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Abstract The Indian Ocean has received increasing attention for its large impacts on regional and global climate. However, sea surface temperature (SST) variability arising from Indian Ocean internal processes has not been well understood particularly on decadal and longer timescales, and the external influence from the Tropical Pacific has not been quantified. This paper analyzes the interannual-to-decadal SST variability in the Tropical Indian Ocean in observations and explores the external influence from the Pacific versus internal processes within the Indian Ocean using a Linear Inverse Model (LIM). Coupling between Indian Ocean and tropical Pacific SST anomalies (SSTAs) is assessed both within the LIM dynamical operator and the unpredictable stochastic noise that forces the system. Results show that the observed Indian Ocean Basin (IOB)-wide SSTA pattern is largely a response to the Pacific ENSO forcing, although it in turn has a damping effect on ENSO especially on annual and decadal timescales. On the other hand, the Indian Ocean Dipole (IOD) is an Indian Ocean internal mode that can actively affect ENSO; ENSO also has a returning effect on the IOD, which is rather weak on decadal timescale. The third mode is partly associated with the Subtropical Indian Ocean Dipole (SIOD), and it is primarily generated by Indian Ocean internal processes, although a small component of it is coupled with ENSO. Overall, the amplitude of Indian Ocean internally generated SST variability is comparable to that forced by ENSO, and the Indian Ocean tends to actively influence the tropical Pacific. These results suggest that the Indian-Pacific Ocean interaction is a two-way process.
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Reconciling Roles of External Forcing and Internal Variability in Indian Ocean Decadal Variability Since 1920
Abstract On decadal time scales, Indian Ocean sea surface temperatures (SSTs) exhibit coherent basin‐wide changes, but their origins are not well understood. Here we analyze observations and model simulations from Coupled Model Intercomparison Project Phase 6 and Community Earth System Model Version 1 to quantify the roles of external forcing and internal climate variability in causing Indian Ocean decadal SST variations. Results show that both external forcing and internal variability since 1920 have contributed to the observed decadal variations in linearly detrended Indian Ocean SSTs, and they exhibit an out‐of‐phase relationship since the 1950s. The internally‐generated variations arise from remote influences from the tropical Pacific and possible contributions from internal local processes, while the influence from the Atlantic Multidecadal Oscillation is opposite to that of the Interdecadal Pacific Oscillation. Decadal SST changes caused by nonlinear variations in greenhouse gases and aerosols are roughly out‐of‐phase with the internal variability, thus dampening observed SST variations since the 1950s.
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- PAR ID:
- 10445845
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 9
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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