bluuebunny/crossref_metadata_2025 huggingface dataset:
The low‐frequency continuum as observed in the solar wind from ISEE 3: Thermal electrostatic noise
Authors: Hoang S. , Steinberg J.‐L. , Epstein G. , Tilloles P. , Fainberg J. , Stone R.G.
Published: February 2008

The low‐frequency (LF) continuum, observed in the solar wind by ISEE 3, is shown to be generated by local electrostatic (thermal) plasma waves and not by electromagnetic waves. The continuum has been investigated between 30 and 200 kHz utilizing the radio astronomy receivers and antennas aboard ISEE 3. This experiment has a noise level 5–20 dB lower than that of previous systems, as well as continuous frequency coverage from 30 to 80 kHz. Not only is the spacecraft itself very quiet but also it is stationed far from terrestrial noise sources. The spin plane wire antenna has a smaller photoemitting area and is consequently less noisy than tubular type antennas previously used. The observed LF noise continuum spectrum is a function of antenna length. For the spin plane S antenna, a 90 m dipole, a spectral index of −3 is found as compared to an index of −1.5 to −2.2 for the 2 to 5‐m Z antenna deployed along the spin axis. This Z antenna shows no spectral cutoff even when one is observed on the S antenna. When an interplanetary shock passes the spacecraft, large noise enhancements occur within a few seconds. The plasma frequency fp and consequently the electron density is obtained from observations of the 2fp line with the S antenna. A low‐frequency cutoff occurs very close to fp, and it is followed on the high‐frequency side by a peak of variable intensity. A cutoff is not observed only when it happens to fall outside the receiver frequency range. The noise voltage variations as a function of fp are deduced from observations of the 2fp line. The observed noise levels are in close agreement with those obtained by Imp 6 and Imp 8 at locations nearer the earth, thus ruling out a magnetospheric origin. The phenomenon is interpreted as local thermal plasma noise. The antenna radiation resistance in the plasma electrostatic mode can be computed and then used to determine the noise. Theory shows, for example, that for f »fp the S antenna spectrum is fp²/f³ provided that the electron density Ne is sufficiently large that the antenna is longer than 7 Debye lengths. In general, the theoretical results for f < fp as well as for f »fp are in excellent agreement with observations. Previous observations are reviewed to show that many of them, postulating a magnetospheric radio source, can be better interpreted instead with the mechanism outlined in the present paper.
Magnetic field directional discontinuities: 1. Minimum variance errors
Authors: Lepping R.P. , Behannon K.W.
Published: February 2008

A statistical investigation of the errors associated with the minimum variance analysis of directional discontinuity normal components has been performed. This study consisted of both computer simulation of discontinuities with controlled properties and examination of actual discontinuities (current sheets) observed by the Mariner 10 spacecraft. The simulated discontinuities were created by adding fluctuations, represented by isotropic random noise, to exactly known but varying (in a plane) magnetic field components. An empirical expression for the magnitude of the error |ΔBz| in an estimated discontinuity normal component, relative to the total field across the discontinuity, was derived, as well as other relevant statistical properties. This formula resulted from studies of the relation between precisely known values of the error and the minimum variance eigenvalues λ, rotation angle in the discontinuity plane ω, and magnitude of the normal component B cos β relative to the total field B. The formula is |ΔBz|=¾ B sin β Λ(3.60+2.44logΛ) {exp [(120° ‐ ω)/120°]³}, where Λ≡λ3(1/λ1 + 1/λ2) and where the subscripts 1, 2, and 3 on the eigenvalues refer to maximum, intermediate, and minimum values, respectively. It is found to give significantly more accurate estimates of the error in the normal component over a wide range of simulated conditions than the formula derived by Sonnerup (1971). Use of this empirical relation in the analysis of Mariner 10 discontinuities has provided a more precise estimate of an upper bound on the relative normal component value for tangential discontinuities that can be used to separate them from rotational discontinuities in studies using only magnetic field data from a single spacecraft in the region of space considered. This upper bound is |ΔBz|/B= 0.30.
Observations of a nonthermal ion layer at the plasma sheet boundary during substorm recovery
Authors: Möbius E. , Ipavich F.M. , Scholer M. , Gloeckler G. , Hovestadt D. , Klecker B.
Published: February 2008

We present measurements of the energy and angular distributions of energetic protons and alpha particles (≳30 keV/charge) in the geomagnetic tail. The measurements were made during the recovery phase of a geomagnetic substorm on April 19, 1978, with the Max‐Planck‐Institut/University of Maryland sensor system on the Isee 1 satellite. The measurements were also correlated with plasma observations made by the LASL/MPE instrument on Isee 1. The data reveal the presence of a thin nonthermal layer of protons and alpha particles at the plasma sheet boundary. The particles have their maximum flux at ∼60 keV/charge and are streaming highly collimated in the earthward direction. The alpha particle layer is confined within the proton layer. Many aspects of the observations are in agreement with an acceleration model near the neutral line proposed by Jaeger and Speiser (1974).
Deceleration of the solar wind in the Earth's foreshock region: Isee 2 and Imp 8 observations
Authors: Bonifazi C. , Moreno G. , Lazarus A. J. , Sullivan J. D.
Published: February 2008

