bluuebunny/crossref_metadata_2025 huggingface dataset:
Iron charge distribution as an identifier of interplanetary coronal mass ejections
Authors: Lepri S. T. , Zurbuchen T. H. , Fisk L. A. , Richardson I. G. , Cane H. V. , Gloeckler G.
Published: January 2004

We present solar wind Fe charge state data measured on the Advanced Composition Explorer (ACE) from early 1998 to the middle of 2000. Average Fe charge states in the solar wind are typically around 9+ to 11+. However, deviations from these average charge states occur, including intervals with a large fraction of Fe≥16+ which are consistently associated with interplanetary coronal mass ejections (ICMEs). By studying the Fe charge state distribution we are able to extract coronal electron temperatures often exceeding 2 × 106 kelvins. We also discuss the temporal trends of these events, indicating the more frequent appearance of periods with high Fe charge states as solar activity increases.
Auroral electron distributions derived from combined UV and X‐ray emissions
Authors: Østgaard N. , Stadsnes J. , Bjordal J. , Germany G. A. , Vondrak R. R. , Parks G. K. , Cummer S. A. , Chenette D. L. , Pronko J. G.
Published: January 2004

The Polar Ionospheric X‐ray Imaging Experiment and the Ultraviolet Imager on board the Polar satellite provide the first simultaneous global scale views of the electron precipitation over a wide range of electron energies. By combining the results from these two remote sensing techniques we have developed a method to derive the electron energy distributions that reproduce the true electron spectra from 1 to 100 keV and that can be used to calculate the energy flux in the energy range from 100 eV to 100 keV. The electron energy spectra obtained by remote sensing techniques in three 5‐min time intervals on July 9 and July 31, 1997, are compared with the spectra measured by low‐altitude satellites in the conjugate hemisphere. In the energy range from 90 eV to 30 keV the derived energy flux is found to be 1.03±0.6 of the measured energy fluxes. The method enables us to present 5‐min time‐averaged global maps of precipitating electron energy fluxes with a spatial resolution of ∼700 km. The study shows that the combination of UV and X‐ray cameras on a polar orbiting spacecraft enables comprehensive monitoring of the global energy deposition from precipitating electrons over the energy range that is most important for magnetosphere‐ionosphere coupling.
Propagation of Z‐mode and whistler‐mode emissions observed by Interball 2 in the nightside auroral region
Authors: Santolík O. , Lefeuvre F. , Parrot M. , Rauch J. L.
Published: January 2004

A case study of VLF (very low frequency) natural emissions propagating at high altitude above the nightside auroral zone is presented. The analysis is based on data of the MEMO experiment on board the Interball 2 spacecraft. In its VLF band the device records waveforms of three magnetic and two electric field components covering a frequency range 1–20 kHz. Several analysis methods are applied in order to obtain the details on the wave propagation and mode structure and to identify possible source regions. We demonstrate that observed band‐limited emission consists of Z‐mode and whistler‐mode waves. Downgoing Z‐mode waves are found just above the lower cutoff at the L=0 frequency. A possible source may be connected with the electron cyclotron resonance mechanism taking place in the nightside sector at altitudes above 21,000 km. Upgoing whistler‐mode waves with upper cutoff at the local plasma frequency are probably generated by upgoing electrons in the auroral region at altitudes lower than the actual satellite position, i.e., below 18,000 km.
Observations and modeling of neutral gas releases from the APEX satellite
Authors: Choueiri E. Y. , Oraevsky V. N. , Dokukin V. S. , Volokitin A. S. , Pulinets S. A. , Ruzhin Y. Y. , Afonin V. V.
Published: January 2004

Results from experiments of neutral xenon gas releases in the ionosphere are presented. The releases were made from the scientific satellite APEX, which had various plasma and field diagnostics. An enhancement of HF wave activity over a broad band (0.1–10 MHz) is shown to occur during releases made in the sunlight at high pitch angles to the magnetic field. No changes of plasma density were detected, but electron temperature measurements indicate electron energy enhancements during the releases. Theoretical calculations based on the conditions of the APEX releases show that charge‐exchange collisions and elastic scattering of the injected Xe neutrals by the ambient plasma can lead to an ion beam instability that may account for the observed wave and electron energy enhancements. The interaction is akin to the critical ionization velocity effect. We calculate that because of the low injection density, this turbulence‐fueled ionization should have a low yield (<1%), which may explain the lack of detectable plasma density enhancement.
Spacecraft potential variations inside the magnetopause during transient events: Geotail observations
Authors: Kim K.‐H. , Cattell C. A. , Lin N. , Fujimoto M. , Wygant J. R. , Johnson M. , Lee D.‐H. , Tsuruda K. , Mukai T.
Published: January 2004

