bluuebunny/crossref_metadata_2025 huggingface dataset:
An apparent shear zone trending north‐northwest across the Mojave Desert into Owens Valley, eastern California
Authors: Savage J. C. , Lisowski M. , Prescott W. H.
Published: February 2008

Strain rates measured at four geodetic networks in eastern California situated between northern Owens Valley and the Transverse Ranges along a small circle drawn about the Pacific‐North America pole of rotation are remarkably consistent. Each exhibits 0.14 μrad/yr simple right‐lateral engineering‐shear‐strain accumulation across the local vertical plane tangent to the small circle. Local faults (e.g., Owens Valley, Garlock, Helendale) traversing these networks are not as closely aligned with the vertical planes of maximum shear‐strain accumulation as is the local tangent to the small circle. A fifth network slightly east of the small circle shows no significant strain accumulation. Thus, a shear zone trending N35° W from near the eastern end of the big bend of the San Andreas fault to northern Owens Valley is indicated by these data. This corresponds to the Eastern California shear zone proposed on geological evidence by Dokka and Travis. The shear zone carries ∼8 mm/yr of the Pacific‐North America relative plate motion from the San Andreas fault north‐northwest across the Mojave Desert into Owens Valley and the northern Basin and Range province. The shear zone observed at the surface may be a manifestation of a through‐going subcrustal fault.
Absorption spectrum and solar photodissociation of gaseous nitrous acid in the actinic ‐ wavelength region
Authors: Vasudev R.
Published: February 2008

The absorption cross section of gaseous nitrous acid (HONO) in the actinic wavelength region (λ≥290 nm) of the solar radiation is mapped through laser photodissociation experiments. HONO is photodissociated by a tunable ultraviolet beam, and the OH product is monitored through fluorescence induced by a frequency‐doubled dye laser. The absorption of HONO is mapped by scanning the photolysis wavelength. Since this technique yields relative cross‐sections, we calibrate our measurements with previous measurements of absolute cross‐section at 354 nm (because there is reasonable agreement among previous measurements at this wavelength). The present experimental approach is insensitive to the presence of NO2, which apparently contributed to inaccuracies in some of the previous conventional measurements on HONO absorption.
On the limitations of general circulation climate models
Authors: Stone Peter H. , Risbey James S.
Published: February 2008

General Circulation Models (GCMs) by definition calculate large‐scale dynamical and thermodynamical processes and their associated feedbacks from first principles. This aspect of GCMs is widely believed to give them an advantage in simulating global scale climate changes as compared to simpler models which do not calculate the large‐scale processes from first principles. However, we point out that the meridional transports of heat simulated by GCMs used in climate change experiments differ from observational analyses and from other GCMs by as much as a factor of two. We also demonstrate that GCM simulations of the large scale transports of heat are sensitive to the (uncertain) subgrid scale parameterizations. This leads us to question whether current GCMs are in fact superior to simpler models for simulating temperature changes associated with global scale climate change.
Relationship between four‐cell and distorted two‐cell convection patterns during northward IMF
Authors: Zhu L. , Kan J. R.
Published: February 2008

Four‐cell convection pattern in the ionosphere during a northward IMF (interplanetary magnetic field) was widely accepted until it was challenged by the distorted two‐cell convection pattern proposed by Heppner and Maynard [1987]. We propose that a four‐cell convection pattern, imposed on the magnetosphere by the solar wind, can be distorted into a wrapped two‐cell pattern by the nonuniform and anisotropic conductance in the ionosphere. This is demonstrated by extending the magnetosphere‐ionosphere coupling model [Kan et al., 1988] to the northward IMF condition. The resulting wrapped two‐cell patterns for positive and negative IMF By are similar to the empirical two‐cell patterns obtained by Heppner and Maynard [1987]. The distributions of the resulting field‐aligned currents are also characteristically consistent with the observed current distributions, including the NBZ currents, during northward IMF.
Ground‐based observations of radio emissions near 2fce and 3fce in the auroral zone
Authors: Weatherwax A. T. , LaBelle J. , Trimpi M. L. , Brittain R.
Published: February 2008

Narrow band emissions at frequencies near twice and three times the ionospheric electron cyclotron frequency have been observed with a ground based receiver located at Two Rivers, Alaska (near Fairbanks). The emissions at twice the local ionospheric electron cyclotron frequency ( ≈ 2.50–2.80 MHz) appear similar in frequency, intensity, local time dependence, and temporal structure to auroral “roar” events previously observed at Churchill, Manitoba [Kellogg and Monson, 1979; 1984]. The observation of emissions near 3fce ( ≈ 3.66–4.24 MHz), sometimes observed simultaneously with the 2fce events, represents a new aspect of this phenomenon. A quantitative theoretical understanding of the phenomenon has not yet been achieved.
On detrending and smoothing random data
Authors: Owens A. J.
Published: February 2008

