Investigation of Mediterranean Sea level between 1961 – 2000 according to SOI data B. Shirman With participation: Y. Melzer, K. Shpitalnik, A. Nahary, I. Perelman The aims of the work: to distinguish tide long time periods; to compare the mean sea level with the current datum.
Sea level measurements during the British Mandate Seasonal variations of MSL in 1929 Survey of Israel has been monitoring sea level along the East Mediterranean Coast 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 record Sea level changes in digital form with 5 -min sampling and 1 cm resolution. Radar sensor (f=24, 125 GHz, p=5 m. W) 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 Moon Sun Z(t) = Zo(t) + T(t) +S(t) Zo(t) – a mean Sea level T(t) –astronomical tide S(t) – meteorological factors Atmosphere
Some astronomical parameters of the Moon and the Sun
The monthly revolution of the Earth and Moon around the barycenter
Spring and neap tides generation Spring tide Neap tide Spring – neap tidal cycles are produced by the relative motions of the moon and sun at 14. 8 -day interval
Unequal semidiurnal tides are produced when the Moon or the Sun is north or south of the equator.
The spectrum shows the main (semidiurnal and diurnal) parts of tides
The influence of atmospheric factors The differences between measured and calculated (astronomical) tide present a meteorological part of the sea level changes.
Correlation between meteorological part of sea level changes and a wind parameters.
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 high frequency noise. Such comparisons justifies arranging the data from all considered stations in one array.
The category of sea level data 1961 – 1984 Ashdod 1964 - 1989 Yafo 1990 - 1995 Ashdod 1996 - 2000 Tel –Aviv analog record digital record
Comparison between the month mean sea levels of Yafo and Ashdod. analog records during 1964 – 1984 were used
The histogram of differences looks like random distribution, which is due to random error. The standard deviation is about 5 cm.
Graph of monthly mean values at Ashdod & Tel-Aviv stations during 1990 – 2000 shows a gradual increase of Mediterranean sea level in the last decade.
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 the Mediterranean sea level by 5 cm over the last fourteen years.
METEOROLOGICAL FACTORS Wind influences
Monthly mean changes of air pressure during 1964 – 1999 and spectrum
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