The deceleration of the solar wind, in the region of the interplanetary space filled by ions backstreaming from the earth's bow shock and associated waves, is studied using a two‐spacecraft technique. This deceleration, which is correlated with the ‘diffuse’ but not with the ‘reflected’ ion population, depends on the solar wind bulk velocity: at low velocities (below 300 km/s) the velocity decrease is ∼5 km/s, while at higher velocities (above 400 km/s) the decrease may be as large as 30 km/s. Along with this deceleration the solar wind undergoes a deflection by ∼1° away from the direction of the earth's bow shock. The energy balance shows that the kinetic energy loss far exceeds the thermal energy which is possibly gained by the solar wind; therefore at least part of this energy must go into waves and/or into the backstreaming ions.
Evidence for a viscous boundary layer at the Venus ionopause from the preliminary Pioneer Venus results
Authors: Pérez‐De‐Tejada H.
Published: February 2008

A comparative study of the preliminary Pioneer Venus results is presented and its implications discussed in connection with the viscous flow interpretation of the ionosheath plasma at the Venusian terminator. It is shown that the various preliminary observations strongly support the case for a flattened ionopause boundary near the terminator as would be expected from the viscously induced deflection of solar wind fluxes in that region. Considerations of mass flux conservation and transfer of momentum are used to prepare an empirical formulation from which estimates of the transport properties of the ionosheath flow can be made. It is suggested that the position of the ionopause downstream from the terminator is not necessarily characterized by a balance condition between the ionospheric thermal pressure below and the magnetic pressure above but that the thermal and kinetic energy densities of the local ionosheath fluxes may be directly responsible for its location.
Photochemistry of SO2 in Venus' upper cloud layers
Authors: Winick J. R. , Stewart A. I. F.
Published: February 2008

A model is presented for the distribution of photochemically active gases in and above the upper cloud layer of Venus. Attention is focused on reproducing the experimental results of the Pioneer Venus (PV) mission, especially the ultraviolet spectrometer results for the cloud top SO2 distribution. The reconciliation of these results with the photochemical oxidation and hydration of SO2 into sulfuric acid aerosol puts limits on the vertical mixing rates in this region, with a value of K around 2 × 104 cm²s−1 being preferred. A model with SO2 being the major sulfur bearing gas is consistent with the PV measurements. The measured SO2 is more than ample to produce the observed H2SO4 in the upper cloud region and balance the sulfur budget in this region. The ClOx chemistry above the clouds and the relatively large SO2 concentration in the cloud top region suppresses the odd hydrogen density and thus inhibits the catalyzed recombination of O2 with CO to form CO2. In conjunction with the slow eddy mixing, this leads to O2 mixing ratios at the cloud tops that are much larger than earth‐based measurements; however, the major features of our sulfur model are not dependent on the O2 abundance.
Measurements of the Venus lower atmosphere composition: A comparison of results
Authors: Hoffman J. H. , Oyama V. I. , von Zahn U.
Published: February 2008

From the Pioneer Venus, as well as the Venera 11 and 12 spacecrafts, data on the chemical composition of the Venus atmosphere from about 700 km to the surface were obtained. In general, reasonable consistency can be found among the results from the seven gas analyzers that encountered Venus in December 1978. One of the more significant findings is the large excess abundance of primordial gases on Venus. The O2 abundances below 30 km must be very small, since none of the instruments detected O2 there. In and near the clouds the O2 mixing ratio may be as much as a few tens of parts per million. The CO mixing ratio is 20–30 ppm. The existence of COS, originally reported to be a major sulfur compound in the lowest part of the atmosphere, is doubtful there, and its mixing ratio at higher altitudes does not exceed a few parts per million. On the other hand, SO2 may exist below the clouds at a mixing ratio of the order of 100 ppm. In the clouds it is less than 10 ppm. A serious discrepancy in the data still exists for the case of the water vapor abundance. As a result of the cross‐checks provided by the number and types of instruments flown to Venus, confidence in the validity of these results on its atmospheric composition has progressed to a reasonable degree of certitude.
The clouds of Venus: A synthesis report
Authors: Knollenberg R. , Travis L. , Tomasko M. , Smith P. , Ragent B. , Esposito L. , McCleese D. , Martonchik J. , Beer R.
Published: February 2008

The results presented represent a synthesis of data from those Pioneer Venus experiments directed toward studying cloud problems. These orbiter and multiprobe experiments show the cloud system to consist of three altitude regions populated by cloud particles and smaller haze particles which extend above and below as well as coexist with the cloud particles. The optical properties derived are only consistent with the largest particles, having platelike morphology. The smallest particles are shown to require changes in chemical composition to explain observed behavior. The medium‐sized H2SO4 droplets of 2 µm diameter appear to be the least volatile and are the best understood. The role of the cloud particles in precipitation dynamical processes, lightning, and radiation are all discussed.
A feature of the behavior of He+ in the nightside high‐latitude ionosphere during equinox
Authors: Heelis R. A. , Murphy J. A. , Hanson W. B.
Published: February 2008

