大气激发和观测极移之间的转换变化分析

本文采用１９８４－１９９２年期间日本气象厅（ＪＡＭ）推算出的大气激发函数序列（χ１，χ２），和美国喷气推进实验室（ＪＰＬ）提供的Ｓｐａｃ３极坐标序理经过反卷积而的测地激发函数（ψ１，ψ２）进行了比较。同时也比较了极移（ｘ，ｙ）和从大气激发序列归算出（经过卷积）激发极移（ｍ１，ｍ２）     

大气激发和观测极移之间的转换变化分析

本文采用１９８４—１９９２年期间日本气象厅（ＪＡＭ）推算出的大气激发函数序列（χ１，χ２），和美国喷气推进实验室（ＪＰＬ）提供的Ｓｐａｃｅ９３极坐标序列经过反卷积而推出的测地激发函数（ψ１，ψ２）进行了比较。同时也比较了极移（ｘ，ｙ）和从大气激发序列归算出（经过卷积）激发极移（ｍ１，ｍ２）。     

不同频段上极移,日长变化与大气角动量变化激发结果的比较

本文用ＪＭＡ大气角动量序列计算了对极移和日长变化的激发量（ｍ＇１、ｍ＇２和ｍ＇３），并分三个频段与天文观测得到的地球自转参数序列（ｍ１、ｍ２和ｍ３）进行了比较．结果表明：在钱德勒和季节性频段上，大气运动确实是固体地球自转变化的主要激发源．     

全球地表水储量再分布对周年极移的激发

利用全球降水和蒸发观测同化资料以及国际大气模式比较计划和国际大气海洋耦合模式比较计划中的陆面过程数值模式，计算比较了地表水储量角动量变化对周年极移的激发，分析结果表明基于3种资料的地表水储量角动量变化对极移周年正向频率的激发约占大气周年正向激发的10%至25%，研究结果尽管显示大气，海洋和地表水的综合周年正向激发与极移测地周年正向激发十分相近，鉴于海洋角动量数值分析的差异和目前对全球水循环观测的水准以及对水循环平衡问题有限的理解，仍然期待更为客观的全球海洋，陆面动力过程和数值分析方法用于完善全球地表水储量变化对周年极移激发的研究。     

极移的半年振荡和大气激发的贡献

本文采用国际地球自转服务（IERS）测定的均匀极坐标序列及日本气象局（JMA）提供的大气激发函数赤道分量而求得的激发极移序列来研究它们的半年振荡变化。两种序列进行了比较，相关估计给出x相对于m1的相关系数为0.69，y相对于m2的相关系数为0.52。因此，我们认为大气质量角动量赤道分量对极移半年项有一部分贡献。这些影响表现在x轴方向稍强于y轴方向。结果表明：观测极移和激发极移的半年振荡的周期及振幅都是随时间而变化的。     

周年极移与旱涝灾害

本文对周年极移年均值序列,用关键年分析的方法划分了周年极移周,研究了周年极移统计分布的特征以及长江中下游地区大面积旱涝年的频率分布,得到了灾害发生的主要规律,并对未来灾害趋势作了预测。     

大气和极移的高频变化比较

采用从1988－1999年的现代技术测定的高精度极移序列EOP（IERS97C04）推导出激发函数χ^m）和美国国家环境预测中心和美国国家大气研究中心（CNEP／NCAR）提供的大气角动量激发函数χp和χib^p，使用几种数据分析方法，分析了大气对极移高频振荡（12－42cpy)激发贡献，复数小波变换和功率谱分析表明，χ^m和χ^p序列在高频段内呈现比较强的谱峰，它们具有相似的谱特征，比较而言，χib^p在这个频率段内比χ^p要弱些，χ^m和χ^p之间的相关系数分别为0．75（逆向）和0．6（顺向），两个序列之间的平方相关谱的估计值分别在0．5－0．9之间（负频）和0．4－0．6（正频），相位谱表明χ^p(AAM)超前x^m一天左右，这些大气是极移高频变化的主要激发源，特别是在逆向运动上具有更大的贡献，由于它们之间位相差和振幅变化的不稳定性，说明可能存在AAM以外的其他激发源，这个问题有待进一步深入研究。χ     

