Investigation of Mediterranean Sea level between 1961 – 2000 according to SOI data

B. Shirman

The aims of the work:

to distinguish tide long time periods;

to compare the mean sea level with the current datum.

With participation: Y. Melzer, K. Shpitalnik, A. Nahary, I. Perelman

Sea level measurements during the British Mandate

Seasonal variations of MSL in 1929

Survey of Israel has been monitoring sea level along the East MediterraneanCoast over decades.The main aim of monitoring is to derive mean sea level

.value in order to determine heights zero level

Tide gauge stations location

Sea level monitoring at the modern period

Tide gauges at Tel-Aviv, Ashqelon,Ashdod and Haifa stations recordSea level changes in digital form with5-min sampling and 1 cm resolution. Radar sensor (f=24,125 GHz, p=5mW)was installed at Haifa port in 2001.

Thales OTT at the Ashqelon marina Kalesto OTT at the port in Haifa

The factors influenced on a Sea level changes

Z(t) = Zo(t) + T(t) +S(t)

Zo(t) – a mean Sea level

T(t) –astronomical tide

S(t) – meteorological factors

Sun Moon

Atmosphere

Some astronomical parameters of the Moon and the Sun

Parameter Moon Sun

Gravit force 11.2 10^-8 g 5.2 10^-8 g

Day duration 24h 50.5m 24h 00m

Orbit:Period (solar days)

27.32(sidereal month)

29.53(synodic month)

365.24

eccentricity 0.0549 0.0168

declination 5.1 deg (to ecliptic) 23.5 deg(to equator)

Period of the moon’s planRotation (to eqliptic)

18.61 years

Earth

E1

E2

E3

M3

M2

M1

Moon

Centerifugal Forceexceeds

lunar attraction

Lunar attractionexceeds

Centerifugal ForceMoon

The monthly revolution of the Earth and Moon around the barycenter

Ashqelon

Tel-Aviv

M ay

A sh q e lo n & T e l-A v iv S e a le v e ls 1 9 9 7

0 7 0 9 1 1 1 3 1 5 1 7 1 9 2 1

0.0

0.2

0.4

Tid

e,

m

0.0

0.2

0.4

Tid

e,

m

Full

Moon Moon

New

Spring Tide

Sun

Sun

Neap TideFirst Quarter

Last Quarter Lunar Tide

Solar Tide

Mean Sea Leval

Combined Tide

Tel-Aviv

Ashdod

Ashdod - Tel-Aviv

m ean = 1 .0 cmst. dev. = 1 .1 cm

260 270 280 290 300 310Ju lian days (16 S ep-13 N ov), 1999

-0 .2

0.0

0.2

0.4

Tid

e, m

-0 .2

0.0

0.2

0.4

Tid

e, m

-0 .2

0.0

0.2

Diff

ere

nce

s, m

è åúù øé

à ëñ ì å

è å ç ù åï

à ç ù åï

Spring and neap tides generation

Spring – neap tidal cycles are produced by the relative motionsof the moon and sun at 14.8-day interval

Spring tide

Neap tide

frequency, 1 /day

0

100

200

300

400

500

Po

we

r260 265 270 275 280 285 290 295 300 305 310 315

Ju lian days (16 Sep t - 13 Nov) 1999

-0 .2

0.0

0.2

0.4

0.6

Se

a le

vel,

m

Sea level record at Tel-Aviv and spectrum

1.0 2.0 3.00.0

א כםלו

טו חשון

א חשון

טו תשרי

Unequal semidiurnal tides are produced when the Moon or the Sun is north or south of the equator.

frequency, 1 /day

0

100

200

300

Po

we

r

1.0 2.0 3.0 4.0

0 1 0 3 0 4 0 6 0 8 1 0 1 2m onth

-0 .4

-0 .2

0.0

0.2

0.4

0.6

Se

a le

vel,

m

Sea levelTel-Aviv 1996

diurnal

sem idiurnal

m onth ly

The spectrum shows the main (semidiurnal and diurnal) parts of tides

T e l-A v iv reco rd s & c a lc u la ted tid e

0 1 0 4 0 7 1 0 1 3 1 6 1 9 2 2 2 5 2 8F ebrua ry 2001

-0 .6

-0 .4

-0 .2

0.0

0.2

0.4

0.6T

el-

Avi

v, m

-0 .6

-0 .4

-0 .2

0.0

0.2

0.4

0.6

Ast

ron

om

ica

l tid

e,

m

-0 .6

-0 .4

-0 .2

0.0

0.2

0.4

0.6

Diff

ere

nce

s, m

The differences between measured and calculated (astronomical) tidepresent a meteorological part of the sea level changes .

The influence of atmospheric factors

0 1 0 4 0 7 1 0 1 3 1 6 1 9 2 2 2 5 2 8F ebrua ry 2001

-0 .4

-0 .2

0.0

0.2

0.4

me

asu

red

- c

alc

1000

1010

1020

1030

air

pre

ssu

re

-0 .20

0.00

0.20

0.40

air

pre

ssu

re c

orr

ect

ion

, m

D ifferences betw een m easured and calculated tides and the ir correcrion of a ir pressure: dZ(cm )=-0.993 d Pa (m Pa)

0 1 0 4 0 7 1 0 1 3 1 6 1 9 2 2 2 5 2 8F ebrua ry 2001

-0 .20

0.00

0.20

0.40M

ea

sure

d -

ca

lcu

late

d,

m

0

4

8

12

16

20

Win

d v

elo

city

, m

/se

c

0

90

180

270

360

Win

d d

ire

ctio

n,

de

g

W ind effect on a sea leve l

Correlation between meteorological part of sea level changes and a wind parameters.

