bluuebunny/crossref_metadata_2025 huggingface dataset:
SALAMMBO: A three‐dimensional simulation of the proton radiation belt
Authors: Beutier Thierry , Boscher Daniel , France Martin
Published: February 2004

Using diffusion theory, we give the first results for a three‐dimensional model of the proton radiation belt. This is based on the numerical solution of a diffusion equation which takes into account the cosmic ray albedo neutron decay source, deceleration of protons by the free and bounded electrons of the medium, the charge exchange loss process, and radial diffusion by magnetic and electric field perturbations. This model used in static conditions gives results which are in a good agreement with those of NASA's AP8 model. However, a better knowledge of thermospheric densities, radial diffusion, and improved measurements of proton flux near synchronous orbit altitudes may be necessary to improve future model results. We prove that an external boundary condition, which plays the part of an injection source, is essential to radiation belt existence and explains the effect of solar activity and magnetotail dynamics on radiation belt dynamics.
The inner magnetosheath of Venus: An analogue for Earth?
Authors: Luhmann J. G.
Published: February 2004

The unmagnetized planets provide examples of solar wind interactions that are free from the complications associated with magnetopause reconnection and with sensitive obstacle response to incident solar wind pressure changes. Using the Venus magnetosheath as a testbed, we search for evidence of standing slow mode “transitions” in the inner subsolar region as reported for Earth by Song et al. [1990a; 1992a; b]. Although the system at Venus is much smaller in scale, the Pioneer Venus Orbiter magnetometer data indicate that for perpendicular interplanetary magnetic field conditions the general behavior of the plasma in the magnetosheath is as expected from the simple depletion layer model. In examples of magnetic field measurements chosen for the apparently steady interplanetary conditions during the spacecraft pass, there is no clear evidence for a slow mode structure near the ionopause as might be expected on the basis of the Song et al. study. The implication is that some aspect of the Venus magnetosheath (such as its small size or the presence of local planetary ion production) makes it physically different from Earth's, that the conditions of the magnetosheath during Song's study differed significantly from those in the Venus study, or that the observations of Song et al. do not represent a steady state.
VLF line radiation observed by satellite
Authors: Rodger Craig J. , Thomson Neil R. , Dowden Richard L.
Published: February 2004

VLF line radiation received by the ISIS 1 and 2 satellites over New Zealand is found to fall into two distinct classes. The first of these consists of magnetospheric lines (MLs) which are characterized by a broadband appearance and by frequency drifts of a few tens of hertz per minute, similar to those reported elsewhere. Both their initial frequencies and their frequency spacings were, however, found to be essentially random rather than multiples of 50 or 60 Hz. The hourly variation in ML occurrence showed no correlation with electrical load in possible electrical mains systems sources. No clear decrease in occurrence on weekends was evident. This first satellite survey with significant numbers of MLs found no evidence of a relationship with power line harmonics. The second class of satellite‐received VLF lines consists of “tram lines” (TLs) which are characterized by their very narrow bandwidth and zero frequency drift. TLs appear to lie close to harmonics of 50 or 60 Hz. An example of this class is presented.
Intensities and polarization rates of whistler mode VLF signals observed from a ground network near L = 4
Authors: Ikeda M. , Nagano I. , Shimbo T. , Carpenter D. L.
Published: February 2004

VLF signals transmitted from Siple station in Antarctica that propagated through the ionosphere and magnetosphere to the northern hemisphere and triggered emissions generated by the Siple signals in the magnetosphere are radiated from wave exit areas on the ionospheric lower boundary. The locations and extent of the wave exit areas are deduced from the wave intensity distributions measured on the ground. In this method we use measurements of wave magnetic intensity made simultaneously at six stations. The validity of this method is assessed by comparing the results with values simply estimated from a mathematical evaluation and with results of full wave calculations carried out by Nagano et al. (1986, 1987). We find close agreement among results obtained from the three methods and conclude that the wave intensity distribution analysis is valid. The observed distribution of polarization rate also agrees well with the results of the full wave calculations carried out by Nagano et al. (1986, 1987) and with those obtained by the mathematical evaluation. As a result of analyzing a triggered emission in detail, the extent of the wave exit area of the downgoing triggered emission is estimated to be 25‐50 km or so at an altitude of 80 km. We believe that this value relates to the horizontal extent of the duct through which the triggered emission propagated in the magnetosphere and ionosphere and that essentially only direct waves transmitted from the wave source arrive within a range of 200 km from the wave intensity peak on the ground.
Neptune radio emission in dipole and multipole magnetic fields
Authors: Sawyer C. B. , King N. V. , Romig J. H. , Warwick J. W.
Published: February 2004

