bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of Pc 1–2 waves in the outer magnetosphere
Authors: Kaye Stanley M. , Kivelson Margaret G.
Published: February 2008

High time resolution measurements made inside the magnetopause from L=7 to L=14 by the University of California at Los Angeles fluxgate magnetometer aboard the Ogo 5 satellite demonstrate that Pc 1–2 magnetic field oscillations are occasionally present in portions of the outer magnetosphere. Eleven events have been studied so far, and all of them occurred in the afternoon sector at geomagnetic latitudes from 0° to ±30°. Both the solar wind dynamic pressure and the magnetospheric cold plasma density were enhanced during events for which the respective data were available. The IMF had a southward component approximately 2 hours before the events; however, there was no significant correlation between the time of the events and either storm recovery phase or substorm onset. The magnetic field perturbations in each event were primarily transverse to the ambient field with amplitudes ranging from 2 to 8 γ; however, small compressional oscillations, evidenced by 1‐ to 2‐γ fluctuations in the total field magnitude, were sometimes present. Most of the transverse perturbations exhibited left‐handed polarization. Brief excursions into the magnetosheath during two of the events revealed a highly disturbed magnetic field with significant power in frequencies of ≥0.1 Hz. Although the magnetosheath was a source of free energy for waves at Pc 1–2 frequencies, the data within the magnetosphere suggest that the observed pulsations were ion cyclotron waves generated at the geomagnetic equator at large radial distances.
High‐latitude field‐aligned current sources and induced electric fields
Authors: Barbosa D.D.
Published: February 2008

Using a simple, planar model of the high‐latitude ionosphere with an enhanced conductivity auroral ring, we compute the electric potential for a pair of field‐aligned current sheets inferred from observations. The relationship of various characteristics of the electric potential pattern to features of the field‐aligned current distribution are elucidated in the context of a generalized field‐aligned current Fourier analysis. On the basis of our analysis and observations to date we conclude that boundary layer dynamo action is the prevalent mechanism in the solar wind/magnetosphere/ionosphere interaction.
Solar cycle variations in IMF intensity
Authors: King Joseph H.
Published: February 2008

Annual averages of logarithms of hourly interplanetary magnetic field (IMF) intensities, obtained from geocentric spacecraft between November 1963 and December 1977, reveal the following solar cycle variation. For 2–3 years at each solar minimum period, the IMF intensity is depressed by 10‐15% relative to its mean value realized during a broad 9‐year period centered at solar maximum. No systematic variations occur during this 9‐year period. The solar minimum decrease, although small in relation to variations in some other solar wind parameters, is both statistically and physically significant.
Intense interplanetary magnetic fields observed by geocentric spacecraft during 1963–1975
Authors: Burlaga L.F. , King J.H.
Published: February 2008

Ninety‐two percent of the intense magnetic fields (>13 γ) observed at 1 AU during solar cycle 20 (1963–1975) were associated with shocks, stream interfaces, or cold magnetic enhancements (CME's). Most (52%) of the magnetic field intensity enhancements occurred at stream interfaces; 27% occurred behind shocks without interfaces; and 11% occurred in CME's. The most intense fields (25–37 γ) followed shocks. Magnetic field intensities at interfaces did not exceed 25 γ, suggesting that some mechanism limits the intensity ahead of streams. The intensities in CME's did not exceed 20 γ. Intense magnetic fields persisted longest behind shocks. During the period 1973–1975, interface‐associated enhancements occurred 3.5 times as frequently as shock‐associated enhancements, and during an earlier period (1967–1969) when the sun was more active, shock‐associated enhancements occurred 1.2 times as frequently as interface‐associated enhancements. The frequency of CME's was the same in both periods. The absolute occurrence frequency of interface‐associated enhancements increased by a factor of 2.4 in going from the early period to the later period, while the absolute occurrence frequency of shock‐associated enhancements decreased by a factor of 1.7 in going from the early to the late period.
A Quasi‐static model of global atmospheric electricity 2. Electrical coupling between the upper and lower atmosphere
Authors: Roble R. G. , Hays P. B.
Published: February 2008

A model of global atmospheric electricity is used to examine the influence of upper atmospheric generators, such as the ionospheric dynamo and the high‐latitude generator associated with magnetospheric convection, upon the global electrical circuit. The model for the lower atmosphere has been described in paper 1 (Hays and Roble, 1979). It includes the effects of orography, and it represents thunderstorms as dipole current generators randomly distributed in areas of known thunderstorm frequency. The electrical conductivity in the model increases exponentially with altitude, and electrical effects are coupled with a passive magnetosphere along geomagnetic field lines. The model determines the electric potential on the basis of an assumed spatial distribution of thunderstorm current sources. The large horizontal‐scale potential differences at ionospheric heights that are associated with the ionospheric dynamo and magnetospheric convection during geomagnetic quiet times, map effectively downward into the lower atmosphere, where perturbations of ±20% in the ground electric field and air‐earth currents at high latitudes are superimposed upon the diurnal variation that is established by worldwide thunderstorm activity. During geomagnetic storms and auroral substorms the perturbations are highly variable but are generally greater and occur futher equatorward. Any current imbalance caused by the superimposed ionospheric potential patterns requires a readjustment of the global fair weather potential difference between the ground and ionosphere to maintain the divergence of air‐earth current on a global scale equal to zero. Changes in upper atmospheric conductivity due to solar flares, polar cap absorptions, and Forbush decreases are shown to alter the downward mapping of the high‐latitude potential pattern and the global distribution of fields and currents.
Ionization, luminosity, and heating of the upper atmosphere of Mars
Authors: Fox J. L. , Dalgarno A.
Published: February 2008

