空间科学学报

2005 Vol. 25, No. 2

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Coronal Flux Rope Catastrophe in Partly-Open Multipolar Magnetic Field

PENG Zhong, HU Youqiu

2005, 25(2): 81-85.

Abstract(2401) PDF 1501KB(1139)

Abstract:
Using a 2.5-dimantional ideal MHD model in spherical coordinates, the catastrophe of a coronal magnetic flux rope embedded in a partly-open multipolar background magnetic field has been studied. The background field consists of a coronal streamer containing three closed bipolar fields and an open magnetic field with an equatorial current sheet. The magnetic flux rope lies below the central bipolar field, characterized by its annular and axial magnetic fluxes. There exists a critical axial flux for a given annular flux, or a critical annular flux for a given axial flux such that below each of these critical fluxes, the magnetic flux rope remains to be attached to the solar surface and the whole system stays in equilibrium. On the other hand, if the critical fluxes are exceeded, the flux rope leaves the solar surface and erupts upward, implying an existence of catastrophe for a coronal flux rope embedded in a partly-open multipolar background magnetic field. For the given example, the corresponding threshold of magnetic energy at the catastrophic point is found to be about 15% larger than the energy of the corresponding partly-open magnetic field in which the central bipolar field is fully open whereas those at the flank remain closed. The excessive energy may serve as an energy source for solar explosions such as coronal mass ejections.

One Case Study About the Development of Coronal Hole and the Correlative Earth Effects

MA Donglan, LIU Siqing, GONG Jiancun

2005, 25(2): 86-92.

Abstract(2605) PDF 2510KB(1230)

Abstract:
The evolutionary features of the coronal hole, the interplanetary and geomagnetic field effects were studied in this paper using the data of a significant coronal hole which recurred between 2003 and 2004, and the data of its correlative solar wind, interplanetary magnetic field (IMF) and geomagnetic field. It is found that the development of the coronal hole can be separated into three phases according to the geomagnetic field effects of coronal hole. That is growth phase, maturation phase and decay phase. There are different characters among these three phases. During maturation phase, the maximum solar wind speed of the high speed stream and the average effect to magnetic field maintain a same level. That means the peak of solar wind speed and the corresponding geomagnetic index (average ∑Kp and maximum ∑Kp) are confined. On the other hand, the structure of this coronal high speed stream and the corresponding recurrent geomagnetic storm are studied. Then it is found that the high speed streams have steady structures on the maturation phase, and the durations of recurrent geomagnetic storms were varied with the high-speed streams. Meanwhile the duration of the high speed is related to the shape and development of the coronal hole, especially to the longitudinal extend of the coronal hole in equator.

Numerical Computation and Analysis on Radiation Field of the Plasma Column

ZHAO Guowei, CHEN Cheng, XU Yuemin

2005, 25(2): 93-98.

Abstract(2589) PDF 1746KB(2953)

Abstract:
There are many ways to excite the plasma, surface waves can be used to excite the plasma from a single end. One of them is by means of capacitively coupled low-pressure Radio-frequency (RF) discharge, plasma surfaces can be suspended in free space to serve as antenna elements. The surface wave driven plasma antenna produces sufficiently low noise so as to be useful for broadcast communications. When frequencies well below the plasma frequency, the plasma surface wave also propagates near the speed of Light just as on a metal-dielectric interface. According to opproach of radiation pattern of metal, the radiation patterns of travelling wave and standing wave transmitting in a column plasma in simple conditions are calculated. When relevant parameters like plasma density are changed, radiation pattern also changes correspondingly. Compared with metal, there are similar results. Using wave vector from dispersion relation of the plasma surface wave for an ideal column plasma, radiation pattern will change greaterly compared with radiation pattern in metal. Radiation pattern of plasma column can be controlled by changing plasma parameters, so utilizing plasma to transmitting the signal, there are certain reference meanings.

Forecasting of Ionospheric Critical Frequency Using Neural Networks

CHEN Yanhong, XUE Bingsen, LI Libin

2005, 25(2): 99-103.

Abstract(2758) PDF 1368KB(1196)

Abstract:
The use of feed-forward back propagation neural networks to predict ionospheric F₂ layer critical frequency, f₀F₂, 24 h ahead, have been examined. The data we used are from Wuhan ionospheric station, China, and Hobart ionospheric station, Australia. The data period is from 1970 to 1990 at Wuhan and from 1962 to 1990 at Hobart. The five day's measurements of f₀F₂ before the day that need forecast are reduced to five coefficients. The inputs used for the BP neural network are the coefficients, the solar 10.7cm flux index, and the outputs are the day's 24 h observed f₀F₂ data. The trained net then can forecast f₀F₂ 24 h advance. The result indicates the predicted f₀F₂ using NN has good agreement with observed data. Comparison with IRI model suggests that NN method is more accurate than IRI. In addition, the error analysis indicates that predicted f₀F₂'s Root-Mean-Square Error (RMSE) is smaller in Hobart than in Wuhan, smaller in low solar activity than in high solar activity, smaller in winter and summer than in spring and autumn. In conclusion, using neural network to predict ionospheric parameters is a feasible method.