At high latitudes during solstice the ray path through the atmosphere to about 400‐km altitude near midnight is either so small that production of O+, He+, and H+ continues at all times or so large that production of these species is negligible. The latter condition will produce an ionospheric ‘hole’ if the plasma stagnates or circulates in the nightside winter pole. Near equinox, however, the shadow height near midnight may ensure that photoproduction of O+ is negligible, while the ray path at higher altitudes may be short enough that significant production of He+ and H+ takes place. Observations made by Atmosphere Explorer D and calculations suggest that an ionospheric hole should also be observable at equinox but will not be so pronounced as that observed during winter. However, the dominance of He+ in the hole between 500 and 1000 km is unique to equinoctial conditions. We note that stagnation of the plasma rather than slow passage across the polar cap is required, since at equinox the field tubes must reach the nightside before the shadow height ensures that the photoproduction of O+ ceases. Stagnation times between 3 and 6 hours are required for He+ to be dominant at altitudes around 600 km.
On the conservation of the first adiabatic invariant in perpendicular shocks
Authors: Pesses M. E.
Published: February 2008

Numerical simulations show that preshock and postshock values of the first adiabatic invariant (magnetic moment) are, on the average, equal for particles transmitted by infinitesimally thin perpendicular magnetosonic fast‐mode shock waves. These results are apparently not explainable by adiabatic theory but are accounted for by the conservation of angular momentum.
Observation of fallout rates of atmospheric 7Be and 22Na produced by cosmic rays—concerning estimation of the fallout rate of atmospheric 26Al
Authors: Hasebe N. , Doke T. , Kikuchi J. , Takeuchi Y. , Sugiyama T.
Published: February 2008

The fallout rates of radionuclides, 7Be and 22Na, in rainwater collected at Tokyo were measured monthly during the period from February 1975 to February 1977, using a low‐background dual NaI(T1) coincidence gamma ray spectrometer. It is found that the contribution from nuclear weapon tests to these nuclides is negligibly small. Therefore these activities (7Be and 22Na) are attributed to the cosmic ray produced nuclides in the atmosphere. The average fallout rates of 7Be and 22Na measured at ground level of Tokyo are 118±13 and (1.66±0.24) × 10−2 pCi/m²/d, respectively. These values are in agreement with values estimated by Lal and Peters, within the experimental error. Using the observed fallout rate of 22Na, the global average fallout rate of 26Al produced in the atmosphere is estimated to be 5.4 × 10−8 pCi/m²/d, which is higher by about a factor of ten than the influx rate of cosmic dust bearing 26Al estimated by Reyss et al. Therefore most of the 26Al activity contained in the terrestrial sample seems to be originated from the 26Al produced by cosmic rays in the atmosphere.
Neutral thermospheric temperature from ion concentration measurements
Authors: Breig E. L. , Donaldson J. S. , Hanson W. B. , Kayser D. C. , Spencer N. W. , Hoffman J. H. , Wharton L. E. , Power R. A.
Published: February 2008

An analysis and evaluation are presented of a technique for extracting information on neutral thermospheric temperature from satellite measurements of the relative abundances of H+ and O+ ions in the F region. Charge‐exchange equilibrium in the neighborhood of 320 km relates the observed altitude distribution of this ion concentration ratio directly to that of the associated neutral species and thus to the neutral temperature. The method has been applied to an extensive set of ion concentration data acquired with the Atmosphere Explorer C and D satellites, and evaluated through direct comparison of these ‘ion‐ratio’ temperatures with other concurrent in situ measurements. A comprehensive orbit‐by‐orbit comparison is presented with both ion temperature data and with calculations from the MSIS model. Select comparisons are also available with direct temperature measurements from the Nate instrument, and with temperatures derived from height distributions of observed neutral particle densities. Statistical analyses emphasize random and systematic differences between these several alternative types of temperature data. Sources and estimates of possible uncertainties unique with the ion‐ratio method are also discussed. Excellent agreement has been achieved between the ion‐ratio and the ion temperatures from the AE‐D satellite; the analysis is, however, unable to account for a small systematic difference between corresponding measurements from AE‐C. A random uncertainty of ∼5% must also be associated with neutral temperatures derived from the ion‐ratio method. Otherwise, a general consistency is demonstrated between the various forms of temperature data. All classes of measurements indicate that nighttime thermospheric temperatures are lower than predicted by the MSIS model.
Mesospheric winds from lidar observations of atmospheric sodium
Authors: Clemesha B. R. , Kirchhoff V. W. J. H. , Simonich D. M. , Batista P. P.
Published: February 2008

Laser radar observations of the atmospheric sodium layer, made by various groups of workers during the past decade, have shown that the layer exhibits considerable time‐varying structure. In this paper we describe horizontally spaced measurements of this structure and use the results of these observations to derive horizontal velocities in the height range 82 to 99 km. The measurements were made with a steerable lidar operating at a fixed zenith angle of 20.9° and pointed at each of three azimuths in turn, the complete sequence taking 5 min. The azimuths were chosen such that the intersections of the lidar beam with the sodium layer formed a triangle with approximately 60 km sides. We present here the analysis of a 10‐hour data run taken on the night of July 21, 1979. After low pass filtering to remove rapid uncorrelated fluctuations, a cross correlation analysis was carried out for each of the height intervals in the range 82 to 99 km. The velocities calculated from the derived time shifts were found to vary with height in an oscillatory manner, with amplitude increasing with height. The east‐west component showed a vertical wavelength of approximately 10 km, the north‐south component a wavelength of 5 km, and the magnitude of the velocity varied between 6 and 146 m s−1.
Wave disturbances in the low latitude ionosphere and equatorial ionospheric plasma depletions
Authors: Sobral J. H. A. , Abdu M. A. , Batista I. S. , Zamlutti C. J.
Published: February 2008

