bluuebunny/crossref_metadata_2025 huggingface dataset:
Australian topography from SEASAT overland altimetry
Authors: Frey Herbert , Brenner Anita C.
Published: February 2008

Retracking of overland returns from the SEASAT altimeter using algorithms originally developed for recovering elevations over ice has led to the successful recovery of high quality continental topography over Australia and other continents. Cross‐over analysis both before and after orbit adjustment shows the altimetric data over land to have a 2–3 m quality. Direct comparison of gridded SEASAT data with surface data re‐averaged in the same way shows excellent agreement except where SEASAT data are sparse, due either to poor track spacing or to dropouts caused by loss of tracker lock over steeply sloping ground. These results suggest that useful topographic data can be derived from SEASAT and the more recent GEOSAT altimeters for parts of the world where surface data are few or of poor quality.
A “universal” wave spectrum for atmospheric temperature and velocity fluctuations in the stratosphere?
Authors: Cot Charles , Barat Jean
Published: February 2008

The first simultaneous power spectral densities of high resolution lower stratospheric temperature and horizontal/vertical velocity fluctuations are presented. Amplitudes are within a factor of 2 or 3 of other observations reported in literature. However, the measured amplitude ratios, which are absolute characteristics of the fluctuating wave field, disagree significantly (multiplicative factor up to 10) with predictions of the saturation theory. Our results disagree with the concept of a universal spectrum controlled by saturated waves.
Triton torus and Neptune aurora
Authors: Cheng Andrew F.
Published: February 2008

Triton is shown to be the dominant source of plasma for L ≳ 7 in the magnetosphere of Neptune. Triton maintains neutral hydrogen torus of average density comparable to or greater than that of the Titan torus at Saturn. The Triton torus may be detectable in H Lyman‐α emissions. However, the energy source from plasma outward transport and mass loading in the Triton torus is insufficient to explain the Neptune aurora. It is proposed that Neptune's aurora is driven mainly by a solar wind interaction.
GLOBAL COLOR AND ALBEDO VARIATIONS ON TRITON
Authors: McEwen Alfred S.
Published: February 2008

Global multispectral mosaics of Triton have been produced from Voyager approach images; six spectral units are defined and mapped. The margin of the south polar cap (SPC) is scalloped and ranges in latitude from + 10° to −30°. A bright fringe is closely associated with the cap's margin; from it, diffuse bright rays extend north‐northeast for hundreds of kilometers. Thus, the rays may consist of fringe materials that were redistributed by northward‐going Coriolis‐deflected winds. From 1977 to 1989, Triton's foil‐disk spectrum changed from markedly red and uv‐dark to nearly neutral white and uv‐bright. This spectral change can be explained by new deposition of nitrogen frost over both the northern hemisphere and parts of a formerly redder SPC. Frost deposition in the southern hemisphere during southern summer is possible over relatively high albedo areas of the cap (Stansbeny et al, 1990), which helps to explain the apparent stability of the unexpectedly large SPC and the presence of the bright fringe.
Liquefaction and foundation failure of Chevron oil and gasoline tanks at Moss Landing, California
Authors: Tuttle Martitia , Cowie Patience , Tinsley John , Benett Michael , Berrill John
Published: February 2008

Liquefaction of gray, coarse‐ to medium‐grained, esturine sand during the October 17, 1989 Loma Prieta (Ms=7.1) earthquake led to foundation failures of oil and tanks at the Chevron Marine Station at Moss Landing located about 25 km south‐southeast of the epicenter. Differential settlement of the foundations resulted in 1° to 6° of the tanks towards one another and an associated 2° to 7° inclination of tank piping. In addition, sand was vented around the bases of the tanks that contained the most oil and adjacent cracks. Liquefaction and related ground failure was not restricted to the vicinity of the Chevron tanks but was a widespread phenomenon at Moss Landing. Analysis of geological and geotechnical data at sites such as the Chevron Marine Station will serve to check and to advance current methods of assessing liquefaction potential at a site and of mapping liquefaction hazard on a regional scale.
Diffuse ions at a quasi‐parallel collisionless shock: Simulations
Authors: Scholer Manfred
Published: February 2008

Large scale one‐dimensional hybrid simulations of a quasi‐parallel (ΘBn = 20°) high Mach number (MS ∼ 5) collisionless shock have been performed. The numerical system is 500 ion inertial lengths long and the shock has been followed up to 150 ion gyroperiods. The omnidirectional distribution function of the ions in the region upstream of the shock exhibits a high energy tail. About 5% of all ions in the upstream region have a velocity exceeding the shock ram velocity. Phase space contour plots show that these ions are diffuse. These are accelerated to high velocities during their first encounter with the shock. They stay very close to the shock for an extended period of time, about 50 gyroperiods, and experience the electric and magnetic field near the constantly reforming shock. Although the electric field at the particle position is highly fluctuating, the particle motion leads to a net energy gain. These particles constitute a seed particle population for a first order Fermi process. The initial state of such a Fermi process can indeed be seen: some particles escape upstream, are turned back by the upstream waves and recross the shock, thus increasing their energy even further.
Low‐dimensional chaos in magnetospheric activity from AE time series
Authors: Vassiliadis D. V. , Sharma A. S. , Eastman T. E. , Papadopoulos K.
Published: February 2008

