Table of Content

    15 September 2007, Volume 27 Issue 5 Previous Issue    Next Issue
    Effect of Interplanetary Transients on Cosmic Ray Anisotropic Variations
    Rajesh K. Mishra
    2007, 27 (5):  353-359.  doi: 10.11728/cjss2007.05.353
    Abstract ( 2627 )   PDF (2273KB) ( 829 )   Save
    In the present work the cosmic ray intensity data recorded with ground-based neutron monitor at Deep River has investigated taking into account the associated interplanetary magnetic field and solar wind plasma data during 1981-1994. A large number of days having abnormally high/low amplitudes for successive number of five or more days as compared to annual average amplitude of diurnal anisotropy have been taken as high/low amplitude anisotropic wave train events (HAE/LAE). The amplitude of the diurnal anisotropy of these events is found to increase on the days of magnetic cloud as compared to the days prior to the event and it found to decrease during the later period of the event as the cloud passes the Earth. The High-Speed Solar Wind Streams (HSSWS) do not play any significant role in causing these types of events. The interplanetary disturbances (magnetic clouds) are also effective in producing cosmic ray decreases. Hα solar flares have a good positive correlation with both amplitude and direction of the anisotropy for HAEs,whereas PMSs have a good positive correlation with both amplitude and direction of the anisotropy for LAEs.The source responsible for these unusual anisotropic wave trains in CR has been proposed.
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    Effect of Guiding Field to Low-Frequency Electromagnetic Instabilities in the Collisionless Current Sheet
    WEI Xinhua;CAO Jinbin
    2007, 27 (5):  360-366.  doi: 10.11728/cjss2007.05.360
    Abstract ( 2587 )   PDF (1778KB) ( 1086 )   Save
    This paper discuss the effect of guiding field to low-frequency electromagnetic instabilities in the collisionless current sheet with the dispersion relation obtained by collisionless and compressible magnetohydrodynamic model. The results show the guiding field affects on the three-dimensional disturbed propagation waves strongly. (1) On the middle plane of current sheet (z = 0), if there is not guiding field, no instability observed, but if there is guiding field, instabilities can take place. (2) Near the middle of current sheet (z = 0.2), the current sheet is instable. With increasing of guiding field, the grow rate increased obviously. The wave mode may be whistler or low-hybrid wave. (3) Near the edge of current sheet (z = 0.8), the effect of guiding field become not clearly. The instability wave mode is quasi-parallel propagation whistler.
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    Calculating Method on Charged Particles Motion in the Near-Earth Region
    HUANG Chaoyan;HAN Jianwe
    2007, 27 (5):  367-373.  doi: 10.11728/cjss2007.05.367
    Abstract ( 1680 )   PDF (3405KB) ( 1254 )   Save
    In this paper, based on the theory of magnetospheric particle dynamics, the charged particles motion character and the calculating method appropriate to these different energy particles in the near-earth region (L 〈 10) are discussed in detail, in terms of the single particle approach and dipole filed model. And then, it is analyzed quantitatively how the electric and magnetic field in the magnetosphere determined these particles drift motion. It is shown that, for the electron and proton with energy lower than 10^5 eV and 10^2 eV, respectively, the Guiding-Center Approximation Appoach (GCAA) is recommended; for 10^5 - 10^8 eV electron and 10^2 - 10^8 eV proton, GCAA or trajectory approach with adaptive step can be adopted in some regions. As for GCAA, the electric drift can be ignored when particle energy is higher than 10^5 eV, and the magnetic drift does not need to be taken into account when particle energy is lower than 10^3 eV. So the guiding-center equations are simplified and the efficiency of numerical calculation is improved.
