bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of halogenated organic compounds near the tropical tropopause
Authors: Schauffler S. M. , Heidt L. E. , Pollock W. H. , Gilpin T. M. , Vedder J. F. , Solomon S. , Lueb R. A. , Atlas E. L.
Published: February 2008

The amount of organic chlorine and bromine entering the stratosphere have a direct influence on the magnitude of chlorine and bromine catalyzed ozone losses. Twelve organic chlorine species and five organic bromine species were measured from 12 samples collected near the tropopause between 23.8°N and 25.3°N during AASE II. The average mixing ratios of total organic chlorine and total organic bromine were 3.50 ± 0.06 ppbv and 21.1 ± 0.8 pptv, respectively. CH3Cl represented 15.1% of the total organic chlorine, with CFC 11 (CCl3F) and CFC 12 (CCl2F2) accounting for 22.6% and 28.2%, respectively, with the remaining 34.1% primarily from CCl4, CH3CCl3, and CFC 113 (CCl2FCClF2). CH3Br represented 54% of the total organic bromine. The 95% confidence intervals of the mixing ratios of all but four of the individual compounds were within the range observed in low and mid‐latitude mid‐troposphere samples. The four compounds with significantly lower mixing ratios at the tropopause were CHCl3, CH2Cl2, CH2Br2, and CH3CCl3. The lower mixing ratios may be due to entrainment of southern hemisphere air during vertical transport in the tropical region and/or to exchange of air across the tropopause between the lower stratosphere and upper troposphere.
Generation of high intensity RF pulses in the ionosphere by means of in situ compression
Authors: Cowley S. C. , Perkins F. W. , Valeo E. J.
Published: February 2008

We demonstrate, using a simple model, that high intensity pulses can be generated, by making use of the dispersive properties of the ionosphere, from a modifier of much lower intensity whose frequency is a parabolic function of time. We show that such a frequency‐chirped pulse can be constructed so that its various components overtake each other at a prescribed height, resulting in large (up to one hundred times) transient intensity enhancements as compared to those achievable from a steady modifier operating at the same power. We examine briefly one possible application: the enhancement of plasma wave amplitudes which occurs as a result of the interaction of such a compressed pulse with pre‐generated turbulence.
CIRRIS 1A observation of 13C16O and 12C18O fundamental band radiance in the upper atmosphere
Authors: Dodd J. A. , Winick J. R. , Blumberg W. A. M. , Lipson S. J. , Armstrong P. S. , Lowell J. R.
Published: February 2008

Fundamental band emission from the ν=1 levels of isotopically substituted 13C16O and 12C18O has been observed for the first time in the earth's atmosphere. High‐resolution earthlimb spectra were obtained in the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) experiment under both nighttime and daytime conditions. Spectral data between 70 and 150 km tangent height were analyzed in the 4.7 µm wavelength region, providing absolute 12C16O, 13C16O, and 12C18O column radiances. The minor isotope column radiances are up to 30 times more intense than predicted, based solely on the natural isotopic abundances of 13C and 18O. The derived line‐of‐sight radiances were accurately modeled using the Phillips Laboratory Atmospheric Radiance Code, and provide a strong test of radiative transport and excitation algorithms, as well as model climatologies.
Recovery of interplanetary cosmic ray intensity following the Great Forbush Decrease of mid‐1991
Authors: Van Allen James A.
Published: February 2008

There was a succession of major solar flares in late‐May to mid‐June 1991. Their effects on cosmic ray intensity were observed by six spacecraft at various points in the heliosphere and by terrestrial neutron monitors. Study of these observations is summarized as follows: (a) An abrupt and extraordinarily large Forbush decrease in intensity occurred at the Earth on DOY 164/1991 (13 June) and ones of similar magnitude (≈ 20 percent) occurred in an orderly sequence of timing thereafter over ranges of heliocentric ecliptic longitude of essentially 360 degrees; of heliographic latitude +32 degrees to −5 degrees; and of radial distance 1.0 to 53 AU. (b) The apparent radial speed of propagation of the presumably causative blast wave was 865 (±75) km s−1 (c) It appears likely that the distinctive solar flare of DOY 162/1991 (11 June) was the dominant cause of the blast wave. (d) Two different representations of the subsequent recoveries of intensity yield substantially different numerical values of “recovery time” but either set of values shows an increase by a factor of about three between 1.0 and 53 AU.
Dusty plasmas: The effect of closely packed grains
Authors: Xu Wenjun , D'Angelo Nicola , Merlino Robert L.
Published: February 2008

A dusty plasma device recently described in the literature has been utilized to study experimentally the charging of dust grains by the surrounding plasma. By varying the ratio d/λD between the intergrain distance and the plasma Debye length, the effects predicted by Goertz and Ip (1984), and subsequently reanalyzed in a more general fashion by Whipple et al. (1985), when “isolated” dust grains become “closely packed” grains have been demonstrated experimentally.
Middle and upper atmosphere radar observations of ionospheric electric fields
Authors: Oliver W. L. , Yamamoto Y. , Takami T. , Fukao S. , Yamamoto M. , Tsuda T.
Published: February 2008

