Reflectance spectra for sodium and potassium doped ammonia frosts: Implications for Io's surface

This paper reports measurements of the reflection spectra of sodium and potassium doped ammonia frosts as a function of alkali metal concentration which cover the wavelength range 0.35–2.5 μm. The purpose of the measurements was to determine whether or not the reflection spectra for such a solid was compatible with the spectral albedo of Io. The data show that with a sufficiently large alkali metal concentration, the reflection spectra of the doped ammonia frost do not display the characteristic ammonia features at 2.0 and 2.25 μm. The high reflectance of the more concentrated samples and the character of the observed reflection spectrum make it difficult to rule out sodium doped ammonia frost as a surface constituent on Io on the basis of existing data.     

Fe57 Mossbauer spectroscopy of the Leoville meteorite

The Mossbauer spectra has been measured for the Leoville meteorite. Experimental results identify it as a type III carbonaceous meteorite. The spectrum shows the principle iron components to be olivine, magnetite, metallic iron, troilite and phyllosilicate material.     

Effect of diffusion-thermal processes on the high-latitude topside ionosphere

We have studied the extent to which diffusion-thermal heat flow affects H⁺ temperatures in the high-latitude topside ionosphere. Such a heat flow occurs whenever there are H⁺?O⁺ relative drifts. From our study we have found that at high-latitudes, where H⁺ flows up and out of the topside ionosphere, diffusion-thermal heat flow acts to reduce H⁺ temperatures by 500–600 K at altitudes above about 900 km.     

The effect of pressure anisotropy on the equilibrium structure of magnetic current sheets

The equilibrium structure of two-dimensional magnetic current sheets is investigated for systems in which the plasma pressure dominates the bulk flow energy, as appears appropriate for the quiet time plasmasheet in the geomagnetic tail. A simple model is studied in which the field is contained between plane parallel boundaries and varies exponentially along the system, while the plasma pressure is anisotropic, the anisotropy being arbitrary but constant along the centre plane. When the field is highly inflated by the plasma current it is found that adiabatic solutions exist only when the plasma pressure is close to isotropic. For the case P_∥ > P_⊥ it is argued that a thin, non-adiabatic current layer will in general form at the sheet centre, usually embedded within a much broader adiabatic current distribution. When P_⊥ > P_∥, a broad region of very depressed fields develops about the centre of the current sheet, terminated at its outer boundary by a spike in the current density. This central region becomes unstable to the mirror mode well before the limiting adiabatic solution is reached.     

Formation of whistler ducts

A theory of whistler duct formation is presented. By means of order of magnitude calculations it is shown that, when the ring current overlaps the outer plasmasphere, irregularities will cause field-aligned currents to flow, which are below the threshold sensitivity of satellite-borne magnetometers. These currents must be continuous with horizontal ionospheric currents, which produce horizontal electric fields. These fields map up to the equatorial plane and are large enough to produce flux tube interchange and hence the formation of whistler ducts in the outer plasmasphere.     

A note on the motion of charged particles in one-dimensional magnetic current sheets

By considering the integrals of the motion of charged particles moving in one-dimensional current sheets, a simple and exact proof is given that particles which are either magnetically or electrostatically trapped about such a current sheet exhibit zero net drift. The transition to the special case of a strictly neutral sheet, a limit remaining unclear from previous studies, is also elucidated. Finally, the relationship between the results and existing self-consistent current sheet solutions is discussed.     

On the dissociation of nitrogen by electron impact and by E.U.V. photo-absorption

The dissociation of N₂ by electron impact and by e.u.v. photo-absorption is studied, and it is shown that the forbidden predissociation of the numerous ¹Π_u and ¹Σ_u⁺ valence and Rydberg states of N₂ in the 11–24eV energy range is the dominant mechanism for N atom production. By measuring the absolute emission cross sections for the e.u.v. singlet bands of N₂ and by using the generalized oscillator strength data of Lassettre (1974), it has been possible to construct a detailed model of the total N₂ dissociation cross section which is in good agreement with the measurements of Winters (1966) and Niehaus (1967) and provides some insights into the maximum possible $\text{N(}{}^2\text{D)}$ yield from dissociative excitation. The total cross section for exciting N₂ e.u.v. radiation in the 800Å–1100Å wavelength range has been measured and found to have a value of 3.4 ×10^?17 cm² at 100 eV under optically thin conditions. Although this result implies that large fluxes of e.u.v. photons should be excited in auroral substorms and in the airglow, they are not observed, and we show that this development is a consequence of radiation entrapment and predissociation. The total cross section for dissociating N₂ by electron impact is given for optically thin and thick media. And some questions concerning the energy budget of a magnetospheric storm which are raised by these results, are discussed.     

Linear force-free fields in the lower corona

We have computed the surface Green's function for linear force-free magnetic fields, where × B = B and is a constant, for application to low coronal levels of the solar atmosphere. Boundary conditions are imposed on the normal component of B on two parallel planes which delineate the force-free volume. This procedure ensures that the magnetic field energy remains bounded, and that the field lines have a smooth behavior. A simple bipolar source distribution is treated and representative field line tracings are shown.     

The polarization of X-ray emission of some solar flares in July 1974

Preliminary results of polarization measurements at three solar flares of July 5 and 6, 1974, are given. The measurements were performed at h 15 keV with Thomson-scattering polarimeter on the Intercosmos 11 satellite.At the decay phase of the flare on July 5 we obtained P = 3.4–5.0%, which did not exclude some contribution from non-thermal processes. At the flares of July 6 we found P =1.0–1.9% and P = 0.1–2.0%, respectively: neither value exceeds the level of statistical fluctuations.Presented at XVIII COSPAR Meeting (VARNA, May–June 1975), contribution III.B.2.9.