bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar wind decrease at high heliographic latitudes detected from Prognoz interplanetary lyman alpha mapping
Authors: Lallement R. , Bertaux J. L. , Kurt V. G.
Published: February 2008

New evidence for a latitudinal decrease of the solar wind mass flux is presented from observations of the interplanetary Lyman alpha emission collected in 1976 and 1977 with satellites Prognoz 5 and 6. The flow of interstellar hydrogen atoms in the solar system is ionized by EUV solar radiation and charge exchange with solar wind protons which accounts for about 80% of the total ionization rate. The resulting gradual decrease of the neutral H density from the upwind region down to the downwind region observed from Ly α intensity measurements allowed the determination of the absolute value of the total ionization rate β for one H atom at 1 AU against ionization. Collected in 1976 and 1977 at five places in the solar system, the measurements are first compared to a model which assumes isotropy of the EUV and solar wind. Strong departures are obvious toward high‐latitude regions, especially when the observer is in the downwind region where the solar wind ionization has had more time to act (cumulative effect). A model was constructed which included a decrease of the ionization rate with heliographic latitude. The adjustment of data allowed for the measurement of the absolute value of the total ionization rate and implies a 50% latitude decrease of the ionization rate due to charge exchange with the solar wind, from βsw = (3.9±0.5) × 10−8; s−1 at the equator to βsw = (2.0±0.5) × 10−8 s−1 at the pole. The corresponding absolute value of the solar wind proton flux is (2.4‐3.6) × 108 cm−2 s−1 at the equator and twice less at the pole if a constant velocity is assumed for the solar wind. Even if the solar wind velocity increases from 400 to 800 km s−1, which would decrease the charge exchange cross section by 25%, there is still a decrease by about 30% of the solar wind mass flux from equator to pole. The Lyman alpha data from Mariner 10 (Kumar and Broadfoot, 1978) had already shown a similar trend in 1974, showing a persistence of the solar wind anisotropy for 3–4 years during a solar minimum. The large‐scale properties of the solar wind mass flux can therefore be monitored at all latitudes by remote sensing of Ly α interplanetary emission, since the solar wind is carving the flow of interstellar H and its anisotropies are ''printed'' on the interplanetary H distribution. With uncalibrated Ly α measurements, an absolute value of the solar wind flux can be determined at all latitudes averaged over a typical 1‐year period.
Recurrent geomagnetic activity: Evidence for long‐lived stability in solar wind structure
Authors: Sargent H. H.
Published: February 2008

The simple index described clearly shows periods of recurrent geomagnetic behavior. The index is based on half‐day values of the geomagnetic aa index for 1868 through 1983, which reveal rather lengthy periods when geomagnetic activity patterns are faithfully repeated every 27 days. It is shown that these recurrent periods occur at the end of each sunspot cycle; that they end fairly abruptly with the beginning of a new sunspot cycle; that they tend to last significantly longer when associated with even‐numbered sunspot cycles; and that the effect is clearly centered on a 27‐day repetition rate. The 27‐day recurrence index indicates those regularly occurring times when the solar wind structure remains relatively stable beyond 1 AU for periods of 1 ½ to 5 years. Correlations have been reported between the index and auroral heights and even the global albedos of Titan and Neptune.
IMF By‐dependent plasma flow and Birkeland currents in the dayside magnetosphere: 1. Dynamics Explorer observations
Authors: Burch J. L. , Reiff P. H. , Menietti J. D. , Heelis R. A. , Hanson W. B. , Shawhan S. D. , Shelley E. G. , Sugiura M. , Weimer D. R. , Winningham J. D.
Published: February 2008

Plasma, magnetic‐field and dc electric‐field observations from Dynamics Explorers 1 and 2 are used to investigate the morphology of solar‐wind ion injection, Birkeland currents, and plasma convection in the morning sector for both positive and negative interplanetary magnetic field (IMF) By components. The results of the study are used to construct a By‐dependent global convection model for southward IMF. A significant element of the model is the coexistence of three types of convection cells (“merging cells,” “viscous cells,” and “lobe cells”). This model can account for observations of a nearly stationary (in local time) convection “throat,” a sunward‐antisunward convection reversal zone at the polar‐cap boundary in both the morning and afternoon quadrants, the morphology of solar‐wind ion injection and transport in the mid‐altitude polar cusp, and the By‐dependent dawn‐dusk asymmetry of polar‐cap electron fluxes.
Bottomside sinusoidal irregularities in the equatorial F region: 2. Cross‐correlation and spectral analysis
Authors: Cragin B. L. , Valladares C. E. , Hanson W. B. , McClure J. P.
Published: February 2008

