Chaos and multifractals in the solar wind

By using the false-nearest-neighbours method, we have argued that the deterministic component of solar wind plasma dynamics should be low-dimensional. In fact, the results we have obtained using the method of topological embedding indicate that the behaviour of the solar wind can be approximately described by a low-dimensional chaotic attractor in the inertial manifold, which is a subspace of system phase space. We have also shown that the multifractal spectrum of the solar wind attractor is consistent with that for the multifractal measure of the self-similar generalized weighted Cantor set with two different scaling parameters and one probability measure parameter responsible for nonuniform compression in phase space and multifractality. The values of the parameters fitted also demonstrate that the complex solar wind system could only be weakly non-conservative (small dissipation) and quantify nonlinear dynamics; some parts of the attractor in phase space are visited much more frequently than other parts. In addition, to quantify the multifractality of space plasma intermittent turbulence, we consider that generalized Cantor set also in the context of scaling properties of solar wind turbulence. We investigate the resulting multifractal spectrum of a one-dimensional phenomenological model of turbulence cascade depending on its parameters, especially for asymmetric scaling. In particular, we have shown that intermittent pulses are stronger for the cascade model with two different scaling parameters. Even thought solar wind turbulence appears to be rather space filling, a better agreement with the data is obtained, especially for the negative index of generalized dimensions. Therefore we argue that there is a need to use a two-scale asymmetric cascade model. We hope that this generalized multifractal model will be a useful tool for analysis of intermittent turbulence in space plasmas. We thus believe that fractal analysis of chaotic systems could lead us to a deeper understanding of their nature, and maybe even to predict their seemingly unpredictable behaviour.     

EUV imaging of near-Venus space

Japan’s Venus Climate Orbiter (the Planet-C spacecraft) will be launched in 2008 and will reach an orbit in the ecliptic plane around Venus in 2009. We propose two eXtreme UltraViolet (XUV) imagers to take global two-dimensional snapshots of near-Venus space, including the Venus ionosphere and the interaction region between the solar wind plasma and the Venus ionospheric plasma. The imagers detect the resonantly scattering emissions of oxygen ions (O II 83.4 nm) and atoms (O I 130.3 nm), neutral helium (He I 58.4 nm), and hydrogen (H Ly-α 121.6 nm). Scientific goals are to investigate mechanisms of momentum and mass transfer across the ionopause, of convection in the upper atmosphere and ionosphere, and of atmospheric escape. Especially, we emphasize that sequential images of the O II 83.4-nm emission will enable us to understand temporal evolution of the vortex produced by the Kelvin–Helmholtz (K–H) instability. Though the wave structure due to the K–H instability is generated also at the terrestrial magnetopause, oxygen ions are too tenuous to detect the emission. On the other hand, at the Venus ionopause oxygen ions have enough density to image the resonance emission, i.e., the Venus ionosphere plays a role as a space laboratory for plasma physics.     

Correlations between neutral and ionized solar wind

We report results of a statistical study correlating ionized solar wind (ISW) fluxes observed by ACE during late 2000 and throughout 2001 with neutral solar wind (NSW) fluxes observed by IMAGE/LENA over the same period. The average correlation coefficient between the neutral and ionized solar wind is 0.66 with correlations greater than 0.80 occurring about 29% of the time. Correlations appear to be driven by high solar wind flux variability, similar to results obtained by in situ multi-spacecraft correlation studies. In this study, however, IMAGE remains inside the magnetosphere on over 95% of its orbits. As a function of day of year, or equivalently ecliptic longitude, the slope of the relationship between the neutral solar wind flux and the ionized solar wind flux shows an enhancement near the upstream direction, but the symmetry point appears shifted toward higher ecliptic longitudes than the interstellar neutral (ISN) flow direction by about 20°. The estimated peak interstellar neutral upstream density inside of 1 AU is about 7 × 10⁻³ cm⁻³.     

Solar orbiter, a high-resolution mission to the sun and inner heliosphere

The scientific rationale of the Solar Orbiter is to provide, at high spatial (35 km pixel size) and temporal resolution, observations of the solar atmosphere and unexplored inner heliosphere. Novel observations will be made in the almost heliosynchronous segments of the orbits at heliocentric distances near 45 R and out of the ecliptic plane at the highest heliographic latitudes of 30° – 38°. The Solar Orbiter will achieve its wide-ranging aims with a suite of sophisticated instruments through an innovative design of the orbit. The first near-Sun interplanetary measurements together with concurrent remote observations of the Sun will permit us to determine and understand, through correlative studies, the characteristics of the solar wind and energetic particles in close linkage with the plasma and radiation conditions in their source regions on the Sun. Over extended periods the Solar Orbiter will deliver the first images of the polar regions and the side of the Sun invisible from the Earth.     