Middle and upper atmosphere (MU) radar observations of electric fields over the period September 1986 to January 1991 are reported in the form of time‐of‐day variations for several different seasonal and solar activity cases. The perpendicular north velocity has on average a smooth and distinct northward excursion from 0600‐1500 LT followed by a period of constant southward velocity until midnight and then a slow linear change to merge with the daytime northward excursion period. This excursion feature is small in summer and enhanced in winter but, seasonally averaged, has only small solar activity variation. The individual seasonal averages show afternoon/evening excursion behavior apparently tied to the time of sunset. The perpendicular east velocity is characterized by a major eastward excursion in the evening and a minor eastward excursion in the morning, with a tendency to level off or form a slight additional local eastward excursion after midnight. The evening excursion is enhanced during winter and at high solar activity, and the postmidnight excursion is enhanced during summer. The morning excursion has no comparable counterpart in existing electric field models or data averages from Arecibo or Jicamarca. We suggest that this may be a semidiurnal component that evidences enhanced propagation of the semidiurnal tide at the location of the MU radar. The maximum daily amplitudes and the time‐of‐day and solar activity trends at the Arecibo and MU radar locations have strong resemblances, but the seasonal trends in the MU data, the Arecibo data, and existing radar models disagree strongly.
Alfven field line resonances at low latitudes (L = 1.5)
Authors: Green A. W. , Worthington E. W. , Baransky L. N. , Fedorov E. N. , Kurneva N. A. , Pilipenko V. A. , Shvetzov D. N. , Bektemirov A. A. , Philipov G. V.
Published: February 2008

The nature of the spatial structure of resonant ULF waves at low latitudes has been studied as part of a joint project between the U.S. Geological Survey, the Institute of Physics of the Earth, Moscow, and the Kyrgyzian Institute of Seismology. Gradient analysis of data taken at a meridional array of three stations in Soviet Central Asia showed that Alfven field line resonances, in the Pc 3 bandwidth, do exist at L = 1.5. Resonant frequencies of 66‐84 mHz (12‐15 s) were measured. Resonance width and the radial gradient of Alfven frequency were determined from our experimental data. When compared with previous published determinations of the resonance width, the resonance width is observed to increase at lower latitudes. This is the result of an increase in ionospheric damping at lower latitudes. Ionospheric damping significantly effects both resonant frequencies and resonance widths. Initial analysis of the data showed that effects of geologic inhomogeneities between two stations can obscure resonant effects that are observed in ground‐based magnetometer data. A method was developed to address these geologic effects so that the response of the resonator can be seen in both amplitude and phase calculations. The cross‐phase spectrum was determined to be the most useful technique to identify the resonant frequency of the field line between two ground stations. The diurnal behavior of resonant frequency was examined using a cross‐phase analysis technique and is shown to agree with theoretical predictions at low latitudes. We can conclude that diurnal variations in resonant frequency are mainly due to diurnal changes in plasma density along the oscillating field line.
Proton whistler interactions near the equator in the radiation belts
Authors: Villalón Elena , Burke William J.
Published: February 2008

The interactions of energetic protons with whistlers propagating near the quasi‐electrostatic limit, are investigated using a test particle, Hamiltonian formalism. We assume that wave packets exist with finite bandwidths of frequencies, which are close to the equatorial electron gyrofrequency and propagate obliquely with respect to the geomagnetic field. Near the equator the protons interact with the waves which appear Doppler shifted to some harmonic of their cyclotron frequency. In an inhomogeneous geomagnetic field the spacing between cyclotron harmonic resonances is very small. The Hamiltonian equations of motion are solved including multiple, independent harmonics for each resonance. The wave frequency varies as a function of the distance along the field line, with only one frequency being resonant at a given point. Thus the inhomogeneity of the magnetic field is compensated by the frequency variation. The proton whistler interactions satisfy the conditions for second‐order resonances for all the harmonics. The resonances may also overlap in phase space, leading to significant changes in the protons energies and pitch angles. The combined contributions of positive and negative harmonics allow protons to diffuse toward smaller pitch angles. Numerical calculations applying this formalism to parameters relevant to the plasmasphere and controlled VLF transmission experiments are presented.
Self‐consistent plasma pressure tensors from the Tsyganenko Magnetic Field Models
Authors: Horton W. , Cheung L. , Kim J. ‐Y. , Tajima T.
Published: February 2008

The high‐pressure plasma trapped in the geomagnetic tail strongly shapes the surrounding magnetic field. Force balance in a steady state requires a balance between the divergence of the total particle momentum stress tensor and the divergence of the magnetic field momentum stress tensor which is the Lorentz force. This condition of stress balance allows strict constraints on the total particle pressure tensor to be derived from the magnetic field structure. The Kp parameterized empirical magnetospheric fields of the Tsyganenko model with local two‐dimensional approximations are used to derive the pressure tensor components implied for the central plasma sheet. The small anisotropies p⊥/p∥ in the gyrotropic pressure tensor required for equilibrium in the central plasma sheet are calculated from the nonpotential values found for the j × B force. The required ratio p⊥/p∥ approaches the marginal stability criterion for the magnetohydrodynamic (MHD) mirror mode and the Alfvén ion cyclotron mode, and we suggest that these instabilities may play a role in establishing the equilibrium structure of the geomagnetic tail. From this perspective the equilibrium and stability constraints for the maximum allowed anisotropy suggest that the Tsyganenko magnetotail field parameterization needs to be modified to support self‐consistent gyrotropic equilibria.
Anomalous absorption during artificial modification at harmonics of the electron gyrofrequency
Authors: Stocker A. J. , Honary F. , Robinson T. R. , Jones T. B. , Stubbe P.
Published: February 2008