‘Filtering’ operations in the time domain are often used to eliminate unwanted short‐ or long‐time scale variations in random data. To suppress long‐period variations, authors often subtract a moving average or fitted polynomial from the raw data. Short‐time variations are often eliminated by using moving‐averaged data. The statistical properties of these processes are derived, and it is shown that they can introduce spurious features in the Fourier spectrum, correlation function, and power spectrum of the data.
Measurements of the Poynting vector of standing hydromagnetic waves at geosynchronous orbit
Authors: Cummings W. D. , DeForest S. E. , McPherron R. L.
Published: February 2008

Particle and magnetic field data from the ATS 6 spacecraft have been combined to study a Pc 4 pulsation event. The event occurred as the satellite passed the dawn meridian during the recovery phase of a moderate magnetic storm, Plasma drifts associated with the wave are determined from the measured modulation of low‐energy protons. Using the observed ambient and perturbation magnetic fields in conjunction with the plasma drift velocity, we calculate the Poynting vector of the wave, assuming that the electric field is given by the frozen field approximation. The Poynting vector gives convincing evidence that the wave is a standing hydromagnetic wave along the magnetic field. In addition, it shows that the wave is propagating predominantly azimuthally from noon toward the dawn meridian. The phase relationships between the magnetic and plasma drift velocity oscillations are consistent with the occurrence of an odd harmonic of the standing wave. Comparison of observed particle fluxes with model predictions demonstrates that the fundamental mode is the most reasonable interpretation of the data. Ambient ion number densities, predicted by the wave data on the basis of a simple model of standing hydromagnetic waves, are found to be somewhat higher than observed values, on the basis of the assumption that the ambient plasma consists of protons and electrons only. Predicted and observed values of the ion number densities can be reconciled if it is assumed that a significant fraction of the ambient plasma consisted of He+ and/or O+. By using the fact that the wave is a standing wave the particle flow velocity is predicted from the observed magnetic variation and a model‐dependent theory. These predictions are found to agree very well with the flow values determined from the data.
Global effect of auroral particle and Joule heating in the undisturbed thermosphere
Authors: Hinton Barry B.
Published: February 2008

From the compositional variations observed with the neutral atmosphere composition experiment on Ogo 6 and a simplified model of thermospheric dynamics, global average values of non‐EUV heating are deduced. These are 0.19–0.25 mW m−2 for quiet days and 0.44–0.58 mW m−2 for ordinary days.
Direct observation of the latitudinal extent of a high‐speed stream in the solar wind
Authors: Schwenn R. , Montgomery M. D. , Rosenbauer H. , Miggenrieder H. , Mühlhäuser K. H. , Bame S. J. , Feldman W. C. , Hansen R. T.
Published: February 2008

Solar wind speeds measured from the Helios 1 solar probe between 0.31 and 1 AU and the earth‐orbiting Imp 7/8 satellites have been correlated with coronal holes as determined from K coronal brightness measurements. In March 1975 during perihelion passage, Helios 1 traversed the range of heliographic latitudes from −6° to +6° in a period of only 20 days. During that time the space probe crossed the northern boundary of the high‐speed stream associated with an equatorward extension of the south polar coronal hole. While this same stream continued to be observed by Imp satellites at −5° latitude, it was no longer observable from Helios 1 at +5° latitude. The conclusion is that sharp boundaries separate high‐speed flows from the surrounding solar wind. The thickness of the boundary in latitude appears to be narrower than about 10°. The local latitudinal gradient in flow speed is at least 30 km s−1 deg−1. With less confidence it can be deduced from the Helios 1 data that the actual gradients at 0.31 AU might even exceed 100 km s−1 deg−1.
On the nature of large auroral zone electric fields at 1‐RE altitude
Authors: Shawhan Stanley D. , Fälthammar Carl‐Gunne , Block Lars P.
Published: February 2008

Mechanisms that may support magnetic‐field‐aligned electric fields in collisionless plasma are discussed in the light of recent magnetospheric observations, which for the first time allow a quantitative test of the theoretical models. Data from barium ion releases which indicate large field‐aligned potential drops and direct electric field probe measurements at high altitude which reveal electric fields of several hundred millivolts per meter are discussed. It is concluded that the large field strengths observed (1) cannot be explained by anomalous resistivity or thermoelectric effects based on wave‐particle interaction, (2) are much larger than required merely to balance the local mirror forces, and (3) are compatible with electric double layers of the same nature as those observed in the laboratory.
Transport properties in the Jovian atmosphere
Authors: Biolsi Louis
Published: February 2008

Transport properties in a Jupiter‐like atmosphere (89 mol % hydrogen and 11 mol % helium) are obtained by using the method of the kinetic theory of gases. The transport collision integrals are calculated by fitting various two‐body semiempirical interaction potentials for which the collision integrals are tabulated to ab initio quantum mechanical calculations of the two‐body interactions. The collision integrals are used to calculate the binary diffusion coefficients, viscosity, and ‘total’ thermal conductivity of the pure gases and the gas mixtures at 1‐atm pressure from 1000°K to 25,000°K.
A theory of triggered emissions
Authors: Roux A. , Pellat R.
Published: February 2008

