bluuebunny/crossref_metadata_2025 huggingface dataset:
On the configuration of the magnetotail near midnight during quiet and weakly disturbed periods: Magnetic field modeling
Authors: West H. I. , Buck R. M. , Kivelson M. G.
Published: February 2008

Energetic‐particle pitch angle data and vector magnetometer data, measured along the Ogo 5 inbound orbit near midnight on three magnetically quiet days, August 2, 4, and 25, 1968, were used to infer the magnetic tail field configuration for each day. For the first 2 days the particles, when initially detected, showed isotropic pitch angle distributions (PAD's) (indicative of nonadiabatic motions resulting from the breakdown of the guiding center invariants µ and J) but later made rapid transitions to the butterfly PAD (indicative of adiabatic guiding center motion). The lower‐rigidity particles made the PAD transitions first and were followed in turn by the higher‐rigidity particles as Ogo neared the earth. We have used a simple algebraic model which has allowed us to fit both the magnetic field and the pitch angle transition data. For the latter data fit, the detailed particle trajectories were followed along the model field lines to the neutral sheet. The particles were required to execute adiabatic guiding center motion if they were started from positions on the satellite orbit nearer earth than the point of observed changes in the PAD. They were required to undergo nonadiabatic motion at some part of their trajectory if they were started at a point on the satellite orbit farther from the earth than the PAD transition point. The results are presented in terms of model coefficients for each day. The model fields are plotted, the cross‐tail currents are derived, and particle motion is studied in the model fields. It was found that 79‐keV electrons were in the nonadiabatic mode when they were on field lines that crossed the neutral sheet beyond 11 RE on August 2; on August 25, a less taillike day, this point was 17 ± 1 RE. For 10‐keV protons the inferred points are 8.5 and 11.7 RE, respectively, for these 2 days. This is interesting because protons of about this energy carry a large part of the cross‐tail current. It is expected that when data from particles of a wide range of rigidity are available, this method of inferring the tail field configuration should be very powerful.
The Martian ionosphere in light of the Viking observations
Authors: Chen R. H. , Cravens T. E. , Nagy A. F.
Published: February 2008

A theoretical model has been constructed in which the ion density and the ion and electron temperature distributions are calculated by solving the coupled continuity‐momentum equations and the coupled energy equations. The latest experimental results from the Viking 1 and 2 landers are used to vary some of the parameters in the model in order to obtain agreement between the theoretical and experimental results. It is found that solar EUV radiation alone is not able to maintain the observed high ion temperatures. It was also established that the energy coupling between the electron and ion gas is insufficient to account for the measured ion temperatures even in the presence of very large electron temperatures. Direct heat input to the ion gas, probably due to solar wind‐ionosphere interactions, can result in ion temperature values in reasonable agreement with the observations. The ion densities calculated with the present model agree well with the Viking observations in the chemically controlled region, but at higher altitudes, dynamic transport processes need to be invoked to achieve consistency among the observed and calculated temperature and density values.
Observations of auroral fading before breakup
Authors: Pellinen R. J. , Heikkila W. J.
Published: February 2008

We have obtained detailed observations of the onset of auroral breakup using a variety of instruments with time resolution of some tens of seconds. Rapid sequences of all‐sky photographs and fast meridian scans by photometers show that breakup is usually preceded by moderate brightening, followed by fading of the auroral brightness lasting 1 or 2 min, before the actual breakup itself. At the time of the fading there is a brief darkening of the poleward sky. Often the breakup is preceded by one or more rapid intensifications, each one preceded by local fading. Pseudobreakups may also occur without the development of a major event. A bona fide breakup may begin on the fading arc, on an adjacent arc, or in an entirely new region nearby. This optical activity is closely correlated with the development of auroral radar echoes, a feature suggesting that variations in the ionospheric and magnetospheric electric and magnetic fields are responsible for the observed auroral variations. Data from the International Magnetospheric Study magnetometer network provide some indication of a correlated response by the local auroral and ionospheric currents, although this could be partly due to changes in conductivity. Riometer recordings show a slow decrease in ionospheric radio wave absorption over a period of about 10 min prior to breakup, with the largest decrease essentially to quiet time values in the region of auroral fading and subsequent breakup. The implications of these observations regarding the trigger mechanism for the expansion phase of a magnetospheric substorm are discussed.
Magnetic‐field‐aligned electric currents in a cold collisionless plasma
Authors: Hruška A.
Published: February 2008

Stationary large‐scale flow of a collisionless zero‐temperature plasma is considered. The relation between the magnetic‐field‐aligned current i and the properties of the plasma flow is analyzed. We find i = (cB/4π)[‐(V/V)·grad α ‐ (1/B⊥)(E/E)·grad B∥ + (1 ‐ β)(B∥/B⊥)K cos α], where V is the velocity of plasma, B∥ and B⊥ are the components of the magnetic field B parallel and perpendicular to V, E is the electric field, β is the ratio of the kinetic energy density to the magnetic energy density, α is the angle between E and the principal normal to the flow lines, and K is the curvature of the flow lines. The treatment is not restricted by imposition of special boundary conditions.
Neutral atmospheric motions manifested in radar echo Doppler shifts from two‐stream Irregularities in equatorial electrojet
Authors: Cohen Robert , Hooke William H.
Published: February 2008