周年极移序列的Markov链概型

本文根据Ｍａｒｋｏｖ随机过程理论，给出了周年极移振幅ｒａ序列的一阶Ｍａｒｋｏｖ链概型，并建立了ｒａ序列增加年Ｒ与减小年Ｄ游程以及（Ｒ十Ｄ）游程循环（周年极移循环）的概率分布模式，经统计假设检验，一阶Ｍａｒｋｏｖ链可以很好拟合。序列的变化过程．得到了ｒａ不同状态的平均首次到达时间矩阵，其值大多与实测符合．ｒａ的基本周期为２年、６．０７年、６．５４年、７．０８－８．５０年、２１．２５－２８．３３年和８５年，而６．０７年是它的一个主要周期．由Ｍａｒｋｏｖ链的遍历性定理得到，预报ｒａ时取用在此之前的第６—１３个以内的样本为宜．     

地球自转极移近120天准周期变化的小波分析及其大气激发机制

本文利用小波变换这一新的频谱分析方法研究了地球自转极移近１２０天准周期变化的时频特征，证实了在极移序列中存在显著的近１２０天准周期振荡，得到了极移准周期变化的周期与振幅随时间变化的规律．以地球自转动力学为基础，在时域内分析了大气变化对自转极移季节内变化的激发．表明大气激发在本文所研究的频段内是极移短周期变化的主要激发源。并发现在极移近１２０天准周期振荡平静时期，发生ＥＬＮｉｎｏ事件，同时日长变化近１２０天准周期变化增强．     

极移速度的周期分析

本文对瞬时极的移动速度用自回归谱估计的Marple算法进行了周期分析，结果表明，瞬时极的移动速度可能存在着2386.天（6.5天）、1168.9天（3.2年）、321.3天、163.7天、130.1天及92.7天等6个周期，同时计算了极移的振幅和周期，发现极移的速度与极移的振幅正相关，与极移的周期负相关，并且发现厄尔尼诺现象都出现在地极移动周期较短的年份。     

大气对地球自转变化的影响-方法和数据的深入分析

大气相对固体地球的运动产生大气相对角动量，它的变化可以激发地球自转多时间尺度的变化．计算大气相对角动量现在采用两种不同的垂直积分高度，一种为从地形表面积分到顶层大气，称之为SP方法；另一种为从1000hPa积分到顶层大气，称之为BP方法，对采用这两种方法所得到的大气相对角动量进行了详细的比较．应用欧洲中距气象预报中心（ECMWF）和美国国家环境预报中心（NCEP）大气再分析数据，重新研究了大气相对角动量变化的时空特征．通过对大气相对角动量季节平均，季节振幅和时空特征的分析，得出ECMWF和NCEP的大气相对角动量变化对地球自转周年极移的影响，在亚洲季风区域和南极洲区域差别最为明显．     

IGS′92联测期间地极坐标的高频波动

本文分析了ＩＧＳ＇９２联测期间七个ＧＰＳ数据处理中心提供的极坐标序列。通过谱分析、最小二乘拟合和Ｆ检验，表明在这些序列中存在一些共同的高频波动：在Ｘ方向上具有２７．０，１６．５，１３．４和１０．４天的周期，在Ｙ方向上的波动周期约为２０．５，１５．８和１０．０天。并且每个序列与ＥＯＰ（ＩＥＲＳ）９２Ｃ０４之间都存在一个系统差。计算与分析表明，这些系统偏离的主要原因是由于在用ＧＰＳ资料解算Ｘ、Ｙ时，不同分析中心采用了不同系统的台站坐标（或者说只有部分台站采用了固定的台站坐标），从而造成这些序列所在的参考架与ＩＴＲＦ９１之间存在一个平移和旋转。最后，计算了该期间的大气角动量激发函数，可部分地解释该期间的Ｘ、Ｙ高频波动的原因。     

Excitation of Annual Polar Wobble by Global Oceans

A reasonable and quantitative result on the variation of polar wobble excited by the oceans is not available at present. Numerous researches have shown that atmospheric motion is the greatest excitation source for the seasonal variations in the polar wobble and that oceanic motion is one of the main remaining excitation sources. The excitation of variation in the annual polar wobble caused by oceans from 1992 to 2004 both globally and in latitude dependence, have been studied in depth by means of the new generation of SODA oceanic data assimilation (SODA-1.4.2 and SODA-1.4.3) and the ECCO oceanic data assimilation. The result shows that the variation in the seasonal polar wobble excited by the SODA oceans is very close to that of the residual after the action of the atmosphere and land water is deducted from the geodesic excitation function for a large part of the investigated time interval, and that there is overall agreement between the two as regards the annual amplitude and phase. In addition, in comparison with the result of early SODA-Bata 7, the new generation of SODA oceanic excitation has achieved obvious improvements. The latitude distributions of the excitations of the annual polar wobble by the SODA and ECCO oceans are consistent in the Greenwich direction, while having obvious differences in the direction of 90° E.     

