A Large-scale travelling ionospheric disturbance of polar origin

Measured direction of arrival variations of 8 MHz signals along a path nearly parallel to the direction of travel of a large-scale travelling ionospheric disturbance of polar origin are compared with those computed by ray tracing through an analytical model for the disturbance deduced from simultaneous ionospheric observations. The results of the comparison and the wide geographic extent of the disturbance suggest the feasibility of using remotely monitored observations of such disturbances.     

Cyclotron amplification of geomagnetic micropulsations Pc1 in the magnetosphere

A numerical analysis of cyclotron instabilities is carried out by computing the dispersion relation for a three component cold plasma-beam system. Rates of growth and damping for various values of the stream density are calculated from the dispersion relation. The rates of growth and damping increase monotonically as the number density of the proton stream increases. It is found that the frequencies at the rates of maximum growth and the damping decrease slightly to lower frequencies and a sharp peak at these frequencies becomes blunt. The minimum e-folding times of an ion cyclotron wave for (a) σ_s = 10⁻⁴, σ_i = 10⁻² and (b) σ_s = 10⁻¹, σ_i = 10⁻² are about 3·84 and 0·16 sec respectively in the vicinity of the equatorial plane at 6 Re, where σ_s and σ_i are the ratios of the beam density N_s and the helium ion (H₆⁺) density N_i to the total positive ions in the plasma-beam system.     

The distribution of stably trapped magnetospheric plasma as determined from Pi2 micropulsations and the auroral electrojet index, AE

The distribution of stably trapped plasma is determined as a function of equatorial geocentric distance, R. Observed Pi2 micropulsation periods and the magnitudes of their associated magnetic bays, measured by the auroral electrojet index, AE, are used in determining this distribution. Plasma density is found to vary inversely as approximately the sixth power of R. When Pi2 period-AE relations are studied for varying time lags, the pulsation periods are found to define prolonged intervals of abnormal AE levels. Thus the periods may be potentially useful in forecasting geomagnetic disturbances or abnormally quiet intervals. A qualitative physical model is proposed to explain the observational relations.     

Modulation of type Pi waves by temporal variations in ionospheric conductivity in a three-dimensional magnetosphere-ionosphere current system

It is suggested that Pi ULF waves are generated from magnetosphere-ionosphere current systems. This current system is modeled by an R (resistance), C (capacitance) and L (inductance) circuit loop in which R = R(t). We studied three cases of modification of ULF waves by variations in ionospheric conductivity: (1) ω ? ω', (2) ω ≈ ω' and (3) ω ? ω', where ω and ω' are the frequency of the driving electric field and ionospheric conductivity variations, respectively, assuming that both variations are sinusoidal. The characteristics of the modification are very different in these three cases. In case 1, the envelope of the ULF wave intensity correlates with the variations in ionospheric conductivity. In case 2, the wave form of the ULF waves is slightly modified from a sinusoidal wave. In case 3, high frequency components are generated in the ULF wave form due to rapid oscillations in ionospheric resistance. We present observational evidence for the existence of the three types of modifications.     

Frequency and period relationships for pi2 micropulsations

Using measurements made at 3 sites, correlation coefficients are calculated between both the period and the frequency of a Pi2, on the one hand, and the planetary magnetic activity index and the magnitude of the accompanying auroral bay, on the other. The coefficients are consistently larger for frequency than for period.     

A generation mechanism for Pc 5 micropulsations in the morning sector

In the companion paper (Lam and Rostoker, 1978) we have shown that Pc 5 micropulsations are intimately related to the behaviour and character of the westward auroral electrojet in the morning sector. In this paper we show that Pc 5 micropulsations can be regarded as LC-oscillations of a three-dimensional current loop involving downward field-aligned current flow near noon, which diverges in part to form the ionospheric westward electrojet and returns back along magnetic field lines into the magnetosphere in the vicinity of the ionosphere conductivity discontinuity at the dawn meridian. The current system is driven through the extraction of energy from the magnetospheric plasma drifting sunwards past the flanks of the magnetosphere in a manner discussed by Rostoker and Boström (1976). The polarization characteristics of the pulsations on the ground can be understood in terms of the effects of displacement currents of significant intensity which flow near the F-region peak in the ionosphere and induced currents which flow in the earth. These currents significantly influence the magnetic perturbation pattern at the Earth's surface. Model current system calculations show that the relative phase of the pulsations along a constant meridian can be explained by the composite effect of oscillations of the borders of the electrojet and variations in the intensity of current flow in the electrojet.     

A sub-class of pi 1 micropulsations associated with the diurnal transit of the neutral sheet

A composite pi 1-hydromagnetic noise class of micropulsations is found to have pronounced local time occurrence maxima at 0930 and 2130. It is shown that the night-time events tend to occur within a geomagnetic local time ‘slot’, the extent of which correlates quasi-linearly with the width of the neutral sheet recombination slot. No such correlation exists for night-time pi 1 bursts. The suggested energy source for these night-time pi 1-hydromagnetic noise events is geotail field-line merging and the concomitant injection and acceleration of the geotail plasma.     

