bluuebunny/crossref_metadata_2025 huggingface dataset:
Quasilinear saturation of forced current sheet tearing modes
Authors: Liewer Paulett C. , Payne David G.
Published: February 2008

Numerical studies of tearing modes in a nearly singular forced current sheet equilibrium [Liewer and Payne, 1990] show that the modes saturate quasilinearly when the width of the magnetic island formed by the reconnection is on the order of several times the linear mode width which scales as Δr ∼ (kS)−2/5, where S is the Lundquist number and k is the wavenumber. The modes saturate quasilinearly by flattening the current profile, converting magnetic energy into plasma energy. The longer wavelength modes, which saturate at higher levels, release the most energy. These modes may, nonlinearly, play a role in coronal heating when sharp current sheets form as a result of global magnetic stresses.
Climatic change due to solar irradiance changes
Authors: Wigley T. M. L. , Raper S. C. B.
Published: February 2008

Solar irradiance reconstructions back to 1874 are used to estimate the effect of the Sun on global‐mean temperature. The importance of the history effect, whereby recent temperature changes may be influenced significantly by past forcing changes, is evaluated. Modelled temperature changes are shown to be relatively insensitive to model uncertainties. The overall range of modelled temperature variations is extremely small, 0.05°C.
Evidence of drift waves at the plasmapause
Authors: Kintner Paul M. , Gurnett Donald A.
Published: February 2008

As the Hawkeye 1 spacecraft crosses the plasmapause at high altitudes (R > 3 RE), a band of electric field noise is often detected in the frequency channels from 1.7 to 178 Hz. No corresponding magnetic field noise is detected, indicating that the noise is electrostatic (or at least quasi‐electrostatic), and the electric field is polarized perpendicular to the plasma density gradient. The noise is only detected when the scale length of the plasmapause is 0.1 RE or less, indicating that a large density gradient is required to produce the noise. These characteristics are all consistent with the interpretation that this noise consists of electrostatic waves excited by the drift mode instability. By using reasonable assumptions concerning the wavelengths of these waves the observed frequency spectrum can be explained as being due to Doppler shifts caused by spacecraft motion through the plasma.
Diffusion‐thermal effects in the topside of the nocturnal equatorial ionosphere
Authors: Bailey G. J. , Moffett R. J.
Published: February 2008

A study is made of the steady state heat balance of the O+, H+, and electron gases in the topside of the nocturnal equatorial ionosphere. The method used is that developed previously by Bailey and others; input plasma concentrations and drift velocities are taken from work by Moffett and Hanson. In the present study, additional terms in the plasma heat flow vectors, as suggested by St.‐Maurice and Schunk, are included. The additional term that depends on relative flow of O+ and H+ gives rise to diffusion‐thermal effects in the O+ and H+ gases. On the other hand, with a zero‐current condition relating the electron, O+, and H+ field‐aligned flows, the electron heat flow vector reduces to the usual thermal conduction form. It is found that for the conditions considered, on the field line with equatorial crossing point at about 800 km at 2200 LT, the H+ temperature is raised by about 50 K and the O+ temperature is raised by about 30 K over the equator in comparison with results obtained when the terms suggested by St.‐Maurice and Schunk are omitted. In the winter hemisphere the H+ temperature may be lowered by about 20 K, and the O+ temperature by about 10 K. It is suggested that diffusion‐thermal effects will become more important with increasing altitude in the equatorial topside ionosphere at night.
Stereoscopic direction finding analysis of a Type III solar radio burst: Evidence for emission at 2fp−
Authors: Gurnett D. A. , Baumback M. M. , Rosenbauer H.
Published: February 2008

Stereoscopic direction finding measurements from the Imp 8, Hawkeye 1, and Helios 2 spacecraft over base line distances of a substantial fraction of an astronomical unit are used to directly determine the three‐dimensional trajectory of a type III solar radio burst. By comparing the observed source positions with the direct in situ solar wind plasma density measurements obtained by Helios 1 and 2 near the sun the relationship of the emission frequency to the local plasma frequency can be determined directly without any modeling assumptions. These comparisons show that the type III radio emission occurs near the second harmonic, 2fp−, of the local electron plasma frequency. Other characteristics of the type III radio emission, such as the source size, which can be obtained from this type of analysis are also discussed.
Energetic ionized helium in the quiet time radiation belts: Theory and comparison with observation
Authors: Spjeldvik Walther N. , Fritz Theodore A.
Published: February 2008

The nonadiabatic behavior of energetic α particles and singly ionized helium ions in the earth's inner magnetosphere is modeled for average quiet time conditions. A quasi‐equilibrium balance among inward radial diffusive transport of both kinds of ions, classical collisional Coulomb interactions, and charge exchange processes is assumed. Ion flux spectra are modeled at the outer boundary of the trapping region of the radiation belts which for this study was taken at L = 7. Radial profiles and energy spectra are computed at all lower L values, and the theory removes one degree of freedom compared to earlier work by predicting absolute intensities of the differential fluxes. The theoretical quiet time predictions are compared with direct observation of energetic helium ions in the lower MeV range obtained from the satellites ATS 6 and Explorer 45 at and below the geostationary orbit, respectively. To the extent of this data it is found that the theory simulates the most important characteristics of the radiation belt helium ion population. A number of spectral features of helium ions are predicted also below 1 MeV, and these can only be observationally tested on future satellites with more sophisticated ion detector systems.
Spectral line profiles in a planetary corona: A collisional model
Authors: Prisco Robert A. , Chamberlain Joseph W.
Published: February 2008