Observations of the anomalous absorption of low‐power HF probe waves caused by the action of a high‐power HF ordinary mode radio wave are presented. At pump frequencies in the vicinity of harmonics of the electron gyrofrequency the anomalous absorption measured on the low‐power probe waves exhibit local minima. Also at these frequencies, large‐scale changes deduced from phase measurements of the low‐power probe waves and heater self‐absorption are reduced, whereas the growth time of the anomalous absorption is increased. The electron gyrofrequency estimated from the frequency of the absorption minimum compares favorably with that derived from the International Geomagnetic Reference Field (IGRF) magnetic field model.
A model of rotating exospheres
Authors: Membrado M. , Pacheco A. F. , Sañudo J.
Published: February 2008

Using a truncated Boltzmann distribution, we analyze the neutral density profile of an isothermal planetary exosphere. In the absence of rotation, the classical result obtained by Chamberlain is recovered. When rotation exists, a latitude‐dependent limit appears and the total bound mass presents a logarithmic divergence. The specific case of atomic hydrogen bound to the Earth is discussed.
Remote X ray measurements of the electron beam from the EXCEDE III Experiment
Authors: Rappaport S. A. , Rieder R. J. , Reidy W. P. , McNutt R. L. , Atkinson J. J. , Paulsen D. E.
Published: February 2008

The EXCEDE III rocket experiment successfully produced an artificial aurora on April 27, 1990, with an injected ∼ 18‐A beam of ∼ 2.5‐keV electrons. The experiment consisted of an accelerator module and a sensor module in a mother‐daughter configuration. The beam was fired along the Earth's magnetic field lines between the altitudes of ∼62 and 115 km during the flight. A major concern prior to the flight was that the injection of such an overdense electron beam into the lower ionosphere would charge the accelerator module to a significant fraction of the beam potential. To monitor the primary electrons remote from the rocket, two X ray proportional counters were included as part of the sensor module. X ray spectra from bremsstrahlung emission yield a direct measure of the primary electron beam energy outside the plasma sheath surrounding the accelerator module. Analysis of these spectra yields a beam energy of 2.2 ± 0.5 keV which indicates no substantial charging of the accelerator module for the entire time that the beam was on. We also find that the X ray intensity was modulated at the few percent level by firings of the attitude control jets.
Ion collection in a spacecraft wake: Laboratory simulations
Authors: Enloe C. L. , Cooke D. L. , Meassick S. , Chan C. , Tautz M. F.
Published: February 2008

Data from a laboratory simulation of current collection by a highly biased body in a spacecraft wake are presented. Ion collection from the plasma stream is investigated for both axisymmetric and nonaxisymmetric geometries. Spatially resolved current collection data, obtained by using a segmented collector, are presented for the first time. A threshold potential for the onset of current collection exists; this threshold depends strongly on the geometry of the problem and is related directly to the details of the trajectories of the collected ions. Results from an approximate numerical model of the laboratory experiment as well as the predictions of a simplified analysis are given. The agreement of the numerical solution with the experimental data is good.
Propagation characteristics of Pc 3 compressional waves generated at the dayside magnetopause
Authors: Zhang X. , Comfort R. H. , Musielak Z. E. , Moore T. E. , Gallagher D. L. , Green J. L.
Published: February 2008

New, three‐dimensional ray tracing of Pc 3 compressional waves from the magnetosheath reveals that the magnetosphere can present a major propagation barrier to the penetration of these waves to the plasmasphere. This barrier is the ion‐ion cutoff between the He+ and O+ gyroresonances. As a result of the frequency‐dependent location of this cutoff, the magnetosphere behaves like a filter for Pc 3 compressional waves, and only low‐frequency components of Pc 3 compressional waves can penetrate to inner magnetosphere. Results are in agreement with previous satellite observations. This “filter action” strongly depends on the relative concentration of He+ and O+ and is therefore sensitive to solar and magnetic activity. Ray‐tracing results are based on a cold plasma dispersion relation, a semi‐empirical model of plasma density, and the Mead‐Fairfield magnetic field model.
Anisotropy and minimum variance of magnetohydrodynamic fluctuations in the inner heliosphere
Authors: Klein L. , Bruno R. , Bavassano B. , Rosenbauer H.
Published: February 2008