Theoretical expressions are derived describing the effect of neutral atmospheric motions (prevailing winds, gravity waves, and tides) on observed propagation velocities of type 1 ionospheric irregularities in the equatorial electrojet. The theory takes account of two ways in which the neutral motions may influence the observed plasma wave phase velocities—directly, through their influence on the ion motion, relative to which the plasma waves propagate, and indirectly, through motion‐associated temperature perturbations which affect the ion acoustic velocity. The theoretical results together with what little independent information is available on neutral motions within the equatorial electrojet suggest that they should produce variations in the observed plasma wave phase velocities of the order of several percent. Results are shown to be consistent with variations in the plasma phase velocity observed at Jicamarca, Peru.
Trajectory traces of charged particles in the magnetosphere
Authors: Ejiri Masaki
Published: February 2008

The characteristic enhancements of ring current particles with energies of about 1–100keV, associated with magnetospheric substorms, were observed by Explorer 45 (S³‐A) around the plasmapause in the afternoon to midnight region and showed the characteristic structure called a ‘nose’ in the proton spectrograms. This paper examines the time‐developing characteristics of newly injected particles in the magnetosphere under a recently proposed convection electric field and a dipole magnetic field. Approximate equations of a bounce period, a second adiabatic invariant, and a bounce‐averaged azimuthal velocity are given with an error of less than about 10−3 for all pitch angles. The complete set of flow patterns of 90° pitch angles is also described by means of inflection lines through which radial and/or azimuthal drifts change their directions and where particle velocities show their local minima, i.e., the flow becomes sluggish. These particle tracings in the magnetosphere, from which time dependent particle fronts can be constructed, give the basic concept and mechanics to explain the complex and dynamical properties of the magnetic storm time particle enhancements.
Multiple‐satellite studies of magnetospheric substorms: Plasma sheet recovery and the poleward leap of auroral zone activity
Authors: Pytte T. , McPherron R. L. , Kivelson M. G. , West H. I. , Hones E. W.
Published: February 2008

Particle observations from pairs of satellites (Ogo 5 and Vela 4A and 5A) during 28 plasma sheet thickening events are examined. These data indicate that thickening of the nighttime plasma sheet during substorms occurs in two main stages, one early stage of single or multiple expansions of the near‐earth (geocentric distances r ≲15 RE) plasma sheet at the onset of substorm expansions (Pi 2 bursts) on the ground and another later stage of plasma sheet recovery that starts near the time of maximum auroral zone bay activity and is characterized by a large‐scale thickening toward higher latitudes that occurs over a broad azimuthal scale and from ionospheric heights to beyond the Vela orbit (r ∼18 RE). A detailed analysis of two‐satellite observations during eight plasma sheet recoveries is presented, showing events that occurred within 5 min in widely separated locations at small (<4 RE) distances from the tail's midplane and events that occurred concurrently in the Vela orbit and at high latitudes in the near‐earth region. Some events were accompanied by clear signatures of a poleward leap (to >71° magnetic latitude) of electron precipitation and the westward electrojet that probably corresponded to an expansion poleward of the ionospheric projection of the recovering plasma sheet. The eight plasma sheet recoveries occurred 10–30 min after a Pi 2 burst on the ground, and mid‐latitude magnetograms showed no indications of a near‐coincident formation of a substorm current wedge in the local time sector of the spacecraft; this indicates that the plasma sheet recoveries and the poleward leaps were not caused directly by a late high‐latitude substorm expansion. Instead, these phenomena seem to represent a transition phase between a substorm expansion sequence and a substorm recovery.
Characteristic electron variations across simple high‐speed solar wind streams
Authors: Feldman W. C. , Asbridge J. R. , Bame S. J. , Gosling J. T. , Lemons D. S.
Published: February 2008

This paper documents electron variations across simple high‐speed streams. Two streams were chosen for full documentation, and hourly averaged parameter plots are presented. Comprehensive scans of the shapes of electron distributions measured at the very highest bulk speeds confirm the results of Rosenbauer and co‐workers and show that they are composed of two parts: a low‐energy nearly isotropic component and a high‐energy strongly beamed component. At 174 eV the high‐energy beam typically has a full width at half maximum of ∼18°; this width decreases with increasing energy. The fact that high‐energy electrons are strongly beamed is consistent with a suggestion made previously that for them, pitch‐angle‐scattering collisions are rare beyond some base radius R0. Their angular widths as a function of energy can be reproduced if it is assumed that their velocity distribution is isotropic below R0 and evolves with heliocentric distance according to Liouville's theorem. The data are consistent with a base radius between about 10 and 30 Rs. The near isotropy and low temperature of low‐energy electrons suggest that binary Coulomb interactions and waves couple them efficiently to one another as well as to the solar wind ions. Beyond the speed maxima but within the constant high‐speed portions of simple streams, systematic trends in most electron parameters are small. This fact reinforces our previous conclusion that high‐speed flows represent a special structure‐free state of the solar wind at 1 AU.
Problems in the chemistry of metallic species in the D and E regions
Authors: Murad Edmond
Published: February 2008