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    Forecasting Auroral Electrojet Activity With BP Neural Networks
    LI Zhitao;XUE Bingsen
    2007, 27 (5):  374-378.  doi: 10.11728/cjss2007.05.374
    Abstract ( 2219 )   PDF (1636KB) ( 1122 )   Save
    Magnetosphere substorm is the result of couplings between solar wind and magneto-sphere. In general, as AE, AL etc indices are used to inspect the turbulence in polar region when sub storms occur, they are the target indices in space environment prediction. The AE index is predicted by data of solar wind and interplanetary magnetic field (IMF), with a back-propagation neural network, which is all-joint one. The data of input comes from ACE satellite, combined into 5 min resolution. There are 4 input variables: The By, Bz components of interplanetary magnetic field, the velocity of solar wind and the density of solar wind proton. The 3 networks with the length of input time series of 20, 40 and 60 minutes are constructed, trained and train them separately. Then the time series of variables on influencing the AE index is discussed. The predictions show that our network model can forecast the trend of fluctuation of AE index, having wonderful veracity in quantitatively computing index value. The correlation between four input variables (By, Bz, v, n) and AE index is very good. As the time extends, the forecasting precision needs some improvements.
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    Strong Range Spread-F Characteristics Observed in Hainan During Intense Storm
    WANG Guojun;SHI Jiankui;WANG Xiao;LIU Zhenxing;Zherebtsov G;Olga P
    2007, 27 (5):  379-383.  doi: 10.11728/cjss2007.05.379
    Abstract ( 2549 )   PDF (1592KB) ( 1285 )   Save
    The response of equatorial ionosphere during geomagnetic storms is one of the important issues related to space weather studies and how they affect the occurrence characteristics of equatorial spread-F is one of the prominent research fields. In this study, the Strong range Spread-F (SSF) data from DPS-4 digisonde during the five strong storms (Dst 〈 -100nT) period in 2004 in Hainan (19.4°N, 109.1°E, MLat. 9.0°N) China are used to investigate the effects of geomagnetic storms on SSF. The results show that there are three storms, the minimum Dst of which lied in the period 2200-0200 LT and SSF occurred during the main or earlier recovery phase of these storms, the role of directly penetrated electric field of magnetosphere maybe the only important factor for occurrence of SSF. The other two storms whose minimum Dst lied in the dayside also trigger SSF during the night of recovery phase of one storm and initial phase of another super intense storm. The SSC of the later super storm led to penetrated electric field towards to lower latitude/equator of ionosphere which triggered SSF. During the storms, SSF occurred only before midnight or started midnight and continued after midnight. The comparisons between the results of Dabas et al. and ours also discussed.
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    Comparison Between GISM Predictions and Ionospheric Scintillation Measurements Over Hainan Region
    HU Lianhuan;NING Baiqi;LI Guozhu
    2007, 27 (5):  384-390.  doi: 10.11728/cjss2007.05.384
    Abstract ( 2186 )   PDF (2143KB) ( 1526 )   Save
    In this paper, the Global Ionospheric Scintillation Model (GISM) has been introduced.Comparison between the model predictions with observations over Hainan region has been made using one year's data. The results show a good overall agreement between GISM predictions and observations in seasonal variation, diurnal variation and spatial distribution. In seasonal variation, GISM predictions agree in general with observations at moderate scintillation level, but there is more deviation at weak or strong scintillation levels. In diurnal variation, GISM predictions accord with observations on the whole, except for a delay of about one hour in the occurrence maximum. In spatial distribution, both observations and predictions show that occurrence in the south of Hainan is higher than that in the north.
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    Morphology of Ionospheric Disturbances Over Kokubunji During Geomagnetic Disturbances
    ZHAN Liang;LIU Libo;WAN Weixing;ZHAO Biqiang
    2007, 27 (5):  391-399.  doi: 10.11728/cjss2007.05.391
    Abstract ( 2388 )   PDF (6037KB) ( 1371 )   Save
    In this paper, with the observed critical frequencies of F2 layer at Kokubunji (139.5°E,35.5°N) during 1959 to 2004, the dependence of the variations of NmF2 on the geomagnetic activity, solar activity, season and local time are statistically investigated. The results show that there are more positive ionospheric storm effects than negative ones over KokuSunji. In summer, negative storm effects prevail during high solar activity, whereas positive storm effects are usually observed during low solar activity; in winter, positive storm effects dominate regardless of solar activity conditions; and in equinox, negative storm effects with smaller amplitude are often seen during high solar activity, and positive storm effects often take place during low solar activity conditions. The correlation analysis between the disturbance of NmF2 and ap index also illustrates the above-mentioned feature. Furthermore, our results show that there is a time delay of 12-15 hours between the ionospheric maximum negative disturbances and the maximum geomagnetic perturbation, and the time delay of the ionospheric positive disturbances are 3 and 10 hours, respectively. In addition, it is also found that under high geomagnetic activity conditions, positive disturbances are often seen in the evening, and negative disturbances in the morning.