An isolated nighttime ionospheric wave disturbance was observed simultaneously by a meridional scanning 6300‐Å photometer, a 6300‐Å zenith photometer, a 30‐MHz riometer, and an ionosonde over Cachoeira Paulista, a low‐latitude station in Brazil. From the results we have identified at least two different scale sizes for the disturbances which could be broadly classified as (1) a larger scale component easily identified in the riometer data and has characteristics similar to those of a large scale TID and (2) smaller scale disturbances observable in the scanning photometer data, occurring during the ascending phases of the larger scale waves. A Fourier analysis of the zenith airglow variations clearly reveals a dominant period of about 104 min that seems to correspond to the period of the larger scale waves and no single dominant period is present for the smaller scale waves. Whereas all these have a poleward velocity component, the smaller scale waves show up this feature more markedly. The equatorial source of the smaller scale disturbances and other characteristics have led us to suggest that these disturbances are perhaps the low‐latitude manifestations of the upward propagating field aligned plasma bubbles in the equatorial ionosphere.
Simultaneous measurements of magnetotail dynamics by IMP spacecraft
Authors: Fairfield D. H. , Lepping R. P. , Hones E. W. , Bame S. J. , Asbridge J. R.
Published: February 2008

Eleven traversals of the magnetotail at 30–40 RE by the IMP 7 and IMP 8 spacecraft occurred while IMP 6 was making magnetotail measurements inside 33 RE. Combined magnetic field and plasma data from these spacecraft provide the first demonstration of pressure balance between the high β plasma of the plasma sheet and the strong magnetic fields of the tail lobes. The time variations of this pressure support the view that a southward interplanetary magnetic field enhances the accumulation of energy in a magnetotail energy reservoir. Sometimes the accumulated magnetic energy is rapidly dissipated during a magnetospheric substorm. At other times the dissipation can occur more gradually during ongoing magnetic activity. At such times the energy supplied by the solar wind may even exceed that being dissipated, thus causing the tail energy to increase. In addition to plasma sheet thinnings seen prior to substorm onsets inside ∽15 RE a gradual decrease in plasma β is detected in the deep tail which precedes onset and the more prominent plasma disappearance that typically accompanies it. The frequency of thinnings and the regions over which they occur indicate that drastic changes in plasma sheet thickness are common features of substorms which occur at all locations across the tail. Several magnetically quiet periods correspond to thick plasma sheets with enhanced BZ components and gradually cooling plasmas.
O++ in the Venusian ionosphere
Authors: Fox J. L. , Victor G. A.
Published: February 2008

It is shown that the revised photochemical theory for O++ in the earth's ionopshere, where double photoionization of O is the dominant source, is consistent with recent O++ measurements on Venus. A rate coefficient of 1.5 × 10−10 cm³ s−1 for O++ + O is obtained, and the possible importance of O++ chemistry on minor atomic ions and airglow emissions is explored.
Effects of charge exchange on the distribution of ionospheric ions trapped in the radiation belts near synchronous orbit
Authors: Lyons L. R. , Moore T. E.
Published: February 2008

Trapped ions believed to have been injected directly into the radiation belts from the ionosphere are persistently observed near synchronous orbit. However, there is an apparent inconsistency between the composition of the trapped ions observed near synchronous orbit and that observed at lower altitudes of ions flowing upward from the ionosphere. The upflowing ionospheric ions are dominated by H+, with a significant but lesser amount of O+, while the small pitch angle ions near synchronous orbit are dominated by O+. In this paper, we show that ion loss from charge exchange with neutral hydrogen is a plausible cause of the differing composition at low and high altitudes. In addition, we find that such charge exchange can simultaneously account for minima near 0° and 180° and maxima near 15°–20° and 160°–165° observed in the pitch angle distributions of the trapped ions.
On the spatial power spectrum of the E × B gradient drift instability in ionospheric plasma clouds
Authors: Keskinen M. J. , Ossakow S. L.
Published: February 2008

Conservation laws, implied by the fundamental plasma fluid equations describing the E × B gradient drift instability in ionospheric plasma clouds, are utilized to obtain an analytic prescription for the power spectrum. Furthermore, it is shown that the two‐dimensional power law power spectra of magnetic field line integrated Pedersen conductivity (density) perturbations, in the plane perpendicular to the ambient magnetic field, computed from numerical simulation studies and experimental results are supported by an analysis of these conservation laws. The numerical simulations suggest a two‐dimensional power spectrum of the form P(k, θ)=P0cosmθ (1 + (k/k0)sup2;)−(n+1)/2, where cos θ=k · E0 and E0 is the ambient electric field. The present analytic formulation suggests 1 <n <3. In addition, if m=2 and n=2, one finds the outer scale wave number k0 ∝ L−1, the plasma cloud gradient scale length.
Simultaneous rocket and radar measurements of currents in an auroral arc
Authors: Robinson Robert M. , Bering Edgar A. , Vondrak Richard R. , Anderson Hugh R. , Cloutier Paul A.
Published: February 2008

