The mean seasonal variation in the transport of atlantic water through the Faroe-Shetland Channel

I

o.28 August 1977

THE rmAN SEASONAL VARIATION IN THE TRANSPORT OF TLANTIC WATER THROUGH THE FAROE-SHETLAND CHANNEL

by

Eyvind Aas

INSTITUTT FOR GEOFYSIKK

UNIVERSITETET I OSLO

ITN§llllllUlllE RlEIPORll §lERITlE§

No.28 August

1977

THE r~AN SEASONAL VARIATION IN THE TRANSPORT OF ATLANTIC WATER THROUGH THE FAROE-SHETLAND CHANNEL

by Eyvind Aas

Abstract

There is a good correlation between the transport and the wind when they are represented by harmonic functions.

A model of zero deflection and linear relation between wind and transport seems to be reasonable. The variation amounts to 20% of the mean annual transport.

- 2 -

CONTENTS

1o A MODEL OF THE RELATION BETWEEN GEOSTROPHIC

TRANSPORT AND WIND EFFECT o o o o o o o o o o o o o • • o o o • • • • • • • • • o 3 2o THE WIJ'.i'D EFFECT o o e o o 1 o o o o • o o o o o o o o o o • o 1 o o o o o o o o o o o o o o 6 3. THE TRANSPORT • o • • • , • • o , o • o , o • • • o o • • • • • , , , , • • • • • • • • • o • 8

4. THE WIND FIELD • o • o • •.• • • • • • • • • o o o • • • • • • , • • • • o , o • • • • • • • 9 5o CORRELATION BETWEEN THE TRANSPORT AND THE

SOUTH-WEST COMPONENT OF THE vliND o o • • • o , • o o • o • • • • , • • • o 11 6o CORRELATION FOR OTHER DIRECTIONS OF THE \viND • • • • • • • • • 13 SUMMARY AND CONCLUSIONS ^t e t I I I I I I t I I t t t I ~ t t I I I I t t I t t t t 13 REFERENCES

. . ^{. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .}

^{' 14}

TABLES I I I I I t I I I I t I I t t t t t t t t t t I I I I I I I t I t t I t t t t I t I I I I t t 15 FIGURES _{• • • •} • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 18

- 3 -

1. A f\10DEL OF THE RELATION BETWEEN GEOSTROPHIC TRANSPORT AND WIND EFFECT.

In this work the velum transport of Atlantic water through the Farce-Shetland Channel into the Norwegian Sea is regarded. The transport has been computed from the gee- strophic model by several authors. Together their values may form an idea about the mean seasonal variation. Meteorological offices have presented data for the mean seasonal wind field.

Since there also exist several theories and empirical formulaes for the relation between wind and ocean currents, it should then be possible to test the correlation between the mean values of wind and transport in this region.

Fig. 1 shows the different sections applied by HELLAND~

HANSEN

(1934),

JACOBSEN

(1943),

TAIT

(1957)

and SlELEN

(1959),

and the core of the Norwegian Atlantic Current as suggested by HELLAND-HANSEN and NANSEN

(1909).

The sections are nearly perpendicular to the direction of the current. The x-axis of a cartesian coordinate system may be placed in the direction of the current, and the z-axis may be let point upwards.

If the streamlines at this point are straight, parallell lines and do not change direction with depth, and if accellerations may be neglected, then the equations of motion are reduced to

0 =

^-a

^1.£

_ax ⁺ _ay ^{a (A} _hay ^{au) +} _az ^l(A _{v az} ^~)

0 =

^-fu

-

^a

^!.E.

_ay

0 =

^-a

^!.E.

_az ^g

Ah and Av are horizontal and vertical eddy viscosity coefficients respectively.

The frictional forces in this model are all in the x-direction and balanced by a pressure force, while the Coriolis force is balanced by a pressure force in the y-direction. In the vertical there is hydrostatic equilibrium.

