2007 Vol. 27, No. 2

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Wavelet Analysis of Quasi-27-Day Oscillations in the Solar Index F10.7
MA Ruiping, JI Qiao, XU Jiyao
2007, 27(2): 89-95. doi: 10.11728/cjss2007.02.089
Abstract(3251) PDF 3861KB(1474)
Abstract:
Using the daily averaged values of the F10.7 for years 1956-2003, the Morlet Wavelet Transform is used to analyze the characteristics of quasi-27-day period oscillation and the relation between the oscillation and the solar 11-year cycle （Schwabe cycle）. The result shows： The amplitude and period of quasi-27-day period oscillation have obvious short-term fluctuations. The change has very large difference in different years. In some years, the amplitude changes more than ten times and the period changes several days, even changes suddenly more than ten days during several days to tens of the day. In other years, the amplitude is large, but the fluctuation is small and the period was steady. The yearly averaged quasi-27-day oscillation amplitude has obvious change year after year and it is correlated with the solar 11-year cycle observably. Generally, the quasi-27-day oscillation amplitude is larger when yearly averaged F10.7 is bigger. But in the solar cycle 19 maximum years, the quasi-27-day oscillation amplitudes is smaller than maximum years of other cycles, although yearly averaged F10.7 of cycle 19 maximum years is bigger than other cycles. The quasi-27-day oscillation amplitude has obvious change year after year except some years （for example 1987）, and the yearly averaged period change range is 24-31 days and is not correlated with the solar cycle. The averaged period of 48 years is 27.3 days. On the whole, the period trends shorter gradually, the period decreases about 1.5 days during 1956-2003. The reasons that conduces to the fluctuations of quasi-27-day oscillation is very complicated, it needs to be studied in the future.
Numerical Study of Low Frequency Wave in Hall MHD Reconnection With Various Plasma β
LI Yi, JIN Shuping, YANG Hongang, LIU Shaoliang
2007, 27(2): 96-103. doi: 10.11728/cjss2007.02.096
Abstract(2488) PDF 3649KB(1102)
Abstract:
The Hall MHD reconnection processes with various plasma β （the ratio of plasma pressure to the magnetic pressure） are numerically studied. The reconnection rate A/ t｜st at the quasi-steady state is in the range of 0.15 ≥ A/ t｜st ≥ 0.095 for the cases with plasma β ranging 0.5 ≤ β ≤ 6.5. In this report, the waves in the Hall MHD reconnection are investigated： The time series of the out-of-plane magnetic field By and the velocity components vx, vz in the xz plane at the given points are transferred into the power spectra by the Fast Fourier Transformation （FFT） for the cases with various plasma β. The results indicate that the frequencies of the By, vx, vz power spectra are in the range of Ωci 〈 ω 〈 8Ωci where Ωci is the proton cyclotron frequency. A shift to low frequency and the energy reduction at the peaks in the power spectrum can be found as the plasma β increases. Using the Minimum Variance Analysis （MVA） on E, the propagation directions k of the waves are determined. The angles α between the wave vector k and the local magnetic field B increase with increasing β： For case 3 with the largest （β = 6.5） α 〈 28°, so that k is approximately parallel to B. In order to investigate the polarized features of waves the hodographs of E are plotted in the plane perpendicular to the wave vector k. The hodographs for all three cases illustrate a right-hand circularly polarized feature. In case 1 with β = 0.5, it is a right-hand elliptical polarization, but in case 2 （β = 2.5） and case 3 （β = 6.5） the hodographs become a complicated right-hand circulation. Such wave behaviors are the signatures of whistler wave, and so the present work might provide a link between the fast reconnection rate and whistler wave.
New Results of Algebraic Reconstruction Techniques to Inverse Ring Current Ions Distribution
WANG Xinyue, LIU Zhenxing, SHEN Chao, LU Li
2007, 27(2): 104-109. doi: 10.11728/cjss2007.02.104
Abstract(2188) PDF 1296KB(805)
Abstract:
Energetic Neutral Atom （ENA） images obtained by the energetic Neutral Atom Detector Unit （NUADU） on board Chinese Double Star mission are used to simulate the changes in the ring current. Changes in the ring current are responsible for global decreases in the Earth surface magnetic field, which are known as geomagnetic storms. ENA imagers provide global pictures of the ring current ions in the space environment. A new technique and arithmetic is explored in this paper to inverse the ring current ions distribution. The technique of seismic tomograpy is introduced into our inversion. Based on the technique, the ring current region of magnetospheric space can be took into grids and use Algebraic Reconstruction Techniques to extract ion＇s flux distribution from the ENA image. The consistency inversion distribution with original one shows the feasibility of this technique. Comparing the original distribution with the inversion results, our arithmetic can obtain ring currents＇ global distribution information with fewer hypotheses and simpler procedures.
