Magnetic clouds and interplanetary particle transport: a numerical model

Magnetic clouds modify the structure of the interplanetary magnetic field on spatial scales of tenth of AU. Their influence on the transport of energetic charged particles is studied with a numerical model that treats the magnetic cloud as an outward propagating modification of the focusing length. As a rule of thumb, the influence of the magnetic cloud on particle intensity and anisotropy profiles increases with decreasing particle mean free path and decreasing particle speed. Three cases are considered: (1) when the magnetic cloud is the driver of a shock that accelerates particles as it propagates outward, (2) when the magnetic cloud interacts with a prior solar energetic particle event, and (3) when a magnetic cloud already is present in interplanetary space at the time of a solar energetic particle event. In the latter case the cloud acts as a barrier, storing the bulk of the particles in its downstream medium.     

Precipitation of energetic magnetospheric electrons and accompanying solar wind characteristics

From 1957 up to the present time, the Lebedev Physical Institute (LPI) has performed regular monitoring of ionizing radiation in the Earth’s atmosphere. There are cases when the X-ray radiation generated by energetic magnetospheric electrons penetrates the atmosphere and is observed at polar latitudes. The vast majority of these events occurs against the background of high-velocity solar wind streams, while magnetospheric perturbations related to interplanetary coronal mass ejections (ICMEs) are noneffective for precipitation. It is shown in the paper that ICMEs do not cause acceleration of a sufficient amount of electrons in the magnetosphere. Favorable conditions for acceleration and subsequent scattering of electrons into the loss cone are created by magnetic storms with an extended recovery phase and with sufficiently frequent periods of negative Bz component of the interplanetary magnetic field (IMF). Such geomagnetic perturbations are typical for storms associated with high-velocity solar wind streams.     

不同起源地磁扰动期间极光沉降能量的统计研究

尽管对极光沉降能量(HP)的研究已经开展很久,但是关于不同行星际扰动源对HP影响的研究仍然很少.本文基于2001—2008年NOAA极轨卫星数据,对三类不同扰动源,即盔状冕流共转相互作用区(CIRs)、伪冕流CIRs和行星际日冕物质抛射(ICMEs)驱动的中等磁暴期间HP的变化进行时序叠加统计分析,讨论了相关太阳风背景参数、地磁活动强度以及耦合函数的有效性;研究了三类磁暴事件期间HP的南北半球不对称性.结果表明,在磁暴之前盔状冕流CIR磁暴的HP明显低于伪冕流CIR磁暴和ICME磁暴,盔状冕流"磁暴前的平静期"与Newell耦合函数关系密切,而与Russell-McPherron效应关系较小.盔状冕流CIR磁暴主相HP高于伪冕流CIR磁暴和ICME磁暴,可能与盔状冕流相应行星际|B_z|和太阳风数密度均较高有关.此外,在Kp≤4时,冬夏季半球HP的差别随着Kp增加而增加,相应的变化规律符合电导率反馈机制的预测;在Kp>4时,盔状冕流磁暴和ICME磁暴冬季半球的HP大于夏季半球的,伪冕流磁暴事件夏季半球的HP大于冬季半球的或与冬季半球的相近.     

Solar connections of geoeffective magnetic structures

Coronal mass ejections (CMEs) and high-speed solar wind streams (HSS) are two solar phenomena that produce large-scale structures in the interplanetary (IP) medium. CMEs evolve into interplanetary CMEs (ICMEs) and the HSS result in corotating interaction regions (CIRs) when they interact with preceding slow solar wind. This paper summarizes the properties of these structures and describes their geoeffectiveness. The primary focus is on the intense storms of solar cycle 23 because this is the first solar cycle during which simultaneous, extensive, and uniform data on solar, IP, and geospace phenomena exist. After presenting illustrative examples of coronal holes and CMEs, I discuss the internal structure of ICMEs, in particular the magnetic clouds (MCs). I then discuss how the magnetic field and speed correlate in the sheath and cloud portions of ICMEs. CME speed measured near the Sun also has significant correlations with the speed and magnetic field strengths measured at 1 AU. The dependence of storm intensity on MC, sheath, and CME properties is discussed pointing to the close connection between solar and IP phenomena. I compare the delay time between MC arrival at 1 AU and the peak time of storms for the cloud and sheath portions and show that the internal structure of MCs leads to the variations in the observed delay times. Finally, we examine the variation of solar-source latitudes of IP structures as a function of the solar cycle and find that they have to be very close to the disk center.     

