共查询到20条相似文献，搜索用时 203 毫秒
1.
Results from a three-dimensional ballistic model of Europa's O2 atmosphere are presented. Hubble Space Telescope (HST) ultraviolet observations show spatially non-uniform O2 airglow from Europa. One explanation for this is that the O2 atmosphere is spatially non-uniform. We show that non-uniform ejection of O2 alone cannot reproduce the required morphology, but that a non-uniform distribution of reactive species in Europa's porous regolith can result in a non-uniform O2 atmosphere. By allowing O2 molecules to react with Europa's visibly dark surface material, we produced a spatially non-uniform atmosphere which, assuming uniform electron excitation of O2 over the trailing hemisphere, compares favorably with the morphology suggested by the HST observations. This model, which requires a larger source of O2 than has previously been estimated, can in principal be tested by the New Horizons observations of Europa's O2 atmosphere. 相似文献
2.
Onkar Nath 《Astrophysics and Space Science》1988,146(1):175-182
The self-similar model of propagation of spherical strong shock waves into non-uniform stellar atmosphere under self-gravitation and non-uniform magnetic field is investigated. The disturbances are headed by a shock surface of variable strength. Gas is assumed to be grey and opaque and the shock tobe transparent. 相似文献
3.
J. B. Singh 《Astrophysics and Space Science》1983,94(1):123-126
An approximate analytical solution for a self-similar flow behind a radiation driven shockwave is obtained using the Laumbach and Probstein's method in non-uniform atmosphere at rest. 相似文献
4.
The self-similar isothermal flow of a gas, moving under the gravitational attraction of a central body of fixed mass behind a spherical shock wave driven out by a propelling contact surface into a non-uniform stationary atmosphere is investigated. The total energy of the wave increases with time obeying a power law. 相似文献
5.
For the evaluation of the effect of the non-uniform surface albedo on the emergent radiation from the atmosphere, the emergent radiation from the atmosphere bounded by the two half Lambert surfaces composed of different albedo is computed. This paper is the improved version of the previous paper (Takashima and Masuda, 1991). The atmosphere is assumed to be homogeneous, which is composed of aerosol, molecules, and absorbent gases. Their optical thicknesses are (1) 0.25, 0.23, and 0.02, and (2) 0.75, 0.23, and 0.02, respectively. The model aerosol is of the oceanic and water soluble types.In the computational procedure, the emergent radiation is calculated approximately by the contributions due to the multiple scattering in the atmosphere, and due to the diffusely or directly transmitted radiation through the atmosphere which is reflected by the surfaces once (4 interactive radiative modes between atmosphere and surface). Furthermore, to perform the hemispherical integration processing the radiative interaction, the transmission function based on the single scattering in the atmosphere is introduced and then the transmission function is averaged over the hemisphere with weighting function. The numerical simulation exhibits the extraordinary effect near the two half surface boundary of different albedoes. The effect decreases exponentially with the distance from the boundary. The effect depends on the atmospheric aerosol type, optical thickness, and surface albedo. The present version enables us to quantitatively discuss the radiative transfer trend near the boundary of two half surfaces. The upward radiance would simply be evaluated using the present scattering approximation method if the surface albedo is less than 0.3. The present method is thought of as a first step extending the one-dimensional radiative transfer model to two-dimensional using the doubling-adding method. 相似文献
6.
A model of self-similar propagation of shock waves driven by a flare energy release in a non-uniform atmosphere has been considered. The total energy content of the model is assumed to be increased with time within the inner expanding surface and shock front. Finally the variation of velocity, pressure, density, and energy of the model have been discussed. The gas is assumed to be grey and opaque. 相似文献
7.
Uriel Vogel 《Planetary and Space Science》1966,14(12):1233-1252
The properties of a neutral lunar atmosphere are investigated theoretically. A non-uniformity is shown to result from the temperature variations and non-uniform gas source distribution on the surface of the Moon. An integral equation governing the distribution of molecular fluxes, in the steady state, is formulated. This equation is solved by computer and analytical methods. Solutions are obtained and discussed for mass numbers ranging from hydrogen to the heavy gases. Characteristic relaxation times for approach to the steady state are estimated and found generally to be a small fraction of the synodic period. It is concluded that in all cases a marked anisotropy of molecular fluxes can be expected. By measuring these fluxes conclusions can be drawn about the distribution of gas sources, the physical properties of the surface and the composition of the lunar atmosphere. 相似文献
8.
