bluuebunny/crossref_metadata_2025 huggingface dataset:
A time dependent model of the Jovian current sheet
Authors: Kivelson Margaret G. , Coleman Paul J. , Froidevaux Lucien , Rosenberg Ronald L.
Published: February 2008

From analysis of vector helium magnetometer measurements obtained during the Pioneer 10 outbound pass through the Jovian magnetosphere it is argued that the average location of the near‐equatorial current sheet is a surface whose shape is determined by the velocity at which the magnetic perturbations produced by a rotating tilted dipole propagate to large radial distances. The equation of the surface in Jovigraphic spherical polar coordinates is cos[ϕs +Ω (rs‐ro)/vr + cot λ cot θs = 0, where Ω is the angular velocity of planetary rotation ϕs = −Ω(t‐to), λ is the angle between Ω and the planetary magnetic moment, vr is an effective velocity for the radial transport of magnetic perturbations, and ro is the Jovicentric distance to the source of the field. This surface rotates rigidly with the planet and so is time independent in a rotating coordinates system, a feature of the model which would change if the obvious asymmetry of external boundary conditions were considered. For appropriately defined vr and ro the expression is applicable to either of the basic models which have been discussed for the outer magnetosphere, i.e., an outflow model or a quasi‐static disk model. Fits to the data are used to evaluate the parameters, and the values vr = 43 RJ/h and ro = 14 RJ are obtained from the least squares fit to the averages of observed current sheet crossings.
Magnetic fields and flows between 1 and 0.3 AU during the primary mission of Helios 1
Authors: Burlaga L. F. , Ness N. F. , Mariani F. , Bavassano B. , Villante U. , Rosenbauer H. , Schwenn R. , Harvey J.
Published: February 2008

Helios 1 moved from 1 AU on December 10, 1974, to 0.31 AU on March 15, 1975, and the sun rotated beneath the spacecraft nearly 4 times during the interval. Recurrent high‐speed streams with uniform magnetic polarity were observed, and they were associated with coronal holes of the same polarity. Although they were recurrent, the streams and their magnetic field patterns were not stationary, because the coronal holes which produced them changed in shape and latitude from one rotation to the next. We estimated that the magnetic field intensity of open field lines in some of these holes was of the order of 10'20 G. Recurrent slow flows were also observed. The magnetic field polarity and intensity in these flows were irregular, and they changed from one rotation to the next. Cold magnetic enhancements (CME's) characterized by a twofold to threefold enhancement of magnetic field intensity and a fivefold to sevenfold depression of proton temperature relative to conditions ahead of the CME's were observed in some slow flows. Some of these CME's were contiguous with interaction regions of streams. At perihelion, Helios observed a recurrent stream which was associated with a lobe of the south polar coronal hole. The longitudinal width of the stream was three times that of the hole. We estimate that the width of the eastern and western boundaries of the streams at the coronal holes was only 2.5° ± 1.5°, and we infer that the width at the northern boundary of the stream was ≲5°. We conclude that between the sun and 0.3 AU there was a diverging stream surrounded by a thin boundary layer in which there was a large velocity shear. There is evidence for compression of the magnetic field in the western boundary layer (interaction region), presumably due to steepening of the stream within 0.31 AU.
An assessment of the role of precipitation in magnetospheric convection
Authors: Southwood D. J. , Wolf R. A.
Published: February 2008

Two ways are examined in which particle precipitation can affect the overall pattern of magnetospheric convection. First, loss due to precipitation may reduce the effectiveness of the shielding process that acts to prevent the high‐latitude convection electric field from penetrating to low latitudes. Second, electron precipitation can strongly influence the flow pattern by modifying the ionospheric conductivity. We conclude that shielding by the plasma sheet electron boundary is likely to be strongly dependent on the loss rate, but at the inner edge of the proton ring current it will always have some importance. We also find that the combined effect of shielding and enhanced conductivity in the auroral zone can be rapid flow in the ionospheric trough, similar to recent observations.
Energy deposition in a gaseous mixture
Authors: Peterson L. R. , Garvey R. H. , Green A. E. S.
Published: February 2008

Current models proposed in planetary aeronomy involve a large variety of possible gaseous mixtures which are subjected to charged particle bombardment. To facilitate the analysis of such problems, we propose a phenomenological approach to electron degradation in gaseous mixtures that is a natural outgrowth of recent studies of yield spectra in pure gases. Existing parameterized yield spectra for a variety of gases, computed by a discrete energy bin method, are used as the basis for constructing a parameterized composite yield spectrum for an arbitrary mixture. For mixtures involving O2, N2, Ar, and He, results are obtained that reproduce the values computed from a complete discrete degradation computation at a few sample mixtures for initial energies greater than 100 eV. Effects of collisional deactivation are not included. An important value of the method lies in its low cost, making it appropriate for widespread application to aeronomy in the energy regions above a few times thresholds. The structure inherent at low energies makes scaling difficult there, but existing discrete deposition codes are easily applied for mixtures at energies below 100 eV.
The height dependence of wave‐normal depression and disturbance amplitude in TID's
Authors: Morgan M. G. , Ballard K. A.
Published: February 2008