Cross-field gradients: general concept, importance of multi-spacecraft measurements and study at 1 AU of the source intensity gradient for E>30 keV solar event electrons

Three main physical processes (and associated properties) are currently used to describe the flux and anisotropy time profiles of solar energetic particle events, called SEP profiles. They are (1) the particle scattering (due to magnetic waves), (2) the particle focusing (due to the decrease of the amplitude of the interplanetary magnetic field (IMF) with the radial distance to the Sun) and (3) the finite injection profile at the source. If their features change from one field line to another, i.e. if there is a cross IMF gradient (CFG), then the shape of the SEP profiles will depend, at onset time, on the relative position of the spacecraft to the IMF and might vary significantly on small distance scale (e.g. 10⁶ km). One type of CFG is studied here. It is called intensity CFG and considers variations, at the solar surface, only of the intensity of the event. It is shown here that drops of about two orders of magnitude over distances of 10⁴ km at the Sun (1° of angular distance) can influence dramatically the SEP profiles at 1 AU. This CFG can lead to either an under or overestimation of both the parallel mean free path and of the injection parameters by factor up to, at least, 2/3 and 18, respectively. Multi-spacecraft analysis can be used to identify CFG. Three basic requirements are proposed to identify, from the observation, the type of the CFG being measured.     

Does the duration of the magnetic storm recovery phase depend on the development rate in its main phase? 2. A new method

In contrast to our previous work (Yermolaev et al., 2015), in which we used the magnetic storm recovery phase duration, the exponential time of the recovery phase of magnetic storms generated by three interplanetary driver types (CIR, Sheath, and ICME) is introduced in the present work. The dependence of these times on the storm development rate |Dst_min|/ΔT (where ΔT is the storm main phase duration) is studied. A similar physical result has been achieved despite the different data analysis method used: the times of the storm recovery and development rates correlate for storms induced by CIR and Sheath compression regions, and any relation between these parameters is absent for storms induced by ICME.     

Geomagnetic Field Disturbances Caused by Heliospheric Current Sheet Crossings

The heliospheric current sheet (HCS) is modified by the solar activity. HCS is highly inclined during solar maximum and almost confined with the solar equatorial plane during solar minimum. Close to the HCS solar wind parameters as proton temperature, flow speed, proton density, etc. differ compared to the region far from the HCS. The Earth’s magnetic dipole field crosses HCS several times each month. Considering interplanetary coronal mass ejections (ICME) and high speed solar wind streams (HSS) free periods an investigation of the HCS influence on the geomagnetic field disturbances is presented. The results show a drop of the Dst index and a rise of the AE index at the time of the HCS crossings and also that the behavior of these indices does not depend on the magnetic polarity.     

Modeling of Physical Processes by Analysis of Hard X-Ray and Microwave Radiations in the Solar Flare of November 10, 2002

For electron acceleration during solar flares, it is very important to determine the pitch-angle and energy dependences of the electron distribution function. At present, this cannot be done directly from observations. Therefore, it is necessary to perform a numerical simulation of the propagation of accelerated electrons in the magnetic field of the flare loop (loops) and calculate the X-ray and radio emissions. For the solar flare of November 10, 2002, we have obtained qualitative and quantitative agreements of modeled X-ray and radio maps with the RHESSI satellite and Nobeyama Radioheliograph data. We have determined the flare model parameters that agree with observations. The pitch-angle anisotropy of electrons determined by highly directional functions of the S(α) = cos⁸(α) type, the energy spectrum consist of two electron populations, the low-energy part of the spectrum up to an energy of break of 350 keV is characterized by a power law with the exponent δ₁ = 2.7–2.9, and the energy spectrum is more rigid above 420 keV (δ₂ = 2–2.3).     

Determining the parameters of coronal mass ejections using the method of MHD modeling ejection evolutions

The initial parameters of disturbing fluxes of coronal mass ejections (CMEs) such as loop, front, spike, multiple structure ejection, and structureless ejection, which cannot be determined from direct observations, are determined using the data on the interplanetary coronal mass ejections (ICMEs) registered on the Helios and Pioneer Venus Orbiter spacecraft in the vicinity of Venus. The method of MHD modeling the modified initial parameters of CMEs has been used for this purpose. The ICME parameters have been analyzed in order to determine the types of the solar sources of the considered plasma flows.     

地球附近第23太阳活动周磁云和非磁云ICME的对比统计

行星际日冕物质抛射（ICME）,作为影响地球空间天气的重要源头之一,根据其磁场结构特点可分为磁云（MC）和非磁云ICME两个子集.本文对第23周的磁云和非磁云ICME结构及其地磁效应进行对比统计研究.第23周ICME事件总数为317个,其中磁云占ICME比例为33.75%,非磁云ICME占66.25%.统计结果表明,非磁云ICME数与太阳黑子数呈现出非常好的正相关性,而磁云与太阳黑子数的这种相关性并不明显.相反,磁云占ICME的比率与太阳黑子数呈现出一定的反相关性.对磁云与非磁云ICME引起的地磁暴的比较研究表明：磁云及其鞘区引发的地磁暴平均水平要高于非磁云ICME及其鞘区.磁云和非磁云ICME的磁场强度、南向磁场强度和传播速度整体上都随地磁暴水平提升而增加.对磁云与非磁云ICME参数的进一步对比分析表明,磁云及其鞘区的平均磁场强度和南向磁场分量平均值都明显要比非磁云ICME的大;而二者的等离子体温度、密度和速度平均值相差并不明显.     