Thermochemical and kinetic data on metal oxides, metal dioxides, and their ions are summarized. Ratios of metal‐to‐metal oxide ions are calculated under steady state conditions and are compared with mass spectrometric data. It is suggested that some of the assignments in the atmospheric composition studies and in atmospheric models need to be revised.
The relationship between ionospheric and field‐aligned currents in the dayside cusp
Authors: Wilhjelm J. , Friis‐Christensen E. , Potemra T. A.
Published: February 2008

Observations of field‐aligned currents determined from magnetic disturbances measured with the Triad satellite near local magnetic noon have been compared to simultaneous magnetic perturbations observed at the ground with a dense chain of magnetic observatories located along the west coast of Greenland. The investigation reveals that the equivalent ionospheric currents at the dayside polar cusp are located between two field‐aligned current sheets and the direction of the equivalent ionospheric current depends upon the directions of the two field‐aligned currents in a manner consistent with the assumption that the equivalent ionospheric current represents an ionospheric Hall current. Previous investigations have shown that the direction of the ionospheric cusp current is determined by the azimuthal component By of the interplanetary magnetic field (IMF). A similar relation therefore exists between the field‐aligned currents and By in the dayside cusp region. When By is positive, the ionospheric current (the DPY current) flows eastward, and the flow of the poleward field‐aligned current (the cusp region field‐aligned current) is away from the ionosphere in the northern hemisphere. When the polarity of By reverses, the flow directions of the ionospheric and field‐aligned currents reverse.
The latitude and longitude structure of the solar wind speed from IPS observations
Authors: Sime D. G. , Rickett B. J.
Published: February 2008

Interplanetary scintillation observations are used to build up a picture of the distribution of solar wind velocities in latitude and longitude. Such a picture is derived for periods of several rotations during the years 1973–1977. The observations are interpreted as if they were point observations and mapped to the sun with the constant radial velocity assumption. Since only eight scintillating radio sources are available, a useful instantaneous picture cannot be obtained, so some integrating in time is required to build up coverage. This integration is restricted to a few solar rotations by both the changing spatial distribution of the radio sources and possible temporal variation of the corona and solar wind. The observed average distributions of velocity are found to be not isotropic or even symmetric about the rotation axis of the sun. The averaged distributions are found to be similar to and to evolve as the distribution of low intensities in white light coronameter data taken at 1.5 R⊙ and suggest that high‐speed solar wind originates in regions of low coronal density. This extends to high latitudes the evidence for coronal holes as the source of high‐speed streams, including the polar holes as the source of high speeds at polar latitudes.
Thermal and wind‐induced variations in thermospheric molecular oxygen as measured on AE‐D
Authors: Potter W. E. , Kayser D. C. , Nier A. O.
Published: February 2008

Simultaneous measurements of ambient [O2], [N2], and temperature were made near winter solstice, 1975, by the open source neutral mass spectrometer (OSS) on Atmosphere Explorer‐D. The data, taken at midmorning and all latitudes, are analyzed by using scatter plots and correlation coefficients. At 200 km the [O2] density exhibits a positive correlation with the magnetic indices. Owing to the latitude dependence, this description of the response of [O2] during or following periods of magnetic activity, while it is useful, is only qualitative. The increase in [O2] with increasing ambient temperature is much better defined over a wide range of latitudes. In addition to temperature, global scale wind systems may play a role in controlling the distribution of [O2]. To study this role further, measurements of [N2] are used to help distinguish between temperature and wind effects in [O2]. A survey of the latitudinal variations in [O2]/[N2] with temperature indicates a positive response in high‐latitude regions and a negative response near the equator. This is further substantiated with the calculation of correlation coefficients. Such an effect can be explained by inferring the existence of upward vertical winds at high latitudes, meridional flow toward lower latitudes, and subsidence near the equator. Such wind systems are in agreement with those predicted by models and measured in the high‐latitude regions. It is concluded that [O2], being a minor constituent, is controlled both by temperature variations and by wind induced diffusion.
Velocity biasing in sampling of the solar wind
Authors: Steinitz Raphael , Eyni Menashe
Published: February 2008

Velocity biasing can lead to erroneous interpretation of temperature and density evolution of the solar wind. It is argued that possibly there is no difference in the physics of the slow and fast components (Helios 1). Finally, it is suggested to use T/u², in order to reduce the strong dependence of temperature on velocity.
Cosmic ray modulation during solar activity cycle 20
Authors: Lockwood J. A. , Webber W. R.
Published: February 2008

