Atmospheric expansion through Joule heating by horizontal electric fields

Incoherent scatter measurements made along a magnetic field line into aurora during a period of high electric field in the recovery phase of a substorm show (1) considerably increased electron densities well above the normal F-region maximum, and (2) field-aligned plasma drifts that increase with altitude. A model invoking atmospheric expansion through Joule heating by the horizontal electric field driving the auroral electrojet is used to explain the observations. From this study it is concluded that during magnetically disturbed periods (1) Joule heating by the auroral electrojet raises the neutral temperature and density in the auroral zone ionosphere at F-region heights, (2) ionization formed by the aurora is transported upward by the expanding atmosphere, at times producing an appreciable increase in lower exospheric plasma densities on the field lines containing the aurora, and (3) combined satellite, radar, and optical observations during periods of aurora and high electric field could provide measured F-region collision frequencies.     

Potential and inductive electric fields in the magnetosphere during auroras

During quiescent auroras the large-scale electric field is essentially irrotational. The volume formed by the plasma sheet and its extension into the auroral oval is connected to an external source by electric currents, which enter and leave the volume at different electric potentials and which supply sufficient energy to support the auroral activity. The location of the actual acceleration of particles depends on the internal distribution of electric fields and currents. One important feature is the energization of the carriers of the cross-tail current and another is the acceleration of electrons precipitated through relatively low-altitude magnetic-field-aligned potential drops.Substorm auroras depend on rapid and (especially initially) localized release of energy that can only be supplied by tapping stored magnetic energy. The energy is transmitted to the charged particle via electric inductive fields.The primary electric field due to changing electric currents is redistributed in a complicated way—but never extinguished—by polarization of charges. As a consequence, any tendency of the plasma to suppress magnetic-field-aligned components of the electric fields leads to a corresponding enhancement of the transverse component.     

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.     

Condensation in Titan's stratosphere during polar winter

In Titan's north polar region stratospheric clouds are expected to form due to a combination of low temperatures and downward motion of volatile-enriched air. Here we investigate possible sources of stratospheric clouds at Titan's pole using data from the Cassini Composite Infrared Spectrometer and a simple condensation model. An upper limit for C₄N₂ gas was determined to be 9×¹⁰⁻⁹, which is less than required to make the C₄N₂ cloud at the Voyager epoch. Hence, the presence of this cloud after equinox remains a mystery. The largest cloud seen in far-infrared spectra has a feature around 220 cm⁻¹ and is located around an altitude of 140 km. The upper limit for propionitrile (C₂H₅CN) gas shows that the feature around 220 cm⁻¹ is probably not due to pure propionitrile ice. Instead, our model calculations show that HCN should cause by far the largest cloud around 140 km. We therefore propose that HCN ice plays an important role in the formation of the massive polar cloud, because of the unavailability of sufficient condensable gas other than HCN to produce a strong enough condensate feature. However, the signature at 220 cm⁻¹ is not consistent with that of pure HCN ice at 172 cm⁻¹ and mixing of HCN ice with other ices, or chemical alteration of HCN ice might mask the HCN ice signature.     

Horizontal electric fields in the middle latitude

Three dimensional electric fields were measured at the altitude of about 27 km in the stratosphere over the Pacific Ocean about 200–400 km away from the Sanriku coast of Honsyu Island (L = 1·4) on 16–17 October 1973, which was magnetically disturbed. The average horizontal electric field thus measured is about 10 mV/m, and the electric field vectors made clockwise semidiurnal rotations rather than diurnal. Daily variation of this electric field was compared with data at L = 2·7–3·5 published by Mozer (1973) and was found to be very similar. This suggests that these electric fields are of common origin in the plasmasphere. From their mean daily variation it is estimated that the plasmaspheric convection is decreased in the night side and is increased in the day side by 200–300 m/sec, and there is an outward flow in the first half of the afternoon and an inward flow in the plasma bulge region of about 500 m/sec.     

The sun's rotation and perturbations of geopotential height and temperature fields in the stratosphere

The morphology of a solar activity effect apparently connected with the Sun's rotation and showing up in 25-day and 13.6-day oscillations of stratospheric geopotential and temperature fields is analysed in this study. The used data cover the height range between roughly 20 and 30 km and a timespan from July 1965 to October 1971. Most prominent responses are found for zonal harmonic wave number 1 at the oscillation period of 25 days (solar rotation period modulated by seasonal changes) and for the zonally averaged meteorological quantities at the oscillation period of 13.6 days. Additional statistically significant effects show up in the zonal harmonics with wave number 1 and 3 at half the solar rotation period and in the zonal means with periodicities near 25–27 days. The results point towards a modulation of the quasistationary stratospheric planetary wave with a positive geopotential anomaly around roughly 180° longitude by solar activity changes. The direct physical mechanisms of this Sun-climate relationship are not yet clear, but it can be concluded that atmospheric dynamics is an important factor for its morphology and that downward propagation of such effects seems possible and should be investigated in future studies.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Large-scale electric fields in post-flare loops

As the electrical conductivity along the magnetic field in solar atmosphere is large, parallel electric fields have been neglected in most investigations. We will first demonstrate their importance for post-flare loops, and then introduce a model for them which takes into account the effect of parallel electric fields. The electric field calculated from the model is consistent with the electric field observed by Foukal et al. (1983).     