The magnetospheric response to the solar wind input, as represented by the time series measurements of the AE index, has been examined using phase space reconstruction techniques. The system was found to behave as a low‐dimensional chaotic system with a fractal dimension of 3.6 and has a Kolmogorov entropy <0.2/min. These are indicative that the dynamics of the system can be adequately described by four independent variables and a corresponding intrinsic time scale is of the order of 5 min. The relevance of the results to magnetospheric modelling is discussed.
Wideband VLF electromagnetic bursts on the DE 1 satellite
Authors: Sonwalkar Vikas S. , Helliwell R. A. , Inan U. S.
Published: February 2008

Wideband VLF electromagnetic bursts are observed on the DE 1 satellite by both the electric and magnetic field sensors in the frequency range of 0.650 kHz to 16.0 kHz. The impulsive signals endure for a relatively short time (∼1 s or less) and exist in the frequency range from well below to well above the local gyrofrequency. They are typically found at L > 4 over a ∼ 40° range of latitudes including the geomagnetic equator and are often accompanied by discrete emissions or a band of hiss. Some observed features are consistent with previous observations of electrostatic plasma waves [Ondoh et al., 1989; Reinleitner et al., 1983]; however, the magnetic measurements clearly indicate that the impulsive signals are electromagnetic in nature, a result that has not been reported before. The possibility of spacecraft discharge effect as the cause of these signals is discussed.
First evidence for high anelastic attenuation beneath the Red Sea from Love Wave Analysis
Authors: Hadiouche Ouiza
Published: February 2008

Attenuation coefficients of Love waves are determined for two seismic paths along the Red sea. The attenuation coefficients are obtained using the multiple filter method for periods from 25 to 130 s along one path and from 40 to 130 s along the second one. The two sets of observations are in good agreement with anomalously high attenuation coefficients similar to those reported across a young part of the Pacific ocean. Indeed, the values lie on average between 3.3 ± 0.6 and 1.1 ± 0.3(10−4km−1), higher values being observed at shorter periods. In a second part of the paper, these apparent attenution observations are interpreted in terms of a distribution of intrinsic absorption in the upper mantle. A frequency independent Qβ model is obtained using a trial‐and‐error method. The best fit to the data required a large and very low Qβ (30–50) zone below a depth of 50 km, underlying a thin and high Qβ (200–300) lid. These results are consistent with high heat flows and low velocities which characterize this tectonically active area, and corroborate the inference of anomalously high temperatures and low viscosity in the upper mantle beneath the Red Sea from recent seismological results.
Observations of potassium in the tenuous lunar atmosphere
Authors: Kozlowski Richard W. H. , Sprague Ann L. , Hunten Donald M.
Published: February 2008

Spectra showing the potassium D1 emission line above the Moon's bright limb (subsolar point) were obtained at first quarter the night of 29 April 1989. The number density at the surface is 9.5 ± 1 atoms cm−3. Linear regression analyses find equally good fits to a one term model with a scale height of 80 km and corresponding temperature of 600 K, or a two term model with a thermal component accommodated to the sub‐solar surface temperature (T=395 K, scale height = 52 km; nt=9.6 K atoms cm−2 sec−1) and with a nonthermal component (represented as T=2500 K, scale height = 329 km; nnt= 1.1 K atoms cm−2 sec−1). In either case there is a large nonthermal component and a deficiency of atoms equilibrated to the surface temperature. The calculated thermalization rate of the nonthermal component through encounters with the lunar surface gives a source strength for the thermal component a factor of 7 greater than loss by photoionization. A possible explanation for the low thermalized population is the existence of a fast and efficient way of depleting the thermal component and supplying the nonthermal by momentary adsorption on the surface and subsequent photo‐desorption by the considerable visible solar irradiance. Also important, this plausible mechanism for the redistribution of thermal and nonthermal components may completely mask the original velocity distribution of the source population.
Ion composition measurements within magnetospheric flux transfer events
Authors: Klumpar D. M. , Fuselier S. A. , Shelley E. G.
Published: February 2008

Impulsive reconnection near the subsolar magnetopause is a fundamental process of interaction between the magnetosphere and the solar wind flow. Flux Transfer Events (FTEs) appear to be a manifestation of this process. It is therefore important to fully characterize the FTE so as to better understand the physics of the interaction process. We use magnetic field signatures from the AMPTE/CCE spacecraft to identify two magnetospheric FTEs. Electron distributions measured in the plane of the magnetopause inside these FTEs complement previously reported electron measurements. We report, for the first time, ion composition measurements in the energy range ∼0 to 20 keV/e within an FTE. We find that the ion distributions, the ion composition, and the flow velocities are unique to the FTE and unlike either the adjacent magnetosphere, the nearby boundary layer, or the nearby magnetosheath. The H+, He+, and He2+ distribution functions in the FTEs have reversed temperature anisotropies and the relative He2+ abundance is depressed with respect to either the magneosheath or the low latitude boundary layer.
A comparison of “GLOBAL” temperature estimates from satellite and instrumental data, 1979–88
Authors: Diaz Henry F.
Published: February 2008

