bluuebunny/crossref_metadata_2025 huggingface dataset:
Quenching rate coefficients for O+(2P) derived from middle ultraviolet airglow
Authors: Stephan A. W. , Meier R. R. , Dymond K. F. , Budzien S. A. , McCoy R. P.
Published: May 2003

O+(2P) is produced in the sunlit thermosphere primarily by photoionization of atomic oxygen. Thermospheric atomic oxygen concentrations can be inferred from measurements of airglow produced near 732.0 nm by the transition of this excited state to the 2D state and at 247.0 nm by the transition to the 4S ground state. The accuracy of these concentrations depends on the accuracy of the important chemical reaction rates used in the airglow model, including quenching of O+(2P). We obtain coefficients for the quenching of O+(2P) by O and N2 by modeling rocket and satellite limb measurements of thermospheric middle ultraviolet (MUV) airglow at 247.0 nm. We derive a reaction rate for N2 of 1.8 × 10−10 cm3 s−1, which is lower than the value obtained by other airglow studies but in agreement with laboratory measurements. We obtain a best fit value for the O reaction rate of 5.0 × 10−11 cm3 s−1, with an upper limit of 8.4 × 10−11 cm3 s−1. The value of the O reaction rate determined by fits to 172 altitude profiles of the 247.0 nm emission shows a strong correlation with the magnitude of the excitation g factor. However, the airglow profile above 260 km favors the upper limit we have identified.
Comparison of the variations of solar indices, interplanetary plasma parameters, and cosmic ray neutron monitor intensities during 1991–2001
Authors: Kane R. P.
Published: May 2003

For the 11‐year interval 1991–2001, the monthly values of three solar indices, interplanetary plasma density N, wind speed V, and total magnetic field B, and cosmic ray neutron monitor intensities at six locations were subjected to spectral analysis. Solar indices showed similar spectra between themselves and so did the cosmic rays between themselves, but the periodicities of solar indices (∼12, 20, 40 months) were diferent from the periodicities of cosmic rays (∼17, 24, 60 months), while interplanetary N, V had ∼13, 17, 28 months, and B had ∼17 and 40 months. Thus solar periodicities do not invariably pervade into the interplanetary space or affect the cosmic rays. On the other hand, interplanetary plasma parameters and cosmic rays develop their own periodicities, unlike each other and unlike solar indices. During two intervals, each of 132 daily values, 11 October 1997–19 February 1998 (Event II) and 20 February–1 July 1998 (Event III), a spectral analysis of the daily values of solar indices showed a strong 27‐day signal, but it was seen only in interplanetary N. Cosmic rays did not show the 27‐day signal. Instead, significant signals were seen in cosmic rays at ∼13.5 and 20 days, seen in solar indices also but much smaller than the 27‐day signal.
Ionospheric electron heating, optical emissions, and striations induced by powerful HF radio waves at high latitudes: Aspect angle dependence
Authors: Rietveld M. T. , Kosch M. J. , Blagoveshchenskaya N. F. , Kornienko V. A. , Leyser T. B. , Yeoman T. K.
Published: May 2003

In recent years, large electron temperature increases of 300% (3000 K above background) caused by powerful HF‐radio wave injection have been observed during nighttime using the EISCAT incoherent scatter radar near Tromsø in northern Norway. In a case study we examine the spatial structure of the modified region. The electron heating is accompanied by ion heating of about 100 degrees and magnetic field‐aligned measurements show ion outflows increasing with height up to 300 m s−1 at 582 km. The electron density decreases by up to 20%. When the radar antenna was scanned between three elevations from near field‐aligned to vertical, the strongest heating effects were always obtained in the field‐aligned position. When the HF‐pump beam was scanned between the same three positions, the heating was still almost always strongest in the field‐aligned direction. Simultaneous images of the 630 nm O(1D) line in the radio‐induced aurora showed that the enhancement caused by the HF radio waves also remained localized near the field‐aligned position. Coherent HF radar backscatter also appeared strongest when the pump beam was pointed field‐aligned. These results are similar to some Langmuir turbulence phenomena which also show a strong preference for excitation by HF rays launched in the field‐aligned direction. The correlation of the position of largest temperature enhancement with the position of the radio‐induced aurora suggests that a common mechanism, upper‐hybrid wave turbulence, is responsible for both effects. Why the strongest heating effects occur for HF rays directed along the magnetic field is still unclear, but self‐focusing on field‐aligned striations is a candidate mechanism, and possibly ionospheric tilts may be important.
Plasma instabilities in meteor trails: Linear theory
Authors: Oppenheim Meers M. , Dyrud Lars P. , Ray Licia
Published: May 2003