Problems related to macroscopic electric fields in the magnetosphere

The macroscopic electric fields in the magnetosphere originate from internal as well as external sources. The fields are intimately coupled with the dynamics of magnetospheric plasma convection. They also depend on the complicated electrical properties of the hot, collisionless plasma. Macroscopic electric fields are responsible for some important kinds of energization of charged particles that take place in the magnetosphere and affect not only particles of auroral energy but also, by multistep processes, trapped high-energy particles.A particularly interesting feature of magnetospheric electric fields is the fact that they can have substantial components along the geomagnetic field. Several physical mechanisms have been identified by which such electric fields can be supported even when collisions between particles are negligible. Comments are made on the magnetic-mirror effect, anomalous resistivity, collisionless thermoelectric effect and electric double layers, emphasizing key features and differences and their significance in the light of recent observational data.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May, 1978.Reprinted, with due permission fromRev. Geophys. Space Phys. 15, (1977), 457     

Particle density in the plasmasphere during quiet periods

Density distribution of plasmaspheric particles in the equatorial plane is derived from a model of plasmaspheric streaming, which may produce S_q current system in the lower ionosphere, and from one integral of motion, which seems to be generally valid for steady-state magnetospheric convection. The results satisfy not only the observed features of S_q variation but also the observed pattern of the density distribution in the magnetospheric equatorial plane during quiet periods.     

Electric conductivities,electric fields and auroral particle energy injection rate in the auroral ionosphere and their empirical relations to the horizontal magnetic disturbances

Recent progress in modeling ionospheric current systems requires global conductivity models which can reflect substorm conditions on an instantaneous basis. For this purpose, empirical relations of the North-South component (ΔH) of the magnetic disturbance field observed at College with the Pedersen (Σ_p) and Hall (Σ_H) conductivities deduced from the Chatanika radar data and their ratio ($\text{Σ}{}_{\mathrm{H}}\text{Σ}{}_{\mathrm{p}}$) are examined. These empirical formulas allow us to construct approximate distribution patterns of Σ_p and Σ_>H over the entire polar region on the basis of the distribution of ΔH at given instants by devising an appropriate weighting function for both the polar cap and the subauroral region. The global conductivity distributions thus obtained are compared with those employed by Kamide et al. (1981) and Spiro et al. (1982). The comparisons show that the gross features are similar among them. In addition, we also examine the relationship of ΔH with the North-South component of the electric field with the particle energy injection rate (u_A) estimated from the Chatanika radar data. Based on the empirical relation between Σ_H and u_A the global distribution of the latter over the entire polar region at particular instants can also be obtained.     

Effects on the plasmasphere of irregular electric fields

A conservative convection electric field model developed by Volland (1973) to describe the solar wind induced plasma flow within the inner magnetosphere is modified to include a noisy spatial component. Under steady state conditions such a random component will result in spatial irregularities in the thermal plasma density distribution in the vicinity of the plasmapause—particularly near dusk. Spatial irregularities in the convection can produce longitudinally restricted perturbations near the plasmapause some of which are detached from the main body of the plasmasphere. Temporal variations in the midnight to noon flow intensity are shown to produce elongated extensions of the plasmasphere known as plasmatails but even short period variations of the overall magnitude of the convection cannot produce longitudinally localized perturbations in the thermal plasma distribution. Convection models based on the 3 hr magnetic index K_p yield plasmasphere structures which are qualitatively similar to those based on shorter period variations, but the exact location at any given time of the plasmapause is dependent upon the characteristic time scale employed.     

Enhancement in wind-driven sand transport by electric fields

Aeolian grain transport is a powerful erosion mechanism and a significant factor affecting atmospheric dynamics by the creation of particulate aerosols. Electric fields, both natural and man-made, occur widely at the Earths surface in environments where granular material is found. Such electric fields may induce electrification of granular material and affect the transport dynamics of the grains. In this laboratory study we show that the influence of such electric fields is significant at field strengths well below that at which breakdown occurs and present a simple semi-empirical expression which allows this mechanism to be quantified.     