A comparison of surface temperature changes over land and ocean areas with tropospheric air temperatures derived from satellite measurements over the period 1979–88 reveals differences in the relative rankings of the individual yearly values over the oceans. The discrepancy occurs mainly in the warm half of the set of years, with good agreement evident during the colder half. Since the land data agrees well with the satellite measurements, unless there is an unknown problem with the surface marine temperatures, it appears that interannual surface temperature variations over the oceans compare poorly with such variations in the troposphere above it, particularly when the oceans are relatively warm. Agreement between the satellite measurements and an index of troposheric temperature derived from a set of globally distributed radiosonde stations is excellent.
Lithospheric thickness and thermal anomalies in the upper mantle inferred from the Love Wave data
Authors: Tanimoto Toshiro , Zhang Yu‐Shen
Published: February 2008

The study of global Earth structure by surface waves can now resolve wavelengths of about 1000 km. Phase velocity maps are detailed enough to test some plate tectonic models. Our results for Love waves indicate (l) continuous thickening and/or velocity increase with age of oceanic plates older than 100 million years, (2) failure of boundary layer scaling laws seen in the rate of thickening of oceanic lithosphere, and (3) asymmetric thickening of plates about ridges. The latter two points suggest that there is a wide variety of differences in the thermal states of oceanic lithosphere. Thermal anomalies, possibly caused by hotspots, are identified in ‘residual’ maps.
Paleomagnetic evidence for Cretaceous age of two volcanoes on the south flank of the Island of Hawaii
Authors: Sager William W. , Pringle Malcolm S.
Published: February 2008

Apuupuu and Dana seamounts are located on the south flank of the island of Hawaii, near the active submarine volcano, Loihi Though previous work suggests that they are older, inactive volcanoes, their ages and relationship to Hawaiian volcanism are uncertain. We make age estimates for these two seamounts by comparing paleomagnetic poles, derived using a magnetic inversion technique, to the Pacific apparent polar wander path. The paleopoles of Apuupuu and Dana seamounts are located at 65.8°N, 9.2°E and 66.7°N, 358.7°E, respectively. Both poles are insignificantly different and located on the Late Cretaceous part of the polar wander path, between the 82 and 72 Ma mean poles, suggesting that the seamounts formed contemporaneously long before their part of the Pacific plate drifted over the Hawaiian hot spot.
Phase height variations and vertical drift in the E region
Authors: Bhar J. N. , Purkait N. N.
Published: February 2008

An attempt has been made to explain the departure of the observed hourly variation of phase height of E region reflections at 2.2 MHz from that expected of a simple undisturbed Chapman layer as the effect of vertical electromagnetic drift. Calculations show that a peak drift velocity ranging between the extreme limits 50.0 and 2.5 m/s located about 2 km below the electron density peak may account for the observed departure. Considering some related observational data it is suggested that the vertical drift velocity would be around 10–20 m/s, which is consistent with a value of α in the vicinity of 2–8 × 10−8 cm3/s.
Ogo 6 observations of small‐scale irregularity structures associated with subtrough density gradients
Authors: Basu Sunanda
Published: February 2008

The high‐resolution Ogo 6 retarding potential analyzer (RPA) data obtained during November 1969 to February 1970 have been utilized to demonstrate the association of small‐scale ionospheric irregularities (several kilometers to hundreds of meters) with sharp F region cross‐L density gradients in the L range of approximately 2–4. These subtrough irregularity structures which often appeared in near‐conjugate locations were observed during periods of quieting following magnetospheric storms and were found to be associated with sharp gradients of O+ ions or of the light ions depending on the height of the satellite. Similar structures in O+ ions were observed at perigee (400 km) altitudes during periods of extended quiet geomagnetic conditions. During such quiet periods the small‐scale density irregularities associated with O+ gradients were found to be correlated with low‐frequency electrostatic fluctuations but not with any appreciable temperature variations. Since gradient scale lengths as small as 1 km were often observed, the drift wave plasma instability is suggested as a possible mechanism for the formation of the small‐scale irregularities. A study of 137‐MHz scintillations at a point L = 2.8 together with model computations based on Ogo 6 irregularity parameters strongly indicates that at least a part of the quiet time mid‐latitude scintillations is caused by the plasma instabilities associated with the subtrough density gradients.
E region coupling effects on the Perkins spread F instability
Authors: Klevans E. H. , Imel G.
Published: February 2008

The Perkins instability theory for mid‐latitude spread F is generalized to include the effects of the E region on growth rates. A three‐layer model, representing the E region, the F region, and a resistive layer of low Pedersen conductivity which separates them, is developed. The E region Pedersen current has a stabilizing effect on the perturbed F region, thereby reducing the growth rate of the instability. For spread F onset on September 17, 1974, the maximum growth rate is found to be only one third of the Perkins growth rate. The resistive layer reduces the electric field perturbation in the E region for short wavelengths but has little effect for long wavelengths.
The form and energy of the shock waves from the solar flares of August 2, 4, and 7, 1972
Authors: Zastenker G. N. , Temny V. V. , D'Uston C. , Bosqued J. M.
Published: February 2008