A model based upon Viking data is constructed of the Martian atmosphere, and a comprehensive quantitative discussion is given of the measurements of the ultraviolet dayglow. A detailed assessment is made of the heating of the neutral and ionized components of the atmosphere arising from the absorption of ultraviolet solar radiation.
A source for the geomagnetic storm main phase ring current
Authors: Lyons L.R. , Williams D.J.
Published: February 2008

It is shown that the flux increases of trapped ions and electrons observed by Explorer 45 at L≤4 during two large geomagnetic storms can be quantitatively explained by a 1–3 RE inward radial displacement of the preexisting trapped particle distribution. This proposed source for the storm time ring current at L≤4 requires only the acceleration of the previously existing trapped particle population via inward displacement under conservation of the first two adiabatic invariants. No source of new trapped particles at L≤4 is required. It was not possible to test whether such an inward radial displacement can account for storm time flux increases at any radial distances beyond L=4; however, the existence of particle losses implies that new particles are injected into the trapping region beyond L=4. The required inward radial displacements of the trapped particles can be explained by an equatorial electric field with an average azimuthal component of ∼0.3–1.0 mV/m, which is a factor of 2 or 3 greater than electric fields observed within the plasmasphere in association with typical, nonstorm time, substorm activity. It is suggested that a significant difference between large geomagnetic storms and typical substorm activity may be inward convection occurring over a large (≳270°) longitude range during storms but only over a small (≲90°) longitude range during typical substorms.
Prompt striations in ionospheric barium clouds due to a velocity space instability
Authors: Simons D.J. , Pongratz Morris B. , Gary S. Peter
Published: February 2008

The linear theory of electrostatic instabilities of the drift loss‐cone type has been developed for a velocity distribution appropriate to the shaped‐charge barium injection experiment Buaro. The dispersion relation for the instability in a Vlasov plasma has been solved numerically. The results show a low‐frequency instability that we interpret as the source of prompt striations observed in Buaro and cyclotron instabilities that appear to correspond to observed ion cyclotron fluctuations. These instabilities have much faster growth rates than drift instabilities of fluid theories and therefore provide a better description of the observations.
Computer studies of the dynamic evolution of the geomagnetic tail
Authors: Birn J.
Published: February 2008

The dynamic evolution of a stretched magnetotail configuration is investigated numerically by means of a two‐dimensional time‐dependant nonlinear resistive MHD code. The initial configuration is shown to be stable in ideal MHD. The unstable evolution is initiated by imposing a finite resistivity.

Rather independently of the boundary conditions, the following phenomena develop spontaneously: plasma sheet thinning, topological changes of the magnetic field configuration, the formation of neutral lines with an almost stationary X line, large induced cross‐tail electric fields, conversion of magnetic to kinetic energy resulting in strong earthward and tailward flow close to the neutral sheet, and outside the neutral sheet a significant part of the flow parallel to the magnetic field. This flow reverses sign across the plasma sheet boundary tailward of the X line. The results support the tearing theory of magnetospheric substorms. At the later stages the configuration around the X line is similar to that obtained from steady state reconnection theory; in particular we found that two current layers form downstream of the magnetic field separatrix, which may represent structures developing into slow shock waves.
Side‐band mutual interactions in the magnetosphere
Authors: Chang D.C.D. , Helliwell R.A. , Bell T.F.
Published: February 2008

Man‐made whistler‐mode waves (WM) in the magnetosphere can interact with other WM waves at nearby frequencies. This interaction must involve nonlinear processes because linear mechanisms cannot explain energy exchange between waves at different frequencies. Using the Siple VLF transmitter, an experiment was performed to determine the critical frequency seperation within which wave‐wave interaction (WWI) occurs. Using frequency‐shift‐keying (FSK) modulation techniques, several constant‐frequency waves (side bands) were generated simultaneously. Preliminary results show that the energetic electrons in the magnetosphere can interact only with side bands generated by signals with short modulation periods, indicating that electrons have a finite ‘memory time’ during interaction with the waves. Using the value of this memory time, the length of the electron interaction region is estimated to lie between 2000 and 4000 km. It is also found that side bands with less than 50‐Hz spacing mutually interact. Suppression and energy coupling among the side bands are often observed. The experiments in general reveal that 50 Hz is the order of magnitude of the critical frequency range within which side bands interact. Mutual interaction between two side bands is explained by the overlap of the ranges of the parallel velocity (V∥) of electrons which the side bands can organize. The electrons in the overlap can exchange energy with both side bands and thus are responsible for the interaction. By estimating the size of the perturbed V∥ range the wave intensity is estimated to be of the order of 2.5–10 mγ, in good agreement with satellite measurements.
Conical distributions of low‐energy ion fluxes at synchronous orbit
Authors: Horwitz J.L.
Published: February 2008

