Magnetosphere

This work builds on and extends our previous effort (Tsyganenko et al., 2003) to develop a dynamical model of the storm-time geomagnetic field in the inner magnetosphere, using space magnetometer data taken during 37 major events in 1996-2000 and concurrent observations of the solar wind and interplanetary magnetic field (IMF). The essence of the approach is to derive from the data the temporal variation of all major current systems contributing to the distant geomagnetic field during the entire storm cycle, using a simple model of their growth and decay. Each principal source of the external magnetic field (magnetopause, cross-tail current sheet, axisymmetric and partial ring currents, and Birkeland current systems) is driven by a separate variable, calculated as a time integral of a combination of geoeffective parameters N l V b B s g , where N, V, and B s are the solar wind density, speed, and the magnitude of the southward component of the IMF, respectively. In this approach we assume that each source has its individual relaxation timescale and residual quiet-time strength, and its partial contribution to the total field depends on the entire history of the external driving of the magnetosphere during a storm. In addition, the magnitudes of the principal field sources were assumed to saturate during extremely large storms with abnormally strong external driving. All the parameters of the model field sources, including their magnitudes, geometrical characteristics, solar wind/IMF driving functions, decay timescales, and saturation thresholds, were treated as free variables, and their values were derived from the data. As an independent consistency test, we calculated the expected Dst variation on the basis of the model output at Earth's surface and compared it with the actual observed Dst. A good agreement (cumulative correlation coefficient R = 0.92) was found, in spite of the fact that $90% of the spacecraft data used in the fitting were taken at synchronous orbit and beyond, while only 3.7% of those data came from distances 2.5 R 4 R E. The obtained results demonstrate the possibility to develop a truly dynamical model of the magnetic field, based on magnetospheric and interplanetary data and allowing one to reproduce and forecast the entire process of a geomagnetic storm, as it unfolds in time and space.

A new model of the quiet-time, near-Earth magnetic field has been derived using a comprehensive approach, which includes not only POGO and Magsat satellite data, but also data from the Ørsted and CHAMP satellites. The resulting model shows great improvement over its predecessors in terms of completeness of sources, time span and noise reduction in parameters. With its well separated fields and extended time domain of 1960 to mid-2002, the model is able to detect the known sequence of geomagnetic jerks within this frame and gives evidence for an event of interest around 1997. Because all sources are coestimated in a comprehensive approach, intriguing north-south features typically filtered out with other methods are being discovered in the lithospheric representation of the model, such as the S Atlantic spreading ridge and Andean subduction zone lineations. In addition, this lithospheric field exhibits significantly less noise than previous models as a result of improved data selection. The F-region currents, through which the satellites pass, are now treated as lying within meridional planes, as opposed to being purely radial. Results are consistent with those found previously for Magsat, but an analysis at Ørsted altitude shows exciting evidence that the meridional currents associated with the equatorial electrojet likely close beneath the satellite. Besides the model, a new analysis technique has been developed to infer the portion of a model parameter state resolved by a particular data subset. This has proven very useful in diagnosing the cause of peculiar artefacts in the Magsat vector data, which seem to suggest the presence of a small misalignment bias in the vector magnetometer.

When high-frequency wave turbulence is present, low-frequency micropulsations can strongly modulate the high-frequency wave amplitudes, leading to finite amplitude pulsations in the loss rate of energetic electrons from the magnetosphere (micropulsation amplitude is small). An extremely idealized model suggests that the precipitation modulation depends exponentially on the micropulsation amplitude, when the micropulsation period is less than the electron precipitation lifetime. 1279

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MES-SENGER) spacecraft, launched on August 3, 2004, is nearing the halfway point on its voyage to become the first probe to orbit the planet Mercury. The mission, spacecraft, and payload are designed to answer six fundamental questions regarding the innermost planet:

It has generally been assumed in the past that the plasmapause is a preferred region for the generation and propagation of electromagnetic ion cyclotron (EMIC) waves in the Earth's magnetosphere. One assumption invoked the overlap of the expanding cold plasmapause with the inner edge of the hot ring current during storm recovery to provide favourable conditions for EMIC instability. The plasmapause was also expected to provide a convenient gradient for guiding the waves from equatorial sources to higher latitudes. The paper commences from a historic perspective and reviews the development of the ideas from the 1960s that relate the source of EMIC waves to the plasmapause. CRRES spacecraft observations of EMIC wave events over L = 3:5-8 and associated plasmapause locations indicate that the plasmapause is a region of wave generation and propagation, with signiÿcant wave power seen in the plasmatrough, but is not necessarily the preferred region. Other results show that wave occurrence predominates in the afternoon and increases with radial distance and a He + slot is seen in the data. These agree with earlier AMPTE-CCE results from Anderson et al. (J. Geophys. Res. 97 (1992) 3075, 3089). New results from CRRES show all wave polarisations (left-hand, linear, and right-hand) are seen within 8 • of the equator whereas linear predominates over 20-30 • latitude. Waves are observed in background plasma densities of 4-300 cm −3 . Wave frequencies above the He + cyclotron frequency are concentrated outside the plasmapause in lower density regions of 2-30 cm −3 .

