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Climate 2018, 6(2), 51; https://doi.org/10.3390/cli6020051

Multi-Decadal Trend and Decadal Variability of the Regional Sea Level over the Indian Ocean since the 1960s: Roles of Climate Modes and External Forcing

1
Department of Atmospheric and Oceanic Sciences, University of Colorado, UCB 311, Boulder, CO 80309, USA
2
Center for Earth System Research and Sustainability, University of Hamburg, Hamburg 20146, Germany
3
Climate and Global Division, National Center for Atmospheric Research, Boulder, CO 80305, USA
4
The Max-Planck-Institute for Meteorology, 20146 Hamburg, Germany
*
Author to whom correspondence should be addressed.
Received: 1 May 2018 / Revised: 5 June 2018 / Accepted: 6 June 2018 / Published: 8 June 2018
(This article belongs to the Special Issue Decadal Variability and Predictability of Climate)
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Abstract

Previous studies suggest that anthropogenic warming has affected the multi-decadal trend patterns of sea level over the Indian Ocean (IO). This effect, however, has not been quantified. Using observational datasets combined with large ensemble experiments from two climate models, this paper assesses the effects of natural internal variability versus external forcing on the observed, multi-decadal trend pattern and the decadal sea level anomaly (SLA) of the IO since the 1960s. Because the global mean sea level rise (SLR), which results largely from external forcing, has been removed before the examination, the paper focuses on the regionally uneven distribution of trend and SLA. The impacts of climate modes are quantified using a Bayesian Dynamic Linear Model. For the regional trend pattern of 1958–2005, the effects of internal variability dominate external forcing. Over the Seychelles area where sea-level variations obtain the maximum, internal variability (external forcing) contributes 81% (19 ± 2.4%) of the observed trend. For decadal SLA, internal variability is the predominant cause, with a standard deviation (STD) ratio of externally forced/observed SLA being 18 ± 17% over Seychelles and 17 ± 11% near the Indonesian Throughflow (ITF) area. Climate modes account for most observed SLA during boreal winter, with the total effects of decadal ENSO, Indian Ocean Dipole (IOD), and monsoon accounting for 78–86% of the observed STD near the Seychelles region, ITF area, and coasts of Sumatra and the Bay of Bengal. During summer, climate modes explain 95% of observed STD near the ITF but only 58–67% in other regions. Decadal ENSO dominates the SLA in the south tropical IO for both seasons and near the coasts of Sumatra and the Bay during winter. Decadal IOD and monsoon, however, control the coastal SLA during summer. Remote and local winds over the IO are the main drivers for decadal SLA, while the Pacific influence via the ITF is strong mainly in the southeast basin. View Full-Text
Keywords: regional sea level; multi-decadal trend; decadal variability; climate mode; internal variability; external forcing; Indian Ocean regional sea level; multi-decadal trend; decadal variability; climate mode; internal variability; external forcing; Indian Ocean
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Han, W.; Stammer, D.; Meehl, G.A.; Hu, A.; Sienz, F.; Zhang, L. Multi-Decadal Trend and Decadal Variability of the Regional Sea Level over the Indian Ocean since the 1960s: Roles of Climate Modes and External Forcing. Climate 2018, 6, 51.

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