A possible precursor for ENSO events: NEC volume transport in the western Pacific

Abstract

To investigate the relationship between ENSO and tropical zonal currents in the northwest Pacific, the monthly average reanalysis data (GLORYS12V1) from January 1993 to May 2020 was analyzed. The reproducibility of the North Equatorial Current (NEC) of the reanalysis data was confirmed by comparing the observed 131°E cross-section (CTD and vessel mounted ADCP) data from 2017 to 2020. The volume transport(VT)s of the NEC and the North Equatorial Countercurrent (NECC), estimated with a thickness of 300 m at selected latitudes (7.5°N<NEC <18.5°N, 3°N<NECC <7.5°N) where the NEC and the NECC appear on average, were closely correlated (r = 0.67). It is shown that the correlation between the volume transport anomaly (VTA) of the currents and the Nino 3.4 index was different depending on the statistical treatment of the data. The 12-month moving average data showed that the NEC VTA changed six months ahead the Nino 3.4 index with the correlation coefficient of 0.46. On the other hand, the NECC VTA changed four months ahead of the Nino 3.4 index with a correlation coefficient of 0.63. This implies that the NEC and the NECC in the western Pacific change continuously with a lag of two months and are reflected in the ENSO signal. The results suggest that the NEC VT can be used for a precursor for the ENSO events.