Advances in modeling gradual solar energetic particle events

Solar energetic particles pose one of the most serious hazards to space probes, satellites and astronauts. The most intense and largest solar energetic particle events are closely associated with fast coronal mass ejections able to drive interplanetary shock waves as they propagate through interplanetary space. The simulation of these particle events requires knowledge of how particles and shocks propagate through the interplanetary medium, and how shocks accelerate and inject particles into interplanetary space. Several models have appeared in the literature that attempt to model these energetic particle events. Each model presents its own simplifying assumptions in order to tackle the series of complex phenomena occurring during the development of such events. The accuracy of these models depends upon the approximations used to describe the physical processes involved in the events. We review the current models used to describe gradual solar energetic particle events, their advances and shortcomings, and their possible applications to space weather forecasting.     

Solar Energetic Particle Charge States: An Overview

The ionic charge distributions of solar energetic particles (SEP) as observed in interplanetary space provide fundamental information about the origin of these particles, and the acceleration and propagation processes at the Sun and in interplanetary space. In this paper we review the measurements of ionic charge states of energetic particles in interplanetary space and discuss their implication for our understanding of SEP sources, and acceleration and propagation processes.     

Energization of Plasma Species by Intermittent Kinetic Alfvén Waves

We propose a new phase-mixing sweep model of coronal heating and solar wind acceleration based on dissipative properties of kinetic Alfvén waves (KAWs). The energy reservoir is provided by the intermittent ∼1 Hz MHD Alfvén waves excited at the coronal base by magnetic restructuring. These waves propagate upward along open magnetic field lines, phase-mix, and gradually develop short wavelengths across the magnetic field. Eventually, at 1.5–4 solar radii they are transformed into KAWs. We analyze several basic mechanisms for anisotropic energization of plasma species by KAWs and find them compatible with observations. In particular, UVCS (onboard SOHO) observations of intense cross-field ion energization at 1.5–4 solar radii can be naturally explained by non-adiabatic ion acceleration in the vicinity of demagnetizing KAW phases. The ion cyclotron motion is destroyed there by electric and magnetic fields of KAWs.     

Ring Current Dynamics

This chapter reviews the current understanding of ring current dynamics. The terrestrial ring current is an electric current flowing toroidally around the Earth, centered at the equatorial plane and at altitudes of ∼10,000 to 60,000 km. Enhancements in this current are responsible for global decreases in the Earth’s surface magnetic field, which have been used to define geomagnetic storms. Intense geospace magnetic storms have severe effects on technological systems, such as disturbances or even permanent damage of telecommunication and navigation satellites, telecommunication cables, and power grids. The main carriers of the ring current are positive ions, with energies from ∼1 keV to a few hundred keV, which are trapped by the geomagnetic field and undergo an azimuthal drift. The ring current is formed by the injection of ions originating in the solar wind and the terrestrial ionosphere into the inner magnetosphere. The injection process involves electric fields, associated with enhanced magnetospheric convection and/or magnetospheric substorms. The quiescent ring current is carried mainly by protons of predominantly solar wind origin, while active processes in geospace tend to increase the abundance (both absolute and relative) of O⁺ ions, which are of ionospheric origin. During intense geospace magnetic storms, the O⁺ abundance increases dramatically. This increase has been observed to occur concurrently with the rapid intensification of the ring current in the storm main phase and to result in O⁺ dominance around storm maximum. This compositional change can affect several dynamic processes, such as species-and energy-dependent charge-exchange and wave-particle scattering loss.     

反铁电陶瓷PLZST纳米粉的制备研究

利用溶胶-水热法制备了PLZST纳米粉,并研究了反应温度、铅过量等因素对产物的影响.溶胶处理确实可以降低制备温度.利用XRD 分析了粉体的结晶性, XRF分析了粉体的化学组成,SEM观察了粉体的形貌以及SAXS测定了粉体的粒度分布.研究发现,经一般超声分散的粉体的颗粒呈球形,而不经分散的粉体颗粒成矩形,表现出自组装的倾向性.     

常增益递推滤波器的次参数选择

设k阶滤波器的尾k 1个参数为a_(0)a_(1)…a_(k),我们称a_(0)。为首参数,a_(1)a_(2)…a_(k)为次参数,选择一组实函数a_(1)(a_0),a_(2)(a_0),a_(2)(a_0),…a_(k)(a_0)使滤波器的某个指标达到最优是属于滤波器的次参数选择问题。本文以滤波器输出误差范数最小为准则选择次参数。     

