Abstract
This study examines the decadal change in the relationship between two major Indian Ocean (IO) sea surface temperature patterns, namely the Indian Ocean dipole (IOD) and northern IO and the East Asia summer monsoon (EASM) in the early 2000s. In 1991–1999, the former epoch, the interannual variability of EASM was associated with the IOD-like pattern in the original paper and its relationship weakened in 2000–2016. There are two possible causes for this decadal change; stronger land-sea thermal contrast as a local forcing in latter epoch, which may result in the weakening of the relationship between the IO and the EASM. In addition, the influence of El Niño-southern Oscillation (ENSO) on the western North Pacific subtropical high (WNPSH) could be changed depending on the frequency of ENSO. In the 2000s, the intensity of the low frequency (LF)-type ENSO (42–86 months period) events was weaker compared to the former epoch but that of quasi-biennial (QB)-type ENSO (16–36 months period) remained persistent. This could explain that the QB-type ENSO is remote forcing that modulates the change in the relationship between the tropical IO patterns and EASM in the 2000s.
Highlights
The Asian summer monsoon includes three monsoon subsystems, namely the East Asian summer monsoon (EASM), western North Pacific summer monsoon (WNPSM) and the Indian summer monsoon (ISM) [1,2]
We investigated the decadal changes in the relationship between East Asian summer monsoon index (EASMI) and the based on distinct shifts in the relationship
The entire period can be divided into four positive Indian Ocean dipole (IOD)-like pattern related to the EASMI is dominant over the tropical Indian Ocean (IO)
Summary
The Asian summer monsoon includes three monsoon subsystems, namely the East Asian summer monsoon (EASM), western North Pacific summer monsoon (WNPSM) and the Indian summer monsoon (ISM) [1,2]. The interdecadal relationship shifts between East Asian summer monsoon index (EASMI) and other phenomena were observed in the late-1970s in many previous studies [21,22,23,24]. Ding et al (2010) [21] showed the interdecadal change in the relationship between EASM and the tropical IO for 1953–1975 and 1979–2000 and the distinct SSTA patterns over the tropical IO were associated with the EASMI during each period. Since it is important to prepare for disasters in near future (within 10-year) such as flood, drought associated with the tropical IO SST pattern, observing the decadal shift in the relationship is meaningful.
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