In situ observations of magnetic field fluctuations

It is well known that the irregularities of the magnetic field are intimately related to the motion of charged particles. Although transport theories need the spatial and time variations of the magnetic field as input, in situ observations are very limited. Ulysses observations have provided a major step forward by entering the unexplored high latitude regions of the heliosphere, the knowledge of which is vital to interpret particle flux measurements, even at the ecliptic. We analyze the magnetic field data of Ulysses during the mission to study the waves and discontinuities in the heliosphere at different locations, covering a total sunspot cycle. Various tools are employed, including power spectral and structure function analysis. A remarkable difference was found between the fluctuations in the fast and slow solar wind. We argue that the latitudinal extent of the high speed solar wind contributes significantly to the latitudinal variation of the transport parameters, which should also affect the 11 (and 22) year modulation cycle.     

Solar wind interaction with lunar crustal magnetic anomalies

Using Lunar Prospector data, we review the magnetic field and electron signatures of solar wind interaction with lunar crustal magnetic sources. Magnetic field amplifications, too large to represent direct measurements of crustal fields, appear in the solar wind over strong crustal sources, with the chance of observing these amplifications depending on upstream solar wind parameters. We often observe increases in low-energy (?100 eV) electron energy fluxes simultaneously with large magnetic field amplifications, consistent with an increase in plasma density across a shock surface. We also often observe low frequency wave activity in the magnetic field data (both broadband turbulence and monochromatic waves), often associated with electron energization, sometimes up to keV energies. Electron energization appears to be correlated more closely with wave activity than with magnetic amplifications. Detailed studies of the interaction region will be necessary in order to understand the physics of the Moon–solar wind interaction. At present, the Moon represents the only natural laboratory available to us to study solar wind interaction with small-scale crustal magnetic fields, though simulation results and theoretical work can also help us understand the physical processes at work.     

Overview of the Solar Polar Orbit Telescope Project for Space Weather Mission

The Solar Polar ORbit Telescope (SPORT) project for space weather mission has been under intensive scientific and engineering background studies since it was incorporated into the Chinese Space Science Strategic Pioneer Project in 2011.SPORT is designed to carry a suite of remote-sensing and in-situ instruments to observe Coronal Mass Ejections (CMEs),energetic particles,solar high-latitude magnetism,and the fast solar wind from a polar orbit around the Sun. The first extended view of the polar regions of the Sun and the ecliptic enabled by SPORT will provide a unique opportunity to study CME propagation through the inner heliosphere,and the solar high-latitude magnetism giving rise to eruptions and the fast solar wind.Coordinated observations between SPORT and other spaceborne/ground-based facilities within the International Living With a Star (ILWS) framework can significantly enhance scientific output.SPORT is now competing for official selection and implementation during China's 13th Five-Year Plan period of 2016-2020.      

太阳风速度及日球电流片对CME渡越时间的影响

基于1996-2005年88个引起重大地磁暴的CME(日冕物质抛射)事件、1996-2000年的47个CME事件以及1997-2002年的29个全晕状CME事件,结合ACE卫星在1AU处的太阳风和行星际磁场观测资料以及Wilcox Solar Observatory(WSO)天文台的太阳光球层磁图,分析了背景太阳风速度和日球电流片对CME到达1AU处渡越时间预报误差的影响.结果表明,背景太阳风速度与CME渡越时间误差并没有明显的相关性,在考虑了磁云通量管轴相对黄道面夹角的影响后相关性依然不明显.然而日球电流片对CME渡越时间却有明显的影响,对于初速度较小的异侧CME事件,其渡越时间大于同侧事件;而对于具有较大初速度的CME事件,异侧事件的渡越时间明显小于同侧事件.研究结果表明,CME与太阳风以及日球电流片的相互作用并不是简单的对流相互作用,造成高速CME异侧事件快于同侧事件到达地球的因素非常复杂,有待深入研究.      

Imaging interplanetary CMEs at radio frequency from solar polar orbit

Coronal mass ejections (CMEs) represent a great concentration of mass and energy input into the lower corona. They have come to be recognized as the major driver of physical conditions change in the Sun–Earth system. Consequently, observations of CMEs are important for understanding and ultimately predicting space weather conditions. This paper discusses a proposed mission, the Solar Polar Orbit Radio Telescope (SPORT) mission, which will observe the propagation of interplanetary CMEs to distances of near 0.35 AU from the Sun. The orbit of SPORT is an elliptical solar polar orbit. The inclination angle between the orbit and ecliptic plane should be about 90°. The main payload on board SPORT will be an imaging radiometer working at the meter wavelength band (radio telescope), which can follow the propagation of interplanetary CMEs. The images that are obtained by the radio telescope embody the brightness temperature of the objectives. Due to the very large size required for the antenna aperture of the radio telescope, we adopt interferometric imaging technology to reduce it. Interferometric imaging technology is based on indirect spatial frequency domain measurements plus Fourier transformation. The SPORT spacecraft will also be equipped with a set of optical and in situ measurement instruments such as a EUV solar telescope, a solar wind ion instrument, an energetic particle detector, a magnetometer, a wave detector and a solar radio burst spectrometer.     

