bluuebunny/crossref_metadata_2025 huggingface dataset:
Satellite observation of discrete VLF line radiation within transmitter‐induced amplification bands
Authors: Koons H. C. , Dazey M. H. , Edgar B. C.
Published: February 2008

Narrow‐band VLF signals with a frequency separation of 100–130 Hz have been detected by a receiver aboard the S3‐3 satellite. The observations were made at L = 2.9 at an altitude of 5700 km. Satellite nadir was 45°N and 151°E. The radiation has the same characteristics as those reported for ground‐based observations of magnetospheric lines resulting from the nonlinear amplification of power line radiation. As is seen in ground‐based observations, the lines are not exact harmonics of the power system frequency, nor are they spaced at exactly 2 or 3 times that frequency. The frequencies of the three dominant lines were typically 7364, 7494, and 7598 Hz. During the time period of these observations the transportable very low frequency (TVLF) transmitter was performing magnetospheric wave injection experiments from a site in Central Otago, New Zealand. The modulation was 0.5 Hz frequency shift keying between 7350 and 8780 Hz. The narrow‐band signals detected by the S3‐3 satellite were observed in the 250‐Hz band above the lower frequency. The narrow‐band magnetospheric lines were apparently observed because power line harmonic radiation was amplified to detectable levels by a nonlinear interaction involving the TVLF signal. The most likely sources of the power line radiation are the 50‐Hz power grids in Tasmania, southeastern Australia, or New Zealand.
Synoptic analysis of interplanetary radio scintillation spectra observed at 34 MHz
Authors: Gotwols B. L. , Mitchell D. G. , Roelof E. C. , Cronyn W. M. , Shawhan S. D. , Erickson W. C.
Published: February 2008

Synoptic observations of the temporal power spectrum of interplanetary scintillations were made in the summer of 1976 on the University of Iowa's Cocoa Cross radio telescope and the University of Maryland's TPT array. Most of the observations were at large (>40°) solar elongations. It was found that the power spectrum broadens when enhanced turbulence at the front of a high‐speed solar wind stream sweeps over the earth. In the case with sufficient synoptic coverage the broadening appeared to result from the relative closeness of the enhanced scattering region rather than from an increase in velocity. A small percentage of the spectra displayed two power law components with a plateau between them. These may result from a flattening in the spatial turbulence spectrum such as has been observed by spacecraft.
The power spectrum of the solar wind speed for periods greater than 10 days
Authors: Fenimore E. E. , Asbridge J. R. , Bame S. J. , Feldman W. C. , Gosling J. T.
Published: February 2008

The Los Alamos Scientific Laboratory experiments on the Vela 2‐6 and Imp 6‐8 satellites have provided more than 11 years of solar wind speed data. The length of this data set provides sufficient frequency resolution to study in detail the power spectrum of speed variations in the range near the solar rotational frequency. Year‐by‐year power spectra show such large differences that the solar wind time series is probably nonstationary. The spectrum of the entire 11‐year time series shows broad bands of power near periods of 27 days (corresponding to the rotational period of the sun), 13.5 days, and higher harmonics. The band of power near 27 days extends from about 25 to about 31.5 days and contains a number of sharply defined peaks. Similar groups of peaks near a period of 27 days in a highly correlated time series, the geomagnetic index aa, have been explained as a solar latitude effect caused by differential rotation. However, recent observations indicate that the source regions of the solar wind during this last solar cycle did not participate in differential rotation; that is, there was a preferred range of longitudes for the sources. We suggest that the individual peaks in both the solar wind and the geomagnetic spectra are probably not due to differential rotation, although the band of power near 27 days almost certainly reflects solar rotation. Rather, the multipeak nature of the power spectra can be explained by a wave packet concept in which recurring high‐speed streams are described as a series of pulses (separated by a constant period) that last for a varying number of solar rotations. Subsequent wave packets have the same period but are shifted in phase to mimic the range of possible longitudes for sources of solar wind streams. Power spectra obtained for such idealized wave packets closely resemble the measured spectra of the solar wind speed and geomagnetic activity. We do not find the frequencies predicted by a theory concerning the nonradial oscillation of the sun.
Laboratory study of the O I (7990 Å) branching ratio
Authors: Christensen A. B. , Cunningham A. J.
Published: February 2008

Branching ratios for several atomic oxygen 3p³D transitions have been studied. A value of 0.0004 ± 20% for the O I (7990 Å) branching ratio was obtained, which is much smaller than the previously accepted value and in accord with recent calculations and interpretations of the auroral extreme ultraviolet spectra. Measurements of the O I (7002 Å) and O I (11,287 Å) multiplets give branching ratios of 0.05 and 0.10, which are in better accord with calculations. As part of this experiment, results of a study of the highly structured O2 photoabsorption cross section in the neighborhood of the multiples are also reported.
The convection electric field model for the magnetosphere based on Explorer 45 observations
Authors: Ejiri M. , Hoffman R. A. , Smith Paul H.
Published: February 2008

