地球自转变化的重力效应

极移对重力测量的影响在前人的研究和工作中已得到了充分的考虑并有不同形式的改正公式。但是由于地轴转动速率变化的重力效应的量级很小,且限于以前的测量精度以及资料处理方法, 因而常常被忽略。随着重力测量精度的提高以及资料处理方法的改进, 有必要重新讨论该项影响。本文从推导地球瞬时自转极运动对地面台站重力测量值影响的公式入手, 将地球自转角速率变化的重力效应和极移的重力效应分离开来, 并对它们的量级分别作了估计。本文着重讨论自转角速率变化对重力测量的影响。用 Ｉ Ｅ Ｒ Ｓ 的日长变化序列和极移序列分别具体地计算了１９８２ ～１９９６ 年期间对武汉的重力测量值的影响, 结果表明, 自转角速率变化对武汉地区重力值的影响最大可达０ ．２５ ｍｉｃｒｏｇａｌ（ｐｅａｋ －ｔｏ － ｐｅａｋ） , 这在高精度的绝对重力测量和相对重力测量中不应再被忽略     

大气参数变化对VLBI对流层时延计算值的影响

本采用我国上海、昆明和乌鲁木齐三个VLBI站的对流层大气高度参数ht和对流层内温度垂直梯度βt参数月均值资料，估计了对干大气时延的影响，结果表明在地平高度ε＝10°－20°时两参数的变化可引起干大气时延周年变化的幅值分别为1-5mm和2-15mm；ht的周日变化也可引起大气时延周日变化约1mm，因此，对于1ps级精度的VLBI物理模型，ht和βt不应当采用测站的固定常数值。     

电磁波在太阳引力场中传播速度的变化对VLBI时延测量的影响

太阳引力场效应对高精度VLBI时延测量有较大影响。本比较了两种改正太阳引力场效应的计算方法－－基于太阳引力偏折的方法和较差光行时方法，并由此得到结论：引力偏折与较差光行时是两个不同的概念；它们两对VLBI时延测量的影响的量级相同，但相差一个主项，即引力场中电磁波速度大小的变化引起的附中时延；另外二还相差一些小项。     

地球自转变化的重力效应

极移对重力测量的影响在前人的研究和工作中已得到了充分的考虑并有不同形式的改正公式。但是由于地轴转动速率变化的重力效应的量级很小,且限于以前的测量精度以及资料处理方法,因而常常被忽略。随着着重力测量精度的提高以及资料处理方法的改进,有必要重新讨论该影响。本文从推导地球瞬时自转极运动对地面台站重力测量值影响的公式入手,将地球自转角速率变化的重力效应和极移的重力效应分离来来,并对它们的量级分别作了估计。     

閃光星(鲸魚UV型星和金牛T型星)

我们在有些恒星上观测到它们的光亮骤然发生变化,例如和太阳隣近的红矮星(鲸鱼UV型)和属於某一星協的星(金牛T型). 本文先列出20颗确定为鲸鱼UV型的星(表1),然後讨论它们的光变情况,如躍变的幅度,光变曲线(表2),闪光的速度(在上昇到极亮时,速度可达0.25星等/秒),躍变的频率等.跟着我们更讨论这些星不在闪光的时候的变化(表3). 这些星的光谱内常有发射线(H与CaⅡ),闪光的时候,光谱上的连续背景加强,并且出现HeⅠ和HeⅡ的谱线,表示温度增加很高,但是这仅限於星的很小的表皮层(1至3％). 鲸鱼UV型星自身亮度很弱(M_(pg)13),数目很多,属星族Ⅰ. 本文内提到几颗御夫RW型星的迅速变化,并且讨论了金牛区(表5),猎户星雲区(表6)和NGC2264里(表7)的闪光星. 我们研究了光变的情况,特别说明鲸鱼UV型星和金牛T型星之间的关系:例如在光曲线、光谱型和同属星族Ⅰ几个方面.我们也讨论了这两型星在绝对星等、光谱和赫-罗图上的位置三者的差异. 最後我们断定鲸鱼UV型星和金牛T型星实在是相同的一群;我们由观测得到的它们之间的差异,其原因一则由於“观测上的选择性”,再则由於这两型星的演化阶段有所不同. 许多恒星的光亮表现突然的增加,或者说很迅速地发出“闪光”,在几分钟、有时在几秒钟内,星光有显著的增加,跟着变暗,初迅速而渐缓慢. 这种星光的躍变在许多型星都观测到,特别是在绝对亮度微弱的星上面.我们现在只讨论下列的主要两类恒星:     