The shape of the shock waves associated with the August 1972 solar flares was determined by comparing the plasma measurement data from the Prognoz, Prognoz 2, Pioneer 9, and Pioneer 10 space probes with observations of radio source scintillations and comet brightness. A nearly spherical shock wave form was obtained for two flares on August 2, and essentially nonspherical shock wave forms were obtained for flares on August 4 and 7. The energy and ejected mass determined from the Prognoz 2 measurements of the additional energy and mass flux behind each shock wave are 1032–1033 ergs and 1016–1017 g, respectively. From the comparison of Prognoz 2 and Pioneer 9 data a significant maximum energy flux near the flare meridian on the shock wave front was deduced for the August 4 flare.
Adiabatic particle motion in a nearly drift‐free magnetic field: Application to the geomagnetic tail
Authors: Stern David P.
Published: February 2008

The guiding center motion of particles in a ‘nearly’ drift‐free magnetic field is analyzed in order to investigate the dependence of the mean drift velocity on equatorial pitch angle, the variation of the local drift velocity along the trajectory, and other properties. The fields considered here are two‐dimensional and depart slightly from a class of drift‐free fields, resembling the field of the geomagnetic tail, with the following properties: (1) no y component and no y dependence, (2) Bx = 0 in the equatorial plane and z = 0, and (3) Bz = B0 = const. In such a field, it has been shown, particles may be trapped, but they exhibit no net drift in the y direction: their instantaneous drifts at any time may be large, but when they are averaged over a sufficiently long time (or, for adiabatic particles, over a bounce period), the result is zero. Here a slight modification of this mode is explored, motion in a field in which Bz slowly varies in the x direction, as is indeed observed in the geomagnetic tail. The mean drift 〈υy〉 for adiabatic particles can now be expressed by means of elliptic integrals: it no longer vanishes but is merely small; if υ0 is the drift velocity for equatorial particles (which is easily derived), 〈υy〉 is typically between υ0 and υ0/3. By contrast, instantaneous guiding center drift velocities at z = 0 may be 50 times larger. Explicit approximations to the twice‐averaged Hamiltonian W(α, μ, J) near z = 0 are also derived, permitting simple representation of drift paths if an electric potential ϕ(α, β) also exists. In addition, the use of W or expressions for the longitudinal invariant allows the derivation of the twice‐averaged Liouville equation and the corresponding Vlasov equation. Bounce times are calculated (by using the drift‐free approximation), as are instantaneous guiding center drift velocities, which are then used to provide a numerical check on the formulas for 〈υy〉.
Energy flow and closure of current systems in the magnetosphere
Authors: Atkinson G.
Published: February 2008

The result of an attempt to express the net energy input to the magnetosphere‐ionosphere system in terms of upstream solar wind parameters is presented. Seven types of electric current system within the magnetosphere are defined and discussed, and it is found that only three of these systematically transfer energy into the magnetosphere from the solar wind. One of these is the magnetotail current system, and the other two form the field‐aligned current observed at the northern edge of the auroral oval. In order to calculate energy input, reasonable models are developed for each of a number of magnetospheric processes. These include (1) flow through the shock, flow in the magnetosheath, and merging; (2) reconnection and the neutral line in the magnetotail; and (3) Alfven layer shielding of the inner magnetosphere from convective flow, nightside pressure balances, and precipitation, and hence from these the width and conductance of the nightside auroral oval. The use of these models permits the development of explicit equations for the total energy input to the magnetosphere‐ionosphere system in terms of upstream solar wind parameters. The interplanetary magnetic field strength and orientation and the solar wind velocity dominate energy input via the nightside plasma sheet. The density of the solar wind is also an important variable for the energy input by the high‐latitude current systems.
Acceleration of protons at 32 Jovian radii in the outer magnetosphere of Jupiter
Authors: Schardt Alois W. , McDonald Frank B. , Trainor James H.
Published: February 2008

During the inbound pass of Pioneer 10 a rapid tenfold increase of the 0.2‐ to 5‐MeV proton flux was observed at 32 RJ (Jovian radii). The total event lasted for 30 min and was made up of a number of superimposed individual events. At the time the spacecraft was in the outer magnetosphere about 7 RJ below the magnetic equator. Before and after the event the proton flux was characteristic of the low flux level normally encountered between crossings of the magnetic equator. Flux changes at different energies were coherent within 1 min, a time comparable to the time resolution of the data. Differential travel time would have led to a greater time difference if the sources had been further than 5–10 RJ from the spacecraft. The angular distributions were highly anisotropic with protons streaming toward Jupiter. A field‐aligned dumbbell distribution was observed initially, and a pancake distribution just before the flux decayed to its preevent value. The alpha particle flux changed as rapidly as the proton flux but peaked at different times. The energetic electron flux behaved differently; it increased gradually throughout the period. This acceleration event was associated with a double crossing of a current sheet, most of the acceleration being coincident with the first crossing. The average shape of the proton energy spectrum (0.3–5 MeV) remained unchanged during the event and resembled the spectrum observed in the magneto‐disk. A superposition of acceleration processes of this type is probably responsible for maintaining the energetic particle population around 30 RJ in the magnetosphere. Random fluctuations in the occurrence of acceleration events would explain the 10–50% flux changes during less than 15 min which were observed most of the time the Pioneer 10 and 11 spacecraft were in the outer Jovian magnetosphere.
Stimulated resonance line scattering in the ionosphere
Authors: Stenflo L. , Trulsen J.
Published: February 2008