(1)

(2)

(3)

- 4 -

Eq.2 implies that the integrated volume transport U in the x-direction may be computed from the geostrophic model:

u = I I

u dydz

= - 1

_f

Ifa

~ ay dydz (4) On the other hand there must be a relation between this transport and the wind stress, due to the frictional forces in eq.l. To get an idea of the form of this relation we have to simplify matters further. If the sum of the

pressure force and the lateral frictional force in eq.l is put equal to a constant

-e,

theH eq.l may be written

a au)

-az (A v a:a • - =

Integration from a depth z to the surface (z

=

^{0) gives}

or

where Tx the depth z gives

rz

au

⁼

is -h

u

=

sz ₊ Tx

r

_v

_~

the wind stress. Integration of where the velocity u vanishes

provided Av is independent of depth.

eq.7 from to a depth

The total volume transport now is obtained by integration from the depth -h to the surface and across the section:

u = f f

udydz = ^{2 8h3}

3 I A;

^{dy +} -2 ^Tx

I

^{-A h2 dy}

v

It has then been assumed that the wind stress Tx does not vary along the y-axis.

(5)

(6)

( 7)

(8)

(9)

- 5 -

If the depth -h equals the reference level of no motion in the geostrophic model, then the geostrophic transport in eq.4 should equal the expression in eq.9.

Eq.9 may also be written:

u =

^{a +} _{bl Tx}

where

2

J

^{eh3 dy}

a

= ₃ r:;

and

1 h2 bl

=

~

f

A dy

v

Another expression for the transport is obtained by putting z

=

0 and 8

=

0 in eq.8. The pure wind drift surface velocity u

0 is then

T

X h

r

_v

Substitution of Tx/Av in eq.8 gives u

=

^{~) h2} _c. ^{+ u} ₀ ^(! _h ^{+ 1)}

If u

0 is independent of y, then the integrated transport from -h to the surface and across the section becomes

where a is given by eq.ll, and

b2

= ~ f

^{h dy}

Note that u

0 is not necessarily equal to the total surface velocity which also includes the effect of f3.

(10)

(11)

(12)

(13)

(14)

(15)

(16)

- 6 ..

2. THE WIND EFFECT.

Eq.lO indicates that the transport may be a linear function of the wind stress. In 1905 EKMAN proposed the relation

where V is the wind speed. However, he also pointed out that the eddy viscosity coefficient Az is likely to in- crease with increasing wind speed. The coefficients a and b

1 in eq,lO will then decrease. Eq.l5 may give a better relation since the coefficient b2 is independent of A • MOHN (1887) found from selected observations

between equator and 20° latitude, with wind and current in v

the same direction, that

=

^0.032

v

In 1909 WITTING found for observations in the Baltic Sea, Kattegat and Ladoga, that a square root form gave better correlation:

= o.o48

These and other results have been examined by ROSSBY and MONTGOMERY (1935). They proposed a theoretical relation in the form of eq.l8, but also the relation

=

^0.00223

^l'i~-/i z

⁺

~ z

²

'v

where

ro

· <21.3

e )

Z

=

0.171 ln V sin ~ ,

is the latitude. At 61°N this relation is very and ~

close to

0.13 0.87 0,033 (~) v

s

Acco~ding to eqs.lO, 15, 17, 18 and 22, the relation between transport and wind may then be of the

( 1 7)

(18)

(19)

(20)

(21)

(22)

- 7 - form

u =

^{a +}

^{b vP}

Where p

=

0.5, 0.87, ¹ or 2. However, the results with

p

=

0.87 are very close to those with p

=

^1, and shall be omitted here.

(23)

In the present model the transport is computed through a section normal to the wind. When applied to the Farce-Shetland Channel where the sections go almost north-west, this means that the geostrophic transports only equal the real ones, when the wind is blowing from south-west or north-east. This is of course a very

severe restriction, but the model has given us the simple relation between geostrophic transport and wind effect in eq.23, and our first aim shall simply be to investigate the correlation between the transport and the south-west component of the wind effect. Later we shall see if

other directions of the component give better correlation.

Generally the relation between transport and wind may then be written

U

=

a + b W(a,p) (24)

where U is transport towards north-east and W(a,p)

is the net component of

vP

with an angle of deflection a.

EKMAN's classic pure wind drift model with infinite depth (1905) has a 45 degrees' deflection of the surface current to the right of the wind stress.

WITTING observed a deflection given by a

=

This deflection decreases with increasing wind speed.

