Current Components (East Component FoUowed by North

Component; Both in arn/s-1) (continued)

Depth

Date Station 10 m 15 m 22 m 30 m

• September 1967 1

2 3.61, 2.07 1.32, 0.66

3 1.36, 0.76

4

5 1.16, -2.96 0.02, 1.28

6 0.14, 0.77 -0.34, -0.30

7 0.24, -1.62

8

9 -1.50, 2.90

11 -1. 94, -0.01 -0.68, 0.11

12 -1.04, -3.78 -1. 70, -3.73 -1. 24, -1. 76

13 -0.59, -1.60

14 -0.67, 1.14 -0.30, -0.09

15 4.47, 8.20

16 -1. 72, 2.72 -1.14, 1.20

17 -0.36, 0.42

October 1967 1

2 7.12, 4.02 7.17, 1.98

3 2.42, 0.68

4

5 2.28, 3.14 0.08, -3.84

6 -0.90, -0.96 -0.82, -1.94

7 0.11, 0.22

8

9 -1. 54, 4.18

11

12

13

14

15

16

17

32
TabZe 1. (PWPCA) Cu!'!'ent Components (East Component Followed by No!'th

Component; Both in orn/s-1) (continued)

Depth

• Date Station 60 m 90 m 120 m 150 m

September 1967 1

2

3 0.67, -0.15

4

5 0.52, -0.74

6

7 0.84, -0.11 -0.29, -0.04

8

9 4.18, 0.92 4.33, 1. 76 4.28, 0.60 -1.16, 0.48

11 -0.70, -0.02

12 -0.72, -1.56

13

14 -0.03, 1.10

15 1.50, 1.29

16

17

October 1967 1

2

3 1.12, 0.51

4

5 4.36, -0.79

6

7 0.94, 0.60 0.76, 0.28

8

9

11

12 -0.54, -0.69

13

14

15 7.20, 10.14

16

17

33
10

34

1-15JUNE

10m •• _

15 m~·..· •..• .

25m ••-----

LAKE SUPERIOR 1973 C.C.I.W 49",

LAKE CURRENT OBSERVATIONS

Figupe 14. (CCIW) haZf-month cweZ'age eJUrTent vector's at 10~ 15~ and 22 m~ 1-15 June 197:5.

i'

i

I !
LAKE SUPERIOR 1973 C.C.I.W

LAKE CURRENT OBSERVATIONS

10

16-30 JUNE

10m •• _

15 mf) ..

25m ••-----_

Figure 15. (CCIW) half-month average current vectors at 10~ 15~ and 22 m~

16-30 June 1973.

35
36

•

--E

LAKE SUPERIOR 1973 C.C.I.W 49"1-

LAKE CURRENT OBSERVATIONS

1-15 JULY 73

10m ••-----

15 m (i) .

25m -----

Figure 16. (eerw) haZf-month average aurrent veators at 103 153 and 22 m3

1-15 JuZy 1973.

i \

JIN..,;;--=--=................;;;;;;o;;;;;;;;;;;;;o;;;;;;;;;;;;;o;;;;;;;........ ....
LAKE SUPERIOR 1973 C.C.I.W

LAKE CURRENT OBSERVATIONS

cm-.-1

~RR~

16 - 31 JULY

10

10m ••-_---

15 m (i) .

25m,••-----

Figu:r>e 17. (CCIW) half-month average cu:r>rent vectors at 10~ 15~ and 22 m~

16-31 July 1973.

37
--E

LAKE SUPERIOR 1973 C.C.I.W 49°1-

LAKE CURRENT OBSERVATIONS

I:

•

1 -16 AUGUST 73

10m •• _

15 me······..··..·..······..····· 25m ••-----

~o

46j

FigUT'e 18. (CCIW) haZf-rrvnth average aurrent vectors at 10, 15, and 22 m,

1-16 August 19?3.

38
LAKE SUPERIOR 1973 C.C.I.W 49°1

LAKE CURRENT OBSERVATIONS

I E3 H cm·.-1

! 10

17 - 31 AUGUST 73

10m••------

15 mlil·..• • •..

