BL Lac天体AO 0235 164在5 GHz上的VLBI观测

应用５ＧＨｚＶＬＢＩ技术在历元１９９７.１２的观测结果,给出ＢＬ　Ｌａｃ天体ＡＯ　０２３５＋１６４在毫角秒尺度上的最新图像．该致密天体的射电结构由一个亮核所支配,另外在东北和西南方向各存在一个相对较弱的子源,其中东北方向的子源要比西南方向的明显得多.模型拟合结果显示,该源的喷流位置角为６６.４°,该数值超过以往的任何一次观测结果．根据流量密度随时间的变化关系,我们发现ＡＯ０２３５＋１６４在波长６ｃｍ上可能存在两种周期性的变化,即１—２年的短周期性变化和３－５年的长周期性变化这两种周期性的变化可能是由于喷流的爆发和旋转两种效应共同作用的结果．     

CCD漂移扫描观测星表ACR和CMC13的系统误差研究

对2000年前后发表的两部用CCD漂移扫描观测的天体测量星表——ACR(As- trometric calibration regions along the celestial equator)和CMC13(Carlsberg Merid- ian Catalog 13)进行误差分析.通过与UCAC2(The second U.S.Naval Observatory CCD Astrograph Catalog)星表比较,采用数值法,分析了误差的形式和量级大小.并从星表观测方式和数据归算的角度,分析了误差的主要可能来源.发现ACR和CMC13在赤纬方向存在明显的星等差,位置差值随赤经存在与CCD视场大小相近的周期性变化,位置差值随赤纬存在与归算带尺寸大小相近的系统性变化.     

卫星双向定时精度分析

介绍了Compass卫星双向定时的基本原理,在讨论双向定时计算模型的基础上,给出了考虑Sagnac效应项的详细计算模型,并计算了Sagnac效应项在几个代表性地区的影响,结果表明:对于距离中心站较远地区的用户,这种影响可达几十个纳秒。最后,对Compass卫星双向定时理论精度进行了分析,并采用几个地区的试验结果进行了验证。     

电视比对电路的改进

目前国内综合原子时系统各台站之间原子时的同步手段,主要是利用长波定时与无线电视同步比对两种方法。因此解决一些“电视比对”之中出现的一些问题就变得相对迫切了。本文是我们在一些改进与实验的基础上提出的改进方法。测地所武昌时辰站地处近郊区。由于相对电视台地势较低,周围建筑林立,因此电视射频场强变化较明显。致使比对结果时而出现跳“场”,时而跳“行”。前者要比原数相差     

近相接双星室女座BF的轨道周期变化

收集了近相接双星ＢＦ Ｖｉｒ的光极小时刻,并对其轨道周期进行分析。结果表明该星的轨道周期在长期减小的财时也含有３０年的周期性变化,对引起轨道周期变化的各种物理机制的分析研究表明：一个质量为０．２８１Ｍ⊙、绕公共质心的轨道半径为１０．２ＵＡ的第３天体的存在能对轨道周期的周期性变化成份作出解释,如果轨道周期的周期性变化成份是由于次子星的周期性磁活动引起,那么系统总光度就应该有振幅０．０９７Ｌ⊙的周期性     

C波段卫星双向时间传递的系统性能验证

中国科学院国家授时中心在全国范围内部署建设了卫星地面观测系统,利用该系统可以进行C波段卫星双向时间频率传递(TWSTFT);TWSTFT是目前国际上远程时间频率标准之间比对精度最高的比对手段之一,但是如何验证TWSTFT的性能,仍是目前研究的难点;为验证该系统TWSTFT的性能,设计了三站闭合方法,在3个站点间两两进行TWSTFT,根据两组比对结果推算第3组比对结果,与第3组实测结果的偏差反映了卫星双向时间传递的精度,最后用实际试验结果对卫星双向时间传递的性能进行了分析;该实验结果表明两两进行TWSTFT得到的三站闭合差数据均优于1 ns。     

国际电离层参考模式在东亚地区的偏离(英文)