The propagation of plane magnetogasdynamic shock waves in an optically-thin grey atmosphere of non-uniform density has been discussed by the use of the similarity method, by use of Planck's diffusion approximation. The distribution of pressure, density, magnetic field, velocity, temperature, and radiation flux have been illustrated through graphs. The numerical integration has been done on a DEC-1090 computer under a RKGS programme. 相似文献
9.
Self-similar flows, behind a radiation-driven shock wave, have been investigated in non-uniform atmosphere. The total energy content of the flow behind the shock increases due to the absorption of radiation and it is assumed to be time-dependent. 相似文献
10.
Self-similar flows of self-gravitating gas behind the spherical shock wave propagating in a non-uniform atmosphere at rest, taking radiation heat flux into consideration, are investigated. The total energy of the wave is non-constant and can be made to vary slowly with time. 相似文献
11.
A comparative study has been made between the effects of transverse and axial components of the magnetic field on the self-similar flow variables of the field behind the cylindrical shock waves propagating into a non-uniform atmosphere at rest. The total energy of the wave is constant. 相似文献
12.
Self-similar MHD shock waves have been studied under the action of monochromatic radiation into a non-uniform stellar atmosphere with a constant intensity on unit area. It has been assumed that the radiation flux moves through the gas. Variation of flow variables have heen shown in tables for two different cases. 相似文献
13.
Investigation of local time dependence of Mercury's sodium exosphere based on a numerical simulation
Mercury has a surface-bounded exosphere (SBE) similar to that of the Moon. One of the atmospheric species, sodium, was found by ground-based observations to be the most prominent component. Mercury's sodium SBE is known to be non-uniform with respect to local time (LT) in low-latitude regions: the sodium column density in the dawn-side region is larger than that in the dusk-side region, and the sodium abundance is the largest in the morning-noon region. To reveal the production processes for the exosphere near Mercury's surface, the LT dependence of the exosphere was investigated through a numerical simulation. Three data sets of sodium column densities observed for the dawn-side hemisphere, observed by Sprague et al. [1997. Distribution and abundance of sodium in Mercury's atmosphere, 1985-1988. Icarus 12, 506-527], were compared with results simulated by a 3D Monte Carlo method, and the source rates and density of sodium of the planetary surface were estimated. In the simulation, the photon-stimulated desorption (PSD) and thermal desorption (TD) processes were assumed as the release mechanisms. The sodium source rates for the three data sets, at respective heliocentric distances of about 0.33, 0.42, and 0.44 AU, were estimated as 1-4×108 Na/cm2/s with weak LT dependence. In contrast, the expected sodium surface density showed clear dependence on LT and the heliocentric distance. The sodium surface density decreases from early morning to noon by a few orders, and, particularly for large heliocentric distances, the surface is in a condition of sodium excess and depletion with respect to the surface sodium density assumed by Killen et al. [2004. Source rates and ion recycling rates for Na and K in Mercury's atmosphere. Icarus 171, 1-19] in the early morning and morning-noon regions, respectively. This study implies that the decrease in sodium surface density from the early morning to noon regions might produce the characteristic LT dependence in the low-latitude dawn-side region. 相似文献
14.
A complete software package has been built for the calibration in m s –1 of the velocity residuals due to solar oscillations in the raw IRIS (International Research on the Interior of the Sun) data. It takes into account all known astronomical components contributing to the line-of-sight velocity between the instrument and the solar surface, and also the apparent velocity due to the non-uniform integration of the solar rotation as seen through an inhomogeneous Earth atmosphere. The IRIS data itself is used for the estimation of the nonlinear instrumental response to the velocity, and the residual can be directly obtained in velocity units, without low frequency filtering. On a day of typical photometric sky quality, the power spectrum obtained appears to be solar noise limited. 相似文献
15.
