太平洋年代际信号中瞬变强迫的作用

发布时间：2018-05-03 01:25

  本文选题：PDO + NPGO　； 参考：《南京大学》2015年硕士论文

【摘要】：中纬度气候存在着显著的年代际信号。在北太平洋最主要的年代际信号有太平洋年代际振荡(PDO)和北太平洋涡旋振荡(NPGO),对应大气中的阿留申低压模态(AL)和北太平洋振荡(NPO)。太平洋年代际信号的产生与维持同中纬度海气相互作用有密切的关系。中纬度海表面温度(SST)异常一方面通过直接热力强迫引起大气环流异常,另一方面还可以通过海洋锋区影响天气尺度涡旋的形成和发展,天气尺度涡旋的非线性作用对低频流产生强迫,后者的作用尤为重要。本文利用1948-2010年北半球冬季NCEP再分析资料诊断了与PDO和NPGO信号相关的大气环流异常和天气尺度瞬变活动异常特征,讨论了海洋锋区天气尺度波与低频流相互作用在大气环流对PDO以及NPGO对应的SST异常响应中的贡献,并建立简单理论模型描述中纬度海洋和大气的耦合过程。本文主要得出以下结论：PDO暖位相时北太平洋海盆区为SST冷异常,对应的SST异常的南北梯度在北太平洋是一个偶极的结构。在北太平洋有两条海洋锋区：副热带锋区和副极地锋区,PDO暖位相时,副极地锋区南移,加强了副热带锋区。伴随着副极地锋区的南移和副热带锋区的加强,风暴轴的活动也随着南移增强。天气尺度瞬变涡旋的涡度输送和热力输送共同作用使得阿留申低压增强并向东南偏移,急流增强。NPGO暖位相时北太平洋SST异常呈现偶极型结构,约以40℃N为界,40℃N以北为冷异常,40℃N以南为暖异常,对应的是副极地锋区的增强和副热带锋区的北移,风暴轴增强。瞬变涡旋的非线性强迫使得阿留申低压和夏威夷上空副热带高压都增强,急流向北移动。对于PDO和NPGO,大尺度环流场都是相当正压结构,温度场都是斜压结构。使用理论模型模拟的结论表明,海气耦合的结果就是被强迫的海洋Rossby波,最不稳定的波长大约10000km,对应的时间尺度基本是年代际时间尺度,与PDO以及NPGO的时间尺度相近。在这个海气耦合过程中,影响SST的主要作用是洋流对SST的南北输送作用,洋流对SST的南北输送使得所有波段都产生不稳定,而洋流异常导致的夹卷作用异常会抑制短波的不稳定,增加长波的不稳定,但作用比平流项弱。
[Abstract]:There are significant Interdecadal signals in the mid-latitude climate. The most important Interdecadal signals in the North Pacific are the Pacific Interdecadal Oscillation (PDO) and the North Pacific Vortex Oscillation (NPGOG), corresponding to the Aleutian low pressure mode (ALL) in the atmosphere and the North Pacific Oscillation (NPO). The generation of the Pacific Interdecadal signal is closely related to the maintenance of mid-latitude sea-air interaction. On the one hand, the SST-anomaly in mid-latitude sea surface temperature can cause the atmospheric circulation anomaly through direct thermal forcing, on the other hand, it can also influence the formation and development of synoptic scale vortices through the oceanic frontal region. The nonlinear action of synoptic vortex forces low frequency flow, the latter is especially important. In this paper, the characteristics of atmospheric circulation anomalies and synoptic scale transient anomalies associated with PDO and NPGO signals are diagnosed by using the NCEP reanalysis data from 1948-2010 in the Northern Hemisphere. The contribution of synoptic scale waves and low-frequency currents in ocean frontal region to the response of atmospheric circulation to SST anomaly corresponding to PDO and NPGO is discussed, and a simple theoretical model is established to describe the coupling process between mid-latitude ocean and atmosphere. In this paper, we draw the following conclusions: the North Pacific basin is a SST cold anomaly during the warm phase of the North Pacific Ocean, and the North and South gradient of the corresponding SST anomaly is a dipole structure in the North Pacific Ocean. There are two ocean fronts in the North Pacific: the subtropical front and the subpolar front. When PDO is warm, the subpolar front moves southward and strengthens the subtropical front. Along with the southward movement of the subpolar front and the strengthening of the subtropical front, the activity of the storm track increases with the southward shift. The vorticity transport and thermal transport of synoptic scale transient vortices make Aleutian low pressure increase and shift to the southeast. The SST anomaly in the North Pacific shows dipole structure during the warm phase of jet enhancement. The north of 40 鈩，

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