基于VLBI资料的ERP高频变化求解方法的研究

在天测与测地VLBI资料分析软件CALC／SOLVE中，对地球自转参数(ERP)高频变化的解算采用了附加约束的连续分段线性拟合方法，即要求在两个历元节点之间ERP变化率小于某事先约定值，并要求ERP在历元节点上连续．实测资料分析表明，当资料点密度较低时，引入约束条件和要求连续均有助于提高解的稳定性，但也人为降低了解的客观性，使各历元节点ERP解算结果之间相关．为此，基于CALC／SOLVE的用户偏导功能，实现了ERP高频变化的直接求解模块，不附加约束，也不要求连续．实测资料分析表明对ERP高频变化的直接求解模式更为可取．对于长时段VLBI资料的ERP高频变化求解，需要考虑岁差和章动模型偏差(天极偏移)的影响，编写相应的求解模块，并成功实现了1979至2003年长时段ERP高频变化求解．比较表明，在考虑了岁差章动模型偏差的影响时能够显著提高解的精度．为此，在基于VLBI资料解算ERP高频变化时，建议采用直接求解模式，并考虑岁差章动模型偏差的影响．     

论地球的钱德勒摆动(一、理论部分)

本文引进了在地球上表层存在一个章动隔离层的概念,从而建立了一种新的章动模型,求出了运动方程及其解。在天体物理中,中子星的自转与章动问题与此类似,本文也许能供研究此类问题时参考。业已证明,地球的隔离层的性质是“软”的,大约位于地表以下300公里的深度。允许的最小厚度小于1公里,它的粘滞率大约为10~(10)泊的量级,相当于沥青在15℃时的情况。结果表明,钱德勒摆动的“主峰”是双频,其一是内主体的章动频率,另一是外体本身的章动频率。由于两个频率的拍频作用而产生钱德勒振幅的40年变化周期。两项的振幅互相影响,因而大小相差不大,它们的近似比值是0.7。著名的钱德勒摆动的振幅-周期关系是本文的直接结果。地极运动弧形的急变与1924—1926年左右的180°相变在本质上是一回事,它们是由内、外体的章动频率的相对变化决定的。过去人们从观测中定出的钱德勒摆动Q值在30—60之间,这是一个假Q值,真正的Q值是200左右,和由地震波定出的Q值一致。本文的解还预言,除两个主频率外,其两旁还对称地分布着一系列(一对以上)次要频率。钱德勒摆动的时间常数约为70年,它近似可由地震激发所维持。它的非平滑运动将主要沿平均迹线方向来回运动。     

晚型巨星FKCom的射电观测研究

本文作者使用美国ＶＬＡ，对快速目转的晚型巨星ＦＫＣｏｍ在３．６、６、１８、２０厘米波长上进行了射电观测，探测到ｍＪｙ量级的射电辐射，而没有探测到圆偏振。我们用热模型对射电频谱进行了拟合，结果都不成功。当发射体内电子密度为９×１０８ｃｍ－３，温度为５×１０７Ｋ时，半径为１２０Ｒ⊙．可获得较为接近的流量，但１０９量级的电子密度不大可能扩展到如此大的范围。这样的发射体用热模型得到的Ｘ射线光度比Ｅｉｎｓｔｅｉｎ天文台所观测到的值大两个数量级。ＦＫＣｏｍ的射电光度和Ｘ射线光度与ＲＳＣＶｎ双星系统相近，如果ＦＫＣｏｍ的射电发射也是由相对论电子在中等强度的磁场中作加速运动产生的话，则在１０高斯磁场中半径为３Ｒ⊙左右的发射区在相应波段即可达到观测的流量值。     

