Vol. 61, n.2, June 2020
Investigating dynamic and static aspects of regional sea level changes in the north-western Indian Ocean
N. Eshghi, A. Barzandeh, F. Hosseinibalam and S. Hassanzadeh
Received: 8 December 2018; accepted: 3 September 2019
Regional sea level changes were studied in the North-West Indian Ocean (NWIO). Basically, the processes affecting regional sea level changes can be divided into dynamic and quasi-static components. In the present study, dynamic sea level changes were evaluated by applying statistical methods such as Trend, Empirical Orthogonal Function (EOF), Spectral and Correlation analyses to the mean sea level anomaly, surface heat flux, and wind stress data. In addition, quasi-static sea level changes were examined by considering the inverted barometer effect. The results indicated that the maximum sea level rise is mostly observed in areas adjacent to the Gulf of Aden, and the minimum sea level rise is seen at the centre of the region, near the equator and oriented towards the SW. In general, in NWIO, the main factors affecting sea level changes are weakened and intensified with a one-year period. The correlation coefficients of heat flux and wind stress with the 2nd EOF of the sea level are larger than those of other modes so that the effect of internal factors, such as seasonal change, is, generally, smaller than the effect of external factors such as El-Nino - Southern Oscillation. The direction of prevailing winds in the region causes the positive sea level anomalies by Ekman suction and increasing the depth of the tropical thermocline. The inverted barometer effect on the sea level changes is significant in most of the months, except December, in such a way that it decreases in the cold months by moving towards high latitudes, while increases in warm months by moving to high latitudes. The distribution of non-barometric effects in the Arabian Sea indicates that they are caused by interactions with the Indian Ocean mostly from the southern areas of the Arabian Sea and the intensity of these effects decreases northwards and westwards during the year.
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