The theory of spectral line profiles for a planetary corona (Chamberlain, 1976) is extended to include the effects of H‐H+ resonant charge exchange in which satellite particles are omitted (Chamberlain, 1977). A computational model is detailed, and sample profiles are presented. Observations of Lyman alpha or Balmer alpha profiles would have an important application to an understanding of the distribution of satellite particles and the nonthermal component of escaping hydrogen. The problem of satellites is seen to merit further investigation.
Rocket‐borne measurements of particles and ion convection in dayside aurora
Authors: Daly P. W. , Whalen B. A.
Published: February 2008

As part of Operation Periquito, two sounding rockets were launched into regions of particle precipitation at invariant latitude 76°N and magnetic local time 13 hours from Cape Parry, Northwest Territories, Canada, in November 1975. On one of the flights, which did not cross any well‐defined auroral arcs, the electron spectra were always soft, the thermal ion drift velocity was variable but generally westward at 500 m/s, and energetic particles (>70 keV) were always well above cosmic ray background, indicating a region of closed magnetic field lines. The other flight crossed two auroral arcs. Electrons with soft (mean energy of 200 eV) power law spectra were observed on the equatorward and poleward sides, whereas intense 1‐keV precipitation was measured within the arcs. The mean drift velocity of thermal ions was seen to change from 1500 m/s westward, parallel to the boundary, on the equatorward side to ∼200 m/s southward on the poleward side of the arcs. Energetic (E > 70 keV) particle measurements showed that the high‐latitude boundary was well poleward of the auroral arcs (Heikkila and Winningham's ‘cleft’ precipitation and ion convection velocity reversals), which indicates that the entire region was on closed magnetic field lines. Comparison of these features with those from midnight aurora shows that the two are qualitatively similar, strongly suggesting that dayside and nightside arcs are different aspects of the same process. No support was seen for the idea that direct penetration of magnetosheath particles is responsible for the dayside aurora.
An extension of the dual magnetometer method for use on a dual spinning spacecraft
Authors: Lepping R. P. , Ness N. F.
Published: February 2008

A method of estimating and correcting for the magnetic field of a dual spinning spacecraft has been developed by employing an extension of the dual magnetometer technique of Ness et al. (1971). This new method is useful for those situations in which a magnetometer boom of modest length (7–10 m) is attached to the spinning part of a large spacecraft (800–1000 kg). The purpose of using a dual spinning spacecraft is to accommodate two types of instruments: (1) imaging and similar ‘pointed’ remote sensing systems on the stationary platform and (2) fields, particles, and other in situ measuring instruments on the spinning portion. Present‐day imaging systems are well known to exhibit large magnetic moments, sometimes displaced from the spacecraft center by a significant amount. The new method assumes that the stationary part of the spacecraft possesses a magnetic field which is represented by a combination of a dipole and a quadrupole field.
A model of the magnetospheric electric convection field
Authors: Volland Hans
Published: February 2008

The observed magnetospheric convection field at ionospheric heights is simulated by a simple analytic quasi‐static electric potential field. In particular, the transition region within the auroral zone where the meridional electric field component reverses is brought into close agreement with Heppner's (1977) observations. The location of zero meridional electric field strength in the model is compared with the observed Harang discontinuity (Maynard, 1974), where the zonal plasma flow reverses. The field‐aligned electric currents associated with the model electric field occur within two regions. In region 1, within the auroral zone, maximum outflow out of the ionosphere occurs at 1600 LT. In region 2, equatorward of the auroral zone, maximum outflow is near 0700 LT, consistent with measurements of Iijima and Potemra (1976).
The frontside boundary layer of the magnetosphere and the problem of reconnection
Authors: Haerendel G. , Paschmann G. , Sckopke N. , Rosenbauer H. , Hedgecock P. C.
Published: February 2008

Further Heos 2 plasma and magnetic field data obtained in the frontside boundary layers of the magnetosphere are presented. They reveal that the low‐latitude extension of the entry layer is of a somewhat different nature. The most pronounced difference with respect to the entry layer in the cusp region is the substantial density jump at the magnetopause. Furthermore, the low‐latitude boundary layer tends to be thinner and less turbulent, and the flow velocity inside the layer is always lower than that of the adjacent magnetosheath. This observation excludes large‐scale reconnection at the front of the magnetosphere as the origin of the layer. It is suggested that diffusive entry of magnetosheath plasma and/or heating of detached plasma from the plasmasphere leads to the formation of the layer. It appears likely that reconnection is dominantly occurring as a transient process in the cusp region and accompanies the eddy convection inside the entry layer. As a consequence, magnetic flux is being eroded from the front of the magnetosphere. This is in agreement with the signature of short‐term large‐amplitude magnetic perturbations observed in the low‐latitude boundary layer.
Direct evidence of transport processes in the thermospheric diurnal tide
Authors: Hedin A. E. , Spencer N. W. , Mayr H. G. , Harris I. , Porter H. S.
Published: February 2008