2D Particle-in-Cell Simulations on Electrostatic Solitary Waves
TAO Jianbao, LU Quanming, WANG Shui
2007, 27(2): 110-116. doi: 10.11728/cjss2007.02.110
Abstract(2275) PDF 2843KB(1068)
Abstract:
With two-dimensional （2D） particle-in-cell simulations, the excitation of electrostatic waves by two-beam instability, and their nonlinear evolution into the electrostatic solitary waves are investigated. The simulation results indicate that the electrostatic waves excited in linear growth stage propagate mainly along the magnetic field. These waves coalesce with each other and form electrostatic solitary waves, and at the same time they can generate electrostatic whistlers. Moreover, we have also surveyed the influence of the strength of the magnetic field and the ion temperature on this process. Electrostatic solitary waves cannot form when the strength of the magnetic field is weak. Only if the strength of the magnetic field is sufficiently strong can the electrostatic waves form. Meanwhile, the ion temperature can affect the stability of electrostatic solitary waves. When the ion temperature is low, the stability of electrostatic solitary waves decrease and they will break up gradually.
Primary Study About the Relationships Between Coronal Holes' Parameters and the Correlative Geomagnetic Disturbances
LUO Bingxian, LIU Siqing, ZHONG Qiuzhen, GONG Jiancun
2007, 27(2): 117-124. doi: 10.11728/cjss2007.02.117
Abstract(2530) PDF 1812KB(1209)
Abstract:
Data from the SOHO EIT284 images are used to analyze the development of coronal holes which existed from 1996 to 2005. In order to investigate the relationship between the coronal hole and earth effect, the correlativity of the coronal hole parameters including coronal holes＇ area and longitude span, with solar wind parameters and geomagnetic index were examined. Our investigation shows that： The correlation between coronal holes＇ longitude extend （20°N-20°S） and geomagnetic disturbance duration is very good. For coronal holes that appeared in 2002, the linear-correlation coefficient is 0.91, and for a long-lived recurrent coronal hole that existed for 15 Carrington rotations from 2002 to 2003, the Pearson Coefficient is 0.934. There is poor correlation between coronal holes＇ areas and maximum solar wind speed in the high speed stream. This result is different from the result that Nolte found in 1976. This might remind us that the solar wind speed in the high speed stream is not only related to the coronal holes＇ areas. The relationship between the high speed stream and the coronal hole must be much more complex. The correlations between the yearly averaged maximum solar wind speed in CHHSS （Coronal Hole-High Speed Stream） and the yearly averaged corresponding geomagnetic field index, for example, Ap index and Kp index are good, especially for the declining phase of solar activity cycle 23. But to the individual samples, fast velocity does not mean intense geomagnetic disturbance, which means that solar wind velocity is not the only major role that causes earth effect. From the study of a recurrent coronal hole that existed for fifteen Carrington rotations, we found that the daily average velocity maximum v^-max shows somewhat correlation to Kp maximum during the the geomagnetic disturbance. The linear-correlation coefficient is about 0.604.