Effects of Extreme Heavy Rainfall in the Troposphere on the Ionosphere

XU Guirong, WAN Weixing, NING Baiqi

2005, 25(2): 104-110.

Abstract(1926) PDF 2163KB(1296)

Abstract:
In this paper, the meteorological influences on ionospheric variability have been studied. We analyzed the effects on the ionosphere from the five extreme heavy rainfall cases happened in Wuhan from 1958 to 1998 by means of the superposed epoch method. The results show that when the extreme heavy rainfall happens:(1) the blanket frequency of Es(f_bE_s) and the critical frequency of Es(f₀E_s) drop distinctly; (2) the minimum virtual height of F-layer (h'F) and the peak height of F-layer (h_pF) decrease limitedly, and when the extreme heavy rainfall is more severe, the decreases of h'F and h_pF are more obvious; (3) the extreme heavy rainfall has few or no effects on the other characters of the ionosphere. In the paper, it is thought that the meteorological influences on the ionosphere are due to dynamical processes; it occurs as the result of upward-propagating tides, planetary waves and gravity waves originating from or accompanying the extreme heavy rainfall.

Effects of Atmospheric Gravity Waves on the Mesosphere and Lower Thermosphere Circulations

HU Xiong, ZHANG Xunxie, ZHANG Dongya

2005, 25(2): 111-117.

Abstract(2015) PDF 409KB(1293)

Abstract:
Atmospheric gravity waves generated in the lower atmosphere, carrying momentum and energies, propagated upward and usually became saturated and breaking in the Mesosphere and Lower Thermosphere (MLT) due to their increasing amplitudes versus increasing height. Linear saturation parameterizations of atmospheric gravity waves were applied with the β-channel quasi-geostrophic mean flow equations to qualitatively investigate influences of gravity waves on MLT circulations. Three waves with 0m·s^-1, 20m·s^-1,-20m·s^-1 horizontal phase speeds respectively were taken as a parameterization of the discrete spectrum of gravity waves. Simulations show that the accelerations due to waves can be 100m·s^-1/d and eddy diffusion coefficients can be 120m²/s in the mesosphere, which balance the Coriolis force due to MLT meridional circulations and induce great departures of the zonal mean zonal winds from the radiation balance zonal winds. The calculations of the zonal mean zonal winds of MLT are qualitatively consistent with the MF radar observations and model profiles both in winter and summer time.Resultsshow gravity waves play significant role in MLT circulations.

Application of GEANT Program to Design Space Particle Detector and Optimize

ZHANG Shenyi, WANG Shijin

2005, 25(2): 118-124.

Abstract(2065) PDF 1981KB(1583)

Abstract:
GEANT is an important Monte Carlo program and this program is in principal applied in high energetic physics. As the scale and complexity of high energy physics experiments increase, simulation studies require more and more care and become essential to the design and optimizing of the detectors, development and test of the reconstruction and analysis of programs, also to interpreting the experimental data. It has been found today applications also outside this domain in areas such as medical and biological sciences, radio-protection. With the development of space technique, design of the particle detector is helped by the Monte Carlo simulation too. The principal applications of GEANT in space particle detection are:the transport of particles through a detector for the simulation of detector response; the graphical representation of the setup and of the particle trajectories. GEANT uses the memory manager ZEBRA, it can help us to manage and store the data easily. In this paper, the primary structure and the process of particle transferring in detector is introduced. With GEANT program, many problems in particle detections can be solved, such as the particle's energy deposition in detector, the linear energy transfer in matter.

Decomposing Algorithm of Laser Altimeter Waveforms

YANG Geng, HUANG Chunming

2005, 25(2): 125-131.

Abstract(2184) PDF 2247KB(1621)

Abstract:
A method to extract the basic information from laser altimeter return waveforms is developed, by which decompose a laser altimeter return waveform into a series of Gaussian components and obtain the number of the Gaussian components and the position, half-width and amplitude of each Gaussian component. From these basic parameters, the topographic information as the elevations and distributions, the surface slope and roughness, and the albedos of distinct reflecting surfaces within the laser footprint can be further induced. Firstly, the initial values of the number of Gaussian components and the position, half-wide of each component are estimated from the number and positions of the waveform's inflection points. Secondly the linear least-squares method are used to calculate the initial amplitudes of each Gaussian component. At last the waveform is fitted with the chosen and ranked Gaussians by Levenberg-Marquardt method, achieving basic optimized parameters of Gaussians. Three types of simulated return waveforms of the laser altimeter from scalariform terrain, woodland and slope surface have been fitted by this decomposing algorithm, the original waveforms are successfully approximated by the fitted ones and the optimized parameters of simulated return waveforms are satisfied. And the results prove that the decomposing algorithm of laser altimeter waveforms obtains a higher precision, it will have a good effect on the analysis of laser altimeter return waveforms.

An Introduction to Displacement Damage Dose Model and Its Applications

ZHANG Qingxiang, HAN Jianwei, SHI Liqin, ZHANG Zhenlong, HUANG Zhi

2005, 25(2): 132-137.