We study the motion of electrons trapped in the potential troughs of a monochromatic whistler wave propagating along geomagnetic field lines. Because of the coupling between inhomogeneity and trapping effects the distribution function of electrons at the termination of this triggering pulse can be very different from the distribution at its front provided that the triggering wave amplitude and duration are large enough to trap electrons over more than one trapping length. Particles which are detrapped at the triggering wave termination have been phase organized and may then act coherently for a while, giving rise to an emission with either rising or falling tones, depending on the sign of the inhomogeneity variation. The spatially averaged part of the distribution function of these suddenly detrapped electrons is shown to generate an instability which amplifies previously emitted waves. These results are compared with existing data. Finally, we show that emitted waves can easily trap electrons, thus explaining how the process of emission can be self‐sustained.
Energization of charged particles to high energies by an induced substorm electric field within the magnetotail
Authors: Pellinen R. J. , Heikkila W. J.
Published: February 2008

Observations have shown that electrons and protons are energized up to at least 1 MeV in the magnetotail during substorms. This magnitude cannot be explained by the cross‐tail electrostatic field, which typically has a modest potential difference of only 50 kV. A rotational electric field induced by a time‐dependent magnetic field does not have such a limitation. In order to evaluate its capabilities a simple model of a localized, growing disturbance in the neutral sheet current was used to calculate perturbation magnetic and electric fields; the model includes the formation of X and O type neutral lines. Plasma sheet test particles were followed in these time‐dependent fields by using the full relativistic equation of motion. The most efficient energizing mechanism is a two‐step process, with an initial linear acceleration along a neutral line up to moderate energies, followed by betatron acceleration. The former imparts a large magnetic moment µ = W⊥/B to the particle as it begins to gyrate and drift in the magnetic field, W⊥ being the transverse kinetic energy. During this drift into regions of stronger magnetic field there is a large increase in W⊥, the relativistic invariant γµ remaining constant. Because of the rotational property of the induced electric field it is possible for a particle to gain energy even when the drift motion by itself would cause a loss. The model also includes acceleration along magnetic field lines in the plasma sheet, with moderate energy gain. A cyclic pattern of electron and proton precipitation is predicted, such as is observed during auroral breakup.
Theory for charge states of energetic oxygen ions in the Earth's radiation belts
Authors: Spjeldvik Walther N. , Fritz Theodore A.
Published: February 2008

Fluxes of geomagnetically trapped energetic oxygen ions have been studied in detail. Ion distributions in radial locations below the geostationary orbit, energy spectra between 1 keV and 100 MeV, and the distribution over charge states have been computed for equatorially mirroring ions. Both ionospheric and solar wind oxygen ion sources have been considered, and it is found that the charge state distributions in the interior of the radiation belts are largely independent of the charge state characteristics of the sources. In the MeV range, oxygen ions prove to be a more sensitive probe for radiation belt dynamics than helium ions and protons.
Interplanetary magnetic field variations and the electromagnetic state of the equatorial ionosphere
Authors: Patel V. L.
Published: February 2008

The effect of interplanetary magnetic field variations on the low‐latitude ionosphere has been studied by using the simultaneous occurrence of three phenomena—the disappearance of equatorial Esq, the reversal or decrease in intensity of the equatorial electrojet as implied from magnetogram signatures, and a northward turning of the z component of the interplanetary magnetic field Bz observed by the Explorer 43 satellite. The search for the simultaneous occurrence of these three phenomena is met with partial success because out of 20 events for which simultaneous data were available, 12 showed no significant change in the interplanetary field near the disappearance of the Esq. Four of the remaining eight showed only small variations. The four best cases are presented in detail. A possible explanation, for these events, is that the induced electric field imposed on the magnetosphere through the change in Bz and coupled to the high‐latitude ionosphere may affect the low‐latitude ionosphere by high‐latitude‐low‐latitude coupling. If the electric field is impressed to the low latitude, the resultant field may suppress cross‐field instability and cause the disappearance of the Esq.
On sudden commencement absorption events at the South Pole and their relation to the latitude of the lower cleft boundary
Authors: Brown R. R.
Published: February 2008

From 7 years (1966–1973) of riometer data from the south pole (74.2° invariant latitude), 43 sudden commencements of magnetic storms were examined for sudden commencement absorption (sca) events and the possible influence of the lower cleft boundary latitude on electron precipitation at that site. For 17 of the events, interplanetary magnetic field (IMF) data are available to predict the position of the lower cleft boundary. Three of the sca events at the south pole occurred during IMF conditions when the predicted cleft boundary, including the effect of magnetic activity (AE) was equatorward of that site by 2°–4°. The observation of sudden commencement electron precipitation at the south pole at these times indicates that the cleft region involves closed field lines.
Auroral excitation of optical emissions of atomic and molecular oxygen
Authors: Feldman Paul D.
Published: February 2008

Rocket measurements of the O I ‘green line’ (¹S‐¹D) at 5577 Å and the O2 (0, 0) atmospheric band at 7620 Å were made in a steady IBC II+ aurora, simultaneously with measurements of N2 emissions and the auroral electron flux. An empirical model based on these data demonstrates that the principal excitation source of O2(b¹Σg+) is energy transfer from O(¹D), with direct electron impact of O2 contributing less than 5%. The altitude profile of the green line emission, taking into account quenching of O(¹S) by O(³P) near the lower border of the aurora, resembles what would be produced by electron impact excitation of O2 but would require a dissociative excitation cross section of 10−16 cm². None of the other known O(¹S) excitation mechanisms are capable of producing the observed emission rate.
Ice sputtering by radiation belt protons and the rings of Saturn and Uranus
Authors: Cheng Andrew F. , Lanzerotti L. J.
Published: February 2008

