Periodic Variations of Drag Coefficient for the ANDE Spherical Satellites During its Lifetime

A drag coefficient (C_D) inversion method is introduced to study the variations of the drag coefficient for orbital satellites with spherical geometry. Drag coefficients of the four micro satellites in the Atmospheric Neutral Density Experiment (ANDE) are compiled out with this new method. The Lomb-Scargle Periodgram (LSP) analysis of the four ANDE satellites' C_D series has shown that there are obvious 5, 7, 9, and 27 days' period in those data. Interesting results are found through comparing the LSP analysis with series of the daily solar radio flux at 10.7 cm (F_10.7 index), the Ap index, and the daily averaged solar wind speed at 1AU. All series in the same time interval have an obvious period of about 27 days, which has already been explained as the association with the 27 days' solar rotation. The oscillating periods less than 27 days are found in series of C_D, Ap and solar wind speed at 1AU, e.g., the 5, 7, 9 days period. However, these short periods disappeared in the time series of F_10.7 index. The same periodicities of 5, 7, 9 days in Ap and solar wind are presented at the same time interval during the declining phase of solar cycle 23. While in the ascending phase of solar cycle 24, these short oscillations are not so obvious as that in the declining phase of solar cycle 23. These results provide definite evidence that the C_D variations with period of 5, 7 and 9 days are produced by a combination of space weather effects caused by the solar wind and geomagnetic activity.      

改进 K-均值算法在雷达辐射源信号预分选中的应用

雷达辐射源信号分选是电子对抗领域一个关键技术,随着电子技术的发展,电磁环境日趋复杂,信号分选的难度越来越大,在这样的条件下,我们应该寻求新的解决问题的方法.本文首先概述了雷达辐射源信号分选意义、系统组成和分选流程,然后介绍了改进 K-均值算法.为了有效实现信号分选,提出了基于改进K-均值算法的信号分选方法,该方法可对到达角、载频和脉宽参数进行分选.最后进行了仿真实验,结果表明该方法实现简单,分选效果较好     

2007-2009谷年期间高热层大气密度的变化

在第23至第24太阳活动周的峰年之间,太阳活动谷年具有持续时间长,极低F_10.7太阳辐射通量（低至65）和超长期的零太阳黑子数记录等特点,因此是观测和研究在这种特殊背景下热层大气变化的极好机会.尤其是能充分理解和掌握在宁静环境下热层大气密度对弱太阳活动和小地磁扰动的响应特性.本文利用高度650 km以上星载大气密度探测器2007—2009年的连续探测数据进行分析,结果表明,在太阳辐射通量F_10.7极低值期间,较高热层大气密度对F_10.7的起伏具有更显著的响应变化.当F_10.7由70降至65时,日均大气密度会有4～5倍的显著降变,远大于通常大气模式中的降变值.同样在F_10.7极低值期间,较高热层大气密度对小地磁扰动也具有显著的响应增变,当日K_p指数之和由23增至30时,较高热层大气密度则会有80%～160%的强增变.     

An alternative Shell inversion technique - Analysis and validation based on COSMIC and ionosonde data

Multi-channel Global Positioning System (GPS) carrier phase signals, received by the six low Earth orbiting (LEO) satellites from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) program, were used to undertake active limb sounding of the Earth’s atmosphere and ionosphere via radio occultation. In the ionospheric radio occultation (IRO) data processing, the standard Shell inversion technique (SIT), transformed from the traditional Abel inversion technique (AIT), is widely used, and can retrieve good electron density profiles. In this paper, an alternative SIT method is proposed. The comparison between different inversion techniques will be discussed, taking advantage of the availability of COSMIC datasets. Moreover, the occultation results obtained from the SIT and alternative SIT at 500 km and 800 km, are compared with ionosonde measurements. The electron densities from the alternative SIT show excellent consistency to those from the SIT, with strong correlations over 0.996 and 0.999 at altitudes of 500 km and 800 km, respectively, and the peak electron densities (N_mF₂) from the alternative SIT are equivalent to the SIT, with 0.839 vs. 0.844, and 0.907 vs. 0.909 correlation coefficients when comparing to those by the ionosondes. These results show that: (1) the N_mF₂ and h_mF₂ retrieved from the SIT and alternative SIT are highly consistent, and in a good agreement with those measured by ionosondes, (2) no matter which inversion technique is used, the occultation results at the higher orbits (∼800 km) are better than those at the lower orbits (∼500 km).     

Effects of solar modulation on the cosmic ray positron fraction

We implemented a 2D Monte Carlo model to simulate the solar modulation of galactic cosmic rays. The model is based on the Parker’s transport equation which contains diffusion, convection, particle drift and energy loss. Following the evolution in time of the solar activity, we are able to modulate a local interstellar spectrum (LIS), that we assumed isotropic beyond the termination shock, down to the Earth position inside the heliosphere. In this work we focused our attention to the cosmic ray positron fraction at energy below ∼10 GeV, showing how the particle drift processes could explain different results for AMS-01 and PAMELA. We compare our modulated spectra with observations at Earth, and then make a prediction of the cosmic ray positron fraction for the AMS-02 experiment.     