We study Neptune's smooth radio emission in two ways: we simulate the observations and we then consider the radio effects of Neptune's magnetic multipoles. A procedure to deduce the characteristics of radio sources observed by the Planetary Radio Astronomy experiment minimizes limiting assumptions and maximizes use of the data, including quantitative measurement of circular polarization. Study of specific sources simulates time variation of intensity and apparent polarization of their integrated emission over an extended time period. The method is applied to Neptune smooth recurrent emission (SRE). Time series are modeled with both broad and beamed emission patterns, and at two frequencies which exhibit different time variation of polarization. These dipole‐based results are overturned by consideration of more complex models of Neptune's magnetic field. Any smooth emission from the anticipated auroral radio source is weak and briefly observed. Dominant SRE originates in complex fields at midlatitude. Possible SRE source locations overlap that of “high‐latitude” emission (HLE) between +(out) and −(in) quadrupoles. This is the first identification of multipolar magnetic structure with a major source of planetary radio emission.
ULF pulsations in a magnetospheric waveguide: Comparison of real and simulated satellite data
Authors: Rickard Graham J. , Wright Andrew N.
Published: February 2004

The representation of the Earth's magnetosphere as an MHD waveguide has prompted much recent speculation. In particular, the signatures associated with ULF pulsations sit well within the waveguide concept. We further explore the appositeness of the waveguide model by simulating data that a spacecraft would see when passing through a stimulated magnetospheric waveguide and by comparing the results with those obtained from a real spacecraft. We find that the waveguide results again compare favorably and can explain many features seen in the data. We also find that the magnetometer signature of the fast mode in a waveguide (unlike a cavity) does not have a regular oscillatory nature with constant period over a range of L shells.
Acoustic‐gravity wave impulse response to a point source in a nonisothermal stratified atmosphere
Authors: Nalesso G. F. , Jacobson A. R.
Published: February 2004

The excitation of pressure waves by a point source in a nonisothermal, stratified atmosphere is studied. Using an ad hoc monotonically increasing thermal profile, Green's function is derived. It is shown that apart from the usual acoustic and acoustic‐gravity branches, waves guided by the atmospheric thermocline are also excited. The leading term of an asymptotic expansion of Green's function is then used to obtain an analytic expression of the acoustic front and the impulse tail.
On possible observational evidence in electron density profiles of a magnetic field in the Martian ionosphere
Authors: Krymskii A. M. , Breus T. , Nielsen E.
Published: February 2004

The purpose of this paper is to examine the effects of a horizontal magnetic field and of horizontal transport of plasma on the vertical electron density profile in the Martian ionosphere. A two‐dimensional magnetohydrodynamic model for the steady state Martian ionosphere is presented. The model takes into account the basic reactions involving O+, O2+, and CO2+ ions and vertical plasma transport as well as horizontal plasma transport along the hypothesized magnetic field lines. The good agreement between model predictions and experimental electron density radio occultation profiles supports the hypothesis of an intrinsic magnetic field of Mars.
Density fluctuations and turbulent Mach numbers in the inner solar wind
Authors: Bavassano B. , Bruno R.
Published: February 2004

At MHD scales the solar wind behaves as an almost incompressible fluid in both the inner and the outer heliosphere, with density fluctuations that, for a relevant fraction of cases, have a relative amplitude less than 0.1. Nearly incompressible MHD theory would seem then appropriate to describe a major part of the solar wind compressive turbulence at these scales. However, in spite of some examples of good agreement between observations and theoretical predictions, an extended applicability of the nearly incompressible theory to the interplanetary plasma turbulence is far from being firmly established. In the present paper, we focus, as a test of the theory, on the scaling properties of density fluctuations with turbulent Mach number. Interplanetary plasma data in the region from 0.3 to 1 AU in a period of low solar activity have been used. The analysis has been performed on the entire data sample and on subsets of it with different ranges of solar wind velocity and heliocentric distance. Our results unambiguously indicate a lack of the expected correlations. This negative outcome might be due to the small dynamic range of the analyzed parameters. Nevertheless, in the light also of recent indications about a low level of correlation between density and temperature fluctuations, it appears reasonable to conclude that experimental observations do not seem in favor of a generalized applicability of the nearly incompressible theory to MHD compressive fluctuations in the inner solar wind.
Ponderomotive wave forces in longitudinal MHD waveguides
Authors: Guglielmi A. V. , Pokhotelov O. A. , Feygin F. Z. , Kurchashov Yu. P. , McKenzie J. F. , Shukla P. K. , Stenflo L. , Potapov A. S.
Published: February 2004

By using a general expression for the ponderomotive wave force, we have evaluated the action of ion cyclotron Alfvén waves on the plasma density in a longitudinal waveguide. The main effect is the condensation of the plasma in the vicinity of the waveguide equator. According to observations onboard the GEOS 1 and Viking satellites, the amplitudes of such geomagnetic pulsations can reach up to several nanoteslas. This is sufficient to cause a strong modification of the cold plasma density in the magnetosphere under the action of ion cyclotron Alfvén pulsations. Furthermore, we have also speculated on the possible effects of the ponderomotive wave force on the problems connected with the so called “wave‐induced substorms” in the neutral sheet of the geomagnetic tail as well as with the phenomenon of “ponderomotive plasma filling,” which determines the relaxation of the plasmasphere after the geomagnetic perturbations.
ULF cusp pulsations: Diurnal variations and interplanetary magnetic field correlations with ground‐based observations
Authors: McHarg Matthew G. , Olson John V. , Newell Patrick T.
Published: February 2004

