bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of the interplanetary sector structure up to heliographic latitudes of 16°: Pioneer 11
Authors: Smith Edward J. , Tsurutani Bruce T. , Rosenberg Ronald L.
Published: February 2008

A study of the interplanetary sector structure at Heliographic latitudes up to 16°N is reported. The study is based on magnetic field measurements made on board Pioneer 11 as the spacecraft traveled along the post‐Jupiter‐encounter trajectory. Preliminary measurements are used to determine the dominant polarity of the interplanetary magnetic field during 43 successive solar rotations including Pioneer's ascent to its maximum latitude and motion inward from 5 to 3.7 AU. As the latitude of Pioneer increased, the dominant polarity became continually more positive, corresponding to an outward‐directed solar interplanetary field. When the spacecraft reached the highest latitude, the usual sector structure had essentially disappeared. A histogram of the field longitude angle, based on data acquired during 1 month at 16° latitude, shows an almost total absence of inward‐directed fields. A comparison with interplanetary field polarities in the ecliptic, as inferred from geomagnetic field variations, rules out the possibility that a time variation rather than a latitude dependence is responsible. The Pioneer 11 observations imply that the boundary between adjacent sectors corresponds physically to a current sheet surrounding the sun and lying nearly parallel to the solar equatorial plane. Above this current sheet, in the northern hemisphere, the field polarity at this phase of the solar cycle is outward, and below the current sheet, in the southern hemisphere, it is inward. The Pioneer observations confirm earlier theoretical suggestions regarding the existence and equatorial orientation of this current sheet. The properties of the current sheet and some major implications and questions associated with it are discussed. It is shown that the radial component of the sheet current is compensated by the distributed currents in the northern and southern hemispheres associated with the spiraled interplanetary field.
A mechanism for current interruption in a collisionless plasma
Authors: Kan J. R. , Akasofu S. ‐I.
Published: February 2008

A mechanism for current interruption in a collisionless plasma is proposed. When a current exceeds the Buneman instability threshold, the instability leads to the growth of Bernstein‐Greene‐Kruskal (BGK) waves in the form of a row of solitary negative potential wells along the current path. As these solitary BGK waves grow, they trap an increasing number of current‐carrying electrons between neighboring potential wells. This trapping process is proposed as a possible mechanism for current interruption in a collisionless plasma. The trapping is complete in about 100 plasma periods, as is indicated by a number of numerical simulation results. The fraction of current interrupted by the proposed mechanism depends on the ratio of the ion thermal energy to the electron streaming energy. In a model examined in this paper it is found that for the unstable current to be interrupted and reduced to one half of its original value, the ion to electron energy ratio must be greater than 2. To interrupt the current by a larger fraction, a higher energy ratio is required. Possible application of this current interruption mechanism to magnetospheric substorms is suggested.
Nonthermal rate coefficients in the ionosphere: The reactions of O+ with N2, O2, and NO
Authors: St.‐Maurice J. ‐P. , Torr D. G.
Published: February 2008

The rate coefficient of a chemical reaction is given by the equation k = ∫0∞ συ f(υ) dυ, where σ is an energy dependent cross section, υ is the relative speed of the reactants, and f(υ) is the relative speed distribution. For certain highly energy dependent ionospheric reactions, k is controlled by the population in the high‐energy tail of the relative speed distribution. This leads to problems in the application of laboratory measurements of rate coefficients to the atmosphere where f(υ) can be significantly different for the same effective temperature. However, we show that the rate coefficients in the laboratory and in the thermosphere are approximately the same for the same value of the mean energy parameter KEcm if a thermal equilibrium apparatus such as a static or flowing afterglow system is used in the laboratory. The rate coefficients are in general not the same in the atmosphere as in drift tube experiments, although for O+ in a helium buffer the difference is about 25% or less. As an application of the present work we derive new expressions for the rate coefficients of O+ reacting with N2, O2, and NO in the ionosphere, using cross sections published by laboratory workers.
Morphological studies of rising equatorial spread F bubbles
Authors: Ossakow S. L. , Chaturvedi P. K.
Published: February 2008

Analytical electrodynamic morphological studies of rising equatorial spread F bubbles, within the context of the collisional Rayleigh‐Taylor regime, are presented. The analogy between bubbles (plasma density depletions) and barium clouds (plasma density enhancements) is noted. Bubbles tend to steepen on their tops and elongate in the vertical direction, and they narrow horizontally as they rise through the equatorial F region ionosphere. Linear and nonlinear models of constant shape bubbles are presented. It is shown for these models that the vertical bubble rise velocity VB = (g/νin)f(δn/n0), where νin is the ion‐neutral collision frequency and f is an increasing function of δn/n0 (fractional density depletion), depending on the shape of the bubble. Consequently, high altitudes and/or large percentage plasma depletions yield large vertical bubble rise velocities. The models are extended to include arbitrary electric fields in addition to the gravitational force.
Induced precipitation of inner zone electrons, 1. Observations
Authors: Vampola A. L. , Kuck G. A.
Published: February 2008