Equatorial bottomside sinusoidal (BSS) irregularities have been studied by applying techniques of cross‐correlation and spectral analysis to the Atmosphere Explorer data set. In order to determine the spatial displacements between the density and transverse velocity components of the irregularities, we have cross‐correlated the ion density data from the retarding potential analyzer with the pitch and yaw ion velocity components as measured by the ion drift meter. The analysis indicates that the pitch velocity component is displaced by somewhat more than 90° (referred to the wavelength of the spectral peak) to the west with respect to the ion density fluctuations. However, the yaw drift component is almost in phase with the density fluctuations. Spectra of the pitch velocity fluctuations show a sharp peak centered at about 1 km E‐W wavelength, and a power law spectral index near +2 in the wavelength range from 10 km to 1 km. Yaw velocity and ion density spectra are also peaked at 1 km, but have more power at long wavelengths than do the pitch velocity spectra. The occurrence frequency of these irregularities maximizes at the solstices, and has a seasonally‐dependent longitude distribution. BSS events are detected most frequently in the local summer hemisphere. Many of these new results can be explained by fairly simple theoretical arguments that emphasize the importance of the ion Larmor flux, interhemispheric plasma flows, and variations in the lower F region Pedersen conductivity. The latter are thought to provide an important boundary condition on the Rayleigh‐Taylor instability dynamics.
Equatorial trapped plasmasphere ion distributions and transverse stochastic acceleration
Authors: Curtis S. A.
Published: February 2008

A theoretical explanation is given for earlier reported observations by the DE 1 and SCATHA satellites which have revealed ion distribution functions in the equatorial plasmasphere which are sharply peaked at 90° pitch angle. The pitch angle anisotropy increases with increasing energy for the observed distributions. Also observed by SCATHA and earlier spacecraft are cyclotron harmonic emissions which are closely confined to the plasmasphere equator. It is shown that the intense equatorial cyclotron turbulence can stochastically accelerate the higher‐energy tail of the plasmasphere thermal ion distribution function. The efficiency of the process increases with higher energies, yielding greater anisotropies at higher energies in agreement with the observations. The rate of diffusion in energy of the ions is proportional to Wn, where W is the ion energy and n > 5 is the cyclotron harmonic number. The number of highly anisotropic ions generated is limited by the initial ion distribution tail population and the time duration of the turbulence. The harmonic cyclotron turbulence is modeled as fast magnetosonic waves which are considered due to highly anisotropic energetic ion distributions in the plasmasphere. The turbulence may be treated in an electrostatic approximation given the high wave phase velocity.
A comparison of precipitating electron energy flux on March 22, 1979 with an empirical model: CDAW 6
Authors: Simons S. L. , Reiff P. H. , Spiro R. W. , Hardy D. A. , Kroehl H. W.
Published: February 2008

Data recorded by Defense Meteorological Satellite Program, TIROS and P‐78‐1 satellites for the CDAW 6 event on March 22, 1979, have been compared with a statistical model of precipitating electron fluxes. Comparisons have been made on both an orbit‐by‐orbit basis and on a global basis by sorting and binning the data by AE index, invariant latitude and magnetic local time in a manner similar to which the model was generated. We conclude that the model flux agrees with the data to within a factor of two, although small features and the exact locations of features are not consistently reproduced. In addition, the latitude of highest electron precipitation usually occurs about 3° more poleward in the model than in the data. We attribute this discrepancy to ring current inflation of the storm time magnetosphere (as evidenced by negative Dst's). We suggest that a similar empirical model based on AL instead of AE and including some indicator of the history of the event would provide an even better comparison. Alternatively, in situ data such as electrojet location should be used routinely to normalize the latitude of the auroral precipitation.
Temporal and spatial variations of the polar cap dimension inferred from the precipitation boundaries
Authors: Makita K. , Meng C.‐I. , Akasofu S.‐I.
Published: February 2008

We examine temporal and spatial variations of the distance between the electron precipitation boundaries across the polar cap: the Defense Meteorological Satellite Program satellite data, within a few hours of the dawn‐dusk and noon‐midnight meridians, are used. It is found that changes in the distance between the precipitation boundaries across the polar region in both the dawn‐dusk and noon‐midnight sectors tend to follow grossly changes of the AE index. On the basis of the simultaneous ISEE 3 data, it is found that the increase of the distance begins at about the time when the southward turning of the interplanetary magnetic field reaches the magnetosphere, but prior to the corresponding increase of the AE index. The period of the maximum distance approximately coincides with the period of the maximum AE value. The decrease of the distance begins at about the same time as the substorm activity begins to subside, but it continues well after the AE index has reduced to very small values. These findings are discussed in terms of changes of the total open magnetic flux by assuming that the precipitation boundaries coincide approximately with the boundaries of the open field line region.
The distant magnetotail's response to a strong interplanetary magnetic field By: Twisting, flattening, and field line bending
Authors: Sibeck D. G. , Siscoe G. L. , Slavin J. A. , Smith E. J. , Tsurutani B. T. , Lepping R. P.
Published: February 2008

During an interval of strong interplanetary magnetic field (IMF) By, while ISEE 3 was in the distant magnetotail, the north lobe was observed south of the ecliptic plane. Lobe field lines were strongly bent in the direction of the IMF, and a dense boundary layer plasma was observed. During the interval, magnetopause normals pointed in the z direction, although ISEE 3 was near the dawnside ecliptic plane. The observations are interpreted in terms of field line bending within a twisted and flattened magnetotail.
Multispectral analysis for electromagnetic wave field components in a magnetoplasma: Application to narrow‐band VLF emissions
Authors: Lagoutte D. , Lefeuvre F.
Published: February 2008