In ROSSBY and lVIONTGOfi1ERY' s first model the deflection is 54.7°, while the model including eqs.20 and 21 gives

a

=

^{arctg 2}

( 25)

(26)

and this deflection increases with increasing wind speed.

- 8 -

A deflection is necessary in a stady-state model if the frictional forces partly or entirely shall balance the Coriolis force. When, however, the Coriolis force is balanced by a pressure force, the deflection may be zero.

3. THE TRANSPORT,

The approximate locations of the hydrographic sections are given in Fig. 1.

Section Source

- ----, -

^Years

^·-.-N---

^u

lsv)--1

I a TAIT (1957) 1927-1952 30 i 2. 3 ± 0.3

i

b JACOBSEN (1943) 1902-1938

I

²⁴ 2.9 ± 0.4

c ^II 1902-1939 31 3.3 ± 0.6

d TAIT (1957) 1927-1952 39 2.3 ± 0,2

I

^e HELLAND-HANSEN (1934) 1927-1929 2 3.0 ± 0.4

I

I f SJELEN (1959)

I

1949-1953 ^I 27 3.8 ± 0,2

l _ ___

^..__

-- -··

In the table above N is the number of observations, U is the mean value of the transports through the section

± the standard deviation of the mean value. (The transport unit 1 SV (1 Sverdrup)

=

106

m3/s.)

HELLAND-HANSEN used 1800 m

as the zero level, or the bottom for depths less than 1800 m.

Likewise JACOBSEN used 800 m or the bottom. TAIT used the 35 0 /oo-isohaline or the bottom, whichever was the smallest, while S£LEN used 1000 m or the bottom. The transports by

HELLAND-HANSEN, TAIT and SJELEN presented here are for Atlantic water, i.e. for water with salinity greater than 35 °/oo.

JACOBSEN's transports also include water of salinity less than 35°/oo, so they may be a little too high.

Since the main part of the observations have been made in summer, the mean values in the table do not represent the annual mean value.

The observations are listed in Table 1. Fig. 2 shows the mean value for each month ± the standard deviation of the mean value. Perhaps due to the great variation of the wind in

the region and the small number of observations, the standard deviations are great.

Since the mean seasonal transport is a periodic

... 9 ~

function, with period one year, it may be described by a Fourier series. Due to the small number of observations, only terms up to the second order have been used. Application of the least squares' method to the data in Table 1 gives the result·

uh(sV)= 3.03+0.22 cosot-0.24 sinot-0.06 cos2ot+O.l0 sin2ot

= 3.03+0.33 cos(ot+48°)-0.12 cos(2ot+59°) (27) The amplitude of the variation becomes 12% of

the mean value, and the total variation becomes 24%. The function (27) is depicted as the dashed line in Fig. 2~

The high mean value of the transport in September (Fig. 2) is remarkable, but its standard deviation is also great, and the harmonic function Uh gives a lower value.

It may be noted that from 9 repeated sections north-west off Stad during the first half of September 1962, LEINEB¢

(1969) calculated the mean net transport of Atlantic water to be 3.05 SV. This result supports the lower value of Uh.

LEINEB¢ used 1400 m or the bottom as zero-leve, :

4. THE WIND FIELD

Wind data from 4 locations in the area (Fig. 1) in the form of percentage frequency in different Beaufort force and ^direct~on intervals, has been ^us~d.

r- · · · ·-·- - ----.. ,--- - - - r - - --- ---· - -·-·--·-

Location Position ⁱ Source

I

^{Torshavn 62°03'N}

Lerwick 60°o8'N

Ocean 62°30'N

or Ocean 61° _{0 N}

'

6° 45

'vJ

1°11'w 00 0 w ^I 50 ₀

' w

50 ⁰

' w

Met.Office (1965)

"

Met. Office (1948) u.s. Dep.Comm. and u.s. Dep.Navy (1959) Table 2 gives the mean annual percentage frequency of different Beaufort forces at Ocean Weather Station M

(S.M. FIKKE, Meteorologisk institutt, personal·communication)J

- 10 -

as well as the resulting calculated mean wind speeds for the different given Beaufort force intervals.