Ablation of micrometeoroids between 70 and 130 km altitude in the atmosphere creates plasma columns with densities exceeding the ambient ionospheric electron density by many orders of magnitude. Density gradients at the edges of these trails can create ambipolar electric fields with amplitudes in excess of 100 mV/m. These fields combine with diamagnetic drifts to drive electrons at speeds exceeding 2 km/s. The fields and gradients also initiate Farley‐Buneman and gradient‐drift instabilities. These create field‐aligned plasma density irregularities which evolve into turbulent structures detectable by radars with a large power‐aperture product, such as those found at Jicamarca, Arecibo, and Kwajalein. This paper presents a theory of meteor trail instabilities using both fluid and kinetic methods. In particular, it discusses the origin of the driving electric field, the resulting electron drifts, and the linear plasma instabilities of meteor trails. It shows that though the ambipolar electric field changes amplitude and even direction as a function of altitude, the electrons always drift in the positive ∇n × direction, where n is the density and B the geomagnetic field. The linear stability analysis predicts that instabilities develop within a limited range of altitudes with the following observational consequences: (1) nonspecular meteor trail echoes will be field‐aligned; (2) nonspecular echoes will return from a limited range of altitudes compared with the range over which the head echo reflection indicates the presence of plasma columns; and (3) anomalous cross‐field diffusion will occur only within this limited altitude range with consequences for calculating diffusion rates and temperatures with both specular and nonspecular radars.
Effects of solar polarity reversals on geoeffective plasma streams
Authors: Baranyi T. , Ludmány A.
Published: May 2003

The present work focuses on the annual/semiannual behavior of those parameters which can be considered to be the most relevant factors from the point of view of geoeffectiveness. These are the interplanetary magnetic field (IMF) components, Bz and By (in both the Geocentric Solar Magnetospheric (GSM) system and Geocentric Solar Ecliptic (GSE) system), the bulk speed of the plasma, and the number of hours spent by the Earth in domains of either positive or negative GSM By. In all cases, monthly mean values were used. As a criterion of geoeffectiveness, we adopted the values Kp > 3. The consecutive solar dipole cycles were separately studied, and definite differences were found between the annual variations of the mean values. When the solar dipole is opposite to the terrestrial one, the mean Bz does not exhibit the Russell‐McPherron effect in the GSM system because there are strong inverse annual variations in the GSE system. However, the Russell‐McPherron effect can be detected in the occurrence of the negative and positive GSM By values. The case is opposite in those years when the solar and terrestrial dipoles are parallel: the Russell‐McPherron effect is detectable in the opposite annual variations of the mean GSM Bz but not in the occurrence of GSM By values. The mean bulk speed of geoeffective events also shows a dipole cycle dependence in its average value, and it shows a semiannual character in the parallel years.
Bounce‐averaged stability of compressional modes in geotail flux tubes
Authors: Crabtree C. , Horton W. , Wong H. V. , Van Dam J. W.
Published: May 2003

The stability of low‐frequency drift magnetosonic waves in the nightside magnetosphere between the outer ring current and the distant neutral line is investigated. As low‐frequency Pi2 oscillations are seen before, during, and after substorm onset, these compressional waves are important for understanding the connection between the two substorm onset mechanisms of (1) the near geosynchronous orbit (NGO) mechanism and (2) the near‐Earth neutral line (NENL) mechanism. It is found that there are two different regions of parameter space where drift‐compressional modes can be unstable: (1) when pressure gradients become sufficiently steep to reverse the magnetic‐guiding center drift and (2) when the temperature gradient is in the opposite direction to the density gradient. Nonlocal bounce‐averaged eigenmode equations are solved with a simple analytic model of the magnetospheric magnetic field and with the Tsyganenko and Stern [1996] magnetic field model. Resulting growth rates, frequencies, and eigenmode structures are reported.
Geotail observations of magnetic flux ropes in the plasma sheet
Authors: Slavin J. A. , Lepping R. P. , Gjerloev J. , Fairfield D. H. , Hesse M. , Owen C. J. , Moldwin M. B. , Nagai T. , Ieda A. , Mukai T.
Published: May 2003

Examination of Geotail measurements in the near‐tail (X > −30 RE) has revealed the presence of small flux ropes in the plasma sheet. A total of 73 flux rope events were identified in the Geotail magnetic field measurements between November 1998 and April 1999. This corresponds to an estimated occurrence frequency of ∼1 flux rope per 5 hours of central plasma sheet observing time. All of the flux ropes were embedded within high‐speed plasma sheet flows with 35 directed Earthward, 〈Vx〉 = 431 km/s, and 38 moving tailward, 〈Vx〉 = −451 km/s. We refer to these two populations as “BBF‐type” and “plasmoid‐type” flux ropes. The flux ropes were usually several tens of seconds in duration, and the two types were readily distinguished by the sense of their quasisinusoidal ΔBz perturbations, i.e., ∓ for the “BBF” events and ± for the “plasmoid” events. Most typically, a flux rope was observed to closely follow the onset of a high‐speed flow within ∼1–2 min. Application of the Lepping‐Burlaga constant‐α flux rope model (i.e., J = αB) to these events showed that approximately 60% of each class could be acceptably described as cylindrical, force‐free flux ropes. The modeling results yielded mean flux rope diameters and core field intensities of 1.4 RE and 20 nT and 4.4 RE and 14 nT for the BBF and plasmoid‐type events, respectively. The inclinations of the flux ropes were small relative to the GSM X–Y plane, but a wide range of azimuthal orientations were determined within that plane. The frequent presence of these flux ropes in the plasma sheet is interpreted as strong evidence for multiple reconnection X‐lines (MRX) in the near‐tail. Hence, our results suggest that reconnection in the near‐tail may closely resemble that at the dayside magnetopause where MRX reconnection has been hypothesized to be responsible for the generation of flux transfer events.
A possible way of understanding the differential motion of minor ions in the solar wind
Authors: Tu C.‐Y. , Wang L.‐H. , Marsch E.
Published: May 2003

