共查询到20条相似文献,搜索用时 15 毫秒
1.
This paper presents a theoretical investigation of the ducting of Pc1 hydromagnetic waves in an ionospheric layer situated above the F2 region. Theoretical calculations show that this upper ionospheric duct may also sustain horizontal propagation of Pc1 pulsations over appreciable distances. It is found that there is a low-frequency cutoff as in the case of the F2 layer waveguide. The group velocity of waves in the upper ionospheric duct is considerably greater, and dispersion is more pronounced compared to the ducted propagation in the F2 region. 相似文献
2.
Incoherent scatter observations of the ionospheric F1 layer above Saint-Santin (44.6°N) are analyzed after correction of a systematic error at 165 and 180 km altitude. The daytime valley observed around 200 km during summer for low solar activity conditions is explained in terms of a downward ionization drift which reaches ?30 m s?1 around 180 km. Experimental determinations of the ion drift confirm the theoretical characteristics required for the summer daytime valley as well as for the winter behaviour without a valley. The computations require an effective dissociative recombination rate of and ionizing fluxes compatible with solar activity conditions at the time when the valley is observed. 相似文献
3.
Incoherent scatter data obtained at Saint-Santin have been analyzed between 1969 and 1972 in the height interval 120–200 km. The summer daytime electron density profiles show a maximum around 150 km followed by a minimum around 165 km, when the solar activity is low. The seasonal and solar cycle variations of this phenomena are discussed. When the day-time valley exists, the maximum density is ca. 20–30 per cent greater than the minimum value. The phenomenon cannot be fully explained on the basis of photochemical equilibrium. A wind-shear mechanism could play an important role. 相似文献
5.
6.
The paper presents a study of large scale travelling ionospheric disturbances detected by riometers operating at 30 MHz, over São José dos Campos (23°S, 45°W) and a nearby location in Sao Paulo, Brasil. The TID's are observed mainly at night and have wavelengths greater than 500 Km. In a few cases it is possible to determine the E-W component of the velocity of propagation, which is of the order of 450 Km per hour. Most of the events are characterized by disperions; the period is found to increase from half an hour to nearly two hours. These and other features are identified with the propagation of atmospheric gravity waves in the F-region, whose source might be located far away from the observing site. The results also suggest that a suitably designed riometer system could profitably be used for future investigation of gravity waves in the F-region in low latitude. 相似文献
7.
The propagation of MHD waves is studied when two ideal fluids, thermal and suprathermal gases, coupled by magnetic field are
moving with the steady flow velocity. The fluids move independently in a direction perpendicular to the magnetic field but
gets coupled along the field. Due to the presence of flow in suprathermal and thermal fluids there appears forward and backward
waves. All the forward and backward modes propagate in such a way that their rate of change of phase speed with the thermal
Mach number is same. It is also found that besides the usual hydromagnetic modes there appears a suprathermal mode which propagates
with faster speed. Surface waves are also examined on an interface formed with composite plasma (suprathermal and thermal
gases) on one side and the other is a non-magnetized plasma. In this case, the modes obtained are two or three depending on
whether the sound velocity in thermal gas is equal to or greater than the sound velocity in suprathermal gas. The results
lead to the conclusion that the interaction of thermal and suprathermal components may lead to the occurrence of an additional
mode called suprathermal mode whose phase velocity is higher than all the other modes. 相似文献
8.
9.
We have performed high-resolution spectral observations at mid-infrared wavelengths of C2H6 (12.16 μm), and C2H2 (13.45 μm) on Saturn. These emission features probe the stratosphere of the planet and provide information on the hydrocarbon photochemical processes taking place in that region of the atmosphere. The observations were performed using our cryogenic echelle spectrometer Celeste, in conjunction with the McMath-Pierce 1.5-m solar telescope in November and December 1994. We used Voyager IRIS CH4 observations (7.67 μm) to derive a temperature profile on the saturnian atmosphere for the region of the stratosphere. This profile was then used in conjunction with height-dependent volume mixing ratios of each hydrocarbon to determine global abundances for ethane and acetylene. Our ground-based measurements indicate abundances of for C2H6 (1.0 mbar pressure level), and for C2H2 (1.6 mbar pressure level). We also derived new mixing ratios from the Voyager mid-latitude IRIS observations; 8.6±0.9×10−6 for C2H6 (0.1-3.0 mbar pressure level), and 1.6±0.2×10−7 for C2H2 (2.0 mbar pressure level). 相似文献
10.
