Effects of rotation on Rayleigh-Taylor instabilities of an accelerating,compressible, perfectly conducting plane layer

The stability of a plane-stratified slab of perfectly conducting, rotating, compressible, inviscid plasma accelerated by a magnetic field is considered. Exact solutions for the growth rates of the unstable modes are determined for a -law gas when the undisturbed equilibrium is an isothermal atmosphere of semi-infinite extent with no frozen-in field. It is shown that the rotation has no effect on the region of unstable modes which has wavelengths long compared with the atmospheric scale height. On the other side, the growth rates in the presence of rotation are less than those in the absence of rotation for unstable modes.     

Dynamic evolution of recurrent mass ejections observed in Hα and Civ lines

During a coordinated SMY program, the consecutive formation of two new active centers merging together within AR 2646 was observed from 28 August, to 5 September, 1980. The two preceding spots compressed an inverse polarity spot on 1 September 1980, causing recurrent ejecta of matter with time intervals around 10 min. The observations of the MSDP spectrograph operating in H at the Meudon Solar tower and of the UVSP spectrometer on SMM in the Civ 1548 Å line show that cold and hot material had the same projection, although the upward Civ velocity structure was more extended than the H one. We present evidence that observed contrasts of the H absorbing structure can be interpreted in terms of a dynamic cloud model overlying the chromosphere. H matter follows a magnetic channel with upward velocity around 20–30 km s^–1 in the first phase of the event and with downward velocity ( - 40 km s^–1) in the second phase. The stored energy is not sufficient to trigger a flare, nor even to propulse matter along the full length of an arch, because of the periodic reorganisation of the magnetic field.     

Simultaneous H and K Ca ii,h and k Mg ii,Lα and Lβ H i profiles of the April 15, 1978 solar flare observed with the OSO-8/L.P.S.P. experiment

Solar flare observations have been performed with the multichannel L.P.S.P. experiment on board OSO-8 NASA Satellite. Simultaneous H and K Caii, h and k Mgii, L and L Hi profiles have been recorded on the plage just before the flare, during the flare onset and relaxation phases. The different behaviour of line profiles and intensities during the flare is evidenced and indicates a downward propagation with relaxation times increasing from the upper part to the lower part of the chromosphere related to line formation processes. Using the H observed profile, an upper limit of 8 × 10¹³ cm^-3 is derived for the electron density.     

Acoustic-gravity waves in the thermosphere of Venus

Properties of acoustic-gravity waves in the upper atmosphere of Venus are studied using a two-fluid model which includes the effects of wave-induced diffusion in a diffusively separated atmosphere. In conjunction with neutral mass spectrometer data from the Pioneer Venus orbiter, the theory should provide information on the distribution of wave sources in the Venus upper atmosphere. Observed wave structure in species density measurements should generally have periods ?30–35 min, small N₂, CO, and O amplitudes, and highly variable phase shifts relative to CO₂. A near resonance may exist between downward phase-propagating internal gravity and diffusion waves near the 165-km level at periods near 29 min. As a result, if very large He wave amplitudes are observed near this level, it will indicate that the wave source is below the 150- to 175-km level and that the exospheric temperature is close to 350°K. Wave energy dissipation may be an important mechanism for heating of the nightside Venus thermosphere. Large-density oscillations in stratospheric cloud layer constituents are also possible and may be detectable by the Pioneer Venus large probe neutral mass spectrometer.     

On the possibility of submillimetric interstellar lines detection by means of laser heterodyne techniques

The search for extraterrestrial and, in particular, interstellar molecules has suddenly increased in the last ten years after the discovery of many complex organic molecules by radioastronomy. Since some very interesting lines are not detectable in the radio region, but only in the middle and far infrared, heterodyne techniques seem to be a powerful tool for interstellar line detection in the submillimetric region and the detection of CO at 870 in Orion (Philipps and Huggins, 1977) represents an encouraging success for further efforts in this new field of research. In this work the possibility of observing interstellar lines at heterodyne laser wavelengths already available in laboratory has been considered. We also computed relative intensities for some representative rotational lines of interstellar molecules at three typical temperatures (10, 20, 50 K) assuming thermodynamic equilibrium and optically thin regions. The results achieved with heterodyne laser techniques developed in the laboratory are discussed here in order to study the possibility for ground and space astronomical observations.     

Spectral reflectance change and luminescence of selected salts during 2–10 KeV proton bombardment: Implications for Io

Radiation damage and luminescence, caused by magnetospheric charged particles, have been suggested by several authors as mechanisms for explaining some of the peculiar spectral/albedo features of Io. We have pursued this possibility by measuring the uv-visual spectral reflectance and luminescent efficiency of several proposed Io surface constituents during 2 to 10-keV proton irradiation at room temperature and at low temperature (120 < T < 140°K). The spectral reflectance of NaCl and KCl during proton irradiation exhibits the well-known F-center absorption bands at 4580 and 5560 Å. Na₂SO₄ shows a generalized darkening which increases toward longer wavelengths. NaNO₃ shows a spectral reflectance change indicative of the partial alteration of NaNo₃ to NaNo₂. NaNO₂ shows no change. The luminescent efficiencies of NaCl and KCl are ～10^?4 at 300°K and increase by one-half order of magnitude at ～130°K. The efficiencies of K₂CO₃, Na₂CO₃, Na₂SO₄, and NaNO₃ are 10^?4, 10^?4, 10^?5 and 10^?6, respectively, at 300°K and they all decrease by one-half order of magnitude at ～130°K. These results indicate that magnetospheric proton irradiation of Io could cause spectral features in its observed ultraviolet and visible reflection spectrum if salts such as those studied here are present on its surface. However, because the magnitude of these spectral effects is dependent on competing factors such as surface temperature, incident particle energy flux, solar bleaching effects, and trace element abundance, we are unable at this time to make a quantitative estimate of the strength of these spectral effects on Io. The luminescent efficiencies of pure samples that we have studied in the laboratory suggest that charged-particle induced luminescence from Io's surface might be observable by a spacecraft such as Voyager when viewing Io's dark side.     

Mariner 9 ultraviolet spectrometer experiment: Vertical distribution of ozone on Mars

The vertical distribution of ozone in the atmosphere of Mars is computed from ultraviolet spectra obtained by the Mariner 9 spacecraft. In the Northern Hemisphere the ozone scale height is much smaller than the atmospheric scale height in midlatitudes and increases rapidly to a maximum farther north. At high latitudes (above 60°) there is no significant difference between the scale heights of ozone in the Northern (winter) Hemisphere and the Southern (summer) Hemisphere. Comparison of the ozone distribution with atmospheric temperature structure indicates that at some locations in the North, the density of water vapor increases with altitude, and the time for vertical mixing is about 3 days or more.     

Temperature domains in the ionosphere

The non-linear stationary temperature waves (domains) is analysed. The exact analytical solutions of the non-linear equation of the heat conductivity determine the region of existence of such domains and the critical values of plasma parameters, correspond to the increase of the periodical temperature profiles in the plasma. A stationary source of heating (photo-electrons or electric fields) may stimulate the existence of domains, when the power of the source reaches a critical value. Conditions in the F-region of the ionosphere near the equator favour the increase of the domains.     

The effect of surface roughness on the transmission of microwave radiation through a planetary surface

To account for surface roughness, the transmission of microwave radiation through a planetary surface to an observer is treated by a Monte Carlo technique. Sizable effects are found near the limb of the planet, and they should be included in analyses of high-resolution observations and high-precision integrated disk observations.