热带海气耦合距平模式中的ENSO循环及其形成机制  

NSO CYCLE IN A TROPICAL COUPLED OCEAN-ATMOSPHERE ANOMALY MODEL AND ITS FORMATION MECHANISM

作　　者：杨修群[1] 谢倩[2] 黄士松[1] 

机构地区：[1]南京大学大气科学系 [2]空军气象学院气象系

出　　处：《气象科学》1995年第4期134-157,共24页Journal of the Meteorological Sciences

基　　金：国家基础研究重大关键项目!"气候动力学和气候预测理论研究";国家自然科学基金

摘　　要：本文研制设计了一包含海洋表面边界层和大气福合反馈过程的热带太平洋海气耦台异常模式，进而利用该模式对ENSO循环进行了成功的模拟。通过对模式ENSO循环的演变特征及其形成机制的细致分析，揭示了ENSO暖位相的一种机制。指出：（1）和观测事实类似，模式ENSO循环涉及了三种时间尺度过程即具有3－4年主周期的甚低频振荡模态（LF）、准两年振荡（QB）和年循环（AC）；（2）ENSO循环的负反馈机制在冷暖态中表现不同，在冷态消亡过程中，这种负反馈过程主要表现为西边界反射产生的时滞效应，但在暖态消亡过程中不存在类似的时滞效应，其负反馈过程主要表现为在海气耦合不稳定充分发展时伴随的赤道两侧冷水上翻过程的加强以及非线性过程的衰减作用抑制了不稳定的发展并最终使得系统恢复至冷态，（3）ENSO循环的3－4年主周期振荡（LF）是一非线性系统的自激振荡现象，其形成是线性系统的本征模即准两年振荡（QB）通过“单向性”大气辐合反馈加热过程减频增幅所致；（4）虽然年循环（AC）过程对ENSO循环形成没有本质影响，但它可明显影响ENSO循环的具体振幅和位相，使得ENSO以季节循环有明显的“销相”特征，并也使ENSO循环在振幅大小和时间长短方面呈现出明显的不规则性。因此，ENSO变化性是LF、QB和AC等多?A tropical Pacific coupled ocean -atmosphere anomaly model was developed for simulat ing ENSO cycle. The coupled model was run 30 years. The key features of the ENSO cycle were successfully simulated both in its horizontal spatial structure and in its temporal variabil. Based on analyses of the simulated results, a new possible negative feedback mechanism responsible for the ENSO cycle was proposed, and further a nonlinear analog model for explaining the time scale selection of the model ENSO variability was also presented. The main results show. that the model ENSO varibility involves a process with three time scales,i. e. the 3-4 year lower-frequency(LF) principle period. quasi- biennial (QB) oscillation and annual cycle (AC), that is qualitatively in agreement with the observational fact. The negative feeback mechanism that checks the unstable air - sea interaction in ENSO cycle warm phase obviously differs form that in cold phase. During the damping period of cold state, the mechanism is related to the delayed effect produced by the wave reflection at the western boundary. However, during the damping period of warm state, instead of reflection effect, the anomalous upwelling of cold water of f the equator accompanied with the strong development of unstable air-sea interaction at the equator and the nonlinear damping effect jointly restrain the instability and finally draw the system from the mature warm phase to the weak cold phase. The 3-4 year principle period oscillation (LF) is a self-exciting oscillation of nonlinear system. The time scale selection results from frequency decreased process of the QB mode that may be the intrinsic mode of the coupled system. via the certain nonlinear mechanism, in which the single-way atmospheric convergence feedback heating process appears mostly important. Although the annual cycle process can not fundamentally influence the formation of ENSO cycle, it can notably fix the phase and modulate the amplitude.Resultantly, the individual warm/cold events in ENSO cycle appear

关 键 词：热带 海气耦合 距平模式 厄尔尼诺 形成机制 

分 类 号：P732.6[天文地球—海洋科学]