基于日心坐标系的PDQG-R剖分模型及编码研究

随着空间数据的海量增长, 为了提高数据存取效率和数据可视化效率, 需要对 数据进行有效的组织和管理. 基于现有的二维表面剖分模型, 针对过太阳质心 的黄道面和子午面, 提出一种新的PDQG-R格网模型--平面退化四叉树格网, 并给出了相应的网格编码方案. 以太阳风模型数据为例, 给出了具体的组织实 例并验证, 结果表明该剖分模型不仅解决了日心附近网格过密问题, 还可以满足径向分辨率与经(纬)向分辨率不同步的需求, 同时还能提供多分辨率层次的数据, 有效地支持海量空间数据的组织管理.      

Russian payload for “interhelioprobe” (“interhelios”) mission

The solar and heliospheric instruments proposed to study the solar atmosphere at close distances and the inner heliosphere onboard the Interhelioprobe mission are described. Remote observations of the solar surface combined with in-situ measurements at optimum orbital parameters (quasi-corotation with the Sun, multiple positions with respect to the Sun-Earth line, and inclination to the ecliptic plane) provide new information on the fine structure and dynamics of the solar surface, solar flares and ejections, solar corona, and solar wind.     

天基X射线掠入射式成像望远镜发展现状

阐述了太阳X射线成像观测在空间天气预报中的地位和作用，叙述了掠入射式X射线聚焦成像的基本原理，简要介绍了在轨成功运行的天体X射线成像望远镜和太阳X射线成像望远镜的基本设计和技术指标，并介绍了国内正开发研制的专门服务于空间天气预报的太阳X射线成像望远镜基本设计和主要特点．     

Sharp boundaries of solar wind plasma structures and their relationship to solar wind turbulence

Sharp (<10 min) and large (>20%) solar wind ion flux changes are common phenomena in turbulent solar wind plasma. These changes are the boundaries of small- and middle-scale solar wind plasma structures which can have a significant influence on Earth’s magnetosphere. These solar wind ion flux changes are typically accompanied by only a small change in the bulk solar wind velocity, hence, the flux changes are driven mainly by plasma density variations. We show that these events occur more frequently in high-density solar wind. A characteristic of solar wind turbulence, intermittency, is determined for time periods with and without these flux changes. The probability distribution functions (PDF) of solar wind ion flux variations for different time scales are calculated for each of these periods and compared. For large time scales, the PDFs are Gaussian for both data sets. For small time scales, the PDFs from both data set are more flat than Gaussian, but the degree of flatness is much larger for the data near the sharp flux change boundaries.     

Some characteristics of propagation of flare- or CME-associated interplanetary shock waves

Many interplanetary shock waves have a fast mode MHD wave Mach number between one and two and the ambient solar wind plasma and magnetic field are known to fluctuate. Therefore a weak, fast, MHD interplanetary shock wave propagating into a fluctuating solar wind region or into a solar wind stream will be expected to vary its strength.It is possible that an interplanetary shock wave, upon entering such a region will weaken its strength and degenerate into a fast-mode MHD wave. It is even possible that the shock may dissipate and disappear.A model for the propagation of a solar flare - or CME (Coronal Mass Ejections) - associated interplanetary shock wave is given. A physical mechanism is described to calculate the probability that a weak shock which enters a turbulent solar wind region will degenerate into a MHD wave. That is, the shock would disappear as an entropy-generate entity. This model also suggests that most interplanetary shock waves cannot propagate continuously with a smooth shock surface. It is suggested that the surface of an interplanetary shock will be highly distorted and that parts of the shock surface can degenerate into MHD waves or even disappear during its global propagation through interplanetary space. A few observations to support this model will be briefly described.Finally, this model of shock propagation also applies to corotating shocks. As corotating shocks propagate into fluctuating ambient solar wind regions, shocks may degenerate into waves or disappear.     

Planet-A mission to Halley

Looking at the chance of the next apparition of the Halley comet in 1986, ISAS decided to send a first Japasanese interplanetary spacecraft for the study of cometary hydrogen coma and solar wind. The Planet-A spacecraft which carries VUV imaging camera and solar wind plasma analyser will be launched in August 1985 and flyby the Halley comet in early March 1986 with the distance of several million kilometers from the comet nucleus. This mission is not only self-consistent but collaborative with other space mission as well as earth-bound observations. In the present paper, the Planet-A mission to Halley is described with brief explanation of the spacecraft.     