磁通量片的Helmholtz不稳定性

本文分析了被等离子体约束由两个间断面组成的有限厚度磁通量片的Helmholtz不稳定性,导出了不稳定条件,若片的厚度趋于无穷则此条件与一个间断面时相同。还给出了两个间断面的色散关系。结果表明,两个间断面时的磁致稳作用比一个间断面时有所减弱,而约束等离子体的致稳作用相对增强,但两种情况具有相同量级的不稳定增长率。     

地震引起地球自转速率变化的分析

由地震引起地球内部质量重新分布将影响地球惯量量矩的变化，从而引起地球自转速率的变化，即日长的变化。一般说，大地震产生大的附加位移违抗和。它对地球自转特性有影响。本文采用Ｈａｒｖａｒｄ目录中１９７７－１９９４年产的地震有关参数，和根据地震激发地球自转的变化理论及Ｄａｈｌｅｒ和Ｌａｍｂｅｃｋ有关公式计算了地震引起地球辆向惯量矩的变化。结果表明：由单个地震引起的日长变化要比观测值小几个量级，它的累积效应     

Viscous flow properties in the transport of solar wind momentum to the Venus upper ionosphere

A comparative study of the viscous transport of solar wind momentum to the upper layers of the Venus ionosphere with that occurring within the trans-terminator flow leads to estimates of the ratio of the viscosity coefficients that are applicable to both cases. Support for viscous forces between the solar wind and the ionospheric plasma in the trans-terminator flow derives from the momentum flux balance between the momentum flux in the latter flow and the deficiency of solar wind momentum along the flanks of the ionosheath. By comparing the relative width of the viscous boundary layer in the Venus ionosheath and the width of the trans-terminator flow we find that the transport of momentum within the upper ionosphere proceeds at a rate similar to that at which momentum is delivered to the upper ionosphere from the solar wind. Comparable values are obtained for the viscosity coefficient of the solar wind that streams over the ionosphere and that implied from momentum transport within the ionospheric trans-terminator flow. It is further suggested that despite the different nature of the processes that give place to the viscous transport of the solar wind momentum to the upper ionosphere (wave-particle interactions) and those responsible for its distribution within the ionosphere (through coulombian collisions) there is a similar response in the behavior of both plasmas to momentum transport. Calculations show that with comparable values of the viscosity coefficient in the ionosheath and in the upper ionospheric plasma the mean free path suitable to wave-particle interactions in the ionosheath is of the same order of magnitude as the mean free path of the planetary O⁺ ions that interact through coulombian collisions in the upper ionosphere. The effects of this similarity are considered in the discussion.     

Detection of a dry-frozen boundary inside Martian regolith

The present work investigates the time oscillations of the temperature at several depths of a Martian soil analogue made of two layers of different physical properties. The maximum temperature-time oscillation inside the Martian soil analogue, DT, and its derivative with depth, d(DT)/dz or DDT, can be analysed to understand the presence of a boundary between dry and frozen soil. The maximum temperature-time oscillation, DT, reduces by about one order of magnitude at the boundary between dry and frozen soil if a frozen layer is present. The reduction of DT at the boundary between two dry soils with different porosity is much smaller. DDT decreases by more than one order of magnitude at the boundary between dry and frozen soil if a frozen layer is present. The reduction of DDT at the boundary between two dry soils with different porosity is much smaller.     