The cosmic ray modulation in the rigidity range 0.34 < P < 50 GV during the period 1965–1976 has been examined using ground‐based neutron monitor data and primary cosmic ray observations made on spacecraft. Numerical solutions to the transport equation were obtained following the method of Fisk (1971). The variation of the energy loss paramter ϕ during the period was determined from the integral cosmic ray intensity (E >60 MeV) measured by satellite cosmic ray telescopes with the rigidity dependence of the diffusion coefficient K2(P) proportional to P for P ≲10 GV. From this study we found that the hysteresis effect between the integral cosmic ray intensity (E > 60 MeV) and the neutron monitor rates at Mount Washington (Pc = 1.24 GV) could be explained by assuming that for P ≥ PT, K2(P) changed from K2 α P to K2 α P², following the theoretical arguments of Jokipii (1971). Furthermore, PT changes from about 25 GV at solar minimum to about 10 GV later in the solar modulation cycle. The hysteresis effect between the count rates of the Mount Washington and Huancayo (Pc=13.5 GV) monitors is explained on the same basis.
Relationship of noise in the frequency range 100 < f < 500 kHz to auroral arcs and field‐aligned current and implications regarding acceleration of auroral electrons
Authors: Kisabeth Jerry L. , Rostoker Gordon
Published: February 2008

The magnetic signatures of field‐aligned and ionospheric currents can be used to determine the geometry and strength of the electrical current systems which couple the ionosphere to the outer regions of the earth's magnetosphere. It is now recognized that the currents flowing in the evening sector are an important clue to the understanding of processes leading to explosive substorm instabilities and episodes of intense ionospheric disruption. In this report we have used a combination of ground‐based magnetometer data and Isis 2 satellite data in the form of energetic particles, auroral luminosity, and electromagnetic and/or electrostatic noise measurements to provide a comprehensive picture of processes which are taking place on field lines penetrating the auroral oval in the evening and midnight sectors. We shall show that noise measurements in the frequency range 100 < f < 500 kHz are characteristic of regions of upward current flow which are found in the region of discrete auroral features. We find that the higher‐energy electrons (a few keV) are associated with the higher‐frequency noise. In addition, the highest noise frequencies are found in the center of discrete auroral arc regions with the frequency decreasing on either side of the center of the arc region. We believe that the source of noise in this frequency range is associated with electron beams in discrete arcs whose velocity space distribution contains a region of positive slope. We shall finally discuss the physics of the relationship among the various electromagnetic and energetic particle signatures presented in this study.
Coupling of ionosphere and troposphere during the occurrence of isolated tornadoes on November 20, 1973
Authors: Hung R. J. , Phan T. , Smith R. E.
Published: February 2008

Gravity waves are the product of Joule heating, the auroral electrojet during geomagnetic substorms, the equatorial electrojet in the thermosphere, severe thunderstorms, tornadoes, and hurricanes in the troposphere, etc. A thorough understanding of sources and sinks of gravity waves can greatly advance our knowledge concerning atmosphere‐ionosphere‐magnetosphere couplings. We have limited ourselves in this paper to discussions of couplings between the ionosphere and the troposphere during the time periods of isolated tornadoes on the stormy day of November 20, 1973. Identification of the location of wave sources for waves detected at F region ionospheric heights was attempted by using the observed characteristics of wave propagation in ray‐tracing computations. Computed locations of wave sources were then compared with conventional meteorological data. The results show that the sources of the gravity waves associated with tornadoes were always on the squall lines and near the tornado touchdown locations. The results also suggest that ionosphere‐troposphere coupling studies can contribute to our understanding of the dynamical development of severe storms.
Energetic neutral atom precipitation during magnetic storms: Optical emission, ionization, and energy deposition at low and middle latitudes
Authors: Tinsley Brian A.
Published: February 2008

Observations of hydrogen Balmer β and He+ 4686‐Å emission made at Huancayo, Peru, during two magnetic storms are consistent with the expectations of energetic neutral atom precipitation resulting from charge exchange loss of ring current ions and support the view that charge exchange is the major loss process for larger geomagnetic storms. The intensities are consistent with previous satellite observations of the emission (called the equatorial aurora) and when translated into ionization rates for the upper E region give production rates an order of magnitude larger than normal nighttime levels. Such ionization enhancements have previously been measured by ionosondes and incoherent scatter at low latitudes and attributed to electron precipitation. New calculations of the latitude variation correct earlier work and show that for a ring current with pitch angle distribution isotropic to the loss cone, located on shells of L value 2 to 6, the maximum influx rate of precipitating neutrals is found at magnetic latitudes 25° to 50°. Most of the energetic neutrals are lost to interplanetary space, and the fraction impacting the thermosphere has been recalculated to range from 11 to 2.2% for L values 2 to 6. For a typical magnetic storm with energy loss rate due to charge exchange, the equivalent to a Dst rate of change of 20 nT/h, the energy input into the thermosphere at the latitude of maximum is calculated to be 0.15 to 0.05 mW/m² from L shells 2 to 6. The ionization production can be of the order of 10 ions cm−3 s−1 at 140 km, and optical emission, of the order of 1 rayleigh (R), both varying according to the species and energy of the impacting neutrals (i.e., the former ring current ions). The latitude distribution shrinks toward the equator after injection has ceased, as the magnetospheric pitch angle distribution evolves toward 90°, on a time scale (for protons <30 keV at L = 3) of the order of 2 hours.
A weekend increase in geomagnetic activity
Authors: Fraser‐Smith A.C.
Published: February 2008