Measurements of neutral composition and temperature obtained between December 6, 1975, and September 17, 1976, with instruments aboard the near‐equatorial AE‐E satellite are analyzed to determine the diurnal variations at altitudes from 145 to 295 km. The general trends, including the shift in oxygen phase from afternoon at high altitudes to morning at low altitudes, are reproduced by circulation theories. The oxygen and helium variations show small departures from diffusive equilibrium below 200 km that are consistent with wind‐induced diffusion and provide the first direct evidence of transport processes in the diurnal tide of the thermosphere.
Tidal variations in thermospheric O, O2, N2, Ar, He, and H
Authors: Forbes Jeffrey M.
Published: February 2008

A formalism is developed for computing tidal variations in thermospheric composition and is used to investigate diurnal and semidiurnal variations in O, O2, N2, Ar, He, and H at minimum and maximum levels of sunspot activity. The model formally accounts for tidal temperatures, horizontal and vertical tidal winds, photochemistry and ion chemistry, thermal diffusion, and exospheric transport in determining the tidal variations of these constituents, as well as deviations from diffusive equilibrium in the time average component due to photochemistry, Jeans escape, or background vertical winds. A procedure is described for using available measurements to calibrate the diurnal and semidiurnal wind and temperature fields, which are used as inputs to the model. Sunspot minimum calculations show excellent agreement with equatorial San Marco 3 Nace measurements in both amplitude and phase for diurnal and semidiurnal variations between 220 and 280 km. Major exceptions are the equatorial diurnal amplitude of Ar, which the model overestimates by 35%, and the equatorial diurnal amplitude of He, which the model underestimates by about 25%. Simulations for sunspot maximum conditions demonstrate substantial solar cycle differences in the vertical structures of amplitude and phase for each constituent and in the relative contribution of semidiurnal and diurnal components at different latitudes and heights. Consequently, a clear need is indicated for continued satellite mass spectrometer and accelerometer measurements over different levels of solar activity if comprehensive empirical models of thermosphere tides are to be developed.
Mariner 10 magnetic field observations of the Venus wake
Authors: Lepping R. P. , Behannon K. W.
Published: February 2008

Magnetic field measurements made over a 21‐hour interval during the Mariner 10 encounter with Venus were used to study the downstream region of the solar wind‐Venus interaction over a distance of ≈ 100 Rv (Venus radii). Mariner 10 encountered Venus on February 5, 1974, with closest approach at 1702 UT. For most of the day before closest approach the spacecraft was located in a sheathlike region which was apparently bounded by the planet's bow shock on the outer side and either a planetary ‘wake boundary’ or a transient boundarylike feature on the inner side. The spacecraft made multiple encounters with the wakelike boundary during the 21‐hour interval with an increasing frequency as it approached the planet. Each pass into the wake boundary from the sheath region was consistently characterized by a slight decrease in magnetic field magnitude, a marked increase in the frequency and amplitude of field fluctuations, and a systematic clockwise rotation of the field direction when viewed from above the plane of Venus' orbit. These boundary crossings were not accompanied strictly by hydromagnetic directional discontinuities, however, but occasionally (∼⅓ of the crossings) such a discontinuity was sufficiently close to the crossing zone to be considered part of the boundary transition. There were a significantly larger number of discontinuities in the overall 21‐hour period than were observed on average during other comparable periods both before and after encounter. A simple large‐scale draped field model in the sense of a magnetic ‘comet tail’ was found not to hold for the downstream region. The sporadic observation of the wake during the near‐encounter period may have been controlled by changes in the direction of the interplanetary field.
Ground‐satellite correlations during presubstorm magnetic field configuration changes and plasma sheet thinning in the near‐Earth magnetotail
Authors: Pytte T. , West H. I.
Published: February 2008

Observations of electron precipitation were made with balloon‐borne X ray detectors and with riometers in Scandinavia on August 9 and 17, 1968, while Ogo 5 was inbound from the magnetotail making observations of the plasma sheet. Clear substorm growth phase effects were observed in terms of changes in field configuration, particle intensity, and pitch angle distributions at Ogo 5 and in the enhanced electron precipitation observed on the ground. For each of the five substorm studies a clear southward turning of the interplanetary magnetic field preceded enhanced plasma sheet thinning, contrasted with the natural thinning during substorm recovery at distances 10–15 RE from the earth near midnight. Pi 2 magnetic pulsations along with mid‐latitude and auroral zone magnetograms established substorm expansion onset. During three of the substorms, conditions were ideal for observing precipitation. The observed precipitation is readily interpreted in terms of eastward azimuthally drifting electrons encountering an increasingly taillike field configuration during the substorm growth phase, a situation resulting in scattering of the electrons near the neutral sheet owing to the taillike magnetic field configuration. As the thinning proceeds, the precipitation region near the earth moves to the lower latitudes, later to move to higher latitudes during expansion. The results are quite in agreement with current growth phase models, at least in the case of isolated substorms.
Solar wind spatial structure: The meaning of latitude gradients in observations averaged over solar longitude
Authors: Hundhausen A. J.
Published: February 2008