Cosmic-ray vector anisotropy and local characteristics of the interplanetary medium

Variations in the cosmic-ray vector anisotropy observed on Earth are closely connected with the state of the near-Earth interplanetary medium. Hourly characteristics of vector anisotropy for the period 1957–2013, which were obtained by the global survey method from the data of the worldwide network of neutron monitors, make it possible to study the relationship between the cosmic-ray anisotropy and solar wind parameters. In the present work, we have studied the connection between the equatorial component of anisotropy of cosmic rays with a rigidity of 10 GV and the following parameters: velocity and density of the solar wind; density of the interplanetary magnetic field; and cosmic-ray density variations, in which the spatial gradient of cosmic rays in the interplanetary medium is manifested. The characteristics of cosmic-ray anisotropy at various combinations of the interplanetary medium parameters are compared. The possibility of diagnosing the solar wind state from data on the cosmic-ray anisotropy is discussed.     

Signatures of interplanetary transients behind shocks and their associated near-surface solar activity

Interplanetary transients with particular signatures different from the normal solar wind have been observed behind interplanetary shocks and also without shocks. In this paper we have selected four well-known transient interplanetary signatures, namely: magnetic clouds, helium enhancements and bidirectional electron and ion fluxes, found in the solar wind behind shocks, and undertaken a correlative study between them and the corresponding solar observations. We found that although commonly different signatures appear in a single interplanetary transient event, they are not necessarily simultaneous, that is, they may belong to different plasma regions within the ejecta, which suggests that they may be generated by complex processes involving the ejection of plasma from different solar regions. We also found that more than 90% of these signatures correspond to cases when an H flare and the eruption of a filament occurred near solar central meridian between 1 and 4 days before the observation of the disturbance at 1 AU, the highest association being with flares taking place between 2 and 3 days before. The majority of the H flares were also accompanied by soft X-ray events. We also studied the longitudinal distribution of the associated solar events and found that between 80% and 90% of the interplanetary ejecta were associated with solar events within a longitudinal band of ±30° from the solar central meridian. An east-west asymmetry in the associated solar events seems to exist for some of the signatures. We also look for coronal holes adjacent to the site of the explosive event and find that they were present almost in every case.     

Dependence of geomagnetic activity during magnetic storms on the solar wind parameters for different types of streams: 2. Main phase of storm

The paper analyses the development of the main phase of magnetic storms with Dst ≤ −50 nT, the interplanetary source of which consists of eight types of solar wind streams: magnetic clouds (MC, 17 storms); corotating interaction regions (CIR, 49 storms); Ejecta (50 storms); compressed region (Sheath) before Ejecta Sh_E (34 storms); the Sheath before a magnetic cloud Sh_MC (6 storms); all Sheath before all ICME, Sh_E + Sh_MC (40 storms); all ICME, MC + Ejecta (67 storms); and an indeterminate type of stream IND (34 storms).     

Observations of flux rope – associated particle bursts with GEOTAIL in the distant tail

Geotail energetic particle, magnetic field data and plasma observations (EPIC, MGF and CPI experiments) have been examined for a number of energetic particle bursts in the distant tail (120Re < |X_GSM| < 130 Re), associated with moving magnetic field structures, following substorm onsets. The features obtained from this data analysis are consistent with the distant magnetotail dynamics determined first by ISEE3 observations and explained in terms of the neutral line model. At the onset of the bursts, before plasma sheet entrance, energetic electrons appear as a field-aligned beam flowing in the tailward direction, followed by anisotro-pic ions. Within the flux rope region, suprathermal ions exhibit a convective anisotropy, which allows determination of the plasma flow velocity, assuming that the anisotropy arises from the Compton-Getting effect. The velocities thus determined in the plasma sheet are estimated to be 200–650 km/s, and compare favourably with the velocities derived from the CPI electron and proton experiment. The estimated length of magnetic field structures varies between 28 and 56 Re and depends on the strength of the westward electrojet intensification. Finally, the three structures reported here show clear magnetic field signatures of flux rope topology. The existence of a strong magnetic field aligned approximately along the Y-axis and centred on the north-to-south excursion of the field, and the bipolar signature in both By and/or Bz components, is consistent with the existence of closed field lines extending from Earth and wrapping around the core of the flux rope structure.     

