Natalia Yu. Ganushkina

Formation of intense nose structures

We examine one well-observed event on November 3, 1997, when clear signatures of intense nose structures were observed during substorm activity on three subsequent inner magnetosphere crossings by Polar and Interball Auroral probe. Tracing particles numerically in stationary electric (Volland-Stern) and magnetic (T96) field models shows that the inward displacement of the intense nose structure in this case could not be formed only by convection in a time-stationary electric field. We add time varying electric and magnetic fields to the tracing procedure which propagate toward the Earth and represent the dipolarization process at a substorm onset. These results show that particles could be moved into the inner magnetosphere within some tens of minutes, consistent with the observations.

Venus Express observes a new type of shock with pure kinematic relaxation

[1] Collisionless shocks are present in the vicinity of many astrophysical objects such as supernova remnants, space jets, stars and planets immersed in the supersonic flow of stellar winds. Understanding the shock structure is crucial for understanding the processes of the redistribution of the upstream flow energy into accelerated particles and formation of downstream thermalized distribution. We report first observations (by Venus Express) of subcritical shocks that do not fit into the well-established classical structure classification. It is shown that its abnormal structure is due to kinematical collisionless relaxation of downstream ions. The spatial gyrophase mixing leads to formation of a downstream thermalized distribution, instead of various instabilities. This type of subcritical shock with kinematic relaxation has never been discussed before in theoretical models (e.g., C. F. Kennel et al., 1985).

CIR versus CME drivers of the ring current during intense magnetic storms

Ninety intense magnetic storms (minimum Dst value of less than −100 nT) from solar cycle 23 (1996–2005) were simulated using the hot electron and ion drift integrator (HEIDI) model. All 90 storm intervals were run with several electric fields and nightside plasma boundary conditions (five run sets). Storms were classified according to their solar wind driver, including corotating interaction regions (CIRs) and interplanetary coronal mass ejections (ICMEs). Data-model comparisons were made against the observed Dst index (specifically, Dst*) and dayside hot-ion measurements from geosynchronous orbiting spacecraft. It is found that the data-model goodness-of-fit values are different for CIR-driven storms relative to ICME-driven storms. The results are also different for the same storm category for different boundary conditions. None of the CIR-driven events was overpredicted by HEIDI, while the dayside comparisons were comparable for the different drivers. The results imply that the outer magnetosphere is responding differently to the two kinds of solar wind drivers, even though the resulting storm size might be similar. That is, for ICME-driven events, magnetospheric currents inside of geosynchronous orbit dominate the Dst perturbation, while for CIR-driven events, currents outside of this boundary have a systematically larger contribution.

Contribution from different current systems to SYM and ASY midlatitude indices

Using empirical magnetospheric models, we study the relative contribution from different current systems to the SYM and ASY midlatitude indices. It was found that the models can reproduce ground-based midlatitude indices with correlation coefficients between the model and real indices being ∼0.8–0.9 for SYM-H and ∼0.6–0.8 and ∼0.5–0.7 for ASY-H and ASY-D, respectively. The good agreement between the indices computed using magnetospheric models and real ones indicates that purely ionospheric current systems, on average, give modest contribution to these indices. The superposed epoch analysis of the indices computed using the models shows that, nominally, the cross-tail current gives the dominant contribution to SYM-H index during the main phase. However, it should be remembered that the model region 2, partial ring current, and cross-tail current systems are not spatially demarcated (the systems are overlapped in the vicinity of geostationary orbit). For this reason, this result should be taken with a precaution. The relative contribution from symmetric ring current to SYM-H starts to increase a bit prior or just after SYM-H minimum and attains its maximum during recovery phase. The ASY-H and ASY-D indices are controlled by interplay between three current systems which close via the ionosphere. The region 1 FAC gives the largest contribution to ASY-H and ASY-D indices during the main phase, though, region 2 FAC and partial ring current contributions are also prominent. In addition, we discuss the application of these results to resolving the long-debated inconsistencies of the substorm-controlled geomagnetic storm scenario.

Challenges associated with near‐Earth nightside current

Every magnetic field of solar and planetary space environments is associated with a current of differentially flowing charged particles. Electric potential patterns in geospace and near other planets are also closely linked with currents. Close to the Earth, particularly in the near-Earth nightside magnetosphere, several current systems wax and wane during periods of space weather activity. The velocity-dependent drift, energization, and loss processes in this region complicate current system evolution. There is a discrepancy about the magnitude, timing, and location of these currents, however, and this Commentary pitches the case for a concerted community effort to resolve this issue.

