Interplanetary streams and their interaction with the earth

Plasma and magnetic field observations of interplanetary streams near 1 AU are summarized. Two types of streams have been identified — corotating streams and flare-associated, and other flow patterns are present due to interactions among streams. The theory of corotating streams, which attributes them to a high temperature region near the Sun, satisfactorily explains many of the effects observed at 1 AU. A correspondingly complete theory of flare-associated streams does not exist. Streams are a key link in the chain that connects solar and geomagnetic activity. The factors that most influence geomagnetic activity are probably related to streams and determined by the dynamics of streams. The evolution of streams on scales of 27 days and 11 years probably determines the corresponding variations of geomagnetic activity.     

Injection and Acceleration Processes in Corotating Interaction Regions: Theoretical Concepts

A brief overview on particle injection and acceleration in corotating interaction regions is presented. After introducing the diffusion-convection transport equation for energetic particles we discuss diffusive acceleration at the corotating shocks, stochastic acceleration within the interaction region, and the injection and acceleration of pickup ions at the corotating shocks. This revised version was published online in August 2006 with corrections to the Cover Date.     

The evolution of the anomalous component of the cosmic rays during the Ulysses mission

We have studied the evolution of the anomalous cosmic ray component at ULYSSES using observations of the quiet time helium fluxes obtained with the COSPIN Low Energy Telescope during the years from launch in October 1990 to the latest data in 1994. Shown are preliminary results of measurements in the energy range from 4.0 to 19 MeV/n. Following the drop in solar activity in late 1991, the low energy cosmic ray helium flux started to increase and continue to rise until the end of 1993, signifying the appearance of the anomalous component at ULYSSES.     

Energetic particle observations at high heliographic latitudes

Energetic particles, accelerated in shocks which were associated with recurrent fast solar wind streams, were observed in high heliographic latitudes; fifteen such steams were included in the present study. Intensity variations ranged up to four orders of magnitude. Energy spectra were typically steeper near forward shocks than near reverse shocks. Electrons were observed only lated to the reverse shocks. Composition ratios in accelerated streams resembled those observed in fast CIR's. In periods between the recurrent acceleration regions elemental abundance ratios were similar to those of the anomalous cosmic rays (ACR). The intensity of the accelerated particles declined as the latitude of ULYSSES increased, probably due to the weakening of the shocks.     

Interplanetary scintillation observations of the high-latitude solar wind

Until the ULYSSES spacecraft reached the polar regions of the solar wind, the only high-latitude measurements available were from indirect techniques. The most productive observations in regions of the solar wind between 5R and 200R have been the family of radio scattering techniques loosely referred to as Interplanetary Scintillation (IPS) (Coles, 1978). Useful observations can be obtained using a variety of radio sources, for example spacecraft beacons, planetary radar echoes and compact cosmic sources (quasars, active galactic nuclei, pulsars, galactic masers, etc.). However for measurement of the high-latitude solar wind cosmic sources provide the widest coverage and this review will be confined to such observations. IPS observations played a very important role in establishing that polar coronal holes (first observed in soft x-ray emission) were sources of fast solar wind streams which occasionally extend down to the equatorial region and are observed by spacecraft. Here I will review the IPS technique and show the variation of both the velocity and the turbulence level with latitude over the last solar cycle. I will also outline recent work and discuss comparisons that we hope to make between IPS and ULYSSES observations.     

A particle event at 5 AU and 20° southern latitude from measurements with the EPAC instrument on Ulysses

In November 1992, the Ulysses spacecraft observed a multiple solar particle event and a CME event at 5.2 AU and a heliographic latitude of 20° S which were superimposed to the recurrent corotating interacting region. Distinct particle flux increases caused by these events were observed in all energy channels of the EPAC experiment. The experimental findings are discussed.     

Voyager Observations of the Magnetic Field in the Distant Heliosphere

The latitudinal structure of the heliospheric magnetic field during much of the solar cycle is determined by a "sector zone", in which both positive and negative magnetic polarities are observed, and by the unipolar regions above and below the sector zone. Distinct corotating streams and interactions regions are found primarily in the sector zone during the declining phase of the solar cycle. Within a few AU, the streams and interaction regions are distinct and are related to solar features. A restructuring of the solar wind occurs between 1 AU and 15 AU, in which the isolated streams, interaction regions and shocks merge to form compound streams and merged interaction regions ("MIRs"). Memory of the source conditions is lost in this process. In the region between 30 AU and the termination shock (the "distant heliosphere"), the pressure of interstellar pickup protons dominates that of the magnetic field and solar wind particles and largely controls the dynamical processes. During 1983 and 1994, corotating streams and corotating interaction regions were observed at 1 AU. Merged interaction regions were observed at 15 AU in 1983, but not at 45 AU during 1994. This result suggests a further restructuring of the solar wind in the distant heliosphere, but variations from one solar cycle to the next might also contribute to the result. Approaching solar minimum in 1996, the latitudinal extent of the sector zone decreased, and Voyager 2 gradually entered the unipolar region below it. The speed was lower in the sector zone than below it. At Voyagers 1 and 2, the change in cosmic ray intensity is related to the magnetic field strength during each year from 1983 through 1996. The magnetic field strength has a multifractal distribution throughout the heliosphere. This fundamental symmetry of the heliosphere has not been incorporated explicitly in cosmic ray propagation models.     