We examine the spacecraft potential (SP) variations near the magnetopause. In the magnetosphere the Geotail satellite often observed transient SP increase accompanied by magnetic field enhancements. This signature (SP increase and magnetic field increase) was also observed inside the magnetopause during the outbound (from the magnetosphere to the magnetosheath) and/or inbound (from the magnetosheath to the magnetosphere) magnetopause crossings. For the interval of the SP increase, the plasma density and temperature were intermediate between those of the magnetosheath and the magnetosphere, and strong enhancements of the field‐aligned bidirectional electron fluxes were observed mainly in the medium energy (∼300–450 eV) range. These observations are consistent with previous studies in the inner part of the low‐latitude boundary layer (LLBL). Thus we suggest that the transient SP increase in the magnetosphere may be a good indicator of the entry into the inner LLBL.
Computational analysis of the near‐Earth magnetospheric current system during two‐phase decay storms
Authors: Liemohn M. W. , Kozyra J. U. , Clauer C. R. , Ridley A. J.
Published: January 2004

Several two‐phase decay magnetic storms are examined using a kinetic transport model to find the spatial and temporal distribution of the perpendicular and field‐aligned currents in the inner magnetosphere. The global morphology of these currents in the calculational domain (inside of geosynchronous orbit) is discussed as a function of storm epoch, obtaining good comparison between the numerically derived features and observed values of stormtime currents in this region. The model results are also consistent with quiet time plasma observations showing an increasing pressure in to L = 3 or 4, including a pressure maximum near midnight for the generation of region 2 Birkeland currents in the proper direction. A detailed analysis of the characteristic features of these currents is also presented and discussed. It is found that most of the ring current (>90%) during the main phase and early recovery phase is partial rather than symmetric, closing mostly (up to 90%) through field‐aligned currents into the ionosphere. Conversely, the quiet time ring current is largely (>60%) symmetric, with most of the asymmetry produced by minor injections of near‐Earth plasma sheet material. In general, the peak asymmetric current (which occurs during the main phase) is 2‐3 times larger than the peak symmetric current (which occurs during the recovery phase) for any particular two‐phase decay event. This is the case for all of the events studied, regardless of storm size, solar wind parameters, or solar cycle. The maximum azimuthal current (integrated over a local time slice) reaches 5 to 20 MA, compared with <2 MA of symmetric current at quiet times.
Prominence eruptions and coronal mass ejections triggered by newly emerging flux
Authors: Lin J. , Forbes T. G. , Isenberg P. A.
Published: January 2004

Using a simple model for the onset of solar eruptions, we investigate how an existing magnetic configuration containing a flux rope evolves in response to new emerging flux. Our results show that the emergence of new flux can cause a loss of ideal MHD equilibrium under certain circumstances, but the circumstances which lead to eruption are much richer and more complicated than one might expect given the simplicity of the model. The model results suggest that the actual circumstances leading to an eruption are sensitive not only to the polarity of the emerging region, but also to several other parameters, such as the strength, distance, and area of the emerging region. It has been suggested by various researchers that the emergence of new flux with an orientation which allows reconnection with the preexisting flux (a process sometimes referred to as tether cutting) will generally lead to destabilization of the coronal or prominence magnetic field. Although our results can replicate such behavior for certain restricted classes of boundary conditions, we find that, in general, there is no simple, universal relation between the orientation of the emerging flux and the likelihood of an eruption.
Theory of type II radio emission from the foreshock of an interplanetary shock
Authors: Knock S. A. , Cairns Iver H. , Robinson P. A. , Kuncic Z.
Published: January 2004

We present an analytical model for type II solar radio bursts and then apply it to an observed type II event. Electron beams are produced in the foreshock of an interplanetary shock via shock drift acceleration. Reflection is treated in the de Hoffman‐Teller frame with efficiencies modeled by a losscone that incorporates the effects of the static cross‐shock potential ϕ. Stochastic growth theory is used to treat electron beam driven Langmuir wave growth in the type II foreshock. Nonlinear wave‐wave interactions are used as the mechanisms for converting Langmuir wave energy into freely propagating radio emission. The electron beams produced in the foreshock have a wide range of speeds and number densities. These electron beams are qualitatively consistent with observations in a type II foreshock as well as earlier theoretical predictions, and observations in Earth's foreshock. Significant levels of Langmuir waves and ƒp and 2ƒp emission are predicted. In particular, the predicted volume emissivities are similar to those predicted for type III bursts. The simple model developed for the source environment of the type II event on August 26, 1998, produces fluxes in reasonable agreement with observation.
Helium ion acceleration and heating by Alfvén/cyclotron fluctuations in the solar wind
Authors: Gary S. Peter , Goldstein Bruce E. , Steinberg John T.
Published: January 2004

The interaction between alpha particles and a given magnetic power spectrum of Alfvén/cyclotron fluctuations at propagation parallel to the background magnetic field Bo is examined in a model of a homogeneous, collisionless, magnetized plasma. Exact solutions of the linear Vlasov dispersion equation and second‐order theory are used to calculate the wave‐particle scattering rates for alpha/proton momentum exchange as well as for proton and alpha heating and anisotropy change. It is well established that alpha velocities are not observed to oscillate when the alpha/proton relative flow speed parallel to Bo matches the phase speed of long‐wavelength Alfvén waves, the “surfing” speed. Second‐order theory predicts that wave‐particle scattering is dominated by the relatively short wavelength, relatively low phase speed Alfvén/cyclotron fluctuations which have a strong cyclotron resonance with the alphas. Thus the theory predicts that at sufficiently high proton β the average alpha/proton speed should be observed to be substantially smaller than the surfing speed associated with long‐wavelength fluctuations.
Mapping Jupiter's outer radiation belt
Authors: Selesnick R. S. , Cohen C. M. S. , Stone E. C.
Published: January 2004

