最新规范的参考系及有关问题

在简要阐明参考系、参考架及其历史重大进程的基础上,对几种重要的、最新规范的参考系/参考架(质心天球参考系和地心天球参考系、国际天球参考系、国际地球参考系、太阳系动力学参考系等)的定义、实现和特点作了评述和分析,并对最新规范中与参考系、参考架有关的某些新概念的定义和新模式的应用(自2003年开始贯彻),如:天球中介极(CIP)、天球历书原点(CEO)、地球历书原点(TEO)、地球自转角的新定义、岁差-章动新模式的应用,作了阐述和讨论。     

大气、陆地水储量和海水质量分布变化与地球低阶引力场球谐系数的关系

大气、固体地球及海洋组成了一个复杂、变化的地球动力学系统，这一系统中的任一质量分布变化都将产生地球引力场变化。采用全球7000多个地面气象台站的月平均降水及温度资料、NCEP提供气压月均值、TOPEX／Poseidon卫星测高资料和WOA98海水温度及盐度模型计算了大气、陆地水储量和海水质量分布变化引起地球低阶引力场系数变化。比较综合大气、陆地水储量和海水质量分布变化对带谐项J2，J3，J4影响的计算结果和人卫激光卫星的测定结果，可以看出，大气、陆地水储量和海水质量分布变化是引起地球低阶引力场系数周年变化的重要激发源。     

天球和地球历书原点

国际天球参考系的使用、观测精度的提高和方法的改善要求采用与地球轨道运动无关的运动赤道上的起算点，Guinot提出的非旋转原点可作为这样一种选择。非旋转原点依赖于天球参考极。IAU决定从2003年起采用天球中间极作为天球参考极。非旋转原点在天球参考系的使用，可给出在天球中间极赤道上的天球历书原点，非旋转原点在地球参考系的使用，可给出在天球中间极赤道上的地球历书原点。回顾了非旋转原点的概念、以历书原点为参考的天球参考系和地球参考系的坐标变换，经出了在微角秒精度下天球参考极的坐标和历书原点的位置，讨论了采用历书原点对测定UT1的影响，指出当岁差章动模型、天极补偿、分点改正得到改善时，基于历书原点的UT1定义不需要更改，从而保证了UT1的连续。     

国际地球参考框架(ITRF)的原点和无整体旋转

目前国际地球参考框架(ITRF)建立和维持中,参考架原点和其定向随时间演变的约束上,并没有遵循协议地球参考系(CTRS)的定义。ITRF的定义和实现不一致的这种特征,将对毫米级地球参考框架的构建产生重要的影响。分析和讨论了最新的国际地球参考框架(ITRF2005)的原点和定向随时间演变的问题,并提出了目前可能解决的办法。     

地球定向参数高精度预报方法研究

<正>地球自转表征了固体地球与大气、海洋、地幔和地核在各种时空尺度上的耦合过程,地球的自转运动可以用地球定向参数(EOP)(主要包括极移两个分量和日长变化)来描述.EOP是地球参考系和天球参考系之间的转换参数,在深空探测、卫星精密定轨和天文地球动力学研究等领域都有重要应用.由于复杂的数据处理过程,空间大地测量技术获取的EOP存在几天至两个星期的延迟.现代空间导航等对EOP预报值的需求日益增长,使得寻求高精度EOP预报方法成为一项需要深入研究的课题.本文     

太阳系天体地面VLBI观测的相对论时延模型

以太阳系质心参考系为基础，根据太阳系的质心参考系和非旋转地球质心参考系的坐标转换关系，推导了太阳系天体地面VLBI观测的相对论时间延迟模型，给出了一个通用的解析表达式．根据这一公式可以得到平劲松博士所采用的公式，以及当地心与源的距离无限大时，可得河外射电源VLBI观测的Zhu—Groten模型、Shapiro模型和IERS(92，96)推荐模型．所推导的公式严格解析且无误差，在实际应用中建议采用这一公式．同时详细地讨论了所推导公式的实用范围和各种舍掉项的量级估计，并详细给出了时间延迟理论模型的计算步骤．     

