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To illustrate the formation mechanisms for the Pacific decadal oscillation (PDO) and the North Pacific gyre oscillation (NPGO) as the dominant and less dominant climate patterns of the North Pacific, and correlations between their periods of oscillation and the length of the ocean in the East-West direction, this paper adopts a mid-latitude channel linear quasi-equilibrium ocean model with reduced gravity to seek the analytical solution of the ocean flow field response to zonal wind forcing, with a special focus on resonance. Main findings include that the response pattern of the bounded ocean resembles the PDO and NPGO modes during winter respectively; specifically, to the east of the west coast of the ocean, the former is characterized by a gyre in an oval shape and the latter by two gyres rotating in opposite directions in the north and the south, constituting a gyre couple; across the entire ocean, the former features basin-wide ocean general circulation, while the latter features basin-wide general circulation in the north and the south respectively, which rotate in opposite directions. The above situations can be forced by anomalous positions of mid-latitude westerlies to the north and the south respectively. The frequency (period) of ocean flow field response to zonal wind field forcing is identical to the frequency (period) of zonal wind forcing; the response is observed after zonal wind forcing while the flow field (stream function) of the response is proportional to the zonal wind in scale. When the frequency (period) of zonal wind forcing equals that of the natural frequency (period) of the ocean, resonance will happen, with the observation of the strongest ocean response; while when the two frequencies differ by wide margins, rather small response will be observed. Smaller frictions correlate with stronger resonance along with more resonance occurrences. The length of the bounded ocean in the East-West direction has an obvious effect on the natural frequency (period), namely, the frequency (period) of resonance, and plays a decisive role in determining such a frequency; the distance between two neighboring resonance periods increases as the length is reduced. Different non-linear air-sea interactions lead to the complexity of the oscillation frequencies of a random wind field, ranging from extremely low to extremely high frequencies; through the resonance, resonance period identical or similar to the natural frequency of the ocean can be identified, at which frequency the ocean flow response to wind fields is the strongest, thus determining the periods of the PDO and NPGO. The final conclusion is that such a non-linear interaction, the effect of wind field forcing on flow field, and resonance are three key factors leading to the PDO and NPGO; the analytical solution is in nature a time-varying resonant Rossby wave.
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Keywords:
- bounded ocean /
- zonal wind /
- resonance /
- Pacific decadal oscillation
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[6] Liu 2010 Deep-Sea Res. Ⅱ 57 1098
[7] Wang S S, Guan Y P, Li Z J, Cao Y, Huang J P 2012 Acta Phys. Sin. 61 169201 (in Chinese)[王闪闪, 管玉平, Li Zhi-Jin, Cao Yi, 黄建平 2012 61 169201]
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[11] Furtado J C, Lorenzo E D, Schneider N, Bond N A 2011 J. Climate 24 3049