The three‐dimensional structure of the solar wind is often studied by searching for solar latitude variations in observed physical properties that have been averaged over solar longitude. The effects of longitude averaging are examined here by using general qualitative arguments and quantitative calculations for a simple class of assumed spatial variations in the solar wind speed. We show that unless the solar wind spatial structure is simply organized about the solar equator, its presence is extremely difficult to infer from longitude averages unless the observations extend to very high solar latitudes. Thus the absence of semiannual variations in ecliptic observations or the absence of large latitude gradients in radio scintillation or comet tail results do not constitute evidence against the presence of strong spatial variations (or large spatial gradients) in the solar wind.
Magnetic field perturbations in the dayside cleft and their relationship to the IMF
Authors: McDiarmid I. B. , Burrows J. R. , Wilson Margaret D.
Published: February 2008

Magnetometers on the Isis 2 satellite have been used to study large‐scale perturbations in the geomagnetic field in the region of the dayside cleft (or cusp). Relatively large perturbations, in a plane perpendicular to the main field direction, are observed on most satellite passes; on the average the perturbations near noon are larger than those observed in the dawn and dusk sectors. The peak perturbations tend to lie in two relatively narrow ranges of direction, pointing approximately eastward or westward depending on the sign of By, the y component of the interplanetary magnetic field (IMF). In general, for this northern hemisphere data set, positive By corresponds to an eastward perturbation, and negative By to a westward perturbation. The invariant latitude of the perturbation is correlated with Bz, the z component of the IMF, while the magnitude of the perturbations is more strongly correlated with By than with Bz. The perturbations are discussed briefly in terms of the tilt of the field direction relative to a model field, and it is suggested that this is related to the direction of convection in the magnetosphere. On the basis of this interpretation the predominant convection direction in the cleft is approximately either eastward or westward.
Energetic particle measurements from within ionospheric structures responsible for auroral acceleration processes
Authors: Sharp R. D. , Johnson R. G. , Shelley E. G.
Published: February 2008

Measurements of energetic electrons (0.07 ≤ E ≤ 24 keV) and ions (0.5 ≤E ≤16 keV) on the S3‐3 satellite show features which are interpreted in terms of parallel potential drops of up to several‐kilovolt magnitude existing simultaneously both above and below the satellite. This leads to the inference that the satellite is within an auroral acceleration region. Two events of this type are examined in which the satellite is in the 7000‐ to 8000‐km altitude range and at auroral latitudes. Both events are interpreted as traversals of an ‘inverted V’ acceleration region of broad latitudinal width (2°–4°). In both cases, one can infer a vertical extent to the acceleration region of ≳10³ km.
A study of magnetosphere dynamics during auroral electrojet events by observations of energetic electron intensity changes at synchronous orbit
Authors: Erickson K. N. , Swanson R. L. , Walker R. J. , Winckler J. R.
Published: February 2008

A statistical study of over 1600 events has established that a close temporal correlation exists between the start of energetic electron directional intensity changes observed at synchronous orbit and the intensification of electrojet currents in the polar ionosphere. This result provides strong evidence that both phenomena are physically linked as part of a large‐scale disturbance and that the electrojet system is closely coupled to other current systems in the distant magnetosphere. The statistical pattern in local time of these electrojet‐associated electron intensity variations consists of decreases observed in the pre‐midnight sector, increases observed over a broad region symmetrical about midnight and spectrum softening increases observed post‐midnight. In the local evening sector intensity decreases and increases are observed with equal probability and typically occur as two parts of a single time sequence such that the decrease directly precedes the increase. Furthermore, while the start times for the decrease and the subsequent increase are both well‐correlated with a marked electrojet intensification the increase is also well‐correlated with a mid‐latitude positive bay but the decrease is not. This difference together with the fact that decreases systematically precede increases in the local time region where both are observed strongly suggests that the decrease corresponds to a distinct ‘precursor’ of the increase event which follows. These results are important for understanding the temporal development of magnetospheric disturbances and are also not consistent with ‘the fault‐line’ concept which suggests that the pre‐midnight decrease corresponds to a simultaneous increase event occurring further eastward in local time. The intensity decreases are closely correlated with a decrease in the local magnetic field and have been interpreted in terms of the electrons responding to a diamagnetic reconfiguration resulting from an enhancement of the particle energy density due to convection of plasma sheet protons into the pre‐midnight region. The subsequent intensity increases are accompanied by an increase in the local magnetic field and can be associated with a tail‐field collapse at expansion onset.
Scattering of ordinary electromagnetic waves by ion cyclotron waves in the ionosphere
Authors: Shukla P. K. , Tagare S. G.
Published: February 2008