大气角动量变化以及对地球自转季节变化的激发

利用日本气象局AMIPⅡ大气数值模式的输出结果，基于BP方法和SP方法计算了1979年至1996年大气角动量变化以及对地球自转季节变化激发的差异。利用最小二乘谐波拟合方法和气候平均图方法，分析了大气角动量的季节变化，并与同时期采用NCEP再分析资料和JMA客观分析资料计算的大气角动量进行比较。     

Atmospheric angular momentum variations of Earth, Mars and Venus at seasonal time scales

Atmospheric angular momentum variations of a planet are associated with the global atmospheric mass redistribution and the wind variability. The exchange of angular momentum between the fluid layers and the solid planet is the main cause for the variations of the planetary rotation at seasonal time scales. In the present study, we investigate the angular momentum variations of the Earth, Mars and Venus, using geodetic observations, output of state-of-the-art global circulation models as well as assimilated data. We discuss the similarities and differences in angular momentum variations, planetary rotation and angular momentum exchange for the three terrestrial planets. We show that the atmospheric angular momentum variations for Mars and Earth are mainly annual and semi-annual whereas they are expected to be “diurnal” on Venus. The wind terms have the largest contributions to the LOD changes of the Earth and Venus whereas the matter term is dominant on Mars due to the CO₂ sublimation/condensation. The corresponding LOD variations (ΔLOD) have similar amplitudes on Mars and Earth but are much larger on Venus, though more difficult to observe.     

研究Chandler摆动的一个随机激发模型

基于同运动激发了Chandler摆动的假设，提出一个研究Chandler摆动的随机非线性模型，它是由一个随机性阶梯函数和一个具有阻尼的线性谐振子的Euler中心差分格式混合而成，研究此模型中各个参数与Chandler摆动振幅的关系，通过对基于实测资料获得的有效大气角动量时间序列的统计分析，初步发现其中含有随机噪声成份，它可以激发目前观测到的Chandler摆动振幅的28－40％，最后，对Chandler摆胡机激发的假设作了一些讨论。     

Bulges versus discs: the evolution of angular momentum in cosmological simulations of galaxy formation

We investigate the evolution of angular momentum in simulations of galaxy formation in a cold dark matter universe. We analyse two model galaxies generated in the N -body/hydrodynamic simulations of Okamoto et al. Starting from identical initial conditions, but using different assumptions for the baryonic physics, one of the simulations produced a bulge-dominated galaxy and the other one a disc-dominated galaxy. The main difference is the treatment of star formation and feedback, both of which were designed to be more efficient in the disc-dominated object. We find that the specific angular momentum of the disc-dominated galaxy tracks the evolution of the angular momentum of the dark matter halo very closely: the angular momentum grows as predicted by linear theory until the epoch of maximum expansion and remains constant thereafter. By contrast, the evolution of the angular momentum of the bulge-dominated galaxy resembles that of the central, most bound halo material: it also grows at first according to linear theory, but 90 per cent of it is rapidly lost as pre-galactic fragments, into which gas had cooled efficiently, merge, transferring their orbital angular momentum to the outer halo by tidal effects. The disc-dominated galaxy avoids this fate because the strong feedback reheats the gas, which accumulates in an extended hot reservoir and only begins to cool once the merging activity has subsided. Our analysis lends strong support to the classical theory of disc formation whereby tidally torqued gas is accreted into the centre of the halo conserving its angular momentum.     

Non-linear dynamics of the corotation torque

The excitation of spiral waves by an external perturbation in a disc deposits angular momentum in the vicinity of the corotation resonance (the radius where the speed of a rotating pattern matches the local rotation rate). We use matched asymptotic expansions to derive a reduced model that captures non-linear dynamics of the resulting torque and fluid motions. The model is similar to that derived for forced Rossby wave critical layers in geophysical fluid dynamics. Using the model we explore the saturation of the corotation torque, which occurs when the background potential (specific) vorticity is redistributed by the disturbance. We also consider the effects of dissipation. If there is a radial transport of potential vorticity, the corotation torque does not saturate. The main application is to the creation, growth and migration of protoplanets within discs like the primordial solar nebula. The disturbance also nucleates vortices in the vicinity of corotation, which may spark further epochs of planet formation.