空间科学学报

2001 Vol. 21, No. 4

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THREE-DIMENSIONAL NUMERICAL CORONAL MODEL OF CARRINGTON ROTATION 1935 AT MAY 1998

YE Zhanyin, WEI Fengsi, FENG Xueshang, SHI Yong, YAO Jiusheng

2001, 21(4): 289-296. doi: 10.11728/cjss2001.04.20010401

Abstract(2328) PDF 666KB(609)

Abstract:
Three-dimensional coronal structure of Carrington rotation 1935 at May 1998 is obtained by using a three-dimensional numerical model of ideal magnetohydro dynamic equations. In this numerical model, MacCormark-Ⅱ scheme is employed for the discretization of the governing equations in computational domain and non- reflecting projected-characteristic condition is adopted at inner boundary to keep the simulation stable and the solution self-consistent. With the numerical model, iteration is carried out with initial magnetic field constructed from photosphere observation at 1935 Carrington rotation by Legendre series expansion and finally approaches a steady state. The iteration results show that:(1) magnetic field on source surface is nearly in radial direction with non-radial magnetic field component no more than 2μT near the neutral line. (2) The value of radial magnetic field component on source surface has no much variation except near the neutral line. This agrees with Ulysess observation. (3) The magnitude of radial magnetic field component at 1 AU, calculated from that on source surface by rule of r^-2, approxi mates observation better than that obtained by potential model. (4) 3-D numerical coronal structure agrees qualitatively with observation. The 3-D numerical results also show that magnetic field dominates global solar wind structure, in which density of solar wind is high and speed is low in close magnetic field and near current sheet, while density is low and speed is high at open magnetic field.

CORRELATIONS OF Dst INDEX WITH THE INTERPLANETARY ELECTRIC FIELD

ZHANG Jichun, TIAN Jianhua, PU Zuyin

2001, 21(4): 297-304. doi: 10.11728/cjss2001.04.20010402

Abstract(2622) PDF 772KB(991)

Abstract:
Correlations of the Dst index with various interplanetary parameters are studied by using the solar wind and interplanetary magnetic field data from the ACE spacecraft. Among all parameters investigated, E_y, the down-dusk component of the interplanetary electric field is found to be best correlated with the Dst index. During strong and moderate geomagnetic storms, it is seen that 2 to 3 hours before the storm main phase starts, E_y suddenly begins to increase and that the increase of E_y, is almost "synchronous" with the decrease of the Dst, with a time a head about 2 to 3 hours. Such an "abruptly changing characteristic curve" of E_y is much easier to be identified than those corresponding curves of V、V²B_z、VB₂ and ε. Weak disturbances in the magnetospheric background field, fluctuations of both the IMF Bz and the interplanetary E_y all strongly influence the development of storms, causing multiple-step main phase decrease and enhancement of the storm intensity. The physical mechanism responsible for the close correlation of Dst with the interplanetary electric field is discussed. A viewpoint that the present study of multiple-step main phase storms needs to be improved is proposed.

NUMERICAL SIMULATION OF NON-STEADY INTERACTION BETWEEN MOVING BODIES AND PLASMA IN COMPRESSION REGION

MA Shanjun, XU Xuexiang

2001, 21(4): 305-310. doi: 10.11728/cjss2001.04.20010403

Abstract(2192) PDF 495KB(931)

Abstract:
The interaction between a body in space and its plasma environment is one of the basic problems in space plasma physics. In this paper, based on the amplitude transport equation of fast varying field and the low frequency disturbance equation of electron density, the evolutions of the density distribution of charged particles and collapse of electric field have been calculated numerically in two dimensions with three field components under the condition of transverse wave. A numerical result of non-steady interaction between moving bodies and plasma in compression region is presented. In numerical simulation, the FTCS method, i.e. time forward difference and space central difference method, has been used. The results of numerical calculation show that the density cavitons and potential solitons are formed due to the modulational instability if the radiation of the antenna as a pump wave source is sufficiently intense. From the distribution of density caviton, the moving body can be traced out by means of observing the structure and intensity of the density caviton although the body may be a stealthy vehicle.

