日长亚季节变化的振幅调制与厄尔尼诺现象

利用Ｈｉｌｂｅｒｔ变换解算了１９６２年至１９９６年日长亚季节振荡的包络变化．结果显示,日长亚季节变化的振幅调制不仅具有一线性增长趋势,而且包含一个超前厄尔尼诺变化历程的年际变化．分别研究日长亚季节准５０天包络变化以及准１２０天包络变化后发现,这种超前性来自日长亚季节准５０天的振幅变化,这一结论与大气的研究结果一致．日长亚季节准１２０天的振幅变化在１９７２年附近发生了位相１８０°反转,因此日长亚季节准１２０天的振幅变化自１９７６年以来与厄尔尼诺的历程正好同步,１９７２年以前则截然相反．众所周知,日长变化在亚季尺度上具有显著的易变性,然而上述的非线性调制现象不仅表明了日长亚季节变化的内在规律性,而且证实了地球自转运动在不同时间尺度上存在极明显的非线性相互作用．同时也表明,日长变化作为全球风系变化的一个有价值的信息指标,将逐渐成为研究气候系统全球状态的有效手段之一．     

同ENSO现象相关联的日长亚季节变化

本文利用小波分析方法研究了地球自转日长亚季节近50天和近120天周期变化的时频特征．结果表明,日长近120天周期变化及近50天周期变化的振幅具有明显的年际变化．ENSO事件发生之前,日长近50天周期变化加强,进入ENSO时期,逐渐减弱,成为ENSO产生的先兆之一,同时,日长近120天周期变化显著增强80年代,日长近50天周期变化明显发生了两次周期分岔分岔的一种趋势经历了一个周期延长的过程,收敛于ENSO时期增强的近120天周期变化,该过程不仅与ENSO现象相关联而且可能受到近10年波动的调制作用.同时证实了日长近120天周期变化及近50天周期变化的激发机制主要是同频段的大气环流变化所导致。     

日长变化与地磁场变化的时滞相关分析

利用历史地磁场模型资料和日长资料,计算和分析了1840~2000年期间地磁场变化与日长变化的互相关特点。结果表明,地磁变化与日长变化存在时滞相关。地磁场强度参数的变化比日长变化超前7.5~10a(年);地磁场西向漂移参数比日长变化滞后,其中,西漂分量.λ12和.λ23滞后7.5a,而地磁场的平均漂移速度和纬度漂移分量滞后20~22.5a。     

空间VLBI数据记录格式RDF解析与数据解码

空间甚长基线干涉测量(Very Long Baseline Interferometry, VLBI)由于基线更长,在相同的观测频率下,可获得比地基甚长基线干涉测量更高的分辨率。我国正在推进空间甚长基线干涉测量科学与技术研究。俄罗斯RadioAstron空间甚长基线干涉测量项目于2018年结束,其成功经验可以借鉴。该项目采用不同于常规地面甚长基线干涉测量的专用数据格式RDF(RadioAstron Data Format)记录观测数据,利用配备的星载或地面上行氢原子频标提供频率基准,数据经采集量化后传输至地面站,打上时标并记录于硬盘。为处理RadioAstron数据,分析了RDF格式,完成了RDF数据解码及相关处理,然后对比分析了Mark5B、VDIF等地面甚长基线干涉测量通用数据格式和RDF格式的特点,为我国未来空间甚长基线干涉测量数据格式设计与处理积累经验。     

关于恒星大气超声对流的注释

1引言尽管有诸多的不满之处,由于其物理上的直观性和应用上的简单性,至今混合长理论仍几乎是唯一一个广泛用于恒星结构、演化和脉动计算的恒星对流理论.混合长理论预言,在红、黄巨星和超巨星大气中,对流是超声速的.我们曾指出,混合长理论隐含了一个假定,对流是亚声速的.对于超声速对流,无论从物理的真实性,还是从混合长公式的数学表述来看,混合长理论都是不正确的.因此超声对流的真实性是存在问题     

恒星初始质量分布函数对伽玛暴爆发率的影响

伽玛射线暴的产生机制比较公认的是:长暴产生于大质量恒星死亡;短暴产生于密近双星合并.因此人们很自然地推测长暴和恒星形成率直接成比例,但是最近数据分析表明这并不能很好地拟合观测.考虑到只有质量大于某一临界质量的大质量恒星才可能产生长暴,因此恒星初始质量分布函数对长暴的产生率会有较大影响.考虑用恒星初始质量分布函数来解释长暴观测个数随红移的分布,得到了比较好的结果.     