Estimates of the wind speeds required for particle motion on Mars

We have obtained estimates of the threshold wind speed V_gt near the top of the atmospheric boundary layer on Mars and of the rotation angle α between this wind velocity and the direction of the surface stress. this calculation has been accomplished by combining wind tunnel determinations of the friction velocity with semi-empirical theories of the Earth's atmospheric boundary layer. Calculations have been performed for a variety of values of the surface pressure, ground temperature, roughness height, boundary layer height, atmospheric composition atmospheric stability, particle density, particle diameter, and strength of the cohesive force between the particles.The curve of threshold wind speed as a function of particle diameter monotonically decreases with decreasing particle diameter for a cohesionless soil but has the classical $\text{U}$ shape for a soil with cohesion. Observational data indicate that the latter condition holds on Mars. Under “favorable” conditions minimum threshold wind speeds between about 50 and 100m/sec are required to cause particle motion. These minimum values lie close to the highest wind speeds predicted by general circulation models. Hence, particle motion should be an infrequent occurence and should be strongly correlated with nearness to small topographic features. The latter prediction is in accord with the correlation found between albedo markings and topographic obstacles such as craters. For equal wind speeds at the midpoint of the boundary layer, particle movement occurs more readily in general at night than during the day, more readily in the winter polar areas than the equatorial areas noon, and more readily for ice particles than for silicate particles.The boundary between saltating and suspendable particles is located at a particle diameter of about 100 μm. This value is close to the diameter at which the V_gt curve has its minimum. Hence, the wind can set directly into motion both saltating and larger-sized suspendable particles, but dust-storm-sized particles usually require impact by a saltating particle for motion to be initiated. Albedo changes occur most often in regions containing a mixture of dust-stoorm-sized particles and saltating particles. The threshold wind speed for surfaces containing large, nonerodible roughness elements can either be larger or smaller than the value for surfaces with only erodible material. The former condition for V_gt holds when the roughness height z₀ is less than about 1 cm and may be illustrated by craters that have experienced less erosion than their environs. The latter condition for V_gt may be partly responsible for albedo changes detected on the elevated shield volcano, Pavonis Mons. Values of the angle α generally lie between 10 and 30°. These figures place a modest limitation on the utility of surface albedo streaks as wind direction indicators.     

The Kelvin-Helmholtz instability in the low-latitude boundary layer

The Kelvin-Helmholtz instability on the magnetopause has frequently been invoked as a mechanism for driving geomagnetic pulsations in the Pc3–Pc5 range, as well as to explain the occurrence of surface waves on the magnetopause observed by satellites. Most theories of the instability represent the magnetopause by a sharp boundary with velocity shear. In this paper a linear theory is developed which takes into account the finite thickness of the low-latitude boundary layer on the magnetopause. The theory is in a form suitable for numerical computation and can take into account the effect of gradients in the plasma pressure, magnetic field magnitude and direction, and density. Computations show that the instability is suppressed at wavelengths short compared with the scale width of the boundary. There is thus a wavelength for which the growth rate is maximum. Extensive computations have been carried out and they show that growth can take place for a very wide range of conditions. The computations confirm earlier results snowing that maximum growth occurs for a wave vector which is perpendicular to the magnetic field. For typical solar wind conditions the theory predicts wavelengths on the magnetopause of the order of 10 times the thickness of the low-latitude boundary layer and periods in the Pc3–Pc5 range. The possible non-linear development of the instability is discussed qualitatively. The predicted results are consistent with satellite observations of pulsations.     

Multipoint observations of low latitude ULF Pc3 waves in south-east Australia

Geomagnetic pulsations recorded on the ground are the signatures of the integrated signals from the magnetosphere. Pc3 geomagnetic pulsations are quasi-sinusoidal variations in the earth’s magnetic field in the period range 10–45 seconds. The magnitude of these pulsations ranges from fraction of a nT (nano Tesla) to several nT. These pulsations can be observed in a number of ways. However, the application of ground-based magnetometer arrays has proven to be one of the most successful methods of studying the spatial structure of hydromagnetic waves in the earth’s magnetosphere. The solar wind provides the energy for the earth’s magnetospheric processes. Pc3–5 geomagnetic pulsations can be generated either externally or internally with respect to the magnetosphere. The Pc3 studies undertaken in the past have been confined to middle and high latitudes. The spatial and temporal variations observed in Pc3 occurrence are of vital importance because they provide evidence which can be directly related to wave generation mechanisms both inside and external to the magnetosphere. At low latitudes (L < 3) wave energy predominates in the Pc3 band and the spatial characteristics of these pulsations have received little attention in the past. An array of four low latitude induction coil magnetometers were established in south-east Australia over a longitudinal range of 17 degrees at L = 1.8 to 2.7 for carrying out the study of the effect of the solar wind velocity on these pulsations. Digital dynamic spectra showing Pc3 pulsation activity over a period of about six months have been used to evaluate Pc3 pulsation occurrence. Pc3 occurrence probability at low latitudes has been found to be dominant for the solar wind velocity in the range 400–700 km/s. The results suggest that solar wind controls Pc3 occurrence through a mechanism in which Pc3 wave energy is convected through the magnetosheath and coupled to the standing oscillations of magnetospheric field lines.     

