Collision frequency and transport properties of electrons in the ionosphere

A unified ionospheric electron collision frequency model profile 〈ν_g〉 has been calculated in the height range 50–500 km. The computed profile accounts for the electron collisions with the neutral particles as well as the ions. Experimental values of momentum transfer cross-sections have been used for electron collisions with N₂, O₂ and Ar and theoretical values for N, O, He and H. It is observed that the electron-ion collisions 〈ν_ei〉 dominate over the electron-neutral collisions 〈ν_en〉 above 170 km. However, 〈ν_e?N〉 is of the same order of magnitude as 〈ν_e?O〉 in the height range 170–210 km. Above 360 km 〈ν_e?O〉 becomes more important among the neutrals. The temporal, seasonal and solar epoch variations of 〈ν_ei〉 are also shown. A typical electron collision frequency profile 〈ν_g〉 corresponding to the exospheric temperature of 1100 K has been compared with the available experimental results for D, E and F-regions obtained from different experimental techniques. This profile has been used to determine the electrical, thermal, heat flow and current flow conductivities, the mobility and the diffusivity of electrons. The results so obtained are found to be in good agreement with the earlier results.     

Inductive electric fields in the magnetosphere

A quantitative estimate of the electric fields induced by the time dependent ring current is made incorporating the drifts and induced electric fields in a self-consistent manner. It has been shown that in the ring current region, the results of the self-consistent calculations deviate substantially from the first order estimates hitherto obtained. Since for a rapidly varying ring current, the induced electric field can be of the same order as the convection electric field in the magnetosphere, these deviations have to be taken into account in substorm studies.     

The excitation of ionic lines and molecular bands in meteor wakes

The appearance of multiplets arising from the 4²P state of CaII (the H and K lines and an infrared triplet), the 1st positive band of N₂ and possibly certain multiplets of FeII in meteor wake spectra is explained semi-quantitatively in terms of the two-step sequence: collisional ionization of major atmospheric species O₂ and N₂ followed by resonant charge exchange with ablated meteoric atoms. Many other features which could arise through this mechanism (multiplets of MgII, SiII and FeII, and bands of O₂ and N₂) are likely to be weak or to have escaped detection owing to observational selection.     

Plasmasphere convection patterns observed simultaneously from two ground stations

Whistler data recorded during a 14 h period on 10–11 July 1973 at Siple (L = 4.17) and Sanae (L = 3.98) have been used to compare the apparent plasma convection patterns observed from these Antarctic stations. Two distinct bulges in the plasmasphere are seen at both stations, each bulge corresponding to an apparent outflowed followed by in flow of plasma. These structures do not coincide in U.T. or M.L.T. The first bulge is seen at Siple almost 1 h earlier in M.L.T. than at Sanae and the second bulge almost 3 h earlier. This is interpreted in terms of a fairly rapid westward and inward movement of the plasmasphere structure.     

On proton and electron acceleration by shock waves during large solar flares

The data on optical, X-ray and gamma emission from proton flares, as well as direct observations of flare-associated phenomena, show energetic proton acceleration in the corona rather than in the flare region. In the present paper, the acceleration of protons and accompanying relativistic electrons is accounted for by a shock wave arising during the development of a large flare. We deal with a regular acceleration mechanism due to multiple reflection of resonance protons and fast electrons from a collisionless shock wave front which serves as a moving mirror. The height of the most effective acceleration in the solar corona is determined. The accelerated particle energy and density are estimated. It is shown in particular that a transverse collisionless shock wave may produce the required flux of protons with energy of 10 MeV and of relativistic electrons of 1–10 MeV.The proposed scheme may also serve as an injection mechanism when the protons are accelerated up to relativistic energies by other methods.     

