A synchrotron-based facility for the in-situ location,chemical and mineralogical characterization of ∼10 μm particles captured in aerogel

NASA’s Stardust mission collected dust from the coma of Comet Wild-2 on January 2nd, 2004, by direct capture into aerogel cells that flew through the dust coma at ∼6 km/s. Stardust collected several hundred comet particles >10 μm in size. These comet samples were delivered to Earth on January 15th, 2006. We developed a facility at the National Synchrotron Light Source at Brookhaven National Laboratory (Upton, NY, USA) for the in-situ characterization of ∼10 μm particles collected in aerogel. These analytical instruments allow us to perform extensive chemical, mineralogical, and size-frequency characterization of particles captured in aerogel. These analyses are conducted without any invasive extraction, minimizing the possibility of contamination or particle loss during preparation. This facility was used to determine the chemical composition, the oxidation state, the mineralogy and to provide an indication of the grain size of the Wild-2 particles before they were removed from the aerogel. This information provides a catalog of particle types, allowing a more reasoned allocation of the particles to subsequent investigators based on a relatively detailed knowledge of the chemical composition and mineralogy of each particle. These measurements allowed a comparison of the chemical and mineralogical properties of the Wild-2 particles with other types of extraterrestrial materials, including interplanetary dust particles and meteorites. The success of in-situ analysis for Wild 2 particles demonstrates that synchrotron-based facilities will be important for the analysis of particles collected in aerogel on future earth-orbiting satellites and spacecraft.     

On the relation of the Forbush decreases detected by ASEC monitors during the 23rd solar activity cycle with ICME parameters

To improve the physical understanding of the Forbush decreases (FD) and to explore the Space Weather drivers, we need to measure as much geospace parameter as possible, including the changing fluxes of secondary cosmic rays. At the Aragats Space Environmental Center (ASEC) are routinely measured the neutral and charged fluxes of secondary cosmic rays. Each of species has different most probable energy of primary “parent” proton/nuclei. Therefore, the energy range of the Galactic Cosmic Rays (GCR) affected by Interplanetary Coronal Mass Ejection (ICME) can be effectively estimated using data of the ASEC monitors. We presented relations of the magnitude of FD observed in different secondary particle fluxes to the most probable energy of the primary protons. We investigate the correlations between the magnitude of FD with the size, speed, density and magnetic field of the ICME. We demonstrate that the attenuation of the GCR flux incident on the Earth’s atmosphere due to passing of the ICME is dependent on the speed and size of the ICME and the magnetic field strength.     

Modeling and data analysis of a Forbush decrease

We study the Forbush decrease of the galactic cosmic ray intensity observed in 9–25 September 2005 using the experimental data and a newly developed time-dependent three dimensional modeling. We analyze neutron monitors and muon telescopes, and the interplanetary magnetic field data. We demonstrate a clear relationship between the rigidity (R) spectrum exponent (γ) of the Forbush decrease and the exponent (ν) of the power spectral density of the components of the interplanetary magnetic field in the frequency range of ∼ 10⁻⁶–10 ⁻⁵ Hz. We confirm that an inclusion of the time-dependent changes of the exponent ν makes the newly developed nonstationary three dimensional model of the Forbush decrease compatible with the experimental data. Also, we show that the changes of the rigidity spectrum exponent γ does not depend on the level of convection of the galactic cosmic rays stream by solar wind; depending on the changes of the exponent ν, i.e. on the state of the turbulence of the interplanetary magnetic field.     

Geoeffectiveness of interplanetary shocks controlled by impact angles: A review

The high variability of the Sun’s magnetic field is responsible for the generation of perturbations that propagate throughout the heliosphere. Such disturbances often drive interplanetary shocks in front of their leading regions. Strong shocks transfer momentum and energy into the solar wind ahead of them which in turn enhance the solar wind interaction with magnetic fields in its way. Shocks then eventually strike the Earth’s magnetosphere and trigger a myriad of geomagnetic effects observed not only by spacecraft in space, but also by magnetometers on the ground. Recently, it has been revealed that shocks can show different geoeffectiveness depending closely on the angle of impact. Generally, frontal shocks are more geoeffective than inclined shocks, even if the former are comparatively weaker than the latter. This review is focused on results obtained from modeling and experimental efforts in the last 15?years. Some theoretical and observational background are also provided.     