Narrow precipitation spikes of energetic electrons observed in the inner zone drift loss cone during the 1968–1970 period by instrumentation on the OV1‐14 and OV1‐19 satellites are shown to have characteristics which are consistent with pitch angle scattering produced through a resonant interaction with ground‐based VLF transmissions. Analysis of the pitch angle distributions indicates that for virtually all of the events the electrons last interacted with the atmosphere in the vicinity of 55°–62° east longitude. The L dependency of the spikes as a function of energy is consistent with scattering by a monochromatic wave. The presumption is that the Russian station UMS, located at 44°E and operating at a frequency of 16.2 kHz during this period, was responsible for these precipitation events.
Collision frequency of artificial satellites: The creation of a debris belt
Authors: Kessler Donald J. , Cour‐Palais Burton G.
Published: February 2008

As the number of artificial satellites in earth orbit increases, the probability of collisions between satellites also increases. Satellite collisions would produce orbiting fragments, each of which would increase the probability of further collisions, leading to the growth of a belt of debris around the earth. This process parallels certain theories concerning the growth of the asteroid belt. The debris flux in such an earth‐orbiting belt could exceed the natural meteoroid flux, affecting future spacecraft designs. A mathematical model was used to predict the rate at which such a belt might form. Under certain conditions the belt could begin to form within this century and could be a significant problem during the next century. The possibility that numerous unobserved fragments already exist from spacecraft explosions would decrease this time interval. However, early implementation of specialized launch constraints and operational procedures could significantly delay the formation of the belt.
Electron density in the plasmasphere: Whistler data on solar cycle, annual, and diurnal variations
Authors: Park C. G. , Carpenter D. L. , Wiggin D. B.
Published: February 2008

Whistler data are used to present a statistical view of equatorial plasmaspheric electron density neq and associated tube electron content NT (defined as the number of electrons in a geomagnetic flux tube of 1cm² cross‐sectional area at 1000km altitude and extending to the magnetic equator). The data were acquired between 1959 and 1973 at Byrd (L ≃ 7), Eights (L ≃ 4), and Siple (L ≃ 4), Antarctica, which are within 1 hour of the same geomagnetic meridian, and from Stanford, California (L ≃ 2). The plasmaspheric neq profile beyond L ≃ 3 is dominated by variations associated with magnetic disturbances and subsequent recovery. In the aftermath of disturbances the plasmasphere tends to be divided into an inner ‘saturated’ region, which is in equilibrium with the underlying ionosphere in a diurnal average sense, and an outer ‘unsaturated’ region, which is still filling with plasma from below. In the outer plasmasphere byond ˜3.5 RE, diurnal variations appear as relatively small effects superimposed on larger storm‐associated variations. Large numbers of whistler traces (as many as 3000 in some cases) were scaled for each of several months. These data sets form the basis for approximations to neq profiles to form log10 (neq) = aL + b. These profiles are offered for reference use in estimating plasmasphere density levels. The previously reported annual and solar cycle variations are further documented by new evidence that these effects diminish with increasing L beyond L ≃ 3.
Vibrational development and quenching effects in the N2(B³Πg‐A³Σu+) and N2+(A2Πu‐X2Σg+) Systems in Auora
Authors: Jones A. Vallance , Gattinger R. L.
Published: February 2008

Quantitative spectra have been obtained of aurora in continuous scans from 7500 Å to 11,400 Å with a spectrometer using an S‐1 photomultiplier. Spectra were obtained of bright and very bright aurora. Significant differences were found between these spectra in the ratio of the N2+ Meinel system and the N I 3F multiplet to the N2 first positive system. These differences are interpreted as quenching effects, and it is estimated on the basis of published values of the quenching rate coefficients that the two spectra spanned a range of 12–18 km in mean excitation heights. These spectra are compared with earlier ones from weaker aurora estimated to originate from still greater heights. From these results we derive reliable values for the relative populations or population rates of N2B³Π and N2+ A²Π states in aurora for υ′ ≤ 5. The values found agree better with theory than previous values based on higher resolution but discontinuous spectra. No variation with height was found in the relative vibrational population rates for either system.
On the role of steepened structures and drift waves in equatorial spread F
Authors: Costa Emanoel , Kelley M. C.
Published: February 2008

A time domain analysis, performed upon electron density data obtained on the bottomside of the F peak during equatorial spread F conditions, indicates that the observed k−2 wave number spectrum is due to sharp gradients in the medium and not to plasma turbulence. The gradients are then shown to be unstable to drift waves with a peak growth rate of about 1 s−1 which occurs at perpendicular wavelengths near the ion gyroradius. These waves may be responsible for some of the intense backscatter detected by VHF radar during equatorial spread F conditions. The linear theory for collisionless drift waves with wavelengths near the ion gyroradius is discussed in a companion paper.
Quiet time pattern of auroral arcs for different directions of the interplanetary magnetic field in the Y‐Z plane
Authors: Lassen K. , Danielsen C.
Published: February 2008