Large‐scale electric fields in the magnetosphere, represented by the scalar potentials of corotation and convection fields, are examined in order to interpret both plasmapause positions at different local times and energetic particle penetrations inside the plasmapause observed by the Explorer 45 (S³‐A) dc E field measurements and particle detectors. The Volland‐Stern type convection electric field is assumed:
, and Φ = ARγ sin ϕ. A uniform dawn‐dusk convection electric field which corresponds to an exponent (γ) of unity is not consistent with the observational data, but the Volland‐Stern model with γ = 2 more likely represents the convection electric field during the hours of electric field increases during magnetic activity. In the time‐independent case the shape of the plasmapause does not depend on the intensity of the convection electric field, so that by using two plasmapause distances at different local times along the S³ outbound and inbound orbits the shape factor γ of the convection field could be determined. The average value of γ for 42 cases was found to be 2.4.
Differential charging and sheath asymmetry of nonconducting spacecraft due to plasma flows
Authors: Parker Lee W.
Published: February 2008

The differential charging of a nonconducting spacecraft is modeled numerically by following charged‐particle trajectories in a self‐consistent space‐charge‐less sheath. In the presence of a plasma flow but independent of any photoelectric or secondary emission a potential difference between the front and wake surfaces of the spacecraft is generated, resulting in an asymmetric sheath and in the creation of a potential barrier for electrons. The potential difference can amount to volts in the ionosphere and kilovolts in the solar wind. As in the more familiar case of photoelectric charging, the asymmetric sheath and potential barrier produced by the plasma flow can lead to erroneous interpretations of experiments measuring space electric fields and low‐energy particle spectra.
Correlated observations of auroral arcs, electrons, and X rays from a DMSP satellite
Authors: Mizera P. F. , Luhmann J. G. , Kolasinski W. A. , Blake J. B.
Published: February 2008

The first simultaneous observations made from a single DMSP satellite of visible auroral arcs, precipitating primary electrons, and atmospheric bremsstrahlung X rays are presented for a magnetically disturbed auroral event. Measured electron fluxes were used to compute absolute X ray distributions expected at the satellite altitude. The agreement between the calculated and measured X ray spectra is sufficiently good to suggest that the primary electron spectra, which produce structured auroral arcs, can be inferred with an orbiting X ray spectrometer.
Neutral thermospheric winds deduced above Millstone Hill, 2. Seasonal wind variations, 1970–1971
Authors: Emery Barbara A.
Published: February 2008

Millstone Hill (42.6°N) incoherent scatter data gathered during 1970–1971 were used as input for a local model of the neutral thermosphere. The pressure gradients in the model were adjusted so as to match the exospheric temperature and neutral wind parallel to the magnetic field observed above the radar. Large seasonal variations in the diurnal average horizontal winds were deduced. Annual average zonal velocities were 5 m/s toward the west with an annual variation of ±43 m/s. Meridional velocities were 21 m/s toward the equator in the annual average with annual variations of ±52 m/s. The mean winds were toward the southwest in the summer and the northeast in the winter and tended to be stronger in 1971 than in 1970. The average vertical velocities were found to be generally downward throughout the year. The mean equatorward winds, large annual variations, and average downward velocities are consistent with a global circulation model presented by Dickinson et al. (1977) and require the existence of significant heating of the thermosphere at high latitudes. Seasonal variations calculated using the MSIS (mass spectrometer/incoherent scatter) model pressure gradients were similar, except that in contrast to the observed behavior the intensity of the annual circulation appeared to decrease from 1970 to 1971, reflecting the decline in the solar flux. Since the magnetic activity tends to lag the sunspot cycle by about a year and remained at about the same level over the 2 years, it is suggested that this difference may be accounted for if the influence of the high‐latitude heating is increased.
The high‐latitude behavior of hmF2 and NmF2 along the noon‐midnight meridian under quiet conditions
Authors: Chacko C. C.
Published: February 2008

The mean latitudinal (corrected geomagnetic) variation of the F2 peak parameters hmF2 and NmF2 from mid‐latitudes to high latitudes along the noon‐midnight meridian is established for midwinter quiet time conditions using Isis 2 topside sounder data.
On gravity wave induced Brunt‐Vaisala oscillations
Authors: Tuan T. F. , Hedinger R. , Silverman S. M. , Okuda M.
Published: February 2008

Airglow oscillations (mostly 5577‐Å oxygen emission) which show a short‐period (4–10 min) oscillation superimposed on a long‐period oscillation (several hours) have frequently been observed. Some data show that the short‐period oscillation is ‘excited’ by the long‐period oscillation as the latter increases in amplitude. The effects often occur in the absence of impulsive energy sources. We propose a model in which the short‐period oscillation is relatively localized and is associated with the natural (Brunt‐Vaisala) oscillation of the atmosphere. This oscillation is triggered off by a long‐period gravity wave through parametric excitation and nonlinear coupling.
A graphical summary of solar wind electron content observations by Pioneer 6, 8, and 9
Authors: Croft Thomas A.
Published: February 2008