Experimental results obtained with multistation rapid‐run ionosondes are presented and discussed for seven large daytime traveling ionospheric disturbances (TID's). There is a sharp maximum in the amplitude of each disturbance in the inflection region of the electron density profile below the F layer peak, and the wave normal is depressed downward in this region from 55° to 85° below the horizontal. At the upper and lower fringes of the disturbance the wave‐normal depression is much less, ranging from 2° to 25°. The reduced depression at the upper side is attributed to a concomitant effect of dissipation of the causative gravity wave, and that at the lower side to trapping of the gravity wave energy below the thermopause. The TID amplitude peak is ascribed to a peak in (1/Ne)(∂Ne/∂z) and to the dissipation which counteracts the exponential growth, with height, of the gravity wave.
Global model of longitude/UT variations in thermospheric composition and temperature based on mass spectrometer data
Authors: Hedin A. E. , Reber C. A. , Spencer N. W. , Brinton H. C. , Kayser D. C.
Published: February 2008

Measurements of N2, O, He, and Ar densities from neutral gas mass spectrometers on four satellites (Ogo 6, Aeros A, AE‐C, and AE‐D) and inferred O2 and H densities from an ion mass spectrometer on AE‐C have been combined to produce a model of longitude/universal time (UT) variations in thermospheric neutral temperature and composition. The longitude/UT model is an extension of the mass spectrometer‐incoherent scatter thermospheric model and uses spherical harmonic terms dependent on geographic latitude, longitude, and universal time. The terms which depend only on longitude indicate a temperature enhancement of about 30°K somewhat equatorward of the magnetic poles. The temperature varies also in universal time, the greatest enhancement being about 30°K near 2130 UT in the northern hemisphere and about 70°K near 0930 UT in the southern hemisphere. The extrapolated 120‐km variations are generally in phase for Ar and O2 and out of phase for He, O, and H. Changes during magnetic storms are relatively small. The combined longitude and UT variations reflect the influence of the earth's magnetic field but indicate that the variations may not be simply represented in magnetic coordinates. The longitude/UT model helps reduce differences in the local time variation between the incoherent scatter stations.
occurrence of the lobe plasma at lunar distance
Authors: Hardy D. A. , Hills H. K. , Freeman J. W.
Published: February 2008

Recent analysis has confirmed and expanded the characterization of the lobe plasma, the extension of the ‘boundary layer’ and ‘plasma mantle’ to lunar distances. Careful statistical analysis has verified that the observation of the ‘lobe plasma’ is strongly correlated with the y component of the Interplanetary Magnetic Field (IMF). When the moon is in the dawnside of the northern lobe or duskside of the southern lobe, the probability for observation of the lobe plasma is greatly increased when, in the hour preceding, the IMF has had a positive y component. Conversely, when the moon is in the duskside of the northern lobe or dawnside of the southern lobe, the probability for observation is much increased when the IMF has a negative y component. Analysis of lobe plasma data in conjunction with high time resolution IMF data has shown the probability of observation also is greater with a southward pointing IMF. The observed correlations with the y and z components the IMF reflect the fact that the asymmetry and changes in magnitude of the polar cap electric field induced by the IMF extends to lunar distances and determines the depth into the tail to which the ions can drift. Generally, the lobe plasma is observed sporadically for a full day after the moon has entered the tail and a full day before the last magnetopause crossing as it exits the tail. An average extent of ∼8–10 RE inward from the magnetopause is inferred; however, the lobe plasma has been seen all across the tail.
Angular and temporal characteristics of partial reflections from the D‐region of the ionosphere
Authors: Hocking W. K.
Published: February 2008

Radio pulses have been used as a probe to investigate scattering characteristics of ionospheric irregularities in the D‐ region at a frequency of 1.98 MHz, at Adelaide, South Australia (35°S). The angular distribution of the returned energy was investigated as a function of time and height. Distinct layers of strong scatter have frequently been detected, the heights of which differ on different days. The layers appear to be of two distinct types—those occurring above 80 km and those below—the two groups having different temporal and angular characteristics. The higher layers exhibit scatter from a much larger range of off‐vertical angles, and the power returned from them varies less in time than for the lower layers, which tend to show short ‘bursts’ of scatter.
Postsunset observations of ionospheric‐protonospheric coupling at Arecibo
Authors: Vickrey James F. , Swartz Wesley E. , Farley Donald T.
Published: February 2008