A detailed study of electric field, current and conductivities associated with an auroral arc was made in a coordinated rocket and radar experiment in Alaska on March 9, 1978. The payload, designated 29.007 UE, was launched at 1013 p.m. local time. It penetrated the diffuse aurora on the upleg and at apogee traversed field lines connected to a stable auroral arc of 40 kR intensity. Among the instruments carried by the payload were a vector magnetometer, a set of electrostatic double probes and a set of electron and proton spectrometers. Simultaneous electron density and line‐of‐sight velocity measurements were made by the Chatanika radar operating in an elevation scan mode in the magnetic meridian plane. Both the radar and rocket measurements indicated that the zonal electric field was westward and approximately constant across the arc with a magnitude of about 7 mV/m. Small differences between the rocket and radar zonal electric field measurements indicated the presence of upward drifting ions in the region of the arc. The meridional field was large and northward equatorward of the arc, but negligible within the arc. Conductivities computed from measured fluxes of energetic electrons agreed well with the conductivities derived from the radar measurements of electron density. The electric field and conductivity measurements indicated that the zonal currents were eastward equatorward of the arc and westward within the arc. These electrojet currents agreed well with those inferred from the rocket magnetometer data. Better agreement was obtained when a westward neutral wind was added. The westward wind was also consistent with differences between the rocket and radar meridional electric fields. The meridional currents computed from the electric field measurements were northward over the entire region. Since the northward current was enhanced within the arc, a pair of oppositely directed field‐aligned current sheets associated with the arc edges was inferred. However, these current sheets were not detected by the rocket‐borne vector magnetometer. The magnetometer measured a downward current in the diffuse aurora equatorward of a wide region of upward current within which the arc was embedded. The differences in the field‐aligned current patterns inferred from the two methods are attributed either to a time dependent field‐aligned current profile or east‐west current divergence in the region of the Harang discontinuity.
5‐ to 50‐m wavelength plasma instabilities in the equatorial electrojet 3. Counter‐electrojet conditions
Authors: Hanuise C. , Crochet M.
Published: February 2008

Measurements of plasma instabilities in the equatorial electrojet with HF and VHF radars have always been performed in a large scale turbulent medium. It is only in the exceptional case of a strong daytime counter‐electrojet, as observed in Africa in 1977, that the background can be considered as almost laminar. Characteristics of the instability during such conditions are presented and appear to be completely different from those observed during electrojet conditions; especially the measured phase velocity varies with elevation angle and wavelength as predicted by the linear theory. The level of turbulence deduced from the measurements is found to be weaker than during usual conditions. Comparisons are made with theoretical works.
Albedo, internal heat, and energy balance of Jupiter: Preliminary results of the Voyager Infrared Investigation
Authors: Hanel R. A. , Conrath B. J. , Herath L. W. , Kunde V. G. , Pirraglia J. A.
Published: February 2008

Full disk measurements recorded 31 days before the Voyager 1 encounter with Jupiter by the radiometer (0.4–1.7 µm) of the infrared instrument Iris indicate a geometric albedo of 0.274±0.013. The given error is an estimate of systematic effects and therefore quite uncertain; the random error in the radiometer measurement is negligible. Combining this measurement with the Pioneer‐derived phase integral of 1.25 of Tomasko et al. (1978) and our error estimate of 0.1 yields a Jovian Bond albedo of 0.343±0.032. Infrared spectra recorded at the same time by the Michelson interferometer (4–55 µm), along with a model extrapolation to low wave numbers not covered by the instrument, yield a thermal emission of 1.359±0.014 × 10−3 W cm−2. This corresponds to an equivalent blackbody temperature of 124.4±0.3 K, in agreement with results of Ingersoll et al. (1975) and Erickson et al. (1978) but lower than all other previous estimates. As in the case of the albedo measurement the quoted errors in the emission measurement reflect estimates of systematic effects and are uncertain, while the random component is negligible. From these measurements the internal heat flux of Jupiter is estimated to be 5.444±0.425 × 10−4 W cm−2, and the energy balance defined as the ratio of emitted thermal to absorbed solar energy is 1.668±0.085.
Flow fields within Jupiter's great red spot and white oval BC
Authors: Mitchell Jim L. , Beebe Reta F. , Ingersoll Andrew P. , Garneau Glenn W.
Published: February 2008

Using sequences of Voyager 1 high‐resolution images of Jupiter's Great Red Spot (GRS) and White Oval BC we map the flow fields within the GRS and Oval BC. We compute relative vorticity within these features as a function of semi‐major axis length and position angle in a coordinate system consisting of concentric ellipses of equal eccentricity. Both the velocity and the relative vorticity profiles are nearly identical for Oval BC and the outer portion of the GRS. Wind speeds of 110–120 m/s are observed near the outer edges of both features. Along their minor axes relative vorticity profiles reach a maximum of ∼6 × 10−5 s−1. This is several times greater than the ambient 1.5 × 10−5 s−1 meridional shear of zonal winds at the latitudes of the GRS and Oval BC. Maximum Rossby numbers of 0.36 are computed for flows within both the GRS and the Oval BC. Generally, the Rossby numbers within these features are much lower, indicating strongly geostrophic constraints on the flow. The difference in streamline curvature within the GRS and the Oval BC is found to compensate for the difference in planetary vorticity at the respective latitudes of the features. Motions within the central region of the GRS are much slower and more random than around the spot’s outer portion.
Thermal structure and dynamics of the Jovian atmosphere 1. The great red spot
Authors: Flasar F. Michael , Conrath Barney J. , Pirraglia Joseph A. , Clark Patrick C. , French Richard G. , Gierasch Peter J.
Published: February 2008