Between 1965 and 1972, solar wind density measurements were obtained by Mariner 5 and Pioneer 6, 7, 8, and 9 using a radio science method called the ‘dual‐frequency experiment.’ The measurements and data processing are now terminated. We present here a graphical summary of the best of the resulting data, showing the average electron number density of the solar wind across radio paths that vary in length up to 1.8 AU and that lie broadside to the flow direction. These graphs summarize 3.4 years of observations with a time resolution of 1 hour; the measurements provided 1‐min resolution and spanned 7 years. Because the orientation and length of the paths change continually and have a major influence on the interpretation of these data, we provide a spacecraft trajectory chart and a plot of the corotation interval.
Interpretation of auroral oval equivalent current flow near dusk using inversion techniques
Authors: Hughes T. J. , Oldenburg D. W. , Rostoker G.
Published: February 2008

Using linear inversion techniques developed by Oldenburg (1976, 1977), the auroral electrojet configuration in the evening sector is studied with a view to finding the local time dependence of the westward electrojet which flows at the poleward edge of the eastward electrojet. Specific current systems whose magnetic field perturbations fit the observations to within a specified rms error are developed which, in conjunction with the inversions, yield useful information on the current density across the electrojets. It is found that the westward electrojet penetrates up to the dusk meridian for periods of moderate activity even though substorms are not necessarily in progress.
Wave propagation experiments at medium frequencies between two ionospheric satellites, 3. Z mode pulses
Authors: James H. G.
Published: February 2008

Intersatellite radio wave propagation in the lower‐frequency branch of the extraordinary mode, or Z mode, has been studied using data recorded by the Isis I and Isis II topside sounder spacecraft during a rendezvous near the north pole. The working frequencies, near 1.0 MHz, lay between the gyrofrequency and the upper hybrid resonance frequency, the former being greater than the plasma frequency. In contrast to the 100‐µs length of the emitted pulses, the received pulses were stretched to about 10 ms and had sharp rising edges. At any given time the range of transmitted frequencies for the Z mode was limited. The central frequency of this ionospheric passband and the time delay of the leading edge of the pulses both increased monotonically with time as the two‐satellite geometry changed. These observations are in good agreement with the predictions of ray optics applied to a smoothly varying medium. However, the detailed pulse shape was quite unlike the theoretical shape predicted under the WKB approximation; this suggests strong scattering. Also, received pulses occasionally had quasi‐sinusoidal modulation envelopes. As in previously reported results for the whistler mode, ionospheric irregularities appear to strongly influence the propagation of a wave that can have large refractive indices.
The near‐wake structure of the Atmosphere Explorer C (AE‐C) Satellite: A parametric investigation
Authors: Samir U. , Gordon R. , Brace L. , Theis R.
Published: February 2008

Measurements of ion current, electron temperature, and values of space potential obtained from the cylindrical electrostatic probe on board the Atmosphere Explorer C (AE‐C) satellite were used to examine, in a parametric manner, the angular distribution of charge around the satellite. Interest is focused on nighttime equatorial data in the altitude range 275–620 km, which yields a wide range for the parameter RD (=R0/λD, where R0 is the radius of the satellite and λD is the ambient value of the Debye lengths), including RD >10², which is of practical significance to large space platforms. The variations of normalized ion current in the wake zone of the AE‐C satellite appear to display an exponential dependence on RD for ‘constant’ values of other relevant parameters. The angular variations of electron temperature (Te) and space potential (ϕs) in the close vicinity of the satellite's surface were examined and compared with results from the Explorer 31 satellite. The variation of the ratio γ=ϕs(measured)/ϕs(computed) with Te was examined using data from both the AE‐C and the Explorer 31 satellites. It was found that γ >1. Possible causes for the above inequality are discussed.
Electromagnetic and electrostatic emissions at the cusp‐magnetosphere interface during substorms
Authors: Curtis S. A. , Wu C. S. , Fairfield D. H.
Published: February 2008

Strongly peaked electrostatic emissions near 10.0 kHz and electromagnetic emissions near 0.56 kHz have been observed by the VLF wave detector on board Imp 6 on crossings from the earth's magnetosphere into the polar cusp during the occurrence of large magnetospheric substorms. The electrostatic emissions were observed to be closely confined to the cusp‐magnetosphere interface. The electromagnetic emissions were of somewhat broader spatial extent and were seen on higher‐latitude field lines within the cusp. Using these plasma wave observations and additional information provided by plasma, magnetometer and particle measurements made simultaneously on Imp 6, theories are constructed to explain each of the two classes of emission. The electromagnetic waves are modeled as whistlers, and the electrostatic waves as electron‐cyclotron harmonics. The resulting growth rates predict power spectra similar to those observed for both emission classes. The electrostatic waves may play a significant role via enhanced diffusion in the relaxation of the sharp substorm time cusp‐magnetosphere boundary to a more diffuse quiet time boundary.
Sunday decreases in magnetospheric VLF wave activity
Authors: Park C. G. , Miller T. R.
Published: February 2008