In this paper we establish the Pc 5 magnetic pulsation signatures of the cusp and boundary regions for the high‐latitude dayside cusp region. These signatures were determined by comparing spectrograms of the magnetic pulsations with optical observations of particle precipitation regions observed at the cusp. The ULF pulsations have a diurnal variation, and a cusp discriminant is proposed using a particular narrow‐band feature in the pulsation spectrograms. The statistical distribution of this pattern over a 253‐day period resembles the statistical cusp description using particle precipitation data from the Defense Meteorological Satellite Program (DMSP). The distribution of the ground‐based cusp discriminant is found to peak 1 hour earlier than the DMSP cusp distribution. This offset is due to the interplanetary magnetic field (IMF) being predominantly negative By for the period when the data were collected. We find the diurnal variations so repeatable that only three main categories of pulsation spectra explain 86 percent of all data observed. We find that these categories have statistically different IMF distributions. The identification of the signatures in the magnetic spectrograms of the boundary regions and central cusp allows the spectrogram to be used as a “time line” that shows when the station passed under different regions of the dayside oval.
A magnetospheric magnetic field model with flexible current systems driven by independent physical parameters
Authors: Hilmer Robert V. , Voigt Gerd‐Hannes
Published: February 2004

A tilt‐dependent magnetic field model of the Earth's magnetosphere with variable magnetopause standoff distance is presented. Flexible analytic representations for the ring and cross‐tail currents, each composed of elements derived from the Tsyganenko and Usmanov (1982) model, are combined with the fully shielded vacuum dipole configurations of Voigt (1981). The ring current, consisting of axially symmetric eastward and westward currents fixed about the dipole axis, resembles that inferred from magnetic field observations yet permits easy control of inner magnetospheric inflation. The cross‐tail current contains a series of linked current sheet segments which allow for the tilt‐dependent flexing of the current sheet in the x‐z plane and arbitrary variations in current sheet position and intensity along the length of the magnetotail. Although the current sheet does not warp in the y‐z plane, changes in the shape and position of the neutral sheet with dipole tilt are consistent with both MHD equilibrium theory and observations. In addition, there is good agreement with observed ΔB profiles and the average equatorial contours of magnetic field magnitude. While the dipole field is rigorously shielded within the defined magnetopause, the ring and cross‐tail currents are not similarly confined, consequently, the model's region of validity is limited to the inner magnetosphere. The model depends on four independent external parameters, namely, (1) the dipole tilt angle, (2) the magnetopause standoff distance, (3) the midnight equatorward boundary of the diffuse aurora, and (4) the geomagnetic index Dst. In addition, we present a simple but limited method of simulating several substorm related magnetic field changes associated with the disruption of the near‐Earth cross‐tail current sheet and collapse of the midnight magnetotail field region. These include the classic dipolarization of the near‐Earth field and the reduction of the far‐tail equatorial field accompanying current sheet thinning. This feature further facilitates the generation of magnetic field configuration time sequences useful in plasma convection simulations of real magnetospheric events.
Ion temperatures in the Io plasma torus
Authors: Thomas Nicolas
Published: February 2004

Observations of the radial dependence of the perpendicular ion temperatures of the four major ion species in the Io plasma torus are reported. Doppler‐resolved forbidden line emissions of S+, S2+, O+, and O2+ were observed within a period of 72 hours on March 3–5 1993, with the 3.6‐m telescope of the European Southern Observatory. The long slit spectra of S+ show a sharp (factor of 4) increase in the perpendicular ion temperature at the position of the “ribbon” where enhanced electron densities and [S II] emission were observed. The observations are broadly consistent with models of line profiles based on average ion temperatures derived from Voyager 1 plasma science data. The signal to noise for the S+ observations was sufficient to reveal two velocity components in the distribution, at 33 and 188 eV, inside Io's orbit. Modeling shows that the two components arise from the superposition of hot outer ions upon a core of cool inner torus ions as a result of line of sight effects. Outside Io's orbit, the temperature of S+ ions was observed to decrease from 120 eV at 6.0 RJ to 80 eV at 6.8 RJ.
A case and statistical study of transient magnetic field events at geosynchronous orbit and their solar wind origin
Authors: Borodkova N. L. , Zastenker G. N. , Sibeck D. G.
Published: February 2004

