bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of neutral iron emission in twilight spectra
Authors: Tepley C. A. , Meriwether J. W. , Walker J. C. G. , Mathews J. D.
Published: February 2008

We present a method for the analysis of twilight airglow spectra that may be contaminated by atmospheric continuum emission of unknown brightness. The necessity of correcting for this continuum emission when measuring weak airglow features in twilight is illustrated by application of the method to the neutral iron line at 3860 Å.
large‐amplitude waves in an anisotropic plasma
Authors: Granik A. T.
Published: February 2008

The propagation of large‐amplitude hydromagnetic waves of a collisionless anisotropic plasma is treated by using the Chew‐Goldberger‐Low equations. The generalization of the usual theory of characteristics as applied to this treatment has been developed. It is shown that in such a plasma there are six different types of waves. They incorporate all modes considered in a small‐amplitude theory. For a special case of a magnetic field almost parallel to the direction of propagation a fast magnetosonic wave has small density variations proportional to the variations of the square of a magnetic field intensity. A wave equation similar to one used in an isotropic plasma describes the behavior of nonplanar Alfvén waves. The simple relation obtained for the averaged large‐amplitude perturbations in the transverse Alfvén wave is identical to the equation derived on the basis of the WKB approximation.
Optical observations of thermospheric dynamics at Arecibo
Authors: Burnside R. G. , Herrero F. A. , Meriwether J. W. , Walker J. C. G.
Published: February 2008

Observations of thermospheric neutral winds have been made at Arecibo, Puerto Rico, by using a Fabry‐Perot interferometer to measure the Doppler shift of the nighttime O(¹D) 630‐nm emission. We have developed a scheme of making observations at eight equally‐spaced azimuth positions with a constant zenith angle. This technique allows us to determine the mean neutral wind velocities in the meridional and zonal directions, as well as any horizontal gradients in the wind field. It also provides a good means of simultaneously monitoring any spatial variations in neutral temperature and the intensity of the O(¹D) emission. In general, the highest equatorward wind velocity is observed at about 2100 LST. The meridional wind velocity usually lessens as midnight approaches and sometimes, but by no means always, reverses after midnight. The magnitude of the equatorward velocity is greater in summer than in winter months. For winter and spring months, the zonal wind blows eastward throughout the night, with the velocity tending to decrease in a fairly regular fashion from about 125 m s−1 at 2100 LST towards zero by 0400 LST. In summer the pattern is similar, but the eastward flow usually reverses earlier, and a westward velocity of some 50 m s−1 may be attained by 0400 LST. Significant horizontal wind gradients are often observed in the meridional direction, but not in the zonal direction. Near midnight especially, during both the equinox and summer months, the equatorward wind is often greater to the north of Arecibo than to the south. We interpret this as being an effect of the passage of the midnight equatorial pressure maximum to the south of the station. Measurements of neutral temperature with the interferometer do indeed show that, between 0100–0200 LST, the neutral temperature to the south of Arecibo is enhanced by some 40°K over that to the north.
Rocket‐borne measurements of particle pulsation in pulsating aurora
Authors: Yau Andrew W. , Whalen Brian A. , McEwen D. J.
Published: February 2008

Rocket‐borne measurements are made of the particle pulsation characteristics in a pulsating aurora. A train of eleven 17‐s pulsations was observed in electron intensities at energies as low as 2 keV and as high as 28 keV. During the pulsations a factor of 2 increase in the electron intensities at the few‐keV range, and a factor of 3–5 increase in the intensities in the 20‐keV range, were measured. Time delays in pulsations of low‐energy electrons are observed; they indicate the source of particle injection to be near the equatorial plane. The electron energy spectra in pulsation maxima are characterized by higher Maxwellian temperatures than their pulsation minima counterparts. The few‐keV electrons have more trapped distributions at pulsation minima than at pulsation maxima. The energetic electrons are isotropic at all times. The altitude profiles of the electron fluxes at various energies are examined, in an attempt to identify the possible existence of thin optical pulsating auroral structure; they are found to be similar to those associated with discrete auroras. Current theoretical pulsation models are discussed in light of the observations.
Chemical fluctuations and incoherent scattering theory in the terrestrial D region
Authors: Kockarts G. , Wisemberg J.
Published: February 2008

The continuum theory of incoherently scattered electromagnetic waves is modified in order to include possible effects of thermally induced chemical fluctuations. These fluctuations are taken into account by introducing fluctuating parts in the production and loss terms of the continuity equations. An equivalent ionospheric model is developed for three types of ionized species, i.e., electrons and negative and positive ions. A matrix formulation gives simultaneous access to fluctuating parts of each charged component. Numerical results indicate that chemical fluctuations are important over the height range where negative ions are comparable or greater than the electron concentration. Strong enhancements of the incoherent scatter cross section occur for frequency shifts smaller than approximately 20 Hz. A simple approximation is given for the contribution of chemical fluctuations.
A model representation of the ionospheric electric field over Millstone Hill (Λ=56°)
Authors: Wand Ronald H.
Published: February 2008