Low‐energy ion fluxes observed at synchronous orbit often display conical pitch angle distributions, that is, peak fluxes between 0° and 90° to the magnetic field direction. They are observed at all local times and are an especially common occurrence near dusk. The conic peaks normally occur in the 15°–35° pitch angle range. Many of the low‐energy ion conics in the late afternoon‐dusk sector appear to be associated with low‐energy plasma from the vicinity of the dusk plasmasphere bulge region. Several hypotheses for the production of these conics are advanced, and it is judged likely that cyclotron acceleration of ions at geocentric distances of 3.1 to 5.1 RE is operative in many cases. It is suggested that cyclotron acceleration in this altitude range may be an effective mechanism in trapping ionospheric ions within the magnetosphere.
Satellite vacuum ultraviolet airglow and auroral observations
Authors: Huffman R.E. , LeBlanc F.J. , Larrabee J.C. , Paulsen D.E.
Published: February 2008

Global observations of the airglow, aurora, and solar scatter radiance of the earth's atmosphere have been made in the 1100‐ to 2900‐Å wavelength region. The spectrometer and photometer utilized were pointed toward the earth center at all times on the polar‐orbiting Department of Defense satellite S3‐4. The experiment is described, and initial measurements are discussed. These measurements include detection of the nitrogen Lyman‐Birge‐Hopfield bands in the nightglow as well as in the dayglow. In addition, nitric oxide delta and gamma bands and oxygen Herzberg bands are found in the nightglow. VUV auroral enhancement and the tropical UV airglow due to atomic oxygen emission are also discussed.
The structure of localized nighttime auroral zone scintillation enhancements
Authors: Rino C.L. , Owen J.
Published: February 2008

Simultaneous observations of the polar‐orbiting Wideband satellite at two auroral zone stations (separated by approximately 200 km along the geomagnetic meridian) were made during November 1977. The latitudinal distribution of the average scintillation occurrence at each station shows a local maximum at the point where the propagation vector lies within an L shell. This supports the hypothesis that the enhancement is a geometrical effect due to L shell aligned, sheetlike irregularities. The detailed structure of the average scintillation occurrence as well as the scintillation patterns on individual passes shows, however, that the source regions are confined in latitude. From a detailed analysis of total electron content data we were able to show that the local scintillation enhancements occur in a region of enhanced F region ionization with a steep gradient at its equatorward edge. The source region lies within the general confines of the diffuse aurora, often with too limited a latitudinal extent to cause an enhancement at both stations. These new results are discussed in light of recent theoretical analysis by Ossakow and Chaturvedi that shows that the current convective instability, which is essentially a stable E×B configuration destabilized by moderate field‐aligned currents, can explain the irregularities. The sheetlike structure is a result of the nonlinear saturation of the instability. The linearly unstable mode, which would give rise to meridional structures, is nonlinearly damped while the dominant nonlinearity favors the perpendicular modes that cause the sheetlike structures.
Plasma line measurements at Chatanika with high‐speed correlator and filter bank
Authors: Kofman Wlodek , Wickwar Vincent
Published: February 2008

In the spring and fall of 1978 we made an extensive series of plasma line and correlative observations with the Chatanika incoherent scatter radar. To make these measurements, we greatly modified the radar receiving system. In addition to enlarging the plasma line filter bank the most significant change was the incorporation of a high‐speed correlator provided by the French. This was the first use of a correlator in a monostatic radar to obtain the intensity spectra of naturally occurring plasma lines. In this paper we develop the signal‐processing theory that we use to obtain the plasma line intensities from these measurements; we also show that these intensities compare well with those obtained from the filter bank. To show the richness of the phenomena and to explore the capabilities of the correlator, we examine a wide variety of spectra that have been enhanced by secondary electrons in the auroral E layer. From the other simultaneous measurements we are able to relate these spectra and their variations to the auroral situation. We also obtained the first measurements in the auroral region of photoelectron‐excited plasma lines in the E and F layers. Perhaps most significant, in the plasma line spectra we detected a Doppler shift that we then used to determine the Birkeland current carried by ambient electrons. Although there is a large estimated uncertainty for this first determination, we obtained a downward Birkeland current of 10 μA/m² in the diffuse aurora in what is, most likely, the equatorward portion of the evening sector auroral oval.
Power threshold for growth of coherent VLF signals in the magnetosphere
Authors: Helliwell R.A. , Carpenter D.L. , Miller T.R.
Published: February 2008

It is well known that coherent VLF signals injected into the magnetosphere from Siple Station, Antarctica, often show temporal growth of 20–30 dB and emission triggering, as observed at the conjugate point, near Roberval, Quebec. In a new kind of experiment it has been found that when the input power to the transmitting antenna is reduced below a ‘threshold’ value Pt, growth and triggering cease. Below Pt the output is proportional to the input. In one typical experiment the peak received power increased by 24 dB when the input power to the antenna crossed the threshold value of 1000 W (estimated radiated power of 10 W). The value of Pt varied widely depending on the duct involved and on the time, changing as much as 10 dB in less than 1 hour. As the power was lowered during multipath propagation, the last duct to be cut off was found to terminate nearly overhead at Siple, as was expected, assuming all ducts to be equally active. Minimum radiated power for growth and triggering was 1 W. One possible explanation for the threshold effect is background noise (e.g., plasmaspheric hiss) that prevents the instability from getting started. Another is a drop in temporal growth rate to below zero at low signal level. Measurement of Pt might possibly serve as a ground‐based diagnostic for magnetospheric flux levels, assuming calibration by satellite particle detectors.
Hydromagnetic wave modulation of substorm particle precipitation at L ∼4
Authors: Lanzerotti L.J. , Maclennan C.G. , Rosenberg T.J.
Published: February 2008