Superposed epoch analyses of a 46.5‐year series of the geomagnetic activity indices Ap and of a 110‐year series of the aa indices show a weekend increase in geomagnetic activity. A similar but not identical increase is observed in 12 years of Pc 1 geomagnetic pulsation occurrence data, and there is a matching decrease in a 7.5‐year interval of VLF whistler‐derived magnetospheric plasma densities. The increases in activity are not large, but standard statistical analyses of the data suggest that the increases are at least marginally significant, and the presence of the same increase in a variety of independent data also suggests that the ‘weekend effect’ is real. It is hypothesized that the increase of activity is related to a generally reduced level of power line harmonic radiation into the magnetosphere during weekends. Power usage data from Quebec show a repetitive weekend decrease and thus support part of this hypothesis.
Inhibition of solar wind impingement on mercury by planetary induction currents
Authors: Hood L.L. , Schubert G.
Published: February 2008

The simple compression of a planetary magnetosphere by varying solar wind stagnation pressure is limited by currents induced in the electrically conducting parts of the planet. This inhibition is especially important for Mercury, since the radius of the electrically conducting iron core is a large fraction of the planetary radius, which in turn is a significant fraction of the subsolar magnetospheric radius b. Previous treatments of solar wind standoff distance variations at Mercury using the terrestrial analogue b−6 assumption have neglected this phenomenon. Using the lowest suggested value of the planetary dipole moment, 2.4 × 1022 G cm³, we estimate that a minimum pressure of ∼38P0, where P0 is the external stagnation pressure in the steady state, is required to force the standoff distance down to the subsolar surface of Mercury if the pressure change persists for at least 1 day. This value is 4.3 times that which would be predicted if Mercury had no core, and it is larger than the maximum pressure predicted at Mercury's orbit (∼25P0) on the basis of hourly averaged solar wind statistics at 1 AU. Thus a direct interaction at any time of solar wind plasma with the surface of Mercury due to external compression effects alone is unlikely for solar wind conditions similar to those at present.
Temperature characteristics of electron beams and ambient particles
Authors: Lin C.S. , Mauk B. , Parks G.K. , DeForest S. , McIlwain C.E.
Published: February 2008

The temperature characteristics of electron beams and trapped particles of large pitch angles during substorms have been studied by examining the plasma data of the University of California at San Diego experiment on board the geostationary ATS 6 satellite. Approximating the observed distribution functions by a single Maxwellian or a superposition of two Maxwellians, we have deduced that the electron distribution function is characterized by two temperatures, ≲1 and ∼3 keV. The 3‐keV component is observed at all pitch angles from ∼10° to 90°. The ≲1‐keV component initially appears only within the electron beams which are confined to small pitch angles (≲30°). With time, this low‐temperature component appears at larger pitch angles (≳30°). This observation has been interpreted in terms of scattering of the electron beams to large pitch angles.
The latitudinal gradient of nitric oxide in the thermosphere
Authors: Cravens T.E. , Gérard J.‐C. , Stewart A.I. , Rusch D.W.
Published: February 2008

Theoretical calculations of nitric oxide altitude profiles are made at five different latitudes by using neutral temperatures and composition primarily from the MSIS (mass spectrometer and incoherent scatter) model. The nitric oxide calculated for an altitude of 105 km remains nearly constant with increasing latitude. Observations made by the ultraviolet nitric oxide instrument on the Atmosphere Explorer C satellite show that at low magnetic activity (Ap ≃4), the NO density at 105 km agrees with the theory; however, at moderate levels of activity it increases with latitude. This discrepancy between the theoretical and observed latitudinal gradients of nitric oxide suggests the transport of NO from a high latitude source to lower latitudes. At 200 km the theoretical and observed latitudinal gradients are in reasonable agreement, an indication that the knowledge of the local composition and temperature is sufficient to model nitric oxide at this altitude.
Stratospheric sounding by infrared heterodyne spectroscopy
Authors: Abbas Mian M. , Kunde Virgil G. , Mumma Michael J. , Kostiuk Theodor , Buhl David , Frerking Margaret A.
Published: February 2008

Intensity profiles of infrared spectral lines of stratospheric constituents can be fully resolved with a heterodyne spectrometer of sufficiently high resolution (∼5 MHz or 0.000167 cm−1 at 10 µ). The constituents' vertical distributions can then be evaluated accurately by analytic inversion of the measured line profiles. Estimates of the detection sensitivity of a heterodyne receiver are given in terms of minimum detectable volume mixing ratios of stratospheric constituents, indicating a large number of minor constituents which can be studied. Stratospheric spectral line shapes and the resolution required to measure them are discussed in light of calculated synthetic line profiles for some stratospheric molecules in a model atmosphere. The inversion technique for evaluation of gas concentration profiles is briefly described, and applications to synthetic lines of O3, CO2, CH4, and N2O are given. Some recent heterodyne measurements of CO2 and O3 absorption lines are analytically inverted, and the vertical distributions of the two gases are determined.
Compression of the Hermaean magnetosphere by the solar wind
Authors: Suess Steven T. , Goldstein Bruce E.
Published: February 2008