Incoherent scatter observations of E and F region drifts over Millstone Hill (42.6°N) were made routinely from May 1976 to November 1977 at monthly intervals. Some 667 hours of data gathered over this 19‐month period were analyzed to yield the F region polarization electric field in the magnetic south and magnetic east directions. The data have been used to construct an analytical model for these two field components as functions of (1) local time, (2) day of year, and (3) magnetic activity (represented by the Kp index). Models were constructed both with and without the constraint that the daily average of the E‐W field be zero. The model employs 35 coefficients for each electric field component which were found by a least mean squares fit to the data and are tabulated.
Wave‐particle interactions near ΩHe+ observed on GEOS 1 and 2 1. Propagation of ion cyclotron waves in He+‐rich plasma
Authors: Young D. T. , Perraut S. , Roux A. , de Villedary C. , Gendrin R. , Korth A. , Kremser G. , Jones D.
Published: February 2008

The GEOS 1 and 2 spacecraft contain a set of particle and wave detectors which allow for a very comprehensive study of wave‐particle interactions occurring within the equatorial region of the magnetosphere. This paper is devoted to interactions involving protons in the energy range 20 keV to 300 keV and ULF waves with frequencies below the proton gyrofrequency. It is shown that most of the ion cyclotron waves (ICW's) detected in this frequency range have spectra whose characteristic frequencies are organized in the vicinity of the He+ gyrofrequency. Simultaneous measurements of the ion composition in the thermal energy range (E ≲110 eV) show these waves to be clearly associated with the abundance of cold He+ as well as the anisotropy of ions above 20 keV. The general characteristics of these helium‐associated ULF events are presented in case studies of four events. The interpretation of this phenomenon is given in the present paper in terms of the propagation of ICW's in a He+‐rich plasma. It is shown that the shape of the cold plasma dispersion curve (for both parallel and non‐parallel propagation) can adequately explain the main characteristics of the observed waves (frequency spectrum, polarization) as well as the differences between observations made onboard GEOS 1 and GEOS 2. The generation conditions of ion cyclotron waves in such a multi‐component plasma, as well as their quasi‐linear effects on both the cold He+ ions and the hot protons, are discussed in a companion paper.
Global ionospheric electric field measurements in April 1978
Authors: Holzworth Robert , Wygant John , Mozer Forrest , Gonzales Cesar , Greenwald Ray , Blanc Michel , Vickrey Jim , Kishi Arlene
Published: February 2008

This paper presents an introduction to a global campaign of simultaneous quasistatic electric field measurements from radars, balloons, and satellites at various places within the earth's environment for April 8–14, 1978. The 7‐day time period encompassed both extended magnetically quiet times as well as two magnetic storms. These storms were related to SSC's that followed solar flares, one of which included a day‐long solar proton event. The wide variety of instrumentation and associated operating modes involved in this campaign is described. Sample conjunctions between satellites and ionospheric measurements are shown that demonstrate that field line mapping is valid under certrain circumstances. Some of the largest ionospheric electric fields ever reported with >100‐km scale size occurred on April 11, and these events are discussed in detail.
Direction findings of medium‐latitude whistlers and their propagation characteristics
Authors: Hayakawa M. , Okada T. , Iwai A.
Published: February 2008

The propagation characteristics of medium‐latitude whistlers are studied on the basis of measurements with a new direction finder at Moshiri (geomag. lat. 34.5°N; L=1.6) during January and February 1978. Detailed analyses are made for two selected events: one with the highest daytime activity on January 22 and the other with the highest nighttime activity on February 20. Daytime whistlers are of multi‐flash or of an isolated type, and the dispersion remains constant during the event. The measured polarization is, on the average, close to exactly circular, indicating a negligible effect of multi‐paths in the earth‐ionosphere waveguide, implying that the ionospheric exit points are determined accurately. The characteristics on the direction finding results are compared with the properties expected for ducted and nonducted pro‐longitudinal mode propagation and it is concluded that the whistlers may be attributed to ducted progagation. Just a single duct is present during the event. The dimension at the lower boundary of the ionosphere, illuminated by the duct which probably terminated at the F2, is found to be ∼100 km. The small apparent movement of the exit regions may be due to a temporal fluctuation of the propagation conditions between the duct endpoint and the lower boundary of the ionosphere. For the nighttime whistlers there are four distinct dispersions, but we concentrate ourselves on the main dispersion which remained constant during the event. The observed polarization is less circular than for the case of daytime whistlers for the measured incident angle ≲60°. For larger incident angles, 60° ≲i ≲75°, we find a great variability in the measured polarization. These indicate that multi‐path propagation may have a significant effect on the propagation in the waveguide at night. Correspondingly, there is a great scatter in the estimated exit points during each time interval. The exit region also shows a large apparent drift. This may be interpreted in terms of a joint effect of the presence of four ducts at the nearly same L shell and the temporal variation of the activity of the lightning sources at the feet of the four ducts in the conjugate zone. The scale of nighttime ducts is difficult to determine due to the great scatter of the data.
Relativistic cosmic rays and corotating interaction regions
Authors: Duggal S. P. , Tsurutani B. T. , Pomerantz M. A. , Tsao C. H. , Smith E. J.
Published: February 2008