In this paper we examine the anisotropy, minimum variance, and related distinguishing plasma parameters of small‐scale fluctuations occurring in the solar wind. We use Helios 2 data taken at solar minimum, at a time when high‐ and low‐speed streams are clearly distinguished and a separation of the characteristics of fluctuations from disparate solar sources is facilitated. We find that while variance directions of fluctuations are generally aligned with the mean magnetic field in regions of high speed and relatively low plasma β, they are more three‐dimensional or isotropic in low‐speed, high‐β intervals. In our analysis period, these latter regions are generally the trailing edges of high‐speed streams and slow‐flow‐containing current sheets. In these low‐speed intervals, we find a tendency for large proton density fluctuations to be associated with a preference for fluctuation variance directions to be three‐dimensional and also a tendency for field and velocity fluctuations to decouple. In the past it has been emphasized that in high‐speed streams, fluctuations are initially outwardly propagating and Alfvénic or two‐dimensional in k space and that this Alfvénicity is destroyed by the production of inwardly traveling waves as the flow evolves. It has been suggested that this admixture of waves is produced in a turbulent cascade initiated by stream shears. Here we suggest that this picture is incomplete, that in addition to inwardly propagating plane waves, compressive waves, convected pressure balances, or other density fluctuations can generate or scatter the original spectrum and produce the observed scattering and decoupling of fluctuation directions. Additionally, while we do not dispute the supposition that the long‐wavelength free energy in stream‐stream interactions can initiate a turbulent cascade in the wind, the role of compressive fluctuations in altering the high‐frequency spectrum cannot be ruled out.
Parametric cyclotron resonance in space plasmas
Authors: Nakamura Tadas K. , Kennel C. F.
Published: February 2008

The parametric interaction of waves with particle cyclotron motion has been studied. A wave with a compressional magnetic field component modifies the cyclotron motion of the particles, which enables them to resonate with other waves which have perpendicular electric fields. Resonance occurs when the frequency difference of the two wave modes (compressional and perpendicular) matches the cyclotron frequency. This so‐called parametric cyclotron resonance mechanism can provide a means to exchange energy between particles and low‐frequency waves. We discuss the specific example of energy exchange between an Alfvén wave and ion Larmor motion.
The uncertainty of the Uranian radio source location due to the nonuniqueness of the planetary magnetic field model
Authors: Ladreiter H. P. , Macher W. , Rabl G. K. F. , Rucker H. O.
Published: February 2008

Since the Voyager 2 encounter in early 1986, several investigators have attempted to localize the source regions of the smooth high‐frequency radio emission which was observed by the planetary radio astronomy experiment at the nightside of Uranus. The various studies (most of them are based on the offset tilted dipole (OTD) model of the Uranian magnetic field) yielded significantly different source locations around the southern magnetic pole of Uranus. This may be a consequence of the individual a priori assumptions of the source model. However, the simplicity of the OTD model (Ness et al., 1986) also cannot adequately represent the complexity of the magnetic field at the radio source locations near the planet. The aim of this study is twofold. (1) We reanalyze the various source locations given in the literature (most of them are based on the OTD model) in the frame of the Q3 magnetic field model (Connerney et al., 1987). Our analysis moves some of the previously determined source locations from open toward closed field lines; however, the uncertainty due to the nonuniqueness of the Q3 model remains too large to exclude the possibility that open field lines are the source of smooth Uranian kilometric radiation. (2) We calculate the uncertainty of the radio source locations imposed by the nonuniqueness of the Q3 and OTD magnetic field models. We construct solutions by using generalized inversion techniques (Connerney, 1981) to obtain estimates of those magnetic field parameters (spherical harmonic coefficients up to degree and order 6) that are constrained by the magnetometer observations. The nonuniqueness of the resulting magnetic field models translates into an uncertainty about the radio source locations of some 20° in Uranocentric coordinates at altitudes of about 1.5 Uranian radii (RU). The present results are important for radio source locations at all the outer planets whose magnetic field geometries are represented by nonunique magnetic field models.
Collisional desorption of NO by fast O atoms
Authors: Sonnenfroh David M. , Caledonia George E.
Published: February 2008

Surface‐adsorbed NO figures largely in the mechanism that produces visible glow around spacecraft in low Earth orbit (LEO). In view of the potential interference to optical observations such a glow represents, we have investigated the collision‐induced desorption of NO from Al, Ni, and Z306 Chemglaze®‐coated surfaces at 96 K by hyperthermal (8 km/s) oxygen atoms. The removal of surface NO was followed by the monitoring of the visible fluorescence of electronically excited NO2* produced through the surface‐mediated reaction O+NO. A variability in collisional desorption rate with material was observed. The limited data suggest a removal efficiency of 4 to 8% of the impinging O atom flux. Implications for the atmospheric scouring of contaminants from external surfaces of LEO spacecraft are discussed.
Acceleration of cometary H2O group pickup ions by obliquely propagating nonlinear magnetosonic waves
Authors: Srivastava Krishna M. , Tsurutani Bruce T. , Goldstein Bruce E. , Sharma V. , Okada M.
Published: February 2008