Recent satellite observations of electrostatic and magnetic noise in the distant magnetotail (Gurnett et al., 1976) can be explained by the excitation of the lower-hybrid-drift instability. In particular, it is shown that (1) existence conditions for the lower-hybrid-drift instability can be met, (2) the observed frequency spectra and polarization are in good agreement with the predictions of linear theory, and (3) the observed amplitudes of fluctuations are consistent with the nonlinear theory of this mode. Moreover, the observation of this instability suggests that the anomalous transport properties associated with these waves, which are important in many laboratory devices, may play a crucial role in the macroscopic evolution of magnetotail processes such as field line merging, tearing instabilities, or 'fireballs.' Paper number 8A0695.

Collisionless shocks at quasi-parallel geometries, i.e., for which the average magnetic field direction upstream of the shock is close to the shock normal, reveal temporally varying quantities, a variety of boundary crossing and kinetic signatures, and magnetic structures, often convecting, of finite extent. These results can be put together by a framework in which the shock can be viewed as an extended region containing three-dimensional Short Large Amplitude Magnetic Structures (SLAMS) which represent individual semi-cycles of the ambient upstream low frequency waves associated with diffuse ions in the ULF foreshock. As SLAMS convect with the flow they grow to large amplitudes and entrain inter-SLAMS regions to form an inhomogeneous downstream state. Their finite transverse extent is probably related to, and interacts with, ion beams, to produce a patchy transition zone which accounts for the variety of spacecraft signatures observed.

C omputers have become indispensable to scientific research. They are essential for collecting and analyzing experimental data, and they have largely replaced pencil and paper as the theorist's main tool. Computers let theorists extend their studies of physical, chemical, and biological systems by solving difficult nonlinear problems in magnetohydrodynamics; atomic, molecular, and nuclear structure; fluid turbulence; shock hydrodynamics; and cosmological structure formation. Beyond such well-established aids to theorists and experimenters, the exponential growth of computer power is now launching the new field of computational science. Multidisciplinary computational teams are beginning to develop large-scale predictive simulations of highly complex technical problems. Large-scale codes have been created to simulate, with unprecedented fidelity, phenomena such as supernova explosions (see figures 1 and 2), inertialconfinement fusion, nuclear explosions (see the box on page 38), asteroid impacts (figure 3), and the effect of space weather on Earth's magnetosphere (figure 4). Computational simulation has the potential to join theory and experiment as a third powerful research methodology. Although, as figures 1-4 show, the new discipline is already yielding important and exciting results, it is also becoming all too clear that much of computational science is still troublingly immature. We point out three distinct challenges that computational science must meet if it is to fulfill its potential and take its place as a fully mature partner of theory and experiment: the performance challenge-producing high-performance computers, the programming challenge-programming for complex computers, and the prediction challenge-developing truly predictive complex application codes. The performance challenge requires that the exponential growth of computer performance continue, yielding ever larger memories and faster processing. The programming challenge involves the writing of codes that can efficiently exploit the capacities of the increasingly complex computers. The prediction challenge is to use all that computing power to provide answers reliable enough to form the basis for important decisions. The performance challenge is being met, at least for the next 10 years. Processor speed continues to increase, and massive parallelization is augmenting that speed, albeit at the cost of increasingly complex computer architectures. Massively parallel computers with thousands of processors are becoming widely available at relatively low cost, and larger ones are being developed. Much remains to be done to meet the programming challenge. But computer scientists are beginning to develop languages and software tools to facilitate programming for massively parallel computers.

We present first results of the magnetospheric magnetic field modeling, based on large sets of spacecraft data and a high-resolution expansion for the field of equatorial currents. In this approach, the field is expanded into a sum of orthogonal basis functions of different scales, capable to reproduce arbitrary radial and azimuthal variations of the geomagnetic field, including its noon-midnight and dawn-dusk asymmetries. Combined with the existing method to model the global field of Birkeland currents, the new approach offers a natural way to consistently represent the field of both the tail and symmetrical/partial ring currents. The proposed technique is particularly effective in the modeling of the inner magnetosphere, a stumbling block for the first-principle approaches. The new model has been fitted to various subsets of data from Geotail, Polar, Cluster, IMP-8, and GOES-8, GOES-9, GOES-10, and GOES-12 spacecraft, corresponding to different activity levels, solar wind IMF conditions, and storm phases. The obtained maps of the magnetic field reproduce most basic features of the magnetospheric structure, their dependence on the geomagnetic activity and interplanetary conditions, as well as characteristic changes associated with the main and recovery phases of magnetic storms.