Ices in the solar system are observed on the surface of planets, satellites, comets and asteroids where they are continuously subordinate at particle fluxes (cosmic ions, solar wind and charged particles caught in the magnetosphere of the planets) that deeply modify their physical and structural properties. Each incoming ion destroys molecular bonds producing fragments that, by recombination, form new molecules also different from the original ones. Moreover, if the incoming ion is reactive (H+, On+, Sn+, etc.), it can concur to the formation of new molecules.Those effects can be studied by laboratory experiments where, with some limitation, it is possible to reproduce the astrophysical environments of planetary ices.In this work, we describe some experiments of 15-100 keV H+ and He+ implantation in pure sulfur dioxide (SO2) at 16 and 80 K and carbon dioxide (CO2) at 16 K ices aimed to search for the formation of new molecules. Among other results we confirm that carbonic acid (H2CO3) is formed after H-implantation in CO2, vice versa H-implantation in SO2 at both temperatures does not produce measurable quantity of sulfurous acid (H2SO3). The results are discussed in the light of their relevance to the chemistry of some solar system objects, particularly of Io, the innermost of Jupiter's Galilean satellites, that exhibits a surface very rich in frost SO2 and it is continuously bombarded with H+ ions caught in Jupiter's magnetosphere. 相似文献
11.
D.J. Southwood 《Planetary and Space Science》1977,25(6):549-554
It is shown that the field line resonance phenomenon that occurs for quasi-transverse signals in a non-uniform cold plasma generally occurs for disturbances with a compressional magnetic component in a hot plasma like the ring current. The equations describing such localised signals are derived and discussed in various limits. It is pointed out that recent observations of low frequency compressional oscillations on spacecraft may be an example of such localised signals. 相似文献
12.
Extreme low frequency electromagnetic waves have been observed below the F peak in the equatorial ionosphere by instruments onboard OGO-6. Electrostatic wave observations indicate that the steep gradient was unstable to the process which causes equatorial spread F above the region where the electromagnetic waves were observed. The data are very similar to observations near the polar cusp and give further evidence that ELF waves are excluded from regions of rapid and irregular density increases. Low level electromagnetic waves with similar properties were occasionally observed on the nightside by the OVI-17 electric field sensor and may be plasmaspheric hiss which has propagated to low altitude. 相似文献
13.
A spectrum of Jupiter between 6000 and 12 000 cm? at high resolution (0.05 cm?) was recorded with a Michelson interferometer at Palomar Mountain in October 1974. An analysis of the R branch of the 3ν3CH4 band with the reflecting-layer model, taking into account the H2 absorption which occurs in the same spectral range, leads to a Lorentzian half-width of 0.09 ± 0.02 cm?1, a rotational temperature of 175 ± 10° K, and a CH4 abundance of order 52m atm. Five lines of the 13CH43ν3 band have been identified; a comparison with new laboratory spectra indicates that the 13CH4/12CH4 ratio in the Jupiter atmosphere is close to the terrestrial ratio. 相似文献
14.
Flower 《Monthly notices of the Royal Astronomical Society》1998,297(1):334-336
We present rate coefficients for rotational transitions induced in collisions between H2 molecules. Rotational levels J ≤ 8 and kinetic temperatures T ≤ 1000 K are considered. The interaction potential computed by Schwenke has been used, together with the quantal coupled channels method of calculating the cross-sections. Comparison is made with the more recent of previous results. 相似文献
15.
E. R. Seaquist 《Astrophysics and Space Science》1972,15(2):284-292
It is shown that relativistic electrons in the presence of circularly polarized hydromagnetic waves emit synchrotron radiation which is partially circularly polarized. The relation between the degree of polarization of the radiation and the energy density and wavelength of the waves is derived, and the factors determining the sense of polarization are discussed. Waves of the type required are generated by pitch angle anisotropies in a relativistic electron gas. An application of the result to conditions expected in quasistellar objects shows that the degree of circular polarization of synchrotron radiation in these objects may be of order 1% or greater. 相似文献
16.
We vapor deposit at 20 K a mixture of gases with the specific Enceladus plume composition measured in situ by the Cassini INMS [Waite, J.H., Combi, M.R., Ip, W.H., Cravens, T.E., McNutt, R.L., Kasprzak, W., Yelle, R., Luhmann, J., Niemann, H., Gell, D., Magee, B., Fletcher, G., Lunine, J., Tseng, W.L., 2006. Science 311, 1419-1422] to form a mixed molecular ice. As the sample is slowly warmed, we monitor the escaping gas quantity and composition with a mass spectrometer. Pioneering studies [Schmitt, B., Klinger, J., 1987. Different trapping mechanisms of gases by water ice and their relevance for comet nuclei. In: Rolfe, E.J., Battrick, B. (Eds.), Diversity and Similarity of Comets. SP-278. ESA, Noordwijk, The Netherlands, pp. 613-619; Bar-Nun, A., Kleinfeld, I., Kochavi, E., 1988. Phys. Rev. B 38, 7749-7754; Bar-Nun, A., Kleinfeld, I., 1989. Icarus 80, 243-253] have shown that significant quantities of volatile gases can be trapped in a water ice matrix well above the temperature at which the pure volatile ice would sublime. For our Enceladus ice mixture, a composition of escaping gases similar to that detected by Cassini in the Enceladus plume can be generated by the sublimation of the H2O:CO2:CH4:N2 mixture at temperatures between 135 and 155 K, comparable to the high temperatures inferred from the CIRS measurements [Spencer, J.R., Pearl, J.C., Segura, M., Flasar, F.M., Mamoutkine, A., Romani, P., Buratti, B.J., Hendrix, A.R., Spilker, L.J., Lopes, R.M.C., 2006. Science 311, 1401-1405] of the Enceladus “tiger stripes.” This suggests that the gas escape phenomena that we measure in our experiments are an important process contributing to the gases emitted from Enceladus. A similar experiment for ice deposited at 70 K shows that both the processes of volatile trapping and release are temperature dependent over the temperature range relevant to Enceladus. 相似文献
17.
