Large-scale propagation properties of interplanetary disturbances revealed from IPS and spacecraft observations

Interplanetary scintillation (IPS) observations may be used to study large-scale propagation properties of transient interplanetary disturbances in a three-dimensional manner, although current IPS observations have several limitations, e.g., poor time resolution and line-of-sight integration. Comparative studies with spacecraft solar wind and white-light coronal mass ejection (CME) observations are quite helpful in interpretation of IPS observations. An interplanetary disturbance apparently in association with a disappearing solar filament, which took place near the central meridian of the Sun on late 22 April, 1979, is discussed to examine previous deductions from IPS observations. Three-station IPS observations of the flow speed and spacecraft observations suggest that a quasi-spherical interplanetary disturbance was formed around the Sun-Earth line, whereas the center of the disturbance derived from the distribution of enhanced IPS across the sky (g-maps) is located to the east of the Sun-Earth line.Permanently at Research Institute of Atmospherics, Nagoya University, Toyokawa 442, Japan.     

CME Disturbance Forecasting

CME disturbances at Earth arise from the sheath that arrives in front of the ICME and from the ICME itself. The geoeffective environment is qualitatively different in the sheath than within the ICME. Consequently two types of forecast procedures using solar observations of phenomena associated with the release of the CME as input parameters have been developed to treat the two types of environment. This chapter surveys efforts that have resulted in implementable (at least in principle) forecast algorithms for sheath and ICME disturbances and discusses uncertainties associated with both.     

Acceleration Profile of the Slow Solar Wind as Inferred from Gradual Mass Ejections Observed by LASCO

The slow solar wind (< 400 km s^-1) appears to initiate from the regions in the corona where magnetic fields are closed, or from the interface between streamers and other coronal regions. The nature of the acceleration of slow solar wind is not yet well known. LASCO observations of gradually evolving mass ejections offer us a good opportunity to study the speed and acceleration profiles of the slow solar wind from a distance of 1.1 up to 30 R_⊙. We present speed and acceleration profiles of slow solar wind, derived on the basis of measurements of mass flows in several cases of gradual mass ejections and present them in perspective of earlier work. This revised version was published online in June 2006 with corrections to the Cover Date.     

Relationship of coronal transients to interplanetary shocks: 3D aspects

More than 1000 coronal mass ejections (CMEs) caused by different types of coronal transients have been analyzed up to now, based on the images from white light coronagraphs on board the OSO 7, Skylab, P78-1, and SMM spacecraft. In many cases, the CME images lead us to the impression of loop-like, more planar structures, similar to those of prominence structures often seen in H pictures. There is increasing evidence, though, for a three-dimensional bubble- or cloud-like structure of CMEs. In several cases, CMEs directed toward the earth (or away from it) were identified, as their outer fronts emerged on all sides of the coronagraph's occulting disk, thus suggesting a bubble-like appearance.There now appears to be unanimity about the crucial role that magnetic reconnection plays during the transient process. Recently, direct evidence was found for the pinch-off of CMEs, both from optical observations and from in situ measurements of isolated magnetic clouds' following transient shock waves. However, the detailed sequence of events during the generation of a CME is still unclear.Interplanetary shock waves associated with the CMEs are usually restricted in latitudinal extent to about the angular width of the optically observed CMEs. They may be somewhat less restricted in longitudinal extent. A nearly 1 1 association between CMEs and shock waves measured in situ from spacecraft (Helios 1 and 2, IMP 7 and 8, ISEE 3, Pioneer Venus) can be established, provided the CME and the spacecraft were in the same longitudinal and latitudinal range and the CME speed exceeds 400 km s^–1. Around the past solar activity minimum all CMEs observed were centered at solar latitudes of less than 60°. Around solar maximum, a significant fraction of CMEs also originated from the polar regions. Thus, there is a good chance that the Ulysses spaceprobe will encounter many shocks caused by both low- and high-latitude CMEs, when it finally starts its journey over the Sun's poles.     

Solar wind and its interaction with the magnetosphere: Measured parameters

The earth's magnetosphere absorbs only a minor fraction (≈ 10^?3) of the incident solar wind energy. Variations of the solar wind can often cause lively reactions in the earth's close environment. However, the physical mechanisms involved are not yet understood. It appears now that the combined action of the solar wind momentum flux, the direction of the interplanetary magnetic field as well as its fluctuations might play the dominant role. The behaviour of these parameters is governed in some characteristic way by the solar wind stream structure which reflects the condition of the solar corona and its magnetic field topology. Transients in the sun's atmosphere associated with solar activity cause reactions in the interplanetary medium which also show some typical, though very different, signatures. Taking into account the interdependence of the solar wind parameters in context with the underlying solar phenomena, we may be able to pinpoint the mechanism which controls the action of the solar wind on the magnetosphere.     