A method for determining many new magnetohydrodynamic shock normal expressions is described that uses both magnetic-field and plasma-flow parameters. These shock normal expressions are useful as a check on the usual magnetic coplanarity expression or for cases in which the most reliable data are mixed. For high Alfv,•n Mach numbers, the exact results are well approximated by the simple velocity coplanarity formula. This is illustrated by calculating shock normals for the 1965 bow shock crossing of Pioneer 6. We present a generalization of the method of calculation using magnetic coplanarity for the unit vector normal to a magnetohydrodynamic shock wave [Colburn and Soneft, 1966; Spreiter et al., 1966]. Two approximate methods for shocks in plasmas with high Alfv•n Mach numbers have also been used. These assumed either

A review of periodic and quasiperiodic VLF emissions observed at ground-based stations and in the Earth's magnetosphere is presented. Emissions with periods below 10 s are divided into three main groups : periodic emissions, hisslers and pulsing hiss, while the quasiperiodic emissions with periods above 10 s are divided into two main groups: QPl, which are definitely related to geomagnetic pulsations, and QP2, which are not obviously related to them, based on ground observations. However, it is pointed out that all types of quasiperiodic emissions with periods over 10 s observed onboard satellites show some association with geomagnetic pulsations which suggests that both QPl and QP2 can have similar mechanisms for their generation. Different approaches to the theoretical modelling of periodic and quasiperiodic emissions are discussed.

From the 27th to the 28th January 2009, the Cassini spacecraft remotely acquired combined observations of Saturn's southern aurorae at radio, ultraviolet and infrared wavelengths, while monitoring ion injections in the middle magnetosphere from energetic neutral atoms. Simultaneous measurements included the sampling of a full planetary rotation, a relevant timescale to investigate auroral emissions driven by processes internal to the magnetosphere. In addition, this interval coincidently matched a powerful substorm-like event in the magnetotail, which induced an overall dawnside intensification of the magnetospheric and auroral activity. We comparatively analyze this unique set of measurements to reach a comprehensive view of kronian auroral processes over the investigated timescale. We identify three source regions in atmospheric aurorae, including a main oval associated with the bulk of Saturn Kilometric Radiation (SKR), together with polar and equatorward emissions. These observations reveal the coexistence of corotational and sub-corototational dynamics of emissions associated with the main auroral oval. Precisely, we show that the atmospheric main oval hosts short-lived sub-corotating isolated features together with a bright, longitudinally extended, corotating region locked at the southern SKR phase. We assign the susbtorm-like event to a regular, internally driven, nightside ion injection possibly triggerred by a plasmoid ejection. We also investigate the total auroral energy budget, from the power input to the atmosphere, characterized by precipitating electrons up to 20 keV, to its dissipation through the various radiating processes. Finally, through simulations, we confirm the searchlight nature of the SKR rotational modulation and we show that SKR arcs relate to isolated auroral spots. We characterize which radio sources are visible from the spacecraft with the fraction of visible southern power estimated to a few percent. The resulting findings are discussed in the frame of pending questions as the persistence of a corotating field-aligned current system within a sub-corotating magnetospheric cold plasma, the occurrence of plasmoid activity and the comparison of auroral fluxes radiated at different wavelengths.

The observation that high speed solar wind streams are correlated with outer radiation belt electrons requires a transducer to convert this mechanical energy to hot electrons. We hypothesize that the high latitude cusp is the ideal location for this acceleration region. We support this hypothesis with two arguments: a forward model to show that the cusp can theoretically accelerate electrons

1] The Cluster mission offers a unique opportunity to investigate the origin of the energy-dispersed ion structures frequently observed at 4.5-5 R E altitude in the auroral region. We present a detailed study of the 14 February 2001 northern pass, characterized by the successive observation by three spacecraft of a series of energy-dispersed structures at $72-75°ILAT in a region of poleward convection. Equatorward, the satellites also observed a localized, steady, and intense source of outflowing energetic (3-10 keV) H + and O + ions. These substructures were modeled by launching millions of H + ions from this ionospheric source and following them through time-dependent electric and magnetic fields obtained from a global MHD simulation of this event. Despite the complexity of ion orbits, the simulations showed that a large number of ions returned to the Cluster location, poleward of their source, in a number of adjacent or overlapping energy-latitude substructures with the correct dispersion. The first dispersed echo was unexpectedly generated by ''half-bouncing'' ions that interacted with the current sheet to return to the same hemisphere. The time-shifted observations made by two Cluster (SC1 and SC3) spacecrafts were correctly reproduced. Almost all the ions returning to the spacecraft underwent a $2-5 keV nonadiabatic acceleration at each interaction with the current sheet in a very confined resonant region. This acceleration explains the overall energy increase from one structure to the next. This event confirms the importance of the ionospheric source in populating bouncing ion clusters within the magnetosphere, even at high latitudes. Citation: Bosqued, J. M., M. Ashour-Abdalla, T. Umeda, M. El Alaoui, V. Peroomian, H. U. Frey, A. Marchaudon, and H. Laakso (2009), Cluster observations and numerical modeling of energy-dispersed ionospheric H + ions bouncing at the plasma sheet boundary layer,