Manh Dung Duong 《Planetary and Space Science》1976,24(10):907-914
This paper derives the basic propagation characteristics of hydromagnetic waves in various layers of the ionosphere. It is shown that propagation in the upper ionosphere and the F2 layer is largely isotropic. In the lower region of the ionosphere there are two possible modes of propagation, both being anisotropic. Propagation characteristics of waves in this lower region, however, are relatively independent of the direction of horizontal propagation. Calculations of intrinsic wave attenuation show that ducted propagation of Pc 1 signals over appreciable horizontal distances may only take place in the upper layers of the ionosphere. 相似文献
18.
About a year's observations of the N2+ band (3914 Å) at Kitt Peak (latitude 32°) are reported. Morning intensities are the same throughout the year, but there is a strong winter maximum in the evening. It is suggested that the additional ionization is produced by photoelectrons from the magnetic conjugate point. Heights are estimated by the zenith-horizon method, which gives 235 km for the constant component and 350 km during the evening enhancement. The intensity variation through twilight is therefore entirely due to changes of the N2+ concentration; each ion scatters light at a constant rate. The rotational distribution resembles that for a temperature of 1600°K, much higher than the temperature of the atmosphere. It is suggested that part of the ions may be produced by charge transfer from metastable O+(2D). N2+ concentrations resulting from photoionization are calculated; they give a fair account of the observed horizon intensities, but not the zenith. Non-local electrons from higher in the atmosphere are suggested as a possible extra source; alternatively, the zenith measurements may be perturbed by scattered horizon light. The band intensity in the nightglow cannot be measured; the upper limit is 1 R. 相似文献
19.
The reactivity of C2(X1Σ+g) with simple saturated (CH4, C2H6 and C3H8) and unsaturated (C2H2 and C2H4) hydrocarbons has been studied in the gas phase over the temperature range 24-300 K using the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in a Uniform Supersonic Flow) technique. All reactions have been found to be very rapid in this temperature range and the rate coefficients are typically ?10−10 cm3 molecule−1 s−1 with the exception of methane for which the rate coefficient is one order of magnitude lower: ∼10−11 cm3 molecule−1 s−1. These results have been analyzed in terms of potential destruction sources of C2(X1Σ+g) in the atmospheres of Titan and the Giant Planets. It appears that the rate coefficient of the reaction 1C2 + CH4 should be updated with our new data and that reactions with C2H2, C2H4 and C2H6 should also be included in the existing photochemical models. 相似文献
20.
Far-IR (25-50 μm, 200-400 cm−1) nadir and limb spectra measured during Cassini's four year prime mission by the Composite InfraRed Spectrometer (CIRS) instrument have been used to determine the abundances of cyanogen (C2N2), methylacetylene (C3H4), and diacetylene (C4H2) in Titan's stratosphere as a function of latitude. All three gases are enriched at northern latitudes, consistent with north polar subsidence. C4H2 abundances agree with those derived previously from mid-IR data, but C3H4 abundances are about 2 times lower, suggesting a vertical gradient or incorrect band intensities in the C3H4 spectroscopic data. For the first time C2N2 was detected at southern and equatorial latitudes with an average volume mixing ratio of 5.5±1.4×10−11 derived from limb data (>3-σ significance). This limb result is also corroborated by nadir data, which give a C2N2 volume mixing ratio of 6±3×10−11 (2-σ significance) or alternatively a 3-σ upper limit of 17×10−11. Comparing these figures with photochemical models suggests that galactic cosmic rays may be an important source of N2 dissociation in Titan's stratosphere. Like other nitriles (HCN, HC3N), C2N2 displays greater north polar relative enrichment than hydrocarbons with similar photochemical lifetimes, suggesting an additional loss mechanism for all three of Titan's main nitrile species. Previous studies have suggested that HCN requires an additional sink process such as incorporation into hazes. This study suggests that such a sink may also be required for Titan's other nitrile species. 相似文献