Observations are presented on the modulation by hydromagnetic waves (irregular periods ∼30 s; Pi 2 classification) of particle (electron) precipitation during two small cosmic noise absorption events observed at geomagnetic latitude ∼60°S (particle drift shell L ≳4). The particle precipitation and modulation occur in the region of a near linearly polarized hydromagnetic wave. The overall particle precipitation appears to be controlled by magnetospheric dynamics, while the modulation of the precipitation is controlled by the hydromagnetic waves.
Seasonal‐latitudinal tidal structures of O, N2, and total mass density in the thermosphere
Authors: Forbes Jeffrey M. , Marcos Frank A.
Published: February 2008

The seasonal‐latitudinal tidal structures of O, N2, and total mass density in the thermosphere for minimum and maximum levels of solar activity are investigated by using a theoretical model and accelerometer data from the Atmosphere Explorer C, D, E, and Air Force S3‐1 satellites. According to theory, oxygen variations are strongly influenced by seasonal differences in the winds, whereas N2 responds primarily to temperature, which has a different seasonal dependence than the winds. The tidal variation of total mass density is complicated by its dependence on the relative amplitudes and phases of the O and N2 variations. The net effect is that rather complicated and different seasonal‐latitudinal tidal structures are predicted to occur. Some representative theoretical profiles are presented. Theoretical height structures of diurnal amplitude and phase of O and N2 near the equator are in good agreement with recently published tidal analyses of Atmosphere Explorer E mass spectrometer data. Tidal analyses of the accelerometer data verify the shift to later times of the diurnal phase of total mass density from the equator to mid‐latitudes in the lower thermosphere as predicted by theory.
Fast fluctuations in the arrival bearing of magnetospherically propagating signals from the Siple, Antarctica, VLF transmitter
Authors: Carpenter D.L.
Published: February 2008

Signals propagating from the Siple, Antarctica, VLF transmitter to the conjugate station at Roberval, Quebec, Canada (L∼4.2), are generally multipath in nature. From previously reported initial observations at Roberval with a tracking receiver/direction finder (TR/DF) it was found that the directional properties of the received signals were stable for only minutes at a time, compared to the tens of minutes that had been expected from earlier dispersion analyses of whistlers. This effect was further investigated in the present study of TR/DF observations of multipath Siple signals in 1977. In a case study from May 20, 1977, the TR/DF consistently obtained directional information on the arrival bearings of multipath signals whose amplitude at the receiver was ∼5 dB or more above that of other signals within the 340‐Hz passband of the frequency‐tracking filter. It was found that the arrival bearing of the strongest signal shifted widely within minutes. The sequence of shifts over a 1‐hour period, coupled with the occasional appearance of power line radiation activity, may possibly be induced by the eastward gradient drift of low‐energy (≃1–2 keV) ‘clouds’ of electrons through a pattern of whistler ducts. This interpretation was suggested by the rapidity (∼10–100 s) with which signal amplitudes rose and fell by greater than ∼10 dB on individual paths. The sudden turn‐ons and turn‐offs are tentatively attributed to the ‘threshold’ effect being reported elsewhere, in which temporal growth of Siple transmitter signals suddenly occurs as the amplitude of the injected waves reaches a particular level. In the present case the phenomenon is believed to occur at constant wave level as the result of changes in particle flux associated with drifting structure in the low‐energy electrons. Other effects observed in the primary case study were a slow northward movement on a time scale of about 30 min of the bearing of the stronger signals. This movement is believed to be associated with quiet‐day convection. Also observed were small‐scale (Δθ ∼10°–20°) fluctuations on a time scale of several minutes in the arrival bearing of signals from a particular path. These fluctuations may be due to a temporal modulation of propagation conditions between the ‘ends’ of magnetospheric ducts and the lower boundary of the ionosphere.
Trigger, An active release experiment that stimulated auroral particle precipitation and wave emissions
Authors: Holmgren G. , Boström R. , Kelley M.C. , Kintner P.M. , Lundin R. , Fahleson U.V. , Bering E.A. , Sheldon W.R.
Published: February 2008