Transient penetration of plasma with magnetosheath origin is frequently observed with the hot plasma experiment on board the Viking satellite at auroral latitudes in the dayside magnetosphere. The injected magnetosheath ions exhibit a characteristic pitch angle/energy dispersion pattern, earlier reported for solar wind ions accessing the magnetosphere in the cusp regions. In contrast to the continuous plasma entry in the cusp, the events discussed here show temporal features which suggest a connection to transient processes at or in the vicinity of the magnetospheric boundary. A single event study confirms previously published observations that the injected ions flow essentially tailward with a velocity comparable to the magnetosheath flow and that the energy spectra inferred for the source population resemble magnetosheath spectra. Those ion injection structures, which were resolved by the Viking mass spectrometer, consist of protons. Based on a statistical study, it is found that these events are predominantly observed around 0800 and 1600 MLT, in a region populated both by ring current/plasma sheet particles and by particles whose source is the magnetosheath plasma. Magnetic field line tracing based on the Tsyganenko magnetic field model yields a scatter of the source locations around the mid-latitude region of the magnetospheric boundary. The probability for these events to occur is highest when the interplanetary magnetic field (IMF) is confined to the ecliptic plane. The event occurrence frequency shows a dawn-dusk asymmetry depending on the azimuthal direction of the IMF. The occurrence frequency is independent of the solar wind velocity but increases with increasing solar wind pressure. For radially directed IMF the probability for observing the events is generally higher than for azimuthally directed IMF. The difference is especially pronounced during times when the solar wind pressure is comparatively low. Some of the most prominent events are obviously associated with significant changes in solar wind plasma density. The connection of the events to transient impulsive solar wind/magnetosphere interaction processes, such as transient reconnection (FTE), impulsive plasma transfer, Kelvin Helmholtz instabilities, and solar wind pressure pulses, is discussed. A relation with transient reconnection can be excluded. 1. INTP•O DU CTION It is well established that the subsolar region of the magnetosphere is a site where the shocked solar wind and the magnetosphere strongly and impulsively interact. One believes that these interaction processes drive or at least contribute significantly to the magnetospheric convection system. Furthermore, the frontside magnetopause is considered one of the prime regions for magnetosheath plasma transfer to the magnetospheric boundary layers. The plasma entry may occur in a more or less continuous way, as in the polar cusp regions, or take place associated with impulsive interaction processes. These transient processes are most often discussed in terms of sporadic intermittent reconnection of magnetosheath and magnetospheric flux tubes, as proposed originaJly by Russell and Elphic [1979]. As an alternative explanation, impulsive penetration of magnetosheath plasma filaments with excess momentum has been suggested, where reconnection of flux tubes is at least not the primary process

The progress in the study of ULF waves in the Earth's magnetosphere made between 1987 and 1989 is reviewed. Topics addressed in the review include satellite and ground-based observations of ULF wave spatial structure, ULF wave resonators and waveguides in the magnetosphere and ionosphere, the ionosphere as a 'passive screen' and an 'active source' for MHD disturbances, 'non-linear language' for ULF waves, and their applications.

1] We use a nonstationary generalization of the higher-order structure function technique to investigate statistical properties of the magnetic field fluctuations recorded by MESSENGER spacecraft during its first flyby (01/14/2008) through the near-Mercury space environment, with the emphasis on key boundary regions participating in the solar windmagnetosphere interaction. Our analysis shows, for the first time, that kinetic-scale fluctuations play a significant role in the Mercury's magnetosphere up to the largest resolvable timescale (∼20 s) imposed by the signal nonstationarity, suggesting that turbulence at this planet is largely controlled by finite Larmor radius effects. In particular, we report the presence of a highly turbulent and extended foreshock system filled with packets of ULF oscillations, broad-band intermittent fluctuations in the magnetosheath, ion-kinetic turbulence in the central plasma sheet of Mercury's magnetotail, and kinetic-scale fluctuations in the inner current sheet encountered at the outbound (dawn-side) magnetopause. Overall, our measurements indicate that the Hermean magnetosphere, as well as the surrounding region, are strongly affected by non-MHD effects introduced by finite sizes of cyclotron orbits of the constituting ion species. Physical mechanisms of these effects and their potentially critical impact on the structure and dynamics of Mercury's magnetic field remain to be understood.

A study of the internal structure of the neutral sheet in the geomagnetic tail has been made from data obtained by the NASA-GSFC magnetic-field experiment on the Explorer 34 spacecraft during its tail passage in the first half of 1968. The data used in the analysis are individual measurements of the vector magnetic field at 2.56-sec intervals. The experimental results consist of statistical studies of relevant properties of the magnetic field as a function of field magnitude. The results do not support nearly one-dimensional field models with characteristic lengths for field variation parallel to the neutral sheet much larger than the neutral-sheet width. The principal conclusion from the data points toward consistency with a quasi-periodic (possibly turbulent) structure with a tendency to formation of magnetic loops as one might expect from stability studies. Numerical results obtained using a simple model with a periodic field pattern in the field reversal region are compared with the observed internal structure. The presence of a neutral sheet in the tail of the geomagnetosphere was first established by Ness [1965]. Later, other measurements confirmed the neutral sheet as a permanent large-scale structural element of the geomagnerosphere (see review by Ness [1969]). For instance, Behannon [1968] has shown that the neutral sheet extends well beyond the orbit of the moon. The picture of a plane current sheet separating regions of magnetic field with opposite directions has become useful for the construction of quantitative models for the gross magnetospheric field. (See review by Roederer [1969].) Speiser and Ness [1967] concluded from Imp I data taken at radial distances between 15 and 32 R• that there is an average south-north field component of a strength of 1-4 •, superimposed; this points towards some connection of the geomagnetic field lines through the neutral sheet. In this picture the field is still approximately one-dimensional, in that the zs• dependence dominates. (Solar magnetospheric coordinates are used throughout this paper; the label sm is sometimes omitted.) Such one-dimensional field descriptions are valid if one is interested in the average field • European Space Research Institute (ESRIN) of the EUropean Space Research Organization structure on time scales larger than several minutes. On smaller time scales one finds a more complicated structure, to which we shall refer as the 'internal structure of the neutral sheet.' Evidence for the existence of the internal

The characteristic features of VLF hiss emissions during quiet and disturbed conditions observed at ground stations and on-board satellites are summarized. The increased intensity of the hiss emissions during magnetic storm period is explained by considering the enhanced flux of energetic electrons during magnetic storm period. The generation and propagation mechanism of VLF hiss are also briefly discussed.

