The IOD signal in the upper-ocean Indonesian Throughflow since mid-1970s

Since the eastern Indian Ocean is located at the exit of the ITF from the Pacific Ocean, the interannual variations in this region could also have a great impact on the ITF variability. IOD is significant interannual signal over the Indian Ocean, characterized by positive SST anomaly in the western tropical Indian Ocean and negative SST anomaly in the east. Based on SODA reanalysis product, the wavelet analysis captures two prominent peaks on the interannual time scales for the upper-ocean ITF volume transport. The other significant period is about 2.67 years. By the correlation and wavelet analysis, we have checked the link between the upper-ocean ITF and IOD. The fact that the maximum correlation coefficient is -0.40 with the upper-ocean ITF lagging the IOD index by 8 months indicates that the 2-4-yr band variability of the upper-ocean ITF is a lagged response to IOD over the tropical Indian Ocean. The peak power in the IOD index wavelet spectrum is strongest within the band of 2-4 yr from the early 1980s till 2001. In the upper-ocean ITF wavelet spectrum, the spectral peak appears the similar frequency during the same times. And both wavelet spectra broaden their peak powers range into lower frequency during 1990s. These similarities illustrate that the signal of IOD over the India Ocean is reflected in the upper-ocean ITF. The evolution of IOD is reproduced by lagged correlation between the upper-ocean ITF volume transport and SSTA over the Indian Ocean. The west/east contrasting correlation structure during 3-month to 9-month lag corresponds to the dipole structure of SSTA in the tropical Indian Ocean. The westward / eastward propagation of negative correlation reproduced the evolution of IOD events. These analyses prove that the 2-4-yr band-scale oscillation of the upper-ocean ITF is related uniquely to the IOD over the tropical Indian Ocean.