Models of auroral processes have been advanced in which the ionosphere plays an active role in stimulating auroral particle precipitation. The validity of these suggestions can be investigated by releasing an artificial plasma cloud into the ionosphere and studying the effects. To this end, the sounding rocket experiment Trigger, comprising a diagnostic and a chemical release payload, was conducted. As a consequence of the release, a drastic increase of the field‐aligned charged particle flux was observed over the approximate energy range 10 eV to more than 300 keV, starting about 150 ms after the release and lasting about 1 s. There is also evidence of a second particle burst, starting 1 s after the release and lasting for tens of seconds. In addition, there is evidence for a periodic train of particle bursts occurring with a 7.7‐s period from 40 to 130 s after the release. A transient electric field pulse of 200 mV/m appeared just before the particle flux increase started. Electrostatic wave emissions around 2 kHz, as well as a delayed perturbation of the E region below the plasma cloud were also observed. Some of the particle observations are interpreted in terms of field‐aligned electrostatic acceleration a few hundred kilometers above the injected plasma cloud. It is suggested that the accelerating electric field was created by an instability driven by field‐aligned currents caused by the plasma cloud release. This paper gives an overview of the experiment design and the general result. Particular observations and their interpretation are discussed in more detail in companion papers.
Mid‐latitude winter nighttime increases in the total electron content of the ionosphere
Authors: Essex E. A. , Klobuchar J. A.
Published: February 2008

A study is made of winter nighttime increases in the total electron content of the ionosphere over the North American region using data from several total electron content stations and from several geostationary satellites for the month of December for the years 1971, 1974, and 1975. The increases are preceded by substorm activity and enhancements in the total electron content of the ionosphere in the auroral regions. Total electron content nighttime increases are accompanied by large increases in the peak density of the F layer and a lowering of the layer height. At mid‐latitudes most of the enhancements occur after midnight (local time) with a marked maximum around 0300 hours (local time). The spatial extent of the enhancements tends to increase with increasing levels of magnetic activity. The enhancements appear to occur at a constant local time, giving an apparent westward motion. The winter nighttime increases are not accompanied by large changes in the plasmaspheric content. Mechanisms to explain the winter nighttime enhancements are discussed. Low mid‐latitude total electron content increases appear to be controlled by mechanisms different from those operating at higher latitudes.
Transport of ionospheric O+ ions across the Venus terminator and implications
Authors: Knudsen William C. , Spenner Karl , Miller Kent L. , Novak Vit
Published: February 2008

Vector velocities of O+ ions in the Venus ionosphere are reported for the dawn and dusk terminator regions. The velocity vectors are generally directed antisunward and radially inward toward the planet with magnitudes ranging from approximately 1 to 8 km/s. The velocity generally increases with altitude. The velocity may increase to still larger values just below the ionopause, but experimental limitations prevent measuring such an increase. The Alfvén and ion Mach numbers are generally greater than 1. The estimated O+ flux across the terminator is equal within a factor of 2 to the total ion recombination rate on the nightside and is evidently a factor of 10 larger than that which could be exiting down the planet wake. The higher velocity flow near the ionopause is hypothesized to converge on the antisolar axis and, after thermalization, to descend into the ionosphere. The kinetic energy and O+ flux in this high‐velocity stream are sufficient to maintain, respectively, the high ion temperature and peak ion concentration, respectively, measured at solar zenith angles in excess of 150°. The nightside ionospheric variability is hypothesized to result from temporal and spatial variations in the ionospheric terminator and wake flow fields. Ion transport contributes substantially and possibly predominantly to the maintenance of the nightside ionosphere.
Electron temperature derived from incoherent scatter radar observations of the plasma line frequency
Authors: Hagfors T. , Lehtinen M.
Published: February 2008

Methods are described whereby it is possible to measure directly electron temperatures by observations of the plasma line in incoherent scatter radar experiments. The method is based on simultaneous observations of plasma lines at different spatial scales. It is described how the observations can be implemented either as a combination of monostatic and bistatic observations at one radar frequency or as a dual frequency backscatter experiment.
The source of proton anisotropy in the high‐speed solar wind
Authors: Schwartz Steven J. , Feldman William C. , Gary S. Peter
Published: February 2008

Two factors which can contribute to proton anisotropy in the high‐speed solar wind are investigated. We present evidence that observed proton T⊥ >T∥ anisotropies are maintained locally by plasma instabilities driven by proton and helium beams. The transfer of beam energy to T⊥ by means of these instabilities is shown to be sufficient to account for the aforementioned proton temperature anisotropy.
Interplanetary ions during an energetic storm particle event: The distribution function from solar wind thermal energies to 1.6 MeV
Authors: Gosling J. T. , Asbridge J. R. , Bame S. J. , Feldman W. C. , Zwickl R. D. , Paschmann G. , Sckopke N. , Hynds R. J.
Published: February 2008

Data from the Los Alamos Scientific Laboratory/Max‐Planck‐Institut fast plasma experiment on Isee 2 have been combined with data from the European Space Agency/Imperial College/Space Research Laboratory low‐energy proton experiment on Isee 3 to obtain for the first time an ion velocity distribution function f(ν) extending from solar wind energies (∼1 keV) to 1.6 MeV during the postshock phase of an energetic storm particle (ESP) event. This study reveals that f(ν) of the ESP population is roughly isotropic in the solar wind frame from solar wind thermal energies out to 1.6 MeV. Emerging smoothly out of the solar wind thermal distribution, the ESP f(ν) initially falls with increasing energy as E−2.4 in the solar wind frame. Above about 40 keV no single power law exponent adequately describes the energy dependence of f(ν) in the solar wind frame. Above ∼200 keV in both the spacecraft frame and the solar wind frame, f(ν) can be described by an exponential in speed (f(ν) ∝ e−ν/ν0) with ν0=1.05 × 108 cm s−1. The ESP event studied (August 27, 1978) was superposed upon a more energetic particle event which was predominantly field‐aligned and which was probably of solar origin. Our observations suggest that the ESP population is accelerated directly out of the solar wind thermal population or its quiescent suprathermal tail by a stochastic process associated with the shock wave disturbance. The acceleration mechanism is sufficiently efficient that ∼1% of the solar wind population is accelerated to suprathermal energies. These suprathermal particles have an energy density of ∼290 eV cm−3.
On 11‐cm irregularities during equatorial spread F
Authors: Huba J. D. , Ossakow S. L.
Published: February 2008