A tidal theory for the origin of the solar nebula

There are two angular momentum (AM) problems associated with the formation of stars in general and the solar system in particular. The first is how to dispose of the AM possessed by turbulent protostellar clouds. Two-dimensional calculations of the gravitational infall of rotating gas clouds by several authors now indicate that stars are formed in groups or clusters rather than as single entities. Added evidence comes from observation of probable regions of star formation and young clusters, plus the fact that most stars are presently members of binaries or other multiples. Thus the first problem is solved by postulating the fragmentation of massive clouds with most of the AM ending up in the relative orbits. These clusters are notoriously unstable and evolve with the ejection of single stars like the Sun.The second problem is the uneven distribution of AM with mass in the solar system. It turns out that the collapse time for the majority of the infalling material is comparable to the time necessary for significant dynamical interaction of the protostellar fragment with its neighbors. It is found here through calculations utilizing very simplified numerical models that the last few tens of percent of infalling material can easily have sufficient AM transferred to it by the tidal action of passing protostars to form a solar nebula and ensure alignment of the solar spin. The most important parameter is the degree of central condensation: fragments without several tenthsM in a central core tend to be torn apart by encounters, or at least stimulated into binary fission. A stabilizing central mass maintains its identity and acquires a rotating envelope of material.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978.     

Observations and interpretation of the close binary system CG Cyg

Photometric observations of the short-period (RS CVn-type) eclipsing binary system CG Cyg have been presented. Two sets of results, obtained from an analysis of theB, V andR light curves, represent ‘occultation’ and ‘transit’ solutions. The occultation solution is preferred as it gives a better fit to the colour curve. This hypothesis may also offer a more promising explanation of the observed peculiarities such as period changes and the light variation outside eclipses.     

Protoplanetary core formation by rain-out of minerals

Models of giant gaseous protoplanets calculated by DeCampli and Cameron (1979) indicate that iron and probably other minerals in the interior of a planet would be in the liquid state during part of the protoplanet evolution. Liquid drops in a protoplanet would grow by coalescence much as cloud drops in the Earth's atmosphere grow to rain drops. We have modeled this process by using the stochastic collection equation (Slattery, 1978) for various initial conditions. In all of the cases considered, the growth time (to centimeter-sized droplets) is much shorter than the time, as estimated by detailed evolutionary calculations, that the drops are in the liquid state. Brownian collection is effective in quickly coalescing tiny liquid droplets to an average radius of about 0.005 cm with very few drops remaining with radii less than 0.001 cm. For radii larger than 0.005 cm gravitational collection is dominant. Since the particles are rapidly swept from interstellar grain sizes to much larger sizes, the opacity in the cloud layer is expected to drop sharply following melting of the grains.     

Some comments on the limb shift of solar lines

We searched for a variation with heliographic latitude of the solar limb effect by comparing the relative wavelengths of weak and strong Fraunhofer lines. The blue shifts associated with the limb effect appear 9%±5% larger in the polar radius vector than in an equatorial radius vector at cos = 0.5. This should perhaps be interpreted as an increase with latitude of either solar convection or of convective overshoot. Recent observations of poleward meridional flows of 30m s^–1 should be corrected for this limb effect variation. This correction increases this flow velocity to 70 m s^–1. A search for a similar variation in plages and in network boundaries had negative results, the variation being +1%±5% and -1%±6% respectively.Now at the Multiple Mirror Telescope Observatory, University of Arizona, Tucson, Ariz. 85721, U.S.A. The MMTO is jointly operated by the University of Arizona and the Smithsonian Institution.The Sacramento Peak Observatory is operated by the Association of Universities for Research in Astronomy, Inc. under contract AST 78-17292 with the National Science Foundation.     

A low β coronal loop model

A localized force-free current is proposed as a model for the observed coronal loops.An upper limit for the growth rate of kink instabilities in this model is found by solving numerically, in cylinder symmetry, the MHD equation of motion, with the boundary condition = 0 outside the loop.For various current densities a spectrum of kinks is found. These instabilities will disrupt the loops that are long or strongly twisted, on a time scale of a few seconds.The kinks in short or barely twisted loops are too long to fit.