The outer portion of the rings of Saturn is probably immersed in intense particle radiation belts. We scale Pioneer 10 and 11 measurements to the Saturnian radiation belts and estimate that sputtering by high‐energy protons from the ice particles in the outer portion of the rings leads to a net erosion rate there of 10−6 cm yr−1 after allowance for the rapid recapture, and thus the redistribution, of water molecules on the ring particles. The lifetime of ice particles in the outer portions of the rings against sputtering may then be less than the age of the solar system. We show that such water ice sputtering can maintain the neutral H atmosphere around the rings detected by Weiser et al. (1977). We also suggest that the very low albedo recently reported for the rings of Uranus could result from the sputtering away of primordial ices on the ring grains by Uranian radiation belt particles.
Ionospheric holes and equatorial spread F: Chemistry and transport
Authors: Szuszczewicz E. P.
Published: February 2008

Existing experimental and theoretical results are synthesized with new ion mass spectrometer data from Atmosphere Explorer C to provide a more comprehensive perspective on the understanding of nighttime equatorial irregularities. Particular attention is given to possible relationships between ionospheric holes and smaller‐scale (3 m) irregularities observed by ground‐based radar. Ion chemistry and transport considerations are found to support the concept that equatorial holes and equatorial spread F can be one and the same phenomenon, with the smaller‐scale irregularities imbedded within the much larger scale ionospheric depletions.
On the coexistence of kilometer‐ and meter‐scale irregularities in the nighttime equatorial F region
Authors: Basu Santimay , Basu Sunanda , Aarons Jules , McClure J. P. , Cousins M. D.
Published: February 2008

Nighttime multifrequency scintillation and 50‐MHz radar backscatter observations simultaneously performed over a nearly common ionospheric volume at the dip equator in Peru during March 1977 were used to study the relationship between the large‐scale irregularities (∼0.1–1 km) giving rise to scintillations and small‐scale irregularities (3 m) causing 50‐MHz backscatter. It is shown that during the generation phase of equatorial irregularities in the evening hours, the kilometer‐ and meter‐scale irregularities coexist, whereas in the later phase, approximately an hour after the onset, the meter‐scale irregularities decay but the large‐scale ones continue to retain their high spectral intensities. Further, multistation scintillation observations from a host of geostationary satellites as well as from the Wideband satellite indicate that eastward‐drifting irregularity structures detected around midnight cause significant scintillations at UHF and L band but generally fail to give rise to appreciable backscatter. Thus, contrary to expectations, it is possible to have even L band scintillations without any plume structure on backscatter maps. This indicates that at later local time a cutoff of the spectral intensity probably occurs at some scale length between 100 and 3 m. These observational results are discussed in the context of current theories of plasma instability in the equatorial ionosphere.
Equatorial ionospheric anomaly and interplanetary magnetic field
Authors: Galperin Yu. I. , Ponomarev V. N. , Zosimova A. G.
Published: February 2008

Measurements of the ion convection velocity (transverse horizontal and vertical components) from asymmetry of the lateral ion flow in the satellite frame and also of the total ion concentration were conducted in October–November 1967 from the Cosmos 184 satellite (circular orbit at 630 km, inclination 81°2′). In this study, first the cases were selected when a reversal of the sign of the By component of the IMF had taken place during the time interval between two successive satellite passes through the equatorial ionospheric anomaly (11 cases). Systematic decreases of the near‐equatorial ion density were observed after reversals from By negative to By positive. These decreases were accompanied by relative enhancements of the upward and the eastward components of the plasma drift velocity of the order of several tens of meters per second. Variations of the opposite direction were observed (though less regularly) after By reversals from positive to negative. Important vertical and horizontal plasma drift velocities appear in the irregular density variations and especially at localized ionization spikes (downward velocity relative to surrounding plasma) and dropouts (upward relative velocity). These density dropouts are very similar to the ‘plasma bubbles’ reported by McClure et al. (1977) and at 630 km are observed mostly when the density profile has a near‐equatorial valley. It was shown by Heppner (1972) that the polar cap convection pattern depends on the sign of the By IMF component. If follows that suitably selected polar plasma drift data from Cosmos 184 can also be used to find the pairs of orbits indicating the reversals of By IMF (‘inferred reversals’). Typical signatures of the plasma drift pattern in the noon region close to the southern (sunlit) dayside polar cusp were constructed from the whole set of Cosmos 184 data. These signatures indeed show high correlation with the sign of By IMF. The reversal of typical signatures on a pair of successive orbits in fact represents the direct indication of the large‐scale electric field variation in the polar ionosphere/outer magnetosphere presumably induced by the reversals of By IMF (9 cases partly overlapping the 11 cases mentioned above). The two sets of data (pairs of orbits) are in general accord (with several doubtful cases but no direct contradictions) both with respect to the By sign reversal evaluation and with respect to the above‐described differential variations in the latitudinal ion density profiles and in the plasma drift velocities in the equatorial ionospheric anomaly. These observations confirm the propagation of the electric field variations from polar ionosphere/outer magnetosphere down to the equatorial latitudes, as was suggested by Rastogi and Patel (1975).
Two‐dimensional turbulence in equatorial spread F
Authors: Kelley M. C. , Ott Edward
Published: February 2008

