2003 Vol. 23, No. 2

Display Method:
HYBRID SIMULATION OF MAGNETIC RECONNECTION IN ANISOTROPIC PLASMA
GUO Jun, LI Yi, LU Quanming, WANG Shui
2003, 23(2): 81-88.
Abstract(2107) PDF 2208KB(1348)
Abstract:
The process of magnetic reconnection in an anisotropic plasma is studied based on two and half dimensional hybrid simulation. The results agree with theories. It is found that the growth rate of instability is enhanced greatly and the speed of magnetic reconnection is increased in the presence of pressure anisotropy (P/P = 1.5) compared with that in pressure isotropy. In a pressure anisotropy (P/P = 0.6) fire hose instability appears, which will restrain the tearing mode instability and magnetic reconnection. Because of the fire hose instability and the restraint of the tearing mode, the width of magnetic island in a pressure anisotropy (P/P = 0.6) is narrower than that in pressure isotropy. In addition, compared with the results based on MHD simulation, the effect of pressure anisotropy in our hybrid simulation is less obvious, which may be caused by the different conditions used in different simulation modes.
A COMPARISON OF APPROACHES TO DERIVING EQUIVALENT WINDS FROM IONOSPHERIC F-LAYER CRITICAL PARAMETERS
LIU Libo, LEI Jiuhou, LUAN Xiaoli, WAN Weixing, NING Baiqi
2003, 23(2): 89-96.
Abstract(1937) PDF 2249KB(1291)
Abstract:
Dynamic information (neutral winds and electric fields) near the peak of the ionospheric F-layer can be obtained from ionospheric critical parameters (f0F2 and hmF2) with different approaches. The physical basis of these approaches is the fact that neutral winds and electric fields strongly control the evolution of the ionosphere near and above the F-layer peak, especially the peak height of the F-layer. These approaches can be classified into three categories: traditional and revised servo approaches, data assimilation and approaches with the aid of ionospheric models, and the new approach introduced by Libo Liu. The first kind of approaches is based on the servo theory which was originally proposed by Rishbeth et al. (1978). A key point of this kind of approaches is that the equivalent wind is assumed to be proportional to the displacement of the peak height of the ionospheric F-layer from its equilibrium height without wind. Although it has achieved great success (Titheridge, 1995), the servo theory approach needs the no-wind equilibrium height, which is difficult to be accurately determined due to the large time constants for the ionosphere reaching an equilibrium state, especially in the day time. The second one includes those with the aid of an ionospheric theoretical model. Some need only an ionospheric model to provide the relationship between the neutral winds and the height displacements. In essence, they should belong to the serve theory approaches. The others make use of the idea of data assimilation, i.e., making the parameters from the model consistent with the observations as well as possible. The adjusted atmospheric parameters during the calculations are assumed to be the values at the actual situations. The approach proposed by Libo Liu avoids deducing equivalent winds from the displacement of the observed peak height from the no-wind equilibrium height, thus it is very simple and does not need to determine the no-wind equilibrium height which may limit the accuracy of the deduced winds as the servo theory approaches did.Equivalent winds derived from F-layer critical parameters by using these approaches are compared with the measurements with Millstone Hill Incoherent Scatter Radar during day 177-180 of the year 1990. Another example shows the consistence of an observation of the FPI wind at Beveridge (37°S, 144°E), Australia, with the equivalent winds derived from the Digisonde 256 observation at the same site. Both case comparisons can qualitatively evaluate the validity of the third approach.
AN IMPROVED GRID-BASED CORRECTION ALGORITHMS FOR SPARSELY OBSERVATION STATION REGION IN WAAS
WANG Yiju, YUAN Hong, WAN Weixing
2003, 23(2): 97-101.
Abstract(2072) PDF 982KB(1490)
Abstract:
The correction method of additional time delay caused by ionosphere and atmosphere plays a more and more important role in satellite timing and positioning system. In many radio projects which using electromagnetic wave as a measuring tool have to deal with the additional time delay, such as GPS, LADGPS, WADGPS and WAAS. In this paper, a new additional time delay algorithm model for a sparsely observation station region in WAAS is established and studied.Based on the improved grid-based correction algorithm for ionospheric delay in WAAS[4] and the model given in this paper, after numerical simulating with GPS data, the result was obtained showing that the precision of new algorithm is better than original one in the case of sparsely observation station region.
THE EFFECT OF POWERFUL HIGH-FREQUENCY RADIO WAVES ON TWO-STREAM INSTABILITY IN THE EQUATORIAL E REGION: THE STUDY OF PIC ELECTROSTATIC PARTICLE SIMULATION
HUANG Wengeng, GU Shifen
2003, 23(2): 102-109.