The multispectral analysis of the wave field components of an electromagnetic wave observed at a fixed point in a magnetoplasma is performed using a maximum entropy method. The validity of the analysis is a posteriori tested comparing the propagation characteristics of the waves, as derived from the spectral matrix estimates, to the propagation characteristics predicted by the magneto‐ionic theory. The techniques so developed are applied to the analysis of ground‐based transmitter signals observed on GEOS 1. Comparisons with results obtained from the Welch (1967) method show the superiority of the maximum entropy method of spectral analysis, at least in the case of narrow‐band electromagnetic emissions.
The substorm as an internal magnetospheric instability: Substorms and their characteristic time scales during intervals of steady interplanetary magnetic field
Authors: Horwitz J. L.
Published: February 2008

Examples of magnetospheric substorms occurring during intervals when the interplanetary magnetic field is steady are used to illustrate the natural, internal instability of the magnetosphere, apart from the recently emphasized classes of substorms more closely associated with interplanetary medium variations. Such substorms have characteristic “expansion” phase and “recovery” phase times such that in virtually all cases Texp < Trec. The average time scales for the substorms examined are 〈Texp〉 = 13 min and 〈Trec〉 = 41 min. These time scales are tentatively identified as indicative of the natural, internal time scales for the basic magnetospheric substorm instability.
Auroral electrodynamics with current and voltage generators
Authors: Lysak Robert L.
Published: February 2008

The electrodynamic structure of auroral currents is studied in the steady state by coupling Maxwell's equations with effective Ohm's laws for ionospheric Pedersen currents, field‐aligned currents and currents in the generator region. An effective generator conductivity is introduced which allows consideration of a variety of states from pure current (ΣG = 0) to pure voltage (ΣG → ∞) generators. On short time scales when Alfvén waves are important, this conductivity mapped to the ionosphere is lower than the ionospheric conductivity, implying a currentlike generator. This is in contrast with previous electrodynamic models of the aurora, which have assumed voltage‐fixed generators. Current generators differ from the voltage generators in that the natural scale size is smaller for current generators, indicating that the narrow discrete arcs may be current driven, while the overall large‐scale auroral currents are voltage driven. In addition, reversals of the electric field occur naturally in the current‐driven case, leading to V‐shaped potential structures. Examination of the effects of ionospheric conductivity gradients and comparison with a time‐dependent MHD model of auroral currents indicate that either regions of nonlinear resistivity or generator motions can decouple the ionospheric currents from the generator. In this case the effective conductivity becomes the Alfvén wave conductivity, which, being small compared to the ionospheric conductivity, leads to a structure typical of a current‐driven system. This implies that the current structure is not affected by ionospheric conductivity gradients, while the ionospheric electric field is enhanced on the low‐conductivity side.
Extreme ultraviolet emissions for monitoring auroras in dark and daylight hemispheres
Authors: Meng C.‐I. , Chakrabarti S.
Published: February 2008

Observations of auroral extreme ultraviolet (EUV) emissions from the noon‐midnight polar‐orbiting Space Test Program (STP) 78‐1 satellite are used to investigate the spectral features of the dayside auroral oval, nightside auroral oval, and the dayglow. The purpose of this study is to evaluate the possibility of using EUV atmospheric emissions for global auroral imaging and to study the temporal variations of the auroral EUV intensity with geomagnetic activity. It is found that during geomagnetically quiet times, O II 834Å, O I 989Å, and N2 1009 Å measurements can provide a clear distinction of the auroral oval above the dayglow background. During the very active period, five other EUV emissions can give good aurora‐to‐dayglow ratios. The auroral EUV emissions are more intense during magnetospheric substorms; however, we have not found a clear one‐to‐one relationship between them. It is also found that the auroral oval brightness, especially the noonside, increased during the initial phase of a geomagnetic storm. Thus, the sudden solar wind dynamic pressure enhancement is another important geophysical parameter that affects the EUV auroral emission.
On the accuracy of spectrum analysis of red noise processes using maximum entropy and periodogram methods: Simulation studies and application to geophysical data
Authors: Fougere Paul F.
Published: February 2008

Power spectra, estimated by the maximum entropy method and by a fast Fourier transform based periodogram method, are compared using simulated time series. The time series are computer generated by passing Gaussian white noise through low‐pass filters with precisely defined magnitude response curves such that the output time series have power law spectra in a limited frequency range: P(f) = Af−p, f1 ≤ f ≤ f2. Ten different values of p between 0.5 and 5.0 are used. Using 4000 independent realizations of these simulated time series, it is shown that maximum entropy results are superior (usually greatly superior) to the periodogram results even when end‐matching or windowing or both are used before the power spectra are estimated. Without the use of end‐matching or windowing or both, the periodogram results are useless at best and very misleading at worst. A 5‐min section of ionospheric scintillation data from the MARISAT satellite has been broken into 60 overlapping sections, each 10 s long and overlapped by 5 s. This section was chosen because it illustrated a transition from low‐level background noise to moderate scintillation and another transition to fully saturated scintillation. Order 5 Burg‐MEM spectra from the raw data are compared with periodograms computed from end‐matched and windowed data. The superiority of Burg‐MEM rests largely in the smoothness of the spectrum: real changes in spectral shape are not obscured by meaningless detail.
A transient‐response theory of Pi 2 pulsations
Authors: Sun W. , Kan J. R.
Published: February 2008