If the percentage frequency of wind speed Vi and direction ~i is denoted fi, then the net south-west

component ~f the wind, W, becomes

W(l) = 100 1 ~ f. Vi cos(<Pi-225°)

1 1

If we want the component of the wind in power p, the expression becomes

W(p) 1 p ⁰

= 100 ~ ^f.

v.

cos(<j>.-225 )

1 1 1 1

The mean value of W(l) for the 4 locations, ± the standard deviation of the mean value, is shown in Fig. 3.

The seasonal variation is great, and the best fit to the 4 sets of W is obtained by

(28)

(29)

Wh(l)(m/s) = 1.60+1.02 coscrt-0.25 sincrt+O.lO cos2crt+0.20sin2crt

= 1.60+1.05 cos(crt+l4°)+0.22 cos(2crt-62°) (30) which is shown as the dashed curve in Fig. 3.

Instead of calculating W at the 4 locations

and then using the resulting mean value, one may also first calculate the mean frequency of wind speed and direction between the locations, and then calculate W from this frequency. The mean frequency is given i Table 3, and the resulting south-west wind component is approximated by Wh(l)(m/s)= 1.60+1.00coscrt-0.30sincrt+0.06cos2crt+O.l0sin2crt

= 1.60+l.04cos(crt+l7°)+0.llcos(2crt-62°) (31) The difference between eqs.30 and 31 is small, and

since the last method saves work, it shall be used here.

With p = 0.5 and 2, Wh becomes

Wh(0.5) ((m/s)0'5)

=

0.50 + 0.31 cos(crt + 23°) -0.05 cos(2crt + 87°)

and

(32)

- 11 -

Wh(2) ((m/s)2

)

=

19.4

~

14.5 cos(crt + 8°) + 2.1 cos(2crt + 7°)

The wind vector W, defined as

w =

where ~ and j are unity vectors towards north and east respectively, has been calculated from Table 3 and is shown for different months in Fig. 4, The vector lies always between north and east, but is far longer in winter than in summer. However, the length of the wind vector is only a small fraction of the mean wind speed in the

different directions (Fig. 5). This means that the wind varies much during the month, and even if the geostrophic model were always valid, one would need a high number of observations to obtain representative values for the mean monthly transports. The number here, 153, may be too small, but it is assumed that the function in eq.27 contains the main features of the variation.

5. CORRELATION BETWEEN THE TRANSPORT AND THE SOUTH-WEST COMPONENT OF THE WIND.

Linear correlation analysis between eq.27 and eqs. 31-33 gives

uh

=

2.53 sv + 1.oo sv wh(0.5) m

0.5

( /s) r

=

0.89

uh

=

2.59 sv + 0.27 sv wh(l) m/s

r

=

0.82

r = 0.68

In Fig. 6 the monthly mean values of Uh (eq.27)

(33)

(34)

(35)

(36)

(37)

are plotted against the monthly mean values of Wh(l) (eq.31).

- 12 -

The straight line represents eq.36. It seems as if the

deviation from the straight line is a function of the season.

From November to June the points lie below the line, wnile the rest of the year they lie above. Some possible causes are:

1) The power of the wind speed.

The correlation between the net wind component Wh(p) and the transport is better for lower values of p.

If p is too high, seasonal variations in the wind speed may cause the deviations described above.

2) The harmonic functions.

The transport and the wind effect are expressed by harmonic functions. Due to inaccuracy in the data these may have a phase difference which gives the described deviations.

3) The linear correlation.

The assumed constants in eq.23 or 24 may vary with the season and thus give the deviations.

4) The wind direction.

The correlation has been performed between the transport towards north-east and the wind component towards the same direction. If the true relation should rather be with an other wind direction, this may give an error which varies with the season and thus creates the described

deviations. (However, as discussed in the next chapter, this does not seem to happen here).

Although p

=

^{0.5 ~} gives a better correlation than p

=

1.0, it may just be that the lower value of p com-

pensates for effects mentioned under point 2-4 above, and it is not possible from this correlation analysis to say what would be the physically most correct value of p.

From eqs. 31-33 and 35-37 it is seen that the annual mean contribution to the transport from the wind is 20%, 17%

or 4% for p

=

0.5, 1 or 2 respectively. For all p-values, however, the induced amplitude of variation is about 10% of the annual mean transport.