Quiet time arcs observed from the Greenland all‐sky camera network have been ordered in corrected geomagnetic latitude/time mass plots according to the values of the Y and Z components of the IMF. Two different patterns of discrete quiet arcs occur. In one system the arcs are ordered along the statistical auroral oval; in the other, which we have called the polar cap pattern of discrete arcs, the arcs are ordered partly in the sun‐earth direction over the polar cap, especially on the dawnside of the pole, partly along the 78°–80° corrected geomagnetic latitude curve in the morning to noon and noon to evening hours. The oval arc pattern is most prominent when Bz is negative. It gradually contracts and finally practically vanishes as the steady IMF is shifted toward a northward direction. The contraction takes place differently, depending on the sign of By. The polar cap pattern is dominant when Bz is positive. The sun‐aligned arcs of the polar cap pattern gradually disappear as Bz goes toward negative values. The high‐latitude arcs in the forenoon sector seem to be present for all values of Bz considered. No dependence on By has been found in the pure polar cap pattern. Apart from periods of extremely great numerical values of Bz, the oval and the polar cap discrete arc patterns are found to coexist, at least in our statistical presentation.
Spaced sensor observations of pattern motion
Authors: Briggs B. H. , Maude A. D.
Published: February 2008

It is shown that the velocity of a moving pattern can be determined from records obtained at spaced sensors without assuming that the spatial and temporal correlation functions have the same functional form.
Structure of current sheets in magnetic holes at 1 AU
Authors: Fitzenreiter R. J. , Burlaga L. F.
Published: February 2008

Current density profiles in several types of interplanetary magnetic holes have been calculated using high‐resolution Imp 6 magnetic field data (12.5 vector measurements/s), assuming that the currents flow in planar sheets and that the magnetic field varies only in the direction normal to the sheet. The planarity was verified in four holes which were observed by two suitably spaced spacecraft. The structure of the current sheets ranges from very simple in some holes to very complex in others. Four types of simple magnetic holes are discussed, in which B varies nearly monotonically on each side of the hole. In two of the holes, B varies in intensity but not in direction as a result of currents normal to B. In the other two holes, B changes in both magnitude and direction as a result of currents both normal and parallel to B. The observed structures are found to be qualitatively consistent with the models of Burlaga and Lemaire, which are based on self‐consistent solutions of Vlasov's equation and Maxwell's equations. Examples of complex irregular magnetic holes are also presented, and they are shown to contain multiple current sheets in which currents flow parallel to one another at various angles with respect to B. There is no model of such magnetic holes at present.
Measurement of the profile and intensity of the solar He I λ584‐Å resonance line
Authors: Maloy J. O. , Carlson R. W. , Hartmann U. G. , Judge D. L.
Published: February 2008

The intensity and profile of the helium resonance line at 584 Å from the entire disc of the sun was investigated by using a rocket‐borne helium‐filled spectrometer and a curve of growth technique. The line profile was found to be accurately represented by a gaussian profile with full width at half maximum of 122 10 mÅ, while the integrated intensity was measured to be (2.6 ± 1.3) × 109 photons s−1 cm−2 at solar activity levels of F10.7 = 90.8 × 10−22 m−2 Hz−1 and Rz = 27. The measured line width is in good agreement with previous spectrographic measurements, but the integrated intensity is larger than most previous photoelectric measurements. However, the derived line center flux of (2.0 ± 1.0) × 1010 photons s−1 cm−2 Å−1 is in good agreement with values inferred from airglow measurements.
Theory of flux anisotropies in a guiding center plasma
Authors: Birmingham T. J. , Northrop T. G.
Published: February 2008

Assuming time stationarity of the one‐particle distribution function f on the scale of the bounce motion of particles in a magnetic field B, we expand the Vlasov equation through O(ϵ) in the adiabatic parameter ϵ, which is the ratio of particle gyroradius to scale length of the magnetic field. Since f is directly proportional to particle flux dΦ/dW dΩ differential in kinetic energy W and solid angle Ω, f is in principle measurable in space experiments, and our analysis is tailored to be explicitly applicable to space problems. To O(1), f is gyrotropic; its first velocity moment is (if nonvanishing) parallel to B, and hence macroscopic parallel flow is included in this term. The O(ϵ) contribution is nongyrotropic, and macroscopic flow perpendicular to B plus additional parallel flow results from these terms. The degree of nongyrotropy and hence the amount of cross‐field macroscopic flow depend on the perpendicular component of the electric field E, on curvature and shear in the magnetic field, and on the spatial gradient ▽f0, pitch angle derivative ∂f0/∂δ, and speed derivative ∂f0/∂υ of the lowest‐order distribution function f0. We also show that the usual expression for the electric field E, which produces plasma corotation in an axisymmetric system such as a dipole, also holds for any nonaxisymmetric but rigidly rotating magnetic field pattern, provided the observed magnetic field is used in place of the dipole field.
Ogo 5 magnetopause structure and classical reconnection
Authors: Sonnerup B. U. Ö. , Ledley B. G.
Published: February 2008

The observations made during one unusual crossing of the magnetopause by the satellite Ogo 5 are compared with the classical reconnection model developed by Levy, Petschek, and Siscoe. The magnetic field observations appear to be generally consistent with this MHD model, although allowance must be made for the fact that the estimated magnetopause thickness was no more than 3.5 ion gyrodiameters. The nature of the finite gyroradius effects in such thin structures is discussed.
Topside ionospheric trough morphology: Occurrence frequency and diurnal, seasonal, and altitude variations
Authors: Ahmed M. , Sagalyn R. C. , Wildman P. J. L. , Burke W. J.
Published: February 2008