The cause of Pi 2 pulsations at substorm onset can be understood in terms of the transient ionospheric response to an enhanced convection in the plasma sheet. A two‐dimensional model is presented to demonstrate how the transient ionospheric response can lead to damped oscillations similar to the Pi 2 pulsations observed at substorm onset. Alfvén waves are launched by the enhanced convection and subsequently reflected between the ionospheres in the opposite hemisphere. The ionospheric conductivity is fully anisotropic and highly nonuniform.
Dependence of Hydromagnetic Energy Spectra Near L = 2 and L = 3 on Upstream Solar Wind Parameters
Authors: Wolfe A. , Meloni A. , Lanzerotti L. J. , Maclennan C. G. , Bamber J. , Venkatesan D.
Published: February 2008

The transmission of fast magnetoacoustic waves generated in the solar wind to the dayside low latitudes deep in the magnetosphere is of vital importance in understanding the physics of some important aspects of the solar wind‐terrestrial interaction. This study provides two examples of such a transmission. Magnetospheric hydromagnetic energies are computed at hourly intervals for four period bands in the Pc 3–5 range (15–30, 30–60, 60–120, and 120–240 s). We use the horizontal component of magnetometer data recorded at AT&T Bell Laboratories and Air Force Geophysics Laboratory stations near L = 2 and L = 3 during January 27–30, 1979, an interval of moderate geomagnetic activity. High correlations are observed between the dayside ground‐based observations of the hourly magnetic energies in the Pc 3 frequency range and the direction of the interplanetary magnetic field. Linear regression and multivariate analysis techniques have been adopted. The statistical results support theories of magnetohydrodynamic wave generation in the solar wind (upstream from the bow shock) and the subsequent wave transmission through the bow shock, magnetosheath, and magnetopause. This leads to the observation of enhancements in Pc 3 at the low‐latitude terrestrial surface. In addition, we also carry out dynamic power spectral analyses of the ground data. These reveal several sudden enhancements in power for variations with periods in the range 15–50 s. At the time of two of these events occurring near local noon we observe large increases of compressional wave power in the solar wind. We take these two events to be specific examples of magnetoacoustic wave transmission of the type indicated by the statistical results.
Model of oval and polar cap arc configurations
Authors: Chiu Y. T. , Crooker N. U. , Gorney D. J.
Published: February 2008

A model of oval and polar cap arc configurations has been formulated by combining the theory of antiparallel magnetic merging and theories of the evening discrete arc and of the morningside arc systems. Aside from incorporating the verified and yet‐to‐be‐verified predictions of the individual component theories this unified model leads to definite predictions of not only arc configurations but also characteristics of the plasmas that produce the various types of arcs. The model predicts two types of polar cap arcs characterized by the plasma sources: the magnetosheath arc and the plasma sheet arc. Their occurrence should be governed by the By component of the interplanetary magnetic field, and the same type should not occur simultaneously in both hemispheres.
Peak flux density spectra of large solar radio bursts and proton emission from flares
Authors: Cliver E. W. , McNamara L. F. , Gentile L. C.
Published: February 2008

We have reexamined the relationship between “U‐shaped” peak flux density microwave spectra and solar proton events for ∼200 large (Sp (≥2 GHz) ≥ 800 solar flux units (sfu)) microwave bursts (1965–1979). The radio spectra fell into two basic classes: U‐shaped, with two maxima (≥ 800 sfu) in the range from 200 MHz to ≥ 10 GHz (59% of all events), and cutoff spectra, with a maximum ≥800 sfu at f ≥ 2 GHz and Sp (200 MHz) < 100 sfu (18%). Nine percent of the events had “intermediate” spectra with a maximum ≥800 sfu at f ≥ 2 GHz and 100 sfu ≤ Sp (200 MHz) < 800 sfu. We were unable to classify 15% of the events because of incomplete data. The associations of the three classes of spectra with type II (and /or type IV) meter wavelength bursts and > 10‐MeV proton events of any size (≥0.01 protons cm−2 s−1 sr−1) are as follows: U‐shaped: type II/IV (90% of large microwave bursts with U‐shaped spectra are associated with type II/IV events), protons (77%); intermediate: type II/IV (78%), protons (73%); and cutoff: type II/IV (22%), protons (33%). These statistics affirm various lines of evidence linking coronal shock waves and interplanetary proton events. They also suggest that the meter wavelength branch of the U‐shaped spectrum may be attributable to second‐phase (versus flash phase) accelerated electrons. We have examined this latter supposition and find that it cannot be true in general. In our sample a type II event was in progress at the time of the peak of the low‐frequency branch for only about half of the bursts with U‐shaped spectrum (U bursts). For these events we cannot rule out a possible contribution to the peak 200‐MHz flux from either the second harmonic of the type II burst or from flare continuum of the type FC II, provided that the starting frequency of the fundamental type II burst is ≳100 MHz. The low‐frequency branch of the U burst appears to be more closely related to impulsive phase type III emission. We note that the small sample of U bursts that lacked type II/IV association is also poorly associated with proton events. We conclude that the observed association between U bursts and proton events probably results from the big flare syndrome rather than a close physical link between these two phenomena. If the current National Oceanic and Atmospheric Administration prediction threshold of J (> 10 MeV) ≥ 10 protons cm−2 s−1 sr−1 had been in effect during the period covered by our data base (1965–1979), the U burst “yes or no” forecast tool would have had a false alarm rate of 50–70% and would have failed to provide warning for 40–50% of the significant prompt proton events attributable to disk flares. We note that several (eight of 46) of the prompt proton events with J (>10 MeV) > 10 protons cm−2 s−1 sr−1 observed from 1965 to 1979 originated in flares that had relatively weak (≤300 sfu) burst emission at 200 MHz.
Polar cap photoionization and the ten‐hour clock at Jupiter
Authors: Goertz C. K. , Baker D. N.
Published: February 2008