The physical processes which couple the mid‐latitude ionosphere and protonosphere are complicated during the postsunset period when temperatures are rapidly changing. We have studied these processes with incoherent scatter measurements of the electron densities and proton and O+ vertical velocities in the topside ionosphere with 10‐min time resolution. Large velocity differences between the H+ and O+ ions in the topside ionosphere occur at times. The two vertical fluxes follow similar temporal trends at high altitudes, where the species have diffusive equilibrium profiles, both of which simply contract after sunset as the ionosphere cools. At lower altitudes, however, the charge exchange reactions can destroy the similarity in the temporal behavior of the two fluxes and can lead to ion counterstreaming at times. Therefore there is no simple relationship between the F2 region O+ flux and the total ion transport between the ionosphere and the protonosphere.
Electromagnetic induction at the South American geomagnetic equator as determined from measured ionospheric currents
Authors: Duhau S. , Romanelli L.
Published: February 2008

The latitudinal distribution of the equatorial height‐integrated current density has been obtained from available experimental data and correlated with the latitudinal distribution of the horizontal component of the daily geomagnetic variations to determine the importance of the internal part of the electrojet field. A simple method is introduced that makes it possible to analyze the importance of the internal electrojet field and simultaneously to separate the planetary field. Contradicting what has been assumed in recent works and confirming earlier results, it has been found that the current induced in the earth by the electrojet contributes significantly to daily geomagnetic variations at South American longitudes.
Late time barium cloud striations and their possible relationship to equatorial spreadF
Authors: Kelley Michael C. , Baker K. D. , Ulwick J. C.
Published: February 2008

An active experiment has been conducted in space that allows a test for the theory of nonlinear development of striations in large barium clouds. The results are in excellent agreement with a computer simulation of theE × Binstability reported by Scannapieco et al. (1976). The power law irregularity spectrum predicted by the theory and verified by the experiment is shown here to be due to wave steepening and not to plasma turbulence. The barium cloud results are remarkably similar to bottomside equatorial spread. A possible role of theE × Binstability in bottomside equatorial spreadFis discussed as a supplement to the Rayleigh‐Taylor instability during the postsunset rise of theFlayer and during anomalous plasma uplifts which occur during geomagnetically active periods.
Development of solar cycle 21 Observed in EUV spectrum and atmospheric absorption
Authors: Hinteregger H. E.
Published: February 2008

Satellite observations of solar EUV irradiance at wavelengths ranging from 140 to 1850 Å show unexpectedly great differences between cycle 21 and the previous cycle 20, posing significant problems to the applicability of current aeronomical models based on observational data gathered primarily during cycle 20. Whereas the O2‐dissociating fluxes for λ >1250 Å show but little change, the irradiance at wavelengths below 1027 Å, known as the major source of ion production in the thermosphere, differs rather drastically not only with respect to the average absolute values but also with respect to the relative amplitudes of temporal variations of EUV compared with the associated amplitudes of the conventional activity indices, F10.7 or Rz. Both the absolute fluxes and the relative variations were found to be considerably higher for the developing new sunspot cycle compared with previously observed characteristics of cycle 20. No simple interpretation seems possible because concurrently obtained observations of atmospheric optical depths at various EUV wavelengths suggest that the actual atmosphere around the 300‐km level does not show any comparable increases in density or temperature (optical depths being essentially proportional to the product of both quantities). This seems to imply that solar‐cycle‐dependent thermospheric heat sources other than the solar EUV irradiance may play an important role not adequately included in the present theoretical basis of atmospheric models.
Coordinated rocket and satellite measurements of an auroral event, 2. The rocket observations and analysis
Authors: Sharp W. E. , Rees M. H. , Stewart A. I.
Published: February 2008

Auroral optical emission rates, thermal ion and electron densities, and low‐energy electron fluxes were measured in an IBC I aurora by a rocket‐borne payload, simultaneously with the overpass of the Atmosphere Explorer C satellite. Auroral ionization rates deduced from the rocket payload and neutral gas densities measured by an instrument on the satellite are used in a model calculation of the thermospheric manifestation of the aurora. The internal consistency of the electron and photometric measurements is demonstrated for the particle‐induced emission of 3371‐Å. A quenching rate of the N2(A³Σu+) state is deduced, by using the measured oxygen densities, and found to be 1.2−.2+.7 × 10−10 cm³ s−1. A discrepancy between the calculated and measured ionospheric densities is discussed in terms of the abundance of nitric oxide. A discrepancy between calculated and measured low‐energy electron fluxes (E <100 eV) is attributed to local plasma processes. The major source of 5577‐Å emission is found to be energy transfer from the N2(A³Σu+) state. The 6300‐Å is found to be unexplained by both electron impact on atomic oxygen and dissociative recombination of O2+.
Seasonal variations of the ionospheric E × B drifts above Saint‐Santin on quiet days
Authors: Blanc Michel , Amayenc Paul
Published: February 2008