The observations made during the encounter with comet Giacobini Zinner show that the character of MHD turbulence is governed by the magnetosonic (MS) waves generated by the pickup ions via a resonant cyclotron instability. Close to the bow shock these waves are highly nonlinear, |ΔB/B0| ∼ 1, and are propagating obliquely to the magnetic field. The interaction of cometary ions in the mass loaded solar wind with MS waves propagating away from the comet and oblique to the interplanetary magnetic field (IMF) is investigated using the test particle approach. Ion trajectories, distribution functions, widths of pitch angle scattering and energy diffusion are obtained. Because of the MS “turbulence”, the particle velocity and acceleration are found to increase with increasing wave amplitude, inclination of the wave vector to the background magnetic field, and the range of resonant mode numbers. It is found that the interaction of water group pickup ions with MS waves propagating obliquely to the IMF gives larger pitch angle scattering and acceleration than that in the case of parallel and antiparallel propagating waves. In particular, obliquely propagating MS waves at angles greater than 40° to the ambient magnetic field are very effective at accelerating particles because of a high phase velocity along the magnetic field. In the case of monochromatic MS waves, Landau damping is found to play an important role; the particles get electromagnetically trapped in a potential well due to Landau damping. In the case of MS turbulence, the particles are stochastically heated and the temperature continues to grow linearly with time. We have also investigated the relationship between pitch angle scattering and the three parameters, namely, α, the angle between the solar wind flow direction and the ambient magnetic field, θBk, the angle between the ambient magnetic field and the wave propagation vector, and the ion injection velocity. The pitch angle scattering rates are obtained using a monochromatic nonlinear MS wave as well as MS turbulence in both the quasi‐parallel (0 < α < 60°) and quasi‐perpendicular (60° < α < 90°) regimes for various values of θBk. In the case of a monochromatic MS wave, pitch angle scattering rates are found to change very slightly with respect to θBk, α and the mode number of the MS wave due to their Landau damping. In the case of MHD turbulence the pitch angle scattering rates decrease with increasing α for θBk < 40° and increase with increasing α for θBk > 40°. They are found to be independent of the injection velocity. The results are in agreement with the observations.
Electron distributions in the inner Jovian magnetosphere: Voyager 1 observations
Authors: Ye G. , Armstrong T. P.
Published: February 2008

Using several improvements in the analysis of the observations of the Low Energy Charged Particle (LECP) experiment on Voyager 1, electron phase space densities in the inner Jovian magnetosphere (5‐10 RJ) were first calculated at constant first and second invariants (represented by µ and K, respectively), based on the LECP measurements. The calculated electron phase space density profiles show that in the inner Jovian magnetosphere there exist evident time and longitude variations, energetic electron injections, and present radial transport and distributed losses. To study the radial and pitch angle diffusions of Jovian electrons, we have calculated the phase space densities in the K‐L space. It is found that the electron population in the inner Jovian magnetosphere seems to consist of two components: electrons radially diffusing from a main external source and electrons generated from local sources. The radially diffusing electrons have a relatively time stationary and isotropic distribution, while the locally created electrons mainly concentrate around the equatorial plane and have relatively lower energies, in comparison with the inward diffusing electrons. Consequently, the sources of precipitation losses to the ionosphere must be primarily electrons transported from outer sources, and the major precipitations occur in the inner magnetosphere (L < 7.5 RJ). In the inner Jovian magnetosphere (L = 5 ∼ 10 RJ) it is estimated that for electrons with magnetic moment µ = 300 MeV/G, the diffusion coefficient D is roughly 10−8 ∼ 10−6 RJ2 s−1, and the lifetime against the diffusion losses is of the order of 104 ∼ 106 s.
Observations of a transverse magnetic field perturbation at two altitudes on the equatorward edge of the magnetospheric cusp
Authors: Peterson W. K. , Abe T. , André M. , Engebretson M. J. , Fukunishi H. , Hayakawa H. , Matsuoka A. , Mukai T. , Persoon A. M. , Retterer J. M. , Robinson R. M. , Sugiura M. , Tsuruda K. , Wallis D. D. , Yau A. W.
Published: February 2008

On January 28, 1990, the Dynamics Explorer 1 and Akebono satellites crossed a magnetic field structure at the equatorward edge of the polar cusp at altitudes of 22,000 and 5000 km, respectively, within 6 min of each other. Locally measured plasma particles and fields and magnetometer data from a ground station near the foot of the magnetic field line are more consistent with an interpretation of the structure as that of a standing Alfvén wave than that of a quasi‐steady field‐aligned current sheet. We discuss the observations supporting this conclusion and other related observations of field‐aligned currents, Alfvén waves, and ion energization near the equatorward edge of the cusp. These observations suggest that Alfvén waves are commonly present near the equatorward edge of the cusp.
Time‐dependent modulation of galactic cosmic rays by merged interaction regions
Authors: Perko J. S.
Published: February 2008

Models that solve the one‐dimensional, solar modulation equation have reproduced the 11‐year galactic cosmic ray cycle using functional representations of global merged interaction regions (MIRs). This study extends those results to the solution of the modulation equation with explicit time dependence. The magnetometers on Voyagers 1 and 2 provide local magnetic field intensities at regular intervals, from which one calculates the ratio of the field intensity to the average local field. These ratios in turn are inverted to form diffusion coefficients. Strung together in radius and time, these coefficients then fall and rise with the strength of the interplanetary magnetic field, becoming representations of MIRs. These diffusion coefficients, calculated locally, propagate unchanged from ∼10 AU to the outer boundary (120 AU). Inside 10 AU, all parameters, including the diffusion coefficient are assumed constant in time and space. The model reproduces the time‐intensity profiles of Voyager 2 and Pioneer 10. Radial gradient data from 1982‐1990 between Pioneer 10 and Voyager 2 are about the same magnitude as those calculated in the model. It also shows agreement in rough magnitude with the radial gradient between Pioneer 10 and 1 AU. When coupled with enhanced, time‐dependent solar wind speed at the probe's high latitude, as measured by independent observers, the model also follows Voyager 1's time‐intensity profile reasonably well, providing a natural source for the observed negative latitudinal gradients. The model exhibits the 11‐year cyclical cosmic ray intensity behavior at all radii, including 1 AU, not just at the location of the spacecraft where the magnetic fields are measured. In addition, the model's point of cosmic ray maximum correctly travels at the solar wind speed, illustrating the well‐known propagation of modulation. Finally, at least in the inner heliosphere this model accounts for the delay experienced by lower‐rigidity protons in reaching their time‐intensity peak. The actual delays in this model, however, are somewhat smaller than the data. In the outer heliosphere the model sees no delays, and the data are ambiguous as to their existence. It appears that strong magnetic field compression regions (merged interaction regions) that are 3‐4 times the average field strength can, at least in a helioequatorial band, disrupt effects, such as drifts, that could dominate in quieter magnetic fields. The question remains: Is the heliosphere ever quiet enough to allow such effects to be unambiguously measured, at least in the midlatitudes?
Electrostatic wave excitation in planetary magnetospheres: Application to Neptune
Authors: Barbosa D. D. , Kurth W. S. , Gurnett D. A. , Sittler E. C.
Published: February 2008