The convective instability of the equatorial ionosphere is known to result in the upwelling of low‐density regions into the topside. We show here that such rising ‘bubbles’ generate a wake consisting of vortices in the background fluid with an initial scale size comparable to the bubble dimension Ls. Since there is a background plasma density gradient, density irregularities will also be created at this scale. The theory of turbulence in two‐dimensional fluids is then applied to predict that velocity and density structures will subsequently develop in the background fluid at both larger and smaller wavelengths. We suggest that this extension to longer wavelengths tends to fill in the region between bubbles with velocity and density structures and contributes to the great horizontal scale over which equatorial spread F is observed, while the wakes themselves account for the extended vertical scale. We also predict that a break in the velocity turbulence spectrum should occur near the stirring length Ls. Under some conditions a well‐defined ‘inertial subrange’ may exist where the velocity wave number spectrum should vary as k−3, and the density spectrum should vary as k−1 in this same range.
High‐resolution energetic particle measurements at 6.6 RE, 2. High‐energy proton drift echoes
Authors: Belian R. D. , Baker D. N. , Higbie P. R. , Hones E. W.
Published: February 2008

Drifting bunches of protons in the 0.14‐ to 1.0‐MeV energy range have been observed with good energy resolution by the charged particle analyzer instruments on the 1976‐059A and 1977‐007A satellites in geostationary orbit. Well‐defined flux peaks are observed corresponding to as many as six circuits of the earth by these proton bunches. Some 52 clear events have been recorded by the instrument on 76‐059 in 8 months of data, and several cases have been observed by both spacecraft. In the twenty‐five cases studied in detail, the proton bunches appear to be injected at locations near midnight. All injections are closely associated with substorm onsets, but fewer than 10% of all substorms have associated high energy proton drift echoes. After injection the magnetic field Structure at ∼6.6 RE often appears to be stable for 1–2 hours, as evidenced by the constant periods between the drift echoes. Observations made using the two spacecraft separated by ∼4 hours of local time show many events which fit a picture of very localized injection and Simple drift in a stable magnetospheric field. The majority of events observed, however, show a more complex behavior than the simple injection‐drift picture would imply.
Sq variation at low latitudes during geomagnetic storms
Authors: Kane R. P.
Published: February 2008

By subtracting the H values at a location (Sabhawala) near the Sq focus from the H values at a low‐latitude station (Alibag) in the Indian longitudes, the Sq pattern at the low‐latitude station is obtained for a continuous period of quiet and disturbed days in February and May 1967. It is shown that the pattern is invariably a near‐noon maximum with amplitudes showing large day‐to‐day variability in quiet days as well as disturbed days. Thus geomagnetic storms have no specific effect on the pattern of the Sq current system.
Quantitative calculations of helium ion escape fluxes from the polar ionospheres
Authors: Raitt W. J. , Schunk R. W. , Banks P. M.
Published: February 2008

Recent experimental measurements of He+ outward fluxes have been obtained for winter and summer hemispheres. The observed fluxes indicate an average He+ escape flux of 2 × 107 cm−2 s−1 in the winter hemisphere and a factor of 10–20 lower in the summer hemisphere. Earlier theoretical calculations had yielded winter fluxes a factor of 4 lower than the measured values and summer fluxes a further factor of 20 below the winter fluxes. We have attempted to reduce this discrepancy between our earlier theoretical model and the experimental observations by improving our theoretical model in the following ways. The helium photo‐ionization cross sections used are accurate to 10%, the latest solar EUV fluxes measured by the Atmosphere Explorer satellites have been incorporated, and the most recent MSIS model of the neutral atmosphere is contained in the model. A range of conditions covering solar cycle, seasonal, and geomagnetic conditions were studied. The results show a maximum He+ escape flux of 1.4 × 107 cm−2 s−1 for solar maximum, winter, low magnetic activity conditions, which is within the scatter of the measured fluxes. The computed summer He+ escape flux is a factor of 20 lower than the winter value, a result which is in reasonable agreement with the summer experimental observations. Possible reasons for the slight discrepancy between theory and experiment in summer are discussed.
Magnetosonic instability driven by an alpha particle beam in the solar wind
Authors: Revathy P.
Published: February 2008

The instability of magnetosonic waves driven by α particle beams and propagating along the magnetic field of the plasma consisting of electrons, protons, and α particles with anisotropic temperatures has been analyzed. The electromagnetic dispersion relation with k⊥ = 0 has been solved numerically for typical solar wind conditions. The growth rate was found to occur near the helium cyclotron frequency.
A theoretical attempt to explain some observed features of the D region
Authors: Chakrabarty D. K. , Chakrabarty Purobi , Witt G.
Published: February 2008