We present a statistical survey of Prognoz 10 solar wind observations at the times of transient (step function and impulsive) variations in the dayside magnetospheric magnetic field strength measured by the GOES 5 and 6 geosynchronous satellites. The results indicate that 51% of the transient magnetospheric events can be associated with corresponding variations in the solar wind dynamic pressure. A further 17% of the events can be associated with fluctuations in the interplanetary magnetic field orientation in the sense previously associated with foreshock pressure pulses. We find no tendency for impulsive events at dayside geosynchronous orbit to be associated with north/south fluctuations in the interplanetary magnetic field (IMF) orientation, nor for the events to occur primarily during intervals of southward IMF. The success rate for associating transient events at dayside geosynchronous orbit with solar wind features decreases as Prognoz 10 moves farther from the Earth‐Sun line. The observations indicate that variations in the solar wind dynamic pressure and foreshock pressure pulses associated with variations in the IMF cone angle are the predominant causes of large‐amplitude transient events observed at dayside geosynchronous orbit.
ISEE 1 and Geotail observations of low‐frequency waves at the magnetopause
Authors: Cattell C. , Wygant J. , Mozer F. S. , Okada T. , Tsuruda K. , Kokubun S. , Yamamoto T.
Published: February 2004

Observations of waves at frequencies below ∼200 Hz obtained near the magnetopause are presented. For one case identified in the ISEE 1 data as a period when steady state reconnection was occurring, there were waves below the lower hybrid frequency with amplitudes up to ∼7 mV/m. Intense low‐frequency waves with amplitudes up to ∼20 mV/m at the subsolar magnetopause have also been observed by the Geotail electric field instrument. In some cases, large spiky fields were embedded in the waves. The waves observed by ISEE 1 and Geotail were large enough to provide the dissipation required for reconnection to occur.
Plasma and magnetic field behavior across the magnetosheath near local noon
Authors: Hill P. , Paschmann G. , Treumann R. A. , Baumjohann W. , Sckopke N. , Lühr H.
Published: February 2004

Using Active Magnetospheric Particle Tracer Explorers/Ion Release Module data from 10 magnetosheath crossings in the 11–13 LT sector, we have investigated the behavior of the proton temperature and the proton temperature anisotropy between the bow shock and the magnetopause. The proton anisotropy increases toward the magnetopause. Comparison with earlier predictions, however, shows that this increase is much more modest than was predicted by assuming the double adiabatic equations. It is shown that neither of the two double‐adiabatic equations holds separately. We conclude that energy is transferred between the perpendicular and the parallel component of the proton temperature. It is well established that instabilities such as the mirror and the ion‐cyclotron instability show such a behavior and lead to a decrease in the temperature anisotropy. Our data show that in the magnetosheath proper, the threshold for the onset of the mirror instability is always marginally met. We show that we can give an empirical relation between the temperature anisotropy and β⊥, as long as β⊥ is not less than 1.
Disturbances of cometary and Earth's magnetospheres by single solar flares
Authors: Saito Takao , Kozuka Yukio , Nishioka Kimihiko , Konno Ichishiro , Saito Masaji , Kojima Masayoshi , Takahashi Tadatoshi
Published: February 2004

Comets P/Brorsen‐Metcalf and C/Okazaki‐Levy‐Rudenko appeared successively in 1989 and displayed various disturbances of their magnetospheres. We observed two cases of a phenomenon in which a disconnection event of the cometary plasma tail (on August 13 and November 16, 1989) was followed by a terrestrial magnetic storm (on August 14 and November 17). A survey of solar flares suggests that an identical solar flare excited successively the cometary magnetosphere and the Earth's magnetosphere in each case. The average velocities of the shock front in interplanetary space were estimated by using the magnetospheric disturbances of both the comets and the Earth together with the assumed responsible solar flare. It is speculated from the results that the propagation of the shock front associated with the flare is not symmetric with respect to the radial axis from the flare region of the Sun.
Preferential heating of light ions during an ionospheric Ar+ injection experiment
Authors: Pollock C. J. , Chandler M. O. , Moore T. E. , Arnoldy R. L. , Kintner P. M. , Chesney S. , Cahill L. J.
Published: February 2004

The Argon Release for Controlled Studies (ARCS) 4 sounding rocket was launched northward into high altitude from Poker Flat Research Range on February 23, 1990. The vehicle crossed geomagnetic field lines containing discrete auroral activity. An instrumented subpayload released 100 eV and 200 eV Ar+ ion beams sequentially, in a direction largely perpendicular to both the local geomagnetic field and the subpayload spin axis. The instrumented main payload was separated along field lines from the beam‐emitting subpayload by a distance which increased at a steady rate of ∼2.4 m s−1. Three‐dimensional mass spectrometric ion observations of ambient H+ and O+ ions, obtained on board the main payload, are presented. Main payload electric field observations in the frequency range 0–16 kHz, are also presented. These observations are presented to demonstrate the operation of transverse ion acceleration, which was differential with respect to ion mass, primarily during 100‐eV beam operations. The preferential transverse acceleration of ambient H+ ions, as compared with ambient O+ ions, during the second, third, fourth, and fifth 100‐eV beam operations, is attributed to a resonance among the injected Ar+ ions, beam‐generated lower hybrid waves, and H+ ions in the tail of the ambient thermal distribution. This work provides experimental support of processes predicted by previously published theory and simulations.
Global equatorial ionospheric vertical plasma drifts measured by the AE‐E satellite
Authors: Fejer B. G. , de Paula E. R. , Heelis R. A. , Hanson W. B.
Published: February 2004