The recent Kwajalein radar backscatter observations of 11‐cm irregularities at high altitudes (∼500 km) during equatorial spread F are explained in terms of the kinetic lower‐hybrid‐drift instability. The absence of radar backscatter from 11‐cm irregularities at lower altitudes (∼240 km) is attributed to the stabilizing influence of electron‐neutral collisions.
Unstable potential of geosynchronous spacecraft
Authors: Besse Arthur L.
Published: February 2008

The potential of a geosynchronous spacecraft and of various portions of its surface may become unstable and undergo large potential jumps. A time varying strongly non‐Maxwellian plasma and secondary electron emission play key roles in the theory.
Double layers and electrostatic shocks
Authors: Hershkowitz Noah
Published: February 2008

It is shown that it is useful to define double layers and shocks so that the ion phase spaces of double layers are shown to be just the mirror image (about zero ion velocity) of the ion phase spaces for laminar electrostatic shocks. The distinguishing feature is the direction of the free ion velocity. It is also shown that double layers can exist without the presence of trapped ions. The Bohm condition for double layers, that the ion drift velocity on the high potential side must be greater than the ion sound velocity, is shown to be related to a requirement of a lower limit on the Mach number of laminar electrostatic shocks.
The Cameo Barium Releases: E∥ fields over the polar cap
Authors: Heppner J. P. , Miller M. L. , Pongratz M. B. , Smith G. M. , Smith L. L. , Mende S. B. , Nath N. R.
Published: February 2008

Four successive thermite barium releases at an altitude of 965 km over polar cap invariant latitudes 84° to 76° near magnetic midnight were conducted from the orbiting second stage of the vehicle that launched Nimbus 7. This was the first opportunity to observe the behavior of a conventional barium release when conducted at orbital velocity in the near earth magnetic field and to demonstrate that the μ▽B force at orbital velocity would accelerate the Ba+ ions to much greater altitudes for measuring E∥ fields by observing perturbations in the motion of the visible ions. The principal unexpected characteristic in the release dynamics was the high, 1.4 to 2.6 km/s, initial Ba+ expansion velocity relative to an expected velocity of 0.9 km/s. Characteristics of the neutral gas expansion are also discussed. Under the combined influence of μ▽B and E∥ forces the finely striated Ba+ streamers from the 8 kg releases elongated along the field to dimensions >10,000 km and were photographed from California and Hawaii as well as higher latitude sites. Although observed up to one hour after release and to elevation angles >55° from Southern California, triangulations of upper tips were limited to the initial 25 min and altitudes <23,000 km. The average E⊥ convection of the Ba+ flux tubes was very normal for Kp=3 conditions and closely followed model patterns for convection between the pole and the midnight auroral zone. However, over shorter space‐time dimensions the E⊥ field is observed to be irregular; this also is a normal polar cap condition. From the analysis of field aligned motions in terms of the potential changes required in the equation of motion to match the altitude versus time observations: (1) E∥ fields do not appear below 1400 km, (2) between 1500 and 4200 km the changes in energy are typically 20–40 eV with a 71 eV maximum, (3) between 4200 and 15,000 km maximum values are in the range 80–720 eV with the highest values coming from the highest latitude releases, and (4) in the case of one release a 6 keV acceleration appears above 15,800 km. These changes appear as both accelerating (upward E∥) and decelerating (downward E∥) fields with an apparent periodicity of 3 to 4 min and are in phase at all four locations for 3, and possibly 4 or 5, cycles within the limitations imposed by a 1 min resolution and data gaps. This apparent wave characteristic could, under selective error assumptions, result from several impulsive decelerations superimposed on a more general, but variable, accelerating field. This possibility is considered to be less likely than a hydromagnetic wave association. The unique capabilities for measuring very weak fields and for separating temporal and spatial variations may explain the lack of precedent from previous E∥ measurements.
Vertical transport and photochemistry in the terrestrial mesosphere and lower thermosphere (50–120 km)
Authors: Allen Mark , Yung Yuk L. , Waters Joe W.
Published: February 2008