Temperatures and thermal winds over the Great Red Spot (GRS) and its environs are derived from Voyager infrared spectroscopy (IRIS) data. The atmosphere over the GRS is characterized by a tropopause which is cold relative to its environment and an upper stratosphere which is relatively warm. The cold tropopause implies a decrease in anticyclonic vorticity with height above 500 mbar through the lower stratosphere. IRIS observations at 5 µm indicate little emission from the GRS itself, but enhanced emission in a ring about it, in agreement with recent ground‐based results. The behavior of the tropopause and 5 µm temperatures can be consistently interpreted as resulting from a circulation which rises within the GRS and subsides in the area around it. The explanation of the upper stratospheric temperatures is not so straightforward. A previous suggestion that they may be a manifestation of the linear vertical propagation of Rossby waves appears inconsistent with the gross east‐west symmetry in the stratospheric temperatures over the GRS. The implications of the present results for various theoretical models of the GRS are examined, and the possibility that latent heat release drives the GRS is discussed. Dynamical scalings based on an axisymmetric, frictionally controlled vortex suggest that, aside from the nonlinearities inherent in the parameterization of small‐scale moist convection, the large‐scale dynamics of the GRS are linear, as distinct from those of a tropical cyclone, which are markedly nonlinear.
Energetic oxygen and sulfur in the Jovian magnetosphere
Authors: Gehrels N. , Stone E. C. , Trainor J. H.
Published: February 2008

This paper reports measurements made by the cosmic ray subsystem onboard Voyager 1 and 2 in the Jovian magnetosphere. Energy spectra of oxygen ions in the energy range 1–20 MeV/nuc between 5 and 20 RJ are presented and used to calculate phase space densities. There is a steep positive radial gradient in the phase space density of the energetic oxygen ions in this region, indicating an inward diffusive flow. Solutions of the diffusion equation assuming a diffusion coefficient D and loss lifetime τ of the forms D=D0Ln and τ=τ0Lm, where D0, τ0, n, and m are constants, and L is the McIlwain parameter, are fit to the radial phase space density profile of oxygen ions with magnetic moments of 680 MeV/nuc‐G. The best fits are found to have n + m ≈ 6 and 3 <n <6. On the basis of the diffusion coefficient upper limit obtained from these fits, the upper limit on the rate at which oxygen ions with >400 MeV/nuc‐G diffuse inward across 10 RJ is 5 × 1021±1 ions s−1. The observations suggest that oxygen and sulfur ions in the Io plasma torus diffuse radially outward, are nonadiabatically accelerated in some region outside 17 RJ and then diffuse inward and outward from the acceleration region.
Global properties of the magnetosphere during a substorm growth phase: A case study
Authors: Baker D. N. , Hones E. W. , Higbie P. R. , Belian R. D. , Stauning P.
Published: February 2008

At approximately 0100 UT on December 29, 1976, a large injection of energetic (>30 keV) particles was observed by Los Alamos instrumentation onboard spacecraft 1976‐059 (35°W longitude) at geostationary orbit. This injection was closely associated with the onset of a major substorm (also at 0100 UT) identified by sharp negative bays in the H components of magnetic records at Leirvogur (22°W) and Narssarssuaq (45°W) and by the occurrence of a positive H component bay at 0100 UT in the mid‐latitude magnetogram record at M'Bour (17°W). This substorm expansion onset (and concomitant particle injection) was preceded (between 2330 and 0100 UT) by a pronounced ‘stretching’ of the magnetic field at synchronous orbit into a taillike configuration and by a development of highly cigarlike (field‐aligned) electron distributions at geostationary orbit that we have in the past identified with the substorm growth phase. Of principal importance in this case are two other auxiliary data sets. The first is a well‐timed set of DMSP auroral images taken during the course of the growth and expansion phases of the substorm. The images before and during the growth (cigar) phase, including one auroral zone crossing at ∼0050 UT, show quiet aurora with no observable substorm activity in the visible polar region. The second relevant data set is a broad set of riometer data from 13 separate stations in three general meridians (west coast Greenland, east coast Greenland, and northern Scandinavia) from magnetic latitudes of ∼65° to ∼90°. The riometer data also show clearly that there was no measurable substorm activity anywhere, either in longitude or latitude, as the magnetosphere developed its very stressed, growth‐phase configuration prior to substorm expansion onset. These results support the concept of a storage of energy (growth phase) prior to its rapid release at substorm onset. IMP 8 observations in the high southern magnetotail lobe at ∼35 RE geocentric radial distance provide strong corroborative evidence of this storage and subsequent release of magnetic energy.
Generation of ELF and VLF waves by polar electrojet modulation: Experimental results
Authors: Stubbe P. , Kopka H. , Dowden R. L.
Published: February 2008