We show that the clocklike modulation of the spectral index of energetic electrons (>2 MeV) in the outer Jovian magnetosphere is due to a periodic shift of the particle energy spectrum toward higher and lower energies. This shift results in a modulation of the spectral index when the spectrum is not a pure power law in energy. We suggest that the periodic energization is due to a periodic modulation of the magnetic field in the outer magnetosphere. This modulation is caused by a variation of the longitudinally averaged Pedersen conductivity due to the asymmetric solar illumination of the trace of the magnetodisc in the high‐latitude ionospheres. Such a modulation requires the presence of a surface magnetic anomaly.
Magnetospheric impulse response for many levels of geomagnetic activity
Authors: Bargatze L. F. , Baker D. N. , McPherron R. L. , Hones E. W.
Published: February 2008

The temporal relationship between the solar wind and magnetospheric activity has been studied using 34 intervals of high time resolution IMP 8 solar wind data and the corresponding AL auroral activity index. The median values of the AL index for each interval were utilized to rank the intervals according to geomagnetic activity level. The linear prediction filtering technique was then applied to model magnetospheric response as measured by the AL index to the solar wind input function VBs. The linear prediction filtering routine produces a filter of time‐lagged response coefficients which estimates the most general linear relationship between the chosen input and output parameters of the magnetospheric system. It is found that the filters are composed of two response pulses speaking at time lags of 20 and 60 min. The amplitude of the 60‐min pulse is the larger for moderate activity levels, while the 20‐min pulse is the larger for strong activity levels. A possible interpretation is that the 20‐min pulse represents magnetospheric activity driven directly by solar wind coupling and that the 60‐min pulse represents magnetospheric activity driven by the release of energy previously stored in the magnetotail. If this interpretation is correct, the linear filtering results suggest that both the driven and the unloading models of magnetospheric response are inportant facets of a more comprehensive response model.
Electrostatic effects in the coupling of upper atmospheric waves to ionospheric plasma
Authors: Jacobson Abram R. , Bernhardt Paul A.
Published: February 2008

Neutral atmosphere waves cause ion motion by neutral‐ion collisions. If the ion motion leads to space charge perturbation, then the neutral‐plasma coupling must be calculated with a self‐consistent electrostatic field. We illustrate such self‐consistent solutions for a variety of examples involving both acoustic and acoustic gravity waves. We find that the electrostatic field introduces three phenomena. First, the plasma perturbation within the neutral disturbance differs from that which would be calculated without an electric field. Second, image plasma perturbations appear above the neutral disturbance. Third, image plasma perturbations appear in the conjugate ionosphere, at least for low L shells. We emphasize the latter two image effects.
Thermospheric winds from the satellite electrostatic triaxial accelerometer system
Authors: Marcos Frank A. , Forbes Jeffrey M.
Published: February 2008

A new thermospheric wind measurement technique is reported, which is based on a satellite electrostatic triaxial accelerometer (SETA) system capable of accurately measuring accelerations in the satellite's in‐track, cross‐track, and radial directions. Cross‐track winds measured on 74 orbits between 170 and 210 km during a 5‐day period of mostly high geomagnetic activity are analyzed to demonstrate the potential contributions of SETA data to studies of thermospheric dynamics. On the basis of an analysis which depends upon alignment of null points in the cross‐track winds, the data are shown to be consistent with a two‐cell polar circulation pattern characterized by a main flow parallel to the 1600/0400 geomagnetic local time meridian and return flows in the late morning and late evening sectors. The flow pattern is asymmetric in that it is displaced about 5°–10° latitude toward the noon (geomagnetic local time) sector, and the evening cell is somewhat more diffuse than the morning cell. The system also covers a greater area of the polar cap and is more intense during active (Kp ≳ 5o) than quiet (Kp ≲ 3o) geomagnetic conditions. Average main flow velocities are characteristically of the order of 150±75 m s−1 for Kp ≈ 2o and 375±100 m s−1 for Kp ≈ 5o, the stated variabilities representing 1σ deviations.
The ultraviolet dayglow at solar maximum: 3. Photoelectron‐excited emissions of N2 and O
Authors: Meier R. R. , Conway R. R. , Anderson D. E. , Feldman P. D. , Eastes R. W. , Gentieu E. P. , Christensen A. B.
Published: February 2008

Rocket observations of the far ultraviolet dayglow spectrum near solar cycle maximum are analyzed using laboratory cross sections, atmospheric composition models, and photoelectron production models. Photoelectron‐excited emissions of N2 and O are used to derive a self‐consistent description of the atmosphere at solar maximum. Spectral synthesis of the N2 Lyman‐Birge‐Hopfield bands shows a departure of a¹Πg state vibrational populations from the direct excitation theory. Observations of the N2 second positive (0, 0) 3371‐Å band and O I 1356‐Å emission indicate an exospheric temperature of 1600 K, 200 K higher than predicted by empirical models. The empirical models are also found to overestimate the O and O2 densities required to fit the data by a factor of 2 and 1.4, respectively. These results are compared to the results of an analysis of similar observations made in 1978 near solar minimum. The derived photoelectron flux at 290 km is a factor of 1.6 times larger than for the 1978 data.
Structure of the plasmapause from ISEE 1 low‐energy ion and plasma wave observations
Authors: Nagai T. , Horwitz J. L. , Anderson R. R. , Chappell C. R.
Published: February 2008

