Zonal overturning circulation and heat flux induced by heaving modes in the world oceans
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Zonal overturning circulation and heat flux induced by heaving modes in the world oceans TAN Wei1, HUANG Rui Xin2, 3*, WANG Weiqiang2, WANG Xin2 1 Hohai University, Nanjing 210098, China 2 State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of
Sciences, Guangzhou 510301, China 3 Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
Received 8 May 2015; accepted 14 July 2015 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2015
Abstract
Zonal overturning circulation (ZOC) and its associated zonal heat flux (ZHF) are important components of the oceanic circulation and climate system, although these conceptions have not received adequate attentions. Heaving induced by inter-annual and decadal wind stress perturbations can give rise to anomalous ZOC and ZHF. Based on a simple reduced gravity model, the anomalous ZOC and ZHF induced by idealized heaving modes in the world oceans are studied. For example, in a Pacific-like model basin intensified equatorial easterly on decadal time scales can lead to a negative ZOC with a non-negligible magnitude (–0.3×106 m3/s) and a considerable westward ZHF with an amplitude of –11.2 TW. Thus, anomalous ZOC and ZHF may consist of a major part of climate signals on decadal time scales and thus play an important role in the oceanic circulation and climate change. Key words: adiabatic motions, heaving, wind-driven circulation, zonal overturning circulation, zonal heat flux Citation: Tan Wei, Huang Rui Xin, Wang Weiqiang, Wang Xin. 2015. Zonal overturning circulation and heat flux induced by heaving modes in the world oceans. Acta Oceanologica Sinica, 34(11): 80–91, doi: 10.1007/s13131-015-0751-3
1 Introduction The oceanic general circulation can be conceptually separated into two components: the wind-driven circulation and thermohaline circulation. Wind-driven circulation occupies the upper kilometer of the world oceans, and it is directly forced by wind stress, but it is not directly linked to the stratification in the ocean. In fact, wind-driven circulation can exist in a homogeneous ocean and the framework of the classical theory of winddriven circulation is built up in separation from the thermodynamics. On the other hand, thermohaline circulation occupies the entire depth of the world oceans, and it is closely linked to density difference induced by the surface thermohaline forcing, such as heat flux and freshwater flux. However, thermohaline circulation is a dissipation system, and its maintenance requires external source of mechanical energy which is supplied by wind stress, tidal dissipation and geothermal heat flux in the world oceans. Ideally, therefore, wind-driven circulation can be treated as adiabatic motions, but thermohaline circulation is intimately linked to diabatic motions. Circulation in the world oceans is a complicated system, and it involves transport of water masses, heat and freshwater in three dimensional space. To describe such complicated phenomena, many two-dimensiona
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