Voyager 2 observations of electrostatic electron and ion cyclotron harmonic waves in Neptune's magnetosphere are addressed. A model of electron Bernstein modes generated by a loss cone distribution of superthermal electrons is scaled to Neptune parameters and a comparison of theory with the observed electron flux shows good agreement. A model of proton Bernstein modes generated by a ring distribution of Tritonogenic nitrogen ions is also investigated and satisfactory agreement with the data are obtained compatible with known properties of the magnetosphere. The success of the model in accounting for electrostatic emissions observed by Voyager over a wide range of sampled parameters recommends its general applicability to planetary magnetospheres.
Linear coupling effects originated in electron nongyrotropy
Authors: Brinca A. L. , Omura Y. , Matsumoto H.
Published: February 2008

In analogy with ion nongyrotropy the gyrophase organization of electron populations also linearly couples the eigenmodes of gyrotropic parallel propagation in magnetoplasmas. The interaction, besides intensifying preexisting instabilities, excites new types of wave activity. Solutions of the nongyrotropic parallel dispersion equation and particle simulations illustrate instability enhancements and the stimulation of electrostatic and electromagetic wave growth in media that, apart from the electron gyrophase organization, are devoid of free energy sources.
Parametric instabilities of parallel‐propagating Alfvén waves: Some analytical results
Authors: Jayanti V. , Hollweg Joseph V.
Published: February 2008

We consider the stability of a circularly polarized Alfvén wave (the pump wave) which propagates parallel to the ambient magnetic field. Only parallel‐propagating perturbations are considered, and we ignore dispersive effects due to the ion cyclotron frequency. The dissipationless MHD equations are used throughout; thus possibly important effects arising from Landau and transit time damping are omitted. We derive a series of analytical approximations to the dispersion relation using A = (ΔB/B0)² as a small expansion parameter; ΔB is the pump amplitude, and B0 is the ambient magnetic field strength. We find that the plasma β (the square of the ratio of the sound speed to the Alfvén speed) plays a crucial role in determining the behavior of the parametric instabilities of the pump. If 0 < β < 1 we find the familiar result that the pump decays into a forward propagating sound wave and a backward propagating Alfvén wave with maximum growth rate γmax ∝ A1/2, but β cannot be too close to 0 or to 1. If β ≈ 1, we find γmax, ∝ A3/4; if β > 1, we find γmax ∝ A3/2, while if β ≈ 0, we obtain γmax ∝ A1/3; moreover, if β ≈ 0 there is a nearly purely growing instability. In contrast to the familiar decay instability, for which the backward propagating Alfvén wave has lower frequency and wavenumber than the pump, we find that if β ≳ 1 the instability is really a beat instability which is dominated by a transverse wave which is forward propagating and has frequency and wavenumber which are nearly twice the pump values. Only the decay instability for 0 < β < 1 can be regarded as producing two recognizable normal modes, namely, a sound wave and an Alfvén wave. We discuss how the different characteristics of the instabilities may affect the evolution of Alfvén waves in the solar wind. However, for a solar wind in which β ≈ 1 the growth times of the instabilities are probably too long for these instabilities to have an appreciable effect inside 1 AU.
European incoherent scatter VHF measurements of gyrolines
Authors: Malnes E. , Bjørnå N. , Hansen T. L.
Published: February 2008

We have observed the incoherent scatter gyrolines with the European Incoherent Scatter VHF radar (224 MHz) pointing northward at 45° elevation, which corresponds to an angle of 54.6° with the magnetic field at 200 km altitude. The lines can be seen after a 30‐min integration almost all the time. Most of the time they are observable after a 10‐min integration and often after only 1‐2 min when the radar is operating at full power. The lines are observed at altitudes of 100‐270 km and are most intense at about 180 km. Typical intensities are 0.5‐2.0% relative to the ion line. The symmetry between upshifted and downshifted lines is good, but the upshifted lines appear to be slightly more powerful. The experiment shows the effect of photoelectron enhancement, the lines being generally stronger in the morning than in the evening. Another indication of the photoelectron effect is the fact that there is a sudden drop in the power of the lines at about 1830 UT which corresponds to the local sunset in the plasma volume we are probing. The data also show examples of enhanced gyrolines in the absence of photoelectrons which we believe are caused by secondary electrons from particle precipitation.
Electron plasma environment at comet Grigg‐Skjellerup: General observations and comparison with the environment at comet Halley
Authors: Reme H. , Mazelle C. , Sauvaud J. A. , D'uston C. , Froment F. , Lin R. P. , Anderson K. A. , Carlson C. W. , Larson D. E. , Korth A. , Chaizy P. , Mendis D. A.
Published: February 2008

