Abstract
Abstract This study uses a series of coupled atmosphere–ocean general circulation model (CGCM) experiments to examine the roles of the Indian and Pacific Oceans in the transition phases of the tropospheric biennial oscillation (TBO) in the Indian–Australian monsoon system. In each of the three CGCM experiments, air–sea interactions are restricted to a certain portion of the Indo-Pacific Ocean by including only that portion of the ocean in the ocean model component of the CGCM. The results show that the in-phase TBO transition from a strong (weak) Indian summer monsoon to a strong (weak) Australian summer monsoon occurs more often in the CGCM experiments that include an interactive Pacific Ocean. The out-of-phase TBO transition from a strong (weak) Australian summer monsoon to a weak (strong) Indian summer monsoon occurs more often in the CGCM experiments that include an interactive Indian Ocean. The associated sea surface temperature (SST) anomalies are characterized by an ENSO-type pattern in the Pacific...
Highlights
Long-term precipitation records show that the interannual variations of Indian summer monsoon rainfall have a tendency to display a quasi-biennial oscillation: years with above-normal summer rainfall tend to be followed by ones with below-normal rainfall and vice versa (Mooley and Parthasarathy 1984; Yasunari 1990; Clarke et al 1998; Webster et al 1998; Meehl and Arblaster 2002a)
The current study aims to identify these different roles by performing experiments with a coupled atmosphere–ocean general circulation model (CGCM) that restricts atmosphere–ocean couplings to only the Indian or Pacific Oceans or both
The values shown are normalized by their respective standard deviations. Based on these two indices, we identify the in-phase transition of the tropospheric biennial oscillation (TBO) as a strong Indian summer monsoon followed by a strong Australian summer monsoon, and the out-ofphase transition of the TBO as a strong Australian summer monsoon followed by a weak Indian summer monsoon in the year
Summary
Interactions between the atmosphere and the tropical Indian and Pacific Oceans have been postulated to play a central role in the TBO (e.g., Nicholls 1978; Meehl 1987, 1993; Clarke et al 1998; Chang and Li 2000). Kim and Lau (2001) performed model experiments with and without an interactive Indian Ocean to demonstrate the contribution of the combination of ocean basin phenomena in the TBO. Interactions between the atmosphere and the tropical Indian and Pacific Oceans have been postulated to play a central role in the TBO (e.g., Nicholls 1978; Meehl 1987, 1993; Clarke et al 1998; Chang and Li 2000). Kim and Lau (2001) performed model experiments with and without an interactive Indian Ocean to demonstrate the contribution of the combination of ocean basin phenomena in the TBO. Meehl and Arblaster (2002b) used (Atmospheric Model Intercomparison Project) AMIPtype experiments to quantify contributions of anomalous sea surface temperatures (SSTs) in the respective Indian
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