电离层参考模式(IRI)提供的环境参数一直受到世界从事电离层物、无线电通讯等科学和技术工作者所重视及普遍应用。制定模式的主要依据是全球电离层台站的观测资料。由于电离层变化的复杂性,以及世界电离层台站分布不均匀,要一次性制定一个普适的模式有一定难度。IRI自1978年公布以来一直处于不断改进与逐步完善的过程中。 最新的IRI版本是1986年公布的IRI—86。为了检验该模式在我国与近邻的日本国的可用性,我们将我国满洲里、北京、武昌、重庆和广州等站及日本国的稚内、秋田、国分寺,山川和冲绳等站在近一个太阳黑子周期内各层临界频率的实测值与IRI—86模式的计算值进行了比较分析。发现两者存在着显著而系统的偏离。在不同的年份和不同的台站偏离表现出相似的变化规律,冬季月份尤为明显。F2层偏离较大,其相对偏离有时超过60％,绝对差值高达3MHz。偏离变化表现为夜间大(子夜最大),白天小(中午最小);冬季大,夏季小;太阳活动低年大,高年小。在中国模式值普遍大于观测值;偏离随纬度降低而增加;纬度较南的广州站偏离变化曲线表现出较大的差异;纬度相近的武昌和重庆两站,偏离大致相同,经度差异不大。在日本国各站的偏离变化基本相似,纬度效应不明显;并且冬季月份模式值明显小于观测值。 E和F1层模式值与观     

磁感应阻力对导体卫星在圆形轨道上的摄动影响

用功能转换原理和摄动理论的两种方法重点研究了导体卫星在地球磁场和有电导率介质空间飞行时磁感应阻力对圆形轨道半径的摄动影响。理论研究表明：导体卫星在圆形轨道上受磁感应阻力后轨道半径有随时间变化的长期摄动效应外还有周期性变化。此外，文中还讨论了磁感应阻力对圆形轨道的其它要素的摄动影响概况。     

1979—1980年ζAur食期间的视向速度

用1979—1980年食期间观测的11夜光谱底片,以做(Δλ)/(Δx)～λ色散曲线的方法,得出了ζAur的视向速度随位相的变化。其结果列于表2,绘于图1。 同以前食期间得到的视向速度相比较,结果基本一致,但在即将全食的大气食期间所得到的视向速度明显偏低。本文对这些结果做了初步讨论。     

基于ITRF97的上海和鹿岛VLBI站地壳垂直形变的VLBI测定

利用美国宇航局(NASA)在1999年的VLBI全球解(glb1123)中关于上海VLBI站与国际上13个VLBI站的基线长变化率高精度测定结果,以及日本鹿岛Kashima和Kashima 34两VLBI站分别与国际VLBI站间的相应结果,基于最近的国际地球参考架ITRF97,估计得到了上海VLBI站和日本鹿岛两VLBI站相对于板块稳定区的地壳垂直形变率分别为-1.91±0.56 mm/yr、-3.72±0.74 mm/yr和-8.81±0.84mm/yr,表明上海VLBI站存在每年近2毫米的下降,讨论并证实日本鹿岛两VLBI站的地壳垂直形变速率是不一致的;基于不同板块运动模型的欧拉旋转矢量,估计得到了上述3站的水平形变速率;还估计给出了太平洋板块中部的形变率结果.     

An empirical model of the daily evolution of the coronal index

Global changes of the solar activity can be expressed by the coronal index that is based upon the total irradiance of the coronal 530.3 nm green line from observations at five stations. Daily mean values of the coronal index of solar activity and other well-correlated solar indices are analyzed for the period 1966–1998 covering over three solar cycles. The significant correlation of this index with the sunspot number and the solar flare index have led to an analytical expression which can reproduce the coronal index of solar activity as a function of these parameters. This expression explains well the existence of the two maxima during the solar cycles taking into account the evolution of the magnetic field that can be expressed by some sinusoidal terms during solar maxima and minima. The accuracy between observed and calculated values of the coronal index on a daily basis reaches the value of 71%. It is concluded that the representative character of the coronal index is preserved even when using daily data and can therefore allow us to study long-term, intermediate and short-term variations for the Sun as a star, in association with different periodical solar–terrestrial phenomena useful for space weather studies.     