This paper deals with the benefits of using a nonlinear model-based approach for controlling magnetically guided therapeutic microrobots in the cardiovascular system. Such robots used for minimally invasive interventions consist of a polymer binded aggregate of nanosized ferromagnetic particles functionalized by drug-conjugated micelles. The proposed modeling addresses wall effects (blood velocity in minor and major vessels' bifurcations, pulsatile blood flow and vessel walls, and effect of robot-to-vessel diameter ratio), wall interactions (contact, van der Waals, electrostatic and steric forces), non-Newtonian behaviour of blood and different driving designs as well. Despite nonlinear and thorough, the resulting model can both be exploited to improve the targeting ability and be controlled in closed-loop using nonlinear control theory tools. In particular, we infer from the model an optimization of both the designs and the reference trajectory to minimize the control efforts. Efficiency and robustness to noise and model parameter's uncertainties are then illustrated through simulations results for a bead pulled robot of radius 250µm in a small artery.

Accurate models of the magnetospheric field during magnetically quiet times are essential for high-resolution mapping of core field dynamics, mantle and ocean induction, crustal fields and ionospheric currents. Satellite data sampled at low-Earth orbit allow for a separate determination of the external contributions from currents in the magnetosphere. We have used Ørsted and CHAMP data from the years 1999-2004 to investigate this field component. In contrast to earlier studies, the field is decomposed here into contributions from sources in the solar-magnetic (SM) frame and those in the geocentric-solar-magnetospheric (GSM) frame. For an observer on the Earth, stable fields in those frames generate different diurnal and annual variations which, in response, induce currents in the subsurface. All of these effects have been modelled here. Our primary findings are: in the GSM frame, there is a dominant constant magnetic field of about 13 nT, pointing due southward. This field component is attributed to the quiet-time tail current system. The interplanetary magnetic field (IMF) contributes to the near-Earth field with 10 per cent of its Bx and about 25 per cent of its By component. For the SM frame, we obtain a constant field of 7.6 nT and a variable part which can be parametrized by the D ST index. The field in SM is attributed to the combined effect of the magnetopause and ring current. A comparison of the external field variations, predicted by our satellite-derived model, with the measurements of five latitudinally distributed ground observatories shows a remarkable agreement.

We present Mars Global Surveyor measurements of bipolar out-of-plane magnetic fields at current sheets in Mars' magnetosphere. These signatures match predictions from simulations and terrestrial observations of collisionless magnetic reconnection, and could similarly indicate differential ion and electron motion and the resulting Hall current systems near magnetic X lines. Thus, these observations may represent passages through or very near reconnection diffusion regions at Mars. Out of 28 events found at 400 km altitude with well-defined current sheet orientations, 26 have magnetic fields consistent with the expected polarities of Hall fields near diffusion regions. For these events, we find an average ratio of Hall field to main field of 0.51 ± 0.13, and an average ratio of normal to main field (reconnection rate) of 0.16 ± 0.09, consistent with terrestrial observations of reconnection. These events do not consistently correlate with the location of crustal fields or with IMF reversals, indicating that magnetic field draping alone (perhaps enhanced by high solar wind dynamic pressure) may generate current sheets capable of reconnection. For some events, we observe field-aligned electrons that may carry parallel currents that close the Hall current loop. Electron distributions around current sheets often indicate magnetic connection to the collisional exosphere. For crossings sunward of the X line, we usually observe an electron flux minimum at the current sheet, consistent with the resulting closed magnetic structure. For crossings antisunward of the X line, we do not observe flux minima, consistent with field lines open downstream. Collisionless reconnection, if common at Mars, could represent a significant atmospheric loss process.

, the Cassini spacecraft performed its Saturn orbit insertion, twice crossing the equatorial plane between the G and F rings. The radio HF receiver observed a peak at the upper-hybrid frequency and weakly banded emissions having well-defined minima at gyroharmonics. We show that through most of the encounter, these emissions do not result from instabilities, but instead are the quasi-thermal noise that can be calculated from the classical theory of plasma fluctuations. The spectroscopy of this noise yields the electron density, the core and the halo temperatures in the range 2.3 < L/R S < 7, À1.2 < z/R S < +0.1. For the first time, we measure the core temperature of the Kronian plasma torus to be about 0.