A seasonal model of the F region electric‐field‐induced plasma drifts prevailing during magnetically quiet periods, and of their day‐to‐day variability, has been established on the basis of 3 years of measurements (1973–1975) above Saint‐Santin (44°39′N, 2° 12′E) with the French quadristatic incoherent scatter facility. It is expressed analytically with the help of a steady component and of the first four diurnal harmonic oscillations and can be used both as a base line for magnetospheric disturbance studies and in itself as a source of information on the morphology of ionospheric wind dynamo electric fields. For all seasons these drifts appear to be dominated by a semidiurnal oscillation in the north‐south direction and by a diurnal one in the east‐west direction. During the daytime the flow is northwestward in the morning and then southeastward in the afternoon. Seasonal effects are dominated by a marked contrast between summer and the two other seasons. Summer is characterized by a disappearance of the morning northward drifts and a more complex harmonic content of the east‐west drifts, with a larger contribution of the secondary semidiurnal and terdiurnal components. Comparison with recent dynamo calculations shows an improved agreement on the north‐south component of the drifts, even though it still leaves a significant gap between theory and experiment. Several elements in our results provide evidence that the attempt to realize a good theory/experiment coincidence meets several difficulties of a fundamental nature: one is the lack of a simple summer/winter symmetry in the observed drifts, which reveals the importance of longitude effects introduced by the real earth's magnetic field; another is the large day‐to‐day variability within each season, which is comparable to the diurnal amplitude itself. Both show the need of worldwide coordinated efforts for the acquisition of simultaneous incoherent scatter data as well as for their interpretation.
The effect of energetically produced O2+ on the ion temperatures of the Martian thermosphere
Authors: Rohrbaugh R.P. , Nisbet J.S. , Bleuler E. , Herman J.R.
Published: February 2008

In the Martian ionosphere the dominant solar ionization products are O+ and CO2+. These ions are rapidly converted to O2+ by ion neutral reactions resulting in O2+ as the dominant ion. As O2+ has a lower ionization potential, each reaction results in approximately 1.2 eV of energy to be shared by the reaction products. The kinetic energy given to the O2+ will affect the ion temperatures. Calculations have been made of the ion heating rates and temperatures which result from the degradation of these energetic ions for various energy production distributions for conditions similar to those encountered by Viking 1. It is shown that the thermalization of the energetic O2+ can greatly increase the ion temperatures above 200 km compared to those calculated using only the ambient electron heating source. The effect of small horizontal magnetic fields, as predicted by current solar wind interaction models on the ion thermal balance was also investigated. These fields act to restrict the ion thermal conductivity and thus also increase the upper altitude ion temperatures. The combination of the heating by the energetic O2+ and the effect of the magnetic field provide a partial agreement with the Viking 1 measurements.
An experimental and theoretical study of the mean diurnal variation of O+, NO+, O2+, and N2+ ions in the mid‐latitude F1 layer of the ionosphere
Authors: Torr D.G. , Torr M.R. , Brinton H.C. , Brace L.H. , Spencer N.W. , Hedin A.E. , Hanson W.B. , Hoffman J.H. , Nier A.O. , Walker J.C.G. , Rusch D.W.
Published: February 2008

Over the past decade, several models have been developed which describe the diurnal behavior of molecular and atomic ions in the altitude range where the atomic and molecular densities are comparable. However, no complete set of diurnal measurements has been available in the past with which to compare these theoretical results, because the altitude regime (130–220 km) lies below the reach of conventional satellites and rocket results give only a transient picture. The Atmosphere Explorer C, D, and E satellites have been taking measurements of ion concentrations together with related aeronomic parameters in the thermosphere for over 4 years. These data have been analyzed to extract the average diurnal variation (i.e., for solar zenith angles less than 105°) of the ion species NO+, O2+, N2+, and O+ as functions of altitude. The AE data have been used in a number of separate studies which have reduced the uncertainties associated with key reaction rate coefficients. As a test of the overall consistency of the photochemistry of the F1 layer we compare the measured ion concentrations with those calculated by using a model which incorporates our latest understanding of the chemistry and which uses, as input parameters, the measured neutral concentrations and temperature, the solar extreme ultraviolet flux, and electron and ion temperatures. The results show that a fairly simple model, in which the free parameters are minimized, reproduces the measurements to a satisfactory degree.
Mesospheric winds and waves over Jicamarca on May 23–24, 1974
Authors: Fukao S. , Sato T. , Kato S. , Harper R.M. , Woodman R.F. , Gordon W.E.
Published: February 2008