The heating facility at Ramfjordmoen near Tromsø, Norway, has been used to modulate the polar electrojet at frequencies in the range 200–5500 Hz. ELF‐VLF signals were received on the ground in the full frequency range, with amplitudes of the order 10 to 100 fT for an effective radiated HF power of 32 MW at 4.04 MHz. A variety of experimental results is presented in this paper.
Simultaneous ground‐satellite observations of quasi‐periodic (QP) ELF‐VLF emissions near L=6
Authors: Sato Natsuo , Fukunishi Hiroshi , Ozaki Takayuki , Yoshino Takeo
Published: February 2008

Simultaneous ground‐satellite observations of ELF‐VLF emissions have been carried out at Syowa station (L∼6) in Antarctica during the IMS period by receiving the telemetry signals from the ISIS 1 and 2 satellites. The quasi‐periodic intensity modulation of ELF‐VLF emissions at the satellite level, which had one‐to‐one correspondence with the intensity modulation of QP emissions at Syowa, was observed in the wide latitude range from −54° to −78° MLAT, and also in the region ∼2 hours apart from Syowa in magnetic local time. The spectral form of QP emissions observed on the ISIS satellite showed a clear dependence on latitude, i.e., emissions in the higher frequency range were observed at lower latitudes, while emissions in the lower frequency range were observed at higher latitudes. Although quasi‐periodic intensity modulation of polar chorus had generally one‐to‐one correspondence between the ground and satellite data, burst‐like discrete emissions did not show always one‐to‐one correspondence between both data. These results give a basis to confirm a phenomenological model proposed by Sato and Fukunishi [1981] for the generation mechanism of QP emissions.
Characteristics of Pc 5 micropulsations as determined with the STARE Experiment
Authors: Villain J. P.
Published: February 2008

Recently, Walker et al. (1979) have shown the suitability of the Scandinavian twin auroral radar experiment facility for Pc 5 pulsation studies. They consider that in the ionosphere the hydromagnetic wave causing the geomagnetic pulsation produces a periodic electric field superimposed on the ambient background field. In this paper STARE measurements of ionospheric electric fields are used to obtain Pc 5 polarization maps covering all the STARE field of view. These fields are deduced from electron Hall drift velocities measured with high spatial (20 × 20 km²) and temporal (20 s or 60 s) resolution over a large area (160,000 km²). The fast Fourier transform algorithm is applied to time series of both the north‐south and east‐west electric field components for each of the ∼400 geographic points within the STARE field of view. By retaining both the amplitudes of and relative phase between the north‐south and east‐west Fourier transformed components, the complete polarization state of the Pc 5 electric field can be determined at each geographic point and for each of the discrete frequencies obtained from the fast Fourier transform algorithm. The analysis of a number of selected events that support the hydromagnetic field line resonance theory of micropulsations is presented.
Ion temperature determination in the ionosphere by retarding potential analyzer aboard sounding rocket
Authors: Minami Shigeyuki , Takeya Yoshio
Published: February 2008

A vertical profile of the ion temperature in the ionosphere at local afternoon in the region from 95 to 310 km has been measured directly by means of an improved retarding potential analyzer (RPA) system aboard a space sounding rocket. This rocket was launched at Kagoshima Space Center of Japan (geomagnetic latitude: 198° 4′E; longitude:20° 0′N). In this paper the method of measurement of the ion temperature by two RPA's and the experimental results are discussed. Two RPA's were flown. One of them measured the probe characteristics and the other one measured the angle of attack of the plasma. To measure the angle of attack, this RPA was tilted at 30° from the rocket spin axis. The probe curves were not distorted, as is often the case with rocket probes, since the clean surfaces of mesh grids and other electrodes were stored in a clean room and the nose cone contained dry N2 gas. The angle of attack is measured directly by the tilted ion trap. The measured angle of attack data agree with the data obtained by geomagnetic and solar aspect sensors aboard the rocket. The tilted probe was most useful in the nighttime experiment when no solar aspect data were available. The results show that the ion temperature below 150 km is the same as that of the neutral temperature at high solar activity. Above 150 km the average ion temperature gradually becomes higher. In this region the ion temperature profile contains a wavelike structure. The peak to trough amplitude of the temperature variation is about 250°K and a vertical wave length of about 25 km is determined. The relationship between this experimental vertical temperature profile and the horizontal atmospheric motions measured by simultaneous ground observations was examined. As a result it was found that these wave data do not fit on the branch of the φ‐k diagram of theoretical internal atmospheric gravity wave (IGW) by Hines (1960). It may also be difficult to regard another vertical profiles showing wave lengths of several tens of kilometers measured by some other workers as simply manifestations of IGW.
Plasma waves near the magnetopause
Authors: Anderson R. R. , Harvey C. C. , Hoppe M. M. , Tsurutani B. T. , Eastman T. E. , Etcheto J.
Published: February 2008