Measurements with Solar and Heliospheric Observatory (SOHO)/Charge, Element, and Isotope Analysis System (CELIAS) in high‐speed solar wind show that some minor ions such as O6+ have a relatively high drift velocity; however, other ions such as Fe9+ tend to lag behind oxygen by a few tens of km/s [Hefti et al., 1998]. This subtle observational feature has not yet been understood. A possible way, based on the quasi‐linear theory of cyclotron resonance, of understanding this phenomenon is presented in this paper. The charge per mass of the ion O6+ and Fe9+ are different, a fact which results in different features of the ion‐cyclotron resonance with waves. In plasma with protons, drifting alpha particles, and electrons, the dispersion relation of cyclotron waves has two branches. The oxygen ions tend to resonate with the inward propagating waves of the left‐hand‐polarized (LHP) first branch and the outward propagating waves of the LHP second branch. These resonances may together lead to a velocity distribution with a central velocity higher than the proton (solar wind) bulk velocity by about 50 km/s at 1 AU. The Fe9+ ions tend to resonate with both the inward and outward propagating waves of the first branch and may thus form a velocity distribution with a central velocity very near the proton bulk velocity. These analytical results are shown to be supported by numerical results from a two‐dimensional simulation based on the quasi‐linear diffusion equation. The limitations of the present analysis and further work, which should be done to support the ideas proposed here, are also discussed.
Nonideal high‐β magnetohydrodynamic Kelvin‐Helmholtz instability driven by the shear in the ion diamagnetic drift velocity at the subsolar magnetopause
Authors: Miura Akira
Published: May 2003

A nonideal magnetohydrodynamic (MHD) Kelvin‐Helmholtz (K‐H) instability peculiar to a high‐β plasma with a nonuniform pressure is studied for the magnetosheath field due north at the subsolar magnetopause, where the ideal MHD K‐H instability driven by the shear in the E × B drift velocity is not operative. This instability is driven by the shear in the ion diamagnetic drift velocity, which is a nonideal MHD drift in a high‐β plasma and is a macroscopic effect not visible at the guiding center level. The two‐dimensional stability (k · B0 = 0) of a model subsolar magnetopause is investigated by solving the eigenmode equation for a polygonal ion diamagnetic drift velocity profile with the density ratio across the magnetopause as a parameter. Near the subsolar magnetopause the fastest growing wave or vortex propagates duskward with a phase velocity from 8 km/s to 14 km/s, and the normalized growth rate decreases with an increase in the ratio of the magnetosheath density to the magnetospheric density. The wavelength and period of the fastest growing mode increases with the density ratio. For realistic parameters near the subsolar magnetopause the wave period becomes 750 s to 2000 s and the wavelength becomes 11000 km to 16000 km. The present K‐H instability (“diamagnetically driven K‐H instability”) may cause a plasma transport across the subsolar magnetopause, since the plasma motion is decoupled from that of the magnetic field owing to nonideal MHD. We discuss a possible dawn‐dusk asymmetry (caused by the ion diamagnetic drift velocity at the magnetopause) of the K‐H instability when the present instability is extended to the dayside magnetopause off the noon meridian, where the tailward E × B drift is no longer negligible. The vortex created by the present instability near the subsolar magnetopause has the same rotational sense as that created by the E × B shear driven K‐H instability within the dusk flank boundary but has the opposite rotational sense to that created by the E × B shear driven K‐H instability within the dawn flank boundary.
Nitric oxide production in collisions of hot O(3P) atoms with N2
Authors: Balakrishnan N. , Dalgarno A.
Published: May 2003

Energetic oxygen atoms play a central role in the heat and energy balance of the terrestrial thermosphere. The reaction between hot O(3P) atoms and N2 has been suggested as a source of shuttle glow in low‐Earth orbits due to the formation of nitric oxide. We report cross sections and rate coefficients for the production of nitric oxide in the reaction between hot O(3P) atoms and N2 and show that vibrational excitation of N2 significantly enhances the reaction rate coefficients. Results are found to be in agreement with shock‐tube experiments as well as with crossed molecular beam data.
MHD tomography using interplanetary scintillation measurement
Authors: Hayashi Keiji , Kojima Masayoshi , Tokumaru Munetoshi , Fujiki Ken'ichi
Published: May 2003

The MHD tomography analysis, an advanced version of the computer‐assisted tomography (CAT) analysis for interplanetary scintillation (IPS) observational data, is presented. When combined with a MHD simulation, the CAT analysis can reconstruct the MHD‐based three‐dimensional solar wind structure within 1 AU from the IPS line‐of‐sight integrated velocity data. At the same time, the MHD code can simulate the actual conditions in the heliosphere beyond 1 AU by utilizing the results of the MHD tomography analysis and extrapolate to r ≥ 1 AU. The present MHD tomography aims to reconstruct the global structure of corotating solar wind, under the assumption that the global solar wind does not vary significantly in time during one Carrington rotation. The reconstructed three‐dimensional solar wind variables including interplanetary magnetic field (IMF) are compared with the in situ measurement data made at the Ulysses spacecraft and nearby Earth, and good correlations are obtained. We anticipate that the combination of MHD simulation and the IPS tomography will enhance solar wind research and space weather prediction algorithms.
Three‐dimensional modeling of Earth's bow shock: Shock shape as a function of Alfvén Mach number
Authors: Chapman J. F. , Cairns Iver H.
Published: May 2003

