Kinetic-Hydrodynamic Models of the Solar Wind Interaction with the Partially Ionized Supersonic Flow of the Local Interstellar Gas: Predictions and Interpretations of the Experimental Data

At present there is no doubt that the local interstellar medium (LISM) is mainly partially ionized hydrogen gas moving with a supersonic flow relative to the solar system. The bulk velocity of this flow is approximately equal ～26 km/s. Although the interaction of the solar wind with the charged component (below plasma component) of the LISM can be described in the framework of hydrodynamic approach, the interaction of H atoms with the plasma component can be correctly described only in the framework of kinetic theory because the mean free path of H atoms in the main process of the resonance charge exchange is comparable with a characteristic length of the problem considered. Results of self-consistent, kinetic-hydrodynamic models are considered in this review paper. First, such the model was constructed by Baranov and Malama (J. Geophys. Res. 98(A9):15,157–15,163, 1993). Up to now it is mainly developed by Moscow group taking into account new experimental data obtained onboard spacecraft studying outer regions of the solar system (Voyager 1 and 2, Pioneer 10 and 11, Hubble Space Telescope, Ulysses, SOHO and so on). Predictions and interpretations of experimental data obtained on the basis of these models are presented. Kinetic models for describing H atom motion were later suggested by Fahr et al. (Astron. Astrophys 298:587–600, 1995) and Lipatov et al. (J. Geophys. Res. 103(A9):20,631–20,642, 1998). However they were not self-consistent and did not incorporate sources to the plasma component. A self-consistent kinetic-hydrodynamic model suggested by Heerikhuisen et al. (J. Geophys. Res. 111:A06110, 2006, Astrophys. J. 655:L53–L56, 2007) was not tested on the results by Baranov and Malama (J. Geophys. Res. 111:A06110, 1993) although it was suggested much later. Besides authors did not describe in details their Monte Carlo method for a solution of the H atom Boltzmann equation and did not inform about an accuracy of this method. Therefore the results of Heerikhuisen et al. (J. Geophys. Res. 111:A06110, 2006) are in open to question and will not be considered in this review paper. That is why below we will mainly consider a progress of the Moscow group on heliospheric modelling endeavours in the kinetic-hydrodynamic approach. Criticism of the models that treat interstellar hydrogen in the heliosphere as several fluids is given. It is shown that the multi-fluid models give rise to unreal results especially for distributions of neutral component parameters. Magnetohydrodynamic (MHD) modelling of the solar wind interaction with the LISM gas is also reviewed.     

Physics of Solar Prominences: II—Magnetic Structure and Dynamics

Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.     

Power Law Distributions of Suprathermal Ions in?the?Quiet Solar Wind

At energies above the bulk solar wind and pick-up ion cutoff, observations reveal an interplanetary suprathermal ion population extending to ～1?MeV/nucleon and even higher energies. These suprathermal ions are found under a wide variety of conditions including periods when there are no obvious nearby accelerating shocks. We review the observational properties of these ions in quiet solar wind periods near 1?AU, including transient Corotating Interaction Region (CIR) events, and other, quieter periods in between transient enhancements. The particle energy spectra are power laws close to E ^?1.5 in the range above the solar wind, rolling over at energies of a few hundred keV/nucleon to a few MeV/nucleon. Although the C/O and Fe/O ratios of the tails is close to that of the solar wind, pickup ions and ³He found in the tails indicate sources distinct from the solar wind. We briefly review several mechanisms that have been proposed to explain these ions.     

Physics of Solar Prominences: I—Spectral Diagnostics and Non-LTE Modelling

This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE (i.e. when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences.     

