The solar chromosphere and its transition to the corona

Our present knowledge on the average physical properties of the chromosphere and of the transition region between chromosphere and corona is reviewed. It is recalled that shock wave dissipation is responsible for the high temperatures observed in the chromosphere and corona and that, due to the non-linear character of the dissipation mechanism, no satisfactory explanation of the structure of the outer solar layers has yet been given. In this paper, the main emphasis is on the observations and their interpretation.Evidence for the non-spherically symmetric structure of the atmosphere is given; the validity of interpreting the observations with the help of a fictitious spherically symmetric atmosphere is discussed.The chromosphere and the transition region are studied separately: for each region, the energy balance is considered and recent homogeneous models derived from ultra-violet, infrared and radio observations are discussed.It is stressed that although in the chromosphere, a study of the radiative losses may lead to the determination, as function of height, of the amount of mechanical energy dissipated as function of height, a more detailed analysis of the velocity field is necessary to find the periods and the wavelengths of the waves responsible for the heating. The methods used for wave detection and some results are presented.Observational and theoretical evidence is given for the non-validity of the assumption of hydrostatic equilibrium which is commonly used in modeling the transition region.We conclude that a better understanding of the heating mechanism will come through a higher spatial resolution (less than 0.2) and more accurate absolute measurements, rather than from sophisticated hydrodynamical calculations.     

Dual spacecraft observations of energetic particles in the vicinity of the magnetopause,bow shock,and the interplanetary medium

This article presents some of the new and important particle features that have been detected in the energy range 1 keV to 290 keV by the ISEE-1 and -2 spacecraft near the magnetopause, bow shock, and the interplanetary space. Only examples of data from the first few orbits, when the spacecraft were on the front side, are shown.Paper presented at 13th ESLAB Symposium, Innsbruck, Austria (June 5, 1978).     

Short-Lived Radionuclides in Meteorites: Constraints on Nebular Timescales for the Production of Solids

Variations in the abundances of short-lived radionuclides such as ²⁶Al (τ_1/2 ≈ 0.74 Ma) and ⁵³Mn (τ_1/2 ≈ 3.7 Ma) in meteoritic solids may be used to infer relative formation intervals of these solids in the nebula at precisions of less than 1 Ma. In a strict chronometric interpretation of the isotopic variations, whereby criteria such as spatial and temporal isotopic homogeneity and closed system isotopic evolution are met, solid formation occurred in the nebula for at least several million years. This is longer than some theoretical and astronomical estimates for the duration of the active nebula. The evidence for live ⁴¹Ca (τ_1/2 ≈ 0.10 Ma) in meteoritic inclusions further indicates that the onset of solid formation occurred quite early, perhaps within a few hundred thousand years after the onset of the collapse of the sun's parent molecular cloud. Failure of the chronometric interpretation may arise for a variety of reasons, including but not limited to, the late, inhomogeneous injection of material from a nearby stellar source or the local production of short-lived radionuclides by an energetic particle irradiation, e. g., from T Tauri (X-wind) or galactic cosmic ray sources. Although some isotopic evidence exists that the criteria required for a strict chronometric interpretation are not met by each of the short-lived chronometers, there is no compelling reason to shorten the interval of solid formation in the nebula to less than 1 Ma. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of clinorotation and fettering stress on tail regeneration of Triturus vulgaris (Urodela).

Tail-amputated adult Triturus vulgaris, fettered in cuvettes of a fast-rotating clinostat were exposed to simulated weightlessness (60 rpm; equiv. to 10(-3)-10(-4) g), during a 14-day period. To feed and clean the animals rotation was stopped once a day for approx. 10 min. To test the influence of the fettering stress, a second series of animals was kept separately under normal earth conditions without rotation. A further control series was kept in a dark container without any handicap. While tail regeneration of the rotated animals was markedly accelerated, the fettered-only animals showed a considerably less marked acceleration effect. At the end of the 14-day period, all regenerates were reamputated together with an additional 5 mm of the tail stump. Although this second level of amputation was distant from the first, the regenerative growth rate of the rotated series was accelerated 123% in contrast to both the control and the fettered-only series. Our results demonstrate that the growth acceleration is induced by clinorotation. Fettering stress has no comparable influence. The growth promoting effect is not limited to the regenerating area.     

An application of embedology to spatio-temporal pattern recognition

The theory of embedded time series is shown applicable for determining a reasonable lower bound on the length of test sequence required for accurate classification of moving objects. Sequentially recorded feature vectors of a moving object form a training trajectory in feature space. Each of the sequences of feature vector components is a time series, and under certain conditions, each of these time series has approximately the same fractal dimension. The embedding theorem may be applied to this fractal dimension to establish a sufficient number of observations to determine the feature space trajectory of the object. It is argued that this number is a reasonable lower bound on test sequence length for use in object classification. Experiments with data corresponding to five military vehicles (observed following a projected Lorenz trajectory on a viewing sphere) show that this bound is indeed adequate     

THE DIGITAL WAVE-PROCESSING EXPERIMENT ON CLUSTER

The wide variety of geophysical plasmas that will be investigated by the Cluster mission contain waves with a frequency range from DC to over 100 kHz with both magnetic and electric components. The characteristic duration of these waves extends from a few milliseconds to minutes and a dynamic range of over 90 dB is desired. All of these factors make it essential that the on-board control system for the Wave-Experiment Consortium (WEC) instruments be flexible so as to make effective use of the limited spacecraft resources of power and telemetry-information bandwidth. The Digital Wave Processing Experiment, (DWP), will be flown on Cluster satellites as a component of the WEC. DWP will coordinate WEC measurements as well as perform particle correlations in order to permit the direct study of wave/particle interactions. The DWP instrument employs a novel architecture based on the use of transputers with parallel processing and re-allocatable tasks to provide a high-reliability system. Members of the DWP team are also providing sophisticated electrical ground support equipment, for use during development and testing by the WEC. This is described further in Pedersen et al. (this issue).