We have found that stimulated resonance line scattering from the ionosphere should be possible with the planned Eiscat radar.
The nature of gravity wave ducting in the thermosphere
Authors: Richmond A. D.
Published: February 2008

It has been widely held that the steep temperature gradient in the lower thermosphere can support one or more surface modes of long‐period gravity wave propagation, thereby acting as a ducting mechanism. This paper shows that such a ducting mechanism in fact does not operate in the earth's thermosphere. It is shown that the thermospheric gravity modes computed by Francis [1973] can instead be explained by internal waves undergoing total reflections in the lower thermosphere and weak partial reflections in the upper thermosphere due to viscosity and heat conduction effects. This ducting mechanism is, however, so weak that the usefulness of the concept of ducted thermospheric gravity modes appears to be limited. An alternative concept of freely propagating waves appears to have more practical applications.
A study of electron density spectra of traveling ionospheric disturbances
Authors: Hearn A. L. , Yeh K. C.
Published: February 2008

Special runs of the Arecibo incoherent scatter radar were made to provide high spatial resolution (8.7 km) and high temporal resolution (about 1 min) electron density data at discrete heights in the altitude range 200–500 km. The observed electron density fluctuations were spectrally analyzed and interpreted in terms of gravity wave induced traveling ionospheric disturbances. In many records, two kinds of persistent spectral dips for all heights were obtained. The first dip, occurring in the frequency range 0.025–0.055 min−1 (18‐ to 40‐min period), is shown to be caused by the absence of ionospheric response when the gravity wave normal is perpendicular to the earth's magnetic field and therefore is of geomagnetic origin. The second dip, occurring in the frequency range 0.09–0.12 min−1 (8‐ to 11‐min period), is shown to be related to high attenuation of those waves whose frequencies are slightly above the Brunt‐Väisälä frequency.
Intensities of N2 bands in proton‐induced polar cap aurora
Authors: Singh Vir , Singhal R. P.
Published: February 2008

The intensities of N2 bands (Vegard‐Kaplan, second positive, and Lyman‐Birge‐Hopfield) in proton‐induced polar cap aurora have been calculated by using the modified results of the loss function of protons and the secondary electron spectrum. It is found that the present results differ significantly from the previous results.
Binary encounter calculations of proton energy deposition in N2
Authors: Singh Vir , Singhal R. P.
Published: February 2008

The problem of proton energy deposition in N2 has been studied by using the more appropriate differential ionization and stripping cross sections. In particular, the loss function and secondary electron spectrum have been calculated. It is found that the shape of the differential cross section has a strong bearing on the loss function and secondary electron spectrum.
Plasma disturbances created by probes in the ionosphere and their potential impact on low‐energy measurements considered for Spacelab
Authors: Stone N. H. , Samir Uri , Wright K. H.
Published: February 2008

An experimental investigation of the perturbations created by small conducting bodies immersed in highly rarefied plasma streams was carried out for spherical and cylindrical geometries in the plasma wind tunnel facility at Marshall Space Flight Center. These measurements, as well as the results of previous studies conducted in that facility, were evaluated for the purpose of demonstrating the potential hazards of interference between instruments mounted on diagnostic packages. The scaling in the laboratory work is sufficiently accurate to provide a rough indication of the spatial extent and magnitude of the disturbances created by small probes of 3–6 cm in diameter mounted on board spacecraft moving at altitudes of 150–200 km. The results of such studies have direct application to the location of probes on instrument packages and design of experiments in future space shuttle/Spacelab missions.
Jovian plasmaspheres
Authors: Siscoe G. L.
Published: February 2008

Plasmaspheres within the Jovian magnetosphere can arise from three distinct types of processes: (1) by a photoelectron (positive ion) flux from the planetary ionosphere (the source type of earth's plasmasphere), (2) by ionization of the atmospheres and neutral particle tori of the satellites, and (3) by ionization of the neutral interstellar medium within the magnetosphere. Loss processes include (1) field‐aligned flux into the planetary atmosphere, (2) recombination, and (3) radial transport. Source strengths are estimated, and the various loss processes are considered to obtain a set of model density profiles for the three types of plasmaspheres. We find that if the photoelectron flux from the planetary atmosphere is strongly trapped, the associated plasmasphere should dominate in number density. However, if the photoelectron flux is in diffusive equilibrium with the atmosphere, the Io‐derived plasmasphere should dominate in number density. In either case the Io‐derived plasmasphere should dominate in mass density because of the heavy ions. The heavy ion plasmasphere can be expected to have important dynamical effects on the magnetosphere in the region beyond about 30 RJ. The interstellar plasmasphere can reach densities approaching 102 cm−3 when Jupiter is in the high‐interstellar‐density portion of its orbit.
Counterelectrojet and interplanetary magnetic field
Authors: Kane R. P.
Published: February 2008