Forecasting space weather: Predicting interplanetary shocks using neural networks

We are developing a system to predict the arrival of interplanetary (IP) shocks at the Earth. These events are routinely detected by the Electron, Proton, and Alpha Monitor (EPAM) instrument aboard NASA’s ACE spacecraft, which is positioned at Lagrange Point 1 (L1). In this work, we use historical EPAM data to train an IP shock forecasting algorithm. Our approach centers on the observation that these shocks are often preceded by identifiable signatures in the energetic particle intensity data. Using EPAM data, we trained an artificial neural network to predict the time remaining until the shock arrival. After training this algorithm on 37 events, it was able to forecast the arrival time for 19 previously unseen events. The average uncertainty in the prediction 24 h in advance was 8.9 h, while the uncertainty improved to 4.6 h when the event was 12 h away. This system is accessible online, where it provides predictions of shock arrival times using real-time EPAM data.     

太阳耀斑行星际激波传播中的追赶效应

本文采用二维MHD模型对具有不同间隔时间的2个耀斑先后爆发,模拟研究它们所对应的行星际激波间的追赶效应,并和单个耀斑所产生的行星际激波相比较。研究结果表明,间隔时间一天以内的2个耀斑激波在行星际空间向外传播时,激波之间有明显的相互作用发生,间隔时间的长短决定了激波传播过程中追赶效应的强弱。根据数值试验结果,追赶效应可归纳为4类,(1)强追赶效应,(2)中等追赶效应,(3)弱追赶效应,(4)无追赶效应。属于强追赶效应的2个耀斑激波传播至1AU处,产生的行星际扰动非常相似于单个耀斑激波的扰动。     

CME dynamics using coronagraph and interplanetary ejecta data

In this work, we present a study of the coronal mass ejection (CME) dynamics using LASCO coronagraph observations combined with in-situ ACE plasma and magnetic field data, covering a continuous period of time from January 1997 to April 2001, complemented by few extreme events observed in 2001 and 2003. We show, for the first time, that the CME expansion speed correlates very well with the travel time to 1 AU of the interplanetary ejecta (or ICMEs) associated with the CMEs, as well as with their preceding shocks. The events analyzed in this work are a subset of the events studied in Schwenn et al. (2005), from which only the CMEs associated with interplanetary ejecta (ICMEs) were selected. Three models to predict CME travel time to Earth, two proposed by Gopalswamy et al. (2001) and one by Schwenn et al. (2005), were used to characterize the dynamical behavior of this set of events. Extreme events occurred in 2001 and 2003 were used to test the prediction capability of the models regarding CMEs with very high LASCO C3 speeds.     

Numeric simulations of in situ observations of interacting ejecta near 1 AU

We use a simple numerical model (González-Esparza, J.A., Santillán, A., Ferrer, J. A numerical study of the interaction between two ejecta in the interplanetary medium: one and two dimensional hydrodynamic simulations, Ann. Geophys. 22, 3741–3749, 2004) to study the evolution of three events in the solar wind reported by Wang et al. (Wang, Y.M., Ye, P.Z., Wang, S. Multiple magnetic clouds: several examples during March–April 2001. J. Geophys. Res. 108, 1370, 2003, doi:10.1029/2003JA009850), where two interacting ejecta detected in situ by ACE near 1 AU were related to CMEs observed previously by SOHO-LASCO. The study is based on a 1-D hydrodynamic model using the ZEUS code (Stone, J.M., Norman, M. ZEUS 2-D: A radiation magnetohydrodynamics code for astrophysical flows in two dimensions, I, the hydrodynamics algorithms and tests, Astrophys. J. 80, 753, 1992). Although this model cannot address either the magnetic field dynamics or the complex geometrical effects intrinsic in the three-dimensional nature of the phenomena, it illuminates the transferring of momentum and evolution of interacting large-scale solar wind disturbances in those cases where there is no merging (magnetic reconnection) between the two ejecta. This model can reproduce, in some cases, characteristics of the events such as transit times and flow signatures as inferred from the two-point measurements from spacecraft.     

行星际南向磁场事件与强磁暴

利用１９７８－１９８８年期间的太阳风和地磁资料对行星际磁场（ＩＭＦ）南向分量Ｂｓ事件（即Ｂｓ〉１０ｎＴ及其所驱动的错向电场ＶＢｓ〉５ｍＶ／ｍ、持续时间△Ｔ〉３ｈ的事件）与弱磁暴（Ｄｓｔ≤－１００ｎＴ）关系进行了分析。结果表明,１００％的Ｂｓ事件能能引起磁暴的发生,但其中只有８４％为强磁暴;强磁暴的发生都与较强的ＩＭＦ Ｂｓ活动密切相关,但只有６８％的强磁共伴随Ｂｓ事件而发生;Ｂｓ事件与强磁暴并不是     

行星际强磁场结构中的亚阿尔文波速流

1982年11月23日开始的极高速太阳风流追赶强磁场结构的事件,形成了高密度前鞘-强磁场本体-高密度后鞘-高速流的组合结构。本文分析了此组合结构的磁流体动力学特征,发现在强磁场本体内出现行星际亚阿尔文波速流,并推论了其可能的成因。