High-latitude Sporadic-E and other Thin Layers – the Role of Magnetospheric Electric Fields

Observations of high-latitude sporadic-E (Es) layers and theories of their formation are reviewed. The layers are found to be composed of metallic ions, they are at times formed by tidal wind shear, and they are more common in summer than in winter. All of these properties are common to Es layers at mid-latitudes. However, the high-latitude layers are rather often formed, modified or transported by the action of magnetospheric electric fields. Taking into account the action of both tides and electric fields leads to an understanding of the daily variation of Es occurrence, the daily variation of Es heights and the occasional appearance of upward migrating Es layers. Correlations between Es and neutral metallic layers at low altitudes can be explained by neutralisation of the metallic ions in the Es layers, but joint Es and neutral layers at higher altitudes are still unexplained. The action of electric fields and the interaction with neutral layers can explain the formation of multiple Es layers and may provide an explanation for the seasonal variation of Es occurrence. Uncertainties remain as to whether the narrowness of Es layers is fully compatible with formation by electric fields, to whether neutralisation at low altitudes can provide a sufficient explanation of the seasonal variation, and to whether the quasi-periodic fine structure observed in mid-latitude Es also appears at high latitudes. The understanding of ion transport by electric fields which results from the study of Es layers leads to new insights and new questions related to other plasma layers (polar mesosphere summer echoes and winter ion layers) which appear in the high-latitude winter ionosphere.     

Electric Fields and Magnetic Fields in the Plasmasphere: A Perspective From CLUSTER and IMAGE

The electric field and magnetic field are basic quantities in the plasmasphere measured since the 1960s. In this review, we first recall conventional wisdom and remaining problems from ground-based whistler measurements. Then we show scientific results from Cluster and Image, which are specifically made possible by newly introduced features on these spacecraft, as follows. 1. In situ electric field measurements using artificial electron beams are successfully used to identify electric fields originating from various sources. 2. Global electric fields are derived from sequences of plasmaspheric images, revealing how the inner magnetospheric electric field responds to the southward interplanetary magnetic fields and storms/substorms. 3. Understanding of sub-auroral polarization stream (SAPS) or sub-auroral ion drifts (SAID) are advanced through analysis of a combination of magnetospheric and ionospheric measurements from Cluster, Image, and DMSP. 4. Data from multiple spacecraft have been used to estimate magnetic gradients for the first time.     

Recent Observations of Plasma and Alfvénic Wave Energy Injection at the Base of the Fast Solar Wind

We take stock of recent observations that identify the episodic plasma heating and injection of Alfvénic energy at the base of fast solar wind (in coronal holes). The plasma heating is associated with the occurrence of chromospheric spicules that leave the lower solar atmosphere at speeds of order 100?km/s, the hotter coronal counterpart of the spicule emits radiation characteristic of root heating that rapidly reaches temperatures of the order of 1?MK. Furthermore, the same spicules and their coronal counterparts (“Propagating Coronal Disturbances”; PCD) exhibit large amplitude, high speed, Alfvénic (transverse) motion of sufficient energy content to accelerate the material to high speeds. We propose that these (disjointed) heating and accelerating components form a one-two punch to supply, and then accelerate, the fast solar wind. We consider some compositional constraints on this concept, extend the premise to the slow solar wind, and identify future avenues of exploration.     

The Influence of the 11-year Solar Cycle on the Stratosphere Below 30 km: a Review

The NCEP/NCAR re-analyses of the global data as high as 10hPa have made it possible to examine the influence of the 11-year sunspot cycle on the lower stratosphere over the entire globe. Previously, the signal of the solar cycle had been detected in the temperatures and heights of the stratosphere at 30hPa and below on the Northern Hemisphere by means of a data set from the Freie Universität Berlin. The global re-analyses show that the signal exists on the Southern Hemisphere too, and that it is almost a mirror image of that on the Northern Hemisphere. The largest temperature correlations with the solar cycle move from one summer hemisphere to the other, and the largest height correlations move poleward within each hemisphere from winter to summer.The correlations are weakest over the whole globe in the northern winter. If, however, one divides the data into the winters when the equatorial Quasi-Biennial Oscillation was easterly or westerly, the arctic correlations become positive and large in the west years, but insignificantly small over the rest of the earth. The correlations in the east years are negative in the Arctic but positive in the subtropics and tropics on both hemispheres.The difference between the east and west years in January-February can be ascribed to the fact that the dominant stratospheric teleconnection and the solar influence work in the same direction in the east years but oppose each other in the west years.NCAR is sponsored by the National Science Foundation.     