The Jovian stratosphere in the ultraviolet

The center-of-disk reflectivity of Jupiter in the wavelength range from 1450 to 3150A?has been computed from 30 low-dispersion IUE spectra taken during solar maximum in 1978–1980. A vertically inhomogeneous radiative transfer program is used to compute model reflectivities of various stratospheric compositions for comparison. Ammonia and acetylene are well determined because they show narrow absorption bands in the ultraviolet. Above 1800A?, these two gases provide a good fit to the data, but not below. At shorter wavelengths the fit would be much improved by a small amount (5–15 ppb) of propadiene/allene (C₃H₄). Voyager IRIS spectra show that the IR bands of allene are not strong enough to be detected in such a small amount. Additional absorption around 1600A?can be reproduced best with the presence of cyclopropane (C₃H₆, <15ppb), although other absorbers (e.g., hydrocarbon molecules with more than three carbon atoms, oxygen- or nitrogen-containing molecules, or a high-attitude haze) could also explain the spectrum in this region. The data are too noisy to detect possible CO Cameron band absorption near 2000A?.     

Magnesium ion chemistry in the stratosphere

Laboratory measurements of reaction rate constants of magnesium ions and magnesium containing ions with O₃, NO, HNO₃, and H₂O₂ have been carried out in a flowing afterglow experiment. Mg⁺ ions react with O₃ to produce MgO⁺ ions, which in turn react with O₃ to produce Mg⁺ ions. Mg⁺ ions react with HNO₃ and H₂O₂ to produce MgOH⁺ ions. MgOH⁺ ions react rapidly with HNO₃ to produce NO⁺₂ ions and Mg(HO)₂. One can therefore conclude that Mg⁺, MgO⁺, or MgOH⁺ ions could not have significant concentrations in the stratosphere if gas phase magnesium compounds were present. The failure to observe these ions therefore cannot be used as evidence that the stratospheric magnesium, resulting from meteor ablation at higher altitudes, is in condensed phases. This is in contrast to the case for sodium where the ion chemistry is such that the failure to observe hydrated Na⁺ ions proves that gas phase sodium compounds are not present in the stratosphere.     

Parallel electric fields accelerating ions and electrons in the same direction

In this contribution we present Viking observations of electrons and positive ions which move upward along the magnetic field lines with energies of the same order of magnitude. We propose that both ions and electrons are accelerated by an electric field which has low-frequency temporal variations such that the ions experience an average electrostatic potential drop along the magnetic field lines whereas the upward streaming electrons are accelerated in periods of downward pointing electric field which is quasi-static for the electrons and forces them to beam out of the field region before the field changes direction.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

Measurement of plasma wave electric fields in solar flares

Measurements of electric fields in solar flares using the Stark effect exhibited by neutral helium atoms are reported. Electric field strengths as high as 700 V cm^–1 are observed. Measurements of electron densities indicate that the electric fields originate from nonthermal plasma waves. Analysis of the plasma wave fields coupled with plasma density and temperature measurements indicate that the Lower Hybrid Drift instability may be present in the flaring region.The National Center for Atmospheric Research is sponsored bythe National Science Foundation.     

Variations of magnetospheric convection electric fields during substorms as inferred from pc1 hydromagnetic waves

The convection electric field in the vicinity of the plasmapause in the midnight sector during magnetospheric substorms has been obtained on the basis of spectral analysis of Pc1 hydromagnetic (HM) waves observed at the low latitude station, Onagawa (Φ = 28.°3, Λ = 206.°8). Variations of the field are consistent for four independent substorm events studied. The calculation implies that the convection electric field increases westwards up to ~1.0 mV/m during the expansion phase of the substorms, changes polarity near the end of the expansion phase, and then points eastwards during the recovery phase.     

Rocket measurements of ULF electric fields and precipitating particles in the aurora

The electric component of ULF waves with a characteristic period of 1.5-3 s and an amplitude of tens of $\text{mV}\text{m}$ has been observed with a double probe on a rocket launched from Andöya in Norway into an aurora. The polarization of the waves was right and left handed nearly circular as well as nearly linear during different intervals of the flight. These measurements are compared with ELF and energetic electron measurements on the rocket and ULF measurements on the ground.Possible interpretations involving generation of the ULF waves by proton cyclotron resonance in the magnetotail or by streaming ions or electrons in the magnetosheath are outlined.     

Space-charge flows and electric fields in the magnetospheres of rotating magnetic stars

We illustrate a method for determining self-consistently the spacial distribution of space-charge currents and electric fields close to the surface of a rotating magnetic star. The unique solution for simple geometries shows that the space-charge flow, required to maintain the surface potentials and to bring the surface electric field parallel to the magnetic field to zero, simultaneously sets E·B to zero at all heights above the surface. Thus this result questions the previous estimates of the parallel electric fields near pulsars.