The phase space density distributions of energetic electrons during two storm periods, including the two storms on 21-23 October 2001 and 4-9 September 2002 selected by Geospace Environment Modeling Inner Magnetosphere/Storms campaign as the radiation belt assessment challenge in 2004 workshop, are presented in this paper. Electron data from the Synchronous Orbit Particle Analysis instrument aboard three Los Alamos National Laboratory geosynchronous satellites as well as the Comprehensive Energetic Particle and Pitch Angle Distribution instrument aboard Polar are used. The Tsyganenko 2001 storm model is chosen for the storm time magnetic field presentation, compared to the best-fitting magnetic model achieved in a previous study. By tracing the temporally evolving radial distributions, we conclude that while the dropout of electron phase space density during storm main phases appears to be energy-independent, the enhancement in recovery phases shows an energy-dependent pattern. The average outwardly decreasing radial gradients of phase space density obtained during the recovery phases of the two storm periods strongly suggest the in situ acceleration is most likely the main source of new energetic electrons, along with a possible contribution from an external source.

Generation of extremely/very low frequency (ELF/VLF) chorus waves in Earth's inner magnetosphere has received increased attention recently because of their significance for radiation belt dynamics. Though past theoretical and numerical models have demonstrated how risingtone chorus elements are produced, falling-tone chorus element generation has yet to be explained. Our new model proposes that weak-amplitude falling-tone chorus elements can be generated by magnetospheric reflection of rising-tone elements. Using ray tracing in a realistic plasma model of the inner magnetosphere, we demonstrate that rising-tone elements originating at the magnetic equator propagate to higher latitudes. Upon reflection there, they propagate to lower Lshells and turn into oblique falling tones of reduced power, frequency, and bandwidth relative to their progenitor rising tones. Our results are in good agreement with comprehensive statistical studies of such waves, notably using magnetic field measurements from THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft. Thus, we conclude that the proposed mechanism can be responsible for the generation of weak-amplitude falling-tone chorus emissions.

The plasmapause position is determined by the innermost equipotential surface which is tangent to the 'Roche-Limit' surface of the ionospheric plasma filling the magnetosphere. When the thermal particles corotate with the Earth's angular velocity, the 'Roche-Limit' equatorial distance is L~ = 5.78 [Rz]. When the angular convectionvelocity is evaluated from the quiet time electric field distribution E3 of McIlwain (1972), Lc depends on the local time. Its minimum value is then L~ : 4-5 near 2400 LT, and the plasmapause shape and position satisfactorily fit the observations. The diffusive equilibrium density distribution appropriated inside the plasmasphere, becomes convectively unstable beyond L --L0, where the collisionless type of model satisfactorily represents the observations. In the intermediate region between the plasmapause and the last closed magnetic field line, continuous ionization fluxes are expected to flow out of the midlatitude ionosphere.

1] The mirror mode is a plasma instability that is typically excited in high-beta plasmas where there is significant pressure anisotropy and is most commonly observed in the magnetosheath. However, it is possible under sufficiently anisotropic conditions to generate the mirror instability inside the magnetosphere, though as yet there are few examples. We present an extended interval of $7 hours of mirror mode activity on 19 March 1998 when the Equator-S spacecraft was traversing the dawnside magnetosphere above the equatorial plane at radial distances of up to L $ 11 and encountered quasi-monochromatic $2-min oscillations in magnetic field and ion number density, temperature, and velocity. The magnetic field strength and number densities were in antiphase, and the plasma and magnetic field pressure perturbations were also in antiphase while the observed total pressure remained constant. This is consistent with excitation via a mirror instability. We are able to discern that the mirror activity must be confined to approximately within ±20°of the equatorial plane through a conjunction with the Geotail spacecraft. We find that the condition for mirror mode waves to grow is strongly met throughout the interval . We believe that this is an excellent high temporal resolution example of the mirror instability exciting ULF waves inside the Earth's magnetosphere. Given the coexistence of toroidal oscillations at almost the same frequency, we suggest coupling between the mirror mode and local standing Alfvén waves. Our observations hence add to the understanding of how energy can be transferred from hot plasma into ULF waves in the magnetosphere before being dissipated in the ionosphere.

This study investigates the role of fluctuations in the solar wind parameters in triggering a magnetic storm and assesses the storm simulation ability of the Space Weather Modeling Framework (SWMF) through a model-data comparison. The event of 22 September 1999 is examined through global magnetosphere simulations, using as input Advanced Composition Explorer (ACE) observations (4 min temporal resolution) along with running averages of this data with windows of 60, 120, and 180 min. It is noted that for this storm the model produces a two phase, fast then slow recovery phase due to a sudden drop in plasma sheet density during the interval of southward interplanetary magnetic field (IMF). Also, smoothing the input with a window larger than 60 min changes the entire magnetosphere and reduces the plasma sheet density and pressure, therefore a less intense storm develops. It is worth mentioning that the main phase (measured from Storm Sudden Commencement to minimum Dst) for this magnetic storm lasted about 3 h. This explains the change in the Dst profile for the 120 and 180 min averaged input. Averaging only IMF B z or solar wind density reveals that all input parameters are important for the development of the storm, but B z is the most significant. Also, comparison with Dst predictions (using the formula of O'Brien and McPherron (2000)) are presented and discussed. For all cases studied, there are no significant differences for Cross Polar Cap Potential (CPCP) in both hemispheres, while the nightside plasma sheet density shows a sharp drop when the input is averaged over 60 min or more. Our results indicate that the magnetosphere responds nonlinearly to the changes in the energy input, suggesting the need for a threshold in the amount of energy transferred to the system in order for the ring current to develop. Further increase of the energy input leads to a saturation limit where the inner magnetosphere response is no longer affected by any additional amount of energy contained within high-frequency oscillations, because the magnetospheric system acts as a low-pass filter on the interplanetary magnetic field.