Earth's bow shock changes its three‐dimensional (3‐D) location in response to changes in the solar wind ram pressure Pram, Alfvén Mach number MA, magnetic field orientation, fast mode Mach number Mms, and sonic Mach number MS. Using shock locations from global 3‐D ideal MHD simulations [Cairns and Lyon, 1995], empirical models are derived for the 3‐D shape and location of Earth's bow shock in the near‐Earth regime as a function of solar wind conditions. Multiple simulations with different MA and Pram but two orientations of the interplanetary magnetic field BIMF are analyzed: θIMF = 45° and 90° with respect to the solar wind direction vsw. Models for the (paraboloid) flaring parameter bs as a function of MA, azimuthal angle ϕ, and θIMF = 45° or 90°, show bs decreasing with MA, corresponding to the shock becoming blunter and less swept back (with a larger cross section), as expected. Together with models for the shock's standoff distance (which increases with decreasing MA) the models for bs(MA, ϕ) predict the shock's 3‐D location. Variations of bs with ϕ represent eccentricities in the shock's cross section (i.e., a departure from circularity), with the shock extending further perpendicular to vms (the fast mode speed) than parallel, as MA → 1. An additional effect is observed in which the shock shape is “skewed” for θIMF = 45° (but not for θIMF = 90°) in the plane containing BIMF and vsw. These latter two effects are consistent with the fast mode velocity varying with propagation direction relative to BIMF.
Ion cyclotron instability due to the thermal anisotropy of drifting ion species
Authors: Gomberoff L. , Valdivia J. A.
Published: May 2003

In a recent study of ion cyclotron waves generated by the thermal anisotropy of oxygen ions, it was shown that the heavy ion drift velocity and a large thermal anisotropy of the heavy ions can destabilize proton‐cyclotron waves [Gomberoff and Valdivia, 2003]. Here this study is extended to alpha particles in order to show that a much smaller thermal anisotropy is required to trigger strong proton‐cyclotron waves. It is also shown that under some conditions, the alpha particle branch of the dispersion relation becomes unstable for frequency values beyond the proton gyrofrequency. This instability occurs for very large alpha particle thermal anisotropy and very low β∥α = vth2/vA2, where vth and vA are the thermal and Alfvén velocity, respectively. The maximum growth rate of this branch of the dispersion relation occurs for drift velocities of the alpha particles larger than those that drive the maximum growth rate of the proton‐cyclotron instability. Finally, it is demonstrated that the combined effect of oxygen ions and alpha particles lead to a complex unstable spectrum, and to an enhancement of the proton‐cyclotron instability. This mechanism is like a cascade effect in which low‐frequency ion cyclotron waves can drive unstable high‐frequency ion cyclotron waves through anisotropic heating and acceleration of heavy ions. These results may be relevant to the understanding of the heating process of the fast solar wind in coronal holes.
Accuracy of epicyclic description of dust grain orbits about Saturn
Authors: Mitchell C. J. , Horányi M. , Howard J. E.
Published: May 2003

We investigate the metamorphosis of charged dust grain orbits in a planetary magnetosphere, the so‐called gravito‐electrodynamic problem. Our primary aim is to determine practical limits to the validity of an epicyclic model. We assume an axisymmetric planet with a centered dipole magnetic field aligned with the planetary spin axis, a good approximation for Saturn and a fair approximation for Jupiter. Nonideal forces, such as planetary oblateness, solar radiation pressure, plasma drag, and the effects of time‐dependent charging are neglected. A standard epicyclic expansion is used to calculate the mean motion and the aspect ratio of the epicyclic ellipse. For gravitationally dominated grains the mean motion is accurately given by the standard expression, but for magnetically dominated grains it can differ significantly even for small excursions from the equilibrium orbit. In some cases this finite gyroradius effect can even cause the mean motion to change direction. Previous studies are extended by examining a wide range of charge‐to‐mass ratios, for positively and negatively charged grains in prograde or retrograde equatorial orbits about Saturn, inside and outside of the synchronous radius. The results show that the epicyclic model is reasonably accurate for the majority of physically interesting orbits about Saturn. For grains suffering large radial excursions, however, major topological changes were often seen which defy an epicyclic description.
Radial evolution of solar wind intermittency in the inner heliosphere
Authors: Bruno R. , Carbone V. , Sorriso‐Valvo L. , Bavassano B.
Published: May 2003