Low‐energy ion pitch angle distributions are compared with plasma density profiles in the near‐earth magnetosphere using ISEE 1 observations. The classical plasmapause determined by the sharp density gradient is not always observed in the dayside region, whereas there almost always exists the ion pitch angle distribution transition from cold, isotropic to warm, bidirectional, field‐aligned distributions. In the nightside region the plasmapause density gradient is typically found, and it normally coincides with the ion pitch angle distribution transition. The sunward motion of the plasma is found in the outer part of the “plasmaspheric” plasma in the dusk bulge region.
Observations of E and F region Mg+ from Spacelab 1
Authors: Mende S. B. , Swenson G. R. , Miller K. L.
Published: February 2008

Images of airglow at 2800 Å were taken on the Spacelab 1 shuttle mission and have been interpreted to be solar resonant emission of magnesium ions. On two orbital passes, observations were made near the magnetic equator while observing in the 2800‐Å channel. The observations were made near the sunset terminator (∼1800 LT), in winter (1983, day 335). Three separate emission clouds were observed, all of which extended well into the F region. The location of the clouds in horizontal space is shown. The processed images have been pseudocolored to highlight the intensity distribution in the clouds. Observations included clouds with apparent magnetic field aligned striations. Bright emissions were observed at the magnetic equator, at 12° north magnetic latitude, and at 12° south magnetic latitude. Cloud center brightnesses varied between 680 rayleighs and 1700 rayleighs.
Inference of high‐latitude ionization and conductivity from AE‐C measurements of auroral electron fluxes
Authors: Vondrak R. , Robinson R.
Published: February 2008

Electron fluxes in the kilovolt energy range measured by the AE‐C satellite have been used to infer the latitudinal distribution of ionization at high latitudes in the altitude range 90 to 200 km. These distributions are compared with simultaneous measurements of electron density by the Chatanika incoherent scatter radar. The study was based on more than 120 electron density profiles obtained on three different nights at magnetic local times between 0200 and 0400. The calculated distributions agree very well with the altitude and latitude distributions measured by the radar. The only obvious difference was the presence in the radar data of additional ionization produced by solar illumination. We also compared the height‐integrated electrical conductivities computed from the measured profiles and those inferred from the satellite measurements. For Hall and Pedersen conductances greater than 5 mhos, the agreement is within 25%. The data were also used to deduce the altitude profile of the effective recombination coefficient. This profile agrees well with the results of previous studies.
Fine structure in mesospheric wind fluctuations observed by the Arecibo UHF Doppler radar
Authors: Fukao Shoichiro , Maekawa Yasuyuki , Sato Toru , Kato Susumu
Published: February 2008

Mesospheric short‐period wind fluctuations are investigated, using two sets of daytime wind data obtained on 15 consecutive days in August 1980 and March 1981 by the UHF Doppler radar at Arecibo, Puerto Rico (18.4°N, 66.8°W). The wind fluctuations are found to have a conspicuous recurring structure with periods of 10–20 min on a vertical scale less than a few kilometers. This structure, appearing as a “grill pattern” in the time‐height sections of wind velocity, seems to indicate that both upward and downward propagating waves with similar wave parameters exist simultaneously in this height range. The wave energy is shown to be almost equally distributed between the upward and downward propagating waves. The frequency power spectrum has a falling gradient gentler than that of the f−5/3 and even of the f−1 power law (f is frequency). Occurrence of these waves seems to be related to strong wind shears associated with long‐period internal inertia‐gravity waves present in the mesospheric region.
The vibrational distribution of N2+ in the terrestrial ionosphere
Authors: Fox J. L. , Dalgarno A.
Published: February 2008

The densities and vibrational distributions of N2+ in the X²Σg+, A²Πu, and B²Σu+ states in the daytime terrestrial ionosphere are computed for both low and high solar activity. Altitude profiles of the relative populations of the vibrational levels of N2+X²Σg+ are presented. The fraction of vibrationally excited N2+ varies from 5% at 100 km to 50% at 450 km. Several models are examined in which loss of N2+(υ) is enhanced for υ > 0 and in which various assumptions are made about the vibrational distributions produced in charge transfer reactions. The N2+ densities are significantly reduced if N2+(υ) reacts with O at rates which are near gas‐kinetic. Vibrational distributions of the A²Πu and B²Σu+ states are also presented, as well as volume emission rates and integrated overhead intensities of the major bands of the Meinel and first negative systems.
Evidence for a nonmagnetospheric origin of fast atmospheric pulsations
Authors: Bhat C. L. , Sapru M. L. , Kaul R. K.
Published: February 2008

An atmospheric fluorescence detection system has been in operation at Gulmarg (India), during 1972–1978, to search for short‐duration (≤ 1 ms) optical pulses produced following the absorption of cosmic X ray and gamma ray photon bursts in the terrestrial atmosphere. A systematic examination of the records reveals no evidence of events with the characteristics of fast atmospheric pulsations (FAP), the millisecond tine scale optical pulses detected during similar studies carried out elsewhere. The complete absence of FAP activity at Gulmarg raises serious doubts about the proposed magnetospheric origin of these events.
Enhanced aurora
Authors: Hallinan T. J. , Stenbaek‐Nielsen H. C. , Deehr C. S.
Published: February 2008