It is shown that an ordinary electromagnetic wave can excite parametric instability by scattering off electrostatic ion cyclotron waves. Application of our result in the European auroral zone of the ionosphere is discussed.
Response of magnetotail plasma at lunar distance to changes in the interplanetary magnetic field, the solar wind plasma, and substorm activity
Authors: Hardy D. A. , Reiff P. H. , Burke W. J.
Published: February 2008

From an analysis of particle and field data obtained on January 19 and 20, 1973, we have determined several important characteristics of the plasma populations in the geomagnetic tail at lunar distance and their relationships to conditions in the solar wind and interplanetary magnetic field (IMF). During an extended period of low geomagnetic activity with the IMF Z component predominantly northward the plasma sheet at lunar distance is observed to cool significantly. Ion temperatures are observed in the range kTi ∼200–400 eV with electron temperatures of ∼100 eV. Number densities are approximately 1 cm−3. During this period the plasma mantle is also present as an extensive but tenuous region of plasma with densities ni = ne ∼10−2 cm−3, bulk velocity VB ∼100 km/s, and ion temperature kTi ∼3 eV. Following a sharp southward turning of the IMF Z component, there is a net transfer of magnetic flux to the tail. At lunar distance the magnetic field in the lobes increases in magnitude, and the density of the plasma mantle increases sharply. The time delay between the southward turning and the observed changes at lunar distance is consistent with the southward IMF being the cause of the increase of the magnetic flux and the plasma mantle density. The electrons in the plasma mantle display a core and halo distribution indicating a solar wind origin. The plasma sheet is observed to become hotter with increasing geomagnetic activity, reaching ion temperatures in excess of 1 keV and electron temperatures up to 900 eV.
On the viscous flow behavior of the shocked solar wind at the Venusian ionopause
Authors: Pérez‐De‐Tejada Héctor
Published: February 2008

The viscous boundary layer concept for the shocked solar wind at the flank regions of the Venusian ionopause is discussed in connection with the most recent experimental results of the Venera 9 and 10 data analysis. The observed dynamics of the plasma in the near wake give further support to the view that the shocked solar wind interacts viscously with the ionospheric material in the vicinity of the planetary terminator. Considerations of mass flux conservation within the ionosheath flow suggest that solar wind protons should be a major component of the plasma density in the wake.
Energetic particle precipitation into the high‐latitude ionosphere and the auroral electrojets, 2. Eastward electrojet and field‐aligned current flow at the dusk meridian
Authors: Rostoker Gordon , Winningham J. D. , Kawasaki Koji , Burrows J. R. , Hughes T. J.
Published: February 2008

Soft particle spectrometer and energetic particle detector data from the Isis 2 polar‐orbiting satellite are organized in the framework of the eastward electrojet flowing in the local time range around dusk. The structure of the ionospheric electrojets is inferred from ground‐based magnetic data using a meridian line of magnetometers through western Canada. Irregularities in latitude profiles of the magnetometer data near the dusk meridian indicate that there is a double structure within the current flow, with strong eastward current flow in the poleward portion of the electrojet. Precipitating energetic electron fluxes are found within this region of strong eastward current flow in the poleward portion of the electrojet. No significant energetic electron or proton fluxes are found in the equatorward portion of the eastward electrojet. Using realistic models of the ionospheric and field‐aligned currents flowing in the evening sector, it is demonstrated that a portion of the eastward electrojet in the postnoon quadrant flows up the field lines into the magnetosphere at the dusk meridian. It is suggested that this segment of the eastward electrojet exists because of the presence of a poleward electric in the sunlit ionosphere and that upward field‐aligned current flow occurs at the conductivity discontinuity between the sunlit and dark ionospheres.
A study of ionospheric scintillations of phase and quadrature components
Authors: Myers W. J. , Gjeldum R. J. , Liu C. H. , Yeh K. C.
Published: February 2008

Statistical properties of the phase as well as the quadrature components of the ionospheric scintillating radio signal are investigated using data received from the ATS 6 radio beacon experiment. For weak scintillation the phase‐quadrature components dominate the fluctuations. When the scintillation level is increased, the multiple scattering seems to have the effect of equalizing the power between the two quadrature components. The phase spectra are consistent with power law irregularity models. For strong scintillations the phase spectra become flattened. The spectra for the quadrature components as well as the frequency dependence of the mean square phase fluctuations are studied. The experimental data were interpreted using existing scintillation theories.
The interaction of electrons in the optical umbra of Venus with the planetary atmosphere—The origin of the nighttime ionosphere
Authors: Gringauz K. I. , Verigin M. I. , Breus T. K. , Gombosi T.
Published: February 2008

The ionization produced by electrons having energies of several tens of electron volts in the nighttime Venusian atmosphere is investigated on the basis of plasma measurements made on board Venera 9 and 10. We conclude that electron fluxes are sufficient to produce a nighttime ionosphere with a maximal electron density of 104 cm−3. Calculated density profiles of the Venusian nighttime ionosphere show shapes closely resembling measured ones with closely agreeing values of maximal density and corresponding altitudes as well.
Gyroharmonic emissions induced by energetic ions in the equatorial plasmasphere
Authors: Curtis S.A. , Wu C.S.
Published: February 2008