A model of the compression of the Hermaean magnetosphere by the solar wind is presented. The model considers the consequences of the finite electrical conductivity of the planetary interior on the magnetopause standoff distance under varying solar wind conditions. Although for average conditions the standoff distance is almost identical to that obtained for a point dipole source embedded in an insulating interior, for periods of above‐average solar wind dynamic pressure the compression of the planetary field between the magnetopause and the conducting interior will increase the standoff distance. From these considerations the solar wind would be expected to impact the dayside surface directly only a very small fraction of the time. Magnetic reconnection may erode the dayside magnetosphere and increase the rate of direct impact upon the surface. However, this effect is not included in the model calculations.
Magnetometer data errors and lunar induction studies
Authors: Daily William D. , Dyal Palmer
Published: February 2008

In this paper we discuss errors in lunar magnetic field data obtained by the Apollo 12, 15, and 16 surface and the orbiting Explorer 35 Ames and Goddard magnetometers and the implications of these errors on investigations of electromagnetic induction in the moon. The Apollo surface instruments measure fields up to 300 γ with fluctuations of about 15 γ and the Explorer magnetometers measure fields of about 10 γ with 5 γ fluctuations. Typical errors of these field measurements are found to be on the order of 1 γ or 1% of the largest fields measured. Comparison of data from the Apollo 12 and Explorer 35 Ames and Goddard magnetometers has allowed measurement of the relative gains and offsets of these three instruments between day 323 of 1969 and day 179 of 1970. During the first half of this period, (i.e., the first four lunations of Apollo 12 magnetometer operation), all three instruments generally are in good agreement with the gains and offsets differing by 1 to 2% and 0.5 γ, respectively. Commencing with the fifth Apollo 12 lunation the two Explorer magnetometer gains and offsets are significantly different. The degraded operation of one or both magnetometers results in gain differences increasing up to 60% and offset differences over 1 γ by the eighth Apollo 12 lunation. Neither Explorer 35 magnetometer agrees well with the Apollo 12 instrument during this later period. The Apollo x Alsep axis gain coincides better with that of the Ames instrument but the y Alsep axis gain corresponds to the Goddard magnetometer. It is probable that both Explorer magnetometers begin to malfunction by the fifth lunation. Coincident with the increase in gain and offset errors an additional data anomaly appears which is associated with exit of the spacecraft from the lunar sun shadow. This error in the spin plane attains a maximum value of 7 γ, which decays monotonically within approximately 3 hours of shadow exit. This malfunction probably results from orientation error in the spin plane sensors. Three other errors in the Apollo surface magnetometer data are also discussed. The effects of magnetic data errors on electrical conductivity are estimated by determining the envelope of conductivity profiles resulting from the errors delineated by this study. Adjustment of previously published bulk lunar magnetic permeability results to account for magnetometer gain uncertainties, yields a lunar permeability of µ=1.012±0.011. We conclude that careful selection of magnetic data used in any study of the moon or its environment is the best procedure for minimizing the effects of these errors.
Pc 3 magnetic pulsations and precipitation of energetic electrons
Authors: Arthur C.W. , Bjordal J. , Rosenberg T.J.
Published: February 2008

Data from the synchronous altitude satellite ATS 1 and near‐conjugate measurements of bremsstrahlung X rays and ground magnetic variations have been used to analyze an event of modulated auroral zone electron precipitation and magnetic pulsations in the Pc 3 range. Transverse, azimuthal, nearly linearly polarized waves, strongly peaked at ∼25‐s period were observed at ATS 1 from 0600 to 1000 LT on August 18, 1967, diminishing in intensity thereafter. Weak pulsations with periods ≲18 s and wave properties similar to the above followed in the interval from 1300 to 1700 LT. Ground magnetic pulsations at College, Alaska, were observed mainly in the transverse H and D components with maximum power spectral density in the period range 25–40 s prior to 1300 LT and from 20 to 30 s thereafter. Four main intervals of modulated electron precipitation, centered roughly on local magnetic noon, were noted in the X ray data obtained near Fort Yukon, Alaska. The intervals, each lasting for ∼30 min, were separated by ∼90 min. Fluctuations of the 50‐ to 150‐keV trapped electrons at ATS 1 during the precipitation event remained typically within 1 or 2σ of the average counting rates and showed no clear association with pulsations in either the X ray or the magnetic data. The origin of the Pc 3 waves is attributed to local field line resonances induced by Kelvin‐Helmholtz instability at the magnetopause. The observed wave periods can be accounted for by a field line distribution of plasma density of the form r−4 with equatorial values at r = 6.6 RE of order 1 cm−3. The wave resonance model can satisfactorily explain observed differences in the pulsation activity at the ground, balloon, and satellite if account is taken of the spatial sensitivities of the different techniques and the location of observing sites with respect to the probable location of resonant field lines. Although the event pertains to a disturbed period, there is insufficient evidence to associate gross temporal changes in the intensity of pulsation activity with the occurrence of specific substorms. However, the data suggest that electron precipitation pulsations will be found to correlate with Pc 3 magnetic pulsations when substorm injections coupled with azimuthal drift provide enhanced energetic particle fluxes within dayside resonance regions.
Thermospheric response to the November 8–9, 1969, magnetic disturbances
Authors: Roble R.G. , Dickinson R.E. , Ridley E.C. , Kamide Y.
Published: February 2008