Seasonal Variation of the Ionospheric Total Electron Content, Maximum Electron Density and Slab Thickness Over Wuhan
XIONG Bo, WAN Weixing, LIU Libo, NING Baiqi, GUO Jianpeng
2007, 27(2): 125-131. doi: 10.11728/cjss2007.02.125
Abstract(2754) PDF 4739KB(1242)
Abstract:
Half-hourly Total Electron Content （TEC） from Faraday rotation measurement in the EST-Ⅱ satellite and half-hourly foF2 ionosonde data obtained at Wuhan （114.4°E, 30.6°N） from 1980 to 1990 are analyzed to show the seasonal variation of TEC, NmF2 （maximum electron density） and the slab thickness. By analyzing and comparing, the results show that the semiannual anomaly of TEC and NmF2 is obvious in high and low solar activity periods during 1980 and 1990 at Wuhan. The season or winter anomaly of TEC and NmF2 is obvious in high solar activity periods during 1980 and 1990 at Wuhan. The nighttime winter anomaly effect had been observed in the northern hemisphere during solar minimum, which is not observed at Wuhan. The occurrence rate of nighttime enhancements of NmF2 is at maximum in summer during high solar activity periods, but at its minimum during wintertime for low solar activity conditions. The slab thickness is mainly between 200 and 800 kilometers, change of which is small from 0700 LT to 1800 LT and is larger at other time. The observed NmF2 values are used to check the validity of International Reference Ionosphere （IRI） and the single-station model over Wuhan to predict the seasonal variability of this parameter. The effect predicted by the single-station model over Wuhan is better than IRI.[
Initial Application of Unequal Step Grid and Explicit Method in the Simulation of Nonlinear Propagation of Gravity Wave
LIU Xiao, XU Jiyao, MA Ruiping
2007, 27(2): 132-139. doi: 10.11728/cjss2007.02.132
Abstract(2408) PDF 3501KB(1192)
Abstract:
An unequal step grid and explicit numerical model is developed in this paper by using the 3rd order TVD explicit time integration method, which is used to simulate the nonlinear propagation of the gravity wave in a 2-dimensional compressible atmosphere. The model can simulate the small-scale complex wave with high resolution while the computer cost doesn＇t increase. It can be used to simulate the nonlinear propagation of gravity waves breaking into small-scale complex wave from the middle-scale wave. The simulation results for the propagation of small amplitude gravity wave indicate that, the model can reproduce the propagation of small amplitude gravity wave and preserve the energy conservation relation and the phase difference between different perturbation variable. The numerical results coincide well with linear gravity wave theory. The simulation results for the nonlinear propagation of finite amplitude gravity wave show that, compared with the equal grid system with the same grid number, the unequal step grid system can simulate the evolution of gravity wave from instable to breakdown with higher resolution. The simulation results in the equal grid system with the grid number increasing one time are same as that for the unequal grid system indicate that, the simulation results in the unequal grid system is correct, and the computer cost is saved greatly. The advantages of explicit method are also preserved in this model, such as, needn＇t iterative method to solve the solution and extend to 3-dimensional easily.
Research on the High-Power Microwave Gaussian Beam Air Breakdown
CAO Jinkun, ZHOU Dongfang, NIU Zhongxia, HOU Deting, YANG Jianhong, RAO Yuping
2007, 27(2): 140-145. doi: 10.11728/cjss2007.02.140
Abstract(2204) PDF 2824KB(1243)
Abstract:
The nonlinear propagation of high-power microwave Gaussian beam in the atmosphere is studied. An appropriate model is presented for calculating the air refractive index when HPM Gaussian beam propagates in the atmosphere. In this model, the cross-section area is treated as a number of concentric annulus, and assuming each has a uniform electric field intensity distribution. Based on the knowledge of air breakdown and the theory of the propagation of Ganssian beam, the air refractive index is calculated for different field intensity, frequency of microwave, width of pulse, pressure, when giving parameters of the Gaussian beam. Then the curves of temporal spatial dispersion are given in the paper. The air breakdown is discussed based on the calculations and some useful results have been obtained.
Structure Analysis of the Hard X-Rays Modulation Telescope (HXMT) Satellite
MA Yi, WANG Sheng, REN Weijia
2007, 27(2): 146-150. doi: 10.11728/cjss2007.02.146
Abstract(2597) PDF 1108KB(1258)
Abstract:
Based on the HXMT satellite＇s structure, the finite element model of this satellite is developed, and static analysis, normal modes and frequency responses are investigated. The maximal stress result of every part of the HXMT satellite and the frequencies in 100 Hz are obtained. The results provide data for optimizing design of the HXMT satellite structure and avoiding synchronous vibration occurring. Considering theory analysis and past design experiences, some reasonable suggestions of optimizing the satellite structure are presented.
Intelligent Control Research of Multibody Satellite for High Stability
LI Guangxing, ZHOU Jun, ZHOU Fengqi
2007, 27(2): 151-156. doi: 10.11728/cjss2007.02.151
Abstract(2126) PDF 1532KB(992)
Abstract:
Control system of multibody satellite is designed to improve attitude stability in this paper. The control law consisting of variable structure control and neural network control is obtained by using Lyapunov stability theory. Variable structure control is a nonlinear control strategy employing feedback of a discontinuous signal, and is very robust to matched plant uncertainties and external disturbances when state variables enter the sliding surface. Neural network systems are physical cellular systems that can acquire, store, and utilize experiential knowledge. The knowledge is in the form of stable states or mappings embedded in networks that can be recalled in response to the presentation of the data input to the network systems. The application of the neural network is made possible by recognizing function approximation capability in this paper. Since dynamics of multibody satellite can not be obtained accurately, the conventional controllers will not ensure the good performance of control system. A suitable technique cope with such system is variable structure control and neural network control. By Integrating their merits, robust capability and high control accuracy can be achieved. In addition, compensation control is introduced into the feedforward loop to eliminate the disturbance caused by the motion of antenna, so convergence of angular velocity is in the form of exponent guaranteed. Simulation results illustrate the control system has the good attitude stable characteristics using the proposed controller in the presence of external disturbances and parameters uncertainties.