Analyses of relativistic galactic cosmic ray intensity variations have been conducted to determine the nature of the modulations that are related to the presence of corotating interaction regions (CIR) in interplanetary space. The corotating interaction regions have been identified from the plasma and field observations recorded by Pioneer 10 and 11 spacecrafts during the period 1972–1974. This investigation has established that the nucleonic intensity recorded at the polar stations Thule and McMurdo decreases as the streams associated with the CIR overtake the earth. However, this modulation occurs only for those CIR‐associated streams in which a neutral sheet is imbedded. In contrast, geomagnetic storms are related to CIR streams with or without neutral sheets. Taken together, these results suggest that the ostensible effect of CIR's on the intensity of high‐energy particles is primarily a consequence of drifts related to neutral sheets, although diffusion effects cannot be ruled out at this stage.
Auroral electron beams: Electric currents and energy sources
Authors: Kaufmann R. L.
Published: February 2008

The equipotential structures and electron beams seen during rocket flight 18∶152 are analyzed. The equipotentials which lead to beam formation can be produced by either a maximum in the high‐altitude potential or a minimum in the low‐altitude potential near a closed U‐shaped structure. Cold ionospheric electrons can enter the acceleration region near a cusplike feature that separates closed and open electric equipotentials. The analysis suggests that some midnight auroras may derive energy from the cross‐tail electric field. Birkeland currents distort magnetic field lines so that plasma flow becomes sheared and the electric field divergence increases near the earth. The observed closed and open equipotential structures develop at still lower altitudes as these electric fields interact with the ionosphere. Finally, horizontal ionospheric electric currents are derived for the flight. Sudden changes in horizontal currents at the edge of an active arc are much larger than can be explained by Birkeland currents. The observed effects can be produced by substantial distortions of horizontal current flow near the rocket.
Active stimulation of the auroral plasma
Authors: Wong A. Y. , Santoru J. , Sivjee G. G.
Published: February 2008

A concept of actively stimulating the auroral plasma using a high‐power pulsed HF radio wave transmitting system is described. A unique feature of a pulsed modular system is the unprecedentedly high power (e.g., 10–100 MW) that can be achieved. This pulsed HF system would be used in the excitation of short‐term nonlinear plasma phenomena, such as resonant enhancement, particle energization, electron density profile modification, excitation of VLF plasma waves, and the modification of auroral optical emission. This excitation is predicted on the basis of previous experience, which includes laboratory simulation experiments at high‐pulsed power, excitation of the ionospheric plasma at low latitudes, and theoretical calculations.
IMF sector effects on the polar geomagnetic field in winter
Authors: Matsushita S. , Xu W.‐Y.
Published: February 2008

IMF sector effects on the polar geomagnetic field, particularly in winter, are examined with a use of the geomagnetic data from 13 northern and 6 southern high‐latitude geomagnetic stations. Detailed behavior of the winter reversal of the sector effects near 70° invariant latitude is investigated. A method to improve the sector estimation from geomagnetic data is suggested, and formation of the winter reversal is briefly discussed, taking electric‐field propagations along field lines from the summer hemisphere as well as upward and downward field‐aligned electric current effects into consideration.
Observations of ions with nuclear charge Z ≧9 in the inner magnetosphere
Authors: Spjeldvik Walther N. , Fritz Theodore A.
Published: February 2008

Ions heavier than protons, such as helium ions and CNO ions, are known to exhibit substantially enhanced trapped fluxes at MeV energies in the interior of the earth's radiation belts associated with some, but not all, magnetic storms. In this report we extend the Explorer 45 heavy ion data analysis to ions heavier than fluorine, i.e., ions with nuclear charge Z ≳9 during and following a major magnetic storm on August 4, 1972. Our heavy ion detector telescope does not permit a precise identification of these ions; but if they are magnesium ions (say), then an equatorially mirroring peak trapped flux of 0.02 ions/(cm² s sr keV) is derived on L shells just below L =3 at energies 12.8–51.2 MeV per ion (533–2133 keV per nucleon). Other possible ion contributions include silicon and iron. The fluxes of these ions are found to decay on time scales typically several tens of days; this is substantially faster than that of helium ions and somewhat faster than that of oxygen ions in the lower MeV range. We infer that the pitch angle distributions of the Z ≳9 ions were quite anisotropic over a range of L shells with the exponent m in the relation jLOC=jEQ sinm αEQ having a value of at least 10; this value is arrived at from two independent techniques.
Synoptic observations of Jupiter's radio emissions: Average statistical properties observed by Voyager
Authors: Alexander J. K. , Carr T. D. , Thieman J. R. , Schauble J. J. , Riddle A. C.
Published: February 2008

