Study On The Multi-scale Variation Of Current / Undercurrent Along The Coast Of New Guinea

New Guinea coastal current/undercurrent is a key channel for the transport of water masses from the southern hemisphere across the equator to the North Pacific.It has played an important role in the exchange of water between the northern and southern hemispheres.And changes were analyzed.This paper uses the submarine observation data from the three sites of 0°,1°S and 1.7°S on the section of 142°E from November 2015 to December 2018 in the Institute of Oceanography,Chinese Academy of Sciences.Current(NGCC)and New Guinea Coastal Undercurrent(NGCUC)multiscale changes were compared and analyzed.The latent target ADCP has well observed the intraseasonal,seasonal and interannual time scale changes above 800 m along the coast of New Guinea.Its relationship with ENSO was studied.The main conclusions are as follows:(1)NGCC is a current with a seasonal reversal of 100 m.It flows northwest in the summer(boreal).In August,it has a maximum westward velocity(about-55cm/s)at a depth of 80 m.In winter,it flows southeast.In February,there is a maximum eastward velocity(about 50cm/s)at a depth of 30 m.The NGCUC in the subsurface layer is an current that flows stably westwards at a depth of 100-400 m,and a maximum westward flow velocity of-39±10cm/s exists at a depth of 200 m.The seasonal changes of NGCUC and NGCC are consistent.The flow velocity in summer is stronger and that in winter is weaker,but its flow direction does not change with the seasons.The current between 400-800 m has the same seasonal variation characteristics as NGCC,and its flow direction will also be seasonally reversed.(2)The currents over 300 m along the coast of New Guinea have obvious 20-40 days of intraseasonal signals.The signal at the depth of 100 m is the strongest in the season,and there is a tendency to spread upward and downward.The analysis results of EEMD show that: NGCC is dominated by seasonal signals,and the interpretation variance of seasonal signals and intra-season signals is 48% and 22%,respectively;while NGCUC is dominated by intraseason signals,and its interpretation of seasonal signals and intra-season signals The variances are 18% and 67%,respectively.(3)NGCC/NGCUC are significantly affected by the coastal monsoon.In the summer(boreal),the velocity of NGCC/NGCUC to the west is enhanced by the anticyclone.In the winter,the velocity of NGCC flows to the southeast and the velocity of NGCUC to the west is obviously weakened by the cyclone.The correlation coefficients of currents above 800 m and monsoon are mostly between 0.8-0.9,and all exceed the 95% confidence level,which shows that the monsoon's forcing effect not only affects 300 m,but also affects 800 m or deeper currents.It is worth noting that the correlation coefficient between the depth of 100-150 m is low,which is caused by the strong semi-annual oscillation between 100-150 m.The temperature and salinity distribution in the coastal waters of New Guinea also have obvious seasonal changes:lower salinity and higher temperature in summer,and higher salinity and lower temperature in winter.(4)NGCUC also showed significant interannual changes.From November 2015 to June 2016,the surface NGCC disappeared,and NGCUC occupied the entire upper layer of the ocean,and the depth of the current core was between 50-100 m,far shallower than the average.The core depth is 200 m.During this period,there was a westward velocity anomaly above 150 m,and an eastward velocity anomaly appeared below 150 m,which corresponds to the shallow depth of the NGCUC core.The cold phase of ENSO is from May 2017 to July 2018,and the change of NGCUC is opposite to the phenomenon of El Ni?o in 2015/2016.The synthesis results of the OFES model show that the depth of the NGCUC flow core will become shallow during El Ni?o,while the depth of the flow core will deepen during La Ni?a,and the flow change of NGCUC has no significant correlation with ENSO.