Thermal and Chemical Evolution of Comet Nuclei and Kuiper Belt Objects

The structure and composition of comet nuclei are mainly altered during two short phases that are separated by a very long hibernation phase. Early evolution—during and immediately after formation—is the result of heating caused by radioactive decay, the most important source being ²⁶Al. Several studies are reviewed, dealing with evolution throughout this phase, calculated by means of 1-D numerical codes that solve the heat and mass balance equations on a fixed spherically symmetric grid. It is shown that, depending on parameters, the interior may reach temperatures above the melting point of water. The models thus suggest that comets are likely to lose the ices of very volatile species during early evolution; ices of less volatile species are retained in the cold subsurface layer. As the initially amorphous ice is shown to crystallize in the interior, some objects may also lose part of the volatiles trapped in amorphous ice. Generally, the outer layers are far less affected than the inner part, resulting in a stratified composition and altered porosity distribution. The second phase of evolution occurs when comet nuclei are deflected into the inner solar system and is dominated by the effect of solar radiation. Now the outer layers are those mostly affected, undergoing crystallization, loss of volatiles, and significant structural changes. If any part of a comet nucleus should retain its pristine structure and composition, it would be well below the surface and also well above the core.     

Relation between the radial speed and theexpansion speed of coronal mass ejections

We have selected 57 limb coronal mass ejections observed by LASCO during the period of January1997 to April 2001. We used the related EIT activity close to the limb to define these CMEs as “limbs”. We measured the radial speed of the leading edge close to the center of these CMEs and the lateral expansion speed of the structures. Comparison of both speeds revealed a high correlation between them, the radial speed being around 88% of the expansion speed of the CME. The expansion speed can also be measured for halo CMEs so that it can be used to infer their radial speed toward earth, which is otherwise inaccessible.     

Theoretical modeling for the stereo mission

We summarize the theory and modeling efforts for the STEREO mission, which will be used to interpret the data of both the remote-sensing (SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The modeling includes the coronal plasma, in both open and closed magnetic structures, and the solar wind and its expansion outwards from the Sun, which defines the heliosphere. Particular emphasis is given to modeling of dynamic phenomena associated with the initiation and propagation of coronal mass ejections (CMEs). The modeling of the CME initiation includes magnetic shearing, kink instability, filament eruption, and magnetic reconnection in the flaring lower corona. The modeling of CME propagation entails interplanetary shocks, interplanetary particle beams, solar energetic particles (SEPs), geoeffective connections, and space weather. This review describes mostly existing models of groups that have committed their work to the STEREO mission, but is by no means exhaustive or comprehensive regarding alternative theoretical approaches.     

Observation of flare-generated shock waves by Helios-2 near the sun

We present the observation of three flare generated shock waves which were measured by Helios-2 at a radial distance from the Sun of 0.476 AU, 0.444 AU, and 0.297 AU. These results show that two of the shocks fulfill the classification scheme of F-events stated in the past while the third shock profile is that of a R-event being interpreted as a driven wave. Because of the close distance to the Sun a flare-association was possible. Only in one case there is some evidence for a piston in the downstream region of the shock. One of the shocks is characterized by a distinct hole in the frequency distribution of directional discontinuities in the downstream region.An invited paper presented at STIP Workshop on Shock Waves in the Solar Corona and Interplanetary Space, 15–19 June, 1980, Smolenice, Czechoslovakia.     

The Galactic Cosmic Ray Intensity over the Past 106–109 Years as Recorded by Cosmogenic Nuclides in Meteorites and Terrestrial Samples

Concentrations of stable and radioactive nuclides produced by cosmic ray particles in meteorites allow us to track the long term average of the primary flux of galactic cosmic rays (GCR). During the past ～10 Ma, the average GCR flux remained constant over timescales of hundreds of thousands to millions of years, and, if corrected for known variations in solar modulation, also during the past several years to hundreds of years. Because the cosmic ray concentrations in meteorites represent integral signals, it is difficult to assess the limits of uncertainty of this statement, but they are larger than the often quoted analytical and model uncertainties of some 30%. Time series of concentrations of the radionuclide ¹⁰Be in terrestrial samples strengthen the conclusions drawn from meteorite studies, indicating that the GCR intensity on a ～0.5 million year scale has remained constant within some ±10% during the past ～10 million years. The very long-lived radioactive nuclide ⁴⁰K allows to assess the GCR flux over about the past one billion years. The flux over the past few million years has been the same as the longer-term average in the past 0.5–1 billion years within a factor of ～1.5. However, newer data do not confirm a long-held belief that the flux in the past few million years has been higher by some 30–50% than the very long term average. Neither does our analysis confirm a hypothesis that the iron meteorite data indicate a ～150 million year periodicity in the cosmic ray flux, possibly related to variations in the long-term terrestrial climate.