A review of thirteen years of video recordings shows that auroras of all types frequently exhibit intensity enhancements in one or more thin horizontal layers having vertical extents that are only a small fraction of the local atmospheric scale height. These layers appear to be stable atmospheric layers that interact more effectively with precipitating auroral electrons than does the bulk atmosphere. The spectrum of the enhanced aurora is grossly similar to that of the background aurora, leading us to suggest that the enhancement is the result of a localized plasma instability that energizes ambient electrons at the expense of the kinetic energy of the precipitating electrons. This is phenomenologically similar to a beam‐plasma discharge. But, whatever the process, it is at least competitive with direct collisional interactions in the enhanced aurora and may be important in normal aurora as well.
High‐latitude mesopause neutral winds and geomagnetic activity: A cross‐correlation analysis
Authors: Johnson R. M. , Luhmann J. G.
Published: February 2008

A cross‐correlation analysis of horizontal winds at 87 km obtained by the Poker Flat mesosphere‐stratosphere‐troposphere (MST) radar and College magnetometer horizontal component fluctuations has been performed on 3 years of summertime data. No consistent, significant peak in the average 4‐day estimate cross‐correlation results is apparent from year to year. Individual estimates similarly do not show evidence of a peak in cross correlation at a variable time lag during geomagnetically active intervals. In addition, the 1‐day 24‐ and 12‐hour wave amplitudes and phases and average zonal and meridional winds do not vary significantly and consistently with the daily averaged magnetometer horizontal component fluctuations or with the standard deviation thereof. The interval following the July 13, 1982, polar cap absorption event and geomagnetic storm, however, shows a different cross‐correlation estimate behavior and is characterized by significantly more westward zonal winds and enhanced 24‐hour zonal wind amplitude.
Oxygen singlet delta 1.58‐micrometer (0–1) limb radiance in the upper stratosphere and lower mesosphere
Authors: Winick Jeremy R. , Picard R. H. , Sharma Ramesh D. , Nadile Richard M.
Published: February 2008

In this paper we analyze daylight 1.58‐µm limb radiance profiles obtained by the Spectral Infrared Rocket Experiment (SPIRE) in the 40‐ to 70‐km tangent height region, near the dawn terminator. Photochemical model calculations indicate that the O2(a¹Δg, υ = 0) → O2(X³Σg−, υ = 1) transition provides the necessary radiance if we choose the Einstein coefficient for the (0, 1) transition, A(0, 1) = 5.0×10−6 s−1. This value is within the range of past field and laboratory measurements but 3 times larger than what the Franck‐Condon principle would predict assuming the accepted value of 2.58×104 s−1 for A(0, 0). One‐dimensional inversions of the radiance give reasonable profiles of O2(¹Δg) for altitudes above the radiance peak. Using the best fit values for A(0, 1), a two‐dimensional model treatment can give good agreement to the limb radiance even below the radiance peak, but there is not enough information in the limb radiance scans to do a two‐dimensional inversion. The two‐dimensional simulation of the limb radiance is more successful since it takes into account the change in the O2 singlet delta density with solar zenith angle and not just altitude, and because the direct calculation avoids the numerical error that accumulates in the one‐dimensional inversion especially below the radiance peak.
On the production of N+ by energetic electrons
Authors: Richards P. G. , Torr D. G.
Published: February 2008

We present calculations of the ratio of N+ to total N2 ion production for auroral electrons which give a value of 0.16 compared to the value of 0.22 that has been assumed in a recent publication. The corresponding ratio for photoelectron production is 0.05, which makes photoelectron production of N+ negligible compared to photodissociative production. The ratio of 3914‐Å to total ion production is found to be 0.07 for auroral electrons and a similar 0.06 for photoelectrons. The 3371‐Å ratio to total N2 ion production is 0.09. This calculation also reveals that the secondary electrons in auroras with energies less than 100 eV produce only about one third of the total number of ions produced. Only one quarter of the N+ ions are created by secondary electrons.
Effects of potential distribution along field lines on field‐aligned current density
Authors: Yamamoto Takashi , Kan J. R.
Published: February 2008

Effects of potential distribution along auroral field lines on the field‐aligned current density are examined for a specific type of field‐aligned potential distribution excluded by the Knight‐Fridman‐Lemaire (KFL) formula. It is shown that the field‐aligned current density can be significantly reduced from the current density originally estimated by the KFL formula if the potential drop is concentrated at low altitudes (4000 km). This result can provide a possible explanation for the observed field‐aligned current pattern across the discrete auroral forms.
A multiple‐satellite observation of the high‐latitude auroral activity on January 11, 1983
Authors: Gorney D. J. , Evans D. S. , Gussenhoven M. S. , Mizera P. F.
Published: February 2008