大气角动量和日长间季节性不平衡

本采用国际时间局（BIH）和美国喷气推进实验室（JPL）提供的日长变化序列（LOD）和美国气象中心（NMC）及日本气象厅（JMA）推导出的大气角动量（AAM）来重新检测固体地球和大气之间的季节性差异。从4种滤波序列中发现由AAM推出的LODatm周年变化高于观测的LOD约17％,而LOD的半年振幅变化超出LODatm的约30％。本还讨论了几种因素，例如洋流中季节性变化，气象中的系统误差，平流层风的贡献，核的惯量矩作用，空气质量的重新分布补尝及其他未知的激发源来解释它们之间不平衡，今后10年，在研究角动量不平衡中，将用固体地球－大气－海洋动力学系统来代替简单的固体地球－－大气的两体动力学系统。海洋对这季节性不平衡可能有重要贡献。     

2000年以来国际天文学联合会(IAU)关于基本天文学的决议及其应用

1991年以来,在国际天文学联合会(IAU)全体大会上,通过了一系列关于天文参考系、时间尺度和地球自转模型的决议,其目的是为了适应不断提高的天文观测精度。其中最重要的3次,分别是在1997年的京都,2000年的曼彻斯特和2006年的布拉格通过的IAU 1997,IAU 2000和IAU 2006决议,主要的变化包括:从与历元有关的动力学参考系到与历元无关的运动学参考系,从参考系的恒星实现到河外射电源实现,从春分点到无旋转原点,以及岁差-章动模型的改进。由于这些决议在参考系转换等方面引入了很多新概念和新方法,对教学、研究和应用都产生了不小的影响,对它们进行解读,澄清概念,规范使用是有必要的。首先介绍IAU关于时间尺度和天文参考系的重要决议,并重点介绍IAU 2000和2006的每一条决议:然后详细介绍其应用:包括时间系统,国际天球参考系和岁差-章动模型,并和对应的旧系统进行比较;最后对这些决议的使用提出建议。     

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．     

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．     

GRACE observations of changes in continental water storage

Signatures between monthly global Earth gravity field solutions obtained from GRACE satellite mission data are analyzed with respect to continental water storage variability. GRACE gravity field models are derived in terms of Stokes' coefficients of a spherical harmonic expansion of the gravitational potential from the analysis of gravitational orbit perturbations of the two GRACE satellites using GPS high–low and K-band low–low intersatellite tracking and on-board accelerometry. Comparing the GRACE observations, i.e., the mass variability extracted from temporal gravity variations, with the water mass redistribution predicted by hydrological models, it is found that, when filtering with an averaging radius of 750 km, the hydrological signals generated by the world's major river basins are clearly recovered by GRACE. The analyses are based on differences in gravity and continental water mass distribution over 3- and 6-month intervals during the period April 2002 to May 2003. A background model uncertainty of some 35 mm in equivalent water column height from one month to another is estimated to be inherent in the present GRACE solutions at the selected filter length. The differences over 3 and 6 months between the GRACE monthly solutions reveal a signal of some 75 mm scattering with peak values of 400 mm in equivalent water column height changes over the continents, which is far above the uncertainty level and about 50% larger than predicted by global hydrological models. The inversion method, combining GRACE results with the signal and stochastic properties of a hydrological model as ‘a priori’ in a statistical least squares adjustment, significantly reduces the overall power in the obtained water mass estimates due to error reduction, but also reflects the current limitations in the hydrological models to represent total continental water storage change in particular for the major river basins.     