The coupled effects of kinetics, solar cycle flux variations and vertical transport on the distribution of long‐lived hydrogen‐carbon‐oxygen compounds in the terrestrial mesosphere and lower thermosphere are studied using a one‐dimensional aeronomy model. The calculations account for the important chemical reactions and use rocket measurements of the solar flux at solar minimum and maximum. Photodissociation rates appropriate for the mesosphere are determined with a spherical shell atmosphere formalism; detailed corrections for the O2 Schumann‐Runge bands and the temperature dependence of the CO2 cross sections are used. Then an eddy diffusion profile is derived which gives agreement with the Aladdin 74 mass spectral measurements of atomic O, O2, CO2, and Ar in the lower thermosphere and observations of the O3 minimum at ∼80 km. The 115 GHz CO radio emission line computed for the CO mixing ratio profile predicted with the new eddy diffusion profile compares well with recent observations of W. J. Wilson. Differences between the calculated CO mixing ratio profile and previous theoretical and observational determinations are discussed. Our derived eddy diffusion profile has a sudden decrease at 92 km which is necessary to produce the atomic O peak at 98 km that appears in the Aladdin 74 measurements. This stagnant region apparently is a recurrent or persistent feature of the upper atmosphere since an atomic O peak around 98 km has been seen by different techniques in different seasons over several years. Slow eddy diffusion in the lower thermosphere through the homopause was also the conclusion of earlier Ar/N2 rocket measurements studies. The analytic approach of this paper could be used in the future to monitor variations in middle atmosphere dynamics, if regularly conducted simultaneous observations of various groups of species were available.
IMF sector behavior estimated from geomagnetic data at South Pole
Authors: Matsushita S. , Xu W. ‐Y.
Published: February 2008

IMF sector behavior which has previously been estimated from the geomagnetic data at Godhavn is confirmed by study of the data at South Pole for 1959–1970 with the same estimation technique, taking the difference between northern and southern hemispheres into consideration. A method to improve (about 18%) the agreement between assigned and actual sector structures by study of the data at the two stations is suggested. Geomagnetic disturbance effects on sector estimation are discussed, and reversed sector effects in winter are given special emphasis.
Asymmetric access and temporal variations of energetic solar protons at the polar caps
Authors: Ifedili S. O.
Published: February 2008

Data from the low‐altitude polar orbiting satellite Ogo 6 showed that the ratio north/south (N/S) of the intensity of solar protons (Ep >50 Mev) over the earth's north (N) polar cap (λ >70°) to that over its south (S) polar cap (−λ >70°) was about 1.61±0.04 for the solar particle event of November 2, 1969, and 1.00±0.03 for the event of December 18, 1969, while the ratio N/S was 0.64±0.02 for the solar particle event of December 19, 1969. These results, considered together with the interplanetary magnetic field polarities and the interplanetary proton anisotropies, favor the open model of the magnetosphere. The data also showed a clear evidence of periodic temporal variations of the proton flux over the polar caps; the pulsation effects had frequencies in the same range as the Pc4 and Pc5 geomagnetic micropulsations and were attributed to magnetohydromagnetic waves.
Stability theory of driftlike electromagnetic waves in two‐dimensional magnetic fields
Authors: Migliuolo S. , Patel V. L.
Published: February 2008

A two‐component (hot and cold) magnetospheric plasma, with spatially varying densities and temperatures, is considered for the case where the equilibrium magnetic field is two‐dimensional: B=êzBz(x, z) + êxBx(x, z). Such a slab geometry includes the effects of field line bending, to first order. A linear theory of low‐frequency electromagnetic perturbations is developed, for long perpendicular wavelength modes (|▽ 1n n|−1 ∼λy ≲λx). We consider modes that are driven unstable by internal sources of free energy: the spatial gradients in density, temperature, and B field. The electrons of the cold component determine the polarization of the perturbed field (Bly <Blx, Blz). The unperturbed orbits of the hot plasma particles consist of the fast cyclotron gyration coupled with the cross‐field drifts and with a slow bounce motion along the principal (i.e., z) direction of the unperturbed B field. A fluidlike instability of the drift‐compressional mode is found to occur, for both the ion‐drift and electron‐drift branches of the mode. A critical value of the field curvature scale length is found, below which this mode is stable. Analytic expressions for the eigenfrequency and eigenvector are given. The perturbed fields are found to be strongly localized in the x direction.
Simultaneous measurements of OH(9,4), (8,3), (7,2), (6,2) and (5,1) bands in the airglow
Authors: Takahashi H. , Batista P. P.
Published: February 2008

Band intensities and the rotational temperatures for the OH(9,4), (8,3), (7,2), (6,2) and (5,1) bands have been measured by means of a multichannel tilting filter photometer at Cachoeira Paulista (22.7°S, 45.0°W), Brazil. It is observed that the nocturnal variations of the five bands show good correlation between them but that there are small differences in the amplitudes of the variations between the bands from the upper vibrational levels and those from the lower levels. Studies of the cross correlation between the band intensities show that the nocturnal variations of the upper vibrational bands lead those of the lower levels. Vibrational populations and initial excitation rates for each vibrational level are calculated. The results show an increase of the initial excitation rate in the v=5 and v=6 levels. The different features of the intensity variations and the excitation rates of the lower vibrational levels suggest the existence of the mechanism HO2 + O → OH* + O2, capable of exciting OH to the v=5 and v=6 levels, in addition to the principal mechanism, assumed to be the reaction H + O3 → OH* + O2. The rotational temperatures derived from the ratios between the Q and R branches show good agreement between the different bands, indicating a high degree of rotational relaxation by thermal collisions.
Composition and thermal profiles of the Jovian upper atmosphere determined by the Voyager Ultraviolet Stellar Occultation Experiment
Authors: Festou M. C. , Atreya S. K. , Donahue T. M. , Sandel B. R. , Shemansky D. E. , Broadfoot A. L.
Published: February 2008