The main trough in the topside ionosphere has been studied using the thermal positive ion and electron densities measured on 15,000 orbits over a 3‐year period (1969–1972) by means of spherical electrostatic analyzers aboard the Isis I and Injun 5 satellites in the 560‐ to 3600‐km altitude range. The trough is found to be a persistent feature at night with an occurrence frequency of approximately 95%. The occurrence frequency decreases to approximately 60% near the dawn‐dusk meridian and to approximately 48% near local noon. At altitudes below about 1500 km during quiet to moderate conditions (Kp ≤30) the trough equatorward boundary is found at L = 3.5±0.5 near midnight and L = 12.5±1.0 near local noon. The equatorward edge of the trough in the nighttime sector lies near the L shell where the plasmapause has been observed. Near local noon the trough occurs at the equatorward edge of the magnetospheric cleft and is at significantly higher L values than those reported for the dayside plasmapause. The seasonal variation of the trough location at a given local time is negligible except near sunrise. With increasing altitude between 1500 and 3600 km the equatorial boundary of the trough moves to continually lower latitudes during the night hours. The equatorward trough wall becomes a dominant feature of the trough, often extending from 15° to 20° in width during quiet magnetic periods. The poleward edge of the trough becomes less well marked with increasing altitude, often being defined only by a sharp spike in ionization extending over a few degrees within the auroral zone. At altitudes above 1500 km on the dayside, two independent troughs or density gradients are observed. The trough at high latitudes located at the equatorward edge of the cusp gradually decreases in amplitude with increasing altitude. This trough is tentatively identified as the dayside analog of the high‐latitude trough observed on the nightside by Ogo 6. Its development is attributed to the depleting effects of enhanced ion chemical reactions in the presence of convective electric fields. The lower latitude dayside trough, observed between L = 2 and 6, results from the partial depletion of flux tubes in the outer plasmasphere.
Proton‐driven electromagnetic instabilities in high‐speed solar wind streams
Authors: Abraham‐Shrauner B. , Asbridge J. R. , Bame S. J. , Feldman W. C.
Published: February 2008

Electromagnetic instabilities of the field‐aligned, right‐hand circularly polarized magnetosonic wave and the left‐hand circularly polarized Alfvén wave driven by two drifted proton components are analyzed for model parameters determined from Imp 7 solar wind proton data measured during high‐speed flow conditions. Growth rates calculated using bi‐Lorentzian forms for the main and beam proton as well as core and halo electron velocity distributions do not differ significantly from those calculated using bi‐Maxwellian forms. Using distribution parameters determined from 17 measured proton spectra, we show that considering the uncertainties the magnetosonic wave may be linearly stable and the Alfvén wave is linearly unstable. Because proton velocity distribution function shapes are observed to persist for times long compared to the proton gyroperiod, the latter result suggests that linear stability theory fails for proton‐driven ion cyclotron waves in the high‐speed solar wind.
Propagation of gravity wave spectra in the thermosphere
Authors: Yeh K. C. , Liu C. H. , Hearn A. L.
Published: February 2008

The ionospheric electron density at discrete heights is obtained with a 1‐min sampling interval using the Arecibo radar for several runs in May 1974. These values are treated as time series in a spectral analysis. Assuming the ionization fluctuations are random traveling ionospheric disturbances, hence are excited by random gravity waves in the neutral atmosphere, the observed spectra are used (1) to compare with the theoretically computed transmittivity functions, where satisfactory agreement has been obtained, and (2) to make inference about the nature of the gravity wave velocity spectrum at the source, which suggests broad bandedness. At least in one case the data suggest the continuous cascading of energy into higher frequency components through a nonlinear process as the spectrum of waves propagates upward into the thermosphere.
Electrostatic noise at the plasma frequency beyond the Earth's bow shock
Authors: Filbert Paul C. , Kellogg Paul J.
Published: February 2008

Electrostatic noise at or near the ambient solar wind plasma frequency, detected by the University of Minnesota plasma waves experiment aboard the Imp 6 satellite beyond the earth's bow shock, is correlated with times when the interplanetary magnetic field probably connects to the shock. The results of this analysis are (1) the noise is present when the field lines connect to the shock, and no noise at the plasma frequency is observed when the field lines do not connect and (2) the noise amplitude is largest along field lines that are tangent to the shock. The measurements are consistent with a two‐stream instability mechanism. The necessary double‐humped distribution function is probably produced by a finite time of flight mechanism; that is, of the energetic electrons generated in the shock, the lower‐energy electrons are swept downstream by the solar wind convection field, leaving a higher‐energy bump on the distribution function. A theoretical discussion shows that the amplitude of the instability is probably limited by the oscillating two‐stream mechanism in the sunward part of the unstable region and by quasilinear diffusion in the downstream part. The amplitude is sufficiently large to generate electromagnetic waves at both the first and the second harmonic of the plasma frequency, and these waves are observed. The instability then leaves a large region, on the flanks of the bow shock, which is filled with electrostatic waves. Spectra and amplitudes in this ‘runout region’ are given and discussed.
Effect of a neutral N2 cloud on the electrical charging of an electron beam‐emitting rocket in the ionosphere: Echo IV
Authors: Israelson Gordon A. , Winckler J. R.
Published: February 2008