Observations of Jupiter's low‐frequency radio emissions collected over one‐month intervals before and after each Voyager encounter have been analyzed to provide a synoptic view of the average statistical properties of the emissions. Compilations of occurrence probability, average power flux density, and average sense of circular polarization are presented as a function of central meridian longitude, phase of Io, and frequency. The results are compared with ground‐based observations. The necessary geometrical conditions and preferred polarization sense for Io‐related decametric emission observed by Voyager from above both the dayside and nightside hemispheres are found to be essentially the same as those observed in earth‐based studies. On the other hand, there is a clear local time dependence in the Io‐independent decametric emission. The emission is prevalent at longitudes >200° when observed from over the dayside hemisphere but is dominant at longitudes <200° when observe from over the postmidnight sector. Decametric emission, which comprises the dynamic spectral lesser arcs near 10 MHz, displays a distinct, bimodal polarization pattern that is predominantly in the left‐hand sense at longitudes below 150° and in the right‐hand sense at longitudes above 150°. The central meridian longitude distributions of occurrence probability and average flux density at hectometric wavelengths appear to depend significantly on both the observer's latitude and local time. Io appears to have an influence on average flux density of the emission down to below 2 MHz. The average power flux density sectrum of Jupiter's emission has a broad peak near 9 MHz. Integration of the average spectrum over all frequencies and all longitudes gives a total radiated power for an equivalent isotropic source of 4 × 1011 W.
Interaction of eddies and mean zonal flow on Jupiter as inferred from Voyager 1 and 2 images
Authors: Ingersoll Andrew P. , Beebe Reta F. , Mitchell Jim L. , Garneau Glenn W. , Yagi Gary M. , Müller Jan‐Peter
Published: February 2008

Voyager 1 and 2 narrow‐angle frames were used to obtain displacements of features at resolutions of 130 km over time intervals of 1 Jovian rotation. The zonal velocity ū was constant to 1.5% during the 4 months between the Voyager 1 and 2 encounters. The latitudes of the zonal jet maxima (extrema of ū) are the same as inferred from earth‐based observations extending over the past 80 years. The curvature of the velocity profile d²ū/dy² varies with latitudinal coordinate y in the range from −3β to +2β, where β is the planetary vorticity gradient. The barotropic stability criterion is violated at about 10 latitudes between ±60°. The eddy momentum flux variation with latitude
is positively correlated with dū/dy for both Voyager 1 and 2 data. The rate of conversion
of eddy kinetic energy into zonal mean kinetic energy is in the range 1.5–3.0 Wm−2, for a layer 2.5 bar deep. The time constant for resupply of zonal mean kinetic energy by eddies is in the range 2–4 months, less than the interval between Voyager encounters. The rate of energy conversion is more than 10% of the total infrared heat flux for Jupiter, in contrast with earth where it is only 0.1% of the infrared heat flux. This hundred‐fold difference suggests that the thermomechanical energy cycles are very different on the two planets.
Multi‐spacecraft observations of heliographic latitude‐longitude structure in the solar wind
Authors: Rhodes Edward J. , Smith Edward J.
Published: February 2008

The heliographic latitude‐longitude structure of high speed solar wind streams observed prior to the maximum of solar cycle 20 has been studied with a multi‐spacecraft comparison. Plasma and magnetic field data obtained near the earth by Explorers 34 and 35 during mid‐1967 were mapped radially inward to the location of Mariner 5, which was making simultaneous measurements at lower heliographic latitudes. For latitude separations less than 3.5°, cross‐correlations of the Explorer‐Mariner velocities showed only the previously reported systematic increase in velocity with latitude. However, for latitude separations ranging from 3.5° to 6.2°, significant differences in the high speed stream structure of up to 250 km/s were seen. For these stream structures, the multi‐spacecraft observations made possible the separation of spatial from temporal variations with little ambiguity. Within one interval, the higher‐latitude Explorers saw a single, broad stream while the lower‐latitude Mariner saw a series of three relatively narrow streams. Within a second interval, a single high speed stream was observed at both locations which was sloped at an angle of 70°–80° from solar north‐south direction. These stream structures, which were also seen by Pioneers 6 and 7, imply the existence of large, temporary, local north‐south velocity gradients, or wind shears, ranging up to 60 km/s/deg. The latitude separations found for these structural differences were the smallest yet observed in spacecraft data and hence involved shorter corotation delays than those of any previous study. The multi‐spacecraft comparisons also led to the identification of several intervals of time when individual high speed streams shifted substantially in either longitude and/or amplitude on a time scale of one solar rotation. Possible flare‐related disturbances were found to be too small to account for these large observed changes.
Simultaneous observations of auroral zone electrodynamics by two satellites: Evidence for height variations in the topside ionosphere
Authors: Rich Frederick J. , Cattell Cynthia A. , Kelley Michael C. , Burke William J.
Published: February 2008