The L5 mission for space weather forecasting

We have studied a number of interplanetary space mission scenarios for space weather research and operational forecasting experiments and concluded that a spacecraft should be deployed at the L5 point of the Sun–Earth system to enable remote sensing of the Sun and interplanetary space and in situ measurements of solar wind plasma and high energy solar particle events. The L5 point is an appropriate position for making side-view observations of geo-effective coronal mass ejections and interplanetary plasma clouds.Here, we describe briefly the mission plan and the ongoing BBM development of important subsystems such as the wide field coronal imager (WCI) and the mission processor. The WCI will have a large CCD array with 16-bit sampling, to achieve a dynamic range of several thousand in order to detect very small deviations due to plasma clouds under zodiacal light contaminations a hundred times brighter than the clouds. The L5 mission we propose will surely contribute to the construction of an international space weather observation network.     

Modelling of galactic Carbon in an asymmetrical heliosphere: Effects of asymmetrical modulation conditions

Observations of galactic cosmic rays (GCRs) from the two Voyager spacecraft inside the heliosheath indicate significant differences between them, suggesting that in addition to a possible global asymmetry in the north–south dimensions (meridional plane) of the heliosphere, it is also possible that different modulation (turbulence) conditions could exist between the two hemispheres of the heliosphere. We focus on illustrating the effects on GCR Carbon of asymmetrical modulation conditions combined with a heliosheath thickness that has a significant dependence on heliolatitude. To reflect different modulation conditions between the two heliospheric hemispheres in our numerical model, the enhancement of both polar and radial perpendicular diffusion off the ecliptic plane is assumed to differ from heliographic pole to pole. The computed radial GCR intensities at polar angles of 55° (approximating the Voyager 1 direction) and 125° (approximating the Voyager 2 direction) are compared at different energies and for both particle drift cycles. This is done in the context of illustrating how different values of the enhancement of both polar and radial perpendicular diffusion between the two hemispheres contribute to causing differences in radial intensities during solar minimum and moderate maximum conditions. We find that in the A > 0 cycle these differences between 55° and 125° change both quantitatively and qualitatively for the assumed asymmetrical modulation condition as reflected by polar diffusion, while in the A < 0 cycle, minute quantitative differences are obtained. However, when both polar and radial perpendicular diffusion have significant latitude dependences, major differences in radial intensities between the two polar angles are obtained in both polarity cycles. Furthermore, significant differences in radial intensity gradients obtained in the heliosheath at lower energies may suggest that the solar wind turbulence at and beyond the solar wind termination shock must have a larger latitudinal dependence.     

Radio sounding of the solar wind acceleration region with spacecraft signals

Data from coronal radio-sounding experiments carried out on various interplanetary spacecraft are used to derive the empirical radial dependence of solar wind velocity and density at heliocentric distances from 3 to 60 solar radii for heliolatitudes below 60° and for low solar activity. The radial dependencies of solar wind power and acceleration are derived from these results. Summaries of the radial behavior of characteristic parameters of the solar wind turbulence (e.g., the spectral index and the inner and outer turbulence scales), as well as the fractional density fluctuation, are also presented. These radio-sounding results provide a benchmark for models of the solar wind in its acceleration region.     

Research Progress of Solar Corona and Interplanetary Physics in China: 2010-2012

The scientific objective of solar corona and interplanetary research is the understanding of the various phenomena related to solar activities and their effects on the space environments of the Earth. Great progress has been made in the study of solar corona and interplanetary physics by the Chinese space physics community during the past years. This paper will give a brief report about the latest progress of the corona and interplanetary research in China during the years of 2010?2012. The paper can be divided into the following parts: solar corona and solar wind, CMEICME, magnetic reconnection, energetic particles, space plasma, space weather numerical modeling by 3D SIP-CESE MHD model, space weather prediction methods, and proposed missions. They constitute the abundant content of study for the complicated phenomena that originate from the solar corona, propagate in interplanetary space, and produce geomagnetic disturbances. All these progresses are acquired by the Chinese space physicists, either independently or through international collaborations.      

Formation and characteristics of low latitude boundary layer

Characteristics of low latitude boundary layer (LLBL) of the Earth’s magnetosphere are investigated using data of Interball/Tail probe observations. The role of different processes of LLBL formation is discussed. The high level of magnetosheath turbulence is taken into account. It is shown that the turbulent nature of magnetic field and plasma fluctuations in the magnetosheath is one of the main factors determining the structure of LLBL. The results of Interball/Tail probe observations of the event 9 March 1996 are analyzed. The thickness of LLBL is determined for the number of cases. The change of LLBL thickness under the influence of the changes of solar wind parameters is investigated. It is shown that variability of solar wind conditions can be the important factor controlling LLBL thickness. Results of observations are compared with the theory which explains the value of LLBL thickness as the result of plasma transport inside the magnetosphere. It is shown that the theory gives the qualitative explanation of the observed dependence of LLBL thickness on solar wind parameters.