北斗系统测站钟差短期预报模型比较及其在单星定轨中的应用

北斗卫星导航系统(BDS)地面跟踪站都配置有高精度的氢原子钟,并基于精密定轨数据处理与主站的时间基准进行同步.在卫星轨道机动以及机动恢复期间,通常采用几何法定轨以及单星定轨确定卫星的轨道.而在这两种定轨模式中,需要提供精确的测站钟差作为输入.为提高定轨的实时性,需要对测站钟差进行预报处理.分析了2次多项式模型、附加周期项模型、灰色模型3种模型对北斗地面跟踪站钟差短期拟合和预报的性能,并将钟差预报结果应用于单星定轨,同时还分析了不同预报钟差用于定轨的精度.试验发现,以上3种模型对6个测站钟差的平均拟合精度分别为0.14 ns、0.05 ns、0.27 ns,预报1 h的平均精度分别为1.17 ns、0.88 ns、1.28 ns,预报2 h的平均精度分别为2.72 ns、2.09 ns、2.53 ns.采用3种模型对测站钟差进行预报并用于单星定轨,采用附加周期项的钟差预报模型轨道3维误差最小,不同模型轨道径向精度差异在3 cm以内.以上结果表明,附加周期项的站钟拟合及预报模型在北斗系统机动期间的轨道恢复数据处理具有最好的效果.     

Lander radioscience for obtaining the rotation and orientation of Mars

The paper presents the concept, the objectives, the approach used, and the expected performances and accuracies of a radioscience experiment based on a radio link between the Earth and the surface of Mars. This experiment involves radioscience equipment installed on a lander at the surface of Mars. The experiment with the generic name lander radioscience (LaRa) consists of an X-band transponder that has been designed to obtain, over at least one Martian year, two-way Doppler measurements from the radio link between the ExoMars lander and the Earth (ExoMars is an ESA mission to Mars due to launch in 2013). These Doppler measurements will be used to obtain Mars’ orientation in space and rotation (precession and nutations, and length-of-day variations). More specifically, the relative position of the lander on the surface of Mars with respect to the Earth ground stations allows reconstructing Mars’ time varying orientation and rotation in space.Precession will be determined with an accuracy better by a factor of 4 (better than the 0.1% level) with respect to the present-day accuracy after only a few months at the Martian surface. This precession determination will, in turn, improve the determination of the moment of inertia of the whole planet (mantle plus core) and the radius of the core: for a specific interior composition or even for a range of possible compositions, the core radius is expected to be determined with a precision decreasing to a few tens of kilometers.A fairly precise measurement of variations in the orientation of Mars’ spin axis will enable, in addition to the determination of the moment of inertia of the core, an even better determination of the size of the core via the core resonance in the nutation amplitudes. When the core is liquid, the free core nutation (FCN) resonance induces a change in the nutation amplitudes, with respect to their values for a solid planet, at the percent level in the large semi-annual prograde nutation amplitude and even more (a few percent, a few tens of percent or more, depending on the FCN period) for the retrograde ter-annual nutation amplitude. The resonance amplification depends on the size, moment of inertia, and flattening of the core. For a large core, the amplification can be very large, ensuring the detection of the FCN, and determination of the core moment of inertia.The measurement of variations in Mars’ rotation also determines variations of the angular momentum due to seasonal mass transfer between the atmosphere and ice caps. Observations even for a short period of 180 days at the surface of Mars will decrease the uncertainty by a factor of two with respect to the present knowledge of these quantities (at the 10% level).The ultimate objectives of the proposed experiment are to obtain information on Mars’ interior and on the sublimation/condensation of CO₂ in Mars’ atmosphere. Improved knowledge of the interior will help us to better understand the formation and evolution of Mars. Improved knowledge of the CO₂ sublimation/condensation cycle will enable better understanding of the circulation and dynamics of Mars’ atmosphere.     