Medium scale gravity waves in the ionospheric F-region and their possible origin in weather disturbances

This study results from a coordinated experiment involving ionospheric observations of Faraday rotation between a geostationary satellite and three ground based receivers at Aberystwyth and Bournemouth in the U.K. and Lannion, France, together with incoherent scatter observations at St. Santin-Nancay, France.Quasi-periodic variations of electron content observed simultaneously at the three stations are interpreted in terms of medium scale gravity waves travelling in the ionospheric F-region. Characteristics of these waves are derived by means of a cross-correlation technique.A reverse ray tracing computation, using data on the neutral atmosphere and neutral wind stratification from the incoherent scatter observations, has been used in an attempt to locate the sources of these waves.The results show that some of the waves are almost certainly generated above 100 km altitude, probably by auroral phenomena, while the others could be produced near ground level by meteorological sources. The reverse ray tracing indicates that the latter sources are in general located in a geographic area in the vicinity of a weather disturbance. A production mechanism for these waves is proposed involving ageostrophic perturbations of the neutral wind in a jet stream.     

The origin of Segue 1

We apply the optimal filter technique to Sloan Digital Sky Survey photometry around Segue 1 and find that the outer parts of the cluster are distorted. There is strong evidence for  ∼1°  elongations of extra-tidal stars, extending both eastwards and southwestwards of the cluster. The extensions have similar differential Hess diagrams to Segue 1. A Kolmogorov–Smirnov test suggests a high probability that both come from the same parent distribution. The location of Segue 1 is close to crossings of the tidal wraps of the Sagittarius stream. By extracting blue horizontal branch stars from Sloan's spectral data base, two kinematic features are isolated and identified with different wraps of the Sagittarius stream. We show that Segue 1 is moving with a velocity that is close to one of the wraps. At this location, we estimate that there are enough Sagittarius stars, indistinguishable from Segue 1 stars, to inflate the velocity dispersion and hence the mass-to-light ratio. All the available evidence is consistent with the interpretation that Segue 1 is a star cluster, originally from the Sagittarius galaxy, and now dissolving in the Milky Way.     

An observational test for the origin of the Titan-Hyperion orbital resonance

If Hyperion's radius is near the upper limit of recent estimates, and tidal dissipation in Hyperion is reasonably well represented by a frequency-independent Q ? 2–300, finding Hyperion rotating in the 3:2 spin-orbit resonance like Mercury would imply a primordial origin for the Titan-Hyperion 4:3 orbital resonance. Independent of this test, observation of Hyperion's spin rate will place an upper bound on the average tidal effective Q for the satellite as a function of its assumed initial angular velocity.     

A family of ionospheric models for different uses

Empirical models of three dimensional electron density distributions in the ionosphere have been constructed for global as well as regional use. The models differ by their degree of complexity and calculation time and therefore have different uses. All are based on “ionogram parameter” (critical frequencies foE, foF1, foF2 and the F2 region transfer parameter M(3000)F2). The models allow the use of global or regional maps for foF2 and M(3000)F2 and use built-in formulations for foE and foF1. Update (instantaneous mapping / nowcasting) versions exist which take foF2 and M(3000)F2 or F2 region peak height and electron density as input. The ground to F2 layer peak part of the profile is identical for all three models and is based on an Epstein formulation. The “quick calculationr” model NeQuick uses a simple formulation for the topside F layer, which is essentially a semi-Epstein layer with a thickness parameter which increases linearly with height. The “ionospheric model” COSTprof is the model which was adopted by COST 251 in its regional “monthly median” form. Its topside F layer is based on O⁺-H⁺ diffusive equilibrium with built-in maps for three parameters, namely the oxygen scale height at the F2 peak, its height gradient and the O⁺-H⁺ transition height. The “ionosphere-plasmasphere” model NeUoG-plas uses a magnetic field aligned “plasmasphere” above COSTprof Typical uses of the models and comparison among them are discussed.     

A terrestrial origin for sulfate veins in CI1 chondrites

Abstract— White sulfate veins are a very well‐known petrological feature of the chemically primitive CI1 carbonaceous chondrites. Sulfate veins were first described in the Orgueil meteorite in 1961, almost one century after its fall. However, we have observed such veins to form easily during typical sample storage. We suggest that all CI1 sulfate veins formed during the terrestrial residence of these heavily brecciated, porous stones. Reacting with atmospheric water, sulfates originally present in the meteorites dissolved and remobilized, and/or sulfides oxidised, filling the many open spaces offered to them by the very porous rock. Sulfate veins in CI1 chondrites can no longer be used as evidence of a late‐stage oxidation event in the CI1 parent body, or of centimeter‐scale fluid transport on the parent asteroid.     