We analyzed intermittency in the solar wind, as observed on the ecliptic plane, looking at magnetic field and velocity fluctuations between 0.3 and 1 AU, for both fast and slow wind and for compressive and directional fluctuations. Our analysis focused on the property that probability distribution functions of a fluctuating field affected by intermittency become more and more peaked at smaller and smaller scales. Since the peakedness of a distribution is measured by its flatness factor we studied the behavior of this parameter for different scales to estimate the degree of intermittency of our time series. We confirmed that both magnetic field and velocity fluctuations are rather intermittent and that compressive magnetic fluctuations are generally more intermittent than the corresponding velocity fluctuations. In addition, we observed that compressive fluctuations are always more intermittent than directional fluctuations and that while slow wind intermittency does not depend on the radial distance from the Sun, fast wind intermittency of both magnetic field and velocity fluctuations clearly increases with the heliocentric distance. We propose that the observed radial dependence can be understood if we imagine interplanetary fluctuations made of two main components: one represented by coherent, nonpropagating structures convected by the wind and, the other one made of propagating, stochastic fluctuations, namely Alfvén waves. While the first component tends to increase the intermittency level because of its coherent nature, the second one tends to decrease it because of its stochastic nature. As the wind expands, the Alfvénic contribution is depleted because of turbulent evolution and, consequently, the underlying coherent structures convected by the wind, strengthen further on by stream‐stream dynamical interaction, assume a more important role increasing intermittency, as observed. Obviously, slow wind does not show a similar behavior because Alfvénic fluctuations have a less dominant role than within fast wind and the Alfvénicity of the wind has already been frozen by the time we observe it at 0.3 AU. Finally, our analysis suggests that the most intermittent magnetic fluctuations are distributed along the local interplanetary magnetic field spiral direction while, those relative to wind velocity seem to be located along the radial direction.
Saturation of IMF Bz influence on the position of dayside magnetopause
Authors: Yang Y.‐H. , Chao J. K. , Dmitriev A. V. , Lin C.‐H. , Ober D. M.
Published: May 2003

The dayside magnetopause moves closer to the Earth with increasing southward IMF Bz. Is the response of magnetopause to solar wind parameters, southward IMF Bz, and dynamic pressure Dp linear or nonlinear? GOES observations on 6 April 2000 shows that the magnetopause is still outside of geosynchronous orbit even though the southward IMF Bz is greater than 25 nT and Dp is near 8 nPa. We suggest that the earthward motion of the dayside magnetopause saturates for large southward IMF Bz. Magnetosheath encounters observed by GOES satellites during 1999–2000 are used as a database for selecting a functional form of the saturation effect based on the calculations of the modified magnetopause model of Chao et al. [2002]. To obtain a relationship of the threshold of southward IMF Bz for saturation occurring as a function of Dp, an iteration procedure is used to minimize the false alarm rate (FAR) and maximize the probability of prediction (PoP). The relationship B′z = −8.1 − 12.0 × log (Dp + 1) is obtained where B′z is the threshold of IMF Bz for saturation. This relationship is applied to a modified Chao et al. [2002] model and the new model is compared against magnetosheath encounters observed by the LANL MPA instruments on 31 March 2001.
Deceleration of streaming alpha particles interacting with waves and imbedded rotational discontinuities
Authors: Kaghashvili Edisher K. , Vasquez Bernard J. , Hollweg Joseph V.
Published: May 2003

Alphas (He42+) and other ions in the interplanetary medium show a tendency to stream near or below the local Alfvén speed (VA) relative to the main component of protons. BecauseVAdecreases with increasing distance from the Sun, forces must exist to slow the heavier ions with increasing distance. We have conducted hybrid simulations in a plasma with particle protons and alphas and with a quasineutralizing electron fluid. Simulation runs with other streaming minor ions were also performed. In our simulations, a group of Alfvén waves steepen and generate imbedded rotational discontinuities (RDs) and compressional waves. We examine cases of almost steady waveforms and RDs and ones with evolving waveforms and RDs due to a significantly nonuniform background. When alphas stream with the waves and imbedded RDs faster than the protons, they decelerate more rapidly from higher speeds and heat. We have concluded that alphas do not remain at one streaming speed due to nonlinear Lorentz forces from the wave compressional component and the presence of collisionless dissipation, which dissipates this component so that bulk alpha kinetic energy is ultimately deposited into alpha thermal energy. Imbedded RDs play no significant role in the overall deceleration of alphas. Protons heat similarly to cases without alphas and are slightly accelerated so that the total ion momentum alongB0is nearly conserved. For small streaming speeds (≲0.5 Alfvén speeds), the deceleration rate can be relatively small because the loss of streaming energy competes with the gain in wave kinetic energy required by large‐amplitude Alfvén waves. Less proton and more alpha heating is also found since alphas can resonate with the left‐handed portion of oblique waves. Starting from rest, alphas and protons can develop a small differential flow in which Lorentz and pressure forces become balanced. The simulation behavior of alphas for streaming speeds near the Alfvén speed is fairly consistent with solar wind observations in high‐speed streams. Turbulent Alfvénic fluctuations do have a small compressional component and so might be responsible for the observed deceleration and heating of alphas. Simulations with other streaming minor ions also gave deceleration, suggesting that the behavior of a wide range of solar wind minor ions might be explained by the same processes that affect alphas.
Self‐consistent magnetosphere‐ionosphere coupling: Theoretical studies
Authors: Khazanov G. V. , Liemohn M. W. , Newman T. S. , Fok M.‐C. , Spiro R. W.
Published: May 2003