Modeling of 3-D Corotating Cosmic-Ray Structures in the Heliosphere

We present a brief review of the modeling of corotating 3-dimensional features in heliospheric cosmic rays. The model heliosphere incorporates a wavy current sheet and Corotating Interaction Regions (CIRs). We find that present models can qualitatively account for the observed extension of recurrent 26-day cosmic-ray variations to high heliospheric latitudes if perpendicular diffusion is significant. The recurrent enhancement of low-energy (MeV) particles accelerated at CIR-s is also shown to fit into this same picture.     

A Brief History of Recurrent Solar Modulation of the Galactic Cosmic Rays (1937-1990)

This brief review of the pre-Ulysses era begins with the first measurements by ionization chambers in 1937 of a cosmic ray 27-day intensity variation that was believed to have its origin in recurrent variations of the geomagnetic field. However, with the introduction of neutron monitor analysis of the nucleonic component, it was shown in the 1940s and 1950s that this cosmic ray intensity variation arose from interplanetary dynamical phenomena. Beginning in the 1960s direct spacecraft investigations in the heliosphere with Pioneer-10, Pioneer-11, Voyager-1 and Voyager-2 proved that Corotating Interaction Regions were not only the source of the cosmic ray recurrent intensity modulation, but also the source of charged particles accelerated in corotating forward and reverse shocks associated with the corotating interaction regions.These early investigations, confined to low latitudes, have contributed to the understanding of solar phenomena, interplanetary dynamics, charge particle acceleration and the Sun-Earth convection.     

Ulysses solar wind observations to 56° south

In the 25 months since Jupiter flyby, the Ulysses spacecraft has climbed southward to a heliolatitude of 56°. This transit has been marked by an evolution from slow, dense coronal streamer belt solar wind through two regions where the rotation of the Sun carried Ulysses back and forth between streamer belt and polar coronal hole flows, and finally into a region of essentially continuous fast, low density solar wind from the southern polar coronal hole. Throughout these large changes, the momentum flux normalized to 1 AU displays very little systematic variation. In addition, the bulk properties of the polar coronal hole solar wind are quite similar to those observed in high speed streams in the ecliptic plane at 1 AU. Coronal mass ejections and forward and reverse shocks associated with corotating interaction regions have also been observed at higher heliolatitudes, however they are seen less frequently with increasing southern heliolatitude. Ulysses has thus far collected data from 20° of nearly contiguous solar wind flows from the polar coronal hole. We examine these data for characteristic variations with heliolatitude and find that the bulk properties in general show very little systematic variation across the southern polar coronal hole so far.     

Corotating Interaction Regions in the Outer Heliosphere

We discuss the structure and evolution of CIRs and their successors in the outer heliosphere. These structures undergo significant evolution as they are convected to greater heliocentric distances. A progression of different types of structure are observed at increasing distance from the Sun. Similar structures are observed at similar heliocentric distance at different portions of the solar cycle. CIRs and their successors are associated with many important physical processes in the outer heliosphere. We discuss the relationship between these structures and recurrent phenomena such as cosmic ray variations, and review some of the associated theoretical models on the role of corotating structures and global merged interaction regions (GMIRs) in global cosmic ray modulation. We also discuss some outstanding questions related to the origin of non-dispersive quasi-periodic particle enhancements associated with CIRs and their successors in the outer heliosphere. This revised version was published online in August 2006 with corrections to the Cover Date.     

Solar wind helium isotopic composition from SWICS/ULYSSES

This is the first study of the isotopic composition of solar wind helium with the SWICS time-of flight mass spectrometer. Although the design of SWICS is not optimized to measure³He abundances precisely,⁴He/³He flux ratios can be deduced from the data. The long term ratio is 2290±200, which agrees with the results obtained with the ICI magnetic mass spectrometer on ISEE-3 and with the Apollo SWC foil experiments.The ULYSSES spacecraft follows a trajectory which is ideal for the study of different solar wind types. During one year, from mid-1992 to mid-1993, it was in a range of heliographic latitudes where a recurrent fast stream from the southern polar coronal hole was observed every solar rotation. Solar wind bulk velocities ranged from 350 km/s to 950 km/s which would, in principle allow us to identify velocity-correlated compositional variations. Our investigation of solar wind helium, however, shows an isotopic ratio which does not depend on the solar wind speed.     

High energy cosmic ray nuclei results on Ulysses: 1. Mission overview

The cosmic ray flux observed with the Kiel Electron Telescope on board the ULYSSES spaceprobe varies with solar activity as well as with heliospheric position. Determination of the latitudinal gradients requires a careful analysis of the influences of the current sheet tilt angle, the number of major solar flares, interplanetary shocks and interaction regions evolving in the expanding solar wind. In this paper we concentrate on nuclei with rigidity above 1 GV. We discuss the effects of the variable solar activity in the declining phase of the present solar cycle and the variation with radial distance as a basis for separating latitudinal effects. We show that during this phase of the solar cycle modulation of GV nuclei is ordered by temporal evolution, radial distance and negligible latitudinal effects even at latitudes between 30° and 50° South.     