Flux maps of energetic ions in Jupiter's outer radiation belt, calculated with the aid of a model of the current sheet magnetic field, are consistent with a spatial distribution that is uniform along field lines and monotonically decreasing with radial distance. This result is supported by numerical ion trajectory calculations that predict uniform filling of drift shells at high L values. Adiabatic compression by radial transport then provides predictions of radial energy dependence and flux gradients. At lower L values, conservation of the second adiabatic invariant predicts some anisotropy with higher equatorial fluxes.
Multisatellite measurements of relativistic electrons: Global coherence
Authors: Kanekal S. G. , Baker D. N. , Blake J. B.
Published: January 2004

In this paper we report on multisatellite measurements of relativistic electrons (energies of ≳2 MeV) in the outer zone using detectors on board SAMPEX, HEO, GOES, and Polar satellites. These satellites are in distinct orbits around the Earth, ranging from polar low‐Earth to geosynchronous orbits. The data thus comprise a broad sampling of the relativistic electron populations of various pitch angles, local times, and energy range and of time resolutions ranging from tens of minutes to a day. By a quantitative intercomparison of these multisatellite electron measurements collected over a period of 2 years (from 1998 to 1999), we find that the relativistic electron populations exhibit a remarkable degree of coherence throughout the outer zone. The correlation coefficients between fluxes measured by different satellites as a function of lag time and at different L shells, are highest at or very near zero lag. The strong correlation between electron fluxes measured at different altitudes is seen over a range of L shells. This suggests that the magnetospheric processes responsible for electron acceleration and decay in the outer zone may be of a global nature. The highest correlation being at nearly zero lag suggests that either the underlying acceleration mechanisms are largely pitch angle independent or that the isotropization timescales for these electrons are quite short (of the order of half a day at most). Our observations thus provide a valuable constraint on the various theoretical models that have been proposed for the acceleration and decay of the relativistic electron population in the outer zone.
Particle‐in‐cell simulations of three‐dimensional collisionless magnetic reconnection
Authors: Hesse Michael , Kuznetsova Masha , Birn Joachim
Published: January 2004

Three‐dimensional simulations of collisionless magnetic reconnection in a current sheet configuration are presented. The study consists of two parts: a simulation of a current sheet with an initial perturbation and another model run without it. Particular emphasis is on the questions (1) whether magnetic reconnection remains two‐dimensional if it initiates so, and (2) whether reconnection favors a patchy, localized mode over long, extended reconnection regions. Our study suggests that results from 2.5‐dimensional models of reconnection are not substantially altered by including variations in the third dimension. In fact, an initially random patchy reconnection structure appear to self‐organize into a more coherent quasi‐two‐dimensional structure. As in 2.5‐dimensional reconnection studies, the dominant contribution to the dissipation stems from off‐diagonal terms of the electron pressure tensor in our simulations. The dominant term is related to oscillatory electron motions between the regions of newly reconnected magnetic field.
Fast evolving spatial structure of auroral parallel electric fields
Authors: Génot V. , Louarn P. , Mottez F.
Published: January 2004

We use a new nonlinear guiding center particle in cell code to investigate the role of Alfvén waves in the auroral particle acceleration. The propagation of an Alfvén wave in an inhomogeneous auroral plasma, described by a density cavity, is considered. Parallel electric fields are generated on the edges of the cavity, leading to an efficient electron acceleration and to the formation of electron beams. A beam‐plasma instability takes place. It evolves nonlinearly, and small‐scale electrostatic structures are created and propagate at a velocity close to the Alfvén velocity. A first category of these structures could be assimilated to weak double layers, whereas a second may be related to electron phase space holes. This study demonstrates the potential importance of Alfvén waves in the auroral acceleration and the coupling between large‐scale electromagnetic and small‐scale electrostatic phenomena.
Relationships between precipitating auroral zone electrons and lower thermospheric nitric oxide densities: 1998 – 2000
Authors: Baker D. N. , Barth C. A. , Mankoff K. E. , Kanekal S. G. , Bailey S. M. , Mason G. M. , Mazur J. E.
Published: January 2004

Data acquired using the Student Nitric Oxide Explorer (SNOE) spacecraft during the years 1998–2000 are presented for nitric oxide (NO) measured at altitudes between 90 and 170 km. These data are compared with energetic electron fluxes (E>25 keV) measured concurrently using a large‐area microchannel plate sensor system (Low‐Energy Ion Composition Analyzer) (LICA) on board the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) spacecraft. Three geomagnetic storm intervals (in May 1998, September 1998, and October 1998) are examined specifically to determine altitude and latitude variations of NO production as it compares to energetic electron precipitation. A broader statistical analysis is then carried out using daily averages of peak NO densities (at 106 km altitudes) and electron intensities measured by SAMPEX. Northern and Southern Hemisphere data are treated separately within the magnetic latitude bands 60°–70° north and south. We find correlation coefficients of 0.56 (north) and 0.73 (south) for NO density versus SAMPEX electron count rates using two complete years of data. We also use the National Oceanic and Atmospheric Administration (NOAA) “hemispherical power index” to compare with SAMPEX and with SNOE measurements. Correlation coefficients of ∼0.6 are found among all the daily‐averaged quantities, suggesting that perhaps 30–40% of the variance in NO density can be accounted for by the particle measurements used. An analysis and adjustment of NO densities to account for seasonal effects increases the NO correlations with particle intensities to ≳0.7.
Modulation of Jovian and galactic electrons in the heliosphere: 1. Latitudinal transport of a few MeV electrons
Authors: Ferreira S. E. S. , Potgieter M. S. , Burger R. A. , Heber B. , Fichtner H.
Published: January 2004