During the Echo IV electron beam rocket flight, 114 moles of neutral N2 was injected for the attitude stabilization system. The interaction of the 40‐kV 80‐mA beam with this relatively dense cloud was studied as a ‘gas plume’ to enhance the flow of neutralizing return current to the rocket body. It was found that the currents preferentially followed a route back through the region where the beam interacted with the N2. A complex luminous discharge was observed photometrically to accompany beam injection. This discharge was strongly roll modulated as the rotating beam swept through the injected gas near the rocket. The neutral N2 number density was measured by observing 3914‐Å emission produced by the beam impact, and reached nearly 1015 cm−3 at times. During a 1‐s 40‐kV 80‐mA beam injection pulse the discharge became oscillatory and ‘flickered’ with a frequency near 22 Hz, somewhat lower than the N2+ ion gyrofrequency. The injected N2 on one occasion apparently acted as a flourescent screen, and a photometric pulse was observed from a conjugate hemisphere beam echo. Ionospheric positive ions have been used to measure E × B drifts by their flow pattern at rocket altitudes, but it was found that the N2 cloud interacted by collision to isotropize and thermalize the flow patterns, so electric fields could not be studied by this technique.
The effect of erosion on the solar wind stand‐off distance at Mercury
Authors: Slavin James A. , Holzer Robert E.
Published: February 2008

Recent studies have provided quantitative measurements of the effect of dayside magnetic reconnection on the position of the earth's forward magnetopause. By scaling these terrestrial observations to Mercury, it is predicted that the mean solar wind stand‐off distance for average solar wind dynamic pressure conditions will be 0.2–0.7Rm inward from its ‘ground state’ position. Furthermore, it is expected that the magnetopause will be eroded and/or compressed to within 0.2Rm of Mercury's surface a significant portion of the time. Empirical formulae derived for the earth's magnetosphere are used to determine both solar wind stand‐off distances and solar wind dynamic pressures for the two Mariner 10 encounters with Mercury's magnetosphere. It is found that for the first encounter when the interplanetary magnetic field was often southward and substorm signatures are observed inside the magnetosphere, the mean stand‐off distance inferred from the boundary crossings is 1.5Rm (for Psw = 6.0 × 10−8 dynes/cm²). At the time of the final encounter, the Mariner 10 magnetometer observed no significant southward component in the IMF and no substorm activity was evident. For this encounter, the mean inferred stand‐off distance is 1.9Rm consistent with the expected effects of magnetic flux transfer within a terrestrial‐type magnetosphere. A dipole moment of 6±2 × 1022 G‐cm³ is calculated from the observed bow shock and magnetopause positions. Finally, the importance of magnetic flux transfer in the solar wind‐magnetosphere‐atmosphere‐surface interaction at Mercury is briefly discussed.
A reexamination of plasma measurements from the Mariner 5 Venus encounter
Authors: Shefer R. E. , Lazarus A. J. , Bridge H. S.
Published: February 2008

Mariner 5 plasma data from the Venus encounter have been analyzed with twice the time resolution of the original analysis of Bridge et al. (1967). The velocity distribution function for each spectrum is used to determine more precisely the locations of boundaries and characteristic flow parameters in the interaction region around the planet. We identify a new region in the flow located between magnetosheathlike plasma inside the shock front and an interior low‐flux region near the geometrical shadow of the planet. The region is characterized by a wide velocity distribution function and a decrease in ion flux. Using the highest time resolution magnetic field data made available by E. J. Smith et al., we propose that rapid magnetic field fluctuations in this region may result in an artificial broadening of the distribution function. We conclude that very high time resolution is required in future experiments in order to determine the true nature of the plasma in this region.
Velocity distribution function and cyclotron wave growth in a modified bi‐Maxwellian two‐ion component solar plasma
Authors: Leubner M.P.
Published: February 2008

Observed double‐humped proton velocity distributions of the solar plasma are represented analytically by a superposition of modified bi‐Maxwellians. Stability and growth rates of the cyclotron mode are calculated in linear Vlasov theory for a warm solar wind at 1 AU. Proton distribution function and cyclotron wave growth are discussed as functions of the beam to plasma particle density and the temperature anisotropy. The presence of a second ion component causes increased growth rates and a second resonant wave particle interaction.
Upper atmosphere tides and the vertical motion of ionospheric sporadic layers at Arecibo
Authors: Mathews J.D. , Bekeny F.S.
Published: February 2008

The vertical motion of ionospheric sporadic layers in the 80‐ to 140‐km altitude region is examined by using a numerical solution for ion trajectories in a wind system composed of diurnal and semidiurnal tides similar to those observed at Arecibo. The confluence of the two tides in the 100‐ to 110‐km altitude region is shown to produce a variety of layer motion possibilities including ‘quasi‐stagnation’ of the layer as well as rapid upward or downward motions. Experimental layer trajectories are presented which confirm the basic theoretical results and which indicate the continuous opportunity for layers to form in the tidal wind system. The availability of metallic ions for layer formation is discussed as is the observed presence of layers below 90‐km altitude.
Rayleigh‐Taylor and wind‐driven instabilities of the nighttime equatorial ionosphere
Authors: Chiu Y.T. , Straus J.M.
Published: February 2008