Magnetospheric wave intensity in the 2‐ to 4‐kHz range was monitored on the ground at Siple, Antarctica, in 1974 and 1975. Sampled broadband spectral data show that the wave activity in the 2‐ to 4‐kHz band is predominantly chorus (discrete narrow band emissions). The measured wave intensity shows a distinct minimum on Sunday in comparison with the rest of the week. The Sunday minimum is confined to the dawn‐afternoon local time sector where the chorus intensity has a diurnal maximum. It is suggested that much of the chorus observed at Siple is triggered in the magnetosphere by power line radiation from its conjugate region in eastern Canada and that the Sunday minimum in magnetospheric wave activity is the result of reduced power consumption on Sunday. This interpretation is supported by the results of an independent study based on broadband spectral data from Siple between 1973 and 1975. The results show weekly variations in the occurrence of strong power‐line‐induced emissions with a pronounced minimum on Sunday. This pattern is similar to the power consumption pattern in Quebec. It appears that power line radiation is an important factor in the overall magnetospheric wave environment. Its role in particle precipitation (through wave‐particle interaction) needs to be investigated.
Bremsstrahlwung produced by precipitating electrons
Authors: Walt M. , Newkirk L. L. , Francis W. E.
Published: February 2008

Theoretical values are presented of the bremsstrahlung flux escaping the atmosphere for various incident electron fluxes. The assumed incident electron fluxes were isotropic with exponential energy spectra. The escaping bremsstrahlung intensity, energy spectra, and angular distributions depend on the incident electron flux characteristics, indicating that measurements of bremsstrahlung can be used to derive information on the electron precipitation.
Atomic oxygen between 80 and 120 km: Evidence for a latitudinal variation in vertical transport near the mesopause
Authors: Wasser Barry , Donahue T. M.
Published: February 2008

Analysis of the Ogo 6 OI green line nightglow photometer experiment has been carried out for eight cases when the alignment of the spacecraft was such that local emission rates could be determined below the altitude of maximum emission and down to about 80 km. The results obtained show that the vertical gradient of the emission rate between 95 and 80 km alternates between regions of very rapid variation and very slow variation spaced on a scale of 5–10 degrees of latitude. Maps showing isoemissivity contours and isodensity contours for [O] in vertical meridional planes are presented. The densities are computed under three assumptions concerning excitation mechanisms. Comparisons of the vertical variations of oxygen density with the results of a time dependent theory suggest the regions of strong downward transport alternate in latitude with regions of weak transport near 90 km. In the first case, conversion of O to O3 at night appears to be overwhelmed by downward transport of O.
Excitation of Balmer alpha and Lyman alpha emissions in collisions of 1.87‐ to 24.6‐keV hydrogen atoms with N2 and O2
Authors: Sheridan J. R. , Vidmar R. J.
Published: February 2008

Measurements of cross sections are presented for excitation of Balmer alpha and Lyman alpha emissions in collisions of 1.98‐ to 24.6‐keV hydrogen atoms with N2 and O2. Estimates of corrections required for cascade contributions and lack of excited state equilibrium are also given. At 1.87 keV, Lyman alpha and Balmer alpha cross sections reach their largest value, indicating maxima in these cross sections at or below 2 keV. Except for differences in absolute values for Lyman alpha cross sections, the results agree well with the work of others where comparison can be made.
Electron temperature profiles measured Up to 8000 km by S3‐3 in the late afternoon sector
Authors: Rich Frederick J. , Sagalyn Rita C. , Wildman Peter J. L.
Published: February 2008

A preliminary survey of thermal electron temperatures in the late afternoon sector (1630–1800 hours magnetic local time) of the high‐altitude ionosphere has been made up to 8000‐km altitude with data from a spherical Langmuir probe onboard the polar‐orbiting satellite S3‐3. The temperature of the thermal electrons is found to be almost independent of altitude along closed field lines above ∼3000 km when both ends of the magnetic field pass through a sunlit ionosphere at 300‐km altitude. Over the sunlit polar cap, a temperature gradient of ∼0.4°K/km is observed up to 5000‐km altitude. The temperature of the thermal electrons at high altitudes is found to have a dependence on invariant latitude similar to previous observations near 1000‐km altitude.
Magnetic fields in flowing magnetotail plasmas and their significance for magnetic reconnection
Authors: Caan Michael N. , Fairfield Donald H. , Hones Edward W.
Published: February 2008

Results of a statistical analysis of 324 intervals of intense bulk plasma flows in the plasma sheet of the geomagnetic tail, measured by the Imp 6 spacecraft, are presented. Measurements of the magnetic field in the plasma sheet during these flows reveal pronounced dependences of the north‐south magnetic field component Bz(GSM) and the earth‐sun component Bx(GSM) on the flow direction; no such dependence of the By(GSM) component is discerned. Specifically, the fraction of field samples that are oriented southward is significantly greater during intervals of tailward flowing plasma than it is during intervals of earthward flowing plasma. Furthermore, this difference increases markedly as the absolute value of the angle of the magnetic field to the equatorial plane steepens. The total fraction of southward field, even during tailward flows, however, is about one third. As for the Bx component of the field, the distribution of samples in earthward flowing plasma is clearly peaked near zero, but the distribution in tailward flowing plasma is flatter and contains proportionately greater numbers of large positive and negative values of Bx. A moderate increase in ground activity, as determined by the AE index, was observed to be associated with the intervals of plasma flows. These results are reviewed in the context of models of magnetic reconnection in the magnetotail and the geometry of the tail plasma sheet.
Possible displacement of Mercury's dipole
Authors: Ng King H. , Beard David B.
Published: February 2008