Abstract(2124) PDF 1894KB(1248)
Abstract:
Two-stream instability is one of some typical instabilities occurred in ionosphere. It exists in equatorial ionospheric and auroral ionospheric E region. Generally speaking, the two-stream instability appears occasionally due to the presence of a relative strong vertical electric field needed. In recent decades, several powerful High-Frequency (HF) radio wave transmitters were set up successively in the world, which provide us convenience to study the interaction of HF radio waves with plasmas. For example, the parametric process between the powerful HF radio waves (pump waves) and the ionospheric plasma, which will excite the electrostatic waves, and some instabilities may be produced under special conditions. In this paper, one dimension PIC (Particle In Cell) electrostatic particle simulation is used to study the interaction of pump waves with the equatorial ionospheric E region. The simulation results show that pump waves can control the two-stream instability. With different parameters, the instability can be stabilized or destabilized by the pump waves. The results are consistent with the theoretical model qualitatively. The simulation studying provides the probabilities for artificial control the irregularities by very strong radio waves on the ground.
A NUMERICAL STUDY ON THE ENERGY PROPAGATION AND CONVERSION OF GRAVITY-WAVE PACKETS EXCITED BY WAVE-LIKE DISTERBANCE IN THE MESOSPHERE
HUANG Chunming, ZHANG Shaodong, YI Fan
2003, 23(2): 110-117.
Abstract(2063) PDF 1769KB(1174)
Abstract:
By using the spectral allocation method, the characteristics of the energy propagation and conversion in the excitation of gravity wave by an initially given Gaussian wave-like disturbance is numerically studied. The simulation results show that any single wave-like disturbance component (horizontal wind, vertical wind, density or temperature) can independently excite two gravity-wave packets, one propagates upward and another propagates downward. With the same wave parameters, the energy propagation paths of the packets under the above mentioned four kinds of disturbances are almost identical with each other and slightly different from the ray paths derived by the linear theory. A further numerical analysis indicates that the characteristic time of the energy conversion from a disturbance to a wave is almost identical for those different disturbances, equal to two times of wave period. However, the energy conversion efficiencies for different disturbances depart significantly from each other.
F2-LAYER RESPONSE TO GEOMAGNETIC DISTURBANCES
MA Ruiping, XU Jiyao, WU Mingliang, JI Qiao
2003, 23(2): 118-126.
Abstract(2117) PDF 2020KB(1173)
Abstract:
Using the data observed in 37 ionosonde stations during 1974-1986 and adopting the correlation analysis method for the deviation of the daily f0F2 value from its monthly median to ap index, the geomagnetic latitude distribution of the F2-layer response to geomagnetic disturbance is obtained for the first time in every year of one solar activity cycle in the East Asia-Australia sector, Europe-Africa sector and America-East Pacific Ocean sector. The results showed that the negative response appeared at the high and middle geomagnetic latitude, the positive response appeared at the low latitude and geomagnetic equator, the response sign changes at the geomagnetic latitude of about ±30°, the maximum positive response appeared at geomagnetic equator and maximum negative response appeared at the geomagnetic latitude of about ±50°, and the amplitude of maximum negative response is larger than the amplitude of maximum positive response. The responses have obvious longitude dependence and the asymmetry between the Southern hemisphere and the Northern hemisphere. The geomagnetic latitude distribution of the response is symmetrical between the Northern and Southern Hemispheres in the East Asia-Australia sector. But in the Europe-Africa sector and America-East Pacific Ocean sector, the asymmetry between the Northern and Southern Hemispheres is obvious, the amplitude of maximum negative response is larger in the Northern Hemispheres than in the Southern Hemispheres.
A METHOD OF CELESTIAL AUTONOMOUS ORBIT DETERMINATION AND ATTITUDE DETERMINATION FOR SATELLITE
LI Linlin, SUN Huixian
2003, 23(2): 127-134.
Abstract(2052) PDF 1610KB(2009)
Abstract:
An autonomous real-time orbit determination for satellite flying around the Earth by the extended Kalman filtering is proposed in this paper. The observables are as follows, Satellite-Sun direction vector measured by Sun sensor, Satellite-Earth direction vector and Satellite-Moon direction vector measured by ultraviolet sensor, and the geocentric distance measured by radar altitude. Moreover, the satellite attitude to the Earth is determined. The simulation results show that orbit determination precision is better than 200m. By simulation experiments of autonomous orbit determination, the effects of sample period, orbit inclination, orbit eccentricity and orbit height on orbit determination precision are analyzed and compared. The changing law is submitted, which can improve satellite autonomous orbit determination precision.