The heliospheric modulation of galactic and Jovian electrons is studied using a fully three‐dimensional, steady state model based on Parker's transport equation including the Jovian source. The modulation of low‐energy electrons is a handy tool to establish and to construct a suitable diffusion tensor to assure compatibility between model computations and observations from the Ulysses spacecraft. This is because electron modulation responds directly to the energy dependence of the diffusion coefficients below ∼500 MeV in contrast to protons which experience large adiabatic energy losses below this energy. The model is used to study the latitudinal transport of both Jovian and 4–20 MeV galactic electrons by illustrating how the electron intensities are affected at different latitudes when enhancing perpendicular diffusion in the polar direction. In particular, the electron intensity‐time profile along the Ulysses trajectory is calculated for various assumptions for perpendicular diffusion in the polar direction and compared to the 3–10 MeV electron flux observed by Ulysses from launch up to the end of the first out of the ecliptic orbit. Comparison of the model computations and the observations give an indication as to the magnitude of this diffusion coefficient. The relative contributions of the Jovian and galactic electrons to the total electron intensity is shown along the Ulysses trajectory.
Dayside erosion during intervals of tenuous solar wind
Authors: Farrugia Charles J. , Mühlbachler Stefan , Biernat Helfried K. , Torbert Roy B.
Published: January 2004

We present six data examples where we infer erosion of the dayside magnetosphere during intervals of very tenuous solar wind (density < 1 cm−3). The interplanetary observations were made by the Wind spacecraft when the average solar wind dynamic pressure Pdyn and the interplanetary magnetic field (IMF) Bz were in the ranges (0.07, 0.62) nPa and (−7.6, −0.9) nT, respectively. The inner magnetospheric signature of erosion we focus on is a decrease in the strength of the geostationary magnetic field, as monitored by NOAA's GOES spacecraft. We obtain this decrease as a function of IMF Bz by comparing each event with a reference day, May 11, 1999. During the reference day the lowest Pdyn of the set was attained (0.07 nPa), IMF Bz > 0, and the geomagnetic field at geostationary orbit was dipolar. The central point we make is that although compared to the reference day the Pdyn in each event is higher, the strength of the geostationary field is weaker. We interpret this as evidence that the field compression due to Pdyn has been overcome by the field depression due to erosion. Correcting empirically for the compression of the geostationary field due to solar wind dynamic pressure, we find that for the tenuous solar winds we consider the decrease of the geostationary field, ΔBGS, is related to IMF Bz as ΔBGS (nT)= −2.8 + 2.3 Bz (nT).
Full polarimetry measurements of stimulated electromagnetic emissions: First results
Authors: Carozzi T. D. , Thidé B. , Leyser T. B. , Komrakov G. , Frolov V. , Grach S. , Sergeev E.
Published: January 2004

A theory and technique for the measurement of the full state of polarization (SOP) for wideband electromagnetic HF emissions from the ionosphere are introduced. The technique was employed in a recent experiment at the Sura ionospheric HF pumping facility near Nizhniy Novgorod, Russia, to measure the full SOP of stimulated electromagnetic emissions (SEE) in their steady state. Measurements were made for O‐mode polarized pump waves at two different frequencies: one below and one slightly above the fourth electron gyroharmonic frequency. The wideband spectral parameters measured in this experiment include the horizontal intensity, the degree of horizontal circular polarization, the degree of horizontal polarization and the tilt angle of the horizontal polarization ellipse. Evaluation of the data collected demonstrates that the technique can be used for HF polarimetry and that, in particular, such measurements provide useful new diagnostics for SEE. Among the most important results regarding the polarimetry of SEE were low degrees of circular polarization in the frequency range between the peak of the broad upshifted maximum and the pump; some SEE features had degree of circularity and tilt angle values that were consistent with slightly oblique waves indicative of a distributed SEE source region; and the pump was found to have changed from an initial left‐handed polarized state to a right‐handed polarized state during steady state.
Temporal fine structure of nighttime spike events in auroral radio absorption, studied by a wavelet method
Authors: Hargreaves J. K. , Ranta A. , Annan J. D. , Hargreaves J. C.
Published: January 2004