Ion drift meter observations from the Atmosphere Explorer E satellite during the period of January 1977 to December 1979 are used to study the dependence of equatorial (dip latitudes ≤ 7.5°) F region vertical plasma drifts (east‐west electric fields) on solar activity, season, and longitude. The satellite‐observed ion drifts show large day‐to‐day and seasonal variations. Solar cycle effects are most pronounced near the dusk sector with a large increase of the prereversal velocity enhancement from solar minimum to maximum. The diurnal, seasonal, and solar cycle dependence of the longitudinally averaged drifts are consistent with results from the Jicamarca radar except near the June solstice when the AE‐E nighttime downward velocities are significantly smaller than those observed by the radar. Pronounced presunrise downward drift enhancements are often observed over a large longitudinal range but not in the Peruvian equatorial region. The satellite data indicate that longitudinal variations are largest near the June solstice, particularly near dawn and dusk but are virtually absent during equinox. The longitudinal dependence of the AE‐E vertical drifts is consistent with results from ionosonde data. These measurements were also used to develop a description of equatorial F region vertical drifts in four longitudinal sectors.
Surface‐induced luminescence in a high‐velocity rarefied atomic oxygen flow regime
Authors: Greer W. A. D. , Stark J. P. W. , Pratt N. H.
Published: February 2004

A comprehensive investigation of surface‐induced luminescence has been carried out, using a beam of fast (1.5 to 3.3 km s−1) atomic oxygen and a painted aluminum target over which NO is effused. Experimental measurements of luminescence intensity as a function of beam fluxes, distance off the surface, and luminscence spectra leads to the conclusion of a surface‐mediated O + NO → NO2 reaction with supporting evidence for a multistep mechanism. Calibration of gas fluxes and luminescence intensity provides an overall rate coefficient [ln {k1(cm² s)} = −40 (+2, −1.5)] which was not found to be sensitive to beam energy over the range investigated. Comparison of laboratory results with spacecraft glow indicates similar trends in both phenomena.
Surface waves on the tailward flanks of the Earth's magnetopause
Authors: Seon J. , Frank L. A. , Lazarus A. J. , Lepping R. P.
Published: February 2004

Forty‐three examples of ISEE 1 tailward flank side magnetopause crossings are examined and directly compared with upstream solar wind parameters. The crossings are classified into two groups. In the first group, a few sudden magnetopause crossings are observed, whereas repeated magnetopause crossings and oscillatory motions, often with boundary layer signatures, are observed in the second group. These distinctive characteristics of the two groups are interpreted in terms of the surface waves due to the Kelvin‐Helmholtz instability. It is found that low solar wind speed tends to favor characteristics of the first group, whereas high solar wind speed yields those of the second group. However, no evident correlations between the groups and the interplanetary magnetic field directions are found.
The response of a gasdynamic termination shock to interplanetary disturbances
Authors: Story T. R. , Zank G. P.
Published: February 2004

A one‐dimensional gasdynamic model is used to analyze the interaction of the solar wind termination shock (TS) with various interplanetary disturbances. These include density enhancements and depletions, Gaussian “shock” pulses, and forward‐reverse shock pairs. Our simulations suggest that the termination shock is unlikely to be stationary. Both the interaction state and the postinteraction state of the termination shock are discussed. The very complicated state and structure of the TS during interaction with interplanetary disturbances is examined carefully. It is found that the TS is not readily identifiable from the other simultaneously present structures (reverse shock, contact discontinuities, forward shocks and so on.). This may complicate the identification of the TS by the Voyager or Pioneer spacecraft significantly. It is also found that a number of interesting structures propagate and evolve downstream after a collision. These include sharp spikes in the density, which advect outward at the postshock flow speed, and secondary damped shock pulses produced in the collision, which propagate supersonically. Some implications of both the density enhancements and the production of damped shock waves in the heliosheath and at the heliopause are discussed.
Cusp currents from ionospheric vorticity generated by gasdynamic and merging flow fields at the magnetopause
Authors: Mei Y. , Crooker N. U. , Siscoe G. L.
Published: February 2004

Cusp currents that arise from ionospheric vorticity generated by the combined merging outflow and gasdynamic flow fields at the magnetopause, as proposed by Saunders (1989), are quantified and compared with those calculated by Mei et al, (1994) from vorticity generated by mapping the solar wind electric field into a limited cusp region of the polar cap, as proposed in the synthesis view of Banks et al. (1984). The results are essentially identical for strong interplanetary magnetic field (IMF) By, thus demonstrating equivalence between mechanical and electrical descriptions of reconnect ion‐driven convection. For southward IMF, however, the mechanical description yields weak cusp currents with dawn‐dusk bipolarity, as deduced from early observations by Iijima and Potemra (1976), whereas the electrical description yields none. The bipolar currents arise from the diverging pattern of gasdynamic flow. The currents become unipolar as By increases and the asymmetry of the merging outflow dominates. Additional cusp currents in both models arise at kinks in the flow contours (additional ionospheric vorticity) around the border of the cusp region, owing to limiting the area of mapping from the magnetopause. The border currents form a bipolar pair that rotates around the circumference of the cusp as the IMF rotates in clock angle. They dominate the currents arising from vorticity within the cusp.
O(1S) 557.7 nm and O(1D) 630 nm emissions in shuttle thruster plumes
Authors: Viereck R. A. , Murad E. , Pike C. P. , Mende S. B. , Swenson G. A. , Elgin J. B. , Bernstein L. S. , Lucid S.
Published: February 2004