Geomagnetic data from 82 northern hemisphere observatories have been used to derive the hemispheric magnetic potential distribution and equivalent ionospheric currents for the 36‐hour geomagnetic storm period from 1200 UT on November 8 to 2400 UT on November 9, 1969. The hemispheric magnetic potential distribution is calculated at 2½‐min intervals during the period. These data are used to parameterize a time‐dependent global distribution of high‐latitude heating due to auroral processes. The zonally averaged high‐latitude heating rate and the calculated solar EUV and UV heating rates appropriate to the date are used in a numerical model of the zonally symmetric thermosphere to calculate the time‐dependent mean meridional circulation and latitudinal variation of temperature during the storm period. The results show that high‐latitude heating during substorms causes considerable variability in the global thermospheric properties and circulation. During two successive large substorms, thermospheric waves are generated that propagate from high latitudes equatorward, producing global scale perturbations in the thermospheric properties and dynamics. With the requirement that the calculated global mean temperature response to the storm heating be consistent with predictions by various empirical models, a crude calibration of equivalent ionospheric current intensity to high‐latitude heating is made.
Direct in situ measurements of thermospheric temperature
Authors: Kayser D.C. , Breig E.L. , Power R.A. , Hanson W.B. , Nier A.O.
Published: February 2008

The Open Source Neutral Mass Spectrometer on the Atmosphere Explorer (AE) satellites, intended primarily to measure neutral constituent densities, has provided direct in situ measurements of the neutral gas temperature by means of the ‘fly‐through’ mode of operation. Evaluation of this new technique is reported here and is facilitated by comparison of the derived neutral temperature (Tn) with ion temperatures (Ti) obtained simultaneously from the on‐board retarding potential analyzer for altitudes and conditions where the two temperatures should be equal. A statistical analysis that compared two sets of these data from the AE‐D satellite indicates an average difference of 2(±3.6)% between concurrently observed values of Tn and Ti. This ∼14°K average excess of ion over fly‐through neutral temperatures is well within the expected absolute errors of the individual experiments. Consistency between localized pairs of Tn and Ti is further demonstrated through profiles depicting their altitude distributions between 150 and 225 km. The overall magnitude of temperatures calculated from the Jacchia (1971) model results in a better representation of the observations than do the relatively higher temperatures predicted for this region by the MSIS model. Reasonable agreement is also found between observed temperatures and those neutral temperatures derived from altitude distributions of N2 particle densities.
A thermospheric model of the annual variations of He, N, O, N2, and Ar from the Aeros Nims data
Authors: Köhnlein W. , Krankowsky D. , Lämmerzahl P. , Joos W. , Volland H.
Published: February 2008

A model of the annual variations of He, N, O, N2, and Ar was derived from the Aeros A and Aeros B neutral and ion mass spectrometer (Nims) data at two local times, 4 and 16 hours, in the altitude range 220–550 km. The Aeros data represent conditions near a solar minimum during the period December 1972 to September 1975. Using the analytical framework of the Ogo 6 model, the number densities of the constituents were expanded into spherical harmonics and the temperature inferred from N2 observations under the assumption of diffusive equilibrium. The average exospheric temperature 〈T∞〉 = 835 K (Kp = 1; 〈F10.7〉 = 80) is in excellent agreement with Thuillier's model value of 840 K (M1 model) but lies about 20 K above the corresponding temperature of the MSIS model. The familiar constituents He, O, N2, and Ar were extended by atomic nitrogen which was deduced from the 30‐amu mass peak. At the poles this constituent shows a density pattern similar to N2 and at the equator like O, but with a much stronger diurnal variation.
Photometric and interferometric observations of the sar arc event of september 25/26, 1978
Authors: Okano S. , Kim J.S.
Published: February 2008

A distinct stable auroral red arc was observed on the night of September 25/26, 1978, with a multicolor meridian scanning photometer and a 6‐inch high‐resolution Fabry‐Perot interferometer. The results obtained include the following: (1) the growth rate of intensity of the arc was very rapid, and the time constant measured as 20 min; (2) the average southward drift velocity was rather fast, v ≃240 km/h or dL/dt ≃ −0.28 per hour; and (3) the temperatures within the arc showed an increase of about 200°K at around 2.7 hours after the appearance of the arc, while no other enhancement of the temperature was observed during the observation period.
Nitric oxide height distribution in the lower ionosphere from rocket ion composition results over a southern temperate latitude station
Authors: Abdu M.A. , Batista Inez S.
Published: February 2008