The general problem of the excitation of ion gyroharmonic electrostatic and electromagnetic waves by energetic ions (E ≳ 0.1 MeV) in a thermal plasma as observed in the earth's plasmasphere is considered. The thermal plasma is taken to be predominantly H+ with trace higher Z ion constituents of ionospheric origin such as He+ and O+. This plasma component has a Maxwellian distribution and supports the waves which may be excited by energetic ions with Z ≳ 1. The energetic ions possess a power law distribution in energy with strong pitch angle anisotropy. Coupling of the free energy source of the energetic ions to the waves is obtained via the velocity dependence of the ion gyrofrequency Ωα. Owing to constraints imposed by free energy coupling, wave amplification, and ion cyclotron damping, the dominant growth rates are found for nearly perpendicularly propagating fast magnetosonic waves closely confined to the magnetic equator. Growth is restricted to frequencies immediately below the ion gyroharmonics by the resonance condition and implies line widths of ∼ 10−3Ωα. The fast magnetosonic waves are found to have a significant electromagnetic component which decreases with increasing gyroharmonic number. The polarization becomes almost entirely electrostatic where the fast magnetosonic and ion Bernstein branches merge above the lower hybrid frequency. When it is compared to observations of ion gyroharmonic emissions, the theory implies that there exist a significant number of charge states for Z ≳ 2 MeV ions in the plasmasphere.
Entry of solar protons to the plasma sheet and lobe of the magnetotail at r=18 RE in the event of April 22, 1971
Authors: Palmer I.D. , Jackson J.C. , Hones E.W.
Published: February 2008

Vela satellites of orbit r=18 RE measured the intensity of ≲1‐MeV solar protons at two points in the plasma sheet and one in the north tail lobe during an 8‐hour period on April 22, 1971. Intensities were isotropic, except when a sharp gradient was convected past a satellite. Several such gradients have been interpreted as the boundary between plasma sheet and north lobe. Movement of this plasma sheet surface has been observed in coincidence with substorm and geomagnetic storm activity. It is inferred that the region of open field lines at Vela orbit was very small in this event. A prolonged intensity difference by a factor of almost 2 existed across the surface between plasma sheet and lobe for >8 hours, implying very little cross‐field transport of ≲1‐MeV protons. One gradient‐induced anisotropy was anomalous in direction and has been explained by a tongue‐shaped distortion in the surface separating plasma sheet and lobe. A second case of anomalous anisotropy from another event has been explained in a similar way. Intercomparison between Vela and Imp 6, the latter in interplanetary space, suggests the following. Access of ≲1‐MeV solar protons to the north tail lobe was delayed by 3–4 hours, giving an access point 602–872 RE from earth. The intensity there was a little higher than the mean of the interplanetary distribution. The intensity in the dusk plasma sheet lay between the mean in interplanetary space and the integrated intensity of the backward moving interplanetary particles (−1 < µ < 0). The intensity in the dawn plasma sheet was lower and tracked the integrated intensity of the backward moving particles in interplanetary space. This gradient across the plasma sheet at r=18 RE implies that there was not a thorough mixing of ≲1‐MeV protons, at least on a time scale of hours.
Seasonal variations in mesospheric molecular oxygen
Authors: Ilyas Mohammad
Published: February 2008

Analysis of molecular oxygen data over the 70‐ to 90‐km range indicates strong seasonal variations at most of the altitudes except 90 km, where the magnitude is rather small. The seasonal variations are in general agreement with the Cira (1972) model (summer maximum).
Doppler line profiles in a planetary corona: An extended approach
Authors: Prisco Robert A. , Chamberlain Joseph W.
Published: February 2008

Measurements of the line profile of the geocoronal Lyman alpha emission by the hydrogen cell aboard Ogo 5 and a marked day‐night asymmetry in the measured intensity distribution have led Bertaux (1974, 1978) to conclude that the population of satellite particles in the exosphere cannot be described by any single value of the satellite critical radius (Chamberlain, 1963). Rather, he concludes (on the basis of a computer simulation of the effect) that Lyman alpha radiation pressure from the sun destroys satellites in a complicated manner which depends upon the initial orbital parameters of each particle and that the satellite critical radius formalism may no longer be a viable way to distinguish a satellite population. He does not, however, consider the alteration of the profile due to proton‐neutral charge exchange when the ionic temperature differs from that of the neutrals (Chamberlain, 1977; Prisco and Chamberlain, 1978), nor does he take into account the fact that the satellite temperature may differ from that of the remaining neutral population. This investigation takes the point of view that Bertaux's interpretation of his data may not be unique. In particular, the influence of these last two effects on the inferred profile (characterized by a ‘reduction factor’) is examined, and several conclusions are reached. First, we find that the perturbation to the reduction factor by charge exchange among the ballistic and escaping populations is negligible. Second, we are able to reproduce the Ogo 5 data satisfactorily by introducing a satellite population characterized by λcs=1.5 and a temperature which equals the neutral temperature beyond about 6 RE but increases inward to about 1.2 times the neutral temperature at 2 RE. We also argue that radiation pressure effects are symmetrical and hence are unlikely to be the cause of the observed asymmetry. Thus the question of how best to describe a satellite population appears still to be open.
A correlation between auroral kilometric radiation and inverted V electron precipitation
Authors: Green James Lauer , Gurnett Donald A. , Hoffman Robert A.
Published: February 2008