无网格SPH法中守恒光滑法的修正

守恒光滑法CSA(Conservative Smoothing Approach)是解决传统SPH(Smoothed Particle Hydrodynamics)法稳定性问题的一种很有效的方法.研究发现在SPH法中运用所谓的守恒光滑法并不能保证系统的总物理量(质量、动量或者能量)在每个时间步均守恒,而是随着时间在理论值附近波动,对计算结果的精度有一定的影响.对此提出了守恒光滑法的修正公式,对SPH控制方程得到的各个粒子的物理量进行CSA光滑,然后运用文中提出的CSA的修正公式把对该粒子物理量的改变量加权平均给邻域内各个粒子,从而确保了SPH算法中系统的总物理量(质量、动量以及能量等)在每个时间步均守恒,而且由于减少了CSA对SPH得到的各个粒子物理量的过分光滑,从而提高了计算精度.物理意义、理论推导以及文中的算例均证明了这种修正的有效性.     

Physics of ion acceleration in the solar flare on 2005 September 7 determines γ-ray and neutron production

Relativistic neutrons were observed by the neutron monitors at Mt. Chacaltaya and Mexico City and by the solar neutron telescopes at Chacaltaya and Mt. Sierra Negra in association with an X17.0 flare on 2005 September 7. The neutron signal continued for more than 20 min with high statistical significance. Intense emissions of γ-rays were also registered by INTEGRAL, and during the decay phase by RHESSI. We analyzed these data using the solar-flare magnetic-loop transport and interaction model of Hua et al. [Hua, X.-M., Kozlovsky, B., Lingenfelter, R.E. et al. Angular and energy-dependent neutron emission from solar flare magnetic loops, Astrophys. J. Suppl. Ser. 140, 563–579, 2002], and found that the model could successfully fit the data with intermediate values of loop magnetic convergence and pitch-angle scattering parameters. These results indicate that solar neutrons were produced at the same time as the γ-ray line emission and that ions were continuously accelerated at the emission site.     

Solar wind low-energy energetic ion enhancements: A tool to forecast large geomagnetic storms

Predicting the occurrence of large geomagnetic storms more than an hour in advance is an important, yet difficult task. Energetic ion data show enhancements in flux that herald the approach of interplanetary shocks, usually for many hours before the shock arrival. We present a technique for predicting large geomagnetic storms (Kp  7) following the arrival of interplanetary shocks at 1 AU, using low-energy energetic ions (47–65 keV) and solar wind data measured at the L1 libration point. It is based on a study of the relationship between energetic ion enhancements (EIEs) and large geomagnetic storms by Smith et al. [Smith, Z., Murtagh, W., Smithtro, C. Relationship between solar wind low-energy energetic ion enhancements and large geomagnetic storms. J. Geophys. Res. 109, A01110, 2004. doi:10.1029/ 2003JA010044] using data in the rise and maximum of solar cycle 23 (February 1998–December 2000). An excellent correlation was found between storms with Kp  7 and the peak flux of large energetic ion enhancements that almost always (93% of time in our time period) accompany the arrival of interplanetary shocks at L1. However, as there are many more large EIEs than large geomagnetic storms, other characteristics were investigated to help determine which EIEs are likely to be followed by large storms. An additional parameter, the magnitude of the post-shock total magnetic field at the L1 Lagrangian point, is introduced here. This improves the identification of the EIEs that are likely to be followed by large storms. A forecasting technique is developed and tested on the time period of the original study (the training data set). The lead times, defined as the times from the arrival of the shock to the start of the 3-h interval of maximum Kp, are also presented. They range from minutes to more than a day; the average for large storms is 7 h. These times do not include the extra warning time given when the EI flux cross the high thresholds ahead of the shock. Because the data-stream used in the original study is no longer available, we extended the original study (1998–2000) to 2001, in order to: (a) investigate EIEs in 2001; (b) present a validation of the technique on an independent data set; (c) compare the results based on the original (P1) energy channel to those of the replacement (P1′) and (d), determine new EIE thresholds for forecasting geomagnetic storms using P1′ data. The verification of this P1′ training data set is also presented, together with lead times.     

轮式起降无人机安全起飞纵向控制

为了提高无人机在风干扰下的起飞安全性,对无人机常规起飞纵向控制方案加以改进,提出了基于直接升力控制的安全起飞纵向控制方案.采用由低通滤波器和超前补偿通道组成的组合滤波方案,用以解决所提出控制方案中无人机升降速度信号的精确获取问题,通过所研制的专用升降测试台和基于频谱分析的设计方法,对组合滤波方案进行了参数选取和仿真验证.基于Matlab/Simulink仿真环境建立某型无人机的全量非线性数学模型,通过仿真设计相应的襟翼偏转控制律.仿真结果表明,应用组合滤波方案获取的升降速度信号精度较高,满足起飞控制的使用要求.安全起飞纵向控制方案可显著增强无人机的抗干扰能力,从而提高起飞过程的安全性.