The depth of the convective boundary layer on Mars

We are using observations obtained with Mars Express to explore the structure and dynamics of the martian lower atmosphere. We consider a series of radio occultation experiments conducted in May-August 2004, when the season on Mars was midspring of the northern hemisphere. The measurements are widely distributed in latitude and longitude, but the local time remained within a narrow range, 17.0-17.2 h. Most of the atmospheric profiles retrieved from these data contain a distinct, well-mixed convective boundary layer (CBL). We have accurately determined the depth of the CBL and its spatial variations at fixed local time through analysis of these profiles. The CBL extends to a height of 3-10 km above the surface at the season and locations of these measurements. Its depth at fixed local time is clearly correlated with variations in surface elevation on planetary scales, with a weaker dependence on spatial variations in surface temperature. In general, the CBL is deep (8-10 km) where the surface elevation is high, as in Tharsis Montes and Syrtis Major, and shallow (4-6 km) where the surface elevation is low, as in Amazonis and Utopia. This variability results from the combined effects of conditions near the surface and in the atmosphere above the CBL. Convection arises from solar heating of the ground, and the impact of this heat source on thermal structure is largest where the surface pressure and atmospheric density are smallest, at high surface elevations. The vertical extent of the CBL is in turn constrained by the static stability of the overlying atmosphere. These results greatly reduce the long-standing uncertainty concerning the depth of the CBL.     

The statistical magnetic signature of magnetospheric substorms

The characteristic magnetic signatures of magnetospheric substorms both on the ground and in space have been determined from the analysis of ～1800 substorm events. The timing and properties of these events were objectively determined according to explicit mathematical criteria by a computer pattern-recognition program. This program processed daily magnetograms from a mid-latitude network of geomagnetic observatories.Ground data analyzed, using onsets determined in this manner, included the AE indices and individual magnetograms at different local times in the auroral zone and at midlatitudes. Superposed epoch averages of these data confirm the local time magnetic substorm signatures, determined in earlier studies of fewer events, and demonstrate the validity of the computerized onset determination procedure.Superposed epoch averages of the interplanetary magnetic field (IMF) associated with the onsets demonstrates both a distinct southward component prior to the onsets and a dependence of the substorm amplitude on the integrated preceding southward IMF flux. Superposed epoch averages of the tail lobe magnetic field magnitude and vector components demonstrates field magnitude changes and rotations in association with the substorm onsets. These lobe field changes are consistent with the growth-phase model of substorm activity and with variations in the magnetopause flaring angle.     

The astroclimatological comparison of the Paranal Observatory and El Roque de Los Muchachos Observatory

The new extremely large telescope projects need accurate evaluation of the candidate sites. In this paper, we present the astroclimatological comparison between the Paranal Observatory, located on the coast of the Atacama Desert (Chile), and the Observatorio del Roque de Los Muchachos (ORM), located in La Palma (Canary Islands). We apply a statistical analysis using long-term data bases from Paranal and Carlsberg Automatic Meridian Circle (CAMC) weather stations. The monthly, seasonal and annual averages of the main synoptical parameters in the two sites are computed. We compare the long-term trends in order to understand the main differences between the two sites. Significant differences between the two analysed sites have been found. Temperature has increasing trends in both observatories with somewhat higher evidence at the ORM. Seasonal variations of pressure at Paranal have been highly decreasing since 1989, and we do not see the same phenomenon at the ORM. The two sites are dominated by high pressure. In cold seasons, relative humidity (RH) is lower than 60 per cent at CAMC and 15 per cent at Paranal. In warm seasons, RH is lower than 40 per cent at CAMC and 20 per cent at Paranal. The analysis of the dew point has shown better conditions at Paranal with respect to CAMC in winter, autumn and spring before 2001, while the two sites are becoming similar afterwards. Winds at the ORM are subject to pronounced local variations.     