Simultaneous observations of energetic electron precipitations and auroral kilometric radiation (AKR) were obtained from the polar orbiting satellites AE‐D and Hawkeye. The Hawkeye observations were restricted to periods when the satellite was in the AKR emission cone in the northern hemisphere and at radial distances ≳7 RE to avoid local propagation cutoff effects. In addition, the AE‐D measurements were restricted to complete passes across the auroral oval in the evening to midnight local time sector (from 20 to 01 hours magnetic local time). This is the local time region where the most intense bursts of AKR are believed to originate. A qualitative survey of AKR and electron particle precipitation shows that AKR is more closely associated with inverted V electron precipitation than with plasma sheet precipitation. Quantitatively, a good correlation is found between the AKR intensity and the peak energy of inverted V events. In addition, in the tail of the most field‐aligned portion (∼0° pitch angle) of the distribution functions of the inverted V events, systematic changes are indicated as the associated AKR intensity increases. When the AKR power flux is weak (<10−17 W/(m² Hz)), the effective tail temperature (T∥) in F(V∥) of the inverted V events is less than 1.8 × 108°K, while for T∥ greater than 1.8 × 108°K the associated AKR power flux is moderate (10−17 to 10−15 W/(m² Hz)) to intense (>10−15 W/(m² Hz)). From a determination of the simultaneous power in the inverted V events and the AKR bursts, the efficiency of converting the charge particle energy into EM radiation increases to a maximum of about 1% for the most intense AKR bursts. However, conversion efficiencies as low as 10−5% are also found. There is some evidence which suggests that the tail temperature, T∥ in F(V∥) of the inverted V events, may play an important role in the efficient generation or amplification of auroral kilometric radiation.
Studies of the sharply defined L dependent energy threshold for isotropy at the midnight trapping boundary
Authors: Imhof W.L. , Reagan J.B. , Gaines E.E.
Published: February 2008

It has previously been reported (Imhof et al., 1977) that near the midnight trapping boundary the onset of isotropy for electrons and protons often occurs at a sharply defined energy threshold which decreases rapidly with increasing L value. In this paper the addition of energy spectrum measurements to the pitch angle distributions provides new information on the magnetic field configuration in the tail region during these cases. The energy dependent characteristics presented here include the positions and total latitude widths of the transition region from locally trapped to precipitating pitch angle distributions, the intensities and locations of near‐coincident enhancements in the trapped fluxes, and the intensities of electron precipitation at energies below the threshold for isotropy. During geomagnetically disturbed times, isotropy at a given energy tends to occur on lower L shells than it does at quiet times, but the widths of the transition region from locally trapped to isotropic pitch angle distributions show no well‐defined dependence upon geomagnetic activity. No evidence is found that unusually broad transition regions occur at any one characteristic phase of a substorm. At energies below the isotropy threshold the ratios of precipitating to trapped electron fluxes display large variations ranging from less than 10−3 to more than 10−1. Near the trapping boundary, enhancements are often observed in the fluxes of locally trapped electrons having minimum drift altitudes of ∼400 km or less. The L shells at which the maximum fluxes occur often display a rigidity dependence which is similar to that associated with the isotropy phenomenon.
An energetic particle perspective of the magnetopause
Authors: Williams D.J. , Fritz T.A. , Wilken B. , Keppler E.
Published: February 2008

We present a detailed analysis of energetic (>24 keV) particle data obtained from the Isee satellites during a series of magnetopause crossings which occurred at 0000–0400 hours UT (∼1030 hours LT) on November 20, 1977. The primary energetic particle data used are the three‐dimensional distributions obtained from the Isee A satellite. Correlative magnetic field measurements are used to relate the particle behavior to magnetic field characteristics at and earthward of the magnetopause. We find that to first order the magnetopause can be regarded as a perfectly absorbing boundary for trapped >24‐keV particles, that it is nearly always in motion, and that boundary waves are often present. We find that the observed dayside magnetopause motion is consistent with a large‐scale radial motion having an ∼10‐min period plus superimposed boundary waves with a 90‐ to 150‐s period. More qualitatively, we find that the data require a third and longer period (∼30 min) magnetopause motion upon which the above, shorter‐period motions are superimposed. Consistent with the picture of absorbing boundary, we find no evidence of microturbulent processes at the magnetopause which significantly affect the directional trapped particle flux to within 9–36 km of the boundary. We therefore conclude that the radial gradient to the magnetopause observed in the directional, >24‐keV, dayside, near‐equatorial, magnetospherically trapped particle flux is due to internal magnetospheric processes. Just outside the magnetopause in the magnetosheath we observe a broad (approximately hemispherical) field‐aligned flow of >24‐keV ions away from the magnetosphere. The absolute intensity and spectral characteristics of this flow and its relation to the magnetopause and the trapped particle population indicate that it is formed by the leakage of trapped particles from the radiation belts onto magnetosheath field lines as their trajectories move to within two gyroradii of the magnetopause.
Thermal ion results from an experiment to produce artificially an ionospheric hole: Lagopedo Uno
Authors: Daly P.W. , Whalen B.A.
Published: February 2008