The VHF radar at Jicamarca (12.0°S, 76.9°W) was used to probe the mesosphere for 24 hours on May 23–24, 1974. The inferred zonal wind shows a strong eastward prevailing component below 75 km for these winter conditions, as would be expected from the annual and semiannual oscillations. The zonal winds are in good agreement in their region of overlap with rocket observations made at Ascension Island (8.0°S, 14.4°W) for the same period. This is the first direct confirmation that Jicamarca VHF observations are measuring mesospheric winds. Substantial wind oscillations are present, but the lack of nighttime echoes precludes a decomposition into tidal components. The dominant periodicity in the short‐period oscillations changes with altitude, with the short‐period cutoff decreasing from around 10 min at 70 km to 4 min at 80 km. This suggests both a local energy source for the oscillations and the importance of the background temperature structure in determining the wave characteristics. The variation of echo power with height in the two antennas that were used shows that 2–10 times more power was received on the average in the nearly vertical antenna than in the antenna offset from the vertical by 3.45° at heights below 75 km, suggesting the possibility that a ‘partial reflection’ mechanism is important in the 55‐ to 75‐km region at a 50‐MHz operating frequency. The powers in the two antennas become nearly equal above 75 km, with the possibility that slightly more power is received in the off‐vertical antenna. The continuous scattered power becomes very small above 80 km; however, meteor echoes are frequently observed. Equatorial electrojet echoes dominate the echo returns above 85 km.
Chemically depleted F2 ion composition: Measurements and theory
Authors: Sjolander Gary W. , Szuszczewicz Edward P.
Published: February 2008

The Lagopedo experiments were the first in situ ion composition measurements of a chemically modified ionosphere. An artificial ionospheric hole was produced by the injection of H2O and CO2 into the O+ dominant F2 region. These released chemicals increased the natural ionospheric depletion rate by approximately two orders of magnitude by changing the rate of molecular ion formation. As the rocket payload passed through the event cloud, O+ was observed at a reduced density, and H2O+, H3O+, and O2+ were observed in enhanced amounts that varied with time after and distance from the event. H3O+ was dominant at times immediately after the event, when the neutral water density was high, but rapidly decreased to 20–40% of the H2O+. A computer model simulated the postevent O+ and O2+ distributions well, but it had mixed success with the H2O+ and H3O+ distributions. Measureable changes in ion composition levels were detected up to 40 km from the release point.
Whistler‐induced anomalies in VLF propagation
Authors: Lohrey B. , Kaiser A.B.
Published: February 2008

Observations of very rapid phase advances of up to 8° for subionospheric VLF transmissions over a path length of 5745 km are found to be associated with whistlers. We show that the energetic electrons that precipitate in the D region and cause the phase advances interacted with the whistler on its second hop, which is consistent with amplification of whistlers by cyclotron resonance with electrons traveling in the opposite direction. No fast amplitude variations were detected. We propose a simple two‐mode model to describe the effects of nighttime D region disturbances on long‐distance subionospheric VLF propagation, and we show how this model can account for our observations and also the amplitude effects seen by Helliwell, Katsufrakis, and Trimpi.
HF radar studies of two‐stream instability during an equatorial counter‐electrojet
Authors: Crochet M. , Hanuise C. , Broche P.
Published: February 2008

A very strong daytime counter‐electrojet was observed on January 21, 1977, near the magnetic equator in Africa. This phenomenon was investigated for the first time using simultaneous magnetic and radar measurements. As predicted by the linear theory, irregularities associated with the two‐stream instability were detected in the absence of the usual turbulence related to the cross‐field effect (or type 2 irregularities). In addition, taking advantage of the refraction of the HF radio waves in the E layer, horizontal or quasi‐horizontal plasma waves were detected for the first time together with the usual oblique waves. Two kinds of spectra were then distinguished from the radar observations: (1) Spectra associated with oblique waves which do not have the usual behavior of type 1 (their phase velocity is dependent on time and angle of incidence) and (2) type H spectra associated with horizontal or quasi‐horizontal waves which have a smaller phase velocity (constant with time and range) and a larger amplitude than oblique waves. Among different hypotheses we presume that the quasi‐linear reduction of the polarization electric field at the bottom of the instability layer explains the constant value of the phase velocity of the horizontal waves. The absence of turbulence (or type 2) would be the source of the difference observed beween oblique waves and usual type 1.
Confidence limits and maximum entropy spectra
Authors: Reid J.S.
Published: February 2008

The maximum entropy method of spectral analysis is examined in terms of the probability density of a finite random sequence. The distribution is found which has maximum entropy within constraints imposed by the stationarity of the sequence. The population power spectral density of the sequence is expressed in terms of the parameters of this distribution. The distribution is shown to be related to a linear regression model for which the parameters may be estimated by the established methods of regression theory. Confidence limits for the spectral estimator are derived, infinite confidence limits being interpreted in terms of cyclic behavior of the ensemble means of the sequence. The null hypothesis that the members of a subset of regression coefficients are all zero is used to estimate the order of the autoregression. Estimated spectra of a sequence of annual mean sunspot numbers are computed using this method and found to have a single significant peak.
Dependence of equatorial F region vertical drifts on season and solar cycle
Authors: Fejer B.G. , Farley D.T. , Woodman R.F. , Calderon C.
Published: February 2008

