Correlation analysis of the North Equatorial Current bifurcation and the Indonesian Throughflow

Based on monthly mean Simple Ocean Data Assimilation （SODA） products from 1958 to 2007, this study analyzes the seasonal and interannual variability of the North Equatorial Current （NEC） bifurcation latitude and the Indonesian Throughflow （ITF） volume transport. Further, Empirical Mode Decomposition （EMD） method and lag-correlation analysis are employed to reveal the relationships between the NEC bifurcation location, NEC and ITF volume transport and ENSO events. The analysis results of the seasonal variability show that the annual mean location of NEC bifurcation in upper layer occurs at 14.33°N and ITF volume transport has a maximum value in summer, a minimum value in winter and an annual mean transport of 7.75×10^6 m^3/s. The interannual variability analysis indicates that the variability of NEC bifurcation location can be treated as a precursor of El Nino. The correlation coefficient between the two reaches the maximum of 0.53 with a time lag of 2 months. The ITF volume transport is positively related with E1 Nifio events with a maximum coefficient of 0.60 by 3 months. The NEC bifurcation location is positively correlated with the ITF volume transport with a correlation coefficient of 0.43.

Observed Near Inertial Waves in the Wake of Typhoon Linfa(2015) in the Northern South China Sea

This study examined the characteristics and vertical propagation of near inertial waves(NIWs)induced by Typhoon Linfa(2015),based on in situ observations conducted southeast of Dongsha Islands in the South China Sea.The results demonstrate that the near inertial currents induced by Linfa had velocities up to 35 cm s^-1 in the mixed layer and 20 cm s^-1 in the ocean interior.The near inertial currents were polarized with predominantly clockwise-rotating components,the magnitudes of which were about 10 times larger than the counter-clockwise rotating components.The energy density spectrum showed that the emergence of NIWs resulted in energy redistribution from the diurnal band to the near inertial band.The wavenumber spectrum and the downward/upward current decomposition demonstrated that the NIWs and energy flux propagated mainly downward.The estimated vertical phase velocity and group velocity are 1.44 and 0.48 m h-1,respectively,corresponding to a vertical wavelength of 49.7 m.The e-folding time scale was 7.5 d based on the near inertial kinetic energy in the ocean interior.We found no obvious wave–wave interaction during the decay process of the NIWs.The frequency was blue-shifted,being 0.03 f0 higher than the local inertial frequency,which was caused by the background vorticity.The normal mode analysis suggests that the higher mode plays a dominant role in the propagation stage of the NIWs.