The S3‐2 and S3‐3 satellites were launched into orbits with identical inclinations but with apogees of 1500 and 8000 km, respectively. Both satellites were equipped to measure magnetic fields, electric fields, and energetic electrons. By comparing a few cases when the satellites were crossing the auroral zone at approximately the same universal time and location, altitude variations in the electrodynamics of the auroral zone can be separated from universal and local time variations. Such comparisons show that there are times when the field‐aligned current per unit of flux in the auroral zone measured by magnetic field deflections at the two satellites is the same at both altitudes. There are also times when the field‐aligned current per unit of flux is larger at high altitudes than at low altitudes. This requires flow of currents perpendicular to the magnetic field. Comparisons of the convection electric field (scale size >0.1°) at the two altitudes show that the electric field does not always map as though field lines were equipotentials. In addition, intense, small‐scale (<0.1°) electric fields perpendicular to the magnetic field, previously associated with electrostatic shocks, and which are observed at high altitudes are usually not seen in simultaneous low‐altitude observations. Only in one of the six passes was there a simultaneous observation of a region of intense, small‐scale electric field variation at 800 and 1000 km.
Incoherent scatter radar observations of wavelike structures in the mesosphere over Arecibo
Authors: Fukuyama K.
Published: February 2008

The 430‐MHz radar at Arecibo has been used to observe the ion component of the incoherent scatter spectrum in the mesosphere. Vertical profiles of the zonal winds deduced from the radar backscatter show excellent agreement with profiles obtained from meteorological rocket soundings from Antigua. Meridional winds and the spectrum parameters (width and relative power) observed on a summer day exhibit wavelike structures which move downward with time. The wavelike structures in the spectrum parameters, pronounded particularly in the D region ledge, are discussed somewhat qualitatively, in relation to transport processes of neutral and ionized particles by the atmospheric motions.
The solar spectral irradiance 1200–3184 Å near solar maximum: July 15, 1980
Authors: Mount George H. , Rottman Gary J.
Published: February 2008

Full‐disk solar spectral irradiances near solar maximum were obtained in the spectral range 1200–3184 Å at a spectral resolution of approximately 1 Å from rocket observations above White Sands Missile Range, New Mexico, on July 15, 1980. Comparison with measurements made in 1979 and during solar minimum confirms a large increase at solar maximum in the solar irradiance near 1200 Å with no change within our measurement errors near 2000 Å. Irradiances in the range 1900–2100 Å are in excellent agreement with previous measurements, and those in the 2100‐ to 2500‐Å range are lower than the Broadfoot results. We find agreement with previous values 2600–2900 Å and then fall below those values 2900–3184 Å.
On the structures and mapping of auroral electrostatic potentials
Authors: Chiu Y. T. , Newman A. L. , Cornwall J. M.
Published: February 2008

We examine the mapping of magnetospheric and ionospheric electric fields in a kinetic model of magnetospheric‐ionospheric electrodynamic coupling proposed for the aurora by Chiu and Cornwall (1980). A new feature is the generalization of the kinetic current potential relationship to the return current region (identified as a region where the parallel potential drop from magnetosphere to ionosphere is positive); such a return current always exists unless the ionosphere is electrically charged to grossly unphysical values. We are able for the first time to give a coherent phenomenological picture of both the low‐energy return current and the high‐energy precipitation of an inverted V. The mapping between magnetospheric and ionospheric electric fields is phrased in terms of a Green’s function that acts as a filter, emphasizing magnetospheric latitudinal spatial scales of order (when mapped to the ionosphere) 50–150 km. We identify this length as roughly the overall size of the inverted V region. Roughly speaking, this scale length, when multiplied by the perpendicular electric field just above the ionosphere, gives the magnitude of the parallel potential drop between the ionosphere and equatorial magnetosphere. A precise relation between these quantities is given—for the first time—in the body of the paper; previous two‐dimensional kinetic models have taken the parallel potential drop as an assumed input.
Birkeland currents as the cause of the low‐latitude asymmetric disturbance field
Authors: Crooker Nancy U. , Siscoe George L.
Published: February 2008

The low‐latitude asymmetric disturbance field, which is so prominent during the developing stage of a magnetic storm and which traditionally has been attributed to a dusk‐centered partial ring current, recently has been interpreted by Harel et al. (1981) to be the result of incomplete cancellation of their computer‐simulated region 1 and region 2 Birkeland currents over local time, with net current flowing into the ionosphere at noon and out at midnight. The new interpretation has the advantage of being based on an observed current system rather than on a hypothetical one. We explore the Birkeland current explanation quantitatively in terms of a simple analytical model, the details of which are given separately in an appendix. The residual current arises as a result of the divergence of the Hall current at the conductivity discontinuity at the poleward boundary of the auroral oval. This effect rotates the pattern of region 1 Birkeland currents relative to region 2 currents and produces the net current at noon and midnight. The model gives a simple expression for the amplitude G of the resulting disturbance at the equator in terms of the polar cap potential Φ and the height‐integrated Hall conductivity ΣAH in the auroral oval: G(nT) ≈ 0.017 Φ (kV) Σ AH (mhos). The equivalent current pattern for the model is presented and compared to the equivalent current pattern for a similar model developed by Vasyliunas for the substorm. Combining the two patterns in a time‐dependent model can account for the observed pattern of phase shifting of the low‐latitude asymmetry during substorms.
The ionospheric peak on the Venus dayside
Authors: Cravens T. E. , Kliore A. J. , Kozyra J. U. , Nagy A. F.
Published: February 2008