25m ••------

Figure 19. (CCIW) haZf-month average current vectors at 10, 15, and 22 m,

17-31 August 1973.

39
Figure 20. (CCIW) half-month average current vectors at 10, 15, and 22 m,

1-15 September 1973.

•........................._....•......_.···6········-...

1-15 SEPTEMBER 73

10m ...-----

15 mlil·........·......•......•....

25ml••-----

cm·.-1

kPH3:EHqb~~A===il,b ...... ....(........ _ I

/.0 ~.~~ • •• •••(j

90

490

LAKE SUPERIOR 1973 C.C.I.W

LAKE CURRENT OBSERVATIONS

40
LAKE SUPERIOR 1973 C.C.I.W 49°/-

LAKE CURRENT OBSERVATIONS

16 - 30 SEPTEMBER 73

10m _

15 m@)o • .

25ffi1 ••-- _

___i}_·_•••.=••.•::::··· o :to

••..·~20.93

10

cm·.-1

~RR6 Ai

Figure 21. (CCIW) half-month average current vectors at 10, 15, and 22 m,

16-30 September 1973.

41
Flows along the northwest shore follow the bathymetry and are stronger

than those measured by the FWPCA. Early in the season (through mid-July)

the flows at CCIW station 10 were in near opposition between 15 and 25 m,

indicating probable downwelling. This is particularly clear in July

(fig. 16-17) when flow at station 8 was onshore while flow at station 10 divided to flow parallel to shore, westward at 15 m, but eastward at 25 m.

Note also the strength measured for the Keweenaw Current.

The entire CCIW data set supports the existence of the counterclockwise

circulation of the whole lake, but wide spacing and absence of data from

the northeastern lake (also not well covered by FWPCA) makes verification

difficult.

The relatively small current at station 5 is a residual of averaged

inertial currents, which are a nearly constant phenomenon during the stratified season. For example, !~ile the net resultant current at 15 m for

station 5 averaged 2.1 cm s for 1-15 September (!!g. 20), the current

speed for the same period ranged from 8 to 11 cm s and the direction

rotated clockwise through 360 0 each 16 hr. The average speed was thus more

than four times the vector resultant average.

A possible period of downwelling is shown in figure 21, the current

map for 16-30 September. Flow was toward shore at stations 6 and 8 and

parallel to shore at 7 and 10. Currents between Isle Royale and Thunder Bay

at stations 12 and 13 are westward, while flow at 11 is eastward.

In summary, the CCIW da!y show a lakewide counteErlockwise flow which

generally averages 5-10 cm s and as fast as 35 cm s in the Keweenaw

Current. Flow near shore paralleled the bathymetry, while deepwater flow

was dominated by inertial currents during stratified conditions.

3.4 Oscillatory Currents at Isle Royale

Interesting periodicities occurred also in the currents at stations 11,

12, and 13. These periodic components were directed parallel to bathymetry

and corresponded to predicted oscillations and seiches of the lake (Rockwell,

1966; Mortimer and Fee, 1976; Rao and Schwab, 1976).

Flows in the channel between Isle Royale and the north shore of the

lake oscillated in two distinct patterns. During the early part of the

measurement season, the lake was thermally unstratified and spectral analysis of flows measured at stations 12 and 13 showed strong coherence between

10- and l5-m levels at periods corresponding to the uninodal longitudinal

seiche, the lunar semidiumal tide, and all periods greater than about

20 hr. The effects of surface oscillations are not generally detectable in

currents, except where amplified by some sort of constriction through which

an oscillatory flow is driven. The periodic current driven by the uninodal

seiche is also strongly coherent between measured east-west flows at 10 m

at stations 12 and 13.

