On the seasonal variability of the Oyashio extension fronts
Previous study reported that the annual-mean eastern Oyashio Extension (OE) front shifts northward while the western OE front has no obvious poleward shift during 1982–2017 by Wu et al. (Geophys Res Lett 45:9042–9048, 2018). Here we revisit this topic and focus on the seasonal variability and shifts of the OE fronts from 1982 to 2018, with observational reanalysis data and a 1.5-layer reduced-gravity model simulation. In winter, both the western and eastern OE fronts demonstrate consistent northward movement. While in summer, the eastern OE front still moves northward but the western OE front has no obvious and even southward shift. It is shown that the trade wind’s expansion during 1982–2018 favours the northward shift of the OE fronts for both winter and summer. However, there is a local cold Ekman heat transport anomaly along the western OE front in summer, which surpasses the effect of trade wind expansion and prohibits northward movement of the front. This cold Ekman advection is due to a westerly wind anomaly induced firstly by the Atlantic Multi-decadal Oscillation (AMO) and secondly by the Pacific Decadal Oscillation (PDO). In winter, the local Ekman heat transport is less effective than in summer in changing the OE front position because of the deep mixed layer. Our study demonstrates the seasonality of the OE front shift and highlights the importance of local Ekman heat transport associated with the AMO. Our results also partly explain the rainfall changes in both winter and summer in the western Pacific Ocean in the past 37 years, since the rainband east of Japan is affected by the sea surface temperature and its front.
Xiaopei Lin is supported by the China’s national key research and development projects (2016YFA0601803), the Qingdao National Laboratory for Marine Science and Technology (2017ASKJ01) and the National Natural Science Foundation of China (41490641, 41521091 and U1606402). The software used to generate all the results in this study is MATLAB.
- Bretherton CS, Widmann M, Dymnidov VP, Wallace JM, Blade I (1999) The effective number of spatial degrees of freedom of a time-varying field. J Clim 12:1990–2009. https://doi.org/10.1175/1520-0442(1999)012%3c1990:TENOSD%3e2.0.CO;2 CrossRefGoogle Scholar
- Deser C, Blackmon ML (1995) On the relationship between tropical and North Pacific sea surface temperature variations. J Clim 8:1677–1680. https://doi.org/10.1175/1520-0442(1995)008%3c1677:OTRBTA%3e2.0.CO;2 CrossRefGoogle Scholar
- Kalnay E, Kanamitsu M, Kistler R, Collins W, Deaven D, Gandin L, Iredell M, Saha S, White G, Woollen J, Zhu Y, Chelliah M, Ebisuzaki W, Higgins W, Janowiak J, Mo KC, Ropelewski C, Wang J, Leetmaa A, Reynolds R, Jenne R, Joseph D (1996) The NCEP–NCAR 40-year reanalysis project. Bull Am Meteorol Soc 77:1057–1072. https://doi.org/10.1175/1520-0477(1996)077%3C0437:TNYRP%3E2.0.CO;2 CrossRefGoogle Scholar
- Locarnini RA et al (2013) World ocean Atlas 2013, volume 1: temperature. In: Levitus S (Ed) A. Mishonov technical Ed.; NOAA Atlas NESDIS 73, 40 ppGoogle Scholar
- Mantua NJ, Hare SR, Zhang Y, Wallace JM, Francis RC (1997) A Pacific interdecadal climate oscillation with impacts on salmon production. Bull Am Meteorol Soc 78:1069–1079. https://doi.org/10.1175/1520-0477(1997)078%3C1069:APICOW%3E2.0.CO;2 CrossRefGoogle Scholar
- Monterey GI, Levitus S (1997) Seasonal variability of mixed layer depth for the world ocean. NOAA Atlas NESDIS 14, 96 ppGoogle Scholar
- Nakamura H, Lin G, Yamagata T (1997) Decadal climate variability in the North Pacific during the recent decades. Bull Am Meteorol Soc 78:2215–2225. https://doi.org/10.1175/1520-0477(1997)078%3c2215:DCVITN%3e2.0.CO;2 CrossRefGoogle Scholar
- Qiu B, Kelly KA (1993) Upper ocean heat balance in the Kuroshio Extension region. J Phys Oceanogr 23:2027–2041. https://doi.org/10.1175/1520-0485(1993)023%3c2027:UOHBIT%3e2.0.CO;2 CrossRefGoogle Scholar
- SSALTO/DUACS (2013) SSALTO/DUACS User Handbook: (M)SLA and (M)ADT Near-real time and delayed time productsGoogle Scholar
- Xie SP, Philander SGH (1994) A coupled ocean-atmosphere model of relevance to the ITCZ in the eastern Pacific. Tellus 46:340–350. https://doi.org/10.1034/j.1600-0870.1994.t01-1-00001.x CrossRefGoogle Scholar
- Zweng MM et al (2013) World ocean Atlas 2013, volume 2: salinity. Levitus S (Ed) A. Mishonov technical Ed.; NOAA Atlas NESDIS 74, 39 ppGoogle Scholar