Ion composition results obtained by Narcisi et al. (1972a) from rocket observations carried out during the November 1966 solar eclipse campaign at Cassino, south Brazil, are analyzed on the basis of the presently known detailed ion chemistry of the lower ionosphere, to deduce the height distribution of nitric oxide concentration in the region from 80 to 110 km. The results are compared with certain available experimental determinations of the NO height distributions carried out by other workers using rocket‐borne radiometric measurement of NO γ band emissions in the dayglow. Other available NO deductions from ion composition data are discussed in the light of the present results.
Io's wobbling flux tube and nonuniform surface conductivity: Longitude control of decametric emission and other magnetospheric interactions
Authors: Nash Douglas B.
Published: February 2008

A model is proposed relating Io's modulation of Jupiter's decametric radio emission (DAM) and other magnetospheric interactions to periodic changes in flux tube orientation with Io’s surface of nonuniform surface electrical conductivity. Spectral reflectance and albedo data suggest that visually bright surface areas on Io may be highly conducting due to the abundance there of irradiation‐altered salts, while relatively dark areas may be extremely insulating due to the abundance of free sulfur. Geometric correlations show that Io's orbital motion through Jupiter's tilted and offset magnetic field results in a 13‐hour periodic variation in the Io‐graphic surface position of Io's flux tube contact junctions. The resulting variation in effective electrical conductivity of Io results in modulation (switching) of Io's motional emf currents and corresponding flux tube currents. This causes the observed magnetic‐longitude dependence of Io‐dependent DAM, while emission beaming accounts for the observed Io‐phase effect. This switching model suggests that Io is a variable unipolar inductor and that its flux tube varies in electrodynamic character as a function of magnetic longitude; the predicted behavior is consistent with pre‐Voyager observed particle‐injection spikes at Io's L shell, auroral emissions from Jupiter, and may reconcile inconsistencies between theoretical and observed particle sweeping effects of Io. The model predicts a relatively inactive flux tube current system and strong particle sweeping during the Voyager 1 flux tube crossing.
Transport properties of monatomic carbon II: Contributions from excited electronic states
Authors: Biolsi Louis , Biolsi Kevin J.
Published: February 2008

It is usually assumed that the transport properties of atoms and molecules in excited electronic states are nearly the same as in the ground state. Using available experimental and theoretical results for interactions between carbon atoms in excited electronic states, reasonably exact calculations of the transport properties of excited state carbon atoms are obtained. These results are compared with results for several models that have been used to estimate transport properties for excited species. It appears that the assumption mentioned above is correct but that the models do not predict the transport properties of excited species very accurately.
Ionospheric electrical currents in the late evening plasma flow reversal
Authors: Behm D.A. , Primdahl F. , Zanetti L.J. , Arnoldy R.L. , Cahill L.J.
Published: February 2008

An instrumented sounding rocket was launched from Andøya, Norway, in January 1977, in the late evening auroral oval. Its trajectory took it northward over a quiet auroral arc and over a region of plasma flow reversal. Horizontal currents were inferred from magnetic field measurements; they were also calculated from the measured electric field and conductivities derived from energetic particle influxes. South of the reversal region the sheet current density of the eastward electrojet was found to be ∼0.1 A/m, while north of the reversal the current density was less than 0.05 A/m. The currents were enhanced in the arc. Current continuity considerations in the meridian plane implied downward field‐aligned currents at the southern edge of the arc and upward field‐aligned currents at the northern edge.
The solar modulation of cosmic ray electrons 1969–1977
Authors: Evenson P. , Caldwell J. , Jordan S. , Meyer P.
Published: February 2008

We discuss the gross morphological features of the cosmic ray electron spectrum from 200 MeV to 6 GeV as measured in eight of the nine years 1969–1977. We find no evidence that the solar magnetic field polarity change of 1970–1971 affected the relative modulation of electrons and protons. However, previously noted problems in explaining the variation of both the electron and proton modulation by one model can at least qualitatively be understood by allowing simultaneous variations in the diffusion coefficient and the boundary of the modulation region in a spherically symmetric solution of the Fokker‐Planck equation. This model also predicts a change in the radial gradient of protons from 1973 to 1974.
Association of corotating magnetic sector structure with Jupiter's decameter‐wave radio emission
Authors: Barrow C.H.
Published: February 2008

Chree (superposed epoch) analyses of Jupiter's decameter‐wave radio emission taken from the new Thieman (1979) catalog show highly significant correlation with solar activity, indicated by the geomagnetic Ap index. The correlation effects can be explained in terms of corotating interplanetary magnetic sector features. At times when the solar wind velocity is relatively low, about 300 to 350 km/s, a sector boundary can encounter the earth and Jupiter almost simultaneously during the period immediately before opposition. After opposition this will not normally occur, as the solar wind velocities necessary are too low. The correlation effects are much enhanced for the three apparitions of 1962–1964, during which a relatively stable and long‐lived sector pattern was present. Chree analyses for this period indicate periodicities, equal to approximately half the solar rotation period, in the Jupiter data.