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    Global Background Wind of Middle Atmosphere From Aura Data
    LIU Sanjun;XIONG Jiangang;WAN Weixing;NIN Baiqi
    2007, 27 (5):  400-408.  doi: 10.11728/cjss2007.05.400
    Abstract ( 2332 )   PDF (3679KB) ( 1427 )   Save
    Global background wind is derived from atmospheric pressure, temperature and density measured by MLS instrument onboard the Aura satellite in this article. The temperal and spacial variations of middle atmospheric wind are also analyzed. Comparisons of the derived Aura wind with WuHan meteor radar and Australian Adelaide observatory prove that the variations of Aura wind associated with time and space are in agreement with the observed results. Comparative result with HWM-93 indicates that the variations of Aura wind associated with time and space are nearly the same as HWM-93, and Aura wind is in better agreement with HWM-93 below 80 km than that above 80 km. The difference of zonal wind from directly observed data is no more than 20 m/s, and the relative difference is less than 18%, and Aura wind speed is larger than HWM-93.
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    Medium-Term Change of the Atmospheric Density at the Altitude From 550 km to 600 km
    CHANG Zheng;WANG Shijin;QIN Guotai
    2007, 27 (5):  409-415.  doi: 10.11728/cjss2007.05.409
    Abstract ( 2390 )   PDF (2960KB) ( 1042 )   Save
    Solar radiation is the main source for heating the thermosphere. The change of radiation intensity can result in the change of Earth's upper atmospheric density. With the same reason, the cycle of solar activities is the main factor to cause the corresponding cycle of thermosphere density change. The consequent change of atmospheric density directly influences orbiter's running and the precision of prediction of orbits of satellites. On the other hand, change of atmospheric density result from cycle of solar activities has something to do with different factors of solar-terrestrial physics, 5ome related phenomena should be taken into account. Although data of atmospheric density detectors which were onboard SZ-2 and SZo3 have already been used to discuss the change of upper atmospheric density, due to limit of their period on running, there are only a few descriptions of medium-term change. In this paper, the data of thermosphere density collected by the Atmospheric Density Detector onboard the satellite with the orbit altitude in 550-600 km. The results show that the value of thermosphere density has two kinds of cycle change, the length of one kind of cycles is 27 days, and the other is close to half a year. The results also show that the difference of the atmospheric density between the sunshine and shade area is one of the principal change of thermosphere density, the ratio of atmospheric density in the sunshine to the density in the shade correlates with solar activity.
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    Preliminary Analysis on the Relationship between Polar Mesosphere Summer Echoes and Frequency
    LI Hailong;WU Jian;HUANG Jiying;WANG Maoyan
    2007, 27 (5):  416-419.  doi: 10.11728/cjss2007.05.416
    Abstract ( 1729 )   PDF (719KB) ( 1054 )   Save
    Polar Mesosphere Summer Echoes (PMSE) are very strong radar echoes primarily stud- ied in the VHF and UHF wavelength band from altitudes near the polar summer mesopause. PMSE have also been detected in the MF and HF wavelength band. In the paper, by analyzing the volume reflectivities of PMSE at different time, stations and frequencies in related references, the volume reflectivities can be found a tremendous decrease with frequencies increasing (or wavenumbers de- creasing). This frequency dependence plays an important part in any physical explanation of PMSE. By studying experimental results in some references, the relationship between volume reflectivity and working frequency is obtained. One finds that the volume reflectivity is inverse proportional to the fourth power of the working frequency, namely the backscattering cross section per unit volume is inverse proportional to the fourth power of the frequency, and the relationship is different from that of the traditional turbulence theory. On the basis of the neutral air turbulence in combination with a large Schmidt number of the electrons, the volume reflectivity is reproduced with the data in the published papers. The result computed by M. Rapp is in an agreement with that mentioned above. Because of the presence of heavy charged ice aerosol particles, electron diffusivity significantly reduces and the irregularity of electron density occurs. The irregularity is the main factor leading to abnormally strong radar echoes. Finally some new problems about PMSE experiments and theories are put forward, the generation mechanism of PMSE may be explained with the theory of dusty plasma.