Exchange of global mean angular momentum between an atmosphere and its underlying planet

This paper investigates the exchange of global mean angular momentum between an atmosphere and its underlying planet by a simple model. The model parameterizes four processes that are responsible for zonal mean momentum budget in the atmospheric boundary layer for a rotating planet: (i) meridional circulation that redistributes the relative angular momentum, (ii) horizontal diffusion that smoothes the prograde and retrograde winds, (iii) frictional drag that exchanges atmospheric angular momentum with the underlying planet, and (iv) internal redistribution of the zonal mean momentum by wave drag. It is shown that under a steady-state or a long-term average condition, the global relative angular momentum in the boundary layer vanishes unless there exists a preferred frictional drag for either the prograde or the retrograde zonal wind. We further show quantitatively that one cannot have either a predominant steady prograde or retrograde wind in the boundary layer of a planetary atmosphere. The parameter dependencies of the global relative angular momentum and the strength of the atmospheric circulation in the boundary layer are derived explicitly and used to explain the observational differences between the atmospheres of Earth and Venus.     

Solar wind energy transfer regions inside the dayside magnetopause—II. Evidence for an MHD generator process

In this paper a quantitative analysis of magnetosheath injection regions observed by PROGNOZ-7 in the dayside high latitude boundary layer is performed. Particular emphasis is laid on describing the consequences of the observed excess transverse momentum of solar wind ions (H⁺ and He²⁺) as compared to the magnetospheric ions (e.g. He⁺ and O⁺) in the magnetosheath injection regions, hereafter referred to as energy transfer regions.An important result of this study is that the observed excess drift velocity of the solar wind ions as compared to the magnetospheric ions can be interpreted as a negative inertia current being present in the boundary layer. This means that the inertia current goes against the local electric field and that particle kinetic energy is converted into electric energy there. The dayside high-latitude boundary layer therefore constitutes a voltage generator (at least with respect to the injected magnetosheath plasma).The MHD-theory predicts a strong coupling of the energy transfer process in the boundary layer and the ionosphere, both regions being connected by field aligned currents. The rate of decay of the inertia current in the injected plasma element is in the range of a few minutes, a value which is directly proportional to the ionospheric resistance. By taking into account both the Hall and the Pedersen conductivities in the ionosphere, the theory also predicts a strong coupling between ionospheric East/West and North/South currents. A considerable part of the inertia current may actually flow in the tangential (East/West) direction due to this coupling. Thus, a consequence of the boundary layer energy transfer process is that it may generate currents, powering other magnetospheric plasma processes, down to ionospheric heights.     

