Abstract
Seasonal variability of the North Equatorial Current (NEC) transport in the western Pacific Ocean is investigated with ECMWF Ocean Analysis/Reanalysis System 3 (ORA-S3). The result shows that NEC transport (NT) across different longitudes in the research area shows a similar double-peak structure, with two maxima (in summer and winter), and two minima (in spring and autumn). This kind of structure can also be found in NEC geostrophic transport (NGT), but in a different magnitude and phase. These differences are attributable to Ekman transport induced by the local meridional wind and transport caused by nonzero velocity at the reference level, which is assumed to be zero in the NGT calculation. In the present work, a linear vorticity equation governing a 1.5-layer reduced gravity model is adopted to examine the dynamics of the seasonal variability of NGT. It is found that the annual cycle of NGT is mainly controlled by Ekman pumping induced by local wind, and westward-propagating Rossby waves induced by remote wind. Further research demonstrates that the maximum in winter and minimum in spring are mostly attributed to wind east of the dateline, whilst the maximum in summer and minimum in autumn are largely attributed to that west of the dateline.
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Antonov J I, Seidov D, Boyer T P, Locarnini R A, Mishonov A V, Garcia H E, Baranova O K, Zweng M M, Johnson D R. 2010. World Ocean Atlas 2009, Volume 2: Salinity. In: Levitus S ed. NOAA Atlas NESDIS 69, US Government Printing Office, Washington DC, America. 184p.
Balmaseda M A, Vidard A, Anderson D L T. 2008. The ECMWF Ocean Analysis System: ORA-S3. Mon thly Wea ther Rev iew, 136(8): 3 018–3 034, http://dx.doi.org/10.1175/2008MWR2433.1.
Capotondi A, Alexander M A, Deser C. 2003. Why are there Rossby wave maxima in the Pacific at 10°S and 13°N?. Journal of Physical Oceanography, 33(8): 1 549–1 563.
Capotondi A, Alexander M A. 2001. Rossby waves in the tropical North Pacific and their role in decadal thermocline variability. Journal of Physical Oceanography, 31(12): 3 496–3 515, http://dx.doi.org/10.1175/1520-0485(2002)031〈3496:RWITTN〉2.0.CO;2.
Carton J A, Giese B S. 2008. A reanalysis of ocean climate using simple ocean data assimilation (SODA). Mo nthly Weather Rev iew, 136(8): 2 999–3 017, http://dx.doi.org/10.1175/2007MWR1978.1.
Chelton D B, deSzoeke R A, Naggar K E, Siwertz N. 1998. Geographical variability of the first-baroclinic Rossby radius of deformation. Journal of Physical Oceanography, 28(3): 433–460, http://dx.doi.org/10.1175/1520-0485(1998)028〈0433:GVOTFB>2.0.CO;2.
Chen Z H, Wu L X. 2011. Dynamics of the seasonal variation of the North Equatorial Current bifurcation. Journal of Geophysical Research, 116(C02018): 1–14, http://dx.doi.org/10.1029/2010JC006664.
Donguy J R, Meyers G. 1996. Mean annual variation of transport of major current in the tropical Pacific ocean. Deep Sea Res. Part 1, 43(7): 1 105–1 122, http://dx.doi.org/10.1016/0967-0637(96)00047-7.
Gu Y H. 1996. Zonal volume transports at 137°E in the northwestern Pacific. Oceanologia et Limnologia Sinica, 27(1): 79–85. (in Chinese with English abstract)
Hosoda S, Ohira T, Nakamura T. 2008. A monthly mean dataset of global oceanic temperature and salinity derived from Argo float observations. JAMSTEC Rep. Res. Dev., 8: 47–59.
Hsin Y C, Qiu B. 2012. Seasonal fluctuations of the surface North Equatorial Countercurrent (NECC) across the Pacific basin. Journal of Geophysical Research, 117(C06001): 1–17, http://dx.doi.org/10.1029/2011JC007794.
Hu D X, Cui M C. 1991. The western boundary current of the Pacific and its role in the climate. Chinese Journal of Oceanology and Limnology, 9(1): 1–14, http://dx.doi.org/10.1007/BF02849784.
Kang L, Wang F, Chen Y L. 2011 Characteristics of temporal and spatial distribution of North Pacific low-lalitude Western Boundary Currents. Marine Forcasts, 28(3): 32–39. (in Chinese with English abstract)
Kashino Y, España N, Syamsudin F, Richards K J, Jensen T, Dutrieux P, Ishida A. 2009. Observations of the North Equatorial Current, Mindanao Current, and Kuroshio Current System during the 2006/07 El Niño and 2007/08 La Niña. Journal of Oceanography, 65(3): 325–333, http://dx.doi.org/10.1007/s10872-009-0030-z.
Kessler W S. 1990. Observations of long Rossby waves in the northern tropical Pacific. Journal of Geophysical Research, 95(C4): 5 183–5 217, http://dx.doi.org/10.1029/JC095iC04p05183.