We present a numerical study of the propagation of VLF whistler waves in the magnetospheric plasma. In this study the plasma is considered to be homogeneous in the direction along the ambient magnetic field and strongly inhomogeneous across it. The goal of this investigation is to understand whistler propagation in magnetic-field-aligned channels (also called ducts) with either enhanced or depleted plasma density. In particular, the paper is focused on situations where the transverse scale size of the duct is comparable to or smaller than the perpendicular wavelength of the whistler. In this case, classical analysis of the whistler dynamics based on the geometrical optic approximation becomes invalid, and numerical solutions of the full wave equations should be performed. Our simulations extend the earlier analysis based on the ray-tracing technique and analytical studies of the very low frequency wave equations. We show that high-density ducts are inherently leaky and this leakage depends on the perpendicular wavelength of the wave inside the duct. We also show that whistler trapping occurs not only at density maxima and minima but also at critical points along a density gradient. This effect can explain whistler guiding along strong transverse plasma density gradients at the plasmapause.

1] We show presence of a mini-magnetosphere above the Reiner Gamma magnetic anomaly (RGA) region in the solar wind, using Lunar Prospector magnetometer (MAG) measurement data. RGA is one of the strongest magnetic anomalies on the Moon. Two magnetic anomalies are found from six MAG datasets at 17-40 km altitudes in the lunar wake or the geomagnetic tail lobe and are well explained by a two-dipole model. When RGA was exposed to the solar wind plasma, two MAG datasets were obtained at 27-29 km altitudes. Although the magnetic anomalies survived against the plasma pressure, they were heavily distorted in comparison with the magnetic field of the two-dipole model. Flow directions and dynamic pressures of the solar wind plasma at those periods indicate that the distortions were caused by forming a mini-magnetosphere over the RGA region in the solar wind. Citation: Kurata, M., H. Tsunakawa, Y. Saito, H. Shibuya, M. Matsushima, and H. Shimizu (2005), Mini-magnetosphere over the Reiner Gamma magnetic anomaly region on the Moon, Geophys. Res. Lett., 32, L24205,

Summary form only given. We will discuss the application of coherent software radio technology to remote sensing of the ionosphere. Using networks of advanced software radio systems it is possible to make observations of the ionosphere with both wide spatial coverage and simultaneous high resolution in space and time. Such observations can be made using a variety of techniques such as active and passive multi-static radar imaging, satellite beacon observations of TEC and scintillation, spectral monitoring, and signal time difference of arrival. Using software radio techniques it is possible to build instrumentation networks which can accomplish these observations using a unified set of hardware and software. While different antennas are often necessary or useful for particular applications the underlying analog and digital hardware systems remain unchanged from application to application. Such multi-role instruments can be highly integrated and can dynamically change their modes of operation and receive antennas precisely relative to a global time reference (e.g. GPS). Networks of such instruments scale rapidly in capability and spatial coverage with increasing number of nodes. The cost of this scaling is primarily in the complexity of control and operations as well as the required computational power needed to analyze data from the software radio array. The Intercepted Signals for Ionospheric Science (ISIS) Array is a coherent software radio network that has recently been deployed. Nodes of this array are installed along the northern United States, primarily in the Northeast and Northwest regions. The ISIS Array is well positioned for observation of the mid-latitude Geospace environment and the plasmasphere boundary layer during active geomagnetic conditions. The array is capable of making coherent observations over a wide range of frequencies with operations focusing on active radar, passive radar, and satellite beacon observations. For coherent scatter radar appl- - ications the array has a field of view that extends over southern Canada. This field of view is well instrumented with complementary data available from the Millstone Hill Incoherent Scatter Radar, GPS total electron content maps, passive optical systems, and the new mid-latitude SuperDARN radars. We will describe the design of the array, the status of its deployment, and give examples of observations from sites in the field. As part of this discussion we will present coherent scatter observations of E-region irregularities made with the array during the Geomagnetic storm of August 3-5, 2010. We will discuss the characteristics of this event and relate them to previous coherent scatter observations. To conclude we will provide an overview of future capabilities and directions for distributed software radio sensor networks that can be used for studies of the Geospace environment.

Abstract[1] The Earth's magnetosphere evolves as an out-of-equilibrium system due to the continuous coupling with the solar wind and the Earth's ionosphere. We test the validity of the symmetries implied in the Fluctuation Theorem for the magnetospheric dynamics by investigating the long-term evolution of the Earth's magnetospheric ring current, as monitored by the geomagnetic Dst index. We find that the symmetries implied by the Fluctuation Theorem are all verified, thus providing a proof of the existence of a steady state far from equilibrium for the Earth's magnetosphere. A possible link between the Dst index and the entropy production rate is also proposed and discussed.