A theoretical examination of the electrodynamical interaction between the ionosphere and the inner magnetosphere is presented. A self‐consistent ring current (RC) model has been developed that couples the electron and ion magnetospheric dynamics with the calculation of the electric field. Two new features were taken into account in order to close the self‐consistent magnetosphere‐ionosphere coupling loop. First, in addition to the RC ions, we have solved an electron kinetic equation in our model. Second, using the relation of Galand and Richmond [2001], we have calculated the height integrated ionospheric conductances as a function of the precipitated high energy magnetospheric electrons and ions that are produced by our model. To validate the results of our model we simulate the magnetic storm of May 2, 1986, a storm that has been comprehensively studied by Fok et al. [2001], and have compared our results with different theoretical approaches. The self‐consistent inclusion of the hot electrons and their effect on the conductance results in deeper penetration of the magnetospheric electric field. In addition, a slight westward rotation of the potential pattern (compared to previous self‐consistent results) is evident in the inner magnetosphere. These effects change the hot plasma distribution, especially by allowing increased access of plasma sheet ions and electrons to low L shells. These results are consistent with recent observations from the IMAGE satellite.
Ground and satellite observations of nighttime medium‐scale traveling ionospheric disturbance at midlatitude
Authors: Shiokawa K. , Otsuka Y. , Ihara C. , Ogawa T. , Rich F. J.
Published: May 2003

We have investigated a nighttime medium‐scale traveling ionospheric disturbance (MSTID) observed by an airglow imager at Shigaraki (34.9°N, 25.4°MLAT), Japan, on 17 May 2001. The structure was identified in the airglow images of OI (630.0 nm and 777.4 nm) as NW‐SE band structures (horizontal wavelength: 230 km) moving southwestward with a velocity of 50 m/s. Neutral wind velocity was measured simultaneously from the Doppler shift of the 630.0‐nm emission by a Fabry‐Perot interferometer at Shigaraki. From these parameters, we performed model calculations of MSTIDs generated by gravity waves and by an oscillating electric field. We found that for the case of gravity waves, the estimated vertical wavelength was too small to explain the observed amplitudes of airglow intensity. For the case of the electric field, we found that an electric field oscillation of ∼1.2 mV/m was sufficient to reproduce the observed airglow amplitudes. This modeled electric field was comparable to that observed by the DMSP F15 satellite as it passed over Shigaraki during our observing period on 17 May 2001. The DMSP ion drift data show that the oscillation of the polarization electric field correlated with the MSTID structure in the airglow image, suggesting that the polarization electric field plays an important role in the generation of MSTIDs.
Kinetic theory of geomagnetic pulsations: 4. Hybrid gyrokinetic simulation of drift‐bounce resonant excitation of shear Alfvén waves
Authors: Dettrick Sean , Zheng Lin‐jin , Chen Liu
Published: May 2003

A one‐dimensional linear hybrid gyrokinetic‐magnetohydrodynamic δf particle in cell simulation code is developed to study the detailed mechanisms of energetic particle drift‐bounce resonant destabilization of Alfvén modes in the ring‐current region of the magnetosphere. The model plasma is composed of a cold (10–100eV) component which provides inertia plus a tenuous energetic (∼10 keV) “ring‐current” component which provides both resonant destabilization and compressional stabilization of MHD modes. Full kinetic effects such as finite Larmor radii and particle magnetic bounce and precessional drift motions are retained nonperturbatively. A simple finite β dipolar equilibrium model is assumed (β is the ratio between plasma and magnetic pressures). Simulations show excellent agreement with earlier perturbative analyses. Results show that when the energetic ion thermal velocity is super‐Alfvénic, the ions destabilize both odd and even parity shear Alfvén MHD modes via the drift‐bounce resonances. The growth rates of the resulting modes scale linearly with plasma β. The most unstable of these modes are found to be drift‐bounce resonance destabilized modes with odd parity, with wave numbers such that k⟂ρ ≈ 0.5 at the equator (ρ is the energetic ion Larmor radius). The destabilization typically occurs at a critical wave number k⟂ρ ≈ 0.3. When the wave number is close to this critical value and the plasma β is close to the ideal MHD critical value, the mode frequency is determined by the energetic particle dynamics, similar to the energetic particle modes (EPMs) observed in laboratory fusion plasma experiments. When the energetic particles have Alfvénic or sub‐Alfvénic thermal velocity, they contribute to damping of the MHD modes via the bounce resonance.
Double‐adiabatic MHD theory for motion of a thin magnetic filament and possible implications for bursty bulk flows
Authors: Ji Shuo , Wolf Richard A.
Published: May 2003

During fast fluid flows in Earth's magnetotail, the plasma distribution function often takes the form of one beam flowing through another, which raises the question of whether bursty bulk flows can reasonably be represented in terms of single‐fluid magnetohydrodynamics, either in global MHD codes or in thin filament theory. An exact kinetic solution is compared with exact fluid solutions for a simplified case of cold, collisionless particles in a pipe, under conditions where there are counterstreaming beams similar to the ones that often occur in Earth's magnetotail. The results from kinetic theory differ from standard fluid theory but are exactly consistent with Chew‐Goldberger‐Low double‐adiabatic fluid theory. Double‐adiabatic MHD equations are derived for the motion of a thin filament through a medium. An initial simulation is presented of a double‐adiabatic filament that starts out with lower gas pressure than nearby flux tubes. As in earlier calculations for the isotropic case, the near‐equatorial part of the filament moves rapidly earthward. A compressional shock wave forms in the filament near the equatorial plane and propagates earthward. The near‐equatorial region of the filament exhibits characteristics similar to a flow burst, while the behavior far from the equatorial plane resembles that of earthward‐streaming plasma sheet boundary layer. The double‐adiabatic filament becomes firehose unstable after the shock wave reflects from the earthward boundary of the simulation and propagates back into the tail.
Geotail observations of the dayside outer boundary region: Interplanetary magnetic field control and dawn‐dusk asymmetry
Authors: Hasegawa H. , Fujimoto M. , Maezawa K. , Saito Y. , Mukai T.
Published: May 2003