Kim Y Y, Qu T D, Jensen T, Miyama T, Misudera H, Kang H W, Ishida A. 2004. Seasonal and interannual variations of the North Equatorial Current bifurcation in a highresolution OGCM. Journal of Geophysical Research, 109(C03040): 1–19, http://dx.doi.org/10.1029/2003JC002013.
Locarnini R A, Mishonov A V, Antonov J I, Boyer T P, Garcia H E, Baranova O K, Zweng M M, Johnson D R. 2010. World Ocean Atlas 2009, Volume 1: Temperature. In: Levitus S ed. NOAA Atlas NESDIS 68, U.S. Government Printing Office, Washington DC, America. 184p.
Masumoto Y, Yamagata T. 1991. Response of the western tropical to the Asian winter Monsoon: the generation of the Mindanao Dome. Journal of Physical Oceanography, 21(9): 1 386–1 398, http://dx.doi.org/10.1175/1520-0485(1991)021〈1386:ROTWTP>2.0.CO;2.
McCreary J P, Lu P. 1994. Interaction between the subtropical and equatorial ocean circulation: the Subtropical Cell. Journal of Physical Oceanography, 24(2): 466–497.
Meyers G. 1979. On the annual Rossby wave in the tropical North Pacific Ocean. Journal of Physical Oceanography, 9(4): 663–674.
Nitani H. 1972. Beginning of the Kuroshio. In: Stommel H eds. Kuroshio: Its Physical Aspects. Tokyo: University of Tokyo Press, Tokyo, Japan. p.129–163.
Qiu B, Chen S M. 2010. Interannual-to-decadal variability in the bifurcation of the North Equatorial Current off the Philippines. Journal of Physical Oceanography, 40(11): 2 525–2 538.
Qiu B, Joyce T M. 1992. Interannual variability in the mid- and low-latitude Western North Pacific. Journal of Physical Oceanography, 22(9): 1 062–1 079.
Qiu B, Lukas R. 1996. Seasonal and interannual variability of the North Equatorial Current, the Mindanao Current and the Kuroshio along the Pacific western boundary. Journal of Geophysical Research, 101(C5): 12 315–12 330.
Qu T D, Mitsudera H, Yamagata T. 1998. On the western boundary currents in the Philippine Sea. Journal of Geophysical Research, 103(C4): 7 537–7 548.
Song D, Hu D X, Zhai F G. 2012. Sea surface height variations in the Mindanao Dome region in response to the northern tropical Pacific winds. Chinese Journal of Oceanology and Limnology, 30(4): 675–683, http://dx.doi.org/10.1007/s00343-012-1155-2.
Stewart R H. 2008. Introduction to Physical Oceanography. Texas A & M University. http://oceanworld.tamu.edu/resources/ocng_textbook/PDF_files/book.pdf. Accessed on 2012-12-12.
Sun X P. 2000. A comparison of characteristics between the subtropical countercurrent, the north Equatorial current and the north Equatorial countercurrent in the northwestern Pacific Ocean. Journal of Oceanography of Huanghai & Bohai Seas, 18(1): 1–12. (in Chinese with English abstract)
Toole J M, Millard R C, Wang Z, Pu S. 1990. Observations of the Pacific North Equatorial bifurcation at the Philippine coast. Journal of Physical Oceanography, 20(2): 307–318.
Toole J M, Zou E, Millard R C. 1988. On the circulation of the upper waters in the western equatorial Pacific Ocean. Deep Sea Research Part A, 35(9): 1 451–1 482.
Wang F, Chang P, Hu D X, Seidel H. 2002. Circulation in the western tropical Pacific Ocean and its seasonal variation. Chinese Science Bulletin, 47(7): 591–595.
Wunsch C. 1997. The vertical partition of oceanic horizontal kinetic energy. Journal of Physical Oceanography, 27(8): 1 770–1 794.
Yaremchuk M, Qu T D. 2004. Seasonal variability of the largescale currents near the coast of the Philippines. Journal of Physical Oceanography, 34(4): 844–855.
Zhai F G, Hu D X. 2012. Interannual variability of transport and bifurcation of the North Equatorial Current in the tropical North Pacific Ocean. Chinese Journal of Oceanology and Limnology, 30(1): 177–185, http://dx.doi.org/10.1007/s00343-012-1194-8.
Zhai F G, Hu D X. 2013. Revisit the interannual variability of the North Equatorial Current transport with ECMWF ORA-S3. Journal of Geophysical Research, 118(3): 1 349–1 366, http://dx.doi.org/10.1002/jgrc.20093.
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Supported by the National Basic Research Program of China (973 Program) (Nos. 2012CB417401, 2013CB956202) and the Major Project of National Natural Science Foundation of China (No. 40890151)
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Yan, Q., Hu, D. & Zhai, F. Seasonal variability of the North Equatorial Current transport in the western Pacific Ocean. Chin. J. Ocean. Limnol. 32, 223–237 (2014). https://doi.org/10.1007/s00343-014-3052-3
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DOI: https://doi.org/10.1007/s00343-014-3052-3