Earlier attempts to model the Hermean magnetospheric field based on a planet‐centered magnetic multipole field have required the addition of a quadrupole moment to obtain a good fit to space vehicle observations. In this work we obtain an equally satisfactory fit by assuming a null quadrupole moment and least squares fitting of the displacement of the planetary dipole from the center of the planet. We find a best fit for a dipole displacement from the planet center of 0.033 RM away from the solar direction, 0.025 RM toward dawn in the magnetic equatorial plane, and 0.189 RM northward along the magnetic dipole axis, where RM is the planet radius. Therefore the presence of a magnetic quadrupole moment is not ruled out. The compressed dipole field more completely represents the field in the present work than in previous work where the intrinsic quadrupole field was not included in the magnetopause surface and field calculations. Moreover, we have corrected a programing error in previous work in the computation of dipole tilt λ away from the sun. We find a slight increase for the planet dipole moment of 190 γ RM³ and a dipole tilt angle λ of only 1.2° away from the sun. All other parameters are essentially unchanged.
The control of the magnetosphere by power line radiation
Authors: Luette J.P. , Park C.G. , Helliwell R.A.
Published: February 2008

Evidence is presented that radiated power line harmonics leak into high‐altitude regions of the magnetosphere with sufficient intensity to control the starting frequencies of chorus emissions. OGO‐3 data from three passes show that the starting frequencies of all measurable chorus emissions were within a few hertz of power line harmonics. It is also found that emissions detected over Western Europe were controlled by harmonics of 50 Hz; over the eastern United States and Canada by 60 Hz; and along the Alaska‐New Zealand meridian by harmonics of both 50 and 60 Hz. These results indicate that man‐made VLF noise plays an important role in the generation of chorus, one of the commonly observed forms of wave activity in the outer magnetosphere.
Electron concentrations in the E and upper D region at Arecibo
Authors: Trost Thomas F.
Published: February 2008

Electron concentrations in the D and E regions of the ionosphere have been measured by incoherent scatter radar from 130‐km altitude down to the D region ledge with an altitude resolution of 900 m. The results are displayed as consecutive 5‐min altitude profiles including sunrise, afternoon, and sunset periods. The ledge is found to undergo systematic variations between 80 and 90 km. A comparison with theoretical models for electron concentrations at 90 and 110 km reveals generally good agreement. However, at 90 km for χ ≲60° the model values are high by a factor of 2, and at 110 km for χ=90° (sunrise and sunset) they are high by a factor of 4. The incoherent scatter results are consistent with rocket measurements and display well‐known patterns of sporadic E as well as the postsunset valley in the E region.
VLF plasma wave excitation due to low‐energy electron beam injection: Laboratory simulation of a rocket experiment
Authors: Tsutsui M. , Hiramoto K. , Matsumoto H. , Kimura I.
Published: February 2008

A laboratory simulation experiment of low‐energy electron beam injection into the ionosphere is performed. Two kinds of waves are excited in VLF frequency range. One with a lower frequency is shown to be caused by an interaction between the beam with a finite cross section and a background plasma. The other with a higher frequency is shown to be caused by a current‐driven ion turbulence due to an electron return current. These two kinds of VLF waves have been observed before in Japanese rocket experiments in the ionosphere. A retarding potential analyzer measurement revealed that the injected beam has a diameter twice as large as the cyclotron radius of beaming electrons. It is shown that the field intensity of the excited VLF waves drops off outside the measured beam column. A correlation measurement of the phase of the VLF wave shows that the phase velocity of the wave excited by the beam instability is equal to that of ion acoustic waves. A dispersion and wave vector measurement has shown that the current‐driven ion turbulence is an ion cyclotron wave whose phase velocity is of the order of the ion acoustic wave velocity Cs.
Dodge satellite observations of Pc 3 and Pc 4 magnetic pulsations and correlated effects in the ground observations
Authors: Patel V. L. , Greaves R. J. , Wahab S.A. , Potemra T.A.
Published: February 2008

The analysis of the magnetic field observations from Dodge satellite magnetometer data at L = 6.25 RE shows dominant low‐frequency waves (Pc 3 and Pc 4) in three major frequency bands: 40–35, 25–20, and 8–12 mHz. During the observation period of July–August 1968 the 25‐ to 20‐mHz band always showed high spectral density, indicating the most dominant wave frequency. Similar results were obtained in the analysis of ground magnetometer observations from L = 6.9 to 1.5 near the local time of the satellite observations. The simultaneous observations of the waves at low as well as high L values are important in wave propagation models. This pattern of observations and the polarizations of certain wave events which occurred when Dodge was close to the ground observatory are discussed in terms of contemporary theoretical models.
Latitudinal beaming of Jupiter's low frequency radio emissions
Authors: Alexander J.K. , Desch M.D. , Kaiser M.L. , Thieman J.R.
Published: February 2008