About a dozen counterelectrojet events both in the afternoon and in the morning hours were compared with interplanetary magnetic field data. It was noticed that in three to four cases there was an association between counterelectrojets and an excursion of Bz from southward to northward. However, in other cases, no such association nor an association with the Bz gradient from northward to southward was noticed. Thus no clear‐cut relationship is indicated.
Temporal development of the energetic particle composition during solar flares
Authors: Scholer M. , Hovestadt D. , Klecker B. , Gloeckler G. , Fan C. Y.
Published: February 2008

The intensity‐time behavior for protons, alpha particles, and carbon, oxygen, and iron ions has been measured during the June 9, 1974, July 4, 1974, and September 19, 1974, solar events for energies in the MeV per nucleon range. Whereas the C/O ratio at the same energy per nucleon is time independent during all three events shown, the Fe/O ratio at the same energy per nucleon during the June and September events decreases by about 1 order of magnitude. A similar decrease is measured for the alpha to proton ratio. This strongly indicates that while carbon and oxygen are essentially fully stripped, iron nuclei are only partially ionized. The Fe/O ratio changes can then be explained by a mean free path increasing with increasing rigidity. During the July 1974 event we observe a small increase of the alpha to proton ratio as well as the Fe/O ratio with time. This is interpreted as being due to a mean free path decreasing with increasing rigidity.
The spiral field inhibition of thermal conduction in two‐fluid solar wind models
Authors: Nerney Steven , Barnes Aaron
Published: February 2008

The two‐fluid solar wind equations, including inhibition of heat conduction by the spiral magnetic field, have been solved for steady radial flow, and the results are compared with those of our previous study of two‐fluid models with straight interplanetary field lines. The main effects of the spiral field conduction cutoff are to bottle up electron heat inside 1 AU and to produce adiabatic electron (and proton) temperature profiles at large heliocentric distances. Otherwise, the spiral field models are nearly identical with straight field models with the same temperatures and velocity at 1 AU, except for models associated with very low coronal base densities (n0 ∼ 106 cm−3 at 1 Rs). Low base density spiral models give a nearly isothermal electron temperature profile over 50–100 AU together with high velocities and temperatures at 1 AU. In general, high‐velocity models do not agree well with observed high‐velocity streams; lower‐velocity states can be represented reasonably well at 1 AU, but only for very high proton temperatures (Tp ∼ 2Te) at the coronal base. For spherically symmetric base conditions the straight field and spiral field models can be regarded, in lowest order, as approximations to the polar and equatorial three‐dimensional flows, respectively. This viewpoint suggests a pole to equator electron temperature gradient in the region 1‐10 AU, which would be associated with a meridional velocity of ∼0.5–1.0 km/s, diverging away from the equatorial plane. The formalism developed in this paper shows rather stringent limits to the mass loss rate for conductively driven winds and, in particular, illustrates that putative T Tauri outflows could not be conductively driven.
On the expected signatures of reconnection in the magnetotail
Authors: Nishida A. , Russell C. T.
Published: February 2008

This paper enumerates basic expected signatures of the reconnection process in the magnetotail. Agreements between expected and observed signatures are pointed out.
The onset of an auroral absorption substorm
Authors: Ranta Hilkka
Published: February 2008

In this report the features of the breakup of an auroral absorption substorm are discussed. In the longitudinal sector where the substorm breaks up, a sharp onset is preceded by weak absorption which intensifies as it moves equatorward. The maximum value of absorption after the onset depends on the intensification of the equatorward‐moving absorption preceding the breakup. On the basis of the studied substorms it seems that before the onset the weak absorption decreases having a minimum just before the onset and that at longitudes near the breakup a sharp onset can be seen without any preceding absorption, or the minimum of the absorption preceding the onset lasts longer.
The radial dependences of the interplanetary magnetic field between 1 and 5 AU: Pioneer 10
Authors: Rosenberg Ronald L. , Kivelson Margaret G. , Coleman Paul J. , Smith E. J.
Published: February 2008