SZ-2" ATMOSPHERIC DENSITY DETECTOR MEASUREMENT RESULT II. CHANGE OF THE THERMOSPHERE DENSITY DURING SOLAR AND GEOMAGNETIC ACTIVITY
QIN Guotai, QIU Shiyan, HE Aiqing, ZHU Yiqiang, SUN Lilin, LIN Xianwen, LI Hong, XU Xuepei
2003, 23(2): 135-141.
Abstract:
Solar radiation is the main source for heating the thermosphere. The change of its intensity can result in the change of Earth’s upper atmospheric density. With the same reason, the difference between the sunlit and shaded area is one of the main reasons for the difference of upper atmospheric density at the same altitude. The consequent change of atmospheric density directly influences orbiter’s running and the precision of prediction of orbit. On the other hand, change of atmospheric density resulted from sunlit and shaded area has something to do with different factors of solar-terrestrial physics, some discussion can be taken into about these related phenomena. Although data of American earlier balloon detection were already used to the discuss the day-change of upper atmospheric density, due to limit of ways and means, there are rare specifications of the change. And the later AE, DE satellite etc. all run at elliptical orbits, it is difficult to provide data for the discussion of the phenomena mensioned above. In this article, we applied the data from "SZ-2" Atmospheric Density Detector, which are the direct measurement results at a quasi-circle orbit and very helpful for the discussion of atmospheric density change in sunlit and shaded area.In this paper, the data on thermosphere density collected by "SZ-2" Atmospheric Density Detector from February to April, 2001 are used to search the change of the thermosphere density in the sunlit and shaded area during solar and geomagnetic active period. The results show that in the sunlit area, the peak value of atmospheric density changes as F10.7 varies; during geomagnetic active periods, the peak value of atmospheric density at shaded area increases as Ap increases, and starts first at higher latitudes, then gradually move to lower latitudes.
DATA RECEIVING AND ALERTING SYSTEM OF FY-2 SATELLITE
GONG Dezhu, SUN Yueqiang, LIU Yiming, LIANG Jinbao, LIN Huaan, ZHU Guangwu, WANG Shijin
2003, 23(2): 142-148.
Abstract(1955) PDF 1643KB(1242)
Abstract:
FY-2 satellite is a geosynchronous meteorological satellite which is produced and lunched by China. The satellite carries the spatial particle detector and the solar X-ray detector used for detection of solar proton-event in high energy particle environment. The whole data receiving and alerting system of FY-2 consists of three systems: the earth-based system of data receiving and demodulating, the system of data processing and alerting. At first, environment detection data are collected, modulated and transmitted in the onboard system of FY-2 and detectors. Then data signals are magnified, demodulated and sent into the earth-based system of data receiving and demodulating. At last, data is received, processed, stored, displayed and judged to make alarm automatically by telephone for solar proton-events and X-ray flare in the system of data processing and alerting. It is an important way for guaranteeing space vehicle’s safety and enhancing antiradiation’s level.
THE STUDY ON IMPROVEMENT OF "BEIDOU" DOUBLE-STAR NAVIGATION SYSTEM AND IT’S ALGORITHM
LIN Xueyuan, LIU Jianye
2003, 23(2): 149-154.
Abstract(2007) PDF 1330KB(2032)
Abstract:
“Beidou” Double-star positioning system is one kind of positioning system for local area (RDSS). In this paper, the disadvantage of double-star navigation system is discussed and a new idea is put forward. The idea is to set an inactive regional navigation system made up of the barometer and the existing two working satellites and the third (spare satellite). The algorithm expression for this navigation idea is presented. The simulation results show that this method for navigation is feasible and can fulfill the media-accuracy navigation positioning, so to offer a new way to develop a relatively simple satellite navigation system.
MODIFIED DESIGN AND STRUCTURALANALYSIS FOR ADJUSTMENT MECHANISM OF THE IMAGING LENS’S FOCAL LENGTH OF A SPACE SOLAR TELESCOPE
YUE Jianru, GUAN Fuling, YANG Yulong
2003, 23(2): 155-160.
Abstract(2459) PDF 1414KB(1969)
Abstract:
Based on the previous work, a modified model of adjustment mechanism of the imaging lens’s focal length of a space solar telescope is designed. Analysis on the environment and contact ifluence of the modified model are also presented in the paper. The design principle is illustrated in the article. The movement of the image lens is controlled by the step motor and screw. According to the result of the contact analysis, the modified mechanism is workable.