H aifa (R adar)

Ashqelon

Haifa - Ashqelon30/03/01 - 05/04/01

D ifferences

30/03/01 01/04/01 03/04/01 05/04/01

-0 .6

-0 .4

-0 .2

0.0

0.2

0.4

0.6

Se

a le

vel,

m

-0 .6

-0 .4

-0 .2

0.0

0.2

0.4

0.6

Se

a le

vel,

m

-0 .6

-0 .4

-0 .2

0.0

0.2

0.4

0.6

Diff

ere

nce

s, m

Comparison between Ashqelon and Haifa records shows that tide waves appear at the same phase and almost the same amplitude at both stations. The differences between records are defined as a highfrequency noise. Such comparisons justifies arranging the data from all considered stations in one array.

The category of sea level data

1961 – 1984 Ashdod analog record1964 - 1989 Yafo analog record 1990 - 1995 Ashdod analog record1996 - 2000 Tel –Aviv digital record

Sea level M onth m ean:Ashdod - Yafa

6 5 6 8 7 1 7 4 7 7 8 0 8 3Year

-30

-20

-10

0

10

20

30

Se

a le

vel,

cm

-30

-20

-10

0

10

20

30

Se

a le

vel,

cm

-30

-20

-10

0

10

20

30

Diff

ere

nce

s, c

m

Ashdod

Yafo

Comparison between the month mean sea levels of Yafo and Ashdod. analog records during 1964 – 1984 were used

-20 -15 -10 -5 0 5 10 15

T ide d iffe rences (Ashdod - ya fo ),cm

0.00

0.05

0.10

0.15

0.20

pro

ba

bili

ty

T ide d iffrences betw een Ashdod & Yafo and the ir probabilities

m edian = 1.9 cmst.dev = 4.8 cm

The histogram of differences looks like random distribution, which is due to random error. The standard deviation is about 5 cm.

Ashdod - Te l-Aviv Sea Level 1990 - 2000

1991 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002Year

-40

-30

-20

-10

0

10

20

30

40

Mo

nth

ly m

ea

n S

ea

leve

l (cm

)

A sh d o d T e l-A v iv

Graph of monthly mean values at Ashdod & Tel-Aviv stations during 1990 –2000shows a gradual increase of Mediterranean sea level in the last decade.

f req ue nc y, 1 /ye ar

0

500

1000

1500

Spe

ctra

l am

plitu

de, c

m

1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000Ye ar

-40

-30

-20

-10

0

10

20

30

40

Sea

leve

l, cm

S pe ctrum

E as t M editer ran ea n S ea lev el cha ng es

1.0 2.0 3.0 4.0 5.0 6.0

58 61 64 67 70 73 76 79 82 85 88 91 94 97 00Years

-8

-4

0

4

8

12

16

Sea

leve

l, cm

On e y ea r a verag ed & eig ht yea rs sm oo the dEa st Me dite rra ne an Se a le ve l (19 58 -20 01 )

Ashdod

m =60

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30January 2000

-20

0

20

40

Tid

e, c

m

-20

0

20

40

Tid

e, c

m

-20

0

20

40

Tid

e, c

m

Sea level

hypothetica l gap

bridged gap

Tel-Aviv

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30F ebrua ry 2000

-20

0

20

40

Tid

e, c

m

-20

0

20

40

Tid

e, c

m

-20

0

20

40

Tid

e, c

m

S ea leve l

hypothetica l gap

bridged gap

Data processing

Missing data were provided by the maximum entropy method

The following results were obtained:

Tide level changes caused by influences from the Moon and the Sun are in the same phase and amplitude along the coast between Tel-Aviv and Ashqelon. This justifies linking together data from different stations into a continuous time series of 40 years.

Spectral analyses of the tide level changes revealed semidiurnal and diurnal periods and long periods of about 20 years, one year and half year.

The influence of meteorological factors on the sea level changes was estimated .

The average tide level relative to the Yafo datum is about 2 cm.

Time series averages during a period of 18.6 years indicate a gradual rise in theMediterranean sea level by 5 cm over the last fourteen years.

31 04 08 12 16 20 24 28 02 06 10 14

-8

-4

0

4

8

12

-8

-4

0

4

8

12

-0 .3-0 .2-0 .10 .00 .10 .20 .3

Oc tob er-De ce mb er 20 00

November December

D ifferences (Te l-Aviv - ca lculated)

N orth com ponent of wind

W est com ponent of w ind

METEOROLOGICAL FACTORS

Wind influences

c ount/ye ar

Spe

ctra

l am

plitu

de, m

b

66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00ye ar

pres

sure

, mb

Air pressure 19 64 - 1 99 9

1 2 3 4 5 60

10 04

10 08

10 12

10 16

10 20

0

2 00

4 00

6 00

8 00

10 00

Monthly mean changes of air pressure during 1964 – 1999 and spectrum