- 13 -

6. CORRELATION FOR OTHER DIREC'I'!ONS OF THE WIND.

The correlation coefficient r, obtained by correlation analysis between Uh and Wh(a,p), where a is the assumed deflection between wind and transport, is presented in Fig.

7.

It shows that the correlation is best for wind directions between south and west, and that there are no significant differences in r for directions around south-west. There is, however, a slight tendency of better correlation for greater deflection, when the applied wind speed power in-

creases. This may indicate that an eventual deflection should increase with increasing wind speed, as in the model of

ROSSBY and MONTGOMERY.

7·

SUMMARY AND CONCLUSIONS.

The mean seasonal volume transport of Atlantic water through the Faroe-Shetland Channel and the south-west component of the mean wind have been represented by harmonic functions.

The analysis shows good correlation between these functions.

The correlation coefficient r is 0.89, 0.82 and 0.68 for wind speed powers 0.5, 1 and 2 respectively. It is, however, not possible to judge from the analysis which power of the wind speed gives the most "true" relation between wind and wind-induced transport. Neither is it possible to determine the angle of deflection between wind and transport. It may seem as if an eventual deflection should increase with in- creasing wind speed.

Due to its simplicity, I then find that a model of zero deflection and linear relation between wind and transport is the most reasonable to work with. In that case the mean annual contribution from the wind to the transport as well as the total variation in the transport created by the wind, becomes about 20% of the mean annual transport of 3.0 SV.

- 14 -_I REFERENCES

EKMAN, V.W., 1905. On the influence of the earth's rotation on ocean-currents. Ark.Mat.Astr.Fys., 2, Nr. 11; 1-53.

HELLAND-HANSEN, B., and NANSEN, F., 1909. The Norwegian Sea.

Rep. Norw. Fish.Invest., 2, No. 2: pp XX+ 390 +XII.

HELLAND-HANSEN, B., 1934.

I"lem. Vol. Liverpool:

The Sognefjord section. J. Johnstone 257-274.

JACOBSEN, J.P., 1943. The Atlantic Current through the Farce- Shetland Channel. Rapp.Cons. Explor. Mer, 112: 5-47.

· ..

LEINEB¢, R., 1969. Den norske atlanterhavsstr¢m. Rapport fra malinger h¢sten 1962. Rep. Univ.Bergen, Geoph.Inst.,

Div.A.: 28 pp.

Meteor, Office, 1965. \'leather in home fleet waters. Vol. 1 - northern seas. Part 2. London. :277 pp.

Meteor. Office, 1948. Monthly meteorological charts of the Atlantic Ocean. London. :122 pp.

MOHN, H., 1887. The Norw. North-Atl. Exped. 1876-78. Vol. 2.

The North Ocean, its depths, temperature and circulation.

:212 pp + 48 charts.

ROSSBY, C.-G., and MONTGOMERY, R.B., 1935. The layer of

frictional influence in wind and ocean currents. Papers Phys.Oceanog. Meteor., 3, no.3 :101 pp.

S~LEN, O.H., 1959. Studies in the Norwegian Atlantic Current.

Part I: The Sognefjord section. Geofys.Publ., 20, nr. 13, :28 pp.

TAIT, J.B., 1957. Recent oceanographical investigations in the Farce-Shetland Channel. Proc.Roy.Soc. Edinburg,

Section A, 64, part 3 (No.l8); 239-289.

U.S.Dep.Comm., Weather Bureau and U.S.Dep. Navy, Hydrogr.Office, 1959. Climatological and oceanographic atlas for mariners.

Vol. 1, North Atlantic Ocean: 7 pp. + 182 charts.

WITTING, R., 1909. Zur Kenntnis der vom Winde erzeugten Ober- flachenstromes. Ann. Hydr.Mar.Meteor., )7 :193-203.