Abstract(2066) PDF 2002KB(1494)

Abstract:
Photonics are increasingly used in space missions to promote performance of space burn system. The radiation issues for photonics are significantly different from those of Si digital microelectronics. It has been found that displacement damage effect is one of the most important damages for photonics used in space radiation environment and a few spacecraft anomalies have been attributed to displacement damage. So displacement damage have been studied seriously in recent year. In this paper, firstly the mechanism for displacement damage is introduced and the ways displacement damage affecting the performances of photonics are discussed; then displacement damage dose model which based on non-ionization energy loss is presented to predict the degradation of CTE in CCD, dark current in Si device and output power in solar cell. Finally, a program based on DDD model for CTE decline prediction in space environment is introduced. The difference between our prediction result with that of ESA SPace ENVironment Information System (SPENVIS) is less than 10%. In addition to that, the program can be used to evaluate the effect o shield for sensitive device and to convert the proton spectrum for a particular mission to a equivalent fluence at a specific proton energy. The study results will find widely applications in satellite radiation-harden design.

Influence of Satellite Departure and Experiment Research on Integrated Positioning With Two Geostationary Satellites and GIS

ZHENG Chong, WU Jie, ZHOU Bozhao, YUAN Yanbo

2005, 25(2): 138-142.

Abstract(2036) PDF 1499KB(1342)

Abstract:
A calculate model is presented in this paper, which is used to study both positioning with two Geostationary satellites and integrated positioning with two Geostationary satellites and geographic Information System (GIS). With the model, how the ephemeris error influence the precision of positioning with two Geostationary satellites and how the position of the satellites influence the integrated positioning when they were added 1° departure in longitude and latitude are studied. The result shows it does not debase the accuracy of the integrated positioning with two Geostationary satellites and geographic information system, to add a small departure on the satellites position. Also, the conclusion is explained by geometry. At the end of the paper, an experiment was done which proved the integrated positioning with two Geostationary satellites and geographic information system can surely improve the precision of positioning with Geostationary satellites.

Spectral Analysis on Time Series of Calibration Parameters of CHAMP Accelerometer

XU Tianhe, YANG Yuanxi

2005, 25(2): 143-148.

Abstract(2394) PDF 1613KB(1433)

Abstract:
The theory and algorithm of determining system errors of CHAMP accelerometer are presented based on energy conservation method. The time series of scale factor, bias and bias drift is analyzed using about two and a half years' accelerometer data of CHAMP from August 2001 to December 2003. The long-term and principal periods variations are obtained by using LS spectral analysis as well as the robust one. The results show that there are clear periodic variations in the time series of scale factor, bias and bias drift. For scale factor, the principal periods are 441 d, 220 d, 126 d and 13.4 d. 441 d and 220 d periods make great contributions to scale factor. For bias, the principal periods are 220 d, 126 d and 13.4 d, and they make almost the same contributions. For bias drift, the principal periods are 220 d, 13.4 d and 9d, and 13.4 d makes the greatest contribution. There are obvious long-term variations in the time series of scale factor and bias except bias drift. It is shown that the results of the robust spectral analysis are superior to that of LS one in the whole. Further investigations about why there are long-term and period variations in system errors of CHAMP accelerometer are necessary.

The Research on Main Satellite Bobbin Cylinder Incorporated With Main Heary Structure and Bracket of Large-Volume Tank

CHEN Changya, WANG Deyu

2005, 25(2): 149-153.

Abstract(2269) PDF 1335KB(1395)

Abstract:
With the background of the large-scale of modern satellite structure and propellant tank, a format of main satellite bobbin cylinder incorporated with main heary structure and bracket of large-volume tank, are proposed aiming at lowering the centroid and increase the fundamental frequency. The new structure type can meet the requirements of both the design of tank volume and the mechanical transferring efficiency from payload of main structure to carry. The numerical computation of finite element method indicates that the proposed structure format can meet the requirement of relevant structure performances and can server as the referential configuration of satellite structural design in the future. The main bobbin structure is weaved by high modulus carbon fiber, the cylinder of which is embedded a carbon fiber board inside. The designability and spreading weavablility should be made full use of to produce it according to the need.

Nonholonomic Motion Planning of Space Robots with Prismatic Joint for Obstacle Avoidance via Hierarchical Lyapunov Methods

GUO Yishen, CHEN Li

2005, 25(2): 154-160.

Abstract(1995) PDF 2577KB(1787)

Abstract:
Based on hierarchical Lyapunov methods, the motion planning of free-flying space robots with prismatic joint for obstacle avoidance is discussed. First, with the momentum conversation and the Jacobian matrix, the system state equations and the control output equations for control design are established. And then the primary and secondary Lyapunov functions are selected. The primary function insures the movement of the endeffector from the start point to the end point. The secondary ascertains obstacle avoidance of the endeffector. Combined the primary and secondary functions, the endeffector implements the specific movement and realizes obstacle avoidance. A planar space robot with prismatic joint is simulated to verify the proposed methods.