共查询到20条相似文献，搜索用时 46 毫秒
1.
Daniel J. Scheeres Sepidehsadat Mirrahimi 《Celestial Mechanics and Dynamical Astronomy》2008,101(1-2):69-103
The rotational dynamics of a small solar system body subject to solar radiation torques is investigated. A set of averaged evolutionary equations are derived as an analytic function of a set of spherical harmonic coefficients that describe the torque acting on the body due to solar radiation. The analysis also includes the effect of thermal inertia. The resulting equations are studied and a set of possible dynamical outcomes for the rotation rate and obliquity of a small body are found and characterized. 相似文献
2.
The principal features which distinguish the atmosphere on Venus from that of the Earth are the slow rotation of the planet, the large mass of the atmosphere, and the opacity of the atmosphere to long-wave radiation. The slow rotation of the planet gives rise, first of all, to nongeostrophuc dynamics (the atmosphere gas has a tendency to move along the pressure gradient), with the result that the region of the main influx of solar energy is located on one side of the planet, and the region of maximum cooling on the other. These considerations lead to a much simpler scheme of circulation than that in the Earth's atmosphere.The large mass of the atmosphere is the cause of a high thermal and mechanical inertia, which explains why the atmospheric circulation is asymmetrical relative to the solar-antisolar axis. The daily center of circulation is displaced to the second half of the Cytherean solar day, i.e., to the line of zero budget of thermal energy corresponding to a height of the Sun abobe the horizon of about 20°. The notions of cold and warm regions are very relative for Venus. While the horizontal temperature differences on the Earth may reach 100°, a mean horizontal temperature drop as small as 3° in the Cytherean atmosphere may be looked upon as an exceptional phenomenon. This high thermal homogeneity is due to a very large thermal inertia, with cooling at the poles never manifesting itself in the temperature fields obtained.The opacity of the Cytherean atmosphere to long-wave radiation results in vertical heat transfer by turbulence, mesoscale convection, and large-scale currents. This produces adiabatic stratification in the troposphere and a high temperature in the lower layers.These phenomena were studied in a general manner using two- and three-level models. Steps have recently been undertaken to investigate in greater detail the vertical structure of the troposphere on Venus using ten-level models. It appeared that the vertical dynamic structure of the troposphere is very much dependent on the distribution in height of the solar energy influx. In the greenhouse model, the entire atmosphere is affected by circulation. Pronounced velocity maxima are observed in the lower and upper layers. In a model with adsorption of solar radiation in the upper layer, the velocity is small in the lower layers, but it rapidly increases and changes its direction several times in the upper layers. The mean kinetic energy of the atmosphere proves to be two to three times smaller than in the greenhouse model.Attempts have been made in the calculations to find the principal modes of the statistical fluctuations. The results obtained show that atmospheric circulation may be represented by a global mean basic state following the rotation of the planet with deviations from that basic state which are indeterminate disturbances. The mean basic state exhibits a high degree of symmetry relative to the equator. On account of nonlinearity, the disturbances were observed in all the models independently of space and time resolution. This phenomenon appears to reflect the actual properties of the Cytherean atmosphere and has no bearing on the details of the numerical scheme. 相似文献
3.
New results of the numerical modeling of the response of the outer atmosphere of the Sun to an impulsive heating are presented.
Features of the general process are considered both for powerful and weak solar flares. For the most powerful flares it is
necessary to take into account the effect of a saturation of the heat flow. Though for the most powerful solar flares the
saturation of a thermal flow is not such large, the influence of this effect is important for cases of powerful flares on
red dwarf stars, strongly limiting the input of the thermal energy downwards. The response of the atmosphere, which consists
of the chromosphere, the transition region and the corona, to weak heating is characterized by creation no one as usually
but two ascending coronal flows. The occurrence of the additional flow at coronal heights is caused by the inhomogeneous initial
heating of the outer atmosphere. Some types of soft X-ray and UV-jets can be associated with such additional flow.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
In a weakly ionized plasma, the evolution of the magnetic field is described by a 'generalized Ohm's law' that includes the Hall effect and the ambipolar diffusion terms. These terms introduce additional spatial and time-scales which play a decisive role in the cascading and the dissipation mechanisms in magnetohydrodynamic turbulence. We determine the Kolmogorov dissipation scales for the viscous, the resistive and the ambipolar dissipation mechanisms. The plasma, depending on its properties and the energy injection rate, may preferentially select one of these dissipation scales, thus determining the shortest spatial scale of the supposedly self-similar spectral distribution of the magnetic field. The results are illustrated taking the partially ionized part of the solar atmosphere as an example. Thus, the shortest spatial scale of the supposedly self-similar spectral distribution of the solar magnetic field is determined by any of the four dissipation scales given by the viscosity, the Spitzer resistivity (electron–ion collisions), the resistivity due to electron–neutral collisions and the ambipolar diffusivity. It is found that the ambipolar diffusion dominates for reasonably large energy injection rate. The robustness of the magnetic helicity in the partially ionized solar atmosphere would facilitate the formation of self-organized vortical structures. 相似文献
5.
