Study On The Character Of Sea Level Variation In The Indian Ocean

Sea-level change affects the human life and environmental change greatly, under the background of global warming and sea-level rising, it has far-reaching significance for human society and nature to study sea level variation and to grasp the law of its change. In this paper, PSMSL tide gauge data, AVSIO sea level abnormal data and the temperature, salinity data of the SODA data were used to study the characteristics and laws of the sea level change in the Indian Ocean. The HYCOM ocean model was also used to simulate the real-time sea surface height and ocean circulation from 1979 to 2008.The sea level is rising at most of the selected tide gauges. Mumbai station located in the northwest of the indian peninsula, Vishakhapatnan station seated in the west side of the Bay of Bengal and Fremantle station have the longest records, the rise rate at the three stations is 0.73mm / yr, 0.99mm/yr and 1.45mm/yr respectively. The average rise rate of the 14 eligible stations from 1978-2008 is 2.1mm/yr, The average rise rate of the 28 eligible stations from 1993-2008 is 1.8mm/yr. 2 -3cm of the amplitude can be caused by the inverse barometric effect around the Indian Ocean. most of the sea level change signal comes from the seasonal cycle which accounts for 60% of the sea-level changes. In addition to significant semiannual and seasonal change in cycle, each tide tauge also has a 2 to 3 years and 6 yeasr period cycle. the wavelet analysis shows that the interdecadal variation period is 15 years at the Mubai station, while the Fremantle station have interdecadal variation of 10 years period.The average rise rate of sea level is 2.35mm/yr in the Indian Ocean from the satellite altimeter data between 1993-2008, it is slightly higher than the corresponding result of the tide tauge data. The average amplitude is 6.36cm obtained from the satellite altimeter data, it is lower than the amplitude from the tide gauge. It is mainly because the tide gauge data is a response to local changes, which is influenced by local weather conditions, but altimeter data reflects the average variation in the Indian Ocean. Amplitude and rise rate of the Steric Sea level is 7.9cm and 0.79mm/yr respectively, the amplitude and rise rate caused by thermal expansion is 8.5cm and 0.73mm/yr respectively. The 3 most important Empirical Orthogonal Functions(EOF) can explain 26% of the sea level change in the Indian Ocean with the first and third EOFs being the seasonal modes, the lowest sea level abnormal appears in August and the peak appears in December or the following January of the next year in the first mode. While the sea level reachs the minimum in March to April and peaks in October to November in the third mode. The second EOF being the ENSO mode. The 3 most important Empirical Orthogonal Functions(EOF) can explain 37.4% of the steric sea level change in the Indian Ocean. The first EOF being the ENSO mode, when its time factor drag the ENSO index two month, its correlation coefficient with the ENSO index can archive -0.66. while its time factor drag sea-level EOF2's time factor one month, the correlation coefficient between them can be as big as 0.85. Both of the second and third EOFs being the seasonal modes, which are also affected by the ENSO at the same time; its second EOFs and the third EOFs of the sea level is positively correlated, the correlation coefficient can reach 0.82, if the former leads the latter one month; the third EOFs of the steric sea level change owns longer decadal oscillation cycle, the steric sea level showed a rising trend during 1994 to 2001, but it began to decline after 2002.The simulated temperature, salinity, sea surface flow field and sea surface height can roughly accurately reflect the corresponding real distribution partern of marine elements in the Indian Ocean. During 1979 to 2008, the simulated average amplitude and average rise rate of sea level change in the Indian Ocean is 18cm and 7.71mm/yr respectively, which are both greater than the altimeter data and tide gauge results obtained. Both of the zonal mean amplitude and rise rate of sea level chenge are increased gradually from south to north.