Vertical drift measurements have been made at Jicamarca for more than half a solar cycle. The data from periods of high and low activity are appreciably different. Daytime drift velocities during sunspot minimum are usually larger than during the maximum, while the opposite is true for nighttime periods. The evening reversal occurs earlier during sunspot minimum than during the maximum, but the morning reversal is not altered. The period of eastward electric field (upward drift) is thus shortest during sunspot minimum and local winter. By integrating the drift velocity data with respect to time, one can obtain a measure of the total potential drop between reversal points (near the terminators). This drop is largest at solar maximum. There is also a pronounced seasonal variation, with a minimum in mid‐December during both solar minimum and maximum. The general features of the data cannot be explained solely on the basis of tidal winds driving an E region dynamo; polarization fields related to the F region dynamo are of major importance, particularly in helping to explain the enhancement of the daytime upward drift which often occurs shortly before the drift reverses to downward in the evening. In order to account quantitatively for the observed variations, however, numerical models considerably more sophisticated than those presently available are needed.
Solar activity changes in the electron temperature at 1000‐km altitude from the Langmuir probe measurements on Isis 1 and Explorer 22 satellites
Authors: Mahajan K.K. , Pandey V.K.
Published: February 2008

Electrostatic probe measurements of electron temperature from the Isis 1 satellite for the equinox season of high solar activity years 1969 and 1970 are analyzed for the 1000‐km altitude. These results are then compared with the Explorer 22 satellite measurements of electron temperature for the years 1965–1967. Large solar activity changes are found to occur in the latitudinal profiles of electron temperature during both day and night. At low and mid‐latitudes, the electron temperature increases from about 2000 to about 3500°K for the daytime and from about 800 to about 1700°K during the nighttime between low and high solar activity conditions. At high latitudes there is an increase in electron temperature by about a factor of 2 from low to high solar activity period. These solar activity changes in electron temperature are interpreted to be mainly due to the heat flux conducted down from the protonosphere, which increases with solar activity.
The shape and location of the sector boundary surface in the inner solar system
Authors: Villante U. , Bruno R. , Mariani F. , Burlaga L.F. , Ness N.F.
Published: February 2008

Simultaneous observations by Helios 1 and Helios 2 over four solar rotations, between January 20 and May 23, 1976, were used to determine the latitudinal dependence of the polarity of the interplanetary magnetic field within ±7.23° of the solar equator and within 1 AU. The longitudinal and latitudinal positions of the sector boundary crossing are consistent with a warped sector boundary which extended from the sun to 1 AU and was inclined ≈ 10° with respect to the heliographic equator. This is consistent with simultaneous Pioneer 11 observations, which showed unipolar fields at latitude ≈ 16° at heliocentric distances greater than 3.5 AU. Two sectors were observed at southern latitudes; however, four sectors were observed at northern latitudes on two rotations, indicating a distortion from planarity of the sector boundary surface.
Auroral motions and magnetic variations associated with the onset of auroral substorms
Authors: Kawasaki Koji , Rostoker Gordon
Published: February 2008

Observations of the aurora borealis were undertaken during the period August 10–20, 1976, from Fort Smith, Northwest Territories, Canada. Two auroral substorm ‘breakup’ events which occurred in the Alberta sector during this period were photographically documented and have been studied together with the associated polar magnetic substorm events. It is found that significant westward‐directed ionospheric current flow occurs for perhaps 2 or 3 minutes prior to the appearance of the auroral breakup surge form. This current appears to lie parallel to the bright arc which forms before onset of the breakup phase. Such an observation is important relative to the timing of the onsets both of auroral and polar magnetic substorms, and also may have critical implications relative to a theoretical understanding of the sequence of events leading to the auroral substorm breakup.
Simultaneous observations of energetic (keV) upstreaming and electrostatic hydrogen cyclotron waves
Authors: Kintner P. M. , Kelley M. C. , Sharp R. D. , Ghielmetti A. G. , Temerin M. , Cattell C. , Mizera P. F. , Fennell J. F.
Published: February 2008

A comparative study of upstreaming energetic ions in the kilovolt energy range and electrostatic hydrogen cyclotron (EHC) waves has been made using the ion mass spectrometer and plasma wave receiver data sets for the first 1200 orbits of the S3‐3 spacecraft. The upstreaming energetic ions and EHC waves are found to coincide in over 90% of the events studied. In addition, both EHC waves and upstreaming ions with energies greater than 500 eV exhibit a lower border in their altitude distribution near 5000 km. The nearly exact correlation suggests either that the upstreaming ions are producing the EHC waves or that the EHC waves are heating the ions. One example of EHC waves and upstreaming energetic ions is analyzed to test the two hypotheses. Evidence that EHC waves are heating ions is presented in the form of conic ion distributions which some theories predict are the consequence of this process. Perpendicular ion heating to at least 6 keV is found to coincide with EHC waves. Evidence that the upstreaming ions are the source of free energy for the EHC waves is presented in the form of an ion distribution function with ∂f/∂ν > 0. However, the stability of that ion distribution function is considered and found to be stable unless other conditions such as filamentation or electron drift are invoked. There also exists the possibility that the source of free energy for EHC waves is drifting thermal electrons. For the one example studied the drifting electron process is consistent with data from the S3‐3 magnetometer. However, it is inconsistent with the S3‐3 electron spectrometer which indicates that the current is carried by keV electrons, not thermal electrons. Consequently, the source of free energy for EHC waves is not yet unambiguously determined.
Idealized Jovian magnetosphere shape and field
Authors: Engle Irene M. , Beard David B.
Published: February 2008