用夏至日影长了解地球

一、简介 我们聪明的祖先很早就开始利用太阳照射到地球上物体产生的投影来测算时间,例如中国的圭表和日晷。而测量某一物体在正午时刻影长,不仅可以计算时间,还可以求出测量所在地的经纬度、地球周长等等一系列地球参数。本文中的实验测量证实了此方法的可行性：已知物体原长与影长,结合测量时间与测量日期,就可以通过公式计算出地球周长和测量地的地理经纬度。     

广义回归神经网络在日长变化预报中的应用

传统的日长变化预报多是基于线性模型,如最小二乘模型、自回归模型等,但是日长变化包含了复杂的非线性因素,线性模型预报的效果往往不甚理想.所以尝试使用一种非线性神经网络—广义回归神经网络(GRNN)模型进行日长变化预报,并将结果与使用BP (Back Propagation)神经网络模型和其它模型的预报结果进行比较.结果表明,GRNN用于日长变化预报是高效可行的.     

大气角动量函数在日长变化非线性预报中的重要作用

日长变化具有复杂的时变特性,传统的线性时间序列分析方法往往难以取得良好的预报效果.采用非线性人工神经网络技术对日长变化进行预报,网络模型的拓扑结构由最小均方误差法来确定.考虑到日长变化与大气环流运动间的密切关系,在神经网络预报模型中引入轴向大气角动量序列.结果表明,联合日长和大气角动量序列,比起单独采用日长资料,预报精度得到显著的提高.     

同NESO现象相关联的日长亚季节变化

本文利用波分析研究了地球自转日长亚季节近５０天和近１２０天周期变化的时频特征。结果表明,日长近１２０周期变化及近５０天周期变化的振幅具有明显的年限变化。     

The Important Role Played by Atmospheric Angular Momentum in the Non-linear Prediction of the Variations in the Length of Day

The variation in the length of day has complicated time-varying characteristics and the traditional method for linear time series analysis is always difficult to obtain good effect of prediction. If the non-linear artificial neural network technique is adopted to predict the variation in the length of day, the topological structure of the network model is determined by the least square error method. By taking into account the close relation between the variation in the length of day and the general circulation of atmosphere, the axial sequence of atmospheric angular momentum is introduced into the forecasting model of neural network. The results show that the forecast accuracy is significantly improved by taking advantage of the combination of the length of day and the atmospheric angular momentum sequence in comparison with the individual adoption of the data of the length of day.     

Periodic variations of the cosmic radiation—III. The 27-day variation

The relation between the 27-day variation of the cosmic radiation and of the terrestrial horizontal magnetic intensity has been investigated by means of the data recorded from 1957 to 1968. The periods have a correlation of about +0.5. The cosmic radiation is undoubtedly modulated by the Sun. A persistent wave with a periodicity of approximately 27.2 days could be proved from the data of several ion chamber and neutron monitor stations, but not underground (14m w.e.). The frequency of the daily period of the cosmic radiation shows a 27.3 day variation, too. The sum total of the relative sunspot numbers has a period length of 27.4 days. Their connection with the cosmic radiation is discussed.     

Continental drift and the rotation of the earth-a new and critical evaluation

Sconzo has proposed that the continental drift of a land mass like Greenland can make a detect-able change in the Earth's rotation rate through a change in the Earth's moment of inertia. The correction of theoretical and numerical errors in his paper results in a change in the length of the day of only 3.5×10^–8 s cy^–1, a rate which is 6 orders of magnitude less than the value he gives. Continental drift does not appear to cause an important change in the length of the day.     