The relative abundance of the carbon isotopes12C and13C in primary cosmic radiation

Mass measurements have been performed on stopping cosmic ray carbon nuclei in a nuclear emulsion stack, which was exposed to the primary radiation in a high altitude balloon flight. The mass determinations are based on measurements of mean track width and residual range in the range intervals 0<R<0.75 mm and 1<R<12 mm. The mean track width measurements have been performed with nuclear track photometers of special construction. The mass measurements in the interval 0<R<0.75 mm have given a nearly symmetrical mass distribution. The width of the distribution is equal to that expected for a distribution which contains only one isotope. The result indicates that one of the stable isotopes is appreciably more abundant than the other. The measurements in the range interval 1<R<12 mm gave the isotopic ratio¹³C/¹²C+¹³C)=0.08. The ratio has been extrapolated to the cosmic ray source. It is found to be smaller in the source than at the point of measurement. Different assumptions about the origin of the cosmic radiation are discussed with regard to the results obtained in this investigation.     

Maximal size of chondrules in shock wave heating model: Stripping of liquid surface in a hypersonic rarefied gas flow

Abstract— We examined partially molten dust particles that have a solid core and a surrounding liquid mantle, and estimated the maximal size of chondrules in a framework of the shock wave heating model for chondrule formation. First, we examined the dynamics of the liquid mantle by analytically solving the hydrodynamics equations for a core‐mantle structure via a linear approximation. We obtained the deformation, internal flow, pressure distribution in the liquid mantle, and the force acting on the solid core. Using these results, we estimated conditions in which liquid mantle is stripped off from the solid core. We found that when the particle radius is larger than about 1–2 mm, the stripping is expected to take place before the entire dust particle melts. So chondrules larger than about 1–2 mm are not likely to be formed by the shock wave heating mechanism. Also, we found that the stripping of the liquid mantle is more likely to occur than the fission of totally molten particles. Therefore, the maximal size of chondrules may be determined by the stripping of the liquid mantle from the partially molten dust particles in the shock waves. This maximal size is consistent with the sizes of natural chondrules.     

The lunar dust environment

Each year the Moon is bombarded by about 10⁶ kg of interplanetary micrometeoroids of cometary and asteroidal origin. Most of these projectiles range from 10 nm to about 1 mm in size and impact the Moon at 10–72 km/s speed. They excavate lunar soil about 1000 times their own mass. These impacts leave a crater record on the surface from which the micrometeoroid size distribution has been deciphered. Much of the excavated mass returns to the lunar surface and blankets the lunar crust with a highly pulverized and “impact gardened” regolith of about 10 m thickness. Micron and sub-micron sized secondary particles that are ejected at speeds up to the escape speed of 2300 m/s form a perpetual dust cloud around the Moon and, upon re-impact, leave a record in the microcrater distribution. Such tenuous clouds have been observed by the Galileo spacecraft around all lunar-sized Galilean satellites at Jupiter. The highly sensitive Lunar Dust Experiment (LDEX) onboard the LADEE mission will shed new light on the lunar dust environment. LADEE is expected to be launched in early 2013.Another dust related phenomenon is the possible electrostatic mobilization of lunar dust. Images taken by the television cameras on Surveyors 5, 6, and 7 showed a distinct glow just above the lunar horizon referred to as horizon glow (HG). This light was interpreted to be forward-scattered sunlight from a cloud of dust particles above the surface near the terminator. A photometer onboard the Lunokhod-2 rover also reported excess brightness, most likely due to HG. From the lunar orbit during sunrise the Apollo astronauts reported bright streamers high above the lunar surface, which were interpreted as dust phenomena. The Lunar Ejecta and Meteorites (LEAM) Experiment was deployed on the lunar surface by the Apollo 17 astronauts in order to characterize the lunar dust environment. Instead of the expected low impact rate from interplanetary and interstellar dust, LEAM registered hundreds of signals associated with the passage of the terminator, which swamped any signature of primary impactors of interplanetary origin. It was suggested that the LEAM events are consistent with the sunrise/sunset-triggered levitation and transport of charged lunar dust particles. Currently no theoretical model explains the formation of a dust cloud above the lunar surface but recent laboratory experiments indicate that the interaction of dust on the lunar surface with solar UV and plasma is more complex than previously thought.     