Cluster Observations of Non–Time Continuous Magnetosonic Waves

Equatorial magnetosonic waves are normally observed as temporally continuous sets of emissions lasting from minutes to hours. Recent observations, however, have shown that this is not always the case. Using Cluster data, this study identifies two distinct forms of these non-temporally-continuous emissions. The first, referred to as rising tone emissions, are characterised by the systematic onset of wave activity at increasing proton gyroharmonic frequencies. Sets of harmonic emissions (emission elements) are observed to occur periodically in the region ±10∘ off the geomagnetic equator. The sweep rate of these emissions maximises at the geomagnetic equator. In addition, the ellipticity and propagation direction also change systematically as Cluster crosses the geomagnetic equator. It is shown that the observed frequency sweep rate is unlikely to result from the sideband instability related to nonlinear trapping of suprathermal protons in the wave field. The second form of emissions is characterised by the simultaneous onset of activity across a range of harmonic frequencies. These waves are observed at irregular intervals. Their occurrence correlates with changes in the spacecraft potential, a measurement that is used as a proxy for electron density. Thus these waves appear to be trapped within regions of localised enhancement of the electron density.

Drivers of the inner magnetosphere

This paper addresses the role of the electric fields in the inner magnetosphere dynamics by reviewing observations and model results, especially whether the stormtime ring current intensification is generated by large-scale convection alone or together with substorm-associated variations. It is discussed that in addition to the large-scale convection electric field partially generated in the magnetospheric boundary layers via reconnection and viscous interaction, there can exist a mechanism for its generation in the magnetotail via plasma pressure gradients. We review the models for this large-scale convection field. One type of these models describe the electric field by the ionospheric potential pattern associated with the solar wind and IMF behavior and then mapped to the magnetotail along the magnetic field lines. The other adjusts the intensity of the model convection field in the tail to the overall level of magnetic activity. It is concluded that these models describe the system only in an average sense. Observations show that particle transport occurs in flow bursts, and that while ions in the energy range 20-80 keV contribute most to the ring current energy density during the storm main phase, during the recovery phase the contribution from the high-energy ions (above 80keV) becomes dominant. It is argued that during inward particle motion, the final energy and the lowest L-shell reached depend on the intensity of the large-scale convection and smaller-scale substorm-associated electric fields, and that only the addition of the substorm-associated electric fields made it able to produce the observed fluxes of high-energy particles.

Can ring current stabilize magnetotail during steady magnetospheric convection

The present study investigates the role of the ring current in stabilizing the magnetotail during steady magnetospheric convection (SMC) events. We develop a method for estimation of the symmetric ring current intensity from the single spacecraft magnetic field observations. The method is applied to a large number of SMC events identified using three different automatic procedures adopted from the literature. It is found that the symmetric ring current can be weak or strong depending on a particular event. We find a significant fraction of events that have a rather weak symmetric ring current in spite of the strong solar wind driving during the event. These findings imply that the symmetric ring current plays no role in the magnetotail stabilization.

Coupling Processes in the Inner Magnetosphere: Inner Magnetosphere Coupling (IMC) Workshop; Espoo, Finland, 28 July to 1 August 2008

In recent years, satellite measurements (e.g., Combined Release and Radiation Effects Satellite (CRRES); Imager for Magnetopause-to-Aurora Global Exploration (IMAGE); Polar; Highly Elliptical Orbit (HEO); Cluster; Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX); and Time History of Events and Macroscale Interactions During Substorms (THEMIS)) and theoretical and modeling studies have significantly advanced the understanding of the dynamics of various plasma populations in the inner magnetosphere. Observations and modeling have revealed that the dynamics of the inner magnetospheric plasma populations not only depend on solar wind conditions but also are coupled to each other bymeans of the electromagnetic field, currents, and wave-particle interactions. The understanding of coupling processes between the plasmasphere, ring current, radiation belts, magnetic field, and waves was the subject of discussion at the recent Inner Magnetospheric Coupling (IMC) workshop, which brought together more than 50 researchers studying various plasma populations and processes that may influence the inner magnetosphere, as well as the effects of the inner magnetosphere on the ionosphere, atmosphere, and global magnetospheric interactions.

Spacecraft surface charging induced by severe environments at geosynchronous orbit

Severe and extreme surface charging on geosynchronous spacecraft is examined through the analysis of 16 years of data from particles detectors on-board the Los Alamos National Laboratory spacecraft. Analysis shows that high spacecraft frame potentials are correlated with 10 to 50 keV electron fluxes, especially when these fluxes exceed 1 × 108 cm−2 s−1 sr−1. Four criteria have been used to select severe environments: 1) large flux of electrons with energies above 10 keV, 2) large fluxes of electrons with energies below 50 keV and above 200 keV, 3) large flux of electrons with energies below 50 keV and low flux with energies above 200 keV, and 4) long periods of time with a spacecraft potential below - 5 kV. They occur preferentially during either geomagnetic storms or intense isolated substorms, during the declining phase of the solar cycle, during equinox seasons and close to midnight local time. The set of anomalies reported in Choi et al. (2011) is concomitant with a new database constructed from these events. The worst-case environments exceed the spacecraft design guidelines by up to a factor of 10 for energies below 10 keV. They are fitted with triple Maxwellian distributions in order to facilitate their use by spacecraft designers as alternative conditions for the assessment of worst-case surface charging.