Identification of the fronts from the Kuroshio Extension to the Subarctic Current using absolute dynamic topographies in satellite altimetry products
The climatologies and variabilities of the fronts associated with the Kuroshio Extension (KE), the Kuroshio Extension Northern Branch (KENB), the flow along the Subarctic Boundary (SAB), and the Subarctic Current (SAC) are identified by a new method based on the absolute dynamic height product from the archiving, validation, and interpretation of satellite oceanographic data (the AVISO product). The fronts are detected by examining the specific contour values of the absolute dynamic topography (ADT) in the AVISO product. The (time-varying) specific contour values are decided from the local maxima of the averaged surface geostrophic velocity along the ADT. Assuming the specific contours as the front locations, we obtain an occurrence frequency map of the four front locations, and determine the monthly variability of the fronts over the 1993–2015 period. The results are validated by hydrographic observations. The KE and KENB east of the Shatsky Rise migrate southward several times at a speed of ~ 0.2 cm s−1, while the SAB and SAC are mostly stationary.
KeywordsFront identification Kuroshio extension Kuroshio bifurcation northern branch Subarctic boundary current Subarctic current AVISO
We thank the members of the Oceanography and Geochemistry Research Department of MRI for many fruitful discussions and comments. This work is funded by MRI and is partly supported by JSPS KAKENHI Grant Number JP 17K05649. Wavelet analysis was conducted using python programs translated from the Fortran by Dr. Toru Miyama. Discussion with Dr. Katsuro Katsumata with regard to the front identification method in the Southern Ocean quite helpful. Comments from the reviewers and the editor, Dr. Eitarou Oka, greatly improve the manuscript. Except for the wavelet analysis, graphics were produced with the Grid Analysis and Display System (GrADS).
- AVISO (2016) Ssalto/Ducas user handbook: (M)SLA and (M)ADT near-real time and delayed time products SALP-MU-P-EA-21065-CLS, 5.0 edGoogle Scholar
- Belkin I, Cornillon P (2007) Fronts in the world ocean’s large marine ecosystems. ICES CM, pp 21–33Google Scholar
- Favorite F, Dodimead AJ, Nasu K (1976) Oceanography of the subarctic Pacific region, 1960–1971. Bull Int N Pac Fish Comm 33:1–187Google Scholar
- Harada N, Sato M, Seki O, Timmermann A, Moossen H, Bendle J, Nakamura Y, Kimoto K, Okazaki Y, Nagashima K, Gorbarenko SA, Ijiri A, Nakatsuka T, Menviel L, Chikamoto M, Abe-Ouchi A, Schouten S (2011) Sea surface temperature changes during the last glacial maximum and deglaciation. Deep Sea Res II 61–64:93–105. https://doi.org/10.1016/j.dsr2.2011.12.007 Google Scholar
- Kawai H (1972) Hydrography of the Kuroshio Extension. In: Stommel H, Yoshida K (eds) Kuroshio: its physical aspects. University of Tokyo Press, Tokyo, pp 235–352Google Scholar
- Kida S, Mitsudera H, Aoki S, Guo X, Ito S, Kobashi F, Komori N, Kubokawa A, Miyama T, Morie R, Nakamura H, Nakamura T, Nakano H, Nishigaki H, Nonaka M, Sasaki H, Sasaki YN, Suga T, Sugimoto S, Taguchi B, Takaya K, Tozuka T, Tsujino H, Usui N (2015) Oceanic fronts and jets around Japan: a review. J Oceanogr 71:469–497CrossRefGoogle Scholar
- Nakamura H, Kazmin AS (2003) Decadal changes in the North Pacific frontal zones as revealed in ship and satellite observations. J Geophys Res 108:C33078Google Scholar
- Rio M-H, Mulet S, Picot N (2013) New global mean dynamic topography from a GOCE geoid model, altimeter measurements and oceanographic in-situ data. In: Proceedings of the ESA living planet symposium, Edinburgh, September 2013Google Scholar
- Torrence C, Compo G (1998) A practical guide to wavelet analysis. Bull Am Meteorol Soc 79:61–78. https://doi.org/10.1175/1520-0477(1998)079\(<\)0061:APGTWA\(>\)2.0.CO;2Google Scholar