Auroral recombination of N and O: A possible source for emission in the γ and δ bands of NO

Radiative recombination of N and O provides a significant source for auroral emission in the γ and δ bands of NO with selective population of vibrational levels in the A²Σ⁺ and C²Π states. This mechanism may account for emissions detected near 2150 Å. Models are derived for the auroral ionosphere and include estimates for the concentrations of N and NO. The concentration of NO is estimated to have a value of about 10⁸ cm^?1 near 140 km in an IBC III aurora. The corresponding density for N is about 5 × 10⁷cm^?3 and the concentration ratio $\text{NO}{}^{\mathrm{+}}\text{O}{}_2{}^{\mathrm{+}}$ has a value of about 5.5.     

Heat flow near obstacles in the solar convection zone

Disturbances in the heat flow in the solar convection zone are calculated with a turbulent thermal diffusion coefficient based on a mixing length approximation. As a consequence of the radiative boundary condition at the surface and the strong increase of the diffusion coefficient with depth, the convection zone resembles a thermally superconducting shell enclosed between a thin surface layer and an interior core of low thermal conductivity. Thermal disturbances originating in the convection zone do not penetrate into the interior, and penetrate only weakly through the solar surface. A thermally isolating obstacle buried entirely in the convection zone casts a shadow of reduced temperature at the solar surface; the brightening surrounding this shadow is undetectable. The shadow is weak unless the object is located close to the surface (less than 2000 km). Assuming a sunspot to be an area of reduced thermal conductivity which extends a finite depth into the convection zone, the heat flow around this obstacle is calculated. The heat flux blocked below the spot (missing flux) spreads over a very extended area surrounding the spot. The brightening corresponding to this missing flux is undetectable if the reduction of the thermal conductivity extends to a depth greater than 1000 km. It is concluded that no effect other than a decrease of the convective efficiency is needed to explain the temperature change observed at the solar surface in and around a sunspot. The energy balance is calculated between magnetic flux tubes, oriented vertically in the solar surface, (magnetic elements in active regions and the quiet network) and their surroundings. Near the visible surface radiation enters the tube laterally from the surrounding convection zone. The heating effect of this influx is important for small tubes (less than a few arcseconds). Due to this influx tubes less than about 1 in diameter can appear as bright structures irrespective of the amount of heat conveyed along the tube itself. Through the lateral influx, small tubes such as are found in the quiet network act as little leaks in the solar surface through which an excess heat flux escapes from the convection zone.     

Tridiurnal variations in cosmic-ray intensity

The tridiurnal wave in cosmic-ray intensity expected from a free space anisotropy is theoretically calculated for different cosmic-ray stations which are characterized by different shapes of asymptotic cones of acceptance. The amplitude A and the time of maximum Tmax are given for latitude dependence of the form cosⁿ λ and rigidity dependence of the form $\text{R}{}^{\mathrm{\beta }}\text{exp (?(R?}\text{1}\text{R}{}_0\text{))}$, where λ and R are the latitude and rigidity respectively and n, β, R₀ are constants. The values of A and Tmax, are calculated for different values of n, β and R₀ for each station. The dependence of A and Tmax on the anisotropy parameters is studied for the proper selection of cosmic-ray stations whose data may be used in determining these parameters.Available experimental data were used to find the observed amplitudes of the tridiurnal variations at five stations using power spectrum analysis with hanning applied on the averaged trains. Minimum variance analysis of the theoretical and experimental amplitudes showed that β has a value between 1 and 2, R₀ greater than 100 GV and n smaller than 3.     

A model for thinning of the plasma sheet

A one-dimensional model for thinning of the plasma sheet is developed on the basis of launching a fast mode MHD rarefaction wave propagating in the tailward direction along the plasma sheet. Behind the rarefaction wave the pressure is reduced, leading to thinning of the plasma sheet and also to an Earthward plasma flow with a speed on the order of the sound speed a₀. The plasma sheet thickness is reduced by a factor of 2 if an Earthward plasma flow speed of 0.8a₀ is induced. The predictions of the model are in reasonable agreement with observations.     