MODELLING STUDY THE VARIATION OF THE EQUATORIAL ANOMALY IONIZATION TROUGH

LIU Libo, WAN Weixing

2001, 21(4): 311-317. doi: 10.11728/cjss2001.04.20010404

Abstract(2209) PDF 680KB(993)

Abstract:
An anomalous feature of low latitude ionosphere is the Equtorial Anomaly, and measurements show that the minimum peak density located between two crests of the Equtorial Anomaly, the equatorial anomaly trough (EAT), is not always located at near the magnetic equator. A two-dimensional theoretical low-latitude ionospheric model is used to simulate the evolution of the EAT and investigate effects of some physical factors on the location of the EAT. Each of them is adjusted respectively to study their influences on the EAT. Simulation results show that there are extinct diurnal, seasonal and longitudinal variations of the location of EAT. The EAT situates at the north of the magnetic dip equator at June solstice and shifts to the south at December solstice. It is found that the seasonal variation of the position of EAT is mainly caused by the neutral winds, not by seasonal changes in photoionization productions directly due to the variation of the geomagnetic solar zenith angle. Longitudinally speaking, the EAT lies north near 285°E and south near 100°E, which is basically consistent with previous observations. And its longitudinal variation is pricipally caused not by the magnetic declination and displacement between the geographical and magnetic equators, but by the longitudinal changes of horizontal neutral wind, which does not support the previous opinion. Only at regions near the 330°E longitudes did the magnetic declination play some larger influence on the EAT location, but it was still much smaller than that of neutral winds. In addition, the displacement between the dip equator and equatorial electrojet is not taken into account because the ionospheric model is under the dipole field assumption.

A CASE STUDY OF WAVE INTERACTIONS IN THE MESOPAUSE REGION

XIONG Jiangang, YI Fan

2001, 21(4): 318-323. doi: 10.11728/cjss2001.04.20010405

Abstract(2154) PDF 556KB(1021)

Abstract:
The nonlinear interaction among waves in the polar mesopause region at height from 83.4 km to 90km has been studied. The 35 h wave, semi-diurnal tides and inertial-gravity waves at period of about 8.9 h existed at almost all heights in the zonal winds and their frequencies satisfied resonance condition. The 33 h wave, semi- diurnal tides and inertial-gravity waves at period of about 19 h in the meridional winds satisfied resonance condition. By using the bispectral analysis, we found that those sets of waves were coupled each other. The maximum amplitude of semi-diurnal tide appeared just at the height where the 35 h or 33 h wave reached its minimum amplitude. The energy exchange between 35 h or 33 h waves and semi-diurnal tide was obvious. That indicates that the nonlinear wave interaction was not local only at lower atmosphere, but also at all heights in the mesopause region. The interaction leads the variation of tide amplitude temporally and spatially. The 35 h and 33 h waves may be generated by nonlinear interaction between diurnal tide and planetary waves at periods of 2-3 days at other sites or other time, and they interacted with semi-diurnal tides when they propagated to the observation site.

IDENTIFICATION OF SOLAR-TERRESTRIAL EVENTS CONNECTED WITH GEOMAGNETIC STORMS FROM THE LATE APRIL TO THE EARLY MAY IN 1998

WANG Yuming, YE Pinzhong, GAO Yufen, WANG Jialong

2001, 21(4): 324-331. doi: 10.11728/cjss2001.04.20010406

Abstract(2384) PDF 894KB(711)

Abstract:
Analyzing the CME observations of SOHO/LASCO and SOHO/EIT, as well as solar wind observations of the WIND spacecraft, we identified the CME sources that led to the geomagnetic storms occurring from the late April to early May in 1998. Also we analyzed the solar-terrestrial events associated with intense geomagnetic storms in early May. The results show that the identification method of solar terrestrial events connected with geomagnetic storms we employed is feasible. In addition, we discussed the relationship between these geomagnetic storms and active regions, the east-west asymmetrical effect and the interactions between magnetic clouds and high-speed streams, etc.

ABUNDANCES AND DISTRIBUTION OF ELEMENTS ON THE LUNAR SURFACE

XU Tao, LI Chunlai

2001, 21(4): 332-340. doi: 10.11728/cjss2001.04.20010407

Abstract(2610) PDF 1003KB(1192)

Abstract:
Recently USA launched two Moon probes which are "Clementine" and "Lunar Prospector". They carried some newly developed or innovated instruments to map the elements abundances on the moon, such as gamma-ray spectrometer, neutron spectrometer and UV-VIS imager. Based on the data of high quality those instruments gained, new progress have been made about the quantification of lunar elements.
This paper summarizes those up to date progress in two ways. First the instruments used by Lunar Prospector and Clementine to map the elements abundances will be introduced, then the progress achieved in the theory of elements quantification will be discussed in detail, especially about the quantification of iron, titanium and Ree.

