The Ulysses fast latitude scans: COSPIN/KET results

International audienceUlysses, launched in October 1990, began its second out-of-ecliptic orbit in December 1997, and its second fast latitude scan in September 2000. In contrast to the first fast latitude scan in 1994/1995, during the second fast latitude scan solar activity was close to maximum. The solar magnetic field reversed its polarity around July 2000. While the first latitude scan mainly gave a snapshot of the spatial distribution of galactic cosmic rays, the second one is dominated by temporal variations. Solar particle increases are observed at all heliographic latitudes, including events that produce >250 MeV protons and 50 MeV electrons. Using observations from the University of Chicago's instrument on board IMP8 at Earth, we find that most solar particle events are observed at both high and low latitudes, indicating either acceleration of these particles over a broad latitude range or an efficient latitudinal transport. The latter is supported by "quiet time" variations in the MeV electron background, if interpreted as Jovian electrons. No latitudinal gradient was found for >106 MeV galactic cosmic ray protons, during the solar maximum fast latitude scan. The electron to proton ratio remains constant and has practically the same value as in the previous solar maximum. Both results indicate that drift is of minor importance. It was expected that, with the reversal of the solar magnetic field and in the declining phase of the solar cycle, this ratio should increase. This was, however, not observed, probably because the transition to the new magnetic cycle was not completely terminated within the heliosphere, as indicated by the Ulysses magnetic field and solar wind measurements. We argue that the new A<0-solar magnetic modulation epoch will establish itself once both polar coronal holes have developed

First imaging of corotating interaction regions using the STEREO spacecraft

Plasma parcels are observed propagating from the Sun out to the large coronal heights monitored by the Heliospheric Imagers (HI) instruments onboard the NASA STEREO spacecraft during September 2007. The source region of these out-flowing parcels is found to corotate with the Sun and to be rooted near the western boundary of an equatorial coronal hole. These plasma enhancements evolve during their propagation through the HI cameras’ fields of view and only becoming fully developed in the outer camera field of view. We provide evidence that HI is observing the formation of a Corotating Interaction Region(CIR) where fast solar wind from the equatorial coronal hole is interacting with the slow solar wind of the streamer belt located on the western edge of that coronal hole. A dense plasma parcel is also observed near the footpoint of the observed CIR at a distance less than 0.1AU from the Sun where fast wind would have not had time to catch up slow wind. We suggest that this low-lying plasma enhancement is a plasma parcel which has been disconnected from a helmet streamer and subsequently becomes embedded inside the corotating interaction region

Data processing for a cosmic ray experiment onboard the solar probes Helios 1 and 2: Experiment 6

The data processing system for the Helios experiment 6, measuring energetic charged particles of solar, planetary and galactic origin in the inner solar system, is described. The aim of this experiment is to extend knowledge on origin and propagation of cosmic rays. The different programs for data reduction, analysis, presentation, and scientific evaluation are described as well as hardware and software of the data processing equipment. A chronological presentation of the data processing operation is given. Procedures and methods for data analysis which were developed can be used with minor modifications for analysis of other space research experiments

Crack initiation and endurance limit of hard steels under multiaxial cyclic loads

