Currents off the Papua New Guinea Coast During and After the El Niño of 2015–2016. Issue 12 (22nd December 2022)

• Record Type: Journal Article
• Authors: Wu, Jie; Zhang, Linlin; Wang, Fan; Kaluwin, Chalapan; Hu, Dunxin
• Is Part Of: Journal of geophysical research. Volume 127:Issue 12(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-22
• Subjects: western Pacific -- low‐latitude western boundary current -- New Guinea coastal undercurrent -- interannual variability -- ENSO; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2022JC018760
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Interannual variation of New Guinea Coastal Undercurrent (NGCUC) along the Papua New Guinea (PNG) coast was investigated using mooring observations during 2015–2019 combined with eddy‐resolving simulations of the Ocean General Circulation Model for the Earth Simulator (OFES) during 1980–2019. Strong interannual variation appears in the upper 800 m of the currents recorded by the mooring, which is well reproduced by OFES outputs. On the interannual time scale, a relatively larger proportion (1.1 Sv) of the transport signals related to El Niño/Southern Oscillation (ENSO) in the Solomon Sea is transmitted through the Solomon Strait, while about 0.84 Sv of ENSO signal is through the Vitiaz Strait due to the topography constraint. As the NGCUC flows along the PNG coast, the mean transport above 400 m gradually increases while its relationship with ENSO rapidly weakens. This weakening is due to its merging with the westward South Equatorial Current (SEC). The westward SEC weakens (strengthens) during El Niño (La Niña) events, which weakens the interannual signal of NGCUC. The interannual variations of the currents above and below the thermocline off the PNG coast are opposite: a clockwise anomalous circulation straddling the equator appears above the thermocline, while a counterclockwise anomalous circulation appears below the thermocline during El Niño, which is connected to the recharge‐discharge oscillation during ENSO cycle. Plain Language Summary: The New Guinea Coastal Undercurrent (NGCUC) as the only cross‐equatorial western boundary current in the South Pacific, influence the exchange of water masses between the south and north hemispheres, which is of particular importance for the filling and draining of the warm pool during the El Niño/Southern Oscillation (ENSO) cycle. Through analyzing mooring observations off the Papua New Guinea (PNG) coast during 2015–2019 and OFES outputs during 1980–2019, we explored interannual variations of the NGCUC transport. The NGCUC carries significant interannual signals from the Solomon Sea, albeit constrained by the complex topography of the Vitiaz Strait. The mean transport gradually increases as the currents flow northwestward along the PNG coast, but its interannual signals are gradually weakened as it is joined by the westward South Equatorial Current (SEC). The circulation above and below the thermocline show opposite interannual variations during ENSO, with currents above the thermocline contribute about 60% of the total transport and dominate the interannual variations above 400 m. This study further complements and refines our understanding of the interannual variability of the western tropical Pacific circulation. Key Points: A relatively larger proportion of ENSO signal in the Solomon Sea is transmitted through Solomon Strait compared with Vitiaz Strait ENSO signal of New Guinea Coastal Undercurrent weakens northwestward along the coast due to the feeding from South Equatorial Current Currents above and below the thermocline exhibit opposite interannual anomalies related to recharge‐discharge oscillation during ENSO