The auroral absorption spike event, occurring generally at the onset of a substorm, is distinguished by its high intensity and short duration. This paper reports the presence of a fine structure within the spike event. Analysis of selected examples using the Morlet wavelet shows that within the 1 – 2 min duration of the spike are significant modulations with periodicities in the bands 15 – 60 s (67 – 16 mHz), and 5 – 10 s (200 – 100 mHz), the former being the stronger. The slower fluctuations can amount to more than 10% of the absorption, and they were observed in every example (seven out of nine) in which the spike was moving poleward. They were absent in the other two cases, when the spike moved equatorward. In the examples studied, the 15 – 60 s absorption pulsations were accompanied by magnetic micropulsations of impulsive type (Pi) having a periodity that was similar or harmonically related. The connection is only close while the spike event is moving. Consideration of the details suggests that both the magnetic and the absorption pulsations are related to the acceleration process at substorm onset, the flux of energetic particles into the auroral zone producing the radio absorption being modulated with, though not by, the geomagnetic field variations. The 5 – 10 s pulsations, which are considerably weaker, appeared in both the absorption and the magnetic records, but in this case with no obvious connection between them.
Tailward electrons at the lobe‐plasma sheet interface detected upon dipolarizations
Authors: Fujimoto M. , Nagai T. , Yokokawa N. , Yamade Y. , Mukai T. , Saito Y. , Kokubun S.
Published: January 2004

We report on highly asymmetric spectra of electrons observed at the lobe‐plasma sheet interface in the near‐Earth (R < 15 RE) magnetotail. The data were obtained as the Geotail spacecraft made the interface crossings when magnetic field dipolarizations were taking place. In the spectra, electrons in the 0.1 keV to a few keV energy range are seen to flow tailward, with their pitch angles highly collimated along the field lines. Energetic ion beams (>10 keV) are occasionally detected flowing earthward counter to the above electrons. The large differences in the bulk flows result in an intense field‐aligned current (FAC) downward into the ionosphere. The estimated vertical thickness of the FAC layer is found to be comparable to the relevant ion inertia length, leading us to propose that the tailward electrons sustain the downward FAC originating from the near‐Earth X line driven by the Hall effects in magnetotail reconnection. Such a FAC structure is indeed shown by a three‐dimensional Hall‐MHD simulation to be located at the high‐latitude edge of the plasma sheet. We also show the currents integrated over the Hall‐FAC layer to be of significant amounts in the context of magnetosphere‐ionosphere coupling.
Are earthward bursty bulk flows convective or field‐aligned?
Authors: Petrukovich A. A. , Baumjohann W. , Nakamura R. , Schödel R. , Mukai T.
Published: January 2004

We use five years of Geotail and AMPTE/IRM measurements in the near‐Earth magnetotail to compute angles between vectors of fast earthward plasma flow and the local magnetic field. In the low‐β parts of the magnetotail, fast flows were found to be nearly field‐aligned with an average angle of ∼20°. In the high‐β plasma sheet the average angle was larger than 45°. The existence of a substantial convective component in the plasma sheet confirms the importance of the bursty bulk flow phenomenon for the magnetotail convection process.
Low‐frequency oscillations and transport processes induced by multiscale transverse structures in the polar wind outflow: A three‐dimensional simulation
Authors: Ganguli Supriya B. , Gavrishchaka Valeriy V.
Published: January 2004

Multiscale transverse structures in the magnetic‐field‐aligned flows have been frequently observed in the auroral region by FAST and Freja satellites. A number of multiscale processes, such as broadband low‐frequency oscillations and various cross‐field transport effects are well correlated with these structures. To study these effects, we have used our three‐dimensional multifluid model with multiscale transverse inhomogeneities in the initial velocity profile. Self‐consistent generation of the low‐frequency mode driven by local transverse gradients in the field‐aligned ion flow and associated transport processes were simulated. Effects of particle interaction with the self‐consistent time‐dependent three‐dimensional wave potential have been modeled using a distribution of test particles. For typical polar wind conditions it has been found that even large‐scale (∼ 50 – 100 km) transverse inhomogeneities in the flow can generate low‐frequency oscillations that lead to significant flow modifications, cross‐field particle diffusion, and other transport effects. It has also been shown that even small‐amplitude (∼ 10 – 20%) short‐scale (∼ 10 km) modulations of the original large‐scale flow profile significantly increases low‐frequency mode generation and associated cross‐field transport, not only at the local spatial scales imposed by the modulations but also on global scales. Note that this wave‐induced cross‐field transport is not included in any of the global numerical models of the ionosphere, ionosphere‐thermosphere, or ionosphere‐polar wind. The simulation results indicate that the wave‐induced cross‐field transport not only affects the ion outflow rates but also leads to a significant broadening of particle phase‐space distribution and tranverse particle diffusion.
Size dependence of the mesospheric dust temperature And its influence on the noctilucent clouds and polar mesosphere summer echo phenomena
Authors: Eidhammer Trude , Havnes Ove
Published: January 2004

The temperature of dust in the Earth's mesosphere, which is determined by collisions with the neutral gas, absorption of radiation from the Sun, the Earth and its own thermal radiation, in general increases with dust size [Grams and Fiocco, 1977]. This may lead to situations where there is a maximum size of the dust rC above which the dust temperature is too high for condensation of water vapor to occur. Dust of this size can still accrete other elements. If they accrete a sufficient amount of elements, with low ionization potential as a surface “contamination,” their photoelectric properties may change. We suggest that this can lead to their charges changing from the “normal” low negative value of pure ice particles to the positive charges which rocket in situ observations have shown to exist. In such cases we will have a situation with small, newly created and negatively charged dust particles coexisting with larger and positively charged dust charges. Agglomeration of dust particles will then be an effective process. We also demonstrate that the changes in the polar surface temperature of the Earth during the polar mesosphere summer echo (PMSE) season can influence the mesospheric dust temperature and by this have a potential effect on the shape of the occurrence rate curve of the PMSE.
Earthward directed CMEs seen in large‐scale coronal magnetic field changes, SOHO LASCO coronagraph and solar wind
Authors: Li Yan , Luhmann Janet G. , Mulligan T. , Hoeksema J. Todd , Arge C. Nick , Plunkett S. P. , St. Cyr O. C.
Published: January 2004