By comparing Rae 1 and Imp 6 satellite measurements of Jupiter's radio emissions near 1 MHz with recent Voyager 1 and 2 observations in the same frequency range it is now possible to study the properties of the low frequency radiation pattern over a 10° range of latitudes with respect to the Jovian rotation equator. These observations, which cover a wider latitudinal range than is possible from the earth, are consistent with many aspects of earlier ground‐based measurements that have been used to infer a sharp beaming pattern for the decameter wavelength emissions. We find marked, systematic changes in the statistical occurrence probability distributions with system III central meridian longitude as the Jovigraphic latitude of the observer changes over this range. Moreover, simultaneous observations by the two Voyager spacecraft, which are separated by up to 3° in Jovigraphic latitude, suggest that the instantaneous beam width may be no more than a few degrees at times. The new hectometer wave results can be interpreted in terms of a narrow, curved sheet at a fixed magnetic latitude into which the emission is beamed to escape the planet.
The annual and semiannual variations of the cosmic radiation
Authors: Khor H.P. , Kwok W.K. , Owens A.J.
Published: February 2008

We determine the annual and semiannual harmonics in the Deep River Neutron Monitor counting rate for the years 1960–1975. A new Fourier analysis technique is used to eliminate solar cycle variations, and we discuss the statistical errors in the determination of the harmonics. The annual and semiannual waves change markedly from year to year. The yearly harmonic has an average amplitude ∼0.6% with a maximum in early March, corresponding to a southward anisotropy of ∼5%/AU perpendicular to the solar equatorial plane. The semiannual harmonic shows no phase coherence and its average amplitude is only marginally significant, ≲0.2%.
diurnal variation of the auroral oval size
Authors: Meng Ching‐I.
Published: February 2008

An examination of the equatorial boundary of the auroral oval (as defined by quiet‐time auroral electron precipitations) reveals a periodic variation of its latitudinal location. The period of oscillation is 24‐hours and the amplitude is about 4°. This diurnal variation seen in the evening and morning sectors of the auroral oval is in phase as is the diurnal variation of the northern and southern hemispheres. The observed latitudinal variation is attributed to UT diurnal variation of the auroral oval size in association with the daily precession of the geomagnetic pole. The auroral oval is smaller when the northern geomagnetic pole is near the local midnight around 0600 UT; it is larger when the northern geomagnetic pole is near the local noon around 1800 UT. The equatorial edges of the evening sector of the quiet auroral oval (1900–2100 MLT) are located at about 72° and 69° CGL, respectively, which correspond to the minimum auroral oval.
The phase of the ten‐hour modulation in the Jovian magnetosphere (Pioneers 10 and 11)
Authors: Fillius Walker , Knickerbocker Paul
Published: February 2008

We have systematized and recorded our study of the phase of the 10‐hour modulation of energetic electrons seen by Pioneers 10 and 11 in the Jovian magnetosphere. To start with, we focus on the peaks rather than the valleys of each cycle because the peaks are where physically interesting features occur, such as particle acceleration, current sheets, etc. To identify the peaks, we demand that the instantaneous intensity be higher than the 5‐hour running average and the 5‐hour running average be greater than the 10‐hour running average. These criteria select an interval rather than a point and we feel that this interval is an appropriate estimate of the experimental uncertainty. When the phases of the peaks are plotted together, they create patterns which we discuss in terms of disk‐like, clock‐like, and rotating anomaly models of the magnetosphere. Each model fits some of the data, but no model explains all of the data convincingly. We conclude that we still do not understand the configuration of the outer Jovian magnetosphere.
Apparent and real fine structures in magnetospheric ULF or VLF emissions
Authors: Gendrin Roger , de Villedary Claude
Published: February 2008

The existence of monochromatic structures in ULF or VLF magnetospheric emissions has often been questioned, and in some cases it has been demonstrated that the apparent frequency structure of these emissions was due to the method of analysis. We present here a theoretical study of the apparent frequency‐time structures which should result from different frequency analysis techniques applied to two kinds of signals. Signals of type I consist of two or more gliding tones (whose frequency varies linearly with time) closely spaced in time. Type II signals consist of two or more quasi‐monochromatic emissions of finite duration, slightly displaced in frequency and time. We show that when very narrow or very wide filter bandwidths are used, similar frequency‐time patterns may be obtained with both signals. These patterns are described, as a function of the characteristics of both the signal and the filter. A procedure is suggested which consists of analyzing the same signal with different filter bandwidths and which enables one to distinguish between type I and type II signals in most cases. The validity of the theory is checked on computer‐simulated wave forms. Application is also made to natural magnetospheric emissions recorded both on the ground and on board satellites. It is shown that whereas the Pc 1 fine structure seems to be a real effect, there is no clear evidence that chorus VLF emissions do present a banded structure.
Magnetic field effects on ionization inhomogeneities advected by motions of the neutral gas
Authors: Hill R.J.
Published: February 2008

A theory is developed for the ambipolar diffusion, drift, distortion, and production of ionization irregularities within weakly ionized plasma in the presence of the geomagnetic field and motions of the neutral gas. The formulation takes into consideration turbulent, wave, or uniform motion of the neutral gas, as well as the effects of uniform electric and gravitational fields. Equations are developed for a multi‐species plasma containing ions of either sign of electric charge; later these equations are specialized to the case of electrons and one species of positive ions. New effects are found relating to the production of ionization irregularities by the coupling of the geomagnetic field with the spatial variation of the velocity field and acceleration field of the neutral gas. The quasi‐neutral approximation and linearization are used to produce a more tractable theory. The length‐scale restrictions necessary for the ionosphere to be treated as a homogeneous plasma are considered. The drift and distortion of ionization irregularities because of the gravitational field, a uniform wind and electric field are considered for the lower ionosphere, as is ambipolar diffusion. The production of ionization irregularities by wind shear and by the convergence of the neutral gas along a magnetic field line and divergence perpendicular to it are investigated, and the fluctuations in electron concentration so produced are estimated.
An equipotential model for auroral arcs: The theory of two‐dimensional Laminar electrostatic shocks
Authors: Swift Daniel W.
Published: February 2008