The three‐dimensional electron spectrometer of the Rème plasma analyzer‐complete positive ion, electron and ram negative ion measurements near comet Halley (RPA‐COPERNIC) experiment aboard the Giotto spacecraft, although damaged during the comet Halley encounter in March 1986, has provided very new results during the encounter on July 10, 1992, with the weakly active comet Grigg‐Skjellerup (G‐S). The main characteristic features of the highly structured interaction region extending from ∼26,500 km inbound to ∼ 37,200 km outbound are: (1) a broad inbound “bow wave transition”, (2) a cometosheath characterized by strong oscillations of the electron fluxes with peak‐to‐valley ratios up to 20∶1; the levels of oscillations are much larger and generally more coherent than at comet Halley or at comet Giacobini‐Zinner, despite the much lower neutral gas production rate, (3) a “mystery” region, identified by significant fluxes of hundreds of eV electrons, and a “mysterious” transition, about halfway between the bow wave transition/bow shock regions; they are observed as for comet Halley, confirming their large importance in the solar wind‐comet interaction at 1 AU, (4) an inner region which coincides with the magnetic pileup region; at closest approach, the cold cometary electron fluxes display a prominent maximum, and (5) a sharp outbound bow shock and its possibily associated electron foreshock. These results are compared to the results obtained by the same instrument during the Giotto comet Halley fly‐by. Despite the large difference in the size of the interaction regions (∼60,000 km for G‐S, ∼2000,000 km for Halley) due to 2 orders of magnitude difference in cometary neutral gas production rate, there are striking similarities in the solar wind interactions with the two comets.
Possible in situ detection of K2+ in the Jovian magnetosphere
Authors: McNutt Ralph L.
Published: February 2008

During the Voyager 1 and 2 encounters with Jupiter in 1979 the positive ion composition of the cold thermal plasma in the Jovian plasma sheet and cold Io torus could be obtained when the plasma Mach number in the spacecraft rest frame was sufficiently large. Clear indication of an ionic species with a mass‐to‐charge ratio between 16 (O+ and/or S2+) and 23 (Na+) is present in two spectra, one from the Voyager 1 encounter and one from the Voyager 2 encounter. Both of these spectra were acquired during apparent crossings of the plasma sheet in the middle magnetosphere. One interpretation is that the most likely identification of the ion is K2+, even though there is no evidence in the data for K+. Such an ion presence would be consistent with reports of neutral potassium associated with the Jovian system and originating at Io as well as with the identification of an ion with a similar mass‐to‐charge ratio at higher energies in the Ulysses data. An alternative interpretation is that the ion is a singly ionized molecular species associated with water products sputtered from Europa, a scenario which may also be consistent with the Ulysses data. However, other species present in the data and the low temperatures favor the Iogenic potassium hypothesis.
Travel times of S and SKS: Implications for three‐dimensional lower mantle structure beneath the central Pacific
Authors: Garnero E. J. , Helmberger D. V.
Published: February 2008

The travel times of S and SKS phases from deep‐focus Fiji‐Tonga events recorded in North America by Canadian Station Network and World Wide Seismographic Station Network stations exhibit a strong azimuthal dependence. The differential times of S‐SKS exhibit relatively little scatter and are used to investigate three‐dimensional mantle models for the central Pacific region. S‐SKS times are corrected for Earth's ellipticity, and residuals are computed with respect to the iasp91 reference model. Anomalously large S‐SKS times, ranging up to 9 s larger than iasp91 predictions for Δ > 100°, suggest a slow lower mantle beneath the central Pacific. These results are compared to the predictions of three tomographic models: MDLSH of Tanimoto (1990), model SH12_WM13 of Su et al. (1992), and model SH. 10c. 17 of Masters et al. (1992). The three‐dimensional whole mantle models have been parameterized into 11 spherical shells. Qualitative agreement between the tomographic model predictions and observations is encouraging, varying from fair to good. However, inconsistencies are present and suggest anomalies in the lower mantle of scale length smaller than the present 2000 + km scale resolution of tomographic models. Laterally varying outer core structure is not necessary to explain the anomalies in this data set, although such a scenario cannot be resolved with this data.
Magnetic fabrics, crystallographic preferred orientation, and strain of progressively Metamorphosed pelites in the Helvetic Zone of the Central Alps (Quartenschiefer Formation)
Authors: Richter Carl , Ratschbacher Lothar , Frisch Wolfgang
Published: February 2008