One picture of coronal mass ejection (CME) initiation relates these events to the expansion into space of previously closed coronal magnetic fields, often part of the helmet streamer belt. The work described here makes use of the potential field source surface model based on updated synoptic photospheric field maps to study the large‐scale coronal field changes. We isolate those field lines that change from closed to open configurations (newly opening field lines) by comparing potential field source surface models from adjacent magnetograph observations, wherein the same starting foot points on the photosphere are used. If there are some newly opening field lines between the times of two maps, we assume there was a possibility for CME occurrence(s) between these times. In particular, if there are newly opening field lines near the solar disk center, an earthward directed CME may have been generated. Monitoring the coronal magnetic field behavior can in principle reinforce (or not) days in advance predictions of magnetic storms based on Solar and Heliospheric Observatory (SOHO) Large‐Angle Spectrometric Coronagraph (LASCO) halo CMEs. Moreover, the coronal field over the visible hemisphere contains information about the possible geoeffectiveness of a particular CME because it shows the approximate orientation and location of the active arcades. By comparing halo CMEs with the newly opening field lines, the solar wind measurements from Wind and ACE spacecraft and the Dst index, we show that, like soft X‐ray sigmoids, disappearing filaments, and Extreme ultraviolet Imaging Telescope (EIT) waves on the disk of the Sun, magnetograph observation‐based coronal field models may provide additional information on the likelihood of CME effects at the Earth.
Response of the quiet auroral arc motion to ionospheric convection variations
Authors: Kozlovsky A. , Lakkala T. , Kangas J. , Aikio A.
Published: January 2004

Equatorward motion of quiet auroral arcs was studied together with the F region ionospheric plasma drift observed by the European Incoherent Scatter radar in Tromsø. Variations in the arc velocity lagged behind corresponding variations in the ionospheric convection velocity by 5–9 min. The same result was obtained from comparison of the arc velocity with variations in the eastward component of ground magnetic field. The variations in the arc and plasma drift velocities followed interplanetary magnetic field Bz variations. The observations indicate that the dawn‐dusk electric potential difference arises at the open polar cap magnetic field lines due to the solar wind ‐ magnetosphere interaction and then propagates to the closed magnetotail field lines through the ionosphere.
Electron hole structure and its stability depending on plasma magnetization
Authors: Singh Nagendra , Loo Sin M. , Wells Earl
Published: January 2004

Observations from Polar have revealed that electron hole (e‐hole) structure critically depends on the plasma magnetization determined by the ratio
, where Ωe and Ωpe are the electron cyclotron and plasma frequencies, respectively. Using three‐dimensional parallel particle‐in‐cell) simulations, we have studied the formation and structure of e‐holes by varying
showing that (1) for
e‐holes are highly transitory while for
long‐lasting e‐holes form, especially when
, (2) in the transitory e‐holes for
, the e‐holes are essentially planar with parallel electric fields E‖ ≫ E⊥, the perpendicular field, (3) when
a variety of structures are possible ranging from spheroidal structures with Ex ∼ Ey ∼ E‖ to a planar one with Ex ∼ Ey ≪ E‖, where Ex and Ey are the x and y components of the perpendicular field E⊥. It is also possible that Ex ≪ Ey ∼ E‖ or Ey ≪ Ex ∼ E‖. We find that e‐holes with long transverse structures undergo a perpendicular modulation, which eventually breaks the long structures into fragments of e‐holes. The fragments are seen to further decay by emitting lower hybrid (LH) waves. A linear model of these instabilities is developed showing an e‐hole is an effective radiator of plasma waves. An e‐hole with long transverse structure is effective in radiating high‐frequency whistler waves which have long perpendicular wavelengths. When such waves are radiated out, the remnant structure is transversely modulated and has relatively short scale length. On the other hand, the fragments with the short perpendicular scale lengths are effective in radiating the LH waves. These findings from the simulations are compared with findings from the data from Polar [Franz et al., 2000].
Dynamic model of the magnetosphere: Case study for January 9–12, 1997
Authors: Alexeev I. I. , Kalegaev V. V. , Belenkaya E. S. , Bobrovnikov S. Y. , Feldstein Ya. I. , Gromova L. I.
Published: January 2004

