太平洋海温年代际变化结构及传播机制的初步研究

【作者】 程智；

【导师】 江志红；

【作者基本信息】 南京信息工程大学 ， 气象学， 2005， 硕士

【摘要】 利用美国Maryland大学的SODA海洋资料集分析了太平洋海温年代际变化的主要形式,并初步探讨了其年代际变化的可能原因,结果表明: (1)太平洋上层海温存在很强的年代际变化,其分布在不同层次有不同的分布形式,但年代际变率的大值层都对应于温度随深度变化的极大值处,表明年代际变率的垂直结构与温度层结有关。 (2)源自北太平洋中部海表的信号向深层延伸,并由窗口地区向西南潜沉,热带西南太平洋的信号越过赤道向东北挺进,两处信号沿20℃等温线传播,在副热带等温线转折处汇合,表明潜沉路径与温跃层的结构有关,海温年代际信号沿着温度随深度变化的极大值处传播,其优势周期在30年左右。 (3)北太平洋的年代际信号起源于海表的海气耦合,并由表面向深层传播,引起深层时间上的滞后。在海气耦合的过程中,海表风场的改变起了主导作用。通过改变潜热通量,风场的年代际变化极大地影响了海表温度,引起了北太平洋海温的年代际变化。 (4)在年代际尺度上,风应力异常通过风驱埃克曼关系改变了洋流,而洋流的年代际变化,会产生3种效应:(1)在经向上产生了异常的经向海流,改变了冷暖平流输送项;(2)在赤道地区,纬向急流的加速或减速产生了异常的Ekman漂流,通过热带和热带外的三维循环影响了海流的垂直运动;(3)洋流旋度的变化,通过辐散辐合引起的抽吸或下沉作用使得海温也发生了很大变化,即表层气旋式旋度加强,海流上升加强或下沉减弱,使海表温度变冷或变暖,若反气旋式旋度加强,则情况正好与之相反。因此,洋流的年代际变化对海温的影响也是不可忽视的。 本文对太平洋海温年代际变化的成因作了分析,但仅局限于诊断分析的初步探讨,至于其具体机制,有赖于洋流数值模式的论证。更多还原

【Abstract】 The main form of Pacific ocean temperature decadal variation and its probable origination investigated using Maryland Ocean Data Assimilation Analysis Datasets. The result show:(1) there is significant variation in the upper level of Pacific ocean, its distribution varies in different levels, but the remarkable levels all locate in the levels of the most variation with depths, which indicates that the vertical structure of Pacific decadal variation has the relationship with the stratificatrion of temperature. In thermocline, cold water is on top and warm water is at below, convection is stable, turbulence and mixture are not the same strong as in mixture level, so its thermal status is more stable. Actually thermocline performs the character that traps the signal propagating to deeper levels, which absorbes and reserves most signals, so the position of significant temperature decadal variation accords with the level of the most variation with depths.(2) The decadal signal from the surface of central north Pacific region extend to lower levels and subduct towards western south, the one from tropical western south Pacific get across equator and push forward to eastern north, the direction of propagation is along the position of most variation of temperature with depth, its main cycle is about 30 yrs. The direct character is that the water mass with greater density subducts below the one with little density, the distribution of density relates with temperature, salinity and pressure, the pressure term is little in upper levels and salinity term is quite less than temperature term. In fact, the distribution of isothermal surface represents the distribution of isopycnal surface in upper levels. So the subducting process lies on the structure of thermocline.(3) The decadal signal of north Pacific originals from ocean-atmosphere coupling, propagates from surface to deeper levels, and bring the lag of deeper levels. During the ocean-atmosphere coupling, the change of surface wind perform the key action. By changing the surface latent heat flux, the decadal change of surface wind greatly affects the surface temperature, which aroses the Pacific decadal variation. This is the direct affection of atmosphere circulation to Pacific ocean.(4) In decadal scale, wind force anomaly changes ocean current by Ekman connection, and current’s change affects ocean temperature, bring its decadal change.The distribution of both current and temperature are correspondent, the decadal change of ocean temperature changes of warm currents and cold currents, and affects the vertical motion by three-dimension circulation, makes the greatly changes of ocean temperature. So the affection of ocean current to ocean temperature is not neglectable. The change of cold currents or warm currents and vertical motion is the main form of ocean current’s affection to ocean temperature, and it’s the indirect affection of atmosphere circulation to ocean temperature.Our article analyse the reason of Pacific ocean temperature decadal variability, but they only focus on diagnoses, the origin lies on ocean numerical models.更多还原