RESEARCH ON SATELLITE PRECISION ORBIT ROBUST ESTIMATION

WEN Yuanlan, YANG Yuanxi, WANG Wei

2001, 21(4): 341-350. doi: 10.11728/cjss2001.04.20010408

Abstract(2770) PDF 817KB(1156)

Abstract:
In this paper, a model is established and weight functions are given for robust batch processor in satellite precision orbit determination. The effects no robustuess weight functions. It is shown that the robust batch processor can give the best estimate results from normal observations by making full use of effective observations, finding limitations of useable observations and eliminating deleterious gross errors. The robust computations steps are also given. Finally, satellite laser ranging (SLR) data of satellite Lageos were processed, the satellite orbit estimated from the robust estimation is more stable than that from least square estimation and this verifies the good robustness of robust batch processor in practice.

PERFORMANCE ANALYSIS FOR REGIONAL SATELLITE POSITIONING SYSTEM BASED UPON GEO/HEO HYBRID CONSTELLATION

LIU Huijie, ZHANG Naitong

2001, 21(4): 351-358. doi: 10.11728/cjss2001.04.20010409

Abstract(2552) PDF 654KB(1164)

Abstract:
As for satellite positioning system, selection of constellation type would greatly influence the performance.of positioning. Connected with Archimedes plan among constellation schemes for GNSS-2, this paper presents a GEO/HEO hybrid positioning constellation by using three HEO satellites and three GEO satellites, here the objective region is chosen as our country. Firstly, the parameters for GEO and HEO satellites are optimized from regional visibility. Secondly, positioning performance analysis for the given hybrid constellation are provided in certain region measured by GDOP and PDOP. Simulation results show that we can expect similar accuracy with GPS in certain region by the hybrid constellation put forward here.

COMPUTER SIMULATION OF TOP-HAT ELECTROSTATIC ANALYZER WITH COLLIMATOR

YU Dejiang, LIU Ying, REN Qiongying

2001, 21(4): 359-362. doi: 10.11728/cjss2001.04.20010410

Abstract(2082) PDF 290KB(790)

Abstract:
Top-hat quadric spherical electrostatic analyzer with a collimator is of large advantage over the bare analyzer (without collimator). The simulation program for the bare analyzer has been already set up successfully[1]. The new simulation program has been developed from the modifications of that for the bare analyzer. These modifications are not significant and substantial, since the difference between two analyzers is only in the structure configuration at entrances, with/without collimator. In effect, the simulation procedures and techniques used in two programs are also similar to each other basically. In addition, the program is applied to a sample of top-hat analyzer with a collimator. The simulation results generated from the program are also reported in this paper.

EXPERIMENTAL REASEARCH ON LEAKAGE RATE OF SPACE SEAL WITH O-RING

WANG Guangzhen, JI Linhong, WEN Shizhu, WANG Zhishan

2001, 21(4): 363-369. doi: 10.11728/cjss2001.04.20010411

Abstract(2343) PDF 559KB(1130)

Abstract:
Experimental research on leakage rate of silastic O-ring at simulative space environment is conducted to investigate the effect of compression ratio, temperature, load decay of O-ring and radialization of atomic oxygen on the leakage rate of O-ring. The results show that the leakage rate of O-ring decreases with the increase of compression ratio, increases with the rise of temperature, and it is affected by the load decay of O-ring and radialization of atomic oxygen at various degrees.

IN-FLIGHT RADIOMETRIC CALIBRATION FOR THERMAL CHANNELS OF FY-1C AND FY-2B METEOROLOGICAL SATELLITE SENSORS USING QINGHAI LAKE

HU Xiuqing, RONG Zhiguo, QIU Kangmu, ZHANG Yuxiang, ZHANG Guangshun, HUANG Yibing

2001, 21(4): 370-380. doi: 10.11728/cjss2001.04.20010412

Abstract(3200) PDF 1016KB(1182)

Abstract:
This Paper describe the in-flight radiometric calibration for thermal channels of FY-1C and FY-2B meteorological satellite sensors using Qinghai lake, water surface radiometric calibration site. The radiance of water surface measured by CE312, and then performed atmosphere correct including gas absorption and path radiance which computed by radiance transfer code MODTRAN37, predict the radiance in the satellite sensor entrance pupil. At the same time the spectral response of Satellite sensor and that of ground-based sensor are coupled. At last the apparent radiance of sensor spectral channels are compared to the digital count of satellite's output to give the calibration coefficient. Several calibration is conducted for the satellite thermal sensors of FY serial satellites. The result show the difference between in-flight and on-board calibration is about 5%, equivalent to a brightness temperature of 3 K.