We have made a thorough re‐examination of the Rayleigh‐Taylor instability in the nighttime equatorial ionosphere from ∼100 km to the bottomside F region. We have taken into account explicitly the following effects which have been ignored by other workers in various combinations: (1) The eastward drift of the ionosphere caused by the nighttime polarization electric field, (2) the eastward nighttime neutral wind, and (3) recombination in the F and E regions. We found that, well below the bottomside F region, the Rayleigh‐Taylor mode can be unstable and is driven by an eastward neutral wind rather than by gravitational drift. Formation of ionospheric bubbles below the bottomside F region is consistent with the observation of lower ionospheric ions in F region ionospheric holes; furthermore, seasonal and shorter term variations in spread‐F occurrence may be associated with variations in the neutral wind and polarization electric field.
A quasi‐static model of global atmospheric electricity, 1. The lower atmosphere
Authors: Hays P. B. , Roble R. G.
Published: February 2008

A model of global atmospheric electricity is constructed and used to examine the electrical coupling between the earth's upper and lower atmospheric regions. The main sources of electric current within the model are thunderstorms, which are considered as dipolar electric generators with a net positive charge at the top of the thundercloud and a net negative charge at the bottom of the cloud. The thunderstorms are assumed to be distributed in geographic areas that are in accordance with the known statistical distribution of thunderstorm frequency at a given universal time. The electric potential at the surface of the earth is assumed to be zero along the earth's orographic surface. Calculations are made with and without the earth's orography. The electrical conductivity increases exponentially with altitude, and electrical effects are eventually coupled into the magnetosphere along geomagnetic field lines. Also, the electrical conductivity is assumed to vary with latitude, simulating the latitudinal variation of known cosmic ray production. The electrostatic model calculates the global distribution of electric potential and current for model conductivities and an assumed spatial distribution of thunderstorm current sources. The results show that large positive electric potentials are generated over thunderstorms and that these perturbations penetrate upward to ionospheric heights. The effect of a thunderstorm region in one hemisphere can be transmitted along geomagnetic field lines into the conjugate hemisphere; however, the potential perturbation in the conjugate hemisphere is damped below stratospheric altitudes. Electric fields over thunderstorm regions may approach 0.25–0.50 mV m−1 at ionospheric heights for nighttime conditions. The return current at the earth’s surface in the fair weather region is greater over mountainous regions than at sea level. The perturbation of the calculated electric potential and current distributions due to an increase in cosmic rays during a solar flare increase and the subsequent Forbush decrease in cosmic ray ionization is also discussed.
Evening sector auroral oval dynamics from DMSP photographs
Authors: Pike C.P. , Dandekar B.S.
Published: February 2008

Expansions and contractions of the auroral oval and substorm activity over a 10‐day period were studied. Changes in latitude of the equatorward boundary of the diffuse aurora, scaled at 2000 CGT from DMSP photographs, reflect expansions and contractions of the oval. Hourly average and 5‐min average IMF Bz component data and AE (11) data are examined relative to the expansions and contractions of the oval and to auroral substorm activity as seen in the photographs. The minimum‐size oval occurs near 73° CGL at 2000 CGT. Over the range of Bz values examined, the oval expands or contracts by less than 2.5° within 102 min, which is the temporal resolution limit imposed by the DMSP satellite orbital period. As was previously reported, Bz appears to control both the expansion and the contraction of the oval. Substorm activity accompanies both the expansion and the contraction. Substorms which occur during the oval expansion are more intense than the substorms which occur during the ensuing contraction. Also, the oval appears to be able to expand more rapidly than it can contract.
Intense electrostatic waves near the upper hybrid resonance frequency
Authors: Kurth W.S. , Craven J.D. , Frank L.A. , Gurnett D.A.
Published: February 2008

Plasma wave measurements using instruments on the Imp 6 and Hawkeye 1 satellites are utilized in a study of very intense electrostatic waves near the upper hybrid resonance frequency in the region just outside the plasmapause. These intense plasma wave events have electric field strengths of ∼1–20 mV m−1 and are among the most intense waves seen in the earth's magnetosphere. Detailed studies of more than 140 of these intense electrostatic disturbances reveal that the events occur at all local times and at magnetic latitudes varying from the equator to as high as 50°. The polarization of these waves is such that the wave electric field vector is oriented perpendicular to the geomagnetic field. In most cases the center frequency of the intense waves appears to correspond to an (n + ½)fg− harmonic near the upper hybrid resonance frequency. A survey of plasma measurements made simultaneously using the Hawkeye 1 Lepedea shows that the occurrence of the intense electrostatic waves is not strongly controlled by the intensities of ∼1‐ to 20‐keV electrons but that specific details of the hot electron distribution function are directly related to the wave turbulence. All events at magnetic latitudes less than about 10° show strong pitch angle anisotropy with the greatest intensities at α ≈ 90°. The hot distribution function f(υ⊥, υ∥) is described for a few events showing two sources of free energy; a temperature anisotropy and a loss cone distribution. One event shown suggests that a bump on tail in υ⊥ may also contribute free energy in some cases. A possible mechanism for producing intense waves near the upper hybrid resonance frequency is suggested which draws upon current theories applied to the generation of (n + ½)fg− bands. Evidence is given which suggests that the intense electrostatic waves may be a source of nonthermal continuum radiation.
A simple model of the magnetosphere
Authors: Luhmann J.G. , Friesen L.M.
Published: February 2008