Several rocket measurements in the D region have revealed the presence of a narrow minimum (dip) and a steep gradient (ledge) in the electron density Ne in the 80‐ to 90‐km altitude region and a rapid drop in the hydronium ions H+·(H2O)n from an altitude above about 85 km during quiet daytime conditions. In this report we have tried to reproduce these features using a detailed positive ion chemical scheme. It is found that the parameters which are responsible for the occurrence of a dip and a ledge in the Ne profile are the height distributions of q(O2) and q(NO), the electron‐ion production rates due to the ionization of O2 and NO, respectively, and Hc, the height of intersection of the q(O2) and q(NO) profiles. The dip in Ne is reproducible when a narrow minimum in the NO density profile is present and the level of this minimum lies below the level of Hc. To reproduce the dip in the Ne profile as observed by Aikin et al. (1964), it is found that the NO density at the minimum should be about 105 cm−3. The ledge in Ne is obtained when the level of Hc lies below the level of the minimum in the NO profile. It is also found that the ledge in the Ne profile follows the ledge in the q(O2) profile. For the disappearance of the hydronium ions above about 85 km the rise of temperature above the mesopause is shown as the major factor which slows down the rate of transfer of molecular ions to hydronium ions, and this, coupled with the decreasing trend of total neutral particle density with height, rapidly decreases the lifetime of hydronium ions above this altitude.
The closed model of the Earth's magnetosphere
Authors: Piddington J. H.
Published: February 2008

The existence of large‐scale motions within the earth's magnetosphere and that of a long magnetotail were predicted in 1960 as results of a hypothetical frictional interaction between the solar wind and the geomagnetic field. The boundary layer model of this interaction involves the flow of magnetosheath plasma in a magnetospheric boundary layer. The flow is across magnetic field lines, and so the layer must be polarized, with a space charge field nearly balancing the induction field
. The space charge tends to discharge through the ionosphere, thus providing some magnetic and related activity as well as the Lorentz frictional force. This closed magnetosphere model has been largely neglected in favor of the reconnection model but is now strongly supported by observational results and their interpretation as follows. (1) The evidence for the reconnection model, increasing activity with a southward interplanetary field and invasion of the polar caps by flare particles, is shown to be equally compatible with the closed field model. (2) The magnetotail grows by the motions of closed flux tubes through the dawn and dusk meridians, a process which depends on the nature of the boundary between magnetosphere and magnetosheath plasmas and perhaps also on the solar wind dynamo. Both of these features depend, in turn, on the direction of the interplanetary magnetic field. (3) Closed field lines entering the tail may be stretched to a few tens of earth radii and then contract back to the corotating magnetosphere. Others enter the long tail and are stretched to hundreds of earth radii and so are pervious to fast solar particles. (4) A new model of the magnetospheric substorm involves the entry of closed field lines into the tail and their rapid return to the corotating magnetosphere. The return is due, first, to the release of their trapped plasma as it becomes electrically polarized and, second, to mounting magnetic and plasma stresses in the inflated magnetotail.
Carbon monoxide mixing ratio in the mesosphere derived from ground‐based microwave measurements
Authors: Goldsmith P. F. , Litvak M. M. , Plambeck R. L. , Williams D. R. W.
Published: February 2008

High‐resolution ground‐based measurements have been made of the J = 0 → 1 and the J = 1 → 2 rotational transitions of carbon monoxide in the earth’s atmosphere. These transitions, which occur at frequencies near 115 and 230 GHz, were observed in absorption against the solar continuum. The two absorption profiles have been used to derive the CO mixing ratio as a function of altitude between 50 and 80 km in the atmosphere.
Particle dynamics in the plasma sheet
Authors: Wagner J. S. , Kan J. R. , Akasofu S.‐I.
Published: February 2008

Trajectories of charged particles in the trail region of the earth’s magnetosphere are studied numerically using a model magnetic field. It is shown that both trapped and untrapped trajectories can be categorized into three groups using two dimensionless parameters. One of the parameters is the ratio of the x and z components of the model magnetic field. The other is the ratio of the plasma sheet thickness to the particle gyroradius in the midplane. Previous trajectory studies are incorporated into our classification scheme which resolves a number of apparent contradictory conclusions among them. The untrapped particles are analyzed in terms of the cross‐tail displacement, the displacement time, the scattering of the final pitch angle, and the coefficient of reflection off the plasma sheet. The results are used to predict the upper limit on particle energization during one neutral sheet interaction.
An equilibrium model of plasmaspheric composition and density
Authors: Chiu Y. T. , Luhmann J. G. , Ching B. K. , Boucher D. J.
Published: February 2008

We have constructed a model of plasmaspheric composition and density in the region bounded by the 500‐km altitude level and by the dipole field line L = 5. We first discuss the collisionless kinetic theory model of quasi‐neutral plasma distributions along a dipole field line under the gravitation field, the ambipolar diffusion electric field and the inhomogeneous magnetic field. A simpler fluid‐equation model of the plasma distribution under the influence of the above force fields is shown to be able to incorporate effects of plasmasphere thermal structure. With O+, H+, and He+ densities at 500 km as input boundary values and with a phenomenological thermal structure of the plasmasphere abstracted from Ogo 5, Prognoz, and S3‐3 satellite data, we show that the plasma density distributions in the fluid‐equation model are consistent with the densities derived from in situ satellite measurements and from whistler observations, both in the topside ionosphere and in the outer plasmasphere.
Field‐aligned currents, convection electric fields, and ULF‐ELF waves in the cusp
Authors: Saflekos N. A. , Potemra T. A. , Kintner P. M. , Green J. Lauer
Published: February 2008

