Mesoscale characteristics of Antarctic Intermediate Water in the South Pacific
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Mesoscale characteristics of Antarctic Intermediate Water in the South Pacific FENG Ying1*, CHEN Xianyao2, WANG Qin3, YUAN Yeli4 1 College of Ocean and Earth Sciences, Xiamen University, Xiamen 361002, China 2 Key Laboratory of Physcial Oceanography, Ocean University of China, Qingdao 266100, China 3 Marine Monitoring and Forecasting Center of Zhejiang, Hangzhou 310007, China 4 Key Laboratory of Marine Science and Numerical Modeling, the First Institute of Oceanography, State Oceanic
Administration, Qingdao 266061, China Received 19 March 2015; accepted 2 June 2015 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2015
Abstract
The Argo float observations are used to investigate the mesoscale characteristics of the Antarctic Intermediate Water (AAIW) in the South Pacific in this paper. It is shown that a subsurface mesoscale phenomenon is probably touched by an Argo float during the float’s ascent-descent cycles and is identified by the horizontal salinity gradient between the vertical temperature-salinity profiles. This shows that the transportation of the AAIW may be accompanied with the rich mesoscale characteristics. To derive the spatial length, time, and propagation characteristics of the mesoscale variability of the AAIW, the gridded temperature-salinity dataset ENACT/ENSEMBLE Version 3 constructed on the in-situ observations in the South Pacific since 2005 is used. The Empirical Mode Decomposition method is applied to decompose the isopycnal-averaged salinity anomaly from 26.8 σθ–27.4 σθ, where the AAIW mainly resides, into the basin scale and two mesoscale modes. It is found that the first mesoscale mode with the length scale on the order of 1 000 km explains nearly 50% variability of the mesoscale characteristics of the AAIW. Its westward-propagation speeds are slower in the mid-latitude (around 1 cm/s) and faster in the low latitude (around 6 cm/s), but with an increasing in the latitude band on 25°–30°S. The second mesoscale mode is of the length scale on the order of 500 km, explaining about 30% variability of the mesoscale characteristics of the AAIW. Its westward-propagation speed keeps nearly unchanged (around 0.5 cm/s). These results presented the stronger turbulent motion of the subsurface ocean on the spatial scale, and also described the significant role of Argo program for the better understanding of the deep ocean. Key words: mesoscale characteristics, subsurface ocean, Antarctic Intermediate Water (AAIW), Argo Citation: Feng Ying, Chen Xianyao, Wang Qin, Yuan Yeli. 2015. Mesoscale characteristics of Antarctic Intermediate Water in the South Pacific. Acta Oceanologica Sinica, 34(11): 92–101, doi: 10.1007/s13131-015-0752-2
1 Introduction Mesoscale variability, containing more energy than any other form of motions in the ocean, plays an important role in the transportation of mass and heat in the global ocean circulation system. Therefore, it received widely interest in a numerous studies, using both the in-situ observations (McWilliams et al., 1986) and the satellite
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