An equatorial sheet current deduced from Pioneer 10 magnetic field observations has been added to a planetary dipole field to construct a model of magnetic field due to sources inside the magnetopause. This internal field has then been used to calculate the magnetopause surface in a cyclic process to a fifth order, in cycles, at which the calculation converges. The resulting magnetopause is considerably flatter in shape than one resulting from a primarily dipole internal field source. The field internal and external to the magnetopause surface due to the currents on the surface has been computed by integrating over the entire magnetopause. A model for the total magnetospheric field of the inflated magnetosphere has been constructed by adding this latter contribution to the internal source fields to obtain a global model of an inflated Jovianlike magnetospheric field.
Uncertainty in ring current parameters due to the quiet magnetic field variability at mid‐latitudes
Authors: Clauer C. Robert , McPherron R.L. , Kivelson M.G.
Published: February 2008

Ground observations of magnetic perturbations can be used to study the spatial and temporal development of magnetospheric disturbances, provided that the magnetic effects of the quiet time ionospheric currents, known as Sq, can be removed from the data. At mid‐latitudes, variability of Sq currents may produce magnetic perturbations comparable to the magnetic effects of the partial ring current on comparable time scales. Thus it is important to know the error associated with the quiet field used as a reference to obtain the magnetic effects of the ring current. To determine this error, we have performed a statistical study using 2 years of quiet data (AE < 100 γ), acquired at 27 mid‐latitude magnetic observatories. We have empirically determined the average quiet magnetic field at each observatory, and the uncertainty of that field as a function of season and local time. Since the Sq currents are confined primarily to the dayside, the uncertainty of the Sq diurnal variation changes as a function of local time. During disturbed periods the quiet field is subtracted from the observations from a worldwide chain of mid‐latitude magnetic observatories to reveal the magnetic effects of substorms and the partial ring current. To obtain a smooth local time profile of the magnetic disturbance, we produce a least squares fit to the resulting data values, using a series of cubic spline functions. Profile uncertainty is estimated to range from approximately ±23 γ near local noon, to ±10 γ near local midnight. At dusk the uncertainty is near ±13 γ. These uncertainties represent uncertainty in the quiet field. The uncertainty can be greatly reduced by examining the changes which occur in some interval of time. This is done by subtracting the local time profile obtained at time t1 from the profile obtained at time t2. For time intervals less than 3 hours the quiet day errors are generally strongly correlated, and the errors are eliminated by the subtraction. The error in the difference profile is typically about ±6 γ. Thus for individual events the local time profile can be used to obtain parameters such as the magnitude, extent, and central meridian, which accurately characterize the magnetic disturbance attributed to a particular current system, provided the duration of the event is less than 3 hours. The more general mid‐latitude indices, such as Dst and the dawn‐dusk asymmetry, are less accurate, but they are still useful, provided the disturbance is sufficiently large.
Seasonal variation of equatorial spread F in the American and Indian Zones
Authors: Rastogi R.G.
Published: February 2008

The occurrence of postsunset range type of spread F at Huancayo (in the American zone) shows a very consistent and strong seasonal variation with maximum around December and minimum around June solstices during any of the years of solar cycle epoch. The occurrence of range spread F at Kodaikanal (in the Indian zone) does not indicate any significant seasonal variation. It is suggested that the range type of equatorial spread F is generated by the action of eastward electric field in the ionospheric region with large plasma density gradient present after sunset, provided enough time is available for the development of irregularities before the electric field reverses to the nighttime westward direction. In the American zone the reversal of the electric field during June solstice occurs in general at about the same time as the sunset at the F region heights, and the spread F irregularities do not get enough time to develop, while during December solstice the electric field reverses more than an hour after the layer sunset, and enough time is provided to the irregularities to develop and produce spread F echoes in the ionograms. In the Indian zone the time of the reversal of electric field varies very little with season. The occurrence of spread F depends on the day to day variation of the time interval between sunset and the reversal of the electric field. The equinoctial maxima in the occurrence of spread F is due to the corresponding maxima in the magnitude of the postsunset peak in the electric field.
The mobility and concentration of ions and the ionic conductivity in the lower stratosphere
Authors: Meyerott R.E. , Reagan J.B. , Joiner R.G.
Published: February 2008