Longitudinal characteristics of Pc5 magnetic pulsations

Data from an East-West line of magnetometer stations stretching approximately along 67° geomagnetic latitude from western Alberta (290° geomagnetic longitude) to western Quebec (350° geomagnetic longitude) in Canada have been used to study the longitudinal characteristics of Pc5 geomagnetic pulsations. This paper concerns the analysis of 3 days' data of relatively intense pulsational activity which occurred around the middle of October in 1976. The intensity variations of Pc5 activity on longitude and time clearly show that the activity is localized in longitude in the morning sector and confused in the afternoon sector. Pulsational activity in the morning sector for two of the events studied appears to be markedly enhanced across the dawn terminator and midway through the pre-noon quadrant. A study of the longitudinal phase variation indicates that the eastern stations lead in phase before noon and lag in phase after noon. This implies that the signals propagate away from noon toward the dawn-dusk meridian. A systematic reversal in the sense of polarization in the horizontal plane was observed when the line of stations rotated across noon. The polarization characteristics in the vertical planes of the events recorded by stations in eastern Canada between 318° and 350° geomagnetic longitude appear to be stationary with respect to time suggesting that the polarization characteristics of pulsations are influenced by geoelectric structures. The implications of these morphological features will be discussed.     

The onset time interval of geomagnetic disturbances in the conjugate areas

The onset time interval of geomagnetic disturbances, as deduced from the numerous cases of rapid changes of K-indices over a cycle in solar activity, was studied for two conjugate auroral stations, Macquarie Island and College. There is a distinct peak in the occurrence number of the disturbances for both stations at an interval 09.00–12.00 U.T., which is close to the local midnight at College but is in the pre-midnight sector at Macquarie Island. For comparison, a similar study was applied to the magnetic data obtained at two more auroral stations, Kiruna and Sodankyla. The onset time of the disturbances for these stations was most frequent at 18.00–21.00 U.T., centered at the conjugate midnight of Kiruna and Sodankyla in the Southern Hemisphere but well ahead of the local midnight of the stations themselves. The specific diurnal occurrences of the disturbances at all four auroral stations are consistent with a difference in the geometry between the southern and northern auroral ovals. It appears that the prevailing onset time of geomagnetic disturbances is associated with the time when both conjugate stations (or conjugate locations) are within the auroral oval and thus accessible to a direct particle influx from the Earth's magnetotail.     

Yearly and seasonal variations of low albedo surfaces on Mars in the OMEGA/MEx dataset: Constraints on aerosols properties and dust deposits

The time variations of spectral properties of dark martian surface features are investigated using the OMEGA near-IR dataset. The analyzed period covers two Mars years, spanning from early 2004 to early 2008 (includes the 2007 global dust event). Radiative transfer modeling indicates that the apparent albedo variations of low to mid-latitude dark regions are consistent with those produced by the varying optical depth of atmospheric dust as measured simultaneously from the ground by the Mars Exploration Rovers. We observe only a few significant albedo changes that can be attributed to surface phenomena. They are small-scaled and located at the boundaries between bright and dark regions. We then investigate the variations of the mean particle size of aerosols using the evolution of the observed dark region spectra between 1 and 2.5 μm. Overall, we find that the observed changes in the spectral slope are consistent with a mean particle size of aerosols varying with time between 1 and 2 μm. Observations with different solar zenith angles make it possible to characterize the aerosol layer at different altitudes, revealing a decrease of the particle size of aerosols as altitude increases.     

Observational features of field line resonances excited by solar wind pressure variations on 4 September 1984

In the course of the magnetic storm of 4 September 1984, after an inverse sudden impulse (SI), geomagnetic pulsations in the Pc5-frequency range were observed at magnetometer stations in the local evening sector. They occurred at L-values of 6, and lasted for several hours, their period increasing from about 320 to 550 s. In this study, two events of enhanced activity are discussed in some detail. During the 16:00 U.T. event, a favourable position of the AMPTE/IRM spacecraft allows conjugate observations in the Northern and Southern Hemispheres and in the magnetosphere. This constellation permits a precise determination of the wave mode. During a later intensification around 18:00 U.T., the AMPTE/CCE spacecraft near local noon monitored poloidal waves, obviously driving the pulsations on the ground. Generally, the observations are consistent with the theory of field line resonance. They are interpreted as being excited by pressure variations in the solar wind. The hydromagnetic cavity mode is assumed to link the magnetopause surface motions to the field line resonances.