- 15 - TABLE 1

VOLUME TRANSPORT OF ATLANTIC WATER

Date and

u

^{i I} I Date and

u

Date and

u

I

section (sv) section (sv) section (sv)

II 19 d 3.31 v 29 f 6.4 VI 23 d 3.69

III 7 a 4.36

I

^{30 c 6.00 24 b 2.11}

9 d 2. 03 . 30 c -1.08 26 b 3.56

12 a 4. 03

I

^{30 e 2.78 26 a 2.31}

IV 9 c 0.81 31 b 3.50 26 f 1.8

13 b _{21 c} 6.00 _2.67 31 c _{31 d 1.17} 4.86

I

_{. VII} ^{28 d} _{1 a} ^1.53 _3.56

21 d 1.33 31 d 1.22 1 f 2.9

26 c .0. 39 VI 1 b 3. 44 ⁱ 4 f 3.4

28 b 2.28 1 a 1. 53

I

4 f 2.1

v 3 c 2.69 1 a 1. 08

i

5 a 1.89

3 a 1.64 1 a 2. 44

I

^{5 d 2.67}

3 a 1.44 1 d 3.67 6 c 2.64

3 d 2.58 1 d 2. 25 ^! 7 ^f 3.2

9 c 5.25 8 c 5.17 7 ^f 3.8

9 a 0.94 9 d 3.75 9 c 2.56

9 d 1.72 10 d 0.81 9 f 2.6

12 b 2.44 11 d 5.36 10 b 4.06

12 a 0.69 12 a 2.47 12 b

o.oo

17 d 0.61 13 b 4. 58

I

^{12 c 3.06}

17 d 3.67 13 c -0.22 12 d 0.86

18 d 0.86 13 d 1. 08 ¹ 13 d 2.89

19 a 0.97 14 c 1. 69 i 14 c 5.39

21 c -0.14 15 f 2. 9

I

_{14 a 0.67}

21 f 3.2 16 a 1. 69 ¹ 17 d 2.72

21 f 4.1 16 a 4. 08 ⁱ 19 d 4.39

21 f 6.5 17 d 1. 58 ⁱ 20 a 1. 36

22 d 2.44 17 d 2. 31 24 d 0.56

22 d 0.94 18 b 5.14 27 f 5.7

23 ^f 4.3 18 c 2.92 29 f 5.6

24 c 5.67 18 a 5. 52

i

^{30 a 3.19}

24 f 2.0 18 ^f 4.0 31 f 3.4

24 f 3.1 20 c

o.

25 ¹ VIII 3 d 1.06

25 e 3.31 20 ^f 3. 9 ⁱ 4 b 0.28

25 ^f 4.5 21 a 1.

oo

¹ 7 b 2.69

27 b 1.83 21 d 1.89

I

^{8 d 0.47}

27 a 0.70 22 c -1.22 9 b 4.31

28 a 3.89 22 c 4.48 13 d 1.31

29 c 3·53 22 ^f 3.5 14 c 1.36

-

-

16

-

TABLE 1 (continued)

Date and

u

Date and

u

I ^{Date and}

section (sv)

^section

(sv) ^section

·viii

.--·

BF 1

2 3 4 5 6 8 7 10 9 11 12

15 a 0.75 VIII 24 c 12.6 XI 4 a

18 c 0.67 24

f

2.3 7 c

18 d 1.03 25 b 2.44 7 a

19 b 3.44 26 d 1.39 9 b

19 a 0.39 28 b 3.61 11 a

20 b 2.47 29 c 3.61 17 d

20 c 8.69 30 b 0.39 18 c

21

f

4.3

IX

1 b 6.81 23 d

21

f

3.9 3 a 3.44 24 b

22 c 4.64 12 d 2.78 XII 10 c

22

f

3.4 19 a 2.78 11 b

23

^f

5.7 X 29 d 3.00 11 d

TABLE 2

PERCENTAGE FREQUENCY OF BEAUFORT FORCES AND ASSUMED WIND SPEED IN THE DIFFERENT GIVEN

INTERVALS •

v ^I

%

(m/s) BF

4.3 0.75 1-2

5.2 2.5 1-3

12.4 4.4 2-3

24.7 6.7 4

19.4 9.4 3-5

18.2 12.3 4-5

9.9 15.5 5-6

4.4 19.0 6-7

1.1 22.6 7

0.3 26.5 8-12

0.04 30.6

0.01 35

u

(sv)

