彗木相撞中的波动

1994年7月18日至24日期间，彗星苏梅克-列维9(SL-9)的超过20块碎片与木星发生了相撞．哈勃空间望远镜(HST)拍摄到的图像揭示了木星大气对撞击的动力学响应．具有重要意义的是观测到5个撞击点周围的圆环，它们以450米／秒的常速度向外运动．环的圆形性表明它们是波．因为对于不同大小的撞击，波速是常量，可以推断出传播速度与爆炸能量无关．这意味着这些波动是线性波．评述现行理论所使用的3类候选波，亦即惯性引力波、声波和地震波，介绍的重点是前面两种．     

彗木相撞的不可压缩分层流体模型

提出了一个彗木相撞的线性模型．在这个模型中，将木星大气看作是一个分层的、不可压缩和无粘滞的流体层，而与撞击相联的引力波则由一个初始冲力所造成．采用初始冲压P(r，z，0)代替初始表面形变作为初始条件．发现这种做法使得问题的数学处理更加方便，特别是在计算流体粒子的垂直位移和摄动势能方面，后者可以表为P(r，z，0)的有限傅立叶正弦和余弦变换．导出了一个联系彗星碰撞参数、木星大气参数和所设初始冲力之间的关系式．还对两种P(r，z，0)的假设形式分析地导出表面波波高．     

近地小行星探测和危险评估

<正>1994年7月,苏梅克-列维9号彗星的21个碎片以约60 km/s的速度撞击木星,这是人类第1次直接观测到的大规模天体相撞.这次事件表明地球面临着天体碰撞的现实威胁.1995年在纽约联合国大厦召开的预防近地天体撞击地球的国际科学会议上,紫金山天文台提出了中国近地天体探测计划(CNEOS).1998年,CNEOS计划正式立项启动.从选址建站、望远镜和CCD系统研制,到投入试观测,实现海量数据处理和碰撞危险评估,经历了7 yr多时间.本论文综述CNEOS观测系统的概     

迎接彗星撞击木星事件的到来

迎接彗星撞击木星事件的到来赵刚１９９３年５月２２日，美国哈佛—一史密松天体物理中心的Ｂ．Ｍａｒｓｄｅｎ等人根据轨道计算结果，预告苏梅克—一利维９周期彗星（Ｐ／ＣｏｍｅｔＳｈｏｅｍａｋｅ’－Ｌ””ｖ９，以下简称Ｓ－Ｌ。彗星）正处于一个将与木星相撞的轨道...     

漫谈地球受撞及影响

漫谈地球受撞及影响韩忠林宇宙间的天体都在运动，碰撞是一种自然现象目睹苏梅克一利维９号彗星分２１块与木星相撞，我们不得不想到地球和人类的安危。人们已经知道，水星、金星、火星及月球、火卫、木卫上星罗棋布的环形山是受撞形成的，地球处在与它们相似的空间环境，...     

彗木相撞的可压缩分层流体模型

提出一个彗木相撞的修正了的线性模型．在这个模型中,将木星大气视为一个转动的、分层的、可压缩和无粘滞的流体层．结果表明,虽然大部分撞击能量仍然转换成内波能量,但不能忽视可压缩效应．     

我国对苏梅克-列维9号慧星撞击木星事件的观测(英)

1994年7月16日─22日，苏梅克－列维9号周期慧星的21颗碎片连续撞击木星事件是一次极为罕见的天文现象．文中概括介绍了我国天文学家对慧木相撞事件的光学和射电观测网点、课题设置以及所取得的主要观测结果．     

SL9彗星碎块穿入木星大气的深度

ＳＬ９慧星撞击木星类似于大气中陨落的流星现象，是替星与木星大气相互作用的过程．慧星碎块的质量取为１０（１２）、１０（１３）和１０（１４）ｋｇ，其密度分别为３．０、１．０、０．８、０．５和０．２ｇ／ｃｍ３．结果表明：这些慧星碎块能穿透木星大气的氨云层，在接近１ｂａｒ的地方爆炸，这与文［１］的模拟结果一致．     

太阳大气中高速喷射柱的MHD稳定性

本文推得了具有流动情形下的磁约束等离子体柱稳定性的色散方程,对内部流动速度为160km/s(冲浪型)和600km/s(喷焰型)两种高速喷射情形,分别算得其增长模的色散曲线。结果表明,不稳定增长率并不随喷射速度增高而无限增长,当喷射速度接近太阳表面逃逸速度时,增长率在短波波段反而下降,色散曲线形状会发生明显的变化。此时,m=0模和m=1模的两种扭折不稳定性会在不同的扰动波长上同时发生,而对极短波长的扰动,不稳定性永远不会发生。通过对物理参数不同取值的计算结果比较,以判断各个物理参数对稳定性的作用及其有效性。最后,利用这些结果对几个特殊的高速喷射现象进行了物理解释。     

