The decadal sea level variability observed in the Indian Ocean tide gauge records and its association with global climate modes

Decadal sea level variability of the Indian Ocean is studied using long-term tide gauge observations of 17 stations. The existence of close association between Indian Ocean sea level and the global decadal climate modes, such as Pacific Decadal Oscillation (PDO) and/or Atlantic Multidecadal Oscillation (AMO) is revealed in most of the tide gauge data sets. An anti-phase sea level evolution with PDO index is identified in the regions such as west coast of India, east coast of India and the western coast of Australia. Moreover, the PDO related sea level variability is found to be stronger at the tide gauge stations along the west coast of India compared to that along the east coast of India, ruling out the remote forcing from the equatorial Indian Ocean. On the other hand, the tide gauge station at Mumbai with more than 100 years of data shows an in-phase relationship with AMO index on the decadal timescales, whereas such relationship is very weak at the tide gauge station Fremantle where similar long-term data is available. The analysis of sea level pressure (SLP), rainfall and winds over the tropical Indian Ocean indicates existence of strong relationship with AMO especially over the Arabian Sea region, strongly suggesting that the variability observed at the tide gauge station Mumbai may have larger spatial signatures. During the positive phase of AMO, the Arabian Sea region is characterized by large fall in SLP and a strong cross equatorial flow towards the Indian land mass, which are primarily responsible for the positive sea level anomalies (SLAs) at the Mumbai tide gauge station and the adjacent regions and positive rainfall over India.

Automated summary

The study found a close association between decadal sea level variability in the Indian Ocean and global decadal climate modes, particularly with the PDO and AMO. The sea level in regions like the west coast of India, east coast of India, and west coast of Australia shows an anti-phase evolution with the PDO index. Furthermore, the relationship between sea level variability and the AMO index is stronger in certain locations, such as Mumbai, than in others like Fremantle, suggesting spatial variations in the impact of these climate modes.