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[19] Zhang Y C, Zhang L F, Luo Y 2010 J. Trop. Meteor. 16 51
[20] Zhang Y C, Zhang L F, Lyu Q P Lyu Q P, Zhang W F, Zhang M 2013 Climatic Environ. Res. 18 124 (in Chinese)[吕庆平, 张维锋, 张铭 2013 气候与环境研究 18 124]
[21] Lyu Q P, Zhang W F, Zhang M 2013 Climatic Environ. Res. 18 124 (in Chinese) [吕庆平, 张维锋, 张铭 2013 气候与环境研究 18 124]
[22] Lyu Q P, Lu X, Zhu J, Dai W H, Zhang M 2015 J. Marin. Sci. 33 1 (in Chinese)[吕庆平, 卢姁, 朱娟, 戴文灝, 张铭 2015 海洋学研究 33 1]
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[27] Qu W Z, Huang F, Zhao J P, Jia Y L, Li C, Yue S H 2008 Oceanol. Limnol. Sin. 39 552 (in Chinese)[曲维政, 黄菲, 赵进平, 加英莱, 李春, 岳淑红 2008 海洋与湖沼 39 552]
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[1] Mantua N J, Hare S R, Zhang Y, Wallace J M, Francis R C 1997 Bull. Amer. Meteor. Soc. 78 1069
[2] Newman M, Alexander M A, Ault T R, et al. 2016 J. Climate 29 4399
[3] Yang X Q, Zhu Y M, Xie Q, Ren X J, Xu G Y 2004 Chin. J. Atmos. Sci. 28 979 (in Chinese)[杨修群, 朱益民, 谢倩, 任雪娟, 徐桂玉 2004 大气科学 28 979]
[4] Wu D X, Lin X P, Wan X Q, Lan J 2006 Acta Oceanol. Sin. 28 1 (in Chinese)[吴德星, 林霄沛, 万修全, 兰健 2006 海洋学报 28 1]
[5] Sun D, Bryan F 2010 Climate Dynamics:Why does Climate Vary? (Washington DC:American Geophys Uninon Press) p123
[6] Liu 2010 Deep-Sea Res. Ⅱ 57 1098
[7] Wang S S, Guan Y P, Li Z J, Cao Y, Huang J P 2012 Acta Phys. Sin. 61 169201 (in Chinese)[王闪闪, 管玉平, Li Zhi-Jin, Cao Yi, 黄建平 2012 61 169201]
[8] Liu Q Y, Li C, Hu R J 2010 Climatic Environ. Res. 15 217 (in Chinese)[刘秦玉, 李春, 胡瑞金 2010 气候与环境研究 15 217]
[9] Lorenzo E D, Schneider N, Cobb K M, Franks P, Chhak K, Miller A, Mcwilliams J, Bograd S, Arango H, Curchitser E 2008 Geophys. Res. Lett. 35 L08607
[10] Cummins P F, Lagerloef G S E, Mitchum G 2005 Geophys. Res. Lett. 32 L17607
[11] Furtado J C, Lorenzo E D, Schneider N, Bond N A 2011 J. Climate 24 3049
[12] Zhang W, Luo M 2016 Atmos. Sci. Lett. 17 437
[13] Rafter P A, Sanchez S C, Ferguson J, Carriquiry J D, Druffel E R M 2017 Quaternary Sci. Rev. 160 108
[14] Chhak K, Lorenzo E D 2009 J. Climate 22 1255
[15] Ceballos L, Lorenzo E D, Hoyos C D 2009 J. Climate 22 5163
[16] Cabanes C, Huck T, Verderee C D 2006 J. Phys. Oceanogr. 36 1739
[17] Qiu B, Chen S M 2010 Deep-Sea Res. Ⅱ. 57 1098
[18] Zhang Y C, Zhang L F 2009 Adv. Earth Sci. 24 1119 (in Chinese)[张永垂, 张立凤 2009 地球科学进展 24 1119]
[19] Zhang Y C, Zhang L F, Luo Y 2010 J. Trop. Meteor. 16 51
[20] Zhang Y C, Zhang L F, Lyu Q P Lyu Q P, Zhang W F, Zhang M 2013 Climatic Environ. Res. 18 124 (in Chinese)[吕庆平, 张维锋, 张铭 2013 气候与环境研究 18 124]
[21] Lyu Q P, Zhang W F, Zhang M 2013 Climatic Environ. Res. 18 124 (in Chinese) [吕庆平, 张维锋, 张铭 2013 气候与环境研究 18 124]
[22] Lyu Q P, Lu X, Zhu J, Dai W H, Zhang M 2015 J. Marin. Sci. 33 1 (in Chinese)[吕庆平, 卢姁, 朱娟, 戴文灝, 张铭 2015 海洋学研究 33 1]
[23] Zhang D L, Lyu Q P, Zhang L F 2015 Chin. J. Atmos. Sci. 39 692 (in Chinese)[张东凌, 吕庆平, 张立凤 2015 大气科学 39 692]
[24] Lyu Q P, Lu K C, Zhang M 2013 Climatic Environ. Res. 18 210 (in Chinese)[吕庆平, 路凯程, 张铭 2013 气候与环境研究 18 210]
[25] Lu K C, Yu J, Lyu Q P, Zhang M 2014 Adv. Marin. Sci. 32 467 (in Chinese)[路凯程, 于杰, 吕庆平, 张铭 2014 海洋科学进展 32 467]
[26] Ding Y H, Sun Y, Liu Y Y, Si D, Wang Z Y, Zhu Y X, Liu Y J, Song Y F, Zhang J 2013 Chin. J. Atmos. Sci. 37 253 (in Chinese)[丁一汇, 孙颖, 刘芸芸, 司东, 王遵娅, 朱玉祥, 柳艳菊, 宋亚芳, 张锦 2013 大气科学 37 253]
[27] Qu W Z, Huang F, Zhao J P, Jia Y L, Li C, Yue S H 2008 Oceanol. Limnol. Sin. 39 552 (in Chinese)[曲维政, 黄菲, 赵进平, 加英莱, 李春, 岳淑红 2008 海洋与湖沼 39 552]
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