Anthony R. Dobrovolskis 《Icarus》1983,56(1):165-175
Diurnal solar heating of Venus' surface produces variable temperatures, winds, and pressure gradients within a shallow layer at the botton of the atmosphere. The corresponding asymmetric mass distribution experiences a tidal torque tending to maintain Venus' slow retrograde rotation. It is shown that including viscosity in the boundary layer does not materially affect the balance of torques. On the other hand, friction between the air and ground can reduce the predicted wind speeds from ∽5 to ∽1 m/sec in the lower atmosphere, more consistent with the observations from Venus landers and descent probes. Implications for aeolian activity on Venus' surface and for future missions are discussed. 相似文献
6.
在太阳大气不同层次连续光谱中叠加有丰富的发射线或吸收线,对这些谱线轮廓进行反演分析可以探测太阳大气的化学成分和物理状态.太阳大气的色球及过渡区由于其密度低难以建立热动平衡,建立相应的大气模型需要采用非局部热动平衡(Non-Local Thermodynamic Equilibrium,N-LTE)理论.根据相对偏离因子计算来研究太阳中低层大气偏离局部热动平衡(Local Thermodynamic Equilibrium,LTE)分布的情况.首先对日全食观测过程中得到色球和过渡区不同高度形成的两条光谱数据进行反演,得到确定观测谱线的参数信息,如连续谱源函数、谱线源函数、多普勒宽度和由此推出的等效动力学温度;根据这些反演出的谱线参量计算出二维视场内每个空间采样点偏离LTE状态的定量结果;其次,根据用于观测的积分视场单元光纤排布阵列重构出辐射强度、等效动力学温度和相对偏离因子二维分布.结果显示:在局部小区域,温度分布和相对偏离因子的分布存在较强相关性,而与辐射强度分布无明显相关.从两条谱线导出的等效温度和相对偏离因子分布存在明显的差异.这两种二维分布揭示出太阳大气某些小尺度区域具有较强的结构性和复杂性,为进一步理解太阳中低层大气物理提供了一种新的视角. 相似文献
7.
A plasmoid may be ejected during a flare and condensed by a radiative instability. The spectral shape of the mean fluxes of Simple 3 (or long-enduring) solar events is interpreted in terms of a thermal emission from this transient condensation in the higher levels of the solar atmosphere. This condensation is thick enough to block the radiation from the underlying S-component. This explanation fits the observed polarization changes, as well as the thermal character of the bursts time profiles. A clue for solar activity forecasting as well as for detailed studies of active sources is indicated. 相似文献
8.
W.B. Hubbard 《Icarus》1978,35(2):177-181
We extend a Jovian convective-cooling model to Uranus and Neptune. The model assumes that efficient interior convection prevails, so that escape of interior heat is governed by the radiative properties of the atmosphere. A comparison of the thermal evolution of Uranus and Neptune indicates that the larger amount of solar radiation absorbed in Uranus' atmosphere tends to differentially suppress the escape of interior heat. The model is shown to be consistent with recent infrared observations of the thermal balance of Uranus and Neptune, and with the presumed age of these planets. 相似文献
9.
R.W. Schunk 《Planetary and Space Science》1978,26(6):605-610
We have studied the extent to which various transport processes affect the dispersal of a gas artificially injected into the night-time atmosphere at F-region altitudes. In addition to diffusion, we have found that nonlinear acceleration, viscous stress, and thermospheric winds affect the dispersal of the injected gas. The magnitude of the effect depends on the atmospheric density, which is a function of solar activity. For an injected H2 gas, non-linear acceleration and viscous stress rapidly become more important than diffusion above about 300 km for low solar activity (T∞ = 750K), 340 km for moderate solar activity (T∞ = 1000K), and 400 km for high solar activity (T∞ = 1500K). For an injected H2O gas, the corresponding altitudes are 350, 400, and 470 km for low, moderate and high solar activity, respectively. The effect of nonlinear acceleration and viscous stress is to retard the expansion of the injected gas. Thermospheric winds of 150–400 m s?1 are important at altitudes near and below the F-region peak electron density. These winds act to transport the injected gas in the wind direction and this affects the shape and temporal development of the subsequent ionospheric hole. Because the H2O diffusion coefficient is smaller than the H2 diffusion coefficient, winds are more important for H2O than for H2. 相似文献
10.