The measurements of the mobility and concentration of ions and the ionic conductivity in the lower stratosphere are reviewed. The measurements are made from rocket, parachute, and balloon platforms. The typical mass of the ions inferred from rocket and parachute platform measurements of the ionic mobilities is ∼30 amu or lower, while that from a balloon platform measurement is ∼1000 amu. Recent in situ ion measurements made at ∼35 km with mass spectrometers on balloon platforms indicate that ion masses as high as ∼140 amu and ∼300 amu for the positive and negative ions, respectively, are present. The ion masses obtained from direct and inferred measurements on rocket platforms are therefore significantly lower than those obtained with balloon platforms. The positive ion concentrations measured from rocket and parachute platforms during quiet times are generally lower than those predicted from a cosmic ray ionization source, while those made from the balloon platforms agree with predictions. During disturbed conditions the measured and predicted ion concentrations agree for high ion densities of ∼105 cm−3. The ionic conductivities appear to be approximately independent of the type of measurement platform used. It is suggested that there may be large ions in the lower stratosphere that are broken up in the sampling process with the experimental techniques employed on the rocket and parachute platforms. The large ionic masses inferred from the mobility measurements on the balloon platform suggest that some fragmentation of the ions may have also taken place in the mass spectrometer samplings on the rocket platform. It is suggested that if these discrepancies are to be resolved, more experiments should be conducted on balloons in which measurements of the ionic mobilities, ionic concentrations, and ionic mass are made on the same platform.
Magnetic storm injection of 0.9‐ to 16‐keV/e solar and terrestrial ions into the high‐altitude magnetosphere
Authors: Balsiger H. , Eberhardt P. , Geiss J. , Young D.T.
Published: February 2008

The Geos 1 ion composition experiment has surveyed the plasma composition in the energy per charge range below 16 keV/e at all local times and at L=3–8. During quiet and moderately disturbed times, H+ is the dominant species with a few percent of heavy (M/Q >1) ions. Substorms and storms increase the relative amount of heavy ions, and occasionally, they can become the dominant species in the outer magnetosphere. Two sources, the solar wind (characterized by 4He++) and the ionosphere (characterized by O+), give on the average comparable contributions to storm time plasma, although in individual storms one or the other may dominate. Data presented here suggest that high‐altitude thermal plasma or the plasmasphere (characterized by He+ and O++) must be considered as a third source. Under storm conditions with Geos in the dawn‐noon local time sector we have observed a mixed composition region just inside the magnetopause where high fluxes of H+, He++, O+, and occasionally He+ ions are present. During several storms a composition profile could be measured down to L ∼3. Both O+ and He+ increase toward low altitudes, and O+ (within our energy range) can become dominant at the inner edge of the ring current. On April 30, 1978, during a storm, O+ contributed ≳8% to the total local energy density of the ring current particles at L=4.1. In no storm has He+ been observed to be the main constituent during the recovery phase. During storm recovery, H+ and O+ are the dominant ions, the H+/O+ ratio remaining constant or even increasing during the days following the main phase of the storms. This suggests that charge exchange is not the only loss mechanism for the storm time ring current and/or that H+ is replenished during the recovery phase.
Theory of the low‐latitude boundary layer
Authors: Sonnerup B.U.Ö.
Published: February 2008

A one‐dimensional steady state fluid mechanical model is developed of the low‐latitude plasma boundary layer inside the dawn and dusk magnetopause. Momentum transfer in the layer is produced by viscosity and/or mass diffusion. Coupling to the ionosphere is achieved via field‐aligned currents, the magnitude of which is limited by parallel potential drops. These currents flow into and out of the ionosphere in the manner described by Iijima and Potemra. The higher‐latitude (region 1) currents are associated with the boundary layer proper, while the lower‐latitude (region 2) ones are associated with a region of sunward return flow adjacent to the boundary layer. The parallel potential drops have a magnitude of typically 2–3 kV and a north‐south extent of 100–200 km. The calculated potential profile corresponds reasonably well to observed inverted V precipitation events.
The SQP magnetic variation, equivalent current, and field‐aligned current distribution obtained from the IMS Alaska Meridian Chain of magnetometers
Authors: Akasofu S.‐I. , Kisabeth J. , Ahn Byung‐Ho , Romick G.J.
Published: February 2008

The solar quiet day daily variation (Sqp) in the polar region is studied by using magnetic records on March 12, 1978 (ΣKp = 6−), and on March 25, 1978 (ΣKp = 6−), from the International Magnetospheric Study Alaska meridian chain. The results are somewhat different from those obtained by earlier studies which dealt with an exceptionally quiet day (ΣKp = ∼1+). The results are discussed in terms of the ionospheric current distribution and field‐aligned current distribution, computed on the basis of the Sqp magnetic field vector distribution. On a quiet day the type I and type II field‐aligned currents and the connected ionospheric currents are mostly confined in the dayside half of the polar region. Comparing these current distributions with those on a moderately disturbed day, one can see that both current systems extend along the auroral oval to the nightside half of the polar cap on a disturbed day. It is also shown that it is not justifiable to infer the convection pattern by using the distribution of magnetic vectors (thus by assuming that Sqp variations are caused mainly by the Hall current).