An impact-melt origin for lithology A of martian meteorite Elephant Moraine A79001

Abstract— Mixing models using major and trace elements show that the bulk composition of lithology A (xenocryst-bearing magnesian basalt) of Elephant Moraine A79001 (EETA79001) can be reasonably approximated as a simple mixture of ～44% EETA79001 lithology B (ferroan basalt) and ～56% of Allan Hills A77005 (ALHA7705) light lithology (incompatible element-poor lherzolite). Micro-instrumental neutron activation analysis (INAA) data on xenocryst-free groundmass samples of lithology A show that about 20–25% of the melt phase could be dissolved lherzolite. The bulk and groundmass samples of lithology A have excesses in Au, which indicates either meteoritic contamination or addition by some unknown martian geochemical process. Previous workers have suggested that lithology A was formed by either assimilation of cumulates (like ALHA77005), by a basalt (like lithology B), or by mixing of basaltic and lherzolitic magmas. The former scenario is energetically improbable and unlikely to explain the normal Fe/Mg zonation in lithology A groundmass pyroxenes, whereas the latter scenario is unlikely to satisfy the constraints of the mixing model indicating the ultramafic component is poor in incompatible elements. We suggest rather that EETA79001 lithology A is an impact melt composed dominantly of basalt like lithology B and lherzolitic cumulates like the trace-element-poor fraction of ALHA77005 or Y-793605. This model can satisfy the energetic, petrologic, and geochemical constraints imposed by the samples. If EETA79001 lithology A is an impact melt, this would have considerable consequences for current models of martian petrologic evolution. It would call into question the generally accepted age of magmatism of martian basalts and preclude the use of lithology A groundmass as a primary martian basalt composition in experimental studies. Regardless, the latter is required because lithology A groundmass is a hybrid composition.     

A technique for the in situ measurement of ionospheric currents

A technique is proposed for determining mean ion and electron “drift” motions from an instrument suitable for sounding rockets and satellites. Some experimental data is shown which confirms the validity of the technique.     

A dynamical effect in the ionospheric f1 layer

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 $\text{2.3 × 10}{}^{\mathrm{?7}}\text{(}\text{300/}\text{T}{}_{\mathrm{e}}\text{)}{}^{0.7}\text{(}\text{cm}{}^3\text{s}{}^{\mathrm{?1}}\text{)}$ and ionizing fluxes compatible with solar activity conditions at the time when the valley is observed.     

Intercomparison among plasma wake models for plasmaspheric and ionospheric conditions

Intercomparisons are made among the angular distributions of ions in the wake of a body moving through a space plasma as computed from three different expressions (models). Both subsonic and supersonic relative flows are considered in order to examine the wake current depletion ratios under conditions realistic for the topside ionosphere and plasmasphere. Results of these comparisons demonstrate the importance of including the thermal flux at low Mach numbers and of taking into account the angular acceptance of ion detectors in making theory-experiment comparisons. Gradients in the angular variations of the fluxes are found to be steeper near the wake-ambient interface than closer to the maximum rarefaction region of all models, although quantitatively there is considerable variation among the models. From examining the variations of the wake depletion ratio parametrically with Mach number and normalized potential over ranges characteristic of the plasmasphere and topside ionosphere, we find considerable variation with both parameters, with sensitivity to normalized potential increasing dramatically with Mach number. Overall, however, the Mach number variation appears to be the more significant over this range of parameters.     

An object within a particle of extraterrestrial origin compared with an object of presumed terrestrial origin

Filamentary objects of submicron size isolated from an extraterrestrial particle and from the Gunflint cherts are compared and shown to have similarities of size, shape and interior structure.     

Comment on “a generation mechanism for Pc5 micropulsations in the morning sector” by Gordon Rostoker and Hing-Lan Lam

It is shown that the combined spatial and temporal oscillation of the auroral electrojet proposed by Rostoker and Lam (1978) gives rise to a second harmonic in the ground recorded pulsation record. An alternate spatial and temporal variation which does not inherently produce higher harmonics is proposed. It is suggested that both proposals require further theoretical and/or experimental investigation.     

Equations of anisotropic hydrodynamics for electron component of the ionospheric plasma

In this paper we have derived a set of transport equations for thermal electron component of the ionospheric plasma in the presence of an anisotropy of the electron energy distribution. Expressions are calculated in a 16-moment approximation for the moments of integrals of elastic and inelastic collisions of thermal electrons with basic neutral ionospheric components. The obtained moments determine variations of the hydrodynamical parameters, such as macroscopic velocity, pressure tensor, viscosity tensor, heat fluxes in respective equations due to collisions. The results have been obtained for an arbitrary degree of electron temperature anisotropy.