On the basis of Geotail observations, we investigate the ion and electron behavior in the dayside low‐latitude magnetosphere just inside the magnetopause in order to obtain clues for understanding the formation mechanism of the low‐latitude boundary layer (LLBL). The dayside region is classified into several categories according to ion energy spectrum characteristics, electron pitch angle anisotropy, the north‐south polarity of the interplanetary magnetic field (IMF), and the observed locations. An important category is the ion mixing region, which contains dense ions of the solar wind origin and hot magnetospheric ions simultaneously. We define this class as data samples for which both the number density and the ion flux at >10 keV exceed certain threshold values. Our statistics show that the ion mixing region thus automatically identified is encountered far more often when the IMF having a northward component lasts for about 4 hours or more. The ion mixing region under extended northward IMF is almost always accompanied by field‐aligned, bidirectional electrons of a few hundreds eV, which energy is higher than that of typical magnetosheath electrons. The flux of >2 keV electrons, that is, electrons of the magnetospheric origin is significantly reduced in the mixing region as compared to that in the region earthward of the mixing region. These facts suggest that the plasma transport process operating for extended northward IMF periods plays an important role both for heating low‐energy (presumably magnetosheath) electrons in field‐aligned directions and for escape/cooling of the magnetospheric electrons. The mixing region exhibits a clear dawn‐dusk asymmetry in the ion energy spectrum, supporting the idea that the transport/heating process of the entrant solar wind ions is different for different sides of the magnetosphere. On the basis of similarities/differences between these observed signatures and those having been found in the tail‐flanks, relationships among the dayside and tail LLBLs under extended northward IMF are discussed.
Observations of dayside convection reduction leading to substorm onset
Authors: Lyons L. R. , Liu S. , Ruohoniemi J. M. , Solovyev S. I. , Samson J. C.
Published: May 2003

We use SuperDARN radar measurements of ionospheric plasma flow on the dayside to evaluate the extent to which substorm onset is the result of interplanetary magnetic field (IMF) changes that lead to a reduction in the strength of magnetospheric convection. We also use this data to evaluate the timing of such convection changes relative to the time of onset. By using direct observations of convection, we avoid the uncertainties in previous studies of substorm triggering arising from their use of IMF measurements from locations away from the magnetosphere. We first identified 12 well‐defined substorm onsets for which sufficient SuperDARN echo coverage on the dayside was available for our analysis. We find that at least 10 of the onsets were associated with a reduction in the strength of large‐scale convection that is imparted to the magnetosphere from the solar wind. This indicates that the majority of substorms with well‐defined onsets are associated with such a convection reduction. We also find that the convection reduction imparted to the magnetosphere initiates a few minutes prior to substorm onset. This is the same time relative to onset that based on auroral observations, the nightside magnetosphere undergoes a transition to an unstable configuration. This suggests that the convection reduction is responsible for the transition to instability that leads to the substorm expansion phase. Our results are consistent with the idea that under enhanced magnetospheric convection, energy builds up within the nightside magnetosphere and can reach a stable equilibrium where energy losses balance further energy input. If the energy accumulated on the nightside during a period of enhanced convection exceeds that of the equilibrium configuration after a reduction in the strength of convection, the nightside magnetosphere undergoes a transition to instability when the strength of convection is reduced and the excess energy is released as the substorm expansion phase. These results indicate that the question of how this instability arises and develops after a decrease in convection is a critical outstanding question for understanding the substorm expansion phase.
Particle simulations of re‐formation at collisionless perpendicular shocks: Coherent behavior of reflected ions
Authors: Nishimura Kazumi , Matsumoto Hiroshi , Kojima Hirotsugu , Gary S. Peter
Published: May 2003

The properties of reformation in perpendicular collisionless shocks are investigated by means of a one‐dimensional particle‐in‐cell simulation. Reformation is associated with ion reflection at the shock ramp and subsequent ion gyromotion in the upstream region. However, if ions are reflected continuously at the ramp, why does the shock reform intermittently at sufficiently high Mach number? The simulations show that the shock potential changes dramatically through the re‐formation cycle, so that it is this potential variation which leads to the intermittent response of the shock.
Pressure‐pulse interaction with the magnetosphere and ionosphere
Authors: Sibeck D. G. , Trivedi N. B. , Zesta E. , Decker R. B. , Singer H. J. , Szabo A. , Tachihara H. , Watermann J.
Published: May 2003

We reexamine traveling convection vortices (TCVs) seen by the Magnetometer Array for Cusp and Cleft Studies on 9 November 1993. IMP‐8 energetic ion observations confirm that the solar wind pressure variations previously associated with these TCVs were generated by kinetic processes within the Earth's foreshock. As expected during this interval of spiral IMF orientation, fast mode waves launched by the pressure variations first arrived in the equatorial ionosphere near dusk and propagated dawnward. We derive a model for the field‐aligned currents generated by transient compressions of the magnetopause and show that it accounts for the number of TCVs seen in the prenoon ionosphere, their sense of rotation, the latitude at which they occur, and their absence in the postnoon ionosphere.
A new O2 band system: The c1∑u−−b1∑g+ transition in the terrestrial nightglow
Authors: Slanger T. G. , Cosby P. C. , Huestis D. L.
Published: May 2003