Configuration Design of Satellite Foramation With Constant Baselines
LIU Lei, XI Xiaoning
2007, 27(2): 157-161. doi: 10.11728/cjss2007.02.157
Abstract(2363) PDF 1034KB(1101)
Abstract:
Constant measurement baselines are very important to satellite formations. So this work stresses on conditions for the constant measurement baselines. Based on the characteristics of relative motion of satellite formations and the definition of baselines in satellite formations, this article firstly studies the relationship between baselines and formation configuration parameters. A criterion called Stabilization Level is then proposed, which can preferably indicate the stabilization of varying baselines. Under the same stabilization level and orbit period, stabilization periods of time of the maximum horizontal and vertical baselines in three particular formations are analyzed. The three formations are at a certain extent similar to foreign formations： Interferometric Cartwheel, Interferometric Pendulum and CarPe. Results show that the three formations cannot meet the requirement of constant horizontal and vertical baselines synchronously. Therefore, the article researches on the conditions for the constant measurement baselines and draws a conclusion： the sufficient and necessary conditions are three constraint formulas for constant horizontal baseline and two for constant vertical baseline. Another important conclusion obtained from the above one is that the formation by two satellites cannot satisfy the above requirement. At end of the article, a formation by three satellites is designed according to the above research, which can attain the constant horizontal and vertical baselines simultaneously and validate the above research
Spline Method for High-Precision Inter-Satellite Relative Positioning Based on Augmented Single-Frequency GPS
LIU Yang, WANG Zhengming, YI Dongyun
2007, 27(2): 162-168. doi: 10.11728/cjss2007.02.162
Abstract(2142) PDF 1409KB(1138)
Abstract:
Autonomous formation flying of multiple vehicles is a key technology for both deep space and orbital applications that involve multiple spacecraft. Many future space applications will benefit from using formation flying technologies to perform distributed observations （e.g., Synthetic Aperture Radar, SAR）. One of the key requirements of distributed SAR is accurate post-progressing knowledge of the relative positions between the vehicles. In order to realize the high-precision intersatellite relative positioning of the distributed SAR, an augmented relative positioning method based on the single-frequency GPS is proposed in this paper. With this method inter-satellite pseudorange measurements based on single-frequency GPS measurements incluing P-code and carrier phase measurements are added, then a spline model of relative positioning based on the continuity of the relative position parameters can be found and, finally the least-square method is used to estimate the parameters. The results of simulation show that this method can not only improve relative positioning precision greatly, but also reduce the epochs needed by fixing the ambiguity. The theoretical analyse proves the correctness of the results of simulations.
Advance in X-Ray Pulsar Navigation Technology
SHUAI Ping, CHEN Shaolong, WU Yifan, ZHANG Chunqing, LI Ming
2007, 27(2): 169-176. doi: 10.11728/cjss2007.02.169
Abstract(2591) PDF 3132KB(1278)
Abstract:
The pulsars are the result of a massive star that has exhausted its nuclear fuel and undergone a core-collapse resulting in a supernova explosion. Its radius is roughly 10 km and mass near 1.4 solar. There are the very strong gravitational, electronic and magnetic fields for the pulsar. The pulsar might emit in the radio, infrared, visible, ultraviolet, X-ray and gamma-ray of the spectrum. Meanwhile, the navigation parameters for the spacecraft on the low earth orbit, deep space and interplanetary flight can, including the position, velocity, attitude and time, be determined highly-accurately by detecting the X-ray radiation of pulsars. And then the spacecrafts are able to flight and operate autonomously. Therefore, the potential of using the X-ray Pulsar Navigation （XPNAV） is very high. Firstly, the history of XPNAV is described briefly in this paper. Secondly, the basic principles, information flow charts and autonomous navigation algorithms are studied in detail as an main part. Moreover.the key techniques of XPNAV, including the all-sky surveying and data processing for the X-ray pulsars, pulse-arrival-time measuring and error correcting, X-ray detector and weak signal processing, establishment and maintenance of the space-time reference, and robust filtering of the autonomous information processing, are also presented. Finally, the essentiality and feasibility to study XPNAV are also shown in some detail.

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