Constraints on the formation of layered tektites from the excavation and analysis of layered tektites from northeast Thailand

Abstract— The size, shape, composition, and vesicle content of 6 kg of layered tektite fragments, excavated near the town of Huai Sai, Thailand, place some constraints on the formation of layered tektites. The mass, shape, and distribution of the fragments are not consistent with an origin as a “puddle” of impact melt but suggest that they were derived from a single equant block. The presence of vesicles up to 7 mm in mean diameter within the tektite fragments suggests that the material was too viscous to allow for significant gravity-driven flow. These results suggest that layered tektites may be analogous to lava bombs, which may have been stretched and deformed in flight but underwent little flow after landing. Rather than being a product of “unusual circumstances,” such as multiple impacts, layered tektites may differ from splash-form tektites only in initial temperature of formation, speed of ejection, and small differences in initial composition.     

1992年6月26日Hα耀斑后环的不均匀性和物质运动的可能解释

本文利用电流不稳定性线性理论讨论了１９９２年６月２５日至２６日耀斑后环中出现不均匀“结”状结构（“ｋｎｏｔ”或“ｂｌｏｂ”）的可能性,并且在同时考虑重力、磁力和环顶物质下落初速的情况下,理论计算了１９９２年６月２６日Ｈα耀斑后环物质运动的规律。理论计算与观测求得的视向速度随高度分布的曲线基本符合。     

Mars low-latitude neutron distribution: Possible remnant near-surface water ice and a mechanism for its recent emplacement

The Mars Odyssey Gamma-Ray Spectrometer/Neutron Spectrometer/High Energy Neutron Detector has provided measurements of near-surface hydrogen, generally interpreted as resulting from water, in the equatorial and mid-latitudes. Water abundances as great as 10% by mass are inferred. Although such high abundances could be present as adsorbed water in clays or water of hydration of magnesium salts, other measurements suggest that this is not likely. The spatial pattern of where the water is located is not consistent with a dependence on composition, topography, present-day atmospheric water abundance, latitude, or thermophysical properties. The zonal distribution of water shows two maxima and two minima, which is very reminiscent of a distribution that is related to an atmospheric phenomenon. We suggest that the high water abundances could be due to transient ground ice that is present in the top meter of the surface. Ice would be stable at tens-of-centimeters depth at these latitudes if the atmospheric water abundance were more than about several times the present value, much as ice is stable poleward of about ±60° latitude for current water abundances. Higher atmospheric water abundances could have resulted relatively recently, even with the present orbital elements, if the south-polar cap had lost its annual covering of CO₂ ice; this would have exposed an underlying water-ice cap that could supply water to the atmosphere during southern summer. If this hypothesis is correct, then (i) the low-latitude water ice is unstable today and is in the process of sublimating and diffusing back into the atmosphere, and (ii) the current configuration of perennial CO₂ ice being present on the south cap but not on the north cap might not be representative of the present epoch over the last, say, ten thousand years.     

MASS FLUX OF ASTEROIDAL ORIGIN METEOROIDS ON PERIODIC COMET NUCLEI

We examine the potential contamination of cometary nuclei through impacts from asteroidal origin meteoroids. The paper uses a simple model and has the goal of determining whether asteroidal contamination is potentially significant. We assume a meteoroid power law mass distribution with index values in the range from s=1.83 to s=2.09. We used maximum and minimum models which we believe will bracket the true meteoroid mass distribution. We identify those comets which are expected to be most significantly contaminated, and find values of up to 3.6 kg of asteroidal meteoroid impact per square meter of the cometary surface per orbital revolution. This is less than the expected mass loss per perihelion passage for most comets. Therefore any remnant effects of the contamination will depend on the penetration depth of the meteoroids in the cometary nucleus, and possibly on the distribution of active and inactive areas on cometary nuclei. We present a simple model which suggests that even small meteoroids will embed relatively deeply into a cometary nucleus.