An instrument designed to determine the three‐dimensional velocity and mass distribution of ions with energy per charge up to 3 eV was flown for the first time as part the Lagopedo Uno rocket experiment, the purpose of which was to deplete artificially the ion concentration in the F layer ionosphere over Hawaii. The device measured relative ion densities and directionality; mass analysis between 1–32 amu/e was performed by using a time‐of‐flight technique. The depletion was achieved by detonating an explosive charge which released 1027 molecules of H2O, accompanied by lesser amounts of NO and CO2. At the time of the explosion the densities of all ion species were reduced below the limit of detectability for 2.5 s. Over the next 60 s, as the instrument package moved 30 km away from the detonation site, O+ was again detected but at a concentration only half that expected from preevent levels and altitude corrections. The O2+ concentration within 60 s and 30 km of the explosion was up to 3 times its earlier value. During the same space and time intervals the O+ mean velocity had a component of velocity perpendicular to the line joining the detector and the detonation location, consistent with an electric field, ∼10 mV/m, pointing toward the center of the ‘hole.’ Later, while the instrument package was 30 km from the explosion site, the O2+ density was seen to increase again, while the O+ density remained below the unperturbed value. The contaminants therefore reached 30 km within 2 min. The behavior of O+ compares favorably with predictions from a simple spherical diffusion model of H2O. H2O+ could not be observed, since it overlapped the O+ mass channel and was expected to be much less than the latter. H+ did not respond to the event except for the dropout of 2.5 s. These measurements of ion composition and depleted region growth pattern are in general agreement with theoretical descriptions of such events, such as that of Bernhardt (1976).
A study of solar flare electron events from October 1972 through December 1974 from Imp 7 and 8
Authors: Decker R. B. , Armstrong T. P.
Published: February 2008

Data from the Johns Hopkins University Applied Physics Laboratory Charged Particle Measurement Experiment aboard Imp H and J were searched for solar flare produced intensity increases in >0.2‐MeV electrons during the 26‐month period from October 1972 through December 1974. Of the 44 solar electron events found during this period, 31 were isolated for a detailed statistical study. Systematics among the characteristics of the electron profiles (e.g., peak intensity times and count rates) and those of the associated flares (e.g., Hα onset times, Hα importance class, heliocentric coordinates, etc.) were examined, and the significant results are presented in several scatter plots. The results reveal that the time delay between the flare onset and the arrival of the peak electron intensity at 1 AU (time to maximum) is a function of the flare's deviation in heliolongitude from the solar region which was well connected to the earth via a magnetic flux tube; the well‐connected flares produced electron intensity maxima in the least time. The data also show that as the flare's deviation from the well‐connected region increases, soft electron events are less likely to be observed, and the peak electron intensities are markedly decreased. No dependence of the time to maximum on the flare's heliolatitude is apparent. It is also found that solar flares with larger Hα areas tend to produce harder electron events.
Artificial aurora conjugate to a rocket‐borne electron accelerator
Authors: Davis T.N. , Hess W.N. , Trichel M.C. , Wescott E.M. , Hallinan T.J. , Stenbaek‐Nielsen H.C. , Maier E.J.R.
Published: February 2008

An accelerator intended to send electron beams upward along an L=1.24 magnetic field line was flown from a rocket launched from Kauai, Hawaii, on October 15, 1972. Though the intent was to produce several hundred observable auroral streaks in the southern hemisphere, imaging instruments operated there aboard jet aircraft detected only a single aurora. Produced by a 0.155‐A beam of energy 22.8 keV, the aurora was of expected brightness, had diameter (210±50 m) somewhat larger than expected, and altitude (top: 116±2 km; bottom: 92±2 km) higher than expected.
Comment on ‘Magnetosheath burst of predominantly medium nuclei observed with Imp 8 on February 16, 1974’ by T. P. Armstrong, S. M. Krimigis, and R. P. Lepping
Authors: Hovestadt Dietrich
Published: February 2008

Armstrong et al. (1978) report the observation of a unique series of charged particle bursts with an unusually high content of Z >2 particles and a high degree of collimation from the direction of the sun. These bursts were observed only with their CPME (charged particle measurement experiment) instrument on Imp 8, while not with the CPME on Imp 7. No indication has been seen for heavy ion bursts comparable in intensity to those reported by Armstrong et al. (1978) with the ULET (ultralow energy telescope) instrument of the University of Maryland/Max‐Planck‐Institut experiment on Imp 8 at the same time. It is noted that the ULET counting rates observed on Imp 8 are fully compatible with the CPME rates observed on the Imp 7 spacecraft. We conclude that the CPME and the ULET data from Imp 8 during these periods do not agree, and this casts doubt on the correctness of the CPME results for these special events.