Plasma waves associated with the magnetopause, from the magnetosheath to the outer magnetosphere, are examined with an emphasis on high time resolution data and the comparison between measurements by using different antenna systems. An early ISEE crossing of the magnetopause region, including passage through two well‐defined flux transfer events, the magnetopause current layer, and boundary layer plasma, is studied in detail. The waves in these regions are compared and contrasted with the waves in the adjoining magnetosheath and outer magnetosphere. Four types of plasma wave emissions are characteristic of the nominal magnetosheath: (1) a very low frequency continuum, (2) short wavelength spikes, (3) ‘festoon‐shaped’ emissions below about 2 kHz, and (4) ‘lion roars.’ The latter two emissions are well correlated with ultra‐low frequency magnetic field fluctuations. The dominant plasma wave features during flux transfer events are (1) an intense low‐frequency continuum, which includes a substantial electromagnetic component, (2) a dramatic increase in the frequency of occurrence of the spikes, (3) quasi‐periodic electron cyclotron harmonics correlated with ∼1‐Hz magnetic field fluctuations, and (4) enhanced electron plasma oscillations. The plasma wave characteristics in the current layer and in the boundary layer are quite similar to the features in the flux transfer events. Upon entry into the outer magnetosphere, the plasma wave spectra are dominated by intense electromagnetic chorus bursts and electrostatic (n + 1/2)fg− emissions. Wavelength determinations made by comparing the various antenna responses and polarization measurements for the different waves are also presented.
Observations of high‐speed plasma flow near the Earth's magnetopause: Evidence for reconnection?
Authors: Eastman T. E. , Frank L. A.
Published: February 2008

In an attempt to confirm the evidence for reconnection reported by Paschmann et al. (1979), we have examined three‐dimensional plasma velocity distributions sampled near the magnetopause by using the LEPEDEA plasma instrument. During the magnetopause crossing of September 8, 1978, we observe high‐speed plasma flow in the magnetospheric boundary layer that is suggestive of the accelerated flow predicted by reconnection models. However, our low‐energy plasma observations reveal an apparent inconsistency with the tangential stress balance condition, and there is no clear evidence available from the plasma measurements for a local, normal flow component υn. Simultaneous measurements of ⩾45‐keV energetic electrons show pancake‐shaped pitch angle distributions and intensity variations that suggest a closed field line regime, whereas the high‐speed plasma flow is predicted to occur on open field lines for the reconnection hypothesis. Allowing for finite gyroradius effects, the energetic particles show no signature of traversing from a closed to an open field line regime upon entering the boundary layer which contains high‐speed ion flow. Since the energetic particle angular distributions indicate that the high‐speed plasma flow occurs partly or entirely on closed field lines, we suggest that the simplest hypothesis is to place the entire boundary layer observed during this crossing on closed field lines. We find that several detailed features of the available measurements can be explained readily in this way. Our ISEE observations appear to be most consistent with impulsive injection of magnetosheath plasma across the magnetopause in a process that involves both MHD and plasma kinetic instabilities.
Evidence for current sheet acceleration in the geomagnetic tail
Authors: Lyons L. R. , Speiser T. W.
Published: February 2008

The existence of the current sheet and the dawn to dusk electric field in the geomagnetic tail implies there is particle energization in the tail current sheet of the order 2–10% of the total solar wind energy incident upon the dayside magnetopause. In this paper we determine that ion acceleration in a current sheet with a small magnetic field across the sheet, via single‐particle motion which violates the guiding center approximation, can account for this large energization in the tail. We calculate the distribution of accelerated ions which result from the current sheet acceleration and compare the results with distributions of accelerated ions frequently observed flowing earthwards along the outer boundary of the plasma sheet. The comparison indicates that the observed earthward‐flowing ions result from current sheet acceleration. Comparison with measurements of auroral ion precipitation at low altitudes implies that the accelerated ions ejected from the current sheet are also an important source of auroral ion precipitation. In addition, these accelerated ions may be an important source of plasma sheet ions.
Saturnian kilometric radiation: Source locations
Authors: Kaiser M. L. , Desch M. D.
Published: February 2008

Using Voyager 1 and 2 Planetary Radio Astronomy data and reasonable assumptions about radiation beam geometry, we deduce the source locations of both polarization components of the Saturn kilometer‐wavelength radiation. The resulting radio source footprints are at high latitudes north and south, and near the noon meridian. These footprints are compared with the surface locations of Saturn's UV aurorae, polar cap boundary, and polar cusp.
Particle precipitation induced by short‐duration VLF waves in the magnetosphere
Authors: Inan U. S. , Bell T. F. , Chang H. C.
Published: February 2008

An extension of a previous test particle simulation model (Inan et al., 1978) of the gyroresonance wave‐particle interaction in the magnetosphere is used to compute the detailed time variation of the precipitated energy flux induced by monochormatic short‐duration VLF waves. The resulting precipitation pulse is found to have a characteristic shape dependent on the L value, cold plasma density, wave frequency, and duration, as well as the energetic particle distribution function. The role of these variables in determining the temporal variation and the magnitude of the precipitated flux is discussed for a wide range of typical magnetospheric parameters. As an example, a 400‐m s wave pulse with a frequency of 6.825 kHz (equatorial half‐gyrofrequency) at L = 4 and for a cold plasma density of 400 el/cc produces a 3.5‐s long precipitation pulse as observed at 1000 km, with the flux reaching its peak value at approximately 3.8 s after the injection of the wave at the same point. Our findings indicate that if the predicted temporal variations can be observed, the results may be used to diagnose some of the details of the energetic particle distribution in the magnetosphere. The magnitude of the precipitated flux is a function of the trapped particle distribution. For example, for typical trapped electron distribution interacting with a 5 kHz wave of 1 pT intensity at L = 4 the peak precipitated energy flux is found to be 5×10−3 ergs/cm² s. The predicted fluxes for typical parameters are 10²–10³ times larger than typical background precipitation levels at these latitudes and would be detectable with presently available instruments.