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    Phase Bias Estimation and Calibration of Meteor Radar System
    CHEN Xiaobo;WAN Weixing;NING Baiqi
    2007, 27 (5):  420-424.  doi: 10.11728/cjss2007.05.420
    Abstract ( 2043 )   PDF (1676KB) ( 2448 )   Save
    A new method was developed to estimate the radar system phase bias and calibrate the radar system. Using the data collected by this radar, the phase differences of the meteor echo between each receiver pairs are estimated, by taking account of the receiver pairs geometries the linear equation matrix is formed, the phase bias between each receiver pairs in the least-squares sense is solved, and finally the location of meteor echoes after calibration is found. Compared with the conventional method, this method can use the history data to find the system phase bias, without the need for additional hardware. It can routinely use for off-line to correct data collected using the bias estimated before. The data of Wuhan Meteor Radar (WHMR) between April 2004 to June 2004 is used as an example, the bias of the radar system is estimated and the data is used after calibration to calculate the location of the meteor echoes. The data calibrated using this method show a more consistent height distribution in terms of number of echoes with the same meridian.
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    Attitude Control of Micro-Satellite With Only Magnetic Actuators
    LIU Haiying;WANG Huinan;CHENG Yuehua
    2007, 27 (5):  425-429.  doi: 10.11728/cjss2007.05.425
    Abstract ( 2463 )   PDF (998KB) ( 1221 )   Save
    This paper researched on the attitude control of Micro-satellite using only magnetic torque for the different control modes including detumbling and attitude acquisition as well as threeaxis stabilization. The satellite model was established relative to orbit frame firstly, then based on the energy considerations and Lyapunov stability analysis methods, the B-dot controller for detumbling was presented, moreover, a new method using global energy control for attitude acquisition and three-axis attitude stabilization was given. At the same time based on the Linearizatlon of the satellite model, a constant gain LQG-controller was designed. Simulating result indicated that the B-dot controller can detumble the satellite's rate effectively; the global energy controller may be used in the large range of attitude capture and stabilization modes; while in small angle range the LQG controller has high precision but the stability properties is not so good compared to the energy controller.
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    Hierarchical Mathematic Model and Hierarchical Routing Algorithm
    GAO Lijuan;ZHAO Hongli;JIANG Taijie
    2007, 27 (5):  430-434.  doi: 10.11728/cjss2007.05.430
    Abstract ( 1914 )   PDF (2070KB) ( 1155 )   Save
    A hierarchical mathematic model of multi-layers satellite network is built in this paper.Based on the research of the mathematic model, a new hierarchical routing algorithm is proposed for multi-layers satellite network. The simulation results show that it has faster computing rate and has better performance in time delay. The routing performance of the multi-layers satellite network is effectively improved.
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    Robust Variable Structure Control for Free-Floating Space Robot System With Dual-Arms in Joints Space
    TANG Xiaoteng;CHEN Li
    2007, 27 (5):  435-440.  doi: 10.11728/cjss2007.05.435
    Abstract ( 1980 )   PDF (1635KB) ( 1291 )   Save
    In this paper, the kinematics and dynamics of free-floating space robot system with dualarms are analyzed. It is shown that the dynamic equations of the system are nonlinearly depending on inertial parameters. In order to overcome these problems, the system is modeled as under-actuated robot system, and the idea of augmentation approach is adopted. It is demonstrated that the dynamic equations of the system can be linearly dependent on a group of inertial parameters. Based on the results, a robust variable structure control scheme for free-floating space robot system with dualarms with uncertain inertial parameters to track the desired trajectory in joint space is proposed, and a planar space robot system with dual arms is simulated to verify the proposed control scheme. The advantage of the control scheme proposed is that it requires neither measuring the position, velocity and acceleration of the floating base with respect to the orbit nor controlling the position and attitude angle of the floating base. In addition to this advantage, it is computationally simple, more suitable for real time applications.
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