The two‐dimensional current‐driven shock theory of Swift (1976) is reformulated in a way that removes previous restrictions on the shock thickness in relation to an ion gyrodiameter and also makes it possible to include effects of finite gyrational energy of the ions. The theory is applied to a shock model consisting of cold streaming electrons of magnetospheric origin and streaming ions of ionspheric origin, and it is shown that shock widths will be slightly less than the gyrodiameter of an ion whose energy is equal to the maximum potential difference across the shock. It is also shown that ions in passing through the shock may gain gyrational energy on the order of 10% of the parallel and the E × B energy gain. The theory also requires that the electron beam flux be largest on field lines where the precipitating electron experiences the largest energy gain.
Photometric studies of the postnoon dayside cleft region
Authors: Duncan C.N. , McEwen D.J.
Published: February 2008

Ground‐based photometric observation of the postnoon dayside cleft region was carried out at Sachs Harbour (Λ=76.7°) during the period November 30–December 19, 1977, by using a 6‐channel meridian‐scanning photometer. Continuous observation of the 6300‐Å O I emission permitted the mapping of the postnoon cleft morphology. The cleft was located at 77°–78°Λ on geomagnetically quiet days and farther equatorward by 2°–3° on the most active days (Kp=4). During each afternoon an equatorward movement of the cleft was observed after about 1400 MLT. The peak intensity of the 6300‐Å emission was usually 1'2 kR. A distinction is made between ‘soft’ cleft characteristics identified early on several afternoons, when the 6300‐Å emission rate is always greater than that at 5577‐Å, and a more structured character seen at all other times. The structure takes the form of transient enhancements of the auroral emissions, particularly 5577 Å. The enhancements have a duration of about 1 min and tend to occur as sequences. On none of the 10 clear days of observations was there optical evidence of energetic electron precipitation equatorward of the cleft.
The linear theory of the Raleigh‐Taylor instability in the equatorial ionosphere
Authors: Russell David A. , Ott Edward
Published: February 2008

We present a linear theory of the Rayleigh‐Taylor instability in the equatorial ionosphere. For a purely exponential density profile, we find that no unstable eigenmode solutions exist. For a particular model ionosphere with an F peak, unstable eigenmode solutions exist only for sufficiently small horizontal wave numbers. In the later case, purely exponential growth at a rate identical to that for the sharp boundary instability is found. To clarify the situation in the case that eigenmodes do not exist, we solve the initial value problem for the linearized ion equation of motion in the long time asymptotic limit. Ion inertia and ion‐neutral collisions are included. Assuming straight magnetic field lines, we find that when eigenmodes do not exist the growth of the response to an impulse is slower than exponential viz., t−1/2 exp (γt) below the F peak and t−3/2 exp (γt) above the peak; and we determine γ.
Solar cycle and seasonal variations of the solar and lunar daily variations of total electron content at Lunping
Authors: Huang Yinn‐Nien
Published: February 2008

The solar and lunar daily variations of the ionospheric total electron content observed at Lunping, which lies close to the crest zone of the so‐called equatorial anomaly, were analyzed by Chapman‐Miller method. The lunisolar diurnal variation L1 and lunar semidiurnal variation L2 were found to have significant seasonal variations, with amplitude increasing steadily from summer to winter. The hours for L1 and L2 variations to attain their respective maximum values also increase steadily from summer to winter. The seasonal variation of the semidiurnal variation L2 was found to be explainable by the additional fountain effect caused by the similar seasonal variation of the lunar semidiurnal electric field induced at the equatorial region. However, the seasonal variation of the lunisolar variation L1 was found not to be explainable by the additional fountain effect. Seasonal variations for the harmonic components of the solar daily variation were found to be different from those of lunar daily variation. Solar cycle variations of the harmonic components of the solar and lunar daily variations were found and described.
Resonance instability of small‐scale field‐aligned irregularities
Authors: Das A.C. , Fejer J.A.
Published: February 2008

The generation of small‐scale field‐aligned irregularities in ionospheric heating experiments is explained in terms of a purely growing parametric instability with thermal coupling based on the scattering of the pump field by the irregularities into plasma oscillations. The standing wave nature of the pump field is a necessary aspect of the present instability which does not require the previous presence of nonthermal irregularities.
Latitude dependence of power spectra of magnetic pulsations near L=4 excited by scc's and si's
Authors: Fukunishi H.
Published: February 2008

Observational evidence from a latitude array of three ground‐based magnetometer stations extending from L ∼ 3.2 to L ∼ 4.4 indicates that the damped‐type oscillations excited by storm sudden commencements and sudden impulses contain many spectral peaks. Each spectral peak appears to have a different localization in latitude. The localization in latitude is quite different for the latitudinal and azimuthal (H and D) components. The conjugate magnetic data show that the H components oscillate in phase, while the D components oscillate out of phase at the conjugate pair stations. These observational facts are discussed using the theoretical result of Chen and Hasegawa (1974b) concerning the response of the magnetosphere to an impulsive driving force.
High‐frequency spontaneous emission of an electron beam injected into the ionospheric plasma
Authors: Lavergnat J. , Pellat R.
Published: February 2008