VLF emissions and substorm activity

The resonant interaction between the whistler mode waves and the energetic electrons near the plasmapause boundary has been studied in the presence of field aligned currents which seem to exist during substorm activity. It is shown that the electrons which carry the current along the direction of the magnetic field enhance the whistler mode growth considerably if the streaming velocity is small compared to the phase velocity of the wave. It is likely that this is one of the mechanisms explaining the intense VLF emissions observed near the plasmapause during substorm activity.     

Energetic protons associated with a forward-reverse interplanetary shock pair at 1 A.U.

A forward-reverse interplanetary shock was observed on 25 March 1969 by the magnetometer and plasma detector on the HEOS-1 satellite. This relatively rare event was described by Chao et al (1972) who concluded that the shock pair was formed at a distance 0.10–0.13 A.U. upstream of the Earth as a result of the interaction between a fast and a slow solar wind streams. Simultaneous observations of 1 MeV solar proton fluxes were also performed on HEOS-1. A characteristic intensity peak was observed as the forward shock passed by the spacecraft. The evolution of the proton intensity, together with a detailed analysis of anisotropies and pitch angle distributions show a complex dynamic picture of the effect of the forward shock on the ambient proton population. Significant changes in particle fluxes are seen to be correlated with fluctuations in the magnetic field. It is suggested that simple geometrical models of shock-associated acceleration should be expanded to include the effect of magnetic fluctuations on particle fluxes. The interaction region limited by the forward and reverse shocks contained a large variety of magnetic fluctuations. Following the tangential discontinuity separating the fast solar wind stream from the preceding slow stream, a sunward flow was observed in the proton data, followed by a small but significant drop in intensity prior to the reverse shock.     

A study of motions in the winter mesosphere using the partial reflection drift technique

Intensive partial reflection drift observations were made at Adelaide (35°S) for a seven day period in June 1973. The results have been analysed to isolate the prevailing motion and oscillations of various time scales: planetary, 24 hr, 12 hr and gravity waves. Each is discussed in turn with particular emphasis on the variability of energy from day to day and as a function of height. Evidence is presented for the local generation of planetary waves, the presence of the evanescent S_?2¹ mode in the 24 hr oscillation, the influence of the S₄² mode in the 12 hr oscillation and a definite polarization of gravity waves. The energies of all the forms of motion are shown to decay exponentially with increasing height and the deposition of energy and momentum in the upper mesosphere and lower thermosphere is discussed.     

Is there Aβ/L relation for any type of qso absorption line system?

The possible correlation noted between the intrinsic quasar luminosity and the absorption line expulsion velocity is re-examined using homogeneous data sets for metal and L only line systems. The method of analysis is chosen to enable any reasonable form of correlation to be found. No correlation is detected at a confidence level >10%.     

Search for variability in hydrogen-poor stars

The evolutionary status of hydrogen-poor stars is analyzed.Photoelectric observations of six objects are reported as a first step of a long-term project devoted to search for variability of a large sample of hydrogen-poor stars.The observed stars show phenomena of microvariability with an amplitude of the order of 0^m. 1 or less.Two extreme helium stars have been examined: a period in the range of 0^d.162-0^d.164 has been found for BD+ 10⁰2179, andP=0^d.1079962 for BD+13⁰3324.The mass-losing O subdwarf (sdO) BD+37⁰ 443 presents short-term fluctuations with a time-scale of several minutes and long-term variations on a scale of months. The standard sdO BD+75⁰325 is probably non-variable, although light variations of very small amplitude (m0.03) with a time-scale of about 1 hr might be present. The high gravity sdO BD+25⁰4655, which is very close to the white dwarf stage, also presents variability on a time-scale of about 13 minutes, and might be an analog of the recently discovered pulsating sdO, or hot white dwarf, PG 1159-035.The variability of the intermediate helium star HD 37776 is finally confirmed.