A phenomenological magnetic field model for the earth's magnetosphere is constructed from a dipole field and a uniform field directed sunward in the northern hemisphere and antisunward in the southern hemisphere. The properties of this simple model are compared with those of several other quantitative models. The present model is found to be more suitable for calculations than some other simple models in cases where the distant (>13 Re) magnetotail configuration is important. Moreover, this model is easily adaptable to changes in the field geometry and to the description of magnetotail asymmetries.
Momentum transport due to atmospheric tides
Authors: Elford W. G.
Published: February 2008

The role of tidal winds between 80 and 100 km in transporting momentum poleward is examined by using meteor wind data collected over 9 years, 1966–1975, at Adelaide, 35°S. It is shown that there is an annual variation in the momentum flux and that in summer the poleward flux is more than sufficient to maintain the mean zonal flow at these heights in middle latitudes. However, the meridional transport of momentum is insufficient to balance that due to the mean flow. Alternative mechanisms are discussed.
Equatorial electric fields during magnetically disturbed conditions 1. The effect of the interplanetary magnetic field
Authors: Fejer B.G. , Gonzales C.A. , Farley D.T. , Kelley M.C. , Woodman R.F.
Published: February 2008

Radar measurements of E and F region drift velocities have been used to look for correlations between changes in equatorial electric fields and the interplanetary magnetic field (IMF). The east‐west component of the IMF appears to be unimportant, but the north‐south component has some effect; rapid reversals from south to north are sometimes correlated with reversals of the equatorial east‐west electric field during both daytime and nighttime. This is not always true, however, the IMF may reverse without any apparent effect at the equator. Furthermore, large equatorial field perturbations are sometimes observed when the IMF Bz is large and southward but not varying drastically. In this latter case the equatorial perturbations start nearly simultaneously with the onset of auroral substorms, while in the previous case they usually correlate with the onset of the substorm recovery phase. These observations indicate that the IMF does not affect the equatorial electric fields directly. Rather, it is changes in the magnetospheric electric fields and the auroral zone electric field and conductivity distribution (which may or may not be triggered by IMF changes) which alter the worldwide ionospheric current flow and electric field pattern, of which the equatorial observations are an indication.
Effect of a parallel electric field on the whistler mode instability in the magnetosphere
Authors: Misra K.D. , Singh B.D. , Mishra S.P.
Published: February 2008

A dispersion relation for the whistler mode wave propagation in an anisotropic warm magnetoplasma in the presence of a weak parallel electrostatic field has been derived from linearized coupled Boltzmann‐Maxwell equations with collision frequency independent of particle velocity. An expression for the growth rate has been derived in the presence of an electric field and for small temperature anisotropy (A<1) for the whistler mode wave. Under suitable approximation we recover the earlier known results. The modifications introduced in the growth rate by the electric field and temperature anisotropy have been discussed using observed plasma parameters at 6.6 RE. It is observed that growth (damping) of whistler mode waves is possible when the wave vector is parallel (antiparallel) to the static electric field. The effect of the electric field is more pronounced at low frequency (higher wave number) wave spectrum.
Effect of a parallel electric field on thermal damping of whistler waves
Authors: Gupta G.P. , Singh R.N.
Published: February 2008

The effect of thermal plasma on the whistler wave propagation in the presence of an electric field parallel to the geomagnetic field lines has been investigated. The dispersion equation accounting for the effect of the parallel electric field in thermal plasma including the resonant particles has been derived. Analysis of the dispersion equation shows that the real part of k is slightly affected by the electric field and the whistler wave suffers damping or growth with varying whistler wave frequencies. It is found that a state of marginal stability is reached at a critical wave frequency counterbalancing the thermal damping by the electric field instability.
Spatial aspects of low‐ and medium‐energy electron degradation in N2
Authors: Singhal R.P. , Jackman C.H. , Green A.E.S.
Published: February 2008

Spatial (radial and longitudinal) yield spectra for electron energy degradation in molecular nitrogen gas for 25‐eV to 10‐keV incident electrons have been generated by using a Monte Carlo technique. These spatial yield spectra associated with the electron degradation process can be employed to calculate a ‘yield’ for any inelastic state at any position in the medium. These have been analytically represented in terms of a model containing three simple ‘microplumes.’ Five‐dimensional yield spectra which contain the information about the polar angle of the electron have also been analytically represented within the framework of the microplume model. Aeronomical and radiological applications of our model are discussed.
The longitudinal distribution of equatorial spreadFplasma bubbles in the topside ionosphere
Authors: Burke William J. , Donatelli Delia E. , Sagalyn Rita C.
Published: February 2008