Nearly simultaneous observations from the Triad and Hawkeye spacecraft at low altitudes over the south polar cap show that in and near the polar cusp there exist several relationships between field‐aligned currents, convection electric fields, ULF‐ELF magnetic noise, broad‐band electrostatic noise and interplanetary magnetic fields. The most important relationships are: (1) The region 1 permanent field‐aligned currents are located inside the region of sunward (eastward) convection and therefore on closed field‐lines. (2) The polar cusp field‐aligned currents are located inside the regions of antisunward (westward) convection. (3) The observations are consistent with a two‐cell convection pattern symmetric in one case and asymmetric in another with stronger convection on the dusk side. This is explainable by models which require interconnection of interplanetary magnetic field lines with those of the geomagnetic field. Furthermore, this region of maximum merging shifts to the morning side in the southern hemisphere for away sectors of the interplanetary magnetic field. (4) In and near the polar cusp, field‐aligned currents and convection velocity gradients (separated only by two hours in MLT) nearly coincide with regions of ULF‐ELF magnetic noise and broadband electrostatic waves. We offer this as evidence consistent with the idea that field‐aligned currents with fine structure are responsible for the presence of ELF noise in the polar cusp.
Diffusion of monoenergetic photoelectron fluxes in the plasmasphere
Authors: Lejeune G.
Published: February 2008

This paper extends the study of Lejeune and Wormser (1976) on the diffusion of photoelectrons in the plasmasphere by considering the diffusion of monoenergetic boundary electron fluxes. Plasmasphere transmission and retrodiffusion coefficients are obtained for monoenergetic electron fluxes and are fitted by formulas which allow the calculation of the transmission and reflection of any boundary photoelectron flux. Knowledge of the diffusion of photoelectron fluxes in the plasmasphere is necessary to understand the coupling of the ionosphere and the plasmasphere. It is also necessary to study the thermal structure of the plasmasphere and to interpret the results of electron release experiments.
Nighttime increases in total electron content observed with the ATS 6 radio beacon
Authors: Davies K. , Anderson D. N. , Paul A. K. , Degenhardt W. , Hartmann G. K. , Leitinger R.
Published: February 2008

Nocturnal winter increases in total electron content are observed at Bozeman, Boulder, and Dallas with the ATS 6 radio beacon. Results of this investigation suggest that the increases take place mainly in the ionosphere. Changes in plasmaspheric contents are much smaller. The downward motion of the F2 layer and the east‐to‐west movement of the nocturnal maximum (NM) suggest the presence of an electric field. A westward electric field will move plasma from higher L shells to lower L shells with smaller volumes and thus increase the plasma pressure, the result being an enhanced flow of plasma from plasmasphere to ionosphere. The total flux required to produce the NM is of the order of 1×1013 m−2 s−1.
Measurement of the north‐south asymmetry in the solar proton albedo neutron flux
Authors: Ifedili S. O.
Published: February 2008

The solar proton albedo neutron flux in the range 10−2–107 eV measured by a neutron detector on board the Ogo 6 satellite was examined for north‐south asymmetry. For the solar proton event of December 19, 1969, the S/N ratio of the solar proton albedo neutron rate at geomagnetic latitude λ > 70° was 1.61±0.27 during the event, while for the November 2, 1969, event at 40° < λ <45° and altitudes ranging from 700 km to 800 km the solar proton albedo neutron rate was 0.40±0.10 count/s in the north and 0.00±0.10 count/s in the south. During the solar proton event of December 18, 1969, the N/S ratio of the solar proton albedo neutron rate at λ > 70° was 1.00±0.26. The results are consistent with the expected N‐S asymmetry in the solar proton flux. An interplanetary proton anisotropy with the interplanetary magnetic field polarity away from the sun corresponded to larger fluxes of solar proton albedo neutrons at the north polar cap than at the south, while an interplanetary proton anisotropy with the interplanetary magnetic field polarity toward the sun corresponded to larger fluxes of solar proton albedo neutrons at the south polar cap than at the north. This evidence favors the direct access of solar protons to the earth's polar caps via the merged interplanetary and geomagnetic field lines.
Unsteady magnetic merging in one dimension
Authors: Cheng Andrew F.
Published: February 2008