Occultation of the star Regulus—α Leo—by the Jovian atmosphere was monitored by the Voyager 2 spacecraft on July 9, 1979. The absorption recorded in the 910–1200 Å range was caused primarily by the H2‐Lyman and Werner bands. These data provide the first complete measurements of atmospheric density and temperature profiles between 330 and 830 km above the ammonia cloud tops. The molecular hydrogen density at 380 km is found to be 3−1+4 × 1013 cm−3, where the atmospheric temperature is 200±50 K. The thermal gradient above 830 km altitude is found to be approximately 1 K km−1 to reconcile the stellar occultation data with the Voyager 1 solar occultation data for the exosphere. Both experiments were performed in the equatorial region. The observed temperature gradient in the upper atmosphere rules out inertia gravity wave propagation as the primary heating mechanism; the heating must be caused by one or many of a host of other potential sources such as magnetospheric electrons (soft or hard), Joule heating and even solar extreme ultraviolet radiation. The data do not present a strong argument in favor of an earthlike mesopause on Jupiter. The absorption in the 1250–1600 Å range yields volume mixing ratios of methane and ethane of 2.5−2+3 × 10−5 and 2.5−1.5+2.0 × 10−6, respectively, at a height of 325 km above the ammonia cloud tops. An upper limit of 2.5 × 10−6 for the mixing ratio of acetylene has been found at the altitude of 300 km. The Voyager infrared data yield mixing ratios of these hydrocarbons deeper in the stratosphere. A study of the density profiles of the hydrocarbons deduced from the stellar occultation data yields a value of the eddy diffusion coefficient at the homopause to be 1.4−0.7+0.8 × 106 cm² s−1 in the equatorial region which is consistent with the value deduced from the hydrogen Lyman alpha and helium 584 Å emission data. Detailed aeronomical implications of the results are discussed elsewhere (Atreya et al., 1981).
Electron‐ion collision effects on the formation of prompt striations in the ionosphere
Authors: Sperling J. L. , Krall N. A.
Published: February 2008

Electron‐ion collisions have been included in the analysis of electrostatic, purely growing, finite ion‐gyroradius, flute instabilities generated by a loss cone distribution of energetic ions in the ionosphere. It is shown that the collisions not only reduce the growth rate below the value predicted by collisionless theory but also result in a second lower growth rate mode not found in collisionless theory. Although the electron‐ion collision frequency is larger than the ion‐gyrofrequency for the parameters of the Buaro barium release experiment, the growth rate of the linearly most unstable mode is not appreciably modified by the collisions from the value predicted from collisionless theory. Electron‐ion collisions have a greater impact on the instability as the electron density is increased. Complete stabilization through electron‐ion collisions requires densities in excess of 8.7 × 107 cm−3.
Distribution of amplitudes of geomagnetic variations and relationships to the K index
Authors: Kane M. L. , Lanzerotti L. J. , Maclennan C. G.
Published: February 2008

We study in this brief report the properties of empirical cumulative distribution functions of geomagnetic signals measured at 3‐hour intervals for two separate 1‐month periods at three stations spaced in latitude from L=3.2 to L=4.0. The cumulative distributions are also compared to theoretical cumulative distribution functions expected from Gaussian distributions. The widths and amplitudes of the empirical distributions, as well as their deviations from Gaussian, are studied and compared to the global and ‘local’ (in longitude) geomagnetic K indices. In general, the widths of the empirical distributions become broader with increasing geomagnetic activity; the widths of the distributions are narrower at lower latitudes for a given level magnetic activity. Many empirical cumulative distribution functions compare favorably to the theoretical functions; deviations show no relation to magnetic activity.
Optical emissions and ionization profiles during an intense pulsating aurora
Authors: Sears Robert D. , Vondrak Richard R.
Published: February 2008

Coordinated spectrophotometric and incoherent scatter radar measurements were made of an intense early‐morning pulsating aurora at Chatanika, Alaska. Both instruments were operated simultaneously with temporal resolution of 1 s and were boresighted at geomagnetic zenith. The goals of the collaborative experiment were to determine the total energy flux Et and the characteristic energy parameter α of the precipitating electrons on a time scale smaller than the pulsation duration and to investigate the response of the ionospheric electron density on a comparable time scale. The relationship between total energy flux and the characteristic energy parameter suggests that during these observations the pulsations were caused by a modulation of α rather than by a modulation of the total precipitating particle flux. The values of Et and α derived from photometric data were used to model the electron density versus altitude in the ionosphere for comparison with the incoherent scatter radar measurements. Measured altitude profiles of ionization did not change significantly on the time scale of the pulsations. The E region maximum electron density typically was 7 × 105 at an altitude of 99 km. Variations in ionospheric conductivity were less than 15% on the pulsation time scale. These results suggest that a magnetospheric modulation mechanism is required to explain diffuse pulsating auroras.