Large-scale Bright Fronts in the Solar Corona: A?Review of?��EIT waves��

??EIT waves?? are large-scale coronal bright fronts (CBFs) that were first observed in 195 Å images obtained using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). Commonly called ??EIT waves??, CBFs typically appear as diffuse fronts that propagate pseudo-radially across the solar disk at velocities of 100?C700 km?s^?1 with front widths of 50?C100 Mm. As their speed is greater than the quiet coronal sound speed (c _s ??200 km?s^?1) and comparable to the local Alfvén speed (v _A ??1000 km?s^?1), they were initially interpreted as fast-mode magnetoacoustic waves ( $v_{f}=(c_{s}^{2} + v_{A}^{2})^{1/2}$ ). Their propagation is now known to be modified by regions where the magnetosonic sound speed varies, such as active regions and coronal holes, but there is also evidence for stationary CBFs at coronal hole boundaries. The latter has led to the suggestion that they may be a manifestation of a processes such as Joule heating or magnetic reconnection, rather than a wave-related phenomena. While the general morphological and kinematic properties of CBFs and their association with coronal mass ejections have now been well described, there are many questions regarding their excitation and propagation. In particular, the theoretical interpretation of these enigmatic events as magnetohydrodynamic waves or due to changes in magnetic topology remains the topic of much debate.     

Measuring the Earth’s Magnetic Field from Space: Concepts of Past, Present and Future Missions

Observations of the Earth’s magnetic field from low-Earth orbiting (LEO) satellites started very early on, more than 50 years ago. Continuous such observations, relying on more advanced technology and mission concepts, have however only been available since 1999. The unprecedented time-space coverage of this recent data set opened revolutionary new possibilities for monitoring, understanding and exploring the Earth’s magnetic field. In the near future, the three-satellite Swarm constellation concept to be launched by ESA, will not only ensure continuity of such measurements, but also provide enhanced possibilities to improve on our ability to characterize and understand the many sources that produce this field. In the present paper we review and discuss the advantages and drawbacks of the various LEO space magnetometry concepts that have been used so far, and report on the motivations that led to the latest Swarm constellation concept. We conclude with some considerations about future concepts that could possibly be implemented to ensure the much needed continuity of LEO space magnetometry, possibly with enhanced scientific return, by the time the Swarm mission ends.     

Selective laser melting of Al–8.5Fe–1.3V–1.7Si alloy: Investigation on the resultant microstructure and hardness

This article presents the microstructure and hardness variation of an Al–8.5Fe–1.3V–1.7Si(wt%, FVS0812) alloy after selective laser melting(SLM) modification. Three zones were distinguished across the melting pool of the SLM-processed FVS0812 alloy: the laser melted zone(LMZ), the melting pool border, and the heat affected zone(HAZ) in the previously deposited area around the melting pool. Inside the LMZ, either an extremely fine cellular-dendritic structure or a mixture zone of the a-Al matrix and nanoscale Al_(12)(Fe,V)_3Si particles appeared. With a decreased laser beam scanning speed, the cellular-dendritic structure zone within the LMZ shrank significantly while the mixture zone expanded. The a-Al and Al_(12)(Fe,V)_3Si mixture zone was also observed in the HAZ, but another phase, submicron h-Al_(13)Fe_4 particles with rectangular or hexagonal shapes,formed along the melting pool border. Microhardness tests indicated that the hardness of the SLM-processed FVS0812 samples far exceeded that of the as-cast FVS0812 alloy.