The magnetohydrodynamics of unsteady magnetic merging flows in one space dimension are investigated by finite difference methods. The evolutions of the x magnetic field, y velocity, z electric current, pressure, and density are followed as functions of y and t in the presence of finite conductivity. For an initial state consisting of a neutral sheet current layer in static mechanical equilibrium the computations indicate significant compressible MHD evolution in times comparable to the Alfven crossing time. Rapid inflow begins behind large‐amplitude magnetosonic expansion waves radiated from the current layer. For the magnetic Reynolds numbers studied (Rm up to 100), this one‐dimensional evolution occurs rapidly compared with the growth time of the tearing mode instability and may have an important effect on its development. The magnitude of the current density near the neutral sheet was found to decrease steadily with time in all cases with static initial states in mechanical equilibrium. This may pose a difficulty for models which invoke an enhancement of the current density there in order to excite plasma micro‐instabilities that yield a large anomalous resistivity and rapid magnetic energy release. The lack of significant current density enhancement can also be seen in previous two‐dimensional simulations which do not invoke large externally imposed inflow velocities. Only with externally imposed stresses do current density enhancements appear in the present one‐dimensional simulations. The effects of varying Rm and the plasma adiabatic index, as well as the initial conditions, are investigated.
Search for worldwide solar eclipse perturbations of geomagnetic activity 1906–1976: Lunar modulation of Ci revisited
Authors: Meisel David D. , Blazejewski Anthony F.
Published: February 2008

Solar eclipses occur with periodicities of 29.53 days, 6 months, 8.85 years, and 18.6 years. Since these are nearly commensurate with known solar‐terrestrial event repetition cycles (27.3 days, semiannual, and 11 years), searches for possible solar eclipse effects in daily geophysical data using standard autocorrelation techniques are likely to have serious side‐band interference problems. Therefore a survey of the geomagnetic Ci index for the years 1906–1976 (164 eclipses) was performed by using a modified version of the well‐known t test for the difference of two means to define eclipse departure probability (Pd). Eclipse epoch Ci changes are shown to satisfy a simple probabilistic model composed of two events—one due to the eclipse E and another due to a ‘background’ of zero ecliptic latitude Ci fluctuations ZL such that the mean values of the departure probabilities are 〈Pd(E|ZL)〉 = 0.5±0.1, 〈Pd(E)〉 = 0.3 ± 0.1, and 〈Pd(ZL|E)〉 = (1.8±0.2)〈Pd(ZL)〉. It is also shown that the derived 〈Pd(E)〉 value is consistent with a simple statistical occulation model and the Pd derived from geomagnetic effects observed during one total solar eclipse. The large and persistent conditional probabilities, however, appear to require some sort of geomagnetic reverberation effect between the earth and moon.
Direct evaluation of the radial diffusion coefficient near L=6 due to electric field fluctuations
Authors: Holzworth R. H. , Mozer F. S.
Published: February 2008

The radial diffusion coefficient for radiation belt particles near L=6 has been calculated from the measured electric field fluctuations. Simultaneous balloon flights in August 1974 from six auroral zone sites ranging 180° in magnetic longitude produced the electric field data. The large scale slowly varying ionospheric electric fields from these flights have been mapped to the equator during the quiet magnetic conditions of this campaign. These mapped equatorial electric fields were then Fourier transformed in space and time to produce power spectra of the first two terms of the global azimuthal electric field. From these power spectra the radial diffusion coefficient has been calculated.
Simultaneous quiet time observations of energetic radiation belt protons and helium ions: the equatorial α/p ratio near 1 MeV
Authors: Fritz Theodore A. , Spjeldvik Walther N.
Published: February 2008

Simultaneous monitoring of energetic helium ions and protons in the earth's radiation belts has been carried out with the satellite Explorer 45 in the immediate vicinity of the equatorial plane. Protons were measured from < 1 keV to 1.6 MeV in differential energy detector channels and above 3.3 MeV in a quasi‐integral channel responsive up to 22 MeV; helium ions were monitored in three differential energy passbands in the range 910 keV to 3.15 MeV and in a differential channel with double passband: 590–910 keV and 2.0–3.99 MeV. The measurements permit determination of the equatorial helium ion to proton flux ratios (α/p) both at equal energy per nucleon and equal energy per particle in the heart of the radiation belts on L shells below the spacecraft apogee at L ∼ 5.25. The flux ratios are found to vary significantly with energy and location in the radiation belts. At equal energy per nucleon a range of variability for α/p from 10−4 to well above 10−3 is found, and at equal energy per ion the corresponding variability is from 10−3 to above 10. The latter findings emphasize the relative importance of the very energetic helium ions in the overall radiation belt ion populations. Comparison is made with theoretical equatorial predictions of the α/p ratios that were made by Cornwall (1972) based on the radial diffusion, charge exchange, and Coulomb interactions; the observational findings support many of the theoretical results.
Electron impact on atmospheric gases, 3. Spatial yield spectra for N2
Authors: Jackman C.H. , Green A.E.S.
Published: February 2008

Spatial yield spectra have been calculated for electron energy degradation into molecular nitrogen gas using a Monte Carlo method for 0.1‐ to 5.0‐keV incident electrons. These spectra contain the spatial yield information about the electron degradation process and can be employed to calculate a ‘yield’ for any inelastic state at any position in the medium. Because of the spectrum's useful nature and simple characteristics, the three‐variable spatial yield spectrum U(E, z, E0) is analytically represented as well. This analytic form can then be easily applied to atmospheric and laboratory problems dealing with energetic electron degradation.