Radiation resulting from interaction between the effluent cloud of a space shuttle thruster and the ambient atmosphere was observed with a spectrograph aboard the shuttle. The spectral measurements were made between 400 and 800 nm with a resolution of 3 nm. The primary emissions are identified as NO2, HNO, O(1D), and O(1S). These are the first observations of O(1S) emission in the shuttle plume. These data are compared with previous measurements, and possible excitation mechanisms are discussed. The results are also compared with a Monte Carlo simulation of thruster plume‐atmosphere interaction radiation.
Visible contrail formation from fuels with different sulfur contents
Authors: Busen R. , Schumann U.
Published: February 2004

As a test for postulated influences of sulfur emissions on nucleation, the contrail formation from a two‐engine jet aircraft was investigated using fuels with different sulfur contents for the two engines during the same flight. The sulfur mass fractions in the fuels were about 2 and 250 ppm, respectively, typical for aviation fuels. Other engine and fuel parameters were about the same for both engines. Contrail formation was observed visually from distances as close as 100 m and documented by video and photos. The flight took place at 302 hPa (9 km altitude), at ambient temperatures of about −50°C, and relative humidity for liquid water of about 34%. Short contrails formed about 30 m after the engines. No visible differences were detected in the contrails forming from the two engines. The observed conditions for contrail formation are close to those predicted by Appleman [1953] if the propulsion efficiency of the aircraft/engine combination during flight is taken into account.
Response of equatorial F layer vertical drift in the dusk sector to the change in the radiative output of the Sun in 1992
Authors: Sastri J. Hanumath
Published: February 2004

A study is made of the effect of the rapid and large decline in the solar radiative output that occurred from March through May 1992 on the postsunset maximum in F layer vertical drift Vzp over Kodaikanal (dip 3°N). Between the periods July 1991 through February 1992 and June 1992 through February 1993, there is a 35% decrease in the mean amplitude of the postsunset peak in F layer vertical drift ( Vzp ) over Kodaikanal, corresponding to the 40% decrease in the mean level of the 10.7‐cm solar radio flux. Changes of the same magnitude are also seen when the comparison is restricted to a shorter interval of two local winter months preceding and following the rapid decline in the 10.7‐cm flux. The results illustrate the sensitivity of equatorial F layer vertical drift in the dusk sector to short‐term variability in the solar radiative output. Solar flux related changes in the longitudinal (local time) gradient in E region conductivity as well as in the F region zonal winds are suggested as the cause of the positive response of the dusktime peak in F layer vertical drift to the rapid decline in solar radiative output that occurred in early 1992.
Density depletions at the 10‐m scale induced by the Arecibo heater
Authors: Kelley M. C. , Arce T. L. , Salowey J. , Sulzer M. , Armstrong W. T. , Carter M. , Duncan L.
Published: February 2004

In June 1992 a NASA sponsored sounding rocket, was flown through the Arecibo heater beam to study the structure of the heated volume. The rocket carried an instrument payload and traversed the 5.1‐MHz reflection height at 268.5 km. Data from the plasma density probe are presented in this paper. The rocket passed through several regions of disturbed plasma both above and below the reflection level. In these regions, over 180 deep filamentary density depletions were detected. Measured perpendicular to the magnetic field, these depletions or filaments have a mean width at half maximum of 7 m which is roughly equal to twice the ion gyroradius (O+) and a mean depletion depth of 6%. The ratio of parallel to perpendicular scale for these structures exceeds 20,000, and the spacing between the filaments is around 15 m. A power spectrum of the rocket data clearly shows the spectral content of the filaments and also reveals peaks at longer wavelengths which we interpret as the spacing between the bunches and between sets of filaments within a given bunch. We believe that previous scintillation and satellite measurements emphasized these longer wavelengths. The power spectrum measured by the rocket instrumentation falls off as k−4 for wavenumber k larger than 0.4/m and remains above the system noise for structure down to 1 m. It is clear that VHF backscatter from these structures can be explained by our data, as can many features of heater‐related, field‐aligned irregularities found in the literature.
Low‐frequency waves in the near‐Earth plasma sheet
Authors: Bauer T. M. , Baumjohann W. , Treumann R. A. , Sckopke N. , Lühr H.
Published: February 2004