The study of excitation of the earthquake to Earth's rotation

The earthquake produces a global static displacement field due to the dislocation in the epicenter. This displacement field in turn changes the Earth's inertia tensor, hence exciting the variation of both polar motion and length of day. In general, large earthquake produces greater displacement field, which has greater effects upon the earth rotational properties. In spite of scientists efforts in the last decades, it is found that the polar motion and the length of day excited by earthquake are at least two orders of magnitude less than those derived from observation. In the future with high observational accuracy the effect of earthquake on polar motion and length of day would be observable.Using the fault plane parameters, the location of epicenter and the expression given by Dahlen as well as the step function, the accumulative change of the axial and equatorial moments of inertia of the Earth earthquake occurring in period of 1977–1994 is estimated in this paper. Results have shown that change of pole axis direction induced by single earthquake is independent of the magnitude of the earthquake, which is random, but large earthquake contributes most to the accumulative change of direction of polar drift. The earthquake tends to make the drift of rotational pole towards the direction of 130–150 E. This direction is roughly different to that inferred from observations. Accumulative changes of both the two equatorial principal moments and the axial moment of inertia of the Earth present the strongest non-randomness and secular behaviour. The change depends upon the slip angle of the fault movement in a large extent.     

Analysis of Guo Shou-Jing's gnomon shadow measurements

The method used by Guo Shou-jing et al to find the times of the solstices from gnomon shadow measurements is discussed. The mean scatter between Guo's measured values of the Sun's shadow and the theoretical values (mean error for a single observation) is found to be between ±1 mm and ±4 mm, and the accuracy of a derived time of the Winter solstice is aobut 0.01 day. The causes for the errors are analysed and a preliminary investigation is made on the derivation of the value of the length of the tropical year adopted in the Shoushi Calendar.     

Observational Study about the Influence of the Solar Wind on the Earth's Rotation

The data on the variation of the Earth's rotation from IERS and the parameters of the solar wind measured by IPM 8 from July 1992 to September 1995 were used for a regression analysis. The results show that there seems to be a weak linear correlation between the velocity of the solar wind near the Earth, V, and the variation of the length of the day, lod₁ calculated from UT1 and averaged over five days. The correlation coefficient is R=0.186. The preliminary conclusion is that the Earth's rotation could be influenced by the variation of the velocity of the solar wind with a short time scale of several days.     

Power spectra of cosmic ray intensity variations at the ground and atmospheric pressure oscillations

Power spectrum estimates are computed for cosmic ray and pressure variations in the frequency range of 1.6 × 10⁻⁶ to 4.15 × 10⁻³ c/sec for three data sets each of 27 days length (2 min interval) recorded at Chacaltaya (Bolivia) during 1965–1966. The general trend of these spectra showy ƒ⁻ fit having exponent values from −1.5 to −1.9 for L.F. side. From the semi-diurnal peaks both in cosmic rays and pressure, the average value of pressure coefficient is found to be 0.3 per cent/mm of Hg. For the same three sets of data, a detailed analysis of cross-spectrum, coherence and phase relationship between cosmic rays and pressure is carried out in the frequency range of 1–12 c/day. Besides semi-diurnal peak, variations of 3, 4, 7 and 8 c/day are found to be common both in cosmic rays and pressure. The value of pressure coefficient and residual amplitude of cosmic rays for these particular frequencies are calculated.     

太阳表面米粒结构观测对比度分析

分析以观测系统焦面上和探测器测到的太阳表面米粒结构的对比度与观测系统口径，大气湍流相干长度以及系统探测灵敏度的关系，给出了不同口径，不同大气湍流相干长度以及不同系统探测灵敏度时的米粒结构对比值计算结果，此外还给出了实验结果。     

A method of evolving synoptic maps of the solar magnetic field,II. Comparison with observations of the polar fields

We describe the application of the synoptic transport equation to simulate the temporal evolution of the magnetic flux over the solar surface. This provides a means of predicting each day both the synoptic maps for the Carrington rotation starting the next day and the instantaneous map of the solar flux over the whole solar surface for the next day. The reliability of the predicted synoptic maps is tested by comparing the locations of the zero-flux contour with those of the observed maps produced by the National Solar Observatory, Kitt Peak and with the locations of Hα filaments measured on filtergrams obtained by the Big Bear Solar Observatory. We conclude that the best match at high latitudes is obtained by long-term simulations (over 20 rotations) with flux updates each rotation between latitudes ± 60°. We illustrate the use of the simulations to describe the evolution of the polar fields at the time of the polarity reversals in Cycle 23. The reconstruction of the instantaneous maps is tested by comparison with full-disk magnetograms. The method provides a simple means of estimating the large-scale flux distribution over the whole surface. It does not take account of flux emerging after the central meridian passage each rotation so it is only approximate in the activity belts but provides a reliable map beyond those latitudes.