A new O2 band system, the c1∑u−‐b1∑g+ transition, has been found in sky spectra of the terrestrial nightglow from the Keck telescopes. The spectral region is 380–550 nm, and emission occurs from highly vibrationally excited levels, exhibiting peak intensities at v = 9 and v = 10 of the c1∑u− state. The spectral lines are relatively sparse, and because of the nature of the transition, they extend to quite high rotational levels in a single Q branch. Population is observed from v = 4 to v = 11 of the c1∑u− state, and the estimated intensity of the entire system is 30 R. A comparison is made between the detectability of the new system and the c1∑u−‐X3∑g+ Herzberg II bands of O2, taking into consideration that the latter are the dominant visible emission in the nightglow of Venus, though only from v′ = 0.
Radial localization of magnetospheric guided poloidal Pc 4‐5 waves
Authors: Denton R. E. , Lessard M. R. , Kistler L. M.
Published: May 2003

The toroidal Alfvén wave, with magnetic field oscillations in the azimuthal direction, exhibits a singularity in the vicinity of the toroidal resonant frequency (field line resonance), so it is not surprising that this wave often exhibits varying frequency as a function of L shell. It is less clear why the poloidal Alfvén wave, with magnetic field oscillations in the radial direction, often exhibits a relatively constant frequency over a range of L shells. So far, the most promising proposal to explain this phenomenon is the theory of Vetoulis and Chen [1994, 1996], who showed that an energetically trapped global poloidal mode can exist in a region where the poloidal Alfvén frequency is lower than the toroidal frequency and where it exhibits a dip (minimum) with respect to L. While this theory is mathematically plausible, it has never been shown that poloidal Alfvén waves actually occur in association with such a dip in poloidal frequency. Here we examine poloidal wave events observed by the AMPTE/IRM spacecraft and calculate the theoretical poloidal frequency as a function of L using the equilibrium parameters obtained from the spacecraft observations. We find that the poloidal Alfvén wave does occur in association with such a dip (or at least a flattening) in poloidal frequency. While Vetoulis and Chen hypothesized that such a dip would occur because of a sharp gradient in plasma pressure, we find that the dip in poloidal frequency may result from the L dependence of the equilibrium density or magnetic field. The observed frequencies are in rough agreement with the theoretical frequencies, though in some cases we must assume that the observed oscillations result from a high harmonic (third or fourth harmonic structure along the magnetic field). We also apply the same analysis to compressional wave events (with oscillations in the direction of the equilibrium magnetic field). Such oscillations may be on the poloidal wave branch or the mirror mode branch. Here also, the observed fluctuations occur in the region of a dip in poloidal frequency. In one case the observed frequency is consistent with the theoretical poloidal frequency, whereas in another case it is not.
SuperDARN observations of the Harang discontinuity during steady magnetospheric convection
Authors: Hughes J. M. , Bristow W. A.
Published: May 2003

We present a study of ionospheric convection patterns observed by the Super Dual Auroral Radar Network (SuperDARN) during two recent steady magnetospheric convection (SMC) events. Our analyses focus on the region near the electrically defined Harang discontinuity (HDE) and indicate, for the first time, that the HDE is often present during SMC events. In comparison with observations made during a typical substorm growth phase, the HDE during the two SMC events studied here is a less pronounced convection feature and often occurs at relatively high geomagnetic latitudes (>70°). In addition the behavior of the HDE during the substorms bounding the SMC events appears to differ from the classic signatures observed during isolated substorms.
Vibrational relaxation of NO(v = 1) by oxygen atoms between 295 and 825 K
Authors: Hwang Eunsook S. , Castle Karen J. , Dodd James A.
Published: May 2003

Vibrational excitation of ground‐state NO through collisions with oxygen atoms produces NO(v = 1) in the lower thermosphere, representing a significant source of atmospheric cooling through the subsequent 5.3‐μm radiative emission. A laser pump‐probe experiment has been used to measure the temperature dependence of the NO(v = 1)‐O vibrational relaxation rate coefficient kO(v = 1) in the 295–825 K range, along with updated measurements of kO(v = 1,2) at room temperature. The experiment employed a continuous wave microwave source to form O atoms, combined with photolysis of a trace amount of added NO2 to produce vibrationally excited NO. Oxygen atoms were detected through two‐photon laser‐induced fluorescence, cross‐calibrated against a normalized O atom signal resulting from photolysis of a known concentration of NO2. No temperature dependence was observed for kO(v = 1) to within the uncertainty in the measurements. The measured room temperature value of kO(v = 1) = (4.2 ± 0.7) × 10−11 cm2 s−1 is 75% larger than the value obtained previously in this laboratory, a significant difference at the 1σ level. The present value is preferred owing to an improved experimental technique. The atmospherically relevant NO(v = 0)‐O vibrational excitation rate coefficient can be derived from measured values of kO(v = 1) through detailed balance. The variable temperature measurements provide key information for aeronomic models of the lower thermospheric energy budget, infrared emission intensities, and neutral constituent densities.