Using magnetometer and plasma instrument data of the Active Magnetospheric Particle Tracer Explorers/Ion Release Module satellite obtained during 3 months of plasma sheet passes, we compute power spectra of magnetic fluctuations in the frequency ranges 0.1–25 mHz, 1–270 mHz, and 0.03–8 Hz and statistically survey their dependence on location, ambient magnetic field, plasma moments, and magnetospheric activity. Average power spectra, S, of the field vectors increase monotonically with decreasing frequency. Whereas for frequencies between 0.03 and 2 Hz power laws, S ∼ ƒ−ϵ with 2 < ϵ < 2.5 hold, the slopes ϵ of the average power spectra fall below 1.5 for frequencies below 1 mHz. In the range 0.03–2 Hz the right‐hand spectrum Sr and the left‐hand spectrum Sl are equal. Being much less than the transverse wave spectra Sr and Sl in the plasma sheet boundary layer, the compressional wave spectrum S∥ surpasses Sr and Sl in the vicinity of the neutral sheet. As expected, the waves are enhanced during substorms. The highest values of all wave spectra Sr, Sl, and S∥ in the range 0.03–2 mHz are connected with high‐speed flows and strong changes in density and temperature in the central plasma sheet as well as with strong changes of the magnetic field in both the central plasma sheet and the plasma sheet boundary layer. Magnetic variations in the range 0.15–1 mHz (periods between 17 min and 2 hours) reflect the substorm dynamics of the near‐Earth plasma sheet and flapping motions of the tail. They have root‐mean‐square amplitudes of a few nanoteslas, the amplitude along XGSM being about twice as high as the amplitudes along YGSM and ZGSM. Close to the neutral sheet we find three events exhibiting compressional narrow‐band fluctuations with spectral peaks at periods of 1–2 min. These fluctuations occur at substorm onset and are accompanied by perturbations of the thermal pressure that are in antiphase with the perturbations of the magnetic pressure.
On the dynamical development of the downward field‐aligned current in the substorm current wedge
Authors: Pellinen R. J. , Pulkkinen T. I. , Huuskonen A. , Glassmeier K.‐H.
Published: February 2004

Data from the Scandinavian magnetometer array, a multichannel scanning photometer, and all‐sky cameras have been combined to study the carriers of the downward field‐aligned current in the substorm current wedge during the first minutes after the substorm onset. The ions are slow and thus cannot contribute much to the downward current immediately after the substorm onset, whereas the precipitating magnetospheric electrons can quickly set up the upward current. On March 4, 1979, magnetometers and all‐sky cameras recorded a substorm onset at ∼2236 UT slightly to the west of the stations. A scanning photometer was located at the center of the downward current during the event. The observations suggest that the downward current in this event was set up less than a minute after the formation of the upward current and that at this stage the current was mainly carried by cold ionospheric electrons.
The double oval UV auroral distribution: 2. The most poleward arc system and the dynamics of the magnetotail
Authors: Elphinstone R. D. , Hearn D. J. , Cogger L. L. , Murphree J. S. , Wright A. , Sandahl I. , Ohtani S. , Newell P. T. , Klumpar D. M. , Shapshak M. , Potemra T. A. , Mursula K. , Sauvaud J. A.
Published: February 2004

The poleward arc system of a double oval distribution is shown to activate at the end of the optical expansion phase signifying the beginning of substorm recovery. The velocity dispersed ion signature (VDIS) can exist coincident with this discrete aurora developing on the most poleward oval. Although the VDlS is usually associated with ion beams in the plasma sheet boundary layer, it is demonstrated that the ionospheric signature is not beamlike but distributed in pitch angle. At the time when the double oval begins to form, the magnetic field in the magnetotail lobe becomes less flared and can show Pc 5 period oscillations. Similar pulsations also exist in the ionosphere associated with the most poleward oval and with stationary surge formation. Theoretical considerations link this phenomenon with a wave source tailward of xGSE = −30RE and fast mode evanescent waves propagating earthward in the tail lobe region. In this case the magnetotail appears to act like a waveguide and the plasma sheet boundary layer as a resonance region. This implies that the coupling of this fast mode wave is with the plasma sheet boundary layer and not with dipolar like field lines. The implications of this for the reconnection model of substorms are discussed.
Intermediate transition in the Venus ionosheath
Authors: Perez‐de‐Tejada H. , Intriligator D. S. , Strangeway R. J.
Published: February 2004

We present the results of an analysis of Pioneer Venus Orbiter (PVO) plasma and electric and magnetic field data with evidence of a plasma transition along the flanks of the Venus ionosheath for 8 PVO passes near the terminator. This transition occurs between the bow shock and the ionopause and represents a stationary change in the properties of the shocked solar wind that streams around the Venus ionosphere. We find that the intermediate transition is characterized by three concurrent features: (1) A noticeable electric field burst measured with the 30 kHz channel of the electric field detector of the PVO; (2) a severe drop of the magnetic field intensity accompanied by a strong rotation of the magnetic field orientation to a direction closer to the Sun‐Venus axis in the inner ionosheath; and (3) substantially enhanced plasma fluxes detected at the time when these changes in the electric and magnetic fields are measured. The peak particle flux and the peak magnetic field intensity measured at this transition in the data of the 17 PVO orbits are also presented. It is found that large values of the enhanced particle fluxes occur mostly when the peak magnetic field intensity is large.
Comparison of Viking onset locations with the predictions of the Thermal Catastrophe Model
Authors: Henderson M. G. , Murphree J. S.
Published: February 2004