The stability equations for localized (or ballooning) modes in the solar atmosphere are formulated. Dissipation due to viscosity, resistivity, and thermal conduction are included using the general forms due to Braginskii (1965). In addition, the effect of gravity, plasma radiation, and coronal heating are included. The resulting equations are one-dimensional and only involve derivatives along the equilibrium magnetic field. Thus, the stabilising influence of photospheric line-tying, which is normally neglected in most numerical simulations, can be studied in a simple manner. Two applications to sound wave propagation and thermal instabilities in a low-beta plasma are considered with a view to determining realistic coronal boundary conditions that model the lower, denser levels of the solar atmosphere in a simple manner.Research Assistant of the Belgian National Fund for Scientific Research. 相似文献
11.
J.A. Pirraglia 《Icarus》1984,59(2):169-176
The meridional energy balance of Jupiter is calculated from high spatial resolution observations by the Voyager 1 infrared spectrometer and radiometer. On a hemispheric scale Jupiter radiates thermal energy to space approximately uniform with latitude while solar energy absorption varies approximately as the solar angle. This implies internal adjustment to the solar energy with a larger contribution poleward of ±45° than in the equatorial zone. The internal flux is modulated by the major visible features of the zone and belt system but, unlike the hemispheric scale where increased internal flux is correlated with decreased solar absorption, on smaller scales the inverse occurs. The energy balance is very likely to be controlled by dynamics, but the relative influence of the upper atmosphere and the interior is not yet clear. Models have been proposed that would explain the pole-to-equator variation in the thermal emission and it is suggested that the smaller scale variations may be the result of forced convective circulation. 相似文献
12.
Alberto Righini 《Solar physics》1972,25(1):242-251
Results on the structure coefficient of the temperature field present in the low atmosphere are presented. Measurements have been performed during the national Italian expedition for solar site testing in Isola delle Correnti (southern Sicily).Calculations have been carried out to show the effect of the observed thermal properties of the low atmosphere on telescope performances, with various assumptions as the structure at greater heights. 相似文献
13.
我们认为存在于太阳高层大气中的一种稳定的物质交换,可以起到冷却日冕和加热色球一日冕过渡区的热机作用。还考虑到来自日冕的热传导和过渡区的辐射损失,计算了太阳过渡区的温度、密度和速度分布。并对物质流通量及速度边值与太阳过渡区厚度之间的关系作了讨论。 相似文献
14.
As part of a study of satellite thermal control, data were obtained on earth-reflected solar radiation and on the stability of thermal-control coatings. The intensity distribution of incoming solar radiation to earth was found to be shifted toward the ultraviolet region upon reflection by the atmosphere. As a result of the shift, the intensity of reflected radiation reaches a maximum in the near ultraviolet. At shorter wavelengths in the ultraviolet region, the intensity drops sharply to zero as a result of absorption of incoming radiation by ozone in the upper atmosphere. Comparisons of calculated intensity distributions with measured distributions for two different atmospheric conditions gave good agreement, except at the shorter ultraviolet wavelengths where the calculations did not adequately include the effect of ozone absorption. Measurements of stability of thermal-control coatings showed a lower degradation rate of white paints than was obtained on other flight experiments flown outside of the protective influence of earth's magnetosphere. The differences in degradation rate were much larger than expected, indicating that further study is required in the development of white coatings for spacecraft thermal control. 相似文献
15.
The damping of MHD waves in solar coronal magnetic field is studied taking into account thermal conduction and compressive
viscosity as dissipative mechanisms. We consider viscous homogeneous unbounded solar coronal plasma permeated by a uniform
magnetic field. A general fifth-order dispersion relation for MHD waves has been derived and solved numerically for different
solar coronal regimes. The dispersion relation results three wave modes: slow, fast, and thermal modes. Damping time and damping
per periods for slow- and fast-mode waves determined from dispersion relation show that the slow-mode waves are heavily damped
in comparison with fast-mode waves in prominences, prominence–corona transition regions (PCTR), and corona. In PCTRs and coronal
active regions, wave instabilities appear for considered heating mechanisms. For same heating mechanisms in different prominences
the behavior of damping time and damping per period changes significantly from small to large wavenumbers. In all PCTRs and
corona, damping time always decreases linearly with increase in wavenumber indicate sharp damping of slow- and fast-mode waves. 相似文献
16.