The radial dependences of the distant interplanetary magnetic field (IMF) between 1 and 5 AU have been investigated by using Pioneer 10 vector helium magnetometer data acquired in 1972–1973 during Bartels solar rotations 1896–1918. Least squares fits were made of the radial dependences of the averages of the magnitudes of IMF components and total field and plane projections. Radial fits were also made of the standard deviations of these variables over the solar rotation, 1 day, and 3‐hour intervals. Results which emerge from the study include the following: (1) Weighted averages of the radial component of the field are found to vary with heliocentric distance R as R−2.10±0.030, in significant agreement with the Parker model. (2) For the entire data set the tangential component of the field is found to vary as R−1.29±0.06. (3) Further analysis was carried out on a subset of the data for which the average solar wind velocity was relatively low. Within this subset of data obtained during solar rotation periods with low average daily ΣKp the tangential field is found to decrease as R−1.23±0.05 and thus to deviate significantly from the Parker model. (4) The deviation between the tangential field variation observed within this subset of the data and the predictions of the model appears to be associated with compressional interaction regions at the leading edges of high‐velocity streams; outside these regions the variations are approximately in accord with the Parker model. (5) The radial decrease of the IMF composite variance (the sum of the variances for all three field components) in a subset of the data obtained during times when the average solar wind velocity was low is consistent with the theory that nonlocally generated Alfvén waves are being swept out from the sun undamped in the interval 1.0‐3.3 AU. (6) The power spectrum in the frequency range 1–8 cycles/d is found to have a slope of approximately 3/2, consistent with spectra near 1 AU.
Satellite observations of impulsive Bremsstrahlung X ray events associated with substorms
Authors: Imhof W. L. , Nakano G. H. , Reagan J. B.
Published: February 2008

With bremsstrahlung X ray data taken on a polar‐orbiting satellite a study has been made of impulsive electron (>50 keV) precipitation events at high latitudes, many of which occurred in the vicinity of local midnight near the beginning of a magnetic substorm. The impulsive events were truly temporal in character and lasted for times of the order of 5 min or less. The angular distributions of the X rays measured at the satellite indicated that the electron precipitation occurred generally near the energetic electron (>155 keV) trapping boundary with a tendency often to be somewhat poleward of that boundary. Just prior to the onset of several of the events there was a significant decrease in X ray flux. The energy spectra often softened during the pronounced increases in X ray flux. For some of the events the maximum total rate of precipitation of electrons of >50 keV into the atmosphere was ∼1023 particles/s over the broad region of observation spanning a MLT range of about 6 hours near the midnight sector. The total energy dissipation rates by electrons of >50 keV over the same MLT interval were found to be in the range from 2.5 × 1014 to 2.8 × 1016 ergs/s.
The energy selective precipitation of inner zone electrons
Authors: Imhof W. L. , Reagan J. B. , Gaines E. E.
Published: February 2008

The occurrence of L dependent peaks in the energy spectra of quasi‐trapped electrons (>130 keV) precipitating from the inner radiation zone has been previously reported (Imhof et al., 1973) and interpreted in terms of the cyclotron resonance interaction of electrons with waves of a nearly constant frequency over the L range (∼1.4 to ∼1.8) of concern. From satellite data taken in 1971‐1972 the longitude variations in the intensities of these peaks observed at ∼800‐km altitude have been studied in order to establish the spatial extent of the responsible mechanism(s). The data acquired over three different longitude intervals show an increase in the frequency of occurrence of the peaked spectra with increasing longitude east of the South Atlantic anomaly. The distribution in equivalent wave frequencies responsible for formation of the peaks is observed to be nearly the same for the three longitude intervals. These two facts suggest that a similar energy selective precipitation mechanism occurs over a broad range of longitudes. It is difficult to unfold uniquely the dependences of the phenomena upon other geophysical parameters from a data set of limited time duration, but certain trends are indicated. L dependent peaks were more prominent in the hours near dawn and dusk than near midnight. This temporal behavior had little dependence on the Kp value. No significant changes with the local time of observation or with the level of geomagnetic activity were observed in the average peak energy at a given L value. Long‐term variations in the peak energies were observed, consistent with a seasonal dependence in the plasma electron density.
Simultaneous multispacecraft observations of energetic proton bursts inside and outside the magnetosphere
Authors: Sarris E. T. , Krimigis S. M. , Bostrom C. O. , Armstrong T. P.
Published: February 2008

Energetic (Ep ≳ 0.21, 0.29 MeV) proton bursts have been observed simultaneously by the Johns Hopkins University Applied Physics Laboratory experiments on three earth‐orbiting (Imp 6, 350 km × ∼32 RE; Imp 7, ∼32 RE × 38 RE; Imp 8, ∼25 RE × 43 RE) spacecraft, separated by several earth radii both inside and outside the earth’s magnetosphere over the period October 1972 through August 1974. It is shown that proton bursts are present nearly simultaneously in the vicinity of the outer belt trapping boundary, in the low‐latitude magnetotail, in the magnetosheath, and upstream from the bow shock. Large intensity differences (up to 10³) are seen among the three spacecraft, with the highest fluxes generally observed near the neutral sheet and outside the outer belt and the lowest inside the tail lobes at |ZSM| > 10 RE. However, intensity gradients can change sign between successive bursts a few minutes apart, a new or moving source being suggested. Time delays in burst onset from one spacecraft to the next ranging up to 30 min are observed and are attributed to propagation effects from the source to the point of observation. In some cases, particle onsets upstream from the bow shock precede those inside the magnetosphere. The energy spectra for a given burst are shown to be harder outside the magnetosphere than inside, a feature suggesting a rigidity‐dependent mechanism for particle escape into the interplanetary medium. Energetic (Ee ≳ 0.22 MeV) electron bursts were generally, but not always, seen to be associated with the protons; intensity differences in the electrons were very large (∼10³) between points within the plasma sheet and outside the magnetosphere, a finding reenforcing the suggestion for rigidity dependence in the propagation process. It is suggested that energetic protons and electrons most likely are accelerated inside the plasma sheet and propagate to various regions both inside and outside the magnetosphere.
The radial variation of corotating energetic particle streams in the inner and outer solar system
Authors: Van Hollebeke M. A. I. , McDonald F. B. , Trainor J. H. , von Rosenvinge T. T.
Published: February 2008

