Recently, scientists from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) and their collaborators from Indonesia and Germany reported their study on the variations of the Indonesian Throughflow under the influence of the western boundary currents. The findings were published in Journal of Physical Oceanography of the American Meteorological Society.
The Maluku Channel is a major opening of the eastern Indonesian Seas to the western Pacific Ocean, the upper-ocean currents of which have rarely been observed historically.
Based on four consecutive years of subsurface moorings observations in the Maluku Channel of the Indonesian Seas, the upper-ocean circulation in the Maluku Sea has been observed for the first time in history, showing a mean northward transport to the Pacific Ocean of about 1.0 Sv (1 Sv = 106 m3 s-1), clarifying the ambiguity of the traditional understanding of the upper-ocean circulation in the area.
The observations unraveled a significant southward increase of the Indonesian Throughflow during the spring and summer of 2014, with a total transport of 14 Sv, of which 3.5 Sv were the interannual variability. These variations were significantly different from the response of the local circulation to the wind forcing and were suggested to be induced by the shifting of the Mindanao Current in the Pacific Ocean.
The variations of the Indonesian Throughflow may have an inhibitory effect on the onset and development of the El Nino event in 2014.
Schematic of the upper-ocean circulation of the Indonesian Seas. Solid and empty triangles mark the positions of the 2012–2014 and 2014–2016 mooring positions, respectively. The solid line across the Maluku Channel indicates the section of the normal transport calculation. (Image by IOCAS)
(a) NCEP winds and the (b) zonal and (c) meridional components of the moored ADCP velocity time series at M00 in the Maluku Channel during December 2012–November 2016. (Image by IOCAS)
Their observations suggested that the interactions between the Rossby waves and the western boundary currents could cause the Indonesian Throughflow to vary significantly, providing solid evidence for the nonlinear reflections of the Rossby waves at the Pacific western boundary.
Prof. YUAN Dongliang from IOCAS discovered that the nonlinear reflection of Rossby waves at the western boundary was significantly different from the classic linear theory nearly 15 years ago, but suffered from no observational data at that time.
The researchers conducted theoretical analysis of the multiple equilibria and hysteresis dynamics of the western boundary currents flowing across a gap (Yuan and Wang, 2011; Wang and Yuan, 2012), which laid a foundation for analyzing the mooring data in the Maluku Sea.
The above researches have laid a solid theoretical and observational foundation for the study of nonlinear dynamics of the western boundary currents in the Pacific Ocean.
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