Observation of an anti-cyclonic mesoscale eddy in the subtropical northwestern Pacific Ocean from altimetry and Argo pro
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Observation of an anti-cyclonic mesoscale eddy in the subtropical northwestern Pacific Ocean from altimetry and Argo profiling floats Yang Wang1, 2, Cheng Li3, 4*, Qingyu Liu1 1 School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China 2 Maritime Environment Construction Office, Beijing 100081, China 3 Guangdong Key Laboratory of Coastal Ocean Variability and Disaster Prediction, College of Ocean and Meteorology,
Guangdong Ocean University, Zhanjiang 524088, China 4 Marine Resources Big Data Center of South China Sea, Southern Marine Science and Engineering Guangdong
Laboratory (Zhanjiang), Zhanjiang 524025, China Received 25 September 2019; accepted 4 February 2020 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
The comprehensive three-dimensional structures of an anti-cyclonic mesoscale eddy (AE) in the subtropical northwestern Pacific Ocean were investigated by combining the Argo floats profiles with enhanced vertical and temporal sampling and satellite altimetry data. The AE originated near the Kuroshio Extension and then propagated westward with mean velocity of 8.9 cm/s. Significant changes and evolutions during the AE’s growing stage (T1) and further growing stage (T2) were revealed through composite analysis. In the composite eddy core, maximum temperature (T) and salinity (S) anomalies were of 1.7 (1.9)°C and 0.04 (0.07) psu in T1 (T2) period, respectively. The composite T anomalies showed positive in almost whole depth, but the S anomalies exhibited a sandwich-like pattern. The eddy’s intensification and its influence on the intermediate ocean became more significant during its growth. The trapping depth increased from 400×104 Pa to 580×104 Pa while it was growing up, which means more water volume, heat and salt content in deeper layers can be transported. The AE was strongly nonlinear in upper oceans and can yield a typical mean volume transport of 0.17×106 m3/s and a mean heat and salt transport anomaly of 3.6×1011 W and –2.1×103 kg/s during the observation period. The Energy analysis showed that eddy potential and kinetic energy increased notably as it propagated westward and the baroclinic instability is the major energy source of the eddy growth. The variation of the remained Argo float trapped within the eddy indicated significant water advection during the eddy’s propagation. Key words: mesoscale eddy, three-dimensional structure, volume transport, available heat and salt content anomaly, energy analysis Citation: Wang Yang, Li Cheng, Liu Qingyu. 2020. Observation of an anti-cyclonic mesoscale eddy in the subtropical northwestern Pacific Ocean from altimetry and Argo profiling floats. Acta Oceanologica Sinica, 39(7): 79–90, doi: 10.1007/s13131-020-1596-y
1 Introduction Oceanic eddies are a kind of vortices in qusi-geostrophic balance or gradient wind balance and most of them have long lifetime and horizontal scales of about 10–100 km and can effectively transport diverse tracers (Wunsch, 1999;
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