Many electron density profiles of the dayside ionosphere of Venus have been measured by the Pioneer Venus orbiter between December 1978 and October 1980, using the dual‐frequency radio occultation technique. The peak electron density as a function of solar zenith angle can be described by a simple Chapman layer theory with proper normalization; however, it does not predict adequately the height variation of the electron density peak. In order to interpret these radio occultation results, we have constructed a theoretical model describing the ion composition and electron density in the vicinity of the ionospheric peak. Good agreement between the model and the measurements was obtained only with a specific choice of the neutral densities, the electron temperature, and the level of solar activity.
Large scale patterns of auroral ionospheric convection observed with the Chatanika Radar
Authors: Foster J. C. , Doupnik J. R. , Stiles G. S.
Published: February 2008

Ionospheric convection at auroral latitudes has been examined during a series of long duration experiments with the Chatanika, Alaska, incoherent scatter radar. These experiments have been carefully designed to obtain maximum latitudinal coverage (56°Λ–75°Λ) while maintaining a temporal resolution of 30 min in order to resolve the effects of individual substorms on the convection pattern. Design criteria for the experiments are described together with presentation of observational data acquired during 400 hr of radar operations during various levels of geophysical disturbance. The data accentuate the repeatability of the gross features of the auroral convection and its basic conformity to the two‐cell pattern predicted from the large‐scale magnetospheric circulation. For moderate to active geomagnetic conditions uniform sunward convection with velocities of 800–1200 m/s spans the 62°Λ to 72°Λ latitude band at both dawn and dusk. In quieter circumstances the sunward convection continues in this region, but has smaller speeds and is centered at higher latitudes. Little evidence of a ‘throat’ in the dayside convection pattern is seen at latitudes below 75°Λ except in very disturbed circumstances. During several experiments coordinated operation of the Chatanika and Millstone Hill, Massachusetts, radars permitted the simultaneous observation of the auroral convection pattern at two different local times. Substorms affect the convection at all local times and appear to generally enhance the rate of convection without seriously changing its direction. Near midnight, latitudinal displacements and expansions of the convection pattern during substorms may result in a local rotation or reversal of the direction of convection, while near dawn and dusk, convection velocities are enhanced and the region of sunward flow expands to lower latitudes.
Vibrational enhancement and the excitation of N2+ and the first negative system in the high‐altitude red aurora and the dayside cusp
Authors: Degen V.
Published: February 2008

Broadfoot’s (1967) theory for fluorescent scattering of sunlight by N2+ in high‐altitude auroral rays is updated with new radiative and electron impact cross sections and extended to include the analogous process of fluorescence induced by low energy electrons. The two mechanisms account successfully for the observed vibrational enhancement of the first negative system in both the sunlit and non‐sunlit phases of the great type‐A red aurora of February 10, 1958, without recourse to proton precipitation as has commonly been suggested, and permit a number of conclusions regarding vibrational temperatures, ion lifetimes, and the role of electron fluxes. In the cusp the agreement is not very conclusive as yet, although a recently published single set of data suggests that the cusp was totally sunlit at the time. Recalculated g‐values for solar scattering and corresponding arrays of band intensities of the first negative and Meinel systems are given. Laboratory beam parameters often lie well within the range of the model prediction, suggesting a means of controlled study of the proposed electron‐induced fluorescence mechanism.
Developing forecasting charts for sunspot numbers
Authors: Kapoor S. G. , Wu S. M.
Published: February 2008

A new statistical modeling approach is used to fit models to 200 years of sunspot data and the adequate models for yearly, monthly, and daily sunspot numbers are employed to obtain the minimum mean squared error forecasts. The analysis of new models revealed a long‐term 76‐year period, a short‐term 27‐year period, and a 2.5‐year period due to stratospheric winds in addition to a commonly known 11‐year periodicity of the sunspots. The forecasting charts are developed in a format that can be easily read to obtain the long‐term (yearly average) and short‐term (daily average) predictions of sunspot numbers.
Solar wind protons: Three‐dimensional velocity distributions and derived plasma parameters measured between 0.3 and 1 AU
Authors: Marsch E. , Mühlhäuser K.‐H. , Schwenn R. , Rosenbauer H. , Pilipp W. , Neubauer F. M.
Published: February 2008

A survey of solar wind three‐dimensional proton velocity distributions as measured by the Helios solar probes between 0.3 and 1 AU is presented. A variety of nonthermal features like temperature anisotropies, heat fluxes, or proton double streams has been observed. The relative speed of the second proton component increases on the average with increasing wind speed and decreasing heliocentric radial distance and shows a correlation with the local Alfvén speed. A marked anisotropy in the core of proton distributions with a temperature larger perpendicular than parallel to the magnetic field (T∥c < T∥c) is a persistent feature of high speed streams and becomes most pronounced in the perihelion (≈0.3 AU). Fairly isotropic distributions have only been measured very close to and directly at magnetic sector boundaries. Low and intermediate speed distributions usually show a total temperature anisotropy T∥p/T⊥p > 1 frequently caused by ‘high‐energy shoulders’ or a resolved second proton component. No clear radial gradient of the temperature anisotropy could be established in these cases. The average dependence of the proton temperature on heliocentric radial distance is given by a power law R−α, where α ≈ 1 for T⊥p and 0.7 < α < 1 for T⊥p are compatible neither with isothermal nor adiabatic expansion. Flattest radial temperature profiles are obtained in high‐speed streams. These observations indicate that local heating or considerable proton heat conduction occurs in the solar wind. Some consequences of nonthermal features of proton distributions for plasma instabilities are discussed as well as kinetic processes that may shape the observed distributions.
Nonlinear evolution of plasma enhancements in the auroral ionosphere, 1, Long wavelength irregularities
Authors: Keskinen M. J. , Ossakow S. L.
Published: February 2008