V. I. Shematovich 《Solar System Research》2017,51(4):249-257
This is a study of the kinetics and transport of hot oxygen atoms in the transition region (from the thermosphere to the exosphere) of the Martian upper atmosphere. It is assumed that the source of the hot oxygen atoms is the transfer of momentum and energy in elastic collisions between thermal atmospheric oxygen atoms and the high-energy protons and hydrogen atoms precipitating onto the Martian upper atmosphere from the solar-wind plasma. The distribution functions of suprathermal oxygen atoms by the kinetic energy are calculated. It is shown that the exosphere is populated by a large number of suprathermal oxygen atoms with kinetic energies up to the escape energy 2 eV; i.e., a hot oxygen corona is formed around Mars. The transfer of energy from the precipitating solar-wind plasma protons and hydrogen atoms to the thermal oxygen atoms leads to the formation of an additional nonthermal escape flux of atomic oxygen from the Martian atmosphere. The precipitation-induced escape flux of hot oxygen atoms may become dominant under the conditions of extreme solar events, such as solar flares and coronal mass ejections, as shown by recent observations onboard NASA’s MAVEN spacecraft (Jakosky et al., 2015). 相似文献
17.
Noboru Takeichi 《Celestial Mechanics and Dynamical Astronomy》2010,108(4):405-416
The parametric excitation of a gravity gradient stabilized spacecraft induced by the periodic solar pressure torque is discussed.
The solar pressure torque in the linearized equations of motion appears as linear terms with periodic coefficients. The attitude
stability is analyzed numerically through the calculation of the Floquet multiplier. The perturbation method is also applied
to identify the instability condition analytically. It is made clear that the periodic solar pressure torque can destabilize
the coupled roll and yaw attitude motion of the spacecraft. It is also shown that the conditions of parametric resonance are
included in the gravity gradient stability condition. Nonlinear simulations are also carried out to verify the effect of the
parametric resonance. The numerical simulation using actual parameters shows that the spacecraft inevitably experiences a
large amplitude attitude motion due to the periodic solar pressure torque even if the gravity gradient stability condition
is satisfied. 相似文献
18.
The spectral window of Jupiter at 3 μm is analyzed and compared with previously published spectra. The two components of the spectrum, the thermal and the solar reflected contributions, are calculated at low resolution (30 cm?1) between 3300 and 3800 cm?1 for preparing the interpretation of the Galileo Near Infrared Mapping Spectrometer experiment. The calculations yield to the following conclusions: (1) NH3 is the main absorber between 3300 and 3600 cm?1 for both the thermal spectrum and the solar reflected spectrum; H2O appears only in the thermal component above 3600 cm?1. (2) The thermal component can be seen only on the dark side of Jupiter; the atmosphere is sounded down to temperature levels of about 210°K. (3) The solar reflected component can be modelized by a reflecting layer between 135 and 140°K with an albedo of 0.3; high spatial resolution maps of Jupiter at 3 μm should give access to the NH3 spatial distribution on Jupiter. 相似文献
19.
The high velocity retrograde circulation of the upper atmosphere of Venus may be an observable consequence of the solar couple upon a thermal semidiurnal atmospheric tide in the stratosphere. A couple of this type would help account for the resonant rotation of the planet. 相似文献
20.
The recent measurements of the vertical distribution and optical properties of haze aerosols as well as of the absorption coefficients for methane at long paths and cold temperatures by the Huygens entry probe of Titan permit the computation of the solar heating rate on Titan with greater certainty than heretofore. We use the haze model derived from the Descent Imager/Spectral Radiometer (DISR) instrument on the Huygens probe [Tomasko, M.G., Doose, L., Engel, S., Dafoe, L.E., West, R., Lemmon, M., Karkoschka, E., See, C., 2008a. A model of Titan's aerosols based on measurements made inside the atmosphere. Planet. Space Sci., this issue, doi:10.1016/j.pss.2007.11.019] to evaluate the variation in solar heating rate with altitude and solar zenith angle in Titan's atmosphere. We find the disk-averaged solar energy deposition profile to be in remarkably good agreement with earlier estimates using very different aerosol distributions and optical properties. We also evaluated the radiative cooling rate using measurements of the thermal emission spectrum by the Cassini Composite Infrared Spectrometer (CIRS) around the latitude of the Huygens site. The thermal flux was calculated as a function of altitude using temperature, gas, and haze profiles derived from Huygens and Cassini/CIRS data. We find that the cooling rate profile is in good agreement with the solar heating profile averaged over the planet if the haze structure is assumed the same at all latitudes. We also computed the solar energy deposition profile at the 10°S latitude of the probe-landing site averaged over one Titan day. We find that some 80% of the sunlight that strikes the top of the atmosphere at this latitude is absorbed in all, with 60% of the incident solar energy absorbed below 150 km, 40% below 80 km, and 11% at the surface at the time of the Huygens landing near the beginning of summer in the southern hemisphere. We compare the radiative cooling rate with the solar heating rate near the Huygens landing site averaging over all longitudes. At this location, we find that the solar heating rate exceeds the radiative cooling rate by a maximum of 0.5 K/Titan day near 120 km altitude and decreases strongly above and below this altitude. Since there is no evidence that the temperature structure at this latitude is changing, the general circulation must redistribute this heat to higher latitudes. 相似文献