The dynamics of the magnetospheric current systems are studied in the course of the specific magnetospheric disturbance on January 9–12, 1997, caused by the interaction of the Earth's magnetosphere with a dense solar wind plasma cloud. To estimate the contribution of the different sources of the magnetospheric magnetic field to the disturbance ground measured, a dynamic paraboloid model of the magnetosphere is used. The model input parameters are defined by the solar wind density and velocity, by the strength and direction of the interplanetary magnetic field, and by the auroral AL index. The total energy of the ring current particles is calculated from the energy balance equation, where the injection function is determined by the value of the solar wind electric field. New analytical relations describing the dynamics of the different magnetospheric magnetic field sources dependent on the model input parameters are obtained. The analysis of the magnetic disturbances during the January 9–12, 1997, event shows that in the course of the main phase of the magnetic storm the contribution of the ring current, the currents on the magnetopause, and the currents in the magnetotail are approximately equal to each other by an order of magnitude. Nevertheless, in some periods one of the current systems becomes dominant. For example, an intense Dst positive enhancement (up to +50 nT) in the course of the magnetic storm recovery phase in the first hours on January 11, 1997, is associated with a significant increase of the currents on the magnetopause, while the ring current and the magnetotail current remain at a quiet level. A comparison of the calculated Dst variation with measurements indicates good agreement. The root mean square deviation is ∼ 8.7 nT in the course of the storm.
Quick ion injection and acceleration at quasi‐parallel shocks
Authors: Sugiyama T. , Fujimoto M. , Mukai T.
Published: January 2004

Particle acceleration processes at quasi‐parallel shocks have been widely discussed; however, the very initial injection from thermal to suprathermal energies is still controversial. Here we show that a nonlinear wave‐particle interaction at quasi‐parallel shocks results in quick injection and quick further acceleration of ions to nonthermal (NT) energies. Instead of an ensemble of small‐amplitude random waves, a large‐amplitude, monochromatic, upstream wave is set to propagate into the shock transition layer and test‐particle orbits are deterministically calculated. First, we superimpose a purely right‐handed, circularly polarized, monochromatic upstream wave whose amplitude is as large as those observed in the upstream of Earth's bow shock. The conversion of the wave at the shock front brings about quick acceleration of selected ions into NT energies. Although the observed orbit is similar to previous results, we propose that the process can be better understood in terms of a nonlinear wave‐particle interaction in which the phase angle between an ion's velocity and the upstream wave field is playing a key role. Next, we add a left‐handed, circularly polarized wave of the same wavelength to make up an elliptically/linearly polarized upstream wave, which is also observed in the bow shock upstream. Some of the NT injected ions that are leaving the shock front are seen to be quickly scattered back to the shock by the wave. These ions experience repeated acceleration within the limited time available for acceleration in the upstream of Earth's bow shock. The resultant energy spectrum has the exponential slope extending up to ∼ 70E0 (where E0 is the upstream bulk flow energy), with the characteristic energy ∼ 7E0. We have compared this energy spectrum with self‐consistent hybrid simulation results and with Geotail satellite observations in the upstream region to find reasonably good agreement.
Mesoscale ionospheric electrodynamics observed with the MIRACLE network: 1. Analysis of a pseudobreakup spiral
Authors: Amm O. , Janhunen P. , Kauristie K. , Opgenoorth H. J. , Pulkkinen T. I. , Viljanen A.
Published: January 2004

A short‐lived auroral spiral is observed on February 3, 1999, around 2204 UT, using the Multi‐Instrument Array for Ionosphere‐Magnetosphere Coupling Studies (MIRACLE) network of ground‐based instruments in Fennoscandia, which consists of magnetometers, coherent scatter radars, and all‐sky cameras. Four minutes later, after this spiral has subsided, the auroral bulge of a fully developed substorm that has set on earlier over Russia intrudes into the MIRACLE field of view from the east. Hence the auroral spiral precedes the substorm spatially (i.e., it is located westward of the substorm bulge) rather than temporarily. Since this spiral is associated with a localized and short‐lived substorm‐type auroral development, we interpret it as a “pseudobreakup spiral,” which is subsequently covered by the intruding auroral bulge, during the decaying phase of the pseudobreakup activity. In contrast to growth phase pseudobreakups that occur temporally before a full breakup, this pseudobreakup is observed spatially ahead (westward) of an already evolving substorm bulge. Our instantaneous spatial analysis of the distributions of ionospheric electrodynamic parameters associated with this spiral shows that all key features are similar to the ionospheric electrodynamics of the westward traveling surge: sharp decrease of conductance toward the west, from Hall conductance values up to 30 S in the spiral to less than 2 S west of it, a cluster of upward field‐aligned currents (FACs) in the spiral area with magnitudes up to 5 A km−2, and anticlockwise spiraling horizontal currents around it. The upward FACs, diverging at least 100 kA of current in total, are fed to a large extent by a “pseudosubstorm electrojet” carried by westward flowing Hall currents. No signs of local current closure by downward FACs from the immediate vicinity of the spiral are found. Our results are inconsistent with the earlier conjecture that insufficient ionospheric conductance would prevent the pseudobreakup to evolve to a full breakup. Since the solar wind data do not provide clear evidence for being a driver of the pseudobreakup‐breakup sequence, the driver has to be an internal magnetospheric one.
Auroral forms and the field‐aligned current structure associated with field line resonances
Authors: Milan Stephen E. , Sato Natsuo , Ejiri Masaki , Moen Jøran
Published: January 2004