Observations from a thermal ion probe on board a Defense Meteorological Satellite Program satellite have been used to study the longitudinal distribution of equatorial spreadFoccurrence in the topside ionosphere. The data were taken in the postsunrise local time sector during the September 1977 magnetic storm. In agreement with previous studies of the longitudinal variability of evening sector spreadF, a higher frequency of occurrence was found in the American than in the Asian sector. No example of spreadFwas observed in the Atlantic‐African sector. The results were interpreted using a quasi‐three‐dimensional model of the collisional Rayleigh‐Taylor instability. It is shown that for the same initial ionospheric conditions and the same initial depletion at the magnetic equator, large plasma bubbles are more apt to reach the topside at longitudes of the American sector than at longitudes of the Asian sector.
Energetic ion beam magnetosphere injection and solar power satellite transport
Authors: Curtis S.A. , Grebowsky J.M.
Published: February 2008

The effects of ion beam injection in the magnetosphere are considered. The beam's parameters are those characteristic of the ion propulsion engines envisioned for use in solar power satellite placement (Hanley and Guttman, 1978a). Specifically, from a detailed analysis of the beam's propagation through the magnetosphere it is shown that the bulk of the ion beam is not stopped in the magnetosphere. However, the relatively small fraction of the beam which is deposited via the beam's sheath loss may give rise to a large distortion in the magnetospheric plasma population. Possible loss mechanisms from the magnetosphere for this artificial energetic ion component are evaluated. Electron coulomb scattering yields the shortest lifetime throughout most of the plasmasphere provided that plasmasphere heating by beam ions is not too intense. Charge exchange dominates beyond the plasmasphere. The effects of pitch angle scattering due to beam ion turbulence may appreciably shorten beam ion lifetimes throughout the magnetosphere.
Monochromatic precursor starts
Authors: Rietveld M.T.
Published: February 2008

Whistler precursors are discrete emissions that precede two‐hop whistlers, starting shortly after the one‐hop delay. More evidence is presented that the precursor and associated whistler propagate through the same duct, and observations of a new type of precursor are presented. This new precursor has a monochromatic precursor start (MPS) which may or may not trigger a riser. Although MPS's may be emissions entrained by power line radiation (PLR), phase analysis of the starting frequencies shows that they are not simply related to harmonics of the power line frequencies in the two conjugate regions (50 Hz in New Zealand, 60 Hz in Alaska). If the MPS is due to entrainment by PLR, then previous theories of precursor generation need not be discarded. Forward triggering of a precursor at a power line harmonic by a hybrid whistler may occur.
Preliminary numerical study of the outer scale size of ionospheric plasma cloud striations
Authors: Keskinen M.J. , McDonald B.E. , Ossakow S.L.
Published: February 2008

The one‐level (one for the plasma cloud and neglect of cloud‐background ionosphere interaction), two‐dimensional fluid equations modeling striation development in large F region ionospheric plasma clouds have been numerically solved, by using an initial one‐dimensional cloud geometry, for three different initial Pedersen conductivity gradient scale lengths L=3, 6, and 10 km. In the nonlinear regime, evidence is presented for an outer scale size of well‐developed striations in a direction (y) perpendicular to the E × B drift (x) of the plasma cloud whose initial Pedersen conductivity varies only along the drift direction. The perpendicular outer scale size 2π/k0y is proportional to the initial gradient scale length L through a constant of order unity, i.e., k0yL/2π ≃1. In addition, for the three scale lengths L studied, the one‐dimensional x power spectra ∝kx−n x with n x ≃2 for 2π/k x between 1 and 80 km, while the y power spectra ∝ky−n y with n y ≃2–2.5 for 2π/k y between 1 and 10 km. These results are consistent with recent experimental and theoretical studies of plasma cloud striations.
The behavior of the O+‐H+ transition level at solar maximum
Authors: Kutiev I. , Heelis R.A. , Sanatani S.
Published: February 2008

An examination of the transition level at which the ionospheric ions O+ and H+ are equal in concentration has been carried out by using the retarding potential analyzer data from the Ogo 6 satellite. Between dip latitudes of 0° and 50° the transition level shows a much more pronounced latitude dependence during solar maximum than during solar minimum. The longitude dependence of the transition level features indicates the roles that zonal and meridional F region winds might play in the distribution of O+ and H+ in the low‐ and mid‐latitude ionosphere.
On a comparison between inferred and observed electron flux in pulsating auroras
Authors: Stenbaek‐Nielsen H.C.
Published: February 2008

Stereo‐TV observations of pulsating auroral patches have demonstrated that they often consist of thin horizontal luminous layers. By the use of computer simulation it is shown that if the layers derive their energy directly from precipitating energetic electrons, the incident electron beam must either be more energetic than typically observed, have an anomalous non‐Maxwellian distribution above 20 keV, or within the thin layer, produce photons at a higher efficiency than in normal collisional energy loss processes. The results could be interpreted as suggesting that the source of energy for the thin pulsating auroral forms is not directly from the precipitation of energetic electrons.
Saturn's satellite situation
Authors: Marsden B. G.
Published: February 2008

The situation with regard to the recent claims of discoveries of Saturnian satellites is reviewed. It appears that Saturn now has twelve definite satellites.