To evalute the effect of the non-uniform surface on the radiation field, the upwelling radiation at the top of the atmosphere bounded by the checkerboard type of terrain is computed using the modified doubling method. The terrain is composed of the square Lambert surfaces with two different albedoes. The dimension of the each square is assumed to be 0.5–6 km. The radiance of the terrain is discussed with respect to the atmospheric effect. The observational site is located at altitude 30 km. The corresponding projected point on the ground is located at the center of a square. The solar and observational direction is located in the plane parallel to the checkerboard squares. The atmosphere is assumed to be homogeneous, which is composed of aerosol and molecules, where the model aerosol is of the oceanic or the water soluble types.Numerical simulation exhibits the extraordinary effect near the edge of each squares. The radiance of the terrain depends upon the difference of albedoes and size of squares. It increases with the increase of the dimension of the square. It decreases with the optical thickness. At large optical thickness, the variation of radiation with zenith direction depends upon the aerosol characteristics. It shows little dependence on the solar zenith angle if less than 20°. 相似文献
16.
Rabindra Nath Das 《Astrophysics and Space Science》1980,67(2):335-342
The key equation which commonly appears for radiative transfer in a finite stellar atmosphere having ground reflection according to Lambert's law is considered in this paper. The exact solution of this equation is obtained for surface quantities in terms of theX-Y equations of Chandrasekhar by the method of Laplace transform and linear singular operators. This exact method is widely applicable for obtaining the solution for surface quantities in a finite atmosphere. 相似文献
17.
For the evaluation of the effect of the nonuniform surface albedo to the emergent radiation from the atmosphere, the emergent radiation from the atmosphere bounded by the two-halves of the Lambert surface with different albedos is computed. The principal plane is assumed to be perpendicular to the boundary of surfaces. The atmosphere is assumed to be homogeneous, which is composed of aerosol, molecules, and absorbent gases. Their optical thicknesses are 0.25, 0.23, and 0.02, respectively. The model aerosol is of the oceanic and water soluble types.In the computational procedure, the emergent radiation is approximated by the contributions due to the multiple scattering in the atmosphere, directly attenuated radiation, and radiation due to single scattering in the atmosphere which is reflected by the Lambert surface (up to 4 interactive radiative modes between atmosphere and surface). For quantitative analysis, results are compared with those of the atmosphere-uniform surface model, where the multiple scattering is considered. The numerical simulation exhibits the extraordinary effect near the surface boundary of different albedos. The effect decreases exponentially with the distance from the boundary. It is a function of the observational position, difference of surface albedos, optical thickness and aerosol type.The upward radiance would simply be evaluated using the present scattering approximation method if the atmosphere is in clear condition. Whereas in hazy condition, the effect of multiple scattering in the atmosphere should be considered more precisely, since the upward radiance exhibit a strong dependence on observational nadir angles due to multiple scattering in the atmosphere. Furthermore, it depends on the optical characteristics of aerosols. 相似文献
18.
Similarity solutions are obtained for spherical radiation-driven shock waves propagating in a non-uniform atmosphere at rest obeying a density power law. Approximate analytical solutions are also obtained and found to be in good agreement with the numerical solutions. The effect of the parameter characterizing the initial density distribution of the gas on solutions of the flow field is studied in detail. It is also shown analytically that the shock wave propagates as an overdriven detonation. 相似文献
19.
This paper considers a spherical shock, in a conducting gas, of self-gravitating gas propagating in a non-uniform atmosphere at rest. Similarity principle has been used to reduce the equations governing the flow to ordinary differential equations under the assumption that the density varies as an inverse-power of distance from the point or explosion. The total energy of the wave is variable.Supported by CSIR, New Delhi under grant No. 7/57/287/81/EMR-I. 相似文献
20.
Tsutomu Takashima 《Earth, Moon, and Planets》1985,33(1):59-97
A procedure of computing the radiance and the polarization parameters of radiation diffusely reflected and transmitted by an inhomogeneous, plane-parallel terrestrial atmosphere bounded by a ruffled ocean surface is discussed with the aid of the adding method. If the atmosphere and the ocean are simulated by a number of homogeneous sublayers, the matrices of radiation reflected and transmitted diffusely by the atmosphere-ocean system can be expressed in terms of these matrices of sublayers by using only a couple of iterative equations in which the polarity effect of radiation is included. Furthermore, the upwelling radiance and the polarization degree of radiation at the top of the atmosphere can be calculated by using a single iterative equation without requiring the equation for the diffuse transmission matrix of radiation. The ruffled ocean surface can be treated as an interacting interface, where the transmitted radiation from beneath the ocean surface into the atmosphere is also taken into account into the derivation of equations. Finally, sample computations of the upwelling radiance and the polarization degree of radiation from the top of the atmosphere are carried out at the wavelength of 0.60 micron. 相似文献