We investigate the relationships between the anisotropy of magnetic susceptibility (AMS), mineral preferred orientation, macroscopic structures, and finite strain in a section of increasing metamorphism in the Helvetic zone of the Central Alps (Switzerland). The Upper Triassic Quartenschiefer Formation, an initially hematite bearing red bed sedimentary rock, can be traced from unmetamophosed shale to amphibolite‐facies schists. The magnetic fabrics of 805 specimens agree well in orientation with the foliation (normal to kmin, kmax≥kint≥kmin are principal susceptibilities) and the mineral stretching lineation (parallel kmax) in all metamorphic grades. The maximum susceptibility axes are in an approximately N‐S orientation and were acquired during the Miocene north directed nappe transport. The effects of the tectonic position and the metamorphic grade on the AMS ellipsoid suggests that deformation has a stronger influence on its shape than the metamorphic grade. The identification and quantification of the sources of magnetic susceptibility was done with (1) a model calculation, (2) the high‐field/low‐field method, and (3) low‐temperature heating curves. The AMS of low‐grade samples is dominated by the paramagnetic minerals (mainly mica) and the AMS of higher susceptible medium‐grade samples by magnetite. The paramagnetic dominated magnetic fabrics correlate well with mica (002) lattice preferred orientations obtained from X ray texture goniometry. A one to one correlation between March “strains” and a magnetic parameter Mi=ln(ki/(kmaxkintkmin)⅓) is predicted by a numerical model and verified empirically. The magnetic fabrics of well characterized samples can thus be used to quantify the degree of mica preferred orientation using relatively simple magnetic anisotropy equipment.
Paleomagnetism and tectonics of the Crescent Formation, northern Olympic Mountains, Washington
Authors: Warnock Andrew C. , Burmester Russell F. , Engebretson David C.
Published: February 2008

A stable prefolding magnetization has been discovered in pillow basalts of the Eocene lower Crescent Formation of the northern Olympic Mountains. The curved outcrop pattern of the Crescent Formation has been the target of several unsuccessful studies to test for oroclinal bending. The success of this study is due, in part, to the development of a small‐diameter electric core drill for sampling the fractured rims of basalt pillows. Thermal demagnetization produced stable endpoints by 580°C in 12 of the 34 sites sampled (large within‐site scatter was common in the remaining sites). Among the accepted sites, within‐site scatter was small and correction for bedding tilt significantly reduced the scatter between sites. The mean paleomagnetic pole for newly sampled pillow basalts (86.4° north latitude, 170.0° east longitude, A95=16.5°) is indistinguishable from the early to middle Eocene pole expected for North America. Including previous results from sites in subaerial basalt of the upper Crescent Formation in and near the easterm Olympic Mountains results in a more regional paleomagnetic pole (80.7° north latitude, 192.0° east longitude, A95 =8.0°, N=46) that shows no significant rotation (0.8° ± 14.4°) or poleward displacement (−3.6 ± 8.5). Analysis of the magnetic mineralogy suggests that the remanence is early, probably primary. The pole, therefore, should be valid for tectonic interpretation of the region. A circular distribution of virtual geomagnetic poles after correction for bedding tilt supports the hypothesis that the northern Crescent Formation experienced deformation due to the rise, in a domelike fashion, of the sediments of the Olympic Core terrane. Erosion of a partial dome open to the west could have produced the curvature seen in the outcrop pattern of the Crescent Formation. The lack of significant rotation of the northernmost Coast Ranges contrasts with the net clockwise rotation seen to the south. The difference could be that irrotational northward translation (paleomagnetically insignificant yet geologically important), driven by oblique convergence, was accommodated by the north‐south trending strike‐slip faults to the east of the Olympic Mountains.
Chemical remanent magnetism related to the Dead Sea Rift: Evidence from Precambrian igneous rocks of Mount Timna, southern Israel
Authors: Marco Shmuel , Ron Hagai , Matthews Alan , Beyth Michael , Navon Oded
Published: February 2008

A paleomagnetic and mineralogical study of shallow intrusive basement rocks on Mount Timna (Arabo Nubian Massif in Sinai) shows that although all the igneous rocks are of late Precambrian age, a remanent magnetic direction similar to the subrecent field (Miocene to present) is identified in samples of quartz‐monzodiorite, monzodiorite, dikes of various composition, and altered gabbro. The average direction of these rock units is (D/I) 359°/41°, α95=4°, and the pole is at 83.6°N,223.2°E. The “subrecent” direction appears both as an overprint direction and as the sole stable vector in dolerite, rhyolite, and andesite dikes. The magnetic mineral assemblage of these rocks includes secondary minerals, such as hematite and goethite, which formed by oxidation and hydration of the original magnetite and Ti‐magnetite. The subrecent direction is interpreted to have been acquired as a chemical remanent magnetization (CRM) by hydrothermal activity and circulation of thermal brines through fractures related to the adjacent Dead Sea transform. The hydrothermal activity occurred before uplift and erosion exposed the basement rocks, i.e., in the middle Miocene, during the early stages of activity of the Dead Sea rift. The north trending declinations indicate that Mount Timna has not rotated about a vertical axis after acquisition of the CRM, a conclusion that confirms a previous structural analysis. An absence of reversals implies that the duration of CRM acquisition was probably less than ∼1 m.y., the maximum length of normal polarities since the Oligocene. Other field directions were found in an alkali granite (one site, 343°/14°, α95=22°), in a dolerite dike (one site, 318°/0°, α95=2°) and in a gabbro (seven sites, 303°/56°, α95=6°). The field direction in the granite is similar to that for Early Cretaceous, a time of magmatic activity in Timna. Northwest trending declinations and shallow inclinations found in several samples of the dikes are carried by unaltered parts of the rocks. These directions are interpreted as late Precambrian‐Early Cambrian in age, indicating a near‐equatorial location of the region at that time.