埋入式涡流发生器在亚音扩压器分离流控制中的应用

本文介绍了在一个大宽高比大扩压角二元亚音扩压器中采用适当几何参数的凹型面埋入式涡流发生器有效地控制扩压壁和角落区域分离流的试验结果。并分析了该型式涡流发生器主要几何参数对扩压器性能的影响。还对该型式涡流发生器与常规翼型式涡流发生器进行了比较。      

Recurrent Solar Modulation of the Galactic Cosmic Rays and the Anomalous Nuclear Component in Three Dimensions of the Heliosphere

Ulysses Mission investigations, extending from pole-to-pole of the Sun and inner heliosphere in the period 1993-1996, have led to discoveries that will change dramatically models to account for the physical phenomena underlying the 26-day modulation of galactic cosmic rays and anomalous nuclear components and their propagation modes. These new findings also relate to the propagation of low energy nucleons and electrons accelerated by corotating interaction region shocks. Also included are some unpublished measurements that will need to be taken into account in any model for the 26-day modulation phenomena. This report is a brief summary of the principal results from the solar wind, magnetic field and charged particle investigations, and their alternate interpretations.     

Ulysses out-of-ecliptic observations of “27-day” variations in high energy cosmic ray intensity

We report the discovery that for latitudes above 40°S, the observed recurring modulation of cosmic rays and anomalous nuclei occurs without the detection byUlysses of the solar wind velocity and magnetic field recurring enhancements that have, heretofore at lower latitudes, defined corotating interaction regions—i.e., the mechanism producing the recurring intensity variations >40°S appears to be located beyond the radial range ofUlysses.     

The elemental composition in energetic particle events at high heliospheric latitudes

The relative abundances of low energy ions (0.6–2.0 MeV/n) in solar energetic particle (SEP) and corotating interaction region (CIR) events have been measured by the EPAC experiment aboard Ulysses since launch in October 1990 until the present time. We give an overview of the abundances of heavy ions (He, C, Ne, Fe) relative to oxygen during energetic particle events lasting longer than 5 days during the in- and out-of-ecliptic phase of the mission. While the period Oct. 1990 to Aug. 1992 was dominated by high solar activity the Ulysses out of ecliptic passage at solar latitudes up to 45° went parallel to the declining phase of solar activity. Thus a very clear structure of corotating interaction regions was observed. While the in-ecliptic composition is in general agreement with measurements made near the Earth, the development of the CIR-composition shows two phases: From Aug. 1992 to May 1993 the C/O-ratio is 0.55–0.70, afterwards it increases to 0.8–0.9. This increase is correlated to the disappearance of the current sheet at 30° solar latitude reported by Smithet al. (1993).     

Interplanetary Shocks and Solar Wind Structure Approaching Solar Maximum: Helios,IMP-8 and Voyager Observations

We studied solar wind observations of five different spacecraft: Helios 1, Helios 2, IMP-8, Voyager 1 and Voyager 2, from November 1977 to February 1978. In this period the large-scale dynamics of the solar wind near of the ecliptic plane was characterized by transient forward shocks (TFSs), ejecta, unstable corotating interaction regions (CIRs), and complex and variable magnetic sector structures. We identified 12 forward shock events of different origin. We did not find any clear tendency of the shock parameters with heliocentric distance nor longitudinal angle, but comparing the observations of each shock event we found local variations in the shock strength and the mean propagation velocities from one spacecraft to another. These unsystematic variations indicate that there were local deformations of the shock fronts, which we attribute to the inhomogenuos solar wind structure that affects the shock propagation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic Domains in the Heliosphere During Solar Maximum Years

The mosaic structure of the magnetic field in the heliosphere is described. It is formed by multiple corotating and propagating magnetic domains which are especially numerous during solar maximum years. This revised version was published online in August 2006 with corrections to the Cover Date.     

Energetic Ions Observed at Low to High Latitudes in the Southern Heliosphere During Declining and Rising Solar Activity

We present and compare observations of energetic protons during the two first transits of the Ulysses spacecraft from low to high latitudes in the southern heliosphere. Protons in the energy range 1.8–3.8 MeV from the COSPIN experiment are studied for global trends and in relation to some ambient structures in the solar wind (corotating interaction region, forward/reverse shock). The global trends show the large dependence on the heliospheric condition and solar activity, including indications of a larger ambient particle population during the rising phase of solar activity and more efficient solar wind particle accelerators during the declining phase. More enhancements in the proton flux intensity are time associated with forward shocks than reverse contrary to first pass. Recurrent structures are found even during the second transit. Some latitude dependent periodicities are observed that could relate to the differential solar rotation. This revised version was published online in August 2006 with corrections to the Cover Date.