The linear stability and nonlinear evolution of plasma enhancements in arbitrary ambient electric fields in the diffuse auroral F region ionosphere have been studied using analytical and numerical simulation techniques. Our results indicate that equatorward convecting plasma slabs initially limited in latitudinal extent are primarily destabilized on their poleward sides by a combination of the effects of convection and field‐aligned currents. Furthermore, we find that the plasma enhancements break up into primary striationlike structures (elongated in the north‐south direction for equatorward convection) which can form and cascade from large (≃100 km) to smaller (≃3 km) scale sizes on the order of an hour. The primary and associated smaller‐scale structures can be oriented in either the north‐south or east‐west (L shell alignment) direction depending on the ambient electric field magnitude and direction. For wave numbers (kx, ky) in Fourier space corresponding to the east‐west and north‐south directions, respectively, the one‐dimensional spatial power spectra of the irregularities in the east‐west direction P(kx) ∝ kx−nx with nx ≃ 2‐2.5 for 2π/kx between 100 km and 3 km while in the north‐south direction, P(ky) ∝ ky−ny with ny ≃ 2 for 2πsol;ky between 256 km and 3 km.
Nonlinear equatorial spread F: The effect of neutral winds and background Pedersen conductivity
Authors: Zalesak S. T. , Ossakow S. L. , Chaturvedi P. K.
Published: February 2008

A simple model of the interaction of the equatorial ionosphere with the eastward F region neutral wind in the presence of evolving spread F bubbles is given. A consequence of the model is that the upper portions of bubbles will take on a westward tilt, while the lower portions will tilt eastward, giving rise to the ‘fishtails’ and ‘C’s’ observed by coherent backscatter radar measurements of field‐aligned small‐scale irregularities. The essence of the model is that the plasma away from the equatorial plane (e.g., a background nighttime E region at higher latitudes) makes a finite contribution to the magnetic field line‐integrated Pedersen conductivity, causing an incomplete coupling of the plasma motion to the neutral wind. The degree of coupling is then a function of the Pedersen conductivities both near the equator in the F region and in the higher‐latitude E region, giving rise to vertical shears of east‐west plasma motion having opposing signs on either side of the equatorial Pedersen conductivity maximum. Evolving spread F bubbles are caught up in this shear as they rise vertically, resulting in the characteristic ‘C’ shape seen by backscatter radar and in the westward motion of plasma bubbles observed by satellite in situ measurements. Numerical simulations, incorporating an eastward neutral wind in the equatorial F region and E region Pedersen conductivity effects, are presented to further support the model and analysis. The simulations also show the result that it may be the eastward as well as the westward wall of a bubble which is subject to secondary instabilities in the presence of an eastward neutral wind. In addition, even without the neutral wind the numerical simulations show that E region Pedersen conductivity effects can result in a slowing down of equatorial spread F and attendant bubble evolution.
Proton temperature anisotropy in the polar wind
Authors: Schunk Robert W. , Watkins David S.
Published: February 2008

We studied the steady state flow of a fully ionized H+‐O+‐electron plasma along geomagnetic field lines in the high‐latitude topside ionosphere. Our theoretical formulation was based on the 13‐moment system of transport equations, which allows for different species temperatures parallel and perpendicular to the geomagnetic field and nonclassical heat flows. Solutions to the plasma transport equations were obtained over the altitude range from 1500 to 12,000 km for a range of lower‐boundary conditions leading to both subsonic and supersonic H+ outflows. For both subsonic and supersonic flows an appreciable H+ temperature anisotropy occurs at all altitudes above 1500 km, and in both cases the H+ temperature anisotropy tends to be regulated at high altitudes. However, the direction of the anisotropy is opposite for the two cases. For supersonic flow, Tp∥ > Tp⊥ at high altitudes, while the reverse occurs for subsonic flow. To some extent, the direction of the temperature anisotropy is related to the direction of the H+ heat flow. For supersonic flow an upward flow of heat from the lower ionosphere is required, while for subsonic flow we were able to obtain solutions with a downward H+ heat flow. For supersonic flow, collisionless transport effects are important at altitudes as low as 1500 km while for subsonic flow H+‐H+ collisions have an important effect on the H+ stress and heat flow balance at all altitudes between 1500 and 12,000 km.
Seasonal variations of the high‐latitude F region for strong convection
Authors: Sojka J. J. , Schunk R. W. , Raitt W. J.
Published: February 2008