In the thermal catastrophe model of substorms, onset is attributed to an explosive heating of the plasma sheet boundary layer (PSBL) due to the resonant absorption of Alfvèn waves. These waves are assumed to have their origins at the magnetopause where solar‐wind‐driven Kelvin‐Helmholtz surface waves launch magnetoacoustic waves through the lobes toward the PSBL which are then mode‐converted to kinetic Alfvèn waves in the PSBL. On the basis of this wave source mechanism, the thermal catastrophe model predicts the locations in the tail where catastrophe and hence onset is most likely to occur. In this paper, the model predictions are extended to include the effects of a realistic tail field (represented by the Tsyganenko 1987 long model) and are compared to observations of substorm onset as determined from Viking auroral images. The use of a realistic tail field causes a deflection of the catastrophe domain towards the dusk (dawn) flanks of the magnetosphere for gardenhose (orthogardenhose) interplanetary magnetic field (IMF) conditions, and it is also found that this region extends into the deep tail only for higher solar wind speeds, thereby confining catastrophe to the relatively near‐Earth portions of the tail for typical conditions. Most of the other results obtained with the inclusion of a realistic tail field produce trends similar to the original model predictions including the results that onset should get closer to midnight for increasing solar wind speed and that onset should occur in the premidnight (postmidnight) sector for gardenhose (orthogardenhose) IMF conditions. Although a weak consistency with measured onset locations is observed, many more events than are contained in the Viking database are required in order to provide a firm conclusion. However, the reasonably well established result that onset occurs very close to the Earth on closed field lines is inconsistent with the predictions of the model which places onset on PSBL field lines. Thus the thermal catastrophe model is not a likely mechanism for typical substorm onsets. Nevertheless, evidence is shown that the mechanism may still operate in the magnetosphere to produce a different type of auroral intensification.
Magnetic field and plasma properties associated with pressure pulses and magnetic reconnection at the dayside magnetopause
Authors: Otto A. , Lee L. C. , Ma Z. W.
Published: February 2004

Most of the models for the formation of magnetic flux transfer events (FTEs) at the dayside magnetopause (MP) are based on magnetic reconnection. However, it has been suggested that a wavy magnetopause motion caused by solar wind pressure variations might provide an alternative explanation. Using two‐dimensional MHD simulations, we study the dynamics and the local field and plasma signatures which are caused by the interaction of enhanced pressure regions with a current layer. The results are compared with two‐dimensional magnetic reconnection processes. The magnetopause motion due to the enhanced pressure agrees qualitatively with the suggested model. The earthward or sunward displacement of the magnetopause is driven by the interaction of a fast mode wave with the current sheet. However, the variation of the magnetic field component normal to the current layer BN is largely monopolar and for the considered cases typically smaller than for the reconnection cases. In addition, the magnetic field signatures depend strongly on the propagation direction of the boundary wave relative to the local magnetic field configuration. The normal magnetic field signature reverses sign across the magnetopause for large magnetic shear and propagation along the direction of antiparallel field components. In the reconnection case, the bipolar BN signature has the same polarity on both sides of the current sheet. Differences between magnetic reconnection and pressure driven boundary motions are manifold and systematic differences are summarized which can be used to test statistical ensembles of such events.
On the spectral asymmetry of type II coherent echoes at large magnetic aspect angles
Authors: Osterried R. , Kustov A. V. , Sofko G. J. , Koehler J. A. , André D.
Published: February 2004

The asymmetry (skewness) of broad type II Doppler spectra collected by the pre Saskatchewan Auroral Polarimetric Phased Array Ionospheric Radar Experiment (SAPPHIRE) coherent radar system during westward electrojet conditions was studied. The system included two 50‐MHz CW links which monitored spatially close regions of the ionosphere with about the same aspect angles of ∼10° but with an azimuth difference of the bisectors of about 90°. Periods of scatter were selected when both radar links recorded echoes with a wide, type II spectrum. Typically, the spectra were asymmetrical on both links and had a magnitude of skewness in between 0.3 and 0.5. For radar links with a positive (negative) mean Doppler shift, the skewness was observed to be positive (negative) contrary to previous reported auroral zone experiments (positive skewness means a longer spectral tail toward higher velocities). The spectra were more skewed for observations along the electrojet, for higher echo power and also for narrower spectral width. The characteristic features of the spectral asymmetry are attributed to the plasma turbulent processes at large off‐orthogonal angles.
Plasma transport through the magnetopause by turbulent interchange processes
Authors: Book David L. , Sibeck David G.
Published: February 2004

The turbulent motion of the plasma compressed behind the Earth's bow shock can cause magnetospheric field lines at the magnetopause to develop localized regions of negative curvature. These regions are unstable with respect to interchange, which can lead to significant transport of mass and energy across the magnetopause. The rate at which magnetosheath plasma crosses the magnetopause is estimated to be of order 1026 s−1, which is consistent with estimates based on observations.