The endurance limit and the mechanisms o f fatigue crack initiation in the high cycle regime were investigated using round specimens o f the bearing steel 52100 under longitudinal forces and torsional moments and combinations o f these loads. Three specimen types were examined: smooth specimens and specimens with circumferential notches with radii o f 1.0 and 0.2 mm. The influence ofmean and multiaxial stresses on the endurance limit can be understood by consideration ofcrack initiation mechanisms and micro-mechanics. Crack initiation took place at oxides, carbonitrides and at the surface. The mechanisms ofcrack initiation could be related to the load type: Loads with rotating principal stresses are more damaging fo r nitrides than fo r oxides. Increasing maximum stresses are more dangerous fo r nitrides than fo r oxides, and introduce more damage to the surface than to the nitrides. Normal stresses are more damaging fo r oxides than shear stresses. The endurance limits were calculated by means o f an extended weakest-link model which combines volume and surface crack initiation with related fatigue criteria. For volume crack initiation the criterion o f Dang Van was used. For the correct description o f the competing surface crack initiation, a new criterion was applied. With this concept, a prediction o f the endurance limit is possible fo r loads which produce critical planes and range within a limited regime ofstress ratios.Исследованы предел выносливости и механизмы зарождения усталостных трещин в многоцикловом режиме, используя круглые образцы из подшипниковой стали 52100, подвергаемые действию продольных сил и крутящих моментов, а также комбинации этих нагрузок. Использовали гладкие образцы и образцы с кольцевыми надрезами радиусами 1,0 и 0,2 мм. Влияние средних и многоосных напряжений на предел выносливости может быть объяснено с учетом механизмов зарождения трещин и микромеханики. Зарождение трещин происходило на оксидах, карбонитридах и на поверхности. Механизмы зарождения трещин могут быть связаны с типом нагрузки: нагрузки с вращательными главными напряжениями более деструктивны для нитридов, чем для оксидов. Возрастающие максимальные напряжения более опасны для нитридов, чем для оксидов, и вызывают большие повреждения поверхности, чем нитридов. Нормальные напряжения вызывают большее повреждение оксидов, чем касательные напряжения Пределы выносливости рассчитывали с помощью модифицированной модели слабого звена, которая объединяет зарождение трещин в объеме и на поверхности с соответствующими критериями усталости. Для зарождения трещин в объеме был использован критерий Данг Вана. Для корректного описания конкурирующего зарождения трещин на поверхности был применен новый критерий. С помощью этой концепции можно предсказать предел выносливости для нагрузок, которые создают критические плоскости и диапазон в рамках ограниченного режима коэффициентов асимметрии цикла

Simultaneous Observations of Cosmic Ray Particles in a Corotating Interplanetary Structure at Different Solar Distances between 0.3 and 1 AU from HELIOS 1 and 2 and IMP 7 and 8

From December 1975 to June 1976 we observed an evolving recurrent proton enhancement with IMP 7/8 and Helios 1/2 at different distances from the sun. The corotating character is established over 4 solar rotations. Due to the unique constellation in March 1976 simultaneous measurements were possible which allowed a study of the radial development undisturbed by temporal effects. The intensity variation of the ~4 - 13 MeV protons between 0.43 and 1 AU revealed a sudden increase to a large positive gradient (+329 %/AU) in the leading edge of the event. This value is consistent with a major source outside 1 AU. We suggest an interplanetary acceleration which becomes sufficiently effective within a fast solar wind stream

Galactic Abundances: Report of Working Group 3

We summarize the various methods and their limitations and strengths to derive galactic abundances from in-situ and remote-sensing measurements, both from ground-based observations and from instruments in space. Because galactic abundances evolve in time and space it is important to obtain information with a variety of different methods covering different regions from the Very Local Insterstellar Medium (VLISM) to the distant galaxy, and different times throughout the evolution of the galaxy. We discuss the study of the present-day VLISM with neutral gas, pickup ions, and Anomalous Cosmic Rays, the study of the local interstellar medium (ISM) at distances <1.5 kpc utilizing absorption line measurements in H I clouds, and the study of galactic cosmic rays, sampling contemporary (~15 Myr) sources in the local ISM within a few kiloparsec of the solar system. Solar system abundances, derived from solar abundances and meteorite studies are discussed in several other chapters of this volume. They provide samples of matter from the ISM from the time of solar system format ion, about 4.5 Gyr ago. The evolution of galactic abundances on longer time scales is discussed in the context of nuclear synthesis in the various contributing stellar objects

Backward correlations and dynamic heterogeneities: a computer study of ion dynamics

We analyse the correlated back and forth dynamics and dynamic heterogeneities, i.e. the presence of fast and slow ions, for a lithium metasilicate system via computer simulations. For this purpose we define, in analogy to previous work in the field of glass transition, appropriate three-time correlation functions. They contain information about the dynamics during two successive time intervals. First we apply them to simple model systems in order to clarify their information content. Afterwards we use this formalism to analyse the lithium trajectories. A strong back-dragging effect is observed, which also fulfills the time-temperature superposition principle. Furthermore, it turns out that the back-dragging effect is long-ranged and exceeds the nearest neighbor position. In contrast, the strength of the dynamic heterogeneities does not fulfill the time-temperature superposition principle. The lower the temperature, the stronger the mobility difference between fast and slow ions. The results are then compared with the simple model systems considered here as well as with some lattice models of ion dynamics.Comment: 12 pages, 10 figure