This paper gives a detailed quantitative analysis of the high‐frequency spontaneous wave emissions produced by an electron beam injected into the ionospheric plasma. A general discussion about individual‐collective and incoherent‐coherent characteristics of the emissions is given. Then attention is focused on the spontaneous coherent emission in three different modes: plasma waves, Bernstein modes, and electromagnetic whistler mode. Comparisons with experimental results obtained by several experiments (electron echo experiment, Araks) are made throughout the paper and suggest that many experimental features are well interpreted in terms of coherent emission.
Enhanced isotropic cosmic ray intensity waves during cosmic ray storms
Authors: Duggal S.P. , Pomerantz M.A.
Published: February 2008

A study of the abnormal cosmic ray storm that followed the solar particle ground level event (GLE) on September 23, 1978, has revealed that the protracted recovery phase is impregnated with wavelike modulations that are associated with the rotational period of the sun. The analysis of data from the global network of stations has demonstrated that these large‐amplitude waves are isotropic. From an analysis of axial and longitudinal anisotropies it is concluded that the observed fluctuations did not originate from periodic changes in the cosmic ray density gradient (▽n) either in or perpendicular to the plane of the ecliptic. Although these long‐duration waves cannot be ascribed to singular features on the sun, it is speculated that they may reflect changes in the topology of active regions on the visible disk. In any case, it is clear that the scope of the classical picture, in which Forbush decreases are associated with short‐term anisotropies, must be expanded to include long‐duration wave phenomena. These new observations provide an important clue in understanding the physical mechanism that gives rise to long‐duration cosmic ray storms.
Counterstreaming electron beams at altitudes of ∼1 RE over the auroral zone
Authors: Sharp R.D. , Shelley E.G. , Johnson R.G. , Ghielmetti A.G.
Published: February 2008

Intense beams of electrons with energies in the keV range have been observed streaming simultaneously both parallel and antiparallel to the magnetic field direction at altitudes between 4000 and 8000 km at auroral latitudes. The peak flux observed was 3 × 1011 (cm² s sr keV)−1 at an energy of 160 eV. The beams are often tightly collimated with widths in pitch angle as narrow as ∼1°. Analysis of the energy spectrums of the beams and the simultaneously observed loss cones in the trapped electron population shows that the energization of the beams cannot be understood as acceleration by a simple quasi‐static parallel electric field. Alternative models include acceleration by wave‐particle interactions or by fluctuating electric fields. One candidate model consistent with the observations is outlined in which the energetic electrons in the counterstreaming electron beams are accelerated from the ambient cold plasma by multiple flickering double layers located in the 1‐RE altitude range.
Thermal diffusion calculations for the ionosphere of Venus
Authors: Nakada M.P. , Sullivan E. .
Published: February 2008

Simplified multicomponent diffusion calculations are made for the ionosphere of Venus. Large differences in temperature between electrons and ions and appreciable temperature gradients that are near those of recent measurements are used. Compositions for which binary thermal diffusion coefficients for ions are the same as multi‐ion ones are examined as well as those that are quite different. An attempt to combine binary coefficients to give multi‐ions ones has not been particularly successful.
Observations of ULF oscillations in the ion fluxes at small pitch angles with ATS 6
Authors: Su S.‐Y. , McPherron R.L. , Konradi A. , Fritz T.A.
Published: February 2008

Ultra‐low‐frequency modulation of ion fluxes is frequently observed by the NOAA low‐energy particle detector on the synchronous satellite ATS 6. This modulation is usually associated with simultaneous periodic variations in the magnetic field. During the first 8 months of operation, 14 ULF modulation events have been identified, all with the unusual property that maximum flux modulation occurs in the smallest pitch angle detector. This paper examines one of these events in detail to determine the properties of the flux and field variations and the phase relations between the magnetic field and the various energy channels of three differently oriented particle telescopes. For this event it is found that maximum flux modulation occurs in the 100‐ to 150‐keV detector at an angle of 32° to the ambient field. The ratio of maximum to minimum flux for this channel is 3.7 during the interval of largest magnetic perturbation. Spectral analysis of the magnetic field data shows that the magnetic perturbation had a 96‐s period and a 5‐γ rms amplitude and was right elliptically polarized, with the major axis tilted about 30° from the dipole meridian plane. The direction of propagation was in the dipole meridian at an angle of about 15° to both the ambient field and the dipole axis. Cross correlations between the principal magnetic field variation and the various proton flux measurements indicate that the lowest energy channel showing modulation in the field‐aligned detector (48–71 keV) lags the field by 180°. Higher energy channels lag by smaller amounts. Comparisons of the observation with three available wave modes, namely, the drift wave, the MHD slow wave, and the bounce resonant interaction associated with a transverse wave, are carried out in detail. It is found that none of the wave modes can explain all the correlated particle and field oscillations satisfactorily.