3.42

-0.64

3.11 4.44 3.86 2.86 5.61 3.97 1.31 5.78

-2.28

6.50

·· - - -

(m!s)

v

1.6 3!2 3.9 7.1 6.7 10.8 8.0 13.4 15.5 20.1

--

- 17 -

TABLE 3

PERCENTAGE FREQUENCY OF WIND SPEED AND DIRECTION

- - -··

January July

· BF N NE E SE

s sw w

^{. NW N NE E SE}

^s sw

^{~T NW}

I

i 1-2 2 1 1 1 2 2 2 3 I 3 3 3 3 4 _{5 3 3}

I

^{3-5 6} 3 4 4 8 10 5 ⁶ 7 5 4 6 7 10 8 6

I

^6-7 3 ^{1 1} 3 5 ⁶ 4 ₃ 1 0 0 1 1 2 2 1

I 8 ... 12 0 1 0 1 3 ^{2 2 1 0 1 0 0 0 0 0 0}

~--·---

-:-~-t

February August

1·. ^{2 1 0 1 2} 3 3 3 3 5 4 _{3 3}

I

^{7 3 3 1 2 2 6 3 8 4 10 5 7 4 5 3}

^I

^{1 8 5 1 4 0 1 6 1 9 10 1 8 1 7 1}

1 o· _{0 1 1 1 1 2 0} 0 0 0 0 0 0 0

-· - -^----·~-

March September

2 1 1 1 3 ^{2 2 2} 3 ^{1 1 2} 4 4 ₃ 3

8 5 4 6 9 9 ⁶ 5 7 4 ₃ 6 12 10 7 5

I

^{1 1 1 2 5 5 3 2 1 1 1 2 3 4 2 1}

1----

^{0 1 0 1 1 1 1 0 0 0 0}

- - - --

^{0 0 0 0}

--- - -

⁰

April October

I

I 3 ^{2 1 1 2 2 2} 3 ^{2 1 1 1} 4 2 3 ²

I 9 5 3 7 8 9 7 6 6 3 3 5 ^{12 10 7 6}

2 2 0 2 2 3 ^{2 2 2 1 1 2} 4 5 ^{4 2}

0 0 0 1 0 1 0 1 0 0 0 1 1 1 1 0

---

I

I _{2 2 4} ^May _{3 3 4 2 3 2 1 1} ^November _{1 2 3 2 3}

I

^{1 8 7 1 1 7 6 2 6 1 8 2 6 2 1 5 7 2 1 3 4 2 6 3 11 5 8 4 6 3 5 2}

i

^{0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0}

1---·---·

I

^{June December}

I

^{2 4 4 3 4 4 1 2 2 1 1 1 2 3 3 3}

I

^{7 1 7 0 4 0 7 2 1 9 2 8 2 6 1 4 5 2 3 1 4 2 6 4 10 5 10 5 6 3 4 2}

I

^{0 0 0 0 0 1 1 1 0 0 0 2 2 2 1 0}

'--·- ^---

F.ig.::... 'I'he mean location of the sections. X de- notes area of wind observati- ons.

Fig.2. The mean net transport or Atlantic wa- tero The number or observations is given for eacn month.

'P1f17:.3. The m~an south-w,.~t ~~m-

w1nd.

sv

4

3

2

1

m/s

l

- 18

u

---

0 ^....

... _...

: I

u

I 11 III IV V

4

, 1

26

I

_ j

3

VI VII VIII IX X X1 X.,.,.

..1. :.

I

L__j

MAY

6 s

- 19 -

3 )I

XII

I

E

Pig.4. The wind vector ror each month.

DECEJIIBER

m/s N

16 14

P1g.5. The wind speed in the eight direction intervals.

1.0 r .6

.6

.4

.2

.o

SE

- 20 -

Wh(l)

2~ ____________ _. __________________ ~---~~

0 1 2 m/s 3

F1g.6. The transport Uh &15 a function or the aov.th-weat wind co.ponent Wh tor eaeh month.

p=0.5

p=l

p=2

s sw w

F1g.7. The correlation eoett1c1ent rasa function or the wind 41rect1on tor d1tt~nt values or p.

NW