42
Figure 22 shows the spectra of east-west oscillations for 22 May-II

August 1973 for stations 12 and 13 at 10 m. The coherence spectrum comparing the two stations clearly shows significant correlations between

the measured oscillations only at line 21 (about 12.5 hr, the lunar tidal

period), line 33 (about 7.9 hr, the uninodal seiche), and line 92 (about

2.8 hr). Rao and Schwab (1976) computed a period of about 2.6 hrs for a

si~th mode of Lake ~uperior; this mode has a significant amplitude only

behind Isle Royale, and no other mode except the first strongly affects

that region. Rao and Schwab (personal communication) stated that their

computations provided better spatial than temporal resolution and that

the period of 2.8 hrs was probably correct for the sixth mode. Mortimer

and Fee (1976) observed in Lake Superior water levels normal modes which

had periods a few percent longer than those Rao and Schwab computed, so

the observations described in the present study appear to fit the actual

situation.

Figure 23 shows east-west current spectra for stations 12 and 13 at

10 m for 12 August-3 October 73. The lake had become stratified and a different oscillatory pattern dominated the currents. Inertial oscillations

prevailed with an order of magnitude more energy than the seiche-driven

motions. There is a suggestion of a hump in the spectrum from station 13

(closer to shore) at the 7.8-hr seiche period, but there is no coherence

between stations 12 and 13 at that period. The strong coherence at the

l6-hr inertial period and a relative phase of 3° between the two meters indicates that both meters were in the same rotating current cell. Inertial

motions at station 12 were nearly circular; with a phase angle of 91° between northward and eastward components at a coherence of 0.949, magnitudes

of the two spectral components were equal within 10 percent. Similar flows

existed at station 13, which in spite of its proximity to shore was in water

l42-m deep. Depth at station 12 was 195 m.

3.5 FWPCA Observations - Winter 1966-67

Monthly resultant currents were calculated for six winter meters on

four moorings (locations shown on fig. 24) at winter stations 1, 2, 7,

and 8. Other records were of insufficient duration or quality to be used.

The data, summarized in table 2, spanned mid-October 1966 throug~ mid-May

1967. Measured speeds were small, generally around 1 to 3 cm ~l ' although

the monthly peak was 8.32 and a half-month value of 11.17 cm s . was recorded at station 1 at 10 m. These data were too sparse to define a circulation pattern, but the resultants generally paralleled the bathymetry, and

station 1 tended to indicate a prevailing counterclockwise pattern of general

circulation. The locations of moorings 7 and 8 in particular were placed

out of the expected general circulation pattern and seemed to respond to

eddies shed by the main flow.

43
16 8

PERIOD (HOURS)

4 2

Figure 22. Spectra of the east-west current components at CCIW moorings 12

(solid line) and 13 (dotted line), depth 10 m, 22 May-11 August 1973.

Broken light line is squared coherence between the two stations. Peak in

coherence at 8-hr period is due to first longitudinal seich~ of the lake;

the peak at 2.8 hr (line 92) may be due to sixth free mode.

w

()

.6 ffi

a:

w

:J:

o

()

Q

w

a:

.4

a

en

.2

.8

99%

60 80 100 120

SPECTRAL LINE NUMBER

o 20 40

tt-----/\

I II

I I I

-3 \ I I

\ A ' I \ I I

\ /'J I

,/\" I \...J

o

>- ...

u; -1

z

wQ

...I

C

a:

...

()

w

a. !!.-2

o

o

...I

44
16 8

PERIOD (HOURS)

4 2 2-r------lL------L. ---lL-

.8

:;- w

(,) t-

.6 ifi U)

z 0 w w Q : ..... 0

c 99% (,)

I Q

(,)

t- , W

w \ .4 Q. !!!. -1 \ 95% 0

<:J \ , l en

0 , I , ..... I , I

,, \

" I I \ ' I I I \ , r l

-2 \ , .2 f\} \

\ , \ , ,

, \ I, , ,

\ '\ , , \ , 1 f I , \

\ I \ I \ I \ /

\I

"

V \V/

-3 0

0 20 40 60 80 100 120

SPECTRAL LINE NUMBER

Figure 23. Same notation as figure 22.. stations 12 and 13 at 10 m.. eastwest components.. 12 August-3 October 1973. Coherence peak at 16 hr is due

to inertial oscillation.