Solar Wind and Chromospheric Network

A physical model of the transition region, including upflow of the plasma in magnetic field funnels that are open to the overlying corona, is presented. A numerical study of the effects of Alfvén waves on the heating and acceleration of the nascent solar wind originating in the chromospheric network is carried out within the framework of a two-fluid model for the plasma. It is shown that waves with reasonable amplitudes can, through their pressure gradient together with the thermal pressure gradient, cause a substantial initial acceleration of the wind (on scales of a few Mm) to locally supersonic flows in the rapidly expanding magnetic field trunks of the transition region network. The concurrent proton heating is due to the energy supplied by cyclotron damping of the high-frequency Alfvén waves, which are assumed to be created through small-scale magnetic activity. The wave energy flux of the model is given as a condition at the upper chromosphere boundary, located above the thin layer where the first ionization of hydrogen takes place.Among the new numerical results are the following: Alfvén waves with an assumed f ^-1 power spectrum in the frequency range from 1 to ⁴ Hz, and with an integrated mean amplitude ranging between 25 and 75 km s⁴, can produce very fast acceleration and also heating through wave dissipation. This can heat the lower corona to a temperature of 5× 10⁵ K at a height of h=12,000 km, starting from 5× 10⁴ K at h=3000 km. The resulting thermal and wave pressure gradients can accelerate the wind to speeds of up to 150 km s^-1 at h=12,000 km, starting from 20 km s^-1 at h=3000 km in a rapidly diverging flux tube. Thus the nascent solar wind becomes supersonic at heights well below the classical Parker-Type sonic point. This is a consequence of the fact that any large wave-energy flux, if it is to be conducted through the expanding funnel to the corona, implies the building-up of an associated wave-pressure gradient. Because of the diverging field geometry, this might lead to a strong initial acceleration of the flow. There is a multiplicity of solutions, depending mainly on the coronal pressure. Here we discuss two new (as compared with a static transition region model) possibilities, namely that either the flow remains supersonic or slows down abruptly by shock formation, which then yields substantial coronal heating up to the canonical 10⁶ K for the proton temperature.     

On the MHD instability of the Earth's magnetopause and its geophysical effects

This paper is concerned with the Kelvin-Helmholtz magnetohydrodynamic (MHD) instability near the low-latitude boundary layer. It is argued that the instability may be responsible both for viscous interaction of solar wind with the magnetosphere and for generation of surface waves over the range of geomagnetic pulsation frequencies. The influence of the inclination angle of the IMF vector with respect to the Earth-Sun line upon the instability growth-rate value is studied numerically. On the basis of the results the morning maximum of surface waves and of geomagnetic pulsations as well as the dependence of the latter on IMF orientation are discussed.     

First order latitude effects in the solar wind

The Weber-Davis model of the solar wind is generalized to include the effects of latitude. The principal assumptions of perfect electrical conductivity, rotational symmetry, a polytropic relation between pressure and density, and a flow aligned magnetic field in a system rotating with the Sun, are retained. A flow aligned magnetic field in the rotating system may be expressed in terms of the flow velocity and density. Rotational symmetry fixes the longitudinal flow velocity V_φ in terms of the flow in the r?θ plane. Thus, the original three dimensional magnetohydrodynamic flow problem is reduced to a two dimensional hydrodynamic flow problem in the r?θ plane.There are three critical surfaces associated with the equations which supply conditions to determine three of six required boundary conditions. The specified boundary conditions at the base of the corona are the temperature, density, and magnitude of the magnetic field. The equations are then expanded about the radial, nonrotating Parker solution and an analytic solution is obtained for the resulting first order equations. The results show that for constant coronal boundary conditions there is a latitudinal flow toward the solar poles, as a result of magnetic stresses, which persists out to large distances for the Sun. Associated with this flow is a latitudinal component of the magnetic field. The radial flow parameters are, to within small first order differences, in agreement with those of the Parker and the Weber-Davis models of the solar wind.The equations are further generalized to permit first order latitudinal variations in the specified coronal boundary conditions. Results at 1 a.u. are presented for 5 per cent latitudinal differences between the equatorial and polar values. These results show that the solution at 1 a.u. is most sensitive to a latitudinal dependence in the boundary temperature and least sensitive to a latitudinal dependence in the magnetic field magnitude.A solution is then obtained for an approximate dipolar variation in the coronal magnetic field magnitude. This solution predicts that the latitudinal flow is initially toward the Equator due to magnetic channeling; however, this effect is rapidly overcome and the latitudinal flow at 1 a.u. is toward the pole and not significantly different from the solution for constant boundary conditions.