Magnetospheric disturbances associated with the 13 December 2006 solar flare and their ionospheric effects over North-East Asia

We present an observational study of magnetospheric and ionospheric disturbances during the December 2006 intense magnetic storm associated with the 4В/Х3.4 class solar flare. To perform the study we utilize the ground data from North–East Asian ionospheric and magnetic observatories (60–72°N, 88–152°E) and in situ measurements from LANL, GOES, Geotail and ACE satellites. The comparative analysis of ionospheric, magnetospheric and heliospheric disturbances shows that the interaction of the magnetosphere with heavily compressed solar wind and interplanetary magnetic field caused the initial phase of the magnetic storm. It was accompanied by the intense sporadic E and F2 layers and the total black-out in the nocturnal subauroral ionosphere. During the storm main phase, LANL-97A, LANL 1994_084, LANL 1989-046 and GOES_11 satellites registered a compression of the dayside magnetosphere up to their orbits. In the morning–noon sector the compression was accompanied by an absence of reflections from ionosphere over subauroral ionospheric station Zhigansk (66.8°N, 123.3°E), and a drastic decrease in the F2 layer critical frequency (foF2) up to 54% of the quite one over subauroral Yakutsk station (62°N, 129.7°E). At the end of the main phase, these stations registered a sharp foF2 increase in the afternoon sector. At Yakutsk the peak foF2 was 1.9 time higher than the undisturbed one. The mentioned ionospheric disturbances occurred simultaneously with changes in the temperature, density and temperature anisotropy of particles at geosynchronous orbit, registered by the LANL-97A satellite nearby the meridian of ionospheric and magnetic measurements. The whole complex of disturbances may be caused by radial displacement of the main magnetospheric domains (magnetopause, cusp/cleft, plasma sheet) with respect to the observation points, caused by changes in the solar wind dynamic pressure, the field of magnetospheric convection, and rotation of the Earth.     

Decadal variability of tropical Pacific temperature in relation to solar cycles

We use the 8-year long satellite temperature data (2002–2010) from Atmospheric InfraRed Sounder (AIRS) and Atmospheric Microwave Sounding Unit (AMSU) on the Aqua satellite to identify temperature trends in the troposphere and low stratosphere over the Niño 3.4 region of the Tropical Pacific Ocean in the most recent 11-year solar cycle. Employing more extended sea surface temperature (SST) data for five solar cycles (1950–2009) in this region we show that the satellite trends reflect a typical decrease of the sea surface temperature (SST) in the Niño 3.4 region in the declining phase of the solar cycle. The magnitude of the SST decrease depends on the solar cycle and ranges between 0.07 K/yr and 0.27 K/yr for the last five solar cycles.     

一种航天器单脉冲差模角跟踪系统的标定及测试方法

介绍了航天器单脉冲差模角跟踪系统的组成和基本原理;针对捕获跟踪系统性能与射频通道相位特性的相关性,提出了在无线状态下通过用户目标在一定范围内按一定轨迹运动进行射频通道相位标定及跟踪性能测试的方法;在此基础上进一步提出了利用信号源模拟用户目标在角跟踪系统天线坐标系下不同位置时天线输出的射频信号,进行有线状态下射频通道性能的测试方法。标定及测试方法通过地面试验验证了可行性和有效性,可用于航天器单脉冲差模角跟踪系统在地面的通道相位标定、跟踪性能测试和射频通道性能测试,以实现角跟踪系统对用户目标高精度、稳定的跟踪。     

再入航天器表面亚波长等离子体薄层对微波信号影响效应研究

为了建立电磁波在亚波长等离子体薄层中传播的物理数学模型,并针对通信频段的电磁波,研究电磁波在再入航天器表面等离子体薄层中的透射问题,相关研究成果可为再入航天器通信“黑障”现象研究提供理论基础。模型从麦克斯韦方程组出发,采用微分薄层法进行数值求解,获得了不同等离子体密度条件下亚波长等离子体中目标电磁波的透射特性及传播规律,揭示了截止反射效应和碰撞吸收效应在其中发挥的作用。本研究对于深入了解亚波长碰撞等离子体薄层中电磁波的传播过程具有意义。     

基于修正差分进化算法确定周期内多载波微放电等效功率

微放电是空间微波部件设计所必须考虑的失效效应之一,随着空间宽带多载波模式的广泛采用,多载波条件下微波部件微放电问题引起广泛关注。针对周期内多载波微放电等效功率计算所采用传统经验公式的不足,提出了一种基于修正差分进化算法的确定周期内多载波微放电等效功率的全局优化方法。该方法通过对多载波合成信号功率特性进行分析,推导获得了 20个电子渡越时间内信号能量的表达式,采用二次插值法进行局部搜索,采用修正差分进化算法进行全局优化,从而高效、准确获得全局最优解。以幅度相等、频率间隔相等的多载波信号为例,进行了等效功率的确定,与经验公式的预测结果相当,验证了所提出方法的有效性;同时,对幅度不同、频率间隔不等的多载波信号进行了处理,获得了能够指导微波部件微放电设计的最坏状态及其等效功率。所提出方法不仅适用于幅度不同、频率间隔不等的多载波信号情况,并且能够提供微放电最坏状态时的相位分布,为多载波微放电实验验证提供相位输入。所提出方法相比传统的基于经验公式的方法具有明显优势,为空间宽带多载波工作微波部件微放电设计提供有效依据,在卫星转发器多载波微放电分析及设计中具有价值。