We assess the statistical spatial distribution of plasma in Mercury's magnetosphere from observations of magnetic pressure deficits and plasma characteristics by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. The statistical distributions of proton flux and pressure were derived from 10 months of Fast Imaging Plasma Spectrometer (FIPS) observations obtained during the orbital phase of the MESSENGER mission. The Magnetometer-derived pressure distributions compare favorably with those deduced from the FIPS observations at locations where depressions in the magnetic field associated with the presence of enhanced plasma pressures are discernible in the Magnetometer data. The magnitudes of the magnetic pressure deficit and the plasma pressure agree on average, although the two measures of plasma pressure may deviate for individual events by as much as a factor of~3. The FIPS distributions provide better statistics in regions where the plasma is more tenuous and reveal an enhanced plasma population near the magnetopause flanks resulting from direct entry of magnetosheath plasma into the low-latitude boundary layer of the magnetosphere. The plasma observations also exhibit a pronounced north-south asymmetry on the nightside, with markedly lower fluxes at low altitudes in the northern hemisphere than at higher altitudes in the south on the same field line. This asymmetry is consistent with particle loss to the southern hemisphere surface during bounce motion in Mercury's offset dipole magnetic field. 1. Introduction Magnetometer [Anderson et al., 2007] observations by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft [Solomon et al., 2001] have proven to be one way to characterize the plasma pressure distribution in Mercury's magnetosphere. The diamagnetic character of plasmas requires a correspondence between plasma pressure and a decrease in magnetic pressure, p B = B 2 /2μ 0 , where B is the magnetic field magnitude and μ 0 is the magnetic permeability of free space. A localized plasma pressure is evident by a depression of the magnetic field. Diamagnetic depressions are frequently observed in the MESSENGER Magnetometer (MAG) data within Mercury's magnetosphere and have been used to determine the distribution of enhanced magnetospheric plasma pressures [Korth et al., 2011, 2012]. In this paper, we extend those earlier analyses with plasma observations. The spatial distribution of plasma pressure is important for understanding the interactions among the solar wind, magnetosphere, and planetary surface. Plasma enhancements near the magnetopause indicate where solar wind plasma enters the magnetosphere via magnetic reconnection [Parker, 1957; Petschek, 1964], diffusion [Eastman et al., 1985], and turbulent mixing [Axford, 1964] processes. Magnetic reconnection occurs both at the dayside magnetopause, where interplanetary and planetary magnetic field lines merge and are subsequently swept anti-sunward by the solar wind, and in the magnetotail, where open field lines connected to the northern and southern magnetic poles reconnect pairwise and cycle back toward the dayside [Dungey, 1961]. In the process, solar wind plasma on interplanetary magnetic field lines is introduced to field lines rooted in the planet, via both convection and accelerated flows from dayside reconnection. Because Mercury's internal magnetic field is weak-the dipole moment is 190 nT R M 3 [Anderson et al., 2012] and the KORTH ET AL.

The collisionless electrical conductivity is calculated for the geomagnetic tail from the stochastic orbits in the plasma sheet. The new conductivity formula is important for the stochastic heating of the plasma sheet and modifies the Galeev-Zeleny• formulas for the collisionless reconnection growth rate for geomagnetic substorms. oentroduction •, 4•0 (• •).

The 24-year-old pulsar problem is reconsidered. New results are obtained by replacing the assumption of steady-state discharges near the polar caps by oscillatory discharges, and by creating the neutral-excess pair plasma via inverse-Compton collisions rather than via curvature radiation. As a result, the electrons and positrons which compose the pulsar wind have different bulk velocities and an oscillating space density, and (strong) coherent curvature radiation is implied (without invoking the excitation of instabilities, and contrary to existing proofs of its impossibility). The magnetospheres of young pulsars are likely to have considerable higher-order multipole components, in particular octupole. Radiation transfer through the pulsar magnetosphere results in fan beams whose polarization is dictated by the bottom of the radiation zone, hence, looks like curvature radiation from dipole-like poiar caps. Wind generation depends mainly on the quantity B~ 2 which takes similar values for the ms pulsars; the latter compensate for (somewhat) weaker fields by wider polar caps and smaller curvature radii.

1] We present observations of periodic magnetospheric substorms and corresponding ionospheric disturbances. Since the periodic substorms occur during a stable interplanetary magnetic field, we are able to identify which ionospheric signatures are caused solely by substorms. We find that the low-latitude ionospheric electric field perturbation after substorm onsets is eastward on the dayside and westward on the nightside and that the ground magnetometer northward (H) deviations at middle and low latitudes show an increase (a positive bay) after each substorm onset, no matter whether the magnetometers are located on the dayside or on the nightside. The nightside magnetometer H deviations are closely correlated with the inner magnetospheric magnetic field B z component during the dipolarization process. The Dst index shows a significant increase of 20-40 nT after each substorm onset. We propose that the increase in the magnetometer H field and Dst index in response to substorm onsets is related to the field dipolarization. In this scenario the nightside magnetosphere earthward of the near-Earth neutral line is highly compressed during the dipolarization, and the magnetic flux density within the inner magnetosphere is greatly enhanced, resulting in an increase in the ground magnetometer H component and in Dst.