Nonlinear mechanism for polar motion with period of 7 months

 The 7 month-period (sub-Chandler) wobble is considered with respect to the nonlinear dynamical equation of polar motion. Starting with the frequency modulation of Chandler wobble (CW) in the model developed by introduction of damping from perturbed visco-elastic deformation, the rotation equation of the CW becomes a resonance model with a time-dependent parameter. According to evolution calculation, the parameter resonance model is essentially identical to the reality of CW observations. If the frequency of CW is modulated about 3 by visco-elastic deformation, then the amplitude of CW will be modulated by greater than 70. On the other hand, bifurcation may occur according to the nonlinear dynamical system of the parameter resonance model, i.e. a pair of solutions splitting from the main CW. One is the 7-month-period wobble and the other is a motion with a period of about 28 months. Although the latter is very weak, the 7-month-period wobble will be observed as the stability condition is satisfied. The maximum amplitude is about 22.89 mas and the average 12.65 mas. This is identical to what is observed in reality. Received: 7 April 2000 / Accepted: 5 March 2001     

New type of pycnostad in the western subtropical-subarctic transition region of the North Pacific: Transition Region Mode Water

A new type of pycnostad has been identified in the western subtropical-subarctic transition region of the North Pacific, based on the intensive hydrographic survey carried out in July, 2002. The potential density, temperature and salinity of the pycnostad were found to be 26.5–26.7 σ _θ , 5°–7°C and 33.5–33.9 psu respectively. The pycnostad is denser, colder and fresher than those of the North Pacific Central Mode Water and different from those of other known mode waters in the North Pacific. The thickness of the pycnostad is comparable to that of other mode waters, spreading over an area of at least 650 × 500 km around 43°N and 160°E in the western transition region. Hence, we refer to the pycnostad as Transition Region Mode Water (TRMW). Oxygen data, geostrophic current speed and climatology of mixed layer depth in the winter suggest that the TRMW is formed regularly in the deep winter mixed layer near the region where it was observed. Analysis of surface heat flux also supports the idea and suggests that there is significant interannual variability in the property of the TRMW. The TRMW is consistently distributed between the Subarctic Boundary and the Subarctic Front. It is also characterized by a wide T-S range with similar density, which is the characteristic of such a transition region between subtropical and subarctic water masses, which forms a density-compensating temperature and salinity front. The frontal nature also tends to cause isopycnal intrusions within the pycnostad of the TRMW.     

On Structure and Temporal Variation of the Bifurcation Current off the Kii Peninsula

The Kii Bifurcation Current is often found along the southwest coast of the Kii Peninsula, and its frequency of occurrence reaches about 70% in the period from 1988 to 1996 (Takeuchi et al., 1998a). In order to clarify the structure and short-period variability of the Kii Bifurcation Current, detailed observations were made four times on board the R/V Seisui-maru of Mie University on October 29–31, 1996, on June 24–26, 1997, October 14–16, 1997, and December 3–4, 1997. The measured horizontal structure of the Kii Bifurcation Current indicates that the eastern portion of the Current (eastward flow near Cape Shionomisaki) consists of a part of the current zone of the Kuroshio. It is shown that the current structure, including the Kii Bifurcation Current in the vicinity of Cape Shionomisaki, is stable when the Kuroshio is flowing in a stationary straight path, but that the current structure is considerably changed when small-scale eddies pass by the cape. Such short-period variation can be monitored by using the daily variation of the sea level difference between Kushimoto and Uragami. In particular, in the case of October 29–31, 1996, when an eminent small-scale eddy passed by Cape Shionomisaki, and when the Kuroshio axis tentatively moved southwards about 50 km apart from the coast, the Kii Bifurcation Current seems to have disappeared.     

Bifurcation of Nonlinear Kelvin Wave-CISK with Conditional Heating in a Truncated Spectral Model:A Possible Mechanism of 30-60-Day Oscillation at the Equator

1.IntroductionSincethe40--50--dayoscillationinthetropicalPacificwasfirstfoundbyMaddenandJulian(1971,1972),ithaslongbeenanimportantresearchtopic.Inobservationalstudies,LauandChan(1985,1986),GhilandMo(1991)showedthattheintraseasonaloscillationsinthetro...     

亮点周围的衍射模式

将衍射问题研究中的回波解析奇性归结为探讨含参量的振荡积分的渐近性态问题,并利用广义函数的算子理论,以十分简捷的方式给出了上述振荡积分的稳定位相公式,以及结合Ｔｈｏｍ理论逐一地算出非退化奇点、岐点和脐点周围的衍射模式．     

冬季平流层波动模型的分岔特性

从描述波流相互作用的Ｈｏｌｔｏｎ－Ｄｕｎｋｅｒｔｏｎ简称Ｈ－Ｄ)模型出发,应用延拓方法求解常微分方程的分岔问题,研究冬季平流层波动模型的分岔特性．给出了大气行星波２与流相互作用的底部边界强迫波、底部边界平均纬向风场、风切变等参数的分岔特性,同时给出了波１与流相互作用的底部边界强迫波的分岔特性的结果．     

对流层强迫与平流层暴发性增温

采用平流层准地转－β通道近似下的波流相互作用模型,考虑大气行星波１和波２与流的相互作用,以平流层底部边界强迫波波１和波２的振幅作为参数,对该模型的分岔特性进行了研究．结果表明,系统具有稳态解支Ａ,Ｂ,Ｃ,在某些参数范围内,多种稳态解同时存在．解支Ａ对应于平流层冷冬状态,解支Ｃ对应于平流层增温状态．由于参数变化系统在稳态解Ａ和Ｃ之间发生灾变是冬季平流层暴发性增温的原因．文中给出了二维参数空间中的分岔集,它表明了对流层顶的波动对平流层暴发性增温的控制作用,能很好地解释观测事实．     

冬季平流层波动模型的分岔特性

从描述波流相互作用的Ｈｏｌｔｏｎ－Ｄｕｎｋｅｒｔｏｎ简称Ｈ－Ｄ)模型出发，应用延拓方法求解常微分方程的分岔问题，研究冬季平流层波动模型的分岔特性．给出了大气行星波２与流相互作用的底部边界强迫波、底部边界平均纬向风场、风切变等参数的分岔特性，同时给出了波１与流相互作用的底部边界强迫波的分岔特性的结果．