We show evidence to suggest that some auroral forms may be related to the field‐aligned current structure associated with magnetohydrodynamic wave activity, specifically field line resonances. These auroras appear as a series of azimuthally spaced east‐west elongated arcs, inclined slightly from north to south. Modeling shows that this “braided” appearance reflects the locations of upward field‐aligned current driven by the wave. Moreover, more complicated auroral structures can be produced if several harmonically related waves occur together. We model a situation in which two harmonic components are present at the latitude of resonance and demonstrate the striking similarity between the resulting field‐aligned current structures and actual auroral observations.
Pi2 pulsations observed with the Polar satellite and ground stations: Coupling of trapped and propagating fast mode waves to a midlatitude field line resonance
Authors: Keiling A. , Wygant J. R. , Cattell C. , Kim K.‐H. , Russell C. T. , Milling D. K. , Temerin M. , Mozer F. S. , Kletzing C. A.
Published: January 2004

Simultaneous measurements from the Polar satellite and several ground stations of two substorm‐related Pi2 pulsation events (separated by ∼6 min) provide evidence for radially trapped and propagating fast mode waves and a coupled field line resonance (FLR). The Pi2 pulsations were observed at five ground stations located between 2130 and 2330 magnetic local time (MLT) ranging from L=1.83 to 3.75, which showed nearly identical waveforms in the H component with a frequency of ∼20 mHz. Five additional ground stations located between L=4.48 and ∼15 (on similar meridians) recorded weaker less‐correlated signals. The pulsations were also detected both simultaneously and with a time delay of ∼38 s at two low‐latitude stations (L=1.17 and 1.23) on the dayside at ∼1030 and ∼0612 MLT, respectively, indicating the global extend of the pulsations. The nightside ground data showed an amplitude maximum and a phase reversal in the H component between L=3.4 and 3.75. During the oscillations the Polar satellite moved (on the same meridian as the ground stations in the nightside) from 14° to 10° magnetic latitude and from L=4.1 to 3.7. Electric and magnetic field measurements also showed two Pi2 pulsation events (∼20 mHz) in both the compressional (Bz and Ey) and transverse (By and Ex) mode components with waveforms almost identical to the ground signals. Whereas the first Pi2 had a standing wave structure in the compressional mode, the second Pi2 was a propagating wave. Both Pi2s had standing wave signatures in the transverse mode. The amplitude of the compressional magnetic field component (Bz) was ∼40% of that of the azimuthal component (By). Although the two Pi2 events showed equal amplitudes in the H component of ground data, Polar recorded much larger oscillations in the azimuthal magnetic field component (By) of the first Pi2 event; the fast mode amplitude (Bz) was nearly unchanged for both Pi2s. This suggests that Polar was at or near a localized FLR excited by the oscillations of the fast mode waves. During the in situ FLR observation, Polar's footpoint was closest to the ground stations which recorded the amplitude maximum and the phase reversal in the H component.
Shock as a black box: 2. Effects of adiabatic deceleration and convection included
Authors: Kallenrode May‐Britt
Published: January 2004

This paper presents an expanded version of a numerical scheme to model the intensity and anisotropy time profiles of energetic particle events associated with interplanetary shocks. The acceleration at the shock is treated as a black box; the subsequent particle propagation is described in a transport model which in addition to the effects of focusing and pitch angle scattering also considers convection with the solar wind and adiabatic deceleration. In addition, the pitch angle transport associated with the passage of energetic particles through the shock is included. Owing to the special description of the shock, corotation is considered too. Results of the model with and without solar wind effects are compared. Owing to the continuous supply of fresh particles from the shock, the influence of solar wind effects is always smaller than that in the case of a simple solar injection for the same set of parameter values. Depending on the radial development of the shock efficiency and the location of the observer relative to the nose of the shock, at 1 AU the effects of adiabatic deceleration and convection are important only at energies below a few MeV. Solar wind effects always show a stronger influence on profiles observed at the shock's eastern flank than those close to the central meridian or on the western flank. Owing to the inclusion of adiabatic deceleration, particle profiles at different energies are coupled: the assumption of a rigidity dependent radial development of the shock's acceleration efficiency, that is, a steepening of the injection spectrum, is required to reproduce the observed energy dependence of intensity time profiles.
An ionospheric convection signature of antiparallel reconnection
Authors: Coleman Iain J. , Chisham Gareth , Pinnock Mike , Freeman Mervyn P.
Published: January 2004

This paper sets out a critical test of the antiparallel merging hypothesis. For the conflicting theories of antiparallel and subsolar reconnection, we model the location of reconnection regions on the dayside magnetopause, their ionospheric footprints, and the resulting ionospheric convection patterns. We show that antiparallel reconnection, under particular seasonal and solar wind conditions, gives rise to a distinctive ionospheric convection signature. Specifically, around midwinter with a quasi‐steady solar wind and IMF Bz < 0 and |By| ∼ |Bz|, we predict equatorward flow in the noon sector with poleward flow either side of noon if the antiparallel merging hypothesis is correct. In contrast, we predict poleward flow in the noon sector in midwinter under these solar wind conditions if the subsolar reconnection hypothesis is correct and in other seasons under both hypotheses. We go on to present radar and spacecraft data for an interval which satisfies the above seasonal and solar wind criteria, demonstrating that the convection signature of antiparallel merging is present. This is not consistent with the subsolar merging hypothesis.