Unusual high‐latitude auroral activity occurred on January 11, 1983, during a period of persistent interplanetary magnetic field Bz > 0, By > 0, and Bx > 0. This activity, which lasted from 0600 to 2100 UT, was characterized by numerous high‐latitude sun‐aligned arcs and a diffuse oval. Near 1500 UT a single broad (250 km) sun‐aligned arc was observed by the optical line scan system on Defense Meteorological Satellite Program (DMSP) F6. The arc was continguous with the dawn auroral oval and extended across the northern polar cap, similar to previously reported “theta aurora” configurations. The fortunate orbital locations of the DMSP F6, NOAA 7, and NOAA 6 satellites allow a detailed analysis of the precipitating particle populations responsible for both the sun‐aligned arc and oval auroras. Specifically, NOAA 7 and DMSP F6 cross the broad sun‐aligned arc almost simultaneously in the northern hemisphere, with NOAA 7 crossing the arc 1500 km farther toward the dayside. During the arc crossing, NOAA 7 observes electron fluxes, temperatures, and accelerations similar to those observed by DMSP F6 but observes ion fluxes diminished by a factor of 50 in comparison with DMSP. Almost simultaneously, NOAA 6 crosses the southern polar cap and observes flux levels in an apparent high‐latitude arc comparable to those observed by DMSP. The results are consistent with, but supplementary to, previous observations of high‐latitude auroral observations and thus place meaningful constraints on emerging theoretical concepts of this phenomenon.
AMPTE lithium tracer releases in the solar wind: Observations inside the magnetosphere
Authors: Krimigis S. M. , Haerendel G. , Gloeckler G. , Mcentire R. W. , Shelley E. G. , Decker R. B. , Paschmann G. , Valenzuela A. , Potemra T. A. , Scarf F. L. , Brinca A. L. , Lühr H.
Published: February 2008

A release of approximately 3.3×1025 lithium atoms was made on September 11 and again on September 20, 1984, by the Active Magnetospheric Particle Tracer Explorers (AMPTE) Ion Release Module (IRM) spacecraft at a geocentric distance of ≈ 18.8 Re in the subsolar direction, creating an ion cloud approximately 4 Re in diameter after one hour. Detailed modeling of ion propagation to the bow shock and transport through the magnetosheath shows that ≳20% (September 11) and ≳50% (September 20) of the ions mapped to a 36‐Re² area around the stagnation point on the magnetopause. The AMPTE Charge Composition Explorer (CCE) satellite, located inside the magnetosphere with an apogee of 8.78 Re and inclination of 4.8°, at a local time of about 1300 MLT, was instrumented to detect lithium ions over the energy range from a few eV to ≳6 MeV. Detailed analysis of the data for the several hours following the lithium releases shows that no measurable lithium ion fluxes reached the location of the CCE; upper limits to the lithium flux at L ≳ 8 are about 50 to 70 (cm2‐sec‐sr)−1 in the range 25–300 keV/e (Li/H ≳ 2×10−5), and about 0.1 to 1 (cm²‐sec‐sr)−1 in the range 45–100 keV/nucleon (Li/H ≈ 1×10−6). The implications of these results are discussed in the context of current theoretical models of plasma entry into and transport within the magnetosphere.
Chaos and nonlinear dynamics of single‐particle orbits in a magnetotaillike magnetic field
Authors: Chen James , Palmadesso Peter J.
Published: February 2008

The properties of charged‐particle motion in Hamiltonian dynamics are studied in a magnetotaillike magnetic field configuration. It is shown by numerical integration of the equation of motion that the system is generally nonintegrable and that the particle motion can be classified into three distinct types of orbits: bounded integrable orbits, unbounded stochastic orbits, and unbounded transient orbits. It is also shown that different regions of the phase space exhibit qualitatively different responses to external influences. The concept of “differential memory” in single‐particle distributions is proposed. Physical implications for the dynamical properties of the magnetotail plasmas and the possible generation of non‐Maxwellian features in the distribution function are discussed.
Shear flow‐ballooning instability as a possible mechanism for hydromagnetic fluctuations
Authors: Viñas Adolfo F. , Madden Theodore R.
Published: February 2008

It is suggested that an MHD instability termed the “shear flow‐ballooning instability,” which unifies both the Kelvin‐Helmholtz and the interchange (“ballooning”) instabilities, can excite hydromagnetic waves in the inner magnetosphere. The stability analysis resembles studies of hydrodynamic flows, where the stabilizing factor is the gravitational buoyancy represented by the Brunt‐Väisälä (or Rayleigh‐Taylor) frequency Ωg(r). Here the “magnetic buoyancy” due to the curvature of the field lines replaces the gravitational buoyancy and allows the derivation of the MHD analogue to Ωg(r). Stability is then found to depend on a dimensionless quantity termed the magnetic Richardson number (similar to hydrodynamic) Ri = [Ωg²(r) + k∥²Ca²](1 + k∥²/k⊥²)/(dVϕ/dr)² representing the relative importance of gravitational, thermal, rotational, magnetic, and shear flow effects. Unstable MHD modes are found to be represented by Alfvén drift waves which are the hydromagnetic, and shear flow effects. Unstable MHD modes are found to be represented by Alfvén drift waves which are the hydromagnetic analogue to hydrodynamic gravity waves and like them are trapped in the shear zone. The study is applied to the plasmapause boundary, and the results indicate that low‐frequency hydromagnetic pulsations (Pc 4‐Pc 5) with typical wave periods between 123 and 428 s and wavelengths in the range of 5×10³ to 17.2×10³ km can be excited in such a region. The analysis can be extended to other shear flow boundaries such as the magnetopause.