45

------------------------------ 
". 90· .9· ..' .,.d

I

1

4

"

I

S.ult St•. W.r"-!

•

4

•• - "':"--~"'wo.C.i..f;'h Pt

.and

....r...

llAuniamg

9

•

46

FWPCA winter 1966-67 mooring sites.

k----J---+--+--+---[-....

•

Figure 24.

KILOWETERS 4~' ~F"3

M 0

~=_=iLE;iT;iiAi;i:T=U::,:T:EE;;iW~I~L~Ei;:iS~~~~"

L'~----L-__....L-__so~_~;--_~__-.!;;-__--;;-__~....---l 9;0 9ro cWo 8g0 A8° R ,. fl f -
Table 2. (FWPCA) CUppent Components at Foup Selected Stations (East Component

Followed by Nopth Component; Both in crn/s-1; Half-Month Data in Bpackets)

Depth

Date Station • 15 m 22 m 30 m 60 m

17-31 Oct. 1966 1 [-5.54, -6.37] [-0.46, 4.96]

2 [ 0.95, 2.55] [-0.23, 2.32]

7

8

Nov. 1966 1 -1. 02, -1. 39 0.56, -0.28

2 -0.50, 1.26 0.27, 0.55

7 -0.72, 0.32

8 -0.60, 2.85

Dec. 1966 1 0.22, -0.68 1.48, 0.90

2 -0.70, 0.72 -1.11, -1.56

7 0.91, -2.08

8 -0.32, 0.19

Jan. 1967 1 -3.18, -4.40 -2.30, 1.28

2 0.30, 0.42 -1.04, -1.92

7 3.23, -1. 76

8 0.26, 0.72

Feb. 1967 1 -6.12, -5.64 -1.44, -0.51

2 -1. 99, 0.16

7 1. 00, 0.57

8 0.02, 1. 35

March 1967 1 -2.16, -2.08 -1. 78, -1.48

2 0.15, 2.47

7 -0.39, 2.16

8

April 1967 1 -1. 82, -2.50 -1. 69, -1.40

2

7 0.90, -0.96

8

1-16 May 1967 1 [-4.92, -10.03] [-1.08, -2.01]

2

7 [0.01, -0.16]

8

47

..
4. REFERENCES

FWQA (Federal Water Quality Administration), 1968: Report on the water

movements and temperature structure in Lake Superior based on 1966-67

field study. U.S. Dept. of the Interior, FWQA, Great Lakes Region,

Chicago, IL., 66 pp.

Millar, F. G., 1952: Surface temperatures of the Great Lakes. Jour. Fish.

Res. Bd.~ Canada 9:329-376.

Mortimer, C. J., and E. J. Fee, 1976: The free surface oscillations and

tides of Lakes Michigan and Superior. Phil. Trans. Roy. Soc. Lond. (AJ

281:1-62.

Rao, D. B., and D. J. Schwab, 1976: Two-dimensional normal modes in arbitrary enclosed basins on a rotating earth: Application to Lakes Ontario

and Superior. Phil. Trans .•Roy. Soc. Lond. (AJ 281:63-96.

Rockwell, D. C., 1966: Theoretical free oscillations of the Great Lakes.

Proc. 9th Conf. Great Lakes Research~ Pub. No. 11, Great Lakes Res.

Div., Univ. Michigan, 362-368.

Sloss, P. W., and J. H. Saylor, 1975: Measurements of current flow during

summer in Lake Huron, NOAA Tech. Report ERL 353-GLERL 5~ National

Oceanic and Atmospheric Administration, Boulder, Colorado, 39 pp.

Smith, N. P., 1972: Summertime temperature and circulation patterns in Lake

Superior. Ph.D. Dissertation, Univ. of Wisconsin. Univ. Microfilms,

Ann Arbor, Mich., 205 pp.

48

"* u. S. GOVERNMENT PRINTING OFFICE: 1976-677-347/1264 REGION NO.8