We combined a plasma convection model with an ionospheric‐atmospheric composition model in order to study the seasonal variations of the high‐latitude F region for strong convection. Our numerical study produced time‐dependent, three‐dimensional, ion density distributions for the ions NO+, O2+, N2+, O+, N+, and He+. We covered the high‐latitude ionosphere above 42°N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. From our study we found the following: (1) For strong convection, the high‐latitude ionosphere exhibits a significant UT variation both during winter and summer. (2) In general, the electron density is lower in winter than in summer. However, at certain universal times the electron density in the dayside polar cap is larger in winter than in summer owing to the effect of the mid‐latitude ‘winter anomaly’ in combination with strong antisunward convection. (3) In both summer and winter, the major region of low electron density is associated with the main or mid‐latitude trough. The trough is deeper and its local time extent is much greater in winter than in summer. (4) Typically, the electron density exhibits a much larger variation with altitude in winter than in summer. (5) The ion composition and molecular/atomic ion transition altitude are highly UT dependent in both summer and winter. (6) The ion composition also displays a significant seasonal variation. However, at a given location the seasonal variation can be opposite at different universal times. (7) High‐speed convection cells should display a marked seasonal variation, with a much larger concentration of molecular ions near the F region peak in summer than in winter.
The probability distribution of S+ gyrospeeds in the Io torus
Authors: Brown Robert A.
Published: February 2008

We report a measured probability distribution for S+ gyrospeeds in the Io torus derived from [S II] 6716 Å, 6731 Å emission line profiles recorded at axial distance 5.9 RJ from Jupiter. This ion species is not in kinetic thermodynamic equilibrium. An artificial spectral decomposition in terms of three Maxwellian distributions finds perpendicular temperatures T⊥ = 2.7, 28, and 192 eV with weights 0.28, 0.50, and 0.22, respectively. The average temeprature is about 60 eV, which would be seriously underestimated by a simple measurement of the line width. We find upper limits of ∼5% or ∼20% to the mixing ratios of S+ ions having the pickup speed of ionized ballistic atoms, assuming a flat or isotropic pitch angle distribution, respectively. Due to the low S+ density and charge, Coulomb collisional power transfer from the observed S+ population to the ambient electrons delivers only 0.01 eV cm−3 s−1, or 1/40 the UV emission power requirement. Existing [S III] linewidth temperatures indicate S2+ is hotter than S+, indicating that kinetic thermodynamic equilibrium exists neither between nor within species in the hot, outer plasma torus.
Electrodynamic properties of the evening sector ionosphere within the region 2 field‐aligned current sheet
Authors: Robinson Robert M. , Vondrak Richard R. , Potemra Thomas A.
Published: February 2008

Chatanika radar measurements were combined with magnetometer data from the Triad satellite to relate the electrodynamic properties of the ionosphere to field‐aligned currents. Radar electric field and electron density data were studied for eight evenings during which the region 2 (downward) field‐aligned current was entirely within the radar field of view. In all cases the downward current region coincided with an E region electron density that increased to the north. The equatorward boundary of the current sheet was associated with maximum E region densities of about 1 × 105 el/cm³. The poleward boundary of the current sheet was always characterized by a local maximum in E region ionization referred to as the interface arc. The ionospheric perpendicular current was generally northeastward within the downward current sheet. The gradient in the northward ionospheric current was used to compute field‐aligned currents, which were in good agreement with those measured by Triad.
EUV emission from Titan's upper atmosphere: Voyager 1 encounter
Authors: Strobel Darrell F. , Shemansky D. E.
Published: February 2008

Analysis of Titan's EUV emission spectra obtained at the Voyager 1 encounter demonstrates that electron impact on N2 above 3600 km accounts for the bulk of the observed emission short of Lyman α. In conjunction with the UVS solar occultation data it is concluded that N2 is the major component of Titan's upper atmosphere, with upper limit mixing ratios at 3900 km on NeI, ArI, CO, H2, and HI of 0.01, 0.06, 0.05, 0.06, and 0.1, respectively. Magnetospheric electrons interact with Titan's sunlit hemisphere to produce a power dissipation rate of ≃2 × 109 W in the exosphere and ≃3 × 109 W below the exobase, with optical signatures from numerous N2 bands, NI, and NII multiplets. The N2 C4′ (0‐0) Rydberg band at 958 Å acts as an optical probe of Titan's exosphere because of transmission losses caused by fluorescence and predissociation. Magnetospheric electron precipitation produces an average dayside electron density of ≃3 × 10³ cm−3 between 3600 and 4000 km, the region of bright limb emission. When Titan is within Saturn's magnetosphere, magnetospheric electron impact dissociation of N2 generates an N atom escape rate of ≃3 × 1026 s−1 from Titan's exosphere. A nonthermal H atom escape rate of ≃2 × 1026 s−1 is estimated from magnetospheric electron impact ionization of N2 followed by reactions with CH4 and H2 and recombination to produce hot H atoms.