Acceleration of interplanetary pick-up ions and anomalous cosmic rays

It may not be doubted anymore that anomalous cosmic rays (ACRs) are produced in the heliosphere from interplanetary pick-up ions through their acceleration at the solar wind termination shock. However, there is no general agreement in the community of heliospheric researchers concerning the mechanism of injection of the pick-up ions into the shock acceleration. We discuss here three possible ways for pick-up ions to be involved into the acceleration process at the termination shock: (1) preacceleration of pick-up ions in the whole region from the Sun up to the termination shock by solar wind turbulences and interplanetary shock waves, (2) local preacceleration of pick-up ions in a vicinity of the termination shock by shock surfing, and (3) formation of high-velocity tails in pick-up ion spectra consisting of secondary pick-up ions which are produced in the supersonic solar wind due to ionization of energetic neutral atoms entering from the inner heliosheath.     

Noise in wireless systems from solar radio bursts

Solar radio bursts were first discovered as result of their interference in early defensive radar systems during the Second World War (1942). Such bursts can still affect radar systems, as well as new wireless technologies. We have investigated a forty-year record of solar radio burst data (1960–1999) as well as several individual radio events in the 23rd solar cycle. This paper reviews the results of a portion of this research. Statistically, for frequencies f  1 GHz (near current wireless bands), there can be a burst with amplitudes >10³ solar flux units (SFU; 1 SFU = 10⁻²² W/m²) every few days during solar maximum conditions, and such burst levels can produce problems in contemporary wireless systems.     

利用MF雷达对耀斑期间电离层D区电子密度的观测研究

利用MF雷达观测资料对X级别耀斑爆发期间在66—80 km高度之间的电子密度进行了研究,观测到了耀斑爆发期间电子密度的突然增加,在较低高度上的电子密度的时间变化趋势与耀斑的软X射线辐射通量相关.电子密度的变化强度依赖于具体的耀斑参数,有些耀斑引起的电子密度增加高达400 cm^-3,有些仅为100 cm^-3左右.但耀斑期间在这一高度区间增加的总电子含量增量仅占耀斑辐射引起的整个电离层总电子含量增量的千分之一左右.最后,利用恢复阶段电子密度的时间变化过程估算了1997年11月4日耀斑期间部分高度上的有效复合系数.     

地磁急始年发生数周期特征的小波分析

采用小波分析方法分析了急始年发生数的时间序列的周期特征,并对急始发生数的特征与太阳黑子相对数的特征进行了简要的对照分析,分析结果表明,急始发生数的周期规律与太阳黑子相对数的周期规律是有差异的。还进行了太阳黑子相对数与急始数的相关性,太阳黑子相对数与急始磁暴的相关性研究,分析结果表明它们之间显著相关。还对急始数与急始磁暴数以及其他的一些参数之间的相关性进行了分析,最后对分析结果进行了讨论。     

单流体二维太阳风结构的磁流体力学模拟

在添加动量项的情况下,对单流体二维磁流体力学方程组进行模拟,得到了子午面上的太阳风结构.结果表明,添加动量项的形式及其被加入的位置对远区太阳风速度和质子密度有苇要的影响,本文在适当的区域加入合适的动量项得出了远区太阳风速和质子密度与Ulysses观测基本符合的结果.文中给出较合适的动量添加区域为3.5-10R_s(R_s为太阳半径).     

太阳风质子束流的演化

太阳神飞船观测表明,太阳风高速流中质子束分量相对于核分量的密度随日心距离增加而增加。提出解释这一观测现象的机理并给出二维数值模拟结果。由于阿尔芬波速随日心距离增加而减少,第二支左旋波将与更多的质子共振,把部分原来属于核分布的质子拉到束分布中来。用数值模拟方程方法求解回旋波共振导致的准线性扩散方程,数值结果与观测结果相符合。     

第23太阳活动周太阳极紫外辐射与磁暴相关性分析

统计第23个太阳活动周内中等及以上强度（Dst_min<-50nT）的磁暴事件,线性拟合分析磁暴主相DDst_min和达到DDst_min前一个表征太阳极紫外辐射强度的F_10.7之间的相关性.结果表明：随着太阳极紫外辐射增强,DDst_min<-50nT的磁暴出现的总数增多,在弱、中等和强太阳极紫外辐射条件下,其数量分别为56,84和85;随着太阳极紫外辐射增强,强磁暴（-200nT ≤ Dst_min<-100nT）和大磁暴（Dst_min<-200nT）发生的数量和相对发生率呈增长趋势,尤其是大磁暴数目（1,4,12）和相对发生率（1.79%,4.76%,14.12%）明显呈增长趋势;大磁暴（|Dst_min|）与太阳极紫外辐射（F_10.7）之间存在中度正相关关系,其相关系数为0.532,并且主要体现在大磁暴（|Dst_min|）与强太阳极紫外辐射（F_10.7）之间的中度正相关性,其相关系数为0.582.大磁暴与强太阳极紫外辐射之间的相关性可为空间天气预报提供参考依据.     

Families of halo orbits in the elliptic restricted three-body problem for a solar sail with reflectivity control devices

Solar sail halo orbits designed in the Sun-Earth circular restricted three-body problem (CR3BP) provide inefficient reference orbits for station-keeping since the disturbance due to the eccentricity of the Earth’s orbit has to be compensated for. This paper presents a strategy to compute families of halo orbits around the collinear artificial equilibrium points in the Sun-Earth elliptic restricted three-body problem (ER3BP) for a solar sail with reflectivity control devices (RCDs). In this non-autonomous model, periodic halo orbits only exist when their periods are equal to integer multiples of one year. Here multi-revolution halo orbits with periods equal to integer multiples of one year are constructed in the CR3BP and then used as seeds to numerically continue the halo orbits in the ER3BP. The linear stability of the orbits is analyzed which shows that the in-plane motion is unstable while the out-of-plane motion is neutrally stable and a bifurcation is identified. Finally, station-keeping is performed which shows that a reference orbit designed in the ER3BP is significantly more efficient than that designed in the CR3BP, while the addition of RCDs improve station-keeping performance and robustness to uncertainty in the sail lightness number.     

A simple control law for reducing the effective characteristic acceleration of a solar sail

The direction and magnitude of a solar sail acceleration are strongly related. For this reason, once the characteristic acceleration has been fixed, it is not possible to modulate the acceleration in a particular direction. In this work, a semi-analytical switching control law is derived, enabling a solar sail to emulate a smaller effective characteristic acceleration (without changes in geometry or optical properties); by periodically changing the pitch (cone) angle of the sail, in average over time, the acceleration produced by the sail matches exactly (in both direction and magnitude) that of a “smaller” sail. The range in which this is possible is determined, and the limitations on this range due to the size difference is computed. The method is validated on optimal Earth-Mars trajectories.     

On the station keeping of a solar sail in the elliptic Sun–Earth system

In this work we focus on the dynamics of a solar sail in the Sun–Earth Elliptic Restricted Three-Body Problem with solar radiation pressure. The considered situation is the motion of a sail close to the L₁ point, but displacing the equilibrium point with the sail so that it is possible to have continuous communication with the Earth. In previous works we derived a station keeping strategy for this situation but using the Circular RTBP as a model.