彗木碰撞时刻及位置的确定

Shoemaker－Levy9号童星于1994年7月与木星碰撞己成为事实．本文依据众多碰撞时刻的观测报道，并结合碰撞预报，对其进行了系统研究．分析了用不同观测技术和观测手段所给出的碰撞时刻的报道，强调了碰撞物理过程的重要性．最后，按照统一的物理模式初步确定了各个碎核的碰撞时刻．并归算出木星南纬碰撞带区的自转速度约为9h55min-周，说明它没有受到营核连续撞击的影响．本文还将各管核撞击点在水面上的位置与预报做了比较．     

The inertia-gravity waves caused by the impact of shoemaker-levy 9 with jupiter

After the collision of Comet Shoemaker-Levy 9 (SL9) with Jupiter, some ring structures were observed propagating outwards at a constant speed (∼450 m/s) on the Jovian surface. These are thought to be linear waves caused by the collision. A linear model of the collision is presented, in which the Jovian atmosphere is considered as an irrotational, inviscid, stratified and incompressible fluid layer moving at a speed of U = b + az. We take an initial impulsive pressure p(r; 0) as the initial condition and solve the fluid dynamics equations for inertia-gravity waves. It is found that most part of the perturbation energy is used to produce internal waves when Jovian atmosphere moves at a constant speed (U = U_o (∼170 m/s)). A relation between the impact depth H and the horizontal phase speed v_p is deduced. Finally, the inertia-gravity waves are discussed for the case U = b + az and it is found that the perturbation energy is then not divided equally between kinetic energy and potential energy because of the effect of a shear.     

A Stratified Compressible Fluid Model of the Comet-Jupiter Collision

A revised linear model is presented to explain the waves from the collisions of Comet Shoemaker-Levy 9 with Jupiter, in which the Jovian atmosphere is taken as a rotating stratified, compressible and inviscid fluid layer. It is shown that the effect of compressibility can not be ignored, although most of the impacting energy is still converted into the energy of internal waves.     

An incompressible stratified fluid model ofComet Shoemaker-Levy 9''s collision with Jupiter

A linear model of Comet Shoemaker-Levy 9's collision with Jupiter ispresented, in which the Jovian atmosphere is taken to be a stratified, incompressible and inviscid fluid layer and the gravity wave associated with the impacts is caused by an initial impulse. Instead of adopting an initial surface deformation, we take an initial impulsive pressure P(r, z, 0) as the initial condition. It is found that this approach is more convenient for the mathematical formulation of the problem, especially for the computation of the vertical displacement of the fluid particles and the perturbation potential energy which can then be expressed by finite Fourier sine and cosine transform of P(r, z, 0).

A relationship among parameters of the impact and the Jovian atmosphereand the assumed initial impulse is deduced. We also derive the wave height of the surface wave analytically for two assumed forms of P(r, z, 0).     

An analytical model of the Comet's collision with Jupiter

An important feature observed in the wake of the Jupiter-comet clash was the appearance of the ring structure axisymmetrically positioned around the center of the impact. The persistent expansion of the dark rings and its speed indicated an outward propagating gravity wave (Benka, 1995). We employ an analytical model of constant density, uniform finite depth and inviscid fluid layer to investigate the wave motion produced by the impact of Comet Shoemaker-Levy 9 on the Jovian atmosphere. The relevant thermal effects are neglected and an explosion resulting from the collision is then described by an initial impulsive pressure at the surface of the Jovian atmosphere. Under the assumption that all the kinetic energy of a comet fragment is completely converted into the energy of wave motions in the Jovian atmosphere, an analytical formula describing the relationship between the resulting wave motion in the atmosphere and the parameters of a comet fragment (the radius, density and speed) is derived. Results from the present simple analytical model give a qualitative agreement with observations regarding the distance and speed of the waves.     

Low order effect of crand input in the Jovian atmosphere

Modeling of the Jovian atmosphere shows that cosmic ray induced albedo neutron decay is inadequate to account for Pioneer 10 and 11 projected electron levels on Jupiter. High energy solar protons must also be excluded as an important neutron decay source. Analysis of neutron flux data near the top of the Jovian atmosphere can lead to the determination of He/H₂ and³He/⁴He ratios for the Jovian atmosphere.     

Light and dark spots in the equatorial regions of Jupiter

The lifetimes and motions of dark and light spots in the equatorial regions of Jupiter have been studied for the 1972 apparition. The difference in lifetimes of the two types of spot is demonstrated, as are their differing modes of formation and disappearance. The way in which the spots interact is examined in detail, and it is pointed out that this may have implications for the fluid dynamics of the Jovian atmosphere,     

Jupiter's outer atmosphere

The current state of the theory of Jupiter's outer atmosphere is briefly reviewed. The similarities and dissimilarities between the terrestrial and Jovian upper atmospheres are discussed, including the interaction of the solar wind with the planetary magnetic fields. Estimates of Jovian parameters are given, including magnetosphere and auroral zone sizes, ionospheric conductivity, energy inputs, and solar wind parameters at Jupiter. The influence of the large centrifugal force on the cold plasma distribution is considered. The Jovian Van Alien belt is attributed to solar wind particles diffused in towards the planet by dynamo electric fields from ionospheric neutral winds and consequences of this theory are given.