Forecast of the solar wind velocity and the interplanetary magnetic field radial component polarity at the phase of decay of solar cycle 23

The solar wind velocity and polarity of the B _x-component of the interplanetary magnetic field have been analyzed for the first eight months of 2005. The interplanetary magnetic field had a four-sector structure, which persisted during nine Carrington rotations. Three stable clusters of a high-speed solar wind stream and one cluster of a low-speed stream were observed during one solar rotation. These clusters were associated with the interplanetary magnetic field sectors. The predicted solar wind velocity was calculated since July 2005 one month ahead as an average over several preceding Carrington rotations. The polarity of the B _x-component of the interplanetary magnetic field was predicted in a similar way based on the concept of the sector structure of the magnetic field and its relation to maxima of the solar wind velocity. The results indicate a satisfactory agreement of the forecast for two rotations ahead in July–August 2005 and pronounced violation of agreement for the next rotation due to a sudden reconfiguration of the solar corona and strong sporadic processes in September 2005.     

Some Features of the Variation of the Magnetic Field Characteristics in the Umbra of Sunspots During Flares and Coronal Mass Ejections

The observed variations of the magnetic properties of sunspots during eruptive events (solar flares and coronal mass ejections (CMEs)) are discussed. Variations of the magnetic field characteristics in the umbra of the sunspots of active regions (ARs) recorded during eruptive events on August 2, 2011, March 9, 2012, April 11, 2013, January 7, 2014, and June 18, 2015, are studied. The behavior of the maximum of the total field strength B_max, the minimum inclination angle of the field lines to the radial direction from the center of the Sun α_min (i.e., the inclination angle of the axis of the magnetic tube from the sunspot umbra), and values of these parameters B_mean and α_mean mean within the umbra are analyzed. The main results of our investigation are discussed by the example of the event on August 2, 2011, but, in general, the observed features of the variation of magnetic field properties in AR sunspots are similar for all of the considered eruptive events. It is shown that, after the flare onset in six AR sunspots on August 2, 2011, the behavior of the specified magnetic field parameters changes in comparison with that observed before the flare onset.     

The structure and origin of magnetic clouds in the solar wind

Plasma and magnetic field data from the Helios 1/2 spacecraft have been used to investigate the structure of magnetic clouds (MCs) in the inner heliosphere. 46 MCs were identified in the Helios data for the period 1974–1981 between 0.3 and 1 AU. 85% of the MCs were associated with fast-forward interplanetary shock waves, supporting the close association between MCs and SMEs (solar mass ejections). Seven MCs were identified as direct consequences of Helios-directed SMEs, and the passage of MCs agreed with that of interplanetary plasma clouds (IPCs) identified as white-light brightness enhancements in the Helios photometer data. The total (plasma and magnetic field) pressure in MCs was higher and the plasma- lower than in the surrounding solar wind. Minimum variance analysis (MVA) showed that MCs can best be described as large-scale quasi-cylindrical magnetic flux tubes. The axes of the flux tubes usually had a small inclination to the ecliptic plane, with their azimuthal direction close to the east-west direction. The large-scale flux tube model for MCs was validated by the analysis of multi-spacecraft observations. MCs were observed over a range of up to 60° in solar longitude in the ecliptic having the same magnetic configuration. The Helios observations further showed that over-expansion is a common feature of MCs. From a combined study of Helios, Voyager and IMP data we found that the radial diameter of MCs increases between 0.3 and 4.2 AU proportional to the distance, R, from the Sun as R^0.8 (R in AU). The density decrease inside MCs was found to be proportional to R^–2.4, thus being stronger compared to the average solar wind. Four different magnetic configurations, as expected from the flux-tube concept, for MCs have been observed in situ by the Helios probes. MCs with left-and right-handed magnetic helicity occurred with about equal frequencies during 1974–1981, but surprisingly, the majority (74%) of the MCs had a south to north (SN) rotation of the magnetic field vector relative to the ecliptic. In contrast, an investigation of solar wind data obtained near Earths orbit during 1984–1991 showed a preference for NS-clouds. A direct correlation was found between MCs and large quiescent filament disappearances (disparition brusques, DBs). The magnetic configurations of the filaments, as inferred from the orientation of the prominence axis, the polarity of the overlying field lines and the hemispheric helicity pattern observed for filaments, agreed well with the in situ observed magnetic structure of the associated MCs. The results support the model of MCs as large-scale expanding quasi-cylindrical magnetic flux tubes in the solar wind, most likely caused by SMEs associated with eruptions of large quiescent filaments. We suggest that the hemispheric dependence of the magnetic helicity structure observed for solar filaments can explain the preferred orientation of MCs in interplanetary space as well as their solar cycle behavior. However, the white-light features of SMEs and the measured volumes of their interplanetary counterparts suggest that MCs may not simply be just H-prominences, but that SMEs likely convect large-scale coronal loops overlying the prominence axis out of the solar atmosphere.