The radial gradient of long‐lived corotating energetic particle streams is measured by using observations of 0.9‐ to 2.2‐MeV protons from Helios 1 and 2 between 0.3 and 1 AU, Imp 7 at 1 AU, Pioneer 11 at 3.8 AU, and Pioneer 10 between 9 and 10 AU. These studies cover several time periods from mid‐1973 to mid‐1976. A positive gradient of ∼350%/AU is found between 0.3 and 1 AU. Between 1 AU and some 3–5 AU the gradient is variable with an average value of 100%/AU, which is consistent with the earlier statistical results obtained from the Imp 7 and Pioneer 11 data. A comparison of measurements at 9 and ∼4 AU shows a negative gradient which is variable from ‐40%/AU to ‐100%/AU. Possible solar latitudinal effects on these gradient studies are also discussed. With the use of solar wind and magnetic field data from Helios 1 between 1 and 0.3 AU the relation between corotating energetic particle events in the inner solar system and the interplanetary medium is examined. It is found that the energetic particles are contained inside the high‐speed solar wind stream in a region adjacent to the interaction region between low‐speed and high‐speed streams.
Evidence for an OH≠ N2≠CO2(ν3) → CO2 +hν (4.3 μm) mechanism for 4.3‐μm airglow
Authors: Kumer J. B. , Stair A. T. , Wheeler Ned , Baker K. D. , Baker D. J.
Published: February 2008

Prior to the study we report here it had been thought that the sole undisturbed nighttime mechanisms for producing CO2 vibrationally excited in the ν3 mode were (1) vibrational excitation by thermal collisions and (2) absorption of 4.3‐µm earthshine by CO2. In this paper we show detailed evidence that the mechanism OH(υ) + N2 → OH(υ ‐ 1) + N2≠, followed by N2≠ + CO2 → N2 + CO2(ν3), may be the dominant excitation mechanism for producing CO2(ν3) in the 85‐km altitude region. The evidence is based on 4.3‐µm zenith radiance data obtained on April 11, 1974, via a rocket‐borne liquid N2 nitrogen cooled circular variable‐filtered radiometer. The rocket was launched at night from the Poker Flat Research Range, Alaska. The data were obtained under conditions of essentially zero auroral activity. There is a feature in these data near 85‐km altitude which can be explained by the mechanism . A column transfer of 0.12 ± 0.025 erg/cm² s from OH≠ to N2 is required to explain the feature. An alternate explanation on the basis of just the mechanisms 1 and 2 which are cited above requires that there existed a very unlikely mesospheric temperature profile on the evening of April 11, 1974. A similar nonauroral feature appears consistently near 85 km in preliminary 4.3‐µm zenith data obtained on March 27, 1973, February 25, 1974, March 6, 1975, and March 12, 1975, thus providing further evidence that the feature most likely results from the OH mechanism rather than a strange mesopheric temperature profile. These data were obtained from the Air Force Geophysics Laboratory and Utah State University as part of the Infrared Chemistry Experiments, Coordinated Auroral Program supported by the Defense Nuclear Agency. In this article we confine our attention to analysis of the April 11, 1974, data.
Toward a unified view of diffuse auroral precipitation
Authors: Ashour‐Abdalla M. , Thorne Richard Mansergh
Published: February 2008

A theoretical description of the mechanisms responsible for diffuse aurora is presented. Emphasis is placed on explaining the origin of the quiet time proton strong diffusion precipitation and its approximate coincidence with the zone of more intense electron precipitation. During quiet geomagnetic conditions, resonant scattering by electrostatic waves is considered the most viable mechanism. It is shown that the broadband electrostatic noise recently detected on auroral field lines by Gurnett and Frank can adequately account for the observed precipitation of ions up to 100 keV. Near the equatorial plane these waves can be destabilized by the normal loss cone pitch angle distribution of plasma sheet protons. Closer to the earth the waves are more readily excited by the field‐aligned currents which are a permanent feature of the auroral flux tubes. A numerical simulation of the convective growth rate in these physically distinct regions is presented, and examples are given of the anticipated polarization and spectral characteristics of the ensuing turbulence. An analysis is also made of the resonant and nonresonant diffusion of plasma on the auroral field lines. Of particular importance is the rapid Landau resonant heating of ionospheric electrons by the ion mode turbulence. The ultimate demise of the outflowing ionospheric electrons is of crucial importance, since a small concentration of cold electrons can quench the loss cone instability of ion cyclotron waves near the equator. This is invoked to explain the restriction of intense broadband electrostatic noise and the concomitant plasma sheet proton precipitation to auroral flux tubes which carry sufficient field‐aligned current to excite ion mode waves (and thus heat electrons) in the topside ionosphere.